@article{belardinelli_li_martin_zeiler_lian_avanzi_wiersma_nguyen_angala_moura_et al._2022, title={2-Aminoimidazoles Inhibit Mycobacterium abscessus Biofilms in a Zinc-Dependent Manner}, volume={23}, ISSN={["1422-0067"]}, DOI={10.3390/ijms23062950}, abstractNote={Biofilm growth is thought to be a significant obstacle to the successful treatment of Mycobacterium abscessus infections. A search for agents capable of inhibiting M. abscessus biofilms led to our interest in 2-aminoimidazoles and related scaffolds, which have proven to display antibiofilm properties against a number of Gram-negative and Gram-positive bacteria, including Mycobacterium tuberculosis and Mycobacterium smegmatis. The screening of a library of 30 compounds led to the identification of a compound, AB-2-29, which inhibits the formation of M. abscessus biofilms with an IC50 (the concentration required to inhibit 50% of biofilm formation) in the range of 12.5 to 25 μM. Interestingly, AB-2-29 appears to chelate zinc, and its antibiofilm activity is potentiated by the addition of zinc to the culture medium. Preliminary mechanistic studies indicate that AB-2-29 acts through a distinct mechanism from those reported to date for 2-aminoimidazole compounds.}, number={6}, journal={INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES}, author={Belardinelli, Juan M. and Li, Wei and Martin, Kevin H. and Zeiler, Michael J. and Lian, Elena and Avanzi, Charlotte and Wiersma, Crystal J. and Nguyen, Tuan Vu and Angala, Bhanupriya and Moura, Vinicius C. N. and et al.}, year={2022}, month={Mar} }
@article{borrel_melander_fourches_2021, title={Cheminformatics Analysis of Fluoroquinolones and Their Inhibition Potency Against Four Pathogens}, volume={40}, ISSN={["1868-1751"]}, DOI={10.1002/minf.202000215}, abstractNote={Drug-resistant bacteria are a worldwide public health concern. As the prevalence of multi-drug resistant pathogens outpaces the discovery of new antibacterials, it is of importance to explore the structure-activity relationships for series of known bactericides with proven scaffolds. Herein, we assembled a set of 507 fluoroquinolone analogues all experimentally tested for their inhibition potency against four pathogens: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pneumoniae. We relied on cheminformatics techniques to characterize and cluster them based on their structural similarity and analyzed the structure-activity relationships identified for each cluster of fluoroquinolones. Then, we utilized machine learning techniques to develop and validate predictive QSAR models for computing the inhibition potencies (pMIC) of analogues for each pathogen. These QSAR models afforded reasonable external prediction performances (R2≥0.6, MAE∼0.4). This study confirmed that (i) there are both global and local inter-pathogen concordance regarding the antibacterial potency of fluoroquinolones, (ii) small clusters of fluoroquinolone analogues are characterized by unique patterns of strain selectivity and potency, the latter being potentially useful to design new analogues with enhanced potency and/or selectivity towards a given pathogen, and (iii) robust QSAR models were obtained allowing for future design of new bioactive fluoroquinolones.}, number={5}, journal={MOLECULAR INFORMATICS}, author={Borrel, Alexandre and Melander, Christian and Fourches, Denis}, year={2021}, month={May} }
@article{jeon_ackart_li_jackson_melander_melander_abramovitch_chicco_basaraba_obregon-henao_2019, title={2-aminoimidazoles collapse mycobacterial proton motive force and block the electron transport chain}, volume={9}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-018-38064-7}, abstractNote={Abstract There is an urgent need to develop new drugs against tuberculosis. In particular, it is critical to target drug tolerant Mycobacterium tuberculosis ( M . tuberculosis ), responsible, in part, for the lengthy antibiotic regimen required for treatment. We previously postulated that the presence of in vivo biofilm-like communities of M . tuberculosis could contribute to this drug tolerance. Consistent with this hypothesis, certain 2-aminoimidazole (2-AIs) molecules with anti-biofilm activity were shown to revert mycobacterial drug tolerance in an in vitro M . tuberculosis biofilm model. While exploring their mechanism of action, it was serendipitously observed that these 2-AI molecules also potentiated β-lactam antibiotics by affecting mycobacterial protein secretion and lipid export. As these two bacterial processes are energy-dependent, herein it was evaluated if 2-AI compounds affect mycobacterial bioenergetics. At low concentrations, 2B8, the lead 2-AI compound, collapsed both components of the proton motive force, similar to other cationic amphiphiles. Interestingly, however, the minimum inhibitory concentration of 2B8 against M . tuberculosis correlated with a higher drug concentration determined to interfere with the mycobacterial electron transport chain. Collectively, this study elucidates the mechanism of action of 2-AIs against M . tuberculosis , providing a tool to better understand mycobacterial bioenergetics and develop compounds with improved anti-mycobacterial activity.}, journal={SCIENTIFIC REPORTS}, author={Jeon, Albert Byungyun and Ackart, David F. and Li, Wei and Jackson, Mary and Melander, Roberta J. and Melander, Christian and Abramovitch, Robert B. and Chicco, Adam J. and Basaraba, Randall J. and Obregon-Henao, Andres}, year={2019}, month={Feb} }
@article{nguyen_minrovic_melander_melander_2019, title={Identification of Anti-Mycobacterial Biofilm Agents Based on the 2-Aminoimidazole Scaffold}, volume={14}, ISSN={["1860-7187"]}, DOI={10.1002/cmdc.201900033}, abstractNote={Tuberculosis (TB) remains a significant global health problem for which new therapeutic options are sorely needed. The ability of the causative agent, Mycobacterium tuberculosis, to reside within host macrophages and form biofilm-like communities contributes to the persistent and drug-tolerant nature of the disease. Compounds that can prevent or reverse the biofilm-like phenotype have the potential to serve alongside TB antibiotics to overcome this tolerance, and decrease treatment duration. Using Mycobacterium smegmatis as a surrogate organism, we report the identification of two new 2-aminoimidazole compounds that inhibit and disperse mycobacterial biofilms, work synergistically with isoniazid and rifampicin to eradicate preformed M. smegmatis biofilms in vitro, are nontoxic toward Galleria mellonella, and exhibit stability in mouse plasma.}, number={9}, journal={CHEMMEDCHEM}, author={Nguyen, T. Vu and Minrovic, Bradley M. and Melander, Roberta J. and Melander, Christian}, year={2019}, month={May}, pages={927–937} }
@article{martin_melander_brackett_scott_chandler_nguyen_minrovic_harrill_ernst_manoil_et al._2019, title={Small Molecule Potentiation of Gram-Positive Selective Antibiotics against Acinetobacter baumannii}, volume={5}, ISSN={["2373-8227"]}, DOI={10.1021/acsinfecdis.9b00067}, abstractNote={In 2016, the World Health Organization deemed antibiotic resistance one of the biggest threats to global health, food security, and development. The need for new methods to combat infections caused by antibiotic resistant pathogens will require a variety of approaches to identifying effective new therapeutic strategies. One approach is the identification of small molecule adjuvants that potentiate the activity of antibiotics of demonstrated utility, whose efficacy is abated by resistance, both acquired and intrinsic. To this end, we have identified compounds that enhance the efficacy of antibiotics normally ineffective against Gram-negative pathogens because of the outer membrane permeability barrier. We identified two adjuvant compounds that dramatically enhance sensitivity of Acinetobacter baumannii to macrolide and glycopeptide antibiotics, with reductions in minimum inhibitory concentrations as high as 256-fold, and we observed activity across a variety of clinical isolates. Mode of action studies indicate that these adjuvants likely work by modulating lipopolysaccharide synthesis or assembly. The adjuvants were active in vivo in a Galleria mellonella infection model, indicating potential for use in mammalian infections.}, number={7}, journal={ACS INFECTIOUS DISEASES}, author={Martin, Sara E. and Melander, Roberta J. and Brackett, Christopher M. and Scott, Alison J. and Chandler, Courtney E. and Nguyen, Catherine M. and Minrovic, Bradley M. and Harrill, Sarah E. and Ernst, Robert K. and Manoil, Colin and et al.}, year={2019}, month={Jul}, pages={1223–1230} }
@article{nguyen_peszko_melander_melander_2019, title={Using 2-aminobenzimidazole derivatives to inhibit Mycobacterium smegmatis biofilm formation}, volume={10}, ISSN={["2040-2511"]}, DOI={10.1039/c9md00025a}, abstractNote={Biofilm formation by mycobacteria can lead to enhanced antibiotic tolerance. Herein, we report on the identification of a series of 2-aminobenzimidazole (2-ABI) derivatives that potently inhibit biofilm formation by Mycobacterium smegmatis.}, number={3}, journal={MEDCHEMCOMM}, author={Nguyen, T. Vu and Peszko, Matthew T. and Melander, Roberta J. and Melander, Christian}, year={2019}, month={Mar}, pages={456–459} }
@article{hubble_hubbard_minrovic_melander_melander_2019, title={Using Small-Molecule Adjuvants to Repurpose Azithromycin for Use against Pseudomonas aeruginosa}, volume={5}, ISSN={["2373-8227"]}, DOI={10.1021/acsinfecdis.8b00288}, abstractNote={A major contributor to fatalities in cystic fibrosis (CF) patients stems from infection with opportunistic bacterium Pseudomonas aeruginosa. As a result of the CF patient’s vulnerability to bacterial infections, one of the main treatment focuses is antibiotic therapy. However, the highly adaptive nature of P. aeruginosa, in addition to the intrinsic resistance to many antibiotics exhibited by most Gram-negative bacteria, means that multi-drug-resistant (MDR) strains are increasingly prevalent. This makes the eradication of pseudomonal lung infections nearly impossible once the infection becomes chronic. New methods to treat pseudomonal infections are greatly needed in order to eradicate MDR bacteria found within the respiratory tract, and ultimately better the quality of life for CF patients. Herein, we describe a novel approach to combatting pseudomonal infections through the use of bis-2-aminoimidazole adjuvants that can potentiate the activity of a macrolide antibiotic commonly prescribed to CF patients as an anti-inflammatory agent. Our lead bis-2-AI exhibits a 1024-fold reduction in the minimum inhibitory concentration of azithromycin in vitro and displays activity in a Galleria mellonella model of infection.}, number={1}, journal={ACS INFECTIOUS DISEASES}, author={Hubble, Veronica B. and Hubbard, Brittany A. and Minrovic, Bradley M. and Melander, Roberta J. and Melander, Christian}, year={2019}, month={Jan}, pages={141–151} }
@misc{melander_zurawski_melander_2018, title={Narrow-spectrum antibacterial agents}, volume={9}, ISSN={["2040-2511"]}, DOI={10.1039/c7md00528h}, abstractNote={While broad spectrum antibiotics play an invaluable role in the treatment of bacterial infections, there are some drawbacks to their use, namely selection for and spread of resistance across multiple bacterial species, and the detrimental effect they can have upon the host microbiome. If the causitive agent of the infection is known, the use of narrow-spectrum antibacterial agents has the potential to mitigate some of these issues. This review outlines the advantages and challenges of narrow-spectrum antibacterial agents, discusses the progress that has been made toward developing diagnostics to enable their use, and describes some of the narrow-spectrum antibacterial agents currently being investigated against some of the most clinically important bacteria including Clostridium difficile, Mycobacterium tuberculosis and several ESKAPE pathogens.}, number={1}, journal={MEDCHEMCOMM}, author={Melander, Roberta J. and Zurawski, Daniel V. and Melander, Christian}, year={2018}, month={Jan}, pages={12–21} }
@article{milton_minrovic_harris_kang_jung_lewis_thompson_melander_zeng_melander_et al._2018, title={Re-sensitizing Multidrug Resistant Bacteria to Antibiotics by Targeting Bacterial Response Regulators: Characterization and Comparison of Interactions between 2-Aminoimidazoles and the Response Regulators BfmR from Acinetobacter baumannii and QseB from Francisella spp.}, volume={5}, ISSN={["2296-889X"]}, DOI={10.3389/fmolb.2018.00015}, abstractNote={2-aminoimidazole (2-AI) compounds inhibit the formation of bacterial biofilms, disperse preformed biofilms, and re-sensitize multidrug resistant bacteria to antibiotics. 2-AIs have previously been shown to interact with bacterial response regulators, but the mechanism of interaction is still unknown. Response regulators are one part of two-component systems (TCS). TCSs allow cells to respond to changes in their environment, and are used to trigger quorum sensing, virulence factors, and antibiotic resistance. Drugs that target the TCS signaling process can inhibit pathogenic behavior, making this a potent new therapeutic approach that has not yet been fully exploited. We previously laid the groundwork for the interaction of the Acinetobacter baumannii response regulator BfmR with an early 2-AI derivative. Here, we further investigate the response regulator/2-AI interaction and look at a wider library of 2-AI compounds. By combining molecular modeling with biochemical and cellular studies, we expand on a potential mechanism for interaction between response regulators and 2-AIs. We also establish that Francisella tularensis/novicida, encoding for only three known response regulators, can be a model system to study the interaction between 2-AIs and response regulators. We show that knowledge gained from studying Francisella can be applied to the more complex A. baumannii system, which contains over 50 response regulators. Understanding the impact of 2-AIs on response regulators and their mechanism of interaction will lead to the development of more potent compounds that will serve as adjuvant therapies to broad-range antibiotics.}, journal={FRONTIERS IN MOLECULAR BIOSCIENCES}, author={Milton, Morgan E. and Minrovic, Bradley M. and Harris, Danni L. and Kang, Brian and Jung, David and Lewis, Caleb P. and Thompson, Richele J. and Melander, Roberta J. and Zeng, Daina and Melander, Christian and et al.}, year={2018}, month={Feb} }
@article{jeon_obregon-henao_ackart_podell_belardinelli_jackson_nguyen_blackledge_melander_melander_et al._2017, title={2-aminoimidazoles potentiate beta-lactam antimicrobial activity against Mycobacterium tuberculosis by reducing beta-lactamase secretion and increasing cell envelope permeability}, volume={12}, number={7}, journal={PLoS One}, author={Jeon, A. B. and Obregon-Henao, A. and Ackart, D. F. and Podell, B. K. and Belardinelli, J. M. and Jackson, M. and Nguyen, T. V. and Blackledge, M. S. and Melander, R. J. and Melander, C. and et al.}, year={2017} }
@article{yuen_walper_melde_daniele_stenger_2017, title={Electrolyte-sensing transistor decals enabled by ultrathin microbial nanocellulose}, volume={7}, journal={Scientific Reports}, author={Yuen, J. D. and Walper, S. A. and Melde, B. J. and Daniele, M. A. and Stenger, D. A.}, year={2017} }
@article{draughn_allen_routh_stone_kirker_boegli_schuchman_linder_baynes_james_et al._2017, title={Evaluation of a 2-aminoimidazole variant as adjuvant treatment for dermal bacterial infections}, volume={11}, journal={Drug Design Development and Therapy}, author={Draughn, G. L. and Allen, C. L. and Routh, P. A. and Stone, M. R. and Kirker, K. R. and Boegli, A. and Schuchman, R. M. and Linder, K. E. and Baynes, R. E. and James, G. and et al.}, year={2017}, pages={153–162} }
@article{byrne-nash_lucero_osbaugh_melander_melander_feldheim_2017, title={Probing the Mechanism of LAL-32, a Gold Nanoparticle-Based Antibiotic Discovered through Small Molecule Variable Ligand Display}, volume={28}, ISSN={["1043-1802"]}, DOI={10.1021/acs.bioconjchem.7b00199}, abstractNote={The unrelenting rise of antimicrobial-resistant bacteria has necessitated the search for novel antibiotic solutions. Herein we describe further mechanistic studies on a 2.0-nm-diameter gold nanoparticle-based antibiotic (designated LAL-32). This antibiotic exhibits bactericidal activity against the Gram-negative bacterium Escherichia coli at 1.0 μM, a concentration significantly lower than several clinically available antibiotics (such as ampicillin and gentamicin), and acute treatment with LAL-32 does not give rise to spontaneous resistant mutants. LAL-32 treatment inhibits cellular division, daughter cell separation, and twin-arginine translocation (Tat) pathway dependent shuttling of proteins to the periplasm. Furthermore, we have found that the cedA gene imparts increased resistance to LAL-32, and shown that an E. coli cedA transposon mutant exhibits increased susceptibility to LAL-32. Taken together, these studies further implicate cell division pathways as the target for this nanoparticle-based antibiotic and demonstrate that there may be inherently higher barriers for resistance evolution against nanoscale antibiotics in comparison to their small molecule counterparts.}, number={7}, journal={BIOCONJUGATE CHEMISTRY}, author={Byrne-Nash, Rose and Lucero, Danielle M. and Osbaugh, Niki A. and Melander, Roberta J. and Melander, Christian and Feldheim, Daniel L.}, year={2017}, month={Jul}, pages={1807–1810} }
@article{barker_martin_chandler_nguyen_harris_goodell_melander_doi_ernst_melander_2017, title={Small molecule adjuvants that suppress both chromosomal and mcr-1 encoded colistin-resistance and amplify colistin efficacy in polymyxin-susceptible bacteria}, volume={25}, ISSN={["1464-3391"]}, DOI={10.1016/j.bmc.2017.08.055}, abstractNote={Bacterial resistance to polymyxin antibiotics has taken on a new and more menacing form. Common are genomically-encoded resistance mechanisms to polymyxins, specifically colistin (polymyxin E), however, the plasmid-borne mobile colistin resistance-1 (mcr-1) gene has recently been identified and poses a new threat to global public health. Within six months of initial identification in Chinese swine in November 2015, the first human clinical isolation in the US was reported (Apr. 2016). Herein we report successful reversion of mcr-1-driven colistin resistance in Acinetobacter baumannii, Klebsiella pneumoniae, and Escherichia coli with adjuvants we previously reported as modulators of chromosomally-encoded colistin resistance. Further screening of our in-house library of nitrogen-dense heterocycles has identified additional chemical scaffolds that actively attenuate colistin resistance. Ultimately, we present a diverse cohort of adjuvants that both sensitize colistin-resistant and colistin-susceptible bacteria to this antibiotic, thus providing a potential avenue to both reduce colistin dosage and toxicity, and overcome colistin resistance.}, number={20}, journal={BIOORGANIC & MEDICINAL CHEMISTRY}, author={Barker, William T. and Martin, Sara E. and Chandler, Courtney E. and Nguyen, T. Vu. and Harris, Tyler L. and Goodell, Christopher and Melander, Roberta J. and Doi, Yohei and Ernst, Robert K. and Melander, Christian}, year={2017}, month={Oct}, pages={5749–5753} }
@article{milton_allen_feldmann_bobay_jung_stephens_melander_theisen_zeng_thompson_et al._2017, title={Structure of the Francisella response regulator QseB receiver domain, and characterization of QseB inhibition by antibiofilm 2-aminoimidazole-based compounds}, volume={106}, ISSN={["1365-2958"]}, DOI={10.1111/mmi.13759}, abstractNote={With antibiotic resistance increasing at alarming rates, targets for new antimicrobial therapies must be identified. A particularly promising target is the bacterial two-component system. Two-component systems allow bacteria to detect, evaluate and protect themselves against changes in the environment, such as exposure to antibiotics and also to trigger production of virulence factors. Drugs that target the response regulator portion of two-component systems represent a potent new approach so far unexploited. Here, we focus efforts on the highly virulent bacterium Francisella tularensis tularensis. Francisella contains only three response regulators, making it an ideal system to study. In this study, we initially present the structure of the N-terminal domain of QseB, the response regulator responsible for biofilm formation. Subsequently, using binding assays, computational docking and cellular studies, we show that QseB interacts with2-aminoimidazole based compounds that impede its function. This information will assist in tailoring compounds to act as adjuvants that will enhance the effect of antibiotics.}, number={2}, journal={MOLECULAR MICROBIOLOGY}, author={Milton, Morgan E. and Allen, C. Leigh and Feldmann, Erik A. and Bobay, Benjamin G. and Jung, David K. and Stephens, Matthew D. and Melander, Roberta J. and Theisen, Kelly E. and Zeng, Daina and Thompson, Richele J. and et al.}, year={2017}, month={Oct}, pages={223–235} }
@article{garcia_blackledge_michalek_su_ptacek_eipers_morrow_lefkowitz_melander_wu_2017, title={Targeting of Streptococcus mutans Biofilms by a Novel Small Molecule Prevents Dental Caries and Preserves the Oral Microbiome}, volume={96}, ISSN={["1544-0591"]}, DOI={10.1177/0022034517698096}, abstractNote={Dental caries is a costly and prevalent disease characterized by the demineralization of the tooth's enamel. Disease outcome is influenced by host factors, dietary intake, cariogenic bacteria, and other microbes. The cariogenic bacterial species Streptococcus mutans metabolizes sucrose to initiate biofilm formation on the tooth surface and consequently produces lactic acid to degrade the tooth's enamel. Persistence of S. mutans biofilms in the oral cavity can lead to tooth decay. To date, no anticaries therapies that specifically target S. mutans biofilms but do not disturb the overall oral microbiome are available. We screened a library of 2-aminoimidazole antibiofilm compounds with a biofilm dispersion assay and identified a small molecule that specifically targets S. mutans biofilms. At 5 µM, the small molecule annotated 3F1 dispersed 50% of the established S. mutans biofilm but did not disperse biofilms formed by the commensal species Streptococcus sanguinis or Streptococcus gordonii. 3F1 dispersed S. mutans biofilms independently of biofilm-related factors such as antigen I/II and glucosyltransferases. 3F1 treatment effectively prevented dental caries by controlling S. mutans in a rat caries model without perturbing the oral microbiota. Our study demonstrates that selective targeting of S. mutans biofilms by 3F1 was able to effectively reduce dental caries in vivo without affecting the overall oral microbiota shaped by the intake of dietary sugars, suggesting that the pathogenic biofilm-specific treatment is a viable strategy for disease prevention.}, number={7}, journal={JOURNAL OF DENTAL RESEARCH}, author={Garcia, S. S. and Blackledge, M. S. and Michalek, S. and Su, L. and Ptacek, T. and Eipers, P. and Morrow, C. and Lefkowitz, E. J. and Melander, C. and Wu, H.}, year={2017}, month={Jul}, pages={807–814} }
@article{melander_melander_2017, title={The Challenge of Overcoming Antibiotic Resistance: An Adjuvant Approach?}, volume={3}, ISSN={["2373-8227"]}, DOI={10.1021/acsinfecdis.7b00071}, abstractNote={Antibiotic resistance is one of the greatest current threats to human health, and without significant action we face the chilling prospect of a world without effective antibiotics. Although continued effort toward the development of new antibiotics, particularly those with novel mechanisms of action, remains crucial, this alone probably will not be enough to prevail, and it is imperative that additional approaches are also explored. One such approach is the identification of adjuvants that augment the activity of current antibiotics. This approach has the potential to render an antibiotic against which bacteria have developed resistance once again effective, to broaden the spectrum of an antibiotic, and to lower the required dose of an antibiotic. In this viewpoint we discuss some of the advantages and disadvantages of the use of adjuvants, and describe various approaches to their identification.}, number={8}, journal={ACS INFECTIOUS DISEASES}, author={Melander, Roberta J. and Melander, Christian}, year={2017}, month={Aug}, pages={559–563} }
@article{nguyen_blackledge_lindsey_minrovic_ackart_jeon_obregon-henao_melander_basaraba_melander_2017, title={The Discovery of 2-Aminobenzimidazoles That Sensitize Mycobacterium smegmatis and M. tuberculosis to beta-Lactam Antibiotics in a Pattern Distinct from beta-Lactamase Inhibitors}, volume={56}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201612006}, abstractNote={A library of 2-aminobenzimidazole derivatives was screened for the ability to suppress β-lactam resistance in Mycobacterium smegmatis. Several non-bactericidal compounds were identified that reversed intrinsic resistance to β-lactam antibiotics in a manner distinct from β-lactamase inhibitors. Activity also translates to M. tuberculosis, with a lead compound from this study potently suppressing carbenicillin resistance in multiple M. tuberculosis strains (including multidrug-resistant strains). Preliminary mechanistic studies revealed that the lead compounds act through a mechanism distinct from that of traditional β-lactamase inhibitors.}, number={14}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Nguyen, T. Vu and Blackledge, Meghan S. and Lindsey, Erick A. and Minrovic, Bradley M. and Ackart, David F. and Jeon, Albert B. and Obregon-Henao, Andres and Melander, Roberta J. and Basaraba, Randall J. and Melander, Christian}, year={2017}, month={Mar}, pages={3940–3944} }
@article{stephens_yodsanit_melander_2016, title={Evaluation of ethyl N-(2-phenethyl) carbamate analogues as biofilm inhibitors of methicillin resistant Staphylococcus aureus}, volume={14}, ISSN={["1477-0539"]}, DOI={10.1039/c6ob00706f}, abstractNote={A small molecule library consisting of 45 compounds was synthesized based on the bacterial metabolite ethyl N-(2-phenethyl) carbamate. Screening of the compounds revealed a potent analogue capabale of inhibiting several strains of Methicillin Resistant S. aureus biofilms with low to moderate micromolar IC50 values.}, number={28}, journal={ORGANIC & BIOMOLECULAR CHEMISTRY}, author={Stephens, Matthew D. and Yodsanit, Nisakorn and Melander, Christian}, year={2016}, pages={6853–6856} }
@article{melander_liu_stephens_bewley_melander_2016, title={Marine sponge alkaloids as a source of anti-bacterial adjuvants}, volume={26}, ISSN={["1464-3405"]}, DOI={10.1016/j.bmcl.2016.11.018}, abstractNote={Novel approaches that do not rely upon developing microbicidal compounds are sorely needed to combat multidrug resistant (MDR) bacteria. The potential of marine secondary metabolites to serve as a source of non-traditional anti-bacterial agents is demonstrated by showing that pyrrole-imidazole alkaloids inhibit biofilm formation and suppress antibiotic resistance.}, number={24}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Melander, Roberta J. and Liu, Hong-bing and Stephens, Matthew D. and Bewley, Carole A. and Melander, Christian}, year={2016}, month={Dec}, pages={5863–5866} }
@article{stephens_hubble_ernst_hoek_melander_cavanagh_melander_2016, title={Potentiation of Francisella resistance to conventional antibiotics through small molecule adjuvants}, volume={7}, ISSN={["2040-2511"]}, DOI={10.1039/c5md00353a}, abstractNote={A screen of 20 compounds identified small molecule adjuvants capable of potentiating anitbiotic activty against Francisella philomiragia. Analogue synthesis of an initial hit compound led to the discovery of a potentially new class of small molecule adjuvants containg an indole core. The lead compound was able to lower the MIC of colistin by 32-fold against intrinsically resistant F. philomiragia.}, number={1}, journal={MEDCHEMCOMM}, author={Stephens, Matthew D. and Hubble, Veroncia B. and Ernst, Robert K. and Hoek, Monique L. and Melander, Roberta J. and Cavanagh, John and Melander, Christian}, year={2016}, pages={128–131} }
@article{stephens_yodsanit_melander_2016, title={Potentiation of the fosmidomycin analogue FR 900098 with substituted 2-oxazolines against Francisella novicida}, volume={7}, ISSN={["2040-2511"]}, DOI={10.1039/c6md00365f}, abstractNote={A library of 33 compounds was screened for potentiation of the antibiotic FR 900098 against the Francisella tularensis surrogate Francisella novicida.}, number={10}, journal={MEDCHEMCOMM}, author={Stephens, Matthew D. and Yodsanit, Nisakorn and Melander, Christian}, year={2016}, pages={1952–1956} }
@article{brackett_furlani_anderson_krishnamurthy_melander_moskowitz_ernst_melander_2016, title={Second generation modifiers of colistin resistance show enhanced activity and lower inherent toxicity}, volume={72}, ISSN={["0040-4020"]}, DOI={10.1016/j.tet.2015.09.019}, abstractNote={We recently reported a 2-aminoimidazole-based antibiotic adjuvant that reverses colistin resistance in two species of Gram-negative bacteria. Mechanistic studies in Acinetobacter baumannii demonstrated that this compound downregulated the PmrAB two-component system and abolished a lipid A modification that is required for colistin resistance. We now report the synthesis and evaluation of two separate libraries of substituted 2-aminoimidazole analogues based on this parent compound. From these libraries, a new small molecule was identified that lowers the minimum inhibitory concentration of colistin by up to 32-fold greater than the parent compound while also displaying less inherent bacterial effect, thereby minimizing the likelihood of resistance evolution.}, number={25}, journal={TETRAHEDRON}, author={Brackett, Christopher M. and Furlani, Robert E. and Anderson, Ryan G. and Krishnamurthy, Aparna and Melander, Roberta J. and Moskowitz, Samuel M. and Ernst, Robert K. and Melander, Christian}, year={2016}, month={Jun}, pages={3549–3553} }
@article{pan_fan_wu_melander_liu_2015, title={A new small molecule inhibits Streptococcus mutans biofilms invitro and in vivo}, volume={119}, DOI={10.1111/jam.12940}, abstractNote={The aim of this study was to identify new small molecules that can inhibit Streptococcus mutans biofilms by in vitro and in vivo model.We evaluated the effect of a small molecule 2-amino-imidazole/triazole conjugate (2-AI/T) on the formation of Strep. mutans biofilms by culturing in 96-well plates. Toxicity was assessed through cell culture and intragastrically administering to mice. The anti-biofilm and anti-caries effects were investigated in vivo. The inhibitive mechanism was detected by isobaric tag for relative and absolute quantification (itraq) and RT-QPCR. In vitro and in vivo study revealed that 2-AI/T significantly inhibited biofilm formation of Strep. mutans and is more so than inhibiting planktonic cells without toxicity. The ribosome and histidine metabolism pathways of Strep. mutans were significantly regulated by this compound.These results suggest that the 2-AI/T conjugate is a potent inhibitor that can be potentially developed into a new drug to treat and prevent dental caries.This is the first study to use small molecule from marine natural products, to protect from dental caries in vivo. It has potential broad range application in clinical caries prevention, or as a bioactive ingredient for food applications.}, number={5}, journal={Journal of Applied Microbiology}, author={Pan, W. and Fan, M. and Wu, H. and Melander, C. and Liu, C.}, year={2015}, pages={1403–1411} }
@article{wahome_beauchesne_pedone_cavanagh_melander_zimba_moeller_2015, title={Augmenting anti-cancer natural products with a small molecule adjuvant}, volume={13}, number={1}, journal={Marine Drugs}, author={Wahome, P. G. and Beauchesne, K. R. and Pedone, A. C. and Cavanagh, J. and Melander, C. and Zimba, P. and Moeller, P. D. R.}, year={2015}, pages={65–75} }
@article{melander_melander_2015, title={From Worms to Targeting Virulence Factors}, volume={22}, ISSN={["1879-1301"]}, DOI={10.1016/j.chembiol.2015.04.005}, abstractNote={Rising antibiotic resistance means that alternative antibacterial strategies are sorely needed. In this issue, Zhu et al. (2015) report the use of a Caenorhabditis elegans model to validate the Pseudomonas aeruginosa virulence factor LasB as a potential therapeutic target and to identify a LasB inhibitor with in vivo efficacy.}, number={4}, journal={CHEMISTRY & BIOLOGY}, author={Melander, Roberta J. and Melander, Christian}, year={2015}, month={Apr}, pages={436–437} }
@article{garrido_simpson_dahl_bresee_whitehead_lindsey_harris_smith_carter_feldheim_et al._2015, title={Gold nanoparticles to improve HIV drug delivery}, volume={7}, ISSN={["1756-8927"]}, DOI={10.4155/fmc.15.57}, abstractNote={Background: Antiretroviral therapy (ART) has improved lifespan and quality of life of patients infected with the HIV-1. However, ART has several potential limitations, including the development of drug resistance and suboptimal penetration to selected anatomic compartments. Improving the delivery of antiretroviral molecules could overcome several of the limitations of current ART. Results & Conclusion: Two to ten nanometer diameter inorganic gold crystals serve as a base scaffold to combine molecules with an array of properties in its surface. We show entry into different cell types, antiviral activity of an HIV integrase inhibitor conjugated in a gold nanoparticle and penetration into the brain in vivo without toxicity. Herein, gold nanoparticles prove to be a promising tool to use in HIV therapy.}, number={9}, journal={FUTURE MEDICINAL CHEMISTRY}, author={Garrido, Carolina and Simpson, Carrie A. and Dahl, Noelle P. and Bresee, Jamee and Whitehead, Daniel C. and Lindsey, Erick A. and Harris, Tyler L. and Smith, Candice A. and Carter, Carly J. and Feldheim, Daniel L. and et al.}, year={2015}, pages={1097–1107} }
@article{richardson_furlani_podell_ackart_haugen_melander_melander_basaraba_2015, title={Inhibition and breaking of advanced glycation end-products (AGEs) with bis-2-aminoimidazole derivatives}, volume={56}, ISSN={["0040-4039"]}, DOI={10.1016/j.tetlet.2015.01.122}, abstractNote={Advanced glycation end-products (AGEs), unregulated modifications to host macromolecules that occur as a result of metabolic dysregulation, play a role in many diabetes related complications, inflammation and aging, and may lead to increased cardiovascular risk. Small molecules that have the ability to inhibit AGE formation, and even break preformed AGEs have enormous therapeutic potential in the treatment of these disease states. We report the screening of a series of 2-aminoimidazloles for anti-AGE activity, and the identification of a bis-2-aminoimidazole lead compound that possesses superior AGE inhibition and breaking activity compared to the known AGE inhibitor aminoguanidine.}, number={23}, journal={TETRAHEDRON LETTERS}, author={Richardson, Mike A. and Furlani, Robert E. and Podell, Brendan K. and Ackart, David F. and Haugen, Jessica D. and Melander, Roberta J. and Melander, Christian and Basaraba, Randall J.}, year={2015}, month={Jun}, pages={3406–3409} }
@article{melander_melander_2015, title={Innovative strategies for combating biofilm-based infections}, volume={831}, journal={Biofilm-based healthcare-associated infections, vol ii}, author={Melander, R. J. and Melander, C.}, year={2015}, pages={69–91} }
@article{stowe_thompson_peng_su_blackledge_draughn_coe_johannes_lapham_mackenzie_et al._2015, title={Membrane-Permeabilizing Activity of Reverse-Amide 2-Aminoimidazole Antibiofilm Agents Against Acinetobacter baumannii}, volume={12}, ISSN={["1875-5704"]}, DOI={10.2174/1567201811666140924125740}, abstractNote={Acinetobacter baumannii has quickly become one of the most insidious and prevalent nosocomial infections. Recently, the reverse-amide class of 2-aminoimidazole compounds (RA-2AI) was found both to prevent A. baumannii biofilm formation and also to disperse preexisting formations, putatively through interactions with cytosolic response regulators. Here we focus on how this class of antibiofilm agent traverses cellular membranes. Following the discovery of dosage-dependent growth rate changes, the cellular effects of RA-2AI were investigated using a combination of molecular assays and microscopic techniques. It was found that RA-2AI exposure has measureable effects on the bacterial membranes, resulting in a period of increased permeability and visible structural aberrations. Based on these results, we propose a model that describes how the structure of RA-2AI allows it to insert itself into and disrupt the fluidity of the membrane, creating an opportunity for increased molecular permeability. Keywords: 2-aminoimidazole, Acinetobacter baumannii, biofilm, membrane permeabilization, reverse amide, SEM.}, number={2}, journal={CURRENT DRUG DELIVERY}, author={Stowe, Sean D. and Thompson, Richele J. and Peng, Lingling and Su, Zhaoming and Blackledge, Meghan S. and Draughn, G. Logan and Coe, William H. and Johannes, Eva and Lapham, Valerie K. and Mackenzie, John and et al.}, year={2015}, pages={223–230} }
@article{furlani_richardson_podell_ackart_haugen_melander_basaraba_melander_2015, title={Second generation 2-aminoimidazole based advanced glycation end product inhibitors and breakers}, volume={25}, ISSN={["1464-3405"]}, DOI={10.1016/j.bmcl.2015.06.080}, abstractNote={The formation of advanced glycation end-products (AGE) as a result of the action of reducing sugars on host macromolecules plays a role in increased morbidity of diabetic patients. There are currently no clinically available therapeutics for the prevention or eradication of AGEs. Following our previous identification of 2-aminoimidazole (2-AI) based AGE inhibitors and breakers, we now report the use of a rapid, scalable, two-step procedure to access a second generation of 2-AI based anti-AGE compounds from commercially available amino acids. Several second generation compounds exhibit increased AGE inhibition and breaking activty compared to the first generation compounds and to the known AGE inhibitor aminoguanidine.}, number={21}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Furlani, Robert E. and Richardson, Mike A. and Podell, Brendan K. and Ackart, David F. and Haugen, Jessica D. and Melander, Roberta J. and Basaraba, Randall J. and Melander, Christian}, year={2015}, month={Nov}, pages={4820–4823} }
@article{melander_minvielle_melander_2014, title={Controlling bacterial behavior with indole-containing natural products and derivatives}, volume={70}, ISSN={["0040-4020"]}, DOI={10.1016/j.tet.2014.05.089}, abstractNote={Indole has recently been implicated as an important small molecule signal utilized by many bacteria to coordinate various forms of behavior. Indole plays a role in numerous bacterial processes, including: biofilm formation and maintenance, virulence factor production, antibiotic resistance and persister cell formation. Intercepting indole-signaling pathways with appropriately designed small molecules provides a n opportunity to control unwanted bacterial behaviors, and is an attractive anti-virulence therapeutic strategy. In this review, we give an overview of the process controlled by indole signaling, and summarize current efforts to design indole-containing small molecules to intercept these pathways, and detail the synthetic efforts towards accessing indole derived bioactive small molecules.}, number={37}, journal={TETRAHEDRON}, author={Melander, Roberta J. and Minvielle, Marine J. and Melander, Christian}, year={2014}, month={Sep}, pages={6363–6372} }
@article{ackart_hascall-dove_caceres_kirk_podell_melander_orme_leid_nick_basaraba_2014, title={Expression of antimicrobial drug tolerance by attached communities of Mycobacterium tuberculosis}, volume={70}, ISSN={["2049-632X"]}, DOI={10.1111/2049-632x.12144}, abstractNote={There is an urgent need to improve methods used to screen antituberculosis drugs. An in vitro assay was developed to test drug treatment strategies that specifically target drug-tolerant Mycobacterium tuberculosis. The H37Rv strain of M. tuberculosis survived antimicrobial treatment as attached microbial communities when maintained in tissue culture media (RPMI-1640) with or without lysed human peripheral blood leukocytes. When cultured planktonically in the presence of Tween-80, bacilli failed to form microbial communities or reach logarithmic phase growth yet remained highly susceptible to antimicrobial drugs. In the absence of Tween, bacilli tolerated drug therapy by forming complex microbial communities attached to untreated well surfaces or to the extracellular matrix derived from lysed human leukocytes. Treatment of microbial communities with DNase I or Tween effectively dispersed bacilli and restored drug susceptibility. These data demonstrate that in vitro expression of drug tolerance by M. tuberculosis is linked to the establishment of attached microbial communities and that dispersion of bacilli targeting the extracellular matrix including DNA restores drug susceptibility. Modifications of this in vitro assay may prove beneficial in a high-throughput platform to screen new antituberculosis drugs especially those that target drug-tolerant bacilli.}, number={3}, journal={PATHOGENS AND DISEASE}, author={Ackart, David F. and Hascall-Dove, Laurel and Caceres, Silvia M. and Kirk, Natalie M. and Podell, Brendan K. and Melander, Christian and Orme, Ian M. and Leid, Jeff G. and Nick, Jerry A. and Basaraba, Randall J.}, year={2014}, month={Apr}, pages={359–369} }
@article{bresee_bond_worthington_smith_gifford_simpson_carter_wang_hartman_osbaugh_et al._2014, title={Nanoscale Structure-Activity Relationships, Mode of Action, and Biocompatibility of Gold Nanoparticle Antibiotics}, volume={136}, ISSN={["0002-7863"]}, DOI={10.1021/ja408505n}, abstractNote={The emergence of resistance to multiple antimicrobial agents by pathogenic bacteria has become a significant global public health threat. Multi-drug-resistant (MDR) Gram-negative bacteria have become particularly problematic, as no new classes of small-molecule antibiotics for Gram-negative bacteria have emerged in over two decades. We have developed a combinatorial screening process for identifying mixed ligand monolayer/gold nanoparticle conjugates (2.4 nm diameter) with antibiotic activity. The method previously led to the discovery of several conjugates with potent activity against the Gram-negative bacterium Escherichia coli. Here we show that these conjugates are also active against MDR E. coli and MDR Klebsiella pneumoniae. Moreover, we have shown that resistance to these nanoparticles develops significantly more slowly than to a commercial small-molecule drug. These results, combined with their relatively low toxicity to mammalian cells and biocompatibility in vivo, suggest that gold nanoparticles may be viable new candidates for the treatment of MDR Gram-negative bacterial infections.}, number={14}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Bresee, Jamee and Bond, Constance M. and Worthington, Roberta J. and Smith, Candice A. and Gifford, Jennifer C. and Simpson, Carrie A. and Carter, Carly J. and Wang, Guankui and Hartman, Jesse and Osbaugh, Niki A. and et al.}, year={2014}, month={Apr}, pages={5295–5300} }
@article{ackart_lindsey_podell_melander_basaraba_melander_2014, title={Reversal of Mycobacterium tuberculosis phenotypic drug resistance by 2-aminoimidazole- based small molecules}, volume={70}, ISSN={["2049-632X"]}, DOI={10.1111/2049-632x.12143}, abstractNote={The expression of phenotypic drug resistance or drug tolerance serves as a strategy for Mycobacterium tuberculosis to survive in vivo antimicrobial drug treatment; however, the mechanisms are poorly understood. Progress toward a more in depth understanding of in vivo drug tolerance and the discovery of new therapeutic strategies designed specifically to treat drug-tolerant M. tuberculosis are hampered by the lack of appropriate in vitro assays. A library of 2-aminoimidazole-based small molecules combined with the antituberculosis drug isoniazid was screened against M. tuberculosis expressing in vitro drug tolerance as microbial communities attached to an extracellular matrix derived from lysed leukocytes. Based on the ability of nine of ten 2-aminoimidazole compounds to inhibit Mycobacterium smegmatis biofilm formation and three of ten molecules capable of dispersing established biofilms, two active candidates and one inactive control were tested against drug-tolerant M. tuberculosis. The two active compounds restored isoniazid susceptibility as well as reduced the in vitro minimum inhibitory concentrations of isoniazid in a dose-dependent manner. The dispersion of drug-tolerant M. tuberculosis with 2-aminoimidazole-based small molecules as an adjunct to antimicrobial treatment has the potential to be an effective antituberculosis treatment strategy designed specifically to eradicate drug-tolerant M. tuberculosis. A class of small molecular weight compounds known to inhibit bacterial biofilms was shown to reverse the in vitro expression of antimicrobial resistance in Mycobacterium tuberculosis.}, number={3}, journal={PATHOGENS AND DISEASE}, author={Ackart, David F. and Lindsey, Erick A. and Podell, Brendan K. and Melander, Roberta J. and Basaraba, Randall J. and Melander, Christian}, year={2014}, month={Apr}, pages={370–378} }
@article{harris_worthington_hittle_zurawski_ernst_melander_2014, title={Small Molecule Downregulation of PmrAB Reverses Lipid A Modification and Breaks Colistin Resistance}, volume={9}, ISSN={["1554-8937"]}, DOI={10.1021/cb400490k}, abstractNote={Infections caused by multi-drug resistant bacteria, particularly Gram-negative bacteria, are an ever-increasing problem. While the development of new antibiotics remains one option in the fight against bacteria that have become resistant to currently available antibiotics, an attractive alternative is the development of adjuvant therapeutics that restore the efficacy of existing antibiotics. We report a small molecule adjuvant that suppresses colistin resistance in multidrug resistant Acinetobacter baumannii and Klebsiella pneumoniae by interfering with the expression of a two-component system. The compound downregulates the pmrCAB operon and reverses phosphoethanolamine modification of lipid A responsible for colistin resistance. Furthermore, colistin-susceptible and colistin-resistant bacteria do not evolve resistance to combination treatment. This represents the first definitive example of a compound that breaks antibiotic resistance by directly modulating two-component system activity.}, number={1}, journal={ACS CHEMICAL BIOLOGY}, author={Harris, Tyler L. and Worthington, Roberta J. and Hittle, Lauren E. and Zurawski, Daniel V. and Ernst, Robert K. and Melander, Christian}, year={2014}, month={Jan}, pages={122–127} }
@article{brackett_melander_an_krishnamurthy_thompson_cavanagh_melander_2014, title={Small-Molecule Suppression of beta-Lactam Resistance in Multidrug-Resistant Gram-Negative Pathogens}, volume={57}, ISSN={["1520-4804"]}, DOI={10.1021/jm501050e}, abstractNote={Recent efforts toward combating antibiotic resistance in bacteria have focused on Gram-positive bacteria; however, multidrug-resistant Gram-negative bacteria pose a significant risk to public health. An orthogonal approach to the development of new antibiotics is to develop adjuvant compounds that enhance the susceptibility of drug-resistant strains of bacteria to currently approved antibiotics. This paper describes the synthesis and biological activity of a library of aryl amide 2-aminoimidazoles based on a lead structure from an initial screen. A small molecule was identified from this library that is capable of lowering the minimum inhibitory concentration of β-lactam antibiotics by up to 64-fold.}, number={17}, journal={JOURNAL OF MEDICINAL CHEMISTRY}, author={Brackett, Christopher M. and Melander, Roberta J. and An, Il Hwan and Krishnamurthy, Aparna and Thompson, Richele J. and Cavanagh, John and Melander, Christian}, year={2014}, month={Sep}, pages={7450–7458} }
@article{gifford_bresee_carter_wang_melander_melander_feldheim_2014, title={Thiol-modified gold nanoparticles for the inhibition of Mycobacterium smegmatis}, volume={50}, ISSN={["1364-548X"]}, DOI={10.1039/c4cc06236a}, abstractNote={We demonstrate that Small Molecule Variable Ligand Display expanded around feed ratio parameter space identified gold nanoparticle conjugates that are potent inhibitors of mycobacterium growth, addressing a lack of innovative approaches to treat infections caused by mycobacteria such as TB.}, number={100}, journal={CHEMICAL COMMUNICATIONS}, author={Gifford, Jennifer C. and Bresee, Jamee and Carter, Carly Jo and Wang, Guankui and Melander, Roberta J. and Melander, Christian and Feldheim, Daniel L.}, year={2014}, pages={15860–15863} }
@article{furlani_yeagley_melander_2013, title={A flexible approach to 1,4-di-substituted 2-aminoimidazoles that inhibit and disperse biofilms and potentiate the effects of beta-lactams against multi-drug resistant bacteria}, volume={62}, ISSN={["1768-3254"]}, DOI={10.1016/j.ejmech.2012.12.005}, abstractNote={The pyrrole-imidazole alkaloids are a 2-aminoimidazoles containing family of natural products that possess anti-biofilm activity. A library of 1,4-di-substituted 2-aminoimidazole/triazoles (2-AITs) was synthesized, and its anti-biofilm activity as well as oxacillin resensitization efficacy toward methicillin resistant Staphylococcus aureus (MRSA) was investigated. These 2-AITs were found to inhibit biofilm formation by MRSA with low micromolar IC50 values. Additionally, the most active compound acted synergistically with oxacillin against MRSA lowering the minimum inhibitory concentration (MIC) 4-fold.}, journal={EUROPEAN JOURNAL OF MEDICINAL CHEMISTRY}, author={Furlani, Robert E. and Yeagley, Andrew A. and Melander, Christian}, year={2013}, month={Apr}, pages={59–70} }
@article{blackledge_worthington_melander_2013, title={Biologically inspired strategies for combating bacterial biofilms}, volume={13}, ISSN={["1471-4973"]}, DOI={10.1016/j.coph.2013.07.004}, abstractNote={Infections caused by bacterial biofilms are a significant global health problem, causing considerable patient morbidity and mortality and contributing to the economic burden of infectious disease. This review describes diverse strategies to combat bacterial biofilms, focusing firstly on small molecule interference with bacterial communication and signaling pathways, including quorum sensing and two-component signal transduction systems. Secondly we discuss enzymatic approaches to the degradation of extracellular matrix components to effect biofilm dispersal. Both of these approaches are based upon non-microbicidal mechanisms of action, and thereby do not place a direct evolutionary pressure on the bacteria to develop resistance. Such approaches have the potential to, in combination with conventional antibiotics, play an important role in the eradication of biofilm based bacterial infections.}, number={5}, journal={CURRENT OPINION IN PHARMACOLOGY}, author={Blackledge, Meghan S. and Worthington, Roberta J. and Melander, Christian}, year={2013}, month={Oct}, pages={699–706} }
@misc{worthington_melander_2013, title={Combination approaches to combat multidrug-resistant bacteria}, volume={31}, ISSN={["1879-3096"]}, DOI={10.1016/j.tibtech.2012.12.006}, abstractNote={The increasing prevalence of infections caused by multidrug-resistant bacteria is a global health problem that has been exacerbated by the dearth of novel classes of antibiotics entering the clinic over the past 40 years. Herein, we describe recent developments toward combination therapies for the treatment of multidrug-resistant bacterial infections. These efforts include antibiotic-antibiotic combinations, and the development of adjuvants that either directly target resistance mechanisms such as the inhibition of β-lactamase enzymes, or indirectly target resistance by interfering with bacterial signaling pathways such as two-component systems (TCSs). We also discuss screening of libraries of previously approved drugs to identify nonobvious antimicrobial adjuvants.}, number={3}, journal={TRENDS IN BIOTECHNOLOGY}, author={Worthington, Roberta J. and Melander, Christian}, year={2013}, month={Mar}, pages={177–184} }
@article{minvielle_eguren_melander_2013, title={Highly Active Modulators of Indole Signaling Alter Pathogenic Behaviors in Gram-Negative and Gram-Positive Bacteria}, volume={19}, ISSN={["1521-3765"]}, DOI={10.1002/chem.201303510}, abstractNote={Abstract Indole is a universal signal that regulates various bacterial behaviors, such as biofilm formation and antibiotic resistance. To generate mechanistic probes of indole signaling and control indole‐mediated pathogenic phenotypes in both Gram‐positive and Gram‐negative bacteria, we have investigated the use of desformylflustrabromine (dFBr) derivatives to generate highly active indole mimetics. We have developed non‐microbicidal dFBr derivatives that are 27–2000 times more active than indole in modulating biofilm formation, motility, acid resistance, and antibiotic resistance. The activity of these analogues parallels indole, because they are dependent on temperature, the enzyme tryptophanase TnaA, and the transcriptional regulator SdiA. This investigation demonstrates that molecules based on the dFBr scaffold can alter pathogenic behaviors by mimicking indole‐signaling pathways.}, number={51}, journal={CHEMISTRY-A EUROPEAN JOURNAL}, author={Minvielle, Marine J. and Eguren, Kristen and Melander, Christian}, year={2013}, month={Dec}, pages={17595–17602} }
@article{minvielle_bunders_melander_2013, title={Indole-triazole conjugates are selective inhibitors and inducers of bacterial biofilms}, volume={4}, ISSN={["2040-2511"]}, DOI={10.1039/c3md00064h}, abstractNote={Herein is described a method of accessing indole/triazole and benzothiophene/triazole analogues that selectively promote or inhibit biofilm formation by Gram-positive and Gram-negative bacteria. Structure/function studies revealed that the addition of a bromine atom at the 2-position of the indole/triazole scaffold altered activity against both Gram-negative and Gram-positive bacteria and could transform a biofilm inhibitor into a biofilm inducer. Isosteric replacement of the indole core by a benzothiophene significantly impaired anti-biofilm activity. A competition assay exposing Escherichia coli to the most potent biofilm inducer and an inhibitor of E. coli biofilm formation was performed. The inducer exhibited the ability to mute the effect of the anti-biofilm compound for this targeted bacterial population.}, number={6}, journal={MEDCHEMCOMM}, author={Minvielle, Marine J. and Bunders, Cynthia A. and Melander, Christian}, year={2013}, month={Jun}, pages={916–919} }
@article{yeagley_su_mccullough_worthington_melander_2013, title={N-Substituted 2-aminoimidazole inhibitors of MRSA biofilm formation accessed through direct 1,3-bis(tert-butoxycarbonyl)guanidine cyclization}, volume={11}, ISSN={["1477-0539"]}, DOI={10.1039/c2ob26469b}, abstractNote={Antibiotic resistance is a significant problem and is compounded by the ability of many pathogenic bacteria to form biofilms. A library of N-substituted derivatives of a previously reported 2-aminoimidazole/triazole (2-AIT) biofilm modulator was constructed via α-bromoketone cyclization with 1,3-bis(tert-butoxycarbonyl)guanidine, followed by selective substitution. Several compounds exhibited the ability to inhibit biofilm formation by three strong biofilm forming strains of methicillin resistant Staphylococcus aureus (MRSA). Additionally, a number of members of this library exhibited synergistic activity with oxacillin against planktonic MRSA. Compounds with this type of dual activity have the potential to be used as adjuvants with conventional antibiotics.}, number={1}, journal={ORGANIC & BIOMOLECULAR CHEMISTRY}, author={Yeagley, Andrew A. and Su, Zhaoming and McCullough, Kara D. and Worthington, Roberta J. and Melander, Christian}, year={2013}, pages={130–137} }
@article{worthington_melander_2013, title={Overcoming Resistance to beta-Lactam Antibiotics}, volume={78}, ISSN={["1520-6904"]}, DOI={10.1021/jo400236f}, abstractNote={β-Lactam antibiotics are one of the most important antibiotic classes but are plagued by problems of resistance, and the development of new β-lactam antibiotics through side-chain modification of existing β-lactam classes is not keeping pace with resistance development. In this JOCSynopsis, we summarize small molecule strategies to overcome resistance to β-lactam antibiotics. These approaches include the development of β-lactamase inhibitors and compounds that interfere with the ability of the bacteria to sense an antibiotic threat and activate their resistance mechanisms.}, number={9}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Worthington, Roberta J. and Melander, Christian}, year={2013}, month={May}, pages={4207–4213} }
@article{blackledge_melander_2013, title={Programmable DNA-binding small molecules}, volume={21}, ISSN={["0968-0896"]}, DOI={10.1016/j.bmc.2013.04.023}, abstractNote={Aberrant gene expression is responsible for a myriad of human diseases from infectious diseases to cancer. Precise regulation of these genes via specific interactions with the DNA double helix could pave the way for novel therapeutics. Pyrrole-imidazole polyamides are small molecules capable of binding to pre-determined DNA sequences up to 16 base pairs with affinity and specificity comparable to natural transcription factors. In the three decades since their development, great strides have been made relating to synthetic accessibility and improved sequence specificity and binding affinity. This perspective presents a brief history of early seminal developments in the field and highlights recent reports of the utility of polyamides as both genetic modulators and molecular probes.}, number={20}, journal={BIOORGANIC & MEDICINAL CHEMISTRY}, author={Blackledge, Meghan S. and Melander, Christian}, year={2013}, month={Oct}, pages={6101–6114} }
@misc{worthington_blackledge_melander_2013, title={Small-molecule inhibition of bacterial two-component systems to combat antibiotic resistance and virulence}, volume={5}, ISSN={["1756-8927"]}, DOI={10.4155/fmc.13.58}, abstractNote={Infections caused by multidrug-resistant bacteria are a considerable and increasing global problem. The development of new antibiotics is not keeping pace with the rapid evolution of resistance to almost all clinically available drugs, and novel strategies are required to fight bacterial infections. One such strategy is the control of pathogenic behaviors, as opposed to simply killing bacteria. Bacterial two-component system (TCS) signal transduction pathways control many pathogenic bacterial behaviors, such as virulence, biofilm formation and antibiotic resistance and are, therefore, an attractive target for the development of new drugs. This review presents an overview of TCS that are potential targets for such a strategy, describes small-molecules inhibitors of TCS identified to date and discusses assays for the identification of novel inhibitors. The future perspective for the identification and use of inhibitors of TCS to potentially provide new therapeutic options for the treatment of drug-resistant bacterial infections is discussed.}, number={11}, journal={FUTURE MEDICINAL CHEMISTRY}, author={Worthington, Roberta J. and Blackledge, Meghan S. and Melander, Christian}, year={2013}, month={Jul}, pages={1265–1284} }
@article{lindsey_worthington_alcaraz_melander_2012, title={2-Aminopyrimidine as a novel scaffold for biofilm modulation}, volume={10}, number={13}, journal={Organic & Biomolecular Chemistry}, author={Lindsey, E. A. and Worthington, R. J. and Alcaraz, C. and Melander, C.}, year={2012}, pages={2552–2561} }
@article{su_peng_melander_2012, title={A modular approach to the synthesis of 1,4,5-substituted-2-aminoimidazoles}, volume={53}, ISSN={["0040-4039"]}, DOI={10.1016/j.tetlet.2011.12.090}, abstractNote={Diversified 1,4,5-substituted-2-aminoimidazoles were rapidly assembled via sequential N–H insertion and Grignard addition to α-diazoesters. Lead compounds were identified as antibiotics against Gram-positive bacteria with an MIC value as low as 2 μg/mL.}, number={10}, journal={TETRAHEDRON LETTERS}, author={Su, Zhaoming and Peng, Lingling and Melander, Christian}, year={2012}, month={Mar}, pages={1204–1206} }
@article{worthington_melander_2012, title={Deconvoluting Interspecies Bacterial Communication}, volume={51}, ISSN={["1433-7851"]}, DOI={10.1002/anie.201202440}, abstractNote={The universal bacterial signal molecule autoinducer-2 (AI-2) is derived from 4,5-dihydroxy-2,3-pentanedione (DPD). DPD exists in a complex equilibrium between multiple forms (see scheme), and NMR spectroscopy has now been used to establish that the extent of the structural diversity displayed by DPD over a broad pH range is even greater than previously posited.}, number={26}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Worthington, Roberta J. and Melander, Christian}, year={2012}, pages={6314–6315} }
@article{stowe_tucker_thompson_piper_richards_rogers_mathies_melander_cavanagh_2012, title={Evaluation of the toxicity of 2-aminoimidazole antibiofilm agents using both cellular and model organism systems}, volume={35}, ISSN={["1525-6014"]}, DOI={10.3109/01480545.2011.614620}, abstractNote={Biofilm formation is a ubiquitous bacterial defense mechanism and has been shown to be a primary element in the antibiotic resistance of many human diseases, especially in the case of nosocomial infections. Recently, we have developed several compound libraries that are extremely effective at both dispersing preexisting biofilms and also inhibiting their initial formation. In addition to their antibiofilm properties, some of these molecules are able to resensitize resistant bacterial strains to previously ineffective antibiotics and are being assessed as adjuvants. In this study, we evaluated the toxic effects of three of our most effective 2-aminoimidazole compounds (dihydrosventrin, RA, and SPAR) using a rapid pipeline that combines a series of assays. A methylthiazolyldiphenyl-tetrazolium assay, using the HaCaT keratinocyte cell line was used to determine epidermal irritants and was combined with Caenorhabditis elegans fecundity assays that demonstrated the effects of environmental exposure to various concentrations of these molecules. In each case, the assays showed that the compounds did not exhibit toxicity until they reached well above their current biofilm dispersion/inhibition concentrations. The most effective antibiofilm compound also had significant effects when used in conjunction with several standard antibiotics against resistant bacteria. Consequently, it was further investigated using the C. elegans assay in combination with different antibiotics and was found to maintain the same low level of toxicity as when acting alone, bolstering its candidacy for further testing as an adjuvant.}, number={3}, journal={DRUG AND CHEMICAL TOXICOLOGY}, author={Stowe, Sean D. and Tucker, Ashley T. and Thompson, Richele and Piper, Amanda and Richards, Justin J. and Rogers, Steven A. and Mathies, Laura D. and Melander, Christian and Cavanagh, John}, year={2012}, month={Jul}, pages={310–315} }
@article{worthington_rogers_huigens_melander_ritchie_2012, title={Foliar-Applied Small Molecule that Suppresses Biofilm Formation and Enhances Control of Copper-Resistant Xanthomonas euvesicatoria on Pepper}, volume={96}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-02-12-0190-re}, abstractNote={We report a small molecule additive, a member of the 2-aminoimidazole (2AI) group that is an analogue of the marine sponge natural product oroidin that suppresses resistance of Xanthomonas euvesicatoria to copper and decreases biofilm formation in an in vitro system. In laboratory experiments, 2AI combined with copper reduced both bacterial multiplication in broth and bacterial recovery on pepper leaf discs of a copper-resistant strain of X. euvesicatoria to a level close to that of a copper-sensitive strain. Compound 2AI used alone exhibited minimal bactericidal activity. In 3 years of field experiments, when combined with a copper-containing material, copper hydroxide (Kocide 3000), and other antibacterial materials, these spray mixtures resulted in decreased bacterial spot foliar disease and increased fruit yields using hybrid bell pepper (Capsicum annuum) cultivars and copper-resistant strains of X. euvesicatoria. This study demonstrates the concept for using small molecules as additives to antibacterial compounds at nonbactericidal concentrations under field conditions that, in the laboratory, were demonstrated to suppress bacterial biofilms and copper-resistant strains.}, number={11}, journal={PLANT DISEASE}, author={Worthington, R. J. and Rogers, S. A. and Huigens, R. W., III and Melander, C. and Ritchie, D. F.}, year={2012}, month={Nov}, pages={1638–1644} }
@article{olson_bobay_melander_cavanagh_2012, title={H-1, C-13, and N-15 resonance assignments and secondary structure prediction of the full-length transition state regulator AbrB from Bacillus anthracis}, volume={6}, ISSN={["1874-2718"]}, DOI={10.1007/s12104-011-9333-2}, abstractNote={The AbrB protein is a transcription factor that regulates the expression of numerous essential genes during the cells transition phase state. AbrB from Bacillus anthracis is, nototriously, the principal protein responsible for anthrax toxin gene expression and is highly homologous to the much-studied AbrB protein from Bacillus subtilis having 85% sequence identity and the ability to regulate the same target promoters. Here we report backbone and sidechain resonance assignments and secondary structure prediction for the full-length AbrB protein from B. anthracis.}, number={1}, journal={BIOMOLECULAR NMR ASSIGNMENTS}, author={Olson, Andrew L. and Bobay, Benjamin G. and Melander, Christian and Cavanagh, John}, year={2012}, month={Apr}, pages={95–98} }
@article{thompson_bobay_stowe_olson_peng_su_actis_melander_cavanagh_2012, title={Identification of BfmR, a Response Regulator Involved in Biofilm Development, as a Target for a 2-Aminoimidazole-Based Antibiofilm Agent}, volume={51}, ISSN={["0006-2960"]}, DOI={10.1021/bi3015289}, abstractNote={2-Aminoimidazoles (2AIs) have been documented to disrupt bacterial protection mechanisms, including biofilm formation and genetically encoded antibiotic resistance traits. Using Acinetobacter baumannii, we provide initial insight into the mechanism of action of a 2AI-based antibiofilm agent. Confocal microscopy confirmed that the 2AI is cell permeable, while pull-down assays identified BfmR, a response regulator that is the master controller of biofilm formation, as a target for this compound. Binding assays demonstrated specificity of the 2AI for response regulators, while computational docking provided models for 2AI–BfmR interactions. The 2AI compound studied here represents a unique small molecule scaffold that targets bacterial response regulators.}, number={49}, journal={BIOCHEMISTRY}, author={Thompson, Richele J. and Bobay, Benjamin G. and Stowe, Sean D. and Olson, Andrew L. and Peng, Lingling and Su, Zhaoming and Actis, Luis A. and Melander, Christian and Cavanagh, John}, year={2012}, month={Dec}, pages={9776–9778} }
@article{melander_margolis_2012, title={Medicinal chemistry: Forcing an enemy into the open}, volume={4}, number={9}, journal={Nature Chemistry}, author={Melander, C. and Margolis, D. M.}, year={2012}, pages={692–693} }
@article{harris_worthington_melander_2012, title={Potent Small-Molecule Suppression of Oxacillin Resistance in Methicillin-Resistant Staphylococcus aureus}, volume={51}, ISSN={["1521-3773"]}, DOI={10.1002/anie.201206911}, abstractNote={Shields down! Adjuvant molecules that have the ability to restore the susceptibility of multi-drug-resistant bacteria, such as MRSA, to clinically available antibiotics are a promising alternative to the development of novel antimicrobials. Pictured is a potent small molecule (1) that, at sub-minimum inhibitory concentration (sub-MIC) levels, lowers the MIC of oxacillin (2) against a number of MRSA strains by up to 512-fold. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={45}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Harris, Tyler L. and Worthington, Roberta J. and Melander, Christian}, year={2012}, pages={11254–11257} }
@article{worthington_bunders_reed_melander_2012, title={Small Molecule Suppression of Carbapenem Resistance in NDM-1 Producing Klebsiella pneumoniae}, volume={3}, ISSN={["1948-5875"]}, DOI={10.1021/ml200290p}, abstractNote={The already considerable global public health threat of multidrug-resistant Gram-negative bacteria has become even more of a concern following the emergence of New Delhi metallo-β-lactamase (NDM-1) producing strains of Klebsiella pneumoniae and other Gram-negative bacteria. As an alternative approach to the traditional development of new bactericidal entities, we have identified a 2-aminoimidazole-derived small molecule that acts as an antibiotic adjuvant and is able to suppress resistance of a NDM-1 producing strain of K. pneumoniae to imipenem and meropenem, in addition to suppressing resistance of other β-lactam nonsusceptible K. pneumoniae strains. The small molecule is able to lower carbapenem minimum inhibitory concentrations by up to 16-fold, while exhibiting little bactericidal activity itself.}, number={5}, journal={ACS MEDICINAL CHEMISTRY LETTERS}, author={Worthington, Roberta J. and Bunders, Cynthia A. and Reed, Catherine S. and Melander, Christian}, year={2012}, month={May}, pages={357–361} }
@article{worthington_richards_melander_2012, title={Small molecule control of bacterial biofilms}, volume={10}, number={37}, journal={Organic & Biomolecular Chemistry}, author={Worthington, R. J. and Richards, J. J. and Melander, C.}, year={2012}, pages={7457–7474} }
@article{budhathoki-uprety_peng_melander_novak_2012, title={Synthesis of Guanidinium Functionalized Polycarbodiimides and Their Antibacterial Activities}, volume={1}, ISSN={["2161-1653"]}, url={http://dx.doi.org/10.1021/mz200116k}, DOI={10.1021/mz200116k}, abstractNote={A family of guanidinium-side-chain functionalized polycarbodiimides has been synthesized by allowing an azido guanidinium salt to react with alkyne polycarbodiimides via the copper catalyzed [3 + 2] cycloaddition (Click) reaction. Poly-2(a-d) are cationic/amphiphilic polymers in which the global hydrophilic/hydrophobic balance has been tailored by local alteration of the length of alkyl side chain in the repeat unit of polymers prior to polymerization. The shorter alkyl chains yield water-soluble polymers, Poly-2c, -2d, and -2e. Antibacterial activities of these cationic polycarbodiimides have been investigated for Gram-positive and Gram-negative bacteria that include Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Acinetobacter baumannii. It was observed that the influence of hydrophobic-hydrophilic balance per repeat unit of these polymers have profound effects for both antimicrobial and hemolytic activities. In addition, these polycarbodiimide-guanidinium-triazole conjugates offered moderate to significant antibacterial activity and rapid interaction with red blood cells causing blood precipitation without significant hemolysis in case of Poly-2(b-e). This latter property has the potential to be exploited in the polymer coatings or wound protection.}, number={3}, journal={ACS MACRO LETTERS}, author={Budhathoki-Uprety, Januka and Peng, LingLing and Melander, Christian and Novak, Bruce M.}, year={2012}, month={Mar}, pages={370–374} }
@article{liu_worthington_melander_wu_2011, title={A New Small Molecule Specifically Inhibits the Cariogenic Bacterium Streptococcus mutans in Multispecies Biofilms}, volume={55}, ISSN={["0066-4804"]}, DOI={10.1128/aac.01496-10}, abstractNote={ABSTRACT Streptococcus mutans is a major cariogenic bacterium. It has adapted to the biofilm lifestyle, which is essential for pathogenesis of dental caries. We aimed to identify small molecules that can inhibit cariogenic S. mutans and to discover lead structures that could give rise to therapeutics for dental caries. In this study, we screened a focused small-molecule library of 506 compounds. Eight small molecules which inhibited S. mutans at a concentration of 4 μM or less but did not affect cell growth or biofilm formation of commensal bacteria, represented by Streptococcus sanguinis and Streptococcus gordonii , in monospecies biofilms were identified. The active compounds share similar structural properties, which are characterized by a 2-aminoimidazole (2-AI) or 2-aminobenzimidazole (2-ABI) subunit. In multispecies biofilm models, the most active compound also inhibited cell survival and biofilm formation of S. mutans but did not affect commensal streptococci. This inhibitor downregulated the expression of six biofilm-associated genes, ftf , pac , relA , comDE , gbpB , and gtfB , in planktonic S. mutans cells, while it downregulated the expression of only ftf , pac , and relA in the biofilm cells of S. mutans . The most potent compound also inhibited production of two key adhesins of S. mutans , antigen I/II and glucosyltransferase (GTF). However, the compound did not alter the expression of the corresponding genes in both S. sanguinis and S. gordonii , indicating that it possesses a selective inhibitory activity against S. mutans .}, number={6}, journal={ANTIMICROBIAL AGENTS AND CHEMOTHERAPY}, author={Liu, Chang and Worthington, Roberta J. and Melander, Christian and Wu, Hui}, year={2011}, month={Jun}, pages={2679–2687} }
@article{harris_worthington_melander_2011, title={A facile synthesis of 1,5-disubstituted-2-aminoimidazoles: Antibiotic activity of a first generation library}, volume={21}, ISSN={["1464-3405"]}, DOI={10.1016/j.bmcl.2011.05.123}, abstractNote={An efficient synthetic route to 1,5-disubstituted 2-aminoimidazoles from readily available amino acids and aldehydes has been developed. A library of simple analogues was synthesized and several compounds were shown to exhibit notable antibiotic activity against a variety of bacterial strains including multi-drug resistant isolates.}, number={15}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Harris, Tyler L. and Worthington, Roberta J. and Melander, Christian}, year={2011}, month={Aug}, pages={4516–4519} }
@misc{stowe_richards_tucker_thompson_melander_cavanagh_2011, title={Anti-biofilm compounds derived from marine sponges}, volume={9}, number={10}, journal={Marine Drugs}, author={Stowe, S. D. and Richards, J. J. and Tucker, A. T. and Thompson, R. and Melander, C. and Cavanagh, J.}, year={2011}, pages={2010–2035} }
@article{su_peng_worthington_melander_2011, title={Evaluation of 4,5-Disubstituted-2-Aminoimidazole-Triazole Conjugates for Antibiofilm/Antibiotic Resensitization Activity Against MRSA and Acinetobacter baumannii}, volume={6}, ISSN={["1860-7187"]}, DOI={10.1002/cmdc.201100316}, abstractNote={Abstract A library of 4,5‐disubstituted‐2‐aminoimidazole–triazole conjugates (2‐AITs) was synthesized, and the antibiofilm activity was investigated. This class of small molecules was found to inhibit biofilm formation by methicillin‐resistant Staphylococcus aureus (MRSA) at low‐micromolar concentrations; 4,5‐disubstituted‐2‐AITs were also able to inhibit and disperse Acinetobacter baumannii biofilms. The activities of the lead compounds were compared against the naturally occurring biofilm dispersant cis ‐2‐decenoic acid and were revealed to be more potent. The ability of selected compounds to resensitize MRSA to traditional antibiotics (resensitization activity) was also determined. Lead compounds were observed to resensitize MRSA to oxacillin by 2–4‐fold.}, number={12}, journal={CHEMMEDCHEM}, author={Su, Zhaoming and Peng, Lingling and Worthington, Roberta J. and Melander, Christian}, year={2011}, month={Dec}, pages={2243–2251} }
@article{bunders_cavanagh_melander_2011, title={Flustramine inspired synthesis and biological evaluation of pyrroloindoline triazole amides as novel inhibitors of bacterial biofilms}, volume={9}, ISSN={["1477-0539"]}, DOI={10.1039/c1ob05605k}, abstractNote={Anti-biofilm agents have been developed based upon the flustramine family of alkaloids isolated from Flustra foliacea. A Garg interrupted Fischer indolization reaction was employed to access a core pyrroloindoline scaffold that was subsequently employed to create a pyrroloindoline triazole amide library. Screening for the ability to modulate biofilm formation against strains of Gram-positive and Gram-negative bacteria identified several compounds with low micromolar, non-toxic IC50 values.}, number={15}, journal={ORGANIC & BIOMOLECULAR CHEMISTRY}, author={Bunders, Cynthia and Cavanagh, John and Melander, Christian}, year={2011}, pages={5476–5481} }
@article{bresee_maier_boncella_melander_feldheim_2011, title={Growth Inhibition of Staphylococcus aureus by Mixed Monolayer Gold Nanoparticles}, volume={7}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201100420}, abstractNote={A library of 120 nanoparticle conjugates is produced by simple one-pot thiol exchange reactions. The antibiotic activity of the conjugates toward Staphylococcus aureus is found to depend upon the combination of thiols assembled on the nanoparticles. Synthetic nanometer-scale systems have the potential to overcome many limitations of conventional small-molecule therapeutic agents.1 For instance, small molecules often have short blood circulation times (half-life, t1/2, of hours), rely on a single high-affinity contact to a disease target, and are typically incapable of disrupting protein–protein interactions that can drive disease pathogenesis. In contrast, nanoscale systems can provide long circulation half-lives (days to weeks), have tunable valency and aqueous solubility, and are adept at preventing protein–protein interactions.2, 3 However, a significant advantage of small-molecule drugs is the ease with which large chemical and structural diversity can be manufactured and screened for biological activity. Synthetic routes to the creation of diversity in nanoparticle composition space would serve to combine many of the advantages of both small-molecule and nanoscale therapeutics. A number of materials have been explored as scaffolds for the design of nanometer-scale therapeutics. Notable recent examples are the pyrimadine-coated gold nanoparticle antibiotics studied by the Zhang laboratory4 and the dextran-coated iron oxide nanoparticles synthesized in Weissleder's laboratory.5, 6 The former experiments suggest that nanoparticles may be able to withstand pathogen evolutionary resistance mechanisms that plague small-molecule drugs, while the latter highlighted the remarkable ability of multivalent binding to strengthen drug-target binding interactions. Our laboratories have focused on gold nanoparticles as a platform for the discovery of novel therapeutics for the treatment of infectious disease. We chose gold for a number of reasons, including the ability to access gold nanoparticles in a range of well-defined sizes from 1 to 10 nm7, 8 and the straightforward gold modification chemistry afforded via formation of gold–thiolate bonds.9-11 In addition, using thiol exchange reactions, combinations of two or more chemically distinct organothiol ligands can be attached to a single particle to create multivalent and multifunctional systems.12 The ability to assemble mixed thiol monolayers on a nanoscale platform provides a powerful tool that can be used to tune binding affinity to a biological target and control cellular internalization and subcellular localization.13, 14 The potential benefits of gold nanoparticle therapeutics were demonstrated recently in our research groups by transforming a weak CCR5 binding small molecule, which by itself was biologically inactive, into a multivalent gold conjugate that effectively inhibited HIV-1 fusion to peripheral blood mononuclear cells (PBMCs) in vitro.15 The biological activity of ligand-coated gold nanoparticles in the prevention of HIV-1 entry suggests that known, weak binding or perhaps even resistance-compromised small-molecule drugs may be transformed into potent therapeutics via conjugation to gold nanoparticles. We were also interested in determining whether completely new biologically active compounds could be discovered using ligand-coated gold nanoparticles. Specifically, could we identify nanoparticle formulations whose biological activity was dictated by a specific combination of ligands displayed on the surface of the particle? Indeed the answer appears to be yes, as we have found that gold nanoparticles with potent activity for Escherichia coli (E. coli) growth inhibition could be discovered from a library of mixed thiol-monolayer-coated gold nanoparticles.16 Here, we show that the gold nanoparticle library created to search for inhibitors of the Gram-negative E. coli could be used to discover inhibitors of the Gram-positive bacterium Staphylococcus aureus (S. aureus). The active nanoparticles that emerged from this screen consisted of a different subset of the library compared to those discovered in the previous search. This suggests that the display of ligand mixtures on gold nanoparticles could present new opportunities in the rapid identification of nanomaterials with biological activity toward a range of microbes. The library of nanoparticle conjugates was assembled by first synthesizing 2.0 nm diameter gold nanoparticles capped with p-mercaptobenzoic acid (pMBA).15, 16 These particles have a proposed empirical formula of [Au144(SC6H4COOH)60].17 The ten thiols shown in Figure 1 were chosen as a representative library of molecules containing H-bond donor/acceptor and hydrophilic/hydrophobic properties. These ligands were incubated with gold nanoparticles in combinations of three (initially at 1:1:1 molar ratios) to build a library of 120 nanoparticle conjugates. The conjugates were purified by salt and methanol precipitation to remove free thiols. A large subset of these formulations (62 combinations) displayed poor aqueous solubility under the equimolar ligand exchange concentrations used initially. This was rectified by simply adjusting the molar ratio of thiols added into the reaction mixture. For example, nanoparticle conjugates 28 and 50 were relatively insoluble in aqueous solution due to the low solubility of thiol 1 (see structure in Figure 1). The amount of thiol 1 in the exchange reaction was thus reduced to 67% of the original feed. With the exchange reaction optimized for solubility, a total of 95 nanoparticle conjugates could be screened for antibiotic activity (see Supporting Information, Table S1 for the composition of the entire library). An initial screen against methicillin- susceptible S. aureus (MSSA) revealed activity that depended upon the combination of thiols conjugated to pMBA-coated gold nanoparticles (Figure 2). The ten thiols chosen as a representative library of molecules containing H-bond donor/acceptor and hydrophilic/hydrophobic properties. Antibiotic activity of several mixed ligand-coated gold nanoparticles. In parentheses are the thiols combined to generate each nanoparticle. Nanoparticle concentrations were 25 μM. POS indicates the positive control, and CFU indicates the colony forming unit. Nanoparticle conjugates that showed >90% growth inhibition at nanoparticle concentrations of 25 μM in the initial screen were chosen for further analysis. Cultures of MSSA were incubated with varying concentrations (10–50 μM) of nanoparticles. Assays were conducted under standard broth dilution procedures followed by colony counting to assess bacterial viability after incubation with nanoparticles. The nanoparticles shown in Table 1 displayed the highest decrease in growth, with conjugate 6 yielding 99.9% growth inhibition at 10 μM. The nanoparticles listed in Table 1 were then tested for activity against methicillin-resistant S. aureus (MRSA) and the Gram-negative bacterium E. coli. This screen allowed us to assess whether nanoparticle formulations could be discovered that were not susceptible to current mechanisms of drug resistance and whether nanoparticle formulations were also active against Gram-negative bacteria. All conjugates were as active against MRSA as they were toward MSSA except conjugate 56, which showed only 99.0% growth inhibition at 50 μM. None of the conjugates were active toward the inhibition of E. coli. The inhibitory activities of the individual, unconjugated thiols were then determined. Thiols 2, 5, 6, 8, 9, and 10 showed little to no inhibition of MSSA growth at concentrations as high as 2 mM (<0.4 log decrease). Thiols 3 and 4 were potent growth inhibitors, which is not surprising since phenols and anilines are known antiseptics. It was also found that thiol 7 showed inhibitory activity of ca. 1 log at 2 mM. However, for this thiol alone to be responsible for the activity of nanoparticles 50 and 56 it would require that more than 100 of them were coordinated to the gold surface, an unlikely scenario given that these nanoparticles can only accommodate 60 ligands total. Thiol 1 could not be screened in solution due to poor solubility in the broth used. However, on agar containing 500 μM 1 and 10% dimethyl sulfoxide (DMSO), no inhibition was observed. Various combinations of the free thiol monomers were then incubated with MSSA. Surprisingly, binary mixtures of 50 μM pMBA and 50 μM thiol 1 or 150 μM pMBA and 150 μM thiol 2 showed 99.9% MSSA growth inhibition. The activity of conjugates containing pMBA and thiols 1 or 2 is thus independent of their attachment to the nanoparticle; however, conjugation of 1 to the nanoparticle has the advantage of converting it into a water-soluble conjugate. Once we had identified active nanoparticle formulations, we employed IR spectroscopy to confirm the presence of thiols on conjugates 6, 28, and 50 (Figure 3). Characteristic vibrations for thiols 1 and 8 were observed for conjugate 6, and thiols 1 and 5 for conjugates 28 and 50. Thiols 2, 8, and 7 were not detected in conjugates 6, 28, and 50, respectively, likely because they were not present in sufficient quantities to be detected by IR or did not have vibrations that could be assigned unambiguously given the other thiols present. IR spectra of active nanoparticle conjugates 6, 28, and 50 confirms the formation of mixed thiol monolayers. A–D) Spectra of nanoparticle conjugates 6, 50, 28, and pMBA-gold nanoparticles, respectively. The * indicates a representative band for pMBA–Au nanoparticle conjugates. The ^, §, and £ correspond to vibrations unique to 3-(nitrobenzyl)mercaptan, glutathione, and 3-mercapto-1-propane sulfonate, respectively, as determined from the spectra of the free thiols. Finally, the toxicity of conjugate 50A was assessed with a hemolysis assay, yielding an HC50 of 40 μM. This value corresponds to a hemolytic index (HC50/MIC99.9) of 2 where HC50 is the concentration capable of causing 50% red blood cell lysis and MIC99.9 is the minimal inhibitory concentration resulting in 99.9% growth inhibition of S. aureus. Nanoscale systems including DNA aptamers, antibodies, proteins, and inorganic nanoparticles such as the gold particles described herein are attractive as therapeutics in part because of their tunable valencies, blood circulation times, and biodistribution profiles. In addition, nanoscale therapeutics are often adept at disrupting protein–protein interactions that can drive disease pathogenesis. In contrast, small-molecule therapeutics typically rely on a single high-affinity contact to a disease target and have difficulty blocking protein–protein interactions. A significant advantage of small-molecule drugs, however, is the ease with which large chemical and structural diversity can be manufactured and screened for biological activity. It has thus been proposed that methods capable of blending the properties of nanoscale systems with the chemical diversity of small molecules will lead to the discovery of superior therapeutic agents.1 We have shown that a library of small-molecule ligand-coated gold nanoparticle conjugates may be generated rapidly via one-pot thiol exchange reactions. The nanoparticle conjugates are prepared at room temperature in aqueous solution and purified using a simple aqueous salt/methanol precipitation and resuspension procedure. Considering solely the number of commercially available thiols (>200), there is potential to access significant chemical and structural diversity with this approach. While the aqueous solubility of the resulting nanoparticle conjugates may in some cases be low (as experienced with many of the compounds in our initial 120-member library), this can be overcome by simply tuning the molar ratios of the ligands during the exchange reaction or by combining thiols with low aqueous solubility with highly water-soluble thiols. The library of 95 unique ligand-coated gold nanoparticles investigated here revealed differential activity toward the inhibition of bacterial growth, with one conjugate displaying 99.9% growth inhibition at 10 μM for both MSSA and MRSA. Whether the bacterial growth inhibition observed for these conjugates is due to efficient internalization, nanoparticle aggregation inside of the cells, or enhanced binding to a biomolecule target located in the cell membrane or inside of the cell is currently not known. As a comparison we note that the minimum inhibitory concentrations of vancomycin, ciprofloxacin, and cefixime against MSSA are ca. 0.7, 1.5, and 17 mM, respectively; thus nanoparticle formulations can be rapidly identified from simple thiol building blocks that are comparable to conventional antibiotics with respect to in vitro bacterial growth inhibition. Synthesis of 2.0 nm Gold Nanoparticles: Two-nanometer diameter [Au144(SC6H4COOH)60] gold nanoparticles were synthesized as previously described.1 In short, a solution of HAuCl4 (11.1 mM), pMBA (37.8 mM), and NaOH (180 mM) in aqueous methanol (55.6% (v/v)) was prepared and allowed to equilibrate for 24 h with constant stirring. Fifty milliliters of this solution were diluted with the addition of methanol (260 mL) and water (740 mL). The Au+ was reduced with the addition of aqueous NaBH4 (10 mL, 0.25 M). The final methanol concentration was adjusted to 25% with the addition of water (100 mL). The reduction of gold was allowed to proceed for 48 h at room temperature with constant stirring. Gold nanoparticles were precipitated with the addition of NaCl (70 mmol) and methanol (500 mL) (final methanol concentration of 47% v/v) followed by centrifugation (3200 rcf, 5 min). The precipitated nanoparticles were reconstituted in water. The concentration was measured by UV–vis spectroscopy, using the molar extinction coefficient at a wavelength of 510 nm, ϵ510 nm, of 409 440 M−1 cm−1. Place Exchange Reactions: One-pot place exchange reactions were conducted with the addition of thiol added in 1:1:1 molar ratio (740 μM total) to gold nanoparticles (7.4 μM) in sodium phosphate buffer, pH 9.5 (20 mM, 15 mL). These solutions were prepared from 20 mM stock solutions of the individual thiols. Thiols 5, 6, 7, 8, 9, and 10 stock solutions were prepared in H2O, while thiols 1, 3, and 4 were dissolved in DMSO, and thiol 2 was dissolved in 20% glycerol. It is important to note that stock solutions of thiol 1 had to be be stored at –80 °C to avoid conversion into a species that fails to place exchange properly onto pMBA-capped gold nanoparticles. Reactions were placed on a plate shaker and agitated for 24 h at room temperature. The exchange product was harvested through the addition of NaCl (11 mL of 4 M stock for a final concentration of 0.8 M) and a volume of methanol equal to that of the reaction volume plus added salt water (26 mL). Reactions were centrifuged (3200 rcf, 30–60 min). Precipitated nanoparticles were resuspended and precipitated with the addition of NaCl and methanol two times to wash out excess unreacted thiol. Particles were allowed to dry to completion overnight at room temperature and resuspended in water. Resuspended nanoparticles were washed with water over a 30 000 MWCO (molecular weight cut-off) centricon filter to remove excess salt and thiol followed by buffer exchange into Mueller–Hinton broth for assay. Optimizing the molar feed ratios resulted in decreasing the concentration of thiols 1, 2, 3, 4, 6, 9, and 10 by 67% of the original value, with the rest of the reaction remaining as described above. The initial screen suggested that thiol 5 (glutathione) was an important ligand in the preparation of gold nanoparticle conjugates with activity toward MSSA. It was thus of interest to determine whether activity could be enhanced by starting with glutathione-capped gold nanoparticles rather than pMBA-capped gold nanoparticles. Glutathione-capped gold nanoparticles were synthesized by mixing HAuCl4•xH2O (0.4 mmol) in methanol (20 mL) with glutathione (1.4 mmol) in H2O (15.4 mL) supplemented with NaOH (0.6 mL of 10 M stock solution). This solution was then divided into thirds. The following was then added to each reaction: methanol (62 mL) and H2O (178 mL), followed by aqueous NaBH4 (2.4 mL, 0.25 M), and finally water (24 mL). Purification of the particles was performed via precipitation of nanoparticles with the addition of NaCl (40 mmol) and methanol (250 mL). Centrifugation of samples allowed for the purification of particles from the solution. Particles were then dissolved in water and washed over a 10 000 MWCO centricon filter to remove excess glutathione and salts. Place exchange reactions were then conducted on these particles as described above. Nanoparticles prepared in this way were designated conjugate 50A. Generation of nanoparticle conjugate 50A occurred through the addition of pMBA (2.95 μmol) and (3-nitrobenzyl)mercaptan (2.95 μmol) to glutathione-capped gold nanoparticles (0.05 μmol) in water (4 mL). These particles did not show enhanced activity versus conjugates prepared with pMBA-capped gold nanoparticles, although batch-to-batch variability was observed to improve. Bacterial Growth Inhibition Assays: Inoculation of S. aureus into Mueller–Hinton broth (3 mL, BD) was carried out by touching the top of 4 well-isolated colonies of MSSA (ATCC 29213), MRSA (ATCC BAA-44), or E. coli (ATCC 25922) from a Mueller–Hinton agar (BD) plate with an inoculation loop. The culture was allowed to grow at 37 °C, 225 rpm until mid-log phase after which it was diluted to 1 × 106 CFU/mL in Mueller–Hinton broth. Equal volumes of diluted inoculum and nanoparticle sample (adjusted to the correct assay concentration in Mueller–Hinton broth) were mixed to make the final inoculum concentration 5 × 105 CFU/mL. Samples were incubated at 37 °C, 225 rpm for 18 h. End points were determined by colony counting on Mueller–Hinton agar after dilution of each sample in phosphate buffered saline (PBS) and incubation of the plates at 37 °C for 24 h. Initial assays were conducted in nutrient broth and nutrient agar with S. aureus ATCC 9144, with final growth inhibition data documented for Mueller–Hinton broth and agar with S. aureus ATCC 29213. Infrared Spectroscopy: Nanoparticle samples were reconstituted and washed of contaminants over a 30 K MWCO centricon filter with water. Samples were then spotted onto potassium bromide Real Crystal IR cards (International Crystal Laboratories) in their appropriate solvent and allowed to dry. IR analysis was carried out on a Thermo Nicolet Avatar 360 FT-IR spectrometer. Blood Hemolysis Assay: Hemolysis assays were performed on mechanically difibrinated sheep's blood (Hemostat Labs: DSB100). Briefly, blood (1.5 mL) was placed into a microcentrifuge tube and centrifuged (10 000 rpm, 10 min). Cells were resuspended and washed with PBS (1 mL). The final cell suspension was then diluted tenfold and nanoparticle compound was added in PBS. PBS alone was used as a zero hemolysis marker and a 1% Triton X sample was used as a 100% lysis marker. Samples were then incubated at 37 °C, 200 rpm for 1 h followed by centrifugation (10 000 rpm, 10 min). The resulting supernatant was diluted by a factor of 40 in distilled water. The absorbance of the supernatant was measured with a UV–vis spectrometer at a 540 nm wavelength. As gold nanoparticles absorb readily at a 540 nm, the nanoparticles of each test sample were precipitated out of solution with NaCl and methanol. The resulting pellet was resuspended and the absorbance was measured with a UV–vis spectrometer at a 540 nm wavelength. This A540 nm reading represents nanoparticles and was subtracted from the initial A540 nm reading of the supernatant to yield A540 nm of cell lysis only. Supporting Information is available from the Wiley Online Library or from the author. The authors wish to thank the Bill and Melinda Gates Foundation for funding. The article is dedicated to Professor Chad Mirkin, a pioneering scientist and devoted mentor. This Communication is part of the Special Issue dedicated to Chad Mirkin in celebration of 20 years of influential research at Northwestern University. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={14}, journal={SMALL}, author={Bresee, Jamee and Maier, Keith E. and Boncella, Amy E. and Melander, Christian and Feldheim, Daniel L.}, year={2011}, month={Jul}, pages={2027–2031} }
@article{peng_desousa_su_novak_nevzorov_garland_melander_2011, title={Inhibition of Acinetobacter baumannii biofilm formation on a methacrylate polymer containing a 2-aminoimidazole subunit}, volume={47}, number={17}, journal={Chemical Communications (Cambridge, England)}, author={Peng, L. L. and DeSousa, J. and Su, Z. M. and Novak, B. M. and Nevzorov, A. A. and Garland, E. R. and Melander, C.}, year={2011}, pages={4896–4898} }
@article{bunders_minvielle_worthington_ortiz_cavanagh_melander_2011, title={Intercepting Bacterial Indole Signaling with Flustramine Derivatives}, volume={133}, ISSN={["1520-5126"]}, DOI={10.1021/ja209836z}, abstractNote={Indole signaling is one of the putative universal signaling networks in bacteria. We have investigated the use of desformylflustrabromine (dFBr) derivatives for the inhibition of biofilm formation through modulation of the indole-signaling network in Escherichia coli and Staphylococcus aureus. We have found dFBr derivatives that are 10–1000 times more active than indole itself, demonstrating that the flustramine family of indolic natural products represent a privileged scaffold for the design of molecules to control pathogenic bacterial behavior.}, number={50}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Bunders, Cynthia A. and Minvielle, Marine J. and Worthington, Roberta J. and Ortiz, Minoshka and Cavanagh, John and Melander, Christian}, year={2011}, month={Dec}, pages={20160–20163} }
@article{rogers_lindsey_whitehead_mullikin_melander_2011, title={Synthesis and biological evaluation of 2-aminoimidazole/carbamate hybrid anti-biofilm and anti-microbial agents}, volume={21}, ISSN={["1464-3405"]}, DOI={10.1016/j.bmcl.2010.12.057}, abstractNote={The successful marriage of structural features from our 2-aminoimidazole and menthyl carbamate classes of anti-biofilm agents has resulted in the development of a novel hybrid scaffold of biofilm modulators. The compounds were evaluated against a panel of four bacterial strains for anti-biofilm and anti-microbial activity.}, number={4}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Rogers, Steven A. and Lindsey, Erick A. and Whitehead, Daniel C. and Mullikin, Trey and Melander, Christian}, year={2011}, month={Feb}, pages={1257–1260} }
@article{su_rogers_mccall_smith_ravishankar_mullikin_melander_2010, title={A nitroenolate approach to the synthesis of 4,5-disubstituted-2-aminoimidazoles. Pilot library assembly and screening for antibiotic and antibiofilm activity}, volume={8}, number={12}, journal={Organic & Biomolecular Chemistry}, author={Su, Z. M. and Rogers, S. A. and McCall, W. S. and Smith, A. C. and Ravishankar, S. and Mullikin, T. and Melander, C.}, year={2010}, pages={2814–2822} }
@article{heinecke_melander_2010, title={Analysis of kinamycin D-mediated DNA cleavage}, volume={51}, ISSN={["0040-4039"]}, DOI={10.1016/j.tetlet.2009.12.142}, abstractNote={Kinamycin D is a potent antitumor antibiotic; however the biological mode of action is poorly understood. Recent efforts suggest the natural product is capable of generating reactive oxygen species under acidic pH to induce DNA damage in the presence of a reducing agent.}, number={11}, journal={TETRAHEDRON LETTERS}, author={Heinecke, Christine L. and Melander, Christian}, year={2010}, month={Mar}, pages={1455–1458} }
@article{rogers_bero_melander_2010, title={Chemical Synthesis and Biological Screening of 2-Aminoimidazole-Based Bacterial and Fungal Antibiofilm Agents}, volume={11}, ISSN={["1439-7633"]}, DOI={10.1002/cbic.200900617}, abstractNote={Abstract A collection of 2‐aminoimidazole/triazole amides has been synthesized and screened for antibiofilm activity. This class of small molecules was found to modulate the biofilm activity of Pseudomonas aeruginosa , a multidrug‐resistant strain of Acinetobacter baumannii (MDRAB), a methicillin‐resistant Staphylococcus aureus strain (MRSA), Escherichia coli , Rhodospirillum salexigens , Staphylococcus epidermidis , Vibrio vulnificus , and vancomycin‐resistant Enterococcus faecium as well as the yeast Candida albicans and Cryptococcus neoformans . Furthermore, lead compounds were found to not lyse red blood cells at active concentrations.}, number={3}, journal={CHEMBIOCHEM}, author={Rogers, Steven A. and Bero, Joseph D. and Melander, Christian}, year={2010}, month={Feb}, pages={396–410} }
@article{bresee_maier_melander_feldheim_2010, title={Identification of antibiotics using small molecule variable ligand display on gold nanoparticles}, volume={46}, number={40}, journal={Chemical Communications (Cambridge, England)}, author={Bresee, J. and Maier, K. E. and Melander, C. and Feldheim, D. L.}, year={2010}, pages={7516–7518} }
@article{bunders_richards_melander_2010, title={Identification of aryl 2-aminoimidazoles as biofilm inhibitors in Gram-negative bacteria}, volume={20}, ISSN={["0960-894X"]}, DOI={10.1016/j.bmcl.2010.04.042}, abstractNote={The synthesis and biofilm inhibitory activity of a 30-member aryl amide 2-aminoimidazole library against the three biofilm forming Gram-negative bacteria Escherichia coli, Psuedomonas aeruginosa, and Acinetobacter baumannii is presented. The most active compound identified inhibits the formation of E. coli biofilms with an IC50 of 5.2 μM and was observed to be non-toxic to planktonic growth, demonstrating that analogues based on an aryl framework are viable options as biofilm inhibitors within the 2-aminoimidazole family.}, number={12}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Bunders, Cynthia A. and Richards, Justin J. and Melander, Christian}, year={2010}, month={Jun}, pages={3797–3800} }
@article{reed_huigens_rogers_melander_2010, title={Modulating the development of E. coli biofilms with 2-aminoimidazoles}, volume={20}, ISSN={["0960-894X"]}, DOI={10.1016/j.bmcl.2010.08.075}, abstractNote={The synthesis of a 20 member 2-aminoimidazole/triazole pilot library is reported. Each member of the library was screened for its ability to inhibit or promote biofilm development of either Escherichia coli and Acinetobacter baumannii. From this screen, E. coli-selective 2-aminoimidazoles were discovered, with the best inhibitor inhibiting biofilm development with an IC(50) of 13μM. The most potent promoter of E. coli biofilm formation promoted biofilm development by 321% at 400μM.}, number={21}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Reed, Catherine S. and Huigens, Robert W., III and Rogers, Steven A. and Melander, Christian}, year={2010}, month={Nov}, pages={6310–6312} }
@article{rogers_huigens_cavanagh_melander_2010, title={Synergistic Effects between Conventional Antibiotics and 2-Aminoimidazole-Derived Antibiofilm Agents}, volume={54}, ISSN={["0066-4804"]}, DOI={10.1128/aac.01418-09}, abstractNote={2-aminoimidazoles are an emerging class of small molecules that possess the ability to inhibit and disperse biofilms across bacterial order, class, and phylum. Herein, we report the synergistic effect between a 2-aminoimidazole/triazole conjugate and antibiotics toward dispersing preestablished biofilms, culminating with a 3-orders-of-magnitude increase of biofilm dispersion toward Staphylococcus aureus biofilms. Furthermore, we document that the 2-aminoimidazole/triazole conjugate will also resensitize multidrug-resistant strains of bacteria to the effects of conventional antibiotics, including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Acinetobacter baumannii.}, number={5}, journal={ANTIMICROBIAL AGENTS AND CHEMOTHERAPY}, author={Rogers, Steven A. and Huigens, Robert W., III and Cavanagh, John and Melander, Christian}, year={2010}, month={May}, pages={2112–2118} }
@article{rogers_whitehead_mullikin_melander_2010, title={Synthesis and bacterial biofilm inhibition studies of ethyl N-(2-phenethyl) carbamate derivatives}, volume={8}, number={17}, journal={Organic & Biomolecular Chemistry}, author={Rogers, S. A. and Whitehead, D. C. and Mullikin, T. and Melander, C.}, year={2010}, pages={3857–3859} }
@article{huigens_reyes_reed_bunders_rogers_steinhauer_melander_2010, title={The chemical synthesis and antibiotic activity of a diverse library of 2-aminobenzimidazole small molecules against MRSA and multidrug-resistant A. baumannii}, volume={18}, ISSN={["1464-3391"]}, DOI={10.1016/j.bmc.2009.12.003}, abstractNote={Multidrug-resistant bacterial infections continue to be a rising global health concern. Herein is described the development of a class of novel 2-aminobenzimidazoles with antibiotic activity. These active 2-aminobenzimidazoles retain their antibiotic activity against several strains of multidrug-resistant Staphylococcus aureus and Acinetobacter baumannii when compared to susceptible strains.}, number={2}, journal={BIOORGANIC & MEDICINAL CHEMISTRY}, author={Huigens, Robert W., III and Reyes, Samuel and Reed, Catherine S. and Bunders, Cynthia and Rogers, Steven A. and Steinhauer, Andrew T. and Melander, Christian}, year={2010}, month={Jan}, pages={663–674} }
@article{rogers_huigens_melander_2009, title={A 2-Aminobenzimidazole That Inhibits and Disperses Gram-Positive Biofilms through a Zinc-Dependent Mechanism}, volume={131}, ISSN={["0002-7863"]}, DOI={10.1021/ja9024676}, abstractNote={A number of 2-aminobenzimidazole derivatives were synthesized and screened for their ability to inhibit and disperse bacterial biofilms. From these compounds, a lead 2-aminobenzimidazole was identified that both inhibited and dispersed MRSA, vancomycin-resistant Enterococcus faecium, and Staphylococcus epidermidis biofilms. Mechanistic studies showed that the activity is Zn(II)-dependent, potentially via a direct zinc-chelating mechanism.}, number={29}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Rogers, Steven A. and Huigens, Robert W., III and Melander, Christian}, year={2009}, month={Jul}, pages={9868-+} }
@article{richards_reyes_stowe_tucker_ballard_mathies_cavanagh_melander_2009, title={Amide Isosteres of Oroidin: Assessment of Antibiofilm Activity and C. elegans Toxicity}, volume={52}, ISSN={["1520-4804"]}, DOI={10.1021/jm900378s}, abstractNote={The synthesis and antibiofilm activities of sulfonamide, urea, and thiourea oroidin analogues are described. The most active derivative was able to selectively inhibit P. aeruginosa biofilm development and is also shown to be nontoxic upward of 1 mM to the development of C. elegans in comparison to other similar isosteric analogues and the natural product oroidin.}, number={15}, journal={JOURNAL OF MEDICINAL CHEMISTRY}, author={Richards, Justin J. and Reyes, Samuel and Stowe, Sean D. and Tucker, Ashley T. and Ballard, T. Eric and Mathies, Laura D. and Cavanagh, John and Melander, Christian}, year={2009}, month={Aug}, pages={4582–4585} }
@article{ballard_richards_aquino_reed_melander_2009, title={Antibiofilm Activity of a Diverse Oroidin Library Generated through Reductive Acylation}, volume={74}, ISSN={["0022-3263"]}, DOI={10.1021/jo802260t}, abstractNote={A diverse 20-compound library of analogues based on the marine alkaloid oroidin were synthesized via a reductive acylation strategy. The final target was then assayed for inhibition and dispersion activity against common proteobacteria known to form biofilms. This methodology represents a significant improvement over the generality of known methods to acylate substrates containing 2-aminoimidazoles and has the potential to have broad application to the synthesis of more advanced oroidin family members and their corresponding analogues.}, number={4}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Ballard, T. Eric and Richards, Justin J. and Aquino, Arianexys and Reed, Catherine S. and Melander, Christian}, year={2009}, month={Feb}, pages={1755–1758} }
@misc{richards_melander_2009, title={Controlling Bacterial Biofilms}, volume={10}, ISSN={["1439-7633"]}, DOI={10.1002/cbic.200900317}, abstractNote={Films you don't want to see: The medical community faces a tremendous challenge in overcoming diseases stemming from the formation and persistence of bacterial biofilms. A concise review of current approaches employed to control bacterial biofilms is discussed. The ubiquitous nature of bacteria in the environment, and the role they play in infectious disease has been one of the most extensively researched areas in biomedical science. It has led to tremendous scientific breakthroughs aimed at eradicating a myriad of diseases and improving the overall quality of life. However, within the past 20–30 years, there has been an increased understanding that bacterial biofilms are a major factor in the morbidity and mortality of most infectious diseases.1–3 This is significant because bacterial biofilms are resistant to common therapeutic approaches that would eliminate their free-floating (planktonic) counterparts. Biofilms are described as surface-associated communities of microorganisms encased in a protective extracellular matrix.4 Approximately 80 % of the world's microbial biomass resides in the biofilm state, and the National Institutes of Health (NIH) estimates that upwards of 75 % of microbial infections that occur in the human body are underpinned by the formation and persistence of biofilms.5 Common diseases associated with the formation of biofilms include lung infections of individuals who suffer from cystic fibrosis (CF), burn wound infections, otitis media, bacterial endocarditis, and tooth decay (Table 1).5, 6 Additionally, the infection of indwelling medical devices (IMDs), such as catheters and heart stents, is also of major concern.3, 7, 8 Biofilms formed on IMDs provide a continual source of infection, thereby often necessitating their complete removal from the patient. Biofilm communities of bacteria differ from the traditional thinking of planktonic bacteria as they are complex, dynamic entities that undoubtedly represent a remarkable evolutionary attempt by the bacteria to survive against a plethora of environmental pressures.9 Organism Biofilm-associated disease Pseudomonas aeruginosa cystic fibrosis lung infection Burkholderia cepacia cystic fibrosis lung infection Acinetobacter baumannii burn wound, trauma infection Helicobacter pylori gastrointestinal infection Escherichia coli urinary, catheter infection Haemophilus influenzae otitis media Bordetella pertussis respiratory infection Legionella pneumophila legionnaires' disease Staphylococcus auerus burn wound, catheter, trauma infection Staphylococcus epidermidis sepsis, catheter infection Streptococcus mutans dental plaques, gingivitis vancomycin-resistant enterococci (VRE) nosocomial infections One of the most significant explanations for interest in biofilm research is the continued emergence and threat of antibiotic-resistant bacteria.10, 11 As the pool of available antibiotic treatments that have not selected for resistance continually diminishes, new avenues for the exploration of suitable therapies to provide adequate health care for the general populous are needed. In the United States alone, antibiotic-resistant infections have been approximated to cost upwards of $20 billion per year.10 Biofilms exacerbate this problem because they are known to be insensitive to the antibiotics and microbicides that would eliminate the bacterium in its planktonic state.12 By understanding the biofilm development model, it becomes clear how biofilms perpetuate many of the problems faced by the medical community in treating bacterial-based infectious diseases. Therefore, this review seeks to highlight how bacteria form biofilms and some of the obstacles faced by the medical field resulting from their development. This will then lead to an overview of a few of the current approaches and research therapies aimed at targeting these communities of bacteria. The purpose of this report is not to be a comprehensive review, but instead to provide the reader with a suitable framework for introduction to the topic of biofilms. Whereas many bacteria need to meet certain requirements to initiate the formation of a biofilm, it is generally thought that most biofilms grow in a cyclic nature and share many similarities to one another.9 The formation of biofilms has been extensively studied in a number of bacteria including, but not limited to, Pseudomonas aeruginosa, Escherichia coli, and Vibrio cholerae.13, 14 Much of what is known about biofilm inception originates from studies documenting the phenomenon of quorum sensing (QS). QS is the term employed to describe how bacteria communicate with one another in an effort to make a coordinated attempt at altering gene expression within the population.15–17 In Gram-negative bacteria, small molecules such as acyl homoserine lactones (AHLs) have been identified as the major players in this communication system (Scheme 1).17 Even across multiple bacterial strains, slight structural modifications in the aliphatic tails of these molecules are often times the only differences documented (1–4). AHLs and AI-2 utilized by various Gram-negative bacteria for QS. In Gram-positive bacteria, autoinducing peptides (AIPs), which bind to receptor histidine kinases embedded within the cellular membranes are commonly used for communication.18 The only definitive quorum-sensing mechanism identified to date shared by both Gram-negative and Gram-positive bacteria involves the production and use of autoinducer-2 (AI-2, 6 and 7) as effective signaling molecules. AI-2 molecules are derived from the common synthetic precursor (S)-4,5-dihydroxy-2,3-pentanedione (DPD) 5, the synthase enzyme of which has been identified in over 55 species of genetically diverse bacteria (Scheme 1).19, 20 Biofilm formation and the production of other virulence factors are known to be heavily influenced by QS pathways. Numerous studies have shown that the inhibition of certain QS pathways can lead to the formation of biofilms exhibiting distinct morphological differences in biomass structure.1, 9, 13, 21 This, coupled to the effect that the local environment can play in shaping biofilm development, explains how biofilms range from flat to highly organized structures. Throughout the biofilm formation process, bacteria are observed to exhibit distinct phenotypic differences from their planktonic counterparts during each subsequent developmental stage.1, 4, 9 Planktonic bacteria first localize on a substrate suitable for attachment to begin the growth cycle (Scheme 2). This attachment is initially characterized as reversible, yet it becomes irreversible once the bacteria begin to secrete an exopolymeric substance (EPS). The EPS is one of the most significant attributes of bacterial biofilms. Composed of a variety of biomolecules originating from both the bacteria and the surrounding environment, it serves as a barrier to defend the gathering microorganisms from microbicides and to provide an enclosed space for the biofilm to mature.22 Early maturation of the biofilm is often observed by the structure becoming three dimensional in space. As development continues, the morphology and topography of the biofilm becomes very distinct. Unique pillar shapes protrude from the biomass that allow for maximization of nutrient adsorption and waste disposal. Additionally, the formation of cavities or hollow channels throughout the biofilm becomes evident. These structural features provide the biofilm with the transport system necessary to funnel water and planktonic bacteria throughout the community and are thought to arise from the production of rhamnolipids by the bacteria. Biofilm growth cycle. A) Planktonic bacteria B) reversibly attach to a surface suitable for growth. C) Bacteria begin secretion of the EPS and attachment becomes irreversible. D) The maturing biofilm begins to take on a 3-dimensional shape. E) The biofilm fully matures, and complex architecture is observed. F) Bacteria disperse from the biofilm to reinitiate biofilm colonization of a distal surface. Rhamnolipids are biomolecules composed of glycolipids containing one or more rhamnose sugars, which have been observed to play a crucial role in the development and maintenance of P. aeruginosa biofilms.23 Studies have documented that these molecules are responsible for the shaping of the maturing biofilm by presumably altering cell-to-cell and cell-to-surface interactions; this ultimately leads to structural changes in the biofilm matrix.24 Mutant biofilms deficient in rhamnolipid production lack a distinct three-dimensional topography; this thus results in a biofilm composed of an uniformly thick layer of cells, whereas those that overexpress the genes encoding for rhamnolipid production have been observed to hyper-detach from surfaces.25 The last stage in the developmental cycle is the detachment of bacteria from the biofilm. These cells shed from the biofilm (which have been documented to be phenotypically similar to their planktonic brethren), move on to further colonize distal sites, and repeat the development cycle. This is consistent with reports of dispersed bacteria reverting back to an antibiotic-susceptible form when treated with antimicrobials.26 The exact mechanism of how or why dispersion occurs is still under investigation, yet most likely it can be attributed to a number of factors including various environmental pressures such as starvation conditions or overcrowding. As discussed in the introduction, antibiotic resistance is the preeminent obstacle faced by the medical community in regard to biofilm-driven infections. Approximately 70 % of bacteria frequently associated with nosocomial infections are resistant to at least one of the drugs commonly used to treat them.27 Many of these resistance mechanisms are tied to the morphology of the biofilm, which provides a unique shelter for the bacteria to thrive (Figure 1). Exchange of genetic material within biofilms through the conjugation process has been observed to occur at rates up to 1000-fold higher than those found in planktonic populations.3, 28, 29 Hypermutation, in which bacteria mutate at higher rates to evolve under stress, also occurs more frequently within biofilms.30, 31 Therefore, development of resistance mechanisms such as specialized efflux pumps or upregulation of porin proteins on the cell surface can quickly be selected for and propagated throughout the community. Conceptual diagram of biofilm resistance mechanisms to antimicrobial therapy. Biofilms are fluid, dynamic structures that can greatly vary in local composition.32 The spider-web-like nature of the biofilm EPS matrix can trap certain classes of microbicides before they can elicit their biological effects. Evidence for this stems from reports of differential penetration distances into biofilm matrices exhibited by a range of antibiotics including tobramycin and ciprofloxacin.33 Many antimicrobials fail to completely penetrate the core of the biofilm by becoming trapped in the EPS or by coming into contact with resistant cells, which block further penetration.32 Biofilms are composed of a heterogeneous population of bacterial cells that exhibit different metabolic properties. Cells that are embedded deep within the biofilm might grow at a slower rate because of lack of nutrients and oxygen in comparison with those located near the surface of the community.34 Because of this, these cells often times display increased insensitivity to antimicrobial compounds due to their reduced metabolic activity. Perhaps one of the most fundamental problems with the treatment of biofilm-associated infections is the high rate of reoccurring infection, which often times results in a more aggressive disease state (Scheme 3). It is now believed that this problem is attributed to the existence of persistor cells.35, 36 These cells are found in both planktonic and biofilm populations and are defined as cells that are inherently resistant to the actions of antibiotics or microbicides.37 It has been suggested that these cells are not mutants or cells that reside in a “special” state of growth or development, but instead might in fact be cells with a disabled programmed death mechanism.36 The progeny of persistor cells can exhibit increased resistance to the particular antimicrobial while simultaneously repopulating the community. In the treatment of infectious diseases underpinned by biofilms, this phenomenon is observed as initial treatment therapies aimed at controlling the infection appear to be successful with dissipation of disease symptoms within the patient. However, when persistor cells repopulate the community, treatment methods are less efficacious with each subsequent infection. Furthermore, persistor cells are not eradicated by the host immune response because they are protected by the biofilm matrix. Persistor cells in the biofilm model. As previously discussed, the implementation of functional QS systems in bacteria is essential for their survival. Work has demonstrated that by inhibiting QS in biofilm-forming bacteria, certain degrees of susceptibility to biocides can be obtained.21, 38 In particular, the use of detergents such as SDS has been documented to disrupt mutant lasI P. aeruginosa biofilms.21 Most of these studies have involved manipulation of the production and use of acyl homoserine lactones (AHLs). From a small-molecule development approach, a considerable amount of effort has been put into the design of potential biofilm controls based on this molecular scaffold (Scheme 4).39, 40 Most derivatives of these analogues are unique in that they elicit their activity in a nonmicrobicidal manner, thus possibly mitigating the development of resistance to the ligand. Various modifications to natural AHLs have resulted in the discovery of analogues that possess the ability to inhibit biofilm formation in P. aeruginosa and a number of QS systems in a multitude of bacteria (8–11).41–45 A few problems associated with the development of AHLs as small-molecule controls of biofilms include their chemical reactivity (prone to hydrolysis) and immunomodulatory properties.46–48 Attempts at overcoming these hurdles include the work of some research groups aimed at tuning the chemical reactivity of AHLs through modification of the lactone head in hopes of obtaining more robust compounds.49–52 In recently related developments, the exogenous addition of the fatty acid messenger cis-2-decenoic acid 12 has also been reported to induce the dispersion of biofilms in a cross-kingdom manner.53 By dispersing established biofilms from bacteria and fungi such as E. coli, S. auerus, and C. albicans, the authors demonstrate that the broad-spectrum activity might result from a evolutionary point that is similarly shared between these organisms. Modulators of biofilms derived from bacterial signaling molecules. In Gram-positive bacteria, the development of peptides as tools to modulate biofilms has garnered the most attention. The RIP peptide (RNA-III-inhibiting peptide) has been documented to possess in vivo activity in a number of animal models including the ability to attenuate infections caused by multi-drug-resistant (MDR) strains.54–56 Furthermore, RIP seems to lack significant toxicological side effects, and no reports of resistance have been observed.57 It is postulated that the mechanism of action of RIP is the prevention of phosphorylation of a key bacterial protein, the involvement of which is crucial in the beginning stages of bacterial swarming and adhesion to a surface. Whereas the development of biofilm controls based on bacterial signaling molecules has provided one avenue for research, another has been the identification of biologically active molecules through high-throughput screening (HTS) processes (Scheme 5). This approach has the obvious advantage of being able to screen a large number of structurally unrelated compounds against a particular target for activity. After the screening of 13 000 compounds, the Wood group reported that ursolic acid (13), a triterpene isolated from an African tree, possessed nonmicrobicidal E. coli antibiofilm activity at low micromolar concentrations, and also affected the regulation of genes commonly associated with biofilm formation.58, 59 Lead antibiofilm compounds obtained through chemical library screening. The Hergenrother group screened over 4500 compounds for activity against P. aeruginosa biofilm formation and found that iron-based salts (for example, ferric ammonium citrate, 14) were successful in both inhibiting the formation of and clearing established P. aeruginosa biofilms in continuous flow experiments.60 Further research by the group showed that chelated iron can suppress biofilm formation in P. aeruginosa;61 this expounded upon earlier work done on lactoferrin as a biofilm disruptor.62 The high-throughput screening of over 66 000 compounds from various chemical libraries by Clardy and Junker also sought to identify modulators of P. aeruginosa development and maintenance.63 Numerous scaffolds demonstrated effective antibiofilm activity, with the most active molecule (15) exhibiting an IC50 value in the midnanomolar range; this makes it one of the most potent inhibitors of P. aeruginosa biofilm formation documented in the literature. Computer-aided drug design (CADD) techniques have been employed in the search for new biofilm modulators. By virtually determining if a small library of compounds exhibited similar docking characteristics in a 3D environment to a known inhibitor of the Agrobacterium tumefaciens QS transcriptional regulator protein TraR, it was hypothesized that hits in the virtual screen would translate into compounds that would also display antibiofilm activity against P. aeruginosa.64 The most active compound, baicalein (16), had no noticeable effect on bacterial growth and was found to possess the ability to sensitize ampicillin-resistant P. aeruginosa biofilms to treatment with the antibiotic. Antibiofilm modulators identified from natural products represent one of the last approaches in the discovery of biologically active agents against biofilms. Salicylic acid,65, 66 cinnamaldehyde,67 and extracts from both garlic68, 69 and cranberries70–73 have all shown various degrees of antibiofilm properties against a number of bacteria in various studies. Halogenated furanones (HFs), isolated from the marine red algae Delisea pulchra, are one the most extensively studied classes of natural products in regards to biofilm modulation (Scheme 6). Giskov and co-workers have published numerous reports of the biological activities of these compounds in both QS and biofilm models. This includes observations of in vitro P. aeruginosa biofilm sensitization to treatment with the antibiotic tobramycin,38 and an in vivo report of accelerated bacterial clearance in the lungs of mice that were given a lethal dose of P. aeruginosa followed by treatment with synthetic furanones 21 and 22.74 Drawbacks associated with the use of these molecules include their associated toxicological properties, carcinogenic affects, and relative instability to aqueous conditions.75 Current efforts have been aimed toward impregnating various IMDs such as catheters with furanones in a covalent or noncovalent manner to help alleviate some of the aforementioned handicaps.76, 77 Halogenated furanones isolated from D. pulchra (17–20) and synthetic furanones (21 and 22) that possess antibiofilm activity. Molecules incorporating a 2-aminoimidazole (2-AI) motif derived from the oroidin class of marine natural products have also been investigated as chemical controls over biofilms (Scheme 7).78 The Melander group has reported the inhibition and dispersion properties of numerous analogues borne from the oroidin (23) and bromoageliferin (25) scaffolds that display antibiofilm activity against a number of medically relevant biofilm-forming bacteria.79–82 The 2-AI natural products oroidin 23 and bromoageliferin 25 are useful leads in the discovery of additional antibiofilm modulators. Phages are commonly defined as viruses that infect bacteria; they carry a single copy of genetic material containing the necessary information needed to reproduce inside a host within a protein or lipoprotein coat.83 Bacteriophages are estimated to be the most abundant life form on the planet, with a total species count believed to be in the range of 1×108.84 Attachment to the host cell is receptor mediated, and specificity of these receptors precludes whether or not the phage can infect at the bacterial-strain level or exhibit more broad-spectrum infection properties. Once infection by a phage has initiated, two life cycles are most commonly observed (Scheme 8). They are referred to as being lytic (in which the phage hijacks the hosts' machinery and the bacteria is killed when cell lysis occurs in the process of releasing progeny) or temperate (in which the phage may incorporate itself into the host genome and lay dormant within the bacteria). Whereas the implementation of phage therapies in human medicine dates back to the early 20th century,85 it was quickly overlooked with the discovery of broad-spectrum antibiotics.86 With the emergence of multiple-drug-resistant bacteria and a paucity of newly discovered antibiotic treatments, renewed interest in this area of late has come from both academic and industrial research. Attempts have been made to employ phage infections of resistant bacteria as a means to circumvent the problem of drug resistance. This is significant because the co-evolution of phages and bacteria is a perpetual struggle, with both mutating in concert in hopes of one gaining the upper hand for continued existence. Harnessing the power of phage-mediated infections of bacteria that form biofilms has led to a few promising results; ultimately this begs the question if these therapies represent a viable avenue for biofilm remediation efforts. General life cycle of bacteriophages. A) Phage outside the bacterial cell B) attach to the membrane through specific receptors. The phage genome is injected into the host cell where it can either C) hijack the host machinery to produce progeny or D) integrate itself into the hosts' genetic material. The phage may then proceed through E) the lytic cycle in which the phage kills the host cell through G) release of its progeny, or F) the temperate cycle in which the phage lays dormant within the host and can become lytic at anytime. One of the most unique characteristics of phages is their ability to produce depolymerases and other surface enzymes that degrade bacterial polysaccharides. These enzymes demonstrate great specificity and have been observed to elicit activity against a number of Gram-negative bacteria.87–89 As previously discussed, biofilms secrete an EPS, which essentially acts as the glue that holds the biofilm together. Additionally, it has been noted that the EPS acts as a defense mechanism by providing the bacteria a barrier from microbicides or other entities that would cause harm. It is believed that phage treatment of a biofilm through this mechanism might expose a small portion of host bacterial cells for infection. Furthermore, due to the fluid architecture of the biofilm, the phage might seek transport to distal sites of biofilm by transporting through channels normally employed for the distribution of planktonic bacteria and nutrients. In one particular study, it was reported that the EPS of E. coli biofilms did not provide resistance to infection with the phage T4.90 Another study noted that phages labeled with fluorescent and chromogenic probes attached to or associated with E. coli biofilm matrices; this further demonstrates that the phage was not inhibited by the EPS.91 Phages have also been observed to diffuse through the EPS of P. aeruginosa92 and Lactococcus lactis.93 There have been other reports that involved the engineering of the E. coli-specific phage T7 to express the protein Dispersin B (DspB) intracellularly during infection so that DspB would be released into the extracellular space upon cell lysis.94 DspB had been previously documented to promote enzymatic degradation of an EPS polysaccharide, and thus it results in reduced biofilm mass when applied exogenously to the biofilms of several different species of bacteria.95 This is similar to reports of the use of other enzymes such as DNAase to break down the bacterial EPS, as DNA is one of its major components.96, 97 The group reported that the engineered phage was able to succeed in dispersing established biofilms in comparison to a number of control phages. Furthermore, as a proof-of-concept work, it was postulated that this approach could be employed in the design and application of other phages to help target a range of medically relevant biofilms. A more recent report in this area documented that other engineered bacteriophages were successful in targeting the SOS gene network in E. coli; this resulted in the enhanced killing of bacterial cells with quinolines by several orders of magnitude in vitro and significantly increased survival times of infected mice in vivo.98 A key observation made in the course of this study was that the engineered phage was also capable of reducing the number of persistor cells in bacterial populations that had already been exposed to antibiotics as well as displaying an increased efficacy against biofilm bacteria. Device-associated infections are of major concern due to the relative inability of the medical community to treat established biofilm infections on many of these substrates. Phage technology has shown promise in reducing the formation of catheter-associated biofilms formed by bacteria such as Staphylococcus epidermidis. One particular experiment focused on hydrogel-coated catheters impregnated with phage 456. This formulation was found to be successful in inhibiting the formation of S. epidermidis biofilms under a number of conditions.99 However, the effect of the phage on established biofilms was not investigated. There are a few examples of clinical uses of phage therapies that provide groundwork for the implementation of phages in the control of biofilms. One approach that has been utilized in treatment is the phage cocktail PhageBioDerm®, a biodegradable polymer wound dressing composed of ciprofloxacin, benzocaine, chymotrypsin, bicarbonate, and six lytic phages. These phages have shown activity against S. aureus, P. aeruginosa, E. coli, Streptococcus species, and Proteus species. Another phage cocktail under evaluation is WPP-201, a blend of eight lytic phages that possess the same spectrum of activity as PhageBioDerm®. Despite the advantages of bacteriophages as controls over biofilms, there are a number of potential drawbacks. Mutations of the proteins that serve as receptor sites on the bacterial cell surface for phages can confer phage resistance to the bacteria. For use as a viable therapy in human treatment, phage immunogenicinity is a concern.100 The immune system recognizes the phage as a foreign substance and therefore triggers an antigenic response. Serum studies have indicated that repeated exposure to phage infection triggers increases in antibody titers.83, 101 Additionally, once cell lysis occurs, the bacterial cells' contents spill into the surrounding environments with the ability to act as toxins. This can lead to a number of biological consequences including inflammation and endotoxic shock.83 Finally, the problem posed by biofilms originating from more than one bacteria are of concern.102 Although phage specificity is high, this could necessitate the use of multiple phages in a cocktail so that complete infection of the biofilm community is obtained. Bacterial biofilms are highly organized structures composed of communities of bacteria encased within extracellular matrices. They represent a significant hurdle to the medical community in terms of the treatment and eradication of numerous infectious diseases. This primarily arises from their ability to confer to the bacteria increased resistance to traditional antimicrobial therapies. This review has highlighted the basic principles of biofilm formation and the subsequent challenges faced by their emergence. Following this, a discussion of a few approaches (that is, small molecules and bacteriophages) that have been implemented in the quest for new biofilm modulators has been presented. Although still in its infancy, the continued development of these various research tools aimed at influencing biofilm growth and maintenance will undoubtedly serve as a firm foundation for others to expound upon in hopes of fully understanding biofilms. Financial support is graciously acknowledged from Jimmy V. NCSU Cancer Therapeutics Training Program (predoctoral fellowship to J.J.R.) and Agile Sciences.}, number={14}, journal={CHEMBIOCHEM}, author={Richards, Justin J. and Melander, Christian}, year={2009}, month={Sep}, pages={2287–2294} }
@article{melander_moeller_ballard_richards_huigens_cavanagh_2009, title={Evaluation of dihydrooroidin as an antifouling additive in marine paint}, volume={63}, ISSN={["0964-8305"]}, DOI={10.1016/j.ibiod.2008.08.009}, abstractNote={Methods used to deter biofouling of underwater structures and marine vessels present a serious environmental issue and are both problematic and costly for government and commercial marine vessels worldwide. Current antifouling methods include compounds that are toxic to aquatic wildlife and marine ecosystems. Dihydrooroidin (DHO) was shown to completely inhibit Halomonas pacifica biofilms at 100 μM in a static biofilm inhibition assay giving precedence for the inhibition of other marine biofilm-forming organisms. Herein we present DHO as an effective paint-based, non-cytotoxic, antifouling agent against marine biofouling processes in a marine mesocosm.}, number={4}, journal={INTERNATIONAL BIODETERIORATION & BIODEGRADATION}, author={Melander, Christian and Moeller, Peter D. R. and Ballard, T. Eric and Richards, Justin J. and Huigens, Robert W., III and Cavanagh, John}, year={2009}, month={Jun}, pages={529–532} }
@article{huigens_rogers_steinhauer_melander_2009, title={Inhibition of Acinetobacter baumannii, Staphylococcus aureus and Pseudomonas aeruginosa biofilm formation with a class of TAGE-triazole conjugates}, volume={7}, ISSN={["1477-0539"]}, DOI={10.1039/b817926c}, abstractNote={A chemically diverse library of TAGE-triazole conjugates was synthesized utilizing click chemistry on the TAGE scaffold. This library of small molecules was screened for anti-biofilm activity and found to possess the ability of inhibiting biofilm formation against Acinetobacter baumannii, Staphylococcus aureus and Pseudomonas aeruginosa. One such compound in this library demonstrated the most potent inhibitory effect against Staphylococcus aureus biofilm formation that has been displayed by any 2-aminoimidazole derivative.}, number={4}, journal={ORGANIC & BIOMOLECULAR CHEMISTRY}, author={Huigens, Robert W., III and Rogers, Steven A. and Steinhauer, Andrew T. and Melander, Christian}, year={2009}, pages={794–802} }
@article{rogers_krayer_lindsey_melander_2009, title={Tandem dispersion and killing of bacteria from a biofilm}, volume={7}, ISSN={["1477-0539"]}, DOI={10.1039/b817923a}, abstractNote={The combined effects of biofilm dispersion with a 2-aminoimidazole–triazole conjugate and bactericidal activity with a photodynamic inactivation agent suggest a novel combination therapy for treating diverse microbial infections.}, number={3}, journal={ORGANIC & BIOMOLECULAR CHEMISTRY}, author={Rogers, Steven A. and Krayer, Michael and Lindsey, Jonathan S. and Melander, Christian}, year={2009}, pages={603–606} }
@article{rogers_melander_2008, title={Construction and screening of a 2-aminoimidazole library identifies a small molecule capable of inhibiting and dispersing bacterial biofilms across order, class, and phylum}, volume={47}, ISSN={["1521-3773"]}, DOI={10.1002/anie.200800862}, abstractNote={A team of three: 2-Aminoimidazole, triazole, and tether units together resulted in conjugates (see picture, n=4–6 for the most active compounds) that are capable of inhibiting and dispersing bacteria biofilms without inducing bacterial death. Such biofilms have been implicated in a plethora of medical problems, including infection of implanted medical devices and the mortality of cystic fibrosis patients. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z800862_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, number={28}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, author={Rogers, Steven A. and Melander, Christian}, year={2008}, pages={5229–5231} }
@article{huigens_ma_gambino_moeller_basso_cavanagh_wozniak_melander_2008, title={Control of bacterial biofilms with marine alkaloid derivatives}, volume={4}, ISSN={["1742-2051"]}, DOI={10.1039/b719989a}, abstractNote={Bacterial biofilms are defined as a community of surface-attached bacteria that are protected by an extracellular matrix of biomolecules. We have recently reported the synthesis of a small molecule, denoted TAGE, based on the natural product bromoageliferin and demonstrated that TAGE has anti-biofilm activity against Pseudomonas aeruginosa. Herein we demonstrate that TAGE: (1) does not have selective toxicity against cells within the biofilm state, (2) will inhibit biofilm development under flow conditions, indicating that the CV staining protocol correlates with the ability to be active under biomimetic conditions, and (3) will disperse preformed P. aeruginosa biofilms. We also present preliminary toxicity work that indicates that TAGE is devoid of cytotoxicity in rat and mice cell lines. Advanced derivatives of TAGE have generated compounds shown to be exceedingly effective as biofilm inhibitors against the γ-proteobacteria in this study (P. aeruginosa strains PAO1, PA14, PDO300, and Acinetobacter baumannii). TAGE derivatives also possessed anti-biofilm activity against the β-proteobacterium Bordetella bronchiseptica (Rb50) and the Gram-positive bacterium Staphylococcus aureus;TAGE derivatives inhibited the formation of biofilms, however, some of this activity is attributed to microbicidal activity. The TAGE derivatives presented in this study, however, do not disperse pre-formed biofilms with the same efficiency as TAGE.}, number={6}, journal={MOLECULAR BIOSYSTEMS}, author={Huigens, Robert W., III and Ma, Luyan and Gambino, Christopher and Moeller, Peter D. R. and Basso, Anne and Cavanagh, John and Wozniak, Daniel J. and Melander, Christian}, year={2008}, pages={614–621} }
@article{richards_reed_melander_2008, title={Effects of N-pyrrole substitution on the anti-biofilm activities of oroidin derivatives against Acinetobacter baumannii}, volume={18}, ISSN={["0960-894X"]}, DOI={10.1016/j.bmcl.2008.06.089}, abstractNote={Bacteria of the genus Acinetobacter spp. are rapidly emerging as problematic pathogens in healthcare settings. This is exacerbated by the bacteria’s ability to form robust biofilms. Marine natural products incorporating a 2-aminoimidazole (2-AI) motif, namely from the oroidin class of marine alkaloids, have served as a unique scaffold for developing molecules that have the ability to inhibit and disperse bacterial biofilms. Herein we present the anti-biofilm activity of a small library of second generation oroidin analogues against the bacterium Acinetobacter baumannii.}, number={15}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Richards, Justin J. and Reed, Catherine S. and Melander, Christian}, year={2008}, month={Aug}, pages={4325–4327} }
@article{richards_ballard_melander_2008, title={Inhibition and dispersion of Pseudomonas aeruginosa biofilms with reverse amide 2-aminoimidazole oroidin analogues}, volume={6}, ISSN={["1477-0539"]}, DOI={10.1039/b719082d}, abstractNote={The marine alkaloid oroidin along with a small library of reverse amide (RA) 2-aminoimidazoles were synthesized and assayed for anti-biofilm activity against PAO1 and PA14, two strains of the medically relevant gamma-proteobacterium Pseudomonas aeruginosa. Analogues that contained a long, linear alkyl chain were more potent inhibitors than the natural product at preventing the formation of PAO1 and PA14 biofilms. The most active compound in the series was also shown to disperse established PAO1 and PA14 biofilms at low micromolar concentrations.}, number={8}, journal={ORGANIC & BIOMOLECULAR CHEMISTRY}, author={Richards, Justin J. and Ballard, T. Eric and Melander, Christian}, year={2008}, pages={1356–1363} }
@article{richards_huigens_ballard_basso_cavanagh_melander_2008, title={Inhibition and dispersion of proteobacterial biofilms}, number={14}, journal={Chemical Communications (Cambridge, England)}, author={Richards, J. J. and Huigens, R. W. and Ballard, T. E. and Basso, A. and Cavanagh, J. and Melander, C.}, year={2008}, pages={1698–1700} }
@article{bowman_ballard_ackerson_feldheim_margolis_melander_2008, title={Inhibition of HIV fusion with multivalent gold nanoparticles}, volume={130}, ISSN={["0002-7863"]}, DOI={10.1021/ja710321g}, abstractNote={The design and synthesis of a multivalent gold nanoparticle therapeutic is presented. SDC-1721, a fragment of the potent HIV inhibitor TAK-779, was synthesized and conjugated to 2.0 nm diameter gold nanoparticles. Free SDC-1721 had no inhibitory effect on HIV infection; however, the (SDC-1721)-gold nanoparticle conjugates displayed activity comparable to that of TAK-779. This result suggests that multivalent presentation of small molecules on gold nanoparticle surfaces can convert inactive drugs into potent therapeutics.}, number={22}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Bowman, Mary-Catherine and Ballard, T. Eric and Ackerson, Christopher J. and Feldheim, Daniel L. and Margolis, David M. and Melander, Christian}, year={2008}, month={Jun}, pages={6896-+} }
@article{ballard_melander_2008, title={Kinamycin-mediated DNA cleavage under biomimetic conditions}, volume={49}, ISSN={["0040-4039"]}, DOI={10.1016/j.tetlet.2008.03.019}, abstractNote={The kinamycins are biologically active secondary metabolites characterized by an uncommon diazobenzo[b]fluorene skeleton. Kinamycin D has been shown to potently cleave DNA under mild biomimetic conditions. Use of the endogenously abundant reductant glutathione at 570 μM, kinamycin D effectively cleaved DNA in a concentration, temperature, and time-dependent fashion. Dithiothreitol also proved effective at low concentration while other reductants failed to induce DNA cleavage. Mechanistic consequences of the DNA cleavage results are described.}, number={19}, journal={TETRAHEDRON LETTERS}, author={Ballard, T. Eric and Melander, Christian}, year={2008}, month={May}, pages={3157–3161} }
@article{ballard_richards_wolfe_melander_2008, title={Synthesis and Antibiofilm Activity of a Second-Generation Reverse-Amide Oroidin Library: A Structure-Activity Relationship Study}, volume={14}, ISSN={["1521-3765"]}, DOI={10.1002/chem.200801419}, abstractNote={A second-generation library of 2-aminoimidazole-based derivatives incorporating a "reversed amide" (RA) motif in comparison to the marine natural product oroidin were synthesized and subsequently assayed for antibiofilm activity against the medically relevant Gram-negative proteobacteria P. aeruginosa and A. baumannii. Most notably, an in-depth activity profile is reported for the most active subclass of derivatives that bear linear aliphatic chains off the amide bond. Additionally, further structural modifications of the core template, such as removal of the amide bond or substitution with a triazole isostere, resulted in the discovery of analogues with antibiofilm activities that varied with respect to their inhibition and dispersal properties of P. aeruginosa and A. baumannii biofilms.}, number={34}, journal={CHEMISTRY-A EUROPEAN JOURNAL}, author={Ballard, T. Eric and Richards, Justin J. and Wolfe, Amanda L. and Melander, Christian}, year={2008}, pages={10745–10761} }
@article{richards_ballard_huigens_melander_2008, title={Synthesis and screening of an oroidin library against Pseudomonas aeruginosa biofilms}, volume={9}, ISSN={["1439-4227"]}, DOI={10.1002/cbic.200700774}, abstractNote={A 50-compound library based on the marine natural product oroidin was synthesized and assayed for anti-biofilm activity against PAO1 and PA14, two strains of the medically relevant gamma-proteobacterium Pseudomonas aeruginosa. Through structure-activity relationship (SAR) analysis of analogues based on the oroidin template, several conclusions can be drawn as to what structural properties of the synthetic derivatives are necessary to elicit a biological response. Notably, the most active analogues identified were those that contained a 2-aminoimidazole (2-AI) motif and a dibrominated pyrrolecarboxamide subunit. Here we disclose the synthesis and subsequently determined biological activity of this unique class of compounds as inhibitors of biofilm formation that have no direct antibiotic effect.}, number={8}, journal={CHEMBIOCHEM}, author={Richards, Justin J. and Ballard, T. Eric and Huigens, Robert W., III and Melander, Christian}, year={2008}, month={May}, pages={1267–1279} }
@article{richards_melander_2008, title={Synthesis of a 2-aminoimidazole library for antibiofilm screening utilizing the Sonogashira reaction}, volume={73}, ISSN={["0022-3263"]}, DOI={10.1021/jo800618q}, abstractNote={The divergent synthesis of a 21-member library composed of 2-aminoimidazole compounds for evaluation as novel antibiofilm molecules is presented. The Sonogashira reaction was employed with three regioisomeric aryl iodides and 11 different alkynes to generate variously substituted diverse ring systems. Good to excellent yields (80-97%) for the reaction were obtained, and the products provide adequate handles for further manipulation into more advanced analogues.}, number={13}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Richards, Justin J. and Melander, Christian}, year={2008}, month={Jul}, pages={5191–5193} }
@article{burns_bobay_basso_cavanagh_melander_2008, title={Targeting RNA with cysteine-constrained peptides}, volume={18}, ISSN={["0960-894X"]}, DOI={10.1016/j.bmcl.2007.11.096}, abstractNote={A combined approach for targeting RNA with novel, biologically active ligands has been developed using a cyclic peptide library and in silico modeling. This approach has successfully identified novel cyclic peptide constructs that can target bTAR RNA. Subsequently, RNA/peptide interactions were effectively modeled using the HADDOCK docking program.}, number={2}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Burns, Virginia A. and Bobay, Benjamin G. and Basso, Anne and Cavanagh, John and Melander, Christian}, year={2008}, month={Jan}, pages={565–567} }
@article{huigens_richards_parise_ballard_zeng_deora_melander_2007, title={Inhibition of Pseudomonas aeruginosa biofilm formation with bromoageliferin analogues}, volume={129}, number={22}, journal={Journal of the American Chemical Society}, author={Huigens, R. W. and Richards, J. J. and Parise, G. and Ballard, T. E. and Zeng, W. and Deora, R. and Melander, C.}, year={2007}, pages={6966-} }
@article{zeng_ballard_tkachenko_burns_feldheim_melander_2006, title={Mimicking the biological activity of diazobenzo[b]fluorene natural products with electronically tuned diazofluorene analogs}, volume={16}, ISSN={["0960-894X"]}, DOI={10.1016/j.bmcl.2006.07.024}, abstractNote={Under appropriate electronic modulation, simple diazofluorene analogs recapitulate the DNA cleavage activity of kinamycin D under thiol-based reducing conditions. Achieving DNA cleavage under these reducing conditions is key to anticancer activity, as the most active compound, 1-methoxydiazofluorene, inhibits the proliferation of HeLa cells.}, number={19}, journal={BIOORGANIC & MEDICINAL CHEMISTRY LETTERS}, author={Zeng, Wei and Ballard, T. Eric and Tkachenko, Alexander G. and Burns, Virginia A. and Feldheim, Daniel L. and Melander, Christian}, year={2006}, month={Oct}, pages={5148–5151} }
@article{zeng_ballard_melander_2006, title={Tuning the oxidation properties of vanadium(V) through ligand stoichiometry}, volume={47}, ISSN={["0040-4039"]}, DOI={10.1016/j.tetlet.2006.06.051}, abstractNote={Vanadium(V) (5 mol %) and hydroxamic acid ligand (45 mol %) were found to promote the selective tert-butyl hydroperoxide-mediated oxidation of allylic and propargylic alcohols to the corresponding aldehydes and ketones.}, number={33}, journal={TETRAHEDRON LETTERS}, author={Zeng, Wei and Ballard, T. Eric and Melander, Christian}, year={2006}, month={Aug}, pages={5923–5926} }