ABSTRACT
Minocycline is one of the few options available to treat infections caused by Acinetobacter baumannii. Acquired resistance to minocycline in A. baumannii is associated with presence of the TetB efflux pump. Previous studies suggested that the absence of tetB may predict minocycline minimum inhibitory concentrations (MICs) of ≤4 µg/mL. In this study, a collection of 258 A. baumannii isolates was used to generate MIC frequency distributions for the tetB-positive and -negative sets of isolates. Of the 93 tetB-negative strains, all had minocycline MICs ≤ 4 µg/mL, resulting in a negative predictive value of 100%. Of the 165 tetB-positive strains, 154 had minocycline MICs > 4 µg/mL, resulting in a positive predictive value of 93.3%. In conclusion, this study shows that tetB is highly associated with MICs above the current US Food and Drug Administration (FDA) and Clinical and Laboratory Standards Institute (CLSI) susceptible breakpoint of 4 µg/mL.
Subject(s)
Acinetobacter baumannii , Anti-Bacterial Agents/pharmacology , Membrane Transport Proteins/genetics , Minocycline/pharmacology , Tetracycline Resistance/genetics , Acinetobacter Infections/drug therapy , Acinetobacter baumannii/drug effects , Acinetobacter baumannii/genetics , Acinetobacter baumannii/isolation & purification , Humans , Microbial Sensitivity TestsABSTRACT
A new series of dihydrofolate reductase (DHFR) inhibitors, the 7-(benzimidazol-1-yl)-2,4-diaminoquinazolines, were designed and optimized for antibacterial potency and enzyme selectivity. The most potent inhibitors in this series contained a five-membered heterocycle at the 2-position of the benzimidazole, leading to highly potent and selective compounds that exploit the differences in the size of a binding pocket adjacent to the NADPH cofactor between the bacterial and human DHFR enzymes. Typical of these compounds is 7-((2-thiazol-2-yl)benzimidazol-1-yl)-2,4 diaminoquinazoline, which is a potent inhibitor of S. aureus DHFR (Ki = 0.002 nM) with 46700-fold selectivity over human DHFR. This compound also has high antibacterial potency on Gram-positive bacteria with an MIC versus wild type S. aureus of 0.0125 µg/mL and a MIC versus trimethoprim-resistant S. aureus of 0.25 µg/mL. In vivo efficacy versus a S. aureus septicemia was demonstrated, highlighting the potential of this new series.
Subject(s)
Anti-Bacterial Agents/chemical synthesis , Benzimidazoles/chemical synthesis , Folic Acid Antagonists/chemical synthesis , Quinazolines/chemical synthesis , Tetrahydrofolate Dehydrogenase/metabolism , Animals , Anti-Bacterial Agents/pharmacokinetics , Anti-Bacterial Agents/pharmacology , Benzimidazoles/pharmacokinetics , Benzimidazoles/pharmacology , Drug Resistance, Bacterial , Folic Acid Antagonists/pharmacokinetics , Folic Acid Antagonists/pharmacology , Humans , Mice , Microbial Sensitivity Tests , Models, Molecular , Quinazolines/pharmacokinetics , Quinazolines/pharmacology , Sepsis/drug therapy , Staphylococcal Infections/drug therapy , Staphylococcus aureus/drug effects , Staphylococcus aureus/enzymology , Streptococcus pneumoniae/drug effects , Structure-Activity RelationshipABSTRACT
The macromolecular synthesis assay was optimized in both S. aureus and E. coli imp and used to define patterns of inhibition of DNA, RNA, protein, and cell wall biosynthesis of several drug classes. The concentration of drug required to elicit pathway inhibition differed among the antimicrobial agents tested, with inhibition detected at concentrations significantly below the minimum inhibitory concentration (MIC) for tedizolid; within 4-fold of the MIC for ciprofloxacin, cefepime, vancomycin, tetracycline, and chloramphenicol; and significantly above the MIC for rifampicin and kanamycin. In a DNA gyrase/topoisomerase IV structure-based drug design optimization program, the assay rapidly identified undesirable off-target activity within certain chemotypes, altering the course of the program to focus on the series that maintained on-target activity.
Subject(s)
Anti-Bacterial Agents/pharmacology , Biological Assay , Escherichia coli/drug effects , Staphylococcus aureus/drug effects , Anti-Bacterial Agents/chemistry , Bacterial Proteins/antagonists & inhibitors , Bacterial Proteins/biosynthesis , Cell Wall/drug effects , DNA Gyrase/chemistry , DNA, Bacterial/antagonists & inhibitors , DNA, Bacterial/biosynthesis , Drug Discovery , Escherichia coli/metabolism , Microbial Sensitivity Tests , RNA, Bacterial/antagonists & inhibitors , RNA, Bacterial/biosynthesis , Staphylococcus aureus/metabolismABSTRACT
Increasing resistance to every major class of antibiotics and a dearth of novel classes of antibacterial agents in development pipelines has created a dwindling reservoir of treatment options for serious bacterial infections. The bacterial type IIA topoisomerases, DNA gyrase and topoisomerase IV, are validated antibacterial drug targets with multiple prospective drug binding sites, including the catalytic site targeted by the fluoroquinolone antibiotics. However, growing resistance to fluoroquinolones, frequently mediated by mutations in the drug-binding site, is increasingly limiting the utility of this antibiotic class, prompting the search for other inhibitor classes that target different sites on the topoisomerase complexes. The highly conserved ATP-binding subunits of DNA gyrase (GyrB) and topoisomerase IV (ParE) have long been recognized as excellent candidates for the development of dual-targeting antibacterial agents with broad-spectrum potential. However, to date, no natural product or small molecule inhibitors targeting these sites have succeeded in the clinic, and no inhibitors of these enzymes have yet been reported with broad-spectrum antibacterial activity encompassing the majority of Gram-negative pathogens. Using structure-based drug design (SBDD), we have created a novel dual-targeting pyrimidoindole inhibitor series with exquisite potency against GyrB and ParE enzymes from a broad range of clinically important pathogens. Inhibitors from this series demonstrate potent, broad-spectrum antibacterial activity against Gram-positive and Gram-negative pathogens of clinical importance, including fluoroquinolone resistant and multidrug resistant strains. Lead compounds have been discovered with clinical potential; they are well tolerated in animals, and efficacious in Gram-negative infection models.
Subject(s)
Anti-Bacterial Agents/chemistry , Anti-Bacterial Agents/pharmacology , DNA Gyrase/metabolism , DNA Topoisomerase IV/antagonists & inhibitors , Drug Design , Topoisomerase II Inhibitors/chemistry , Topoisomerase II Inhibitors/pharmacology , Animals , Anti-Bacterial Agents/chemical synthesis , Bacteria/drug effects , Bacteria/enzymology , DNA Gyrase/chemistry , DNA Topoisomerase IV/chemistry , Drug Resistance, Bacterial/drug effects , Female , Indoles/chemical synthesis , Indoles/chemistry , Indoles/pharmacology , Mice , Microbial Sensitivity Tests , Models, Molecular , Protein Conformation , Topoisomerase II Inhibitors/chemical synthesisABSTRACT
The 2.25 A crystal structure of a complex of Aurora A kinase (AIKA) with cyclopropanecarboxylic acid-(3-(4-(3-trifluoromethyl-phenylamino)-pyrimidin-2-ylamino)-phenyl)-amide 1 is described here. The inhibitor binding mode is novel, with the cyclopropanecarboxylic acid moiety directed towards the solvent exposed region of the ATP-binding pocket, and several induced structural changes in the active-site compared with other published AIK structures. This structure provides context for the available SAR data on this compound class, and could be exploited for the design of analogs with increased affinity and selectivity for AIK.