Novel DNA gyrase inhibitors: microbiological characterisation of pyrrolamides.

Pyrrolamides are a novel class of antibacterial agents that target DNA gyrase, resulting in inhibition of DNA synthesis and bacterial cell death. In these studies, advanced compounds were shown to have potent in vitro activity against selected Gram-positive and Gram-negative pathogens, including meticillin-resistant Staphylococcus aureus, meticillin- and quinolone-resistant S. aureus, vancomycin-resistant enterococci, penicillin-resistant Streptococcus pneumoniae and ß-lactamase-producing Haemophilus influenzae and Moraxella catarrhalis. Representatives of the class were demonstrated to be bactericidal, with frequencies of spontaneous resistance ≤1×10(-7) when plated at concentrations equivalent to their minimum inhibitory concentration. Mode of action studies suggested that the activity of these compounds is due to inhibition of the GyrB subunit of DNA gyrase in key pathogens. The antibacterial activity, spectrum and mode of action of these compounds underscore the promise of the pyrrolamide series as attractive candidates for the treatment of several clinical indications, including respiratory and soft tissue infections.

Pyrrolamide DNA gyrase inhibitors: fragment-based nuclear magnetic resonance screening to identify antibacterial agents.

DNA gyrase is an essential enzyme in bacteria, and its inhibition results in the disruption of DNA synthesis and, subsequently, cell death. The pyrrolamides are a novel class of antibacterial agents targeting DNA gyrase. These compounds were identified by a fragment-based lead generation (FBLG) approach using nuclear magnetic resonance (NMR) screening to identify low-molecular-weight compounds that bind to the ATP pocket of DNA gyrase. A pyrrole hit with a binding constant of 1 mM formed the basis of the design and synthesis of a focused library of compounds that resulted in the rapid identification of a lead compound that inhibited DNA gyrase with a 50% inhibitory concentration (IC(50)) of 3 µM. The potency of the lead compound was further optimized by utilizing iterative X-ray crystallography to yield DNA gyrase inhibitors that also displayed antibacterial activity. Spontaneous mutants were isolated in Staphylococcus aureus by plating on agar plates containing pyrrolamide 4 at the MIC. The resistant variants displayed 4- to 8-fold-increased MIC values relative to the parent strain. DNA sequencing revealed two independent point mutations in the pyrrolamide binding region of the gyrB genes from these variants, supporting the hypothesis that the mode of action of these compounds was inhibition of DNA gyrase. Efficacy of a representative pyrrolamide was demonstrated against Streptococcus pneumoniae in a mouse lung infection model. These data demonstrate that the pyrrolamides are a novel class of DNA gyrase inhibitors with the potential to deliver future antibacterial agents targeting multiple clinical indications.

Utilization of target-specific, hypersensitive strains of Saccharomyces cerevisiae to determine the mode of action of antifungal compounds.

Target-specific hypersusceptible strains of Saccharomyces cerevisiae were used to screen antifungal compounds. Two novel Erg7p inhibitors were identified, providing proof of principle of the approach taken. However, observed hypersensitivities to antifungals acting via other targets imply that use of this tool to identify the mode of action requires significant deconvolution.

Pyridines and pyrimidines mediating activity against an efflux-negative strain of Candida albicans through putative inhibition of lanosterol demethylase.

The first step in ergosterol biosynthesis in Saccharomyces cerevisiae consists of the condensation of two acetyl coenzyme A (acetyl-CoA) moieties by acetoacetyl-CoA thiolase, encoded by ERG10. The inhibition of the sterol pathway results in feedback activation of ERG10 transcription. A cell-based reporter assay, in which increased ERG10 transcription results in elevated specific beta-galactosidase activity, was used to find novel inhibitors of ergosterol biosynthesis that could serve as chemical starting points for the development of novel antifungal agents. A class of pyridines and pyrimidines identified in this way had no detectable activity against the major fungal pathogen Candida albicans (MICs > 64 micro g. ml(-1)). However, a strain of C. albicans lacking the Cdr1p and Cdr2p efflux pumps was sensitive to the compounds (with MICs ranging from 2 to 64 micro g. ml(-1)), suggesting that they are efficiently removed from wild-type cells. Quantitative analysis of sterol intermediates that accumulated during growth inhibition revealed the accumulation of lanosterol at the expense of ergosterol. Furthermore, a clear correlation was found between the 50% inhibitory concentration at which the sterol profile was altered and the antifungal activity, measured as the MIC. This finding strongly suggests that the inhibition of growth was caused by a reduction in ergosterol synthesis. The compounds described here are a novel class of antifungal pyridines and pyrimidines and the first pyri(mi)dines to be shown to putatively mediate their antifungal activity against C. albicans via lanosterol demethylase.