Identification of antimicrobial activity among FDA-approved drugs for combating Mycobacterium abscessus and Mycobacterium chelonae.

OBJECTIVES: Rapidly growing mycobacteria have long been neglected in drug discovery efforts and this neglect is reflected in the paucity of therapeutic options available for diseases resulting from these infections. The purpose of this work is to identify new candidate drugs for treating non-tuberculous mycobacteria (NTM) by testing FDA-approved drugs for antimicrobial activity against Mycobacterium abscessus and Mycobacterium chelonae, two emerging NTM drug-resistant pathogens. METHODS: In this study, we screened 1040 FDA-approved drugs against M. abscessus and M. chelonae. RESULTS: Of the drugs screened, 32 compounds exhibited significant antimicrobial activity, with an MIC ≤ 8 mg/L, against M. chelonae, while only 7 compounds showed such activity against M. abscessus. Notably, neostigmine bromide and cinnarizine exhibited highly significant antimicrobial activity against M. chelonae, but had little potency against M. abscessus. Metronidazole and puromycin were the only drugs that acted equipotently against both strains, in decreasing order of effectiveness. CONCLUSIONS: The dearth of identified compounds active against M. abscessus exemplifies its ability to resist drugs as well as the resilience of rapidly growing NTM. Repurposing of approved drugs is a viable alternative to de novo drug discovery and development.

A high-throughput fluorescence polarization assay for inhibitors of gyrase B.

DNA gyrase, a type II topoisomerase that introduces negative supercoils into DNA, is a validated antibacterial drug target. The holoenzyme is composed of 2 subunits, gyrase A (GyrA) and gyrase B (GyrB), which form a functional A(2)B(2) heterotetramer required for bacterial viability. A novel fluorescence polarization (FP) assay has been developed and optimized to detect inhibitors that bind to the adenosine triphosphate (ATP) binding domain of GyrB. Guided by the crystal structure of the natural product novobiocin bound to GyrB, a novel novobiocin-Texas Red probe (Novo-TRX) was designed and synthesized for use in a high-throughput FP assay. The binding kinetics of the interaction of Novo-TRX with GyrB from Francisella tularensis has been characterized, as well as the effect of common buffer additives on the interaction. The assay was developed into a 21-µL, 384-well assay format and has been validated for use in high-throughput screening against a collection of Food and Drug Administration-approved compounds. The assay performed with an average Z' factor of 0.80 and was able to identify GyrB inhibitors from a screening library.