Abstract 1657 Interactions of established and novel antibacterials with Acinetobacter baumannii gyrase and topoisomerase IV

Acinetobacter baumannii is a common nosocomial infection that has major therapeutic challenges due to increasing antibacterial resistance. Fluoroquinolones, which target the bacterial type II topoisomerases, gyrase, and topoisomerase IV, were commonly used as part of the treatment regimen for A. baumannii until the rise of widespread resistance in the 1990s. It is critical to identify novel classes of antibacterials with activity against this pathogen. Consequently, we examined the effects of new gyrase/topoisomerase IV-targeted antibacterials, such as triazaacenaphthelenes (TAANs) and spiropyrimidinetriones (SPTs), on A. baumannii gyrase and topoisomerase IV. The lead members of these new classes, gepotidacin and zoliflodacin, have finished phase III clinical trials for urinary-tract infections and gonorrhea, respectively. The clinical efficacy of antibacterials targeting type II topoisomerases is linked to their ability to stabilize covalent enzyme-cleaved DNA complexes that are requisite enzyme intermediates. Fluoroquinolones and SPTs are associated with the generation of enzyme-mediated double-stranded DNA breaks, while TAANs are associated with the generation of single-stranded breaks. We tested the abilities of fluoroquinolones, TAANs, and SPTs to enhance A. baumannii topoisomerase-mediated DNA cleavage and their abilities to inhibit the catalytic activity of the enzymes. Fluoroquinolones (moxifloxacin and ciprofloxacin) induced similar levels of double-stranded breaks (∼20% of substrate) and inhibited the catalytic activity of the wild-type enzyme. Zoliflodacin induced ∼20% cleavage with gyrase but lower levels (with reduced potency) with topoisomerase IV. It showed a surprisingly strong ability to inhibit the DNA supercoiling activity of gyrase (IC50 ∼ 2.5 μM), but a lesser ability to inhibit decatenation by topoisomerase IV. Gepotidacin was very active against topoisomerase IV (maximal DNA cleavage ≈ 25%, EC50 ≈ 0.02 μM). In addition to its hallmark generation of single-stranded DNA breaks, gepotidacin induced ∼5% double-stranded DNA breaks with a similar EC50. Gepotidacin showed the strongest inhibition of catalytic activity of the compounds tested (IC50: gyrase ∼ 1 μM, topoisomerase IV ∼ 0.4 μM). Our results suggest that new classes of gyrase/topoisomerase IV-targeted antibacterials may be useful for treating A. baumannii infections. This work was funded by the V NIH Grant R01 GM126363, and NIH Grant R01 AI170546.