Discovery, characterization and comparison of inhibitors of Bacillus anthracis and Staphylococcus aureus replicative DNA helicases

Antibacterial compounds with new mechanisms of action are needed for effective therapy against drug-resistant pathogens in the clinic and in biodefense. Screens for inhibitors of the essential replicative helicases of Bacillus anthracis and Staphylococcus aureus yielded 18 confirmed hits (IC50 ⩽ 25 μM). Several (5 of 18) of the inhibitors were also shown to inhibit DNA replication in permeabilized polA-deficient B. anthracis cells. One of the most potent inhibitors also displayed antibacterial activity (MIC ∼5 μg/ml against a range of Gram-positive species including bacilli and staphylococci) together with good selectivity for bacterial versus mammalian cells (CC50/MIC > 16) suitable for further optimization. This compound shares the bicyclic ring of the clinically proven aminocoumarin scaffold, but is not a gyrase inhibitor. It exhibits a mixed mode of helicase inhibition including a component of competitive inhibition with the DNA substrate (Ki = 8 μM) and is rapidly bactericidal at 4 × MIC.

High throughput screening revealed several inhibitors of the replicative DNA helicase of Bacillus anthracis. Compound 2 exhibited potency in vitro (Ki = 8 μM) and in vivo (MIC ∼3 μg/ml) as well as selectivity for bacterial cell growth inhibition (CC50/MIC > 16).Figure optionsDownload as PowerPoint slide