Evidence for Inhibition of Topoisomerase 1A by Gold(III) Macrocycles and Chelates Targeting Mycobacterium tuberculosis and Mycobacterium abscessus

Mycobacterium tuberculosis and the fast-growing speciesMycobacterium abscessus are two important human pathogens causing persistent pulmonary infections that are difficult to cure and require long treatment times. The emergence of drug-resistantM. tuberculosis strains and the high level of intrinsic resistance ofM. abscessus call for novel drug scaffolds that effectively target both pathogens. In this study, we evaluated the activity of bis(pyrrolide-imine) gold(III) macrocycles and chelates, originally designed as DNA intercalators capable of targeting human topoisomerase types I and II (Topo1 and Topo2), againstM. abscessus andM. tuberculosis . We identified a total of 5 noncytotoxic compounds active against both mycobacterial pathogens under replicatingin vitro conditions. We chose one of these hits, compound 14, for detailed analysis due to its potent bactericidal mode of inhibition and scalable synthesis. The clinical relevance of this compound was demonstrated by its ability to inhibit a panel of diverseM. tuberculosis andM. abscessus clinical isolates. Prompted by previous data suggesting that compound 14 may target topoisomerase/gyrase enzymes, we demonstrated that it lacked cross-resistance with fluoroquinolones, which target theM. tuberculosis gyrase.In vitro enzyme assays confirmed the potent activity of compound 14 against bacterial topoisomerase 1A (Topo1) enzymes but not gyrase. Novel scaffolds like compound 14 with potent, selective bactericidal activity againstM. tuberculosis andM. abscessus that act on validated but underexploited targets like Topo1 represent a promising starting point for the development of novel therapeutics for infections by pathogenic mycobacteria.