Usnic Acid Derivatives as Inhibitors of Mycobacterium tuberculosis Uracil-DNA Glycosylase

Tuberculosis (TB) remains a global health issue exacerbated by spreading drug resistance and lengthy treatment regimens. Targeting bacterial DNA-repair pathways, particularly those counteracting host-generated genotoxic stress, represents a promising strategy to sensitize Mycobacterium tuberculosis to existing antibiotics. Through structure-based virtual screening of a compound library, we identified novel small-molecule inhibitors of M. tuberculosis uracil-DNA glycosylase (MtbUng), an enzyme essential for the repair of DNA damage inflicted by macrophage-produced reactive nitrogen species. Experimental validation revealed that four derivatives of usnic acid, a lichen-derived metabolite, significantly inhibited MtbUng activity, with the most potent compound, OL10-88-1, exhibiting IC₅₀ 26 ± 7 µM. Molecular docking suggests that OL10-88-1 inhibits MtbUng by occupying both the active site and the DNA-binding groove, thereby disrupting multiple steps of uracil recognition. The compounds also showed variable inhibitory activity against uracil-DNA glycosylases from Escherichia coli, humans, and vaccinia virus. Our findings establish that the compound could potentially be used in combination therapies to enhance the efficacy of current anti-TB drugs by exploiting the vulnerability of DNA-repair-deficient mycobacteria.