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.