8‑Hydroxyquinoline\nSeries Exerts Bactericidal\nActivity against Mycobacterium tuberculosis Via Copper-Mediated Toxicity

New drugs and mechanisms of action targeting Mycobacterium\ntuberculosis are urgently needed to solve the global\npandemic of tuberculosis. We previously demonstrated that the 8-hydroxyquinoline\nseries has rapid bactericidal activity against M. tuberculosis. In this work, we determined that the activity of the 8HQ series\nis potentiated by copper ions and that the activity is dependent on\ncopper since activity was reduced when copper was depleted from the\nmedium. We determined that exposure to 8HQs led to an increase in\nintracellular copper. The increase in copper ions was specific since\nwe saw no changes for other metal cations (zinc, iron, magnesium,\nmanganese, or calcium). We observed the transient generation of reactive\noxygen species after 8HQ exposure which disappeared by 24 h. Inhibition\nof growth could be partially relieved by scavenging hydroxyl radicals.\nWe excluded the possibility that 8HQs are toxic by DNA intercalation.\nWe screened a panel of hypomorph strains and identified sensitized\nstrains. The pattern of sensitized strains did not suggest a specific\ntarget, but metalloenzymes, proteins with Fe–S clusters, and\ncell envelope biosynthetic enzymes were highlighted. These data suggest\nthat 8HQs do not have a specific intracellular target, but act as\ncopper ionophores, and that the mode of action is via copper-dependent\ntoxicity.