Repurposing ethacridine as a potent MMPL3 Inhibitor for the treatment of tuberculosis

Mycobacterium tuberculosis (Mtb), the pathogen responsible for tuberculosis, remains a major global health threat, particularly with the rise of multidrug-resistant and extensively drug-resistant strains. This has renewed interest in repurposing existing drugs and exploring new cellular targets. The mycobacterial cell envelope is a key barrier to antibiotics and an attractive site for therapeutic intervention. In this study, we identify the FDA-approved drug ethacridine as a strong inhibitor of MmpL3, an essential transporter required for exporting trehalose monomycolate and building the cell wall. Computational docking and molecular dynamics indicate that ethacridine engages the MmpL3 binding pocket at residues also targeted by SQ109. Ethacridine shows potent activity against drug-sensitive and resistant Mtb isolates, with an MIC of 1 g/mL, and remains effective against non-replicating bacteria and intracellular infection. Ethacridine-resistant mutants, overexpression strains, and a spheroplast TMM-flipping assay confirm MmpL3 as the target. The compound also disrupts the membrane potential, and flow-cytometry assays