MmpL3 drug discovery in Mycobacterium abscessus: from target validation to therapeutic development

Mycobacterium abscessus ( Mab ) pulmonary disease remains difficult to treat because of extensive intrinsic resistance, the limited bactericidal activity of current drugs, and the physiological diversity of bacterial populations encountered during infection. MmpL3, an essential transporter required for trehalose monomycolate (TMM) trafficking during mycomembrane assembly, has emerged as one of the best-characterized experimental drug targets in M. abscessus . Chemically distinct MmpL3-directed series include piperidinols, indole-2-carboxamides, benzimidazoles, benzothiazole amides, and naphthalen-1-ylmethanamines. Across these series, resistance genetics and mycolate transport phenotypes support MmpL3 engagement, although the nature and strength of the supporting evidence differ among chemotypes. Some compounds predominantly disrupt TMM transport and cell envelope assembly, whereas others additionally alter membrane integrity, adenosine triphosphate (ATP) homeostasis, or respiration. These observations show that target identity alone does not define the full antibacterial mechanism of an MmpL3 inhibitor. In this study, we integrate the chemical, genetic, biochemical, and physiological evidence defining MmpL3 inhibition in M. abscessus and discuss how chemotype-specific resistance and cellular pharmacology may influence bactericidal activity, combination therapy, and lead optimization. We argue that future MmpL3-directed drug development should prioritize not only potency but also bactericidal activity, resistance resilience, and pharmacological compatibility with multidrug regimens.