Active Benzimidazole Derivatives Targeting the MmpL3 Transporter in <i>Mycobacterium abscessus</i>

Abstract

The prevalence of pulmonary infections due to nontuberculous mycobacteria such as <i>Mycobacterium abscessus</i> has been increasing and surpassing tuberculosis (TB) in some industrialized countries. Because of intrinsic resistance to most antibiotics that drastically limits conventional chemotherapeutic treatment options, new anti-<i>M. abscessus</i> therapeutics are urgently needed against this emerging pathogen. Extensive screening of a library of benzimidazole derivatives that were previously shown to be active against <i>Mycobacterium tuberculosis</i> led to the identification of a lead compound exhibiting very potent in vitro activity against a wide panel of <i>M. abscessus</i> clinical strains. Designated EJMCh-6, this compound, a 2-(2-cyclohexylethyl)-5,6-dimethyl-1<i>H</i>-benzo[<i>d</i>]imidazole), also exerted very strong activity against intramacrophage-residing <i>M. abscessus</i>. Moreover, the treatment of infected zebrafish embryos with EJMCh-6 was correlated with significantly increased embryo survival and a decrease in the bacterial burden as compared to those for untreated fish. Insights into the mechanism of action were inferred from the generation of spontaneous benzimidazole-resistant strains and the identification of a large set of missense mutations in MmpL3, the mycolic acid transporter in mycobacteria. Overexpression of the mutated <i>mmpL3</i> alleles in a susceptible <i>M. abscessus</i> strain was associated with high resistance levels to EJMCh-6 and to other known MmpL3 inhibitors. Mapping the mutations conferring resistance on an MmpL3 three-dimensional homology model defined a potential EJMCh-6-binding cavity. These data emphasize a yet unexploited chemical structure class against <i>M. abscessus</i> with promising translational development for the treatment of <i>M. abscessus</i> lung diseases.