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BTZ-043 exposure in vitro selects efflux pump mutants and BTZ-043, bedaquiline and clofazimine resistance in Mycobacterium tuberculosis

A Ghodousi(1) I Iannucci(1) F Saluzzo(1) D M Cirillo(2)

1:Vita-Salute San Raffaele University; 2:IRCCS San Raffaele Scientific Institute


With the emergence of drug-resistant strains of Mycobacterium tuberculosis complex (MTBC), substantial efforts have been directed towards the development of innovative drugs for Tuberculosis treatment. Among the most encouraging lead compounds is the benzothiazinones BTZ-043 which is presently undergoing phase IIb clinical trials.


In light of the potential clinical significance of BTZ-043, we aimed to pinpoint potential synergistic interactions and novel resistance mechanisms using a stepwise approach, exposing wild-type strain of M. tuberculosis H37Rv ATCC 27294 to escalating concentrations of BTZ-043, and the generated resistance-associated variants (RAVs) were identified using the whole genome sequencing method. Mutant MIC values were confirmed for BTZ-043 in broth microdilution and for bedaquiline/clofazimine in MGIT960.


Results and conclusion

Genomic analysis of these BTZ-043-resistant mutants revealed the emergence of mutations in Rv0678, the negative regulator of the mmpS5/L5 drug efflux pump, and dprE1. Mutant MIC values showed a 4-16 fold and a 1000 fold increase compared to baseline for Rv0678 and dprE1 mutants, respectively. Moreover, all Rv0678 mutants were found to be resistant to both bedaquiline and clofazimine.

Our experiments confirmed that in vitro generated Rv0678 mutations confer a low-level cross-resistance to BTZ-043. While it remains uncertain whether Rv0678 mutations would render benzothiazinones ineffective in TB treatment, these results underscore the significance of monitoring the clinically prevalent Rv0678 mutations during the ongoing BTZ043 and other benzothiazinones clinical trials.

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