ABSTRACTDrug resistance is a major problem inMycobacterium tuberculosiscontrol, and it is critical to identify novel drug targets and new antimycobacterial compounds. We have previously identified an imidazo[1,2-a]pyridine-4-carbonitrile-based agent, MP-III-71, with strong activity againstM. tuberculosis. In this study, we evaluated mechanisms of resistance to MP-III-71. We derived three independentM. tuberculosismutants resistant to MP-III-71 and conducted whole-genome sequencing of these mutants. Loss-of-function mutations inRv2887were common to all three MP-III-71-resistant mutants, and we confirmed the role ofRv2887as a gene required for MP-III-71 susceptibility using complementation. The Rv2887 protein was previously unannotated, but domain and homology analyses suggested it to be a transcriptional regulator in the MarR (multiple antibiotic resistance repressor) family, a group of proteins first identified inEscherichia colito negatively regulate efflux pumps and other mechanisms of multidrug resistance. We found that two efflux pump inhibitors, verapamil and chlorpromazine, potentiate the action of MP-III-71 and that mutation ofRv2887abrogates their activity. We also used transcriptome sequencing (RNA-seq) to identify genes which are differentially expressed in the presence and absence of a functional Rv2887 protein. We found that genes involved in benzoquinone and menaquinone biosynthesis were repressed by functional Rv2887. Thus, inactivating mutations ofRv2887, encoding a putative MarR-like transcriptional regulator, confer resistance to MP-III-71, an effective antimycobacterial compound that shows no cross-resistance to existing antituberculosis drugs. The mechanism of resistance ofM. tuberculosisRv2887mutants may involve efflux pump upregulation and also drug methylation.
Investigation of the Rv3065, Rv2942, Rv1258c, Rv1410c, and Rv2459 efflux pump genes expression among multidrug-resistant Mycobacterium tuberculosis clinical isolates
