Efflux Attenuates the Antibacterial Activity of Q203 in Mycobacterium tuberculosis.

New and improved treatments for tuberculosis (TB) are urgently needed. Recently, it has been demonstrated that verapamil, an efflux inhibitor, can reduce bacterial drug tolerance caused by efflux pump activity when administered in combination with available antituberculosis agents. The aim of this study was to evaluate the effectiveness of verapamil in combination with the antituberculosis drug candidate Q203, which has recently been developed and is currently under clinical trials as a potential antituberculosis agent. We evaluated changes in Q203 activity in the presence and absence of verapamil in vitro using the resazurin microplate assay and ex vivo using a microscopy-based phenotypic assay for the quantification of intracellular replicating mycobacteria. Verapamil increased the potency of Q203 against Mycobacterium tuberculosis both in vitro and ex vivo, indicating that efflux pumps are associated with the activity of Q203. Other efflux pump inhibitors also displayed an increase in Q203 potency, strengthening this hypothesis. Therefore, the combination of verapamil and Q203 may be a promising combinatorial strategy for anti-TB treatment to accelerate the elimination of M. tuberculosis.