Relative contributions of the novel diarylquinoline TBAJ-876 and its active metabolite to the bactericidal activity in a murine model of tuberculosis

Background TBAJ-876 is a next-generation diarylquinoline. In vivo, diarylquinoline metabolites are formed with activity against Mycobacterium tuberculosis. Species-specific differences in parent drug-to-metabolite ratios might impact the translational value of animal model-based predictions. This study investigates the contribution of TBAJ-876 and its major active metabolite, TBAJ-876-M3 (M3), to the total bactericidal activity in a mouse tuberculosis model. Methods In vitro activity of TBAJ-876 and M3 was investigated and compared to bedaquiline. Subsequently, a dose-response study was conducted in M. tuberculosis-infected BALB/c mice treated with TBAJ-876 (1.6/6.3/25 mg/kg) or M3 (3.1/12.5/50 mg/kg). Colony-forming units in the lungs and TBAJ-876 and M3 plasma concentrations were determined. M3's contribution to TBAJ-876's bactericidal activity was estimated based on M3 exposure following TBAJ-876 treatment and corresponding M3 activity observed in M3-treated animals. Results TBAJ-876 and M3 demonstrated profound bactericidal activity. Lungs of mice treated for 4 weeks with 50 mg/kg M3 were culture negative. Following TBAJ-876 treatment, M3 exposures were 2.2 to 3.6-fold higher than for TBAJ-876. TBAJ-876 activity was substantially attributable to M3, given its high exposure and potent activity. Conclusions These findings emphasize the need to consider metabolites and their potentially distinct exposure and activity profiles compared to parent drugs to enhance the translational value of mouse model-driven predictions.