Novel, potent, orally bioavailable and selective mycobacterial ATP synthase inhibitors that demonstrated activity against both replicating and non-replicating M. tuberculosis

Abstract

The mycobacterial F0F1-ATP synthase (ATPase) is a validated target for the development of tuberculosis (TB) therapeutics. Therefore, a series of eighteen novel compounds has been designed, synthesized and evaluated against M. smegmatis ATPase. The observed ATPase inhibitory activities (IC50) of these compounds range between 0.36 to 5.45 µM. The lead compound 9d [N-(7-chloro-2-methylquinolin-4-yl)-N-(3-((diethylamino)methyl)-4-hydroxyphenyl)-2,3-dichlorobenzenesulfonamide] with null cytotoxicity (CC50 > 300 µg/mL) and excellent anti-mycobacterial activity and selectivity (mycobacterium ATPase IC50 = 0.51 µM, mammalian ATPase IC50 > 100 µM, and selectivity > 200) exhibited a complete growth inhibition of replicating M. tuberculosis H37Rv at 3.12 µg/mL. In addition, it also exhibited bactericidal effect (approximately 2.4 log10 reductions in CFU) in the hypoxic culture of non-replicating M. tuberculosis at 100 μg/mL (32-fold of its MIC) as compared to positive control isoniazid [approximately 0.2 log10 reduction in CFU at 5 μg/mL (50-fold of its MIC)]. The pharmacokinetics of 9d after p.o. and i.v. administration in male Sprague-Dawley rats indicated its quick absorption, distribution and slow elimination. It exhibited a high volume of distribution (Vss, 0.41 L/kg), moderate clearance (0.06 L/h/kg), long half-life (4.2h) and low absolute bioavailability (1.72 %). In the murine model system of chronic TB, 9d showed 2.12 log10 reductions in CFU in both lung and spleen at 173 µmol/kg dose as compared to the growth of untreated control group of Balb/C male mice infected with replicating M. tuberculosis H37Rv. The in vivo efficacy of 9d is at least double of the control drug ethambutol. These results suggest 9d as a promising candidate molecule for further preclinical evaluation against resistant TB strains.