Efficacy of Quinoxaline-2-Carboxylate 1,4-Di- N -Oxide Derivatives in Experimental Tuberculosis

This study extends earlier reports regarding the in vitro efficacies of the 1,4-di- N -oxide quinoxaline derivatives against Mycobacterium tuberculosis and has led to the discovery of a derivative with in vivo efficacy in the mouse model of tuberculosis. Quinoxaline-2-carboxylate 1,4-di- N -oxide derivatives were tested in vitro against a broad panel of single-drug-resistant M. tuberculosis strains. The susceptibilities of these strains to some compounds were comparable to those of strain H 37 Rv, as indicated by the ratios of MICs for resistant and nonresistant strains, supporting the premise that 1,4-di- N -oxide quinoxaline derivatives have a novel mode of action unrelated to those of the currently used antitubercular drugs. Specific derivatives were further evaluated in a series of in vivo assays, including evaluations of the maximum tolerated doses, the levels of oral bioavailability, and the efficacies in a low-dose aerosol model of tuberculosis in mice. One compound, ethyl 7-chloro-3-methylquinoxaline-2-carboxylate 1,4-dioxide, was found to be (i) active in reducing CFU counts in both the lungs and spleens of infected mice following oral administration, (ii) active against PA-824-resistant Mycobacterium bovis , indicating that the pathway of bioreduction/activation is different from that of PA-824 (a bioreduced nitroimidazole that is in clinical trials), and (iii) very active against nonreplicating bacteria adapted to low-oxygen conditions. These data indicate that 1,4-di- N -oxide quinoxalines hold promise for the treatment of tuberculosis.