Nitroimidazopyrazinones with oral activity against tuberculosis and Chagas disease in mouse models of infection
Tuberculosis remains one of the leading causes of death from a single infectious agent, surpassing both AIDS and malaria. In recent years, two bicyclic nitroimidazole drugs, delamanid and pretomanid have been approved to treat this airborne infection. This has spurred a renewed interest in developing new and improved nitroimidazole analogs. We have previously identified a new bicyclic heteroaromatic subclass, the nitroimidazopyrazinones, with substituted analogs showing promising activity against Mycobacterium tuberculosis under both aerobic and hypoxic environments. A second generation of nitroimidazopyrazinones with extended biaryl side chain also possessed good antiparasitic activity against Trypanosoma brucei brucei and Trypanosoma cruzi, suggesting the utility of this new scaffold for development into potential candidates against both tuberculosis and the kinetoplastid parasites which cause neglected tropical diseases. In this study, we further evaluated the properties of nitroimidazopyrazinone derivatives by assessing their selectivity against different mycobacterial species, measuring their reduction potential, and determining the kinetic parameters as substrates of the deazaflavin-dependent nitroreductase (Ddn), which is the activating enzyme of delamanid and pretomanid in M. tuberculosis. We also conducted an in vivo evaluation of a lead compound, MCC8967 that demonstrated a favorable pharmacokinetic profile, with good oral bioavailability and efficacy in an acute M. tuberculosis infection model. Two other promising compounds MCC9481 and MCC9482, with good in vitro activity (IC50 = 0.016 and 0.10 µM, respectively) against T. cruzi, the causative agent for Chagas diseases, were similarly tested for in vivo activity. These compounds also exhibited good oral bioavailability, and transiently reduced the acute-stage parasite burden by >98‒99% at doses of 50 mg/kg once or twice daily, similar to benznidazole at 100 mg/kg once daily. Overall, we have demonstrated that active nitroimidazopyrazinones have potential to be developed as clinical candidates against both tuberculosis and Chagas disease.