In Vitro and In Vivo Trypanocidal Synergistic Activity of N-Butyl-1-(4-Dimethylamino)Phenyl-1,2,3,4-Tetrahydro-β-Carboline-3-Carboxamide Associated with Benznidazole

American trypanosomiasis, or Chagas' disease, is caused by Trypanosoma cruzi and affects around 15 million people throughout the American continent. The available treatment is based on two nitroheterocyclic drugs, nifurtimox and benznidazole, both only partially effective and toxic. In this context, new drugs must be found. In our previous work, the tetrahydro-β-carboline compound N-butyl-1-(4-dimethylamino)phenyl-1,2,3,4-tetrahydro-β-carboline-3-carboxamide, named C4, showed a potent in vitro trypanocidal effect. The goal of this study was to evaluate the in vitro and in vivo trypanocidal effects of the compound C4 associated with other drugs (benznidazole, ketoconazole, and amphotericin B). For this, we used the checkerboard technique to analyze the effect of combinations of C4 reference drugs. C4 was assayed in a murine model alone as well as in association with benznidazole. We also evaluated the parasitemia, mortality, weight, and presence of amastigote nests in cardiac tissue. A synergic effect of C4 plus benznidazole against epimastigote and trypomastigote forms was observed in vitro, and in the murine model, we observed a substantial reduction in parasitemia levels and lowered mortality rates. These findings encourage supplementary investigations of carboline compounds as potential new trypanocidal drugs.