In vitro and in vivo study of the inhibition of ubiquinone biosynthesis in Leishmania (Leishmania) amazonensis using the combination of buparvaquone and 4-nitrobenzoate as a strategy for the discovery of new therapeutic targets

Leishmaniasis is a parasitic disease caused by several species of the genus Leishmania, considered one of the most dangerous neglected tropical diseases in the world. Treatment options are limited and toxicity exists, requiring an urgent search for new therapies. Leishmania differs from mammalian cells by having unique mitochondria, which have been considered an important therapeutic target. Ubiquinone is found in the inner membrane of mitochondria and plays a critical role in the electron transport chain, which is essential for cell viability. The combination of buparvaquone and 4-nitrobenzoate seems an interesting option due to their action on these targets. The aim of the present work was to investigate the effects of this combination against Leishmania (Leishmania) amazonensis infections in vitro and in vivo and to elucidate the possible mechanism of action of 4-nitrobenzoate. The results showed that the drug combination tested in promastigotes has an additive or indifferent effect. In the intracellular amastigotes, when buparvaquone was tested with fixed concentrations of 4-nitrobenzoate, concentrations that had no effect alone potentiated the effect of buparvaquone by two to four times. The mechanism of action of 4-nitrobenzoate in promastigote forms suggests a reduction in ubiquinone 6 levels, an alteration in mitochondrial membrane potential, and an increase in reactive oxygen species. In vivo treatment with a topical formulation (buparvaquone 0.1% and 4-nitrobenzoate 0.1%) in infected mice showed a reduction in parasite burden of 57% compared to the control group, suggesting that this combination may represent a promising therapeutic strategy for future treatment of this disease.