SQ109 inhibits proliferation of Leishmania donovani by disruption of intracellular Ca2+ homeostasis, collapsing the mitochondrial electrochemical potential (ΔΨm) and affecting acidocalcisomes.

Leishmania donovani is the causative agent of visceral leishmaniasis. Annually, 500 million new cases of infection are reported mainly in poor communities, decreasing the interest of the pharmaceutical industries. Therefore, the repositioning of new drugs is an ideal strategy to fight against these parasites. SQ109, a compound in phase IIb/III of clinical trials to treat resistant Mycobacterium tuberculosis, has a potent effect against Trypanosoma cruzi, responsible for Chagas' disease, and on Leishmania mexicana, the causative agent of cutaneous and muco-cutaneous leishmaniasis. In the latter, the toxic dose against intramacrophagic amastigotes is very low (IC50 ~ 11 nM). The proposed mechanism of action on L. mexicana involves the disruption of the parasite intracellular Ca2+ homeostasis through the collapse of the mitochondrial electrochemical potential (ΔΨm). In the present work, we show a potent effect of SQ109 on L. donovani, the parasite responsible for visceral leishmaniasis, the more severe and uniquely lethal form of these infections, obtaining a toxic effect on amastigotes inside macrophages even lower to that obtained in L. mexicana (IC50 of 7.17 ± 0.09 nM) and with a selectivity index > 800, even higher than in L. mexicana. We also demonstrated for first time that SQ109, besides collapsing ΔΨm of the parasite, induced a very rapid damage to the parasite acidocalcisomes, essential organelles involved in the bioenergetics and many other important functions, including Ca2+ homeostasis. Both effects of the drug on these organelles generated a dramatic increase in the intracellular Ca2+ concentration, causing parasite death.

Potentiation of the leishmanicidal activity of nelfinavir in combination with miltefosine or amphotericin B.

The present work assesses the effect in vitro of combining the antiretroviral drug nelfinavir (NFV), a drug used against HIV but also a strong in vitro inhibitor of the growth of Leishmania promastigotes and amastigotes, with amphotericin B or miltefosine on different strains of Leishmania infantum. The isobolograms revealed a synergistic effect for both combinations, with a fractional inhibitory concentration index (∑FIC) <0.5. The ∑FIC values obtained with reference strain MCAN/ES/98/LLM-724 were 0.25 ± 0.1 (95% CI: 0.178-0.322) for the combination NFV+AMB and 0.48 ± 0.2 (95% CI: 0.377-0.573) for the combination NFV+MTF. The effect of NFV on visceral leishmaniasis induced by L. infantum in BALB/c mice was also examined, and the results confirmed a leishmanicidal effect when administered alone, with approximately 60% (P<0.05) reductions in the liver and spleen parasite burdens. This is the first time this has been reported in an in vivo model. A significant reduction in the liver (77%; P<0.01) and spleen (76%; P<0.01) parasite burdens was also observed for NFV+MTF compared with those obtained when these drugs were used alone. This indicates that such combinations may be useful treatment options in patients with visceral leishmaniasis who are also infected with HIV.

In vitro 4-Aryloxy-7-chloroquinoline derivatives are effective in mono- and combined therapy against Leishmania donovani and induce mitocondrial membrane potential disruption.

The present study evaluates in vitro the effect of two synthetic compounds of the 7-chloro-4-aryloxyquinoline series, QI (C17H12ClNO3) and QII (C18H15ClN4O2S), on Leishmania donovani parasites. The results obtained demonstrate that these compounds are able to inhibit the proliferation of L. donovani promastigotes in a dose-dependent way (QI IC50 = 13.03 ±â€¯3.4 and QII IC50 = 7.90 ±â€¯0.6 µM). Likewise, these compounds significantly reduced the percentage of macrophage infection by amastigotesand the number of amastigotes within macrophage phagolysosomes, the clinical relevant phase of these parasites. Compound QI showed an IC50 value of 0.66 ±â€¯0.2 µM, while for derivative QII, the corresponding IC50 was 1.02 ±â€¯0.17 µM. Interestingly, the amastigotes were more susceptible to the drug treatment when compared to promastigotes. Furthermore, no cytotoxic effect of these compounds was observed on the macrophage cell line at the concentrations tested. The combination of these compounds with miltefosine and amphotericin B on both parasite morphotypes was evaluated. The isobolograms showed a synergistic effect for both combinations; with a Fractional Inhibitory Concentration (FIC) Index lower than 1 for promastigotes and less than 0.3 for intracellular amastigotes. The effect of QI and QII on mitochondrial membrane potential was also studied. The combination of quinolone derivatives compounds with miltefosine and amphotericin B showed 5-8-fold stronger depolarization of membrane mitochondrial potential when compared to drugs alone. The present work validates the combination of drugs as an effective alternative to potentiate the action of anti-Leishmania agents and points to the quinoline compounds studied here as possible leishmanicidal drugs.