Targeting the Cytochrome bc ₁ Complex of Leishmania Parasites for Discovery of Novel Drugs

Abstract

c Endochin-like quinolones (ELQs) are potent and specific inhibitors of cytochrome bc 1 from Plasmodium falciparum and Toxoplasma gondii and show promise for novel antiparasitic drug development. To determine whether the mitochondrial electron transport chain of Leishmania parasites could be targeted similarly for drug development, we investigated the activity of 134 structurally diverse ELQs. A cohort of ELQs was selectively toxic to amastigotes of Leishmania mexicana and L. donovani, with 50% inhibitory concentrations (IC 50 s) in the low micromolar range, but the structurally similar hydroxynaphthoquinone buparvaquone was by far the most potent inhibitor of electron transport, ATP production, and intracellular amastigote growth. Cytochrome bc 1 is thus a promising target for novel antileishmanial drugs, and further improvements on the buparvaquone scaffold are warranted for development of enhanced therapeutics.

Orally Bioavailable and Effective Buparvaquone Lipid-Based Nanomedicines for Visceral Leishmaniasis

“…However, BPQ formulations were more variable in inhibiting parasite replication in the liver. Studies on promastigotes and amastigotes of several species of Leishmania indicated that ETC is critical for the survival of these pathogens as application of antimycin A, an inhibitor of cytochrome bc1, or cyanide, an inhibitor of complex IV, resulted in death of promastigotes or amastigotes [57][58][59] . BPQ has been recently shown to be a potent inhibitor of cytochrome bc1 activity and the ETC, ATP production and intracellular amastigote growth at nanomolar concentrations 24, 57 .…”

“…Both BPQ and BPQ SNEDDS showed excellent selectivity for parasite versus mammalian cells with a high selectivity index that are well above DNDi (Drug for Neglected Diseases initiative) accepted hit selection levels 54 and that of miltefosine. The high selectivity of BPQ is expected as there is a high degree of sequence divergence between the Leishmania and human cytochrome b proteins 57 .…”

“…Napthoquinones interact with biological targets by forming covalent bonds or via their ability to undergo reversible oxidation-reduction reactions by generation of ROS (reactive oxygen species) by the redox cycle under aerobic conditions, by the inhibition of electron transport. The electron transport chain (ETC) entails the sequential transfer of electrons via multiprotein complexes (complex I to IV) present in the inner mitochondrial membrane with electron transfer between several complexes being mediated by ubiquinone57 . Compounds that are analogs of ubiquinone that can act as competitive inhibitors of cytochrome bc1 by complexing to the Qi ubiquinone binding site (one of two ubiquinone binding sites on cytochrome bc1 and the one that is oriented toward the luminal side of the inner mitochondrial membrane, as distinct from the Qo site, which is oriented toward the external surface of that membrane)57 .…”

Leishmania mexicana can utilize amino acids as major carbon sources in macrophages but not in animal models

“…Paradoxically, the dependence of Leishmania amastigotes on sugars as their major carbon source, and down-regulation of NEAA uptake, means that these stages are dependent on anapleurotic mitochondrial reactions involved NEAA biosynthesis. Indeed a number of studies have shown that inhibitors of mitochondrial metabolism have potent anti-leishmania activity (Fidalgo and Gille, 2011;Ortiz et al, 2016;Saunders et al, 2014). These studies suggest that Leishmania amastigote metabolism is highly constrained in vivo, which offers new opportunities for drug development.…”

“…Reactive oxygen species (ROS) were detected using a plate based assay adapted from (Ortiz et al, 2016;Mukherjee et al, 2002). Briefly, log phase parasites were pelleted and resuspended in fresh RPMI supplemented with 10% iFCS (400 ml, 1 3 10 7 cell ml 21 ) in the presence of selected ROS-inducing compounds (H 2 O 2 and menadione [MEN], 75 mM and 2.5 mM respectively) and incubated at 278C for 2 h. Cells were pelleted, resuspended in fresh RPMI media supplemented with 10% iFCS (400 ml) containing 20 mM H 2 DCFDA (Sigma) and incubated in the dark at 278C for 30 min.…”