Diversity-Oriented Synthesis Probe TargetsPlasmodium falciparumCytochrome b Ubiquinone Reduction Site and Synergizes With Oxidation Site Inhibitors

Abstract

Background. The emergence and spread of drug resistance to current antimalarial therapies remains a pressing concern, escalating the need for compounds that demonstrate novel modes of action. Diversity-Oriented Synthesis (DOS) libraries bridge the gap between conventional small molecule and natural product libraries, allowing the interrogation of more diverse chemical space in efforts to identify probes of novel parasite pathways.Methods. We screened and optimized a probe from a DOS library using whole-cell phenotypic assays. Resistance selection and whole-genome sequencing approaches were employed to identify the cellular target of the compounds.Results. We identified a novel macrocyclic inhibitor of Plasmodium falciparum with nanomolar potency and identified the reduction site of cytochrome b as its cellular target. Combination experiments with reduction and oxidation site inhibitors showed synergistic inhibition of the parasite.Conclusions. The cytochrome b oxidation center is a validated antimalarial target. We show that the reduction site of cytochrome b is also a druggable target. Our results demonstrating a synergistic relationship between oxidation and reduction site inhibitors suggests a future strategy for new combination therapies in the treatment of malaria.

Advancing Biological Understanding and Therapeutics Discovery with Small-Molecule Probes

“…To determine the compound’s mechanism of action, MLP generated ML238-resistant parasites and conducted whole-genome sequencing. These studies revealed that ML238 acts at the quinone reductase site of the bc 1 complex (Q 1 ) (Lukens et al , 2014), which is on the opposite side of the cell membrane from the quinol oxidase site targeted by the antimalarial drug atovaquone. ML238 and atovaquone lacked cross-resistance and were synergistic in combination, highlighting the quinone reductase site as a antimalarial therapeutic target that may overcome atovaquone resistance (Lukens et al , 2014).…”

Subtle Changes in Endochin-Like Quinolone Structure Alter the Site of Inhibition within the Cytochrome bc 1 Complex of Plasmodium falciparum

“…Inhibition at either site is sufficient to block the catalytic cycle of cyt bc 1 (Q cycle), which ultimately leads to pyrimidine starvation and cell death in P. falciparum (4,5). To date, pyridones (6,7), naphthoquinones (8,9), acridones (10), quinolones (11)(12)(13), and benzene sulfonamides (14) have been identified as potent inhibitors of Plasmodium cyt bc 1 (15). This includes atovaquone (ATV), which targets the Q o site of the P. falciparum cytochrome bc 1 complex (16).…”

Identification and Validation of Novel Drug Targets for the Treatment of Plasmodium falciparum Malaria: New Insights

“…Aside of atovaquone, other bc1 complex inhibitors were described, as acridones [78], quinolones [79][80][81], pyridones [82,83], and benzene sulfonamides [84]. Although many compounds have presented inhibitory potential against bc1 complex, this target might be considered underexploited, since the majority of these compounds target the Qo site [85].…”