Determination of the active stereoisomer of the MEP pathway-targeting antimalarial agent MMV008138, and initial structure–activity studies

Abstract

Compounds that target isoprenoid biosynthesis in Plasmodium falciparum could be a welcome addition to malaria chemotherapy, since the methylerythritol phosphate (MEP) pathway used by the parasite is not present in humans. We previously reported that MMV008138 targets the apicoplast of P. falciparum and that its target in the MEP pathway differs from that of Fosmidomycin. In this article, we determine that the active stereoisomer of MMV008138 is 4a, which is (1R,3S)-configured. 2′,4′-Disubstitution of the D ring was also found to be crucial for inhibition of the parasite growth. Limited variation of the C3-carboxylic acid substitutent was carried out, and methylamide derivative 8a was found to be more potent than 4a; other amides, acylhydrazines, and esters were less potent. Finally, lead compounds 4a, 4e, 4f, 4h, 8a, and 8e did not inhibit growth of Escherichia coli, suggesting that protozoan-selective inhibition of the MEP pathway of P. falciparum can be achieved.

Validation of Putative Apicoplast-Targeting Drugs Using a Chemical Supplementation Assay in Cultured Human Malaria Parasites

“…Although IPP is now used increasingly to discriminate whether or not a drug has a target in the apicoplast, we performed IPP supplementation trials on parasites exposed to two definite nonapicoplast drugs (chloroquine and atovaquone) and two validated apicoplast drugs (azithromycin and fosmidomycin) to establish a comprehensive set of assays focused on apicoplast target validation (Table 1 and Fig. 1) (30,(37)(38)(39)(40)(41)(42). Chloroquine targets the food vacuole in which the parasite digests ingested hemoglobin (43,44), and atovaquone targets the cytochrome bc 1 complex in the mitochondrion (45,46).…”

“…This unique feature allows us to separate out the effect of any drug on the apicoplast from effects on any alternative target during the asexual blood stage of P. falciparum. Here, we used a chemical supplementation approach (37), a technique now routinely in use (30,(38)(39)(40)(41)(42), to test the target of 23 presumed apicoplast drugs, including compounds with confirmed apicoplast targets, confirmed nonapicoplast targets, and compounds with putative apicoplast targets.…”

Metabolomic Profiling of the Malaria Box Reveals Antimalarial Target Pathways

“…The unclassified group of compounds remains of interest, and expanding our metabolomic methodologies beyond focusing on hydrophilic metabolites may allow us to discern the unique signatures within this class. Interestingly, MMV008138 is among the unclassified compounds, although it is an established inhibitor of the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway of isoprenoid biosynthesis (14,30,110,111), which is beyond the detection capabilities of our methodology. However, this compound might be used as a known signature of MEP pathway disruption for future analytical optimization.…”

New Insight into Isoprenoids Biosynthesis Process and Future Prospects for Drug Designing in Plasmodium

“…However, cytotoxicity of these pseudilins in mammalian cell also suggests additional molecular targets apart from IspD (Kunfermann et al, 2014 ). Recently, another inhibitor MMV008138 (shortlisted from Malaria Box) was found effective against Pf IspD enzyme showing competitive inhibition with CTP substrate (Wu et al, 2015 ; Yao et al, 2015 ), whereas, in P. vivax , it is effective only at a lower concentration of CTP substrate (Imlay et al, 2015 ). In addition, MMV008138 does not exhibit activity against liver stages of P. yoelli nor does it have activity against sexual stages of P. falciparum (Bowman et al, 2014 ).…”