Download Full Text (2.0 MB)

Presentation date


College, Institute, or Department

Pathology and Microbiology

Faculty Mentor

Rakesh Singh

Research Mentor

Caroline Ng


In 2019, ~ 229 million malaria cases were reported globally, causing 409,000 deaths. Malaria is caused by the Plasmodium parasite with cyclical infection in human and Anopheles mosquito host. P. falciparum is the most common species, causing approximately 75% of malaria. Asexual, blood stage parasites cause malaria symptoms. The lifecycle begins with merozoites that invade red blood cells and they develop into rings, then trophozoite, and mature into schizonts. Artemisinin-based combination therapy (ACT) is the first-line treatment for uncomplicated falciparum malaria. Resistance to all artemisinin (ART) is a widespread problem, which is conferred by point mutations in Kelch 13. The K13C580Y mutation is the most abundant in SE Asia. P. falciparum’s apicoplast, an essential organelle that generates fatty acids, heme, and isoprenoid precursors, is a promising drug target since humans lack this organelle. The apicoplast’s primary function in asexual life stages is to produce isoprenoid precursor isopentenyl phosphate (IPP) via the methylerythritol phosphate (MEP) pathway. IPP supplementation has been shown to chemically rescue MEP inhibited cultures. Delayed death phenotype is defined as growth of treated parasite is unaffected, but growth arrest is observed in the progeny. This is seen when apicoplast biosynthesis and apicoplast metabolic pathways are inhibited. The apicoplast-located PfClpC/P complex degrades proteins and has chymotrypsinlike proteolytic activity. PfClpC is a chaperone to the PfClpP protease. P. falciparum 26S proteasome is a cytoplasmic protease with β1, β2, and β5 subunits that have caspase-like, trypsin-like and chymotrypsin-like activity, respectively. WLL, a proteasome inhibitor, targets the β2 and β5 subunits. An analog of MAS1-86 effectively inhibited multi-drug resistant Staphylococcus aureus ClpX, a homolog of PfClpC, in multi-drug resistant S. aureus. Analogs of MAS1-86 were then tested against P. falciparum and MAS1-86 was identified as the most potent inhibitor. We show that MAS1-86 selected parasites display a 6 - 23-fold increase in resistance to MAS1-86. IPP failed to rescue MAS1-86 parasite inhibition nor did MAS1-86 inhibition display a delayed death phenotype, defined as a 10-fold reduction in IC50 values at 120 hours compared to72 hours. We conclude that MAS1-86 does not target the MEP pathway. MAS1-86 inhibition caused a delay in late trophozoite stages through schizont stages, with fewer nuclei observed in schizonts. This observation is of interest since aberrant scizont morphology with fewer nuclei has been reported in auto-inhibited ClpC P. falciparum. There was no shift in the K13 mutant dose response curves, thus K13 haplotype does not influence parasite susceptibility to MAS1-86. MAS1-86-resistant parasites did not show cross-resistance to proteasome β2 and β5 subunit inhibitor, WLL, which has the same chymotrypsin-like activity as ClpP.


Plasmodium falciparum, ClpC/P, MEP pathway, artemisinin-resistance, apicoplast

Characterization of MAS1-86 Activity in Malaria Parasites