Conference Agenda

Artemisinin resistance in Plasmodium parasites, driven by mutations in the parasite's Kelch 13 (K13) protein, threatens global malaria control. K13 is important for regulating the cytostome, a double-membraned invagination used to ingest host-cell haemoglobin. This process is important because haemoglobin digestion releases haem-iron as a toxic byproduct, which is required to activate artemisinin. Mutations in K13 cause slowed-feeding and lower haem levels, allowing parasites to survive drug exposure. However, the precise mechanisms by which K13 mutations impairs parasite feeding remains unclear.
We performed a variety of high-resolution and spatial-temporal microscopy techniques to investigate cellular changes when K13 is mutated. By expansion microscopy, we confirmed K13 to localise to distinctive ring-shaped structures (~160 nm) surrounding cytostomal necks. Using a machine-learning segmentation and automated quantification pipeline, we found K13 mutant parasites produced new cytostomes at significantly slower rates than the wild-type. K13 mutants had a 4h egress delay, producing fewer total K13 rings compared to wild-type, despite maintaining normal progeny counts. Furthermore, these mutants occasionally exhibited aberrant cytostome morphologies where K13 was absent from the cytostomal neck, correlating with decreased haemoglobin uptake efficiency.

These findings fundamentally advance understanding of artemisinin resistance by providing a mechanistic explanation for K13-mediated feeding defects.

Malaria is a disease of significant and ongoing global burden, caused by parasites of the Plasmodium genus, with Plasmodium falciparum responsible for 90% of global malaria mortality. Effective drug treatment is instrumental to control of this disease, and the World Health Organisation (WHO) recommends artemisinin (ART) combinations for treatment of uncomplicated P. falciparum malaria. In this process of treatment, intentionally or otherwise, ART derivatives may be coadministered with apicoplast-targeting antibiotics such as doxycycline or clindamycin. However, previous work from our laboratory indicated an antagonistic relationship between these drugs. Antagonism between ART derivatives and apicoplast-targeting drugs may reduce efficacy and lengthen duration of treatment, as well as potentially increasing susceptibility to resistance mutations. In order to shed light on the mechanism of this antagonism, we are optimising a novel mass spectrometry assay that directly measures the degradation of ART under different conditions. Despite the discrete cellular targets of the drugs of interest, we posit that the downstream effects of these antibiotics on haemoglobin uptake are critical to ART activation and may be responsible for the antagonistic effect. Clarification of these drug class interactions may hold clinical significance for coadministration of antimalarial therapeutics.