Dihydroartemisinin - Ferriprotoporphyrin IX Adduct Abundance in Plasmodium falciparum Malarial Parasites and Relationship to Emerging Artemisinin Resistance.

Previously (Heller L. and Roepe, P.D.; preceeding paper, this issue) we quantified free ferriprotoporphyrin IX (FPIX) heme abundance for control vs delayed clearance phenotype (DCP) intraerythrocytic Plasmodium falciparum malarial parasites. Since artemisinin drugs are activated by free FPIX, these data predict that the abundance of long - hypothesized toxic artemisinin drug - FPIX covalent adducts might differ for control vs DCP parasites. If so, this would have important repercussions for understanding the mechanism of the DCP, also known as emerging artemisinin resistance. To test these predictions, we studied in vitro formation of FPIX- dihydroartemisinin (DHA) adducts and then for the first time quantified the abundance of FPIX-DHA adducts formed within live P. falciparum vs the stage of intraerythrocytic development. Using matched isogenic parasite strains we quantified adduct for DCP vs control parasite strains and find that mutant PfK13 mediates lower adduct abundance for DCP parasites. The results suggest improved models for the molecular pharmacology of artemisinin-based antimalarial drugs and the molecular mechanism of the DCP.