Reductive Activation of Artefenomel (OZ439) by Fe(II)-Heme, Related to Its Antimalarial Activity

The 1,2,4-trioxolane antimalarial drug, OZ439 (artefenomel), exhibits cross-resistance to artemisinins in vitro with similar survival rates of artemisinin-resistant parasites after dihydroartemisinin or OZ439 exposure, suggesting that this drug shares some mechanisms of action with artemisinins. In this way, we investigated the in vitro reductive activation of OZ439 by heme in the presence of dithionite, demonstrating the formation of covalent heme-drug adducts. However, in the presence of the biologically abundant reductant glutathione instead of dithionite, heme-drug adducts were not detected, contrary to artemisinin that efficiently alkylates heme regardless of the reductant used. Conversely, the C-centered radical of OZ439 resulting from heme-mediated activation of the drug reacts with the thiol function of glutathione, thus confirming the ability of this drug to alkylate proteins or other biological targets. So, the difference in the mechanism of action between artemisinin and OZ439 in vivo may rely on the different proportions between heme alkylation and protein alkylation.