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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.

Background: Ganaplacide, also known as KAF156, is among the new antimalarial drug candidates that have successfully reached Phase III clinical trials, and is proposed in combination with lumefantrine. This combination could replace the current front-line artemisinin-based combination therapies (ACTs) in case of Plasmodium falciparum resistance to both artemisinins and partner drugs. Indeed, the African continent, where the malaria burden is the highest, is currently experiencing worrying multiple emergences and spread of artemisinin resistance, which urges for the exploration of the antiparasitic properties of KAF156 in this context., Objectives and Methods: The objectives of this work were firstly to evaluate the risk of cross-resistance between artemisinins and KAF156 alone, and in combination with lumefantrine, using a panel of artemisinin-resistant strains carrying different pfk13 mutations and markers of other antiplasmodial drug resistances; secondly to explore in vitro the relevance of combining KAF156 and lumefantrine with artemisinins, based on the model of triple ACTs., Results: Our results highlighted that KAF156 activity was not impaired by mutations in pfk13, pfcrt, pfmdr1, pfmdr2, pfdhps and pfdhfr genes or by pfmdr1 amplification. Moreover, we demonstrated that KAF156 alone and in combination with lumefantrine was active against artemisinin-resistant parasites, including when they are quiescent., Conclusions: All these in vitro results evidence that multi-drug resistant parasites currently in circulation in the field might not affect KAF156 efficacy, and are encouraging signs for KAF156 use in a triple ACT to preserve the use of artemisinins for as long as possible., (© The Author(s) 2024. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy.)

In response to the spread of artemisinin (ART) resistance, ART-based hybrid drugs were developed, and their activity profile was characterized against drug-sensitive and drug-resistant Plasmodium falciparum parasites. Two hybrids were found to display parasite growth reduction, stage-specificity, speed of activity, additivity of activity in drug combinations, and stability in hepatic microsomes of similar levels to those displayed by dihydroartemisinin (DHA). Conversely, the rate of chemical homolysis of the peroxide bonds is slower in hybrids than in DHA. From a mechanistic perspective, heme plays a central role in the chemical homolysis of peroxide, inhibiting heme detoxification and disrupting parasite heme redox homeostasis. The hybrid exhibiting slow homolysis of peroxide bonds was more potent in reducing the viability of ART-resistant parasites in a ring-stage survival assay than the hybrid exhibiting fast homolysis. However, both hybrids showed limited activity against ART-induced quiescent parasites in the quiescent-stage survival assay. Our findings are consistent with previous results showing that slow homolysis of peroxide-containing drugs may retain activity against proliferating ART-resistant parasites. However, our data suggest that this property does not overcome the limited activity of peroxides in killing non-proliferating parasites in a quiescent state., Competing Interests: The authors declare no conflict of interest.