Why are iron chelators not as effective as artemisinin in killing malaria parasites?

Artemisinin resistance endangers current artemisinin combination therapy (ACT), necessitating new ACT development. Artemisinin kills malaria parasites by generating free radicals via heme/iron activation, while iron chelators disrupt iron utilization. The combination of these two mechanisms may form a better antimalarial therapy. It is known that iron chelators have significantly weaker antimalarial effects than artemisinin, but the mechanism is unclear. Thus, clarifying this reason is essential for elucidating artemisinin's antimalarial action and developing strategies to enhance ACT.

We assessed the effects of artemisinin derivatives (dihydroartemisinin, DHA; artemether, ATM) and the iron chelator desferrioxamine (DFO) on parasite infection rate and morphology in vitro/in vivo. Single-cell RNA sequencing was used to compare Plasmodium falciparum 3D7's sensitivity to DHA/DFO at 3, 9, and 24 h post-treatment, analyzing differential gene expression and affected functions. Transmission electron microscopy (TEM) was used to observe artemisinin's impact on parasites.

Although all developmental stages of P. falciparum 3D7 exhibited sensitivity to 24-h DHA treatment, parasite counts at 12-30 h postinfection (hpi) decreased more rapidly following 9-h DFO treatment than 9-h DHA treatment. Notably, DHA upregulated iron utilization-related genes at 3 h post-treatment (hpt), whereas DFO did not. DHA and DFO exerted distinct effects on gene expression, particularly in parasites at 12-30 hpi, where DHA induced the expression of genes related to ribosome biogenesis and protein translation pathways. In functional assays, DFO reduced P. falciparum parasitic infection in vitro but failed to inhibit P. yoelii proliferation in vivo; the combination of ATM and DFO was less potent than ATM monotherapy. TEM observations revealed that ATM localized to the parasites' digestive vacuoles and disrupted heme aggregation.

Artemisinin and its derivatives exhibit more potent antimalarial activity than iron chelators, likely stemming from their ability to accumulate in the parasite's digestive vacuoles, interact more effectively with heme and iron, and thereby disrupt heme/iron homeostasis and utilization.