Artemisinins target the SERCA of Plasmodium falciparum

Abstract

Artemisinins are extracted from sweet wormwood (Artemisia annua) and are the most potent antimalarials available, rapidly killing all asexual stages of Plasmodium falciparum. Artemisinins are sesquiterpene lactones widely used to treat multidrug-resistant malaria, a disease that annually claims 1 million lives. Despite extensive clinical and laboratory experience their molecular target is not yet identified. Activated artemisinins form adducts with a variety of biological macromolecules, including haem, translationally controlled tumour protein (TCTP) and other higher-molecular-weight proteins. Here we show that artemisinins, but not quinine or chloroquine, inhibit the SERCA orthologue (PfATP6) of Plasmodium falciparum in Xenopus oocytes with similar potency to thapsigargin (another sesquiterpene lactone and highly specific SERCA inhibitor). As predicted, thapsigargin also antagonizes the parasiticidal activity of artemisinin. Desoxyartemisinin lacks an endoperoxide bridge and is ineffective both as an inhibitor of PfATP6 and as an antimalarial. Chelation of iron by desferrioxamine abrogates the antiparasitic activity of artemisinins and correspondingly attenuates inhibition of PfATP6. Imaging of parasites with BODIPY-thapsigargin labels the cytosolic compartment and is competed by artemisinin. Fluorescent artemisinin labels parasites similarly and irreversibly in an Fe2+-dependent manner. These data provide compelling evidence that artemisinins act by inhibiting PfATP6 outside the food vacuole after activation by iron.

Characterization of noncovalent complexes of antimalarial agents of the artemisinin-type and Fe(III)-heme by electrospray mass spectrometry and collisional activation tandem mass spectrometry

“…Furthermore, it has been shown that covalent artemisinin-heme adducts mimick heme in binding to the enzyme histidine-rich protein II and as such have the ability to inhibit heme polymerization [16]. Recently, evidence has been obtained that iron-activated artemisinin-type drugs act by alkylating an essential enzyme of Plasmodium falciparum, i.e., a sarco/endoplasmic reticulum Ca 2ϩ -ATPase ortholog [17].…”

“…Formation of a relatively stable noncovalent complex between antimalarial drugs of the artemisinin-type and Fe(II)-heme can be regarded as the first step in covalent interaction, since Fe 2ϩ is required for activation of artemisinin derivatives, i.e., generation of alkyl radicals [17,18]. Experimental evidence using spectrophotometry has demonstrated that noncovalent interaction indeed occurs prior to covalent association in in vitro experiments [19].…”

Reaction of artemisinin with haemoglobin: implications for antimalarial activity

“…Several studies have suggested that the haem-promoted cleavage of the peroxide in artemisinin, leading to the formation of C-radicals which alkylate some proteins of the malaria parasite [18], also contributes to its antimalarial action. Specific reactions of artemisinin with TCTP (translationally controlled tumour protein) [19], inhibition of the SERCA (sarcoplasmic/endoplasmic-reticulum Ca 2+ -ATPase) orthologue (PfATP6) of P. falciparum [20] and inhibition of P. falciparum cysteine proteases have also been proposed to contribute to its drug activity [21]. On the other hand, Hong et al [22] reported that artemisinin forms covalent adducts with haem in artemisinintreated parasite cultures.…”

Activity of artemether and OZ78 against triclabendazole-resistant Fasciola hepatica

“…A long-standing hypothesis to account for the antimalarial specificity of the artemisinins is that the peroxide bond undergoes reductive activation by haem released by parasite Hb digestion producing carbon-centred free radicals (Golenser et al, 2006). Another likely target of the artemisinins is the PfATP6, a SERCA-type Ca 2+ -ATPase (Eckstein-Ludwig et al, 2003). As Plasmodium, Schistosoma spp.…”