Investigating the Antimalarial Action of 1,2,4-Trioxolanes with Fluorescent Chemical Probes

Abstract

The 1,2,4-trioxolanes are a new class of synthetic peroxidic antimalarials currently in human clinical trials. The well known reactivity of the 1,2,4-trioxolane ring towards inorganic ferrous iron and ferrous iron heme is proposed to play a role in the antimalarial action of this class of compounds. We have designed structurally relevant fluorescent chemical probes to study the sub-cellular localization of 1,2,4-trioxolanes in cultured Plasmodium falciparum parasites. Microscopy experiments revealed that a probe fluorescently labeled on the adamantane ring accumulated specifically in digestive vacuole-associated neutral lipid bodies within the parasite while an isosteric, but non-peroxidic congener did not. Probes fluorescently labeled on the cyclohexane ring showed no distinct localization pattern. In their sub-cellular localization and peroxidative effects, 1,2,4-trioxolane probes behave much like artemisinin-based probes studied previously. Our results are consistent with a role for adamantane-derived carbon-centered radicals in the antimalarial action of 1,2,4-trioxolanes, as hypothesized previously on the basis of chemical reactivity studies.

System-wide biochemical analysis reveals ozonide antimalarials initially act by disrupting Plasmodium falciparum haemoglobin digestion

“…Neutral lipid bodies are thought to concentrate free haem and catalyse its biocrystallisation into non-toxic haemozoin [ 76 – 78 ], placing them proximal to the location where peroxide antimalarials are thought to be activated. Furthermore, fluorescently-tagged artemisinin and ozonide derivatives have been shown to accumulate in neutral lipid bodies [ 70 , 71 ]. Activated drug, or potentially alkylated haem adducts [ 58 ], may therefore promote oxidative damage to DGs and TGs within neutral lipid bodies and limit the availability of key neutral lipids that are required for parasite development [ 74 ].…”

The Lipophilic Bullet Hits the Targets: Medicinal Chemistry of Adamantane Derivatives

“…This clearly shows that the C -centered radicals that act as alkylating agents must be adamantane-derived. 351 …”

Hemozoin and Antimalarial Drug Discovery

“…Trophozoites were treated with adamantane-linked fluorescent 1,2,4-trioxolanes and allowed to incubate prior to confocal microscopy. Fluorescence was observed solely within spherical neutral lipid bodies that were closely associated with the digestive vacuole [54]. However, cyclohexane-linked fluorescent trioxolanes were observed uniformly throughout the cytoplasm, indicating the importance of the endoperoxide moiety for specific localization (Figure 4).…”