No abstract

The antihistamine clemastine inhibits multiple stages of thePlasmodiumparasite that causes malaria, but the molecular targets responsible for its parasite inhibition were unknown. Here, we applied parallel chemoproteomic platforms to discover the mechanism of action of clemastine and identify that clemastine binds to thePlasmodium falciparumTCP-1 ring complex or chaperonin containing TCP-1 (TRiC/CCT), an essential heterooligomeric complex required for de novo cytoskeletal protein folding. Clemastine destabilized all eightP. falciparumTRiC subunits based on thermal proteome profiling (TPP). Further analysis using stability of proteins from rates of oxidation (SPROX) revealed a clemastine-induced thermodynamic stabilization of thePlasmodiumTRiC delta subunit, suggesting an interaction with this protein subunit. We demonstrate that clemastine reduces levels of the major TRiC substrate tubulin inP. falciparumparasites. In addition, clemastine treatment leads to disorientation ofPlasmodiummitotic spindles during the asexual reproduction and results in aberrant tubulin morphology suggesting protein aggregation. This clemastine-induced disruption of TRiC function is not observed in human host cells, demonstrating a species selectivity required for targeting an intracellular human pathogen. Our findings encourage larger efforts to apply chemoproteomic methods to assist in target identification of antimalarial drugs and highlight the potential to selectively targetPlasmodiumTRiC-mediated protein folding for malaria intervention.

No abstract

Malaria remains a global health burden partly due to parasite resistance to first-line therapeutics. The molecular chaperone heat shock protein 90 (Hsp90) has emerged as an essential protein for blood-stage parasites, but details about its function during malaria's elusive liver stage are unclear. We used target-based screens to identify compounds that bind to and human Hsp90, which revealed insights into chemotypes with species-selective binding. Using cell-based malaria assays, we demonstrate that all identified Hsp90-binding compounds are liver- and blood-stage inhibitors. Additionally, the Hsp90 inhibitor SNX-0723 in combination with the phosphatidylinositol 3-kinase inhibitor PIK-75 synergistically reduces the liver-stage parasite load. Time course inhibition studies with the Hsp90 inhibitors and expression analysis support a role for Hsp90 in late-liver-stage parasite development. Our results suggest that Hsp90 is essential to liver- and blood-stage parasite infections and highlight an attractive route for development of species-selective Hsp90 inhibitors that may act synergistically in combination therapies to prevent and treat malaria.

Highlights d PfPK9-binding compounds were discovered d PfPK9-binding compounds inhibit K63-linked ubiquitination in Plasmodium d Takinib and PfPK9-selective HS220 inhibit liver-stage Plasmodium d Takinib and PfPK9-selective HS220 increase liver-stage parasite size

There is a pressing need for compounds with broad-spectrum activity against malaria parasites at various life cycle stages to achieve malaria elimination. However, this goal cannot be accomplished without targeting the tenacious dormant liver-stage hypnozoite that causes multiple relapses after the first episode of illness. In the search for the magic bullet to radically cure Plasmodium vivax malaria, tafenoquine outperformed other candidate drugs and was approved by the U.S. Food and Drug Administration in 2018. Tafenoquine is an 8-aminoquinoline that inhibits multiple life stages of various Plasmodium species. Additionally, its much longer half-life allows for single-dose treatment, which will improve the compliance rate. Despite its approval and the long-time use of other 8-aminoquinolines, the mechanisms behind tafenoquine’s activity and adverse effects are still largely unknown. In this Perspective, we discuss the plausible underlying mechanisms of tafenoquine’s antiparasitic activity and highlight its role as a cellular stressor. We also discuss potential drug combinations and the development of next-generation 8-aminoquinolines to further improve the therapeutic index of tafenoquine for malaria treatment and prevention.

No abstract

Phosphatidylinositol 3-phosphate (PI(3)P) levels in Plasmodium falciparum correlate with tolerance to cellular stresses caused by artemisinin and environmental factors. However, PI(3)P function during the Plasmodium stress response was unknown. Here, we used PI3K inhibitors and antimalarial agents to examine the importance of PI(3)P under thermal conditions recapitulating malarial fever. Live cell microscopy using chemical and genetic reporters revealed that PI(3)P stabilizes the digestive vacuole (DV) under heat stress. We demonstrate that heat-induced DV destabilization in PI(3)P-deficient P. falciparum precedes cell death and is reversible after withdrawal of the stress condition and the PI3K inhibitor. A chemoproteomic approach identified PfHsp70-1 as a PI(3)P-binding protein. An Hsp70 inhibitor and knockdown of PfHsp70-1 phenocopy PI(3)P-deficient parasites under heat shock. Furthermore, PfHsp70-1 downregulation hypersensitizes parasites to heat shock and PI3K inhibitors. Our findings underscore a mechanistic link between PI(3)P and PfHsp70-1 and present a novel PI(3)P function in DV stabilization during heat stress.