Torins are potent antimalarials that block replenishment of Plasmodium liver stage parasitophorous vacuole membrane proteins

Abstract

Residence within a customized vacuole is a highly successful strategy used by diverse intracellular microorganisms. The parasitophorous vacuole membrane (PVM) is the critical interface between Plasmodium parasites and their possibly hostile, yet ultimately sustaining, host cell environment. We show that torins, developed as ATP-competitive mammalian target of rapamycin (mTOR) kinase inhibitors, are fast-acting antiplasmodial compounds that unexpectedly target the parasite directly, blocking the dynamic trafficking of the Plasmodium proteins exported protein 1 (EXP1) and upregulated in sporozoites 4 (UIS4) to the liver stage PVM and leading to efficient parasite elimination by the hepatocyte. Torin2 has single-digit, or lower, nanomolar potency in both liver and blood stages of infection in vitro and is likewise effective against both stages in vivo, with a single oral dose sufficient to clear liver stage infection. Parasite elimination and perturbed trafficking of liver stage PVM-resident proteins are both specific aspects of torin-mediated Plasmodium liver stage inhibition, indicating that torins have a distinct mode of action compared with currently used antimalarials.host-parasite interactions | malaria | protein trafficking | P. falciparum

Plasmodium berghei EXP-1 interacts with host Apolipoprotein H during Plasmodium liver-stage development

“…The same membrane topology was reported for other small PVM-resident proteins of the ETRAMP family, which are, together with EXP-1, organized in nonoverlapping oligomeric arrays within the PVM (36,37). Because EXP-1 was found to be continuously trafficked to the PVM throughout at least the first half of liver-stage development, there was speculation as to whether the protein might also be trafficked back from the PVM to the PV or even the parasite cytosol (38). PfEXP-1 is one of the most abundantly transcribed loci during ring and early trophozoite-stage development; it is therefore not surprising that it seems to exert vital functions during blood-stage development and was shown to be refractory to gene deletion (39)(40)(41).…”

“…Interestingly, Hanson et al recently reported that both known PVM-resident proteins, EXP-1 and UIS4, must be continuously exported to the PVM, at least during the first 30 h of intrahepatic development. This finding raises the possibility that these proteins may be trafficked back into the PV or even into the parasite's cytoplasm (38). If EXP-1 is indeed subjected to retrograde trafficking, it might serve as a shuttle protein for ApoH.…”

Vacuolin-1 potently and reversibly inhibits autophagosome-lysosome fusion by activating RAB5A

“…Some of these compounds have been widely used to dissect the mechanisms underlying autophagy. 17 Popular autophagy inducers include MTOR kinase inhibitors, e.g., rapamycin and torin 1, 18 and chemicals inhibiting inositol monophosphatase, e.g., lithium and carbamazepine. 19 Notably, rapamycin is an immunosuppressant and has recently been used as an anticancer agent.…”

In Vitro Alterations Do Not Reflect a Requirement for Host Cell Cycle Progression during Plasmodium Liver Stage Infection

“…To address both of these issues, we asked whether the likelihood of mitosis in the host cell would be similarly altered at 24 h in cells harboring nondeveloping parasites that had undergone normal invasion. To block parasite development as early as possible after invasion, we treated cells with decoquinate (DCQ), a cytochrome bc 1 inhibitor and potent antimalarial (23,24) that is active against very early liver stages, such that a 6-h treatment from 2 to 8 h after sporozoite addition prevents parasite growth but does not lead to parasite elimination (25). A representative image of such a DCQ-treated parasite in a metaphase HepG2 cell 24 h postinfection is shown in Fig.…”