A non-radiolabeled heme–GSH interaction test for the screening of antimalarial compounds

Intraerythrocytic Plasmodium produces large amounts of toxic heme during the digestion of hemoglobin, a parasite specific pathway. Heme is then partially biocristallized into hemozoin and mostly detoxified by reduced glutathione. We proposed an in vitro micro assay to test the ability of drugs to inhibit heme-glutathione dependent degradation. As glutathione and o-phthalaldehyde form a fluorescent adduct, we followed the extinction of the fluorescent signal when heme was added with or without antimalarial compounds. In this assay, 50 microM of amodiaquine, arthemether, chloroquine, methylene blue, mefloquine and quinine inhibited the interaction between glutathione (50 microM) and heme (50 microM), while atovaquone did not. Consequently, this test could detect drugs that can inhibit heme-GSH degradation in a fast, simple and specific way, making it suitable for high throughput screening of potential antimalarials

Maternally supplied S-acyl-transferase is required for crystalloid organelle formation and transmission of the malaria parasite.

Transmission of the malaria parasite from the mammalian host to the mosquito vector requires the formation of adequately adapted parasite forms and stage-specific organelles. Here we show that formation of the crystalloid-a unique and short-lived organelle of the Plasmodium ookinete and oocyst stage required for sporogony-is dependent on the precisely timed expression of the S-acyl-transferase DHHC10. DHHC10, translationally repressed in female Plasmodium berghei gametocytes, is activated translationally during ookinete formation, where the protein is essential for the formation of the crystalloid, the correct targeting of crystalloid-resident protein LAP2, and malaria parasite transmission

Antiplasmodial activity of 3-trifluoromethyl-2-carbonylquinoxaline di-N-oxide derivatives

The in vitro antiplasmodial activity of some 3-trifluoromethyl-2-carbonylquinoxaline di-N-oxide derivatives is reported. The evaluation was performed on cultures of FcB1 strain (chloroquine-resistant) of P. falciparum and the most interesting compounds were then evaluated on MCF7 tumor cells in order to evaluate an index of selectivity. The 7-methyl (2b, 4b, 5b, 6b) and nonsubstituted (3c, 4c, 5c) quinoxaline 1,4-dioxide derivatives presented the best level of activity

Antiplasmodial Activities of Homogentisic Acid Derivative Protein Kinase Inhibitors Isolated from a Vanuatu Marine Sponge Pseudoceratina sp.

As part of our search for new antimalarial drugs in South Pacific marine sponges, we have looked for inhibitors of Pfnek-1, a specific protein kinase of Plasmodium falciparum. On the basis of promising activity in a preliminary screening, the ethanolic crude extract of a new species of Pseudoceratina collected in Vanuatu was selected for further investigation. A bioassay-guided fractionation led to the isolation of a derivative of homogentisic acid [methyl (2,4-dibromo-3,6-dihydroxyphenyl)acetate, 4a] which inhibited Pfnek-1 with an IC50 around 1.8 μM. This product was moderately active in vitro against a FcB1 P. falciparum strain (IC50 = 12 μM). From the same sponge, we isolated three known compounds [11,19-dideoxyfistularin-3 (1), 11-deoxyfistularin-3 (2) and dibromo-verongiaquinol (3)] which were inactive against Pfnek-1. Synthesis and biological evaluation of some derivatives of 4a are reported

Creation and preclinical evaluation of genetically attenuated malaria parasites arresting growth late in the liver.

Whole-sporozoite (WSp) malaria vaccines induce protective immune responses in animal malaria models and in humans. A recent clinical trial with a WSp vaccine comprising genetically attenuated parasites (GAP) which arrest growth early in the liver (PfSPZ-GA1), showed that GAPs can be safely administered to humans and immunogenicity is comparable to radiation-attenuated PfSPZ Vaccine. GAPs that arrest late in the liver stage (LA-GAP) have potential for increased potency as shown in rodent malaria models. Here we describe the generation of four putative P. falciparum LA-GAPs, generated by CRISPR/Cas9-mediated gene deletion. One out of four gene-deletion mutants produced sporozoites in sufficient numbers for further preclinical evaluation. This mutant, PfΔmei2, lacking the mei2-like RNA gene, showed late liver growth arrest in human liver-chimeric mice with human erythrocytes, absence of unwanted genetic alterations and sensitivity to antimalarial drugs. These features of PfΔmei2 make it a promising vaccine candidate, supporting further clinical evaluation. PfΔmei2 (GA2) has passed regulatory approval for safety and efficacy testing in humans based on the findings reported in this study

Replication of Plasmodium in reticulocytes can occur without hemozoin formation, resulting in chloroquine resistance

Most studies on malaria-parasite digestion of hemoglobin (Hb) have been performed using P. falciparum maintained in mature erythrocytes, in vitro. In this study, we examine Plasmodium Hb degradation in vivo in mice, using the parasite P. berghei, and show that it is possible to create mutant parasites lacking enzymes involved in the initial steps of Hb proteolysis. These mutants only complete development in reticulocytes and mature into both schizonts and gametocytes. Hb degradation is severely impaired and large amounts of undigested Hb remains in the reticulocyte cytoplasm and in vesicles in the parasite. The mutants produce little or no hemozoin (Hz), the detoxification by-product of Hb degradation. Further, they are resistant to chloroquine, an antimalarial drug that interferes with Hz formation, but their sensitivity to artesunate, also thought to be dependent on Hb degradation, is retained. Survival in reticulocytes with reduced or absent Hb digestion may imply a novel mechanism of drug resistance. These findings have implications for drug development against human-malaria parasites, such as P. vivax and P. ovale, which develop inside reticulocytes

A Novel ‘Gene Insertion/Marker Out’ (GIMO) Method for Transgene Expression and Gene Complementation in Rodent Malaria Parasites

Research on the biology of malaria parasites has greatly benefited from the application of reverse genetic technologies, in particular through the analysis of gene deletion mutants and studies on transgenic parasites that express heterologous or mutated proteins. However, transfection in Plasmodium is limited by the paucity of drug-selectable markers that hampers subsequent genetic modification of the same mutant. We report the development of a novel ‘gene insertion/marker out’ (GIMO) method for two rodent malaria parasites, which uses negative selection to rapidly generate transgenic mutants ready for subsequent modifications. We have created reference mother lines for both P. berghei ANKA and P. yoelii 17XNL that serve as recipient parasites for GIMO-transfection. Compared to existing protocols GIMO-transfection greatly simplifies and speeds up the generation of mutants expressing heterologous proteins, free of drug-resistance genes, and requires far fewer laboratory animals. In addition we demonstrate that GIMO-transfection is also a simple and fast method for genetic complementation of mutants with a gene deletion or mutation. The implementation of GIMO-transfection procedures should greatly enhance Plasmodium reverse-genetic research

Correction: Variant Exported Blood-Stage Proteins Encoded by Plasmodium Multigene Families Are Expressed in Liver Stages Where They Are Exported into the Parasitophorous Vacuole.

[This corrects the article DOI: 10.1371/journal.ppat.1005917.]

Validation of use of a traditional antimalarial remedy from French Guiana, Zanthoxylum rhoifolium Lam

Zanthoxylum rhoifolium bark (Rutaceae) is a medicinal plant, traditionally used in French Guiana to treat and prevent malaria. Bioassay-guided extractions of Zanthoxylum rhoifolium bark have shown that antiplasmodial activity is concentrated in the alkaloid fraction. Further fractionation of this extract has yielded seven benzophenanthridine alkaloids, dihydroavicine 1, dihydronitidine 2, oxyavicine 3, oxynitidine 4, fagaridine 5, avicine 6 and nitidine 7. Antimalarial activity of the last five compounds has been evaluated, and nitidine was the most potent, displaying an IC50 < 0.27 mu M against Plasmodium falciparum. Investigation of the traditional remedy, a trunk bark decoction in water, has shown that fagaridine 5, avicine 6 and nitidine 7 are also present in the decoction, therefore justifying the traditional use of Zanthoxylum rhoifolium bark as antimalarial. (c) 2006 Elsevier Ireland Ltd. All rights reserved

Nouveaux extraits à activités anti-paludiques issus de matières premières végétales

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