Similarly efficacious anti-malarial drugs SJ733 and pyronaridine differ in their ability to remove circulating parasites in mice.

BACKGROUND: Artemisinin-based combination therapy (ACT) has been a mainstay for malaria prevention and treatment. However, emergence of drug resistance has incentivised development of new drugs. Defining the kinetics with which circulating parasitized red blood cells (pRBC) are lost after drug treatment, referred to as the "parasite clearance curve", has been critical for assessing drug efficacy; yet underlying mechanisms remain partly unresolved. The clearance curve may be shaped both by the rate at which drugs kill parasites, and the rate at which drug-affected parasites are removed from circulation. METHODS: In this context, two anti-malarials, SJ733, and an ACT partner drug, pyronaridine were compared against sodium artesunate in mice infected with Plasmodium berghei (strain ANKA). To measure each compound's capacity for pRBC removal in vivo, flow cytometric monitoring of a single cohort of fluorescently-labelled pRBC was employed, and combined with ex vivo parasite culture to assess parasite maturation and replication. RESULTS: These three compounds were found to be similarly efficacious in controlling established infection by reducing overall parasitaemia. While sodium artesunate acted relatively consistently across the life-stages, single-dose SJ733 elicited a biphasic effect, triggering rapid, partly phagocyte-dependent removal of trophozoites and schizonts, followed by arrest of residual ring-stages. In contrast, pyronaridine abrogated maturation of younger parasites, with less pronounced effects on mature parasites, while modestly increasing pRBC removal. CONCLUSIONS: Anti-malarials SJ733 and pyronaridine, though similarly efficacious in reducing overall parasitaemia in mice, differed markedly in their capacity to arrest replication and remove pRBC from circulation. Thus, similar parasite clearance curves can result for anti-malarials with distinct capacities to inhibit, kill and clear parasites.

(+)-SJ733, a clinical candidate for malaria that acts through ATP4 to induce rapid host-mediated clearance of Plasmodium.

Drug discovery for malaria has been transformed in the last 5 years by the discovery of many new lead compounds identified by phenotypic screening. The process of developing these compounds as drug leads and studying the cellular responses they induce is revealing new targets that regulate key processes in the Plasmodium parasites that cause malaria. We disclose herein that the clinical candidate (+)-SJ733 acts upon one of these targets, ATP4. ATP4 is thought to be a cation-transporting ATPase responsible for maintaining low intracellular Na(+) levels in the parasite. Treatment of parasitized erythrocytes with (+)-SJ733 in vitro caused a rapid perturbation of Na(+) homeostasis in the parasite. This perturbation was followed by profound physical changes in the infected cells, including increased membrane rigidity and externalization of phosphatidylserine, consistent with eryptosis (erythrocyte suicide) or senescence. These changes are proposed to underpin the rapid (+)-SJ733-induced clearance of parasites seen in vivo. Plasmodium falciparum ATPase 4 (pfatp4) mutations that confer resistance to (+)-SJ733 carry a high fitness cost. The speed with which (+)-SJ733 kills parasites and the high fitness cost associated with resistance-conferring mutations appear to slow and suppress the selection of highly drug-resistant mutants in vivo. Together, our data suggest that inhibitors of PfATP4 have highly attractive features for fast-acting antimalarials to be used in the global eradication campaign.

Synthesis and structure-activity relationship of disubstituted benzamides as a novel class of antimalarial agents.

Malaria is a devastating world health problem. Using a compound library screening approach, we identified a novel series of disubstituted benzamide compounds with significant activity against malaria strains 3D7 and K1. These compounds represent a new antimalarial molecular scaffold exemplified by compound 1, which demonstrated EC(50) values of 60 and 430 nM against strains 3D7 and K1, respectively. Herein we report our findings on the efficient synthesis, structure-activity relationships, and biological activity of this new class of antimalarial agents.

Evaluation of Jatropha isabelli natural products and their synthetic analogs as potential antimalarial therapeutic agents.

Protozoal diseases such as malaria are a leading world health concern. We screened a library of fractionated natural products to identify new potential therapeutic leads and discovered that jatrophone (a product of Jatropha isabelli) exerts significant activity against Plasmodium falciparum strains 3D7 and K1. A focused jatrophone-scaffold library was synthesized to evaluate jatrophone's mode of action and identify more selective analogs. Compounds 25 and 32 of this natural product-inspired compound library exhibited micromolar EC50 values against strains 3D7 and K1, thus providing a new antimalarial molecular scaffold. Our report describes an efficient derivatization approach used to evaluate the structure-activity relationship of jatrophone analogs in search of potential new antimalarial agents.