The pharmacokinetics and biodistribution of the (14) C-labeled actinide decorporation agent 3,4,3-LI(1,2-HOPO) were investigated in young adult Swiss Webster mice and Sprague Dawley rats, after intravenous, intraperitoneal, and oral dose administration. In all routes investigated, the radiolabeled compound was rapidly distributed to various tissues and organs of the body. In mice, the 24 h fecal elimination profiles suggested that the biliary route is the predominant route of elimination. In contrast, lower fecal excretion levels were observed in rats. Tissue uptake and retention of the compound did not differ significantly between sexes although some differences were observed in the excretion patterns over time. The male mice eliminated a greater percentage of (14) C through the renal pathway than the female mice after receiving an intravenous or intraperitoneal dose, while the opposite trend was seen in rats that received an intravenous dose. Metabolite profiling performed on selected rat samples demonstrated that a putative major metabolite of [(14) C]-3,4,3-LI(1,2-HOPO) is formed, accounting for approximately 10% of an administered oral dose. Finally, to improve its oral bioavailability, 3,4,3-LI(1,2-HOPO) was coformulated with a proprietary permeability enhancer, leading to a notable increase in oral bioavailability of the compound.

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.