The spiroindolone
cipargamin, a new
antimalarial compound that inhibits Plasmodium ATP4, is currently in clinical development. This study aimed to characterize the
antimalarial activity of
cipargamin in healthy volunteers experimentally infected with blood-stage Plasmodium falciparum Eight subjects were intravenously inoculated with parasite-infected erythrocytes and received a single oral dose of 10 mg
cipargamin 7 days later. Blood samples were collected to monitor the development and clearance of
parasitemia and plasma
cipargamin concentrations. Parasite regrowth was treated with
piperaquine monotherapy to clear asexual parasites, while allowing gametocyte transmissibility to mosquitoes to be investigated. An initial rapid decrease in
parasitemia occurred in all participants following
cipargamin dosing, with a parasite clearance half-life of 3.99 h. As anticipated from the dose selected, parasite regrowth occurred in all 8 subjects 3 to 8 days after dosing and allowed the pharmacokinetic/pharmacodynamic relationship to be determined. Based on the limited data from the single subtherapeutic dose cohort, a MIC of 11.6 ng/ml and minimum parasiticidal concentration that achieves 90% of maximum effect of 23.5 ng/ml were estimated, and a single 95-mg dose (95% confidence interval [CI], 50 to 270) was predicted to clear 109 parasites/ml. Low gametocyte densities were detected in all subjects following
piperaquine treatment, which did not transmit to mosquitoes. Serious adverse liver function changes were observed in three subjects, which led to premature study termination. The
antimalarial activity characterized in this study supports the further clinical development of
cipargamin as a new treatment for P.
falciparum malaria, although the hepatic safety profile of the compound warrants further evaluation. (This study has been registered at ClinicalTrials.gov under identifier NCT02543086.).