Imidazolopiperazines Kill both Rings and Dormant Rings in Wild-Type and K13 Artemisinin-Resistant Plasmodium falciparum In Vitro

Artemisinin (ART) resistance has spread through Southeast Asia, posing a serious threat to the control and elimination of malaria. ART resistance has been associated with mutations in the Plasmodium falciparum kelch-13 (Pfk13) propeller domain. Phenotypically, ART resistance is defined as delayed parasite clearance in patients due to the reduced susceptibility of early ring-stage parasites to the active metabolite of ART dihydroartemisinin (DHA). Early rings can enter a state of quiescence upon DHA exposure and resume growth in its absence. These quiescent rings are referred to as dormant rings or DHA-pretreated rings (here called dormant rings). The imidazolopiperazines (IPZ) are a novel class of antimalarial drugs that have demonstrated efficacy in early clinical trials. Here, we characterized the stage of action of the IPZ GNF179 and evaluated its activity against rings and dormant rings in wild-type and ART-resistant parasites. Unlike DHA, GNF179 does not induce dormancy. We show that GNF179 is more rapidly cidal against schizonts than against ring and trophozoite stages. However, with 12 h of exposure, the compound effectively kills rings and dormant rings of both susceptible and ART-resistant parasites within 72 h. We further demonstrate that in combination with ART, GNF179 effectively prevents recrudescence of dormant rings, including those bearing pfk13 propeller mutations.