Identification of Compound <b>15</b> (MMV1581361) as a <i>Pf</i> ATP4 Inhibitor with Transmission-Blocking Activity and <i>In Vivo</i> Efficacy in a SCID Mouse Model of Malaria

Focused structure-activity-relationship studies of MMV020136, <b>1</b>, a whole-cell phenotypic screening hit originating from the Pathogen Box against the human malaria parasite, <i>Plasmodium falciparum</i>, led to the identification of compound <b>15</b> (MMV1581361). Compound <b>15</b> retained nanomolar activity against drug-sensitive, drug-resistant, and field isolates of <i>Plasmodium falciparum</i> blood-stage parasites. It was found to display a moderate rate-of-kill profile similar to pyrimethamine <i>in vitro</i> and efficacy in the humanized <i>P. falciparum</i> <i>Pf3D7</i>^0087/N9 NODscidIL2Rγ^null mouse model at a single dose of 25 mg/kg, with similar kinetics to chloroquine. Furthermore, compound <b>15</b> demonstrated significant transmission-blocking potential, achieving 90% inhibition of male gamete exflagellation, a 98% reduction in mean oocyst intensity, and an 88% block in transmission. Mechanism-of-action studies revealed that compound <b>15</b> disrupts Na⁺ ion homeostasis in <i>P. falciparum</i>, indicating that it functions as a <i>Pf</i>ATP4 inhibitor. However, due to the resistance risk associated with the <i>Pf</i>ATP4 target and the presence of more advanced clinical candidates, further development of <b>15</b> into a viable antimalarial drug is currently deprioritised.