Structural and mechanistic insights into the inhibition of Plasmodium falciparum MDR1

Malaria, caused by the parasite Plasmodium falciparum, remains a significant global health threat, with multidrug resistance posing a major challenge to treatment. The P-glycoprotein homolog P. falciparum Multidrug Resistance Protein 1 (PfMDR1) is a key determinant of resistance to first-line antimalarials like mefloquine (MFQ) and chloroquine. ACT-451840, a clinical phase I drug, has been developed as an antimalarial candidate, but its mechanism of action and interaction with drug resistance markers remain to be fully understood. Here, we present the cryo-electron microscopy structure of PfMDR1 in complex with ACT-451840, determined at a resolution of 3.42 Å. The structure reveals that ACT-451840 binds within the central cavity and locks PfMDR1 in an inward-open conformation, inhibiting its basal ATPase activity. A structural comparison of the ACT-451840-bound state with the previously reported MFQ-bound state provides a molecular explanation for how ACT-451840 resistance mutations can lead to the sensitization of MFQ. Furthermore, a comparative structural analysis and biochemical characterization with human ABCB1 reveal the selective mechanism of ACT-451840 against PfMDR1. Our findings provide a structural basis for the inhibitory mechanism of ACT-451840, which may inform the future development of antimalarial candidates targeting PfMDR1.