Plasmodium falciparum protein kinase 6 and hemozoin formation are inhibited by a type II human kinase inhibitor exhibiting antimalarial activity

Abstract

Kinase inhibitors are potent therapeutics, but most essential Plasmodium kinases remain unexploited as antimalarial targets. We identified compound 12, a type II kinase inhibitor based on aminopyridine and 2,6-benzimidazole scaffolds, as a lead compound with nanomolar potency, fast action, and in vivo activity in the Plasmodium berghei rodent malaria model. Three-hybrid luciferase fragment complementation, enzymatic studies, and cellular thermal shift assays implicated Plasmodium protein kinase 6 (PfPK6) as the target. However, conditional knockdown of PfPK6 did not alter 12 potency, suggesting complex mechanisms of action. In vitro selection for compound 12 resistance revealed mutations in three transporters: multidrug-resistance protein 1, chloroquine resistance transporter and V-type ATPase, indicating a digestive vacuole site of action. Compound 12 inhibited β-hematin and hemozoin formation while increasing free heme levels, suggesting antimalarial activity via blockade of heme detoxification. Our studies repurpose a safe human kinase inhibitor as a potent, fast-acting antimalarial with established in vivo efficacy.