A type II human kinase inhibitor with antimalarial activity inhibits Plasmodium falciparum protein kinase 6 and hemozoin formation

To address the need for new antimalarials, we are repurposing human kinase inhibitors. This endeavor has identified compound 12 (YLIU-06-026-1), a type II kinase inhibitor based on aminopyridine and 2,6-benzimidazole scaffolds. This compound exhibited nanomolar antiplasmodial activity, fast-action, and in vivo activity in P. berghei infected mice. Our comprehensive in vitro analysis based on three-hybrid luciferase fragment complementation, enzymatic and cellular thermal shift assays point to Plasmodium protein kinase 6 as the protein target of 12. Using a conditional knock down of PfPK6 expression, we found unchanged compound 12 EC 50 , implicating a complex mode of action. In vitro selection of parasites resistant to compound 12 selected for parasites carrying mutations in two digestive vacuole transporters: multidrug-resistance protein 1 (PfMDR1) and chloroquine resistance transporter (PfCRT), suggesting a digestive vacuole site of action. Perturbation of b-hematin formation, cellular heme and hemozoin levels provided evidence that compound 12 acted via inhibition of hemozoin formation in Plasmodium.