The Human Chk1 Inhibitor CHIR-124 Shows Multistage Activity against the Human Malaria Parasite Plasmodium falciparum via Polypharmacological Inhibition of PfArk1 and Hemozoin Formation.

The high burden of malaria and growing resistance to frontline antimalarials demand new drug target combinations with reduced propensities for conferring parasite resistance. An attractive approach for circumventing antimalarial drug resistance is target repurposing, in which known drugs that act through protein targets of human origin that are also active against the human malaria parasite Plasmodium falciparum are exploited to identify novel antimalarial drug targets. Here, we show that the human checkpoint kinase 1 (Chk1) inhibitor CHIR-124 is active in vitro against both drug-sensitive and drug-resistant asexual blood stage parasites and competitively binds to several Plasmodium kinases. The compound also shows moderate activity against both the liver and gametocyte forms of the parasite. Further target investigation of CHIR-124 via conditional knockdown experiments confirmed that P. falciparum Aurora-related kinase 1 (PfArk1) is implicated in its parasiticidal activity. Notably, CHIR-124 also inhibits β-hematin (synthetic hemozoin) formation and causes a dose-dependent increase in free heme that correlates with inhibition of parasite growth. These findings suggest that polypharmacology is involved in the activity of CHIR-124 against P. falciparum via the dual inhibition of Plasmodium PfArk1 and hemozoin formation, both essential for parasite proliferation. This is further supported by in vitro drug combination experiments, morphological studies, and resistance generation attempts. This study validates the feasibility of dual Plasmodium kinase/hemozoin formation inhibitors active against resistant strains with decreased resistance risks in the fight against malaria.