Identification of Plasmodium falciparum-specific kinase inhibitors: candidates for a potent antimalarial drug

Abstract

Background: Malaria is a disease caused by protozoan parasites of the genus Plasmodium and results in almost a million deaths annually. Currently, the resistance to the available anti-malarial drugs is the biggest obstacle to control the disease. Thus, there is an urgent need for developing a new drug having different parasitic targets. Plasmodium kinases are emerging attractive targets for a novel antimalarial drug because they play essential roles for the parasites while they are very different from the mammalian kinases structurally and even functionally. Therefore, in this study, I looked for the small molecules that can inhibit kinases of malaria parasites, which can be developed into a novel antimalarial drug in the future. Methods: In order to find Plasmodium falciparum-specific kinase inhibitors, 4000 kinase-directed inhibitors were screened using a SYBR green I assay against wild type (3D7) and drug resistant strains (Dd2) of P. falciparum. Some of the hits were tested using fluorescence-based thermal shift assay (FSA) and kinase assay to find their kinase targets. They were also tested in a related apicomplexan parasite, Toxoplasma gondii to prove the suggested target. In silico molecular docking analysis was performed to propose the possible binding modes between the small molecules and the target protein. Results: The primary screening resulted in the identification of 23 compounds that are highly active for both 3D7 and Dd2 strains but have low toxicity profiles in human cell lines. Plasmodium falciparum calcium-dependent protein kinase 1 (PfCDPK1) was found to be a possible target for three compounds using the enzyme-based FTA and kinase assay. The three compounds inhibited invasion of T. gondii into U2OS cells, supporting the target of these particular compounds is CDPK1. Molecular docking analysis suggests the three compounds might have ATP-competitive but not ATP-mimetic mode of binding with the enzyme, which is different from conventional kinase inhibitors. Conclusions: The present study will contribute to develop a new antimalarial drug targeting Plasmodium kinases in the future. Particularly, the three compounds targeting PfCDPK1 will be a good start to design a novel PfCDPK1 inhibitor for an antimalarial drug.