Characterization of Competitive Inhibitors of P. falciparum cGMP-Dependent Protein Kinase

P. falciparum cGMP-dependent protein kinase (PfPKG) is an enticing anti-malarial drug target. Novel chemotypes are needed because existing inhibitors have safety issues that may prevent further development. This work demonstrates isoxazole-based compounds are potent ATP competitive inhibitors of PfPKG and discloses a new analog in this series. Isoxazoles 3 and 5 had K i values that are comparable to a known standard, 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H pyrrol-3-yl] pyridine. They also exhibited excellent selectivity for PfPKG over the human ortholog and the gatekeeper mutant T618Q PfPKG, which mimics the less accessible binding site of the human ortholog. The human ortholog’s larger binding site volume was predicted to explain the selectivity of the inhibitors for the P. falciparum enzyme. Drugs with novel mechanisms of action are needed to combat malaria. Isoxazole-based compounds were found to be potent, selective and ATP-competitive inhibitors of P. falciparum cGMP-dependent protein kinase.