Hypervalent organotellurium compounds as inhibitors of P. falciparum calcium-dependent cysteine proteases

Hypervalent organotellurium compounds (organotelluranes) have shown several promising applications, including their use as potent and selective cysteine protease inhibitors and antiprotozoal agents. Here, we report the antimalarial activities of three organotellurane derivatives (RF05, RF07 and RF19) in two Plasmodium falciparum strains (CQ_S 3D7 and CQ_R W2), which demonstrated significant decreases in parasitemia in vitro. The inhibition of intracellular P. falciparum proteases by RF05, RF07 and RF19 was determined and the IC₅₀ values were 3.7 ± 1.0 μM, 1.1 ± 0.2 μM and 0.2 ± 0.01 μM, respectively. Using an assay performed in the presence of the ER Ca^2 +-ATPase inhibitor we showed that the main enzymatic targets were cysteine proteases stimulated by calcium (calpains). None of the compounds tested caused haemolysis or a significant decrease in endothelial cell viability in the concentration range used for the inhibition assay. Taken together, the results suggest promising compounds for the development of antimalarial drugs.