Antiplasmodial activity of [(aryl)arylsulfanylmethyl]pyridine

A series of [(aryl)arylsufanylmethyl]pyridines (AASMP) have been synthesized. These compounds inhibited hemozoin formation, formed complexes (K-D = 12 to 20 mu M) with free heme (ferriprotoporphyrin IX) at a pH close to the pH of the parasite food vacuole, and exhibited antimalarial activity in vitro. The inhibition of hemozoin formation may develop oxidative stress in Plasmodium falciparum due to the accumulation of free heme. Interestingly, AASMP developed oxidative stress in the parasite, as evident from the decreased level of glutathione and increased formation of lipid peroxide, H2O2, and hydroxyl radical (center dot OH) in P. falciparum. AASMP also caused mitochondrial dysfunction by decreasing mitochondrial potential (Delta Psi m) in malaria parasite, as measured by both flow cytometry and fluorescence microscopy. Furthermore, the generation of center dot OH may be mainly responsible for the antimalarial effect of AASMP since center dot OH scavengers such as mannitol, as well as spin trap alpha-phenyl-n-tertbutyinitrone, significantly protected P. falciparum from AASMP-mediated growth inhibition. Cytotoxicity testing of the active compounds showed selective activity against malaria parasite with selectivity indices greater than 100. AASMP also exhibited profound antimalarial activity in vivo against chloroquine resistant P. yoelii. Thus, AASMP represents a novel class of antimalarial.