The effect of ascaridole on the in vitro development of Plasmodium falciparum.

Ascaridole is a terpene isolated from the plant Chenopodium ambrosioides (American wormseed); it is one of the few naturally occurring endoperoxidases. Artemisinin, which also belongs to this group, is a potent antimalarial. We therefore undertook a study to determine the effect of ascaridole, a known anthelmintic, on the in vitro development of Plasmodium falciparum. Ascaridole was found to be a potent inhibitor of plasmodial growth; after 3 days, development was arrested by a drug concentration of 0.05 microM, and at 0.1 microM no parasites were visible in the culture. At lower concentrations the effect was observed mainly at the trophozoite stage, whereas the ring stage was marginally affected. However, even at these lower concentrations, the ring culture could not continue normal development and ceased to grow at a later stage. The peroxide group is essential for the antimalarial activity of ascaridole, as judged from the fact that cineol, which bears an epoxide group instead of the peroxide group found in ascaridole, was totally inactive at identical concentrations.