In Vitro Activity of Antimalarial Compounds on the Exoerythrocytic Stages of Plasmodium cynomolgi and P. Knowlesi

Tamara L. FiskMalaria Branch, Division of Parasitic Diseases, Center for Infectious Diseases, Centers for Disease Control, Atlanta, Georgia

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Pascal MilletMalaria Branch, Division of Parasitic Diseases, Center for Infectious Diseases, Centers for Disease Control, Atlanta, Georgia

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William E. CollinsMalaria Branch, Division of Parasitic Diseases, Center for Infectious Diseases, Centers for Disease Control, Atlanta, Georgia

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Phuc Nguyen-DinhMalaria Branch, Division of Parasitic Diseases, Center for Infectious Diseases, Centers for Disease Control, Atlanta, Georgia

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Primary cultures of Macaca mulatta hepatocytes infected with sporozoites of Plasmodium knowlesi, P. cynomolgi (Cambodian strain), and P. cynomolgi bastianellii were exposed in vitro to 7 antimalarial compounds. The number of exoerythrocytic schizonts present after 4–7 days of culture was used to assess the activity. With pyrimethamine, proguanil, cycloguanil, primaquine, and 2 of its analogues (WR242511 and WR238605), marked inhibition of schizont formation could be achieved at concentrations below those causing a cytotoxic effect on the host hepatocytes. Chloroquine had only minimal schizonticidal activity at a concentration that produced severe hepatocyte toxicity. This simian in vitro system provides a reliable model for screening antimalarial compounds and for investigating their effects on the hepatic stage of malaria parasites.

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