The experimental chemotherapy of leishmaniasis. II. The activity in tissue culture of some antiparasitic and antimicrobial compounds in clinical use.

A variety of compounds used in the treatment of parasitic or bacterial infections in man, including leishmaniasis itself, were examined for their activity against three lines of Leishmania in tissue culture. The organisms used were L. mexicana mexicana, L. tropical major and L. donovani; they were grown in dog sarcoma and hamster peritoneal exudate cell lines. Leishmanicidal activity was observed in a number of compounds currently in clinical use for the treatment of one or other form of leishmaniasis. Cycloguanil, nifurtimox, amphotericin B and monomycin were effective but pentamidine showed poor activity. In each case marked differences were observed in the level of response in the different parasite lines. Organic antimonials were most active when anmastigotes were exposed to them prior to entry of the parasites into host cells. This suggests that such compounds may exert an effect on amastigotes during their brief extracellular transit from one host cell to another in vivo. A number of antimalarials showed good to moderate leishmanicidal action, particularly against L. mexicana and L.t. major. Several schistosomicidal agents also possessed leishmanicidal properties. The commonly used broad spectrum antibiotics showed little if any activity. In discusssion a comparison is drawn between data published on the action of some of these drugs against L.t. major in mice and our observations with the same strain and L. mexicana in tissue culture. A remarkably good agreement is found for most of the compounds examined. General agreement is also noted between these data and reports of clinical trials although it is not possible to draw too many conclusions because of the failure in most clinical studies to make an accurate identification of the causative Leishmania. It is concluded that, although the tissue culture model is not to be considered as ideal and can probably be improved, data obtained by its use do bear relevance to the action compounds in vivo, and the model may be use in the screening of drugs for leishmanicidal activity.