The antileukemic action of two thiadiazole derivatives.

]'he thiadiazole derivatives ~-amino-l,S-4-thiadiazole and 5~-ethylamino-l,gAthiadiazole retarded the growth of leukemia LI~10 and extended the survival time of the mice. The thiadiazoles were approximately as effective as the folie acid antagonist aminopterin but considerably less effective than amethopterin in inereasing the life span of the leukemic mice. The antileukemie action and host toxicity of the thiadiazoles were blocked by administration of nieotinamide. In vitro exehange of thiadiazole with the nieotinamide moiety of DPN was obtained, resulting in the formation of the thiadiazole analog of DPN. C~qabeled thiadiazole was readily incorporated in the various tissues of the leukemic host. Preliminary attempts to demonstrate formation of the thiadiazole analog of DPN [~ ,'i,,o were inconclusive.