Leukemia induced in rats but not mice by dimethyl morpholinophosphoramidate, a simulant anticholinesterase agent.

Dimethyl morpholinophosphoramidate (DMMPA), an organophosphate, caused leukemia in male and female Fischer 344/N rats. DMMPA was administered in corn oil by oral intubation to groups of 50 male and 50 female rats at 0, 150, 300, or 600 mg/kg body weight, five times per week for 2 years. B6C3F1 mice were given 0, 150 (males only), 300, and 600 (females only) mg/kg body weight under the same schedule. DMMPA induced a dose-related enhancement in the incidence of mononuclear cell leukemia in rats--males: controls = 14/50, 150 mg group = 21/50; 300 mg group = 19/50; 600 mg group = 25/50; females: controls = 9/50, 150 mg group = 13/50; 300 mg group = 12/49; 600 mg group = 18/50. Survival-adjusted rates strengthen the DMMPA effect: males--31%, 50%, 47%, and 63%; females--20%, 32%, 30%, 50%. Latent periods for mononuclear cell leukemia development in exposed rats were not shortened compared to controls. No carcinogenic effects in mice were detected. DMMPA was not mutagenic in Salmonella, was mutagenic for mouse lymphoma cells, and induced both chromosome aberrations and sister chromatid exchanges in Chinese hamster ovary cells.