Prophylaxis of 3-methylcholanthrene-induced tumorigenesis in mice with the yeast polysaccharide preparation.

: Prophylaxis of 3-methylcholanthrene-induced epithelial tumor formation in ddI mice with our Candida utilis glucomannan preparation (YPS) was confirmed further in the present system of fibrosarcoma production. A single subcutaneous dose of MCA (0.5 mg per mouse) was either preceded by or followed by 10 or 30 daily intraperitoneal (i.p.) injections of YPS at the dosage of 100 mg/kg per dose according to various time schedules. Protective effect of YPS was demonstrable by a significantly lengthened latent period before the tumor appearance and a slower rate of the subsequent tumor production until around day 100. All the schedules of pre- or post-treatment were found to be effective, although the one delayed until two weeks post MCA was so only marginally. It was also disclosed by prolonging the observation period that this protection was of a transient nature, 100 per cent tumor incidence being found by around 150 days post MCA in all the experimental groups. A longer latency due to the treatment with YPS was generally found in association with a faster growth of the tumor and a shorter life span of the host animal. Temporary protection of MCA-induced tumorigenesis in ddI mice was not reproducible in C3H/He mice, and was thus suggested the possible strain-dependent nature of YPS effect.