Enhanced resistance to an antigenic tumor in immunosuppressed mice by dietary retinyl palmitate plus canthaxanthin

Retinoids and certain carotenoids, e.g., beta-carotene and canthaxanthin, have been found to prevent photocarcinogenesis in mice and also to act as immunoenhancers. The hypothesis that retinoids and carotenoids inhibit photocarcinogenesis by preventing UV induction of immunosuppression predicts that mice treated with these agents before and during periods of UV radiation treatments should be as resistant as unirradiated mice to an antigenic UV-induced tumor. To test this prediction, mice were fed 120 IU of retinyl palmitate per gram of diet, and/or 1% canthaxanthin, before UV irradiation treatments began, and during the entire experiment. After 4.95 x 10(5) Jm-2, delivered over 12 weeks, resistance of mice to antigenic UV-induced tumor implants (UV20) was studied. Dietary supplementation with retinyl palmitate plus canthaxanthin, but not with either agent alone at these doses, prevented the enhanced growth of UV20 in UV irradiated mice.