Combined chronic low dose radiation-caloric restriction: a model for regression of spontaneous mammary tumor

This study was carried out to determine whether chronic low dose radiation can act alone or in synergy with restricted diet in down-regulating spontaneously occurring mammary tumor in tumor-susceptible female C3H/He mice and whether immune cells are involved.

At 7 months of age, one-half of the experimental mice were maintained on an ad lib diet, and the other half was adapted over a period of 1 month to a diet of 70% of the daily amount of food consumed by the ad lib-fed mice. The food of the restricted diet was enriched such that the vitamin and mineral intake was the same for both groups. Half of the mice in each group was then subjected to chronic low dose radiation (0.04 Gy per exposure from a 60Co source, 3 x-per-week for 4 weeks) and the other half was sham irradiated. The 70% calorically restricted diet was maintained throughout the study.

Chronic low dose radiation alone was ineffective in down-regulating spontaneous mammary tumor, unlike caloric restriction. However, chronic low dose radiation when combined with caloric restriction promoted regression of mammary tumors, which were infiltrated with massive numbers of CD8+ T cells. These phenomena were not seen in mice subjected to caloric restriction alone.

Combined chronic low dose radiation-caloric restriction appears to be a useful model for promoting spontaneous mammary tumor regression.