Inhibition of skin carcinogenesis in vivo by caffeine and other agents.

The induction of skin cancer in mice of the Swiss (Carshalton) strain, by repeated irradiation with UV-light, was strikingly reduced by the local application of caffeine prior to each exposure. Theophylline displayed the same activity. These two substances have been selected as probable inhibitors of error-prone, postreplicative DNA repair. Conversely, reductone and chloroquine, which are considered as inhibitors of the error-free, prereplicative excision repair, did not modify the incidence of the tumors. Special emphasis has been given to the histologic behavior of radiolabeled caffeine in the normal and UV-irradiated epidermis of the mouse in vivo and to the ability of mouse epidermal cells in vitro to repair DNA after UV irradiation.