The inefficacy of riboflavin against ultraviolet-induced carcinogenesis.
Flavins are reported to protect cellular DNA against UV irradiation injury in vitro. The possible photoprotective effects of riboflavin in vivo on UV-induced carcinogenesis were studied in three groups of HR-hairless mice. Group I served as control. Group II was painted daily with a 15 mg per ml solution of riboflavin. In Group III, drinking water was replaced with a 15 mg per ml solution of riboflavin in water. All three groups were simultaneously irradiated in a light box with two Westinghouse FS20 sunlamps from a distance of 30 cm for 5 min daily 6 days a week throughout the experiment. By the 11th month all surviving mice developed several histologically proven squamous cell carcinomas. The total numbers and times of onset of tumors did not vary in the three groups. Thus, no protective effect of massive amounts of riboflavin on ultraviolet-induced carcinogenesis in the hairless mouse could be demonstrated when such high dose rates of UV were used.