Effect of Massive Doses of Riboflavin, and Other Vitamins of the B Group, on Skin Carcinogenesis in Mice

IT came to our notice that a large group of Strong A mice in another institute fed on a diet known as " P.R.M. " unexpectedly failed to develop skin tumours in response to twice weekly applications of 0*1 ml. 0.1 per cent 3,4-benzopyrene for over one year. Because P.R.M. diet has a high content of vitamins of the B group, and because there are certain theoretical reasons for believing that riboflavin, in particular, might influence carcinogenesis, the experiments described below were undertaken. Previously Boutwell, Brush and Rusch (1949) investigated the effect of different levels of dietary vitamins of the B group on skin carcinogenesis by 3,4-benzopyrene. They reported a somewhat lower incidence of tumours in a group given a diet low in all B vitamins, but saw no difference in groups receiving diets rich in all, or individual, B vitamins. However, in their experiments the highest dietary level of riboflavin was less than 100,tg. per mouse per day. Moreover, their treatment with benzopyrene (0.3 per cent in benzene twice weekly, volume of solution not stated) was probably vastly in excess of that necessary to induce tumours, and a small inhibitory effect may have been swamped. In the experiments reported below, the dose-levels of riboflavin were much higher and the concentration of benzopyrene (in Experiments II and III) much lower. MATERIALS AND METHODS Mice.- " 101 " strain mice of both sexes were used in all experiments. Animals were vaccinated on the tail at the age of 6-8 weeks, as a precaution against ectromelia, and began treatment at 8-10 weeks of age. Chemicals.-3,4-Benzopyrene (BP) and 9,10,-dimethyl-1,2-benzanthracene (DMBA) were obtained from L. Light and Co. and used without further purification. Croton oil was obtained from Messrs. Stafford Allen and Co., Wharf Road, London, N. 1, in 1953 and thereafter stored in the dark at room temperature. Acetone (Analar grade) and Thiamine B.P. were obtained from British Drug Houses