Carcinogenic effects of intracolonic benzo[a]pyrene in beta-naphthoflavone-induced mice

Benzo[a]pyrene (BP) was administered intracolonically to ICR/Ha and C57Bl/6 female mice, 1 mg/mouse, once weekly for 14 weeks. Half of the mice received beta-naphthoflavone (beta-NF, a mixed-function oxygenase inducer) i.p. 24 h prior to the BP. No colonic neoplasms were found in any of the mice after 18 months. However, the BP treatment did cause a significant increase in numbers of primary lung tumors, forestomach papillomas, mammary carcinomas, and sarcomas in one or both strains, relative to controls, and the incidence of all of these except for the sarcomas was significantly reduced by treatment with beta-NF prior to BP. Overall, the beta-NF pretreatment reduced total incidence of neoplasms by about 30% in the ICR/Ha mice and by about 60% in the C57Bl/6 mice, and did not potentiate the action of the carcinogen in any organ.