Tumorigenicity Studies with Diol-Epoxides of Benzo(a)pyrene Which Indicate That (±)-trans-7β,8α-Dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene Is an Ultimate Carcinogen in Newborn Mice

The tumorigenic activities of benzo(a)pyrene (BP), (±)-trans-7β,8α-dihydroxy-9β,10β-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (diol-epoxide 1), (±)-trans-7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (diol-epoxide 2), (±)-trans-7,8,-dihydroxy-7,8-dihydrobenzo(a)pyrene (BP 7,8-dihydrodiol), and the tetraols derived from the hydrolysis of diol-epoxide 2 were evaluated in newborn mice. The mice were given injections sequentially of 4, 8, and 16 nmoles of each compound on the first, eighth, and fifteenth days of life, and the animals were killed when they were 28 weeks old. Diol-epoxide 1 was highly toxic in newborn mice, and most of the animals treated with this compound died before weaning. Diol-epoxide 2 and BP 7,8-dihydrodiol were, respectively, about 40- and 15-fold more active than BP in causing pulmonary adenomas. Vehicle-treated control animals had an average of 0.13 lung adenoma/mouse, whereas animals treated with BP, BP 7,8-dihydrodiol, or diol-epoxide 2 had, respectively, 0.24, 1.77, and 4.42 pulmonary adenomas/mouse. Diol-epoxide 1 and the tetraols derived from diol-epoxide 2 did not induce pulmonary adenomas. The inactivity of diol-epoxide 1 under the conditions of our study should be interpreted with caution because of the high toxicity of this compound. The results of our study provide evidence that BP 7,8-dihydrodiol is a proximate carcinogenic metabolite and that diol-epoxide 2 is an ultimate carcinogenic metabolite of BP in the newborn mouse.