Tumor-initiating activity of dihydrodiols formed metabolically from 5-methylchrysene

The major dihydrodiols formed from 5-methylchrysene by rat liver 9000 x g supernatant were tested for tumor-initi-ating activity on mouse skin. The compounds tested were 1,2-dihydro-1,2-dihydroxy-5-methylchrysene, 7,8-dihydro-7,8-di-hydroxy-5-methylchrysene, 9, 10-dihydro-9, 10-dihydroxy-5-methylchrysene, and 5-methylchrysene. Each compound was applied in a total initiating dose of 30 μg and was followed by promotion with tetradecanoylphorbol acetate. 1,2-Dihydro-1,2-dihydroxy-5-methylchrysene was the most powerful tumor initiator, inducing tumors in 95% of the animals and 7.3 tumors per animal. 5-Methylchrysene and 7,8-dihydro-7,8-dihydroxy-5-methylchrysene induced tumors in 75 and 50% of the animals and gave 3.0 and 1.1 tumors per animal, respectively. 9,10-Dihydro-9,10-dihydroxy-5-methylchrysene was not tumorigenic. The results indicate that 1,2-dihydro-1,2-dihydroxy-5-methylchrysene is a major proximate carcinogen of 5-meth-ylchrysene. Both 1,2-dihydro-1,2-dihydroxy-5-methylchrysene and 7,8-dihydro-7,8-dihydroxy-5-methylchrysene can theoretically form bay-region dihydrodiol epoxides, but the former was more tumorigenic than the latter. The high activity of 1,2-dihydro-1,2-dihydroxy-5-methylchrysene is typical of hydrocarbon derivatives with a methyl group in the bay region adjacent to an unsubstituted angular ring.