The initiation of tumours on mouse skin by dihydrodiols derived from 7,12‐dimethylbenz(a)anthracene and 3‐methylcholanthrene

The cis‐2a,3‐diol and the trans‐4,5‐, trans‐7,8‐, trans‐9,10‐ and trans‐11,12‐dihydrodiols of 3‐methylcholanthrene and the trans‐3,4, trans‐5,6‐, trans‐8,9‐ and trans‐10,11‐ dihydrodiols of 7,12‐dimethylbenz[a]‐anthrancene have been tested, in comparison with the parent hydrocarbons, for their abilities to initiate skin tumours in female CDI mice. Groups of mice received a single topical application (25 μg) of a diol or of a hydrocarbon, and 1 week later repeated topical applications (1 μg) of 12–0‐tetradecanoyl‐phorbol‐13‐acetate were commenced. The results show that the diols capable of being converted into bay‐region vicinal diol‐epoxides, i.e. the 9,10‐diol of 3‐methylcholanthrene and the 3,4‐diol of 7,12‐dimethylbenz[a]anthrancene were active as initiating agents but that they were no more active than their parent hydrocarbon. The K‐region 5,6‐diol of 7,12‐dimethylbenz[a]anthrancene, which cannot be converted directly into a vicinal diol‐epoxide, was also active as a tumour‐initiating agent when applied to mouse skin.