The importance of the "bay region" diol-epoxide in 7,12-dimethylbenz[a]anthracene skin tumor initiation and mutagenesis

The skin tumor-initiating and V79 mutagenic activities of various derivatives of 7,12-dimethylbenz[a]anthracene (DMBA) were investigated to determine what possible cellular metabolite(s) may be responsible for its carcinogenicity and/or mutagenicity. 1-,2-,3-,4- and 5-hydroxyDMBA were found to be essentially inactive as skin tumor initiatrs whereas 9- and 10-hydroxy DAMBA had weak activity. The (±)-trans DMBA 8,9- and 5,6-dihydrodiols were also essentially inactive as skin tumor initiators and (±)-DMBA 8β,9α-diol-10α,11α-epoxide had weak skin tumor initiating activity. All of the above tested derivatives of DMBA were essentially inactive as mutagens in the cell-mediated or direct V79 mutagenesis systems. A methyl or fluoro addition to the 1, 2 or 5 positions almost completely blocked the skin tumor initiating and V79 mutagenic activities of DMBA, whereas a fluoro addition to position 11 did not. From our data we suggest that a 'bay region' diol-epoxide may be important in DMBA carcinogenicity and mutagenicity.