In contrast to 5-methylchrysene and 5,9-dimethylchrysene, 5,6-dimethylchrysene and 5,7-dimethylchrysene are weak tumor initiators on mouse skin. In order to investigate the basis for this, we have evaluated the mutagenic activities toward Salmonella typhimurium TA 100 and reactivity with DNA of (+/-)-anti-1,2-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydro-5,6-dimethyl-ch rys ene (anti-5,6-diMeC-1,2-diol 3,4-epoxide) and anti-5,7- and anti-5,9-diMeC-1,2-diol 3,4-epoxide. The tumorigenic activities of anti-5,6- and anti-5,7-diMeC-1,2-diol 3,4-epoxides in newborn mice were also investigated. anti-5,9-diMeC-1,2-diol 3,4-epoxide was the most mutagenic of the three diol epoxides. anti-5,6-diMeC-1,2-diol 3,4-epoxide was highly tumorigenic in newborn mouse lung, with activity significantly greater than that of either anti-5-MeC- or anti-5,7-diMeC-1,2-diol 3,4-epoxide. Although the amounts of total binding of the diol epoxides to calf thymus DNA were similar, anti-5,6-diMeC-1,2-diol 3,4-epoxide bound extensively to deoxyadenosine residues. High binding to deoxyadenosine is related to the presence of a sterically hindered bay or fjord region as present in 5,6-diMeC, 7,12-dimethylbenz[a]anthracene, benzo-[g]chrysene, and benzo[c]phenanthrene. The conformations of the anti- and syn-diol epoxides of 5,6-diMeC and benzo[c]phenanthrene were similar, with both having pseudodiequatorial hydroxyl groups, in contrast to less sterically crowded diol epoxides. The high tumorigenicity of anti-5,6-diMeC-1,2-diol 3,4-epoxide in newborn mice is of interest with respect to its high deoxyadenosine binding.(ABSTRACT TRUNCATED AT 250 WORDS)

5,6-Dimethylchrysene (5,6-diMeC) is a weaker tumor initiator on mouse skin than 5-methylchrysene (5-MeC). To investigate the reasons for the unexpectedly low activity of 5,6-diMeC, we have studied its metabolism and DNA binding in mouse skin, particularly with respect to metabolic activation via its anti-1,2-diol 3,4-epoxide. The metabolism of 5,6-diMeC was first examined with liver 9000g supernatant from Aroclor 1254 pretreated rats. Three major metabolites were identified as 1- or 7-hydroxy-5-(hydroxymethyl)-6-MeC, 1,2-dihydroxy-1,2-dihydro-5,6-diMeC (5,6-diMeC-1,2-diol), and 1-hydroxy-5,6-diMeC. The formation of 5,6-diMeC-1,2-diol was then assessed in mouse epidermis, following topical application of [3H]5,6-diMeC. Levels of 5,6-diMeC-1,2-diol in epidermis exceeded those of 5-MeC-1,2-diol formed from 5-MeC under similar conditions. The binding of [3H]5,6-diMeC and that of [3H]5-MeC to mouse epidermal DNA were then compared. 5,6-DiMeC-deoxyribonucleoside adducts were prepared as markers by reaction of anti- and syn-5,6-diMeC-1,2-diol 3,4-epoxide with calf thymus DNA. HPLC analysis of enzymatic hydrolysates of mouse epidermal DNA, isolated 18 h after topical treatment with [3H]5,6-diMeC or [3H]5-MeC, demonstrated the formation from [3H]5,6-diMeC of two major adducts produced by reaction of its anti-1,2-diol 3,4-epoxide with deoxyguanosine and deoxyadenosine, respectively, while the major adduct formed from [3H]5-MeC resulted from reaction with deoxyguanosine, in agreement with previous results. Total DNA binding of [3H]5-MeC as well as formation of deoxyguanosine adducts exceeded that of [3H]5,6-diMeC by 3-4-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

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The 3'-monophosphates of the major deoxyribonucleoside adducts of five representative polynuclear aromatic hydrocarbons (PAH)-benzo[a]pyrene, benz[a]anthracene, chrysene, 5-methylchrysene and 6-methylchrysene--were prepared by reaction with DNA of the appropriate bay-region diol epoxides followed by enzymatic hydrolysis and HPLC purification. These standards were converted to 3',[32P]-5'-bisphosphates as in the Randerath 32P-postlabeling assay. TLC and HPLC systems for their separation are described. HPLC conditions for separation of the corresponding 3'- and 5'-monophosphates are also reported. These data will be useful for determining whether unknown DNA adducts detected by the 32P-postlabeling assay may have resulted from reactions of DNA with PAH diol epoxides.

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