Identification of various deoxyribonucleoside adducts formed in primary cultures of mouse keratinocytes exposed to dibenz[a,j]anthracene (DB[a,j]A) is presented. A preliminary analysis of the DNA adducts formed from 7-methyldibenz[a,j]anthracene (7MeDB[a,j]A) also is presented. Cultures of keratinocytes obtained from dorsal skins of female SENCAR mice were exposed to 0.5 microgram of tritium-labeled hydrocarbons/mL of medium for 24 h. The total DNA binding was 2.23 +/- 0.54 and 5.28 +/- 0.97 pmol of hydrocarbon/mg of DNA for DB[a,j]A and 7MeDB[a,j]A, respectively. These binding values represented the radioactivity associated with the modified deoxyribonucleosides separated from the normal deoxyribonucleosides on Sephadex LH-20 columns following enzymatic digestion of isolated DNA. Treatment of keratinocytes with DB[a,j]A produced adduct peaks corresponding to marker adducts derived from trans addition of both deoxyguanosine as well as deoxyadenosine residues to the (+) enantiomer of the anti-diol epoxide where the deoxyadenosine adducts were predominant. In addition, DNA adduct peaks corresponding to markers of trans and cis addition, respectively, of deoxyguanosine and deoxyadenosine to the (+)-syn-diol epoxide were also noted in these chromatograms. A major DNA adduct in cells exposed to DB[a,j]A was tentatively identified as resulting from the addition of deoxyadenosine to DB[a,j]A-5,6-oxide. Several other later eluting DNA adduct peaks, not corresponding to any of the marker adducts, were also present in these chromatograms. In comparison, when cells were exposed to the more biologically potent 7-methyl analogue, at least 12 DNA adduct peaks were consistently observed in HPLC chromatograms.(ABSTRACT TRUNCATED AT 250 WORDS)

This study was designed to evaluate the point mutations in the murine c-Ha-ras gene of skin papillomas induced by initiation with dibenz[a,j]anthracene (DB[a,j]A), its bay-region anti-diol epoxide ((+/-)anti-DB[a,j]A-DE), and a 7,14-dimethyl analogue (7,14-diMeDB[a,j]A). Recent studies (Nair RV, et al., Chem Res Toxicol 4:115-122, 1991) in our laboratory have revealed both deoxyguanosine (dGuo) and deoxyadenosine (dAdo) adducts formed from the anti- and syn-diol epoxides of DB[a,j]A in cultured mouse epidermal cells after exposure to this hydrocarbon. Using PCR amplification and direct sequencing, we found specific A182----T transversion mutations (eight of 10 tumors) in codon 61 of c-Ha-ras in papillomas induced by initiation with DB[a,j]A. Analysis of papillomas generated by initiation with the more biologically potent analogue 7,14-diMeDB[a,j]A revealed that five of five tumors exhibited A182----T transversions in codon 61. The nature of the changes in the two DB[a,j]A tumors not showing codon 61 mutations in Ha-ras is currently not known since these tumor DNAs also did not possess c-Ha-ras mutations at codons 12, 13, or 59. Interestingly, papillomas produced by initiation with (+/-)anti-DB[a,j]A-DE also possessed A182----T transversion mutations in codon 61 of c-Ha-ras (five of five tumors). These data suggest that dAdo adducts derived from both parent hydrocarbons may play an important role in their tumor-initiating activity and possibly implicate a specific diol epoxide-dAdo adduct in this process.