Covalent DNA adducts formed by benzo[c]chrysene in mouse epidermis and by benzo[c]chrysene fjord-region diol epoxides reacted with DNA and polynucleotides.

The metabolic activation in mouse skin of benzo[c]chrysene (B[c]C), a weakly carcinogenic polycyclic aromatic hydrocarbon (PAH) present in coal tar and crude oil, was investigated. Male Parkes mice were treated topically with 0.5 mumol of B[c]C, and DNA was isolated from the treated areas of skin at various times after treatment and analyzed by 32P-postlabeling. Seven adduct spots were detected, at a maximum level of 0.89 fmol of adducts/microgram of DNA. Four B[c]C-DNA adducts persisted in skin for at least 3 weeks. Treatment of mice with 0.5 mumol of the optically pure putative proximate carcinogens (+)- and (-)-trans-benzo[c]chrysene-9,10-dihydrodiols [(+)- and (-)-B[c]C-diols] led to the formation of adducts which comigrated on TLC and HPLC with some of those formed in B[c]C-treated mice. The major adduct formed in mouse skin treated with B[c]C coeluted on TLC and HPLC with an adduct formed in mouse skin treated with (-)-B[c]C-diol. These results suggested that the detected adducts were formed by the fjord-region B[c]C-9,10-dihydrodiol 11,12-epoxides (B[c]CDEs). To test this, the four optically pure synthetic B[c]CDEs were reacted in vitro with DNA and with synthetic polynucleotides and these samples were 32P-postlabeled. Cochromatography, both on TLC and HPLC, of in vitro and in vivo adducts indicated that B[c]C is activated in mouse skin through formation of the (-)-anti- and (+)-syn-B[c]CDE with 9R,10S,11S,12R- and 9S,10R,11S,12R- absolute configuration, respectively, both of which formed two DNA adducts in vivo. However, the major adduct present in the B[c]C-treated skin DNA was not a fjord-region B[c]CDE adduct but was possibly derived from a bay region B[c]CDE at the 1,2,3,4-position. The extent of DNA adduct formation by B[c]C in mouse skin DNA was lower than that of moderately carcinogenic PAHs previously studied by this method, suggesting a correlation between extent of DNA adduct formation and carcinogenic potential.

Covalent DNA adducts formed in mouse epidermis by benzo[g]chrysene.

The metabolic activation in mouse skin of benzo[g]chrysene (B[g]C), a moderately carcinogenic polycyclic aromatic hydrocarbon (PAH) present in coal tar, was investigated. Male Parkes mice were treated topically with 0.5 micromol B[g]C and DNA was isolated from the treated areas of skin at various times after treatment and analysed by 32P-post-labelling. Seven major adduct spots were detected, at a maximum level of 6.55 fmol adducts/microg DNA. Mouse skin treated with the PAH benzo[c]phenanthrene (B[c]Ph) gave a total of 0.24 fmol adducts/microg DNA. B[g]C-DNA adducts persisted in skin for at least 3 weeks. Treatment of mice with 0.5 micromol of the optically pure putative proximate carcinogens, the (+)- and (-)-trans benzo[g]chrysene-11,12-dihydrodiols, led to the formation of adducts which comigrated on TLC and HPLC with those formed in B[g]C-treated mice, which suggested that the detected adducts were formed by the fjord region B[g]C-11,12-dihydrodiol-13,14-epoxides (B[g]CDEs). To test this, the four optically pure synthetic B[g]CDEs were reacted in vitro with DNA and the heteroco-polymers poly(dA x dT) and poly(dG x dC) and these samples 32P-postlabelled. Co-chromatography, on both TLC and HPLC, of in vitro and in vivo adducts indicated that B[g]C is activated in mouse skin through formation of the (-)-anti-(11R,12S,l3S,14R) and (+)-syn-(11S,12R,13S,14R) B[g]CDEs. (-)-anti-B[g]CDE formed five adducts with DNA, two of them with adenine and three with guanine bases. (+)-syn-B[g]CDE formed one adduct with each of these bases in DNA. The adenine adducts accounted for 64% of the total major adducts formed in B[g]C-treated mouse skin. The route of metabolic activation or B[g]C is similar to that reported for B[c]Ph, but the extent of activation to the fjord region diol-epoxides is significantly greater in the case of B[g]C, as demonstrated by the higher levels of adduct formation in vivo.

In vitro reaction with DNA of the fjord-region diol epoxides of benzo[g]chrysene and benzo[c]phenanthrene as studied by 32P-postlabeling.

The chemical reactivities of the optically-pure fjord-region syn- and anti-benzo[g]chrysene 11,12-dihydrodiol 13,14-epoxides (B[g]CDEs) toward DNA in vitro have been compared with those of the optically-pure fjord-region syn- and anti-benzo[c]phenanthrene 3,4-dihydrodiol 1,2-epoxides (B[c]PhDEs), using the standard 32P-postlabeling assay. The (+)-anti-, (+)-syn-, and (-)-syn-isomers of the two sets of diol epoxides showed similar extents of reaction with DNA, but the (-)-anti-B[c]PhDE was 2.5 times more reactive toward DNA than the corresponding B[g]CDE isomer and was the most reactive of the eight diol epoxides studied. When the reactions of the B[g]CDEs with DNA were analyzed by the nuclease P1-enhanced method of 32P-postlabeling, the observed adduct levels were between 3 and 10 times lower than were obtained using the standard method of 32P-postlabeling. By analyzing by TLC and HPLC the 32P-postlabeled products of the reactions of the diol epoxides with synthetic polynucleotides, the relative reactions of the B[g]CDEs and B[c]PhDEs with guanine and adenine bases in DNA were determined. All four B[g]CDE isomers reacted with adenine residues in similar proportions to those seen for the B[c]PhDE isomers. Thus, the presence of an additional benzene ring on the benzo[c]phenanthrene structure, distant from the fjord region, does not radically alter the reactivity or base selectivity of the fjord-region diol epoxides, except in the case of the (-)-anti-isomer of benzo[g]chrysene. The reasons for the lower reactivity of this isomer compared with that of the corresponding isomer of benzo[c]phenanthrene are unclear.(ABSTRACT TRUNCATED AT 250 WORDS)