Reactivity of benzo[a]pyrene-7,8-dione with DNA. Evidence for the formation of deoxyguanosine adducts

Polycyclic aromatic hydrocarbon (PAH) o-quinones are productsof the dihydrodiol dehydrogenase-catalyzed oxidation of trans-dihydrodiolswhich are proximate carcinogens. The PAH o-quinones are highlyreactive molecules and have the potential to alkylate DNA. Inthis study, the reactivity of [³H](+/–)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene([³H](+/–)-anti-BPDE), [³H]benzo[a]pyrene-7,8-dione ([³H]BPQ)and [³H](+/–)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene ([³H](+/–)-B[a]P-diol) with DNA were compared.(+/–)-anti-BPDE reacted equally well with native, deproteinatedand deproteinated/sheared calf thymus DNA. In each case DNAadducts were formed which upon digestion to deoxyribonucleosidescomigrated on reverse-phase (RP)-HPLC with adducts synthesizedby reacting (+/–)-anti-BPDE with oligo-p(dG)₁₀. (+/–)-anti-BPDEalso reacted with plasmid (pGEM-3) DNA to yield multiple adductsone of which comigrated with the (+)-anti-BPDE-deoxyguanosineadduct. Under identical conditions [³H]BPQ reacted preferentiallywith native calf thymus DNA but displayed low reactivity withdeproteinated and deproteinated/sheared calf thymus DNA. RP-HPLCanalysis of deoxyribonucleoside—BPQ adducts indicatedthat the predominant adduct formed comigrated with a standardsynthesized by reacting BPQ with oligo-p(dG)₁₀. BPQ also reactedwith pGEM-3 DNA to yield multiple adducts one of which comigratedwith the BPQ—deoxyguanosine adduct. Reactions between[³H]BPQ and poly(dA), poly(dT), poly(dC) and oligo-p(dG)₁₀ indicatedthat BPQ preferentially formed deoxyguanosine adducts. In thisstudy, [³H]BPQ and [³H](+/–)-anti-BPDE covalently labelednative calf thymus DNA to an equal extent, however, less [³H]BPQwas recovered as deoxyguanosine adducts. By contrast, no covalentmodification of calf thymus DNA, pGEM-3 DNA or oligonucleotideswas observed with [³H](+/–)-B[a]P-diol. These studiesindicate that BPQ has the potential to be genotoxic in vitro;that reactivity is heightened in the presence of protein orcircular DNA and that the major adduct formed is a deoxyguanosineadduct.