Reaction of cyclopenta[c,d]pyrene-3,4-epoxide with DNA and deoxynucleotides

Cyclopenta[c,d]pyrene (CPP) is a widespread polycyclic aromatic hydrocarbon with potent mutagenic and carcinogenic activity. The trans isomer of 3,4-dihydro-3,4-dihydroxy-cyclopenta[c,d]pyrene has been shown to be the major metabolic product of CPP in rat, mouse or human microsomal systems, as well as in peroxyl radical-generating systems, indicating the preferential formation of its obligatory precursor, CPP-3,4-epoxide. The direct mutagenicity of CPP-3,4-epoxide, the inactivity of 3,4-dihydro-CPP and the DNA adduct forming capacity of CPP in vivo has prompted analysis of the DNA adducts produced by CPP-3,4-epoxide to provide information pertaining to: (i) the role this postulated major ultimate mutagenic metabolite may play in the formation of DNA adducts in vivo; (ii) the base selectivity of CPP-3,4-epoxide DNA adducts; and (iii) the role of CPP-3,4-epoxide in the mutagenicity/carcinogenicity of CPP. CPP-3,4-epoxide was reacted with calf thymus DNA, dGp, dAp, dTp, dCp, poly dG-dC, poly dA-dT and poly dG. Adducts were analyzed by the butanol-enhanced version of 32P-postlabeling. Four major and at least three minor adducts formed with DNA in vitro, which were further analyzed for their base selectivity. A similar spectrum of adducts was exhibited by dGp, poly dG-dC and poly dG. dCp, dTp, and dAp formed one, two, and four adducts respectively. The relative binding in adducts per 10(7) nucleotides was in the following descending order: dGp (6000), poly dG-dC (5800), dTp (5300), dAp (4800), calf thymus DNA (3800), poly dA-dT (2300), poly dG (2600) and dCp (20). Adducts derived from either dGp, poly dG-dC or poly dG co-migrated with the DNA adducts in three solvent systems, indicating that CPP-3,4-epoxide forms DNA adducts almost exclusively with deoxyguanosine.