Critical parameters for adduct formation of the carcinogen (+)-anti-benzo[a]pyrene-7,8-dihydrodiol 9,10-epoxide with oligonucleotides.

Various parameters relevant for the formation of dG adducts produced in the reaction of individual benzo[a]pyrene diol epoxide (BPDE) stereoisomers with oligonucleotides have been studied. Reaction time, temperature, pH, molar ratio of diol epoxide and oligonucleotide, base sequence, and buffer system were shown to affect the amount of (+)-anti-BPDE dG adducts formed. Optimum experimental conditions for dG adduct formation were different depending on the base sequence context of the oligonucleotide employed [5'-d(CCTATAGATATCC) or 5'-d(CCTATTGCTATCC)]. In general, low temperature to allow a longer reaction time, slightly alkaline Tris-HCl (pH 7.5-8.0) or alkaline phosphate buffer (pH 11), low concentration of organic solvent, and a molar excess of (+)-anti-BPDE promote dG adduct formation with an oligonucleotide. Low incubation temperature and Tris-HCl buffer also favor dG adduct formation of (-)-anti-BPDE and both enantiomers of syn-BPDE to both 5'-d(CCTATAGATATCC) and 5'-d(CCTATTGCTATCC).