IDENTIFICATION OF N-(DEOXYGUANOSIN-8-YL)-2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE AS THE MAJOR ADDUCT FORMED BY THE FOOD-BORNE CARCINOGEN, 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE, WITH DNA

The covalent binding of the N-acetoxy-, N-hydroxy-, and nitro derivatives of the food-borne carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to 2'-deoxyribonucleosides or DNA was investigated in vitro and in vivo. N-Acetoxy-PhIP reacted with deoxyguanosine (dG), but not with the other deoxyribonucleosides, to form N-(deoxyguanosin-8-yl)-PhIP (dG-C8-PhI]P), whose structure was determined by NMR and mass spectral analyses and by ultraviolet absorption and pH-solvent partitioning characteristics. While reaction of N-acetoxy-PhIP with calf thymus DNA at pH 5.0 yielded 5.38 +/- 1.16 nmol of bound PhIP residues/mg of DNA, N-hydroxy-PhIP gave only 0.13-0.23 nmol binding/mg of DNA under identical reaction conditions. Nitro-PhIP produced no detectable binding under these conditions. HPLC analysis of 1-butanol extracts of enzymatically hydrolyzed DNA that had been modified by N-acetoxy-PhIP PhIP in vitro showed a major adduct which coeluted with and had an ultraviolet absorption and a mass spectrum that were identical to that of authentic dG-C8-PhIP. P-32-Postlabeling analysis of DNA isolated from colon, pancreas, lung, heart, and liver of rats treated orally with revealed the presence of a major PhIP-DNA adduct. This adduct had chromatographic properties identical to that of the P-32-labeled bis(phosphate) derivative of dG-C8-PhIP and represented 35-45 % of the total adducts. Thus, these results indicate that PhIP is similar to other carcinogenic aromatic amines, forming dG-C8-PhIP as a major DNA adduct in vitro by reaction of N-acetoxy-PhIP with DNA and also in vivo in a variety of rat tissues after oral dosing with PhIP.