PYRIDYLOXOBUTYL ADDUCT O-6-[4-OXO-4-(3-PYRIDYL)BUTYL] GUANINE IS PRESENT IN ETHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE-TREATED DNA AND IS ASUBSTRATE FOR O-6-ALKYLGUANINE-DNA ALKYLTRANSFERASE

The lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NN K) is activated to reactive metabolites that methylate or pyridyloxobu tylate DNA. Previous studies demonstrated that pyridyloxobutylated DNA interferes with the repair of O-6-methylguanine (O-6-mG) by O-6-alkyl guanine-DNA alkyltransferase (AGT). The AGT reactivity of pyridyloxobu tylated DNA was attributed to (pyridyloxobutyl)guanine adducts. One po tential AGT substrate adduct, 2'deoxy-O-6-[4-oxo-4-(3-pyridyl)butyllgu ano (O-6-pobdG), was prepared. This adduct was stable at pH 7.0 for gr eater than 13 days and to neutral thermal hydrolysis conditions (pH 7. 0, 100 degrees C, 30 min). Under mild acid hydrolysis conditions (0.1 N HCl, 80 degrees C), O-6-pobdG was depurinated to yield O-6-[4-oxo-4- (3-pyridyl)butyl]guanine (O-6-pobG). O-6-pobdG was hydrolyzed to 4-hyd roxy-1-(3-pyridyl)-1-butanone and guanine under strong acid hydrolysis conditions (0.8 N HCl, 80 degrees C). O-6-pobG was detected in 0.1 NC l hydrolysates of DNA alkylated with the model pyridyloxobutylating ag ent 4-(acetoxymethylnitrosamino)-1-(3-[5-H-3] ([5-H-3]MVKOAc). When [5 -H-3]NNKOAc-treated DNA was incubated with either rat liver or recombi nant human AGT, O-6-pobG was removed, presumably a result of transfer of the pyridyloxobutyl group from the O-6-position of guanine to AGT's active site.