Pyridyloxobutyl adduct O6-[4-oxo-4-(3-pyridyl)butyl]guanine is present in 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone-treated DNA and is a substrate for O6-alkylguanine-DNA alkyltransferase

Chem Res Toxicol. 1997 May;10(5):562-7. doi: 10.1021/tx9602067.


The lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is activated to reactive metabolites that methylate or pyridyloxobutylate DNA. Previous studies demonstrated that pyridyloxobutylated DNA interferes with the repair of O6-methylguanine (O6-mG) by O6-alkylguanine-DNA alkyltransferase (AGT). The AGT reactivity of pyridyloxobutylated DNA was attributed to (pyridyloxobutyl)guanine adducts. One potential AGT substrate adduct, 2'-deoxy-O6-[4-oxo-4-(3-pyridyl)butyl]guanosine (O6-pobdG), was prepared. This adduct was stable at pH 7.0 for greater 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), O6-pobdG was depurinated to yield O6-[4-oxo-4-(3-pyridyl)butyl]guanine (O6-pobG). O6-pobdG was hydrolyzed to 4-hydroxy-1-(3-pyridyl)-1-butanone and guanine under strong acid hydrolysis conditions (0.8 N HCl, 80 degrees C). O6-pobG was detected in 0.1 N HCl hydrolysates of DNA alkylated with the model pyridyloxobutylating agent 4-(acetoxymethylnitrosamino)-1-(3-[5-3H]pyridyl)-1-butanone ([5-3H]NNKOAc). When [5-3H]NNKOAc-treated DNA was incubated with either rat liver or recombinant human AGT, O6-pobG was removed, presumably a result of transfer of the pyridyloxobutyl group from the O6-position of guanine to AGT's active site.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • DNA / drug effects*
  • DNA Adducts / analysis*
  • Guanine / analogs & derivatives*
  • Guanine / analysis
  • Humans
  • Liver / enzymology
  • Methyltransferases / metabolism*
  • Nitrosamines / toxicity*
  • O(6)-Methylguanine-DNA Methyltransferase
  • Pyridines / toxicity*
  • Rats
  • Substrate Specificity


  • DNA Adducts
  • Nitrosamines
  • O(6)-benzyl-8-oxoguanine
  • Pyridines
  • 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone
  • Guanine
  • DNA
  • Methyltransferases
  • O(6)-Methylguanine-DNA Methyltransferase