O6-pyridyloxobutylguanine adducts contribute to the mutagenic properties of pyridyloxobutylating agents

Renée S. Mijal, Natalia A. Loktionova, Choua C. Vu, Anthony E. Pegg, Lisa A. Peterson

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


The tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK) and N′-nitrosonornicotine (NNN) are potent carcinogens in animal models and likely human carcinogens. Both NNK and NNN can be activated to a pyridyloxobutylating agent. This alkylating agent contributes to the carcinogenic effects of NNK and NNN via the formation of miscoding DNA adducts. One of these adducts, O6-[4-oxo-4-(3-pyridyl)butyl]guanine (O 6-pobG) has been characterized as a mutagenic adduct which is a substrate for the repair protein O6-alkylguanine-DNA alkyltransferase (AGT). Repair of O6-alkylguanine adducts by AGT protects cells from the mutagenic and carcinogenic effects of alkylating agents and is likely to play a similar role in shielding cells from the adverse effects of pyridyloxobutylating agents. Therefore, we examined the mutagenicity of the model pyridyloxobutylating agent, 4-(acetoxymethyl-nitrosamino)-1-(3-pyridyl)-1- butanone (NNKOAc), in Salmonella typhimurium YG7108 expressing hAGT. Expression of hAGT protected cells from NNKOAc-induced mutagenicity. Interestingly, hAGT did not shield cells from the toxicity of this agent. To confirm that the repair of O6-pobG was increased in the bacteria expressing hAGT, we measured levels of this adduct in NNKOAc-treated cultures. The levels of O 6-pobG were lower in DNA from bacteria expressing hAGT. This work establishes an important role for O6-pobG in mediating the mutagenic, and possibly carcinogenic, effects of pyridyloxobutylating compounds.

Original languageEnglish (US)
Pages (from-to)1619-1625
Number of pages7
JournalChemical research in toxicology
Issue number10
StatePublished - Oct 2005

All Science Journal Classification (ASJC) codes

  • Toxicology


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