Formation and Repair of Pyridyloxobutyl DNA Adducts and Their Relationship to Tumor Yield in A/J Mice

Abstract

The nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a known human carcinogen. It generates methyl and pyridyloxobutyl DNA adducts. The role of the methyl DNA adducts has been well-established in the tumorigenic properties of NNK. However, the role of the pyridyloxobutyl DNA adducts is unclear. Four pyridyloxobutyl DNA adducts have been characterized: 7-[4-3-(pyridyl)-4-oxobut-1-yl]guanine (7-pobG), O2-[4-3-(pyridyl)-4-oxobut-1-yl]-cytodine (O2-pobC), O2-[4-3-(pyridyl)-4-oxobut-1yl]thymidine (O2-pobdT), and O6-[4-3-(pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O6-pobdG). Mutagenic O6-pobdG is thought to contribute to the tumorigenic properties of the pyridyloxobutylation pathway. It is repaired by O6-alkylguanine-DNA alkyltransferase (AGT). To explore the role of O6-pobdG formation and repair in the tumorigenic properties of NNK, A/J mice were given single or multiple doses of the model pyridyloxobutylating agent 4-(acetoxymethyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNKOAc) in the presence or absence of the AGT depletor, O6-benzylguanine. Levels of the four pyridyloxobutyl DNA adducts were measured in the lung at 8, 48 or 96 h following treatment and compared to the lung tumorigenic activity of these treatments. AGT depletion had only a modest effect on the levels of O6-pobdG and did not increase tumor formation. Three pyridyloxobutyl DNA adducts, 7-pobG, O2-pobdT, and O6-pobdG, persisted in lung DNA at significant levels for up to 96 h post-treatment, suggesting that all three adducts may contribute to the tumorigenic properties of NNK.

Multiclass Carcinogenic DNA Adduct Quantification in Formalin-Fixed Paraffin-Embedded Tissues by Ultraperformance Liquid Chromatography–Tandem Mass Spectrometry

“…25,35,48,52 For pulmonary dG- N 2 -B[ a ]PDE, bladder dG-C8-4-ABP, hepatic O 6 -Me-dG, O 6 -POB-dG, no direct comparison can be drawn as adduct levels are not reported in the literature. We observed similar carcinogenic DNA adduct distribution among different organs within the same animals as previously reported.…”

Liquid Chromatography-Tandem Mass Spectrometry for the Quantification of Tobacco-Specific Nitrosamine-Induced DNA Adducts in Mammalian Cells

“…6 Pyridyloxobutylated DNA adducts, 7-POBG, O 2 -POBdT, and O 6 -POBdG, persisted in lung DNA of A/J mice at significant levels for up to 96 h post-treatment. 12 These DNA lesions also accumulate in normal lung tissues of lung cancer patients 15 and in lung stem cells, 22 indicating that the formation and persistence of these adducts may be important in tobacco-derived human lung cancer. Other types of pyridyloxobutylated DNA adducts were also discovered recently.…”

“…This adduct induced only GC → AT transition mutations in bacteria, whereas GC → TA transversions and more complex mutations were observed in the K-ras oncogene of NNKOAc-induced lung tumor in A/J mice. 6 There were few reports about how O 2 -POBdT perturbs DNA replication, 12,18,21 where the lesion was found to be strongly blocking to DNA replication, and direct significant frequencies of nucleotide misincorporations during replication in bacterial and human cells. 21,25 Similar findings were made for other O 2 -alkylated thymidine lesions.…”

“…31–36 There were several reports about the use of solid-phase extraction followed by LC-MS/MS analysis on a triple-quadrupole mass spectrometer to quantify different pyridyloxobutyl DNA adducts, directly or after conversion of the modified nucleosides to the respective modified nucleobases with acid hydrolysis. 12,15,18 …”

Mechanistic relationships between hepatic genotoxicity and carcinogenicity in male B6C3F1 mice treated with polycyclic aromatic hydrocarbon mixtures

“…For example, DNA adducts can cause miscoding events in critical genes (Hecht 2012). Many DNA adducts serve as biomarkers of carcinogenic PAH exposure and cancer risk (Phillips and Venitt 2012; Poirier 1997; Urban et al 2012). Significant positive linear correlations between levels of PAH-DNA adducts and cancer incidence have been reported in both epidemiological studies (Agudo et al 2012; Tang et al 2001; Veglia et al 2008) and animal experiments (Culp et al 1998).…”