Characterization of DNA adducts formed in vitro by reaction of N-hydroxy-2-amino-3-methylimidazo[4,5-f]quinoline and N-hydroxy-2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline at the C-8 and N2 atoms of guanine

Abstract

The covalent binding of the carcinogenic N-hydroxy metabolites of 2-amino-3-methylimidazo-[4,5-f]quinoline (IQ) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) to deoxynucleosides and DNA was investigated in vitro. Two major adducts were formed by the reaction of the N-acetoxy derivatives of IQ and MeIQx with deoxyguanosine (dG); however, no adducts were formed with deoxycytidine, deoxyadenosine, or thymidine. From proton NMR and mass spectroscopic characterization the adducts were identified as 5-(deoxyguanosin-N2-yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-N2-IQ),N-(deoxyguanosin-8-yl)-2-amino-3-methylimidazo-[4,5-f]q uinoline (dG-C8-IQ), 5-(deoxyguanosin-N2-yl)-2-amino-3,8-dimethylimidazo[4,5-f]qu inoxaline (dG-N2-MeIQx), and N-(deoxyguanosin-8-yl)-2-amino-3,8-dimethylimidazo[4,5-f]qui noxaline (dG-C8-MeIQx). The level of dG-C8 adducts was approximately 8-10 times greater than the amount of dG-N2 adducts formed from the reaction of dG with the N-acetoxy derivatives of IQ and MeIQx. The C-8-substituted dG adduct was also the major adduct formed from reactions of DNA with N-acetoxy-IQ and N-acetoxy-MeIQx. Approximately 60-80% of the bound carcinogens were recovered from DNA as dG-C8 adducts upon enzymatic digestion. The dG-N2 adducts also were detected and accounted for approximately 4% of the bound IQ and 10% of the bound MeIQx. These results suggest that the relative contributions of the nitrenium and carbenium ion resonance forms as well as DNA macromolecular structure are major determinants for DNA adduct substitution sites. Investigations on adduct conformation of 1H NMR spectroscopy revealed that the anti form is preferred for the dG-N2 adducts of IQ and MeIQx, while the syn form is preferred for the dG-C8 adducts. The possible role of these adducts in the initiation of carcinogenesis is discussed.

New insights in the formation of deoxynucleoside adducts with the heterocyclic aromatic amines PhIP and IQ by means of ion trap MSn and accurate mass measurement of fragment ions

“…The chemical shifts observed for IQ protons are reported in Figure 5. These data are in good agreement with published results [14], and confirm that the primary amine function of IQ is bonded to the guanine moiety.…”

“…Deoxynucleoside adducts of IQ were prepared according to a previously described protocol [14]. N-N N Hydroxy-IQ (100 g) was directly reacted with 2-fold molar excess of deoxynucleosides dissolved in 2.5 mL of NaH 2 PO 4 /EDTA (100 mM/100 M, pH 7) in the pre -sence of acetic anhydride (1.3 L).…”

“…Powerful analytical methods mainly based on capillary high-performance liquid chromatography (HPLC) or capillary electrophoresis coupled to mass spectrometry have been developed for the characterization of these structurally known adducts formed in vivo. However, although analytical systems have been dramatically improved, no work has revisited the adduct formation between HAAs and deoxynucleosides in the past decade [14]. Therefore, a systematic investigation on HAA-deoxynucleoside adduct formation was performed in this study, by assessing the reactivity of the four deoxynucleosides (dG, dA, dC, and dT) with PhIP and IQ, whose structures are reported in Figure 1.…”

Carcinogen–DNA adducts in human breast epithelial cells

“…If there is excessive exposure, increased activation, or decreased detoxification, some of the reactive metabolites may bind to DNA, forming DNA adducts, and lead to the initiation of the carcinogenic cascade [Kadlubar, 1987[Kadlubar, , 1994. The major sites of DNA damage are C8 and N 2 atoms of guanine [Kadlubar et al, 1980;Turesky et al, 1992] and mutagenic consequences are mainly transversions and frameshift mutations [Schut and Snyderwine, 1999].…”

Versatility of Y-family Sulfolobus solfataricus DNA Polymerase Dpo4 in Translesion Synthesis Past Bulky N2-Alkylguanine Adducts

“…The N2 atom of guanine is susceptible to modification by various potential carcinogens, including formaldehyde (4), acetaldehyde (5)(6)(7)(8), styrene oxide (9), N-nitrosopyrrolidine (10), oxidation products of heterocyclic aromatic amines (e.g. N-hydroxy-2-amino-3-methylimidazo [4,5-f]quinoline and N-hydroxy-2-amino -3,8-dimethylimidazo [4,5-f]quinoxaline (11)), and the oxidation products of various polycyclic aromatic hydrocarbons (e.g. benzo [a]pyrene (BPDE) 3 ) (12,13).…”