An Unusual DNA Adduct Derived from the Powerfully Mutagenic Environmental Contaminant 3-Nitrobenzanthrone

Abstract

The covalent binding of an N-hydroxy metabolite of the powerfully mutagenic 3-nitrobenzanthrone (NBA) to 2'-deoxyguanosine (dG) and calf thymus DNA has been investigated in vitro. The major adduct obtained from the reaction of the N-acetoxy-N-acetyl derivative (N-Aco-N-Ac-ABA) of 3-aminobenzanthrone (ABA) and dG was identified as N-acetyl-3-amino-2-(2'-deoxyguanosin-8-yl)benzanthrone (dG-N-Ac-ABA) by 1H NMR and mass spectroscopies as well as by the reaction of N-Aco-N-Ac-ABA with the double-stranded calf thymus DNA. The coupling with the dG moiety occurred exclusively at C-2 of benzanthrone (BA), suggesting a significant contribution of a resonance-stabilized arenium ion intermediate derived from BA to the production of this new type of adduct. The preferred conformation of the adduct has been shown to be syn by 1H and 13C NMR.

Identification of three major DNA adducts formed by the carcinogenic air pollutant 3‐nitrobenzanthrone in rat lung at the C8 and N2 position of guanine and at the N6 position of adenine

“…Although a variety of unusual dA and dG adducts were characterised previously from reaction with N-acetoxy-N-acetyl-3-aminobenzanthrone (N-Aco-N-Ac-ABA) as the reactive metabolite, these adducts were different to those found in vivo, 22,26,35 indicating that DNA adducts derived from N-Aco-N-Ac-ABA and activation pathways reported earlier based on in-vitro synthesis might not entirely represent the situation in vivo. 22,35 Two of these adducts have been characterised as Nacetyl-3-amino-2-(2 0 -deoxyguanosin-8-yl)benzanthrone (dG-C8-C2-N-Ac-ABA) and an unusual 3-Ac-ABA adduct of dA, which involves a double linkage between adenine and benzanthrone (N1-C1, N 6 -C11b), creating a five-membered imidazo-type ring system. 35 Although treatment of 3 0 -phosphates of both these novel adducts with alkali generated two authentic nonacetylated standards for 32 P-postlabeling, these were also shown to differ from those formed in vivo.…”

“…29 N-OH-ABA was prepared as reported. 22,32 The authenticity of 3-NBA and 3-ABA was confirmed by UV, liquid chromatography-mass spectrometry (LC-MS), and high field proton nuclear magnetic resonance (NMR) spectroscopy. The authenticity of N-OH-ABA and N-Aco-ABA was confirmed by UV and LC-MS analyses.…”

“…The synthesis of dG-C8-C2-ABA and dG-C8-N-ABA was reported previously. 22,34 Details concerning the structural identification of dG-N 2 -ABA will be published elsewhere (Takamura-Enya et al, manuscript in preparation). Yields of dG3 0 p-N 2 -ABA, dG3 0 p-C8-C2-ABA and dG3 0 p-C8-N-ABA based on the initial amount of N-OH-ABA were about 0.6%, 1.1% and 5.5%, respectively.…”

“…9 Its genotoxicity has been further documented by the detection of specific DNA adducts formed in various chemical and enzymatic in-vitro assays, in cells and in vivo in rodents treated with 3-NBA. [22][23][24][25][26][27][28][29][30][31][32][33][34][35] The main metabolite of 3-NBA, 3-aminobenzanthrone (3-ABA, Fig. 1), has been found in urine samples of underground salt mine workers occupationally exposed to diesel emissions, 10 and this metabolite forms the same DNA adducts as those formed by its nitroaromatic counterpart 3-NBA.…”

Mutagenicity Analysis of C8-Phenoxy-Guanine in the NarI Recognition DNA Sequence

“…Due to the ambident electrophilicity of phenoxyl radicals (C vs O) both carbonand oxygen-linked C8-dG adducts have been observed (Figure 1). The phenolic C-linked C8-dG adducts belong to a larger class of C8-aryldG lesions produced by a number of chemical mutagens that include polycyclic aromatic hydrocarbons (PAHs) [15], estrogens [16], nitroaromatics [17] and arylhydrazines [18]. The phenolic O-linked C8-dG adducts are unique to phenol precursors, but are expected to be structurally similar to the corresponding nitrogen-linked C8-dG adducts produced by aromatic amine carcinogens [19][20][21].…”