Guanine−Adenine DNA Cross-Linking by 1,2,3,4-Diepoxybutane: Potential Basis for Biological Activity

1,2,3,4-Diepoxybutane (DEB) is a prominent carcinogenic metabolite of 1,3-butadiene (1,3-BD), an important industrial chemical and an environmental pollutant found in cigarette smoke
and automobile exhaust. DEB is capable of inducing a variety of genotoxic effects, including
point mutations, large deletions, and chromosomal aberrations. The mutagenicity and
carcinogenicity of DEB are thought to result from its ability to form bifunctional DNA−DNA
adducts by sequentially alkylating two nucleobases within the DNA double helix. We recently
reported that DEB-induced DNA−DNA cross-linking leads to the formation of 1,4-bis-(guan-7-yl)-2,3-butanediol (bis-N7G-BD) adducts [Park, S., and Tretyakova, N. (2004) Structural
characterization of the major DNA−DNA cross-link of 1,2,3,4-diepoxybutane. Chem. Res.
Toxicol. 17 (2), 129−136]. However, guanine−guanine cross-linking by DEB cannot explain
the development of A:T base pair mutations following exposure to DEB and 1,3-BD. In the
present work, four asymmetrical DNA−DNA cross-links involving both adenine and guanine
nucleobases were identified in double-stranded DNA treated with racemic DEB. These novel
lesions were assigned the structures of 1-(aden-1-yl)-4-(guan-7-yl)-2,3-butanediol (N1A-N7G-BD), 1-(aden-3-yl)-4-(guan-7-yl)-2,3-butanediol (N3A-N7G-BD), 1-(aden-7-yl)-4-(guan-7-yl)-2,3-butanediol (N7A-N7G-BD), and 1-(aden-N6-yl)-4-(guan-7-yl)-2,3-butanediol (N6A-N7G-BD),
based on the comparison of their MS/MS spectra, HPLC retention times, and UV spectra with
those of the corresponding authentic standards prepared independently. Although guanine−adenine lesions are ∼10 times less abundant in DEB-treated double-stranded DNA than the
corresponding bis-N7G cross-links, N1A-N7G-BD and N6A-N7G-BD are more hydrolytically
stable and, if formed in vivo, may accumulate in target tissues. HPLC-ESI-MS/MS analysis of
guanine−adenine DEB cross-links induced in synthetic DNA duplexes 5‘-(GGT)5, 5‘-(GT)7G,
and 5‘-(GAA)5 (+-strand) demonstrate that G−A cross-linking by DEB produces primarily 1,3-interstrand N1A-N7G lesions. The formation of bifunctional guanine−adenine adducts is likely
to contribute to AT base pair substitutions and deletion mutations following DEB exposure.