Synthesis, Characterization, and Quantitation of a 4-Aminobiphenyl-DNA Adduct Standard

(32)P-Postlabeling is a powerful technique for the detection of DNA adducts; however, quantitation of DNA adducts by this method can result in errors due to differences in hydrolysis and labeling efficiencies between adducted and normal nucleotides. We have synthesized a DNA sample modified with 4-aminobiphenyl to serve as a quantitation standard for (32)Ppostlabeling and other DNA adduct detection methodologies. [2,2ʹ-3H]-N-Hydroxy-4-aminobiphenyl was reacted with calf thymus DNA at pH 5 to give 62 ± 0.8 adducts/10^8 nucleotides (mean ± SD) on the basis of 3H content. HPLC analyses following enzymatic hydrolysis to nucleosides indicated one major adduct, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-4ABP). The adduct identity was confirmed by HPLC/electrospray ionization mass spectrometry, which indicated a modification level of 19 ± 1.7 dG-C8-4-ABP/10^8 nucleotides. 32P-Postlabeling analysis gave a value of 0.84 dG-C8-4-ABP/10^8 nucleotides, while a dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA) indicated levels of 82 ± 26 and 63 ± 20 dG-C8-4ABP/10^8 nucleotides after enzymatic hydrolysis to nucleotides and nucleosides, respectively. The utility of the DNA adduct standard was determined by assessing the level of dG-C8-4ABP in liver DNA from mice treated with [2,2ʹ-3H]-4-aminobiphenyl. (32)P-Postlabeling analyses, based upon measuring the extent of the (32)P incorporation, underestimated the levels of dGC8-4-ABP, while DELFIA, using a G-C8-4-ABP quantitation standard, overestimated the adduct levels. The adduct levels determined by HPLC/electrospray ionization mass spectrometry best reflected those obtained from 3H incorporation. When the (32)P-postlabeling analyses and the DELFIA were conducted using the DNA modified in vitro with dG-C8-4-ABP as a quantitation standard, accurate estimations of the extent of in vivo formation of dG-C8-4-ABP were obtained.