METABOLIC-ACTIVATION OF N-HYDROXY-4-ACETYLAMINOBIPHENYL BY CULTURED HUMAN BREAST EPITHELIAL-CELL LINE MCF 10A

Metabolism and nucleic acid binding of the mammary gland carcinogen N- hydroxy-4-acetylaminobiphenyl (N-OH-AABP) was investigated using the h uman mammary epithelial cell line MCF 10A. Chromatographic analysis of the ethyl acetate extract of the media from cultured MCF 10A after 24 h exposure to N-OH-AABP revealed the formation of two metabolites, 4- aminobiphenyl (ABP) and 4-acetylaminobiphenyl (AABP). Iincubation of [ H-3]N-OH-AABP with calf thymus DNA in the presence of the cytosols or microsomes revealed a binding of 0.21 and 2.36 nmol/mg DNA/mg protein respectively. In contrast to cytosol-mediated binding, the microsome-m ediated binding of [H-3]N-OH-AABP to DNA was inhibited by paraoxon. Fu rthermore, exogenous addition of non-labelled N-hydroxy-4-aminobipheny l (N-OH-ABP) to the incubation mixture blocked the binding of [H-3]N-O H-AABP to DNA, suggesting that the metabolic activation process involv es inter-molecular transacetylation. Cytosols from MCF 10A also cataly zed acetyl coenzyme A (AcCoA)dependent binding of [H-3]N-OH-ABP to DNA ; the amount of binding was 0.51 nmol/mg DNA/mg protein. HPLC of the D NA hydrolysate obtained after incubation of [H-3]N-OH-AABP and [H-3]N- OH-ABP with the MCF 10A microsomes and cytosols showed N-(deoxyguanosi n-8-yl) 4-aminobiphenyl (dG-ABP) as the primary adduct, based on the m obility of the radioactive peak in comparison with the synthetic stand ard. P-32-postlabelling of adducted DNA obtained on incubation,vith N- OH-ABP or N-OH-AABP showed similar adduct profiles, with the major add uct corresponding with the bisphospho derivative of dG-ABP and a minor adduct corresponding with N- (deoxyadenosin-8-yl)-4-aminobiphenyl (dA -ABP). Additionally, the cellular DNA isolated from MCF 10A following exposure to N-OH-AABP also revealed a major spot corresponding,vith th e dG-ABP derivative. These results suggest that the mammary gland carc inogen N-OB-AABP is activated to reactive electrophilic species in the target human mammary tissues by acetyl transferase(s) enzyme systems.