Inhibition of Cell Death in Human Mammary Epithelial Cells by the Cooked Meat-Derived Carcinogen 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

Abstract

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mammary gland carcinogen present in the human diet in cooked meat. To examine if PhIP and its reactive metabolite N-hydroxy-PhIP inhibit apoptosis in human mammary epithelial MCF-10A cells, confluent cultures deprived of serum and growth factors were incubated for 24 h with either compound. The percentages of dead cells (mean ± SEM, n = 3) as measured by trypan blue exclusion were 5.7 ± 0.6, 3.4 ± 0.3, 2.7 ± 0.3, and 0.2 ± 0.003%, in control, 1 μM N-hydroxy-PhIP-, 5 μM N-hydroxy-PhIP-, and 100 μM PhIP-treated dishes, respectively. The expression of Bcl-2 and Bcl-xL as quantitated by Western blotting was 1.2- to 1.9-fold higher in the treated groups. PhIP–DNA adducts induced by N-hydroxy-PhIP in MCF-10A cells measured by the 32P-postlabeling assay were low (<1 × 107, relative adduct labeling). No adducts were detected after incubation with PhIP. Western blot analysis indicated that PhIP increased ERK2 phosphorylation concomitant with Bcl-2. The results suggest that the inhibition of cell death in mammary epithelial cells by PhIP occurs independently of PhIP–DNA adducts and may involve enhanced signaling through the MAP kinase pathways.