Bioactivation of the cooked food mutagen N-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by estrogen sulfotransferase in cultured human mammary epithelial cells

Abstract

Cooked food mutagens from fried meat and fish have recently been suggested to contribute to the etiology of breast cancer. Thus, the most prevalent of these compounds, i.e. 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, or rather its more mutagenic N-hydroxylated metabolite (N-OH-PhIP), forms DNA adducts in mammary cells, including human mammary epithelial (HME) cells. The objective of this study was to determine the involvement of estrogen sulfotransferase (EST), the only sulfotransferase identified in HME cells, in the further bioactivation of N-OH-PhIP. These studies were done in vitro using human recombinant EST and in intact HME cells. Human recombinant EST increased the covalent binding of [3H]N-OH-PhIP to calf thymus DNA ~ 3.5-fold in the presence of the sulfotransferase co-substrate 3'-phosphoadenosine-5'-phosphosulfate at each N-OH-PhIP concentration (1, 10 and 100 μM) (n = 6, P < 0.001). In contrast, EST did not catalyze the DNA binding of two other cooked food mutagens, N-hydroxy-2-amino-3-methylimidazo[4,5-f]quinoline and N-hydroxy-2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, which are mainly hepatocarcinogens. Cultured HME cells displayed high EST activity, which could be completely inhibited by 1 μM estrone. When the cells were incubated with [3H]N-OH-PhIP, binding to native DNA occurred at 60-240 pmol/mg DNA. This binding was inhibited to 55% of control by 1 μM estrone (P < 0.01, n = 8), suggesting that EST plays a significant role in carcinogen bioactivation in human breast tissue.