Determination of the enzymes responsible for activation of the heterocyclic amine 2-amino-3-methylimidazo [4,5-f]quinoline in the human breast

The heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is a po tent mutagen and is a mammary carcinogen in rodents. In man, hepatic activa tion is carried out by cytochrome P450 (CYP) 1A2 and the ultimate DNA-react ive species is thought to be a nitrenium ion formed via an acetoxy ester of an exocyclic amino group. Because most human breast tumours are ductal in origin, we investigated the ability of cell types present in the mammary gl and (breast epithelial cells and neutrophils present in milk) to activate I g to DNA-binding species using P-32-postlabelling, Phorbol myristate acetat e-stimulated neutrophils produced a similar pattern of IQ-DNA adducts to th at produced by human mammary epithelial cells, Adduct formation in stimulat ed neutrophils was inhibited 80% by the myeloperoxidase inhibitor sodium az ide (1 mM) but was not affected by proadifen (100 mu M), indomethacin (100 mu M), or eicosatetraynoic acid (100 mu M), inhibitors of cytochrome P450, prostaglandin synthetase, and lipoxygenase, respectively. Similar experimen ts in human mammary epithelial cells showed no azide inhibition of IQ-DNA a dduct formation. Analysis of gene expression by reverse transcription-polym erase chain reaction showed that CYP1A1 and CYP1B1, but not CYP1A2, were ex pressed at detectable levels in untreated mammary epithelial cells, whereas in neutrophils cytochrome P450 expression was confined to low levels of CY P1A1, In cultured epithelial cells, IQ-DNA adduct formation and CYP1A1, but not CYP1B1 expression were induced threefold by benz[a]anthracene treatmen t; IQ-DNA adduct. formation was inhibited by a-naphthoflavone. Our results indicate possible mechanisms for the metabolic activation of dietary carcin ogens in the human breast. Pharmacogenetics 8:519-528. (C) 1998 Lippincott Williams & Wilkins.