ACTIVATION OF PROMUTAGENS IN A HUMAN BRONCHIAL EPITHELIAL-CELL LINE STABLY EXPRESSING HUMAN CYTOCHROME-P450 1A2

Normal human bronchial epithelial (NHBE) cells are the putative progen itor cells of all types of lung cancer. NHBE cells immortalized by SV4 0 T-antigen retain many characteristics of the primary cells and are a useful model for investigating the role of oncogenes, tumor suppresso r genes, and certain chemical carcinogens in the molecular pathogenesi s of lung cancer. In this study, SV40 T-antigen-positive cells (BEAS-2 B) were characterized for their metabolic functions and were shown to continue to express epoxide hydrolase, glutathione S-transferase pi, g lutathione peroxidase, and catalase. To increase their metabolic activ ity towards human procarcinogens, human cytochrome P450 1A2 (CYP1A2) w as stably expressed by introducing CYP1A2 cDNA into BEAS-2B cells eith er by infection with a high-titer recombinant retrovirus (pXT-1A2) or by transfection with a CYP1A2 expression vector (pCMV1A2), which produ ced the cell lines B-1A2 and B-CMV1A2, respectively. Cell lines establ ished with either expression system expressed enzymatically active CYP 1A2 protein and were 50- to 400-fold more sensitive to the cytotoxic e ffect of the carcinogen aflatoxin B-1 (AFB(1)) than the corresponding control cell lines. The cytotoxic effects of AFB(1) were paralleled by increased metabolism of AFB(1) and enhanced formation of the AFB(1)-N -7 guanine adduct in B-CMV1A2 cells. Cytotoxicity and adduct formation correlated with a significantly higher protein expression of CYP1A2 b y the cytomegalovirus promoter-driven plasmid. Since this human epithe lial cell line is the precursor cell type of lung cancer, has normal p hase II enzymes, and exhibits highly reproducible expression of phase I enzymes, this in vitro model should aid in the evaluation of putativ e human carcinogens and anticarcinogens. (C) 1994 Wiley-Liss, Inc.