Neoplastic transformation of rat mammary cells exposed to 7,12-dimethylbenz[alpha]anthracene or N-nitrosomethylurea in cell culture.

Primary cultures of mammary cells from virgin Lewis rats were seeded at 5 X 10(5) cells per cm2 in medium 199 supplemented with 10% fetal calf serum, insulin (5 microgram/ml), prolactin (5 microgram/ml), estradiol (5 ng/ml), progesterone (0.5 microgram/ml), and hydrocortisone (0.5 microgram/ml). On the second or third day of culture, cells were exposed to either 7,12-dimethylbenz[alpha]anthracene (0.1 microgram/ml for 24 hr) or N-nitrosomethylurea (80 microgram/ml for 2 hr). The cells were later assayed for transformation by transplanting 10(6) or 10(5) cells into gland-free mammary fat pads of 3-week-old female hosts. Untreated cells produced only normal mammary outgrowths when transplanted. Cells treated with 7,12-dimethylbenz[alpha]anthracene or N-nitrosomethylurea produced abnormal outgrowths in 11% of the transplants. These abnormal outgrowths ranged from rapidly growing adenocarcinoma to alveolar and ductal hyperplastic lesions. The results indicate that rat mammary epithelial cells can be transformed by exposure to chemical carcinogens in culture and thus represent a potential in vitro model for epithelial cell transformation.