A critical approach to the malignant transformation of human breast epithelial cells with chemical carcinogens.

This work was undertaken with the purpose of clarifying the factors that modulate the transformation of human breast epithelial cells. For accomplishing this goal, it was necessary to establish the adequate culture conditions for maintaining primary cultures of breast tissue for their treatment with genotoxic agents. It also was determined whether primary cultures generated from these tissues maintained the basic biological properties of the host. In this work we have been able to show that the in vivo developmental stage of the gland is important in the expression of an early transformation phenotype after treatment with chemical carcinogens in vitro; furthermore, that the culture conditions, mainly the calcium concentration in the medium, are important in the selection of that specific phenotype. Four carcinogens, 7,12-dimethylbenz(a)anthracene (DMBA), benzo(a)pyrene (BP), methyl-N-nitro-nitrosoguanidine (MNNG), and N-methyl-N-nitrosourea (NMU) were used for treating primary human breast epithelial cell (HBEC) cultures. Ten out of 20 samples tested expressed survival efficiency in agar methocel. The immortalized human breast epithelial cell line MCF-10 was treated with the same chemical carcinogens, which induced point mutations in codons 12 and 61 and the expression of malignant phenotypes in treated cells. MCF-10 cells transfected with the mutated c-Ha-ras gene exhibited the same malignant phenotypes shown by carcinogen-treated cells, mainly tumorigenesis in SCID mice. It was concluded that both chemical carcinogens and mutated ras gene induce malignant transformation of immortalized HBEC, which suggests that the critical point in the transformation pathway is the immortalization of the cell.