Transformation of human breast epithelial cells by chemical carcinogens

The present study was carried out to determine whether human breast epithelial cells (HBEC) are transformed by chemicals that have been proven to be carcinogenic in other model systems. A spontaneously immortalized human breast epithelial cell line, MCF-10F, was treated with dimethylbenz[a]anthracene (DMBA), benzo[a]pyrene (B[a]P), N-methyl-N-nitrosoguanidine (MNNG) or N-methyl-N-nitrosourea (NMU) for 24 h. MCF-7 and T24 malignant cell lines were used as positive controls. All the carcinogens induced alterations in both cell morphology and pattern of growth, increased growth rate and anchorage-independent growth in agar-methocel, which became evident by the 8th to 10th passages post-treatment, at approximately 157 days in culture. Colonies formed in agar-methocel were isolated and expanded. The following clones were successfully grown: D1, D2 and D3, from DMBA, M4 from MNNG, and BP1, BP2, BP5, BP6, BP7, and BP10 from B[a]P treated cells. From clones BP1 and BP2, selected cell populations were isolated and the derived cell lines or clones were named BP1-E and BP2-B respectively; the D3-1 cell line was derived from clone D3. BP1 and BP1-E clones showed increased anchorage-independent growth, chemotaxis and invasiveness. Clone D3-1 showed increased chemotactic and invasive capabilities, but to a lesser degree than BP1-E. The tumorigenic potential of the cells was tested by inoculation into SCID mice. MCF-7, T24 and BP1-E cells formed tumors in 100% of the SCID mice at 28, 10 and 101 days of inoculation respectively. None of the other clones formed tumors. It was concluded that both polycyclic hydrocarbons and aromatic amines induced in the immortal cells MCF-10F changes indicative of neoplastic transformation. Our data show that the phenotypes associated with neoplastic transformation appear in a progressive fashion, and that the emergence of clones is associated with the expression of higher proliferative rate, anchorage independence, chemotactic and chemoinvasive abilities and, in certain cases, tumorigenicity.