Clonal variation of MCF-7 breast cancer cells in vitro and in athymic nude mice.

Abstract The MCF-7 human breast cancer cell line and four derived variant sublines (R27, R3, R3–12, and R3–98), which were all estrogen receptor positive, as well as the receptor-deficient line, MDA-MB-231, were compared both in vitro and as heterotransplants into athymic nude mice. The cell lines and heterotransplanted tumors were evaluated in terms of growth, receptor status, morphology by light and electron microscopy, karyotype, and allozyme phenotype analyses. The R3 and R3–12 variant lines exhibited markedly retarded growth rates in vitro as compared with those of the MCF-7 parent line. The R3-12 line, which had the slowest growth rate in vitro as compared to those of the other cell lines, failed to produce tumors in nude mice after many attempts using various concentrations of tumor cell inocula. The MCF-7 and derived lines would not grow in oophorectomized animals without 17β-estradiol replacement, with one rare exception, while the MDA-MB-231 receptor-deficient line was able to grow in oophorectomized mice with and without 17β-estradiol replacement. Compared to the parent MCF-7 and R27 line in vivo and in vitro , the R3 line and its subclones had reduced progesterone receptor markedly. By light microscopy, all of the cell lines in vivo and in vitro could be identified as adenocarcinoma. Using electron microscopy, the MCF and variant lines showed better tissue organization and more squamous features in vivo than in vitro where glandular features were more prominent. The R27 line in vivo and in vitro showed the most cellular polarity and differentiation as compared to the MCF or R3 lines (R3, R3–12, and R3–98), while the R3 lines were the least differentiated of all the lines. The MDA-MB-231 line in vivo and in vitro had the most pronounced glandular features of all the lines and was not affected by changes in media additions of fetal calf serum, 17β-estradiol, or charcoal-treated calf serum as were the MCF-7- and MCF-7-derived lines. All the tumors in vivo and in vitro showed a human karyotype, and the MCF-7 and each of the derived lines showed both common and unique chromosome markers. The original cell line (MCF-7), the derived sublines (R27 and R3), and tumors derived in nude mice from these lines were typed for species identity using standard isozyme procedures and were found to be human. The allozyme phenotype at seven polymorphic human loci (allozyme genetic signature) demonstrated that the MCF-7 line and its derivatives were derived from the same individual and were distinct from the signatures of HeLa and a variety of other human breast cancer lines. This multifaceted study, using both in vivo and in vitro systems, may provide a model for better understanding the nature of tumor heterogeneity and its implications in therapeutic designs.