Isolation and characterization of a spontaneously transformed malignant mouse mammary epithelial cell line in culture

A method is described that permits the selection of spontaneously transformed mammary epithelial colonies from an untransformed mouse mammary epithelial cell line, NMuMG, and utilizes a long-term anchorage-independent growth of the transformants on soft agarose. These transformed cells (NMuMG-ST) are shown to be distinguishable from the untransformed cells by morphology, growth characteristics, induced carcinomas when transplanted into nude mice and ability to metastasize. This transformed phenotype displayed focal, multilayer growth and higher saturation density in comparison with the untransformed phenotype. Transplanted tumors as well as metastatic lung tumors in nude mice were adenocarcinomas morphologically similar to typical mammary tumors in humans. This selection procedure of mutant mammary cells from an immortalized cell line derived from normal mammary glands could be very useful to identify the genomic biomarkers in the growth regulation and malignant progression of breast cancer.