QUANTITATIVE DEMONSTRATION OF SPONTANEOUS METASTASIS BY MCF-7 HUMAN BREAST-CANCER CELLS COTRANSFECTED WITH FIBROBLAST GROWTH FACTOR-IV AND LACZ

We recently established transfectants of MCF-7 human breast cancer cel ls with fibroblast growth factor 4 (fgf-4) that showed rapid growth an d spontaneous metastasis in ovariectomized and tamoxifen-treated nude mice. To establish a spontaneous metastatic model of human breast canc er cells in nude mice with a sensitive marker for detection of microme tastasis, the transfection of fgf-4 was combined with transfection of the bacterial lacZ gene encoding beta-galactosidase. MKL-4 cells, a la cZ transfectant of an fgf-4-transfected cell line, showed the same lev el of fgf-4 expression as parental cells and expressed a high level of beta-galactosidase activity. When MKL-4 cells were injected s.c. into female nude mice, rapidly growing tumors developed. Whole organ stain ing for beta-galactosidase activity was able to detect even small numb ers of metastatic tumor cells. Micrometastases in lymph nodes, lung, a nd brain were detected 3 weeks after the tumor cell injections, the fi rst time point tested. Within 12 weeks, metastases were observed in ly mph nodes, lung, brain, kidney, perirenal fatty tissues, liver, spleen , retroperitoneum, heart, and gallbladder. The frequency of metastasis and number of foci were correlated with the volume of the primary tum ors. The distribution of metastatic sites was similar to that in breas t cancer patients. MKL-4 cells may be a useful model for studying the malignant progression of hormone-dependent breast cancer, antimetastat ic drugs, or early events in metastasis.