FIBROBLAST GROWTH-FACTOR OVEREXPRESSING BREAST-CARCINOMA CELLS AS MODELS OF ANGIOGENESIS AND METASTASIS

Progression of breast cancer from an estrogen-dependent, slowly growin g tumor amenable to tamoxifen treatment to an aggressive, metastatic, estrogen-independent phenotype has been mimicked by the transfection o f MCF-7 breast carcinoma cells with fibroblast growth factors 1 or 4. FGF-transfected cells are aggressively tumorigenic in ovariectomized o r tamoxifen-treated nude mice, conditions under which the parental cel ls would not produce tumors. When detection of metastasis was enhanced by lacZ transfection, the FGF-transfected MCF-7 cells were reliably m etastatic to lymph nodes and frequently metastatic to lungs, in furthe r contrast to parental cells. An antiangiogenic drug, AGM-1470, given to mice bearing tumors produced by FGF-transfected MCF-7 cells, produc ed a decrease in tumor size. The decreased tumor size was not as marke d as that produced by treatment with pentosan polysulfate, an agent wh ich would abrogate all autocrine or paracrine effects of the transfect ed FGF. Thus, increased angiogenesis may be a component of the phenoty pic change produced by the FGF transfection, but other autocrine or pa racrine effects may also be important. Since a clonal FGF-4 and lacZ d oubly-transfected cell line, MKL-4, progressively lost expression of t he transfected lacZ gene in individual cells, we performed successive rounds of fluorescence-activated cell sorting to select high-expressin g cells. High-expressing cell populations thus obtained rapidly lost e xpression of beta-gal activity in continued culture. High beta-gal exp ressing clonal cell lines of MKL-4 cells established by either one or two rounds of low-density cloning also lost lacZ expression with conti nued culture. Southern analysis of DNA from lacZ transfected cell line s showed the transfected sequences to be present and grossly intact in both high and low expressing populations. However, Northern analysis revealed that high-expressing populations of MKL-4 cells contained the most lacZ mRNA, implying that in the unstable MKL-4 cell line, indivi dual cells are down-regulating mRNA levels of lacZ. Stable lacZ expres sion has been obtained in other FGF-transfected and parental MCF-7 cel l lines using the same expression vector. Thus, the MKL-4 cell line is down-regulating mRNA encoding the transfected gene through a mechanis m not dependent on the CMV promotor utilized in the expression vector. This evidence suggests that lacZ expression is not a benign modificat ion in certain cells.