FGFB binding sites in cancers of the human breast]

We investigated binding characteristics of bFGF in membranes prepared from 4 human breast cancer cell lines (MCF-7, T-47D, BT-20 and MDA-MB-231) and 38 primary breast cancer biopsies. Results of competitive binding experiments were analysed using the "Ligand" program to determine binding site concentrations and affinities. bFGF mitogenic activity was also measured by 3H]-thymidine incorporation into DNA of breast cancer cell lines. The presence of high-affinity binding sites was demonstrated in each cell type (Kd: 0.5 nM). The presence of these high-affinity binding sites was confirmed by saturation experiments. A second class of low-affinity binding sites was detected in the 2 hormono-independent cells (BT-20: Kd = 2.9 nM; MDA-MB-231: Kd = 2.7 nM). bFGF stimulated the proliferation of MCF-7, 7-47D, BT-20 and not of MDA-MB-231 cell lines. In breast cancer biopsies, binding sites were detectable in 36/38 cases; high-affinity binding sites (Kd < 1 nM) were present in 19/39 cases and low-affinity binding sites (Kd > 2 nM) were present in 29/36 cases (the 2 classes of binding sites were present in 12 biopsies). No relation between FGF binding sites and node involvement nature or grade of tumor was evidenced. Negative correlations (Spearman test) were found between total bFGF binding site concentrations and estradiol receptor concentrations (P = 0.05) or progesterone receptor concentrations (P = 0.009). The demonstrations of 1), bFGF specific binding sites in breast cancer membranes; and 2) bFGF growth stimulation of some breast cancer cell lines, indicate that this factor could be involved in the growth of most breast cancers, and could act (among other factors) directly on the growth of cancer cells.