Figure 4

Combination treatment with hormone drugs and taxanes. A: Effect of combination treatment with hormone drugs and taxanes using a constant ratio design. The combination effect was evaluated using the Combination Index (C.I). Combination treatment with fulvestrant and taxanes showed a synergistic effect. Combination treatment with tamoxifen and taxanes had an antagonistic effect at low doses, but this effect became additive in both cell lines as the tamoxifen dose increased. (Data for MCF-7 cells are shown.) C.I, Combination Index; Fa, fraction affected. B: Effect of combination treatment with hormone drugs and taxanes using a non-constant ratio design. Cells were cultivated with 1 μM paclitaxel alone, with tamoxifen at various concentrations, with fulvestrant alone at various concentrations, and with combinations of these agents. The combination effect was evaluated using the Combination Index (C.I). In combination treatment with tamoxifen and paclitaxel, an antagonistic effect was observed at low concentrations, while an additive effect was found at high concentrations. The strongest antagonistic effect was observed at 500 nM. Combinations of fulvestrant and taxanes gave a synergistic effect. (Data are shown for MCF-7 cells with paclitaxel.) Pacli, paclitaxel; Tam, tamoxifen; Ful, fulvestrant; C.I, Combination Index. C: Evaluation of combination treatment by flow cytometry. Cells were cultivated with 50 nM paclitaxel alone, 100 nM tamoxifen alone, 75 nM fulvestrant alone, or with combinations of these agents. Combination treatment with fulvestrant and paclitaxel increased the percentage of cells in G2/M phase, compared with paclitaxel alone or combination treatment with paclitaxel and tamoxifen. (Data are shown for MCF-7 cells with paclitaxel.) D: Evaluation of combination treatment using immunofluorescence. Cells were cultivated with 50 nM paclitaxel alone, 100 nM tamoxifen alone, 75 nM fulvestrant alone, or combinations of these agents. An increase in apoptotic cells and repression of cell proliferation occurred in the combination treatment with fulvestrant and paclitaxel, compared with paclitaxel alone. These changes did not occur in combination treatment with tamoxifen. Apoptotic cells occurred in 11/100 cells with paclitaxel treatment alone; in 12/100 cells in combination treatment using tamoxifen; and in 25/100 cells in combination treatment using fulvestrant. (Arrows indicate apoptotic MCF-7 cells.)