Synergistic Effects Of Everolimus And Paclitaxel On Cell Proliferation And Apoptosis In Drug-resistant Human Breast Cancer Cells

Objective Resistance to chemotherapeutics agents has become a problem leading to failure of chemotherapy for breast cancer. This study aimed to investigate the effects of combination therapy with paclitaxel and the m TOR inhibitor, everolimus, in a multidrug-resistant cell line of MCF-7/ADR.Methods MCF-7/ADR cells were cultured in RPMI1640 containing 10% FBS, 1000ng/ml ADR.Then we treated the cells with paclitaxel or everolimus alone or combined. 1, MTT method were used to detect IC50 of the paclitaxel and everolimus, and the combination effect according to the IC50 result; 2, Flow cytometry were used to detect the cell growth, cell cycle, apoptosis; 3, Western blot assay were used to detect expression of PI3K、m TOR、4EBP1、p-p I3K、p-AKT、p-m TOR and p-4EBP1.Results1. MTT assay showed that paclitaxel and everolimus inhibited cell proliferation in a dose-dependent manner with IC50 of 9.59 μg/ml and 32.582μg/m L. The combination of paclitaxel and everolimus showed greater anti-proliferative effects than that of paclitaxel or everolimus alone with a combination index of 0.9.2. The cells treated with paclitaxel and everolimus alone or combined tuned to apoptosis. Paclitaxel was used in combination with everolimus, the cells turned to apoptosis significantly, compared with the other group(P < 0.05). Combination treatment of paclitaxel and everolimus has synergistic effect in inducing apoptosis when compared to the treatment with paclitaxel alone.3. Western blot analysis showed that treatment with paclitaxel and everolimus resulted in decreased expression of PI3 K, m TOR, 4EBP1 and phosphorylated-PI3 K, p-AKT,p-m TOR, and p-4EBP1 forms. After treated with paclitaxel in combination with everolimus, changes of these protein was more significant, compared with the other group(P<0.05).Conclusion1.These results suggest that everolimus enhances the effect of paclitaxel in MCF-7/ADR cell line by inducing of apoptosis and inhibiting of cell proliferation.2.The ability of everolimus to restore sensitivity to paclitaxel is associated with downregulation of m TOR signaling pathway, such as m TOR, p-m TOR and its downstream substrate, 4EBP1.