The Mechanism Of Apoptosis Induced By Paclitaxel Combined With TRAIL In MCF-7 Breast Cancer Cell Lines

Objective:To determine the interaction between Paclitaxel and TRAIL,(tumor necrosis factor-related apoptosis inducing ligand,TRAIL)in MCF-7 breast cancer cell line and investigate the possible mechanism.Methods:The inhibitory rates of Paclitaxel and TRAIL alone at different concentrations on MCF-7 cells were examined by MTT assay.The inhibitory rates of different combinations of Paclitaxel and TRAIL on MCF-7 cells were examined by MTT assay.MCF-7 cells of control group,TRAIL group,Paclitaxel group and the combination group were stained by Annexin V-FITC/PI and the apoptosis rates were detected by flow cytometry.MCF-7 cells of control group,TRAIL group,Paclitaxel group and the combination group were stained by PI and the cell cycles distribution were detected by flow cytometry.At mRNA levels,the DR4,DR5 of MCF-7 cells treated by Paclitaxel were semi-qualified by RT-PCR.Results:MTT assay showed that MCF-7 cells were sensitive to Paclitaxel in a dose-dependent manner,the IC50 of Paclitaxel was 4.85μM.Meanwhile the MCF-7 cells were less sensitive to TRAIL.When TRAIL＜0.5μM,the differences were not statistically significant between experimental groups and control group(P＞0.05),but when TRAIL≥0.5μM,the differences were statistically significant between experimental groups and control group(P＜0.05),and the differences were not statistically significant within experimental groups of different concentrations (P＞0.05).Paclitaxel 0.5μM and TRAIL 0.5μM were selected as the suitable combination concentrations.MTT assay also showed different combination schemes had different inhibitory effects.There was not synergistic effect in Scheme 1(MCF-7 cells were treated by Paclitaxel and TRAIL simultaneously)and Scheme 2(MCF-7 cells were treated with inhibitory effects.There was not synergistic effect in Scheme 1(MCF-7 cells were treated by Paclitaxel and TRAIL simultaneously)and Scheme 2(MCF-7 cells were treated with TRAIL firstly and successively treated with Paclitaxel),but the synergistic effect was seen in Scheme 3(MCF-7 cells treated with Paclitaxel firstly and successively treated with TRAIL).3.By Annexin V-FITC/PI assay,the apoptosis rates of control group,Paclitaxel group,TRAIL group and the combination group(cells were treated with Paclitaxel firstly and successively treated with TRAIL)were(7.56±2.23)%,(22.6±2.44)%, (12.36±0.47)%and(61.56±5.52)%respectively.4.PI assay confirmed the differences of the cell cycle distribution were not statistically significant between TRAIL group and control group(P＞0.05);the differences were not statistically significant between Paclitaxel group and the combination group(P＞0.05).5.DR4,DR5 were detected by RT-PCR at mRNA levels,DR5 was up-regulated by Paclitaxel,but DR4 was not changed significantly.Conclusion:The MCF-7 breast cancer cell line was sensitive to Paclitaxel and showed resistance to TRAIL at a degree.A synergism had been seen when MCF-7 cells were treated with Paclitaxel firstly and successively treated with TRAIL.TRAIL didn't affect the cell cycle distribution or the cell cycle blockage of MCF-7 cells induced by Paclitaxel.The synergistic mechanism may be related to the up-regulation of DR5 induced by Paclitaxel.