Background and purpose:Radiotherapy and endocrine therapy are both important parts of adjuvant therapy for breast cancer, yet few studies have been conducted focusing on the interaction between radiation and endocrine therapy. Up to now, no conclusion has been drawn on the timing sequence of adjuvant radiation and endocrine therapy, which is indeed crucial in clinical practice. This study intended primarily to investigate the effect of concurrent or sequential exemestane combined with radiation on radiosensitivity of MCF-7 cells and its possible mechanism,and further to provide rationale for optimal clinical treatment modality.Methods:MCF-7 cells were arranged into three trial groups: the radiation group, exemestane sequenced with radiation group and exemestane followed radiation group. Radiosensitivity was evaluated by clonogenic assay, cell proliferation was measured by MTT assay, the ability to induce cell apoptosis was evaluated by DAPI staining assay, the changes of Bcl-2 and Bax were detected by Western blot.Results:Sensitive enhancement ratios (SER) were 1.51 and 1.37 in the exemestane sequenced with radiation group and exemestane followed radiation group, respectively. Compared with the radiation group, the percentage of cellular proliferation inhibition and apoptosis increased obviously in the exemestane sequenced with radiation group and exemestane followed radiation group. Exemestane combined with radiation made the Bax protein increase obviously and the Bcl-2 protein lowered significantly.Conclusion:Exemestane can enhance the radiosensitivity of MCF-7 cells, whose mechanism might be relevant to the promotion of cellular apoptosis. However,the treatment sequence does not affect the outcome.

Objective: To investigate the properties of radiation-induced changes of cell cycle and apoptosis in breast cancer cell lines MDA-MB-231 and MCF-7, and to further explore its relationship with radiosensitivity. Methods: The two cell lines MCF-7 and MDA-MB-231 were irradiated with 6 MV X-rays. The cell survival curves were fitted by clonogenic formation assay, then according to the radiosensitivity parameters average lethal dose (D₀), quasi-threshold dose (D_q) and survival fraction after 2 Gy irradiation (SF₂), the radiosensitivity of the two cell lines was compared. The apoptosis rate and cell cycle distribution of the two cell lines were detected by Hoechst 33342 and PI staining. Results: The survival curve of MDA-MB-231 cell line shifted to the right compared with that of MCF-7 cell line. The values of D₀, D_q and SF₂ of MDA-MB-231 cell line were higher than those of MCF-7 cell line (1.603±0.023 vs. 1.233±0.027, 1.76±0.04 vs. 1.03±0.10, 0.639 3±0.008 2 vs. 0.398 1±0.018 5, t values were -17.981, -11.745, -20.596, P values were 0.000, 0.003, 0.000). The apoptosis rate of MCF-7 cell line was significantly higher than that of MDA-MB-231 cell line at the doses of 2, 4, 8 Gy irradiated 24 h and at the 12, 48 h after 6 Gy X-irradiation (t values were 4.441, 7.299, 10.499, 6.375, 7.743, P values were 0.011, 0.002, 0.000, 0.003, 0.001). Compared with the non-irradiated group, G₂ phase arrest appeared in both cell lines after irradiation. The percentage of the G₂/M phase in MDA-MB-231 cell line increased as the time or dosage accumulated. Furthmore, the percentage didn't go down even after 48 hours later. However, the blockage began to gradually release in MCF-7 cell line at the dose of 8 Gy irradiated 24 h and the 48 h after 6 Gy X-irradiation. Followed with that, it turned out the percentage of the G₀/G₁ phase increased [(65.80±0.56)%, (62.53±0.67)%]. Conclusions 6 MV X-irradiation with the doses of 2-8 Gy can induce the cell cycle arrest at G₁ and G₂ phase in MCF-7 cell line, G₂ phase in MDA-MB-231 cell line. Thus more apoptosis appears in MCF-7 cell line, which may cause the difference in radiosensitivity between the two cell lines.

Objective To investigate the effects of metformin on the radiosensitivity of breast carcinoma cells with different estrogen receptors stasus (MCF-7 and MDA-MB-231) and to explore the underlying mechanisms.Methods Two cell lines,MCF-7 and MDA-MB-231 in logarithmic phase were divided into four groups:control group,drug group (mefformin),irradiation group and experimental group (irradiation plus metformin).MTT assay and the clonogenic assay were performed to evaluate the effects of metformin on the proliferation and survival of breast carcinoma cell lines,respectively.The change of cell cycle distribution and apoptosis rates were measured by propidium iodide (PI) and Hoechst 33342 staining analysis repectively.Western blot was used to detect the expression of p-AMPK and p-mTOR.Resutls Metformin could obviously inhibit the proliferation of the two breast carcinoma cell lines in a dose dependent manner.The cloning formation capacity was decreased in the group of metformin plus irradiation,which displayed the values of Dq,D0 and SF2 significantly lower than those of irradiation alone group (MCF-7:t =9.305,14.528,13.708,P ＜0.05;MDA-MB-231:t =19.560,16.893,36.048,P ＜0.05),and the sensitizing enhance rate (SER) of D0 were 1.29 and 1.21 for MCF-7 and MDA-MB-231 cell lines,respectively.Compared with irradiation alone,metformin plus irradiation obviously increased the proportion of cells in the G2/M phase in both cell lines (t =6.103,38.431,P ＜ 0.05).Metformin plus irradiation also enhanced radiation-induced apoptosis in both cell lines so that the apoptosis rates were higher than that in the metformin group or irradiation alone group (t =9.143,14.561,P ＜ 0.05).In MCF-7 cell lines,the expression of p-AMPK in the metformin combined with irradiation group was significantly higher than other treatment groups (t =35.194,8.647,10.316,P ＜ 0.05),but no significant changes of p-AMPK expression in MDA-MB-231 cell lines was observed (P ＞ 0.05).While inhibition of p-mTOR by metformin was observed in both cell lines (MCF-7:t =80.133,31.820,11.308,P＜0.05;MDA-MB-231:t=12.436,15.757,8.402,P＜0.05).Conclusions This study suggests that metformin possessed a strong radiosensitizing potential in both breast carcinoma cell lines of MCF-7 (ER positive) and MDA-MB-231 (ER negative).This radiosensitizing effect may result from the activation of AMPK or AMPK-independent pathway,inhibition of mTOR signaling pathway,and the enhancement of radiation-induced G2/M phase arrest and cell apoptosis after metformin treatment.

Objective:To investigate the value of postoperative radiotherapy in patients with cT 1-2N 1M 0 breast cancer after neoadjuvant chemotherapy and modified radical mastectomy which postoperative pathology showed that the number of axillary lymph node metastases was 0-3. Methods:One hundred and twenty-eight patients diagnosed with cT 1-2N 1M 0 breast cancer admitted to our hospital from January 1, 2000 to December 31, 2014 were retrospectively reviewed. All patients underwent neoadjuvant chemotherapy and modified radical mastectomy. The number of postoperative axillary lymph node metastases was 0-3. According to whether there was postoperative radiotherapy or not, the whole group of patients was divided into radiotherapy group ( n=87) and non-radiotherapy group ( n=41). In the two groups after operation, there were 43 and 11 patients with 1-3 axillary lymph node metastases (ypN 1), while there were 44 and 30 patients without axillary lymph node metastases (ypN 0) respectively. The 5-year locoregional recurrence-free survival (LRFS) rate, disease-free survival (DFS) rate and overall survival (OS) rate were calculated by Kaplan-Meier method, and the differences were compared by log-rank test. Univariate analysis was performed to analyze the effects of clinical features and treatment on prognosis. Results:The 5-year LRFS rate, DFS rate and OS rate of 128 patients were 91.4%, 82.8% and 93.0% respectively. The 5-year LRFS rates of the patients in the radiotherapy group and the non-radiotherapy group were 94.3% and 85.4% respectively, and the difference was not statistically significant ( χ2=3.055, P=0.080). As well as the 5-year DFS rates were 89.7% and 68.3% respectively, and the difference was statistically significant ( χ2=9.312, P=0.005). The 5-year OS rates were 94.3% and 90.2% respectively, and the difference was not statistically significant ( χ2=0.810, P=0.368). In the subgroup analysis, the 5-year LRFS rates of the patients who had achieved ypN 1 in the radiotherapy group and the non-radiotherapy group were 93.0% and 72.7%, and the 5-year DFS rates were 88.4% and 63.6%, with statistically significant differences ( χ2=4.248, P=0.039; χ2=4.525, P=0.033). The 5-year OS rates were 90.7% and 81.8% respectively, and the difference was not statistically significant ( χ2=0.713, P=0.399). The 5-year LRFS rates of the patients who had achieved ypN 0 in the radiotherapy group and the non-radiotherapy group were 95.5% and 90.0% respectively, with no statistically significant difference ( χ2=0.872, P=0.350). The 5-year DFS rates were 90.9% and 70.0% respectively, with statistically significant difference ( χ2=5.439, P=0.019). The 5-year OS rates were 97.7% and 93.3% respectively, with no statistically significant difference ( χ2=0.876, P=0.349). The univariate analysis indicated that age ( χ2=11.709, P=0.001) and blood vessel invasion ( χ2=7.608, P=0.006) were significant influencing factors for 5-year LRFS rate. Postoperative radiotherapy ( χ2=9.312, P=0.002) was a prognostic factor for 5-year DFS rate. Age ( χ2=6.093, P=0.014) and hormone receptor status ( χ2=3.974, P=0.046) were prognostic factors for OS. Conclusion:For the cT 1-2N 1M 0 breast cancer patients with 1-3 positive axillary lymph nodes after neoadjuvant chemotherapy, postmastectomy radiotherapy has local control benefit, and it can improve DFS. However, the benefit of postoperative radiotherapy needs to be further investigated in patients with pathological negative axillary lymph nodes after neoadjuvant chemotherapy.