Study of the effect of concurrent use of letrozole with radiotherapy to the cell death mechanisms in the breast cancer cell line

Purpose:Breast cancer is the third most common cancer worldwide and the most common malignancy in women. It is responsible for 37% of cancer cases in women. Recently, there have been important changes regarding standard adjuvant endocrine therapy in breast cancer patients. According to the results of preclinical and clinical studies, hormone receptor-positive tumors have molecular, biological and clinical differences. Using hormonal treatment prolongs survival for the majority of hormone receptor positive breast cancerIn premenopausal women standard endocrine therapy is tamoxifen; the optimal adjuvant hormonal therapy in ER (+), postmenopausal patients is aromatase inhibitors as initial therapy or after tamoxifen treatment. In the third-generation aromatase inhibitors studies, progression and disease-free survival rates have shown that aromatase inhibitors are at least as effective and are superior to tamoxifenPostoperative radiotherapy (RT) decreases the risk of locoregional recurrence. RT is also associated with improved survival in high-risk premenopausal and postmenopausal women with breast cancer. Experimental and clinical studies show that concurrent use of tamoxifen sensitizes cells to radiotherapy and increases radiotherapy induced pulmonary fibrosis. Whether letrozole sensitizes breast cancer cells to RT has not been determined with sufficient number of studies. There is a single experimental study of breast cancer cells that revealed increased radiation sensitivity with letrozole.The purpose of this study is to investigate the effect of concurrent use of letrozolewith radiotherapy to the cell death mechanisms in the breast cancer cell line.Materials and methods:In our study in vitro cell culture methods were used, as a model MCF-7 aro breast cancer cell lines were chosen as model and MCF-7 cells were chosen as the control group.Letrozole was used with varying doses of 100, 500, 1000 nM, and cell lines were exposed to letrozole for 1, 3 and 6 days; Irradiations were performed using a cobalt-60 source with doses 2 and 4 Gy. Experiments were held 24 hours after radiotherapy. Apoptotic cell death was evaluated with "Fluorometric Caspase 3 Assay Kit?; by measurement of the apoptotic behavior ,with ?Annexin-V FITC Apoptoz Detection Kit " by showing of dead cells with PI staining in flow analysis. Western blot technique was used for determination Beclin gene expression which has a role in autophagy in cell line. The experiments were repeated three times for MCF-7 cells but experiments with MCF-7 aro cells could be done only one time because of the problems to optain the cell line.Results:In our experiments with MCF-7 cell line, we evaluated caspase-3 and Annexin-V results for 1,3, and 6 day incubation with letrozole. There was no significant difference for early apoptoz, late apoptoz and necrosis. Apoptozis was reduced by increasing radiation doses in MCF-7 aro cells under Letrozol effect. The experimental results of decreasing necrosis showed that there was a trend from necrosis to apoptoz.Our study showed a increased autophagy in cells which received 4 Gy irradiation and incubated with letrozole for 1 day compared with the control group. There was no difference in cells which received 2-4 Gy irradiation and incubated for 3 and 6 days. Also we found a increased autophagy in MCF-7 Aro cells which received 2 - 4 Gy irradiation and incubated with letrozole for 1 day compared with the control group.Conclusion:In accordance with the data obtained, we had positive effect on cell death mechanisms for hormone-sensitive, receptor-positive and aromatase enzyme expressed cells with concurrent use of letrozole. The results of ongoing studies are needed to provide better information. This study must be supported by improved results because there isn?t sufficient information for this topic in the literatureKey Words: MCF-7 and MCF-7 aro cell line, Radiotherapy, Letrozole, Apoptoz, Autophagy