Tamoxifen effect on isolated breast cancer stem cells and MCF-7 breast cancer cells in the aspect of autophagy and apoptosis

Cancer stem cell hypothesis emphasizes that cancers are driven by a cellular component having stem cell properties, including self-renewal, tumorigenicity, and multi-lineage differentiation capacity. It has been thought that cancer stem cells may also be responsible for resistance against therapeutic approaches and reforming tumors. Therefore, understanding cancer stem cells? role during carcinogenesis has become a major focus in stem cell biology and cancer research. Breast cancer is the most common cancer among women. It has been thought that breast stem cells play an important role in initiating breast cancer since biology of breast requires large amount of stem cells. A better characterization of breast cancer stem cells which initiate and drive tumor growth seems an essential step to improve breast cancer knowledge and management.Scope of this study was to isolate breast cancer stem cells from breast cancer cell line (MCF-7) using CD44 and CD24 cell surface markers, and test if these cells have any resistance to hormonal therapy as it shows some resistancy to chemotherapy compared to MCF-7 cells. Also, it was aimed to observe whether there is autophagic cell death mechanism in breast cancer stem cells as in the case of autophagy induction in MCF-7 cells due to Tamoxifen application. For this purpose, CD44+, CD24-/low breast cancer stem cells were treated with Doxorubicin for chemotherapy experiments and Tamoxifen for hormonal therapy studies after they were sorted from MCF-7 cells by FACS system. MTS assay was then performed for cell proliferation studies following drug treatment. In addition, flow cytometry was carried out to check apoptosis and autophagic cell death on these cells and on MCF-7 cells. Western blot and LC3-GFP aggregation assays were also performed for autophagic studies. As a result of the study, isolated breast cancer stem cells showed some resistance to chemotherapeutic drug Doxorubicin, but did not show significant difference towards the hormonal therapy drug Tamoxifen in the aspect of apoptosis and autophagy.