In Vitro Evaluation of Cytotoxic and Antitumor Activities of The Tamoxifen and Doxorubicin Combination on MCF-7 and BT-474 Breast Cancer Cell Lines

The combination therapy of breast cancer has preferred for the patients to minimize possible side effects, drug resistance, recurrence and toxic effects. In this study, we aim to investigate the cytotoxic and antitumor activities the tamoxifen and doxorubicin combination in breast cancer cell lines, MCF-7 and BT-474. Tamoxifen (Tam) and doxorubicin (Dox) and their combination with different concentrations (0.625–20 μM Tam; 0.0625–2 μM Dox and 5 μM Tam+ 0.5/1.0/1.5 μM Dox combination were applied to MCF-7 and BT-474 cells for 48 hours. Afterthat, their cytotoxic activities were analyzed with MTT assay. Bcl-2, Mapt and Mrp1 are genes that induce cell proliferation, inhibit apoptosis and play role in drug resistance in cancer cells. To evaluate the antitumor activities of these genes in combination treatment, mRNA levels were analyzed by quantitative PCR. According to the MTT assay, it was determined that IC50 values as 17.26 μM and 16.65 μM for tamoxifen on MCF-7 and BT-474 breast cancer cell lines. IC50 values of doxorubicin in MCF-7 and BT-474 cells were 1.65 μM and 1.57 μM, respectively. It was found that the application of the combination drugs (15 μM tamoxifen and 1.5 μM doxorubicin) in MCF-7 and BT-474 cells have the lowest combination index values as 1.09 and 1.26, respectively. Therefore, the combination of 15 μM tamoxifen and 1.5 μM doxorubicin was selected and applied to both breast cancer cell lines for gene expression analysis. It was found that while Mrp1 and Mapt genes expressions were significantly upregulated, Bcl-2 gene expression was downregulated in MCF-7 cells. However, Bcl-2, Mrp1 and Mapt genes expressions in BT-474 cells were not significantly regulated. Altogether, these findings suggest that the combination of these two drugs may have a potential antagonistic interaction according combination index values.