Tamoxifen and the PI3K Inhibitor: LY294002 Synergistically Induce Apoptosis and Cell Cycle Arrest in Breast Cancer MCF-7 Cells.

Breast cancer is considered as one of the most aggressive types of cancer. Acquired therapeutic resistance is the major cause of chemotherapy failure in breast cancer patients. To overcome this resistance and to improve the efficacy of treatment, drug combination is employed as a promising approach for this purpose. The synergistic cytotoxic, apoptosis inducing, and cell cycle effects of the combination of LY294002 (LY), a phosphatidylinositide-3-kinase (PI3K) inhibitor, with the traditional cytotoxic anti-estrogen drug tamoxifen (TAM) in breast cancer cells (MCF-7) were investigated. LY and TAM exhibited potent cytotoxic effect on MCF-7 cells with IC50 values 0.87 µM and 1.02 µM. The combination of non-toxic concentration of LY and TAM showed highly significant synergistic interaction as observed from isobologram (IC50: 0.17 µM, combination index: 0.18, colony formation: 9.01%) compared to untreated control. The percentage of early/late apoptosis significantly increased after treatment of MCF-7 cells with LY and TAM combination: 40.3%/28.3% (p < 0.001), compared to LY single treatment (19.8%/11.4%) and TAM single treatment (32.4%/5.9%). In addition, LY and TAM combination induced the apoptotic genes Caspase-3, Caspase-7, and p53, as well as p21 as cell cycle promotor, and significantly downregulated the anti-apoptotic genes Bcl-2 and survivin. The cell cycle assay revealed that the combination induced apoptosis by increasing the pre-G1: 28.3% compared to 1.6% of control. pAKT and Cyclin D1 protein expressions were significantly more downregulated by the combination treatment compared to the single drug treatment. The results suggested that the synergistic cytotoxic effect of LY and TAM is achieved by the induction of apoptosis and cell cycle arrest through cyclin D1, pAKT, caspases, and Bcl-2 signaling pathways.

Extra virgin olive oil potentiates the effects of aromatase inhibitors via glutathione depletion in estrogen receptor-positive human breast cancer (MCF-7) cells.

There have been numerous evidences supporting the relationship between olive oil and cancer, with most of the attention being directed toward its fat and phenolic content. The aims of this study were to investigate whether EVOO and OA could enhance the effects of aromatase inhibitors (letrozole and anastrozole) in ER-positive MCF-7 cells, as well as to investigate its influence on cytochrome c release and GSH levels. It was observed that upon combination treatment, anti-proliferation effects and apoptosis induction were augmented. Apoptosis was triggered via the intrinsic pathway in accordance with cytochrome c release into the cytosol based on IF-IC and ELISA observations. Intracellular GSH levels were also reduced upon EVOO/OA treatment in combination with aromatase inhibitors, and were found to be inversely correlated to cytosolic cytochrome c levels. Additionally, the estrogenic suppressive effects of letrozole and anastrozole were amplified when used in combination with EVOO/OA. Therefore, the employment of aromatase inhibitors in combination with EVOO/OA could orchestrate a reduction in intracellular estrone biosynthesis which feeds ER-positive cells, while simultaneously depleting GSH levels and increasing ROS generation, thus releasing cytochrome c and subsequent induction of apoptosis in MCF-7 cells.