Investigation of the effect of everolimus and melatonin combination on mtor pathway-mediated cell death and mitochondrial respiration in MCF-7 cells

The majority of breast cancer patients are hormone receptor positive and human epidermal growth factor receptor-2 negative. This type of cancer cells is highly sensitive to hormonal therapy. However, resistance to such hormonal therapies develops over time, and mechanism responsible for the resistance can also occur de novo in some types of cancer. One of the most important reasons for the developing resistance mechanism against endocrine therapy is the increase in PI3K/Akt/mTOR pathway activity. mTOR, a serine/threonine kinase, is involved in the downstream signaling pathway of the PI3K/Akt pathway and plays a role in cell growth, proliferation, protein synthesis and cell survival. Therefore, mTOR suppression in cancer cells is important for the development and understanding of the anti-tumor effect. Everolimus is an mTOR inhibitor and melatonin is a hormone with anti-oxidan and anti-inflammatory properties. As a result of everolimus and melatonin co-administration, changes in cell viability, apoptosis, autophagy activation and mitochondrial respiration were examined in this study. In this context, cell viability test, migration test, mTOR pathway protein expressions, autophagic protein expressions, differences in apoptotic cell death and cell cycle stages by flow cytometry, formation of LC3 clusters and membrane potential by JC-1 staining were determined. It has been shown that as a result of the combination of melatonin and everolimus, apoptotic cell death increases, mTOR protein expressions are suppressed, autophagic activation occurs and there is an improvement in respiration via complex II.