In Vitro Evaluation of Olive Leaf (Olea europaea L.) Extract as a Functional Food Component in Combination with Chemotherapeutics in MCF-7 Breast Cancer Cells

<b>Background</b>: Since breast cancer is a major cause of mortality, investigation of the synergistic effect of <i>Olea europaea</i> L. leaf extract in combination with some cancer medications is important for obtaining cost-effective and high-achieving treatments for breast cancer. This study aims to investigate the potential effects of <i>Olea europaea</i> L. extract in inhibiting breast cancer cell growth and enhancing the efficacy of chemotherapy agents against breast cancer under in vitro conditions. <b>Methods</b>: We conducted an analysis of some minerals and vitamins of three different viscosities (200 V, 300 V, and 400 V as a natural food product) of <i>Olea europaea</i> L. leaf water-based extract (OWE) derived from a natural cold maceration. We investigated the cytotoxic effects of <i>Olea europaea</i> L. extract with different viscosities (200-400 V) and various chemotherapy agents, either alone or in combination, in estrogen receptor-positive MCF-7 human breast carcinoma cells by MTT assay. <i>Olea europaea</i> L. extract treatment of cells resulted in growth inhibition in a dose- and time-dependent manner. <b>Results</b>: The 400 V OWE showed the highest calcium (301 ± 12 mg/100 g), potassium (1744 ± 33 mg/100 g), and vitamin E (0.36 ± 0.01 mg/100 g) amounts. Based on MTT results, combinations of 400V <i>Olea europaea</i> L. extract, which exhibited the strongest inhibitory effect with an IC₅₀ value of 940 µg/mL, and anticancer drugs were next assessed for their synergistic efficacy towards cell growth inhibition. <b>Conclusions</b>: Combinations of the IC₅₀ value of 400 V OWE with docetaxel, paclitaxel, and trastuzumab (1 µg/mL) treatment showed a strong synergistic effect in the growth inhibition of MCF-7 cells.