Investigation of the treatment potential of "olea europaea leaf extract" in gastri̇c cancer cells

Gastric cancer (Gastric cancer; GK) is one of the most common gastrointestinal system cancers worldwide. The current treatment of advanced stage GK is surgical resection followed by radiotherapy and chemotherapy treatment. 5-Fluorouracil (5-FU) and cisplatin are generally used as chemotherapy drugs in advanced GCs. However, in advanced stage GC patients, the treatment results in negative results due to the aggressiveness of the tumor and the development of drug resistance in the patients. Today, plant extracts are used in the development of new strategies for use in cancer treatment, and combined treatment methods with different chemotherapeutic drugs are focused on in various cancers. In the current thesis, it is aimed to evaluate the possible effects of Olea europea leaf extract (OLE) alone or in combination with the chemotherapy drug 5-FU and cisplatin on the viability and death, suppressing the aggressiveness of tumor cells, breaking the tumor size and treatment resistance developed in the cells and playing a role in these processes and evaluation of possible effects on epigenetic mechanisms of GK cells. For this purpose, RT-PCR method was used to determine the effects of OLE on MDR genes related to drug resistance, EMT and CSC markers associated with tumor aggressiveness, and expression levels of LncRNAs associated with epigenetic mechanisms. The effects of OLE on cell proliferation, WST, cell death, Annexin V analyzes in GK tumors, and the effects of OLE on wound healing, colony formation, tumor size and angiogenesis were performed by functional analyzes in cell culture. As a result, it has been determined that OLE reduces cell proliferation, kills cells apoptotically, suppresses tumor aggressiveness by inhibiting EMT and CSC markers together with chemotherapeutics, and also prevents drug resistance by reducing the expression levels of MDR genes. At the same time, it was determined that OLE alone and in combination with chemotherapeutics reduced tumor size and suppressed angiogenesis.