Over kanseri hücrelerinde hücre yoğunluğu bağımlı sisplatin direncinde P53 ve P21'in rolü

Chemoresistance is one of the major challenges in ovarian cancer. Resistant cancer cells which lead to disease relapse are the most prominent causes of death in ovarian cancer patents. Cisplatin is one of the most common platinum-based chemotherapeutic agents used to treat ovarian cancer. It's main mechanism of action involves inhibiting transcription by covalently binding to DNA, forming adducts which cause DNA damage and resulting in cell death. Tumor suppressor p53 exhibits great importance in determining whether the cells will go into apoptosis or repair DNA damage upon exposure to cisplatin. Associated with p53 is p21, a cyclin dependent kinase inhibitor (CDK) that is directly responsible for cell cycle arrest and cellular repair at the G1/S and G2/ phases of the cell cycle. Despite that the use of cisplatin increased effectiveness of chemotherapy in ovarian cancer, resistance to cisplatin is a major handicap in the clinic. Recent studies have suggested a new mode of cisplatin resistance in ovarian cancer cells, which is cell density-dependent cisplatin resistance at which ovarian cancer cells exhibit increased resistance to cisplatin as the cell density in cancer cell populations increase. Although cell density-dependent cisplatin resistance may have important clinical implications, its underlying mechanisms are not clear. To understand how cellular density affects cisplatin resistance in ovarian cancer, in this thesis we investigated the responses of sensitive (A2780) and resistant (CP16) ovarian cancer cell lines to cisplatin at low, confluent, and overconfluent culture conditions. In order to evaluate the contribution of p53 and p21's functions in cell density dependent chemoresistance we assessed the differential protein expression of p53 and p21 along with their phosphorylated forms at different subcellular fractions. Hence, we aimed to shed light on possible mechanisms of cisplatin resistance at increasing confluence levels. Moreover, we investigated the changes in the influx and efflux pumps that determine intracellular cisplatin accumulation to understand whether the degree of cell – cell interaction at different confluency levels affects the cells' cisplatin uptake or efflux capabilities. Our study suggests that p53 and p21 are regulated in a cell density dependent manner in response to cisplatin, including changes in their phosphorylation and subcellular localization. In CP16 cells, the confluence dependent pattern of p53 and p21 regulation seem to support cisplatin resistance at higher cell densities, while in A2780, the opposite pattern is observed.