Sensitization of P53-mutated Epithelial Ovarian Cancer to CD95-mediated Apoptosis is Synergistically Induced by Cisplatin Pretreatment

Epithelial ovarian carcinoma (EOC) remains a highly lethal malignancy. Despite the progress in surgical and therapeutic strategies, resistance to chemotherapy is still a major concern. Cytotoxic therapies mediate killing of cancer cells by activating the intrinsic mitochondrial apoptotic pathway, and p53 status is a key factor in determining the efficacy of apoptotic signaling. The extrinsic (CD95) death receptor-dependent signaling pathway also contributes to the efficacy of cancer therapy. We previously showed that EOC are generally resistant to CD95-dependent apoptosis. In p53 wild-type EOC tumors, CD95-mediated apoptosis is impaired at the receptor level by the long form of cellular FLICE-inhibitory protein, whereas this mechanism does not account for resistance in tumors with mutated p53 (p53mu). In the present study, we examined both intrinsic and death receptor-dependent apoptotic signaling in p53mu OVCAR3 EOC cell line, showing that these cells are less susceptible to cisplatin treatment as compared with p53 wild-type EOC cells and also resist CD95-mediated apoptosis due to inefficient formation of the death-inducing signaling complex and weak mitochondrial signal amplification. However, pretreatment of OVCAR3 cells with clinically relevant cisplatin concentrations significantly improved receptor-dependent apoptotic signaling by up-modulating CD95 receptor expression and increasing death-inducing signaling complex formation efficiency. The synergy of cisplatin pretreatment and CD95 triggering in inducing cell death was also shown in p53mu tumor cells derived from ascitic fluid of advanced-stage EOC patients. These findings support the effectiveness of a combined therapeutic treatment able to sensitize cancer cells to apoptosis even when p53 is functionally inactivated.