Cisplatin chemotherapy plus adenoviral p53 gene therapy in EBV-positive and -negative nasopharyngeal carcinoma

We have previously shown that the introduction of human recombinant wild-ty pe p53 mediated by an adenoviral vector (Ad5CMV-p53), either alone or deliv ered in combination with ionizing radiation, was cytotoxic to two nasophary ngeal carcinoma (NPC) cell lines. To further explore the potential therapeu tic role for gene therapy, the combination of Ad5CMV-p53 and cisplatin was examined in two NPC cell lines, CNE-1 and C666-1. The C666-1 cells are part icularly relevant because they express Epstein-Barr virus latent gene produ cts analogous to human NPC in situ. Cel Is were infected with 5 pfu/cell of Ad5CMV-p53 or Ad5CMV-beta -gal, followed by exposure to increasing doses o f cisplatin. Clonogenic and MTT assays were used to assess the sensitivity of cells to these treatments, and apoptosis was also quantified. The combin ation of Ad5CMV-p53 and cisplatin resulted in approximately 25% greater cyt otoxicity compared to that observed with cisplatin alone in either cell lin e. Apoptosis was induced in approximately 50% of cells following administra tion of both Ad5CMV-p53 and cisplatin, but was induced in considerably fewe r cells following either treatment alone. The two modalities appeared to in teract in an additive manner. Ad5CMV-p53 gene therapy resulted in the expre ssion of biologically active p53 protein, shown by induction of p21(WAF1/Cl P1). Cisplatin treatment showed little Effect on either p53 or p21(WAF1)/(C IP1) expression. Therefore, both p53 gene therapy and cisplatin chemotherap y demonstrated cytotoxicity mediated by apoptosis despite the presence of E BV gene products in the C666-1 cells, but it appears that the two modalitie s induce cytotoxicity by independent pathways.