Cytotoxic effects of Ad5CMV-p53 expression in two human nasopharyngeal carcinoma cell lines.

Nasopharyngeal carcinoma (NPC) is a malignant disease of the head/neck region with a 5-year survival level of approximately 65%. To explore novel therapeutic strategies in the management of this disease, the potential of Ad5CMV-p53-mediated gene transfer to NPC cells was investigated in vitro. Two NPC cell lines, CNE-1 and CNE-2Z, were infected with either Ad5CMV-p53 or Ad5CMV-beta-galactosidase and evaluated for transduction efficiency and cytotoxicity. At a multiplicity of infection of 50 plaque-forming units (pfu)/cell, Ad5CMV-beta-galactosidase infection and beta-galactosidase expression were detected in almost 100% of treated NPC cells. High levels of recombinant p53 protein expression were also observed in the NPC cell lines when treated with Ad5CMV-p53 at 50 pfu/cell. Expression of recombinant p53 was dose and time dependent, with peak levels observed at 24 h. A marked increase in WAF1/CIP1 expression was also observed in NPC cells after Ad5CMV-p53 infection. Expression of bcl-2 and bax were minimally detectable at baseline; infection with Ad5CMV-p53 induced no changes in the protein levels in the NPC cells. Growth of NPC cells treated with Ad5CMV-p53 was observed to be significantly inhibited when determined by either the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide or clonogenic assay. Infection with Ad5CMV-p53 at 25 pfu/cell resulted in survival levels of 0.35 and 11% in CNE-1 and CNE-2Z cells, respectively. Chromatin condensation and DNA fragmentation were also observed, demonstrating that these cells were undergoing apoptosis. However, when GM38 (normal human fibroblasts) were subjected to identical treatments, they demonstrated significantly lower infection efficiency and transgene expression and were resistant to Ad5CMV-p53-mediated cytotoxicity. These data demonstrate the efficacy of Ad5CMV-p53-mediated gene therapy in human NPC, thus warranting additional investigations of this therapeutic strategy.