The effects of combining ionizing radiation and adenoviral p53 therapy in nasopharyngeal carcinoma

Purpose: Nasopharyngeal carcinoma (NPC) is a malignant disease of the head/ neck region, with a 5-year survival level of approximately 65 %. To explore gene therapy as a novel approach which might improve outcome, we have show n previously that introduction of human recombinant wild-type p53 mediated by the adenoviral vector (Ad5CMV-p53) was cytotoxic in two human nasopharyn geal carcinoma (NPC) cell lines (CNE-1 and CNE-2Z). The current work was de signed to determine whether this strategy, combined with ionizing radiation (XRT), was more effective than either treatment alone. Methods and Materials: CNE-1, CNE-2Z, and a normal human nasopharyngeal fib roblast strain, KS1, were infected with 2- and 6-plaque-forming units (pfu) /cell of Ad5CMV-p53, respectively. These doses were isoeffective for beta-g alactosidase activity in the CNE-1 and CNE-2Z cells. XRT was administered 2 4 h post-infection, and Western blot analyses were conducted for p53, p2l(w aF1/C1P1), bar, and bcl-2 2 days after XRT. Cell survival was assessed usin g a clonogenic assay. Presence of DNA ladders reflecting apoptosis was dete cted using DNA agarose gel electrophoresis, and cell cycle was analyzed usi ng how cytometry. Results: The combination of Ad5CMV-p53 plus XRT (2, 4, and 6 Gy) resulted i n an approximately 1-log greater level of cytotoxicity compared to that obs erved with XRT alone for both NPC cell lines. The two modalities appear to be interacting in a synergistic manner in cancer cells, but not in KS1 fibr oblasts. XRT alone stimulated minimal p53 expression in control cells; Ad5C MV-p53 alone induced significant recombinant p53 expression, which was not further enhanced by the addition of XRT. Similar observations were made for p2l(WAF1/CIP1) expression. No changes were observed for bar or bcl-2 expre ssion with any of these treatments. Apoptosis was induced following 4 Gy of XRT alone, but was observed after only 2 Gy when combined with Ad5CMV-p53. Cell cycle analysis indicated that Ad5CMV-p53 infection did not perturb th e cell cycle beyond that observed with XRT alone. Conclusion: p53 gene therapy and XRT appears to interact in a synergistic m anner; underscoring the significant potential of this novel strategy in the treatment of NPC. (C) 1999 Elsevier Science Inc.