Background: This study was undertaken to determine the status of cyclooxygenase-2 (COX-2) in nasopharyngeal cancer (NPC) in Taiwanese patients and its relationship to survival after radiotherapy (RT). In addition, the effect of NS-398, a potent selective COX-2 inhibitor, was tested in vitro alone and in combination with radiation on NPC-BM1 human NPC cells as a prelude to using this drug along with RT in the treatment of patients with NPC.
Methods: Thirty-seven patients diagnosed with T4N0-3M0 NPC were enrolled into this study. COX-2 expression was determined by immunohistochemical staining of formalin-fixed, paraffin-embedded tumor tissue. Patient survival was the clinical end point. The effects of COX-2 expression on cell survival and radioresistance was tested in vitro using the selective COX-2 inhibitor NS-398 in conjunction with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide (MTT) and clonogenic assays.
Results: COX-2 immunoreactivity was detected in 62% of NPC tumors, and expression levels were high in 43%. Survival analysis showed the 5-year overall survival rates for patients who had high COX-2 expression was 27% compared with 60% for those with low/absent expression (p = .047). Pattern of failure analysis showed no significant difference between high and low COX-2 expression in locoregional failure (27% vs 25%, p = .91). However, patients with N0 to N1 disease and high COX-2 expression had a significantly higher incidence of distant metastasis compared with patients with stage N0 to N1 disease and low COX-2 expression (83% vs 15%, p = .004). This difference was not observed in patients with N2 to N3 disease. This difference contributed to worse survival of patients whose tumors had high COX-2 expression levels. The selective COX-2 inhibitor NS-398 was directly cytotoxic to NPC-BM1 cells in vitro, as judged in an MTT assay (viable cells decreased from 92% to 76%, 52%, and 22%, with increases of NS-398 from 20 to 40, 60, and 80 microM, respectively). Radiation-induced cell death was also increased by treatment with NS-398. At a 10% survival level, 40 microM NS-398 increased radiation cytotoxicity by a factor of 1.37, whereas 60 microM increased it by a factor of 4.9.
Conclusions: COX-2 overexpression is a predictor for poor survival for advanced stage NPC. In vitro, NS-398 radiosensitizes the NPC-BM1 cell line, providing a basis for testing the combination of COX-2 inhibitors with radiation in the treatment of patients with NPC.
(c) 2005 Wiley Periodicals, Inc.