Inhibition of cyclooxygenase-2 activity by celecoxib does not lead to radiosensitization of human prostate cancer cells in vitro

Purpose: To evaluate the potential radiosensitizing effect of the specific COX-2 inhibitor celecoxib (Celebrex'(R)) on prostate carcinoma cells in vitro. Materials and methods: The influence of celecoxib (concentration range 5 to 75 mu M) on radiation-induced cellular and clonogenic survival was investigated in prostate carcinoma cell lines PC-3, DU145, LNCaP and normal prostate epithelial cells (PrEC). Western blot analysis and ELISA were used to determine the impact of radiation alone or radiation combined with celecoxib treatment on COX-2 expression and prostaglandin E2 synthesis. To evaluate induction of celecoxib-induced apoptosis cell cycle analysis has been performed. Results: Celecoxib (5, 10 and 25 mu M) in combination with single-dose irradiation of 2 Gy induced a significant radiosensitization in normal prostate epithelial cells which could not be observed for any of the prostate carcinoma cell lines investigated. Increased COX-2 protein expression in PC-3 cells was obvious only after IR with 15 Gy, while PGE2 production was elevated following irradiation (2-15 Gy) in a dose-dependent manner. Treatment with celecoxib alone or in combination with IR led to a dose-dependent increase in COX-2 protein expression. Nevertheless pre-treatment with celecoxib caused a marked reduction of radiation-induced enzyme activity as tested at the level of PGE2 production, both in PC-3 and DU145 cells. Following fractionated irradiation with single doses of 2 Gy, elevated COX-2 protein expression as well as enhanced PGE2 production was observed already after the second fraction in PC-3 cells. Pretreatment with celecoxib reduced the amount of PGE2 significantly, but not of COX-2 protein. Conclusions: Our data obtained for the human prostate cancer cell lines do not indicate that a marked inhibition of prostaglandin E2 synthesis by celecoxib leads to enhanced radiosensitization. Thus, in terms of radiosensitization the analysed prostate cancer cells can be classified as non-responders to celecoxib treatment. (c) 2006 Elsevier Ireland Ltd. All rights reserved.