DNA-PKcs-Dependent Modulation of Cellular Radiosensitivity by a Selective Cyclooxygenase-2 Inhibitor

Elisabeth Kodym, Reinhard Kodym, Benjamin P. Chen, David J. Chen, Keiko Morotomi-Yano, Hak Choy, Debabrata Saha

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Purpose: Inhibition of cyclooxygenase-2 has been shown to increase radiosensitivity. Recently, the suppression of radiation-induced DNA-dependant protein kinase (DNA-PK) activity by the selective cyclooxygenase-2 inhibitor celecoxib was reported. Given the importance of DNA-PK for repair of radiation-induced DNA double-strand breaks by nonhomologous end-joining and the clinical use of the substance, we investigated the relevance of the DNA-PK catalytic subunit (DNA-PKcs) for the modulation of cellular radiosensitivity by celecoxib. Methods and Materials: We used a syngeneic model of Chinese hamster ovarian cell lines: AA8, possessing a wild-type DNK-PKcs; V3, lacking a functional DNA-PKcs; and V3/WT11, V3 stably transfected with the DNA-PKcs. The cells were treated with celecoxib (50 μM) for 24 h before irradiation. The modulation of radiosensitivity was determined using the colony formation assay. Results: Treatment with celecoxib increased the cellular radiosensitivity in the DNA-PKcs-deficient cell line V3 with a dose-enhancement ratio of 1.3 for a surviving fraction of 0.5. In contrast, clonogenic survival was increased in DNA-PKcs wild-type-expressing AA8 cells and in V3 cells transfected with DNA-PKcs (V3/WT11). The decrease in radiosensitivity was comparable to the radiosensitization in V3 cells, with a dose-enhancement ratio of 0.76 (AA8) and 0.80 (V3/WT11) for a survival of 0.5. Conclusions: We have demonstrated a DNA-PKcs-dependent differential modulation of cellular radiosensitivity by celecoxib. These effects might be attributed to alterations in signaling cascades downstream of DNA-PK toward cell survival. These findings offer an explanation for the poor outcomes in some recently published clinical trials.

Original languageEnglish (US)
Pages (from-to)187-193
Number of pages7
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number1
StatePublished - Sep 1 2007


  • Celecoxib
  • Cellular radiosensitivity
  • Chinese hamster ovarian
  • Cycloxoygenase-2 inhibitors
  • DNA-PKcs

ASJC Scopus subject areas

  • Radiation
  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Cancer Research


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