Inhibition of DNA repair as a mechanism of enhanced radioresponse of head and neck carcinoma cells by a selective cyclooxygenase-2 inhibitor, celecoxib

Journal Article · Sat Oct 01 04:00:00 EDT 2005 · International Journal of Radiation Oncology, Biology and Physics

DOI:https://doi.org/10.1016/j.ijrobp.2005.06.007· OSTI ID:20702162

Raju, Uma ^[1]; Ariga, Hisanori ^[2]; Dittmann, Klaus ^[3]; Nakata, Eiko ^[4]; Ang, Kian K ^[5]; Milas, Luka ^[1]

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1. Department of Experimental Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX (United States)
2. Department of Radiation Oncology, Miyagi Cancer Center, Miyagi (Japan)
3. Department of Radiation Oncology, Eberhard Karls-University, Tubingen (Germany)
4. Department of Radiology, Tohoku University School of Medicine, Sendai (Japan)
5. Department of Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX (United States)

Purpose: Previously, we reported that inhibitors of cyclooxygenase-2 (COX-2) enzyme enhanced murine and human tumor cell response to radiation in vitro and in vivo. However, the molecular mechanisms mediating the effects of COX-2 inhibitors are not clear. The present study was designed to investigate the ability of celecoxib, a selective COX-2 inhibitor, to sensitize human head-and-neck cancer cell line, HN5, to radiation, and examine its effects on DNA repair, which may be a potential mechanism of radiosensitization. Methods and Materials: Cells were assessed for the effect of celecoxib (5-50 {mu}M), by 3-[4,5-dimethylthiozol-2-yl]-2,5-diphenyltetrazolium bromide assay for growth inhibition and by clonogenic cell survival assay for the radiosensitizing effect. Kinase assay and Western analysis were conducted to assess the effect of celecoxib on DNA-dependent protein kinase catalytic subunit (PKcs) and Ku proteins. Electrophoretic mobility shift assays (EMSA) were performed to determine the DNA-binding activity of Ku/DNA-PKcs protein complex and nuclear factor kappa B (NF{kappa}B). Results: Celecoxib (10 and 50 {mu}M, for 2 days) inhibited the HN5 cell growth and significantly enhanced the cell radiosensitivity in a dose-dependent manner. It also reduced the shoulder region on the radiation-survival curve, suggesting that inhibition of DNA repair processes may have occurred. Western blot analysis demonstrated that celecoxib downregulated the expression of Ku70 protein and inhibited the kinase activity of DNA-PKcs, which are involved in the double-stranded DNA-break repair machinery. By EMSA, it was further shown that celecoxib reduced DNA-binding activity of Ku/DNA-PKcs protein complex. In addition, celecoxib inhibited the constitutively active NF{kappa}B and the radiation-induced NF{kappa}B in HN5 cells, suggesting that NF{kappa}B may play a role in mediating the effects of celecoxib. Conclusions: Celecoxib strongly enhanced the sensitivity of HN5 carcinoma cells to radiation, which, mechanistically, can be attributed to the inhibition of DNA repair processes in radiation-damaged cells.

• OSTI ID: 20702162
• Journal Information: International Journal of Radiation Oncology, Biology and Physics, Journal Name: International Journal of Radiation Oncology, Biology and Physics Journal Issue: 2 Vol. 63; ISSN IOBPD3; ISSN 0360-3016
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
BROMIDES
CARCINOMAS
DNA REPAIR
ENZYMES
HEAD
IN VITRO
IN VIVO
INHIBITION
NECK
RADIATION DOSES
RADIOSENSITIVITY
SENSITIVITY
SURVIVAL CURVES
TUMOR CELLS