TY - JOUR
T1 - Inhibition of DNA repair as a mechanism of enhanced radioresponse of head and neck carcinoma cells by a selective cyclooxygenase-2 inhibitor, celecoxib
AU - Raju, Uma
AU - Ariga, Hisanori
AU - Dittmann, Klaus
AU - Nakata, Eiko
AU - Ang, Kian K.
AU - Milas, Luka
PY - 2005/10/1
Y1 - 2005/10/1
N2 - 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 μM), 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 (NFκB). Results: Celecoxib (10 and 50 μM, 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 NFκB and the radiation-induced NFκB in HN5 cells, suggesting that NFκB 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.
AB - 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 μM), 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 (NFκB). Results: Celecoxib (10 and 50 μM, 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 NFκB and the radiation-induced NFκB in HN5 cells, suggesting that NFκB 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.
KW - Celecoxib
KW - Inhibition of DNA repair
KW - Ku70
KW - NFκB
KW - Radiosensitization
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U2 - 10.1016/j.ijrobp.2005.06.007
DO - 10.1016/j.ijrobp.2005.06.007
M3 - Article
C2 - 16168844
AN - SCOPUS:24944579985
SN - 0360-3016
VL - 63
SP - 520
EP - 528
JO - International Journal of Radiation Oncology Biology Physics
JF - International Journal of Radiation Oncology Biology Physics
IS - 2
ER -