International Journal of Radiation Oncology*Biology*Physics
Biology ContributionCelecoxib Induced Tumor Cell Radiosensitization by Inhibiting Radiation Induced Nuclear EGFR Transport and DNA-Repair: A COX-2 Independent Mechanism
Introduction
Celecoxib belongs to the group of specific cyclooxygenase 2 (COX-2) inhibitors that originally were approved by the Food and Drug Administration for treatment of rheumatoid arthritis. COX-2 inhibitors were found to be effective also in prevention of development of intestinal 1, 2 and skin cancers (3). Therapeutic benefit can be achieved by combining celecoxib with radiation and chemotherapy during treatment of glioblastomas (4), prostate carcinomas (5), and lung cancer 6, 7. Taken together, there exists solid evidence that inhibition of COX-2 with selective inhibitors prevents carcinogenesis, slows the growth of established tumors, and enhances tumor response to radiation without appreciably affecting normal tissue radioresponse 8, 9. Albeit intensive investigations to understand the cellular consequences of celecoxib treatment, it has not been fully resolved which molecular processes are involved in radiosensitization. Celecoxib and other COX-2 selective inhibitors inhibit proliferation of and induce apoptosis in a variety of tumor cells 10, 11. They affect some normal cells as well. For example, at high concentrations, both rofecoxib and celecoxib induce apoptosis in endothelial cells, but do not effect either the induction of apoptosis or inhibition of cell-cycle progression in human vascular smooth muscle cells 11, 12, suggesting a cell type–dependency of these effects of COX-2 inhibitors. Some other effects of COX-2 inhibitors such as reduction of angiogenesis and inhibition of invasiveness of tumor cells may also be cell type–dependent (13).
At the molecular level, COX-2 inhibitors affect signal transduction pathways involved in cell proliferation, cell-cycle, and apoptosis development 14, 15. Among these is the phosphatidylinositol 3-kinase/Akt pathway reported recently to be affected by celecoxib 16, 17, 18. The exact signaling for phosphatidylinositol 3-kinase/Akt activation is unclear, but some recent findings suggest that both PGE2, a major metabolite of COX-2, and epidermal growth factor receptor (EGFR) are involved (17). Buchanan et al.(17) found that PGE2-induced migration and invasion involved rapid transactivation and phosphorylation of EGFR. Within minutes after treatment, PGE2 induced activation of Akt, which was completely abolished by EGFR-specific tyrosine kinase inhibitors, providing evidence for a distinct role of EGFR during this process. It was reasoned that the rapid transactivation of EGFR occurred probably via an intracellular Src-mediated event without release of extracellular epidermal growth factor-like ligand (17). Ionizing radiation is also able to induce EGFR transactivation (18), in which case this molecular process was found to be essential for cell survival 19, 20. The crucial role of EGFR during cell survival after exposure to radiation or some other cellular stresses is accentuated by our recent observation (21). We found that EGFR became translocated into the cell nucleus and regulated DNA-PK activity essential for repair of DNA double-strand breaks (21).
The antitumor effects of COX-2 inhibitors, used either as single treatments or in combination with radiation or chemotherapeutic agents, have commonly been attributed to selective COX-2 inhibitory activities of coxibs 8, 9. However, increasing evidence suggests that these agents may exert antitumor actions by COX-2 independent mechanisms as well. Reports show that these agents (1) inhibit in vitro growth of cells (22) and in vivo growth of tumors (23), lacking COX-2; (2) need to be given in higher doses to block cell proliferation than those that inhibit the enzyme (24); and (3) retain inhibitory properties for cells in vitro and tumors in vivo when derivatives of celecoxib lack COX-2 suppressive activity 4, 25.
Using cell lines expressing or lacking COX-2, the present study assessed the effect of celecoxib on radiosensitivity and molecular mechanisms underlying celecoxib-induced radiosensitization, concentrating on the involvement of EGFR. Data presented show that celecoxib inhibited radiation-induced nuclear translocation of EGFR in responding cells, which was associated with inhibition of DNA repair processes, and thus provide a novel explanation for the radiosensitizing effects of COX-2 inhibiting agents.
Section snippets
Cell culture and irradiation
Celecoxib was kindly provided by Pfizer Corp. (Karlsruhe, FRG). Human bronchial carcinoma cells, designated A549 (26), normal foreskin fibroblasts HSF7, transformed fibroblasts HH4dd (27), HCT116 cells (ATCC, origin colon carcinoma), and the human squamous carcinoma cell line FaDu (ATCC, origin head-and-neck cancer) were used. Cells were trypsinized and seeded for colony formation assay in 78 cm2 plates. Twenty-four hours after plating cells were treated with celecoxib (10 μM) for 48 hours and
Radiosensitization of tumor cells and normal cells by celecoxib
Celecoxib pretreatment in a clinical relevant dose of 10 μM led to a clear radiosensitization in the human bronchial adenocarcinoma cell line A549 (surviving fraction at 2 Gy (SF2) = 0.57 vs. 0.39 in presence of celecoxib, dose enhancement rate = 1.46) (Fig. 1a). Likewise, the normal fibroblast cell strain HSF7 (SF2 = 0.42 vs. 0.16) and the colon carcinoma cell line HCT116 (SF2 = 0.72 vs. 0.55) responded to celecoxib treatment with a clear radiosensitization (Fig. 1c, e). In contrast, the human
Discussion
The data presented herein clearly demonstrate a differential effect of combined celecoxib/radiation treatment on clonogenic survival of human tumor cells and normal fibroblasts in vitro. Unlike in the bronchial cancer cell line A549, the colon carcinoma cell line HCT116 and normal fibroblasts responded with a marked radiosensitization, the head-and-neck tumor cell line FaDu as well as the tumorigenic, transformed fibroblast line HH4dd did not respond. These differential effects seem to be
References (52)
- et al.
Suppression of Peutz-Jeghers polyposis by inhibition of cyclooxygenase-2
Gastroenterology
(2004) - et al.
Topical application of a selective cyclooxygenase inhibitor suppresses UVB mediated cutaneous inflammation
Prostaglandins Other Lipid Mediat
(2000) Cyclooxygenase-2 (COX-2) enzyme inhibitors as potential enhancers of tumor radioresponse
Semin Radiat Oncol
(2001)- et al.
Effects of the selective COX-2 inhibitors celecoxib and rofecoxib on human vascular cells
Biochem Pharmacol
(2004) - et al.
Inhibitors of cyclo-oxygenase 2: A new class of anticancer agents?
Lancet Oncology
(2003) - et al.
Prostaglandin E2 regulates cell migration via the intracellular activation of the epidermal growth factor receptor
J Biol Chem
(2003) - et al.
Radioresistance of K-Ras mutated human tumor cells is mediated through EGFR-dependent activation of PI3K-AKT pathway
Radiother Oncol
(2005) - et al.
Radiation-induced epidermal growth factor receptor nuclear import is linked to activation of DNA-dependent protein kinase
J Biol Chem
(2005) - et al.
Cyclooxygenase-2 (COX-2)-dependent and -independent anticarcinogenic effects of celecoxib in human colon carcinoma cells
Biochem Pharmacol
(2004) - et al.
Inhibition of radiation-induced EGFR nuclear import by C225 (Cetuximab) suppresses DNA-PK activity
Radiother Oncol
(2005)
Physical interaction between epidermal growth factor receptor and DNA-dependent protein kinase in mammalian cells
J Biol Chem
In vitro enhancement of tumor cell radiosensitivity by a selective inhibitor of cyclooxygenase-2 enzyme: mechanistic considerations
Int J Radiat Oncol Biol Phys
Inhibition of cyclooxygenase-2 activity by celecoxib does not lead to radiosensitization of human prostate cancer cells in vitro
Radiother Oncol
Non-homologous end joining requires that the DNA-PK complex undergo an autophosphorylation-dependent rearrangement at DNA ends
J Biol Chem
Cell cycle dependence of DNA-dependent protein kinase phosphorylation in response to DNA double strand breaks
J Biol Chem
Inhibition of DNA repair as a mechanism of enhanced radioresponse of head and neck carcinoma cells by a selective cyclooxygenase-2 inhibitor, celecoxib
Int J Radiat Oncol Biol Phys
Celecoxib but not rofecoxib inhibits the growth of transformed cells in vitro
Clin Cancer Res
Differential effects of selective COX-2 inhibitors on cell cycle regulation and proliferation of glioblastoma cell lines
Cancer Biol Ther
A pilot study of use of the cyclooxygenase-2 inhibitor celecoxib in recurrent prostate cancer after definitive radiation therapy or radical prostatectomy
BJU Int
A phase I clinical trial of thoracic radiotherapy and concurrent celecoxib for patients with unfavorable performance status inoperable/unresectable non-small cell lung cancer
Clin Cancer Res
Chemotherapy induces the expression of cyclooxygenase-2 in non-small cell lung cancer
Clin Cancer Res
Enhancing radiotherapy with cyclooxygenase-2 enzyme inhibitors: A rational advance?
J Natl Cancer Inst
Improvement of radiotherapy or chemoradiotherapy by targeting COX-2 enzyme
Oncology (Williston Park)
Anti-cancer effects of COX-2 inhibitors and their correlation with angiogenesis and invasion in gastric cancer
World J Gastroenterol
The cyclooxygenase-2 inhibitor celecoxib blocks phosphorylation of Akt and induces apoptosis in human cholangiocarcinoma cells
Mol Cancer Ther
Forkhead box transcription factor FOXO3a regulates estrogen receptor alpha expression and is repressed by the Her-2/neu/phosphatidylinositol 3-kinase/Akt signaling pathway
Mol Cell Biol
Cited by (0)
Supported by Deutsche Krebshilfe Grant 106401, the National Institutes of Health (NIH) Grant CA06294 and National Cancer Institute (NCI) Cancer Center Core Grant CA16672.
Conflicts of interest: none.