Cyclooxygenase-2 (COX-2) enzyme inhibitors as potential enhancers of tumor radioresponse

Molecular mechanisms of resveratrol as chemo and radiosensitizer in cancer

One of the primary diseases that cause death worldwide is cancer. Cancer cells can be intrinsically resistant or acquire resistance to therapies and drugs used for cancer treatment through multiple mechanisms of action that favor cell survival and proliferation, becoming one of the leading causes of treatment failure against cancer. A promising strategy to overcome chemoresistance and radioresistance is the co-administration of anticancer agents and natural compounds with anticancer properties, such as the polyphenolic compound resveratrol (RSV). RSV has been reported to be able to sensitize cancer cells to chemotherapeutic agents and radiotherapy, promoting cancer cell death. This review describes the reported molecular mechanisms by which RSV sensitizes tumor cells to radiotherapy and chemotherapy treatment.

Modern Stereotactic Radiotherapy for Brain Metastases from Lung Cancer: Current Trends and Future Perspectives Based on Integrated Translational Approaches

Brain metastases (BMs) represent the most frequent metastatic event in the course of lung cancer patients, occurring in approximately 50% of patients with non-small-cell lung cancer (NSCLC) and in up to 70% in patients with small-cell lung cancer (SCLC). Thus far, many advances have been made in the diagnostic and therapeutic procedures, allowing improvements in the prognosis of these patients. The modern approach relies on the integration of several factors, such as accurate histological and molecular profiling, comprehensive assessment of clinical parameters and precise definition of the extent of intracranial and extracranial disease involvement. The combination of these factors is pivotal to guide the multidisciplinary discussion and to offer the most appropriate treatment to these patients based on a personalized approach. Focal radiotherapy (RT), in all its modalities (radiosurgery (SRS), fractionated stereotactic radiotherapy (SRT), adjuvant stereotactic radiotherapy (aSRT)), is the cornerstone of BM management, either alone or in combination with surgery and systemic therapies. We review the modern therapeutic strategies available to treat lung cancer patients with brain involvement. This includes an accurate review of the different technical solutions which can be exploited to provide a "state-of-art" focal RT and also a detailed description of the systemic agents available as effective alternatives to SRS/SRT when a targetable molecular driver is present. In addition to the validated treatment options, we also discuss the future perspective for focal RT, based on emerging clinical reports (e.g., SRS for patients with many BMs from NSCLC or SRS for BMs from SCLC), together with a presentation of innovative and promising findings in translational research and the combination of novel targeted agents with SRS/SRT.

The COX-2 inhibitor NS398 selectively sensitizes hypoxic HeLa cells to ionising radiation by mechanisms both dependent and independent of COX-2

It is widely accepted that the hypoxic nature of solid tumors contribute to their resistance to radiation therapy. There is increasing evidence that cyclooxygenase-2 (COX-2) contributes to increased resistance of tumors to radiation therapy. Several studies demonstrate that combination of COX-2 selective inhibitors with radiation therapy selectively enhances radio responsiveness of tumor cells. However, the majority of these studies utilised suprapharmacological concentrations under normoxic conditions only. Furthermore, the mechanism by which these agents act remain largely unclear. Therefore, the aim of this study was to determine the impact of COX-2 selective inhibitors on both normoxic and hypoxic radiosensitivity in vitro and the mechanisms underlying this. Because of the close, reciprocal relationship between COX-2 and p53 we investigated their contribution to radioresistance. To achieve this we exposed HeLa, MCF-7 and MeWo cells to the COX-2 selective inhibitor, NS398 (10μM). NS398 (10μM) selectively sensitized hypoxic HeLa and MCF-7 but not MeWo cells to ionising radiation (5 Gy). Furthermore, while knockdown of COX-2 with siRNA did not affect either normoxic radiosensitivity in HeLa cells, the radiosensitisation observed with NS398 was lost suggesting both COX-2 dependent and independent mechanisms. We also show that ionising radiation at 5 Gy results in phosphorylation of p53 at serine 15, a key phosphorylation site for p53-mediated apoptosis, and that hypoxia attenuates this phosphorylation. Attenuated phosphorylation of p53 under hypoxic conditions may therefore contribute to hypoxic radioresistance. We also show that NS398 selectively phosphorylates p53 under hypoxic conditions following irradiation at 5 Gy. p53 phosphorylation could be an underlying mechanism by which this agent and other COX-2 inhibitors sensitize tumors to radiation therapy.

Cyclooxygenase-2 inhibitors delay relapse and reduce Prostate Specific Antigen (PSA) velocity in patients treated with radiotherapy for nonmetastatic prostate cancer: a pilot study

Introduction

A common treatment for localized prostate cancer (PCa) is radiotherapy; however, effectiveness is hampered because of toxicities and tumor resistance. Cyclooxygenase-2 (COX-2) inhibitors have been identified as potential agents that could improve treatment outcomes and have demonstrated ability to increase the radiosensitivity of many human carcinomas. This retrospective human study aims to investigate the ability of COX-2 inhibitors, celecoxib, and meloxicam, to improve treatment outcomes after radiotherapy.

Methods

Prostate Specific Antigen (PSA) data of eligible patients were obtained from Genesis Cancer Care, Southport, Australia. The primary outcome was the percentage of patients in each group that had reached biochemical relapse at two and five years after treatment. Secondary outcomes included time to biochemical relapse and PSA velocity.

Results

At two and five years after treatment, both the celecoxib (6.7%, 18.3%) and meloxicam (0.0%, 18.9%) showed lower relapse rates than the control (8.6%, 31.0%). Although not statistically significant, these results are clinically significant. In addition, the two treatment groups were found to increase the time to relapse, 46.20 months for celecoxib and 54.15 months for meloxicam, compared with the control group, 35.53 months. A similar trend was shown for PSA velocity with both treatment groups demonstrating lower PSA velocities compared with control.

Conclusions

This study provides further evidence to the potential for COX-2 inhibitors to address gaps in localizedz PCa treatment by demonstrating high clinical significance for the use of celecoxib and meloxicam. Further research should be conducted including larger retrospective studies and prospective studies to fully evaluate the benefits of COX-2 inhibitors in combination with radiotherapy for PCa.

Not Only Redox: The Multifaceted Activity of Cerium Oxide Nanoparticles in Cancer Prevention and Therapy

Much information is accumulating on the effect of cerium oxide nanoparticles (CNPs) as cell-protective agents, reducing oxidative stress through their unique ability of scavenging noxious reactive oxygen species via an energy-free, auto-regenerative redox cycle, where superoxides and peroxides are sequentially reduced exploiting the double valence (Ce³⁺/Ce⁴⁺) on nanoparticle surface. In vitro and in vivo studies consistently report that CNPs are responsible for attenuating and preventing almost any oxidative damage and pathology. Particularly, CNPs were found to exert strong anticancer activities, helping correcting the aberrant homeostasis of cancer microenvironment, normalizing stroma-epithelial communication, contrasting angiogenesis, and strengthening the immune response, leading to reduction of tumor mass in vivo. Since these homeostatic alterations are of an oxidative nature, their relief is generally attributed to CNPs redox activity. Other studies however reported that CNPs exert selective cytotoxic activity against cancer cells and sensitize cancer cells to chemotherapy- and radiotherapy-induced apoptosis: such effects are hardly the result of antioxidant activity, suggesting that CNPs exert such important anticancer effects through additional, non-redox mechanisms. Indeed, using Sm-doped CNPs devoid of redox activity, we could recently demonstrate that the radio-sensitizing effect of CNPs on human keratinocytes is independent from the redox switch. Mechanisms involving particle dissolution with release of toxic Ce⁴⁺ atoms, or differential inhibition of the catalase vs. SOD-mimetic activity with accumulation of H₂O₂ have been proposed, explaining such intriguing findings only partially. Much effort is urgently required to address the unconventional mechanisms of the non-redox bioactivity of CNPs, which may provide unexpected medicinal tools against cancer.

Recent advances in arsenic trioxide encapsulated nanoparticles as drug delivery agents to solid cancers

Since arsenic trioxide was first approved as the front line therapy for acute promyelocytic leukemia 25 years ago, its anti-cancer properties for various malignancies have been under intense investigation. However, the clinical successes of arsenic trioxide in treating hematological cancers have not been translated to solid cancers. This is due to arsenic's rapid clearance by the body's immune system before reaching the tumor site. Several attempts have henceforth been made to increase its bioavailability toward solid cancers without increasing its dosage albeit without much success. This review summarizes the past and current utilization of arsenic trioxide in the medical field with primary focus on the implementation of nanotechnology for arsenic trioxide delivery to solid cancer cells. Different approaches that have been employed to increase arsenic's efficacy, specificity and bioavailability to solid cancer cells were evaluated and compared. The potential of combining different approaches or tailoring delivery vehicles to target specific types of solid cancers according to individual cancer characteristics and arsenic chemistry is proposed and discussed.

Celecoxib mitigates genotoxicity induced by ionizing radiation in human blood lymphocytes

Ionizing radiation causes DNA damage and chromosome abbreviations on normal cells. The radioprotective effect of celecoxib (CLX) was investigated against genotoxicity induced by ionizing radiation in cultured human blood lymphocytes. Peripheral blood samples were collected from human volunteers and were incubated at different concentrations at 1, 5, 10 and 50 μM of CLX for two hours. At each dose point, the whole blood was exposed in vitro to 150 cGy of X-ray, and then the lymphocytes were cultured with mitogenic stimulation to determine the micronucleus frequency in cytokinesis blocked binucleated lymphocytes. Incubation of the whole blood with CLX exhibited a significant decrease in the incidence of micronuclei in lymphocytes induced by ionizing radiation, as compared with similarly irradiated lymphocytes without CLX treatment. The maximum reduction on the frequency of micronuclei was observed at 50 μM of CLX (65% decrease). This data may have an important possible application for the protection of human lymphocytes from the genetic damage induced by ionizing irradiation in human exposed to radiation.

Therapeutic response to a novel enzyme-targeting radiosensitization treatment (Kochi Oxydol-Radiation Therapy for Unresectable Carcinomas) in patients with recurrent breast cancer

Linear accelerator-based radiotherapy has little effect on the majority of locally advanced neoplasms. Thus, the novel radiosensitizer Kochi Oxydol Radiation Therapy for Unresectable Carcinomas, Type II (KORTUC II), which contains hydrogen peroxide and sodium hyaluronate, was developed. The effectiveness of KORTUC II for the treatment of chemotherapy-resistant supraclavicular lymph node metastases has been previously demonstrated. The present study evaluated the safety and effectiveness of KORTUC II in patients with recurrent breast cancer. A total of 20 patients (age range, 39–84 years) were enrolled in the study. The majority of patients underwent positron emission tomography (PET)-computed tomography (CT) examinations prior to and 1–7 months following KORTUC II treatment, and every 6 months thereafter when possible. The radiotherapy regimen was 2.75 Gy/fraction, 5 fractions/week, for 16–18 fractions, with a total radiation dose of 44.00–49.50 Gy (X-ray irradiation), or 4.00 Gy/fraction, 3 fractions/week, for 10–12 fractions, with a total radiation dose of 40.00–48.00 Gy (electron beam irradiation). The injection of 3–6 ml of the KORTUC II agent was initiated at the fifth radiotherapy fraction, and was performed twice/week under ultrasonographic guidance. The therapeutic effects were evaluated by PET-CT examinations prior and subsequent to KORTUC II treatment, which was observed to be well tolerated with minimal adverse effects. Of the 24 lesions presented by the 20 patients, 18 exhibited complete response, 5 partial response, 0 stable disease and 1 progressive disease. The overall survival rate was 100% at 1 year and 95% at 2 years. The mean duration of follow-up at the end of June 2014 was 51 months. Based on the results of the PET-CT studies conducted, KORTUC II treatment demonstrated marked therapeutic effects, with satisfactory treatment outcomes and acceptable adverse events.

Nuclear EGFR as a molecular target in cancer

The epidermal growth factor receptor (EGFR) has been one of the most targeted receptors in the field of oncology. While anti-EGFR inhibitors have demonstrated clinical success in specific cancers, most patients demonstrate either intrinsic or acquired resistance within one year of treatment. Many mechanisms of resistance to EGFR inhibitors have been identified, one of these being attributed to alternatively localized EGFR from the cell membrane into the cell's nucleus. Inside the nucleus, EGFR functions as a co-transcription factor for several genes involved in cell proliferation and angiogenesis, and as a tyrosine kinase to activate and stabilize proliferating cell nuclear antigen and DNA dependent protein kinase. Nuclear localized EGFR is highly associated with disease progression, worse overall survival in numerous cancers, and enhanced resistance to radiation, chemotherapy, and the anti-EGFR therapies gefitinib and cetuximab. In this review the current knowledge of how nuclear EGFR enhances resistance to cancer therapeutics is discussed, in addition to highlighting ways to target nuclear EGFR as an anti-cancer strategy in the future.

Predicting factors for locoregional failure of high-dose-rate brachytherapy for early-stage oral cancer

AIM

Brachytherapy is an alternative to surgery in the treatment of the early stages of oral tongue cancer. The aim of this retrospective study was to analyze the clinical risk factors and possible candidate biomarkers of local and regional tumor control.

PATIENTS & METHODS

Twenty-four patients were treated between the years 2001 and 2010. Median follow-up was 37.4 months. Correlation between disease-free survival and clinical stage, tumor grade, resection margin, depth of invasion, and p16, EGF receptor, NF-κB, HIF-1α, HER2, Ku-80, COX-2 and VEGF expression was evaluated.

RESULTS

The estimated 5-year local control was 81% and locoregional control was 62%. Depth of tumor invasion (p = 0.018) and higher VEGF expression (p = 0.016) were significantly predictive for worse disease-free survival in Cox multivariate analysis.

CONCLUSION

Intensity of VEGF expression and depth of tumor invasion may be significantly negative predictors of disease-free survival in tongue cancer patients treated by brachytherapy alone. Predictive value of VEGF deserves evaluation in larger studies.

Plasma levels of vascular endothelial growth factor during and after radiotherapy in combination with celecoxib in patients with advanced head and neck cancer

Celebrex and radiotherapy in advanced head and neck cancer. This phase I dose-escalation study seeks to determine the phase II recommended dose of cyclooxygenase type 2 (COX-2) inhibitor in patients with locally advanced squamous cell head and neck (H&N) cancer, treated with accelerated radiotherapy. Anti-vasculogenic effect of this treatment on serum vascular endothelial growth factor (VEGF) is examined. Patients were irradiated with curative intent (72Gy in 6weeks). Celecoxib was administered throughout the radiotherapy course. Serum VEGF level were tested during radiotherapy and in follow-up. Tumor specimens were stained to quantify the COX-2 expression. Thirty-two patients completed the treatment. The dose of celecoxib was escalated (200, 400 and 800mg bid, then de-escalated to 600mg bid). The acute toxicity related to the treatment in the first and second cohort did not reach grade III; in the third cohort three patients had grade III radiation toxicity and one had celecoxib-related toxicity. In the last fourth cohort the toxicity was acceptable. Significant VEGF level drop (p=0.011) was found between radiation day 1 and post-treatment visit. Significant decrease (p=0.022) of the VEGF level was shown in patients with high COX-2 expression in the tumor. Phase II recommended dose of celecoxib combined with accelerated radiotherapy in advanced H&N cancer was 600mg bid. A significant decrease of the post-treatment serum VEGF level compared to the initial level was noticed only in patients with high COX-2 expression in tumors.

Estrogen-dependent prognostic significance of cyclooxygenase-2 expression in early-stage invasive breast cancers treated with breast-conserving surgery and radiation

PURPOSE

To evaluate the prognostic significance of cyclooxygenase-2 (COX-2) in breast cancer patients treated with conservative surgery and radiation therapy (CS+RT).

METHODS AND MATERIALS

Between 1975 and 2003, we retrieved specimens from 504 breast cancer patients treated with CS+RT. The specimens were constructed into tissue microarrays processed and stained for estrogen receptor (ER), progesterone receptor, Her2/neu, and COX-2. Each core was scored as positive or negative. All data including demographics, clinical, pathologic, staging, and outcome variables were entered into a computerized database.

RESULTS

Expression of COX-2 was positive in 58% of cases and correlated with younger age (p = 0.01) and larger tumor size (p = 0.001). Expression of COX-2 was predictive of local relapse (relative risk[RR], 3.248; 95% confidence interval [CI], 1.340-7.871; p = 0.0091), distant metastasis (RR, 2.21; 95% CI, 1.259-3.896; p = 0.0058), and decreased survival (RR, 2.321; 95% CI, 1.324-4.071; p = 0.0033). Among ER-positive patients, COX-2 expression was predictive of worse local control (85% vs. 93%, p = 0.04), distant metastasis (75% vs. 95%, p = 0.002) and worse survival (65% vs. 94%, p = 0.002). Among ER-negative tumors COX-2 expression was not significantly correlated with local control (87 vs. 95%, p = 0.12), distant metastasis (73% vs. 78%, p = 0.39), or survival (77% vs. 87%, p = 0.15).

CONCLUSIONS

In breast cancer patients treated with CS+RT, COX-2 expression is associated with younger age, larger tumor size, worse local control, distant metastasis, and worse overall survival. The significance is limited to hormone receptor-positive tumors, consistent with the known effect of COX-2/PGE2 on aromatase activity. Use of COX-2 inhibitors in estrogen-dependent breast cancers warrants further investigation.

Radiosensitization of human glioma cells by cyclooxygenase-2 (COX-2) inhibition: independent on COX-2 expression and dependent on the COX-2 inhibitor and sequence of administration

PURPOSE

Patients with a malignant glioma have a very poor prognosis. Cyclooxygenase-2 (COX-2) protein is regularly upregulated in gliomas and might be a potential therapeutic target. The effects of three selective COX-2 inhibitors were studied on three human glioma cell lines.

MATERIALS AND METHODS

The selective COX-2 inhibitors NS-398, Celecoxib and Meloxicam and three human glioma cell lines (D384, U251 and U87) were used. Cell growth was assessed by a proliferation assay, the interaction with radiation (0 - 6 Gy) was studied using the clonogenic assay and cell cycle distribution was determined by FACS (fluorescence-activated cell sorting) analysis.

RESULTS

All COX-2 inhibitors reduced proliferation of the glioma cell lines irrespective of their COX-2 expression level. Incubation with 200 microM NS-398 24 h before radiation enhanced radiation-induced cell death of D384 cells and 750 microM Meloxicam resulted in radiosensitization of D384 and U87 cells. No radiosensitization was observed with COX-2 inhibitor administration after radiotherapy. Treatment of D384 with NS-398 (200 microM) or Celecoxib (50 microM) and U87 with NS-398 (200 microM) after radiation resulted even in radioprotection.

CONCLUSIONS

Effectiveness of COX-2 inhibitors on cell proliferation and radio-enhancement was independent of COX-2 protein expression. The sequence of COX-2 inhibitor addition and irradiation is very important.

Celecoxib induced tumor cell radiosensitization by inhibiting radiation induced nuclear EGFR transport and DNA-repair: a COX-2 independent mechanism

PURPOSE

The purpose of the study was to elucidate the molecular mechanisms mediating radiosensitization of human tumor cells by the selective cyclooxygenase (COX)-2 inhibitor celecoxib.

METHODS AND MATERIALS

Experiments were performed using bronchial carcinoma cells A549, transformed fibroblasts HH4dd, the FaDu head-and-neck tumor cells, the colon carcinoma cells HCT116, and normal fibroblasts HSF7. Effects of celecoxib treatment were assessed by clonogenic cell survival, Western analysis, and quantification of residual DNA damage by gammaH(2)AX foci assay.

RESULTS

Celecoxib treatment resulted in a pronounced radiosensitization of A549, HCT116, and HSF7 cells, whereas FaDu and HH4dd cells were not radiosensitized. The observed radiosensitization could neither be correlated with basal COX-2 expression pattern nor with basal production of prostaglandin E2, but was depended on the ability of celecoxib to inhibit basal and radiation-induced nuclear transport of epidermal growth factor receptor (EGFR). The nuclear EGFR transport was strongly inhibited in A549-, HSF7-, and COX-2-deficient HCT116 cells, which were radiosensitized, but not in FaDu and HH4dd cells, which resisted celecoxib-induced radiosensitization. Celecoxib inhibited radiation-induced DNA-PK activation in A549, HSF7, and HCT116 cells, but not in FaDu and HH4dd cells. Consequentially, celecoxib increased residual gammaH2AX foci after irradiation, demonstrating that inhibition of DNA repair has occurred in responsive A549, HCT116, and HSF7 cells only.

CONCLUSIONS

Celecoxib enhanced radiosensitivity by inhibition of EGFR-mediated mechanisms of radioresistance, a signaling that was independent of COX-2 activity. This novel observation may have therapeutic implications such that COX-2 inhibitors may improve therapeutic efficacy of radiation even in patients whose tumor radioresistance is not dependent on COX-2.

Cyclooxygenase-2 expression in human irradiated uveal melanomas

AIM

Previous studies have shown that radiotherapy is a stimulus for cyclooxygenase-2 (COX-2) expression and that use of COX-2 inhibitors enhances the radio sensitivity of tumor cells. The objective of this study was to evaluate COX-2 expression, and its correlation with tumor regrowth after irradiation, in enucleated eyes with uveal melanomas.

METHODS

Fifteen tissue samples from patients who underwent enucleation after radiotherapy between 1988 and 2001 were used. Nine cases (60%) were enucleated because of tumor regrowth and six (40%) because of severe complications of radiotherapy. Specimens were immunostained for COX-2, and tumor cells were evaluated for specific cytoplasmic and granular immunostaining. COX-2 expression for these cases was compared with that in the previous study including 40 non-irradiated uveal melanoma cases. COX-2 expression was also correlated with tumor regrowth after radiotherapy.

RESULTS

Two cases (13.3%) were positive and thirteen (86.7%) were negative for COX-2 expression. One of the positive cases had been enucleated because of tumor regrowth and one because of radiotherapy complications. There was no relationship between tumor regrowth and COX-2 expression. COX-2 expression was significantly lower in irradiated cases than in non-irradiated cases in the previous study (p<0.001).

CONCLUSIONS

In contrast with studies showing an increase of COX-2 expression in other irradiated malignancies, irradiation was not a factor inducing COX-2 in uveal melanomas. Radiotherapy may, moreover, be a factor that reduces COX-2 expression in uveal melanomas.

Radiosensitizing potential of the selective cyclooygenase-2 (COX-2) inhibitor meloxicam on human glioma cells

The COX-2 protein is frequently overexpressed in human malignant gliomas. This expression has been associated with their aggressive growth characteristics and poor prognosis for patients. Targeting the COX-2 pathway might improve glioma therapy. In this study, the effects of the selective COX-2 inhibitor meloxicam alone and in combination with irradiation were investigated on human glioma cells in vitro. A panel of three glioma cell lines (D384, U87 and U251) was used in the experiments from which U87 cells expressed constitutive COX-2. The response to meloxicam and irradiation (dose-range of 0-6 Gy) was determined by the clonogenic assay, cell proliferation was evaluated by growth analysis and cell cycle distribution by FACS. 24-72 h exposure to 250-750 microM meloxicam resulted in a time and dose dependent growth inhibition with an almost complete inhibition after 24 h for all cell lines. Exposure to 750 microM meloxicam for 24 h increased the fraction of cells in the radiosensitive G(2)/M cell cycle phase in D384 (18-27%) and U251 (17-41%) cells. 750 microM meloxicam resulted in radiosensitization of D384 (DMF:2.19) and U87 (DMF:1.25) cells, but not U251 cells (DMF:1.08). The selective COX-2 inhibitor meloxicam exerted COX-2 independent growth inhibition and radiosensitization of human glioma cells.

Enhancement of glioblastoma radioresponse by a selective COX-2 inhibitor celecoxib: inhibition of tumor angiogenesis with extensive tumor necrosis

PURPOSE

Toward improved glioblastoma multiforme treatment, we determined whether celecoxib, a selective cyclooxygenase (COX)-2 inhibitor, could enhance glioblastoma radiosensitivity by inducing tumor necrosis and inhibiting tumor angiogenesis.

METHODS AND MATERIALS

U-87MG cells treated with celecoxib, irradiation, or both were assayed for clonogenic survival and angiogenic factor protein analysis (angiopoietin-1, angiopoietin-2, and vascular endothelial growth factor [VEGF]). In vivo, survival of mice intracranially implanted with U-87MG cells and treated with celecoxib and/or irradiation was monitored. Isolated tumors were assessed for tumor necrosis and tumor microvascular density by von Williebrand's factor (vWF) immunohistochemical staining.

RESULTS

Celecoxib (4 and 30 microM; 24, 48, and 72 h) enhanced U-87MG cell radiosensitivity by significantly reducing clonogenic survival of irradiated cells. Angiopoietin-1 and VEGF proteins were decreased, whereas angiopoietin-2 expression increased after 72 h of celecoxib alone and when combined with irradiation. In vivo, median survival of control mice intracranially implanted with U-87MG cells was 18 days. Celecoxib (100 mg/kg/day, 2 weeks) significantly extended median survival of irradiated mice (24 Gy total) from 34 to 41 days, with extensive tumor necrosis [24.5 +/- 8.6% of tumor region, compared with irradiation alone (2.7 +/- 1.8%)]. Tumor microvascular density was significantly reduced in combined celecoxib and irradiated tumors (52.5 +/- 2.9 microvessels per mm2 tumor region), compared with irradiated tumors alone (65.4 +/- 4.0 microvessels per mm2).

CONCLUSION

Celecoxib significantly enhanced glioblastoma radiosensitivity, reduced clonogenic survival, and prolonged survival of glioblastoma-implanted mice by inhibition of tumor angiogenesis with extensive tumor necrosis.

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) on prostate carcinoma cells in vitro.

MATERIALS AND METHODS

The influence of celecoxib (concentration range 5 to 75 microM) 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 microM) 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. Pre-treatment with celecoxib reduced the amount of PGE(2) 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.

Tumor radiosensitizers--current status of development of various approaches: report of an International Atomic Energy Agency meeting

PURPOSE

The International Atomic Energy Agency (IAEA) held a Technical Meeting of Consultants to (1) discuss a selection of relatively new agents, not those well-established in clinical practice, that operated through a variety of mechanisms to sensitize tumors to radiation and (2) to compare and contrast their tumor efficacy, normal tissue toxicity, and status of development regarding clinical application. The aim was to advise the IAEA as to which developing agent or class of agents would be worth promoting further, by supporting additional laboratory research or clinical trials, with the eventual goal of improving cancer control rates using radiotherapy, in developing countries in particular.

RESULTS

The agents under discussion included a wide, but not complete, range of different types of drugs, and antibodies that interfered with molecules in cell signaling pathways. These were contrasted with new molecular antisense and gene therapy strategies. All the drugs discussed have previously been shown to act as tumor cell radiosensitizers or to kill hypoxic cells present in tumors.

CONCLUSION

Specific recommendations were made for more preclinical studies with certain of the agents and for clinical trials that would be suitable for industrialized countries, as well as trials that were considered more appropriate for developing countries.

COX-2 inhibitors act as radiosensitizer in tumor treatment

Since cyclooxygenase-2 (COX-2) is overexpressed in malignant tissues, the COX-2 mediated signaling pathway has been recognized as potential target for therapeutic intervention. In most human tumors, COX-2 overexpression has been associated with tumor aggressiveness and poor clinical outcome. In vitro studies show inhibition of cell proliferation by selective COX-2 inhibitors alone, and enhancement of the response to irradiation. In vivo experimental reports demonstrate enhanced tumor response and impediment of tumor neovascularization following radiotherapy combined with COX-2 inhibition. Clinical studies on the combination of irradiation with COX-2 inhibitors are emerging. Taken together, the perspective for the combined approach of radiotherapy with COX-2 inhibition yields clinical significance since preclinical data demonstrate selective COX-2 inhibitors to act as radiosensitizer in tumor treatment.

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

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 microM), 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 (NFkappaB).

RESULTS

Celecoxib (10 and 50 microM, 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 NFkappaB and the radiation-induced NFkappaB in HN5 cells, suggesting that NFkappaB 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.

Chemosensitization and radiosensitization of tumors by plant polyphenols

The treatment of cancer with chemotherapeutic agents and radiation has two major problems: time-dependent development of tumor resistance to therapy (chemoresistance and radioresistance) and nonspecific toxicity toward normal cells. Many plant-derived polyphenols have been studied intently for their potential chemopreventive properties and are pharmacologically safe. These compounds include genistein, curcumin, resveratrol, silymarin, caffeic acid phenethyl ester, flavopiridol, emodin, green tea polyphenols, piperine, oleandrin, ursolic acid, and betulinic acid. Recent research has suggested that these plant polyphenols might be used to sensitize tumor cells to chemotherapeutic agents and radiation therapy by inhibiting pathways that lead to treatment resistance. These agents have also been found to be protective from therapy-associated toxicities. How these polyphenols protect normal cells and sensitize tumor cells to treatment is discussed in this review.

Expression of cyclooxygenase-2 and epidermal growth factor receptor in primary and recurrent glioblastoma multiforme

PURPOSE

To investigate the pattern and level of cyclooxygenase-2 (COX-2) expression in a series of high grade primary and recurrent glioblastoma multiforme (GBM) and correlation with time to recurrence and patients' survival following therapy. The relationship between COX-2 and epidermal growth factor receptor (EGFR) immunoreactivities was evaluated.

MATERIALS AND METHODS

Specimens of 14 primary and 14 recurrent GBMs (eight pairs) following surgery and full course radiation therapy were processed for immunostaining on COX-2 and EGFR. Tumor cell positivity was semi-quantitatively scored. COX-2 scores of the primary tumor and recurrence were correlated with the time to radiological tumor progression and patients' survival.

RESULTS

COX-2 positive tumor cells were disseminated throughout the tumor parenchyma. The intensity and pattern of COX-2 expression were heterogeneous, with predominant expression in areas surrounding tumor necrosis. Scoring of COX-2 positivity revealed values between 1 and 80% of the cells. Primary GBMs with COX-2 expression levels between 25% and 70% of the tumor cells showed a shorter time to radiological recurrence than GBMs with <10% COX-2 positive tumor cells (respectively, 219 +/- 50 and 382 +/- 77 days). No correlation was found between the COX-2 expression in the primary tumor and patients' survival (r (s) = -0.073) following therapy. No correlation was found either between COX-2 and EGFR immunoreactivity.

CONCLUSIONS

Immunohistochemical expression of COX-2 in GBM showed large variation. Hence, determination of COX-2 expression in tumor specimen for each individual might be relevant for selection of those patients, who could benefit from adjuvant therapy with selective COX-2 inhibitors.

A phase I clinical trial of thoracic radiotherapy and concurrent celecoxib for patients with unfavorable performance status inoperable/unresectable non-small cell lung cancer

OBJECTIVES

Preclinical observations that selective cyclooxygenase-2 inhibitors enhance in vitro cell radiosensitivity and in vivo tumor radioresponse led to clinical trials testing therapeutic efficacy of these agents. Our study was designed to determine whether the COX-2 inhibitor celecoxib could be safely administered in doses within those approved by the Food and Drug Administration when used concurrently with thoracic radiotherapy in patients with poor prognosis non-small cell lung cancer (NSCLC).

PATIENTS AND METHODS

The trial consisted of three cohorts of patients: (a) locally advanced NSCLC with obstructive pneumonia, hemoptysis, and/or minimal metastatic disease treated with 45 Gy in 15 fractions; (b) medically inoperable early-stage NSCLC treated with definitive radiation of 66 Gy in 33 fractions; and (c) patients who received induction chemotherapy but who were not eligible for concurrent chemoradiotherapy trials. These patients received 63 Gy in 35 fractions. Celecoxib was administered p.o. on a daily basis 5 days before and throughout the course of radiotherapy. Celecoxib doses were escalated from 200, 400, 600, to 800 mg/d given in two equally divided doses. Two to eight patients of each cohort were assigned to each dose level of celecoxib.

RESULTS

Forty-seven patients were enrolled in this protocol (19 in cohort I, 22 in cohort II, and 6 in cohort III). The main toxicities were grades 1 and 2 nausea and esophagitis, and they were independent of the dose of celecoxib or radiotherapy schedule. Only two patients in group II developed grade 3 pneumonitis 1 month after treatment, one on 200 mg, and the other on 400 mg celecoxib. Celecoxib-related toxicity developed in 3 of 47 patients: an uncontrolled hypertension in one patient on 800 mg celecoxib and hemorrhagic episodes in 2 patients (shoulder hematoma in one and hemoptysis in the other) on 200 mg celecoxib who were on warfarin for other medical reasons. Of 37 patients evaluable for tumor response, 14 had complete response, 13 partial responses, and 10 stable or progressive disease. The actuarial local progression-free survival was 66.0% at 1 year and 42.2% at 2 years following initiation of radiotherapy.

CONCLUSIONS

These results show that celecoxib can be safely administered concurrently with thoracic radiotherapy when given up to the highest Food and Drug Administration-approved dose of 800 mg/d, which we used. A maximal tolerated dose was not reached in this study. The treatment resulted in actuarial local progression-free survival of 66.0% at 1 year and 42.2% at 2 years, an encouraging outcome that warrants further assessment in a phase II/III trial.

Cyclooxygenase-2 Expression in Postmastectomy Chest Wall Relapse

PURPOSE

Cyclooxygenase-2 (COX-2) expression has been shown to be associated with radiation resistance, which theoretically could be overcome with the use of COX-2 inhibitors. The purpose of this study was to assess the prognostic significance and clinical correlations of COX-2 expression (COX) in a cohort of patients treated with radiation for postmastectomy chest wall relapse.

EXPERIMENTAL DESIGN

Between 1975 and 1999, 113 patients were treated for isolated postmastectomy chest wall relapse. All patients were treated with biopsy and/or excision of the chest wall recurrence followed by radiation therapy. Median follow-up was 10 years. All clinical data, including demographics, pathology, staging, receptor status, HER-2/neu status, and adjuvant therapy, were entered into a computerized database. Paraffin-embedded chest wall recurrence specimens were retrieved from 42 patients, of which 38 were evaluated, created into a tissue microarray, stained by immunohistochemical methods for COX, and graded 0 to 3+. A score of 2 to 3+ was considered positive.

RESULTS

Overall survival from original diagnosis for entire cohort was 44% at 10 years. Survival rate after chest wall recurrence was 28% at 10 years. The distant metastasis-free survival rate after chest wall recurrence was 40% at 10 years. Local-regional control of disease was achieved in 79% at 10 years after chest wall recurrence. COX was considered positive in 13 of 38 cases. COX was inversely correlated with estrogen receptor (P = 0.045) and progesterone receptor (P = 0.028), and positively correlated with HER-2/neu (P = 0.003). COX was also associated with a shorter time to postmastectomy chest wall relapse. The distant metastasis-free rate for COX-negative patients was 70% at 10 years, compared with 31% at 10 years for COX-2-positive patients (P = 0.029). COX positive had a poorer local-regional progression-free rate of 19% at 10 years, compared with 81% at 10 years for COX negative. This was of high statistical significance with a P value of 0.003.

CONCLUSIONS

Outcome following radiation therapy for postmastectomy chest wall relapse is relatively poor. Positive COX correlated with other markers of poor outcome, including a shorter time to local relapse, negative estrogen receptor/progesterone receptor, and positive Her-2/neu status. Positive COX correlated with higher distant metastasis and lower local-regional control of disease. If confirmed with larger studies, these data have implications with respect to the concurrent use of COX-2 inhibitors and radiation for postmastectomy chest wall relapse.

Molecular biological design of novel antineoplastic therapies

Novel therapies represent a new strategy for the development of anticancer agents. New targets derived from the knowledge of the molecular structure and genetic defects has been useful in developing anticancer drugs that prolong or stabilise the progression of tumours with minimal systemic toxicities. In this review, the mechanism of action and the most significant trials regarding monoclonal antibodies, tyrosine kinase inhibitors, angiogenesis and cyclooxygenase inhibitor-based therapies, farnesyl transferase inhibitors and proteasome inhibitors are discussed. The potential biological end points and toxicities are also described. In conclusion, novel therapies present a promising class of anticancer agents, acting through different mechanisms and offering a new perspective in the treatment of cancer.

Angiogenesis inhibitors: a rational strategy for radiosensitization in the treatment of non-small-cell lung cancer?

Angiogenesis is a precondition to invasion and metastasis for all solid tumors. Vascular endothelial growth factor (VEGF) and its family of receptors (VEGFR) play a critical role in cancer progression by promoting new blood vessel formation. Overexpression of VEGF and VEGFR has been correlated with poor prognosis in a variety of malignancies. In this era of targeted therapies for cancer, inhibiting angiogenesis through antiangiogenic and/or vascular targeting agents seems logical. Disturbing the angiogenesis process is an alternative or complementary strategy to inhibition of growth factor signaling. Blocking angiogenesis may enhance conventional anticancer treatments such as radiation therapy in situations where tumors are unresponsive to current antigrowth factor efforts. Compounds currently under investigation in cancer therapy include anti-VEGF/VEGFR antibodies, small molecule VEGFR tyrosine kinase inhibitors, antisense suppression of VEGF, immunotherapy, viral-directed targeting of VEGFR signaling, ribozymes, and various toxin conjugates. Preclinical investigations are exploring the benefits of combining angiogenic inhibitors with radiation. This article will provide an overview of these preclinical studies and the rationale for this therapeutic strategy in the treatment of non-small-cell lung cancer.

Multifaceted roles of cyclooxygenase-2 in lung cancer

Lung cancer is the leading cause of cancer death in the United States. Although the low 5-year survival rate (under 15%) has changed minimally in the last 25 years, new agents and combinations of agents that target tumor proliferation, invasion, and survival may lead to improvement in patient outcomes. There is evidence that cyclooxygenase-2 (COX-2) is overexpressed in lung cancer and promotes tumor proliferation, invasion, angiogenesis, and resistance to apoptosis. COX-2 inhibitors have been found to inhibit tumor growth in animal models and have demonstrated responses when combined with conventional therapy in phase II clinical trials. Further understanding of the mechanisms involved in COX-2-mediated tumorigenesis and its interaction with other molecules in lung cancer may lead to improved therapeutic strategies for this disease. In addition, delineation of how COX-2-dependent genes modulate the malignant phenotype will provide novel insights in lung cancer pathogenesis.

Tissue Microarray Analysis Reveals Prognostic Significance of COX-2 Expression for Local Relapse in T1???2N0 Larynx Cancer Treated with Primary Radiation Therapy

OBJECTIVE

The purpose of this analysis is to determine whether a significant correlation exists between cyclooxygenase-2 (COX-2) expression and local relapse in a large cohort of patients with T1 to 2N0 laryngeal cancer treated with primary radiation therapy.

METHODS AND MATERIALS

Clinical and molecular analyses were conducted on 123 patients with biopsy-proven T1 to 2N0 laryngeal cancer. Clinical prognostic factors included pretreatment hemoglobin, age, sex, race, T stage, tumor subsite, beam energy, biologically equivalent dose, therapy duration, and treatment date. Molecular prognostic factors included COX-2, p53, and Ki-67 expression. Expression levels were determined by immunohistochemistry on paraffin-embedded tissues arrayed on tissue microarrays. Multivariate analysis was done with the Cox proportional hazards model.

RESULTS

Thirty-two patients have locally relapsed, for an actuarial 5-year local relapse-free rate of 70.4%. On multivariate analysis, positive COX-2 expression predicted local relapse after radiation therapy. The relative risk (RR) for local relapse with COX-2 positivity was 2.57 (95% CI, 1.21-5.47; P = .01). Other prognostic factors for local relapse included negative Ki-67 expression (RR = 5.72; 95% CI, 2.04-16.1; P < .001), T2 stage (RR = 2.98; 95% CI, 1.39-6.38; P = .005), and therapy duration greater than 43 days (RR = 6.04; 95% CI, 1.37-26.7; P = .02).

CONCLUSIONS

Positive COX-2 expression predicts for local relapse in T1 to 2N0 larynx cancer in a multivariate model. This relationship may have potential therapeutic implications regarding the use of COX-2 inhibitors during radiation therapy for optimal outcome.

Prognostic significance of cyclooxygenase-2 in oropharyngeal squamous cell carcinoma

PURPOSE

To determine the relative prognostic significance of cyclooxygenase (COX)-2 expression in patients with oropharyngeal squamous cell carcinoma (SCC).

EXPERIMENTAL DESIGN

This retrospective cohort study included 82 patients with SCC referred to the Department of Therapeutic Radiology at Yale-New Haven Hospital (Connecticut) between 1980 and 1999 who were treated with primary external beam radiotherapy or gross total surgical resection and postoperative radiotherapy. A microarray of archival tumor tissue was constructed and stained with monoclonal antibodies directed against COX-2 and scored for intensity by a pathologist blinded to the clinical outcomes of the patients. COX-2 immunoreactivity and clinicopathological data were analyzed with respect to survival endpoints using bivariate and multivariate techniques.

RESULTS

Frequency of COX-2 overexpression was 45%. In multivariate analysis, COX-2 positivity predicted poor 3-year survival (P = 0.02; odds ratio = 0.41; 95% confidence interval, 0.20-0.84). Increasing age was significantly associated with increased 3-year survival (P = 0.03; odds ratio = 1.04; 95% confidence interval, 1.004-1.09). Positive COX-2 status trended toward predicting decreased 3-year disease-free survival.

CONCLUSIONS

COX-2 was the most important predictor of poor survival in this patient cohort. In patients with oropharyngeal SCC treated with external-beam radiation therapy, overexpression of COX-2 may affect clinical outcome, and COX-2 may therefore prove valuable both as a prognostic factor and as a therapeutic target.

C225 antiepidermal growth factor receptor antibody enhances the efficacy of docetaxel chemoradiotherapy

PURPOSE

C225 anti-EGFR (epidermal growth factor receptor) antibody has been shown to enhance tumor response to radiation and a number of chemotherapeutic agents. Because of increased use of concurrent chemoradiotherapy in cancer treatment, it is important to determine whether C225 enhances also the antitumor efficacy of radiation when combined with chemotherapy. This study assessed the effect of C225 on tumor response when combined with docetaxel plus single or fractionated radiation.

METHODS AND MATERIALS

MDA468 human adenocarcinoma and A431 human epidermoid carcinoma cells growing as xenografts in the right hind leg of nude mice were used. Mice bearing 8-mm tumors were treated with C225 antibody at a dose of 1 mg given i.p. once, twice, or three times 3 days apart, 10 or 30 mg/kg docetaxel given i.v., and/or local tumor irradiation of 8 or 10 Gy single dose or fractionated irradiation consisting of 2 Gy daily for 5 days. When all three agents were combined, C225 was given 6 h before or 18 h after docetaxel, and radiation was given 24 h after docetaxel. The treatment end point was tumor growth delay.

RESULTS

C225 enhanced the antitumor efficacy of docetaxel, local tumor irradiation, and docetaxel combined with radiation. The response of both MDA468 and A431 carcinomas was enhanced. The enhancement factors ranged from 1.19 to 8.52, the degree of the enhancement depending on experimental conditions such as administration of multiple vs. single dose C225 or single or fractionated irradiation. C225 given twice or 3 times was more effective than when administered as a single dose. The effect of C225 was more pronounced when combined with single than fractionated irradiation with or without docetaxel. The triple-agent therapy was more effective than a single agent or double combination therapies, expressed by both increased tumor growth delay and the rate of tumor cure.

CONCLUSIONS

Our results show that C225 anti-EGFR antibody is a potent enhancer of tumor response to docetaxel or radiation as single agents, and to docetaxel when combined with radiation. Thus, these findings provide strong preclinical evidence in support of combination of anti-EGFR blockade with chemoradiotherapy.

Multiple roles of COX-2 in tumor angiogenesis: a target for antiangiogenic therapy

Angiogenesis is required for multistage carcinogenesis. The inducible enzyme cyclooxygenase-2 (COX-2) is an important mediator of angiogenesis and tumor growth. COX-2 expression occurs in a wide range of preneoplastic and malignant conditions; and the enzyme has been localized to the neoplastic cells, endothelial cells, immune cells, and stromal fibroblasts within tumors. The proangiogenic effects of COX-2 are mediated primarily by three products of arachidonic metabolism: thromboxane A(2) (TXA(2)), prostaglandin E(2) (PGE(2)), and prostaglandin I(2) (PGI(2)). Downstream proangiogenic actions of these eicosanoid products include: (1) production of vascular endothelial growth factor; (2) promotion of vascular sprouting, migration, and tube formation; (3) enhanced endothelial cell survival via Bcl-2 expression and Akt signaling; (4) induction of matrix metalloproteinases; (5) activation of epidermal growth factor receptor-mediated angiogenesis; and (6) suppression of interleukin-12 production. Selective inhibition of COX-2 activity has been shown to suppress angiogenesis in vitro and in vivo. Because these agents are safe and well tolerated, selective COX-2 inhibitors could have clinical utility as antiangiogenic agents for cancer prevention, as well as for intervention in established disease alone or in combination with chemotherapy, radiation, and biological therapies.

Expression of cyclooxygenase-2 in canine epithelial nasal tumors

Cyclooxygenase-2 (COX-2) is an enzyme upregulated in some human and animal tumors. Enzymatic products are associated with tumorigenic activities. Given the poor response of canine nasal tumors to radiation, we considered the possibility that some of this resistance may be associated with COX-2 expression. To test this, 21 formalin-fixed, paraffin-embedded, and archived biopsy samples from canine epithelial nasal tumors were analyzed for COX-2 expression using immunohistochemistry. The biopsies were collected from dogs prior to radiation therapy. COX-2 expression was present in 17 of 21 (81%) tumors. The expression was observed in several different tumor types, including nasal carcinomas, adenocarcinomas, and squamous cell carcinomas. Samples from five control dogs without nasal neoplasia were also analyzed for COX-2 staining. These specimens were characterized by varying degrees of lymphoplasmacytic rhinitis with scattered regions of COX-2 positive respiratory epithelial and stromal cells. Whether the intensity and distribution of COX-2 expression in nasal tumors can be used as a prognostic marker requires further investigation. A combination therapy of irradiation and a selective COX-2 inhibitor appears worthy of clinical investigation in the treatment of canine epithelial nasal tumors.

A Sense of Danger from Radiation1

Tissue damage caused by exposure to pathogens, chemicals and physical agents such as ionizing radiation triggers production of generic "danger" signals that mobilize the innate and acquired immune system to deal with the intrusion and effect tissue repair with the goal of maintaining the integrity of the tissue and the body. Ionizing radiation appears to do the same, but less is known about the role of "danger" signals in tissue responses to this agent. This review deals with the nature of putative "danger" signals that may be generated by exposure to ionizing radiation and their significance. There are a number of potential consequences of "danger" signaling in response to radiation exposure. "Danger" signals could mediate the pathogenesis of, or recovery from, radiation damage. They could alter intrinsic cellular radiosensitivity or initiate radioadaptive responses to subsequent exposure. They may spread outside the locally damaged site and mediate bystander or "out-of-field" radiation effects. Finally, an important aspect of classical "danger" signals is that they link initial nonspecific immune responses in a pathological site to the development of specific adaptive immunity. Interestingly, in the case of radiation, there is little evidence that "danger" signals efficiently translate radiation-induced tumor cell death into the generation of tumor-specific immunity or normal tissue damage into autoimmunity. The suggestion is that radiation-induced "danger" signals may be inadequate in this respect or that radiation interferes with the generation of specific immunity. There are many issues that need to be resolved regarding "danger" signaling after exposure to ionizing radiation. Evidence of their importance is, in some areas, scant, but the issues are worthy of consideration, if for no other reason than that manipulation of these pathways has the potential to improve the therapeutic benefit of radiation therapy. This article focuses on how normal tissues and tumors sense and respond to danger from ionizing radiation, on the nature of the signals that are sent, and on the impact on the eventual consequences of exposure.

Biologic premises of combined radiation therapy and chemotherapy in lung cancer

When radiation is combined with concurrent chemotherapy, independent cell kill and enhancement of tumor response may be expected. On the other hand, spatial cooperation may be the main rationale for sequential combination of the two modalities. Among many new agents being investigated, radiation-activated antitumor prodrugs have a therapeutic potential as a new method to effectively combine radiation and concurrent chemotherapy.

Potentiation of tumor response to radiation or chemoradiation by selective cyclooxygenase-2 enzyme inhibitors

Cyclooxygenase-2 (COX-2) is an enzyme expressed primarily in pathologic states, such as inflammatory disorders and cancer, where it mediates prostaglandin production. Its overexpression is associated with more aggressive biologic tumor behavior and adverse patient outcome. Increasing evidence shows that agents that selectively inhibit COX-2 enhance tumor response to radiation or chemotherapeutic agents. This article gives an overview of some of this evidence. In addition, we describe new results showing that celecoxib, a selective COX-2 inhibitor, enhanced response of A431 human tumor xenografts in nude mice to radiation by an enhancement factor (EF) of 1.43 and to the chemotherapeutic agent docetaxel by an EF of 2.07. Celecoxib also enhanced tumor response when added to the combined docetaxel plus radiation treatment (EF = 2.13). Further experiments showed that selective COX-2 inhibitors enhanced tumor cell sensitivity to ionizing radiation, involving inhibition of cellular repair from radiation damage and cell cycle redistribution as mechanisms for some cell types. The results show that selective COX-2 inhibitors have the potential to improve tumor radiotherapy or radiochemotherapy, and this therapeutic strategy is currently under clinical testing.

Improvement strategies for molecular targeting: cyclooxygenase-2 inhibitors as radiosensitizers for non-small cell lung cancer

Cyclooxygenase-2 (COX-2) is an enzyme involved in prostaglandin production in pathologic states such as inflammatory processes and cancer. The enzyme is often overexpressed in premalignant lesions and various cancers, including cancer of the lung. Inhibition of this enzyme with selective COX-2 inhibitors was found to enhance tumor response to radiation in preclinical studies, suggesting that these agents can improve the response of various cancers to radiotherapy. On the basis of these preclinical findings, we initiated clinical trials of the combination of celecoxib, a selective COX-2 inhibitor, with radiotherapy in patients with lung cancer. Here we discuss the rationale for using selective COX-2 inhibitors and describe current clinical protocols and the initial findings.

Improved free vascular graft survival in an irradiated surgical site following topical application of rVEGF

PURPOSE

Wound healing disorders following surgery in preirradiated tissue are clinically well known and may even become more crucial with the increasing use of neoadjuvant chemoradiation protocols. Both the expression of vascular endothelial growth factor (VEGF) and endoglin (CD105) play a key role in neovascularization and wound healing after soft tissue grafts in irradiated and nonirradiated tissue. Modulation of neovascularization through the application of recombinant VEGF (rVEGF) may be a therapeutic option to reduce wound healing disorders in irradiated tissue. An experimental in vivo model was used to study the possible role of rVEGF for reduction of wound healing disorders and the promotion of neovascularization.

METHODS AND MATERIALS

A free myocutaneous gracilis flap was transplanted from the groin into the neck region of Wistar rats (weight 300-500 g) with and without previous irradiation of the neck region with 40 Gy: Group 1 (n = 7) radiotherapy alone; Group 2 (n = 14) flap transplantation alone and rVEGF; Group 3 (n = 14) radiotherapy, transplantation, and rVEGF. Time interval between irradiation and grafting was 10 +/- 1 day. 1.0 micro g rVEGF/500 microL phosphate-buffered saline was applied s.c. intraoperatively and on Days 1 through 7. Neovascularization (CD105) and endogenous VEGF expression were analyzed by means of immunohistochemistry on Days 3, 5, 7, 14, and 28 postoperatively and quantified as labeling indices (LI).

RESULTS

After irradiation there was a continuous significant reduction of the cytoplasmic VEGF expression (MEAN LI: 0.018 +/- 0.048) compared with the nonirradiated control (mean LI: 0.042 +/- 0.006) (p < 0.001). VEGF expression after flap transplantation without irradiation after VEGF application was at a constantly higher level from Day 3 (mean LI: 0.044 +/- 0.01) to Day 28 postoperatively compared with the control group (Day 3, mean LI: 0.028 +/- 0.006) (p < 0.001). As an indication of increased neovascularization after the local application of rVEGF, a significantly increased expression of CD105 was found in the transition area and graft bed from Day 7 on (p < 0.001). After irradiation and grafting there was a significant overall increase in the VEGF- and CD105-expression throughout Day 28 after rVEGF in the transition area (p < 0.001).

CONCLUSION

Whereas irradiation alone led to a downregulation of the endogenous VEGF expression, rVEGF application resulted in an increased expression and in a CD105 associated neovascularization after soft tissue grafting in irradiated tissues. Application of rVEGF may enable modulation of wound healing by influencing neovascularization. This could indicate a possible clinical approach for reducing fibrosis and chronic wound healing disorders in irradiated tissues.

Myeloid differentiation factor 88-dependent post-transcriptional regulation of cyclooxygenase-2 expression by CpG DNA: tumor necrosis factor-alpha receptor-associated factor 6, a diverging point in the Toll-like receptor 9-signaling

The immune stimulatory unmethylated CpG motifs present in bacterial DNA (CpG DNA) induce expression of cyclooxygenase-2 (cox-2). The present study demonstrates that CpG DNA can up-regulate cox-2 expression by post-transcriptional mechanisms in RAW264.7 cells. To determine the CpG DNA-mediated signaling pathway that post-transcriptionally regulates cox-2 expression, a cox-2 translational reporter (COX2-3'-UTR-luciferase) was generated by inserting sequences within the 3'-untranslated region (UTR) of cox-2 to the 3' end of the luciferase gene under control of the SV40 promoter. CpG DNA-induced COX2-3'-UTR-luciferase activity was completely inhibited by an endosomal acidification inhibitor chloroquine, a Toll-like receptor 9 antagonist inhibitory CpG DNA, or overexpression of a dominant negative (DN) form of MyD88. However, overexpression of DN-IRAK-1 or DN-TRAF6 resulted in substantial, but not complete, inhibition of the CpG DNA-induced COX2-3'-UTR-luciferase activity. Activation of all three MAPKs (ERK, p38, and JNK) was required for optimal COX2-3'-UTR-luciferase activity induced by CpG DNA. Overexpression of DN-TRAF6 suppressed CpG DNA-mediated activation of p38 and JNK, but not ERK, explaining the partial inhibitory effects of DN-TRAF6 on CpG DNA-induced COX2-3'-UTR-luciferase activity. Co-expression of DN-TRAF6 and N17Ras completely inhibited CpG DNA-induced COX2-3'-UTR-luciferase activity, indicating the involvement of Ras in CpG DNA-mediated ERK and COX2-3'-UTR regulation. Collectively, our results suggest that MyD88 and MAPKs play a key regulatory role in CpG DNA-mediated cox-2 expression at the post-transcriptional level and that TRAF6 is a diverging point in the Toll-like receptor 9-signaling pathway for CpG DNA-mediated MAPK activation.

Report from the Radiation Oncology Committee of the Southwest Oncology Group (SWOG)

To achieve the ultimate goal of cancer treatment, which is 100% cancer control with negligible toxicity, the therapeutic window must be enlarged, allowing for higher doses of beneficial treatments with reduced toxicity. The advent of image- and metabolism-guided therapy offers the best opportunity to date for combining modern radiation targeting and imaging techniques. Indeed, for the first time, it is reasonable to locally target metastatic disease with the goal of sterilization. Combining these focal radiation techniques with novel targeted antiproliferative agents and full-dose classic cytotoxic chemotherapy will become more effective as we learn to use these compounds in a less systemically toxic manner and as radiation fields become more defined. In addition, increasing numbers of biologic modifiers of normal tissue response are becoming available, and they suggest great promise for decreasing the normal tissue toxicity resulting from both radiation and chemotherapy treatments. Thus, radiation metastectomy for gross metastases, used together with systemic control of micrometastatic disease, may yield improved survival rates. This hypothesis is ready for testing in cancers of the breast, prostate, colon, and in sarcomas. Enlarging the therapeutic window is a major goal that would allow for an increasingly favorable therapeutic gain.

Molecular markers in clinical radiation oncology

Radiation therapy plays a critical role in the management of a majority of patients diagnosed with cancer. Identification of factors that help predict which patients are at risk for relapse within the irradiated field remains an active area of investigation. Although conventional clinical and pathologic factors have been helpful in identifying risk and guiding clinical decision-making for both local and systemic management, there is clearly a need to identify additional prognostic markers, which can aid in refining our treatment strategies and improving outcomes. A substantial amount of research efforts have been devoted to identifying molecular markers for prognostic and therapeutic strategies. The recent emergence of a powerful armamentarium of molecular tools has resulted in rapid expansion of our fund of knowledge and understanding of the molecular biology underlying tumor behavior and response. While a majority of these efforts have been focused on risk factors for metastatic disease and survival, there is a rapidly growing body of literature focused on molecular factors associated with radiation resistance and locoregional failure. In this review, we summarize recent advances and the available literature evaluating molecular markers as they relate to radiation sensitivity of solid tumors. Literature regarding the potential application of expression of genes related to apoptosis, angiogenesis, cell cycle, DNA repair and growth factors will be reviewed. Some of the basic biology and laboratory evidence demonstrating how the marker relates to radiation response and available correlative clinical studies employing these markers as prognostic tools are presented. The majority of molecular markers that have potential clinical significance with respect to radiation sensitivity and local control will be highlighted.

Celecoxib reduces skin damage after radiation: selective reduction of chemokine and receptor mRNA expression in irradiated skin but not in irradiated mammary tumor

Inflammatory cytokine and chemokine production is mediated, at least in part, by prostaglandin E (PGE2). Cyclooxygenases, COX-1 and COX-2, are two key enzymes in the conversion of arachidonic acid to PGE2. Radiation induces the overproduction of cytokines and chemokines, and it also increases PGE2 production, both locally and systemically. In this study, we tested the effects of a COX-2 inhibitor (celecoxib) after 50 Gy radiation of MCa-35 tumor and cutaneous tissues of C3H/He mice. Preclinical toxicity endpoints and associated alterations in chemokine production and cellular infiltrates were measured. Celecoxib was given by daily gavage (50 mg/kg for 15 days), with the first dose delivered either 2 hours before, 2 days after, or 7 days after a single dose of radiation. Celecoxib-treated animals had less inflammation of the dermis compared with saline-treated controls. Severe skin dermatitis occurred in 23.8% (5/21) of mice treated with 50 Gy, whereas only 17.6%, 5.3%, and 11.1% of mice in the 2-hour pre-, or the 2-day post-, and 7-day postirradiation groups, respectively, had severe dermatitis on day 20. The decreased skin toxicity scores were associated with a reduction of both blood vessels and focal necrosis in MCa-35 tumors. Celecoxib also significantly decreased C-C family chemokine (Rantes and MCP-1) mRNA expression in irradiated skin tissues, but not in tumor tissues, which was accompanied by a decrease in skin mRNA expression of both C-C (CCR2 and CCR5) and C-X-C (CXCR2 and CXCR4) chemokine receptors. A significant positive correlation was also found between skin damage (skin scores) and chemokine and its receptor mRNA expression in radiation-treated mice. Finally, celecoxib also decreased the infiltration of monocytes and neutrophils in locally irradiated tumor and surrounding normal tissue. The differential effects of celecoxib on inflammation help to explain the selective protection by celecoxib of irradiated cutaneous tissues without a concurrent protection of MCa-35 tumors.

Combination of a COX-2 inhibitor with radiotherapy or radiochemotherapy in the treatment of thoracic cancer

Cyclooxygenase-2 (COX-2) is an enzyme involved in prostaglandin production in pathologic states such as inflammatory processes and cancer. The enzyme is often overexpressed in premalignant lesions and cancer, including cancers of the lung and esophagus. Inhibition of this enzyme with selective COX-2 inhibitors was found to enhance tumor response to radiation in preclinical studies, suggesting that these agents can improve the response of various cancers to radiotherapy. On the basis of these preclinical findings, clinical trials of the combination of celecoxib, a selective COX-2 inhibitor, with radiotherapy were initiated in patients with lung carcinoma and with chemoradiotherapy in patients with esophageal carcinoma. The rationale for using selective COX-2 inhibitors is discussed, and the current clinical protocols and the initial findings are described.