Eicosanoids and radiation

Antrodia salmonea induces G2 cell-cycle arrest in human triple-negative breast cancer (MDA-MB-231) cells and suppresses tumor growth in athymic nude mice

ETHNOPHARMACOLOGICAL RELEVANCE

Antrodia salmonea (AS), is a well-known folk medicinal mushroom in Taiwan, has been reported to exhibit anti-oxidant, anti-angiogenic, and anti-inflammatory effects.

MATERIALS AND METHODS

In the present study, we examined the effects of AS on cell-cycle arrest in vitro in MDA-MB-231 cells and on tumor regression in vivo using an athymic nude mice model.

RESULTS

AS (0-200μg/mL) treatment significantly induced G₂ cell-cycle arrest in MDA-MB-231 cells by reducing the levels of cyclin B1, cyclin A, cyclin E, and CDC2 proteins. In addition, N-acetylcysteine (NAC) pretreatment prevented AS induced G₂ cell-cycle arrest, indicating that ROS accumulation and subsequent cell cycle arrest might be a major mechanism of AS-induced cytotoxicity. Further, AS treatment decreased COX-2 expression and induced PARP cleavage was significantly reversed by NAC pretreatment in MDA-MB-231 cells. The in vivo study results revealed that AS treatment was effective in terms of delaying the tumor incidence and reducing the tumor growth in MDA-MB-231-xenografted nude mice. TUNEL assay, immunohistochemical staining and Western blotting confirmed that AS significantly modulated the xenografted tumor progression as demonstrated by induction of apoptosis, autophagy, and cell-cycle arrest.

CONCLUSION

Our data strongly suggest that Antrodia salmonea could be an anti-cancer agent for human breast cancer.

Phase I clinical trial of nasopharyngeal radiotherapy and concurrent celecoxib for patients with locoregionally advanced nasopharyngeal carcinoma

We evaluated the incidence of acute toxicity of concurrent cyclooxygenase-2 inhibitor (celecoxib) plus radiotherapy in patients with locoregionally advanced nasopharyngeal carcinoma (NPC). Thirty-four patients received an accumulated radiation dose of 72-76Gy in 36-38 fractions to the primary lesion and 60Gy in 30 fractions to cervical lymph-node lesions. Palpable residual nodes were boosted to 70Gy at the 90% isodose level with an electron field. Celecoxib was administered at escalating doses of 400, 600, and 800mg/day, starting 3days before the first fraction of radiotherapy and continuing throughout the course of radiotherapy. The majority of toxicities were grade 1, with mucositis and weight loss most frequently observed (28 of 34, 82.4%), followed by dermatitis (27 of 34, 79.4%) and otitis (14 of 34, 41.2%). The toxicities were not related to celecoxib dose (all P>0.05). Stomach pain was considered related to celecoxib, which developed in 2 patients at doses of 400mg and 800mg/day. No grade-3 or -4 toxicities or episodes of toxic death occurred. The tumors in 31 patients (31/34, 91.2%) showed a complete response, and 3 patients (3/34, 8.8%) had partial responses. The actuarial local progression-free survival was 96.6% at 1year, and the 2year overall survival rate was 84.6%. Celecoxib can be safely administered concurrently with nasopharyngeal radiotherapy at doses up to 800mg/day. The tumors responded well to treatment warranting further assessment in a phase II trial.

The effects of celecoxib, a COX-2 selective inhibitor, on acute inflammation induced in irradiated rats

The potential value of selective and non-selective COX-2 inhibitors in preventing some of the biochemical changes induced by ionizing radiation was studied in rats exposed to carrageenan-induced paw edema and 6-day-old air pouch models. The animals were exposed to different exposure levels of gamma-radiation, namely either to single doses of 2 and 7.5 Gy or a fractionated dose level of 7.5 Gy delivered as 0.5 Gy twice weekly for 7.5 weeks. The inflammatory response produced by carrageenan in irradiated rats was markedly higher than that induced in non-irradiated animals, and depended on the extent of irradiation. Celecoxib, a selective COX-2 inhibitor, in doses of 3, 5, 10, and 15 mg/kg was effective in reducing paw edema in irradiated and non-irradiated rats in a dose-dependent manner as well as diclofenac (3 mg/kg), a non-selective COX inhibitor. Irradiation of animals before the induction of the air pouch by an acute dose of 2 Gy led to a significant increase in leukocytic count, as well as in the level of interleukin-6 (IL-6), interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), LTB(4), PGE(2) (as an index of COX-2 activity), TXB(2) (as an index of COX-1 activity), and the plasma level of MDA. This increase in level of these parameters was more marked than that observed in the non-irradiated animals subjected to the inflammagen. The blood GSH level was not affected by the dose of irradiation used, whereas superoxide dismutase (SOD) activity was suppressed. In many respects, celecoxib (5 mg/kg) was as potent as diclofenac in decreasing the elevated levels of IL-6, IL-1beta, TNF-alpha, LTB(4), PGE(2), but lacked any significant effect on TXB(2) level. Since it is mostly selective for COX-2 with a rare effect on COX-1 enzyme, both drugs at the selected dose levels showed no effect on level of MDA, GSH, and SOD activity.

Combined action of celecoxib and ionizing radiation in prostate cancer cells is independent of pro-apoptotic Bax

BACKGROUND AND PURPOSE

The cyclooxygenase-2-inhibitor celecoxib has been shown to inhibit cell growth and to reduce prostatic intraepithelial neoplasia in mice. The drug was suggested to increase efficacy of ionizing radiation. However, extent and mechanisms of the suggested benefit of celecoxib on the radiation response are still unclear. The aim of the present study was to analyze cytotoxic efficacy of celecoxib in combination with irradiation on human prostate cancer cell lines and to define the importance of pro-apoptotic Bax in this process.

MATERIALS AND METHODS

Induction of apoptosis and global and clonogenic cell survival upon irradation- (2-10Gy), celecoxib- (10-75microM) or combined treatment were evaluated in prostate cancer cells by fluorescence microscopy, WST-1 assay and standard colony formation assays.

RESULTS

Celecoxib <25microM caused morphological changes and growth inhibition without substantial apoptosis or radiosensitization in terms of decreased clonogenic cell survival. In contrast, celecoxib 25microM increased radiation-induced cell death and clonogenic kill. While radiation-induced clonogenic death was increased in the presence of Bax, effects of celecoxib or combined treatment were Bax independent.

CONCLUSIONS

Our findings reveal Bax-independent beneficial effects of celecoxib on radiation-induced apoptosis and eradication of clonogenic prostate cancer cells in vitro providing a rationale for clinical evaluation of high-dose celecoxib in combination with irradiation in prostate cancer patients.

Preoperative radiochemotherapy is successful also in patients with locally advanced rectal cancer who have intrinsically high apoptotic tumours

BACKGROUND

Not all patients with locally advanced rectal cancer (LARC) respond equally to neo-adjuvant radiochemotherapy (RCT). Patients with highly apoptotic less advanced rectal cancers do not benefit from short-term radiotherapy. This study investigates whether this is also the case in the setting of RCT for LARC.

PATIENTS AND METHODS

Tissue microarrays were constructed of biopsy and resection specimens of 201 LARC patients. Apoptosis (M30) and several apoptosis-regulating proteins [p53, Bcl-2, Bax, cyclooxygenase-2 (Cox-2) and mamma serine protease inhibitor (maspin)] were studied with immunohistochemistry. Subsequently, predictive values for local recurrence (LR), overall survival (OS) and histological tumour regression were analysed.

RESULTS

Apoptotic levels, quantified as the number of apoptotic cells/mm(2) tumour epithelium, were higher in posttherapy tissues compared with biopsies (P < 0.001). Biopsies from clinical T4 stage tumours demonstrated significantly higher levels of apoptosis than clinical T3 stage tumours (P = 0.020). Therapy-induced apoptosis was higher when the interval between the last day of irradiation and surgery increased (P < 0.001, correlation coefficient = 0.355). Pre- and posttherapy apoptosis, p53, Bcl-2, Bax and Cox-2 were not associated with LR, OS or tumour regression. Intense pretherapy cytoplasmatic staining of maspin indicated a higher risk on LR (P = 0.009) only.

CONCLUSION

Combined RCT is also successful in highly apoptotic tumours and is therefore independent of intrinsic apoptosis.

Targeted agents and esophageal cancer--the next step?

Esophageal cancer (EC) is an aggressive cancer and is a leading cause of cancer-related death worldwide. In the United States and Western Europe, there has been a decline in the incidence of squamous cell carcinomas coupled with a rapid rise in incidence of adenocarcinoma of the esophagus and gastroesophageal junction. Although the 5-year survival rates have slowly increased over time from 4% to 14%, the outcomes are still dismal. The lack of adequate preventative strategies, inadequate screening techniques, early lymphatic and hematogenous spread, and lack of truly effective therapeutic agents all contribute to the poor outcome. This review will highlight the current status of targeted therapies in EC. This will include a review of agents targeting the vascular endothelial growth factor and epidermal growth factor receptor pathways and trials planned or ongoing to incorporate these and other agents into therapy for advanced disease and into combined modality therapy for early-stage tumors. Further work is required regarding the rational integration of these targeted agents and the optimal selection of patients who will most likely benefit.

Inhibition of cyclooxygenase-2 and induction of apoptosis in estrogen-nonresponsive breast cancer cells by Antrodia camphorata

The objective of this study was to investigate the fermented culture broth of Antrodia camphorata (A. camphorata) to induce apoptosis and inhibit cyclooxygenase-2 (COX-2) in estrogen-nonresponsive (MDA-MB-231) human breast cancer cells. Treatment of the highly invasive MDA-MB-231 cells with A. camphorata (40-240 microg/ml) resulted in dose and time-dependent sequences of events marked by apoptosis, as evidenced by loss of cell viability, chromatin condensation, and internucleosomal DNA fragmentation. Apoptosis in the MDA-MB-231 cells was accompanied by release of cytochrome c, activation of caspase-3, -8, and -9, and specific proteolytic cleavage of poly (ADP-ribose) polymerase (PARP). Although the A. camphorata-induced apoptosis was associated with a reduction in Bcl-2 protein levels, negligible Bax increase was observed. Furthermore, A. camphorata treatment inhibited COX-2 protein expression and prostaglandin E2 (PGE2) production in MDA-MB-231 cells. Analysis of the study data suggests that A. camphorata exerts growth inhibition on (highly invasive) estrogen-nonresponsive human breast cancer cells through apoptosis induction associated with COX-2 inhibition, and that it may possess anticancer properties potentially valuable for application in drug products.

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.

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.

Abdominal radiation exposure elicits inflammatory responses and abscopal effects in the lungs of mice

An inflammatory reaction is a classical feature of radiation exposure and appears to be a key event in the development of the acute radiation syndrome. We have investigated the radiation-induced inflammatory response in C57BL6/J mice after total abdominal or total-body irradiation at a dose of 15 Gy. Our goal was to determine the radiation-induced inflammatory response of the gut and to study the consequences of abdominal irradiation for the intestine and for the lungs as a distant organ. A comparison with total-body irradiation was used to take into account the hematopoietic response in the inflammatory process. For both irradiation regimens, systemic and intestinal responses were evaluated. A systemic inflammatory reaction was found after abdominal and total-body irradiation, concomitant with increased cytokine and chemokine production in the jejunum of irradiated mice. In the lungs, the radiation-induced changes in the production of cytokines and chemokines and in the expression of adhesion molecules after both abdominal and total-body irradiation indicate a possible abscopal effect of radiation in our model. The effects observed in the lungs after irradiation of the abdomino-pelvic region may be caused by circulating inflammatory mediators consequent to the gut inflammatory response.

Cyclooxygenase-2 Inhibits Novel Ginseng Metabolite-Mediated Apoptosis

Recently, a novel intestinal bacterial metabolite of ginseng protopanaxadiol saponins, i.e., 20-O-(beta-D-glucopyranosyl)-20(S)-protopanaxadiol (IH-901), has been reported to induce apoptosis in a variety of cancer cells. Here we show a differential effect of IH-901 on several cell types. Exposure to IH-901 for 48 hours at a supposedly subapoptotic concentration of 40 mumol/L led to both apoptotic cell death and G1 arrest in Hep3B cells, but only resulted in G1 arrest in MDA-MB-231, Hs578T, and MKN28 cells. Additionally, the treatment of MDA-MB-231, but not of Hep3B, with IH-901 up-regulated cyclooxygenase-2 (COX-2) mRNA (2 hours) and protein (6 hours), and enhanced the production of prostaglandin E2. In MDA-MB-231 cells, IH-901 induced the sustained activation of extracellular signal-regulated kinase (ERK), whereas inhibition of mitogen-activated protein/ERK kinase blocked IH-901-mediated COX-2 induction and resulted in apoptosis, suggesting the involvement of an ERK-COX-2 pathway. Combined treatment with IH-901 and nonsteroidal anti-inflammatory drugs inhibited COX-2 enzyme and induced apoptosis in MDA-MB-231 and Hs578T cells. Adenovirus-mediated COX-2 small interfering RNAs also effectively inhibited COX-2 protein expression and enhanced IH-901-mediated apoptosis without inhibiting ERK 1/2 phosphorylation, thus providing direct evidence that COX-2 is an antiapoptotic molecule. Moreover, IH-901-mediated G1 arrest resulted from an increase in p27Kip1 mRNA and protein expression followed by a decrease in CDK2 kinase activity that was concurrent with the hypophosphorylation of Rb and p130. In conclusion, IH-901 induced both G1 arrest and apoptosis, and this apoptosis could be inhibited by COX-2 induction.

Phase I/II study of selective cyclooxygenase-2 inhibitor celecoxib as a radiation sensitizer in patients with unresectable brain metastases

PURPOSE

The primary goal of this phase I/II study was to evaluate the feasibility, safety and efficacy of celecoxib administered concomitant to radiotherapy to treat unresectable BM.

PATIENTS AND METHODS

Patients with measurable BM by CT or MRI, unresectability criteria by a neurosurgeon and RPA-RTOG class II were eligible. Celecoxib was administered at 400 mg/day during the entire course of radiotherapy. All patients were irradiated with 60Co beams to whole-brain dose of 32 Gy (20 fractions of 1.6 Gy each two times a day with a 6 h interval between treatments) followed by a 22.4 Gy boost (same fractionation schedule) over evident lesions.

RESULTS

Twenty-seven patients were treated. The concurrent regimen was well tolerated with 15 cases of mild dyspepsia. Alopecia (NCI grades 1-2) was the most important side effect. Three patients presented rash/desquamation of moderate intensity. Radiological responses occurred in 18 of 25 valuable patients (72), with five complete responses (CR). Symptomatic responses were reported in 25 of 27 patients (92.6), with 20 CR. The overall response rate (considering complete plus partial responses) was 66.7. Percentile 50 for time-to-progression, time-to-neurological-progression and functional-independence-time were 3, 6.25 and 6.7 months, respectively. Median survival time was 8.7 months.

CONCLUSION

Our initial results suggest that radiotherapy plus celecoxib is safe and a possible active treatment for patients with BM. Further investigation in a randomized trial is warranted to validate its clinical utility.

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.

COX-2 and its inhibition as a molecular target in the prevention and treatment of lung cancer

Lung cancer is the leading cause of cancer death in the USA. Conventional therapy using chemotherapy, radiation therapy, and a combination of the two, has yielded modest improvement in patient outcome. Dysfunction and dysregulation of many molecular processes and signaling pathways are involved in the development and growth of malignant lung tumors, and in conferring resistance to standard cancer treatments. Cyclooxygenase (COX)-2, an enzyme involved in prostaglandin production in pathologic states, is often overexpressed in premalignant and malignant lesions. Overexpression of COX-2 in lung cancer is associated with more aggressive biologic tumor behavior and adverse patient outcome. In preclinical studies, inhibition of this enzyme with selective COX-2 inhibitors enhances tumor response to radiation and chemotherapeutic agents. These findings quickly led to clinical studies. Phase I and II clinical trials of the combination of selective COX-2 inhibitors with radiotherapy, chemotherapy, or both in patients with lung cancer have been initiated and some preliminary results are available. In this review, the relationship between overexpression of COX-2 and lung cancer, the antitumor effect of selective COX-2 inhibitors, and the rationale for using selective COX-2 inhibitors combined with radiotherapy and chemotherapy, will be described. Current clinical protocols and preliminary findings will also be summarized.

Overexpression of cyclooxygenase-2 is associated with radioresistance in oral squamous cell carcinoma

Cyclooxygenase-2 (COX-2), an inducible isoform of cyclooxygenase, is overexpressed in many types of malignant tumors, which in turn may stimulate tumor growth and protect against damage by irradiation or cytotoxic agents. The purpose of this study is to investigate the relationship between the radiation sensitivity and elevated level of COX-2. Radiation sensitivity of the eight oral SCC cell lines differed greatly in their response to radiation. Further, the level of the COX-2 expression correlated inversely with increased tumor radiation sensitivity. The similar significant association between the response to preoperative radiation therapy and COX-2 overexpression was observed in the oral SCC patients. In addition, treatment with a COX-2 selective inhibitor enhanced the radioresponse of HSC-2 cell, which constitutively expressed COX-2. These results suggested that COX-2 expression level correlates to radiation tolerance and the COX-2 selective inhibitor may be a potent enhancer for tumor radioresponse in oral SCC.

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.

NS 398 radiosensitizes an HNSCC cell line by possibly inhibiting radiation-induced expression of COX-2

PURPOSE

Cyclooxygenase-2 (COX-2) protein is frequently elevated in squamous cell carcinoma of the head and neck (HNSCC). The aim of this study was to determine if COX-2 inhibitors have radiosensitizing effects in HNSCC and understand the mechanism by which this occurs.

MATERIALS AND METHODS

The radiosensitizing effects of a selective COX-2 inhibitor, NS398, on a HNSCC cell line HEp3, were determined using clonogenic survival assay. Cells were pretreated with the dose of NS398 at which 50% growth inhibition occurred (IC(50)) and then irradiated. COX-2 protein and mRNA were then determined in the presence and absence of NS398.

RESULTS

NS398 significantly decreased (p < 0.0001) the calculated survival fraction (SF) for all radiation doses (0.79 to 0.41 at 2 Gy). A significant increase in COX-2 protein of 2.8 fold for 2 Gy and 3.5 fold for 6 Gy was noted 48 h after radiation. Interestingly, the upregulation of COX-2 protein with radiation was suppressed when cells were pretreated with NS398. Quantitative reverse transcriptase polymerase chain reaction showed no significant corresponding increase in COX-2 mRNA at 48 h with ionizing radiation.

CONCLUSIONS

The radiosensitizing effect of NS398 could be due to inhibition of radiation-induced COX-2 upregulation by this drug. NS398, known as an inhibitor of COX-2 enzyme activity, down-regulated COX-2 protein expression, which may indicate that NS398 can act upstream of COX-2, and this change appears to be post-transcriptional.

Indomethacin and ibuprofen induce Hsc70 nuclear localization and activation of the heat shock response in HeLa cells

It has been established that non-steroidal anti-inflammatory drugs (NSAIDs), such as sodium salicylate, sulindac, ibuprofen, and indomethacin, induce anti-inflammatory and anti-proliferative effects independent of cyclooxygenase. These cyclooxygenase-independent pharmacodynamic effects appear to regulate several signaling pathways involving proliferation, apoptosis, and heat shock response. However, the mechanisms of these actions remain an area of ongoing investigation. Hsc70 is a cytoplasmic chaperone protein involved in folding and trafficking of client proteins to different subcellular compartments, plays roles in signal transduction and apoptosis processes, and translocates to the nucleus following exposure to heat shock. Since NSAIDs induce some aspects of the heat shock response, we hypothesized that they may also induce Hsc70 nuclear translocation. Western immunoblotting and indirect cellular immunofluorescence showed that indomethacin and ibuprofen induce Hsc70 nuclear translocation at concentrations previously shown to induce HSF DNA-binding activity. Chemical inhibition of both p38(MAPK) and Erk42/44 had no effect on localization patterns. In addition, while indomethacin has been shown to behave as an oxidative stressor, the radical scavenging agent, N-acetyl cysteine, did not inhibit nuclear translocation. These results indicate that induction of the heat shock response by NSAIDs occurs at concentrations fivefold greater than those required to inhibit cyclooxygenase activity, suggesting a cyclooxygenase-independent mechanism, and in the presence or absence of kinase inhibitors and a free radical scavenger, suggesting independence of Erk42/44 or p38(MAPK) activities and intracellular oxidoreductive state.

Lipid a radiosensitizes hypoxic EMT-6 tumor cells: role of the NF-κB signaling pathway

PURPOSE

Lipid A has shown promising immunostimulatory effects in both experimental tumor models and advanced stage cancer patients. This study examines whether lipid A may directly modulate the radioresponse of tumor cells by activating inducible nitric oxide synthase (iNOS) or cyclooxygenase-2 (COX-2) through nuclear factor-kappaB (NF-kappaB) signaling.

METHODS AND MATERIALS

Hypoxic EMT-6 tumor cells were exposed to lipid A and analyzed for the level of COX-2 and iNOS by Western blotting and enzymatic assays. The hypoxic radioresponse of EMT-6 cells was estimated by clonogenic survival. The activation of NF-kappaB was examined by immunostaining of its p65 subunit and by luciferase reporter gene assay.

RESULTS

Lipid A dose-dependently increased the expression and activity of iNOS with a maximal effect at plasma achievable concentrations of 3-30 micro g/mL. The COX-2 mediated production of prostaglandin E2 was constitutively high and further upregulated by lipid A. The radiosensitivity of hypoxic EMT-6 cells was increased up to 2.5 times and counteracted by the iNOS inhibitor aminoguanidine but not by the COX-2 inhibitor NS-398. The mechanism of radiosensitization was linked to NF-kappaB signaling, because its inhibition by phenylarsine oxide impaired both iNOS activation and radioresponse.

CONCLUSION

Lipid A is an efficient hypoxic cell radiosensitizer at plasma relevant concentrations, which provides a rationale to combine lipid A with radiotherapy in further studies.

Cyclo-oxygenase 2 inhibition in colorectal cancer therapy

BACKGROUND

Cyclo-oxygenase inhibition for the treatment of colorectal neoplasia has been studied with renewed interest since the discovery of cyclo-oxygenase (Cox) 2 and the introduction of specific Cox-2 inhibitors. These drugs have implications for both the prevention of colorectal carcinoma and the potential treatment of the disease.

METHODS AND RESULTS

A Medline database search was performed for articles using the keywords "colonic, colon or rectal and neoplasia or cancer" and "cyclo-oxygenase or Cox-2." Cross-references of relevant historical papers were also included. There is substantial evidence that Cox-2 plays a role in the development and progression of colorectal cancer. The specific inhibition of this enzyme has been shown to inhibit cancer growth in in vitro and in vivo models. The mechanisms of action for these effects are poorly understood and potential clinical applications at present remain under investigation.

CONCLUSION

Cox-2 inhibitors have great promise as useful additions to current cancer treatments. There is a need for randomized clinical trials to define a role for these drugs in chemoprevention, recurrence prophylaxis, and adjuvant therapy for colorectal and other solid tumours.

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.

Targeted therapies for stage III non-small cell lung cancer: integration in the combined modality setting

Combined modality therapy represents current standard therapy for locoregionally advanced non-small cell lung cancer. In particular, concomitant chemoradiotherapy has emerged as the preferred approach. At the same time, efforts to increase locoregional and systemic antitumor activity are necessary to further improve long-term survival rates for these patients. In recent years, multiple cellular targets have emerged in the development of novel antitumor therapies. Several of these are of high relevance in the carcinogenesis of lung cancer including the epidermal growth factor receptor (EGFR), the ras signaling pathway, tumor angiogenesis, and cyclooxygenase-2 (COX-2) expression. Novel agents directed against these targets are currently under development with promising early results in non-small cell lung cancer when administered as single agents or in combination with chemotherapy in stage IV or recurrent disease. Similarly their use with concurrent radiation therapy is supported by preclinical models. Selected early clinical trials utilizing these agents in combination with radiotherapy or chemoradiotherapy are discussed.

Initial experience combining cyclooxygenase-2 inhibition with chemoradiation for locally advanced pancreatic cancer

Pancreatic cancer is a lethal disease that is resistant to chemotherapy and radiotherapy. Gemcitabine has recently been shown to be an improvement over 5-fluorouracil in patients with advanced disease. It is also a potent radiosensitizer, which has led to the investigation of gemcitabine with concurrent radiotherapy. However, preliminary results indicate that there are significant limitations to this approach in this challenging disease. Pancreatic cancer cells have alterations in many molecular signaling pathways that may be responsible for their resistance to cytotoxic therapy and aggressive behavior. Cyclooxygenase-2 (COX-2) is commonly overexpressed in pancreatic tumors, and preclinical evidence indicates that selective COX-2 inhibition enhances both chemotherapy and radiotherapy response, without affecting normal tissue damage. We have initiated preclinical studies as well as a phase I clinical protocol evaluating the combination of gemcitabine and celecoxib (Celebrex) with radiotherapy. In preclinical studies, celecelecoxib strongly enhanced the antitumor efficacy of chemoradiation. However, preliminary observations from both the preclinical experiments as well as the clinical protocol have revealed more toxicity with this combination than with gemcitabine and radiotherapy alone. These observations require further study, but are cause for concern when combining gemcitabine, radiotherapy, and celecoxib.

Cyclooxygenase-2 (COX-2) enzyme inhibitors and radiotherapy: preclinical basis

Cyclooxygenase-2 (COX-2), an enzyme induced by proinflammatory cytokines, mitogenic substances, oncogenes, growth factors, and hypoxia, among others, is involved in the metabolic conversion of arachidonic acid to prostaglandins in inflamed tissues and neoplasia. COX-2 is often overexpressed in malignant tumors and premalignant lesions and is linked to carcinogenesis, maintenance of progressive tumor growth, and facilitation of metastatic spread. Because COX-2 may also be a determinant of tumor radioresistance, its inhibition or inhibition of its products (prostaglandins) may improve tumor response to radiotherapy. Preclinical studies have shown that treatment with selective COX-2 inhibitors significantly enhances tumor response to radiation without appreciably affecting normal tissue radioresponse. The underlying mechanisms of the COX-2 inhibitor-radiation interactions seem to be multiple, with the enzyme inhibitor directly or indirectly augmenting tumor cell destruction by radiation. Thus, use of selective COX-2 inhibitors is a potential approach for improving cancer radiotherapy.

Role of Cyclooxygenase-2 Inhibitors in Combination with Radiation Therapy in Lung Cancer

Cyclooxygenase-2 (COX-2) is an enzyme involved in prostaglandin production in pathologic states such as inflammatory disorders and cancer. The enzyme is often overexpressed in premalignant lesions and cancer of the lung. Overexpression of COX-2 in lung cancer is associated with more aggressive biological tumor behavior and adverse patient outcome. In preclinical studies, inhibition of this enzyme with selective COX-2 inhibitors enhances tumor response to radiation and chemotherapeutic agents. These findings have been rapidly advanced to clinical oncology. Clinical trials of the combination of selective COX-2 inhibitors with radiation therapy, chemotherapy, or both in patients with lung cancer have been initiated and some preliminary results are available. In this review, we describe the relationship between overexpression of COX-2 and lung cancer, the antitumor effect of selective COX-2 inhibitors, discuss the rationale for using selective COX-2 inhibitors combined with radiation therapy and chemotherapy, and summarize current clinical protocols and initial findings.

Chemoradiotherapy: emerging treatment improvement strategies

BACKGROUND

The use of chemotherapeutic drugs in combination with radiotherapy has become a common strategy for the treatment of advanced cancer. Solid evidence exists showing that chemotherapy administered during the course of radiotherapy (concurrent chemoradiotherapy) increases both local tumor control and patient survival in a number of cancer sites, including head and neck cancer. These therapy improvements, however, have been achieved at the expense of considerable toxicity, which underscores the need for further improvements.

METHODS

The current status of chemoradiotherapy clinical trials for head and neck cancer and research on the emerging treatment improvements were reviewed. A review of potential treatment improvement strategies focused on preclinical investigations on newer chemotherapeutic agents, notably taxanes and nucleoside analogues, as well as on molecular targets such as epidermal growth factor receptor (EGFR) or cyclooxygenase-2 (COX-2) enzyme.

RESULTS

Concurrent, but not induction (drugs given before radiotherapy), chemoradiotherapy improves locoregional tumor control and survival benefit in head and neck carcinoma relative to radiotherapy alone. In comparison, both concurrent and induction chemoradiotherapy showed therapeutic advantage over radiotherapy alone in the treatment of lung cancer. These therapeutic improvements were achieved with standard chemotherapeutic drugs, most commonly cisplatin-based chemotherapy. Biologically, chemotherapy interacts with radiation through a number of mechanisms, including inhibition of cellular repair, cell cycle effects, and inhibition of tumor cell regeneration. Potential avenues emerged to further improve chemoradiotherapy. One of these involves the newer chemotherapeutic agents, taxanes and nucleoside analogues, which in preclinical studies exhibited strong tumor radiosensitization and therapeutic gain. The clinical benefit of these agents is currently under testing. Another approach for improvement of chemoradiotherapy consists of inhibiting molecules selectively or preferentially expressed on tumor cells, such as EGFR and COX-2, both shown to render cellular resistance to drugs or radiation. Agents that selectively inhibit these molecules are becoming available at a rapid rate, and many of them have been shown in preclinical testing to be highly effective in improving tumor radioresponse or chemoresponse without affecting normal tissues.

CONCLUSIONS

Concurrent chemoradiotherapy, using standard chemotherapeutic agents, has emerged as an effective treatment for advanced cancer, but unfortunately at the expense of considerable increase in normal tissue toxicity. There are a number of potential emerging treatment strategies to further improve chemoradiotherapy. One consists of using newer chemotherapeutic drugs, which in preclinical studies are potent enhancers of tumor radioresponse. Another approach consists of targeting EGFR or COX-2 with selective inhibitors of these molecules.

In vitro enhancement of tumor cell radiosensitivity by a selective inhibitor of cyclooxygenase-2 enzyme: mechanistic considerations

PURPOSE

Selective cyclooxygenase-2 inhibitors have been reported to enhance the tumor response to radiation in vivo, but the cellular mechanisms underlying the radiosensitizing effect are not understood. In the present study, we investigated several possible mechanisms using a murine sarcoma cell culture system.

METHODS AND MATERIALS

Cells derived from a murine sarcoma, designated NFSA, were cultured in vitro and exposed to different (either single or split) doses of radiation with and without a pretreatment of SC-236 (4-[5-(4-chlorophenyl)-3-(trifluoromethyl)-1H-pyrazol-l-yl] benzene sulfonamide), a selective cyclooxygenase-2 (COX-2) inhibitor. The cells were assayed for clonogenic survival to determine the radiosensitizing effect of SC-236. In addition, MTT assay and TUNEL assay were performed to determine the effects of SC-236 and radiation on the cell survival and cell cycle distribution. RNase protection assay was performed on the total RNA extract using probes that encoded for selected cell cycle regulatory proteins, such as cyclins and cyclin-dependent kinases. To monitor the extent of COX-2 activity and its role in radiosensitization, the cellular content of prostaglandin E2, a major metabolite of COX-2 activity on arachidonic acid, was also determined.

RESULTS

The cell clonogenic survival assay showed that SC-236 significantly enhanced tumor cell radiosensitivity: 50 microM SC-236 increased it by a factor of 1.51 at the 0.1 cell survival level. Treatment with SC-236 (50 microM, 3 days) removed the "shoulder" region on the radiation survival curve, suggesting that the drug inhibited repair of sublethal radiation damage. The inhibition was confirmed by split-dose experiments where two doses (3 Gy each) of radiation were given 4 h apart. The cells exposed to radiation only repaired the damage by a factor of 1.44, whereas those treated with SC-236 plus radiation repaired it by a factor of 1.1 only. Whereas SC-236 induced apoptosis in these NFSA cells, radiation did not. No further increase in apoptosis was observed when the cells were exposed to both SC-236 and radiation, suggesting that SC-236 did not render tumor cells more susceptible to radiation-induced apoptosis. The RNase protection assay showed that SC-236 (50 microM, 3 days) inhibited the expression of cyclins A and B, as well as cyclin-dependent kinase-1. Inhibition of these cell cycle regulatory elements by SC-236 was associated with the arrest of cells in the radiosensitive G2-M phase (67%), determined by flow cytometry.

CONCLUSIONS

SC-236 significantly enhanced radiosensitivity of tumor cells; the magnitude of sensitivity was dependent on the drug's concentration. The likely mechanisms involve accumulation of cells in the radiosensitive G2-M phase of the cell cycle and inhibition of repair from sublethal radiation damage.

Radiosensitizing and anti-proliferative effects of resveratrol in two human cervical tumor cell lines

Resveratrol is a polyphenol isolated from the skins of grapes that has been shown to significantly alter the cellular physiology of tumor cells, as well as block the process of initiation and progression. At least one mechanism for the intracellular actions of resveratrol involves the suppression of prostaglandin (PG) biosynthesis. The involvement of PGs and other eicosanoids in the development of human cancer is well established. PGs are synthesized from arachidonic acid via the cyclooxygenase pathway and have multiple physiological and pathological functions. In addition, evidence has arisen suggesting that PGs may be implicated in the cytotoxic and/or cytoprotective response of tumor cells to ionizing radiation (IR). As such, we hypothesized that tumor cells may exhibit changes in the cellular response to IR following exposure to resveratrol, a naturally occurring compound that inhibits cyclooxygenase-1 (COX-1) activity. Thus, clonogenic cell survival assays were performed using irradiated HeLa and SiHa cells pretreated with resveratrol prior to IR exposure, and resulted in enhanced tumor cell killing by IR in a dose-dependent manner. Further analysis of COX-1 inhibition indicated that resveratrol pretreatment: (1), inhibited cell division as assayed by growth curves; and (2), induced an early S phase cell cycle checkpoint arrest, as demonstrated by fluorescence-activated cell sorting, as well as bromodeoxyuridine pulse-chase analysis. These results suggest that resveratrol alters both cell cycle progression and the cytotoxic response to IR in two cervical tumor cell lines.

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

Cyclooxygenase-2 (COX-2) is an enzyme induced by a variety of factors including tumor promoters, cytokines, growth factors and hypoxia. It is involved in the metabolic conversion of arachidonic acid to prostanoids, primarily in inflammatory states and tumors. In normal tissues, prostanoids are synthesized by COX-1, and they exert numerous homeostatic physiologic functions. COX-2 overexpression is linked to carcinogenesis, maintenance of progressive tumor growth and facilitation of metastatic spread. COX-2 and its products may act as protectors against cell damage by ionizing radiation. I describe findings showing that inhibition of COX-2 or prostanoids by selective COX-2 inhibitors or commonly used nonsteroidal antiinflammatory drugs (NSAIDs) has antitumor activity and may improve tumor response to radiation without significantly affecting normal tissue radioresponse. COX-2 inhibitors and radiation interact in multiple complex ways, with the enzyme inhibitor directly or indirectly augmenting tumor cell destruction by radiation. COX-2 represents a potential molecular target for improvement of cancer radiotherapy.

Biology-based combined-modality radiotherapy: workshop report

PURPOSE

The purpose of this workshop summary is to provide an overview of preclinical and clinical data on combined-modality radiotherapy.

METHODS AND MATERIALS

The 8th Annual Radiation Workshop at Round Top was held April 13-16, 2000 at the International Festival Institute (Round Top, TX).

RESULTS

Presentations by 30 speakers (from Germany, Netherlands, Australia, England, and France along with U.S. participants and M. D. Anderson Cancer Center faculty) formed the framework for discussions on the current status and future perspectives of biology-based combined-modality radiotherapy.

CONCLUSION

Cellular and molecular pathways available for radiation modification by chemical and biologic agents are numerous, providing new opportunities for translational research in radiation oncology and for more effective combined-modality treatment of cancer.

Characterization of the acute inflammatory response after irradiation in mice and its regulation by interleukin 4 (Il4)

The aim of this study was to determine the effects of total-body irradiation of mice on the acute release of a panel of several mediators of inflammation and to evaluate the efficacy of Il4 in regulating these radiation-induced modifications. We studied the effects of exposure of C57BL6/J mice to 8 Gy gamma rays on the early release of cytokines, chemokines, acute-phase proteins, prostaglandins and corticosterone in either plasma or tissues compared to those observed after intraperitoneal injection of lipopolysaccharide from 1 h to 3 days after stimulation. During the characterization of the acute inflammatory response induced by radiation or lipopolysaccharide, we observed differences both in the type of mediators produced and in the time course of release. We next determined the anti-inflammatory potential of Il4 in this model of total-body irradiation. We found that Il4 was able to down-regulate the radiation-induced production of mediators of inflammation such as Gro1 (also known as KC, N51) in plasma and lung, corticosterone in blood, Il1b in lung, and prostaglandin E(2) in colon, suggesting the anti-inflammatory potential of Il4 in regulating the radiation-induced response.

Radiation induces upregulation of cyclooxygenase-2 (COX-2) protein in PC-3 cells

PURPOSE

To investigate the impact of gamma-irradiation on cyclooxygenase-2 (COX-2) expression and its enzymatic activity in PC-3 cells. Cell cycle redistribution, viability, and apoptosis were quantitated in control and irradiated cells with or without the COX-2 inhibitor NS-398.

METHODS AND MATERIALS

Western blot analysis was used to assess COX-2 protein expression. Prostaglandin (PGE(2)) was measured after addition of arachidonic acid (AA) using a Monoclonal Immunoassay Kit. Cell cycle and apoptosis were assessed using flow cytometry.

RESULTS

We observed a dose-dependent increase in COX-2 of 37.0%, 79.7%, and 97.5% following irradiation with 5, 10, and 15 Gy, respectively. The PGE(2) level of irradiated cells was higher than in controls (1512 +/- 157.5 vs. 973.7 +/- 54.2 rhog PGE(2)/mL; p < 0.005, n = 4) while cells irradiated in the presence of NS-398 had reduced PGE(2) levels (218.8 +/- 80.1 rhog PGE(2)/mL; p < 0.005; n = 4). We found no differences in cell cycle distribution or apoptosis between cells irradiated in the presence or absence of NS-398.

CONCLUSIONS

COX-2 protein is upregulated and enzymatically active after irradiation, resulting in elevated levels of PGE(2). This effect can be suppressed by NS-398, which has clinical implications for therapies combining COX-2 inhibitors with radiation therapy.

Low-doses of ionising radiation induce melanoma metastases and trigger the immune system--adrenal axis feedback loop

Low-doses of ionising radiation are frequently implicated in triggering and/or accelerating the growth of skin and other malignancies. It seemed probable that the radiation at similar dose levels might initiate metastasis from already existing tumours. Highly pigmented human melanoma xenograft that had lost its ability for a spontaneous metastasising and grown subcutaneously in athymic mice was exposed to very low and well-defined doses of ionising radiation to determine whether low linear energy transfer radiation can restore metastatic potential of the tumour. To ensure that all effects derived from radiation-activated neoplastic cells only, I was delivered selectively to the cutaneous melanoma instead of using the external beam. The direct response of these tumours to radiation was monitored by determining the growth rate of the lesions. Histopathological methods were employed to detect metastases. The lowest radiation dose of approximately 6 cGy deposited in the tumours initiated metastatic spread in all animals. Gradual increase of the radiation doses diminished both the frequency of the appearance of metastases and their distance from the primary lesions. There were no metastases from non-irradiated melanomas. The highest dose used (60 cGy) did not affect significantly the growth of cutaneous (primary) tumours, but lower doses that enhanced inflammatory infiltration of the lesions reduced tumour growth. Such radiation-stimulated immune responses were accompanied by increased pigmentation in cutaneous lesions and activation of the adrenal cortex indicating that the immune system-adrenal axis feedback loop had been triggered. The results demonstrate that very low-doses of ionising radiation induce melanoma metastases. The phenomenon is accompanied by the stimulation of the immune system-adrenal axis feedback loop that regulates eicosanoid synthesis, thereby suggesting an involvement of these molecules in the process. Radiation doses approaching the therapeutic level do not initiate melanoma dissemination.

Toxicity antagonists in head and neck cancer

Clinical trials of altered fractionation and concurrent chemoradiation regimens have better elucidated the limits of both acute and late normal tissue toxicities in the head and neck. Acute effects on mucosal epithelium represent the principal barrier to intensification of radiation or chemoradiation schedules. Late soft tissue injury and organ dysfunction limit efforts to escalate radiation total dose. New insights into the cellular and molecular mechanisms of injury repair allow new strategies in the management and prevention of treatment-related toxicity. Toxicity antagonists are agents that directly interfere with the mechanism of toxicity or modulate the normal tissue response to injury. This article reviews 10 agents under development. Not only could such interventions reduce treatment-related morbidity, but they may also allow treatment intensification in advanced disease.

The response of tumours with Gompertzian growth characteristics to fractionated radiotherapy

Proliferation of tumour cells during radiotherapy may be a significant factor determining response to treatment. In previous work based on the linear-quadratic (LQ) model, tumour cell proliferation was assumed to be independent of both tumour size and the temporal structure of treatment. This paper examines a form of tumour cell proliferation that is exponential at small tumour sizes and Gompertzian at larger sizes. This is integrated with the LQ description of tumour cell sterilization. It is assumed that exposure to therapeutic radiation changes the state of tumour cells from viable to doomed. Doomed cells are assumed to be lost from the tumour mass with exponential kinetics. Six parameters are used to describe tumour response. Three of these are the standard 'LQ+time' (alpha, beta, Tpot) parameters. Two additional parameters are required to describe the shape of the tumour growth/regrowth curve (VG, Vmax). The sixth parameter (Ts) represents the rate of loss of doomed cells from the tumour. The model may be used to describe the effects of radiation therapy, both in terms of cure response (clonogenic cell sterilization) and also remission response (tumour regression and regrowth). An important feature of the model is that it enables the effects of temporally non-uniform treatments to be described. Preliminary modelling studies suggest that it may be possible to manipulate the temporal structures of fractionation schedules to increase the duration of remission at the expense of the probability of cure.

The effect of azelastine on acute radiation dermatitis in mice models

PURPOSE

In our previous report we described the clinical value of azelastine, an oral antiallergic agent, as an inhibitor of radiation dermatitis. Here we studied the effect of azelastine on normal skin and tumor size after irradiation in a mouse model.

METHODS AND MATERIALS

The modifying effects of azelastine on both the degree of radiation dermatitis and antitumoral effect of radiation therapy were investigated in the normal skin as well as in SCC VII tumors of C3H/He mice. The right hind legs, with or without tumors, were irradiated with 20-60 Gy at 0.62 Gy/min. Azelastine was administered via the mouse chow, and acute skin reactions and tumor growth curves were compared between the azelastine and control groups.

RESULTS

The acute skin reactions of the azelastine group were significantly less prominent than those of the control group (p < 0.01). At a dose of 40 Gy the dose modification factors were 1.19-1.25. The tumor growth curves of the azelastine and control groups were almost identical, indicating that the treatment response of irradiation was not affected by administration of azelastine.

CONCLUSIONS

Application of azelastine reduces the degree of acute radiation dermatitis without affecting the antitumoral effect of radiation therapy.