Selected eicosanoids increase the proliferation rate of human colon carcinoma cell lines and mouse colonocytes in vivo

Cyclooxygenase-2: a novel target in human solid tumors

The enzyme cyclooxygenase-2, which is involved in the conversion of arachidonic acid-to-prostanoid synthesis, plays a key role in many inflammatory and proliferative reactions. Experimental data have shown that prostaglandins have a central action in therapeutic targeting not only in the treatment of many inflammatory diseases but also in several types of human cancers. Inhibitors of cyclooxygenase activity seem to protect against carcinoma development and show promise as chemopreventive agents and possible target therapies. Data support new treatments for patients with solid cancers tailored to the molecular characteristics of the individual tumor.

Celecoxib treatment alters the gene expression profile of normal colonic mucosa

A clinical trial was recently conducted to evaluate the safety and efficacy of a selective inhibitor of cyclooxygenase-2 (celecoxib) in hereditary nonpolyposis colon cancer patients. In a randomized, placebo-controlled phase I/II multicenter trial, hereditary nonpolyposis colon cancer patients and gene carriers received either celecoxib at one of two doses or placebo. The goal was to evaluate the effects of these treatment arms on a number of endoscopic and tissue-based biomarker end points after 12 months of treatment. As part of this trial, we analyzed gene expression by cDNA array technology in normal descending (rectal) colonic mucosa of patients before and after treatment with celecoxib or placebo. We found that treatment of patients with celecoxib at recommended clinical doses (200 and 400 mg p.o. bid), in contrast to treatment with placebo, leads to changes in expression of >1,400 genes in the healthy colon, although in general, the magnitude of changes is <2-fold. Twenty-three of 25 pairs of colon biopsies taken before and after celecoxib treatment can be classified correctly by the pattern of gene expression in a leave-one-out cross-validation. Immune response, particularly T- and B-lymphocyte activation and early steps of inflammatory reaction, cell signaling and cell adhesion, response to stress, transforming growth factor-beta signaling, and regulation of apoptosis, are the main biological processes targeted by celecoxib as shown by overrepresentation analysis of the distribution of celecoxib-affected genes across Gene Ontology categories. Analysis of possible cumulative effects of celecoxib-induced changes in gene expression indicates that in healthy colon, celecoxib may suppress the immune response and early steps of inflammation, inhibit formation of focal contacts, and stimulate transforming growth factor-beta signaling.

Therapeutic options for 5-lipoxygenase inhibitors

5-Lipoxygenase (5-LO) catalyzes the conversion of arachidonic acid (AA) into leukotriene (LT) A(4) and 5-hydroperoxyeicosatetraenoic acid. LTA(4) can then be converted into LTB(4) by LTA(4) hydrolase or into LTC(4) by LTC(4) synthase and the LTC(4) synthase isoenzymes MGST2 and MGST3. LTB(4) is a potent chemoattractant for neutrophils, eosinophils and monocytes leading to adherence of phagocytes to vessel walls, neutrophil degranulation and release of superoxide anions. LTC(4) and its metabolite, LTD(4), are potent bronchoconstrictors that increase vascular permeability and stimulate mucus secretion from airways. Recent data also suggest that LT have an immunomodulatory role. Due to these properties, the increased biosynthesis of LT in asthma, and based upon clinical data obtained with CysLT(1) receptor antagonists in asthma patients, there is a consensus that CysLT play a prominent role in asthma. In this review, we summarize the knowledge on possible functions of the 5-LO pathway in various diseases like asthma, cancer and cardiovascular events and review the corresponding potential therapeutic roles of 5-LO inhibitors.

Mediators of PGE2 synthesis and signalling downstream of COX-2 represent potential targets for the prevention/treatment of colorectal cancer

Colorectal cancer is a major cause of mortality and whilst up to 80% of sporadic colorectal tumours are considered preventable, trends toward increasing obesity suggest the potential for a further increase in its worldwide incidence. Novel methods of colorectal cancer prevention and therapy are therefore of considerable importance. Non-steroidal anti-inflammatory drugs (NSAIDs) are chemopreventive against colorectal cancer, mainly through their inhibitory effects on the cyclooxygenase isoform COX-2. COX enzymes represent the committed step in prostaglandin biosynthesis and it is predominantly increased COX-2-mediated prostaglandin-E2 (PGE2) production that has a strong association with colorectal neoplasia, by promoting cell survival, cell growth, migration, invasion and angiogenesis. COX-1 and COX-2 inhibition by traditional NSAIDs (for example, aspirin) although chemopreventive have some side effects due to the role of COX-1 in maintaining the integrity of the gastric mucosa. Interestingly, the use of COX-2 selective NSAIDs has also shown promise in the prevention/treatment of colorectal cancer while having a reduced impact on the gastric mucosa. However, the prolonged use of high dose COX-2 selective inhibitors is associated with a risk of cardiovascular side effects. Whilst COX-2 inhibitors may still represent viable adjuvants to current colorectal cancer therapy, there is an urgent need to further our understanding of the downstream mechanisms by which PGE2 promotes tumorigenesis and hence identify safer, more effective strategies for the prevention of colorectal cancer. In particular, PGE2 synthases and E-prostanoid receptors (EP1-4) have recently attracted considerable interest in this area. It is hoped that at the appropriate stage, selective (and possibly combinatorial) inhibition of the synthesis and signalling of those prostaglandins most highly associated with colorectal tumorigenesis, such as PGE2, may have advantages over COX-2 selective inhibition and therefore represent more suitable targets for long-term chemoprevention. Furthermore, as COX-2 is found to be overexpressed in cancers such as breast, gastric, lung and pancreatic, these investigations may also have broad implications for the prevention/treatment of a number of other malignancies.

15-deoxy-Delta12,14-prostaglandin J2 inhibits the expression of microsomal prostaglandin E synthase type 2 in colon cancer cells

Prostaglandin (PG) E(2) (PGE(2)) plays a predominant role in promoting colorectal carcinogenesis. The biosynthesis of PGE(2) is accomplished by conversion of the cyclooxygenase (COX) product PGH(2) by several terminal prostaglandin E synthases (PGES). Among the known PGES isoforms, microsomal PGES type 1 (mPGES-1) and type 2 (mPGES-2) were found to be overexpressed in colorectal cancer (CRC); however, the role and regulation of these enzymes in this malignancy are not yet fully understood. Here, we report that the cyclopentenone prostaglandins (CyPGs) 15-deoxy-Delta(12,14)-PGJ(2) and PGA(2) downregulate mPGES-2 expression in the colorectal carcinoma cell lines Caco-2 and HCT 116 without affecting the expression of any other PGES or COX. Inhibition of mPGES-2 was subsequently followed by decreased microsomal PGES activity. These effects were mediated via modulation of the cellular thiol-disulfide redox status but did not involve activation of the peroxisome proliferator-activated receptor gamma or PGD(2) receptors. CyPGs had antiproliferative properties in vitro; however, this biological activity could not be directly attributed to decreased PGES activity because it could not be reversed by adding PGE(2). Our data suggest that there is a feedback mechanism between PGE(2) and CyPGs that implicates mPGES-2 as a new potential target for pharmacological intervention in CRC.

Endometriosis as a model for inflammation–hormone interactions in ovarian and breast cancers

Chronic inflammation has been implicated in a variety of cancers. In this review, we consider associations between endometriosis and cancers both local (ovarian) and distant (breast). We review the epidemiological data linking endometriosis to ovarian and breast cancers. We then consider evidence for a role for sex steroid hormones and for inflammation in the aetiology of each of these cancers. Finally, we consider that endometriosis may promote alterations in sex steroid hormones and inflammatory mediators. A possible explanation for the association between endometriosis and these reproductive cancers may then be local and systemic enhancement of aberrant inflammatory and hormonal mediators. If this hypothesis is true, endometriosis may need to be considered as a risk factor for ovarian and breast cancers, triggering increasingly intensive surveillance. Moreover, treatments for endometriosis may require consideration of the impact on long-term cancer risk.

Increased EP4 Receptor Expression in Colorectal Cancer Progression Promotes Cell Growth and Anchorage Independence

Cyclooxygenase-2 and prostaglandin E(2) (PGE(2)) levels are increased in colorectal cancers and a subset of adenomas. PGE(2) signaling through the EP4 receptor has previously been associated with colorectal tumorigenesis. However, changes in EP4 expression during adenoma to carcinoma progression have not been investigated, neither has whether levels of EP4 influence important markers of malignant potential, such as anchorage-independent growth or the tumors growth response to PGE(2). We report using immunohistochemistry that in vivo EP4 receptor protein expression was increased in colorectal cancers (100%) as well as adenomas (36%) when compared with normal colonic epithelium. EP4 expression was also higher in colorectal carcinoma compared with adenoma cell lines and increased with in vitro models of tumor progression. Adenoma (PC/AA/C1 and RG/C2) and carcinoma cell lines (HT29) were growth stimulated by PGE(2) up to 0.5 micromol/L. However, although carcinoma and transformed adenoma (PC/AA/C1SB10C, a transformed derivative of PC/AA/C1) cells remain stimulated by higher doses of PGE(2) (10 micromol/L), the adenoma cell lines were inhibited. Interestingly, enforced expression of EP4 in the adenoma cell line, RG/C2, resulted in stimulation of growth by 10 micromol/L PGE(2) and promoted anchorage-independent growth. Both in vivo and in vitro data from this study suggest that increased EP4 receptor expression is important during colorectal carcinogenesis. We propose that high levels of PGE(2) in a tumor microenvironment would select for cells with increased EP4 expression, and that the EP4 receptor may therefore represent an important target for colorectal cancer prevention and treatment.

Cyclooxygenase-2 plays a suppressive role for induction of apoptosis in isoliquiritigenin-treated mouse colon cancer cells

Cellular damage induced by chronic inflammation is a well known cause of colon carcinogenesis. Cyclooxygenase-2 (COX-2), the enzyme that converts arachidonic acid to prostanoids, is known to play an important role in inflammation. Herbal flavonoid isoliquiritigenin (ILTG) has previously been reported to be a strong suppresser of the COX-2 pathway as well as an inducer of apoptosis. Here we report that the susceptibility to apoptosis by ILTG is dependent on the level of COX-2 in mouse colon adenocarcinoma Colon 26, which spontaneously expresses COX-2. This dependency was observed to be enhanced by blockage of the lipoxigenases (LOXs)-mediated metabolic pathway and attenuated by addition of a number of prostaglandins and thromboxanes. Taken together, these findings indicate that ILTG-induced apoptosis is negatively regulated by the COX-2 expression level.

Is COX-2 a 'collateral' target in cancer prevention?

NSAIDs (non-steroidal anti-inflammatory drugs) prevent colon and other cancers. The fact that NSAIDs inhibit the eicosanoid pathway prompted mechanistic drug-developmental work focusing on COX (cyclo-oxygenase) and its products. The increased prostaglandin E2 levels and the overexpression of COX-2 in colon and many other cancers provided the rationale for clinical trials with COX-2 inhibitors for cancer prevention or treatment. However, one COX-2 inhibitor has been withdrawn from the market because of cardiovascular side effects, and there are concerns about a class effect. Evidence suggests that COX-2 may not be the only, or the ideal, target for cancer prevention; for example, COX-2 is not expressed in human aberrant crypt foci, the earliest recognizable pre-malignant lesion in the colon; COX-2 is expressed in less than half of the adenomas; in vitro data show that NSAIDs do not require the presence of COX-2 to prevent cancer; in familial adenomatous polyposis, the COX-2 inhibitor, celecoxib, had a modest effect, which was weaker than that of a traditional NSAID; and COX-2-specific inhibitors have several COX-2-independent activities, which may account for part of their cancer-preventive properties. The multiple COX-2-independent targets, and the limitations of COX-2 inhibitors, suggest the need to explore targets other than COX-2.

Prostaglandin E2 promotes colon cancer cell growth through a Gs-axin-beta-catenin signaling axis

How cyclooxygenase-2 (COX-2) and its proinflammatory metabolite prostaglandin E2 (PGE2) enhance colon cancer progression remains poorly understood. We show that PGE2 stimulates colon cancer cell growth through its heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptor, EP2, by a signaling route that involves the activation of phosphoinositide 3-kinase and the protein kinase Akt by free G protein betagamma subunits and the direct association of the G protein alphas subunit with the regulator of G protein signaling (RGS) domain of axin. This leads to the inactivation and release of glycogen synthase kinase 3beta from its complex with axin, thereby relieving the inhibitory phosphorylation of beta-catenin and activating its signaling pathway. These findings may provide a molecular framework for the future evaluation of chemopreventive strategies for colorectal cancer.

Non-COX-2 targets and cancer: Expanding the molecular target repertoire of chemoprevention

Chemoprevention represents a highly promising approach for the control of cancer. That nonsteroidal anti-inflammatory drugs (NSAIDs) prevent colon and other cancers has led to novel approaches to cancer prevention. The known inhibitory effect of NSAIDs on the eicosanoid pathway prompted mechanistic and drug development work focusing on cyclooxygenase (COX), culminating in clinical trials of cyclooxygenase 2 (COX-2) inhibitors for cancer prevention or treatment. However, two COX-2 inhibitors have been withdrawn due to side effects. Here we review several pathways of the eicosanoid cascade that are relevant to cancer; summarize the evidence regarding the role of COX-2 as a target for cancer prevention; and discuss several of the molecular targets that may mediate the chemopreventive effect of NSAIDs. The clinically modest results obtained to date with COX-2 specific inhibitors used in cancer prevention; the multiple COX-2-independent targets of both NSAIDs and COX-2 inhibitors; and the limitations of some COX-2 inhibitors indicate that exploiting these (non-COX-2) molecular targets will likely yield effective new approaches for cancer chemoprevention.

Leukotriene B4 receptor inhibitor LY293111 induces cell cycle arrest and apoptosis in human anaplastic large-cell lymphoma cells via JNK phosphorylation

Anaplastic large-cell lymphoma (ALCL) is a heterogeneous lymphoma category in which a subset of cases carry the t(2;5)(p23;q35) or variant translocations resulting in overexpression of anaplastic lymphoma kinase (ALK). LY293111 (2-[2-propyl-3-[3-[2-ethyl-4-(4-fluorophenyl)-5-hydroxyphenoxy]-propoxy]-phenoxy] benzoic acid sodium salt) is a leukotriene B4 receptor antagonist, which was found to be safe and tolerable in Phase I clinical trials. In this study, we investigated the potential therapeutic effects and mechanisms of action of LY293111 in ALCL cell lines. LY293111 inhibited proliferation of both ALK(+) and ALK(-) ALCL cell in a dose-dependent fashion and induced complete G(1)-S cell cycle arrest, which was accompanied by upregulation of p27 and downregulation of cyclin E. Pretreatment with LY293111 for 4 h resulted in profound inhibition of serum-induced phosphorylation of extracellular-regulated kinases-1 and 2 and Akt and a concomitant increase in the phosphorylation of the stress-activated kinase c-jun N-terminal kinases (JNK). Simultaneously, LY293111 induced caspase-dependent apoptosis via activation of the intrinsic pathway, including early loss of mitochondrial inner transmembrane potential and the production of reactive oxygen species (ROS), cleavage of caspases-9, -3, poly ADP-ribose polymerase (PARP) and X-linked inhibitor of apoptosis. The phospho-JNK inhibitor SP600125 partially protected Sup-M2 cells from LY293111-induced apoptosis, PARP cleavage and ROS generation, suggesting a role for JNK in LY293111-induced cell death. These results warrant further studies of LY293111 in ALCL.

Cancer prevention: a new era beyond cyclooxygenase-2

The seminal epidemiological observation that nonsteroidal anti-inflammatory drugs (NSAIDs) prevent colon and possibly other cancers has spurred novel approaches to cancer prevention. The known inhibitory effect of NSAIDs on the eicosanoid pathway prompted studies focusing on cyclooxygenase (COX) and its products. The increased prostaglandin E2 levels and the overexpression of COX-2 in colon and many other cancers provided the rationale for clinical trials with COX-2 inhibitors for cancer prevention or treatment. Their efficacy in the prevention of sporadic colon and other cancers remains unknown; one COX-2 inhibitor has been withdrawn because of side effects, and there are concerns about whether these effects are class-specific. There is evidence to suggest that COX-2 may not be the only or ideal eicosanoid pathway target for cancer prevention. Six sets of observations support this notion: the relatively late induction of COX-2 during carcinogenesis; the finding that NSAIDs may not require inhibition of COX-2 for their effect; the modest effect of coxibs in cancer prevention; that currently available coxibs have multiple non-COX-2 effects that may account for at least some of their efficacy; the possibility that concurrent inhibition of COX-2 in non-neoplastic cells may be harmful; and the possibility that COX-2 inhibition may modulate alternative eicosanoid pathways in a way that promotes carcinogenesis. Given the limitations of COX-2-specific inhibitors and the biological evidence mentioned above, we suggest that targets other than COX-2 should be pursued as alternative or complementary approaches to cancer prevention.

The effects of L-748706, a selective cyclooxygenase-2 inhibitor, on N-nitrosomethylbenzylamine-induced rat esophageal tumorigenesis

Epidemiological studies suggest that the frequent intake of non-steroidal anti-inflammatory drugs (NSAIDs) is associated with a decreased risk of developing esophageal squamous cell carcinoma (SCC). This decrease is thought to correlate with the inhibition of cyclooxygenase (COX) activity. The production of prostaglandin E2 (PGE2), a major metabolite of COX, is increased in numerous human cancers including esophageal SCC, therefore, inhibition of COX activity and subsequent suppression of the formation of PGE2 may be chemopreventive in the esophagus. The objective of the present study was to determine whether L-748706 (L-706), a novel selective COX-2 inhibitor, would prevent N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumor progression in the Fischer 344 (F344) rat. In rats pretreated with a low-dose of NMBA (0.25 mg/kg body weight), L-706 at 100 p.p.m. in the diet significantly reduced tumor multiplicity but not tumor incidence. At 150 p.p.m. in the diet, L-706 alone and in combination with 200 p.p.m. piroxicam produced significant reductions in both tumor incidence and multiplicity. Inhibition of tumor development in low-dose NMBA-treated rats was associated with reductions in esophageal cell proliferation rates and PGE2 levels in preneoplastic tissues. In contrast, in rats treated with a higher dose of NMBA (0.5 mg/kg body weight), neither L-706 alone nor in combination with piroxicam reduced esophageal tumor incidence or multiplicity in spite of the fact that they reduced esophageal PGE2 levels in preneoplastic tissues and in papillomas. Cell proliferation rates were reduced only in animals treated with L-706 + piroxicam. Our data suggest that the chemopreventive treatments were effective in inhibiting tumor development in NMBA-treated animals only when they reduced PGE2 levels in preneoplastic esophageal tissues approximately to those levels found in normal esophagus.

Inhibition of the expression and activity of cyclooxygenase-2 by chicory extract

Chicory is a major source of fructans with reported prebiotic-bifidogenic properties. In the present study, the potential anti-inflammatory activities of chicory were investigated. Ethyl acetate chicory root extract produced a marked inhibition of prostaglandin E(2) (PGE(2)) production in human colon carcinoma HT29 cells treated with the pro-inflammatory agent TNF-alpha. Two independent mechanisms of action were identified: (1) a drastic inhibition of the induction by TNF-alpha of cyclooxygenase 2 (COX-2) protein expression and (2) a direct inhibition of COX enzyme activities with a significantly higher selectivity for COX-2 activity. The inhibition of TNF-alpha-dependent induction of COX-2 expression was mediated by an inhibition of NF-kappaB activation. A major sesquiterpene lactone of chicory root, the guaianolide 8-deoxylactucin, was identified as the key inhibitor of COX-2 protein expression present in chicory extract. Altogether, the data presented strongly support chicory root as a promising source of functional food ingredient, combining prebiotic and anti-inflammatory properties.

Signal transduction network leading to COX-2 Induction: a road map in search of cancer chemopreventives

Cancer is still a major global health concern even after an everlasting strive in conquering this dread disease. Emphasis is now given to chemoprevention to reduce the risk of cancer and also to improve the quality of life among cancer afflicted individuals. Recent progress in molecular biology of cancer has identified key components of the cellular signaling network, whose functional abnormality results in undesired alterations in cellular homeostasis, creating a cellular microenvironment that favors premalignant and malignant transformation. Multiple lines of evidence suggest an elevated expression of cyclooxygenase-2 (COX-2) is causally linked to cancer. In response to oxidative/pro-inflammatory stimuli, turning on unusual signaling arrays mediated through diverse classes of kinases and transcription factors results in aberrant expression of COX-2. Population-based as well as laboratory studies have explored a broad spectrum of chemopreventive agents including selective COX-2 inhibitors and a wide variety of anti-inflammatory phytochemicals, which have been shown to target cellular signaling molecules as underlying mechanisms of chemoprevention. Thus, unraveling signaling pathways regulating aberrant COX-2 expression and targeted blocking of one or more components of those signal cascades may be exploited in searching chemopreventive agents in the future.

Effect of LY293111 in combination with gemcitabine in colonic cancer

New adjuvant therapies are needed for the treatment of stage III colon cancer. The essential fatty acids, linoleic and arachidonic acid enhance tumorigenesis through the cyclooxygenase and lipoxygenase pathways. Leukotriene B4 (LTB4) is a product of 5-lipoxygenase (5-LOX) which has tumor-promoting effects. The LTB4 receptor antagonist, LY293111 inhibited tumor growth and induced apoptosis in vitro. The effectiveness of LY293111, alone and in combination with gemcitabine was investigated in a heterotopic xenograft model in athymic mice using HT29 and LoVo human colonic cancer cells. The combined therapy markedly inhibited tumor growth and could warrant consideration as a new therapeutic option.

Prostaglandin EP receptors: Targets for treatment and prevention of colorectal cancer?

The importance of the prostaglandin (PG) synthesis pathway, particularly the rate-limiting enzymatic step catalyzed by cyclooxygenase, to colorectal carcinogenesis and development of novel anticolorectal cancer therapy is well established. The predominant PG species in benign and malignant colorectal tumors is PGE2. PGE2 acts via four EP receptors termed EP1 to EP4. Recently, EP receptors have been identified as potential targets for treatment and/or prevention of colorectal cancer. This review summarizes existing knowledge of the expression and function of the EP receptor subtypes in human and rodent intestine during tumorigenic progression and describes the current literature on targeting EP receptor signaling during intestinal tumorigenesis.

Expression of cyclooxygenase-2 in human esophageal squamous cell carcinomas

AIM: To determine whether cyclooxygenase-2 (COX-2) was expressed in human esophageal squamous cell carcinoma.

METHODS: Quantitative reverse transcription-polymerase chain reaction (RT-PCR), western blotting, immunohistoc-hemistry and immunofluorescence were used to assess the expression level of COX-2 in esophageal tissue.

RESULTS: COX-2 mRNA levels were increased by > 80-fold in esophageal squamous cell carcinoma when compared to adjacent noncancerous tissue. COX-2 protein was present in 21 of 30 cases of esophageal squamous cell carcinoma tissues, but was undetectable in noncancerous tissue. Immunohistochemistry was performed to directly show expression of COX-2 in tumor tissue.

CONCLUSION: These results suggest that COX-2 may be an important factor for esophageal cancer and inhibition of COX-2 may be helpful for prevention and possibly treatment of this cancer.

Cyclooxygenase-2 and Gastrointestinal Cancer

The cyclooxygenase (COX) enzymes (COX-1 and COX-2) are key enzymes of prostaglandin (PG) biosynthesis. Nonselective non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the enzymatic activity of both COX-1 and COX-2. Selective COX-2 inhibitors have been developed that appear to have 50% less gastrointestinal toxicity than traditional nonselective NSAIDs. Experimental evidence suggests that the COX pathway is involved in tumor promotion. Evidence to support this comes from both clinical and laboratory findings suggesting that chronic NSAID use reduces the relative risk for developing colorectal cancer (CRC). Although the precise mechanism or mechanisms by which these drugs affect tumor progression is not completely understood, it is likely that part of their anti-tumor effect is due to inhibition of the COX- 2 enzyme. COX-2 levels are increased in CRC as well as in several other solid malignancies. COX-2-derived bioactive lipid products promote tumor-associated n eovascularization, inhibit cell death, and stimulate cell proliferation and motility. Additionally, treatment with COX-2-selective inhibitors reduces polyp burden in animal models of intestinal neoplasia and in humans with familial adenomatous polyposis (FAP). Ongoing human clinical trails are under way to test the efficacy of COX-2-selective inhibitors in a number of human cancers.

Nutritional and botanical modulation of the inflammatory cascade--eicosanoids, cyclooxygenases, and lipoxygenases--as an adjunct in cancer therapy

Emerging on the horizon in cancer therapy is an expansion of the scope of treatment beyond cytotoxic approaches to include molecular management of cancer physiopathology. The goal in these integrative approaches, which extends beyond eradicating the affected cells, is to control the cancer phenotype. One key new approach appears to be modulation of the inflammatory cascade, as research is expanding that links cancer initiation, promotion, progression, angiogenesis, and metastasis to inflammatory events. This article presents a literature review of the emerging relationship between neoplasia and inflammatory eicosanoids (PGE2 and related prostaglandins), with a focus on how inhibition of their synthesizing oxidases, particularly cyclooxygenase (COX), offers anticancer actions in vitro and in vivo. Although a majority of this research emphasizes the pharmaceutical applications of nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors, these agents fail to address alternate pathways available for the synthesis of proinflammatory eicosanoids. Evidence is presented that suggests the inhibition of lipoxygenase and its by-products-LTB4, 5-HETE, and 12-HETE-represents an overlooked but crucial component in complementary cancer therapies. Based on the hypothesis that natural agents capable of modulating both lipoxygenase and COX may advance the efficacy of cancer therapy, an overview and discussion is presented of dietary modifications and selected nutritional and botanical agents (notably, omega-3 fatty acids, antioxidants, boswellia, bromelain, curcumin, and quercetin) that favorably influence eicosanoid production.

Piroxicam selectively inhibits the growth of premalignant and malignant human oral cell lines by limiting their progression through the S phase and reducing the levels of cyclins and AP-1

Studies have shown that nonsteroidal antiinflammatory drugs (NSAIDs) reduce the risk of and mortality from a variety of cancers. Although cyclooxygenase (COX)-dependent and -independent pathways may be involved, the mechanisms responsible for these effects remain unknown. In our study, we found that piroxicam inhibited cell growth in premalignant and malignant, but not normal, human oral epithelial cell lines in a concentration- and time-dependent manner. After 6 days of exposure, the concentration that inhibited growth by 50% was 181 and 211 microM for premalignant and malignant cells, respectively. Piroxicam did not induce apoptosis. The growth inhibitory effect was COX and PGE2 independent. Adding PGE2 or infecting cells with a COX-1 transgene did not abrogate piroxicam-induced growth inhibition. After treatment of the premalignant and malignant cell lines with piroxicam, cells accumulated in the S phase of the cell cycle. Upon removal of piroxicam, cells entered the G2 phase. The S phase block was accompanied by a reduction in the protein levels of cyclin A, cyclin B1, cyclin D1, cdc2, PCNA and the c-jun AP-1 component. Therefore, piroxicam may exert its growth inhibitory effects selectively on the premalignant and malignant human oral epithelial cells lines via signaling pathways regulating the progression of cells through the S phase of the cell cycle.

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.

Cyclooxygenase-2 and 5-lipoxygenase converging functions on cell proliferation and tumor angiogenesis: implications for cancer therapy

Cyclooxygenase (COX) and lipoxygenase (LO) metabolic pathways are emerging as key regulators of cell proliferation and neo-angiogenesis. COX and LO inhibitors are being investigated as potential anticancer drugs and results from clinical trials seem to be encouraging. In this article we will review evidence of COX-2 and 5-LO involvement in cancer pathobiology, propose a model of integrated control of cell proliferation by these enzymes, and discuss the pharmacologic implications of this model.

Leukotriene A4 hydrolase in rat and human esophageal adenocarcinomas and inhibitory effects of bestatin

BACKGROUND

Esophageal adenocarcinoma (EAC) is increasing at the most rapid rate of any cancer in the United States. An esophagogastroduodenal anastomosis (EGDA) surgical model in rats mimics human gastroesophageal reflux and results in EAC. Leukotriene A4 hydrolase (LTA4H), a protein overexpressed in EAC in this model, is a rate-limiting enzyme in the biosynthesis of leukotriene B4 (LTB4), a potent inflammatory mediator. We used this model and human EAC and non-tumor tissues to elucidate the expression pattern of LTA4H and to evaluate it as a target for chemoprevention.

METHODS

LTA4H expression was examined by western blotting and immunohistochemistry. The functional role of LTA4H in carcinogenesis was investigated by use of an LTA4H inhibitor, bestatin, in the rat EGDA model. All statistical tests were two-sided.

RESULTS

LTA4H was overexpressed in all 10 rat EACs examined, compared with its level in normal rat tissue; it was also overexpressed in four of six human EAC tumor samples, compared with its level in adjacent non-tumor tissue. In tissue sections from 20 EGDA rats and 92 patients (86 with EAC, one with dysplasia, and five with columnar-lined esophagus), LTA4H was expressed in infiltrating inflammatory cells and overexpressed in the columnar cells of preinvasive lesions and cancers, especially in well-differentiated EACs, as compared with the basal cells of the normal esophageal squamous epithelium. Bestatin statistically significantly inhibited LTB4 biosynthesis in the esophageal tissues of EGDA rats (without bestatin = 8.28 ng/mg of protein; with bestatin = 4.68 ng/mg of protein; difference = 3.60, 95% CI = 1.59 to 5.61; P = .002) and reduced the incidence of EAC in the EGDA rats from 57.7% (15 of 26 rats) to 26.1% (6 of 23 rats) (difference = 31.6%, 95% CI = 0.3% to 56.2%; P = .042).

CONCLUSION

LTA4H overexpression appears to be an early event in esophageal adenocarcinogenesis and is a potential target for the chemoprevention of EAC.

Cyclooxygenase-2 in human non-small cell lung cancer

AIM

Recent studies report that the expression of cyclooxygenase (COX) in non-small cell lung cancer (NSCLC) is increased, especially in adenocarcinoma. Platelet activating factor (PAF), n-sodium butyrate (n-BT), and phorbol myristate acetate (PMA) are important mediators of the inflammatory process.

METHOD

Expression of COX-2 in 67 stage 1 NSCLC paraffin-embedded tumor samples was determined by immunohistochemistry (IHC). Four NSCL cell lines were incubated and stimulated by PAF, n-BT and PMA for 48 h. Expression of COX-2 was determined by IHC, immunoblotting, and reverse transcription-polymerase chain reaction (RT-PCR).

RESULT

IHC showed increasing immunoreactivity in 35 of 67 (52%) in stage I NSCLC, 31 of 53 (59%) in adenocarcinoma and 13 of 15 (87%) in bronchoalveolar cell carcinoma, but only 2 of 12 (17%) in epidermoid carcinoma. The COX-2 expression in NSCLC cells was 75% (3/4) and the COX-1 expression in NSCLC cells was 100% (4/4). After stimulation with PMA, n-BT, PAF and n-BT + PAF, the COX-2 expression in NSCLC cells was significantly increased in all cell lines.

CONCLUSIONS

The expression of COX-2 in NSCLC cells is high and was up-regulated by PMA, n-BT and PAF. We consider that COX-2 inhibitors will play an important role in the therapy of NSCLC.

New avenues for the prevention of colorectal cancer: targeting cyclo-oxygenase-2 activity

Carcinoma of the colon and/or rectum represents the second most common gastrointestinal malignancy worldwide. Despite this prevalence, current therapeutic regimens remain largely ineffectual, particularly when the disease is diagnosed at an advanced stage. Recent work in the field of colorectal cancer has established that a chronic intake of non steroidal anti-inflammatory drugs can reduce the risk of developing colorectal cancer. Although the precise mechanism(s) by which these drugs inhibit tumour growth is not completely understood, it is likely that at least a part of their anti-tumorigenic effects results from an inhibition of the cyclo-oxygenase-2 enzyme. This chapter will focus on this emerging research area and the promise it brings for identifying new strategies for the prevention of colorectal cancer.

Gamma-tocopherol inhibits human cancer cell cycle progression and cell proliferation by down-regulation of cyclins

Effects of gamma-tocopherol on the cell cycle and proliferation were examined in human prostate carcinoma, colorectal adenocarcinoma, and osteosarcoma cells. Many epidemiological studies have suggested an anticancer activity of vitamin E, yet mechanistic studies are sparse to date. Vitamin E consists of four tocopherols (alpha-, beta-, gamma-, delta-) and the corresponding tocotrienols. Because gamma-tocopherol is the predominant form of tocopherol found in the U.S. diet, while alpha-tocopherol is the form of vitamin E most readily found in dietary supplements, we compared physiologically relevant concentrations of these tocopherols and found a more significant growth inhibition effect for gamma- than for alpha-tocopherol. Flow cytometry analysis of gamma-tocopherol treated prostate carcinoma DU-145 cells showed decreased progression into the S-phase. This effect was associated with reduced DNA synthesis as measured by 5-bromo-2'-deoxy-uridine incorporation. Furthermore, Western-blot analysis of gamma-tocopherol treated cells showed decreased levels of cyclin D1 and cyclin E. Taken together, the results indicate that gamma-tocopherol inhibits cell cycle progression via reduction of cyclin D1 and cyclin E levels. Because gamma-tocopherol has a weaker antioxidant capacity than a-tocopherol and gamma-tocopherol more significantly inhibited cell proliferation as well as DNA synthesis than alpha-tocopherol, we suggest a non-antioxidant mechanism to be at the basis of this effect.

Human colorectal adenomas demonstrate a size-dependent increase in epithelial cyclooxygenase-2 expression

Non-steroidal anti-inflammatory drugs are chemopreventive for colorectal cancer. This effect is due in part to their ability to inhibit the inducible isoform of cyclooxygenase (COX-2). However, the cellular expression and role of COX-2 in the premalignant stages of colorectal tumourigenesis is unclear. COX-2 expression was assessed in 35 human colorectal adenomas and 38 sporadic invasive colorectal adenocarcinomas. Adenomas were classified as small (<5 mm in diameter), medium (5-10 mm), and large (>10 mm). All tissues were paraffin-embedded and formalin-fixed. COX-2 protein expression was determined using immunohistochemistry. COX-2 was detected in the epithelial cells in 35 of 38 carcinomas (92%) and in 8 of 8 (100%) lymph node metastases. All of the epithelial cells expressed COX-2 in 30 of 35 (86%) carcinomas and in 100% of the lymph node metastases. Twenty-three of 35 (66%) adenomas expressed COX-2 in the tumour epithelium. With an increase in the size of adenoma (<5 mm, 5-10 mm, >10 mm), there was an increase in (i) the proportion of adenomas with immunoreactive COX-2 in the epithelium (p = 0.036)-this was 38% in small adenomas and 82% in large adenomas; (ii) the extent of epithelial COX-2 staining within a given tumour (p = 0.003)-100% of epithelial cells were COX-2-positive in 15% of small adenomas and in 73% of large adenomas; and (iii) the intensity of epithelial COX-2 staining (p = 0.009)-strong COX-2 staining occurred in 8% of small adenomas and in 36% of large adenomas. COX-2 immunoreactivity was not detected in adjacent normal epithelium but was apparent in fibroblasts and inflammatory mononuclear cells of adjacent normal, adenoma, and carcinoma tissue. These results suggest that epithelial COX-2 activity is important for the growth and/or survival of adenomatous epithelial cells from an adenoma diameter of less than 5 mm and that there is a selective advantage for adenoma epithelial cells expressing higher levels of COX-2.

Inhibition of DNA replication by fish oil-treated cytoplasm is counteracted by fish oil-treated nuclear extract

We have recently noted that cells treated with fish oil and n-3-fatty acids show slower DNA replication rates than cells treated with a control emulsion or corn oil only. However, it is not clearly understood how such an effect is induced. Fish oil and its metabolites are known to have several modulating effects on signal transduction pathways. Alternatively, they may influence DNA replication by interacting directly with nuclear components. To investigate this problem in greater detail, we have studied the kinetics of DNA synthesis in a cell-free system derived from HeLa cells. Nuclei and cytosolic extract were isolated from cells synchronized in early S phase after treatment with control emulsion, corn oil, or fish oil, respectively. The nuclei were reconstituted with cytosolic extract and a reaction mixture containing bromodeoxyuridine (BrdU) triphosphate to label newly synthesized DNA. The rate of DNA synthesis was measured by bivariate DNA/BrdU analysis and flow cytometry. We show that fish oil-treated cytosol inhibits the elongation of newly synthesized DNA by ~80% in control nuclei. However, nuclei treated with fish oil escape this inhibitory effect. We also show that addition of nuclear extract from fish oil-treated cells reverses the inhibitory effect seen in the reconstitution system of control nuclei and fish oil-treated cytosol. These results indicate that polyunsaturated fatty acids can modulate DNA synthesis through cytosolic as well as soluble nuclear factors.

Dysplasia and carcinoma development in a repeated dextran sulfate sodium-induced colitis model

BACKGROUND

As an important mechanism underlying the increased risk of colorectal carcinoma development in patients with long-standing ulcerative colitis, promotion as a result of the regenerative process has been proposed. In the present study, a dysplasia-carcinoma sequence in a novel repeated colitis model in mice is documented.

METHODS

Repeated colitis was induced by nine administration cycles of 3% dextran sulfate sodium (DSS; molecular weight, 54 000): each administration cycle comprised 3% DSS for 7 days followed by distilled water for the subsequent 14 days, to give conditions similar to the clinically observed active and remission phases in humans.

RESULTS

Multiple colorectal tumors (nine low- and four high-grade dysplasias and two carcinomas) developed in 25 mice. These neoplastic lesions consisted of tubular structures, presenting as various types of elevated, flat and depressed tumor, similar to those in ulcerative colitis patients. A time-course study with assessment of the severity of colitis and in vivo bromodeoxyuridine uptake during a single 3% DSS administration cycle revealed a high level of regenerative activity in the colitis-affected mucosal epithelia.

CONCLUSION

Thus, with the present repeated colitis model, regeneration and neoplastic lesions were apparent, the biological features of which provide evidence of a colorectal dysplasia-invasive carcinoma sequence in ulcerative colitis.

Angiogenic markers, neovascularization and malignant deformation of Barrett's esophagus

The molecular events underlying progression of Barrett's esophagus to adenocarcinoma remain an area of active investigation. Neovascularization and angiogenesis have been studied in esophageal adenocarcinomas by counting of microvessels after staining with vascular markers, and by immunohistochemistry for vascular endothelial growth factor. Angiogenesis appears to be increased early in the neoplastic process, but has poor prognostic value. We have demonstrated that expression levels of two important genes that regulate cell growth, namely inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, are frequently upregulated in Barrett's esophagus and associated adenocarcinomas. COX-2 expression may be related to reflux of bile salts, which induce COX-2 expression in Barrett's tissues and esophageal adenocarcinoma cells in vitro. COX-2 inhibition induces apoptosis and blocks proliferation in COX-2-expressing esophageal adenocarcinoma cells in vitro, and blocks angiogenesis in both in vivo and in vitro models. Although controversial, recent evidence suggest that iNOS-derived NO can inhibit angiogenesis in some model systems. In conclusion, both iNOS and COX-2 appear to be involved in Barrett's-associated neoplastic progression, but COX-2 inhibition is more promising as a chemopreventive strategy. COX-2 inhibition may exert beneficial effects by decreasing angiogenesis and epithelial proliferation, and by facilitating apoptosis of epithelial cells that have undergone DNA damage.

Design, synthesis, and biological evaluation of a cephalosporin-monohydroguaiaretic acid prodrug activated by a monoclonal antibody-beta-lactamase conjugate

A novel cephalosporin derivative of monohydroguaiaretic acid (cephem-M(3)N, 7) was synthesized and found to possess anticancer activity against human leukemia (K562), breast carcinoma (MCF7), human lung cancer (A549), human colon cancer (Colo205) and pancreatic cancer cells (Capan2 and MiaPaCa2). A tumor targeting fusion protein (dsFv3-beta-lactamase) was also used in conjunction with cephem-based M(3)N 7 and its potency toward K562, MCF7, A549, Colo205, Capan2, and MiaPaCa2 was found to approach that of the free M(3)N (4). In the presence of dsFv3-beta-lactamase, tumor cells were found to be much more susceptible to conjugate 7 than normal human embryonic lung (HEL) cells and normal fibroblasts (Hef522). These notions provide a new approach to the use of nordihydroguaiaretic acid (NDGA) and its derivatives for antitumor therapy.

Dual function of nonsteroidal anti-inflammatory drugs (NSAIDs): inhibition of cyclooxygenase and induction of NSAID-activated gene

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used drugs for the treatment of inflammatory disease and have a chemopreventive effect on colorectal cancer. NSAIDs inhibit cyclooxygenase (COX)-1 and/or COX-2 activity, but the chemopreventive effect may be, in part, independent of prostaglandin inhibition. NSAID-activated gene (NAG-1) was previously identified as a gene induced by some NSAIDs in cells devoid of COX activity. NAG-1 has proapoptotic and antitumorigenic activity in vitro and in vivo. To determine whether the induction of NAG-1 by NSAIDs is influenced by COX expression, we developed COX-1- and COX-2-overexpressing HCT-116 cells. COX expression did not affect NSAID-induced NAG-1 expression as assessed by transient and stable transfection. Also, NAG-1 expression was not affected by PGE(2) and arachidonic acid, suggesting that NAG-1 induction by NSAIDs occurs by a prostanoid-independent manner. We also report that indomethacin increased NAG-1 expression in a number of cells from tissues other than colorectal. In conclusion, NSAIDs have dual function, induction of NAG-1 expression and inhibition of COX activity that occurs in a variety of cell lines.

Up-regulation of cyclooxygenase-2 expression in lymphocytic thyroiditis and thyroid tumors: significant correlation with inducible nitric oxide synthase

To cast light on relations of cyclooxygenase-2 (COX-2) expression to lymphocytic thyroiditis and thyroid tumorigenesis, protein levels were immunohistochemically assessed and compared with inducible nitric oxide synthase (iNOS) in a total of 181 cases: follicular adenoma, 23; well-differentiated papillary carcinoma, 85; poorly differentiated papillary carcinoma, 25; anaplastic carcinoma, 7; and follicular carcinoma, 41. In addition, 72 specimens of normal follicular epithelia and 36 of lymphocytic thyroiditis were used as control samples. Immunohistochemical results were confirmed in 2 cases each of normal thyroid, lymphocytic thyroiditis, and well-differentiated and poorly differentiated papillary carcinoma, by Western blotting assay. Stepwise increments in overexpression of COX-2 and iNOS were revealed in epithelial cells of lymphocytic thyroiditis, follicular adenoma, and papillary carcinoma; normal thyroid epithelium showed little expression. A significant positive correlation between the 2 enzymes was found with all cases. Enhanced expression of both COX-2 and iNOS suggests important roles in the inflammatory processes underlying lymphocytic thyroiditis and thyroid tumorigenesis.

The antiproliferative effects of biologically active isomers of conjugated linoleic acid on human colorectal and prostatic cancer cells

The antiproliferative effects of two commercial preparations of conjugated linoleic acid (CLA) and their constituent isomers, cis-9, trans-11 (c9,t11)-CLA, c9,c11-CLA, and t10,c12-CLA, were determined in vitro using human colorectal (HT-29, MIP-101) and prostate (PC-3) carcinoma cells adapted to serum-free medium. The antiproliferative effects of the preparations were dependent upon the type and concentration of CLA isomer present. The t10,c12-CLA isomer exhibited the greatest potency against colorectal cancer proliferation, and the c9,t11 and t10,c12 isomers were moderately effective against prostate cancer. The t10,c12 isomer induced caspase-dependent apoptosis in MIP-101 and PC-3 cells. The results are the first to demonstrate that physiologic levels of two CLA preparations, their constituent isomers, and the c9,t11-CLA elongation product, c11,t13-conjugated eicosadienoic acid, induce dose-dependent inhibitory effects on cancer proliferation in vitro. Novel CLA preparations may prove effective as chemopreventive supplements for individuals at risk of or diagnosed with colorectal or prostate cancer.

Nonsteroidal anti-inflammatory drugs, apoptosis, and colon-cancer chemoprevention

Nonsteroidal anti-inflammatory drugs (NSAIDs) can inhibit colorectal tumorigenesis and are among the few agents known to be chemopreventive. Epidemiological studies and experiments with animals have shown that NSAIDs have powerful anticolorectal cancer properties, but the mechanism of these effects remains unclear. NSAIDs can inhibit neoplastic growth by inducing apoptosis in cancer cells; the way they do this is currently an area of intense investigation. The most well-characterised pharmacological feature of NSAIDs is their inhibition of the enzyme cyclo-oxygenase (COX), which catalyses the synthesis of prostaglandins. Several studies have shown that COX inhibition prevents cell proliferation and promotes apoptosis. The chemopreventive effects of NSAIDs are thought to occur via this pathway. Other observations indicate that NSAIDs also promote apoptosis through mechanisms that are independent of COX inhibition. This idea is supported by the finding that compounds that are structurally similar to NSAIDs, but do not inhibit COX, also have chemopreventive and proapoptotic properties. COX-dependent and COX-independent mechanisms of apoptosis induction are not mutually exclusive, and it is likely that both have a role in the biological activity of NSAIDs. Knowledge of how NSAIDs prevent neoplastic growth will greatly aid the design of better chemopreventive drugs and novel treatments for colorectal cancer.

New indene-derivatives with anti-proliferative properties

Metabolites of the non-steroidal anti-inflammatory drug Sulindac inhibit cell proliferation by affecting several intracellular signaling pathways including the tumorigenic Ras/Raf/MAPK pathway. Here, we report the synthesis of eight new indene derivatives derived from the Sulindac structure, and present data on their anti-proliferative properties and their effects on the p21ras protein.

Cyclooxygenase-2 regulates apoptosis in rat epididymis through prostaglandin D2

In previous studies, cyclooxygenase (COX)-1 and COX-2 isozymes have been detected in the rat epididymis. COX-1 mediates electrolyte and fluid secretion induced by a number of peptide hormones, including bradykinin, angiotensin, and endothelin, via local formation of prostaglandin (PG) E2; however, the physiological role of COX-2 remains largely unknown. Marked apoptotic cell death in the rat epididymis following androgen depletion has been reported. Because expression of both COX isozymes is dependent on androgen, we investigated whether these isozymes control apoptosis in the epididymis. Apoptosis was detected in rat epididymal epithelial cells by in situ staining using the TUNEL method and by the presence of internucleosomal DNA fragmentation using capillary electrophoresis with laser-induced fluorescence detection. Specific COX inhibitors were used to delineate the roles of the 2 isozymes. There was no significant apoptotic cell death in normal and specific COX-1 inhibitor (SC-560)-treated epididymal cells. However, application of a specific COX-2 inhibitor (NS-398) induced apoptosis in a dose- and time-dependent manner. A similar apoptotic effect of COX-2 inhibitor was seen in the in vivo study. The drastic DNA fragmentation induced by COX-2 inhibitor could be reversed completely by PGD2 and partially by PGE2. In addition, the protective effect of PGD2 against COX-2 inhibition was significantly blocked by a PGDP-receptor antagonist, BWA868C. These results indicate that the COX-2 products PGD2 and, to a lesser extent, PGE2 control apoptosis in cultured rat epididymal cells in vitro.

Antidepressants, eicosanoids and the prevention and treatment of cancer. A review

Among the mechanisms of carcinogenesis are oncogene synthesis and expression, upregulation of cyclooxygenase, accelerated cell replication, failed apoptosis, viral activation, disruption of signaling pathways, autoimmunity, immunosuppression, angiogenesis and metastasis. All fall within the orbit of eicosanoids and the enzymes that synthesize them. Antidepressants may be of benefit in the prevention and treatment of cancer, as they inhibit the synthesis, antagonize the actions and accelerate the degradation of such eicosanoids as prostaglandins and thromboxanes.

A Fas-associated death domain protein-dependent mechanism mediates the apoptotic action of non-steroidal anti-inflammatory drugs in the human leukemic Jurkat cell line

Non-steroidal anti-inflammatory drugs (NSAIDs) are inhibitors of cyclooxygenase-1 and -2 and are useful for prevention and cure of cancers, especially colon and rectal cancers. The NSAIDs indomethacin and sulindac sulfide have been shown to induce apoptosis of colon epithelial cancer cells by a Bax-dependent mechanism that involves mitochondria-mediated activation of a caspase-9-dependent pathway. In this report, we demonstrate that indomethacin and sulindac sulfide induce apoptosis of human leukemic Jurkat cells by a mechanism that requires the Fas-associated Death Domain Protein-mediated activation of a caspase-8-dependent pathway. Therefore, NSAIDs induce apoptosis by different mechanisms depending on the cell type.

COX-2 expression in dysplasia of the head and neck: correlation with elF4E

BACKGROUND

COX-2 inhibitors have shown promise in chemoprevention of epithelial tumors. eIF4E is a biomarker that has identified individuals at high risk for relapse after definitive treatment for head and neck squamous cell cancer (HNSCC). Hence, the authors wanted to determine if COX-2 is expressed in dysplasia of the head and neck and to study the correlation of expression of COX-2 with eIF4E as a potential surrogate endpoint for determining response to COX-2 inhibitors.

METHODS

The authors studied the expression of COX-2 and eIF4E in normal epithelium (n = 8), dysplasia (n = 51), mucosa adjacent to tumors (n = 11), and cancer of the head and neck (n = 19) using immunohistochemistry. In addition, Western blot analysis was performed on a subset of the above patient samples and HNSCC cell lines.

RESULTS

Immunohistochemical analysis showed expression of COX-2 and eIF4E in all cancers and no expression in normal tissues. In dysplastic epithelium, there was a significant correlation between the expression of eIF4E and COX-2 for all groups of dysplasia combined (chi-square = 40.3, P < 0.001). A Cochran-Armitage trend test showed a significant increase in the proportion of cases that expressed both molecular markers with increasing grades of dysplasia (P = 0.001). Western blot analysis showed increased expression of COX-2 and eIF4E in tumors compared with adjacent mucosa. All three HNSCC cell lines analyzed had increased expression of eIF4E, although only two had increased COX-2 expression.

CONCLUSIONS

Expression of COX-2 in dysplasia suggested that COX-2 inhibitors may play a role in chemoprevention of head and neck cancers and that the correlation of Cox-2 with eIF4E indicates that eIF4E can be a potential surrogate marker in chemoprevention trials.

Molecular mechanisms underlying chemopreventive activities of anti-inflammatory phytochemicals: down-regulation of COX-2 and iNOS through suppression of NF-kappa B activation

A wide array of phenolic substances, particularly those present in edible and medicinal plants, have been reported to possess substantial anticarcinogenic and antimutagenic activities. The majority of naturally occurring phenolics retain antioxidative and anti-inflammatory properties which appear to contribute to their chemopreventive or chemoprotective activity. Cyclooxygenase-2 (COX-2) inducible and nitric oxide synthase (iNOS) are important enzymes that mediate inflammatory processes. Improper up-regulation of COX-2 and/or iNOS has been associated with pathophysiology of certain types of human cancers as well as inflammatory disorders. Since inflammation is closely linked to tumor promotion, substances with potent anti-inflammatory activities are anticipated to exert chemopreventive effects on carcinogenesis, particularly in the promotion stage. Examples are curcumin, a yellow pigment of turmeric (Curcuma longa L., Zingiberaceae), the green tea polyphenol epigallocatechin gallate (EGCG), and resveratrol from grapes (Vitis vinifera, Vitaceae) that strongly suppress tumor promotion. Recent studies have demonstrated that eukaryotic transcription factor nuclear factor-kappa B (NF-kappa B) is involved in regulation of COX-2 and iNOS expression. Several chemopreventive phytochemicals have been shown to inhibit COX-2 and iNOS expression by blocking improper NF-kappa B activation. Multiple lines of compelling evidence indicate that extracellular-regulated protein kinase and p38 mitogen-activated protein kinase are key elements of the intracellular signaling cascades responsible for NF-kappa B activation in response to a wide array of external stimuli. Curcumin, EGCG and resveratrol have been shown to suppress activation of NF-kappa B. One of the plausible mechanisms underlying inhibition of NF-kappa B activation by aforementioned phytochemicals involves repression of degradation of the inhibitory unit I kappa B alpha, which hampers subsequent nuclear translocation of the functionally active subunit of NF-kappa B.

Role of intracellular interleukin-1 receptor antagonist in skin carcinogenesis

Interleukin 1 (IL-1) is a major mediator of inflammation and exerts pleiotropic effects on many systems. To elucidate the role of its endogenous inhibitor, intracellular IL-1 receptor antagonist (icIL-1Ra), in mouse skin, we produced an icIL-1Ra-overexpressing skin carcinoma cell line (icIL-1Ra-JWF2). Altered expression of icIL-1Ra did not change IL-1alpha mRNA levels in these transfected cells. In icIL-1Ra-JWF2 cells, however, cyclooxygenase-2 mRNA levels were dramatically reduced and shown to be transcriptionally regulated by icIL-1Ra. To determine the effect of icIL-1Ra on cell proliferation, cell counts were done 24 h after plating equal numbers of cells. Cells from three icIL-1Ra-JWF2 clones showed significantly reduced growth rates compared with parental JWF2 cells. We subcutaneously injected five independent clones of icIL-1Ra-JWF2 cells into nude mice and measured the tumor doubling time by weekly measurements of tumor volume. IcIL-1Ra appeared to significantly slow the growth of tumors in vivo. Collectively these observations suggest that IL-1Ra has antiproliferative effects in murine skin carcinoma cells.

Suppression of N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis in F344 rats by JTE-522, a selective COX-2 inhibitor

Recent studies have demonstrated that overexpression of cyclooxygenase-2 (COX-2) and elevation of COX-2-mediated synthesis of prostaglandin E(2) (PGE(2)) were observed in various cancers including esophageal cancer, but their roles in carcinogenesis of the esophagi still remain unclear. To address the issue, we observed the reduction of N:-nitrosomethylbenzylamine (NMBA)-induced tumorigenesis in rat esophagi via JTE-522 (4-[4-cyclohexyl-2-methyloxazol-5-yl]-2-fluorobenzenesulfonamide), a selective COX-2 inhibitor. In this study, 54 F344 male rats were divided into nine groups; JTE-522 (3, 9 and 30 mg/kg) was administered orally. We also examined the effects of JTE-522 on COX-2 mRNA and synthesis of PGE(2). In the group in which JTE-522 was administered intermittently at a daily dose of 30 mg/kg, the number of NMBA-induced esophageal tumors per rat significantly reduced, to 62% (P< 0.05), but the size of the tumors was not significantly inhibited. In the group in which JTE-522 was administered continuously five times weekly for 24 weeks at a daily dose of 9 mg/kg, both the number and size of tumors significantly reduced, to 29 and 44%, respectively (P<0.05). Furthermore, JTE-522 suppressed not only tumor formation but also developing carcinomas (P<0.0021) [corrected]. In this study, treatment with NMBA alone resulted in an approximately 5-fold rise in expression of COX-2 mRNA detected by semi-quantitative RT-PCR analysis and an approximately 7-fold increase in the production of PGE(2) measured by ELISA compared with the normal esophageal mucosa. The up-regulated COX-2 expression did not decrease with the treatment of JTE-522 at the 3, 9 and 30 mg/kg doses; however, the increased levels of PGE(2) synthesis were significantly decreased by administering JTE-522 (P<0.01). Our study suggests that COX-2-mediated PGE(2) is important in NMBA-induced esophageal tumorigenesis in rats, and therefore may be a promising chemotherapeutic target for the prevention and treatment of esophageal cancer, especially with selective COX-2 inhibitors.

Nonsteroidal anti-inflammatory drugs and the gastrointestinal tract. Extent, mode, and dose dependence of anticancer effects

Regular intake of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with a decreased incidence of colorectal, esophageal, gastric, and lung cancer. The relative risk of colorectal cancer is about 0.6 in large cohort studies--in other words, the risk is reduced by 40%. Also, in experimental models, the frequency of colonic cancer is reduced by NSAIDs. Both human and experimental tumors contain increased amounts of prostaglandin E(2), which may have a role in the accelerated proliferation taking place in tumor tissue. This may be the result of activation of cyclooxygenase-2 (COX-2) in response to mitogens and growth factors, for example, which will result in an increased production of prostaglandins. The current theory is that the mechanism for the suppressor effect of NSAIDs on carcinogenesis is COX-2 inhibition. However, reliable data on the dose of aspirin or other NSAIDs for optimal benefit for tumor suppression are lacking, and it is still premature to give general recommendations on using NSAIDs for chemoprevention of gastrointestinal cancer.

Aspirin induces apoptosis through release of cytochrome c from mitochondria

Nonsteroidal anti-inflammatory drugs (NSAID) reduce the risk for cancer, due to their antiproliferative and apoptosis-inducing effects. A critical pathway for apoptosis involves the release of cytochrome c from mitochondria, which then interacts with Apaf-1 to activate caspase proteases that orchestrate cell death. In this study we found that treatment of a human cancer cell line with aspirin induced caspase activation and the apoptotic cell morphology, which was blocked by the caspase inhibitor zVAD-fmk. Further analysis of the mechanism underlying this apoptotic event showed that aspirin induces translocation of Bax to the mitochondria and mitochondrial release of cytochrome into the cytosol. The release of cytochrome c from mitochondria was inhibited by overexpression of the antiapoptotic protein Bcl-2 and cells that lack Apaf-1 were resistant to aspirin-induced apoptosis. These data provide evidence that the release of cytochrome c is an important part of the apoptotic mechanism of aspirin.

Investigation into the involvement of phospholipases A(2) and MAP kinases in modulation of AA release and cell growth in A549 cells

1. We have investigated the contribution of specific PLA(2)s to eicosanoid release from A549 cells by using specific inhibitors of secretory PLA(2) (ONO-RS-82 and oleyloxyethylphosphocholine), cytosolic PLA(2) (AACOCF(3) and MAFP) and calcium-independent PLA(2) (HELSS, MAFP and PACOCF(3)). Similarly, by using specific inhibitors of p38 MAPK (SB 203580), ERK1/2 MAPK (Apigenin) and MEK1/2 (PD 98059) we have further evaluated potential pathways of AA release in this cell line. 2. ONO-RS-82 and oleyloxyethylphosphocholine had no significant effect on EGF or IL-1beta stimulated (3)H-AA or PGE(2) release or cell proliferation. AACOCF(3), HELSS, MAFP and PACOCF(3) significantly inhibited both EGF and IL-1beta stimulated (3)H-AA and PGE(2) release as well as cell proliferation. Apigenin and PD 98509 significantly inhibited both EGF and IL-1beta stimulated (3)H-AA and PGE(2) release and cell proliferation whereas, SB 203580 had no significant effect on EGF or IL-1beta stimulated (3)H-AA release, or cell proliferation but significantly suppressed EGF or IL-1beta stimulated PGE(2) release. 3. These results confirm that the liberation of AA release, generation of PGE(2) and cell proliferation is mediated largely through the actions of cPLA(2) whereas, sPLA(2) plays no significant role. We now also report a hitherto unsuspected contribution of iPLA(2) to this process and demonstrate that the stimulating action of EGF and IL-1beta in AA release and cell proliferation is mediated in part via a MEK and ERK-dependent pathway (but not through p38MAPK). We therefore propose that selective inhibitors of MEK and MAPK pathways may be useful in controlling AA release, eicosanoid production and cell proliferation.

Cyclooxygenase-2 expression in Helicobacter pylori-associated premalignant and malignant gastric lesions

Expression of cyclooxygenase-2 (COX-2) in various stages of the Helicobacter pylori-associated gastric carcinogenesis pathway has not been elucidated. We investigated the distribution and intensity of COX-2 expression in premalignant and malignant gastric lesions, and monitored the changes after H. pylori eradication. Gastric biopsies from H. pylori-infected patients with chronic active gastritis, gastric atrophy, intestinal metaplasia (IM), gastric adenocarcinoma, and noninfected controls were studied. Expression of COX-2 was evaluated by immunohistochemistry and in situ hybridization. Endoscopic biopsies were repeated 1 year after successful eradication of H. pylori in a group of IM patients for comparing COX-2 expression and progression of IM. In all H. pylori-infected patients, COX-2 expression was predominantly found in the foveolar and glandular epithelium and, to a lesser extent, in the lamina propria. In the noninfected group, only 35% of cases demonstrated weak COX-2 expression. Intensity of COX-2 was not significantly different between the chronic active gastritis, gastric atrophy, IM, and gastric adenocarcinoma groups. In 17 patients with IM, COX-2 expressions in the epithelial cells and stromal cells were reduced 1 year after H. pylori eradication. However, the changes in COX-2 expression did not correlate with progression/regression of IM. Both premalignant and malignant gastric lesions demonstrate strong COX-2 expression. Successful eradication of H. pylori leads to down-regulation of COX-2 expression but failed to reverse IM at 1 year.