Cyclooxygenase 2 selective inhibitors in cancer treatment and prevention

Prostaglandin synthesis by a number of enzymes is important at all stages during the genesis of cancer. The availability of prostaglandin H₂ as a substrate for prostaglandin production is a critical control point in its synthesis. Cyclooxygenase (COX) occurs in two forms (COX-1 and -2) and acts as the rate-limiting enzyme that generates prostaglandin H₂. COX-1 is produced as a steady-state enzyme, while COX-2 is heavily involved in inflammation and tumorigenesis. Differences in the catalytic sites of these enzymes are utilised to generate COX-2 selective inhibitors. Certain chemical characteristics of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors make some of these inhibitors more effective against COX-2 than others. Epidemiological, animal and preclinical data demonstrate the promise of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors as anticancer agents. Ongoing clinical trials are designed to determine the efficacy of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors in the prevention and treatment of many types of cancer.     

Cyclooxygenase inhibitors: drugs for cancer prevention

Evidence that chronic intake of non-steroidal anti-inflammatory drugs, especially aspirin, prevents cancer development continues to accumulate. The data are particularly convincing for colorectal cancer; however, because of well-known side effects, they cannot routinely be recommended for this purpose. An appreciation of the mechanisms that underlie their anti-cancer effects might permit the development of safer agents. Intensive investigation has led to the characterization of several potential chemopreventive mechanisms of action of these drugs. Antineoplastic actions could result from effects on overlapping processes in the different cell-types that comprise tumors, such as epithelial and stromal cells.     

Cyclooxygenase inhibition in cancer prevention and treatment

Several lines of evidence suggest that the cyclooxygenase enzymes (specifically COX-2) might be an important molecular target for the intervention of cancer at both early and late stages of some cancers, providing an opportunity for both cancer prevention and therapy. COX-2 is overexpressed during carcinogenesis, and appears to have a role in both tumour initiation and promotion and is amenable to intervention. This review discusses the importance of COX modulation via non-specific, as well as COX-2 specific COX inhibitors (NSAIDs and COX-2 selective inhibitors [COXIB]). A brief discussion on the pharmacoeconomic considerations of NSAID and COXIB use and safety issues that have recently been the focus of debate, will be presented.     

Cyclooxygenase inhibition in cancer prevention and treatment

Several lines of evidence suggest that the cyclooxygenase enzymes (specifically COX-2) might be an important molecular target for the intervention of cancer at both early and late stages of some cancers, providing an opportunity for both cancer prevention and therapy. COX-2 is overexpressed during carcinogenesis, and appears to have a role in both tumour initiation and promotion and is amenable to intervention. This review discusses the importance of COX modulation via non-specific, as well as COX-2 specific COX inhibitors (NSAIDs and COX-2 selective inhibitors [COXIB]). A brief discussion on the pharmacoeconomic considerations of NSAID and COXIB use and safety issues that have recently been the focus of debate, will be presented.     

Role of COX-2 selective inhibitors for prevention and treatment of cancer

Cyclooxygenase-2 (COX-2) is an enzyme induced by inflammatory and mitogenic stimuli and results in enhanced synthesis of PGs in inflamed and neoplastic tissues. It is associated with cell proliferation and growth, in various cancerous conditions. We review the potential mechanisms of cancer reduction with COX-2 inhibitors and the preclinical evidence suggesting their effectiveness. Results of our study show that COX-2 is a regulatory factor for a number of pathways that can result in cancer. COX-2 makes cells resistant to apoptosis and promote angiogenesis, metastasis and cancer cell cycle by controlling number of targets. We found that, COX-2 selective inhibitors (like celecoxib and NS-398) can suppress the cancer both by COX-2 dependent and COX-2 independent pathways. COX-2 inhibitors can also produce synergic effects when used with other anti-cancer therapies. Thus, it is concluded that COX-2 selective inhibitors may be promising agents for prevention and treatment of cancer.     

Cyclooxygenase 2: a molecular target for cancer prevention and treatment

Cyclooxygenase2 (COX-2), an inducible prostaglandin G/H synthase, is overexpressed in several human cancers. Here, the potential utility of selective COX-2 inhibitors in the prevention and treatment of cancer is considered. The mechanisms by which COX-2 levels increase in cancers, key data that indicate a causal link between increased COX-2 activity and tumorigenesis, and possible mechanisms of action of COX-2 are discussed. In a proof-of-principle clinical trial, treatment with the selective COX-2 inhibitor celecoxib reduced the number of colorectal polyps in patients with familial adenomatous polyposis. Selective COX-2 inhibitors appear to be sufficiently safe to permit large-scale clinical testing and numerous clinical trials are currently under way to determine whether selective inhibitors of COX-2 are effective in the prevention and treatment of cancer.     

Cyclooxygenase isoenzymes and newer therapeutic potential for selective COX-2 inhibitors

Cyclooxygenase (COX), also known as prostaglandin G/H synthase, is a membrane-bound enzyme responsible for the oxidation of arachidonic acid to prostaglandins that was first identified over 20 years ago. In the past decade, however, more progress has been made in understanding the role of cyclooxygenase enzymes in various pathophysiological conditions. Two cyclooxygenase isoforms have been identified and are referred to as COX-1 and COX-2. COX-1 enzyme is constitutively expressed and regulates a number of housekeeping functions such as vascular hemostasis and gastroprotection, whereas COX-2 is inducible (i.e., sites of inflammation) by number of mediators such as growth factors, cytokines and endotoxins. Nonsteroidal antiinflammatory drugs (NSAIDs) produce their therapeutic effects through inhibition of COX, the enzyme that makes prostaglandins. Nonselective inhibition of COX isoenzyme leads to not only beneficial therapeutic effects but also a number of detrimental effects. Beneficial effects are due to inhibition of COX-2 and detrimental effects are due to inhibition of physiological COX-1. The present review discusses the biology as well as the role of these COX isoenzymes in various pathophysiological conditions.     

COX-2 inhibitors in cancer treatment and prevention, a recent development

Epidemiological and experimental studies have demonstrated the effect of non-steroidal anti-inflammatory drugs (NSAIDs) in the prevention of human cancers. NSAIDs block endogenous prostaglandin synthesis through inhibition of cyclooxygenase (COX) enzymatic activity. COX-2, a key isoenzyme in conversion of arachidonic acid to prostaglandins, is inducible by various agents such as growth factors and tumor promoters, and is frequently overexpressed in various tumors. The contribution of COX-2 to carcinogenesis and the malignant phenotype of tumor cells has been thought to be related to its abilities to (i) increase production of prostaglandins, (ii) convert procarcinogens to carcinogens, (iii) inhibit apoptosis, (iv) promote angiogenesis, (v) modulate inflammation and immune function, and (vi) increase tumor cell invasiveness, although some studies indicated that NSAIDs have COX-2-independent effects. A number of clinical trials using COX-2 inhibitors are in progress, and the results from these studies will increase our understanding of COX-2 inhibition in both cancer treatment and prevention. The combination of COX-2 inhibitors with radiation or other anti-cancer or cancer prevention drugs may reduce their side effects in future cancer prevention and treatment. Recent progress in the treatment and prevention of cancers of the colon, esophagus, lung, bladder, breast and prostate with NSAIDs, especially COX-2 inhibitors, is also discussed.     

Cyclooxygenase inhibition and mechanisms of colorectal cancer prevention

Colorectal cancer is a leading cause of cancer death throughout the world. The high prevalence and mortality associated with colon cancer make effective prevention and treatment an important public health and economic concern. Among the few agents known to inhibit colorectal tumorigenesis are the nonsteroidal anti-inflammatory drugs or NSAIDs, as well as newer agents such as celecoxib and rofecoxib. Both epidemiologic studies and investigations with animals show that these compounds possess marked anti-colorectal cancer properties. NSAIDS are widely known to be inhibitors of the cyclooxygenase (COX) enzymes, and it is thought that the chemopreventive effects of NSAIDs are at least in part due to this ability to inhibit COX. More recent studies, however, have suggested that NSAIDs may also exert anti-cancer effects through mechanisms independent of COX inhibition. COX-dependent and COX-independent mechanisms are not mutually exclusive and it is likely that both are involved in the biological activity of NSAIDs.     

Cyclooxygenase (COX)-2 selective inhibitors: aspirin, a dual COX-1/COX-2 inhibitor, to COX-2 selective inhibitors

Aspirin was developed as a non-steroidal anti-inflammatory drug (NSAID) in 1899. During the century after that, aspirin has been found to show its anti-inflammatory, analgesic and anti-pyretic activities by reducing prostaglandins biosynthesis through inhibition of cyclooxygenase (COX); and then COX was found to be constituted of two isoforms, constitutive COX-1 and inducible COX-2. Currently, novel NSAIDs, acting through selective inhibition of COX-2, that have efficacy as excellent as aspirin with significantly lower incidence of gastrointestinal adverse effects are available in America and some other countries, but not in Japan. Physiological and pathophysiological roles of COX-1 and COX-2 have been explained from studies in experimental animals, but there are many differences in species and diseases between animals and humans. Thus, physiological and pathophysiological roles of COX-2 were considered from the standpoint of clinical effects of the two latest COX-2 selective inhibitors, celecoxib and rofecoxib, on inflammation, pain, fever and colorectal cancer together with their adverse effects on gastrointestinal, renal and platelet functions; and the usefulness and limits of COX-2-selective inhibitors were discussed with the trends of new NSAIDs development.     

环氧合酶及其抑制剂与肿瘤防治的研究进展

环氧合酶（COX）及其抑制剂是近年肿瘤防治研究的热点之一。目前认为，COX通过多种途径参与肿瘤的发生发展，COX抑制对结肠癌等多种肿瘤有预防作用，也可能增强肿瘤的放化疗疗效，但安全性及有效性均不理想，且可能存在非COX途径。因此，COX作为肿瘤防治靶点的临床价值还有待进一步评价。     

The role of COX-2 in oral cancer development, and chemoprevention/ treatment of oral cancer by selective COX-2 inhibitors

Oral cancer is challenging for clinicians due to its high mortality and increasing incidence rate. Cyclooxygenase-2 (COX-2) is extensively expressed in oral cancer and oral premalignant lesions and seems to be enhanced specifically in high-risk oral lesions. Mounting evidence suggests that these inhibitors may represent a promising approach for chemoprevention or treatment of oral cancer. This review reports on Medline and PubMed literature searches of published articles from 1995 to 2003. Our purpose is to provide a comprehensive examination and discussion of the potential role of COX-2 in oral cancer development and the use of COX-2 inhibitors for oral cancer chemoprevention or treatment. The data in the literature strongly indicate that COX-2 is significantly upregulated in oral cancer and premalignant lesions, and we believe that inhibition of COX-2 would suppress development of oral lesions by affecting several pathways of oral carcinogenesis. Therefore, the COX-2 inhibitors should be investigated as a new treatment, particularly new chemoprevention agents, for patients who are at high risk for developing oral cancer.     

Cyclooxygenase 2 inhibitors: discovery, selectivity and the future.

The recent marketing of two selective cyclooxygenase 2 (COX-2) inhibitors climaxes the first phase of an exciting and fast-paced effort to exploit a novel molecular target for nonsteroidal anti-inflammatory drugs (NSAIDs). Much has been written in the lay and scientific press about the potential of COX-2 inhibitors as anti-inflammatory and analgesic agents that lack the gastrointestinal side-effects of traditional NSAIDs. Although research on COX-2 inhibitors has focussed mainly on inflammation and pain, experimental and epidemiological data suggest that COX-2 inhibitors could be used in the treatment or prevention of a broader range of diseases. In this review, some key points and unresolved issues related to the discovery of COX-2 inhibitors, the kinetic and structural basis for their selectivity, and possible complications in their development and use will be discussed.     

Cyclooxygenase-2 selective inhibitors

The identification of two cyclooxygenase (COX) enzymes has been a tremendous advance in understanding the role of prostaglandins in inflammation and the actions of nonsteroidal antiinflammatory drugs (NSAIDs). COX-1 activity appears to be related to "constitutive" or "housekeeping" functions in the gastric mucosa, kidney and platelets. COX-2 activity is "inducible" and generally occurs in response to a specific stimulus to enhance inflammatory actions. Current NSAIDs inhibit both COX-1 and COX-2, although the clinical benefit of NSAIDs appears to be associated with inhibition of COX-2 activity. The inhibition of COX-1 activity by NSAIDs is related to adverse side effects in general, particularly gastrointestinal toxicity. Recently, COX-2 selective inhibitors have been developed. Current data would suggest that by inhibiting COX-2 action, these agents may have efficacy similar to that of standard NSAIDs and that by not inhibiting COX-1 activity, they may have less toxicity than standard NSAIDs. Thus, these actions indicate that COX-2 selective inhibitors will have similar clinical efficacy to the traditional NSAIDs with fewer adverse side effects.     

Aromatase inhibitors and breast cancer prevention

INTRODUCTION: Endocrine therapy with selective estrogen receptor modulators (SERMs) has been the mainstay of breast cancer prevention trials to date. The aromatase inhibitors, which inhibit the final chemical conversion of androgens to estrogens, have shown increased disease-free survival benefit over tamoxifen in patients with primary hormone receptor-positive breast cancer, as well as reducing the risk of developing contralateral breast cancers. The aromatase inhibitors are being actively evaluated as prevention agents for women with a history of ductal carcinoma in situ as well as for women who are considered to be at high risk for developing primary invasive breast cancer. AREAS COVERED: This review evaluates the available prevention data, as evidenced by the decrease in contralateral breast cancers, when aromatase inhibitors are used in the adjuvant setting, as well as the emerging data of the aromatase inhibitors specifically tested in the prevention setting for women at high risk. EXPERT OPINION: Exemestane is a viable option for breast cancer prevention. We continue to await further follow-up on exemestane as well as other aromatase inhibitors in the prevention setting for women at high risk of developing breast cancer or with a history of ductal carcinoma in situ.     

COX-2 selective inhibitors and bone

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely prescribed medications for relief of pain and inflammation. Recent animal studies using models of fracture healing and bone ingrowth suggest that NSAIDs (both non-selective NSAIDs and selective COX-2 inhibitors) adversely affect these bone-related processes. The dose and time-relationships of these medications and their resulting effects on bone have not yet been fully elucidated. Furthermore, whether COX-2 inhibitors and non-selective NSAIDs lead to clinically relevant adverse effects on bone healing in humans is unknown.     

选择性环氧合酶-2抑制剂的研究现状及进展

非甾体抗炎药（NSAIDs）是临床上应用非常广泛的一类药物，但严重的不良反应使其应用受到很大限制。研究已经发现，NSAIDs对炎症的有效治疗源干其对环氧合酶-2（COX-2）的抑制作用。综述了选择性COX-2抑制剂作用的分子基础、构效关系及其目前研究开发的现状和最新进展。     

The development of MetAP-2 inhibitors in cancer treatment

Methionine aminopeptidases (MetAPs), which remove methionine residue from newly synthesized polypeptide chains, are a class of metalloproteases ubiquitously distributed in both eukaryotes and prokaryotes. MetAP-2 inhibition can induce G1 cell cycle arrest, cytostasis in tumor cells in vitro and inhibition of tumor growth in vivo. The discovery of fumagillin with potent antiangiogenic and antiproliferative activities promoted the development of fumagillin analogues as a novel class of anticancer agents. Early drug discovery efforts have focused on analogs of fumagillin, which irreversibly inhibit MetAP-2 through covalent modification of an epoxide. Several fumagillin analogs, like CKD-732, TNP-470 and PPI-2458, were found to be potent selective inhibitors of MetAP-2 (proteolytic activity) and endothelial cell proliferation. Further, they have entered in clinical trials for the treatment of different types of tumors. Recently, attention has been paid to reversible human MetAP-2 inhibitors, such as bengamides, 2-hydroxy-3-aminoamides, anthranilic acid sulfonamides and triazole analogs, which have demonstrated their potential to inhibit angiogenesis and tumor growth in vivo as well. This review article mainly discussed the development of MetAP-2 inhibitors in cancer therapy and also summarized their structure-activity relationships.