A hypothesis: nonsteroidal anti-inflammatory drugs reduce the incidence of large-bowel cancer

Modulation of DNA hypomethylation as a surrogate endpoint biomarker for chemoprevention of colon cancer

Surrogate end-point biomarkers are being developed as indicators of the efficacy of chemopreventive agents. These biomarkers are molecular and biological end-points that can be modulated by chemopreventive agents in accordance with their efficacy to prevent cancer. DNA hypomethylation is a common alteration found in colon tumors that has the potential of being modulated by chemopreventive agents and thus being useful as a surrogate end-point biomarker. Agents that were either effective or ineffective in preventing colon cancer were evaluated for the ability to modulate DNA hypomethylation in azoxymethane-induced colon tumors in male F344 rats. DNA methylation was determined by Dot Blot Analysis using a mouse monoclonal anti-5-methylcytosine antibody. Colon tumors had a 70% reduction in DNA methylation relative to normal colonic mucosa. DNA methylation in the tumors was increased by 7 days of treatment with agents that have been shown to prevent colon cancer (calcium chloride, alpha-diflouromethylornithine [DFMO], piroxicam, and sulindac), whereas agents shown not to prevent colon cancer in rats (low dose aspirin, 2-carboxyphenyl retinamide [2-CPR], quercetin, 9-cis retinoic acid, and rutin) did not increase DNA methylation. The results suggest that the ability to reverse the DNA hypomethylation in colon tumors could be useful as a surrogate end-point biomarker for chemoprevention of colon cancer.

Celecoxib: a potent cyclooxygenase-2 inhibitor in cancer prevention

Non-steroidal anti-inflammatory drugs (NSAIDs) are the most widely used therapeutic agents in the treatment of pain, inflammation and fever. They may also have a role in the management of cancer prevention, Alzheimer's disease and prophylaxis against cardiovascular disease. These drugs act primarily by inhibiting cyclooxygenase enzyme, which has two isoforms, cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). Selective COX-2 inhibitors provide potent anti-inflammatory and analgesic effects without the side effects of gastric and renal toxicity and inhibition of platelet function. Celecoxib is a potent COX-2 inhibitor being developed for the treatment of rheumatoid arthritis and osteoarthritis. Chemoprevention is the use of pharmacological or natural agents to prevent, suppress, interrupt or reverse the process of carcinogenesis. For this purpose, celecoxib is being used for different cancer types. The effects of NSAIDs on tumor growth remain unclear, but are most likely to be multifocal. In this article, we reviewed COX-2 selectivity, the pharmacological properties of celecoxib, the use of celecoxib for cancer prevention and the mechanisms of chemoprevention.

Studies with the azoxymethane-rat preclinical model for assessing colon tumor development and chemoprevention

During recent years, multidisciplinary studies in epidemiology and molecular biology have contributed to our understanding of the etiology of colorectal cancer; more importantly they have enabled us to approach its prevention. An impressive body of epidemiological data suggests an inverse relationship between colorectal cancer risk and consumption of diets rich in omega (omega)-3 fatty acids (n-3 PUFAs) or the regular use of nonsteroidal antiinflammatory drugs (NSAIDs), including aspirin. The development of strategies for the chemoprevention of colorectal cancer have been facilitated by the use of relevant animal models mimicking the neoplastic processes that occur in humans, including similarities in histopathology and molecular and genetic lesions during both the early and promotion/progression stages of carcinogenesis. Studies with the azoxymethane-F344 rat model indicate that diets rich in n-3 PUFAs, NSAIDs, selective cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS) inhibitors, and curcumin can reduce the incidence of colon cancer. Advances in the knowledge of the mechanisms by which chemopreventive agents act offer opportunities to use combinations of specific chemopreventive agents, having clinically beneficial aggregate activity with minimal toxicity. This approach is extremely important when a promising chemopreventive agent demonstrates apparent efficacy but may produce toxic effects at high doses. Our studies show that a combination of very low doses of piroxicam (NSAID) and difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, or very low doses of COX-2 and HMG-CoA reductase inhibitors are more effective in inhibiting colon carcinogenesis than administration of these compounds as single agents even at higher levels. The natural history of colorectal cancer, from dysplastic aberrant crypts to adenomas and adenocarcinomas, offers multiple opportunities for assessment and intervention. Of further importance is to identify whether the molecular targets that are critical in the growth and survival of the malignant colorectal cell are modulated by n-3 PUFAs, NSAIDs, or COX-2 and iNOS inhibitors.

Aspirin use and lung cancer in men

We examined prospectively the relation between regular aspirin use and lung cancer risk in the Health Professionals Follow-Up Study. Of 49,383 US men aged 40-75 years who completed biennial self-administered questionnaires that assessed aspirin use beginning in 1986, 328 developed lung cancer during 601,453 person-years of follow-up through 31 December 2000. No information on aspirin dose was available. Controlling for current age, smoking status, and age at starting to smoke regularly, the relative risk (RR) of total lung cancer for regular users of aspirin (twice or more per week) at baseline compared to nonusers was 1.13 (95% confidence interval (CI) =0.89-1.43). Results were similar for non-small-cell lung cancer (RR=1.16; 95% CI=0.88-1.54). No apparent dose-dependent association was observed for the frequency of aspirin use and lung cancer risk (P for trend=0.64), and results remained null when consistent use of aspirin over time was examined. These findings do not suggest that regular aspirin use is associated with a reduced lung cancer risk.

Regulation of cell growth by selective COX-2 inhibitors in oral carcinoma cell lines

Evidence indicates that NSAIDs that inhibit prostaglandin (PG) synthesis can reduce the incidence of colorectal cancers and that inhibition of cyclooxygenase-2 (COX-2) may be the underlying mechanism. The objective of this study was to investigate this putative mechanism by examining the effect of selective COX-2 inhibitors (Celebrex, DFU, NS-398) and COX-1 inhibitors (Aspirin) on the growth of two human oral carcinoma cell lines (OEC-M1 and KB) and one normal fibroblast cell line (NF). We found that the growth of OEC-M1 cells could be significantly inhibited by DFU concentrations above 30 microM (31%) after 4 days, and above 50 microM (35%) after 2 days in culture; by Celebrex at concentrations above 20 microM (52%) after 6 days, above 30 microM (36%) after 5 days, and above 40 microM (33%) after 4 days in culture; and by NS-398 above 1 microM (30%) after 6 days, and above 10 microM (35%) after 5 days in culture. The growth of KB cells could be significantly inhibited by DFU concentrations above 10 microM (33%) after 6 days, above 20 microM (35%) after 4 days in culture; and by Celebrex at concentrations above 10 microM (33%) after 5 days, and above 50 microM (30%) after 4 days in culture; and by NS-398 above 1 microM (45%) after 5 days, above 20 microM (36%) after 4 days in culture. The growth of NF cells could be significantly inhibited by DFU above 30 microM (45%) after 6 days, and above 40 microM (32%) after 3 days in culture, and by Celebrex at concentrations above 10 microM (42%) after 6 days, above 30 microM (31%) after 4 days, above 50 microM (32%) after 3 days in culture, and by NS-398 above 0.1 microM (35%) after 4 days, and above 1 microM (32%) after 3 days in culture. The growth-inhibitory concentration (IC50) values for DFU on OEC-M1, KB, and NF cells were about 39.1, 14.8, and 42.9 microM at 144 h, respectively, and on KB was about 45.2 microM at 120 h. The IC50 values for Celebrex on OEC-M1, KB, and NF cells were about 19.1, 8.6, and 15.8 microM at 144 h, respectively, and on KB and NF were about 27.7 and 35.3 microM, respectively, at 120 h. The IC50 values for NS-398 on OEC-M1, KB, and NF were about 18.9, 0.7 and 1 microM, respectively, at 144 h; on KB and NF values were about 10.8 and 1.4 microM, respectively, at 120 h and on KB and NF were about 26.6 and 4.1 microM, respectively, at 96 h. The results show that the growth of these cell lines is inhibited by three COX-2 selective inhibitors but not by any COX-1 selective inhibitors. These findings suggest that COX-2 may play an important role in the generation of biochemical mediators that stimulate the growth of human oral cancer and normal fibroblast cell lines.

Polyamines reverse non-steroidal anti-inflammatory drug-induced toxicity in human colorectal cancer cells

Naproxen, sulindac and salicylate, three NSAIDs (non-steroidal anti-inflammatory drugs), were cytotoxic to human colorectal cancer cells in culture. Toxicity was accompanied by significant depletion of intracellular polyamine content. Inhibition of ornithine decarboxylase (the first enzyme of the polyamine biosynthetic pathway), induction of polyamine oxidase and spermidine/spermine N(1)-acetyltransferase (the enzymes responsible for polyamine catabolism) and induction of polyamine export all contributed to the decreased intracellular polyamine content. Morphological examination of the cells showed typical signs of apoptosis, and this was confirmed by DNA fragmentation and measurement of caspase-3-like activity. Re-addition of spermidine to the cells partially prevented apoptosis and recovered the cell number. Thus polyamines appear to be an integral part of the signalling pathway mediating NSAID toxicity in human colorectal cancer cells, and may therefore also be important in cancer chemoprevention in humans.

Review article: the data supporting a role for aminosalicylates in the chemoprevention of colorectal cancer in patients with inflammatory bowel disease

The chemoprevention of colorectal cancer (CRC) with long-term sulfasalazine and 5-aminosalicyclic acid (5-ASA) treatment has been demonstrated through epidemiological and experimental studies, in patients with ulcerative colitis. In a large case-controlled study, there was a trend for long-term nonsteroidal anti-inflammatory consumption to be protective against CRC in patients with inflammatory bowel disease (IBD) (OR, 0.84). Sulfasalazine treatment over a 3-month period was shown to be protective (OR, 0.38), independently of disease activity. A longer-term study of sulfasalazine also revealed a relationship with treatment compliance, where 3% of compliant patients developed CRC compared with 31% of the noncompliers. Treatment with 5-ASA was associated with an increase in apoptosis, a decrease in proliferation of colorectal mucosa and has been shown to lower the rate of spontaneous mutation. In a retrospective, matched case-control study conducted in the UK, 102 patients with ulcerative colitis and CRC were matched with ulcerative colitis patients without CRC. Incidence was correlated to treatment protocols, family history and other risk factors. Mesalazine was the only treatment to be associated with a statistically significant reduction in the risk of developing cancer. Even after adjusting for variables, mesalazine at doses > 1.2 g / day reduced the risk of cancer by 81% (P = 0.006). Frequent visits to the clinician were also associated with a protective effect.

Effect of nonsteroidal anti-inflammatory drugs on stage of colon cancer at diagnosis

BACKGROUND AND OBJECTIVE

We investigated the effect of nonsteroidal anti-inflammatory drug (NSAID) use on stage of colon cancer and presence of distant metastases at diagnosis.

METHODS

Cases of incident colon cancer diagnosed between 1981 and mid-1995 were selected from the Saskatchewan Cancer Registry. Cases with more extensive cancer at diagnosis were compared with cases with less extensive cancer (characterized using the Dukes system). NSAID exposure was assessed using the Saskatchewan Prescription Drug Plan database.

RESULTS

Compared with non-users in the same period, nonmetastatic cancer was found to be less extensive in those with low NSAID use (odds ratio [OR] 0.67, 95% confidence interval [CI] 0.53-0.87) and high NSAID use (OR 0.55, 95%CI 0.36-0.84) during the 6 to 10 year periods preceding diagnosis, regardless of the cut-off used to define "more extensive cancer." NSAID use in the 2 to 5 year periods was also found to protect (although not statistically significantly) against the occurrence of distant metastasis.

CONCLUSION

Results are consistent with the hypothesized mechanism of the action of NSAIDs, but confounding by healthy lifestyle cannot be ruled out.

Effects of the selective cyclooxygenase-2 inhibitor Celebrex on the expressions of PGE2 and VEGF in pancreatic carcinoma

AIM

To investigate the effects of Celebrex, a selective cyclooxygenase-2 inhibitor, on tumor growth and the expression of vascular endothelial growth factor (VEGF) and PGE2 in pancreatic carcinoma of xenografted nude mice induced by pancreatic carcinoma PC-3 cell lines.

METHODS

The effects of Celebrex on tumor growth, and the expression of VEGF and PGE2 were assayed by using enzyme-linked immuno-adsordent assay (ELISA) and radioimmunoassay (RIA), respectively.

RESULTS

Compared to control mice, the growth curve of treated mice was much lower and flatter. Average tumor volume from control mice was 0.438 cm³ as compared with 0.212 cm³ from treated mice (51.6% inhibition, P<0.05). The expression of PGE₂ in control mice (66±12 ng/g) was significantly higher than that in treated mice(29±5 ng/g) (P<0.01). VEGF expression was significantly down regulated in the Celebrex-treated tumors. ELISA revealed the expression of VEGF was 1.11±0.11 μg/g in control mice, while 0.66±0.11 μg/g in treated mice (P<0.05). The inhibitory rate of VEGF was 40.6%

CONCLUSION

COX-2 may play an important role in the angiogenesis of pancreatic carcinoma, PGE₂ is likely to act as an important intermediate part between COX-2 and tumor generation. The selective COX-2 inhibitor, Celebrex, can inhibit angiogenesis and tumor growth.

Risk of cancer in a large cohort of nonaspirin NSAID users: a population-based study

There is increasing evidence of an inverse association between use of nonsteroidal anti-inflammatory drugs (NSAIDs) and risk of colorectal cancer. However, data regarding other cancer sites are limited. Using data from the population-based North Jutland Prescription Database and the Danish Cancer Registry, we compared cancer incidence among 172 057 individuals prescribed nonaspirin NSAIDs with expected incidence (based on county-specific cancer rates) during a 9-year study period. A total of 6081 incident cancer cases were diagnosed among NSAID users vs 5722 expected (standardised incidence ratio (SIR) 1.1, 95% confidence interval (CI)1.0-1.1). The SIRs for colon and rectal cancer among persons who obtained 10 or more prescriptions were 0.7 (95% CI 0.6-0.9) and 0.6 (95% CI 0.4-0.9), respectively. Similarly, reduced risk estimates were found for stomach (SIR 0.7, 95% CI 0.4-1.1) and ovarian cancer (SIR 0.7, 95% CI 0.4-1.0). Standardised incidence ratios for other cancers among those with 10 or more prescriptions tended to be close to 1.0, except for lung, kidney, and prostate cancers with SIRs of 1.3 (95% CI 1.1-1.6), 1.4 (95% CI 0.9-2.1), and 1.6 (95% CI 1.3-2.0), respectively. We found protective associations of NSAIDs against colon, rectal, stomach, and ovarian cancer. Reasons for the increased risk for some cancer sites are not clear.

Cytokine dependent inverse regulation of CD54 (ICAM1) and major histocompatibility complex class I antigens by nuclear factor kappaB in HEp2 tumor cell line: effect on the function of natural killer cells

The aim of this study is to investigate the mechanisms by which elevated nuclear factor kappaB (NFkappaB) activity in HEp2 cells can modulate the function and survival of immune effector cells. Inhibition of NFkappaB functional activity by stable expression of IkappaB super-repressor rendered HEp2 cells (HEp2-IkappaB((S32AS36A))) susceptible to natural killer (NK) cell mediated cytotoxicity. Increase in surface ICAM1 expression was greater on HEp2-IkappaB((S32AS36A)) cells than on the surface of vector alone transfected HEp2 cells when these cells were treated with IFN-gamma. In contrast, tumor necrosis factor alpha (TNF-alpha) treatment augmented ICAM-1 expression on the surface of vector-alone transfected HEp2 cells and not on the HEp2-IkappaB((S32AS36A)) cells. Moreover, synergistic augmentation of ICAM-1 by a combination of TNF-alpha and interferon-gamma (IFN-gamma) treatment was completely abrogated on the surface of HEp2-IkappaB((S32AS36A)) cells. The addition of blocking antibody to ICAM-1 surface antigen partially inhibited the increased cytotxicity mediated by interleukin-2 treated NK cells against HEp2-IkappaB((S32AS36A)) cells. In contrast to ICAM-1, the expression of major histocompatibility complex (MHC) class I antigens were downregulated when the function of nuclear NFkappaB was inhibited in HEp2 cells. The addition of IFN-gamma to HEp2-kappaB((S32AS36A)) cells increased the expression of MHC class I antigen and rendered these cells less susceptible to NK cell mediated cytotoxicity. Secretion of IFN-gamma and granulocyte macrophage-colony-stimulating factor (GM-CSF) by NK cells was also significantly increased in the presence of HEp2-IkappaB((S32AS36A)) cells, and the treatment of these tumor cells with IFN-gamma prior to their addition to the cultures of NK cells decreased the released IFN-gamma and GM-CSF by NK cells. However, the levels of NK cell mediated cytotoxicity and IFN-gamma secretion remained significantly higher in the presence of both untreated and IFN-gamma treated HEp2-IkappaB((S32AS36A)) cells when compared with vector-alone transfected HEp2 cells. Thus, NFkappaB regulates inversely the expression of ICAM-1 and MHC class I antigens on HEp2 tumor cells and this may contribute to the resistance of these cells to NK cell mediated cytotoxicity.

Fish consumption and colorectal cancer: a case-reference study in Japan

Several clinical studies have suggested that supplementation with fish oils can suppress the proliferation of colorectal mucosa and therefore inhibit the development of colorectal cancer. However, epidemiological evidence concerning fish consumption and risk is inconsistent and limited. To clarify the association between intake of fish and the likelihood of developing colorectal cancer, we conducted a large sample size case-reference study with 928 cases of colon cancer, 622 of rectal cancer and 46886 cancer-free outpatient references aged 40-79 years. The data showed frequent raw/cooked fish intake to be associated with decreased odds ratio (OR) 0.68 with 95% confidence interval (CI) 0.47-0.99 for male colon cancer, especially for males aged over 60 years, smokers and frequent meat eaters. A marginal decrease in the OR (OR 0.58, 95% CI 0.31-1.07) was also detected for female rectal cancer, especially in the regular physical exercise subgroup. However, frequent dried/salted fish intake was found to be associated with increased OR in females younger than 60 years old and alcohol drinkers. Although there is some possible bias in epidemiological studies, the results suggest that frequent raw/cooked fish intake may decrease the risk while dried/salted fish, in contrast, may exert a detrimental effect.

Correlation of COX-2 expression and clinicopathological features of colorectal cancer

AIM: To investigate the expression of COX-2 on different stages of colorectal cancer and the correlation between the expression of COX-2 and its clinicopathological features.

METHODS: The expression of COX-2 was determined by immunohistochemical staining in seventy-six surgical specimens of colorectal cancer (late stage 44 and early stage 32), 33 adenomas and 18 normal colonic mucosal tissues were biopsied endocscopically. The correlation of COX-2 with the survival rate was evaluated with Kaplan-Meier survival curves and Cox proportional hazards regression.

RESULTS: The degree of expression of COX-2 was categorized into 4 grades ranged from "-" to "+++", the expression grades in series in normal colonic mucosal tissues was 83.3%, 16.7%, 0%, 0%, respectively; that in adenomas was 12.1%, 42.4%, 36.4%, 9.1%, respectively. The difference of the expression of COX-2 between late stage and early stage of colorectal cancer, and that between the late stage of cancer and adenoma were statistically significant (P < 0.01); however, no significant difference in the expression of COX-2 between early stage of cancer and adenoma was observed. A significant difference in the survival curves between low COX-2 expression group and high COX-2 expression group was showed by Kaplan-Meier survival analysis (P < 0.05). Cox proportional hazards regression indicated that the correlation of the expression of COX-2 with the poor long-term prognosis was existed with a hazard ratio of 2.665 unadjusted for other variables (P < 0.05); the expression of COX-2 was an independent risk factor for poor prognosis.

CONCLUSION: The expression of COX-2 is gradually up-regulated in the evolution of normal epithelium to adenoma or from early stage to advanced stage of colorectal cancer. The expression of COX-2 is an independent risk factor of poor prognosis for postoperative patients with advanced colorectal cancer.

A randomized trial of aspirin to prevent colorectal adenomas in patients with previous colorectal cancer

BACKGROUND

Experimental studies in animals and observational studies in humans suggest that regular aspirin use may decrease the risk of colorectal adenomas, the precursors to most colorectal cancers.

METHODS

We conducted a randomized, double-blind trial to determine the effect of aspirin on the incidence of colorectal adenomas. We randomly assigned 635 patients with previous colorectal cancer to receive either 325 mg of aspirin per day or placebo. We determined the proportion of patients with adenomas, the number of recurrent adenomas, and the time to the development of adenoma between randomization and subsequent colonoscopic examinations. Relative risks were adjusted for age, sex, cancer stage, the number of colonoscopic examinations, and the time to a first colonoscopy. The study was terminated early by an independent data and safety monitoring board when statistically significant results were reported during a planned interim analysis.

RESULTS

A total of 517 randomized patients had at least one colonoscopic examination a median of 12.8 months after randomization. One or more adenomas were found in 17 percent of patients in the aspirin group and 27 percent of patients in the placebo group (P=0.004). The mean (+/-SD) number of adenomas was lower in the aspirin group than the placebo group (0.30+/-0.87 vs. 0.49+/-0.99, P=0.003 by the Wilcoxon test). The adjusted relative risk of any recurrent adenoma in the aspirin group, as compared with the placebo group, was 0.65 (95 percent confidence interval, 0.46 to 0.91). The time to the detection of a first adenoma was longer in the aspirin group than in the placebo group (hazard ratio for the detection of a new polyp, 0.64; 95 percent confidence interval, 0.43 to 0.94; P=0.022).

CONCLUSIONS

Daily use of aspirin is associated with a significant reduction in the incidence of colorectal adenomas in patients with previous colorectal cancer.

Colorectal cancer in 2003: old principles, new strategies

In the last two decades the prognosis of colorectal cancer has improved for two reasons: (i) the proportion of patients with localized disease has increased and treatment has been standardized, and (ii) new chemotherapeutic agents have led to a longer life expectancy for patients with advanced disease. In this review the current insights in disease etiology and treatment of localized and disseminated colorectal cancer are discussed.

Prostate Development and Carcinogenesis

The process involved in the development and carcinogenesis of the prostate gland is complex. During early prostate development, the androgenic hormone from embryonic testicles is required for ductal formation, growth, and branching morphogenesis of the prostate gland. From this early stage, interactions between the epithelium and mesenchyme become firmly established through paracrine influence (i.e., growth factors) from mesenchyme (stroma), in response to testosterone, acting on epithelium to stimulate its proliferation, morphogenetic differentiation, and function. In return, the epithelium also exerts its paracrine effects on mesenchyme by regulating the differentiation and specific organizational pattern of its stromal smooth muscle. In a normal adult prostate, the maintenance of normal glandular structure and function is dependent not only on the constant presence of testosterone, but also on a normal intact and stable stroma. This chapter will concentrate first on factors involved in the normal development of the prostate gland and then on the aberrant changes in the homeostatic balance arising either from within (i.e., mutations) or outside (i.e., changes in hormonal balance) that result in derangements of the prostate gland. Finally, environmental and genetic factors that lead to prostate carcinogenesis including activation of oncogenes and mutations of tumor suppressor genes are also discussed.

Update on the cost-effectiveness of screening for colorectal neoplasia

Colorectal cancer is an ideal target for population screening because it is a prevalent disease with an identifiable precursor lesion that, when treated, favorably alters the natural history of the disease. Several strategies for screening have illustrated efficacy, including fecal occult blood testing, sigmoidoscopy and colonoscopy. Cost-effectiveness analyses have been performed to determine whether the resources required to implement screening are justified by potential gains. The U.S. Preventive Services Task Force recently commissioned a study on the cost-effectiveness of colorectal cancer screening, which revealed that screening was cost-effective compared to no screening. However, it could not be confirmed which strategy would save the most life-years, nor which was most cost-effective. Since publication of this review, several additional cost-effectiveness analyses have been performed. These studies confirm that screening average risk patients at age 50 by a variety of available strategies is likely to be reasonable by current standards for resource utilization, and that either colonoscopy every 10 years (or once at age 65) or the combination of annual fecal occult blood testing with sigmoidoscopy every 5 years are viable alternatives. Additional economic analyses have examined the use of aspirin chemoprophylaxis to prevent colorectal cancer either alone or as an adjunct to screening strategies. These studies reaffirm the cost-effectiveness of colorectal cancer screening, but illustrate that aspirin chemoprophylaxis is unlikely to be associated with gains for which society would be willing to pay. At present, the decision to choose one colorectal screening strategy over another is based on availability of screening modalities, patient and provider preferences, and associated adherence to screening recommendations. Assessment of preference and development of interventions to increase adherence to screening should be a focus of research in the future.

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.

Modifiable risk factors for colon cancer

Although many mechanisms remain unclear, a large body of evidence indicates that several dietary and lifestyle factors are likely to have a major influence on the risk of colon cancer. Physical inactivity, excess body weight, and a central deposition of adiposity are consistent risk factors. Overconsumption of energy is likely to be one of the major contributors to the high rates of colon cancer in Western countries. Beyond their influence on energy balance, the independent role of specific macronutrients remain controversial. Red meat, processed meats, and perhaps refined carbohydrates contribute to risk. Recent evidence indicate that chronic hyperinsulinemia may increase risk of colon cancer. As insulin resistance and subsequent hyperinsulinemia is induced by excess energy intake and some aspects of the Western diet (e.g., saturated fats and refined carbohydrates), insulin may be a focus of factors influencing colon cancer risk. Recent evidence also points to a role of IGF-1, but our understanding of modifiable factors that influence levels of these is poor at present. Of note is that hyperinsulinemia increases free IGF-1 exposure [25]. High alcohol consumption, probably in combination with a diet low in some micronutrients such as folate and methionine, and smoking early in life are likely to increase risk of colon cancer. Recent epidemiologic studies have tended not to support a strong influence of fiber; instead, some micronutrients or phytochemicals in fiber-rich foods may be important. Folate is one such nutrient that has received attention lately and is being studied in randomized intervention trials. Agents with chemopreventive properties, such as aspirin and postmenopausal estrogens, have potential adverse effects so a careful consideration of the risk-benefit ratio is required before general recommendations can be made. Other NSAIDs with a potential for reduced toxicity, such as celecoxib, are currently being evaluated for efficacy and toxicity. The overwhelming evidence indicates that primary prevention of colon cancer is feasible. At least 70% of colon cancers may be preventable by moderate changes in diet and lifestyle [197]. Secondary prevention, through screening by sigmoidoscopy and colonoscopy, is also critically important to prevent mortality from colon cancer; however, many of the diet and lifestyle risk factors for colon cancers are the same for cardiovascular disease and for some other cancers, so focusing on the modifiable risk factors for colon cancer is likely to have many additional benefits beyond this cancer.

Aspirin and cancer risk: an update to 2001

Evidence of a protective role of aspirin on the risk of colorectal and other common cancers has been building up since the end of the 1980s. There are now more than 15 epidemiological (case-control and cohort) studies indicating that long-term use of aspirin is associated with a reduced risk of colorectal cancer. The overall relative risk (RR) estimate for regular aspirin users was 0.71 (95% confidence interval (CI) 0.66-0.77) from case-control studies, and 0.84 (95% CI 0.72-0.98) from cohort studies. A recent meta-analysis reported a RR of breast cancer for aspirin use of 0.70 (95% CI 0.61-0.81) in case-control studies, and of 0.79 (95% CI 0.59-1.06) in cohort studies. Furthermore, various epidemiological studies have suggested that aspirin use might have a favourable effect on ovarian cancer as well: the overall RR estimate was 0.82 (95% CI 0.69-0.99), although the evidence is too limited to permit firm conclusions. Data are more scanty, though in the same direction, for other neoplasms, including in particular stomach and oesophageal cancer.

The combination of 1alpha,25(OH2)-vitamin D3, calcium and acetylsalicylic acid affects azoxymethane-induced aberrant crypt foci and colorectal tumours in rats

Effects of 1alpha,25(OH)(2)-vitamin D(3) and acetylsalicylic acid at various dietary levels of calcium (CaCO(3)) on development of aberrant crypt foci (ACF) and tumours in colon were examined in groups of 16 male F344 rats initiated with azoxymethane and observed for 16 weeks. Calcium was the most potent modulator of ACF development. The total number of ACF increased with low calcium and decreased with high calcium. The number of large ACF decreased with any addition of calcium, acetylsalicylic acid and 1alpha,25(OH)(2)-vitamin D(3). High levels of calcium alone or in combination with 1alpha,25(OH)(2)-vitamin D(3) increased the incidence of tumour-bearing animals. 1alpha,25(OH)(2)-vitamin D(3) and acetylsalicylic acid at 5,000 ppm calcium increased the incidence as well.

The role of cyclooxygenase-2 (COX-2) in breast cancer, and implications of COX-2 inhibition

The cyclooxygenase (COX) enzyme system is composed of two isoenzymes, COX-1 and COX-2. Recent sources of experimental and epidemiological evidence suggest a significant role for the COX enzymes, particularly COX-2, in the pathogenesis of breast cancer. This has important implications for treatment of the disease. This article reviews the evidence for a relationship between the COX enzyme system and mammary carcinogenesis, and discusses the likely therapeutic roles and potential pitfalls of COX inhibition.

Cyclooxygenase-2 promotes prostate cancer progression

BACKGROUND

Cyclooxygenase (COX) -2, an inducible isoform of COX, has been observed to be expressed in prostate cancer. Several studies have reported that COX-2 overexpression is associated with carcinogenesis, cell growth, angiogenesis, apoptosis, and invasiveness in a variety of tumor types.

METHODS

To investigate the function of COX-2 in prostate cancer directly, we stably transfected human full-length COX-2 cDNA into LNCaP cells (LNCaP-COX-2), which express low levels of endogenous COX-2.

RESULTS

The level of COX-2 mRNA and protein and the COX activity in COX-2 LNCaP-COX-2 cells was significantly increased compared with parent and control-transfected cells. Overexpression of COX-2 increased both proliferation in vitro and tumor growth rate in vivo. However, the pro-tumor effect was neither associated with changes of androgen receptor (AR) expression level nor AR activity. Furthermore, addition of the major metabolites of COX-2-mediated arachidonic acid metabolism did not alter the proliferation of LNCaP-COX-2 cells in vitro. LNCaP-COX-2 cells had increased secretion of vascular endothelial growth factor (VEGF) protein, suggesting that angiogenesis induced by COX-2 stimulates tumor growth in vivo.

CONCLUSION

These data demonstrate that COX-2 contributes to prostate cancer progression and suggest that it mediates this effect, in part, through increased VEGF.

The role of cyclooxygenase-2 (COX-2) in two different morphological stages of intestinal polyps in APC(Delta474) knockout mice

The expression of COX-2 participates strongly in polyp formation of adenomatous polyposis coli (APC)-mutated mice. However, the mechanism of growth inhibition by COX-2 inhibition remains unclear. The aims of this study were to assess the role of COX-2 during the process of polyp formation in APC(Delta474) knockout mice. Starting at 4 weeks of age, the treated group (T group) were given a diet containing JTE-522, a selective COX-2 inhibitor, and the control group (C group) were given a control diet. At 12 weeks of age, mice were killed and polyps located in a proximal 10 cm of the small intestine were classified into two morphological stages: large adenomas (>300 microm in diameter) which lacked normal villous structure, and small adenomas (</=300 microm) covered with normal villous epithelia. In both classes, after counting the incidence, adenomas were examined for vascularity, expression of COX-2 and VEGF protein, labeling proliferating cell nuclear antigen (PCNA) and apoptosis with the TdT-mediated dUTP nick end labeling method, including expression of Bcl-2 and Bcl-X. JTE-522 significantly reduced the incidence of large adenomas, but not of small adenomas. Although it did not affect the proliferating potential of adenomas, the apoptosis index increased significantly in the T group accompanied by a reduction in Bcl-X expression in both small and large adenomas. In the C group, macrophages with both COX-2 and VEGF expression were observed in the submucosa of large adenomas, where some large vessels were also observed. JTE-522 inhibited the VEGF expression of these macrophages, resulting in a decrease in vascular area. In conclusion, macrophages with COX-2 and VEGF expression in the submucosal layer are responsible for angiogenesis in large adenomas, and a selective COX-2 inhibitor reduced the growth of adenoma mainly by its inhibitory effect on angiogenesis.

The effect of nonsteroidal antiinflammatory drugs ibuprofen, flurbiprofen, and diclofenac on in vitro and in vivo growth of mouse fibrosarcoma

For suppression of primary G:5:113 fibrosarcoma growth, three structurally different cyclooxygenase (COX) inhibitors (ibuprofen, flurbiprofen, and diclofenac) were administered intraperitoneally (i.p.) in two regimens starting on day 5 after tumor-cell inoculation. Repeated application of 0.15 mg/mouse/day during 14 consecutive days significantly suppressed the tumor growth and increased the percentage of surviving mice. Similar tendency, however without significant differences, was observed when animals were given 0.5 mg/day for five consecutive days. These results suggest that a time schedule of drug application is important for the therapeutic effect. Suppressive effect of diclofenac and flurbiprofen on tumor growth was also observed under in vitro conditions. We conclude that suppressive effect of these drugs on tumor growth in vivo comprises both direct effects of COX inhibitors on fibrosarcoma cells and indirect effects that are presumably mediated by extratumoral sources. Our findings encourage the use of COX inhibitors in the therapy of fibrosarcoma.

NSAIDs and gastrointestinal cancer prevention

Numerous studies report the relationship between aspirin and other nonsteroidal anti-inflammatories (NSAIDs) and cancer incidence, in particular for colorectal cancer. This paper systematically reviews the evidence of the effect of aspirin and other NSAIDs on the primary prevention of colorectal and other gastrointestinal cancers in the general population. In 25 investigations of NSAIDs and colorectal cancer, 23 observational studies reported a relative risk reduction but estimates vary widely. Cohort studies generally indicate lesser reductions than case-control studies suggesting possible biases in the latter. Clear evidence of a dose relationship generally appears lacking but data do not indicate useful effects of aspirin in cardioprophylactic doses. Differences have otherwise not been detected between aspirin and other NSAIDs, nor between non-aspirin NSAIDs. There is some evidence that the risk of colorectal cancer reduces with increased duration of NSAID use. The lower incidence of oesophageal and gastric cancers results in smaller numbers of cases in the studies reporting these cancers, particularly in the cohort studies. The trend is for a risk reduction for oesophageal and gastric cancers in people taking NSAIDs, which is more likely to be statistically significant in the case-control studies. A very small number of observational studies have reported the relationship between NSAIDs and the incidence of pancreatic, gallbladder and liver cancers. These show no consistent relationship. In view of the inadequate information about optimal dose and duration of NSAIDs for colorectal cancer reduction, and the adverse effects of NSAIDs, we are not yet in a position to recommend NSAIDs for the primary prevention of colorectal cancer in the general population.

Cyclooxygenase-2 (COX-2), aromatase and breast cancer: a possible role for COX-2 inhibitors in breast cancer chemoprevention

Interest in chemoprevention in oncology using suppressants of prostaglandin (PG) synthesis has been stimulated by epidemiological observations that the use of aspirin and other non-steroidal inflammatory drugs (NSAIDs) is associated with reduced incidence of some cancers, including cancer of the breast. The main target of NSAID activity is the cyclooxygenase (COX) enzyme. Two isoforms of COX have been identified: COX-1, the constitutive isoform; and COX-2. the inducible form of the enzyme. COX-2 can undergo rapid induction in response to many factors such as bacterial lipopolysaccharides, growth factors, cytokines and phorbol esters. COX-2 is overexpressed in some malignancies including carcinoma of the breast. It has been suggested that such enhanced expression may lead to increased angiogenesis such that the inhibition of COX-2 might have a general anticancer effect via decreased blood vessel formation. In addition, an association between COX-2, its main product PGE2 and aromatase activity in human breast cancer suggests that such inhibitors might have an additional, specific prophylactic mechanism for this tumour. New COX-2 inhibitors are already licensed for use in the treatment of arthritis and are well tolerated. Their potential role in chemoprevention of mammary carcinogenesis in rats has already been investigated. What remains to be seen is if these findings can be extrapolated to human studies.

Reducing the risk of colorectal cancer by intervening in the process of carcinogenesis: a status report

Risk factors for colorectal cancer have been identified, and significant advances have been made in understanding the process of colorectal carcinogenesis. The transition from normal colonic mucosa to adenomatous polyp to adenocarcinoma is a gradual process involving genetic and epigenetic instability that can take decades, offering numerous opportunities for early detection (e.g., colonoscopy screenings), lifestyle changes (e.g., reduced red meat intake, increased physical activity, and reduced alcohol/ tobacco exposure), and chemopreventive interventions. Aspirin and various other nonsteroidal anti-inflammatory drugs may have chemopreventive benefits for colorectal cancer and other human epithelial carcinomas, butthe long-term use of nonsteroidal anti-inflammatory drugs is associated with serious gastrointestinal side effects. Recently, overexpression of cyclooxygenase-2 has been documented in colorectal tumors and numerous other pre-cancers and cancers. The development of selective cyclooxygenase-2 inhibitors, such as celecoxib, provides an opportunity for preventive intervention in the carcinogenic process. Celecoxib has been approved for the management of familial adenomatous polyposis and is under investigation for the management of sporadic colorectal polyps and for its potential as a chemopreventive agent for other cancers.

Chemoprevention of gastrointestinal malignancies with nonsteroidal antiinflammatory drugs

In multiple studies, the chronic use of nonsteroidal antiinflammatory drugs (NSAIDs) has been associated with a decreased incidence of several types of gastrointestinal (GI) neoplasia. This effect may be mediated by one of several intracellular mechanisms, some of which involve the inhibition of the cyclooxygenase-2 (COX-2) isoenzyme. In multiple studies of colorectal carcinoma, chronic NSAID use has shown a protective effect, with the majority of studies demonstrating a 30-70% risk reduction associated with NSAID use. The effect of NSAIDs on other types of GI neoplasia is less clear, but evidence suggests that chronic NSAID use may diminish the risk of esophageal and gastric carcinomas. Data assessing the effects of NSAIDs on the incidence of pancreatic and hepatic malignancies currently are too sparse and inconsistent to draw any conclusions. The newer COX-2 specific agents may provide a less GI-toxic alternative to nonselective NSAIDs as chemoprotective agents.

Rationale and feasibility of chemoprovention of hepatocellular carcinoma by cyclooxygenase-2 inhibitors

Hepatocellular carcinoma (HCC) is a growing health problem worldwide. The limited treatment and poor prognosis of this disease emphasizes the importance of developing effective prevention, including chemoprevention. Improvement in early diagnosis of HCC and regular screen of individuals with increased risk for HCC provide the possibility of effective chemoprevention for HCC in the future. Hepatocarcinogenesis is best described as a continuity of regeneration, proliferation, unregulated hyperplasia, dysplasia, and malignant transformation. Uncontrolled proliferation of hepatocytes clearly plays a key role in hepatocarcinogenesis. Overexpression of cyclooxygenase-2 (COX-2) has been associated with tumorigenesis of colon cancer. Selective COX-2 inhibitors possess potent suppression on the growth of colon cancer. Overexpression of COX-2 has also recently been demonstrated in patients with HCC, especially in nontumorous tissue with cirrhosis and well-differentiated tumorous tissue. In vitro studies have revealed that both NS-398, a selective COX-2 inhibitor, and sulindac, an analog of nonsteroidal anti-inflammatory drugs, effectively inhibit growth of human hepatoma cell lines, which is mediated by a decreased rate of cell proliferation. Although further in vivo studies are required in animal models to confirm these findings and define optimal doses for future clinical trials in human subjects, these findings provide a rationale for the use of COX-2 inhibitors as HCC chemoprevention.

Cyclooxygenase-2 expression is increased in early intestinal-type gastric cancer and gastric mucosa with intestinal metaplasia

OBJECTIVE

Cyclooxygenase-2 (COX-2) expression is increased in gastric cancer. We examined COX-2 expression in early stage gastric cancer and background mucosa to elucidate the role of COX-2 in gastric carcinogenesis.

METHODS

Thirty-three early gastric cancers obtained from 30 patients infected with Helicobacter pylori were studied. Twenty-three patients had an intestinal, four patients had a diffuse, and three patients had both an intestinal and a diffuse type cancer. Expression of COX-2 protein was detected by immunohistochemistry by counting the number of positive staining cells per 100 cells.

RESULTS

Mean COX-2 expression was 84.1 (SD 11.4) in 26 intestinal type cancers and was significantly higher than that in seven diffuse type cancers (23.1 +/- 9.7) (P < 0.001). In three patients who had both the intestinal and the diffuse type cancer, COX-2 expression was 92, 90 and 83 in the intestinal type cancer and only 25, 24 and 7 in the corresponding diffuse type cancer. In 18 patients who had intestinal metaplasia (15 had incomplete metaplasia), COX-2 expression was 60.2 (24.2) in the crypts with metaplasia while it was only 16.8 (10.7) in the crypts without metaplasia (P < 0.001).

CONCLUSIONS

COX-2 expression may be associated with the carcinogenesis of the intestinal type gastric cancer and, speculatively, inhibition of COX-2 might have preventative effects on the intestinal type gastric cancer.

Screening for colon cancer and evaluation of chemoprevention with coxibs

Although colorectal cancer is one of the most preventable forms of visceral cancer, it remains the second leading cause of cancer death in the United States. Most colorectal cancers are believed to arise from adenomatous polyps, premalignant mucosal masses that account for up to two thirds of colorectal polyps. Early identification and removal of adenomas prevent the development of colorectal cancer. Colonoscopy has emerged as the dominant method for evaluating symptomatic patients with colorectal cancer and for surveillance of patients with previous colon polyps or cancer. In the United States, fecal occult blood testing and flexible sigmoidoscopy are the most commonly used screening methods in average-risk persons, although there is an emerging trend toward the use of colonoscopy. For both screening and surveillance, the type of screening test used and the intervals at which it is performed are based on risk stratification, which also serves as the basis for selecting potential candidates for chemoprevention. Because colonoscopy, like most screening procedures, has several disadvantages, including risk of perforation and bleeding and an inherent "miss rate," alternative methods of prevention are being explored. A variety of agents with potential chemopreventive benefits have been identified, including cyclooxygenase (COX)-2-specific inhibitors (coxibs) even though these agents have not been approved for this use in the United States. COX-2 is overexpressed in colonic adenomas and cancers, and its inhibition has been shown to produce regression of polyps in familial adenomatous polyposis. Nonselective COX inhibition with nonsteroidal anti-inflammatory drugs (NSAIDs) has been consistently associated with reductions in the risk of mortality and the incidence of colorectal adenomas and cancers in case-control studies. Thus, selective COX-2 inhibition is a potential method of risk reduction in high-risk screening and surveillance groups, and large-scale trials of coxibs for the prevention of recurrence of adenomas after polypectomy are currently underway.

A population-based study of daily nonsteroidal anti-inflammatory drug use and prostate cancer

OBJECTIVE

To investigate the association between daily use of nonsteroidal anti-inflammatory drugs (NSAIDs) and prostate cancer.

PATIENTS AND METHODS

Subjects were 50- to 79-year-old white men randomly selected in January 1990 from the Olmsted County, Minnesota, community (n=1362) from among participants in a longitudinal study of lower urinary tract symptoms. At the beginning of the study, all medications that were used daily, including prescription and nonprescription NSAIDs, were ascertained by trained interviewers. Men who developed a histologically proved diagnosis of prostate cancer during a median of 66 months (maximum, 6 years) of follow-up were identified from a complete review of the community medical record.

RESULTS

Twenty-three (4%) of 569 NSAID users and 68 (9%) of 793 nonusers developed prostate cancer during follow-up (P=.001). The relative odds of prostate cancer were 0.45 (95% confidence interval [CI], 0.28-0.73) in NSAID users compared with nonusers. This inverse association with NSAID use increased with increasing age at study onset. Thus, the relative odds of prostate cancer among NSAID users were 0.9 (95% CI, 0.4-2.2) in men aged 50 to 59 years, 0.4 (95% CI, 0.2-0.8) in men aged 60 to 69 years, and 0.2 (95% CI, 0.1-0.5) in men aged 70 to 79 years compared with similarly aged men who did not use NSAIDs.

CONCLUSION

The study findings suggest that daily use of NSAIDs may be associated with a lower incidence of prostate cancer in men aged 60 years or older. The stronger effect among older men suggests that NSAIDs may prevent the progression of prostate cancer from latent to clinical disease.

The diet-induced proinflammatory state: a cause of chronic pain and other degenerative diseases?

BACKGROUND

It is the rare physician who includes diet therapy and nutritional supplements in patient care. Perhaps this is because chiropractic and medical schools devote very few classroom hours to nutrition. It is also possible that physicians are under the misconception that a detailed biochemical understanding of each individual disease is required before nutritional interventions can be used.

OBJECTIVE

The purpose of this article is two-fold: (1) to demonstrate that chronic pain and other degenerative conditions encountered in clinical practice have similar biochemical etiologies, such as a diet-induced proinflammatory state, and (2) to outline a basic nutritional program that can be used by all practitioners.

DATA SOURCES

The data were accumulated over a period of years by reviewing contemporary articles and books and subsequently by retrieving relevant articles. Articles were also selected through MEDLINE and manual library searches.

RESULTS

The typical American diet is deficient in fruits and vegetables and contains excessive amounts of meat, refined grain products, and dessert foods. Such a diet can have numerous adverse biochemical effects, all of which create a proinflammatory state and predispose the body to degenerative diseases. It appears that an inadequate intake of fruits and vegetables can result in a suboptimal intake of antioxidants and phytochemicals and an imbalanced intake of essential fatty acids. Through different mechanisms, each nutritional alteration can promote inflammation and disease.

CONCLUSION

We can no longer view different diseases as distinct biochemical entities. Nearly all degenerative diseases have the same underlying biochemical etiology, that is, a diet-induced proinflammatory state. Although specific diseases may require specific treatments, such as adjustments for hypomobile joints, beta-blockers for hypertension, and chemotherapy for cancer, the treatment program must also include nutritional protocols to reduce the proinflammatory state.

Association between acetaminophen or nonsteroidal antiinflammatory drugs and risk of developing ovarian, breast, or colon cancer

STUDY OBJECTIVE

To explore the association between exposure to acetaminophen (paracetamol) or nonsteroidal antiinflammatory drugs (NSAIDs) and risk of developing ovarian, breast, or colon cancer.

DESIGN

Retrospective case-control study

SETTING

General practice offices.

SUBJECTS

Four hundred eighty-three women with ovarian cancer and 1877 women matched for age, years of medical history in computer record, general practice attended, and calendar time; 3706 women with breast cancer and 14,155 matched control subjects; and 635 women with colon cancer and 2434 matched control subjects.

INTERVENTION

United Kingdom-based General Practice Research Database was searched for women aged 50-89 years with a first-time diagnosis of ovarian, breast, or colon cancer and for matched controls to assess prescription analgesic exposure.

MEASUREMENTS AND MAIN RESULTS

Regular acetaminophen exposure (> or = 30 prescriptions) was associated with a slightly decreased risk of developing breast (odds ratio [OR] 0.8, 95% confidence interval [CI] 0.7-1.0) but not ovarian (OR 1.0, 95% CI 0.6-1.5) or colon (OR 1.0, 95% Cl 0.7-1.4) cancer. Regular NSAID exposure was associated with a reduced risk of colon (OR 0.5, 95% CI 0.3-0.9) but not ovarian or breast cancer.

CONCLUSION

We found no evidence for a decreased ovarian cancer risk for women with regular acetaminophen or NSAID exposure.

Celecoxib: a specific COX-2 inhibitor with anticancer properties

In addition to the well-established pathophysiological role that COX-2 plays in inflammation, recent evidence implies that this isoform may also be involved in multiple biologic events throughout the tumorigenic process. Many epidemiological studies demonstrate that nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of a wide range of tumors. Further, COX-2 is chronically overexpressed in many premalignant, malignant, and metastatic human cancers, and levels of overexpression have been shown to significantly correlate to invasiveness, prognosis, and survival in some cancers. Pharmacological studies consistently demonstrate that COX-2 inhibitors dose-dependently inhibit tumor growth and metastasis in various relevant animal models of cancer. Importantly, several investigators have also shown COX-2 inhibitors may act additively or synergistically with currently used cytotoxics and molecularly targeted agents. Here we present a broad overview of the growing evidence that COX-2 plays a pivotal role throughout oncogenesis and summarize the rationale to explore the use of COX-2 inhibitors for the prevention and/or treatment of cancer as a single agent or in combination with current anticancer modalities.

NSAID inhibition of GI cancer growth: clinical implications and molecular mechanisms of action

Epidemiological studies suggest that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) reduce the incidence of and mortality from colorectal, gastric, and esophageal cancers. The precise mechanisms by which NSAIDs exert their chemopreventive effects are not fully explained, but likely involve inhibition of cyclo-oxygenase, the enzyme that converts arachidonic acid to prostaglandins. Two isoforms of this enzyme, cyclo-oxygenase 1 (COX-1) and COX-2, have been identified. COX-2 is absent in normal mucosa but is overexpressed in colonic, gastric, and esophageal cancers, as well as their precursor lesions. The inhibition of COX-2 through either pharmacological agents or gene deletion results in suppression of colonic polyp formation. NSAIDs reduce colonic, gastric, and esophageal cancer cell growth, in part, by inducing apoptosis. However, the antineoplastic effects of NSAIDs may be partly independent of their ability to inhibit COX-2. The mechanisms involved in the antineoplastic actions of NSAIDs include inhibition of angiogenesis (essential for delivery of oxygen and nutrients to a growing tumor), induction of apoptosis (which is usually reduced in cancer cells) by stimulation of proapoptotic genes, and direct inhibition of cancer cell growth by blocking signal transduction pathways responsible for cell proliferation.

Nonsteroidal anti-inflammatory drugs as anticancer agents: mechanistic, pharmacologic, and clinical issues

Numerous experimental, epidemiologic, and clinical studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs), particularly the highly selective cyclooxygenase (COX)-2 inhibitors, have promise as anticancer agents. NSAIDs restore normal apoptosis in human adenomatous colorectal polyps and in various cancer cell lines that have lost adenomatous polyposis coli gene function. NSAIDs also inhibit angiogenesis in cell culture and rodent models of angiogenesis. Many epidemiologic studies have found that long-term use of NSAIDs is associated with a lower risk of colorectal cancer, adenomatous polyps, and, to some extent, other cancers. Two NSAIDs, sulindac and celecoxib, have been found to inhibit the growth of adenomatous polyps and cause regression of existing polyps in randomized trials of patients with familial adenomatous polyposis (FAP). However, unresolved questions about the safety, efficacy, optimal treatment regimen, and mechanism of action of NSAIDs currently limit their clinical application to the prevention of polyposis in FAP patients. Moreover, the development of safe and effective drugs for chemoprevention is complicated by the potential of even rare, serious toxicity to offset the benefit of treatment, particularly when the drug is administered to healthy people who have low annual risk of developing the disease for which treatment is intended. This review considers generic approaches to improve the balance between benefits and risks associated with the use of NSAIDs in chemoprevention. We critically examine the published experimental, clinical, and epidemiologic literature on NSAIDs and cancer, especially that regarding colorectal cancer, and identify strategies to overcome the various logistic and scientific barriers that impede clinical trials of NSAIDs for cancer prevention. Finally, we suggest research opportunities that may help to accelerate the future clinical application of NSAIDs for cancer prevention or treatment.

The role of eicosanoids, cyclooxygenases, and nonsteroidal anti-inflammatory drugs in colorectal tumorigenesis and chemoprevention

There is mounting evidence from studies on experimental cancer in rodents, interventional studies in patients with familial adenomatous polyposis, and some, but not all, epidemiologic investigations, that suggests a chemopreventive effect of aspirin and nonaspirin nonsteroidal anti-inflammatory drugs (NSAIDs) against colorectal cancer. In addition, the mechanisms by which these agents modulate tumorigenesis are being elucidated in laboratory experiments. Currently available NSAIDs are unlikely to have an acceptable benefit-to-risk ratio for long-term use in an asymptomatic population. Once the discrete chemopreventive mechanisms are established and the genetic background and risk factor profile of individuals who will benefit from chemoprevention are clarified, a low-dose combination of NSAIDs with different targets may optimize efficacy and minimize toxicity. At present, however, colectomy is still the treatment of choice for patients with familial adenomatous polyposis, and early screening and regular surveillance colonoscopies are the choices for those at risk for hereditary nonpolyposis colorectal cancer. In the average-risk individual, endoscopic screening and surveillance will remain the core of efforts to prevent sporadic colorectal cancer.

Chemoprevention of colorectal cancer

Colorectal cancer is the third most incident cancer in the United States and is second only to lung cancer as a cause of cancer-related mortality. Colorectal cancer develops through a multistep process characterized by histopathological precursor lesions and molecular genetic alterations. This sequential process of tumorigenesis provides opportunities for the development and testing of both primary and secondary prevention strategies. This review focuses on chemoprevention, which is defined as the use of natural or synthetic agents to reverse the process of carcinogenesis. Epidemiological studies have consistently shown that chronic intake of nonsteroidal anti-inflammatory drugs (NSAIDs), principally aspirin, can reduce the incidence of colorectal adenomas and carcinomas. Evaluation of NSAIDs, including newer selective cyclo-oxygenase-2 inhibitors, in carcinogen-induced and genetically manipulated animal models of colorectal cancer demonstrates that these drugs are effective chemopreventive agents. In humans, the NSAID sulindac has been studied in familial adenomatous polyposis patients and was found to regress colorectal adenomas in a placebo-controlled trial. More recently, the selective cyclo-oxygenase-2 inhibitor Celebrex was also shown to be effective in familial adenomatous polyposis and was approved by the Food and Drug Administration as a adjuct to usual care in these patients. NSAIDs, as well as other chemopreventive agents, are currently being studied in patients at increased risk of colorectal cancer, including those with sporadic adenomas. The outcome of these studies has the potential to impact patient management practices. However, chemopreventive agents cannot be recommeded at present for average-risk individuals or for those with sporadic colorectal neoplasia. In addition to demonstrating efficacy, chemopreventive agents must be safe and well tolerated for chronic administration and should be relatively cost-effective. Although still in its infancy, the field of chemoprevention is an exciting and rapidly advancing area of investigation. Chemopreventive strategies, if effective, offer the promise of producing a paradigm shift in our current approach to colorectal cancer.

Epidemiology of colorectal cancer

Colorectal cancer is a important public health problem: there are nearly one million new cases of colorectal cancer diagnosed world-wide each year and half a million deaths. Recent reports show that, in the US, it was the most frequent form of cancer among persons aged 75 years and older. Given that the majority of cancers occur in elder people and with the ageing of the population in mind, this observation gives further impetus to investigating prevention and treatment strategies among this subgroup of the population. Screening research, recommendations and implementation is an obvious priority. While there are many questions to be resolved, it is apparent that many facets of colorectal cancer are becoming increasingly understood and prospects for prevention are becoming apparent. Achieving colorectal cancer control is the immediate challenge.

Characterization of cyclooxygenase-2 (COX-2) during tumorigenesis in human epithelial cancers: evidence for potential clinical utility of COX-2 inhibitors in epithelial cancers

Increased prostaglandins (PGs) are associated with many inflammatory pathophysiological conditions; and are synthesized from arachidonic acid by either of 2 enzymes, cyclooxygenase-1 (COX-1) or -2 (COX-2). Recent epidemiologic, expression, and pharmacologic studies suggest COX-2 derived metabolites also play a functional role in the maintenance of tumor viability, growth and metastasis. Archival and/or prospectively collected human tissues were prepared for immunohistochemistry, and representative cases assayed via Western blot, RT-PCR, or TAQman analysis. Consistent overexpression of COX-2 was observed in a broad range of premalignant, malignant, and metastatic human epithelial cancers. COX-2 was detected in ca. 85% of the hyperproliferating, dysplastic, and neoplastic epithelial cells, and in the existing and angiogenic vasculature within and adjacent to hyperplastic/neoplastic lesions. These data collectively imply COX-2 may play an important role during premalignant hyperproliferation, as well as the later stages of invasive carcinoma and metastasis in various human epithelial cancers.

Aspirin and epithelial ovarian cancer

BACKGROUND

Epidemiological evidence suggests that chronic inflammation may influence ovarian carcinogenesis. The study objective was to examine the association between the commonly used anti-inflammatory drug aspirin and epithelial ovarian cancer.

METHODS

The authors conducted a case-control study based in the New York University Women's Health Study cohort enrolled between 1985 and 1991 in New York City. After a median follow-up period of 12 years, 68 incident cases of epithelial ovarian cancer were identified. Data about regular aspirin use were collected during the 1994-1996 follow-up questionnaire. Using a case-control study design, 10 controls per case were randomly selected among study participants who matched the case by age and menopausal status. Conditional logistic regression analysis was used to study the relationships between aspirin and epithelial ovarian cancer by generating odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Relative to no aspirin use, the OR for epithelial ovarian cancer among women who reported aspirin use three or more times per week for a period of at least 6 months was 0.60 (95% CI 0.26, 1.38), after adjustment for age at menarche, parity, oral contraceptive use, and first-degree family history of breast cancer before age 50. Among recent, within the previous 5 years, users of aspirin, the adjusted OR was 0.36 (95% CI 0.11, 1.18).

CONCLUSION

Although confidence intervals included unity, the observed risk estimates seem to be compatible with previous studies suggesting that regular aspirin use could be inversely associated with risk of epithelial ovarian cancer.