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

Tissue prostaglandin levels in familial adenomatous polyposis patients treated with sulindac

BACKGROUND

Recent work has demonstrated a correlation between frequency of aspirin ingestion and colorectal cancer prevention. Sulindac, another nonsteroidal anti-inflammatory drug (NSAID), has been shown to cause polyp regression and a fall in cell proliferation in patients with familial adenomatous polyposis, who are destined to develop colorectal cancer unless the colon is removed. However, the mode of action of NSAIDs in colorectal carcinogenesis prevention remains to be determined, although a prostaglandin-mediated mechanism seems likely.

METHODS

Rectal or duodenal biopsies from 20 patients with familial adenomatous polyposis, who had been randomized to sulindac or placebo, were analyzed for prostaglandin (PG) E2 and F2 alpha levels before and after treatment.

RESULTS

A significant fall in prostaglandin E2 and F2 alpha levels was seen in patients who were on sulindac; this correlated with a visual improvement in number and size of polyps in the same patients (P = 0.0096; PGE2, P = 0.036; PGF2 alpha, Spearman's rank correlation).

CONCLUSIONS

Nonsteroidal anti-inflammatory drugs may prevent colorectal cancer by their inhibition of prostaglandin synthesis. Prostaglandins may be implicated in carcinogenesis through an increase in cell proliferation, through immunosuppression, by increasing neovascularization, or via a mutagenic effect.

NSAID use and decreased risk of gastrointestinal cancers

The accumulating evidence suggests that aspirin or other NSAIDs may prevent or inhibit the development of colon and perhaps other digestive tract cancers. Although the clinical, experimental, and epidemiologic evidence is promising, the hypothesis remains unproven except in the models of chemically induced colon cancer in rodents and adenomatous polyps in patients with FAP. Clinicians should await the results of randomized trials before using NSAIDs for cancer prevention or treatment. Recommendations are as follows: 1. Experimental studies should define the mechanism or mechanisms by which NSAIDs inhibit tumorigenesis in the rodent model. 2. Experimental and clinical studies should define the optimal drug, dosage, and treatment regimen. The new, selective COX-2 inhibitors should be studied for efficacy and toxicity. 3. Epidemiologic studies should continue to explore the issues of dosage, duration, drug, and toxicity. Because full-scale, randomized trials are feasible only for studying intermediate end points such as polyp recurrence or proliferative indices in high-risk populations, epidemiologic studies have an ongoing role. 4. Carefully designed randomized, clinical trials, now underway, are needed to test the efficacy of NSAIDs in inhibiting colorectal polyps or cancer in humans. 5. Better criteria are needed as to who should take aspirin and who should not.

Prostaglandins, their inhibitors and cancer

Prostaglandins (PGs) and their analogs endoperoxides are a large series of compounds which mainly enhanced cancer development and progression, acting as cocarcinogens or tumor promoters, and having profound effects on carcinogenesis. Although PGs are ubiquitous tissue hormones exerting pleiotropic effects on cancer cells, their mechanism(s) of action at molecular and cellular levels are not yet elucidated. Autoradiographic, ultrastructural, antigenic, and cell surface studies revealed that PGs act namely by their specific receptors and by interfering with DNA, RNA and protein synthesis, cell membranes and cell communications. PGs also play a role in tumor immunology and transplantation, acting as immunomodulators. Prostaglandins exert their effects by autocrine and paracrine mechanisms similar to hormone-like substances, and hypophysectomy reduces some of their tumor-promoting effects. PGs may act synergistically with hormones, growth factors (GFs), and vitamins. Several drugs called PG-synthesis inhibitors or PG-antagonists are found to markedly inhibit the cyclooxygenase activity. Most of these PG-inhibitors (aspirin, ibuprofen, indomethacin, piroxicam, sulindac) or commonly called NSAIDs (nonsteroidal antiinflammatory drugs) also significantly inhibit cancer development and cancer progression, and are recently used in epidemiological studies for cancer prevention and treatment. Developing more active and less toxic NSAIDs, which can also more selectively inhibit PG synthesis, is a promising field in prostaglandin research.

Distinct isoforms (COX-1 and COX-2) of cyclooxygenase: possible physiological and therapeutic implications

The discovery of an inducible isoform of cyclooxygenase (COX-2) requires a refinement of the theory that inhibition of cyclooxygenase activity explains both therapeutic and side effects of non-steroidal anti-inflammatory drugs (NSAIDs). Indeed, new pharmacological results suggest that COX-2 inhibition provides the therapeutic (ie, anti-inflammatory) activity of NSAIDs, whereas inhibition of constitutive COX-1 is responsible for their gastric and renal side effects as well as for their antithrombotic activity. However, a role of COX-1 in inflammation cannot be excluded. Furthermore, the functional relevance of COX-2 expression and induction in various tissues warrants further investigation. These studies should help in predicting potential adverse effects as well as new indications for selective COX-2 inhibitors.

Sulindac and indomethacin inhibit formation of aberrant crypt foci in the colons of dimethyl hydrazine treated rats

Aberrant crypt foci are microscopic lesions found in the colons of rodents treated with carcinogens, and in patients with premalignant colorectal conditions. They consist of single or multiple abnormal crypts and show cellular changes ranging from dysplasia to microscopic adenomacarcinoma. It is thought that these lesions represent the initial stages of the adenomacarcinoma path that results in the development of colorectal neoplasia. We have examined the effect of sulindac and indomethacin on the formation of aberrant crypt foci in rats treated with dimethylhydrazine (DMH). Aberrant crypt foci were induced in male Sprague-Dawley rats with two oral doses of dimethyl hydrazine at 25 mg/kg per dose. Rats were randomized to receive sulindac at 3 mg/kg (n = 20) or 10 mg/kg (n = 18) b.d., indomethacin at 1 mg/kg per day (n = 18) or 2 mg/kg per day (n = 19) or control (n = 37). Drug treatment was started on the day following the first dose of carcinogen and continued for 3 weeks. Colons were fixed flat overnight in 10% formalin and stained with 0.2%. Methylene Blue solution before being studied. There was a significant reduction in the number of aberrant crypt foci in rats treated with 10 mg/kg b.d., sulindac (P = 0.001) and indomethacin at 2 mg/kg per day (P = 0.0002). Sulindac, at 3 mg/kg b.d., and indomethacin, at 1 mg/kg per day, did not have a statistically significant effect (P = 0.089 and P = 0.052, respectively). None of the drug treatments affected the relative frequency of single crypt vs multiple crypt foci. Previous studies have shown that sulindac and indomethacin will significantly inhibit the growth and development of tumours in DMH treated rats. The current data suggest that one of the pathways of action of NSAID is to inhibit the formation of early preneoplastic lesions.

Apoptosis and gastrointestinal pharmacology

Apoptosis is a fundamental biological process that regulates cell number and removes cells that are neoplastic or infected by viruses. This review summarises present knowledge of the mechanisms and genetic regulation of apoptosis in the gastrointestinal tract and highlights areas of pharmacological relevance. In the intestine, apoptosis occurs in the crypt and possibly at the villus tip. Abnormal apoptosis plays a role in a number of gastrointestinal disease including colorectal cancer. The effects of cytotoxic drugs, chemical carcinogens, nonsteroidal anti-inflammatory drugs, short-chain fatty acids, bile salts and anthraquinolones on apoptosis in the gastrointestinal tract are reviewed.

Aspirin, non-steroidal anti-inflammatory drugs and protection from colorectal cancer: a review of the epidemiological evidence

There is substantial experimental, clinical and epidemiological evidence that regular use of non-steroid anti-inflammatory drugs (NSAIDs), particularly aspirin, is associated with a reduced risk of colorectal cancer. The protective effect is thought to arise from inhibition of prostaglandin synthesis, although the precise mechanism remains unclear. Of the epidemiological studies carried out, all but one have found that regular use of NSAIDs reduces the risk of colorectal cancer by 30-50%. The consistency of this finding across studies and the magnitude of the reduced risk tend to support a causal association between NSAID use and reduced risk of colorectal cancer. Further, the protective effect increases with longer duration of use, and persists after controlling for other colorectal cancer risk factors. However, these observational studies are limited by inherent biases, potential confounding with other lifestyle factors, and sparse information on dose and duration of use. Only one randomized controlled trial has been carried out, and no reduction in risk was associated with intake of one aspirin per day, though this may be due to the short follow-up period and the low dose of aspirin taken. Further observational studies and randomized controlled trials are needed to confirm the association, to quantify the dosage required for a protective effect, and to identify those patients most likely to benefit.

Basis and consequences of primary and secondary prevention of gastrointestinal tumors

Carcinomas of the gastrointestinal tract (GI) are among the most common malignancies with regard to their incidence and mortality. Nutritional factors play an important role in the tumor development. The strength of their influence varies with the localization in the GI tract. Epidemiological studies focusing on GI cancer incidence or mortality as an endpoint necessitate large numbers of subjects to achieve significant results. Generally, a low energy and fat intake and a high intake of antioxidative vitamins (vitamin C, E, beta-carotene) and secondary plant metabolites (especially polyphenols) appear to be protective in GI carcinogenesis. Moderate drinking of alcohol and increased consumption of whole grain products, as opposed to highly refined carbohydrates, may help to reduce the risk of colon cancer. The recommended type of diet is low in fat, especially in saturated fatty acids, includes monounsaturated fatty acids, and includes moderate amounts of polyunsaturated fatty acids (no more than 10% of calories). Moderate consumption of salt and of highly salted, smoked, and barbecued foods should be encouraged. Obesity should be avoided by trying to match energy intake with expenditure while increasing physical activity levels. The mechanisms by which nutritional factors act especially on molecular events still remain to be examined. The use of molecular biomarkers will help us better understand cancer development as well as the role and significance of nutritional factors in this process.

Dietary fat and colon cancer

Dietary fat in general, and perhaps animal and polyunsaturated fats in particular, appear to increase colon carcinogenesis in animal models and epidemiologic studies. This observation holds the potential to shed light on the underlying mechanisms of colorectal carcinogenesis and reduce morbidity and mortality from the disease by dietary and chemoprevention. While research continues into the relationship between prostglandins and other putative mediators of the effects of fats on the colon, we can suggest that a diet which protects against colorectal cancer would be low in fat with most of that fat coming from vegetable sources. Prospective dietary trials are ongoing which may strengthen or modify these preliminary recommendations.

Quinacrine: sclerosing agent of the utero-tubal junction in women, with anticarcinogenic actions in transplanted tumors in mice

Quinacrine, an acridine derivative that was in widespread use as an anti-malarial, has been shown to have both sclerosant and anticarcinogenic actions. The sclerosant action of quinacrine has been used to produce occlusion of Fallopian tube in both experimental animals and women, and several clinical studies are reviewed. Both actions of quinacrine are potentiated by steroidal and non-steroidal antiprostaglandins as well as by ionic copper. Combinations of quinacrine with antiprostaglandin drugs, and also with copper, improved the efficacy of quinacrine when used for female sterilization and reduced side effects. A review of the experimental and epidemiological evidence suggests that quinacrine has no carcinogenic effects.

Effects of dietary fibre on dimethylhydrazine-induced changes in prostanoid concentrations in rat colonic mucosa

1. This study was designed to elucidate the effects of guar gum, a dietary fibre, on changes in prostanoid contents induced by 1,2-dimethylhydrazine, a carcinogenic agent, in rat colonic mucosa. 2. Prostanoid contents were determined using high performance liquid chromatography; five prostanoids, namely 6-keto-prostaglandin F1 alpha, prostaglandin F2 alpha, prostaglandin E2, prostaglandin D2 and thromboxane B2, were detected. 3. Four subcutaneous injections of dimethylhydrazine, 60 mg/kg every 6 days, increased the mucosal concentrations of prostaglandin E2 and thromboxane B2 by approximately 50%. Other prostanoids did not change significantly throughout the experiments. 4. In rats treated with dimethylhydrazine and a fibre diet a significant increase in thromboxane B2 content was not observed, although a significant increase in prostaglandin E2 content was observed. These effects were observed in rats fed with fibre diet over 20 days but not observed in rats fed with fibre diet over 10 days. 5. From these results and the report that aspirin use at low doses is effective in the reduction of the risk of fatal colonic cancer, inhibiting thromboxane B2 synthesis by fibre diet might be involved in the protective effect against the occurrence of colonic cancer.

Aspirin and reduced risk of esophageal carcinoma

BACKGROUND

Aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs) have been shown experimentally to inhibit chemically induced esophageal cancers. An epidemiologic study of more than 600,000 adults in the United States followed for 6 years found that aspirin use was associated with a reduced risk of death from esophageal cancer.

METHODS

The relation of aspirin use and esophageal cancer was examined using data from the National Health and Nutrition Examination Survey (NHANES I) and the National Epidemiologic Follow-up Studies (NEFS). Of the 14,407 United States residents followed for 12-16 years, esophageal cancer developed in 15. Persons were classified as nonusers, occasional users, or regular users of aspirin based on their response to two questions at the baseline examination: whether they had taken aspirin in the past 30 days and whether they had used pain medications regularly during the prior 6 months.

RESULTS

Occasional use was associated with a 90% decreased risk (95% confidence interval, 0.01-0.76) of developing esophageal cancer, and no person classified as a regular user developed the disease. Adjusting for cigarette smoking (ever vs. never) and alcohol intake (at least monthly vs. not) did not explain the finding.

CONCLUSION

Aspirin use was associated with a 90% decreased risk of developing esophageal carcinoma. Further studies to determine whether aspirin is protective against both squamous cell esophageal carcinoma and adenocarcinoma of the esophagus are indicated.

Do patients with epistaxis have drug-induced platelet dysfunction?

Aspirin and other non-steroidal anti-inflammatory drugs (NSAID) are being used increasingly. A positive correlation has been shown between epistaxis and the use of NSAID in the over 50s. This prospective study compared the NSAID intake and platelet function in 50 patients with epistaxis and 50 controls. Standard haematological parameters and the platelet response to collagen and arachidonic acid aggregation and adenosine triphosphate release were measured. The patients showed a significant increase in NSAID intake (P < 0.01, 95% confidence for the difference in the medians = 4-36%) and hypertension (for diastolic blood pressure > 100 mmHg, P < 0.01, 95% confidence for the difference in the medians = 5.9-16.1). The patients showed a significant reduction in platelet aggregation to collagen (P = 0.025). Non-steroidal anti-inflammatory drugs produce a significant platelet dysfunction which should be considered in the multifactorial aetiology of epistaxis.

Effect of extended ibuprofen administration on the acute phase protein response in colorectal cancer patients

The regulation of acute phase protein production and the relationship of the acute phase protein response to tumour growth was examined in colorectal cancer patients (n = 9). Ibuprofen (1200 mg/d) was administered for 8-11 days. Following ibuprofen administration there were reductions in circulating concentrations of C-reactive protein (P = 0.01), interleukin-6 (P = 0.06), cortisol (P = 0.04) and also in the platelet count (P = 0.01). There was no significant change in albumin, insulin and carcinoembryonic antigen. These results indicate that ibuprofen administered over a prolonged period substantially reduces acute protein production via its effect on interleukin-6 and cortisol. It remains to be determined whether ibuprofen is useful in moderating tumour growth in colorectal cancer patients.

A prospective study of tumor recurrence and the acute-phase response after apparently curative colorectal cancer surgery

BACKGROUND

Approximately 70% of patients who are going to develop tumor recurrence following curative colorectal surgery do so within 24 months of surgery.

PATIENTS AND METHODS

The relationship was prospectively examined between an ongoing acute-phase response and subsequent clinical relapse in 36 colorectal cancer patients who had undergone a curative resection. Approximately 4 months after their operation, patients were grouped according to the presence (n = 15) or absence (n = 21) of an acute-phase response (C-reactive protein > 5 mg/L) and were followed-up for a minimum of 24 months.

RESULTS

Age, tumor site, and serum carcinoembryonic antigen concentrations were similar in both groups. There was a significantly higher recurrence rate in patients with an acute-phase response (11 of 15) compared to those with no acute-phase response (2 of 21, P < 0.01).

CONCLUSIONS

These results are consistent with the presence of an acute-phase response being an important predictive factor in the early stages of tumor recurrence in patients who have had apparently curative colorectal surgery.

Aspirin and the risk of colorectal cancer in women

BACKGROUND

Most data suggest that the regular use of aspirin reduces the risk of colorectal cancer, but some apparently conflicting evidence exists. The effects of the dose and the duration of aspirin consumption on the risk of colorectal cancer are not well understood.

METHODS

We determined rates of colorectal cancer according to the number of consecutive years of regular aspirin use (defined as two or more tablets per week) among women in the Nurses' Health Study who reported regular aspirin use on three consecutive questionnaires (1980, 1982, and 1984) and compared the rates in this group with the rates among women who said they did not use aspirin. Cases of cancer occurring from 1984 through 1992 (the eight years after the 1984 questionnaire) were included.

RESULTS

From 1984 through 1992, we documented 331 new cases of colorectal cancer during 551,651 person-years of follow-up. Women who consistently took two or more aspirin tablets per week had no appreciable reduction in the risk of colorectal cancer as compared with nonusers after four years (relative risk, 1.06; 95 percent confidence interval, 0.78 to 1.45) or after five to nine years (relative risk, 0.84; 95 percent confidence interval, 0.55 to 1.28). There was a slight reduction in risk among women who took aspirin for 10 to 19 years, but it was not statistically significant (relative risk, 0.70; 95 percent confidence interval, 0.41 to 1.20). However, there was a statistically significant reduction after 20 years of consistent use of aspirin (relative risk, 0.56; 95 percent confidence interval, 0.36 to 0.90; P for trend = 0.008). The maximal reduction in risk was observed among women who took four to six tablets per week; higher doses had a similar apparent benefit. Controlling for risk factors for colorectal cancer, including diet, did not change the results, and the earlier diagnosis and removal of colorectal adenomas among aspirin users did not account for the results.

CONCLUSIONS

Regular aspirin use, at doses similar to those recommended for the prevention of cardiovascular disease, substantially reduces the risk of colorectal cancer. However, this benefit may not be evident until after at least a decade of regular aspirin consumption.

Coronary artery disease and colorectal neoplasia

PURPOSE

This study was designed to determine whether patients with coronary artery disease are at elevated risk for colorectal neoplasia.

METHODS

A case-control study was conducted among consecutive patients in three colonoscopy practices in New York City from 1986 to 1988. All study participants completed an interview questionnaire covering demographics, diet, environmental and behavioral exposures, family and personal medical history, and other variables. For the present study, 298 newly diagnosed colorectal adenoma cases and 107 incident cancer cases were compared with 507 colonoscoped controls without colorectal neoplasia or other significant findings on colonoscopy. Data on history of coronary artery disease (angina and/or heart attack) were obtained solely from the study participants' questionnaire responses.

RESULTS

No association was observed between angina, heart attack, or either and colorectal adenomas in males. However, prior coronary artery disease was found to be associated with colorectal cancer in males more than 60 years of age and with colorectal adenomas in females aged 50 years or younger.

CONCLUSION

Men with coronary artery disease may be at elevated risk for subsequent colorectal cancer. Young women with coronary artery disease also may be at elevated risk for colorectal neoplasia.

Eicosanoids and the gastrointestinal tract

Determining the role of eicosanoids in gastrointestinal physiology and pathophysiology has been an active area of investigation over the past 20 years. The landmark discovery of prostaglandin endoperoxide synthase and other enzymes involved in the production of arachidonic acid products (lipoxygenases and epoxygenases) ushered in a new era of research. The goal of this review is to distill a large body of work pertaining to studies of eicosanoids in the gastrointestinal tract. This review has been organized according both to functional (secretion and motility) and disease-related (inflammation, mucosal injury, and neoplasia) effects. The aim of this article is to present a clear summary of this area of gastroenterology so that future research can be directed in a logical and productive manner.

The role of nonsteroidal anti-inflammatory drugs in colorectal cancer prevention

Colorectal cancer is the second leading cause of cancer death in the U.S.A. Recent research suggests that nonsteroidal anti-inflammatory drugs (NSAIDs) are effective in the prevention of colorectal neoplasia. This review summarises the results of research in animals and humans of these compounds in preventing tumours of the colorectum.

Effect of sulindac on sporadic colonic polyps

BACKGROUND/AIMS

We sought to determine in a double-blinded, placebo-controlled study if the nonsteroidal anti-inflammatory drug sulindac causes regression of sporadic colonic polyps. The impetus for this study is the profound regressive effect of sulindac on polyps in familial adenomatous polyposis.

METHODS

Asymptomatic patients undergoing routine screening flexible sigmoidoscopy were enrolled if they had polyps of < or = 1 cm in size. Of 162 patients screened, 22 patients were randomly enrolled to take 150 mg of sulindac twice daily, and 22 patients took a placebo. Treatment duration was 4 months and was followed by colonoscopy with removal of all polyps.

RESULTS

Four patients were dropped from the study (sulindac group) due to urosepsis (1 patient), heartburn (2 patients), and anemia (1 patient). Compliance (determined by monthly pill counting), mean age, and the effect of sulindac vs. placebo on polyp regression or size were not statistically different in the two treatment groups. Analysis of our data indicated that there is only a 0.8% chance that the probability of polyp regression with sulindac is as large as 50%.

CONCLUSIONS

Four months of treatment with sulindac does not result in a clinically significant regression of sporadic colonic polyps, although a small effect may not have been detected by the size of our study. Our data suggest that the biological response of sporadic and familial polyposis polyps to sulindac is different.

Aspirin, age, and proximity to lymphoid nodules influence cell proliferation parameters in rat colonic crypts

Recent epidemiological studies have demonstrated a correlation between regular aspirin (acetylsalicylic acid) use and decrease risk for the development of fatal colorectal cancer. An increase in the size of the cell proliferation compartment in colorectal crypts has been correlated with an increased risk for the development of colon cancer in animals and in humans. To determine if acetylsalicylic acid acts to decrease the size of the cell proliferation compartment, young (3 month) and old (22 month) rats were treated intragastrically with: 1 the vehicle for acetylsalicylic acid delivery (0.25% wt/vol carboxymetylcellulose in 0.15 N (HCl), 2 a single dose of acetylsalicylic acid (100 mg/kg), or 3 acetylsalicylic acid (30 mg/kg) given daily for 30 days. One day after the last treatment, colons were resected, fixed, sectioned and mounted on slides for immunohistochemical staining with a monoclonal antibody to proliferating cell nuclear antigen to assess cell proliferation parameters in the colonic crypts. The results were subjected to three way analysis of variance to assess the effects of: 1 rat age, 2 acute or chronic acetylsalicylic acid treatment, and 3 location of crypts over and away from aggregates of lymphoid nodules on the crypt proliferative parameters. Results demonstrated that: 1 acetylsalicylic acid treatment caused on overall decrease in the proliferative zone height, as measured in number of cells in the crypt column, 2 that crypts located over aggregates of lymphoid nodules had significantly higher proliferative activity than crypts located away from aggregates of lymphoid nodules, and 3 after chronic acetylsalicylic acid treatment there was a greater suppression of proliferative zone height in the crypts of old rats than in the crypts of young rats. In conclusion, acute and chronic intragastric delivery of acetylsalicylic acid caused an overall downward shift in the cell proliferation compartment of colonic crypts of young and of old rats. Whether or not acetylsalicylic acid administration will cause the same proliferative zone height response in carcinogen-treated rats is not yet established.

Do NSAIDs exert their colon cancer chemoprevention activities through the inhibition of mucosal prostaglandin synthetase?

Nonsteroidal antiinflammatory drugs (NSAIDs) have considerable potential as chemopreventive agents for colorectal cancer. Recent case-control drug surveillance and large cohort studies found that patients with regular aspirin use had a reduced incidence of colorectal cancer and/or decreased death rate from this disease. Several different NSAIDs reduce formation of both colon adenomatous polyps (the precursor lesion of colon cancer) and cancers in experimental animals given known carcinogens. Perhaps most convincing are reports that the NSAID sulindac promotes regression and inhibits recurrence of adenomatous colon polyps in patients with adenomatous polyposis coli. The best characterized pharmacologic effect of the NSAIDs is their reduction of prostaglandin synthesis by inhibiting prostaglandin synthetase PGE2, which catalyzes the formation of prostaglandin precursors from arachidonic acid. Several lines of evidence are contrary to the concept that inhibition of prostaglandin synthesis is central to the NSAIDs' chemopreventive effects. Relatively high levels of prostaglandins have been reported to inhibit tumor cell growth both in vivo and in vitro, and to inhibit differentiation in some tumor cell lines. We evaluated comparative chemopreventive effects on colon tumor formation in an azoxymethane (AOM)-induced colon carcinogenesis rat model using the NSAIDs piroxicam, sulindac, and sulindac sulfone, a metabolite of sulindac which lacks the anti-prostaglandin synthetase activity typically associated with NSAID-induced gastrointestinal toxicities. The results demonstrate that sulindac sulfone, a compound lacking anti-prostaglandin synthetase activity, inhibits AOM-induced colon cancer in rats. Substantial dose-dependent reductions in both tumor burden and tumor multiplicity were observed in the sulindac sulfone-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of prostaglandin H synthase isozymes during multistage carcinogenesis in mouse epidermis

An anti-tumor-promoting effect of indomethacin and related nonsteroidal anti-inflammatory drugs (NSAIDs) as well as the ability of the tumor promoter 12-O-tetradecanoylphorbol-13- acetate (TPA) to increase the level of prostaglandins in murine keratinocytes and mouse epidermis in vivo has been repeatedly documented. Here, the expression of prostaglandin H synthase (PGHS) isozymes, which are major targets of NSAIDs, was investigated in different stages of tumor development in mouse skin. Mouse epidermis in vivo constitutively expressed PGHS-1. PGHS-1 steady-state levels remained unchanged upon induction of acute or chronic epidermal hyperplasia by TPA and in papillomas and carcinomas generated by the initiation-promotion procedure, with 7,12-dimethylbenz[a]anthracene as initiator and TPA as promoter. Thus, the elevated prostaglandin level in the acute hyperplastic epidermis was very likely due to PGHS-2 induction. Repeated applications of TPA resulted in stationary hyperplasia and downregulation of PGHS-2 expression and prostaglandin levels, suggesting that the epidermis had adapted to the TPA stimulus. In papillomas and carcinomas, however, constitutive overexpression of PGHS-2 was found, with a large amount of prostaglandin E2 and prostaglandin F2 alpha. Keratinocyte cell lines corresponding to different stages of tumor development also constitutively over-expressed PGHS-2. Considered with inhibitor studies, these data suggest that PGHS-2 has a critical role in skin carcinogenesis. The anti-tumor-promoting effect of the PGHS inhibitor indomethacin is specifically reversed by prostaglandin F2 alpha, indicating that this prostaglandin type has a significant role in tumor development.

Diet, body mass index, and colonic epithelial cell proliferation in a healthy population

Using 63 healthy subjects, we conducted an observational study to assess associations between colonic epithelial cell proliferation and dietary intake of selected nutrients. Study subjects exhibited no personal or family history of colon carcinoma, familial polyposis coli, sporadic adenomas, or chronic inflammatory bowel diseases. In this study population, a negative association between the tritiated thymidine-labeling index and dietary intake of calcium (p < 0.003) was found after the effects of age, sex, body mass index (kg/m2), dietary fat, and total energy were controlled in a linear regression model. The association for calcium indicated that a daily calcium intake of 1,200 mg was associated with a predicted thymidine-labeling index of 6%. In the same model, a positive association with the thymidine-labeling index was found for body mass index (p < 0.002) and was suggested for female gender (p < 0.09). No association was found between the thymidine-labeling index and intake of fat, protein, carbohydrate, retinol, ascorbic acid, phosphorus, or iron. Repeat measures of diet in this investigation were used to estimate a subject's daily intake of selected nutrients.

Regulation of prostaglandin synthase-1 and prostaglandin synthase-2

It has been assumed that the rate-limiting step in the ligand-induced synthesis of prostaglandins is the release of arachidonic acid from membrane phospholipid stores as a result of the activation of phospholipase. The assumption has been that the arachidonic acid is converted to PGH2 by the constitutive prostaglandin synthase/cyclooxygenase EC1.14.99.1 (PGS-1) enzyme present in cells. In this model, PGS-1 is proposed to be present in excess, and the production of arachidonic acid is thought to be rate limiting. However, a second prostaglandin synthase gene, PGS-2 has recently been described. The PGS-2 gene is induced by a variety of ligands, in cells as diverse as fibroblasts, monocytes, macrophages, smooth muscle cells, ovarian granulosa cells, epithelial cells, endothelial cells, and neurons. Moreover, PGS-2 induction is inhibited in nearly all contexts by glucocorticoids. It seems likely, therefore, that the regulation of PGS-2 expression plays a critical role in the production of prostanoids, both in normal physiological processes and in pathophysiological processes involving these paracrine mediators. In this review, we consider the regulation of the two genes, PGS-1 and PGS-2, that encode the isoforms of prostaglandin synthase.

Nonsteroidal antiinflammatory drugs and human cancer. Report of an interdisciplinary research workshop

BACKGROUND

Since the 1970s, work in several disciplines (toxicology, pharmacology, clinical medicine, epidemiology) increasingly has suggested that aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs) may reduce the occurrence or progression of colorectal cancers and polyps and perhaps of other gastrointestinal tumors. The potential application of these findings for chemoprevention of such cancers in man now deserves serious consideration.

METHODS

An interdisciplinary workshop was held by the American Cancer Society in March 1994 to review the current knowledge of NSAIDs and cancer and to seek a consensus on future research directions, particularly concerning the possibility of randomized prevention trials in human populations.

RESULTS

A wide-ranging review was conducted of past and current research regarding (1) NSAIDs' effects in experimental animal cancer models; (2) clinic experience in NSAID treatment, particularly in familial polyposis; (3) pharmacologic studies regarding the enzymatic and metabolic actions of NSAIDs; and (4) epidemiologic observations on the relationship of aspirin/NSAID usage to colorectal cancer occurrence in human populations.

CONCLUSIONS

Combined evidence from different research disciplines strongly supports the notion that aspirin and other NSAIDs act to prevent the development or progression of certain human gastrointestinal cancers, especially colorectal cancer. Consequently, the workshop recommended that randomized prevention trials be undertaken. For various logistic reasons, such trials probably should focus on NSAID effects on the occurrence and progression of colorectal polyps rather than on carcinoma itself. Continued research also is needed to clarify further the pharmacologic, clinical, and epidemiologic nature of NSAIDs' influences on human carcinogenesis.

Diseases preceding colon cancer. A case-control study among veterans

Patients with regular use of nonsteroidal antiinflammatory drugs (NSAIDs) appear to have a reduced mortality from colon cancer. As NSAID use is associated with gastrointestinal bleeding, endoscopic exploration of patients on NSAID may lead to more efficient screening and frequent detection of colon cancer. A case-control study was conducted among 12,304 veterans with a colon cancer diagnosed between 1988 and 1992. Four controls were matched by age, sex, and race to each case. The frequency distributions of previous discharge diagnoses in cases and controls were compared. Arterial embolism and thrombosis, spondylosis, peripheral vascular disease, angina, osteoarthrosis, and ischemic heart disease protected against future development of colon cancer. On the other hand, atrial fibrillation and flutter, as well as phlebitis and thrombophlebitis, were associated an increased occurrence of colon cancer after 5-10 years. The study contrasts diseases that are treated with aspirin with those that are treated with other anticoagulants. Both cause bleeding, but the reduced risk of colon cancer was seen only in conditions treated with aspirin. The difference between the two disease groups from the same VA patient population suggests that chronic use of NSAID truly protects against future development of colon cancer.

Phospholipases A2 in ras-transformed and immortalized human mammary epithelial cells

Phospholipase A2 (PLA2) activities of non-tumorigenic and tumorigenic human mammary epithelial cells, 184B5 cells (immortalized cell line from a reduction mammoplasty) and B5KTu cells (cells from a tumor induced by ras-transformed 184B5 cells), are characterized, with emphasis on lipid biomediator-related phospholipases A2. Phospholipases A2 associated with regulation of arachidonic acid metabolism include the high molecular mass cytosolic PLA2 (cPLA2) and group II PLA2. The major PLA2 activity in the mammary epithelial cells has the characteristics of cPLA2; this activity is higher in the B5KTu cells. In contrast, the 184B5 and B5KTu cells have similar levels of a Ca(2+)-independent, cytosolic PLA2 activity and low levels of a particulate fraction PLA2 activity, which does not have the properties of group II PLA2. Thus, cPLA2 activity is selectively elevated in the tumorigenic human mammary epithelial cells and this may result in increased generation of lipid biomediators such as arachidonic acid metabolites.

Nonsteroidal antiinflammatory drugs and colorectal cancer

BACKGROUND

The association between the use of nonsteroidal antiinflammatory drugs (NSAID) and large bowel cancer was examined in a hospital-based case-control study of 511 patients with colorectal cancer and 500 age-sex matched control subjects.

METHODS

Regular NSAID use was defined as at least 3 times per week for 1 or more years before the date of hospital admission. Odds ratios (OR) were calculated by the duration of NSAID use and according to the medical reasons given for taking NSAIDs.

RESULTS

The prevalences of regular NSAID use were 15% for male patients, 8% for female patients, and 20% for control subjects. Overall, NSAID use was associated with a statistically significant risk reduction in men (OR = 0.64; 95% confidence interval [CI], 0.42-0.97) and in women (OR = 0.32; 95% CI, 0.18-0.57). The estimate decreased with duration among men but increased with duration among women. The risk reduction among patients who took NSAIDs to prevent heart disease was 0.67 (95% CI, 0.38-1.13) for men and 0.43 (95% CI, 0.12-1.59) for women. For treating headache pain, the OR was 0.5 (95% CI, 0.23-1.09) for men and 0.64 (95% CI, 0.25-1.62) for women. The use of NSAID was not found to be associated with the stage of cancer at diagnosis. The OR for daily acetaminophen use was 1.07 (95% CI, 0.35-3.23) for men and 0.59 (95% CI, 0.27-1.25) for women.

CONCLUSIONS

The regular use of NSAIDs was associated with an overall significant risk reduction of colorectal cancer in men and in women. Among female patients, the greater protective effect associated with short term NSAID use compared with long term NSAID use may reflect a sampling bias.

Nonsteroidal antiinflammatory agents in chemoprevention of colorectal cancer. At what cost?

The objective was to provide a comparison of the known toxicities of nonsteroidal antiinflammatory drugs (NSAIDS) and the likelihood of benefit from colorectal cancer (CRC) chemoprevention attributed to them. Chemoprevention trials require large numbers of subjects followed over many years and are therefore very expensive and difficult. Hence, it is important that agents tested in these trails have a realistic expectation of actual use in the population. Data sources were published literature on the toxicity and CRC chemopreventive activity of NSAIDS. Presently available NSAIDS, used at their usual therapeutic doses, have a serious toxicity rate that quickly exceeds any benefit from CRC prevention. In contrast, low-dose aspirin is worth evaluating, especially because of the potential for simultaneous cardiovascular risk reduction. Possibly, low doses of other NSAIDS may have benefit, but this remains unproven. Synthesis of other NSAIDS, with less toxicity, is another approach towards making the toxicity-benefit ratio more favorable for the use of these agents for CRC prevention.

Up-regulation of cyclooxygenase 2 gene expression in human colorectal adenomas and adenocarcinomas

BACKGROUND/AIMS

Several clinical, epidemiological, and animal studies indicate that nonsteroidal anti-inflammatory drugs (NSAIDs) may alter the incidence of colorectal cancer. A likely target for NSAIDs is cyclooxygenase, a key enzyme in arachidonic acid metabolism. Two isoforms of this enzyme have been identified; cyclooxygenase (COX) 1 and COX-2. The present study was undertaken to determine if there is differential expression of these isoforms in colorectal neoplasia, and, if so, at what stage in malignant transformation this occurs.

METHODS

COX-1 and COX-2 messenger RNA (mRNA) levels were determined by Northern blot analysis of poly(A)+ RNA isolated from human colorectal cancers, adenomas, and accompanying normal mucosa.

RESULTS

There was a marked increase in COX-2 mRNA levels in 12 of 14 carcinomas (86%) compared with paired normal mucosa. In contrast, there was equivalent intensity of the COX-1 mRNA transcript between the normal mucosa and cancer in all 14 cases. In six pairs of colorectal adenomas and normal mucosa, three showed up-regulation of COX-2 in the adenoma compared with the normal mucosa. Because COX-2 expression is low to undetectable in normal colorectal mucosa, 14 unpaired adenomas were examined for COX-2 expression; a clearly detectable transcript was identified in six (43%).

CONCLUSIONS

COX-2, but not COX-1, gene expression is markedly elevated in most human colorectal cancers compared with accompanying normal mucosa. Furthermore, COX-2 expression seems to be increased in a subset of adenomas. COX-2 may provide an attractive therapeutic target in colorectal neoplasia.

Regression of rectal polyps by indomethacin suppository in familial adenomatous polyposis. Report of two cases

PURPOSE

The effect of indomethacin suppository on rectal polyps was evaluated in two patients with familial adenomatous polyposis who had undergone total colectomy and ileoproctostomy.

METHODS

Both patients received intrarectal administration of 50 mg of indomethacin suppository once or twice daily to control the rectal remnant polyps.

RESULTS

With this treatment, an almost complete regression was achieved within three months, in both patients. Polyps recurred after the interruption of indomethacin treatment in one patient. At the present follow-up of two to three years, no cancer has developed.

CONCLUSIONS

Indomethacin suppository treatment was effective in controlling rectal remnant polyps in the two patients with familial adenomatous polyposis. Intraluminal administration of indomethacin in suppository form seems more beneficial since it allows for direct contact of the drug with the lesions and produces a high local concentration of the drug.

Lipid peroxidation and prostaglandins in colorectal cancer

Dietary fat, arachidonic acid metabolism and lipid peroxidation have all been implicated in colorectal carcinogenesis. Fatty acids, prostaglandins (PGE2, PGF2 alpha) and malondialdehyde (MDA), the stable end-product of lipid peroxidation of polyunsaturated fatty acids (PUFAs), were studied in paired tumour and normal mucosa of 20 patients with colorectal cancer. Levels of arachidonic acid and total PUFAs were increased in the phospholipid fraction of tumours (P < 0.05). Levels of PGE2 and MDA were also higher in tumours (P < 0.001) and there was a significant correlation between MDA and PGE2 concentrations (rs = 0.69, P < 0.01). In contrast to previously reported in vitro studies, this work suggests that lipid peroxidation may be enhanced in human colorectal tumours. As PGE2 and MDA have been shown to be involved in carcinogenesis, these may be considered potential therapeutic targets for preventing or treating colorectal carcinoma.

Non-steroidal anti-inflammatory drugs and tumor progression: inhibition of fibroblast hyaluronic acid production by indomethacin and mefenamic acid

The antitumor effects of non-steroidal anti-inflammatory drugs (NSAIDs) have been documented in a variety of both clinical and experimental settings, although the mechanisms responsible remain unclear. In the present study, we show that the NSAIDs indomethacin and mefenamic acid inhibit the calf serum-stimulated production of hyaluronic acid (HA) in murine Swiss 3T3 fibroblasts, at concentrations where DNA synthesis is unaffected. HA is an extracellular matrix glycosaminoglycan associated with cell migration and tumor invasion. Our data suggest that one mechanism whereby NSAIDs inhibit tumor progression may be to inhibit the synthesis of HA by host fibroblasts, and that the eicosenoid pathway may represent an important control point in the growth-factor-mediated production of HA in fibroblasts. Thus the use of an agent which inhibits HA synthesis may be a novel approach to alter the invasive and metastatic properties of tumor cells in a non-cytotoxic fashion.

Similarity of colorectal cancer in Crohn's disease and ulcerative colitis: implications for carcinogenesis and prevention

Colorectal cancer is the most frequent malignant complication in patients with inflammatory bowel disease. Eighty patients with colorectal cancer complicating Crohn's disease (CD) or ulcerative colitis (UC) with median ages at diagnosis of colorectal cancer of 54.5 years and 43.0 years respectively were studied. The median duration of disease to the diagnosis of cancer was long (CD 15 years; UC 18 years). Most cancers developed after more than eight years of disease (CD 75%; UC 90%). Patients with multiple carcinomas at diagnosis were equally common (CD 11%; UC 12%). Carcinoma occurred in the area of macroscopic disease in most patients (CD 85%; UC 100%). Mucinous and signet ring histological features were equally common (CD 29%; UC 21%). Dysplasia was present with similar frequency in both diseases (CD 73%; UC 79%). The overall five year survival rates were also similar (CD 46%; UC 50%). These findings show that carcinomas complicating CD and UC have strikingly similar clinicopathological features and suggest that a common underlying process, such as chronic inflammation, maybe important in the pathogenesis of colorectal carcinoma.

Aspirin reduces the incidence of colonic carcinoma in the dimethylhydrazine rat animal model

BACKGROUND

Epidemiological studies in humans suggest that regular use of non-steroidal anti-inflammatory drugs (NSAIDS) especially aspirin significantly decreases the risk of developing colorectal cancer.

AIMS

The purpose of this study was to investigate the effect of aspirin on colonic carcinogenesis using the dimethylhydrazine (DMH) colonic cancer model in rats.

METHODS

Groups of animals were given daily doses of aspirin either 0, 5, 30 or 60 mg/kg for 18 weeks. Half of each group also received 18 x 30 mg/kg/wk injections of DMH.

RESULTS

Aspirin at doses of 5, 30 or 60 mg/kg/dy had a progressive effect on the reduction of tumour numbers and the percentage of tumours greater or equal to 5 mm in diameter. Aspirin at doses of 30 and 60 mg/kg/dy significantly reduced tumour incidence.

CONCLUSION

These findings support the epidemiological studies in humans. The rat DMH model would appear to be suitable for investigating the mechanism of action of aspirin in reducing colonic tumour formation.

Aspirin and the prevention of colorectal cancer: a review of the evidence

In all but one of seven recent epidemiologic case-control and cohort studies directly examining the association between aspirin and colorectal cancer and polyps, regular aspirin use reduced the risk of these diseases by about half. Although these studies show a biologically plausible relationship between aspirin and colorectal cancer, information regarding dose and duration and risk change after discontinuation of aspirin is limited and contradictory. Additionally, selection bias, recall bias, and confounding cannot be completed discounted. The one randomized trial of aspirin and placebo showed that aspirin at a dose adequate for preventing myocardial infarction (325 mg every other day) did not reduce colorectal cancer incidence during five years of randomized treatment and follow-up. Further studies need to determine the biologic effects of aspirin, the minimum dose required, and whether other factors, such as age, illnesses, and reasons for aspirin use, modify or confound colorectal cancer development.

Opposing effects of indomethacin and nordihydroguaiaretic acid on macrophage function and tumor growth

The effects of indomethacin (INDO) and nordihydroguaiaretic acid (NDGA) were compared on macrophage function and tumor growth. Intraperitoneal injections (5 mg/kg/day, 6, 8 or 9 days) of INDO in C57BL/6 mice stimulated the cytotoxicity of peritoneal macrophages and inhibited growth of subcutaneous B16 melanoma, whereas NDGA injections suppressed macrophage cytotoxicity, increased macrophage prostaglandin-E2 (PGE2) release, and enhanced the tumor growth. Further, pretreatment of macrophages in vitro with the INDO group serum increased cytostasis against B16 tumor cells, while the use of NDGA group serum reduced it. Incubation of tumor-bearer's macrophages in vitro with INDO (10(-6) M and 10(-7) M) or 10(-6) M NDGA for 4 h reduced PGE2 release, but 10(-7) M NDGA markedly enhanced the PGE2 release. Our data indicate that INDO and NDGA are able to modulate the macrophage function directly, and produce opposing effects on macrophage function and tumor growth. Inhibitory actions of INDO and NDGA on the cyclooxygenase or lipoxygenase pathway of arachidonic acid metabolism appear to contribute to their effects.

Regulation of eicosanoid production and mitogenesis in rat intestinal epithelial cells by transforming growth factor-alpha and phorbol ester

Growth factors and tumor promoters have been shown to play a role in intestinal epithelial growth regulation and transformation. In this study, transforming growth factor-alpha (TGF alpha) and the tumor promoter, tetradecanoyl phorbol acetate (TPA), are shown to stimulate the production of eicosanoids by rat intestinal epithelial (RIE-1) cells in culture. A 4.5-kb mRNA, which hybridizes to the mouse cyclooxygenase-2 cDNA probe, is elevated 18-fold within 30 min after TGF alpha or TPA treatment. Stimulation of RIE-1 cells with TGF alpha leads to the increase of a protein (M(r) approximately 69,000), which binds a monospecific antibody to the mouse cyclooxygenase-2 protein. Dexamethasone markedly inhibits the increase of the 4.5-kb mRNA. Pretreatment of TGF alpha or TPA-stimulated RIE-1 cells with dexamethasone or cyclooxygenase inhibitors prevents the increase in eicosanoid production by these cells. Treatment of quiescent RIE-1 cells with TGF alpha stimulates mitogenesis. This mitogenic activity is blocked by pretreating the cells with dexamethasone or cyclooxygenase inhibitors. A mitogen-inducible cyclooxygenase gene is thus shown to be regulated by TGF alpha and TPA in rat intestinal epithelial cells. We suggest that products of an intestinal growth factor-inducible cyclooxygenase may play a role in the regulation of mitogenesis.

Effect of aspirin on incidence and growth of aberrant crypt foci induced in the rat colon by 1,2-dimethylhydrazine

The aim of this work was to investigate if the possible chemopreventive effect of aspirin (ASA) on rat colon carcinogenesis could be detected with a medium-term assay. The end-point chosen was the inhibition of incidence and growth of putative preneoplastic lesions, the aberrant crypt foci (ACF) induced in the rat colon by two administrations of 1,2-dimethylhydrazine (DMH, 25 mg/kg p.o.). At both 4 and 8 weeks after the starting of the carcinogenic treatment the incidence of total ACF was reduced of 60% in rats receiving ASA (10 mg/kg/day p.o.) for 12 consecutive days during the initiation treatment with DMH. Also the number of the larger foci (with 3 or more crypts) was significantly lower in ASA-treated rats at both time-points (about 70% reduction). Moreover, concomitant ASA treatment determined a significant decrease of the mean number of crypts per focus at week 8. These results indicate that the chemopreventive effect of ASA on chemically-induced rat colon carcinogenesis observed in long-term studies may be detected in this relatively short assay.

Chemoprevention of cancer

Chemoprevention is a strategy used to block the development of cancers in human beings. This emerging field has broad potential for influencing cancer incidence rates in defined high-risk groups and the general population. In this review, we define some of the mechanisms of carcinogenesis, describe some of the genetic markers of carcinogenesis, and list possible biomarkers that may serve as surrogate end points in chemoprevention studies. A major component of this review is a description of the agents that are currently under investigation in animal systems or in human trials. They are grouped according to the agents that block or suppress mutation, such as oltipraz, selenium, vitamin C and the flavones, or according to agents that block promotion and proliferation, such as difluoromethylornithine, tamoxifen, nonsteroidal antiinflammatory drugs, and the vitamin A derivatives. We describe the issues that are considered in the design of chemoprevention trials and in the phase I, II, and III components of these trials. The following national trials are discussed: the Breast Cancer Prevention Trial, which uses tamoxifen; the Prostate Cancer Prevention Trial, which uses finasteride; and a Lung Cancer Prevention Trial, which uses 13-cis-retinoic acid. The review ends with some insights about future studies in chemoprevention.