Relationship between blood plasma prostaglandin E2 and liver and lung metastases in colorectal cancer

Inhibition of COX-2 Impairs Colon Cancer Liver Metastasis through Reduced Stromal Cell Reaction

Liver colonization is initiated through the interplay between tumor cells and adhesion molecules present in liver sinusoidal endothelial cells (LSECs). This crosstalk stimulates tumor COX-2 upregulation and PGE₂ secretion. To elucidate the role of the LSEC intercellular adhesion molecule-1 (ICAM-1) in the prometastatic response exerted by tumor and stromal COX-2, we utilized celecoxib (CLX) as a COX-2 inhibitory agent. We analyzed the in vitro proliferative and secretory responses of murine C26 colorectal cancer (CRC) cells to soluble ICAM-1 (sICAM-1), cultured alone or with LSECs, and their effect on LSEC and hepatic stellate cell (HSC) migration and in vivo liver metastasis. CLX reduced sICAM-1-stimulated COX-2 activation and PGE₂ secretion in C26 cells cultured alone or cocultured with LSECs. Moreover, CLX abrogated sICAM-1-induced C26 cell proliferation and C26 secretion of promigratory factors for LSECs and HSCs. Interestingly, CLX reduced the protumoral response of HSC, reducing their migratory potential when stimulated with C26 secretomes and impairing their secretion of chemotactic factors for LSECs and C26 cells and proliferative factors for C26 cells. In vivo, CLX abrogated the prometastatic ability of sICAM-1-activated C26 cells while reducing liver metastasis. COX-2 inhibition blocked the creation of a favorable tumor microenvironment (TME) by hindering the intratumoral recruitment of activated HSCs and macrophages in addition to the accumulation of fibrillar collagen. These results point to COX-2 being a key modulator of processes initiated by host ICAM-1 during tumor cell/LSEC/HSC crosstalk, leading to the creation of a prometastatic TME in the liver.

Association between plasma prostaglandin E2 level and colorectal cancer

Evidences for the personalized use of nonsteroidal anti-inflammatory drugs (NSAIDs) in colorectal cancer (CRC) prevention and treatment that include consideration of prostaglandin E2 levels are necessary. This study was designed as a case-control study including 60 CRC patients and 120 cancer-free controls. A sensitive empirical method, precolumn derivatization HPLC, was used to determine plasma PGE2 levels. The TaqMan SNP Genotyping Assay was used for the genotyping of prostaglandin-endoperoxide synthase 2 (PTGS2) polymorphisms. Multivariate logistic regression analysis suggested that 1 log10(PGE2) increase would result in a 3.64-fold increase in the risk of CRC. Moreover, subjects with log10(PGE2) level in the 75th percentile had a significantly higher risk of CRC than those with log10(PGE2) levels in the 25th percentile [odds ratio (OR), 3.50; 95% confidence interval (CI), 1.35-9.05]. This association was more evident after adjustment for history of NSAIDs use (OR, 3.85; 95% CI, 1.46-10.16). Preliminarily, 260.02 and 414.95 pg/ml might be proposed as the preventive and warning cutoff values of plasma PGE2 for CRC. The preferred NSAIDs dose for patients with the AG+GG (rs689466) and CC+CT (rs5275) genotypes should be higher than that of patients carrying AA or TT genotypes, despite the presence of equal plasma PGE2 levels. We show for the first time that the plasma PGE2 level is associated with the risk of CRC. We provide a preliminary suggestion for NSAIDs doses adjustment according to PTGS2 genotypes after consideration of plasma PGE2 levels.

Immunosuppressive Factors: Role in Cancer Development and Progression

The concept of the immunological surveillance against neoplastic cells was initially proposed by Erlich in 1909 and later elaborated by Burnet. This hypothesis states that the normal function of the immune system, in particular the cell-mediated immunity, is to recognize and destroy the transformed and proliferating tumor cells. The role of cell-mediated immunity during the first steps of tumorigenesis remains controversial. However, there is certain evidence about its importance in the progression and dissemination of cancer. The frequent immunosuppressed condition of cancer patients at tumor relapse or recurrence of secondary tumors is a clinical sign supporting this hypothesis, and many studies have demonstrated a defective immune response in patients diagnosed with advanced cancer. Several mechanisms of escape from the immune surveillance have been described, including the immunoselection of tumor antigen-negative variants, the downregulation of MHC class I expression, suppressive T cells, and the elaboration of immunosuppressive cytokines and other factors. Because of the technical difficulty of isolating the very small amounts from culture supernatants or body fluids, only a few of these substances have been characterized and studied with respect to their biological activity: transforming growth factor-β (TGF-β), the protein p15E, interleukin 10 (IL-10), prostaglandin E2 (PGE2), mucins, suppressive E-receptor (SER), immunosuppressive acidic protein (IAP), and adhesion molecules. The possibility of monitoring cancer patients by testing biochemical factors related to cancer growth led to a proposal to measure a number of these factors as tumor markers. Some of them, e.g mucins, enjoy the consensus of the oncologic community, as for some indications they can help the clinician in the management of cancer patients. Except for the class of mucins, the other above-mentioned immunosuppressive factors have not found any clinical application in the laboratory routine because the information deriving from their measurement, although of speculative and scientific interest, has limited clinical value at present. Nevertheless, even if they have no impact on patient management, these substances do have a potential role to play in the study of cancer patients, and should be taken into account when developing new therapeutic strategies.

Rectal Cancer in a Patient with Bartter Syndrome: A Case Report

A woman with rectal cancer was scheduled for surgery. However, she also had hypokalemia, hyperreninemia, and hyperaldosteronism in the absence of any known predisposing factors or endocrine tumors. She was given intravenous potassium, and her blood abnormalities stabilized after tumor resection. Genetic analysis revealed mutations in several genes associated with Bartter syndrome (BS) and Gitelman syndrome, including SLC12A1, CLCNKB, CASR, SLC26A3, and SLC12A3. Prostaglandin E2 (PGE2) plays an important role in BS and worsens electrolyte abnormalities. The PGE2 level is reportedly increased in colorectal cancer, and in the present case, immunohistochemical examination revealed an increased PGE2 level in the tumor. We concluded that the tumor-related PGE2 elevation had worsened the patient’s BS, which became more manageable after tumor resection.

Intratumoral forkhead box P3-positive regulatory T cells predict poor survival in cyclooxygenase-2-positive uveal melanoma

BACKGROUND

Forkhead box P3 (FOXP3)-positive regulatory T cells (Tregs) are key mediators of peripheral tolerance and suppress efficient antitumor responses. Prostaglandin E(2) (PGE(2)) produced by inducible cyclooxygenase-2 (COX-2) can lead to Treg induction. COX-2 expression has been linked to tumorigenesis and growth in various malignancies. The objective of the current study was to investigate whether Tregs infiltrate uveal melanomas (UMs) and whether their prevalence is linked to COX-2 expression and the prediction of overall survival (OS).

METHODS

One hundred patients who underwent enucleation after they were diagnosed with UM were included in the study. Immunohistochemical staining with monoclonal anti-FOXP3, anti-CD4, and anti-COX-2 antibodies was performed, and immunoreactivity was assessed. Correlations of COX-2 expression with the presence of Tregs, established clinicopathologic parameters, and OS were evaluated in univariate and multivariate analyses.

RESULTS

High expression of COX-2 was predictive of shortened OS. FOXP3-positive Tregs were detectable in 24% of UMs and were restricted to malignant tissue. The extent of COX-2 expression was associated significantly with Treg prevalence (P = .004) and Treg intratumoral localization (P = .005). Intratumoral Tregs (but not the prevalence of Tregs) were independent marker for worse OS with a hazard ratio of 5.36 in patients with COX-2-positive tumors.

CONCLUSIONS

The current results demonstrated that high COX-2 expression is associated with OS and Treg prevalence in UM. These findings are in line with the observations that COX-2/PGE(2) induces Tregs and that Tregs may alter antitumor responses, resulting in a negative effect on the clinical disease course. Intratumoral Tregs are an independent prognostic marker for COX-2-positive UM, and these results put COX-2 inhibitors and Treg depletion into the spotlight of potential novel treatment modalities for patients with UM.

Reduced risk of human lung cancer by selective cyclooxygenase 2 (COX-2) blockade: results of a case control study

We conducted a case control study of selective cyclooxygenase-2 (COX-2) blocking agents and lung cancer. A total of 492 newly diagnosed lung cancer cases were ascertained during January 1, 2002 to September 30, 2004, at The Ohio State University Medical Center, Columbus, Ohio. All cases were confirmed by examination of the pathology report. Healthy population controls without cancer were ascertained during the same time period. Controls were frequency matched at a rate of 2:1 to the cases by age, gender, and county of residence. We collected information on type, frequency, and duration of use of selective COX-2 inhibitors (primarily celecoxib or rofecoxib) and nonselective NSAIDs such as ibuprofen and aspirin. Estimates of odds ratios (OR) were obtained with adjustment for cigarette smoking, age and other potential confounders using logistic regression analysis. Odds Ratios for selective COX-2 inhibitors were adjusted for past use of other NSAIDs. Use of any selective COX-2 inhibitor for more than one year produced a significant (60%) reduction in the risk of lung cancer (OR=0.40, 95% CI=0.19-0.81). Observed risk reductions were consistent for men (OR=0.26, 95% CI=0.10-0.62) and women (OR=0.52, 95% CI=0.24-1.13) and for individual COX-2 inhibitors (OR=0.28, 95% CI=-0.12-0.67, for celecoxib and OR=0.55, 95% CI=0.19-1.56, for rofecoxib). Intake of ibuprofen or aspirin also produced significant risk reductions (OR=0.40, 95% CI=0.23-0.73 and OR=0.53, 95% CI=0.34-0.82, respectively), whereas acetaminophen, an analgesic with negligible COX-2 activity, had no effect on the risk (OR=1.36, 95% CI=0.53-3.37). This investigation demonstrates for the first time that selective COX-2 blocking agents have strong potential for the chemoprevention of human lung cancer.

Cancer chemoprevention by cyclooxygenase 2 (COX-2) blockade: results of case control studies

Significant use of selective cyclooxygenase-2 (COX-2) blocking agents prescribed for the treatment of arthritis during 1999 to 2005 facilitates epidemiologic investigations to illuminate their chemopreventive effects against human cancer. We therefore conducted a set of case control studies of selective COX-2 blocking agents to determine their chemopreventive potential for the four major cancers: breast, prostate, colon, and lung. Newly diagnosed cases (323 breast cancer patients, 229 prostate cancer patients, 326 colon cancer patients, and 486 lung cancer patients) were ascertained during 2002 to September 30, 2004, at The James Cancer Hospital and Solove Research Institute, The Ohio State University Medical Center, Columbus, Ohio. All cases of invasive cancer were confirmed by examination of the pathology report. Healthy controls without cancer were ascertained from hospital screening clinics during the same time period. Controls were frequency matched at a rate of 2:1 to the cases by age, gender, and county of residence. We collected information on type, frequency, and duration of use of selective COX-2 inhibitors and nonselective nonsteroidal anti-inflammatory drugs (NSAIDs). Other potentially important risk factors (smoking, drinking, body mass, medical history, blood pressure and cholesterol medications, family history of cancer, occupational history, and reproductive history for women) were also recorded for each subject. Estimates of odds ratios were obtained with adjustment for age and other potential confounders using logistic regression analysis. Use of selective COX-2 inhibitors resulted in a significant risk reduction for each type of cancer (71% for breast cancer, 55% for prostate cancer, 70% for colon cancer, and 79% for lung cancer) and an overall 68% risk reduction for all four cancers. This investigation demonstrates that COX-2 blocking agents have strong potential for the chemoprevention of cancers of the breast, prostate, colon and lung.

Distribution and metabolism of dihomo-gamma-linolenic acid (DGLA, 20:3n-6) by oral supplementation in rats

We compared the dietary effects of dihomo-gamma-linolenic acid (DGLA) contained in the DGLA oil produced by a fungus with gamma-linolenic acid (GLA) on the fatty acid composition. Wistar rats were fed with three kinds of oil for two weeks as follows: (i) control group: corn oil; (ii) GLA group: borage oil; (iii) DGLA group: DGLA oil/safflower oil = 55:45. The DGLA concentrations in the liver, serum, and brain of the DGLA group were higher than those of the GLA oil group. We also examined the dose effect of DGLA. The DGLA levels in the liver, serum, and brain significantly increased with increasing dosage of DGLA in the diet. DGLA administration significantly increased the ratio of PGE1/PGE2 in the rat plasma. The mechanism for GLA administration to improve atopic eczema is thought to involve an increase in the concentration of DGLA metabolized from GLA, so these results suggest that the dietary effect of DGLA would be more dominant than GLA.

Suppression of prostate carcinogenesis by dietary supplementation of celecoxib in transgenic adenocarcinoma of the mouse prostate model

Epidemiological studies and clinical observations suggest that nonsteroidal anti-inflammatory drugs and certain selective cyclooxygenase (COX)-2 inhibitors may reduce the relative risk of clinically evident prostate cancer. This prompted us to investigate the chemopreventive potential of celecoxib, a selective COX-2 inhibitor, against prostate carcinogenesis in a transgenic adenocarcinoma of the mouse prostate (TRAMP) model. Similar to prostate cancer in humans, prostate malignancies in TRAMP mice progress from precursor intraepithelial lesions, to invasive carcinoma that metastasizes to lymph nodes, liver, lungs, and occasionally to bone. The basal enzyme activity and protein expression of COX-2 is significantly higher (>4-fold) in the dorsolateral prostate of TRAMP mice up to 24 weeks of age compared with their nontransgenic littermates. Eight-week-old TRAMP mice were randomly divided and fed either control diet (AIN 76A) or a custom prepared AIN 76A diet containing 1500-ppm celecoxib ad libitum for 24 weeks, a dosage that would compare with the normal recommended dose for the treatment of human disease. Studies from two independent experiments, each consisting of 10 mice on test, showed that the cumulative incidence of prostate cancer development at 32 weeks of age in animals fed with AIN 76A diet was 100% (20 of 20) as observed by tumor palpation, whereas 65% (13 of 20), 35% (7 of 20), and 20% (4 of 20) of the animals exhibited distant site metastases to lymph nodes, lungs, and liver. Celecoxib supplementation to TRAMP mice from 8-32 weeks of age exhibited significant reduction in tumor development (5 of 20) with no signs of metastasis. Celecoxib feeding resulted in a significant decrease in prostate (56%; P < 0.0003) and genitourinary weight (48%; P < 0.008). Sequential magnetic resonance imaging analysis of celecoxib-fed mice documented lower prostate volume compared with the AIN 76A-fed group. Histopathological examination of celecoxib-fed animals showed reduced proliferation, and down-modulation of COX-2 and prostaglandin E2 levels in the dorsolateral prostate and plasma, respectively. These results correlated with retention of antimetastasis markers, viz E-cadherin, and alpha- and beta-catenin, along with a significant decrease in vascular endothelial growth factor protein expression. Celecoxib supplementation also resulted in enhanced in vivo apoptosis in the prostate as monitored by several techniques including a recently perfected technique of 99mTc-labeled annexin V in live animals followed by phosphor imaging. One striking observation in an additional study was that celecoxib feeding to mice with established tumors (16 weeks of age) significantly improved their overall survival (P = 0.014), compared with AIN 76A-fed group. Our findings suggest that celecoxib may be useful in chemoprevention of prostate cancer.

The relationship between cyclooxygenase-2 expression and characteristics of malignant transformation in human colorectal adenomas

BACKGROUND AND AIMS

Cyclooxygenase 2 (COX-2) is a target of aspirin and other non-steroidal anti-inflammatory drugs and is implicated in the pathogenesis of colorectal cancer. The objective of this study was to evaluate the extent of COX-2 in pre-malignant colorectal polyps and to assess the relationship between COX-2 and the level of dysplasia in these lesions.

METHODS

Whole polypectomy specimens were retrieved from 123 patients by endoscopic or surgical resection. Following formalin fixation and paraffin embedding, the polyps were evaluated histologically for size, type and grade of dysplasia. The extent of COX-2 expression was measured by the avidin-biotin immunohistochemical technique using a monoclonal COX-2 antibody. The extent of COX-2 expression was graded according to percentage epithelial COX-2 expression.

RESULTS

The polyps were of the following histological types: 10 hyperplastic, 35 tubular adenomas, 61 tubulovillous adenomas and 17 villous adenomas. Twenty showed mild dysplasia, 65 moderate dysplasia, and 28 focal or severe dysplasia (including eight with focal invasion). The average polyp size was 1.7 cm. Nine hyperplastic polyps were COX-2-negative and one was COX-2-positive. COX-2 expression was more extensive in larger polyps and in polyps with a higher villous component. There was a significant increase in the extent of COX-2 protein with increasing severity of dysplasia. Within a polyp, there was a focal corresponding increase in COX-2 expression within epithelium showing a higher grade of dysplasia.

CONCLUSIONS

COX-2 expression is related directly to colorectal adenomatous polyp size, type and grade of dysplasia. This suggests that the role of COX-2 in colorectal cancer may be at an early stage in the adenoma-to-carcinoma sequence and supports the suggestion that inhibition of COX-2 may be useful chemoprevention for this disease.

Effects of dietary linseed, evening primrose or fish oils on fatty acid and prostaglandin E2 contents in the rat livers and 7,12-dimethylbenz[a]anthracene-induced tumours

We examined the influence of diets supplemented with fish and vegetable oils on fatty acid and prostaglandin E2 (PGE2) contents in livers of non-7,12-dimethylbenz[a]anthracene (DMBA)- and DMBA-treated rats, and in DMBA-induced tumours. Decreased concentrations of saturated fatty acids and increased unsaturated fatty acid levels were observed in liver phospholipids of rats fed these oils. There was a marked difference in the concentrations of fatty acids found in the tumours and those present in liver lipids. Oleic acid was the main unsaturated fatty acid found in the tumour tissue. Both liver and tumour PGE2 contents were clearly correlated to the diet. The PGE2 concentrations were decreased in livers and tumours of rats fed fish (FO) and linseed oils (LO).

Tumor invasiveness and liver metastasis of colon cancer cells correlated with cyclooxygenase-2 (COX-2) expression and inhibited by a COX-2-selective inhibitor, etodolac

Non-steroidal anti-inflammatory drugs (NSAIDs) have been reported to reduce the risk and mortality of colorectal cancer (CRC). Although the exact mechanisms remain unclear, the inhibition of cyclooxygenase (COX) by NSAIDs appears to abort, if not prevent, CRC carcinogenesis or metastatic tumor progression. The aim of our study was to investigate the association between COX-2 expression and CRC tumor cell invasiveness. The differences in immunoblot-detectable COX-2 protein contents in primary CRCs, metastatic hepatic lesions and corresponding normal mucosa from the same individual were evaluated in 17 patients. Three different colon cancer cell lines, SW620, Lovo, HT-29 and a metastatic variant of HT-29, HT-29/Inv3, were employed to evaluate COX-2 expression and prostaglandin E(2) (PGE2) production in relation to their invasive abilities in vitro. The effects of a COX-2-selective inhibitor, etodolac, on cell proliferation and invasive activity were also determined. The results showed that 15 of 17 (88%) metastatic CRC cells from the liver and 14 of 17 (82%) primary CRC tissue exhibited much higher levels of COX-2 than corresponding adjacent normal mucosa from the same patient. Among those patients with relatively high COX-2 expression in the primary tumors, almost all exhibited even higher levels of COX-2 in their hepatic metastases. Among the 4 colon cancer cell lines, HT-29/Inv3 manifested the highest COX-2 expression, PGE2 production and in vitro invasive activity. The selective COX-2 inhibitor, etodolac, could especially exert cytotoxicity and markedly suppress the invasive property and PGE(2) production, although not the COX-2 protein level, in HT-29/Inv3 cells. Our results imply that COX-2 expression may be associated with the invasive and metastatic properties of CRC tumor cells.

Xenobiotic-metabolizing cytochromes P450 convert prostaglandin endoperoxide to hydroxyheptadecatrienoic acid and the mutagen, malondialdehyde

Cyclooxygenases catalyze the oxygenation of arachidonic acid to prostaglandin endoperoxides. Cyclooxygenase-2- and the xenobiotic-metabolizing cytochrome P450s 1A and 3A are all aberrantly expressed during colorectal carcinogenesis. To probe for a role of P450s in prostaglandin endoperoxide metabolism, we studied the 12-hydroxyheptadecatrienoate (HHT)/malondialdehyde (MDA) synthase activity of human liver microsomes and purified P450s. We found that human liver microsomes have HHT/MDA synthase activity that is concentration-dependent and inhibited by the P450 inhibitors, ketoconazole and clotrimazole with IC(50) values of 1 and 0.4 microM, respectively. This activity does not require P450 reductase. HHT/MDA synthase activity was present in purified P450s but not in heme alone or other heme proteins. The catalytic activities of various purified P450s were determined by measuring rates of MDA production from prostaglandin endoperoxide. At 50 microM substrate, the catalytic activities of purified human P450s varied from 10 +/- 1 to 0.62 +/- 0.02 min(-1), 3A4 >> 2E1 > 1A2. Oxabicycloheptane analogs of prostaglandin endoperoxide, U-44069 and U-46619, induced spectral changes in human P450 3A4 with K(s) values of 240 +/- 20 and 130 +/- 10 microM, respectively. These results suggest that co-expression of cyclooxygenase-2 and P450s in developing cancers may contribute to genomic instability due to production of the endogenous mutagen, MDA.

Treatment and survival study in the C57BL/6J-APC(Min)/+(Min) mouse with R-flurbiprofen

Our previous studies with the mouse model of familial adenomatous polyposis (FAP), C57BL/6J-APC(Min)/+ or Min mouse, demonstrated the optimal dose for adenoma reduction with R-flurbiprofen was 10 mg/kg/day as an undivided dose. Divided doses exhibited no increased efficaciousness. This study examines 10 mg/kg R-flurbiprofen daily (qd) on survival as well as a second daily (q.o.d.) schedule and compares it with sulindac sulfone. The q.o.d. schedule at 10 mg/kg was equally efficacious as qd treatment at the same dose. For the q.o.d. group, tumor number decreased similarly (p<0.01); while body weight gain (p<0.01), hematocrit and average tumor area (both, p<0.05) were improved compared with qd treatment. Treatment with R-flurbiprofen (10 mg/kg/day) increased survival significantly (p=0.0004, log-rank) compared to vehicle treated animals. Major biological endpoints (hematocrit, weight gain, tumor number, average and total area [99% reduction]) were significantly improved in treated animals (p<0.01). Sulindac sulfone treatment (50 mg/kg/day) of the Min mouse produced no significant biological benefit. The dose schedule study suggests that for tumor reduction it is necessary to attain a threshold drug-level but not necessarily sustain it over 24 hrs (pharmacodynamic t1/2 >> pharmacokinetic t1/2). During the period of administration R-flurbiprofen dramatically prolongs survival for the mouse model of the human disease, FAP.

Prostaglandin production in mouse mammary tumour cells confers invasive growth potential by inducing hepatocyte growth factor in stromal fibroblasts

Interactions between stromal and mammary tumour cells play a crucial role in determining the malignant behaviour of tumour cells. Although MMT mouse mammary tumour cells do not produce hepatocyte growth factor (HGF), addition of conditioned medium (CM) from MMT cells to cultures of human fibroblasts derived from skin and breast tissues stimulated the production of HGF, thereby indicating that MMT cells secrete an inducing factor for HGF. This HGF-inducing factor, purified from MMT-derived CM, proved to be prostaglandin E2 (PGE2). Consistently, treatment of MMT cells with indomethacin, an inhibitor of cyclooxygenase, abolished this HGF-inducing activity in MMT-derived CM, while treatment of MMT cells with HGF stimulated cell growth and cell motility. Likewise, HGF strongly enhanced urokinase-type plasminogen activator activity and invasion of MMT cells through Matrigel: a 15-fold stimulation in the invasion of MMT cells was seen by HGF. Finally, MMT cells in the upper compartment were co-cultivated with fibroblasts in the lower compartment of the Matrigel chamber, HGF levels in the co-culture system exceeded the level in fibroblasts alone and suppression occurred with exposure to indomethacin. Together with increase in the HGF level, the invasion of MMT cells was enhanced by co-cultivation with fibroblasts, whereas the increased invasion of MMT cells was significantly inhibited by an anti-HGF antibody and by indomethacin. These results indicate mutual interactions between MMT cells and fibroblasts: MMT-derived PGE2 plays a role in up-regulating HGF production in fibroblasts, while fibroblast-derived HGF leads to invasive growth in MMT cells. The mutual interactions mediated by HGF and prostaglandins may possibly be a mechanism regulating malignant behaviour of mammary tumour cells, through tumour-stromal interactions.

Early expression of cyclo-oxygenase-2 during sporadic colorectal carcinogenesis

Regular administration of non-steroidal anti-inflammatory drugs (NSAIDs) may reduce the incidence of colorectal cancer by targeting cyclo-oxygenase-2 (Cox-2), a key enzyme in arachidonic acid metabolism. To evaluate the role of Cox-2 in sporadic colorectal cancer development, Cox-2 expression was investigated by immunohistochemistry in 85 adenomas, 53 carcinomas, 34 hyperplastic lesions and 104 samples of histologically normal mucosa adjacent to adenoma or carcinoma. In addition, Cox-2 mRNA expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR) in six adenomas and 14 carcinomas with paired grossly normal mucosa. Immunohistochemistry for the proliferation-associated antigen Ki-67 and in situ end labelling for demonstrating apoptotic bodies were also used to analyse the associations between Cox-2 expression and proliferation and apoptosis. Cox-2 protein expression was increased in 76/85 (89.4 per cent) adenomas and 44/53 (83.0 per cent) carcinomas compared with normal mucosa. Cox-2 protein expression was unrelated either to the degree of dysplasia or to the size of the adenomas (p > 0.50, p > 0.10, respectively) or to differentiation, Dukes stage or lymph node metastasis of carcinomas (all p > 0.50). Interestingly, 20/34 (58.8 per cent) hyperplastic lesions adjacent to adenomas or carcinomas displayed expression higher than in normal mucosa (18.3 per cent) (p < 0.0001) but lower than in adenomas or carcinomas (p < 10(-5), p < 0.001, respectively). There were no correlations between Cox-2 protein expression and proliferative or apoptotic index in either adenomas or carcinomas (all p > 0.25). Cox-2 mRNA expression was significantly increased in adenomas and carcinomas compared with normal mucosa (p < 0.005, p < 0.001, respectively). There were no differences between adenomas and carcinomas in either protein or mRNA levels (p > 0.25, p > 0.90, respectively). These data indicate that enhanced expression of Cox-2 occurs early during colorectal carcinogenesis and may contribute to tumour formation.

Non steroidal anti-inflammatory drugs and colorectal cancer: is there a way forward?

Non steroidal anti-inflammatory drugs (NSAIDs) have diverse clinical applications through modulation of oxidative processes and cell signalling. Observations that these agents may inhibit human colorectal carcinogenesis have produced great excitement. However, comparative data relating to their chemopreventative effectiveness or to relevant mechanisms of action remains unclear. This review considers the clinical and epidemiological evidence for colorectal tumour prevention by NSAIDs against current concepts of drug mechanisms. We also propose areas of further research for potential therapeutic advancement.

Prevention by aspirin and its combination with alpha-difluoromethylornithine of azoxymethane-induced tumors, aberrant crypt foci and prostaglandin E2 levels in rat colon

The dose-response relationship in male F344 rats was determined for the ability of aspirin administered in the diet to prevent azoxymethane (AOM)-induced colon cancer and aberrant crypt foci (ACF) and to reduce prostaglandin E2 (PGE2) levels. Starting at either 7 or 22 weeks of age, the rats received aspirin. All rats received two doses of AOM (15 mg/kg each on days 7 and 14) and were killed on day 36. The lowest concentrations of aspirin to prevent ACF or reduce PGE2 levels were 600 and 400 mg/kg, respectively. To evaluate the prevention of tumors, rats received either 0 or 400 mg/kg aspirin for a total of 39 weeks with AOM (30 mg/kg) administered 7 days after the start of treatment. Aspirin had no effect on the yield of colon tumors. In a second experiment, rats started to receive 0, 200, 600 or 1800 mg/kg aspirin or 1000 mg/kg alpha-difluoromethylornithine (DFMO) +/- aspirin. Eight and 15 days later, all the rats received 15 mg/kg AOM. Eleven weeks later, animals that were receiving the control diet started to receive 0, 200, 600 or 1800 mg/kg aspirin; 1000 or 3000 mg/kg DFMO; or 1000 mg/kg DFMO + 200 or 600 mg/kg aspirin. The animals were killed 32 weeks later. DFMO effectively reduced the yield of colon tumors when administered starting either before or after AOM while aspirin was much weaker. The combination of aspirin + DFMO administered after AOM was synergistic. Both aspirin and DFMO decreased the Mitotic Index, while apoptosis was increased only by DFMO. Our results demonstrated that aspirin and DFMO could prevent colon cancer when administered after AOM. Furthermore, aspirin reduced ACF, PGE2 levels and mitosis at concentrations that did not prevent cancer. In contrast, the ability to enhance apoptosis did correlate with the prevention of cancer.

Early expression of cyclo-oxygenase-2 during sporadic colorectal carcinogenesis

Regular administration of non-steroidal anti-inflammatory drugs (NSAIDs) may reduce the incidence of colorectal cancer by targeting cyclo-oxygenase-2 (Cox-2), a key enzyme in arachidonic acid metabolism. To evaluate the role of Cox-2 in sporadic colorectal cancer development, Cox-2 expression was investigated by immunohistochemistry in 85 adenomas, 53 carcinomas, 34 hyperplastic lesions and 104 samples of histologically normal mucosa adjacent to adenoma or carcinoma. In addition, Cox-2 mRNA expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR) in six adenomas and 14 carcinomas with paired grossly normal mucosa. Immunohistochemistry for the proliferation-associated antigen Ki-67 and in situ end labelling for demonstrating apoptotic bodies were also used to analyse the associations between Cox-2 expression and proliferation and apoptosis. Cox-2 protein expression was increased in 76/85 (89.4 per cent) adenomas and 44/53 (83.0 per cent) carcinomas compared with normal mucosa. Cox-2 protein expression was unrelated either to the degree of dysplasia or to the size of the adenomas (p > 0.50, p > 0.10, respectively) or to differentiation, Dukes stage or lymph node metastasis of carcinomas (all p > 0.50). Interestingly, 20/34 (58.8 per cent) hyperplastic lesions adjacent to adenomas or carcinomas displayed expression higher than in normal mucosa (18.3 per cent) (p < 0.0001) but lower than in adenomas or carcinomas (p < 10(-5), p < 0.001, respectively). There were no correlations between Cox-2 protein expression and proliferative or apoptotic index in either adenomas or carcinomas (all p > 0.25). Cox-2 mRNA expression was significantly increased in adenomas and carcinomas compared with normal mucosa (p < 0.005, p < 0.001, respectively). There were no differences between adenomas and carcinomas in either protein or mRNA levels (p > 0.25, p > 0.90, respectively). These data indicate that enhanced expression of Cox-2 occurs early during colorectal carcinogenesis and may contribute to tumour formation.

Cyclooxygenase-2 inhibitors in tumorigenesis (Part II)

The rate-limiting step in arachidonate metabolism is mediated by enzymes known as cyclooxygenases (COXs). These enzymes catalyze the biosynthesis of prostaglandin H2, the precursor of molecules such as prostaglandins, prostacyclin, and thromboxanes. The COX enzyme family consists of the classical COX-1 enzyme, which is constitutively expressed in many tissues, and a second isozyme, i.e., COX-2, which is induced by various stimuli, such as mitogens and cytokines, and is involved in many inflammatory reactions. Because nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit both COX-1 and COX-2, these drugs also cause unwanted side effects, exemplified by gastrointestinal bleeding. Accumulating evidence indicates that NSAIDs can reduce the incidence of colorectal cancers in human and experimental animals and can reduce the number and size of polyps in patients with familial adenomatous polyposis. This Part II (of a two-part review) focuses on the growing clinical and experimental evidence that NSAIDS and COX-2 inhibitors can influence the risk of colon (and possibly of other) cancers.

Suppression of human colorectal mucosal prostaglandins: determining the lowest effective aspirin dose

BACKGROUND

A variety of studies have supported the finding that regular intake of aspirin (acetylsalicylic acid) or nonsteroidal anti-inflammatory agents can affect colorectal cancer carcinogenesis. These agents inhibit the synthesis of prostaglandins. High levels of prostaglandins are observed in colon cancer tissues.

PURPOSE

Experiments were planned to determine the lowest dose of aspirin that can markedly suppress the levels of mucosal prostaglandins E2 and F(2alpha) in colorectal mucosa and to determine whether a relationship exists between these levels and plasma levels of both acetylsalicylic acid and its metabolite, salicylic acid.

METHODS

Healthy men and women aged 18 years or older participated in the study. The participants took a single, daily dose of aspirin (40.5, 81, 162, 324, or 648 mg) or a placebo for 14 days. Colorectal biopsy specimens were taken at baseline, 24 hours after the first dose of aspirin, and 24-30 hours and 72-78 hours after the last, i.e., fourteenth, daily dose of aspirin. The biopsy specimens were assayed for prostaglandins E2 and F(2alpha) by use of a competitive enzyme immunoassay. Plasma concentrations of acetylsalicylic acid and salicylic acid were determined by use of high-performance liquid chromatography. All P values are two-sided.

RESULTS

A total of 65 subjects (10 receiving placebo, groups of 10 each receiving 40.5, 81, 162, or 324 mg of aspirin, and a group of 15 receiving 648 mg of aspirin) completed the protocol. One subject reported unacceptable drug-induced toxic effects and did not complete the protocol; other subjects reported acceptable side effects. The lowest dose to significantly suppress colorectal mucosal prostaglandin E2 concentrations from baseline at 24 hours after the first dose (by 22.6%; P = .002) and at 24-30 hours after the last dose (by 14.2%; P = .021) was 162 mg. At 72-78 hours after the last dose, there was significant suppression for subjects receiving 81 mg (by 23.7%; P = .008). The lowest dose to significantly suppress colorectal mucosal prostaglandin F(2alpha) concentrations from baseline at 24 hours after the first dose (by 18.3%; P = .032) was 324 mg. The lowest dose causing a marked reduction in the level of prostaglandin F(2alpha) at 24-30 hours (by 15.1%; P = .003) and 72-78 hours (by 23.0%; P = .0002) after the last dose was 40.5 mg. No detectable amounts of acetylsalicylic acid or salicylic acid were present in the plasma at any of the biopsy time points.

CONCLUSIONS

The lowest doses of aspirin taken daily for 14 days to significantly suppress concentrations of colorectal mucosal prostaglandins E2 and F(2alpha) were 81 and 40.5 mg, respectively. The suppression occurred without detectable amounts of aspirin or salicylic acid in the plasma at the time points studied. On the basis of these observations, we recommend a single, daily dose of 81 mg of aspirin in future studies of this drug as a chemopreventive agent for colorectal cancer.

The role of cyclic AMP and oxygen intermediates in the inhibition of cellular immunity in cancer

Cell-mediated immunity is often impaired in cancer. This may be partly due to increased amounts of prostaglandin E2 (PGE2) and histamine in the blood of cancer patients, since PGE2 and histamine possess inhibitory effects on cellular immunity. These effects are mediated by cyclic AMP (cAMP), which is increased in leukocytes by PGE2 through EP2 and by histamine through H2 receptors and also by epinephrine through beta 2-adrenergic receptors. Increased cAMP activates protein kinase A, which inhibits the formation of interleukin 2 (IL-2) in T cells. The formation of interferon gamma is concomitantly decreased, and cellular immunity is attenuated. In monocyte/macrophages the formation of IL-1 beta, IL-12 and tumor necrosis factor alpha is decreased by cAMP or through the increased formation of IL-10, which is up-regulated by cAMP. This attenuates cellular immunity. In monocytes histamine may decrease the formation of oxygen intermediates, which can induce apoptosis of natural killer cells and thus inhibit immunity. The superoxide anion is a potent inducer of the cyclooxygenase-2 enzyme, which is upregulated in colorectal cancer. Cyclooxygenase-2 catalyzes the formation of PGE2, e.g. in cancer cells. Thus the inhibition of cellular immunity in cancer may be at least partly mediated by cAMP and oxygen intermediates. This may offer new options for cancer immunotherapy.

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.

The effect of leukotrienes B and selected HETEs on the proliferation of colon cancer cells

Eicosanoids have been implicated in colon carcinogenesis, but very little is known on the potential role of leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) in this process; such compounds are produced by colonocytes and tumor infiltrating leukocytes. We studied the effect of LTB4, LTB4 methyl ester, LTB5, 12(R)-HETE, 12(S)-HETE and 15(S)-HETE (10(-10), 10(-8), 10(-6) M) on the proliferation rate, the cell cycle distribution, and the rate of apoptosis in HT-29 and HCT-15 human colon carcinoma cells. Our data show that LTB4, a lipoxygenase product, increased the proliferation rate of both cell lines in a time- and concentration-dependent manner. In HT-29 cells the concentration-response curve was bell-shaped (maximal effect at 10(-8) M). The proliferative effects of LTB4 in HT-29 cells were inhibited by SC-41930, a competitive antagonist of LTB4, suggesting the existence of an LTB4 receptor in epithelial cells. The methyl ester of LTB4 stimulated the proliferation of these cells, but LTB5, an isomer of LTB4 derived from eicosapentaenoic acid, did not. Of the HETEs, only 12(R)-HETE, a P-450 product, stimulated the proliferation of both cell lines; the other HETEs, all lipoxygenase products, failed to affect the proliferation of these cells. None of these eicosanoids had any effect on cell cycle distribution or apoptosis in either cell line. Taken together with our previous data showing that PGs stimulate colon cancer cell proliferation (Qiao et al. (1995) Biochim. Biophys. Acta 1258, 215-223), these findings indicate that arachidonic acid products synthesized via at least three different pathways (cyclooxygenase, lipoxygenase, P-450) may not be able to modulate the growth of colon cancer, and suggest a potential role in human colon carcinogenesis for LTB4 and 12(R)-HETE.

Complete reversion and prevention of rectal adenomas in colectomized patients with familial adenomatous polyposis by rectal low-dose sulindac maintenance treatment. Advantages of a low-dose nonsteroidal anti-inflammatory drug regimen in reversing adenomas exceeding 33 months

PURPOSE

This nonrandomized, controlled Phase II pilot study aims at the lowest effective dose of rectally applied sulindac to achieve and maintain adenoma reversion in colectomized patients with familial adenomatous polyposis (FAP).

METHODS

The study group (n = 15) underwent proctoscopic and laboratory follow-up for polyp reversion every 6 to 12 weeks. Polyp reversion was followed by dose reduction in predefined steps. Proliferating cell nuclear antigen/cyclin (PCNA) and KI-67 proliferation indices (PI) were performed by point counting. Prostaglandin (PG)E2 and PGF2 alpha were quantified by time-resolved competitive fluorescence immunoassay.

RESULTS

All patients responded to therapy within 6 to 24 weeks. Sixty and 87 percent of patients achieved complete adenoma reversion after 48 weeks at 53 and 67 mg of sulindac per day per patient on average, respectively. Reversion was evident compared with the control group. Dose reduction by one-sixth to one-eighth of the usual oral dose was significant (Mann's trend test, P < 0.05). PCNA and KI-67 PIs of adenomatous and flat mucosa were significantly reduced (Wilcoxon's test, P < 0.05). Correlation of PCNA and KI-67 PIs indicate similar reaction of different tissue structures (Spearman's rank correlation test, P < 0.01). Nonsteroidal anti-inflammatory drug-induced redifferentiation from high-grade to low-grade dysplasia occurred in all but two patients. Tissue-PGE2 levels were greatly reduced. Unwanted, curable side effects were rare (gastritis, n = 2), and laboratory controls are within detection limits.

CONCLUSIONS

Low-dose rectal sulindac maintenance therapy is highly effective in achieving complete adenoma reversion without relapse in 87 percent of patients after 33 months. Rectal FAP phenotype should be crucial for the surgical decision. Colectomy with ileorectal anastomosis and regular chemoprevention might proceed to be a promising alternative to pouch procedures. Chemoprevention with lower incidence of FAP-related tumors via dysplasia reversion may be possible in the future.

Activities of phospholipase A2 and diacylglycerol lipase are increased in human colorectal cancer

Experimental, clinical and epidemiological studies have implicated arachidonic acid and its metabolites as important mediators in colorectal carcinogenesis. Although arachidonic acid levels are increased in tumour membrane lipids, its availability for metabolic processes is not known. The activities of phospholipase A2 (PLA2) and diacylglycerol lipase therefore were assessed in tumour and normal mucosal specimens from 20 patients with colorectal cancer using 14C-radiolabelled substrates. The median (interquartile range) PLA2 activity was increased in tumour tissue (10.5 (6.0, 18.5) pmol arachidonic acid mg-1 h-1) compared with that in normal mucosa (5.6 (2.5, 8.5) pmol arachidonic acid mg-1 h-1) (P < 0.001, Wilcoxon signed rank test). Activity of diacylglycerol lipase was also greater in tumoral tissue (47.4 (21.6, 82.1) pmol arachidonic acid mg-1 h-1) than in mucosa (19.1 (9.4, 42.9) pmol arachidonic acid mg-1 h-1) (P < 0.005). There was no correlation between either PLA2 or diacylglycerol lipase activity and myeloperoxidase activity, suggesting that these increases were not directly attributable to tumour inflammatory cell infiltrate. Augmentation of arachidonic acid release in colorectal tumours may have implications for therapy.

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)

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.

Patients with adenomatous polyps and carcinomas have increased colonic mucosal prostaglandin E2

Colorectal carcinoma in humans and animal models is associated with increased synthesis of prostaglandin E2 (PGE2). PGE2 synthesis was measured in normal and neoplastic human colorectal mucosa to investigate its role in the adenoma-carcinoma sequence. Paired mucosal biopsy specimens for PGE2 synthesis and histological examination were obtained during 39 diagnostic colonoscopies. Twelve control patients in whom colonoscopies and histology were normal synthesised similar amounts of PGE2 at all sites. Their results were (mean (SD) pg PGE2/mg tissue) caecum 102.8 (15.9) (n = 6), ascending colon 110.8 (24.3) (n = 10), transverse colon 103.9 (19.5) (n = 11), descending colon 102.9 (23.2) (n = 12), sigmoid colon 96.4 (18.0) (n = 12), and rectum 107.1 (17.6) (n = 12). Nineteen patients had a total of 27 adenomatous polyps (rectum (1), sigmoid (22), descending (1), transverse (1), and ascending colon (1): histology-tubular (16), tubulo-villous (8), and villous adenomous (3)). The polyps (178.0 (55.0), n = 27) synthesised more PGE2 than controls (p < 0.001), but the values in polyp-associated mucosa (mean (SD) 115.4 (21.9), n = 15) were not different to control results. Eight patients had carcinomas (rectal (2), sigmoid (4), and caecal (2)) all of which were adenocarcinomas. The cancers (193.6 (40.2), n = 8) synthesised more PGE2 than control specimens (p < 0.001), but were not different to polyps. Cancer-associated mucosa (140.3 (27.7) n = 8) synthesised more PGE2 than control and polyp-associated mucosa. Colorectal neoplasia is associated with a progressive increase in PGE2 synthesis which may have a role in tumourigenesis and be a pathophysiological explanation for the beneficial effects of NSAIDs in animal models and human disease.

Optimal follow-up in colorectal cancer patients: what tests and how often?

Patients' benefit from follow-up examinations after curative surgery for colorectal cancer is unproven in spite of numerous different programs' having been designed for that purpose. Unfortunately, no final results from prospective randomized studies have been published yet and no ideal marker for recurrent cancer is available to identify patients in whom new curative treatment may be possible. So far, screening for metachronous neoplasia with intervals of several years may influence survival, whereas benefit from detecting recurrent colorectal cancer may be claimed only by using historical or other inappropriate controls. The tradition of follow-up is expensive and prospective evidence for any cost benefit is needed to justify continuous use of our limited resources in this area of patient care.

The effect of misoprostol on colon cancer

A synthetic prostaglandin E1 (PGE1) analogue, misoprostol, was investigated for its effects on the growth of colon cancer in two in vivo models. Human colon cancer cell lines C170, LIM2412 and LIM2405 were grown as subcutaneous xenografts on T-lymphocyte deficient ARC(s) nu/nu mice. Tumour volumes were found to be significantly inhibited compared with control in misoprostol-treated animals with two cell lines. C170 was inhibited by 70.5% (P = 0.0001) and LIM2412 by 68.2% (P = 0.01). LIM2405 was inhibited by 33% (P = 0.14) which was not significantly different from the control. In a second experiment, colon cancers were induced in Sprague-Dawley rats using 1,2 dimethyl-hydrazine (DMH). After 10 weeks of treatment, rats were randomized to receive a 5 week course of 20 micrograms/kg per day of oral misoprostol. Misoprostol-treated rats were found to have a similar tumour incidence and staging compared with control animals. Oral administration of misoprostol has an inhibitory effect on early tumour growth of some colonic cancers, but not on established tumours.

Prostaglandin E2 levels and lymphocyte subsets in portal venous drainage of colorectal cancers

Local immunosurveillance may play an important role in the growth and spread of tumors. To investigate the local immune response, we determined prostaglandin E2 (PGE2) levels (n = 23) and lymphocyte subsets (n = 10) in the portal vein draining the tumors of patients with colorectal cancer. PGE2 levels in the portal vein were significantly higher than those in the radial artery. Portal PGE2 levels in patients with advanced stage tumors (Duke's C and D) and lymph node metastases were significantly higher than those of patients with Duke's A and B tumors without lymph node metastases. Moreover, four of the nine patients with portal PGE2 levels greater than 100 pg/mL had liver metastases within 2 years of surgery. There were no differences in lymphocyte subsets between the portal vein and the radial artery. PGE2 levels in the portal vein draining colorectal tumor may thus be closely related to tumor progression and recurrence and may serve as a predictor of tumor recurrence in patients with colorectal cancer.

Effect of omega-3 fatty acids on rectal mucosal cell proliferation in subjects at risk for colon cancer

The effects of 12 weeks of omega-3 fatty acid supplementation on rectal mucosal proliferation were assessed with [3H]thymidine autoradiography in a double-blind, placebo-controlled study of 20 patients with sporadic adenomatous colorectal polyps. In the group of 10 that received fish oil containing eicosapentaenoic acid (4.1 g/day) and docosahexaenoic acid (3.6 g/day), the mean percentage of replicative "S"-phase cells in the upper part of colonic crypts (considered a reliable marker of colon cancer risk) significantly dropped from the baseline level after only 2 weeks of treatment and remained lower throughout the study period; no change in upper-crypt labeling was observed in the 10 placebo patients. Rectal mucosal eicosapentaenoic acid content increased in fish oil patients, whereas arachidonic acid levels decreased. The fish oil-induced kinetic changes represent contraction of the proliferative compartment to the levels of a low-risk population and may be related to omega-3 fatty acid effects on the arachidonic prostaglandin pathway. In this short-term trial, fish oil appeared to exert a rapid effect that may protect high-risk subjects from colon cancer.