Adenocarcinoma in the rectal segment in familial polyposis coli is not prevented by sulindac therapy

Chemoprevention in hereditary digestive neoplasia: A comprehensive review

Hereditary syndromes, such as familial adenomatous polyposis (FAP), MUTYH polyposis or Lynch syndrome, are particularly predisposing to the development of colorectal cancer. These situations have necessitated the development of adapted prevention strategies based largely on reinforced endoscopic surveillance and the search for complementary prevention strategies. This is the case for chemoprevention, which is the long-term administration of chemical agents limiting carcinogenesis, used as primary or secondary prophylaxis. The aim of this review is to present the available literature and the latest advances in chemoprevention in patients with FAP or MUTYH and other polyposis as well as in patients with Lynch syndrome. The main conclusions of the few available guidelines in these situations are also discussed.

Long-term chemoprevention in patients with adenomatous polyposis coli: an observational study

Prospective short-term studies on effectiveness of non-steroidal anti-inflammatory drugs (NSAIDs) point towards a decrease in the number and size of polyps. Effectiveness and safety in the prevention of progression in familial polyposis with NSAIDs in long-term use, which is the prerequisite for therapeutic evaluation in prospective studies, is unknown. The total absolute observation period of 54 patients under sulindac was 399 patient years with a mean of 7.4 (2-19) years per patient. 36 patients (66.7%) showed a fast decrease of polyp burden, 8 (14.8%) were slow responders, and 9 (16.7%) had stable disease; one patient had a slow progression. Upper gastrointestinal (GI) polyp burden remained stable in 47% patients, increased in 31%, and improved in 22%. Advanced adenomas were found in 8 patients only within the first 5 years of chemoprevention, no patient developed desmoid disease, anamnestically evaluated on every follow-up. There were no life-threatening side-effects. Dosage and delivery pattern were essential for effectiveness. This study provides evidence that chemoprevention with sulindac is effective and safe and can, either alone or in combination with other drugs, become a long-term management option in cases of adenomatous polyposis. These results justify further long-term prospective chemoprevention studies to elaborate treatment protocols and guidelines.

Combination of Sulindac and Eflornithine Delays the Need for Lower Gastrointestinal Surgery in Patients With Familial Adenomatous Polyposis: Post Hoc Analysis of a Randomized Clinical Trial

BACKGROUND

Colectomy and proctocolectomy are the initial standard of care for patients with familial adenomatous polyposis. Pharmacotherapy to prevent the progression of polyposis and surgeries in the lower GI tract would be beneficial to patients with this disease.

OBJECTIVE

This analysis aimed to evaluate the impact of eflornithine-sulindac combination versus monotherapy in delaying time to disease progression in the lower GI tract of patients with familial adenomatous polyposis.

DESIGN

This is a post hoc analysis of a randomized phase 3 trial.

SETTING

This study was conducted in 21 hospitals in 7 countries treating patients with familial adenomatous polyposis.

PATIENTS

Adults with familial adenomatous polyposis were randomly assigned 1:1:1 into 3 arms.

INTERVENTIONS

Patients received either eflornithine (750 mg), sulindac (150 mg), or both once daily for up to 48 months.

MAIN OUTCOME MEASURES

Efficacy was evaluated as the time from randomization to predefined primary disease progression end points.

RESULTS

A total of 158 patients were included in the study. Disease progression was observed in 2 of 54 (3.7%), 9 of 53 (17.0%), and 10 of 51 (19.6%) patients with at least partial lower GI tract in the combination, sulindac, and eflornithine arms, corresponding to risk reductions of 80% (p = 0.02) and 83% (p = 0.01) between combination and sulindac or eflornithine. When endoscopic excision of adenomas ≥10 mm in size was censored, the need for major surgery was observed in 0 of 54, 7 of 53 (13.2%), and 8 of 51 (15.7%) patients in the combination, sulindac, and eflornithine arms, corresponding to risk reductions approaching 100% between combination and sulindac (p = 0.005) or combination and eflornithine (p = 0.003).

LIMITATIONS

This was a post hoc analysis, the sample size was small, and there were fewer than expected events.

CONCLUSIONS

Eflornithine-sulindac combination therapy was superior to either drug alone in delaying or preventing the need for lower GI tract surgery in patients with familial adenomatous polyposis. See Video Abstract at http://links.lww.com/DCR/B658.

REGISTRATION

ClinicalTrials.gov, NCT01483144; EU Clinical Trials Register, EudraCT 2012-000427-41.

LA COMBINACIN DE SULINDAC Y EFLORNITINA RETRASA LA NECESIDAD DE CIRUGA DEL TUBO DIGESTIVO BAJO EN PACIENTES CON PAF ANLISIS POSTHOC DE UN ENSAYO CLNICO ALEATORIZADO

ANTECEDENTES:La colectomía y la proctocolectomía son el estándar inicial de atención para los pacientes con poliposis adenomatosa familiar. La farmacoterapia para prevenir la progresión de la poliposis y las cirugías en el tracto gastrointestinal inferior sería beneficiosa para los pacientes con esta enfermedad.OBJETIVO:Este análisis tuvo como objetivo evaluar el impacto de la combinación de eflornitina-sulindac versus la monoterapia en el retraso del tiempo hasta la progresión de la enfermedad en el tracto gastrointestinal inferior de pacientes con poliposis adenomatosa familiar.DISEÑO:Este es un análisis posthoc de un ensayo de fase 3 aleatorizado.ENTORNO CLINICO:Veintiún hospitales en 7 países que tratan a pacientes con poliposis adenomatosa familiar.PACIENTES:Adultos con poliposis adenomatosa familiar fueron aleatorizados 1: 1: 1 en 3 brazos.INTERVENCIONES:Los pacientes recibieron eflornitina (750 mg), sulindac (150 mg) o ambos una vez al día durante un máximo de 48 meses.PRINCIPALES MEDIDAS DE VALORACION:La eficacia se evaluó como el tiempo desde la aleatorización hasta los criterios de valoración primarios predefinidos de progresión de la enfermedad.RESULTADOS:Los resultados se informan para la población de estudio excluyendo a los pacientes que se habían sometido a ileostomías permanentes (n = 158). Se observó progresión de la enfermedad en 2/54 (3,7%), 9/53 (17,0%) y 10/51 (19,6%) pacientes con al menos tracto gastrointestinal inferior parcial en los brazos de combinación, sulindac y eflornitina, respectivamente, correspondientes al riesgo de reducciones del 80% (p = 0,02) y del 83% (p = 0,01) entre la combinación y el sulindaco o la eflornitina, respectivamente. Cuando se censuró la escisión endoscópica de adenomas ≥10 mm de tamaño, se observó la necesidad de cirugía mayor en 0/54, 7/53 (13,2%) y 8/51 (15,7%) pacientes en la combinación, sulindac y eflornitina, respectivamente, correspondientes a reducciones de riesgo cercanas al 100% entre combinación y sulindac (p = 0,005) o combinación y eflornitina (p = 0,003).LIMITACIONES:Este fue un análisis posthoc, el tamaño de la muestra fue pequeño y hubo menos eventos de los esperados.CONCLUSIONES:La terapia de combinación de eflornitina-sulindac fue superior a cualquier fármaco solo para retrasar o prevenir la necesidad de cirugía del tracto gastrointestinal inferior en pacientes con poliposis adenomatosa familiar. Consulte Video Resumen en http://links.lww.com/DCR/B658.

Natural history of colonic polyposis in young patients with familial adenomatous polyposis

BACKGROUND AND AIMS

Proctocolectomy prevents colorectal cancer in familial adenomatous polyposis (FAP). Colorectal polyp progression is one of the indications for surgery. No data exist regarding the natural history of colorectal polyposis in young patients with FAP. This study examined the rate of polyposis progression and factors associated with it.

METHODS

Patients with FAP <30 years old who had undergone ≥2 colonoscopies since 2000 were identified. Rate of polyposis progression was calculated by review of polyp counts obtained from baseline and last colonoscopy, accounting for any polyps removed during the observation period. Endoscopic and non-endoscopic factors affecting the rate of polyposis progression were evaluated. Multivariate analysis was performed to identify factors associated with rate of polyposis progression.

RESULTS

One hundred sixty-eight patients (52% female; median age, 13.5 years) were included. Median rate of polyposis progression was 25.4 polyps/year (interquartile range, 9.5-69.8). Highest median rate of polyposis progression (89 polyps/year) was associated with mutation in codon 1309. The rate of polyposis progression was independently associated with the location of mutation in the adenomatous polyposis coli gene, the number of polyps at the initial colonoscopy, and exposure to chemoprevention. Of the 39.9% of patients who underwent surgery, an increase in polyp number was the most common indication (53.7%).

CONCLUSIONS

The rate of polyposis progression in young patients with FAP varies with a median of about 25 new polyps per year. Progression is associated with distinct factors, which can be used in discussion with patients regarding the need for and timing of prophylactic colorectal surgery.

Alternative treatments for prophylaxis of colorectal cancer in familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is a rare, hereditary disease characterized by the presence of 100 or more adenomas distributed throughout the colon and rectum. If untreated, colorectal cancer develops in almost 100% of FAP patients. As prophylactic treatment, proctocolectomy with ileal pouch-anal anastomosis remains the surgical treatment of choice. High rates of postoperative complications, however, have been reported with this procedure, including bowel dysfunction, incontinence, and reduced female fecundity. Some novel strategies for preventing hereditary colon cancers have been reported. This review summarizes alternative treatments, including the laparoscopic approach, chemoprevention, endoscopic management, and subtotal colectomy combined with endoscopic treatment, for prophylaxis of colorectal cancer in FAP patients.

Use of NSAIDs for the Chemoprevention of Colorectal Cancer

OBJECTIVE:

To discuss the role of nonsteroidal antiinflammatory drugs (NSAIDs) in the chemoprevention of colorectal cancer.

DATA SOURCES:

A MEDLINE search (1966–May 2003) was performed to identify key literature. Search items included, but were not limited to, NSAIDs, colorectal cancer, chemoprevention, cyclooxygenase-2 (COX-2)–specific inhibitors, and familial adenomatous polyposis (FAP).

STUDY SELECTION AND DATA EXTRACTION:

The search included experimental (in vitro and animal models) and clinical studies evaluating the use of NSAIDs for the chemoprevention of colorectal cancer. The MEDLINE search was supplemented by references from selected articles.

DATA SYNTHESIS:

Numerous experimental, epidemiologic, and clinical studies suggest that NSAIDs have promise as anticancer agents. The mechanism by which NSAIDs lead to decreased colon carcinogenesis is not fully understood, but may involve restoration of apoptosis and inhibition of prostaglandin-mediated angiogenesis. Compelling evidence from many observational studies has consistently documented a 40–50% reduction in the risk of adenomatous polyps, colorectal cancer incidence, and mortality in patients using NSAIDs. Recent randomized, controlled trials have demonstrated a benefit with aspirin in reducing the rate of development of new or recurrent adenomas in high-risk patients. In addition, randomized studies using sulindac and celecoxib in patients with FAP have documented significant regression of existing adenomatous polyps.

CONCLUSIONS:

Inhibition of COX-2 is an example of a targeted approach to the chemoprevention of colorectal cancer. However, controversy exists about the safety, efficacy, and optimal treatment regimen of NSAIDs as long-term chemopreventive agents in the general population. Ongoing studies in high-risk patients with both selective and nonselective COX inhibitors will provide important information in the area of colorectal chemoprevention, but clinical trials' use of adenomas as surrogate markers for chemoprevention trials makes their application to the general population limited.

Chemoprevention of hereditary colon cancers: time for new strategies

Colorectal cancer (CRC) is potentially preventable. Chemoprevention, a focus of research for the past three decades, aims to prevent or delay the onset of cancer through the regression or prevention of colonic adenomas. Ideal pharmacological agents for chemoprevention should be cheap and nontoxic. Although data indicate that aspirin can reduce the risk of CRC in the general population, the highest return from chemopreventive strategies would be expected in patients with the highest risk of developing the disease, particularly those with a defined hereditary predisposition. Despite compelling data showing that a large number of chemopreventive agents show promise in preclinical CRC models, clinical studies have yielded conflicting results. This Review provides a historical and methodological perspective of chemoprevention in familial adenomatous polyposis and Lynch syndrome, and summarizes the current status of CRC chemoprevention in humans. Our goal is to critically focus on important issues of trial design, with particular attention on the choice of appropriate trial end points, how such end points should be measured, and which patients are the ideal candidates to be included in a chemopreventive trial.

Effect of Sulindac and Erlotinib vs Placebo on Duodenal Neoplasia in Familial Adenomatous Polyposis: A Randomized Clinical Trial

IMPORTANCE

Patients with familial adenomatous polyposis (FAP) are at markedly increased risk for duodenal polyps and cancer. Surgical and endoscopic management of duodenal neoplasia is difficult and chemoprevention has not been successful.

OBJECTIVE

To evaluate the effect of a combination of sulindac and erlotinib on duodenal adenoma regression in patients with FAP.

DESIGN, SETTING, AND PARTICIPANTS

Double-blind, randomized, placebo-controlled trial, enrolling 92 participants with FAP, conducted from July 2010 through June 2014 at Huntsman Cancer Institute in Salt Lake City, Utah.

INTERVENTIONS

Participants with FAP were randomized to sulindac (150 mg) twice daily and erlotinib (75 mg) daily (n = 46) vs placebo (n = 46) for 6 months.

MAIN OUTCOMES AND MEASURES

The total number and diameter of polyps in the proximal duodenum were mapped at baseline and 6 months. The primary outcome was change in total polyp burden at 6 months. Polyp burden was calculated as the sum of the diameters of polyps. The secondary outcomes were change in total duodenal polyp count, change in duodenal polyp burden or count stratified by genotype and initial polyp burden, and percentage of change from baseline in duodenal polyp burden.

RESULTS

Ninety-two participants (mean age, 41 years [range, 24-55]; women, 56 [61%]) were randomized when the trial was stopped by the external data and safety monitoring board because the second preplanned interim analysis met the prespecified stopping rule for superiority. Grade 1 and 2 adverse events were more common in the sulindac-erlotinib group, with an acne-like rash observed in 87% of participants receiving treatment and 20% of participants receiving placebo (P < .001). Only 2 participants experienced grade 3 adverse events. [table: see text].

CONCLUSIONS AND RELEVANCE

Among participants with FAP, the use of sulindac and erlotinib compared with placebo resulted in a lower duodenal polyp burden after 6 months. Adverse events may limit the use of these medications at the doses used in this study. Further research is necessary to evaluate these preliminary findings in a larger study population with longer follow-up to determine whether the observed effects will result in improved clinical outcomes.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT 01187901.

Regression of Colonic Adenomas After Treatment With Sulindac in Familial Adenomatous Polyposis: A Case With a 2-Year Follow-up Without a Prophylactic Colectomy

Familial adenomatous polyposis (FAP) is an autosomal dominant disorder characterized by hundreds of colorectal adenomatous polyps that progress to colorectal cancer. Management of patients with FAP is with a total colectomy. Chemopreventive strategies have been studied in FAP patients in an effort to delay the development of adenomas in the upper and the lower gastrointestinal tract and to prevent recurrence of adenomas in the retained rectum of patients after prophylactic surgery. Sulindac, a nonsteroidal anti-inflammatory drug, causes regression of colorectal adenomas in the retained rectal segment of FAP patients. However, evidence regarding long-term use of this therapy and its effect on the intact colon has been insufficient. We report a case in which the long-term use of sulindac was effective in reducing the size and the number of colonic polyps in patients with FAP without a prophylactic colectomy and polypectomy; we also present a review of the literature.

Sulindac selectively inhibits colon tumor cell growth by activating the cGMP/PKG pathway to suppress Wnt/β-catenin signaling

Nonsteroidal anti-inflammatory drugs (NSAID) display promising antineoplastic activity for colorectal and other cancers, but toxicity from COX inhibition limits their long-term use for chemoprevention. Previous studies have concluded that the basis for their tumor cell growth inhibitory activity does not require COX inhibition, although the underlying mechanism is poorly understood. Here, we report that the NSAID sulindac sulfide inhibits cyclic guanosine 3',5'-monophosphate phosphodiesterase (cGMP PDE) activity to increase intracellular cGMP levels and activate cGMP-dependent protein kinase (PKG) at concentrations that inhibit proliferation and induce apoptosis of colon tumor cells. Sulindac sulfide did not activate the cGMP/PKG pathway, nor affect proliferation or apoptosis in normal colonocytes. Knockdown of the cGMP-specific PDE5 isozyme by siRNA and PDE5-specific inhibitors tadalafil and sildenafil also selectively inhibited the growth of colon tumor cells that expressed high levels of PDE5 compared with colonocytes. The mechanism by which sulindac sulfide and the cGMP/PKG pathway inhibits colon tumor cell growth involves the transcriptional suppression of β-catenin to inhibit Wnt/β-catenin T-cell factor transcriptional activity, leading to downregulation of cyclin D1 and survivin. These observations suggest that safer and more efficacious sulindac derivatives can be developed for colorectal cancer chemoprevention by targeting PDE5 and possibly other cGMP-degrading isozymes.

Utilizing endoscopic technology to reveal real-time proteomic alterations in response to chemoprevention

Cancer chemoprevention approaches use either pharmacological or dietary agents to impede, arrest or reverse the carcinogenic process. Although several agents have shown effectiveness against colon cancer, present intervention strategies provide only partial reduction. In this study, we utilized high-resolution endoscopy to obtain colon tumor biopsy specimens from Apc mutant mice before and after 2-wk sulindac intervention. To acquire information beyond genomics, proteome analysis using the ProteomeLab PF2D platform was implemented to generate 2-D protein expression maps from biopsies. Chromatograms produced common signature profiles between sulindac and nonsulindac treated samples, and contrasting profiles termed "fingerprints". We selected a double peak that appeared in tumor biopsies from sulindac-treated mice. Further analyses using MS sequencing identified this protein as histone H2B. The location of H2B in the 1(st) dimension strongly suggested PTM, consistent with identification of two oxidized methionines. While further studies on sulindac proteomic fingerprints are underway, this study demonstrates the feasibility and advantages of "real-time" proteomic analysis for obtaining information on biomarker discovery and drug activity that would not be revealed by a genetic assay. This approach should be broadly applicable for assessing lesion responsiveness in a wide range of translational and human clinical studies.

Chemoprevention in familial adenomatous polyposis

Familial adenomatous polyposis (FAP) predictably leads to adenomas and eventual adenocarcinomas in the lower gastrointestinal tract and less frequently, the upper gastrointestinal tract. Chemopreventive strategies have been studied in FAP patients to delay the development of adenomas in the upper and lower gastrointestinal tract, as well as to prevent recurrence of adenomas in the retained rectum of patients after prophylactic surgery with colectomy and ileorectal anastamosis (IRA). The nonsteroidal anti-inflammatory drug (NSAID) sulindac and selective cyclooxygenase-2 (COX-2) inhibitor celecoxib reduce polyposis of the retained rectum after colectomy with IRA. Reports of cardiovascular risks of some NSAIDs and selective COX-2 inhibitors have led to promising studies of lower doses in combination with ursodeoxycholic acid, statin, and difluoromethylornithine. Curcumin and eicosapentaenoic acid show efficacy in small clinical trials of FAP chemoprevention. This article will review the concept of chemoprevention and the current clinical literature in FAP chemoprevention.

Molecular alterations associated with sulindac-resistant colon tumors in ApcMin/+ mice

Although nonsteroidal anti-inflammatory drugs (NSAID), including sulindac, have been used extensively as chemopreventive agents for colorectal cancer, results are not consistent. NSAIDs, most reportedly sulindac, often do not cause a complete regression of adenomas and some patients develop resistance to NSAID treatment. In this study, we evaluated the effect of sulindac on colon tumorigenesis in the Apc(Min/+) mouse model. Sulindac (180 ppm) given in drinking water for 9 weeks to Apc(Min/+) mice significantly reduced the size of colon tumors, but actually caused an increase in colon tumor multiplicity relative to untreated controls (average of 5.5 versus 1.6 tumors per mouse, respectively; P < 0.0001). This indicated that the drug could inhibit colon tumor progression but not initiation. As expected, in the small intestine, sulindac significantly reduced tumor size and multiplicity relative to untreated controls (average of 2.3 versus 42.0 tumors per mouse, respectively; P < 0.0001). Generation of a panel of prostanoids was comparably suppressed in the small intestine and colon by sulindac treatment. Sulindac is also known to exert its growth inhibitory effects through regulation of many noncyclooxygenase targets, including p21, beta-catenin, E-cadherin, mitochondrial apoptotic proteins, and peroxisome proliferator-activated receptor-gamma. We found that sulindac treatment protected against E-cadherin loss in colon tumors, with associated inhibition of nuclear beta-catenin accumulation. Importantly, p21(WAF1/cip1) and peroxisome proliferator-activated receptor-gamma expression were absent in colon tumors from sulindac-treated mice, suggesting that loss of these proteins is necessary for drug resistance. Together, these observations may be translatable to designing novel clinical therapies using combinations of agents that target multiple molecular pathways to overcome sulindac resistance.

NSAIDs: Old Drugs Reveal New Anticancer Targets

There is compelling evidence that nonsteroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase-2 selective inhibitors have antineoplastic activity, but toxicity from cyclooxygenase (COX) inhibition and the suppression of physiologically important prostaglandins limits their use for cancer chemoprevention. Previous studies as reviewed here suggest that the mechanism for their anticancer properties does not require COX inhibition, but instead involves an off-target effect. In support of this possibility, recent molecular modeling studies have shown that the NSAID sulindac can be chemically modified to selectively design out its COX-1 and COX-2 inhibitory activity. Unexpectedly, certain derivatives that were synthesized based on in silico modeling displayed increased potency to inhibit tumor cell growth. Other experiments have shown that sulindac can inhibit phosphodiesterase to increase intracellular cyclic GMP levels and that this activity is closely associated with its ability to selectively induce apoptosis of tumor cells. Together, these studies suggest that COX-independent mechanisms can be targeted to develop safer and more efficacious drugs for cancer chemoprevention.

Basal cell carcinoma chemoprevention with nonsteroidal anti-inflammatory drugs in genetically predisposed PTCH1+/- humans and mice

In vitro and epidemiologic studies favor the efficacy of nonsteroidal anti-inflammatory drugs (NSAID) in preventing skin squamous photocarcinogenesis, but there has been relatively little study of their efficacy in preventing the more common skin basal cell carcinoma (BCC) carcinogenesis. We first compared the relative anti-BCC effects of genetic deletion and NSAID pharmacologic inhibition of cyclooxygenase (COX) enzymes in the skin of Ptch1(+/-) mice. We then assessed the effects of celecoxib on the development of BCCs in a 3-year, double-blinded, randomized clinical trial in 60 (PTCH1(+/-)) patients with the basal cell nevus syndrome. In Ptch1(+/-) mice, genetic deletion of COX1 or COX2 robustly decreased (75%; P < 0.05) microscopic BCC tumor burden, but pharmacologic inhibition with celecoxib reduced microscopic BCCs less efficaciously (35%; P < 0.05). In the human trial, we detected a trend for oral celecoxib reducing BCC burden in all subjects (P = 0.069). Considering only the 60% of patients with less severe disease (<15 BCCs at study entry), celecoxib significantly reduced BCC number and burden: subjects receiving placebo had a 50% increase in BCC burden per year, whereas subjects in the celecoxib group had a 20% increase (P(difference) = 0.024). Oral celecoxib treatment inhibited BCC carcinogenesis in PTCH1(+/-) mice and had a significant anti-BCC effect in humans with less severe disease.

Sulindac effects on inflammation and tumorigenesis in the intestine of mice with Apc and Mlh1 mutations

We have previously reported that sulindac, a non-steroidal anti-inflammatory drug, inhibited tumor formation in the small intestine but increased tumors in the colon of Apc(Min/+) mice, a model of human familial adenomatous polyposis. To further explore intestinal regional responses, we studied effects of sulindac on additional gene-targeted mouse models of human intestinal tumorigenesis; these were (i) Apc(1638N/+) mouse (chain termination mutation in exon 15 of the Apc gene); (ii) Mlh1(+/-) mouse (DNA mismatch repair deficiency, a mouse model of human hereditary non-polyposis colorectal cancer) and (iii) double-heterozygous Mlh1(+/-)Apc(1638N/+) mutant mouse. Mice were fed AIN-76A control diet with or without 0.02% sulindac for 6 months. Intestinal regional tumor incidence, multiplicity, volume and degree of inflammation were used as end points. The results showed the following: (i) sulindac inhibited tumor development in the small intestine of Apc(1638N/+) mice; (ii) in contrast, sulindac increased tumors in the small intestine of Mlh1 mutant mice, a neoplastic effect which persisted in heterozygous compound Mlh1(+/-)Apc(1638N/+) mutant mice; (iii) sulindac increased tumors in the cecum of all mice regardless of genetic background; (iv) sulindac decreased inflammation in the small intestine of Apc(1638N/+) mice, but it increased inflammation in the small intestine of Mlh1(+/-) mice and Mlh1(+/-)Apc(1638N/+) mice and (v) sulindac enhanced inflammation in the cecum of all mutant mice. Findings indicate that the effects of sulindac in the intestine of these mutant mouse models are probably related to genetic background and appear to be associated with its inflammatory-inducing response.

A novel sulindac derivative that does not inhibit cyclooxygenases but potently inhibits colon tumor cell growth and induces apoptosis with antitumor activity

Nonsteroidal anti-inflammatory drugs such as sulindac have shown promising antineoplastic activity, although toxicity from cyclooxygenase (COX) inhibition and the suppression of prostaglandin synthesis limits their use for chemoprevention. Previous studies have concluded that the mechanism responsible for their antineoplastic activity may be COX independent. To selectively design out the COX inhibitory activity of sulindac sulfide (SS), in silico modeling studies were done that revealed the crucial role of the carboxylate moiety for COX-1 and COX-2 binding. These studies prompted the synthesis of a series of SS derivatives with carboxylate modifications that were screened for tumor cell growth and COX inhibitory activity. A SS amide (SSA) with a N,N-dimethylethyl amine substitution was found to lack COX-1 and COX-2 inhibitory activity, yet potently inhibit the growth of human colon tumor cell lines, HT-29, SW480, and HCT116 with IC(50) values of 2 to 5 micromol/L compared with 73 to 85 micromol/L for SS. The mechanism of growth inhibition involved the suppression of DNA synthesis and apoptosis induction. Oral administration of SSA was well-tolerated in mice and generated plasma levels that exceeded its in vitro IC(50) for tumor growth inhibition. In the human HT-29 colon tumor xenograft mouse model, SSA significantly inhibited tumor growth at a dosage of 250 mg/kg. Combined treatment of SSA with the chemotherapeutic drug, Camptosar, caused a more sustained suppression of tumor growth compared with Camptosar treatment alone. These results indicate that SSA has potential safety and efficacy advantages for colon cancer chemoprevention as well as utility for treating malignant disease if combined with chemotherapy.

Sulindac, a nonsteroidal anti-inflammatory drug, selectively inhibits interferon-gamma-induced expression of the chemokine CXCL9 gene in mouse macrophages

Sulindac, a non-steroidal anti-inflammatory drug, has been shown to exert an anti-tumor effect on several types of cancer. To determine the effect of sulindac on intracellular signaling pathways in host immune cells such as macrophages, we investigated the effect of the drug on interferon gamma (IFNgamma)-induced expression of signal transducer and activator of transcription 1 (STAT1) and other genes in mouse macrophage-like cell line RAW264.7 cells. Sulindac, but not aspirin or sodium salicylate, inhibited IFNgamma-induced expression of the CXC ligand 9 (CXCL9) mRNA, a chemokine for activated T cells, whereas the interferon-induced expression of CXCL10 or IFN regulatory factor-1 was not affected by sulindac. Luciferase reporter assay demonstrated that sulindac inhibited IFNgamma-induced promoter activity of the CXCL9 gene. Surprisingly, sulindac had no inhibitory effect on IFNgamma-induced STAT1 activation; however, constitutive nuclear factor kappaB activity was suppressed by the drug. These results indicate that sulindac selectively inhibited IFNgamma-inducible gene expression without inhibiting STAT1 activation.

Clinical Implications of Our Advancing Knowledge of Colorectal Cancer Genetics: Inherited Syndromes, Prognosis, Prevention, Screening and Therapeutics

Recent genetic advances in our knowledge of colorectal cancer genetics are beginning to pay translational dividends in the management of this common clinical problem. We are now able to accurately screen and counsel individuals at risk of rare inherited cancer syndromes. We have recently introduced two of what are sure to be numerous biologic-based therapies, and have shown that colorectal neoplasia risk can be modestly reduced by various chemopreventative agents. Finally, our advancing knowledge has led to significant inroads into understanding what genetic alterations define prognosis and predict response to specific chemotherapeutic agents, and we are beginning to explore the utility of this knowledge in mass genetic-based clinical screening efforts. Enthusiasm must be tempered, however, by the extraordinary cost that often accompanies relatively modest gains. Finally, although genetic-based therapy often receives the greatest attention, molecular genetics, will likely have the greatest cost-effective impact in primary prevention and early diagnosis.

Effect of the non-steroidal anti-inflammatory drug sulindac on colorectal adenomas of uncolectomized familial adenomatous polyposis

BACKGROUND

The aim of the present study was to elucidate the effect of sulindac on uncolectomized familial adenomatous polyposis (FAP).

METHODS

Seven FAP patients (SU group) without proctocolectomy were given sulindac 300 mg/day orally for 12 months. Six FAP patients without sulindac (non-SU group) served as controls. Colorectal lesions were assessed by protrusion index (no. radiolucent areas/cm(2); PI) under barium enema examination and non-polypoid lesion were assessed under chromoscopy prior to and at the end of the observation period. In the SU group, germline adenomatous polyposis coli (APC) mutation was determined by protein truncation test.

RESULTS

In the SU group, PI decreased significantly in the distal colon (from 3.0 +/- 1.1 to 1.1 +/- 0.8/cm(2), P < 0.02) and in the proximal colon (from 3.4 +/- 2.4 to 0.9 +/- 1.3/cm(2), P < 0.02). The PI in the non-SU group slightly but significantly increased in the distal colon (from 1.0 +/- 0.8 to 1.2 +/- 0.9/cm(2); P < 0.05) and it remained unchanged in the proximal colon (from 0.6 +/- 0.3 to 0.7 +/- 0.3/cm(2); P > 0.05). Chromoscopy at the end of observation identified non-polypoid lesions in five patients in the SU group, whereas such lesions were not found in the non-SU group (71% vs 0%, P = 0.016). Decrease in PI was not different among distal APC mutation (exons 1-9), proximal APC mutation (exons 10-15) and negative mutation.

CONCLUSION

Sulindac reduces colorectal adenomas of protruding type in uncolectomized FAP. The effect of sulindac may be unrelated to genotype of FAP.

Prophylaktische Chirurgie der familiären adenomatösen Polyposis coli

Familial adenomatous polyposis coli (FAP) may not be considered a single disease entity with standardized guidelines for operative treatment. However, prophylactic colectomy after the manifestation of polyps but prior to the development of colorectal cancer is essential. The optimal timing of prophylactic surgery remains a clinical decision taken independently of mutation analysis. In case of the classic FAP phenotype, restorative proctocolectomy and ileal pouch-anal anastomosis is the procedure of choice. The development of reliable guidelines for attenuated FAP variants requires further evidence from clinical studies on surgical strategy and the advantages of prophylactic surgery over regular endoscopic screening with removal of polyps.

Sulindac sulfide–induced apoptosis is enhanced by a small-molecule Bcl-2 inhibitor and by TRAIL in human colon cancer cells overexpressing Bcl-2

Sulindac is a nonsteroidal anti-inflammatory drug (NSAID) that induces apoptosis in cultured colon cancer cells and in intestinal epithelia in association with its chemopreventive efficacy. Resistance to sulindac is well documented in patients with familial adenomatous polyposis; however, the molecular mechanisms underlying such resistance remain unknown. We determined the effect of ectopic Bcl-2 expression upon sulindac-induced apoptotic signaling in SW480 human colon cancer cells. Sulindac sulfide activated both the caspase-8-dependent and mitochondrial apoptotic pathways. Ectopic Bcl-2 attenuated cytochrome c release and apoptosis induction compared with SW480/neo cells. Coadministration of sulindac sulfide and the small-molecule Bcl-2 inhibitor HA14-1 increased apoptosis induction and enhanced caspase-8 and caspase-9 cleavage, Bax redistribution, and cytochrome c and second mitochondria-derived activator of caspase release. Given that sulindac sulfide activated caspase-8 and increased membrane death receptor (DR4 and DR5) protein levels, we evaluated its combination with the endogenous death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Coadministration of sulindac sulfide and TRAIL cooperatively enhanced apoptotic signaling as effectively as did HA14-1. Together, these data indicate that HA14-1 or TRAIL can enhance sulindac sulfide-induced apoptosis and represent novel strategies for circumventing Bcl-2-mediated apoptosis resistance in human colon cancer cells.

Primary and secondary prevention in colorectal cancer

Colorectal cancer is an important public health problem: there are nearly one million cases of colorectal cancer diagnosed worldwide each year and half a million deaths. The geographic distribution of colorectal cancer follows the division between westernized versus developing countries, The highest rates are in North America, Australia and Europe. Rates in Africa and Asia are low, but are increasing in countries adopting western-style dietary habits. Given that the majority of cancers occur in older people, and with the ageing of the population in mind, this observation adds impetus to investigating prevention strategies to avoid some of this increase. High vegetable and fruit consumption has been associated with decreased risk of colorectal cancer in numerous observational studies, while high fibre intake seems to have a similar effect. Promising data have been obtained for aspirin and other non-steroidal anti-inflammatory drugs, and dietary calcium. A physically active lifestyle and maintenance of normal body weight are behavioural tools for prevention of colorectal cancer. Faecal occult blood testing has been shown to be effective in the prevention of about 20% of deaths from colorectal cancer, but few population-based screening programs have been initiated. Sigmoidoscopy and colonoscopy are potentially effective screening modalities; however, no randomized trial data have yet been reported. Overall, primary and secondary prevention, chemoprevention and screening research and implementation of these prevention strategies are priorities for reduction of colorectal cancer incidence and mortality.

Non steroidal anti-inflammatory drugs (NSAID) and Aspirin for preventing colorectal adenomas and carcinomas

EDITORIAL NOTE

This review was split in 2012 and the review question was to be addressed according to three new protocols: (See: http://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD010267.pub2; http://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD010291.pub2; http://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD010325.pub2). These titles were withdrawn at the protocol stage in 2020 as the authors did not make any progress on the reviews. This original review will no longer be updated and may be superseded by new titles hosted by Cochrane Gut in the future.

BACKGROUND

There is evidence from experimental animals studies, prospective and retrospective observational studies that nonsteroidal anti-inflammatory drugs (NSAIDS) may reduce the development of sporadic colorectal adenomas (CRAs) and cancer (CRC) and may induce the regression of adenomas in familial adenomatous polyposis (FAP).

OBJECTIVES

To conduct a systematic review to determine the effect of NSAIDS for the prevention or regression of CRAs and CRC.

SEARCH STRATEGY

Randomized controlled trials (RCTs) up to September 2003 were identified.

SELECTION CRITERIA

NSAIDS and aspirin (ASA) were the interventions. The primary outcomes were the number of subjects with at least one CRA, the change in polyp burden, and CRC. The secondary outcome was adverse events.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and assessed trial quality. Dichotomous outcomes were reported as relative risks (RR) with 95% confidence intervals (CI). The data were combined with the random effects model if clinically and statistically reasonable.

MAIN RESULTS

Nine trials with 150 familial adenomatous polyposis (FAP) and 24,143 population subjects met the inclusion criteria. The interventions included sulindac, celecoxib, or aspirin (ASA). From the combined results of three trials, significantly fewer subjects in the low dose ASA group developed recurrent sporadic CRAs [RR 0.77 (95% CI 0.61, 0.96), (NNT 12.5 (95% CI 7.7, 25)] after one to three years. In another three trials, phenotypic FAP subjects that received sulindac or celecoxib had a greater proportional reduction (range: 11.9% to 44%) in the number of CRAs compared to those in the control group (range: 4.5% to 10%). There was no significant difference for the outcomes of CRC or adverse events in any of the trials.

REVIEWERS' CONCLUSIONS

There was evidence from three pooled RCTs that ASA significantly reduces the recurrence of sporadic adenomatous polyps after one to three years. There is evidence from short-term studies to support regression, but not elimination or prevention of CRAs in FAP.

Effect of sulindac treatment for attenuated familial adenomatous polyposis with a new germline APC mutation at codon 161: report of a case

INTRODUCTION

Patients with familial adenomatous polyposis develop colorectal cancers if left untreated. As indicated in patients with familial adenomatous polyposis, prophylactic colectomy has been recommended even in a milder colonic phenotype referred to as attenuated familial adenomatous polyposis. However, therapeutic strategies in attenuated familial adenomatous polyposis are still controversial.

METHODS

We report a patient with attenuated familial adenomatous polyposis who has been treated with sulindac for five years. During the period of observation, she has been carefully followed up by chromoscopic and radiographic surveillance. Immunohistochemical study for cyclooxygenase-2 and genetic analysis in the adenomatous polyposis coli gene was also performed.

RESULTS

Continuous administration of sulindac resulted in obvious regression of both colorectal adenomatous polyps and gastric fundic gland polyps, and no cancers developed during the observation period. Immunohistochemical study showed the decrease of cyclooxygenase-2-positive epithelial cells in colorectal polyps by the treatment. The genetic analysis revealed a C to A substitution at nucleotide 481 of her germline adenomatous polyposis coli gene, which resulted in a nonsense mutation at codon 161.

CONCLUSIONS

Our case suggests that treatment with sulindac accompanied by intensive colonoscopic surveillance may be a choice of management for attenuated familial adenomatous polyposis.

Primary chemoprevention of familial adenomatous polyposis with sulindac

BACKGROUND

Familial adenomatous polyposis is caused by a germ-line mutation in the adenomatous polyposis coli gene and is characterized by the development of hundreds of colorectal adenomas and, eventually, colorectal cancer. Nonsteroidal antiinflammatory drugs can cause regression of adenomas, but whether they can prevent adenomas is unknown.

METHODS

We conducted a randomized, double-blind, placebo-controlled study of 41 young subjects (age range, 8 to 25 years) who were genotypically affected with familial adenomatous polyposis but phenotypically unaffected. The subjects received either 75 or 150 mg of sulindac orally twice a day or identical-appearing placebo tablets for 48 months. The number and size of new adenomas and side effects of therapy were evaluated every four months for four years, and the levels of five major prostaglandins were serially measured in biopsy specimens of normal-appearing colorectal mucosa.

RESULTS

After four years of treatment, the average rate of compliance exceeded 76 percent in the sulindac group, and mucosal prostaglandin levels were lower in this group than in the placebo group. During the course of the study, adenomas developed in 9 of 21 subjects (43 percent) in the sulindac group and 11 of 20 subjects in the placebo group (55 percent) (P=0.54). There were no significant differences in the mean number (P=0.69) or size (P=0.17) of polyps between the groups. Sulindac did not slow the development of adenomas, according to an evaluation involving linear longitudinal methods.

CONCLUSIONS

Standard doses of sulindac did not prevent the development of adenomas in subjects with familial adenomatous polyposis.

Long-term treatment with sulindac in familial adenomatous polyposis: a prospective cohort study

BACKGROUND & AIMS

Management of patients with familial adenomatous polyposis (FAP) can consist of colectomy with ileorectal anastomosis (IRA). Sulindac, a nonsteroidal anti-inflammatory drug, causes regression of colorectal adenomas in the retained rectal segment of FAP patients, although long-term use of this therapy has not been studied. We evaluated the long-term effectiveness and toxicity of sulindac in attempting to maintain retained rectal segments free of adenomas.

METHODS

Twelve FAP patients (5 women), mean age 37.1 years, with IRA received sulindac (mean dosage, 158 mg/day) for a mean period of 63.4 +/- 31.3 months (range, 14-98 months). Number, size, and histologic grade of polyps, side effects, and medication compliance were assessed every 4 months.

RESULTS

Seven of 12 patients (58%) remained in the study (6 of these polyp-free) for a mean of 76.9 +/- 27.5 months. Five of 12 patients (42%) withdrew from the trial after a mean follow-up period of 44 +/- 28 months (range, 14-89 months). A significant regression of polyp number was observed in all patients at 12 months (P = 0.039) and at a mean of 63.4 +/- 31.3 months (P = 0.006). Prevention of recurrence of higher-grade adenomas (tubulovillous, villous adenomas) was also observed (P = 0.004). At 35 months of follow-up, 1 patient developed stage III cancer in the rectal stump. The most common side effect was rectal mucosal erosions in 6 patients.

CONCLUSIONS

Long-term use of sulindac seems to be effective in reducing polyp number and preventing recurrence of higher-grade adenomas in the retained rectal segment of most FAP patients. Erosions at the IRA site can preclude adequate dose maintenance.

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

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

Prevention and chemoprevention of colorectal neoplasms

Main purpose of the review is to analyse the impact of the current approaches for colorectal cancer prevention, including chemoprevention. Available evidence does not support the contention that a more appropriate diet can be of great help in the prevention of these neoplasms, either because the scientific evidence is poor and highly controversial, or because changes in diet are difficult to implement, at least in many Western countries. Similarly, a preventive approach based on the modification of lifestyle remains improbable, either in the short --or in the long period of time. Secondary prevention--i.e., the systematic removal of adenomatous polyps--can hardly be applied in the general population, with the exception of individuals at risk because members of families with Adenomatosis coli or Lynch syndrome, or affected by inflammatory bowel diseases. Finally, chemoprevention (i.e., the attempt to prevent tumour development through the administration of drugs or natural compounds that interfere with various phases of carcinogenesis) is still in its infancy Though attractive, this approach requires well-designed studies which should be carried out for years before being evaluated and interpreted; so far most of these investigations gave inconsistent or controversial results. In conclusion, both primary and secondary prevention of colorectal malignancies appear difficult to apply in the general population, and chemoprevention is still at the beginning of a (presumably] long story. The final impression is that notwithstanding the remarkable advancements made in the last two decades in colorectal cancer research, the practical application of these new concepts remains difficult.

Chemoprevention of colorectal cancer

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

Familial and inherited colorectal cancer: endoscopic screening and surveillance

Familial risk of colorectal cancer is very common. The high-risk inherited syndromes are well described and much is known about the genetics and the effectiveness of registration, endoscopic surveillance, and appropriate intervention in these patients. The inherited syndromes, however, are extremely rare. There is a large group of patients in our population who can benefit from risk stratification based on the number of their relatives with colon cancer or adenomas and the age at which those relatives developed neoplasm. The GI endoscopist has a vital role in recommending and providing colonoscopic screening for this large group of patients.

Decision analysis in the surgical treatment of patients with familial adenomatous polyposis: a Dutch-Scandinavian collaborative study including 659 patients

BACKGROUND AND AIMS

The choice of colorectal surgery in patients with familial adenomatous polyposis lies between the morbidity of proctocolectomy and ileum-pouch-anal anastomosis (IPAA) and the mortality from rectal cancer after total colectomy and ileorectal anastomosis (IRA). The aims of the present study were: (1) to assess the risk of dying from rectal cancer after IRA, (2) to compare the life expectancy between patients with an IRA and those with an IPAA, and (3) to investigate whether regular endoscopic examination of the rectum leads to detection of cancer at an earlier stage.

METHODS

Clinical and pathological data on 659 patients who underwent colectomy and ileorectal anastomosis were collected from four national polyposis registries-that is, in Denmark, Finland, Sweden, and the Netherlands. Data were analysed using survival analysis methods. Decision analysis was used to compare the life expectancy between patients with an IRA and those with an IPAA.

RESULTS

A total of 47 patients developed rectal cancer after IRA. The risk of dying from rectal cancer was 12.5% (95% confidence interval 7.1--17.9%) by age 65. Compared with IRA, IPAA would lead to an increase in life expectancy of 1.8 years. Seventy five per cent of patients with rectal cancer had a negative rectoscopy within 12 months before the diagnosis.

CONCLUSION

IRA is associated with substantial mortality due to rectal cancer. Follow up examinations of the rectum does not have sufficient preventive effect on morbidity and mortality of rectal cancer.

Relationship between APC genotype, polyp distribution, and oral sulindac treatment in the colon and rectum of patients with familial adenomatous polyposis

PURPOSE

Familial adenomatous polyposis is an inherited colorectal cancer syndrome characterized by the presence of multiple adenomatous colorectal polyps. Molecular studies have revealed that germline mutations in the APC gene are the underlying cause of the disease. The nonsteroidal anti-inflammatory agent sulindac has been shown to reduce the number of colorectal adenomas. Most sulindac trials in the large bowel have focused on the distal colon and relatively little is known about its effect on the proximal colon. Moreover, it is unknown whether the site of the APC mutation affects the efficacy of sulindac.

METHODS

This study investigated whether there were regional differences in the effect of sulindac on the colon and whether response to sulindac was dependent on the site of mutation in the APC gene. In an open prospective study 17 patients with familial adenomatous polyposis were treated with 300 mg oral sulindac daily for four months followed by a washout phase of six months. Ten of the patients had an intact colon and seven had rectal stumps only. The number, size, and the degree of dysplasia of the adenomas were evaluated by colonoscopy at entry, end of treatment and end of the study.

RESULTS

Overall, a statistically significant decrease in the number of adenomas was observed (120 +/- 112 to 28 +/- 64, P = 0.007). After cessation of sulindac treatment the number of adenomas increased to 48 +/- 44.5, but remained significantly lower than the values observed at baseline. In the ten patients with intact colons, adenomas decreased by sevenfold in the proximal colon (103 +/- 73 to 15.1 +/- 47.4, P = 0.011) and twofold in the distal colon (80 +/- 52 to 29.6 +/- 37.2, P = 0.005). The size of adenomas and the grade of dysplasia also decreased. No correlation could be seen between the APC mutation site and the response to treatment.

CONCLUSION

These data indicate that sulindac reduces the number of adenomas in the entire colon and that the effect seems to be more pronounced in the proximal colon.