Chemoprevention of colorectal cancer

Non-Steroidal Anti-Inflammatory Drugs in Colorectal Cancer Chemoprevention

Simple Summary

There is growing evidence from epidemiologic, preclinical and clinical studies suggesting that non-steroidal anti-inflammatory drugs (NSAIDs) play a beneficial role in colorectal cancer chemoprevention. They reduce the risk of colorectal polyps, mostly by cyclooxygenase-2 inhibition. The aim of our work was to describe the current state of scientific knowledge on the potential added value of the use of NSAIDs (such as aspirin, sulindac, and celecoxib) as chemopreventive agents in patients at risk of colorectal cancer. The study confirmed that there is a link between the long-term use of the NSAIDs and a decrease in the risk of colorectal cancer.

Abstract

Since colorectal cancer is one of the world’s most common cancers, studies on its prevention and early diagnosis are an emerging area of clinical oncology these days. For this study, a review of randomized controlled, double-blind clinical trials of selected NSAIDs (aspirin, sulindac and celecoxib) in chemoprevention of colorectal cancer was conducted. The main molecular anticancer activity of NSAIDs is thought to be a suppression of prostaglandin E₂ synthesis via cyclooxygenase-2 inhibition, which causes a decrease in tumor cell proliferation, angiogenesis, and increases apoptosis. The lower incidence of colorectal cancer in the NSAID patients suggests the long-lasting chemopreventive effect of drugs studied. This new approach to therapy of colorectal cancer may transform the disease from a terminal to a chronic one that can be taken under control.

Quercetin ameliorates reactive oxygen species generation, inflammation, mucus depletion, goblet disintegration, and tumor multiplicity in colon cancer: Probable role of adenomatous polyposis coli, β-catenin

1,2 Dimethyl hydrazine (DMH), a cogent environmental toxicant, targets the colon. Previous reports suggest that DMH-mediated dysregulation of the Wnt/β-catenin pathway plays a vital role in the initial events of colon carcinogenesis. Our study was designed to investigate the effect of quercetin on DMH-mediated colon cancer by targeting adenomatous polyposis coli (APC) and β-catenin in Wistar rats. Animals were pretreated orally with quercetin at doses of either 25 or 50 mg/kg bodyweight (bw) and DMH at a dose of 20 mg/kg bw subcutaneously up to the 15th week and sacrificed after the 30th week. DMH administration leads to reactive oxygen species generation, resulting in an imbalance in redox homeostasis and causing membrane lipid peroxidation, which is also partly due to the decrease in the level of tissue antioxidant machinery. Increased inflammatory and proliferative proteins were observed in DMH-induced colon cancerous rats. DMH treatment also led to dysregulation in the apoptotic pathway with decreased Bax:Bcl-2 ratio. Quercetin pretreatment ameliorates DMH-induced proliferation, activities of detoxifying enzymes, and putative early markers (mucin depletion and goblet cell disintegration) in colonic tissue. It also significantly regulates APC and β-catenin expression and inhibits tumor incidence and multiplicity. Histological results further confirm the beneficial role of quercetin in averting DMH-induced pathological alterations.

Colon targeted beads loaded with pterostilbene: Formulation, optimization, characterization and in vivo evaluation

Background

Pterostilbene has a proven chemopreventive effect for colon carcinogenesis but suffers low bioavailability limitations and therefore unable to reach the colonic tissue.

Objective and methodology

To overcome the issue of low bioavailability, pterostilbene was formulated into an oral colon targeted beads by ionic gelation method using pectin and zinc acetate. Optimization was carried out by 2³ factorial design whereby the effect of pectin concentration (X₁), zinc acetate concentration (X₂) and pterostilbene:pectin ratio (X₃) were studied on entrapment efficiency (Y₁) and in vitro drug release till 24 h (Y₂). The optimized beads were characterized for shape and size, swelling and surface morphology. The optimized beads were uniformly coated with Eudragit S-100 using fluidized bed coater. Optimized coated beads were characterized for in vitro drug release till 24 h and surface morphology. Pharmacokinetic and organ distribution study were performed in rats to ascertain the release of pterostilbene in colon.

Results

The optimized formulation comprised of 2% w/v of pectin concentration (X₁), 2% w/v of zinc acetate concentration (X₂) and 1:4 of pterostilbene:pectin ratio (X₃), which showed a satisfactory entrapment efficiency (64.80%) and in vitro release (37.88%) till 24 h. The zinc pectinate beads exhibited sphericity, uniform size distribution, adequate swelling and rough surface. The optimized coated beads achieved 15% weight gain, displayed smooth surface and optimum drug release. Pterostilbene from optimized coated beads appeared in the plasma at 14 h and reached the C_max at 22 h (T_max), whereas plain pterostilbene exhibited T_max of 3 h.

Discussion and conclusion

Thus, larger distribution of pterostilbene was obtained in the colonic tissue compared to stomach and small intestinal tissues. Thus, delayed T_max and larger distribution of pterostilbene in colonic tissue confirmed the targeting of beads to colon.

Cyclic-GMP-Elevating Agents Suppress Polyposis in ApcMin mice by Targeting the Preneoplastic Epithelium

The cGMP signaling axis has been implicated in the suppression of intestinal cancers, but the inhibitory mechanism and the extent to which this pathway can be targeted remains poorly understood. This study has tested the effect of cGMP-elevating agents on tumorigenesis in the Apc^Min/+ mouse model of intestinal cancer. Treatment of Apc^Min/+ mice with the receptor guanylyl-cyclase C (GCC) agonist linaclotide, or the phosphodiesterase-5 (PDE5) inhibitor sildenafil, significantly reduced the number of polyps per mouse (67% and 50%, respectively). Neither of the drugs affected mean polyp size, or the rates of apoptosis and proliferation. This was possibly due to increased PDE10 expression, as endogenous GCC ligands were not deficient in established polyps. These results indicated that the ability of these drugs to reduce polyp multiplicity was primarily due to an effect on nonneoplastic tissues. In support of this idea, Apc^Min/+ mice exhibited reduced levels of endogenous GCC agonists in the nonneoplastic intestinal mucosa compared with wild-type animals, and this was associated with crypt hyperplasia and a loss of goblet cells. Administration of either sildenafil or linaclotide suppressed proliferation, and increased both goblet cell numbers and luminal apoptosis in the intestinal mucosa. Taken together, the results demonstrate that targeting cGMP with either PDE5 inhibitors or GCC agonists alters epithelial homeostasis in a manner that reduces neoplasia, and suggests that this could be a viable chemoprevention strategy for patients at high risk of developing colorectal cancer. Cancer Prev Res; 11(2); 81-92. ©2018 AACR.

Berberine binds RXRα to suppress β-catenin signaling in colon cancer cells

Berberine, an isoquinoline alkaloid, is a traditional oriental medicine used to treat diarrhea and gastroenteritis. Recently, we reported that it could inhibit the growth of intestinal polyp in animals and in patients with the familial adenomatous polyposis by downregulating β-catenin signaling. However, the intracellular target mediating the effects of berberine remains elusive. Here, we provide evidence that berberine inhibits β-catenin function via directly binding to a unique region comprising residues Gln275, Arg316 and Arg371 in nuclear receptor retinoid X receptor alpha (RXRα), where berberine concomitantly binding to and synergistically activating RXRα with 9-cis-retinoic acid (9-cis-RA), a natural ligand binding to the classical ligand-binding pocket of RXRα. Berberine binding promotes RXRα interaction with nuclear β-catenin, leading to c-Cbl mediated degradation of β-catenin, and consequently inhibits the proliferation of colon cancer cells. Furthermore, berberine suppresses the growth of human colon carcinoma xenograft in nude mice in an RXRα-dependent manner. Together, our study not only identifies RXRα as a direct protein target for berberine but also dissects their binding mode and validates that berberine indeed suppresses β-catenin signaling and cell growth in colon cancer via binding RXRα, which provide new strategies for the design of new RXRα-based antitumor agents and drug combinations.

Role of GSK-3β in Regulation of Canonical Wnt/β-catenin Signaling and PI3-K/Akt Oncogenic Pathway in Colon Cancer

Non-steroidal anti-inflammatory drugs (NSAIDs) are emerging as novel chemopreventive agents because of their ability in blocking cellular proliferation, and thereby tumor development, and also by promoting apoptosis. GSK-3β, a serine threonine kinase and a negative regulator of the oncogenic Wnt/β-catenin signaling pathway, plays a critical role in the regulation of oncogenesis. Celecoxib and etoricoxib, the two cyclooxygenase-2 (COX-2) selective NSAIDs, and Diclofenac, a preferential COX-2 inhibitory NSAID, had shown uniformly the chemopreventive and anti-neoplastic effects in the early stage of colon cancer by promoting apoptosis as well as an over-expression of GSK-3β while down-regulating the PI3-K/Akt oncogenic pathway.

Prostaglandin E receptor 4 (EP4) promotes colonic tumorigenesis

Colorectal cancer (CRC) continues to be a major cause of morbidity and mortality. Although the factors underlying CRC development and progression are multifactorial, there is an important role for tumor-host interactions, especially interactions with myeloid cells. There is also increasing evidence that cyclooxygenase-derived prostaglandins are important mediators of CRC development and growth. Although prevention trials with either nonselective NSAIDs or COX-2 selective agents have shown promise, the gastrointestinal or cardiovascular side effects of these agents have limited their implementation. The predominant prostaglandin involved in CRC pathogenesis is PGE2. Since myeloid cells express high levels of the PGE2 receptor subtype, EP4, we selectively ablated EP4 in myeloid cells and studied adenoma formation in a mouse model of intestinal adenomatous polyposis, ApcMin/+ mice. ApcMin/+mice with selective myeloid cell deletion of EP4 had marked inhibition of both adenoma number and size, with associated decreases in mTOR and ERK activation. Either genetic or pharmacologic inhibition of EP4 receptors led to an anti-tumorigenic M1 phenotype of macrophages/dendritic cells. Therefore, PGE2-mediated EP4 signaling in myeloid cells promotes tumorigenesis, suggesting EP4 as a potentially attractive target for CRC chemoprevention or treatment.

Targeting Notch Signaling in Colorectal Cancer

The activation of Notch signaling is implicated in tumorigenesis in the colon due to the induction of pro-survival signaling in colonic epithelial cells. Chemoresistance is a major obstacle for treatment and for the complete eradication of colorectal cancer (CRC), hence, the inhibition of Notch is an attractive target for CRC and several groups are working to identify small molecules or monoclonal antibodies that inhibit Notch or its downstream events; however, toxicity profiles in normal cells and organs often impede the clinical translation of these molecules. Dietary agents have gained momentum for targeting several pro-survival signaling cascades, and recent studies demonstrated that agents that inhibit Notch signaling result in growth inhibition in preclinical models of CRC. In this review, we focus on the importance of Notch as a preventive and therapeutic target for colon cancer and on the effect of WA on this signaling pathway in the context of colon cancer.

Ulcerative colitis: From inflammation to cancer. Do estrogen receptors have a role?

Ulcerative colitis (UC) is a condition at increased risk for colorectal carcinoma (CRC) development. Nowadays, screening and follow-up programs are routinely performed worldwide to promote the early detection of CRCs in subjects with well known risk factors (extent, duration and severity of the disorder). The diffusion of these procedures is presumably the main reason for the marked reduction of cancer incidence and mortality in the course of UC. In addition, chemoprevention has been widely investigated and developed in many medical fields, and aspirin has shown a preventive effect against CRC, while mesalazine has been strongly invoked as a potential chemopreventive agent in UC. However, available studies show some limitations due to the obvious ethical implications of drug withdrawal in UC in order to design a control group. The estrogen receptors (ER) alpha/beta balance seems to have a relevant influence on colorectal carcinogenesis and ER beta appears to parallel apoptosis, and hence an anti-carcinogenic effect. Phytoestrogens are compounds acting as ER beta agonists and have shown a promising chemopreventive effect on sporadic as well as genetically inherited CRC. There is evidence suggesting a role for ERs in UC-related carcinogenesis. In this perspective, since these substances can be considered as dietary supplements and are completely free from side effects, phytoestrogens could be an interesting option for CRC prevention, even when the disease is a consequence of long-term chronic inflammation, as in the course of UC. Further studies of their effects are warranted in both the basic research and clinical fields.

Molecular diagnostics in colorectal carcinoma

Molecular pathogenesis and classification of colorectal carcinoma are based on the adenoma-carcinoma sequence in the Vogelstein model, serrated polyp pathway, and microsatellite instability. The genetic basis for hereditary nonpolyposis colorectal cancer is based on detection of genetic mutations. Genetic testing for Lynch syndrome includes microsatellite instability, methylator phenotyping, BRAF mutation, and molecular testing. Molecular makers include quantitative multigene reverse transcriptase-polymerase chain reaction assay and KRAS and BRAF mutation analysis. Potential biomarkers include one-step nucleic acid amplification and epigenetic inactivation of endothelin 2 and endothelin 3 in colon cancer. Molecular screening approaches in colorectal cancer using stool DNA are under investigation.

Insulin therapy and risk of colorectal cancer: an updated meta-analysis of epidemiological studies

OBJECTIVE

An increasing number of studies show that exogenous insulin therapy may promote colorectal carcinogenesis. However, the results of the association between insulin therapy and risk of colorectal cancer (CRC) among type 2 diabetes patients are inconsistent. The purpose of our study is to examine the effect of insulin therapy on CRC risk among patients with type 2 diabetes in an updated meta-analysis.

RESEARCH DESIGN AND METHODS

Medline and Embase were searched for the reference lists of pertinent articles published from January 1970 to April 2013. Two investigators independently extracted the data and reached consensus on the inclusion and exclusion criteria. Pooled relative risks and 95% confidence intervals were calculated with a random-effects model.

RESULTS

Analysis of six studies, including 374,950 participants, showed that compared with non-insulin or metformin treatment, insulin treatment was associated with an increase of 37% in the risk of colorectal neoplasm among patients with type 2 diabetes, with moderate heterogeneity (I2=40%). The sensitivity analysis showed that exclusion of one small case-control study had no appreciable changes on the pooled results. Subgroup analyses suggested that there were significant positive associations between insulin therapy and risk of CRC in some subgroups, rather than all subgroups.

CONCLUSIONS

Our meta-analysis supports a relationship between insulin therapy and increased risk of CRC in patients with type 2 diabetes. Because of bias and confounding of included studies, caution is needed when interpreting our results. Further investigations are needed.

Epithelial-specific deletion of 11β-HSD2 hinders Apcmin/+ mouse tumorigenesis

Cyclooxygenase-2 (COX-2)-derived prostaglandin E2 (PGE2) promotes colorectal tumorigenesis. Glucocorticoids are endogenous and potent COX-2 inhibitors, and their local actions are downregulated by 11β-hydroxysteroid dehydrogenase type II (11β-HSD2)-mediated metabolism. Previously, it was reported that 11β-HSD2 is increased in human colonic and Apc(min/+) mouse intestinal adenomas and correlated with increased COX-2, and 11β-HSD2 inhibition suppressed the COX-2 pathway and decreased tumorigenesis. Because 11β-HSD2 is expressed in Apc(min/+) mouse intestinal adenoma stromal and epithelial cells, Apc(min/+) mice were generated with selective deletion of 11β-HSD2 in intestinal epithelial cells (Vil-Cre-HSD2(-/-) Apc(min/+)). Deletion of 11β-HSD2 in intestinal epithelia led to marked inhibition of Apc(min/+) mouse intestinal tumorigenesis. Immunostaining indicated decreased 11β-HSD2 and COX-2 expression in adenoma epithelia, whereas stromal COX-2 expression was intact in Vil-Cre-HSD2(-/-) Apc(min/+) mice. In Vil-Cre-HSD2(-/-) Apc(min/+) mouse intestinal adenomas, both p53 and p21 mRNA and protein were increased, with a concomitant decrease in pRb, indicating glucocorticoid-mediated G1-arrest. Further study revealed that REDD1 (regulated in development and DNA damage responses 1), a novel stress-induced gene that inhibits mTOR signaling, was increased, whereas the mTOR signaling pathway was inhibited. Therefore, in Vil-Cre-HSD2(-/-) Apc(min/+) mice, epithelial cell 11β-HSD2 deficiency leads to inhibition of adenoma initiation and growth by attenuation of COX-2 expression, increased cell-cycle arrest, and inhibition of mTOR signaling as a result of increased tumor intracellular active glucocorticoids.

IMPLICATIONS

Inhibition of 11β-HSD2 may represent a novel approach for colorectal cancer chemoprevention by increasing tumor glucocorticoid activity, which in turn inhibits tumor growth by multiple pathways.

Prospective of colon cancer treatments and scope for combinatorial approach to enhanced cancer cell apoptosis

Colorectal cancer is the leading cause of cancer-related mortality in the western world. It is also the third most common cancer diagnosed in both men and women in the United States with a recent estimate for new cases of colorectal cancer in the year 2012 being around 103,170. Various risk factors for colorectal cancer include life-style, diet, age, personal and family history, and racial and ethnic background. While a few cancers are certainly preventable but this does not hold true for colon cancer as it is often detected in its advanced stage and generally not diagnosed until symptoms become apparent. Despite the fact that several options are available for treating this cancer through surgery, chemotherapy, radiation therapy, immunotherapy, and nutritional-supplement therapy, but the success rates are not very encouraging when used alone where secondary complications appear in almost all these therapies. To maximize the therapeutic-effects in patients, combinatorial approaches are essential. In this review we have discussed the therapies previously and currently available to patients diagnosed with colorectal-cancer, focus on some recent developments in basic research that has shaded lights on new therapeutic-concepts utilizing macrophages/dendritic cells, natural killer cells, gene delivery, siRNA-, and microRNA-technology, and specific-targeting of tyrosine kinases that are either mutated or over-expressed in the cancerous cell to treat these cancer. Potential strategies are discussed where these concepts could be applied to the existing therapies under a comprehensive approach to enhance the therapeutic effects.

Dietary intakes of retinol, carotenes, vitamin C, and vitamin E and colorectal cancer risk: the Fukuoka colorectal cancer study

It has long been a matter of interest whether antioxidant vitamins are protective against colorectal cancer as well as human cancers in general, but epidemiological evidence is inconclusive. We investigated associations of dietary intakes of retinol and antioxidant vitamins with colorectal cancer risk in 816 incident cases of histologically confirmed colorectal cancer and 815 controls randomly selected for the Fukuoka colorectal cancer study in Japan. Dietary intakes were assessed by a PC-assisted interview regarding 148 food items. Statistical adjustment was made for body mass index, physical activity, calcium, and n-3 fatty acid intake and other factors. Retinol intake was significantly, inversely associated with colorectal cancer risk; the odds ratio for the highest vs. lowest was 0.55 (95% CI: 0.35, 0.88; P (trend) = 0.01) in women, but a modest increase in the risk was observed among men with the highest intake of retinol. Liver was the major source of retinol intake and showed similar associations with colorectal cancer risk in men and women. Intake of carotenes, vitamin C, and vitamin E were not related to colorectal cancer risk in either men or women. The study did not support a hypothesis that dietary intake of antioxidant vitamins is protective in the development of colorectal cancer.

COX-2 inhibition alters the phenotype of tumor-associated macrophages from M2 to M1 in ApcMin/+ mouse polyps

Macrophages are a major component of tumor stroma. Tumor-associated macrophages (TAMs) show anti- (M1) or protumor (M2) functions depending on the cytokine milieu of the tumor microenvironment. Cyclooxygenase-2 (COX-2) is constitutively expressed in a variety of tumors including colorectal cancer. TAMs are known to be a major source of COX-2 in human and mice intestinal tumors. COX-2 inhibitor reduces the number and size of intestinal adenomas in familial adenomatous polyposis patients and Apc(Min/+) mice. Although COX-2 inhibitor is thought to regulate cancer-related inflammation, its effect on TAM phenotype remains unknown. Here, we examined the effects of COX-2 inhibition on TAM phenotype and cytokine expression both in vivo and in vitro. Firstly, the selective COX-2 inhibitor celecoxib changed the TAM phenotype from M2 to M1, in proportion to the reduction in number of Apc(Min/+) mouse polyps. Concomitantly, the expression of M1-related cytokine interfron (IFN)-γ was significantly upregulated by celecoxib, although the M2-related cytokines interleukin (IL)-4, IL-13 and IL-10 were not significantly altered. Secondly, IFN-γ treatment attenuated M2 phenotype of mouse peritoneal macrophages and oriented them to M1 even in the presence of M2-polarizing cytokines such as IL-4, IL-13 and IL-10. Thus, our results suggest that COX-2 inhibition alters TAM phenotype in an IFN-γ-dependent manner and subsequently may reduce intestinal tumor progression.

Studies on the metabolism and biological activity of the epimers of sulindac

Sulindac is a nonsteroidal, anti-inflammatory drug (NSAID) that has also been studied for its anticancer activity. Recent studies suggest that sulindac and its metabolites act by sensitizing cancer cells to oxidizing agents and drugs that affect mitochondrial function, resulting in the production of reactive oxygen species and death by apoptosis. In contrast, normal cells are not killed under these conditions and, in some instances, are protected against oxidative stress. Sulindac has a methyl sulfoxide moiety with a chiral center and was used in all of the previous studies as a mixture of the R- and S-epimers. Because epimers of a compound can have very different chemical and biological properties, we have separated the R- and S-epimers of sulindac, studied their individual metabolism, and performed preliminary experiments on their effect on normal and lung cancer cells exposed to oxidative stress. Previous results had indicated that the reduction of (S)-sulindac to sulindac sulfide, the active NSAID, was catalyzed by methionine sulfoxide reductase (Msr) A. In the present study, we purified an enzyme that reduces (R)-sulindac and resembles MsrB in its substrate specificity. The oxidation of both epimers to sulindac sulfone is catalyzed primarily by the microsomal cytochrome P450 (P450) system, and the individual enzymes responsible have been identified. (S)-Sulindac increases the activity of the P450 system better than (R)-sulindac, but both epimers increase primarily the enzymes that oxidize (R)-sulindac. Both epimers can protect normal lung cells against oxidative damage and enhance the killing of lung cancer cells exposed to oxidative stress.

Statin use and risk of colorectal cancer in a cohort of middle-aged men in the US: a prospective cohort study

BACKGROUND

Numerous modifiable factors have been associated with a reduced risk of colorectal cancer, including the chronic use of NSAIDs. Thus, it is biologically plausible that HMG-CoA reductase inhibitors (statins), therapeutic agents that also possess anti-inflammatory effects, are also associated with a lowered risk of colorectal cancer.

OBJECTIVE

To examine the association between statin use and the risk of colorectal cancer in a large cohort of middle-aged men enrolled in a prepaid, integrated health maintenance organization.

METHODS

We conducted a prospective cohort study of 69 115 Northern and Southern California Kaiser Permanente (KP) members aged 45-69 years who enrolled in the California Men's Health Study in 2002-3. Colorectal cancer cases were identified by linkage to the KP California Cancer Registries. Statin exposure, estimated from automated KP outpatient pharmacy records (available since 1991 in Southern California and 1994 in Northern California), was treated as time-varying. Cox proportional hazards regression analyses were used to estimate hazard ratios and 95% confidence intervals (CIs), while controlling for potential confounders.

RESULTS

During a maximum of 3.5 years of follow-up, 171 colorectal cancer cases were identified. Compared with nonuse, the adjusted hazard ratio for ever use of statins was 0.89 (95% CI 0.61, 1.30). The hazard ratio for statin use of >or=5 years was 0.83 (95% CI 0.43, 1.63). The results did not differ markedly by type or severity of disease. There was also no evidence of effect modification by regular NSAID use. However, the stratified analyses were limited by small numbers.

CONCLUSION

These findings provide little support for an association between the use of statins and the risk of colorectal cancer in men. There was some suggestion of a modest inverse association between statin use for >or=5 years and risk of colorectal cancer; however, the possibility that this observation may be related to regular NSAID use cannot be ruled out.

Inhibition of peroxynitrite-mediated DNA strand cleavage and hydroxyl radical formation by aspirin at pharmacologically relevant concentrations: implications for cancer intervention

Epidemiological studies have suggested that the long-term use of aspirin is associated with a decreased incidence of human malignancies, especially colorectal cancer. Since accumulating evidence indicates that peroxynitrite is critically involved in multistage carcinogenesis, this study was undertaken to investigate the ability of aspirin to inhibit peroxynitrite-mediated DNA damage. Peroxynitrite and its generator 3-morpholinosydnonimine (SIN-1) were used to cause DNA strand breaks in phiX-174 plasmid DNA. We demonstrated that the presence of aspirin at concentrations (0.25-2mM) compatible with amounts in plasma during chronic anti-inflammatory therapy resulted in a significant inhibition of DNA cleavage induced by both peroxynitrite and SIN-1. Moreover, the consumption of oxygen caused by 250 microM SIN-1 was found to be decreased in the presence of aspirin, indicating that aspirin might affect the auto-oxidation of SIN-1. Furthermore, EPR spectroscopy using 5,5-dimethylpyrroline-N-oxide (DMPO) as a spin trap demonstrated the formation of DMPO-hydroxyl radical adduct (DMPO-OH) from authentic peroxynitrite, and that aspirin at 0.25-2mM potently diminished the radical adduct formation in a concentration-dependent manner. Taken together, these results demonstrate for the first time that aspirin at pharmacologically relevant concentrations can inhibit peroxynitrite-mediated DNA strand breakage and hydroxyl radical formation. These results may have implications for cancer intervention by aspirin.

Endogenous damage-associated molecular pattern molecules at the crossroads of inflammation and cancer

Inflammatory mediators play important roles in the development and progression of cancer. Cellular stress, damage, inflammation, and necrotic cell death cause release of endogenous damage-associated molecular pattern (DAMP) molecules or alarmins, which alert the host of danger by triggering immune responses and activating repair mechanisms through their interaction with pattern recognition receptors. Recent studies show that abnormal persistence of these molecules in chronic inflammation and in tumor microenvironments underlies carcinogenesis and tumor progression, indicating that DAMP molecules and their receptors could provide novel targets for therapy. This review focuses on the role of DAMP molecules high-mobility group box 1 and S100 proteins in inflammation, tumor growth, and early metastatic events.

Effects of selenite and genistein on G2/M cell cycle arrest and apoptosis in human prostate cancer cells

Combination of chemopreventive agents with distinct molecular mechanisms is considered to offer a potential for enhancing cancer prevention efficacy while minimizing toxicity. Here we report two chemopreventive agents, selenite and genistein, that have synergistic effects on apoptosis, cell cycle arrest, and associated signaling pathways in p53-expressing LNCaP and p53-null PC3 prostate cancer cells. We show that selenite induced apoptosis only, whereas genistein induced both apoptosis and G2/M cell cycle arrest. Combination of these two agents exhibited enhanced effects, which were slightly greater in LNCaP than PC3 cells. Selenite or genistein alone upregulated protein levels of p53 in LNCaP cells only and p21(waf1) and Bax in both cell lines. Additionally, genistein inhibited AKT phosphorylation. Downregulation of AKT by siRNA caused apoptosis and G2/M cell cycle arrest and masked the effects of genistein. Treatment with insulin-like growth factor I (IGF-I) elevated levels of total and phosphorylated AKT and suppressed the effects of genistein. Neither downregulation of AKT nor IGF-I treatment altered the cellular effects of selenite. Our study demonstrates that selenium and genistein act via different molecular mechanisms and exhibit enhanced anticancer effects, suggesting that a combination of selenium and genistein may offer better efficacy and reduction of toxicity in prostate cancer prevention.

Sulindac enhances the killing of cancer cells exposed to oxidative stress

Background

Sulindac is an FDA-approved non-steroidal anti-inflammatory drug (NSAID) that affects prostaglandin production by inhibiting cyclooxygenases (COX) 1 and 2. Sulindac has also been of interest for more than decade as a chemopreventive for adenomatous colorectal polyps and colon cancer.

Principal Findings

Pretreatment of human colon and lung cancer cells with sulindac enhances killing by an oxidizing agent such as tert-butyl hydroperoxide (TBHP) or hydrogen peroxide. This effect does not involve cyclooxygenase (COX) inhibition. However, under the conditions used, there is a significant increase in reactive oxygen species (ROS) within the cancer cells and a loss of mitochondrial membrane potential, suggesting that cell death is due to apoptosis, which was confirmed by Tunel assay. In contrast, this enhanced killing was not observed with normal lung or colon cells.

Significance

These results indicate that normal and cancer cells handle oxidative stress in different ways and sulindac can enhance this difference. The combination of sulindac and an oxidizing agent could have therapeutic value.

Statins and the risk of colorectal carcinoma: a nested case-control study in veterans with diabetes

OBJECTIVES

Experimental data indicate a possible preventive effect for statins in colorectal cancer (CRC). However, the available epidemiological data are conflicting.

METHODS

We conducted a nested case-control study of veterans with diabetes in national databases of the Department of Veterans Affairs (VA) and Medicare-linked files. Cases were defined as incident CRC during January 2001-December 2002, sampled on incidence density. VA pharmacy benefits management (PBM) files were used to identify filled prescriptions for statins. Multivariable conditional logistic regression models were used to estimate odds ratios (ORs) after adjusting for potential confounding variables. Stratified analyses were conducted for potential effect modifiers.

RESULTS

A total of 6,080 cases and 24,320 controls were examined. The mean age was 74 years, and the majority of patients were Caucasian (88%) and male (99%). Filled prescriptions of statins were recorded less frequently in cases (49%) than in controls (52%; OR: 0.88; 95% confidence interval (95% CI): 0.83-0.93). This inverse association remained significant after adjusting for inflammatory bowel disease, diabetes severity, cholecystectomy, liver disease, filled prescriptions for sulfonylurea, aspirin or NSAID use, or colorectal evaluation. Simvastatin comprised the majority (87%) of statin-filled prescriptions, and the association with risk of CRC with simvastatin was very similar to that of any statin. No significant associations were observed between the risk of CRC and nonstatin cholesterol (OR: 1.02; 95% CI 0.88-1.18) or triglyceride-lowering medications (OR: 0.96; 95% CI: 0.87-1.05). The significant inverse association was limited to Caucasians, patients without history of polyps, patients aged 65 years and older, and patients with colon cancer (excluding rectum).

CONCLUSIONS

The use of statins was associated with a small reduction in the risk of colon cancer in patients with diabetes. However, the causal link is not clear.

Inhibition of 11beta-hydroxysteroid dehydrogenase type II selectively blocks the tumor COX-2 pathway and suppresses colon carcinogenesis in mice and humans

Colorectal cancer (CRC) is a leading cause of cancer death, yet primary prevention remains the best approach to reducing overall morbidity and mortality. Studies have shown that COX-2-derived PGE2 promotes CRC progression, and both nonselective COX inhibitors (NSAIDs) and selective COX-2 inhibitors (such as glucocorticoids) reduce the number and size of colonic adenomas. However, increased gastrointestinal side effects of NSAIDs and increased cardiovascular risks of selective COX-2 inhibitors limit their use in chemoprevention of CRC. We found that expression of 11beta-hydroxysteroid dehydrogenase type II (11betaHSD2), which converts active glucocorticoids to inactive keto-forms, increased in human colonic and Apc+/min mouse intestinal adenomas and correlated with increased COX-2 expression and activity. Furthermore, pharmacologic inhibition or gene silencing of 11betaHSD2 inhibited COX-2-mediated PGE2 production in tumors and prevented adenoma formation, tumor growth, and metastasis in mice. Inhibition of 11betaHSD2 did not reduce systemic prostacyclin production or accelerate atherosclerosis in mice, thereby avoiding the major cardiovascular side effects seen with systemic COX-2 inhibitors. Therefore, 11betaHSD2 inhibition represents what we believe to be a novel approach for CRC chemoprevention and therapy by increasing tumor glucocorticoid activity, which in turn selectively blocks local COX-2 activity.

Antioxidant supplements for preventing gastrointestinal cancers

BACKGROUND

Oxidative stress may cause gastrointestinal cancers. The evidence on whether antioxidant supplements are effective in preventing gastrointestinal cancers is contradictory.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements in preventing gastrointestinal cancers.

SEARCH STRATEGY

We identified trials through the trials registers of the four Cochrane Review Groups on gastrointestinal diseases, The Cochrane Central Register of Controlled Trials in The Cochrane Library (Issue 2, 2007), MEDLINE, EMBASE, LILACS, SCI-EXPANDED, and The Chinese Biomedical Database from inception to October 2007. We scanned reference lists and contacted pharmaceutical companies.

SELECTION CRITERIA

Randomised trials comparing antioxidant supplements to placebo/no intervention examining occurrence of gastrointestinal cancers.

DATA COLLECTION AND ANALYSIS

Two authors (GB and DN) independently selected trials for inclusion and extracted data. Outcome measures were gastrointestinal cancers, overall mortality, and adverse effects. Outcomes were reported as relative risks (RR) with 95% confidence interval (CI) based on random-effects and fixed-effect model meta-analysis. Meta-regression assessed the effect of covariates across the trials.

MAIN RESULTS

We identified 20 randomised trials (211,818 participants), assessing beta-carotene (12 trials), vitamin A (4 trials), vitamin C (8 trials), vitamin E (10 trials), and selenium (9 trials). Trials quality was generally high. Heterogeneity was low to moderate. Antioxidant supplements were without significant effects on gastrointestinal cancers (RR 0.94, 95% CI 0.83 to 1.06). However, there was significant heterogeneity (I(2) = 54.0%, P = 0.003). The heterogeneity may have been explained by bias risk (low-bias risk trials RR 1.04, 95% CI 0.96 to 1.13 compared to high-bias risk trials RR 0.59, 95% CI 0.43 to 0.80; test of interaction P < 0.0005), and type of antioxidant supplement (beta-carotene potentially increasing and selenium potentially decreasing cancer risk). The antioxidant supplements had no significant effects on mortality in a random-effects model meta-analysis (RR 1.02, 95% CI 0.97 to 1.07, I(2) = 53.5%), but significantly increased mortality in a fixed-effect model meta-analysis (RR 1.04, 95% CI 1.02 to 1.07). Beta-carotene in combination with vitamin A (RR 1.16, 95% CI 1.09 to 1.23) and vitamin E (RR 1.06, 95% CI 1.02 to 1.11) significantly increased mortality. Increased yellowing of the skin and belching were non-serious adverse effects of beta-carotene. In five trials (four with high risk of bias), selenium seemed to show significant beneficial effect on gastrointestinal cancer occurrence (RR 0.59, 95% CI 0.46 to 0.75, I(2) = 0%).

AUTHORS' CONCLUSIONS

We could not find convincing evidence that antioxidant supplements prevent gastrointestinal cancers. On the contrary, antioxidant supplements seem to increase overall mortality. The potential cancer preventive effect of selenium should be tested in adequately conducted randomised trials.

Effect of aspirin on DNA damage induced by MMC in Drosophila

In our previous paper, we found that aspirin suppressed the genotoxicity of mitomycin C (MMC) in a somatic mutation and recombination test (SMART) in Drosophila melanogaster. In order to reveal the mechanism of antigenotoxicity of aspirin, we evaluated the protective effects of aspirin against the genotoxicity of MMC with the DNA repair test in Drosophila melanogaster. Three types of treatment of aspirin were performed as co-, post- and pre-treatment. Aspirin co-treatment suppressed effectively the genotoxicity of MMC in a dose-dependent manner and the sex ratio at a dose of aspirin 10mg/bottle elevated from 0.01 (without aspirin) to 0.65 at sc z(1) w(+(TE)) mei-9(a) mei-41(D5)/-C(1)DX, y f [mei-9 mei-41, Rec(-) male.Rec(+) female] consists of DNA repair-deficient (Rec(-)) males and -proficient (Rec(+)) females. The antigenotoxic effect of aspirin on [mei-41, Rec(-) male.Rec(+) female] was similar to that on [mei-9, Rec(-) male.Rec(+) female]. But post- and pre-treatment by aspirin did not affect the genotoxicity of MMC on [mei-9 mei-41, Rec(-) male.Rec(+) female].

Synthesis and in vitro antitumor effect of diclofenac and fenoprofen thiolated and nonthiolated polyaspartamide-drug conjugates

This paper reports the synthesis and antiproliferative effects of new thiomer-diclofenac and fenoprofen conjugates, hydrophilic, bioadhesive, polymeric prodrugs, as well as antiproliferative effects of diclofenac, fenoprofen and a series of previously described polymer-fenoprofen conjugates on five tumor cell lines. Thiolated and nonthiolated polyaspartamides were the chosen polymeric components. Drug-loading ranged from 5.6 to 22.4%, and the amount of SH groups ranged from 6.9 to 45.6micromol g(-1). Tensile studies demonstrated a clear correlation between the amount of thiol and the mucoadhesive properties of the conjugates. The growth-inhibitory activity of the tested polymer-drug conjugates demonstrates that polyaspartamide-type polymers, especially thiolated polymers, enable inhibition of tumor cell growth with significantly lower doses of the active substance.

Expression of cyclo-oxygenase-2 in ependymal tumors

Up-regulation of cyclo-oxygenase-2 (COX-2), a cytokine-induced enzyme that metabolizes arachidonic acid into prostaglandins, has been described in some brain tumors, including astrocytomas. Little is known about its expression in ependymal neoplasms. The objective of the present study was to assess COX-2 immunostaining of ependymal tumors. Retrospective COX-2 immunohistochemical analysis was conducted on 117 ependymal tumors. Statistical analysis was performed using Student t-test. The study group (56 men and 44 women, mean age, 30.8 years) was comprised of 48 low-grade ependymomas (WHO grade II), 12 anaplastic ependymomas (WHO grade III), 27 myxopapillary ependymomas (WHO grade I) and 13 subependymomas (WHO grade I). At last known follow-up (range, 12-226 months; mean, 74 months), 52 patients were alive with no evidence of tumor, 16 patients were alive with residual tumor, nine patients died with tumor, one patient died with no tumor and three died with tumor status unknown. Nineteen patients had less than 12 months of follow-up. Thirty-six (36%) patients had tumors, which demonstrated positive COX-2 staining, including 16/27 (59%) myxopapillary ependymomas, 3/13 (23%) subependymomas, 14/48 (29%) ependymomas and 3/12 (25%) anaplastic ependymomas. Statistically significant COX-2 positive immunostaining was observed in myxopapillary ependymomas versus WHO grade II (P = 0.03) and grade III (P = 0.02) tumors. Increased COX-2 expression in myxopapillary ependymoma as compared to the WHO grade II and II ependymoma was observed. The reason for this apparent increased immunoexpression in these low-grade tumors is uncertain. COX-2 inhibitors may play a role in treatment of the subset of ependymal tumors that demonstrate increased expression. COX-2 staining did not reliably predict tumor behavior.

Meta-analysis: antioxidant supplements for primary and secondary prevention of colorectal adenoma

BACKGROUND

Colorectal cancer may be prevented by reducing the development of adenomatous polyps.

AIM

To assess the benefits and harms of antioxidant supplements in preventing colorectal adenoma.

METHODS

Using the Cochrane Collaboration methodology we reviewed all randomized clinical trials comparing antioxidant supplements with placebo or no intervention. We searched electronic databases and the reference lists until October 2005. Outcome measures were development of colorectal adenoma adverse events. We analysed dichotomous outcomes with fixed- and random-effects model meta-analyses and calculated the relative risk with 95% confidence interval.

RESULTS

We identified eight randomized trials (17 620 participants). Neither fixed-effect (relative risk: 0.93, 95% CI: 0.81-1.1) nor random-effect model meta-analyses (0.82, 0.60-1.1) showed statistically significant effects of supplementation with beta-carotene, vitamins A, C, E and selenium alone or in combination. Antioxidant supplements seemed to increase the development of colorectal adenoma in three low-bias risk trials (1.2, 0.99-1.4) and significantly decrease its development in five high-bias risk trials (0.59, 0.47-0.74). The estimates difference is significant (P < 0.0001). There was no significant difference between the intervention groups regarding adverse events, including mortality (0.82, 0.47-1.4).

CONCLUSION

We found no convincing evidence that antioxidant supplements have significant beneficial effect on primary or secondary prevention of colorectal adenoma.

15-deoxy-Δ12,14-prostaglandin J2 inhibits the expression of microsomal prostaglandin E synthase type 2 in colon cancer cells

Prostaglandin (PG) E(2) (PGE(2)) plays a predominant role in promoting colorectal carcinogenesis. The biosynthesis of PGE(2) is accomplished by conversion of the cyclooxygenase (COX) product PGH(2) by several terminal prostaglandin E synthases (PGES). Among the known PGES isoforms, microsomal PGES type 1 (mPGES-1) and type 2 (mPGES-2) were found to be overexpressed in colorectal cancer (CRC); however, the role and regulation of these enzymes in this malignancy are not yet fully understood. Here, we report that the cyclopentenone prostaglandins (CyPGs) 15-deoxy-Delta(12,14)-PGJ(2) and PGA(2) downregulate mPGES-2 expression in the colorectal carcinoma cell lines Caco-2 and HCT 116 without affecting the expression of any other PGES or COX. Inhibition of mPGES-2 was subsequently followed by decreased microsomal PGES activity. These effects were mediated via modulation of the cellular thiol-disulfide redox status but did not involve activation of the peroxisome proliferator-activated receptor gamma or PGD(2) receptors. CyPGs had antiproliferative properties in vitro; however, this biological activity could not be directly attributed to decreased PGES activity because it could not be reversed by adding PGE(2). Our data suggest that there is a feedback mechanism between PGE(2) and CyPGs that implicates mPGES-2 as a new potential target for pharmacological intervention in CRC.

Aged garlic extract has chemopreventative effects on 1,2-dimethylhydrazine-induced colon tumors in rats

Garlic has been reported to have chemopreventive effects against a variety of cancers. However, different garlic preparations contain different constituents. We investigated the chemopreventive effect of aged garlic extract (AGE), an odorless product from prolonged extraction of fresh garlic, on colon carcinogenesis and cell proliferation in 1,2-dimethylhydrazine (DMH)-induced colon neoplastic rats. Rats were given weekly subcutaneous injections of DMH (20 mg/kg) for 20 wk, and fed either a basal diet or one containing 4% AGE. Serum from AGE-treated rats contained detectable S-allylcysteine. The AGE diet significantly reduced the number of colon tumors and aberrant crypt foci compared to the basal diet. Cell proliferation of normal-appearing colonic mucosa was assessed by MIB-5 immunohistochemistry. AGE treatment significantly decreased the mean MIB-5-labeling index. These findings suggest AGE has a chemopreventive effect on colon carcinogenesis through suppression of cell proliferation.

Suppression of tumor cell invasion by cyclooxygenase inhibitors is mediated by thrombospondin-1 via the early growth response geneEgr-1

Cyclooxygenase (COX) inhibitors have antitumorigenic activity and increase the expression of the early growth response gene Egr-1, a tumor suppressor gene and transcription factor. In this study, we have investigated the gene regulatory and anti-invasive activity of two traditional nonsteroidal anti-inflammatory drugs (NSAID), sulindac sulfide and indomethacin. These compounds inhibited tumor cell invasion and induced Egr-1 expression in lung adenocarcinoma A549 cells. Overexpression of Egr-1 reduced cellular invasion in the Matrigel system, whereas suppression of Egr-1 by small interference RNA (siRNA) attenuated the inhibition of Matrigel invasion by these compounds, indicating that Egr-1 is responsible for the decrease in invasion reported following treatment with NSAIDs. Egr-1-overexpressing cells were analyzed for genes involved in invasion and metastasis. Thrombospondin-1 (TSP-1) an antiangiogenic and anti-invasion protein was up-regulated by Egr-1 overexpression, which was confirmed following treatment with sulindac sulfide. Furthermore, the induction of TSP-1 by sulindac sulfide was blocked by Egr-1 siRNA. When TSP-1 was sequestered by the addition of anti-TSP-1 antibody, the inhibition of invasion by sulindac sulfide was attenuated, indicating that TSP-1 is involved in the inhibition of invasion by NSAIDs. We used the Min mouse model to determine if sulindac sulfide would increase Egr-1 and TSP-1 in vivo, because this model is widely used to study the effects of NSAIDs on tumor formation. Treatment of Min mice with concentrations of sulindac sulfide that inhibit tumor formation increased the expression of Egr-1 and TSP-1 in colonic tissues and in the polyps of these mice. This is the first report suggesting that COX inhibitors suppress tumor cell invasion via TSP-1, which occurs downstream of Egr-1.

5-ASA and colorectal cancer chemoprevention in inflammatory bowel disease: can we afford to wait for 'best evidence'?

Patients with inflammatory bowel disease have a higher risk of developing colorectal cancer. The main risk factors for colorectal cancer are not suitable targets for therapeutic intervention, and primary chemoprevention is an intriguing therapeutic option. The analogies between acetyl-salicylic acid and 5-amino-salicylic acid, and the results obtained by using acetyl-salicylic acid as a chemopreventive agent in patients with sporadic colorectal cancer have prompted the study of potential chemopreventive effects of 5-amino-salicylic acid in inflammatory bowel disease. The results of both epidemiological and experimental studies have shown that long-term 5-amino-salicylic acid treatments appear to have a chemopreventive effect. The evidence for this effect is provided by retrospective and case-control studies whose results, however, do not reach the highest grades for evidence-based recommendations. Nevertheless, these results are supported by a series of experimental studies demonstrating the multiplicity of actions of 5-amino-salicylic acid. Although data regarding the chemopreventive effect of 5-amino-salicylic acid may not be rigorous enough to meet the criteria for the highest evidence-based medicine recommendations, we feel that the argument to wait until we have Grade A evidence is not necessarily rational in this case, because discontinuation of 5-amino-salicylic acid treatment to perform a randomised controlled trial would be unethical secondary to their proven efficacy for maintenance treatment.

Oxidation of anthracyclines by peroxidase metabolites of salicylic Acid

Oxidation of anthracyclines leads to their degradation and inactivation. This process is carried out by peroxidases in the presence of a catalytic cofactor, a good peroxidase substrate. Here, we investigated the effect of salicylic acid, a commonly used anti-inflammatory and analgesic agent, on the peroxidative metabolism of anthracyclines. We report that at pharmacologically relevant concentrations, salicylic acid stimulates oxidation of daunorubicin and doxorubicin by myeloperoxidase and lactoperoxidase systems and that efficacy of the process increases markedly on changing the pH from 7 to 5. This pH dependence is positively correlated with the ease with which salicylic acid itself undergoes metabolic oxidation and involves the neutral form of the acid (pKa = 2.98). When salicylic acid reacted with a peroxidase and H2O2 at acid pH (anthracyclines omitted), a new metabolite with absorption maximum at 412 nm was formed. This metabolite reacted with anthracyclines causing their oxidation. It was tentatively assigned to biphenyl quinone, formed by oxidation of biphenol produced by dimerization of salicylic acid-derived phenoxyl radicals. The formation of this product was inhibited in a concentration-dependent manner by the anthracyclines, suggesting their scavenging of the salicylate phenoxyl radicals. Altogether, this study demonstrates that oxidation of anthracyclines is mediated by peroxidase metabolites of salicylic acid, such as phenoxyl radicals and the biphenol quinone. Given that cancer patients undergoing anthracycline chemotherapy may be administered salicylic acid-based drugs to control pain and fever, our results suggest that liberated salicylic acid could interfere with anticancer and/or cardiotoxic actions of the anthracyclines.

Cost implications of post-surgical morbidity following blood transfusion in cancer patients undergoing elective colorectal resection: an evaluation in the US hospital setting

OBJECTIVE

To estimate the cost implications of blood transfusions and related surgical site infections (SSIs) in cancer patients undergoing elective colorectal resection in the hospital setting in the United States (US).

STUDY DESIGN

A modelling study was performed from the perspective of the hospital sector, based on published clinical outcomes from a study in Taiwan involving 2809 cancer patients who underwent elective colorectal resection using laparotomy and American treatment patterns.

METHODS

Data on resource use were retrieved from published literature and from two American hospital centres specialising in colorectal cancer management. Decision analytical modelling was used to estimate the treatment costs and consequences of managing patients undergoing elective colorectal resection with and without blood transfusions.

RESULTS

The expected treatment costs of managing patients who required and did not require a blood transfusion were estimated to be US dollars 19,869 (95% CI: 15 797; 23 150) and US dollars 14,586 (95% CI: 14 263; 14 886) per patient respectively. Expected treatment costs for those patients transfused with 1-3 units and > 3 units of blood were estimated to be US dollars 17,449 and US dollars 22,588 per patient respectively.

CONCLUSION

This is one of the first studies to specifically address the cost implications of postsurgical morbidity following colorectal resection in cancer patients. The cost of managing cancer patients undergoing elective colorectal resection who require a blood transfusion is expected to be 36% more than that of non-transfused patients, largely resulting from the development of SSIs.

Prevention of colorectal cancer through the use of COX-2 selective inhibitors

Colorectal cancer is a major cause of morbidity and mortality accounting for an estimated 550,000 deaths annually worldwide. Colonic neoplasia develops in a stepwise fashion progressing from normal mucosa to adenomatous polyps to carcinoma, a process that takes years, thereby providing a prime opportunity for intervention. Although early detection by fecal occult blood testing and sigmoidoscopy can decrease the risk of cancer-related death by 20-30%, most persons never undergo appropriate screening. Population-based studies have previously determined that long-term ingestion of aspirin or other nonsteroidal antiinflammatory drugs (NSAIDs) leads to a 40-50% reduction in mortality. from colorectal cancer. These observational studies fueled subsequent mechanistic investigations that led to the identification of a molecular target, cyclooxygenase-2 (COX-2). COX-2 has tumor-promoting properties. Expression of COX-2 is virtually undetectable in normal intestinal mucosa, but is increased in approximately 50% of colonic adenomas and in 90% of colorectal carcinomas. Experimental studies in mice have revealed that genetic ablation or pharmacologic inhibition of COX-2 attenuates the number and size of intestinal polyps that develop in animals harboring a mutation in Apc, which confers an increased risk for intestinal neoplasia. Recent clinical studies using specific COX-2 inhibitors have shown that these compounds can: (1) reduce intestinal polyp burden in patients with familial adenomatous polyposis; (2) prevent the occurrence and/ or recurrence of colorectal adenomas and cancers; and (3) negatively regulate angiogenesis in colorectal cancer liver metastases. Compared to nonselective NSAIDs, COX-2 specific inhibitors cause substantially fewer gastrointestinal side effects. These findings indicate that a widely used and relatively safe class of drugs may represent a viable and effective anticancer strategy for a disease that causes over a half-million deaths per year.

Methionine sulfoxide reductases: history and cellular role in protecting against oxidative damage

An enzyme that can reduce methionine sulfoxide in proteins was first discovered in Escherichia coli about 25 years ago. It is now apparent that there is a family of enzymes, referred to as methionine sulfoxide reductases (Msr), and in recent years there has been considerable interest in one of the members of the Msr family, MsrA. This enzyme has been shown to protect cells against oxidative damage, which suggests a possible role in a large number of age-related diseases. This review summarizes the history of the discovery of MsrA, properties of the enzyme and its role in protecting cells against oxidative damage. Other members of the Msr family that differ in substrate specificity and localization are described as well as a possible role for the Msr system in drug metabolism. The concept that the Msr system can be used to develop novel drugs that could be catalytic anti-oxidants is discussed.

Antioxidant supplements for preventing gastrointestinal cancers

BACKGROUND

Oxidative stress may cause gastrointestinal cancers. The evidence on whether antioxidant supplements are effective in preventing gastrointestinal cancers is contradictory.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements in preventing gastrointestinal cancers.

SEARCH STRATEGY

We identified trials through the trials registers of the four Cochrane Review Groups on gastrointestinal diseases, The Cochrane Central Register of Controlled Trials on The Cochrane Library (Issue 1, 2003), MEDLINE, EMBASE, LILACS, and SCI-EXPANDED from inception to February 2003, and The Chinese Biomedical Database (March 2003). We scanned reference lists and contacted pharmaceutical companies.

SELECTION CRITERIA

Randomised trials comparing antioxidant supplements to placebo/no intervention examining the incidence of gastrointestinal cancers.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected trials for inclusion and extracted data. The outcome measures were incidence of gastrointestinal cancers, overall mortality, and adverse events. Outcomes were reported as relative risks (RR) with 95% confidence interval (CI) based on fixed and random effects meta-analyses.

MAIN RESULTS

We identified 14 randomised trials (170,525 participants), assessing beta-carotene (9 trials), vitamin A (4 trials), vitamin C (4 trials), vitamin E (5 trials), and selenium (6 trials). Trial quality was generally high. Heterogeneity was low to moderate. Neither the fixed effect (RR 0.96, 95% CI 0.88 to 1.04) nor random effects meta-analyses (RR 0.90, 95% CI 0.77 to 1.05) showed significant effects of supplementation with antioxidants on the incidences of gastrointestinal cancers. Among the seven high-quality trials reporting on mortality (131,727 participants), the fixed effect (RR 1.06, 95% CI 1.02 to 1.10) unlike the random effects meta-analysis (RR 1.06, 95% CI 0.98 to 1.15) showed that antioxidant supplements significantly increased mortality. Two low-quality trials (32,302 participants) found no significant effect of antioxidant supplementation on mortality. The difference between the mortality estimates in high- and low-quality trials was significant by test of interaction (z = 2.10, P = 0.04). Beta-carotene and vitamin A (RR 1.29, 95% CI 1.14 to 1.45) and beta-carotene and vitamin E (RR 1.10, 95% CI 1.01 to 1.20) significantly increased mortality, while beta-carotene alone only tended to do so (RR 1.05, 95% CI 0.99 to 1.11). Increased yellowing of the skin and belching were non-serious adverse effects of beta-carotene. In four trials (three with unclear/inadequate methodology), selenium showed significant beneficial effect on gastrointestinal cancer incidences.

REVIEWERS' CONCLUSIONS

We could not find evidence that antioxidant supplements prevent gastrointestinal cancers. On the contrary, they seem to increase overall mortality. The potential cancer preventive effect of selenium should be studied in adequately conducted randomised trials.

Arachidonic acid and colorectal carcinogenesis

Colorectal carcinoma is a leading cause of cancer related death worldwide. This deadly disease advances through a series of clinical and histopathological stages, initiated by single crypt lesions to small benign tumors and finally to malignancy. Although some progress has been made in elucidating the formation of colorectal tumors at molecular/genetic levels, the possible mechanisms of dietary lipids in inducing and promoting colorectal tumorigenesis are poorly understood. Recent epidemiological studies, however, indicate that lipid-rich diet containing omega-6 fatty acids (i.e. linoleic acid, arachidonic acid, etc.) may somehow be related with the disease process. Rapid metabolism of arachidonic acid, increased activities of phospholipases (i.e. phospholipase-A2s), and the elevated levels of cyclooxygenase (COX) and lipoxygenase (LOX) in colonic cells were reported in various stages of the malignancy, suggesting a possible link between dietary lipids and the incidence of colorectal cancer. The major focus of this review is to delineate the recent findings on enhanced arachidonic acid metabolism and its conversion into eicosanoids during the initiation and progression of colorectal carcinogenesis. In addition, the identification and participation of various phospholipases are also discussed. It is speculated that many of these phospholipases can be used as targets for developing new drugs against colorectal as well as other adenocarcinomas.

Arachidonic acid and colorectal carcinogenesis

Colorectal carcinoma is a leading cause of cancer related death worldwide. This deadly disease advances through a series of clinical and histopathological stages, initiated by single crypt lesions to small benign tumors and finally to malignancy. Although some progress has been made in elucidating the formation of colorectal tumors at molecular/genetic levels, the possible mechanisms of dietary lipids in inducing and promoting colorectal tumorigenesis are poorly understood. Recent epidemiological studies, however, indicate that lipid-rich diet containing omega-6 fatty acids (i.e. linoleic acid, arachidonic acid, etc.) may somehow be related with the disease process. Rapid metabolism of arachidonic acid, increased activities of phospholipases (i.e. phospholipase-A2s), and the elevated levels of cyclooxygenase (COX) and lipoxygenase (LOX) in colonic cells were reported in various stages of the malignancy, suggesting a possible link between dietary lipids and the incidence of colorectal cancer. The major focus of this review is to delineate the recent findings on enhanced arachidonic acid metabolism and its conversion into eicosanoids during the initiation and progression of colorectal carcinogenesis. In addition, the identification and participation of various phospholipases are also discussed. It is speculated that many of these phospholipases can be used as targets for developing new drugs against colorectal as well as other adenocarcinomas.

Selective nonsteroidal anti-inflammatory drugs induce thymosin beta-4 and alter actin cytoskeletal organization in human colorectal cancer cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used for their anti-inflammatory effects and have been shown to have chemopreventive effects as well. NSAIDs inhibit cyclooxygenase (COX) activity to exert their anti-inflammatory effects, but it is not clear whether their antitumorigenic ability is through COX inhibition. Using subtractive hybridization, we previously identified a novel member of the transforming growth factor-beta superfamily that has antitumorigenic activity from indomethacin-treated HCT-116 human colorectal cancer cells. On further investigation of this library, we now report the identification of a new cDNA corresponding to the thymosin beta-4 gene. Thymosin beta-4 is a small peptide that is known for its actin-sequestering function, and it is associated with the induction of angiogenesis, accelerated wound healing, and metastatic potential of tumor cells. However, only selective NSAIDs induce thymosin beta-4 expression in a time- and concentration-dependent manner. For example, indomethacin and SC-560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole] induce thymosin beta-4 expression whereas sulindac sulfide does not. We show that selective NSAIDs induce actin cytoskeletal reorganization, a precursory step to many dynamic processes regulating growth and motility including tumorigenesis. This is the first report to link thymosin beta-4 induction with NSAIDs. These data suggest that NSAIDs alter the expression of a diverse number of genes and provide new insights into the chemopreventive and biological activity of these drugs.

Cell Proliferation and Apoptotic Indices Predict Adenoma Regression in a Placebo-Controlled Trial of Celecoxib in Familial Adenomatous Polyposis Patients

Background: Celecoxib was shown to regress colorectal adenomas in familial adenomatous polyposis (FAP) patients relative to placebo. To address the mechanism of polyp regression, we determined whether celecoxib can modulate cell proliferation, apoptosis, and prostaglandin E2 (PGE2) levels in colorectal epithelia from FAP trial participants and whether such alterations correlate with observed reductions in polyp number. Materials and Methods: Colorectal mucosal biopsies were obtained at baseline and on last day of celecoxib (100 or 400 mg twice daily) or placebo administration (6 months). Residual paraffin-embedded adenomas and normal mucosa from the same patients (n = 17) or normal tissue alone (n = 15) were analyzed. Immunoperoxidase staining for Ki-67 was performed and apoptotic cells were identified by their morphology. Ki-67 and apoptotic labeling indices and their ratios were calculated in superficials (s) and nonsuperficial (ns) regions of adenomas and normal mucosa, and baseline to 6-month differences were calculated. PGE2 levels were analyzed by mass spectroscopy (normal, n = 64; adenoma, n = 56). Biomarkers were analyzed by treatment arm and correlated with previously determined mean percentage reductions in colorectal polyp number. Results: In adenomas, a reduction in the superficial proliferative activity i.e., Ki-67s labeling index, accompanied polyp regression (r = −0.76, P = 0.006). An increase in the apoptotic ratio [i.e., superficial apoptotic index (AIs)/nonsuperficial apoptotic index (AIns)] was found to correlate with reduced polyp counts in that higher apoptotic ratios correlated with better response to celecoxib (r = 0.71, P = 0.004). Furthermore, the AIs/Ki-67s ratio (r = 0.58, P = 0.026) accompanied polyp regression. In normal mucosa, a trend toward increased AIs (r = 0.33, P = 0.053) and polyp regression was found. PGE2 levels did not significantly correlate with polyp regression. Changes in biomarker levels (baseline to 6 months) were correlated in adenomas and normal mucosa (AIs, r = 0.29, P = 0.024; AIns, r = 0.34, P = 0.009; PGE2, r = 0.50, P = 0.059) within individual patients. Conclusion: Suppression of cell proliferation and an increased apoptotic ratio, as well as the ratio of apoptosis to cell proliferation, accompany polyp regression in a chemoprevention trial in FAP patients. These findings suggest potential mechanisms for the efficacy of celecoxib and warrant further study of these biomarkers as intermediate endpoints in FAP patients.

Reduction of Sulindac to its active metabolite, sulindac sulfide: assay and role of the methionine sulfoxide reductase system

Sulindac is a known anti-inflammatory drug that functions by inhibition of cyclooxygenases 1 and 2 (COX). There has been recent interest in Sulindac and other non-steroidal anti-inflammatory drugs (NSAID) because of their anti-tumor activity against colorectal cancer. Studies with sulindac have indicated that it may also function as an anti-tumor agent by stimulating apoptosis. Sulindac is a pro-drug, containing a methyl sulfoxide group, that must be reduced to sulindac sulfide to be active as a COX inhibitor. In the present studies we have developed a simple assay to measure sulindac reduction and tested sulindac as a substrate for 6 known members of the methionine sulfoxide reductase (Msr) family that have been identified in Escherichia coli. Only MsrA and a membrane associated Msr can reduce sulindac to the active sulfide. The reduction of sulindac also has been demonstrated in extracts of calf liver, kidney, and brain. Sulindac reductase activity is also present in mitochondria and microsomes.

Chemoprevention for pancreatic cancer

For a number of solid tumors, including pancreatic cancer, efforts aimed at disease prevention may be more successful than currently available anticancer treatments. While specific interventions are emerging to prevent breast, prostate, lung, and colorectal cancer, no trials of chemoprevention are being conducted in pancreatic cancer. Importantly, there are significant obstacles to the conduct of such research. However, preclinical and epidemiologic studies suggest that several drugs may have chemopreventive potential in pancreatic cancer. These include aspirin and other non-steroidal antiinflammatory drugs (NSAIDs), selective cyclooxygenase inhibitors, somatostatin analogs, selective estrogen receptor modulators (SERMs), and anti-androgenic agents. As the oncology community evaluates some of these agents in large chemoprevention trials for breast, colon, and prostate cancer, it may be found that pancreatic cancer prevention occurs as an unintended, but desirable consequence. Moreover, other general societal trends, such as smoking cessation and the widespread use of cholesterol-lowering agents and aspirin, could have a role in reducing the risk of pancreatic cancer, and in the future, may lead to a decrease in its incidence.

Review article: chemoprevention of colorectal cancer

Colorectal cancer is a disease with a high mortality at present, due to the late stage at which many cases present. Attention is therefore focusing on preventative strategies for colorectal cancer given that polyps appear to be identifiable and treatable precursor lesions of this disease. Endoscopic polypectomy has been shown to reduce the incidence of colorectal cancer and there is a good case for endoscopic screening of the general population. However, this will require a large amount of manpower and resources and its success will also depend on the overall compliance of the population. Epidemiological studies have shown that individuals reporting a regular intake of aspirin and other non-steroidal anti-inflammatory drugs have a reduced risk of developing colorectal polyps and cancer. Similarly, a number of natural substances, such as calcium and folate, when supplemented regularly in the diet, have also been linked to a possible decreased incidence of colorectal cancer. This has led to the concept of using such agents to reduce the number of cases of colorectal cancer. In this article, we review the current evidence for the use of these and other agents for the chemoprevention of colorectal cancer, together with theories as to their possible mechanisms of action.