beta-Catenin-accumulated crypts in the colonic mucosa of juvenile ApcMin/+ mice

Sunitinib malate inhibits intestinal tumor development in male ApcMin/+ mice by down-regulating inflammation-related factors with suppressing β-cateinin/c-Myc pathway and re-balancing Bcl-6 and Caspase-3

Sunitinib is a tyrosine kinase inhibitor for many tumors. Inflammation is one of the most important factors in the development of intestinal tumors. Many inflammation-related factors are regulated by tyrosine kinase receptors. It is reasonable to hypothesize that sunitinib can regulate the development of intestinal tumors by regulating the expression and/or activity of inflammation-related factors. Here, ApcMin/+ male mouse model was used to investigate the effect and mechanism of sunitinib malate against intestinal cancer. Results show that compared to vehicle, after sunitinib malate treatment, overall survival of ApcMin/+ mice was lengthened up to 25 days, with a gain of body weight, reduction of spleen/body weight index, and RBC, WBC and HGC regulated to normal levels of wild type mice, and a number of polyps no less than 1 mm significantly reduced. Meanwhile, in the intestines, the nuclear β-Catenin protein and c-Myc mRNA were both down-regulated, and Bcl-6 was significantly reduced with Caspase-3 up regulated. Furthermore, inflammation-related factors including IL-6, TNF-α, IL-1α, IL-1β and IFN-γ were down-regulated at mRNA levels in the intestines. These results suggest that sunitinib malate can significantly improve the survival status and inhibit intestinal tumor development in male ApcMin/+ mice, through inhibiting inflammation-related factors, while suppressing β-cateinin/c-Myc pathway and re-balancing protein levels of Bcl-6 and Caspase-3.

Lipocalin 2 performs contrasting, location-dependent roles in APCmin tumor initiation and progression

Evidence that lipocalin 2 (LCN2) is oncogenic has grown in recent years and comes from both animal models and expression analysis from a variety of human cancers. In the intestine, LCN2 is overexpressed in colitis patients and its overexpression is a negative prognostic indicator in colorectal cancer. Functionally, LCN2 has a number of different activities that may contribute to its oncogenic potential, including increasing matrix metalloproteinase activity, control of iron availability and stimulating inflammation. In this report, we examined APCmin intestinal tumorigenesis in an LCN2-deficient background. We found that the loss of LCN2 increased tumor multiplicity specifically in the duodenum, suggesting a potential tumor-suppressive activity. Concurrently, however, LCN2 increased the average small intestinal tumor size particularly in the distal small intestine. We found that this increase was correlated to tumor iron(II) content, suggesting that an iron-scavenging role is important for LCN2 oncogenic activity in the intestine.

Development of an inflammation-associated colorectal cancer model and its application for research on carcinogenesis and chemoprevention

Chronic inflammation is a well-recognized risk factor for development of human cancer in several tissues, including large bowel. Inflammatory bowel disease, including ulcerative colitis and Crohn's disease, is a longstanding inflammatory disease of intestine with increased risk for colorectal cancer development. Several molecular events involved in chronic inflammatory process may contribute to multistep carcinogenesis of human colorectal cancer in the inflamed colon. They include overproduction of reactive oxygen and nitrogen species, overproduction and upregulation of productions and enzymes of arachidonic acid biosynthesis pathway and cytokines, and intestinal immune system dysfunction. In this paper, I will describe several methods to induce colorectal neoplasm in the inflamed colon. First, I will introduce a protocol of a novel inflammation-associated colon carcinogenesis in mice. In addition, powerful tumor-promotion/progression activity of dextran sodium sulfate in the large bowel of Apc^Min/+ mice will be described. Finally, chemoprevention of inflammation-associated colon carcinogenesis will be mentioned.

Monosodium glutamate-induced diabetic mice are susceptible to azoxymethane-induced colon tumorigenesis

Obese people and diabetic patients are known to be high risk of colorectal cancer (CRC), suggesting need of a new preclinical animal model, by which to extensively study the diverse mechanisms, therapy and prevention. The present study aimed to determine whether experimental obese and diabetic mice produced by monosodium glutamate (MSG) treatment are susceptible to azoxymethane (AOM)-induced colon tumorigenesis using early biomarkers, aberrant crypts foci (ACF) and β-catenin-accumulated crypts (BCACs), of colorectal carcinogenesis. Male Crj:CD-1 (ICR) newborns were daily given four subcutaneous injections of MSG (2 mg/g body wt) to induce diabetes and obesity. They were then given four intraperitoneal injections of AOM (15 mg/kg body wt) or saline (0.1 ml saline/10 g body wt). Ten weeks after the last injection of AOM, the MSG-AOM mice had a significant increase in the multiplicity of BCAC (13.83 ± 7.44, P < 0.002), but not ACF (78.00 ± 11.20), when compare to the Saline-AOM mice (5.45 ± 1.86 of BCAC and 69.27 ± 8.06 of ACF). Serum biochemical profile of the MSG-treated mice with or without AOM showed hyperinsulinemia, hypercholesteremia and hyperglycemia. The mRNA expression of insulin-like growth factor-1 receptor (IGF-1R, P<0.01) was increased in the MSG-AOM mice, when compared with the mice given AOM alone. IGF-1R was immunohistochemically expressed in the BCAC, but not ACF, in the AOM-treated mice. Our findings suggest that the MSG mice are highly susceptible to AOM-induced colorectal carcinogenesis, suggesting potential utility of our MSG-AOM mice for further investigation of the possible underlying events that affect the positive association between obese/diabetes and CRC.

C57BL/KsJ-db/db-Apc mice exhibit an increased incidence of intestinal neoplasms

The numbers of obese people and diabetic patients are ever increasing. Obesity and diabetes are high-risk conditions for chronic diseases, including certain types of cancer, such as colorectal cancer (CRC). The aim of this study was to develop a novel animal model in order to clarify the pathobiology of CRC development in obese and diabetic patients. We developed an animal model of obesity and colorectal cancer by breeding the C57BL/KsJ-db/db (db/db) mouse, an animal model of obesity and type II diabetes, and the C57BL/6J-Apc(Min/+) (Min/+) mouse, a model of familial adenomatous polyposis. At 15 weeks of age, the N9 backcross generation of C57BL/KsJ-db/db-Apc(Min/+) (db/db-Min/+) mice developed an increased incidence and multiplicity of adenomas in the intestinal tract when compared to the db/m-Min/+ and m/m-Min/+ mice. Blood biochemical profile showed significant increases in insulin (8.3-fold to 11.7-fold), cholesterol (1.2-fold to 1.7-fold), and triglyceride (1.2-fold to 1.3-fold) in the db/db-Min/+ mice, when compared to those of the db/m-Min/+ and m/m-Min/+ mice. Increases (1.4-fold to 2.6-fold) in RNA levels of insulin-like growth factor (IGF)-1, IRF-1R, and IGF-2 were also observed in the db/db- Min/+ mice. These results suggested that the IGFs, as well as hyperlipidemia and hyperinsulinemia, promoted adenoma formation in the db/db-Min/+ mice. Our results thus suggested that the db/db-Min/+ mice should be invaluable for studies on the pathogenesis of CRC in obese and diabetes patients and the therapy and prevention of CRC in these patients.

Mthfd1 is a modifier of chemically induced intestinal carcinogenesis

The causal metabolic pathways underlying associations between folate and risk for colorectal cancer (CRC) have yet to be established. Folate-mediated one-carbon metabolism is required for the de novo synthesis of purines, thymidylate and methionine. Methionine is converted to S-adenosylmethionine (AdoMet), the major one-carbon donor for cellular methylation reactions. Impairments in folate metabolism can modify DNA synthesis, genomic stability and gene expression, characteristics associated with tumorigenesis. The Mthfd1 gene product, C1-tetrahydrofolate synthase, is a trifunctional enzyme that generates one-carbon substituted tetrahydrofolate cofactors for one-carbon metabolism. In this study, we use Mthfd1(gt/+) mice, which demonstrate a 50% reduction in C1-tetrahydrofolate synthase, to determine its influence on tumor development in two mouse models of intestinal cancer, crosses between Mthfd1(gt/+) and Apc(min)(/+) mice and azoxymethane (AOM)-induced colon cancer in Mthfd1(gt/+) mice. Mthfd1 hemizygosity did not affect colon tumor incidence, number or load in Apc(min/+) mice. However, Mthfd1 deficiency increased tumor incidence 2.5-fold, tumor number 3.5-fold and tumor load 2-fold in AOM-treated mice. DNA uracil content in the colon was lower in Mthfd1(gt/+) mice, indicating that thymidylate biosynthesis capacity does not play a significant role in AOM-induced colon tumorigenesis. Mthfd1 deficiency-modified cellular methylation potential, as indicated by the AdoMet: S-adenosylhomocysteine ratio and gene expression profiles, suggesting that changes in the transcriptome and/or decreased de novo purine biosynthesis and associated mutability cause cellular transformation in the AOM CRC model. This study emphasizes the impact and complexity of gene-nutrient interactions with respect to the relationships among folate metabolism and colon cancer initiation and progression.

Carcinogenic effects of exogenous and endogenous glucagon-like peptide-2 in azoxymethane-treated mice

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent intestinotropic hormone that promotes intestinal growth, via increased intestinal proliferation and decreased apoptosis, as well as increases in nutrient absorption and barrier function. The long-acting analog h(Gly(2))GLP-2[1-33] is currently being tested for treatment of short bowel syndrome and Crohn's disease. However, the role of GLP-2 in colon carcinogenesis is controversial. To assess the intestinotropic effects of exogenous and endogenous GLP-2, C57BL6/J mice were injected with 1 microg h(Gly(2))GLP-2[1-33]; 30 or 60 ng hGLP-2[3-33], a GLP-2 receptor antagonist; or PBS (4 wk, twice a day, sc). Chronic h(Gly(2))GLP-2[1-33] increased small intestinal weight/body weight (P < 0.001), villus height (P < 0.001), crypt depth (P < 0.001), and crypt cell proliferation, as measured by expression of the proliferative marker Ki67 (P < 0.05-0.01). In contrast, chronic hGLP-2[3-33] decreased small intestinal weight/body weight (P < 0.05) and colon weight/body weight (P < 0.05). To assess the carcinogenic effects of endogenous and exogenous GLP-2, separate mice were injected with azoxymethane (10 mg/kg, 4 wk, every 7 d, ip), followed by 1.5 microg h(Gly(2))GLP-2[1-33], 30 ng hGLP-2[3-33], or PBS (4 wk, twice a day, sc) 2 or 12 wk thereafter. At 10 or 46 wk after azoxymethane treatment, the numbers of aberrant crypt foci increased with h(Gly(2))GLP-2[1-33] (P < 0.001) and decreased with hGLP-2[3-33] (P < 0.01-0.05) treatment. Furthermore, mucin-depleted aberrant foci, consistent with progressive dysplasia, were almost exclusively present in h(Gly(2))GLP-2[1-33]-treated mice (P < 0.01-0.001). Additionally, adenocarcinomas developed in h(Gly(2))GLP-2[1-33]-treated mice but not in those receiving hGLP-2[3-33] or PBS. Taken together, these studies indicate that chronic treatment with GLP-2 enhances colon carcinogenesis, whereas antagonism of the GLP-2 receptor decreases dysplasia, with possible implications for human therapy.

Supplementation with branched-chain amino acids inhibits azoxymethane-induced colonic preneoplastic lesions in male C57BL/KsJ-db/db mice

PURPOSE

Obesity and related metabolic abnormalities, including insulin resistance and activation of the insulin-like growth factor (IGF)/IGF-I receptor (IGF-IR) axis, are risk factors for colon cancer. Supplementation with branched-chain amino acids (BCAA) reduces the risk of liver cancer in cirrhotic patients who are obese, and this has been associated with an improvement of insulin resistance. The present study examined the effects of BCAA on the development of azoxymethane (AOM)-initiated colonic premalignant lesions in C57BL/KsJ-db/db (db/db) mice that were obese and had hyperinsulinemia.

EXPERIMENTAL DESIGN

Male db/db mice were given 4 weekly s.c. injections of AOM (15 mg/kg of body weight) and then they were fed a diet containing 3.0% BCAA or casein, a nitrogenc content-matched control diet, for 7 weeks.

RESULTS

Feeding with BCAA caused a significant reduction in the number of total aberrant crypt foci and beta-catenin accumulated crypts, both of which are premalignant lesions of the colon, compared with the control diet-fed groups. BCAA supplementation caused a marked decrease in the expression of IGF-IR, the phosphorylated form of IGF-IR, phosphorylated glycogen synthase kinase 3beta, phosphorylated Akt, and cyclooxygenase-2 proteins on the colonic mucosa of AOM-treated mice. The serum levels of insulin, IGF-I, IGF-II, triglyceride, total cholesterol, and leptin were also decreased by supplementation with BCAA.

CONCLUSION

BCAA supplementation in diet improves insulin resistance and inhibits the activation of the IGF/IGF-IR axis, thereby preventing the development of colonic premalignancies in an obesity-related colon cancer model that was also associated with hyperlipidemia and hyperinsulinemia. BCAA, therefore, may be a useful chemoprevention modality for colon cancer in obese people.

(-)-Epigallocatechin gallate suppresses azoxymethane-induced colonic premalignant lesions in male C57BL/KsJ-db/db mice

Obesity and diabetes mellitus are risk factors for colon cancer. The activation of the insulin-like growth factor (IGF)/IGF-IR axis plays a critical role in this carcinogenesis. (-)-Epigallocatechin gallate (EGCG), the major constituent of green tea, seems to have both antiobesity and antidiabetic effects. This study examined the effects of EGCG on the development of azoxymethane-induced colonic premalignant lesions in C57BL/KsJ-db/db (db/db) mice, which are obese and develop diabetes mellitus. Male db/db mice were given four weekly s.c. injections of azoxymethane (15 mg/kg body weight) and then they received drinking water containing 0.01% or 0.1% EGCG for 7 weeks. At sacrifice, drinking water with EGCG caused a significant decrease in the number of total aberrant crypt foci, large aberrant crypt foci, and beta-catenin accumulated crypts in these mice, all of which are premalignant lesions of the colon. The colonic mucosa of db/db mice expressed high levels of the IGF-IR, phosphorylated form of IGF-IR (p-IGF-IR), p-GSK-3beta, beta-catenin, cyclooxygenase-2, and cyclin D1 proteins, and EGCG in drinking water caused a marked decrease in the expression of these proteins. Treating these mice with EGCG also caused an increase in the serum level of IGFBP-3 while conversely decreasing the serum levels of IGF-I, insulin, triglyceride, cholesterol, and leptin. EGCG overcomes the activation of the IGF/IGF-IR axis, thereby inhibiting the development of colonic premalignant lesions in an obesity-related colon cancer model, which was also associated with hyperlipidemia, hyperinsulinemia, and hyperleptinemia. EGCG may be, therefore, useful in the chemoprevention or treatment of obesity-related colorectal cancer.

Citrus compounds inhibit inflammation- and obesity-related colon carcinogenesis in mice

Dietary polyphenols are important potential chemopreventive natural agents. Other agents, such as citrus compounds, are also candidates for cancer chemopreventives. They act on multiple key elements in signal transduction pathways related to cellular proliferation, differentiation, apoptosis, inflammation, and obesity. This short review article provides our findings of preclinical studies on potential chemopreventive activities of dietary citrus compounds, auraptene, collinin, and citrus unshiu segment membrane (CUSM), using clitis- and obesity-related colon tumorigenesis models. Dietary feeding with auraptene and collinin at dose levels of 0.01% and 0.05% significantly lowered the incidence (50-60% reduction) and multiplicity (67-80% reduction) of colonic adenocarcinomas induced by azoxymetahene [AOM, single intraperitoneal injection of 10 mg/kg body weight (bw)] and dextran sodium sulfate (1% in drinking water). Anti-inflammatory potency of aurapene and collinin may contribute to the effects. Administration with CUSM at 3 doses in diet significantly inhibited development of aberrant crypts foci induced by 5 weekly subcutaneous injections of AOM (15 mg/kg bw) in male db/db mice: 53% inhibition by 0.02% CUSM, 54% inhibition by 0.1% CUSM, and 59% inhibition by 0.5% CUSM. CUSM treatment also decreased serum level of triglycerides. Our findings suggest that certain citrus materials are capable of inhibiting clitis- and obesity-related colon carcinogenesis.

A simple colostomy implantation model for evaluating colon cancer

PURPOSE

Realistic models of colorectal cancer are necessary to study cancer biology and evaluate therapeutic interventions. Real-time observation and repeated sampling of implanted tumor is difficult to achieve in the current orthotopic animal colorectal cancer model. The aim of this study was to establish a simple colostomy implantation mouse model for evaluating colon cancer.

EXPERIMENTAL DESIGN

The human colon cancer cell line LoVo was injected subcutaneously into the necks of five mice to generate a solid tumor. Colostomies were created from the ceca of 14 nude mice. Fragments from the solid tumors were then harvested and implanted into the submucosa of the stoma. Half of the tumor-bearing mice were treated with 5-fluorouracil (5-FU) and all were monitored for tumor growth and survival. Tumor tissue was taken at different time points to evaluate pathological changes, expression of hMSH2 and P53, and microsatellite instability (MSI).

RESULTS

The stoma healed 2 weeks after the surgery. Twelve mice had developed detectable colon tumor 2 to 3 weeks after implantation of human colon cancer LoVo cells into the colostomy with mesenteric lymph node metastases. The median survival was 13 weeks. Histopathological and immunohistochemical examinations of tumor tissues collected at different time points of tumor progression showed similar histopathological changes and hMSH2 and P53 expression patterns to the original cell line. MSI analysis showed that five tumors were MSI-L from the second week after tumor implantation and all 12 colostomy tumors were MSI-H from 4 weeks after implantation. The tumors were highly sensitive to 5-FU treatment, which lead to a longer median survival of 15 weeks (P = 0.0374) and significant tumor growth inhibition.

CONCLUSION

This study demonstrates that a colostomy implantation mouse model is an ideal model for evaluating colon cancer. Its advantages include high tumor take rate, easy real-time visualization, easy repeated sampling of the implanted tumor in live animals, and significant sensitivity to a commonly used chemotherapeutic agent.

Mouse models for the study of colon carcinogenesis

The study of experimental colon carcinogenesis in rodents has a long history, dating back almost 80 years. There are many advantages to studying the pathogenesis of carcinogen-induced colon cancer in mouse models, including rapid and reproducible tumor induction and the recapitulation of the adenoma-carcinoma sequence that occurs in humans. The availability of recombinant inbred mouse panels and the existence of transgenic, knock-out and knock-in genetic models further increase the value of these studies. In this review, we discuss the general mechanisms of tumor initiation elicited by commonly used chemical carcinogens and how genetic background influences the extent of disease. We will also describe the general features of lesions formed in response to carcinogen treatment, including the underlying molecular aberrations and how these changes may relate to the pathogenesis of human colorectal cancer.

Effect of exercise on biological pathways in ApcMin/+ mouse intestinal polyps

Many epidemiological studies have demonstrated that level of exercise is associated with reduced colorectal cancer risk. Treadmill training can decrease Apc(Min/+) mouse intestinal polyp number and size, but the mechanisms remain unclear. Understanding the molecular changes in the tumor following exercise training may provide insight on the mechanism by which exercise decreases Apc(Min/+) mouse polyp formation and growth. The purpose of this study was to determine if exercise can modulate Apc(Min/+) mouse intestinal polyp cellular signaling related to tumor formation and growth. Male Apc(Min/+) mice were randomly assigned to control (n = 20) or exercise (n = 20) treatment groups. Exercised mice ran on a treadmill at a moderate intensity (18 m/min, 60 min, 6 days/wk, 5% grade) for 9 wk. Polyps from Apc(Min/+) mice were used to quantify markers of polyp inflammation, apoptosis, and beta-catenin signaling. Exercise decreased the number of macrophages in polyps by 35%. Related to apoptosis, exercise decreased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells by 73% in all polyps. Bax protein expression in polyps was decreased 43% by exercise. beta-Catenin phosphorylation was elevated 3.3-fold in polyps from exercised mice. Moderate-intensity exercise training alters cellular pathways in Apc(Min/+) mouse polyps, and these changes may be related to the exercise-induced reduction in polyp formation and growth.

Diet supplemented with citrus unshiu segment membrane suppresses chemically induced colonic preneoplastic lesions and fatty liver in male db/db mice

The modulatory effects of dietary citrus unshiu segment membrane (CUSM) on the occurrence of aberrant crypt foci (ACF) and beta-catenin accumulated crypts (BCACs) were determined in male C57BL/KsJ-db/db (db/db) mice initiated with azoxymethane (AOM). Male db/db, db/+ and +/+ mice were given 5 weekly subcutaneous injections of AOM (15 mg/kg body weight), and then they were fed the diet containing 0.02%, 0.1% or 0.5% CUSM for 7 weeks. At Week 12, a significant increase in the numbers of ACF and BCAC was noted in the db/db mice in comparison with the db/+ and +/+ mice. Feeding with CUSM caused reduction in the frequency of ACF in all genotypes of mice and the potency was high in order of the db/db mice, db/+ mice and +/+ mice. The number of BCACs was also reduced by feeding with CUSM, thus resulting in a 28-61% reduction in the db/db mice, possibly due to suppression of cell proliferation activity in the lesions by feeding with CUSM-containing diet. Clinical chemistry revealed a low serum level of triglyceride in mice fed CUSM. In addition, CUSM feeding inhibited fatty metamorphosis and fibrosis in the liver of db/db mice. Our findings show that CUSM in the diet has a chemopreventive ability against the early phase of AOM-induced colon carcinogenesis in the db/db as well as db/+ and +/+ mice, indicating potential use of CUSM in cancer chemoprevention in obese people.