Response of Apc(min) and A33 (delta N beta-cat) mutant mice to treatment with tea, sulindac, and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

Dietary spinach reshapes the gut microbiome in an Apc-mutant genetic background: mechanistic insights from integrated multi-omics

Complex interrelationships govern the dynamic interactions between gut microbes, the host, and exogenous drivers of disease outcome. A multi-omics approach to cancer prevention by spinach (SPI) was pursued for the first time in the polyposis in rat colon (Pirc) model. SPI fed for 26 weeks (10% w/w, freeze-dried in the diet) exhibited significant antitumor efficacy and, in the Apc-mutant genetic background, β-catenin remained highly overexpressed in adenomatous polyps. However, in both wild type and Apc-mutant rats, increased gut microbiome diversity after SPI consumption coincided with reversal of taxonomic composition. Metagenomic prediction implicated linoleate and butanoate metabolism, tricarboxylic acid cycle, and pathways in cancer, which was supported by transcriptomic and metabolomic analyses. Thus, tumor suppression by SPI involved marked reshaping of the gut microbiome along with changes in host RNA-miRNA networks. When colon polyps were compared with matched normal-looking tissues via metabolomics, anticancer outcomes were linked to SPI-derived linoleate bioactives with known anti-inflammatory/ proapoptotic mechanisms, as well as N-aceto-2-hydroxybutanoate, consistent with altered butanoate metabolism stemming from increased α-diversity of the gut microbiome. In colon tumors from SPI-fed rats, L-glutamate and N-acetylneuraminate also were reduced, implicating altered mitochondrial energetics and cell surface glycans involved in oncogenic signaling networks and immune evasion. In conclusion, a multi-omics approach to cancer prevention by SPI provided mechanistic support for linoleate and butanoate metabolism, as well as tumor-associated changes in L-glutamate and N-acetylneuraminate. Additional factors, such as the fiber content, also warrant further investigation with a view to delaying colectomy and drug intervention in at-risk patients.

Optimization of Erlotinib Plus Sulindac Dosing Regimens for Intestinal Cancer Prevention in an Apc-Mutant Model of Familial Adenomatous Polyposis (FAP)

A clinical trial in patients with familial adenomatous polyposis (FAP) demonstrated that sulindac plus erlotinib (SUL+ERL) had good efficacy in the duodenum and colon, but toxicity issues raised concerns for long-term prevention. We performed a biomarker study in the polyposis in rat colon (Pirc) model, observing phosphorylated Erk inhibition in colon polyps for up to 10 days after discontinuing ERL+SUL administration. In a follow-up study lasting 16 weeks, significant reduction of colon and small intestine (SI) tumor burden was detected, especially in rats given 250 ppm SUL in the diet plus once-a-week intragastric dosing of ERL at 21 or 42 mg/kg body weight (BW). A long-term study further demonstrated antitumor efficacy in the colon and SI at 52 weeks, when 250 ppm SUL was combined with once-a-week intragastric administration of ERL at 10, 21, or 42 mg/kg BW. Tumor-associated matrix metalloproteinase-7 (Mmp7), tumor necrosis factor (Tnf), and early growth response 1 (Egr1) were decreased at 16 weeks by ERL+SUL, and this was sustained in the long-term study for Mmp7 and Tnf. Based on the collective results, the optimal dose combination of ERL 10 mg/kg BW plus 250 ppm SUL lacked toxicity, inhibited molecular biomarkers, and exhibited effective antitumor activity. We conclude that switching from continuous to once-per-week ERL, given at one-quarter of the current therapeutic dose, will exert good efficacy with standard-of-care SUL against adenomatous polyps in the colon and SI, with clinical relevance for patients with FAP before or after colectomy. PREVENTION RELEVANCE: This investigation concludes that switching from continuous to once-per-week erlotinib, given at one-quarter of the current therapeutic dose, will exert good efficacy with standard-of-care sulindac against adenomatous polyps in the colon and small intestine, with clinical relevance for patients with FAP before or after colectomy.

Interactions of tea polyphenols with intestinal microbiota and their implication for cellular signal conditioning mechanism

Tea polyphenols (TP) is the main functional substances in tea. It has been reported that TP can modulate the composition of gut microbes in the human body, in addition, after the bio-transformation by intestinal flora, the metabolites of TP also have positive effects on the health of the host. Lots of researches have shown that TP have possible therapeutic effect against high fat diet induced obesity, which is closely related to the gut flora of the host. Therefore, this review focused on the interactions of TP with intestinal microbiota and their implication for cellular signal conditioning mechanism that will enable us to better study the two-way effects of TP and intestinal microbiota on host health improvement. PRACTICAL APPLICATIONS: TP have been widely concerned for their health care properties. As the functional food components, TP have strong antioxidant and physiological activities for human body. A better understanding on the interactions of TP with intestinal microbiota and their implication for cellular signal conditioning mechanism will lead us to better evaluate the contribution of the microbial metabolites of TP, as well as the regulation of intestinal bacterial diversity and abundance for host health.

Polyphenols in Colorectal Cancer: Current State of Knowledge including Clinical Trials and Molecular Mechanism of Action

Polyphenols have been reported to have wide spectrum of biological activities including major impact on initiation, promotion, and progression of cancer by modulating different signalling pathways. Colorectal cancer is the second most major cause of mortality and morbidity among females and the third among males. The objective of this review is to describe the activity of a variety of polyphenols in colorectal cancer in clinical trials, preclinical studies, and primary research. The molecular mechanisms of major polyphenols related to their beneficial effects on colorectal cancer are also addressed. Synthetic modifications and other future directions towards exploiting of natural polyphenols against colorectal cancer are discussed in the last section.

Wnt Signalling-Targeted Therapy in the CMS2 Tumour Subtype: A New Paradigm in CRC Treatment?

Colorectal cancers (CRC) belonging to the consensus molecular subtype 2 (CMS2) have the highest incidence rate, affect mainly the distal colon and rectum, and are characterized by marked Wnt/β-catenin/Transcription Factor 7-Like 2 (TCF7L2) pathway activation and also by activation of epidermal growth factor receptor (EGFR) signalling. Despite having the highest overall survival, CMS2 tumours are often diagnosed at stage III when an adjuvant chemotherapy-based regimen is recommended. Nevertheless, colorectal cancer stem cells (CSCs) and circulating tumour cells may still evade the current therapeutic options and metastasize, stressing the need to develop more tailored therapeutic strategies. For example, activation of EGFR signalling is being used as a target for tailored therapy, however, therapy resistance is frequently observed. Therefore, targeting the Wnt signalling axis represents an additional therapeutic strategy, considering that CMS2 tumours are "Wnt-addicted". Several efforts have been made to identify Wnt antagonists, either of synthetic or natural origin. However, an inverse gradient of Wnt/β-catenin/TCF7L2 signalling activity during CRC progression has been suggested, with early stage and metastatic tumours displaying high and low Wnt signalling activities, respectively, which lead us to revisit the "just-right" signalling model. This may pinpoint the use of Wnt signalling agonists instead of antagonists for treatment of metastatic stages, in a context-dependent fashion. Moreover, the poor immunogenicity of these tumours challenges the use of recently emerged immunotherapies. This chapter makes a journey about CMS2 tumour characterization, their conventional treatment, and how modulation of Wnt signalling or immune response may be applied to CRC therapy. It describes the newest findings in this field and indicates where more research is required.

Divergent roles of p120-catenin isoforms linked to altered cell viability, proliferation, and invasiveness in carcinogen-induced rat skin tumors

The heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) targets multiple organs for tumorigenesis in the rat, including the colon and the skin. PhIP-induced skin tumors were subjected to mutation screening, which identified genetic changes in Hras (7/40, 17.5%) and Tp53 (2/40, 5%), but not in Ctnnb1, a commonly mutated gene in PhIP-induced colon tumors. Despite the absence of Ctnnb1 mutations, β-catenin was overexpressed in nuclear and plasma membrane fractions from PhIP-induced skin tumors, coinciding with loss of p120-catenin from the plasma membrane, and the appearance of multiple p120-catenin-associated bands in the nuclear extracts. Real-time RT-PCR revealed that p120-catenin isoforms 1 and 4 were upregulated in PhIP-induced skin tumors, whereas p120-catenin isoform 3 was expressed uniformly, compared with adjacent normal-looking tissue. In human epidermoid carcinoma and colon cancer cells, transient transfection of p120-catenin isoform 1A enhanced the viability and cell invasion index, whereas transient transfection of p120-catenin isoform 4A increased cell viability and cell proliferation. Knockdown of p120-catenin revealed a corresponding reduction in the expression of β-catenin and a transcriptionally regulated target, Ccnd1/Cyclin D1. Co-immunoprecipitation experiments identified associations of β-catenin with p120-catenin isoforms in PhIP-induced skin tumors and human cancer cell lines. The results are discussed in the context of therapeutic strategies that might target different p120-catenin isoforms, providing an avenue to circumvent constitutively active β-catenin arising via distinct mechanisms in skin and colon cancer.

A hypermorphic epithelial β-catenin mutation facilitates intestinal tumorigenesis in mice in response to compounding WNT-pathway mutations

Activation of the Wnt/β-catenin pathway occurs in the vast majority of colorectal cancers. However, the outcome of the disease varies markedly from individual to individual, even within the same tumor stage. This heterogeneity is governed to a great extent by the genetic make-up of individual tumors and the combination of oncogenic mutations. In order to express throughout the intestinal epithelium a degradation-resistant β-catenin (Ctnnb1), which lacks the first 131 amino acids, we inserted an epitope-tagged ΔN(1-131)-β-catenin-encoding cDNA as a knock-in transgene into the endogenous gpA33 gene locus in mice. The resulting gpA33(ΔN-Bcat) mice showed an increase in the constitutive Wnt/β-catenin pathway activation that shifts the cell fate towards the Paneth cell lineage in pre-malignant intestinal epithelium. Furthermore, 19% of all heterozygous and 37% of all homozygous gpA33(ΔN-Bcat) mice spontaneously developed aberrant crypt foci and adenomatous polyps, at frequencies and latencies akin to those observed in sporadic colon cancer in humans. Consistent with this, the Wnt target genes, MMP7 and Tenascin-C, which are most highly expressed in benign human adenomas and early tumor stages, were upregulated in pre-malignant tissue of gpA33(ΔN-Bcat) mice, but those Wnt target genes associated with excessive proliferation (i.e. Cdnn1, myc) were not. We also detected diminished expression of membrane-associated α-catenin and increased intestinal permeability in gpA33(ΔN-Bcat) mice in challenge conditions, providing a potential explanation for the observed mild chronic intestinal inflammation and increased susceptibility to azoxymethane and mutant Apc-dependent tumorigenesis. Collectively, our data indicate that epithelial expression of ΔN(1-131)-β-catenin in the intestine creates an inflammatory microenvironment and co-operates with other mutations in the Wnt/β-catenin pathway to facilitate and promote tumorigenesis.

The activating mutation R201C in GNAS promotes intestinal tumourigenesis in Apc(Min/+) mice through activation of Wnt and ERK1/2 MAPK pathways

Somatically acquired, activating mutations of GNAS, the gene encoding the stimulatory G-protein Gsα subunit, have been identified in kidney, thyroid, pituitary, leydig cell, adrenocortical and more recently, in colorectal tumours, suggesting that mutations such as R201C may be oncogenic in these tissues. To study the role of GNAS in intestinal tumourigenesis, we placed GNAS R201C under the control of the A33-antigen promoter (Gpa33), which is almost exclusively expressed in the intestines. The GNAS R201C mutation has been shown to result in the constitutive activation of Gsα and adenylate cyclase and to lead to the autonomous synthesis of cAMP. Gpa33^{tm1(GnasR201C)Wtsi/+} mice showed significantly elevated cAMP levels and a compensatory upregulation of cAMP-specific phosphodiesterases in the intestinal epithelium. GNAS R201C alone was not sufficient to induce tumourigenesis by 12 months but there was a significant increase in adenoma formation when Gpa33^{tm1(GnasR201C)Wtsi/+} mice were bred onto an Apc^Min/+ background. GNAS R201C expression was associated with elevated expression of Wnt and extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase (ERK1/2 MAPK) pathway target genes, increased phosphorylation of ERK1/2 MAPK, and increased immunostaining for the proliferation marker Ki67. Furthermore, the effects of GNAS R201C on the Wnt pathway were additive to inactivation of Apc. Our data strongly suggest that activating mutations of GNAS cooperate with inactivation of APC and are likely to contribute to colorectal tumourigenesis.

Overcoming multidrug resistance in human cancer cells by natural compounds

Multidrug resistance is a phenomenon whereby tumors become resistant to structurally unrelated anticancer drugs. P-glycoprotein belongs to the large ATP-binding cassette (ABC) transporter superfamily of membrane transport proteins. P-glycoprotein mediates resistance to various classes of anticancer drugs including vinblastine, daunorubicin, and paclitaxel, by actively extruding the drugs from the cells. The quest for inhibitors of anticancer drug efflux transporters has uncovered natural compounds, including (-)-epigallocatechin gallate, curcumin, capsaicin, and guggulsterone, as promising candidates. In this review, studies on the effects of natural compounds on P-glycoprotein and anticancer drug efflux transporters are summarized.

Endogenous expression of the sodium iodide symporter mediates uptake of iodide in murine models of colorectal carcinoma

The sodium iodide symporter (NIS) mediates iodide uptake into the thyroid. Because of this mechanism, differentiated thyroid cancer is susceptible for radioiodine therapy. Functional NIS expression in extrathyroidal tumors has been reported mainly in breast cancer. We screened colorectal tumors for NIS expression and investigated the mechanisms regulating NIS activity. Cell lines were screened for iodide uptake in vitro and NIS expression was evaluated by real-time RT-PCR, immunocytochemistry and immunoblotting. Iodide and pertechnetate uptake were evaluated in allograft tumors by biodistribution studies and scintigraphy. Tumors of transgenic mouse models for colorectal cancer harboring mutations in the oncogenes KRAS, beta-catenin or the tumor-suppressor gene adenomatous-polyposis coli (APC) were screened for NIS expression by RT-PCR. In vitro, functional NIS activity was detected in murine CMT93 rectal carcinoma cells and NIS expression was verified on mRNA and protein level. Inhibition of tyrosine kinases increased iodide uptake. Inhibition of tyrosine phosphatases decreased iodide uptake. In vivo, functional NIS expression was preserved in CMT93 tumors and tumor uptake could be enhanced by treatment of mice with tyrosine kinase inhibitors. In transgenic murine models of colorectal cancer, 14% of endogenous tumors expressed elevated levels of NIS mRNA. We conclude that NIS is functionally expressed in a subset of murine colorectal tumors and its activity is regulated by tyrosine phosphorylation. Therefore, with specific tyrosine kinase inhibition, these tumors might be susceptible for radioiodine treatment. Further studies are justified to identify the specific pathways regulating NIS activity and to transfer these findings to human cell lines and tissues.

Elevated Dnmt3a activity promotes polyposis in Apc(Min) mice by relaxing extracellular restraints on Wnt signaling

BACKGROUND & AIMS

Aberrant DNA methylation is a common early event in neoplasia, but it is unclear how this relates to dysregulation of DNA (cytosine-5) methyltransferases (Dnmts). Here we use knock-in transgenic mice to investigate the consequences of intestinal epithelium-specific overexpression of de novo Dnmt3a.

METHODS

A novel gene targeting strategy, based on the intestinal epithelium-specific, uniform expression of the A33 glycoprotein, is employed to restrict Dnmt3a overexpression in homozygous A33(Dnmt3a) mutant mice.

RESULTS

A33(Dnmt3a) mice infrequently develop spontaneous intestinal polyps. However, when genetically challenged, tumor multiplicity in A33(Dnmt3a);Apc(Min) compound mice is 3-fold higher than in Apc(Min) mice. Although we observe a requirement for spontaneous loss of heterozygosity of the adenomatous polyposis coli (Apc) gene to trigger tumorigenesis in Apc(Min) mice, lesions in A33(Dnmt3a);Apc(Min) mice frequently retain the wild-type Apc allele. However, epithelia from normal mucosa and polyps of A33(Dnmt3a);Apc(Min) mice show hypermethylation-mediated transcriptional silencing of the Wnt antagonists Sfrp5, and to a lesser extent, Sfrp1 and increased nuclear beta-catenin alongside activation of the Wnt-target gene Axin2/Conductin. Conversely, enforced Sfrp5 expression suppresses canonical Wnt-signaling more effectively in wild-type than in Apc(Min) cells.

CONCLUSIONS

Aberrant activation of the canonical Wnt pathway, either by mono-allelic Apc loss or transcriptional silencing of Sfrp5 is largely insufficient to promote polyposis, but epistatic interactions between these genetic and epigenetic events enables initiation and promotion of disease. This mechanism is likely to play a role in human colorectal cancer, because we also show that elevated DNMT3A expression coincides with repressed SFRP5 and enhanced AXIN2/CONDUCTIN expression in paired patient biopsies.

Detection of metabolic alterations in non-tumor gastrointestinal tissue of the Apc(Min/+) mouse by (1)H MAS NMR spectroscopy

In this study, we have used metabolic profiling (metabolomics/metabonomics) via high resolution magic angle spinning (HRMAS) and solution state (1)H NMR spectroscopy to characterize small bowel and colon tissue from the Apc(Min/+) mouse model of early gastrointestinal (GI) tumorigenesis. Multivariate analysis indicated the presence of metabolic differences between the morphologically normal/non-tumor tissue from approximately 10 week-old Apc(Min/+) mice and their wild-type litter mates. The metabolic profile of isolated lamina propria and epithelial cells from the same groups could also be discriminated on the basis of genotype. Accounting for systematic variation in individual metabolite levels across different anatomical regions of the lower GI tract, the metabolic phenotype of Apc(Min/+) lamina propria tissue was defined by significant increases in the phosphocholine/glycerophosphocholine ratio (PC/GPC, +21%) and decreases in GPC (-25%) and the gut-microbial cometabolite dimethylamine (DMA, -40%) relative to wild type. In the whole tissue, elevated lactate (+15%) and myo-inositol (+19%) levels were detected. As the metabolic changes occurred in non-tumor tissue from animals of very low tumor burden (<2 polyps/animal), they are likely to represent the specific consequence of reduced Apc function and very early events in tumorigenesis. The observed increase in PC/GPC ratio has been previously reported with immortalisation and malignant transformation of cells and is consistent with the role of Apc as a tumor suppressor. Phospholipase A2, which hydrolyses phosphatidylcholine to Acyl-GPC, is a known modifier gene of the model phenotype (Mom1), and altered expression of choline phospholipid enzymes has been reported in gut tissue from Apc(Min/+) mice. These results indicate the presence of a metabolic phenotype associated with "field cancerization", highlighting potential biomarkers for monitoring disease progression, for early evaluation of response to chemoprevention, and for predicting the severity of the polyposis phenotype in the Apc(Min/+) model.

Activator protein 2alpha suppresses intestinal tumorigenesis in the Apc(min) mouse

Activator protein 2alpha (AP-2alpha) is a putative tumor suppressor, and various reports have described the loss or reduction of AP-2alpha expression in cutaneous malignant melanomas, as well as in cancers of the prostate, breast and colon. Previously, AP-2alpha was shown to attenuate beta-catenin/T-cell factor-4 (TCF-4) nuclear interactions and beta-catenin/TCF-4-dependent transcriptional activity in human colorectal cancer cells [Q. Li, R.H. Dashwood, Activator protein 2alpha associates with adenomatous polyposis coli/beta-catenin and Inhibits beta-catenin/T-cell factor transcriptional activity in colorectal cancer cells, J. Biol. Chem. 279 (2004) 45669-45675]. Here, we show that in vivo gene delivery of AP-2alpha suppressed intestinal polyp formation in the Apc(min) mouse, and protected against the development of anemia and splenomegaly. Immunoblot analyses and immunohistochemistry following gene delivery revealed an increase in AP-2alpha expression in the mouse intestinal mucosa and liver. Co-immunoprecipitation experiments provided evidence for interactions between AP-2alpha, beta-catenin, and adenomatous polyposis coli (APC) proteins in mouse intestinal mucosa, as well as in a primary human colorectal cancer. Collectively, these studies support a tumor suppressor role for AP-2alpha in the gastrointestinal tract, and suggest that AP-2alpha represents a novel target for therapeutic intervention in human cancers characterized by dysregulated Wnt signaling.

Conjugated linoleic acids differentially alter polyp number and diameter in the Apc(min/+) mouse model of intestinal cancer

OBJECTIVE

Dietary conjugated linoleic acids (CLA) have had many health benefits claimed for them, including antineoplastic actions.

MATERIALS AND METHODS

The effects of the predominant forms of CLA, namely the c9t11 and t10c12 isomers, or a mixture of these on polyp development, were investigated in the Apc(Min/+) mouse. CLAs have also been linked to altered rates of cell renewal and cell proliferation so this was also studied, as was a further means of increasing tissue mass, namely crypt fission.

RESULTS

The stomach and small intestine were significantly heavier in the t10c12, and in the mixture-treated groups (P < 0.001). Crypt fission was increased in the middle small intestine by the t10c12 diet while colonic weight was reduced by c9t11 provision and crypts were 20% shorter. The t10c12 and the mixture significantly reduced polyp number in the proximal small intestine but they increased polyp diameter in the middle and distal small intestine, to an extent that the polyp burden was significantly increased at these sites. All CLAs significantly reduced polyp number in the colon, but the mixture significantly increased polyp diameter in the colon.

CONCLUSION

Increased polyp diameter associated with t10c12 diet and especially with the mixture is a cause of concern, as this is the commercially available form. The naturally occurring isomer, c9t11 decreased colonic polyp number and did not increase diameter, suggesting that this natural isomer is the most likely to be protective.

Cancer chemoprevention and chemotherapy: dietary polyphenols and signalling pathways

Prevention of cancer through dietary intervention recently has received an increasing interest, and dietary polyphenols have become not only important potential chemopreventive, but also therapeutic, natural agents. Polyphenols have been reported to interfere at the initiation, promotion and progression of cancer. They might lead to the modulation of proteins in diverse pathways and require the integration of different signals for the final chemopreventive or therapeutic effect. Polyphenols have been demonstrated to act on multiple key elements in signal transduction pathways related to cellular proliferation, differentiation, apoptosis, inflammation, angiogenesis and metastasis; however, these molecular mechanisms of action are not completely characterized and many features remain to be elucidated. The aim of this review is to provide insights into the molecular basis of potential chemopreventive and therapeutic activities of dietary polyphenols with emphasis in their ability to control intracellular signalling cascades considered as relevant targets in a cancer preventive approach.

Effect of genistein on the bioavailability and intestinal cancer chemopreventive activity of (-)-epigallocatechin-3-gallate

The green tea (Camellia sinensis) catechin, (-)-epigallocatechin-3-gallate (EGCG), has shown cancer-preventive activity in animal models. Previously, we have reported the bioavailability of EGCG in rats and mice. Here, we report that cotreatment of HT-29 human colon cancer cells with genistein (from soy) increased cytosolic EGCG by 2- to 5-fold compared with treatment with EGCG only. Inclusion of genistein, at non-cytotoxic concentrations, increased the growth inhibitory effects of EGCG against HT-29 cells (up to 2-fold at 20 microM genistein). Intragastric coadministration of EGCG (75 mg/kg) and genistein (200 mg/kg) to CF-1 mice resulted in an increase in plasma half-life (t(1/2) 148.7 +/- 16.4 versus 111.5 +/- 23.4 min) and exposure (AUC(0-->infinity) 183.9 +/- 20.2 versus 125.8 +/- 26.4 microg/ml x min) of EGCG. Cotreatment with genistein also increased the maximal concentration (C(max)), 6 h exposure (AUC(0-->360 min)), and t(1/2) of EGCG in the small intestine by 2.0-, 4.7- and 1.4-fold, respectively, compared with mice treated with EGCG only. Contrary to our expectations, the combination of 0.01% EGCG in the drinking fluid and 0.2% genistein in the diet enhanced intestinal tumorigenesis in male adenomatous polyposis coli (APC)(min/+) mice. This combination increased the multiplicity of tumors in the medial and distal small intestine: the largest increase was in tumors >2 mm in diameter (4.3-fold compared with controls). This study demonstrates that although genistein can enhance EGCG bioavailability and in vitro growth inhibitory activity, this combination enhances tumorigenesis in the APC(min/+) mouse. These results further show the need for careful cancer prevention studies in animal models and for caution when interpreting data from in vitro studies.

Dual inhibition of VEGFR and EGFR signaling reduces the incidence and size of intestinal adenomas in Apc(Min/+) mice

Both the epidermal growth factor (EGF) and the vascular endothelial growth factor (VEGF) pathways are associated with intestinal cancer, and therapeutic approaches targeting either EGF receptor (EGFR) or VEGF receptor (VEGFR) signaling have recently been approved for patients with advanced colorectal cancer. The Apc(Min/+) mouse is a well-characterized in vivo model of intestinal tumorigenesis, and animals with this genetic mutation develop macroscopically detectable adenomas from approximately 6 weeks of age. Previous work in the Apc(Min/+) mouse has shown that therapeutic approaches targeting either VEGFR or EGFR signaling affect predominantly the size or number of adenomas, respectively. In this study, we have assessed the effect of inhibiting both these key pathways simultaneously using ZD6474 (Vandetanib, ZACTIMA), a selective inhibitor of VEGFR and EGFR tyrosine kinases. To assess the effects of ZD6474 on early- and later-stage disease, treatment was initiated in 6- and 10-week-old Apc(Min/+) mice for 28 days. ZD6474 markedly reduced both the number and the size of polyps when administered at either an early or a later stage of polyp development. This reduction in both adenoma number and size resulted in a total reduction in tumor burden in the small intestine of nearly 75% in both studies (P < 0.01). The current data build on the concept that EGFR-dependent tumor cell proliferation and VEGF/VEGFR2-dependent angiogenesis and survival are distinct key mechanisms in polyp development. Pharmacologic inhibition of both signaling pathways has significant antitumor effects at both early and late stages of polyp development. Therefore, targeting both VEGFR- and EGFR-dependent signaling may be a beneficial strategy in early intestinal cancer.

Resistant carbohydrates stimulate cell proliferation and crypt fission in wild-type mice and in the Apc(Min/+) mouse model of intestinal cancer, association with enhanced polyp development

Fermentation of carbohydrates in the colon can stimulate cell proliferation and could thus be a cancer risk. The effects of resistant carbohydrates, i.e. those not digested and absorbed in the small intestine, on cell proliferation, crypt fission and polyp development were investigated in wild-type and adenomatous polyposis coli multiple intestinal neoplasia (Apc(Min/+)) mice. Fifteen 4-week-old female wild-type and fifteen Apc(Min/+) mice were used for each group and fed a chow diet, a semi-synthetic diet or the semi-synthetic supplemented with wheat bran or an apple pomace preparation, both high in resistant carbohydrates, for 8 weeks. Tissue from all mice was used to measure cell proliferation and crypt fission and tissue from the Apc(Min/+) mice was scored for polyp number and tumour burden. There were slight reductions in intestinal mass in the mice fed the semi-synthetic diets and this was increased by the inclusion of resistant carbohydrates. The Apc(Min/+) mice had elevated cell proliferation and crypt fission in the distal small intestine and colon and these were increased by the resistant carbohydrates. Bran or apple pomace significantly increased polyp number in the proximal third of the small intestine. Apple pulp more than doubled polyp number throughout the small bowel (99.2 (SEM 11.1) v. 40.0 (SEM 8.2), P<0.004). Bran and apple pomace increased polyp diameter and hence burden in the colon by 243 and 150 %, respectively (P<0.05). In conclusion, both types of resistant carbohydrates increased polyp number and tumour burden and this was associated with elevated epithelial cell proliferation and crypt fission.

Inhibition of tumorigenesis in ApcMin/+ mice by a combination of (-)-epigallocatechin-3-gallate and fish oil

The effect of a combination of (-)-epigallocatechin-3-gallate (EGCG) with fish oil on intestinal tumorigenesis in Apc (Min/+) mice fed a high-fat diet was investigated in the present study. The combined treatment of EGCG and fish oil for 9 weeks reduced the tumor number by 53% as compared to controls while neither agent alone had a significant effect. Apoptosis was significantly increased in all treatment groups. beta-Catenin nuclear positivity in adenomas from the combination group was lower than control mice, implicating the modulation of Wnt signaling by the combination. Fish oil and the combination significantly reduced prostaglandin E 2 (PGE 2) levels in small intestinal tumors as compared to controls, suggesting modulation of aberrant arachidonic acid metabolism by fish oil. Akt phosphorylation in adenomas was significantly reduced in all treatment groups, which may have contributed to the observed increase in apoptosis. The results indicate that a combination of low doses of EGCG and fish oil can inhibit tumor multiplicity in Apc (Min/+) mice.

Conditional mouse models of cancer

The development of inducible and conditional technologies allowed us to generate transgenic mouse models that faithfully recapitulate human tumorigenesis. It is possible to control, in time and space, the development of tumors in almost every mouse tissue. The result is that now we have available mouse models for all major human cancers. Novel noninvasive approaches to tumor imaging will enable us to follow tumor development and metastasis in vivo, as well as the effects of candidate therapeutic drugs. Such new generation tumor models, which accurately emulate the disease state in situ, should provide a useful platform with which to experimentally test drugs targeted to specific gene products, or combinations of genes that control rate-limiting steps of tumor development. In this review, we focus on the different mouse models for colon cancer.

Induction of aberrant crypt foci in DNA mismatch repair-deficient mice by the food-borne carcinogen 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP)

Disruption of the DNA mismatch repair (MMR) pathway results in elevated mutation rates, inappropriate survival of cells bearing DNA damage, and increased cancer risk. Relatively little is known about the impact of environmentally relevant carcinogens on cancer risk in individuals with MMR-deficiency. We evaluated the effect of MMR status (Mlh1(+/+) versus Mlh1(-/-)) on the carcinogenic potential of the cooked-meat mutagen, 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) in mice. PhIP exposure did not obviously increase lymphoma or small intestinal tumorigenesis in either Mlh1-deficient or -proficient mice. In contrast, the frequency of aberrant crypt foci (ACF), a preneoplastic biomarker for colon tumorigenesis, was increased by PhIP, and the increase due to PhIP was significantly greater in Mlh1(-/-) versus wild-type littermates. This apparent heightened susceptibility to induction of ACF parallels the previously reported hypermutability of Mlh1-deficient mice to PhIP and is consistent with the hypothesis that MMR-deficiency would increase the likelihood of PhIP-induced carcinogenic mutations. Further evaluation of the risk that consumption of heterocyclic amines may impart to MMR-deficient individuals therefore is warranted.

How good are rodent models of carcinogenesis in predicting efficacy in humans? A systematic review and meta-analysis of colon chemoprevention in rats, mice and men

Tumours in rodent and human colon share many histological and genetic features. To know if rodent models of colon carcinogenesis are good predictors of chemopreventive efficacy in humans, we conducted a meta-analysis of aspirin, beta-carotene, calcium, and wheat bran studies. Controlled intervention studies of adenoma recurrence in human volunteers were compared with chemoprevention studies of carcinogen-induced tumours in rats, and of polyps in Min (Apc(+/-)) mice: 6714 volunteers, 3911 rats and 458 mice were included in the meta-analyses. Difference between models was small since most global relative risks were between 0.76 and 1.00. A closer look showed that carcinogen-induced rat studies matched human trials for aspirin, calcium, carotene, and were compatible for wheat bran. Min mice results were compatible with human results for aspirin, but discordant for calcium and wheat bran (no carotene study). These few results suggest that rodent models roughly predict effect in humans, but the prediction is not accurate for all agents. Based on three cases only, the carcinogen-induced rat model seems better than the Min mouse model. However, rodent studies are useful to screen potential chemopreventive agents, and to study mechanisms of carcinogenesis and chemoprevention.

The promise of genetically engineered mice for cancer prevention studies

Sophisticated genetic technologies have led to the development of mouse models of human cancers that recapitulate important features of human oncogenesis. Many of these genetically engineered mouse models promise to be very relevant and relatively rapid systems for determining the efficacy of chemopreventive agents and their mechanisms of action. The validation of such models for chemoprevention will help the selection of appropriate agents for large-scale clinical trials and allow the testing of combination therapies.

Inhibition of carcinogenesis by polyphenols: evidence from laboratory investigations

Many plant polyphenolic compounds have been shown to have cancer-preventing activities in laboratory studies. For example, tea and tea preparations have been shown to inhibit tumorigenesis in a variety of animal models of carcinogenesis, involving organ sites such as the skin, lungs, oral cavity, esophagus, stomach, liver, pancreas, small intestine, colon, and prostate. In some of these models, inhibitory activity was demonstrated when tea was administered during the initiation, promotion, or progression stage of carcinogenesis. The cancer-preventing activities of these and other polyphenols, such as curcumin, genistein, and quercetin, are reviewed. In studies in vitro, many of these compounds have been shown to affect signal transduction pathways, leading to inhibition of cell growth and transformation, enhanced apoptosis, reduced invasive behavior, and slowed angiogenesis. However, the concentrations used in cell culture studies were much higher than those found in vivo. If we propose mechanisms for cancer prevention on the basis of cell line experiments, then these activities must be demonstrated in vivo. The bioavailability, ie, tissue and cellular concentrations, of dietary polyphenols is a determining factor in their cancer-preventing activity in vivo. For example, compounds such as curcumin are effective when applied topically to the skin or administered orally to affect the colon but are not effective in internal organs such as the lungs. More in-depth studies on bioavailability should facilitate correlation of mechanisms determined in vitro with in vivo situations, increase our understanding of dose-response relationships, and facilitate extrapolation of results from animal studies to human situations.

Effect of nonsteroidal anti-inflammatory drugs on beta-catenin protein levels and catenin-related transcription in human colorectal cancer cells

Elevated β-catenin levels in human colorectal cancer (CRC) cells lead to increased trans-activation of ‘protumorigenic’ β-catenin/T-cell factor (TCF) target genes such as cyclin D1. Therefore, possible targets for the anti-CRC activity of nonsteroidal anti-inflammatory drugs (NSAIDs) are β-catenin and catenin-related transcription (CRT). We tested the antiproliferative activity and the effects on levels of β-catenin and cyclin D1 protein, as well as CRT (measured using a synthetic β-catenin/TCF-reporter gene [TOPflash]), of a panel of NSAIDs (indomethacin, diclofenac, sulindac sulphide and sulphone, rofecoxib; range 10–600 μM) on SW480 human CRC cells in vitro. Following NSAID treatment, there was no consistent relationship between reduced cell proliferation, induction of apoptosis and changes in β-catenin protein levels or CRT. All the NSAIDs, except rofecoxib, decreased nuclear β-catenin content and cyclin D1 protein levels in parallel with their antiproliferative activity. However, cyclin D1 downregulation occurred prior to a decrease in total β-catenin protein levels and there was no correlation with changes in CRT, suggesting the existence of CRT-independent effects of NSAIDs on cyclin D1 expression. In summary, NSAIDs have differential effects on β-catenin protein and CRT, which are unlikely to fully explain their effects on cyclin D1 and their antiproliferative activity on human CRC cells in vitro.

Cancer chemoprevention with dietary phytochemicals

Chemoprevention refers to the use of agents to inhibit, reverse or retard tumorigenesis. Numerous phytochemicals derived from edible plants have been reported to interfere with a specific stage of the carcinogenic process. Many mechanisms have been shown to account for the anticarcinogenic actions of dietary constituents, but attention has recently been focused on intracellular-signalling cascades as common molecular targets for various chemopreventive phytochemicals.

Age-related difference in susceptibility of Apc(Min/+) mice towards the chemopreventive efficacy of dietary aspirin and curcumin

The nonsteroidal anti-inflammatory drug aspirin and the spice curcumin retard adenoma formation when administered long-term to Apc(Min/+) mice, a model of human familial adenomatous polyposis coli. Both agents interfere with cyclooxygenase activity. When aspirin is administered to Apc(Min/+) mice only postweaning, but not before, it is inefficacious, while curcumin given postweaning is active. Here the hypothesis was tested that dietary aspirin (0.05%) or curcumin (0.2%) prevent or delay adenoma formation in offsprings when administered to Apc(Min/+) mothers and up to the end of weaning, but not afterwards. Whereas curcumin was without effect when administered in this way, aspirin reduced numbers of intestinal adenomas by 21%. When aspirin given up to the end of weaning was combined with curcumin administered from the end of weaning for the rest of the animals' lifetime, intestinal adenoma numbers were reduced by 38%. The combination was not superior to intervention postweaning with curcumin alone. These results show that aspirin exerts chemopreventive activity in the Apc(Min/+) mouse during tumour initiation/early promotion, while curcumin is efficacious when given at a later stage of carcinogenic progression. Thus, the results suggest that in this mouse model aspirin and curcumin act during different 'windows' of neoplastic development.

Use of transgenic and mutant animal models in the study of heterocyclic amine-induced mutagenesis and carcinogenesis

Heterocyclic amines (HCAs) are potent mutagens generated during the cooking of meat and fish, and several of these compounds produce tumors in conventional experimental animals. During the past 5 years or so, HCAs have been tested in a number of novel in vivo murine models, including the following: lacZ, lacI, cII, c-myc/lacZ, rpsL, and gptDelta. transgenics, XPA-/-, XPC-/-, Msh2+/-, Msh2-/- and p53+/- knock-outs, Apc mutant mice (ApcDelta716, Apc1638N, Apcmin), and A33DeltaNbeta-cat knock-in mice. Several of these models have provided insights into the mutation spectra induced in vivo by HCAs in target and non-target organs for tumorigenesis, as well as demonstrating enhanced susceptibility to HCA-induced tumors and preneoplastic lesions. This review describes several of the more recent reports in which novel animal models were used to examine HCA-induced mutagenesis and carcinogenesis in vivo, including a number of studies which assessed the inhibitory activities of chemopreventive agents such as 1,2-dithiole-3-thione, conjugated linoleic acids, tea, curcumin, chlorophyllin-chitosan, and sulindac.

Inhibition of beta-catenin/Tcf activity by white tea, green tea, and epigallocatechin-3-gallate (EGCG): minor contribution of H(2)O(2) at physiologically relevant EGCG concentrations

Epigallocatechin-3-gallate (EGCG) is the major polyphenol present in white tea and green tea. Recently, it was reported that the addition of EGCG and other tea polyphenols to cell culture media, minus cells, generated significant levels of H(2)O(2), with the corollary that this might represent an "artifact" in cell culture studies which seek to examine the chemopreventive mechanisms of tea. We show here that in cell growth media with and without serum, and in growth media containing human embryonic kidney 293 (HEK293) cells plus serum, physiologically relevant concentrations of EGCG (< or =25 microM) generated H(2)O(2) with a peak concentration of the order of 10-12 microM. However, addition of 20 microM H(2)O(2) directly to HEK293 cells transiently transfected with wild-type or mutant beta-catenin constructs and TCF-4 had no significant effect on beta-catenin/TCF-4 reporter activity or beta-catenin expression levels. In contrast, 2-25 microM EGCG inhibited beta-catenin/TCF-4 reporter activity in a concentration-dependent fashion and there was a concomitant reduction in beta-catenin protein levels in the cell lysates without changes in TCF-4 expression. The inhibition of reporter activity was recapitulated by white tea and green tea, each tested at a 25 microM EGCG equivalent concentration in the assay, and this was unaffected by the addition of exogenous catalase. The results indicate that physiologically relevant concentrations of tea and EGCG inhibit beta-catenin/TCF-4 reporter activity in HEK293 cells due to reduced expression of beta-catenin and that this is unlikely to be an artifact of H(2)O(2) generation under the assay conditions used here. These data are consistent with the findings from in vivo studies, showing the suppression of intestinal polyps by tea, via an apparent down-regulation of beta-catenin and Wnt target genes.

Inhibition by white tea of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced colonic aberrant crypts in the F344 rat

There is growing interest in the potential health benefits of tea, including the anticarcinogenic properties. We report here that white tea, the least processed form of tea, is a potent inhibitor of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced colonic aberrant crypts in the rat. Male Fischer 344 rats were treated for 8 wk with white tea (2% wt/vol) or drinking water alone, and on alternating days in experimental Weeks 3 and 4 the animals were given PhIP (150 mg/kg body wt p.o.) or vehicle alone. At the end of the study there were 5.65 +/- 0.81 and 1.31 +/- 0.27 (SD) aberrant crypt foci per colon in groups given PhIP and PhIP + white tea, respectively (n = 12, P < 0.05). No changes were detected in N-acetyltransferase or arylsulfotransferase activities compared with controls, but there was marked induction of ethoxyresorufin O-deethylase, methoxyresorufin O-demethylase, and UDP-glucuronosyltransferase after treatment with white tea. Western blot revealed corresponding increases in cytochrome P-450 1A1 and 1A2 proteins. Enzyme assays and Western blot also revealed induction of glutathione S-transferase by white tea. There was less parent compound and 4'-hydroxy-PhIP but more PhIP-4'-O-glucuronide and PhIP-4'-O-sulfate in the urine from rats given PhIP + white tea than in urine from animals given carcinogen + drinking water. The results indicate that white tea inhibits PhIP-induced aberrant crypt foci by altering the expression of carcinogen-metabolizing enzymes, such that there is increased ring hydroxylation at the 4' position coupled with enhanced phase 2 conjugation.