Importance of epidermal growth factor receptor signaling in establishment of adenomas and maintenance of carcinomas during intestinal tumorigenesis

Insulin-like growth factor 1 activates methionine adenosyltransferase 2A transcription by multiple pathways in human colon cancer cells

We have previously reported that the expression of MAT2A (methionine adenosyltransferase 2A) is increased in human colon cancer and in colon cancer cells treated with IGF-1 (insulin-like growth factor-1), which was required for its mitogenic effect. The aim of the present study was to elucidate the molecular mechanisms of IGF-1-mediated MAT2A induction. Nuclear run-on analysis confirmed that the increase in MAT2A expression lies at the transcriptional level. DNase I footprinting of the MAT2A promoter region revealed a similar protein-binding pattern in colon cancer and IGF-1-treated RKO cells. IGF-1 induced MAT2A promoter activity and increased nuclear protein binding to USF (upstream stimulatory factor)/c-Myb, YY1 (Yin and Yang 1), E2F, AP-1 (activator protein 1) and NF-κB (nuclear factor κB) consensus elements. IGF-1 increased the expression of c-Jun, FosB, MafG, p65, c-Myb, E2F-1 and YY1 at the pre-translational level. Knockdown of p65, MafG, c-Myb or E2F-1 lowered basal MAT2A expression and blunted the inductive effect of IGF-1 on MAT2A, whereas knockdown of YY1 increased basal MAT2A expression and had no effect on IGF-1-mediated MAT2A induction. Consistently, mutation of AP-1, NF-κB, E2F and USF/c-Myb elements individually blunted the IGF-1-mediated increase in MAT2A promoter activity, and combined mutations completely prevented the increase. In conclusion, IGF-1 activates MAT2A transcription by both known and novel pathways. YY1 represses MAT2A expression.

EGFR signals downregulate tumor suppressors miR-143 and miR-145 in Western diet-promoted murine colon cancer: role of G1 regulators

Epidermal growth factor receptors (EGFR) contribute to colonic tumorigenesis in experimental models of colon cancer. We previously showed that EGFR was also required for colonic tumor promotion by Western diet. The goal of this study was to identify EGFR-regulated microRNAs that contribute to diet-promoted colonic tumorigenesis. Murine colonic tumors from Egfr(wt) and hypomorphic Egfr(wa2) mice were screened using micro RNA (miRNA) arrays and miR-143 and miR-145 changes confirmed by Northern, real-time PCR, and in situ analysis. Rodent and human sporadic and ulcerative colitis (UC)-associated colon cancers were examined for miR-143 and miR-145. Effects of EGFR on miR-143 and miR-145 expression were assessed in murine and human colonic cells and their putative targets examined in vitro and in vivo. miR-143 and miR-145 were readily detected in normal colonocytes and comparable in Egfr(wt) and Egfr(wa2) mice. These miRNAs were downregulated in azoxymethane and inflammation-associated colonic tumors from Egfr(wt) mice but upregulated in Egfr(wa2) tumors. They were also reduced in human sporadic and UC colon cancers. EGFR signals suppressed miR-143 and miR-145 in human and murine colonic cells. Transfected miR-143 and miR-145 inhibited HCT116 cell growth in vitro and in vivo and downregulated G(1) regulators, K-Ras, MYC, CCND2, cdk6, and E2F3, putative or established targets of these miRNAs. miRNA targets Ras and MYC were increased in colonic tumors from Egfr(wt) but not Egfr(wa2) mice fed a Western diet. EGFR suppresses miR-143 and miR-145 in murine models of colon cancer. Furthermore, Western diet unmasks the tumor suppressor roles of these EGFR-regulated miRNAs.

Muscarinic receptor subtype-3 gene ablation and scopolamine butylbromide treatment attenuate small intestinal neoplasia in Apcmin/+ mice

M3 subtype muscarinic receptors (CHRM3) are over-expressed in colon cancer. In this study, we used Apc(min/+) mice to identify the role of Chrm3 expression in a genetic model of intestinal neoplasia, explored the role of Chrm3 in intestinal mucosal development and determined the translational potential of inhibiting muscarinic receptor activation. We generated Chrm3-deficient Apc(min/+) mice and compared intestinal morphology and tumor number in 12-week-old Apc(min/+)Chrm3(-/-) and Apc(min/+)Chrm3(+/+) control mice. Compared with Apc(min/+)Chrm3(+/+) mice, Apc(min/+)Chrm3(-/-) mice showed a 70 and 81% reduction in tumor number and volume, respectively (P < 0.01). In adenomas, β-catenin nuclear staining was reduced in Apc(min/+)Chrm3(-/-) compared with Apc(min/+)Chrm3(+/+) mice (P < 0.02). Whereas Apc gene mutation increased the number of crypt and Paneth cells and decreased villus goblet cells, these changes were absent in Apc(min/+)Chrm3(-/-) mice. To determine whether pharmacological inhibition of muscarinic receptor activation attenuates intestinal neoplasia, we treated 6-week-old Apc(min/+) mice with scopolamine butylbromide, a non-subtype-selective muscarinic receptor antagonist. After 8 weeks of continuous treatment, scopolamine butylbromide-treated mice showed a 22% reduction in tumor number (P = 0.027) and a 36% reduction in tumor volume (P = 0.004) as compared with control mice. Compared with Chrm3 gene ablation, the muscarinic antagonist was less efficacious, most probably due to shorter duration of treatment and incomplete blockade of muscarinic receptors. Overall, these findings indicate that interplay of Chrm3 and β-catenin signaling is important for intestinal mucosal differentiation and neoplasia and provide a proof-of-concept that pharmacological inhibition of muscarinic receptor activation can attenuate intestinal neoplasia in vivo.

Muscarinic receptor agonists stimulate human colon cancer cell migration and invasion

Muscarinic receptors (CHRM) are overexpressed in colon cancer. To explore a role for muscarinic receptor signaling in colon cancer metastasis, we used human H508 and HT29 colon cancer cells that coexpress epidermal growth factor (ERBB) and CHRM3 receptors. In a wound closure model, following 8-h incubation of H508 cells with 100 μM ACh we observed a threefold increase in cell migration indistinguishable from the actions of epidermal growth factor (EGF). Atropine blocked the actions of ACh but not of EGF. In SNU-C4 colon cancer cells that express ERBB but not CHRM, EGF caused a threefold increase in migration; ACh had no effect. ACh-induced cell migration was attenuated by chemical inhibitors of ERBB1 activation, by anti-ERBB1 antibody, and by inhibitors of ERK and phosphatidylinositol 3-kinase (PI3K) signaling. Consistent with matrix metalloproteinase-7 (MMP7)-mediated release of an ERBB1 ligand, heparin binding epidermal growth factor-like growth factor (HBEGF), ACh-induced migration was inhibited by an MMP inhibitor and by anti-MMP7 and -HBEGF antibodies. ACh-induced cell migration was blocked by inhibiting RhoA and ROCK, key proteins that interact with the actin cytoskeleton. ACh-induced RhoA activation was attenuated by agents that inhibit ERBB1, ERK, and PI3K activation. Collectively, these findings indicate that ACh-induced cell migration is mediated by MMP7-mediated release of HBEGF, an ERBB ligand that activates ERBB1 and downstream ERK and PI3K signaling. In a cell invasion model, ACh-induced HT29 cell invasion was blocked by atropine. In concert with previous observations, these findings indicate that muscarinic receptor signaling plays a key role in colon cancer cell proliferation, survival, migration, and invasion.

Activation of epidermal growth factor receptor signaling by the prostaglandin E(2) receptor EP4 pathway during gastric tumorigenesis

Cyclooxygenase-2 (COX-2) plays an important role in tumorigenesis through prostaglandin E(2) (PGE(2)) biosynthesis. It has been shown by in vitro studies that PGE(2) signaling transactivates epidermal growth factor receptor (EGFR) through an intracellular mechanism. However, the mechanisms underlying PGE(2)-induced EGFR activation in in vivo tumors are still not fully understood. We previously constructed transgenic mice that develop gastric tumors caused by oncogenic activation and PGE(2) pathway induction. Importantly, expression of EGFR ligands, epiregulin, amphiregulin, heparin-binding EGF-like growth factor, and betacellulin, as well as a disintegrin and metalloproteinases (ADAMs), ADAM8, ADAM9, ADAM10, and ADAM17 were significantly increased in the mouse gastric tumors in a PGE(2) pathway-dependent manner. These ADAMs can activate EGFR by ectodomain shedding of EGFR ligands. Notably, the extensive induction of EGFR ligands and ADAMs was suppressed by inhibition of the PGE(2) receptor EP4. Moreover, EP4 signaling induced expression of amphiregulin and epiregulin in activated macrophages, whereas EP4 pathway was required for basal expression of epiregulin in gastric epithelial cells. In contrast, ADAMs were not induced directly by PGE(2) in these cells, suggesting indirect mechanism possibly through PGE(2)-associated inflammatory responses. These results suggest that PGE(2) signaling through EP4 activates EGFR in gastric tumors through global induction of EGFR ligands and ADAMs in several cell types either by direct or indirect mechanism. Importantly, gastric tumorigenesis of the transgenic mice was significantly suppressed by combination treatment with EGFR and COX-2 inhibitors. Therefore, it is possible that inhibition of both COX-2/PGE(2) and EGFR pathways represents an effective strategy for preventing gastric cancer.

Genomic instability and oncogene amplifications in colorectal adenomas predict recurrence and synchronous carcinoma

Individual colorectal adenomas have different propensities to progress to invasive disease. In this study, we explored whether these differences could be explained by gene copy number alterations. We evaluated 18 adenomas of patients without synchronous or subsequent carcinoma (6.5 years follow-up), 23 adenomas of carcinoma patients, and 6 related carcinomas. All samples were measured for their DNA ploidy status. Centromere probes for chromosomes 17 and 18, as well as gene-specific probes for SMAD7, EGFR, NCOA3, TP53, MYC, and RAB20 were assessed by multicolor fluorescence in situ hybridization. An increased genomic instability index of CEP17, SMAD7, and EGFR, as well as TP53 deletions and MYC amplifications defined adenomas of patients with synchronous carcinoma (P<0.05). Diploid NCOA3 signal counts were associated with longer adenoma recurrence-free surveillance (P=0.042). In addition, NCOA3, MYC, EGFR, and RAB20 amplifications, as well as TP53 deletions correlated with increased DNA stem line values and/or aneuploidy in adenomas (P<0.05). Furthermore, aberrations of NCOA3, MYC, and RAB20 were associated with histopathologically defined high-risk adenomas (P<0.05). RAB20 amplifications were also correlated with high-grade dysplastic adenomas (P=0.002). We conclude that genomic instability in colorectal adenomas is reflected by EGFR, MYC, NCOA3, and RAB20 amplifications that do correlate with histomorphological features and are indicative for adenoma recurrence and the presence of synchronous carcinomas.

Claudin-2 expression increases tumorigenicity of colon cancer cells: role of epidermal growth factor receptor activation

Claudin-2 is a unique member of the claudin family of transmembrane proteins as its expression is restricted to the leaky epithelium in vivo and correlates with epithelial leakiness in vitro. However, recent evidence suggests potential functions of claudin-2 that are relevant to neoplastic transformation and growth. In accordance here we report, based upon analysis of mRNA and protein expression using a total of 309 patient samples, that claudin-2 expression is significantly increased in colorectal cancer and correlates with cancer progression. We also report similar increases in claudin-2 expression in inflammatory bowel disease (IBD)-associated colorectal cancer. Most importantly, we demonstrate that the increased claudin-2 expression in colorectal cancer is causally associated with tumor growth as forced claudin-2 expression in colon cancer cells that do not express claudin-2 resulted in significant increases in cell proliferation, anchorage-independent growth, and tumor growth in vivo. We further show that the colonic microenvironment regulates claudin-2 expression in a manner dependent on signaling through the EGF receptor (EGFR), a key regulator of colon tumorigenesis. In addition, claudin-2 expression is specifically decreased in the colon of waved-2 mice, naturally deficient in EGFR activation. Furthermore, genetic silencing of claudin-2 expression in Caco-2 , a colon cancer cell line, prevents the EGF-induced increase in cell proliferation. Taken together, these results uncover a novel role for claudin-2 in promoting colon cancer, potentially via EGFR transactivation.

[Colorectal oncogenesis]

Recent progress in the field of molecular biology has allowed us to identify at least two different molecular mechanisms implicated in colorectal carcinogenesis (CRC): chromosomal instability (CIN) and genetic instability. Even though the two molecular mechanisms differ, their signalling pathways, implicated in malignant transformation of colonic epithelial cells, appear to be similar. The most frequent group of CRC, which represents 80% of sporadic CRC, is characterized by allelic losses on the short arm of chromosome 17 and 8 and on the long arm of chromosome 5, 18 and 22. These allelic losses are associated with mutations in TP53, APC, SMAD2 and SMAD4 genes. All of these alterations are grouped under the phenotype CIN. A genetic instability termed MSI (microsatellite instability), which results from a mismatch repair (MMR) deficiency, appears in 12-15% of CRC cases. The presence of MMR deficiency leads to the accumulation of mutations in genes controlling cell cycle and apoptosis (TGFBRII, BAX or CASPASE5). More recently, the existence of a third phenotype was suggested. The main alteration associated with this group of tumors is the hypermethylation of the promoter region of numerous genes, leading to their inactivation. An activating mutation of BRAF is frequently associated with this phenotype. As described above, CRC shows genetic heterogeneity, however the consequences in terms of signalling pathway alterations are similar. For example, the activation of Wnt signalling pathways can result from the inactivation of the APC gene in the CIN phenotype or from an activating mutation in the β-catenin gene in MSI tumors. The inactivation of TGFβ pathways is also present in both tumor types and is driven by SMAD4, and more rarely by a SMAD2 inactivating mutation in CIN tumors, or by the existence of a frame-shift mutation occurring in a polyG coding track of the TGFβ (transforming growth factor) receptor type II in MSI tumors. The RAS-MAP kinase pathway is activated by KRAS mutations in CIN tumors or by BRAF mutations in MSI tumors. The p53 pathway is inactivated by TP53 inactivation in CIN tumors or by BAX inactivating mutations in MSI tumors.

EGFR/Ras/MAPK signaling mediates adult midgut epithelial homeostasis and regeneration in Drosophila

Many tissues in higher animals undergo dynamic homeostatic growth, wherein damaged or aged cells are replaced by the progeny of resident stem cells. To maintain homeostasis, stem cells must respond to tissue needs. Here we show that in response to damage or stress in the intestinal (midgut) epithelium of adult Drosophila, multiple EGFR ligands and rhomboids (intramembrane proteases that activate some EGFR ligands) are induced, leading to the activation of EGFR signaling in intestinal stem cells (ISCs). Activation of EGFR signaling promotes ISC division and midgut epithelium regeneration, thereby maintaining tissue homeostasis. ISCs defective in EGFR signaling cannot grow or divide, are poorly maintained, and cannot support midgut epithelium regeneration after enteric infection by the bacterium Pseudomonas entomophila. Furthermore, ISC proliferation induced by Jak/Stat signaling is dependent upon EGFR signaling. Thus the EGFR/Ras/MAPK signaling pathway plays central, essential roles in ISC maintenance and the feedback system that mediates intestinal homeostasis.

The intestinal stem cell

The intestinal epithelium is one of the most rapidly proliferating organs in the body. A complete turnover of the epithelium occurs every 3-5 days in the mouse, a process that is maintained by a small population of intestinal stem cells (ISCs) that reside in the crypt bases. The signals that regulate the behavior of these ISCs are still unknown. This has been due, until recently, to the singular lack of definitive ISC markers. The recent identification of genes that mark functional stem cells has yielded insights into how ISCs are regulated and maintained by their surrounding niche. Herein, we examine the body of literature regarding the precise identity and location of the ISCs, the role of the surrounding niche in ISC maintenance and regulation, as well as the hypothesis that the ISCs are the cells of origin in colorectal cancer.

Oncogenic KRAS desensitizes colorectal tumor cells to epidermal growth factor receptor inhibition and activation

Epidermal growth factor receptor (EGFR)-targeting therapeutics have shown efficacy in the treatment of colorectal cancer patients. Clinical studies have revealed that activating mutations in the KRAS protooncogene predict resistance to EGFR-targeted therapy. However, the causality between mutant KRAS and resistance to EGFR inhibition has so far not been demonstrated. Here, we show that deletion of the oncogenic KRAS allele from colorectal tumor cells resensitizes those cells to EGFR inhibitors. Resensitization was accompanied by an acquired dependency on the EGFR for maintaining basal extracellular signal-regulated kinase (ERK) activity. Deletion of oncogenic KRAS not only resensitized tumor cells to EGFR inhibition but also promoted EGF-induced NRAS activation, ERK and AKT phosphorylation, and c-FOS transcription. The poor responsiveness of mutant KRAS tumor cells to EGFR inhibition and activation was accompanied by a reduced capacity of these cells to bind and internalize EGF and by a failure to retain EGFR at the plasma membrane. Of 16 human colorectal tumors with activating mutations in KRAS, 15 displayed loss of basolateral EGFR localization. Plasma membrane localization of the EGFR could be restored in vitro by suppressing receptor endocytosis through Rho kinase inhibition. This caused an EGFR-dependent increase in basal and EGF-stimulated ERK phosphorylation but failed to restore tumor cell sensitivity to EGFR inhibition. Our results demonstrate a causal role for oncogenic KRAS in desensitizing tumor cells not only to EGFR inhibitors but also to EGF itself.

Non-germline genetically engineered mouse models for translational cancer research

Genetically engineered mouse models (GEMMs) of cancer have affected virtually all areas of cancer research. However, the accelerated discovery of new cancer genes emerging from large-scale cancer genomics and new chemical entities pouring from the drug discovery pipeline have strained the capacity of traditional germline mouse models to provide crucial insights. This Review introduces new approaches to modelling cancer, with emphasis on a growing collection of non-germline GEMMs (nGEMMs). These offer flexibility, speed and uniformity at reduced costs, thus paving the way for much needed throughput and practical preclinical therapeutic testing models.

Suppressor of cytokine signaling-2 gene disruption promotes Apc(Min/+) tumorigenesis and activator protein-1 activation

Epigenetic in vitro and in vivo studies suggest that suppressor of cytokine signaling-2 (SOCS2) may normally limit tumorigenesis in the intestine; however, this theory has not been directly tested. We hypothesized that SOCS2 deficiency promotes spontaneous intestinal tumorigenesis in Apc(Min/+) mice. Therefore, we quantified tumor number, size, and load in the small intestine and colon using SOCS2(+/+)/Apc(Min/+), SOCS2(+/-)/Apc(Min/+), and SOCS2(-/-)/Apc(Min/+) mice and assayed hematocrit as an indirect marker of disease severity. Biochemical and histological assays were used to assess mechanisms. Heterozygous and homozygous disruption of SOCS2 alleles promoted 166 and 441% increases in tumor load in the small intestine, respectively, accelerated development of colon tumors, and caused severe anemia. SOCS2 deletion promoted significant increases in intestinal insulin-like growth factor-I mRNA but did not affect plasma insulin-like growth factor-I. Western blots and immunohistochemical analysis demonstrated that tumor and nontumor intestinal tissue of SOCS2(-/-)/Apc(Min/+) mice had increased serine 727 phosphorylation of signal transducer and activator of transcription 3 compared with SOCS2(+/+)/Apc(Min/+) mice. Moreover, electromobility shift assays showed that SOCS2 deletion did not alter signal transducer and activator of transcription 3 DNA binding. However, tumors and small intestine from SOCS2(-/-)/Apc(Min/+) showed dramatic increases in activator protein-1 (AP-1) DNA binding, and SOCS2 overexpression in vitro reduced levels of AP-1. These studies indicate that SOCS2 deletion promotes the spontaneous development of intestinal tumors driven by mutations in the adenomatous polyposis coli/beta-catenin pathway and activates AP-1. Therefore, reduced expression or epigenetic silencing of SOCS2 may serve as a useful biomarker for colorectal cancer risk.

APC and its modifiers in colon cancer

Colon cancer closely follows the paradigm of a single "gatekeeper gene." Mutations inactivating the APC (adenomatous polyposis coli) gene are found in approximately 80% of all human colon tumors and heterozygosity for such mutations produces an autosomal dominant colon cancer predisposition in humans and in murine models. However, this tight association between a single genotype and phenotype belies a complex association of genetic and epigenetic factors that together generate the broad phenotypic spectrum ofboth familial and sporadic colon cancers. In this Chapter, we give a general overview of the structure, function and outstanding issues concerning the role of Apc in human and experimental colon cancer. The availability of increasingly close models for human colon cancer in genetically tractable animal species enables the discovery and eventual molecular identification of genetic modifiers of the Apc-mutant phenotypes, connecting the central role of Apc in colon carcinogenesis to the myriad factors that ultimately determine the course of the disease.

Mutant EGFR is required for maintenance of glioma growth in vivo, and its ablation leads to escape from receptor dependence

Epidermal growth factor receptor (EGFR) gene amplification is the most common genetic alteration in high-grade glioma, and approximately 50% of EGFR-amplified tumors also harbor a constitutively active mutant form of the receptor, DeltaEGFR. Although DeltaEGFR greatly enhances tumor growth and is thus an attractive target for anti-glioma therapies, recent clinical experiences with EGFR kinase inhibitors have been disappointing, because resistance is common and tumors eventually recur. Interestingly, it has not been established whether DeltaEGFR is required for maintenance of glioma growth in vivo, and, by extension, if it truly represents a rational therapeutic target. Here, we demonstrate that in vivo silencing of regulatable DeltaEGFR with doxycycline attenuates glioma growth and, therefore, that it is crucial for maintenance of enhanced tumorigenicity. Similar to the clinical experience, tumors eventually regained aggressive growth after a period of stasis, but interestingly, without re-expression of DeltaEGFR. To determine how tumors acquired this ability, we found that a unique gene, KLHDC8, herein referred to as SDeltaE (Substitute for DeltaEGFR Expression)-1, is highly expressed in these tumors, which have escaped dependence on DeltaEGFR. SDeltaE-1 is also expressed in human gliomas and knockdown of its expression in DeltaEGFR-independent "escaper" tumors suppressed tumor growth. Taken together, we conclude that DeltaEGFR is required for both glioma establishment and maintenance, and that gliomas undergo selective pressure in vivo to employ alternative compensatory pathways to maintain aggressiveness in the event of EGFR silencing. Such alternative pathways function as substitutes for DeltaEGFR signaling and should therefore be considered as potential targets for additional therapy.

Diacylglycerol kinase delta and protein kinase C(alpha) modulate epidermal growth factor receptor abundance and degradation through ubiquitin-specific protease 8

Many human epithelial cancers are characterized by abnormal activation of the epidermal growth factor receptor (EGFR), which is often caused by its excessive expression in tumor cells. The abundance of EGFR is modulated, in part, by its ubiquitination, which targets it for degradation. The components responsible for adding ubiquitin to EGFR are well characterized, but this is a reversible process, and the mechanisms that modulate the removal of ubiquitin from the EGFR are not well known. We found that de-ubiquitination of EGFR was regulated by diacylglycerol kinase delta (DGKdelta), a lipid kinase that terminates diacylglycerol signaling. In DGKdelta-deficient cells, ubiquitination of EGFR was enhanced, which attenuated the steady-state levels of EGFR and promoted its ligand-induced degradation. These effects were not caused by changes in the ubiquitinating apparatus, but instead were due to reduced expression of the de-ubiquitinase, ubiquitin-specific protease 8 (USP8). Depletion of protein kinase Calpha (PKCalpha), a target of diacylglycerol, rescued the levels of USP8 and normalized EGFR degradation in DGKdelta-deficient cells. Moreover, the effects of PKCalpha were caused by its inhibition of Akt, which stabilizes USP8. Our data indicate a novel mechanism where DGKdelta and PKCalpha modulate the levels of ubiquitinated EGFR through Akt and USP8.

Bile acids induce cdx2 expression through the farnesoid x receptor in gastric epithelial cells

Clinical and experimental studies showed that the reflux of bile into the stomach contributes to the induction of intestinal metaplasia of the stomach and gastric carcinogenesis. Caudal-type homeobox 2 (Cdx2) plays a key role in the exhibition of intestinal phenotypes by regulating the expression of intestine-specific genes such as goblet-specific gene mucin 2 (MUC2). We investigated the involvement of the farnesoid X receptor (FXR), a nuclear receptor for bile acids, in the chenodeoxycholic acid (CDCA)-induced expression of Cdx2 and MUC2 in normal rat gastric epithelial cells (RGM-1 cells). RGM-1 cells were treated with CDCA or GW4064, an FXR agonist, in the presence or absence of guggulsterone, an FXR antagonist. CDCA induced dose-dependent expression of Cdx2 and MUC2 at both the mRNA and protein levels. The maximum stimulation of Cdx2 and MUC2 mRNA induced by CDCA was observed at 3 h and by 6 h, respectively. GW4064 also induced expression of these molecules. The effects of CDCA and GW4064 on expression of Cdx2 and MUC2 were abolished by guggulsterone. These findings suggest that bile acids may induce gastric intestinal metaplasia and carcinogenesis through the FXR.

Prognostic effect of activated EGFR expression in human colon carcinomas: comparison with EGFR status

BACKGROUND

Evidence suggests that epidermal growth factor receptor (EGFR)-activation status may better predict the clinical behaviour of colon cancers than does EGFR expression. However, the prognostic effect of phospho-EGFR in primary colon cancer remains undefined.

METHODS

Phospho-EGFR (Tyr-1173) and EGFR expression were analysed by immunohistochemistry (IHC) in tissue microarrays of TNM stage II and III colon cancers from completed adjuvant therapy trials (n=388). Staining intensity was scored and correlated with clinicopathological variables, DNA mismatch repair (MMR) status, rates of cell proliferation (Ki-67), apoptosis (caspase-3), and patient survival.

RESULTS

Phospho-EGFR expression was detected in 157 of 388 (40%) tumours, whereas EGFR was found in 214 of 361 (59%). Although phospho-EGFR was unrelated to clinicopathological variables, strong EGFR intensity was associated with higher tumour stage (P=0.03). Tumours overexpressing EGFR (P=0.0002) or phospho-EGFR (P=0.015) showed increased Ki-67, but not caspase-3 expression. Phospho-EGFR was not prognostic. EGFR intensity was associated with worse disease-free survival (DFS) (hazard ratio (HR): 1.21 (1.03, 1.41); P=0.019) and overall survival (OS) (HR: 1.19 (1.02, 1.39); P=0.028). Tumours expressing both EGFR and phospho-EGFR had similar survival as EGFR alone. Stage and lymph node number were prognostic for DFS and OS, and histological grade for OS. EGFR was an independent predictor of DFS (P=0.042) after adjustment for stage, histological grade, age, and MMR status.

CONCLUSION

Phospho-EGFR and EGFR expression were associated with tumour cell hyperproliferation. Phospho-EGFR was not prognostic, whereas increased EGFR intensity was independently associated with poor DFS.

The role of COX-2 in intestinal inflammation and colorectal cancer

Colorectal cancer (CRC) is a heterogeneous disease, including at least three major forms: hereditary, sporadic and colitis-associated CRC. A large body of evidence indicates that genetic mutations, epigenetic changes, chronic inflammation, diet and lifestyle are the risk factors for CRC. As elevated cyclooxygenase-2 (COX-2) expression was found in most CRC tissue and is associated with worse survival among CRC patients, investigators have sought to evaluate the effects of nonsteroidal anti-inflammatory drugs (NSAIDs) and selective COX-2 inhibitors (COXIBs) on CRC. The epidemiological studies, clinical trials and animal experiments indicate that NSAIDs are among the most promising chemopreventive agents for this disease. NSAIDs exert their anti-inflammatory and antitumor effects primarily by reducing prostaglandin production by inhibition of COX-2 activity. In this review, we highlight breakthroughs in our understanding of the roles of COX-2 in CRC and inflammatory bowel disease. These recent data provide a rationale for re-evaluating COX-2 as both the prognostic and the predictive marker in a wide variety of malignancies and for renewing the interest in evaluating relative benefits and risk of COXIBs in appropriately selected patients for cancer prevention and treatment.

Epidermal growth factor receptor is required for colonic tumor promotion by dietary fat in the azoxymethane/dextran sulfate sodium model: roles of transforming growth factor-{alpha} and PTGS2

PURPOSE

Colon cancer is a major cause of cancer deaths. Dietary factors contribute substantially to the risk of this malignancy. Western-style diets promote development of azoxymethane-induced colon cancer. Although we showed that epidermal growth factor receptors (EGFR) controlled azoxymethane tumorigenesis in standard fat conditions, the role of EGFR in tumor promotion by high dietary fat has not been examined.

EXPERIMENTAL DESIGN

A/J x C57BL6/J mice with wild-type Egfr (Egfr(wt)) or loss-of-function waved-2 Egfr (Egfr(wa2)) received azoxymethane followed by standard (5% fat) or western-style (20% fat) diet. As F(1) mice were resistant to azoxymethane, we treated mice with azoxymethane followed by one cycle of inflammation-inducing dextran sulfate sodium to induce tumorigenesis. Mice were sacrificed 12 weeks after dextran sulfate sodium. Tumors were graded for histology and assessed for EGFR ligands and proto-oncogenes by immunostaining, Western blotting, and real-time PCR.

RESULTS

Egfr(wt) mice gained significantly more weight and had exaggerated insulin resistance compared with Egfr(wa2) mice on high-fat diet. Dietary fat promoted tumor incidence (71.2% versus 36.7%; P < 0.05) and cancer incidence (43.9% versus 16.7%; P < 0.05) only in Egfr(wt) mice. The lipid-rich diet also significantly increased tumor and cancer multiplicity only in Egfr(wt) mice. In tumors, dietary fat and Egfr(wt) upregulated transforming growth factor-alpha, amphiregulin, CTNNB1, MYC, and CCND1, whereas PTGS2 was only increased in Egfr(wt) mice and further upregulated by dietary fat. Notably, dietary fat increased transforming growth factor-alpha in normal colon.

CONCLUSIONS

EGFR is required for dietary fat-induced weight gain and tumor promotion. EGFR-dependent increases in receptor ligands and PTGS2 likely drive diet-related tumor promotion.

Advances in research on hereditary colorectal neoplasms

Colorectal cancer is one of the most common digestive malignant tumors in China. Its incidence and mortality rates rank top among all malignant tumors. Previous studies show that nearly one-third of colorectal cancers are associated with hereditary colorectal tumors. Hereditary colorectal tumors are mainly divided into two categories: hereditary nonpolyposis colorectal cancer and hereditary colorectal polyposis. In this article, we will review the recent advances in research on hereditary colorectal neoplasms.

Regulation of miRNA expression by Src and contact normalization: effects on nonanchored cell growth and migration

Transformation by the Src tyrosine kinase (Src) promotes nonanchored cell growth and migration. However, nontransformed cells can force Src-transformed cells to assume a normal morphology and phenotype by a process called 'contact normalization'. It has become clear that microRNA (miRNA) can affect tumorigenesis by targeting gene products that direct cell growth and migration. However, the roles of miRNA in Src transformation or contact normalization have not yet been reported. We examined the expression of 95 miRNAs and found 9 of them significantly affected by Src. In this study, we report that miR-218 and miR-224 were most significantly induced by Src, but not affected by contact normalization. In contrast, miR-126 was most significantly suppressed by Src and was induced by contact normalization in transformed cells. Mir-126 targets Crk, a component of the focal adhesion network that participates in events required for tumor cell migration. Accordingly, we show that miR-126 expression correlates inversely with Crk levels, motility and the invasive potential of human mammary carcinoma cells. Moreover, we show that miR-224 expression promotes nonanchored growth of nontransformed cells. These data reveal novel insights into how Src regulates miRNA expression to promote hallmarks of tumor cell growth and invasion, and how nontransformed cells can affect miRNA expression in adjacent tumor cells to inhibit this process.

Epidermal growth factor receptor regulates pancreatic fibrosis

The development of pancreatic fibrosis has been shown to be a major component in several diseases of the pancreas including pancreatic cancer, chronic pancreatitis, and type 2 diabetes mellitus, but its actual role in the progression of these disorders is still unknown. This fibrosis is characterized by stromal expansion and the excessive deposition of extracellular matrix (ECM) that replaces pancreatic tissue. This eventually leads to dysregulation of ECM turnover, production of cytokines, restriction of blood flow, and often exocrine and endocrine insufficiencies. Activated pancreatic stellate cells (PSCs) have been identified as key mediators in the progression of pancreatic fibrosis, serving as the predominant source of excess ECM proteins. Previously, we found that overexpression of the growth factor heparin-binding epidermal growth factor-like growth factor (HB-EGF) in pancreatic islets led to intraislet fibrosis. HB-EGF binds to and activates two receptors, epidermal growth factor receptor (EGFR) and ErbB4, as well as heparin moieties and CD9/DRAP27. To understand the mechanism underlying the induction of fibrogenesis by HB-EGF, we utilized a hypomorphic allele of Egfr, the Waved-2 allele, to demonstrate that EGFR signaling regulates fibrogenesis in vivo. Using an in vitro cell migration assay, we show that HB-EGF regulates both chemoattraction and stimulation of proliferation of PSCs via EGFR activation.

Saccharomyces boulardii inhibits EGF receptor signaling and intestinal tumor growth in Apc(min) mice

BACKGROUND & AIMS

Saccharomyces boulardii (Sb) is a probiotic yeast with anti-inflammatory and anti-microbial activities and has been used for decades in the prevention and treatment of a variety of human gastrointestinal disorders. We reported previously that Sb modulates host inflammatory responses through down-regulation of extracellular signal-regulated kinase (Erk)1/2 activities both in vitro and in vivo. The aim of this study was to identify upstream mediators responsible for extracellular signal-regulated kinase (Erk)1/2 inactivation and to examine the effects of Sb on tumor development in Apc(Min) mice.

METHODS

Signaling studies of colon cancer cells were done by western blot. Cell proliferation was measured by MTS and BrdU assay. Apoptosis was examined by flow cytometry, tunel assay and caspase assay. Apc(Min) mice were orally given Sb for 9 weeks before sacrifice for tumor analysis.

RESULTS

We found that the epidermal growth factor receptor (EGFR) was deactivated upon exposure to Sb, leading to inactivation of both the EGFR-Erk and EGFR-Akt pathways. In human colonic cancer cells, Sb prevented EGF-induced proliferation, reduced cell colony formation, and promoted apoptosis. HER-2, HER-3, and insulin-like growth factor-1 receptor were also found to be inactivated by Sb. Oral intake of Sb reduced intestinal tumor growth and dysplasia in C57BL/6J Min/+ (Apc(Min)) mice.

CONCLUSIONS

Thus, in addition to its anti-inflammatory effects, Sb inhibits EGFR and other receptor tyrosine kinase signaling and thereby may also serve a novel therapeutic or prophylactic role in intestinal neoplasia.

Tumor-specific apoptosis caused by deletion of the ERBB3 pseudo-kinase in mouse intestinal epithelium

Pharmacologic blockade of EGFR or the closely related receptor ERBB2 has modest efficacy against colorectal cancers in the clinic. Although the upregulation of ERBB3, a pseudo-kinase member of the EGFR/ERBB family, is known to contribute to EGFR inhibitor resistance in other cancers, its functions in normal and malignant intestinal epithelium have not been defined. We have shown here that the intestinal epithelium of mice with intestine-specific genetic ablation of Erbb3 exhibits no cytological abnormalities but does exhibit loss of expression of ERBB4 and sensitivity to intestinal damage. By contrast, intestine-specific Erbb3 ablation resulted in almost complete absence of intestinal tumors in the ApcMin mouse model of colon cancer. Unlike nontransformed epithelium lacking ERBB3, intestinal tumors lacking ERBB3 had reduced PI3K/AKT signaling, which led to attenuation of tumorigenesis via a tumor-specific increase in caspase-3-mediated apoptosis. Consistent with the mouse data, which suggest that ERBB3-ERBB4 heterodimers contribute to colon cancer survival, experimentally induced loss of ERBB3 in a KRAS mutant human colon cancer cell line was associated with loss of ERBB4 expression, and siRNA knockdown of either ERBB3 or ERBB4 resulted in elevated levels of apoptosis. These results indicate that the ERBB3 pseudo-kinase has essential roles in supporting intestinal tumorigenesis and suggest that ERBB3 may be a promising target for the treatment of colorectal cancers.

Placental and embryonic growth restriction in mice with reduced function epidermal growth factor receptor alleles

Embryos lacking an epidermal growth factor receptor (EGFR) exhibit strain-specific defects in placental development that can result in mid-gestational embryonic lethality. To determine the level of EGFR signaling required for normal placental development, we characterized congenic strains homozygous for the hypomorphic Egfr(wa2) allele or heterozygous for the antimorphic Egfr(Wa5) allele. Egfr(wa2) homozygous embryos and placentas exhibit strain-dependent growth restriction at 15.5 days post-coitus while Egfr(Wa5) heterozygous placentas are only slightly reduced in size with no effect on embryonic growth. Egfr(wa2) homozygous placentas have a reduced spongiotrophoblast layer in some strains, while spongiotrophoblasts and glycogen cells are almost completely absent in others. Our results demonstrate that more EGFR signaling occurs in Egfr(Wa5) heterozygotes than in Egfr(wa2) homozygotes and suggest that Egfr(wa2) homozygous embryos model EGFR-mediated intrauterine growth restriction in humans. We also consistently observed differences between strains in wild-type placenta and embryo size as well as in the cellular composition and expression of trophoblast cell subtype markers and propose that differential expression in the placenta of Glut3, a glucose transporter essential for normal embryonic growth, may contribute to strain-dependent differences in intrauterine growth restriction caused by reduced EGFR activity.

A two-step model for colon adenoma initiation and progression caused by APC loss

Aberrant Wnt/beta-catenin signaling following loss of the tumor suppressor adenomatous polyposis coli (APC) is thought to initiate colon adenoma formation. Using zebrafish and human cells, we show that homozygous loss of APC causes failed intestinal cell differentiation but that this occurs in the absence of nuclear beta-catenin and increased intestinal cell proliferation. Therefore, loss of APC is insufficient for causing beta-catenin nuclear localization. APC mutation-induced intestinal differentiation defects instead depend on the transcriptional corepressor C-terminal binding protein-1 (CtBP1), whereas proliferation defects and nuclear accumulation of beta-catenin require the additional activation of KRAS. These findings suggest that, following APC loss, CtBP1 contributes to adenoma initiation as a first step, whereas KRAS activation and beta-catenin nuclear localization promote adenoma progression to carcinomas as a second step. Consistent with this model, human FAP adenomas showed robust upregulation of CtBP1 in the absence of detectable nuclear beta-catenin, whereas nuclear beta-catenin was detected in carcinomas.

Placental overgrowth and fertility defects in mice with a hypermorphic allele of epidermal growth factor receptor

Epidermal growth factor receptor (EGFR) is a member of the ERBB family of receptor tyrosine kinases that has been shown to play an important developmental and physiologic role in many aspects of pregnancy. We have previously shown in mice that Egfr(tm1Mag) nullizygous placentas have fewer proliferative trophoblasts than wild-type and exhibit strain-specific defects in the spongiotrophoblast and labyrinth layers. In this study we used mice with the hypermorphic Egfr(Dsk5) allele to study the effects of increased levels of EGFR signaling on placental development. On three genetic backgrounds, heterozygosity for Egfr(Dsk5) resulted in larger placental size with a more prominent spongiotrophoblast layer and increased expression of glycogen cell-specific genes. The C3HeB/FeJ strain showed additional placental enlargement of Egfr(Dsk5) homozygotes with a significant number of homozygous embryos dying prior to 15.5 days post-coitus (dpc). We also observed strain-specific subfertility in Egfr(Dsk5) heterozygous females and pregnancy loss was dependent on maternal factors rather than embryo genotype. Higher levels of phospho-EGFR were detected in the uterus of Egfr(Dsk5) heterozygotes but the structure of Egfr(Dsk5) heterozygous nonpregnant uteri appeared similar to wild-type. Collectively, our results demonstrate that mice with increased levels of EGFR signaling exhibit an extensive level of genetic background-dependent phenotypic variability. In addition, EGFR promotes growth of the placental spongiotrophoblast layer in mice, and EGFR expressed in the uterine stroma may play an underappreciated role in preparation of the uterus for embryo implantation.

Murine models of colorectal cancer

Colorectal cancer is one of the most prevalent cancers of humans. To experimentally investigate this common disease, numerous murine models have been established. These models accurately recapitulate the molecular and pathologic characteristics of human colorectal cancers, including activation of the myelocytomatosis oncogene (MYC), which has recently been suggested to be a key mediator of colorectal cancer development. This review focuses on the variety of murine models of human colorectal cancer that are available to the research community and on their use to identify common and distinct characteristics of colorectal cancer.

Inhibition of cell proliferation and invasion in a human colon cancer cell line by 5-aminosalicylic acid

BACKGROUND

5-Aminosalicylic acid lacks the well-known side effects associated with the long-term use of non-steroidal anti-inflammatory drugs. We investigated anti-carcinogenic mechanisms of 5-aminosalicylic acid on a colon cancer cell line.

METHODS

MTT analysis was performed for various colon cancer cell lines. The expression of NF-kappaB and metalloproteinases was examined in either HT-29 cells treated with IL-1beta and/or 5-aminosalicylic acid. Matrigel assay was used to evaluate invasive potential of HT-29 cells. Analysis of a cDNA microarray containing 8700 genes was performed to identify the alteration of gene expression in response to treatment to 5-aminosalicylic acid.

RESULTS

The use of MTT analysis showed that 5-aminosalicylic acid suppressed the growth of HT-29 cells. The activity of NF-kappaB was also decreased by combined-treatment with IL-1beta and 5-aminosalicylic acid. The use of an ELISA and zymography demonstrated that MMP-2 and MMP-9 enzyme activity were decreased in HT-29 cells by treatment with various concentration of 5-aminosalicylic acid. A matrigel analysis demonstrated that 5-aminosalicylic acid treatment on HT-29 significantly inhibited the invasiveness of the cells. In cDNA microarray, 163 genes following 5-aminosalicylic acid exposure showed altered expression.

CONCLUSIONS

This study indicated that 5-aminosalicylic acid suppresses the growth of human colon cancer cells and is able to inhibit MMPs expression via NF-kappaB mediated cell signals and invasiveness.

Chemoprevention of colorectal cancer: feasibility in everyday practice?

Chemoprevention means the use of agents to prevent, delay, or reverse carcinogenesis. This review was designed to critically discuss the most promising agents in colorectal cancer (CRC) chemoprevention. Aspirin is the best studied chemopreventive agent for CRC. Optimal chemoprevention requires long-term use and high dose of aspirin that may increase the risk of gastrointestinal bleeding. Nonsteroidal anti-inflammatory drugs and selective cyclooxygenase-2 inhibitors may also be candidates for chemoprevention. The regular use of nonsteroidal anti-inflammatory drugs, however, causes adverse effects including gastrointestinal bleeding, and cyclooxygenase-2 inhibitors may increase the risk of cardiovascular events. In patients with ulcerative colitis 5-aminosalicylates reduce the risk of CRC and dysplasia. Ursodeoxycholic acid can reduce the risk of dysplasia or CRC in patients with primary sclerosing cholangitis and ulcerative colitis. Current data are insufficient to support the use of hormone replacement therapy to reduce the risk of CRC. Statins may have chemopreventive effects, but further investigation of their overall benefits in preventing CRC is warranted. Antioxidant supplements cannot prevent CRC. The usefulness of selenium, folate, calcium, and vitamin D awaits further evaluation. Chemoprevention cannot yet be accepted as standard medical practice. Use of chemopreventive agents cannot be a substitute for colorectal surveillance.

Optical methodology for detecting histologically unapparent nanoscale consequences of genetic alterations in biological cells

Recently, there has been a major thrust to understand biological processes at the nanoscale. Optical microscopy has been exceedingly useful in imaging cell microarchitecture. Characterization of cell organization at the nanoscale, however, has been stymied by the lack of practical means of cell analysis at these small scales. To address this need, we developed a microscopic spectroscopy technique, single-cell partial-wave spectroscopy (PWS), which provides insights into the statistical properties of the nanoscale architecture of biological cells beyond what conventional microscopy reveals. Coupled with the mesoscopic light transport theory, PWS quantifies the disorder strength of intracellular architecture. As an illustration of the potential of the technique, in the experiments with cell lines and an animal model of colon carcinogenesis we show that increase in the degree of disorder in cell nanoarchitecture parallels genetic events in the early stages of carcinogenesis in otherwise microscopically/histologically normal-appearing cells. These data indicate that this advance in single-cell optics represented by PWS may have significant biomedical applications.

A plant flavonoid fisetin induces apoptosis in colon cancer cells by inhibition of COX2 and Wnt/EGFR/NF-kappaB-signaling pathways

Overexpression of cyclooxygenase 2 (COX2) and uncontrolled wingless and Int (Wnt)-signaling pathway have long been suggested to play crucial roles in colorectal cancer. Studies show that selective COX2 inhibitors possess great potential as chemopreventive agents for colon cancer. Recent studies suggest that targeting COX2 and epidermal growth factor receptor (EGFR) may provide better therapeutic strategy than inhibiting either single target and that this may alleviate the problem of COX2 inhibitor-associated side effects. Therefore, there have been intensive efforts to develop novel dietary substances that target COX2 and EGFR activation. Fisetin is a naturally occurring flavonoid commonly found in various vegetables and fruits. We found that the treatment of COX2-overexpressing HT29 human colon cancer cells with fisetin (30-120 microM) resulted in induction of apoptosis, downregulation of COX2 protein expression without affecting COX1 and inhibited the secretion of prostaglandin E2. Treatment of cells with fisetin also inhibited Wnt-signaling activity through downregulation of beta-catenin and T cell factor 4 and decreased the expression of target genes such as cyclin D1 and matrix metalloproteinase 7. Fisetin treatment of cells also inhibited the activation of EGFR and nuclear factor-kappa B (NF-kappaB). Finally, the formation of colonies in soft agar was suppressed by fisetin treatment. Taken together, we provide evidence that the plant flavonoid fisetin can induce apoptosis and suppress the growth of colon cancer cells by inhibition of COX2- and Wnt/EGFR/NF-kappaB-signaling pathways. We suggest that fisetin could be a useful agent for prevention and treatment of colon cancer.

ERBBs in the gastrointestinal tract: recent progress and new perspectives

The gastrointestinal epithelium does much more than provide a physical barrier between the intestinal lumen and our internal milieu. It is actively engaged in absorption and secretion of salt and water via ion transporters, exchangers and selective ion channels. It is also a continuously self-renewing epithelium that undergoes ordered growth and differentiation along its vertical axis. From this dual perspective, we will consider the actions of the ERBB family of ligands and receptors in the maintenance of gastrointestinal homeostasis and discuss instances when the actions of this family go awry such as in cancer and Ménétrier's disease.

Betacellulin stimulates growth of the mouse intestinal epithelium and increases adenoma multiplicity in Apc+/Min mice

We employed transgenic mice overexpressing betacellulin (BTC) to study its effects in the gut. BTC stimulated crypt cell proliferation and markedly increased intestinal size, while the crypt-villus architecture was preserved. Introduction of a dominant negative epidermal growth factor receptor (EGFR) completely abolished the intestinal hyperplasia. BTC increased polyp multiplicity but did not change the mean size or the histological quality of intestinal polyps in Apc(+/Min) mice. Analysis of intact and cleaved caspase-3 levels indicated that BTC has anti-apoptotic effects in the intestinal epithelium. We conclude that increased BTC levels support the survival of nascent adenomas in Apc(+/Min) mice, resulting in a larger total polyp number at later stages.

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.

Epidermal growth factor receptor controls flat dysplastic aberrant crypt foci development and colon cancer progression in the rat azoxymethane model

PURPOSE

Colonic carcinogenesis deranges growth-regulating epidermal growth factor receptors (EGFR). We previously showed that EGFR signals were up-regulated in human aberrant crypt foci (ACF), putative colon cancer precursors. The azoxymethane model of colon cancer recapitulates many aspects of human colonic tumors. Recent studies indicate that flat dysplastic ACF with increased beta-catenin are tumor precursors in this model. We asked, therefore, if EGFR signals are required for flat dysplastic ACF development and cancer progression.

EXPERIMENTAL DESIGN

Rats received azoxymethane or saline, and standard chow or chow supplemented with gefitinib, an EGFR inhibitor, for 44 weeks. EGFR signals were quantified in normal colon, flat ACF, and tumors by computerized analysis of immunostains and Western blots. K-ras mutations were assessed by PCR and mRNA for egfr ligands by quantitative real-time PCR.

RESULTS

EGFR inhibition with gefitinib decreased the incidence of flat dysplastic ACF from 66% to 36% and tumors from 71% to 22% (P < 0.05). This inhibitor also reduced the overexpressions of cyclin D1 and Cox-2 in flat ACF. Furthermore, in flat ACF, EGFR blockade decreased the up-regulation of c-Jun, FosB, phosphorylated active signal transducers and activators of transcription 3, and CCAAT/enhancer binding protein-beta, potential regulators of cyclin D1 and Cox-2. In colonic tumors, EGFR blockade significantly decreased angiogenesis, proliferation, and progression while also increasing apoptosis (P < 0.05). Gefitinib also inhibited the activations of extracellular signal-regulated kinase, Src, and AKT pathways in tumors.

CONCLUSIONS

We have shown for the first time that EGFR promotes the development of flat dysplastic ACF and the progression of malignant colonic tumors. Furthermore, we have mechanistically identified several transcription factors and their targets as EGFR effectors in colonic carcinogenesis.

Helicobacter hepaticus infection promotes colon tumorigenesis in the BALB/c-Rag2(-/-) Apc(Min/+) mouse

Adenomatous polyposis coli (APC) mutations are linked to human and mouse colorectal cancers. The Apc multiple intestinal neoplasia (Min) mouse mutation causes adenomas to develop throughout the small and large intestines. The BALB-Min (C.B6-Apc(Min/+)) congenic strain was generated by backcrossing into BALB/c the Apc(Min) allele from C57BL/6J-Apc(Min/+) mice. BALB-Min mice have a low tumor multiplicity (27.4 small intestine tumors/mouse) and a relatively long life span (>1 year) that makes them amenable to long-term studies. To investigate the interplay of the adaptive immune system and intestinal tumorigenesis, the immunodeficient compound mutant strain BALB-RagMin (C.Cg-Rag2(-/-) Apc(Min/+)) was generated. BALB-RagMin mice had a significant increase in tumors in the small, but not large, intestine relative to their BALB-Min counterparts (43.0 versus 24.0 tumors/mouse, respectively). The results suggest that the adaptive immune system plays a role in either the elimination or the equilibrium phase of cancer immunoediting in the small intestine in this model. We investigated the effect of the enterohepatic bacterial pathogen Helicobacter hepaticus on liver and intestine tumorigenesis in BALB-RagMin mice. H. hepaticus-infected BALB-RagMin mice developed moderate hepatitis, moderate typhlitis, and mild colitis. There were no differences in small intestine and cecal tumor multiplicity, regionality, or size relative to that in uninfected mice. However, H. hepaticus-infected BALB-RagMin mice had a significant increase in colon tumor incidence relative to uninfected BALB-RagMin mice (23.5% versus 1.7%, respectively). The data suggest that H. hepaticus, which is present in many research colonies, promotes colon tumorigenesis in the BALB-RagMin mouse and that it has the potential to confound colon tumorigenesis studies.

Deoxycholyltaurine rescues human colon cancer cells from apoptosis by activating EGFR-dependent PI3K/Akt signaling

Recent studies indicate that secondary bile acids promote colon cancer cell proliferation but their role in maintaining cell survival has not been explored. We found that deoxycholyltaurine (DCT) markedly attenuated both unstimulated and TNF-alpha-stimulated programmed cell death in colon cancer cells by a phosphatidylinositol 3-kinase (PI3K)-dependent mechanism. To examine the role of bile acids and PI3K signaling in maintaining colon cancer cell survival, we explored the role of signaling downstream of bile acid-induced activation of the epidermal growth factor receptor (EGFR) in regulating both apoptosis and proliferation of HT-29 and H508 human colon cancer cells. DCT caused dose- and time-dependent Akt (Ser(473)) phosphorylation, a commonly used marker of activated PI3K/Akt signaling. Both EGFR kinase and PI3K inhibitors attenuated DCT-induced Akt phosphorylation and Akt activation, as demonstrated by reduced phosphorylation of a GSK-3-paramyosin substrate. Transfection of HT-29 cells with kinase-dead EGFR (K721M) reduced DCT-induced Akt phosphorylation. In HT-29 cells, EGFR and PI3K inhibitors as well as transfection with dominant negative AKT attenuated DCT-induced cell proliferation. DCT-induced PI3K/Akt activation resulted in downstream phosphorylation of GSK-3 (Ser(21/9)) and BAD (Ser(136)), and nuclear translocation (activation) of NF-kappaB, thereby confirming that DCT-induced activation of PI3K/Akt signaling regulates both proproliferative and prosurvival signals. Collectively, these results indicate that DCT-induced activation of post-EGFR PI3K/Akt signaling stimulates both colon cancer cell survival and proliferation.

Chronic pharmacologic inhibition of EGFR leads to cardiac dysfunction in C57BL/6J mice

Molecule-targeted therapies like those against the epidermal growth factor receptor (EGFR) are becoming widely used in the oncology clinic. With improvements in treatment efficacy, many cancers are being treated as chronic diseases, with patients having prolonged exposure to several therapies that were previously only given acutely. The consequence of chronic suppression of EGFR activity may lead to unexpected toxicities like altered cardiac physiology, a common organ site for adverse drug effects. To explore this possibility, we treated C57BL/6J (B6) mice with two EGFR small molecule tyrosine kinase inhibitors (TKIs), irreversible EKB-569 and reversible AG-1478, orally for 3 months. In B6 female mice, chronic exposure to both TKIs depressed body weight gain and caused significant changes in left ventricular (LV) wall thickness and cardiac function. No significant differences were observed in heart weight or cardiomyocyte size but histological analysis revealed an increase in fibrosis and in the numbers of TUNEL-positive cells in the hearts from treated female mice. Consistent with histological results, LV apoptotic gene expression was altered, with significant downregulation of the anti-apoptotic gene Bcl2l1. Although there were no significant differences in any of these endpoints in treated male mice, suggesting sex may influence susceptibility to TKI mediated toxicity, the LVs of treated male mice had significant upregulation of Egf, Erbb2 and Nppb over controls. Taken together, these data suggest that chronic dietary exposure to TKIs may result in pathological and physiological changes in the heart.

Widespread hyperplasia induced by transgenic TGFalpha in ApcMin mice is associated with only regional effects on tumorigenesis

Using a mouse predisposed to neoplasia by a germ line mutation in Apc (Apc(Min)), we tested whether induced hyperplasia is sufficient to increase intestinal tumor multiplicity or size in the intestine. We found that hyperplasia in the jejunum correlated with a significant increase in tumor multiplicity. However, tumor multiplicity was unchanged in the hyperplastic colon. This result indicates that even an intestine predisposed to neoplasia can, in certain regions including the colon, accommodate net increased cell growth without developing more neoplasms. Where hyperplasia correlated with increased tumor multiplicity, it did not increase the size or net growth of established tumors. This result suggests that the event linking hyperplasia and neoplasia in the jejunum is tumor establishment. Two novel observations arose in our study: the multiple intestinal neoplasia (Min) mutation partially suppressed both mitosis and transforming growth factor alpha-induced hyperplasia throughout the intestine; and zinc treatment alone increased tumor multiplicity in the duodenum of Min mice.

Trisomy represses Apc(Min)-mediated tumours in mouse models of Down's syndrome

Epidemiological studies spanning more than 50 yr reach conflicting conclusions as to whether there is a lower incidence of solid tumours in people with trisomy 21 (Down's syndrome). We used mouse models of Down's syndrome and of cancer in a biological approach to investigate the relationship between trisomy and the incidence of intestinal tumours. Apc(Min)-mediated tumour number was determined in aneuploid mouse models Ts65Dn, Ts1Rhr and Ms1Rhr. Trisomy for orthologues of about half of the genes on chromosome 21 (Hsa21) in Ts65Dn mice or just 33 of these genes in Ts1Rhr mice resulted in a significant reduction in the number of intestinal tumours. In Ms1Rhr, segmental monosomy for the same 33 genes that are triplicated in Ts1Rhr resulted in an increased number of tumours. Further studies demonstrated that the Ets2 gene contributed most of the dosage-sensitive effect on intestinal tumour number. The action of Ets2 as a repressor when it is overexpressed differs from tumour suppression, which requires normal gene function to prevent cellular transformation. Upregulation of Ets2 and, potentially, other genes involved in this kind of protective effect may provide a prophylactic effect in all individuals, regardless of ploidy.

Concurrent EGFr and Cox-2 expression in colorectal cancer: proliferation impact and tumour spreading

BACKGROUND

Many reports were produced on single epidermal growth factor receptor (EGFr) and cyclo-oxygenase-2 (Cox-2) evaluation using immunohistochemical techniques (IHC), but very few works considered concurrent expression of these two proteins in the light of their impact on proliferation and tumour spreading. At least three molecular pathways (EGFr, Cox-2, and APC/beta-catenin molecular cascade) may interact in this malignancy giving rise to cross talking effects on proliferation and cancer spreading.

PATIENTS AND METHODS

To better detail these two latter aggressive features, we studied 205 sporadic colorectal cancer patients, comparing concurrent expression of EGFr, Cox-2, Ki-67, Cyclins D1-A, and E, with tumour spreading (budding) (BUD) and pN status.

RESULTS

Our results point to a different aggressive molecular profile due to Cox-2 expression. Cox-2 High expressing cases showed a clear EGFr proliferation-promoting role. On the contrary, EGFr seems directly involved in cancer cells spreading rather than in promoting cancer proliferation in Cox-2 Low/Negative cases.

CONCLUSIONS

Immunohistochemical profiling of colorectal cancer seems to be a promising approach, not only to define prognostic impact, but also to detail proliferation-related molecular interplays between EGFr and Cox-2 pathways, with these two latter proteins, at present, being the hottest pharmacological targets for colorectal cancer (CRC) chemoprevention and therapy.

Investigation of two dosing schedules of vandetanib (ZD6474), an inhibitor of vascular endothelial growth factor receptor and epidermal growth factor receptor signaling, in combination with irinotecan in a human colon cancer xenograft model

PURPOSE

This in vivo study was designed to determine the optimal doses and schedules of vandetanib, a dual epidermal growth factor receptor (EGFR)-vascular endothelial growth factor receptor tyrosine kinase inhibitor, in combination with irinotecan in a murine xenograft model of human colon cancer.

EXPERIMENTAL DESIGN

HT-29 tumor-bearing nude mice were treated with two doses of vandetanib (12.5 and 25 mg/kg/d) with or without irinotecan (100 mg/kg) using either sequential or concurrent schedules for 30 days. Tumor size was measured using standard variables, whereas the antiangiogenic response was evaluated using dynamic contrast-enhanced magnetic resonance imaging. Additionally, effects on EGFR-dependent signal transduction pathways and proliferation were assessed using immunohistochemistry. These pharmacodynamic end points were then evaluated for associations with antitumor efficacy and/or to plasma/tumor concentrations of vandetanib.

RESULTS

The greatest antitumor efficacy was observed in the groups receiving the highest dose of vandetanib given continuously (concurrent schedule), alone or in combination with irinotecan. These dosing schedules resulted in significant effects on tumor vasculature, with decreased volume transfer constants, area under the curve, and permeability surface factor as well as increased gadolinium clearance after 30 days of treatment. In addition, these groups showed the greatest inhibition of EGFR signaling. Interestingly, tumor concentrations of vandetanib were increased by irinotecan in the concurrent schedule, possibly due to decreased tumor perfusion in this group.

CONCLUSIONS

These data suggest that higher, sustained concentrations of vandetanib (versus intermittent), alone and in combination with irinotecan, result in optimal antitumor efficacy in this model and may have implications for the design of future clinical studies with this drug.