Beta-catenin antisense treatment decreases beta-catenin expression and tumor growth rate in colon carcinoma xenografts

Effect of vitamin E δ-tocotrienol and aspirin on Wnt signaling in human colon cancer stem cells and in adenoma development in APCmin/+ mice

In this study, we evaluated the effects of vitamin E δ-tocotrienol (DT3) and aspirin on Wnt signaling in human colon cancer stem cells (CCSCs) and in the prevention of adenoma formation in APCmin/+ mice. We found that knockdown of the adenomatous polyposis coli (APC) gene led to subsequent activation of Wnt signaling in colon epithelial cells (NCM460-APCsiRNA) and induction of β-catenin and its downstream target proteins c-MYC, cyclin D1, and survivin. When aspirin and DT3 were combined, cell growth and survival were inhibited and apoptosis was induced in colon epithelial cells and CCSCs. However, DT3 and/or aspirin had little or no effect on the control of normal colon epithelial cells (NCM460-NCsiRNA). The induction of apoptosis was directly related to the activation of caspase 8 and cleavage of BH3-interacting-domain (BID) to truncated BID. In addition, DT3- and/or aspirin-induced apoptosis was associated with cleaved Poly (ADP-ribose) polymerase (PARP), elevated levels of cytosolic cytochrome c and BAX, and depletion of antiapoptotic protein BCl-2 in CCSCs. The combination of aspirin and DT3 inhibited the self-renewal capacity, Wnt/β-catenin receptor activity, and expression of β-catenin and its downstream targets c-MYC, cyclin D1, and survivin in CCSCs. We also found that treatment with DT3 alone or combined with aspirin significantly inhibited intestinal adenoma formation and Wnt/β-catenin signaling and induced apoptosis, compared with vehicle, in APCmin/+ mice. Our study demonstrated a rationale for further investigation of the combination of DT3 and aspirin for colorectal cancer prevention and therapy.

Human Papillomaviruses as Infectious Agents in Gynecological Cancers. Oncogenic Properties of Viral Proteins

Human papillomaviruses (HPVs), which belong to the Papillomaviridae family, constitute a group of small nonenveloped double-stranded DNA viruses. HPV has a small genome that only encodes a few proteins, and it is also responsible for 5% of all human cancers, including cervical, vaginal, vulvar, penile, anal, and oropharyngeal cancers. HPV types may be classified as high- and low-risk genotypes (HR-HPVs and LR-HPVs, respectively) according to their oncogenic potential. HR-HPV 16 and 18 are the most common types worldwide and are the primary types that are responsible for most HPV-related cancers. The activity of the viral E6 and E7 oncoproteins, which interfere with critical cell cycle points such as suppressive tumor protein p53 (p53) and retinoblastoma protein (pRB), is the major contributor to HPV-induced neoplastic initiation and progression of carcinogenesis. In addition, the E5 protein might also play a significant role in tumorigenesis. The role of HPV in the pathogenesis of gynecological cancers is still not fully understood, which indicates a wide spectrum of potential research areas. This review focuses on HPV biology, the distribution of HPVs in gynecological cancers, the properties of viral oncoproteins, and the molecular mechanisms of carcinogenesis.

The multidimensional role of the Wnt/β-catenin signaling pathway in human malignancies

Several signaling pathways have been identified as important for developmental processes. One of such important cascades is the Wnt/β-catenin signaling pathway, which can regulate various physiological processes such as embryonic development, tissue homeostasis, and tissue regeneration; while its dysregulation is implicated in several pathological conditions especially cancers. Interestingly, deregulation of the Wnt/β-catenin pathway has been reported to be closely associated with initiation, progression, metastasis, maintenance of cancer stem cells, and drug resistance in human malignancies. Moreover, several genetic and experimental models support the inhibition of the Wnt/β-catenin pathway to answer the key issues related to cancer development. The present review focuses on different regulators of Wnt pathway and how distinct mutations, deletion, and amplification in these regulators could possibly play an essential role in the development of several cancers such as colorectal, melanoma, breast, lung, and leukemia. Additionally, we also provide insights on diverse classes of inhibitors of the Wnt/β-catenin pathway, which are currently in preclinical and clinical trial against different cancers.

Cytotoxic activity of broussochalcone a against colon and liver cancer cells by promoting destruction complex-independent β-catenin degradation

Aberrant activation of β-catenin-response transcription (CRT) is a well-recognized characteristic of colorectal and liver cancers and thus a potential therapeutic target for these malignancies. Broussonetia papyrifera (paper mulberry) has been used as a herbal medicine to treat various diseases. Using a sensitive cell-based screening system, we identified broussochalcone A (BCA), a prenylated chalcone isolated from Broussonetia papyrifera, as an antagonist of CRT. BCA accelerated the turnover of intracellular β-catenin that was accompanied by its N-terminal phosphorylation at Ser33/37/Thr41 residues, marking it for ubiquitin-dependent proteasomal degradation. Pharmacological inhibition of glycogen synthase kinase-3β could not abrogate BCA-mediated degradation of β-catenin. BCA decreased the intracellular β-catenin levels in colon and liver cancer cells with mutations in β-catenin, adenomatous polyposis coli, and Axin. BCA repressed the expressions of cyclin D1, c-Myc, and Axin2, which are β-catenin/T-cell factor-dependent genes, and thus decreased the viability of colon and liver cancer cell. Moreover, apoptosis was elicited by BCA, as indicated by the increase in the population of Annexin V-FITC positive cells and caspase-3/7 activities in colon and liver cancer cells. These findings indicate that BCA exerts its cytotoxic effects by promoting phosphorylation/ubiquitin-dependent degradation of β-catenin and may potentially serve as a chemopreventive agent for colonrectal and liver cancers.

Mutation Hotspots in the β-Catenin Gene: Lessons from the Human Cancer Genome Databases

Mutations in the β-catenin gene (CTNNB1) have been implicated in the pathogenesis of some cancers. The recent development of cancer genome databases has facilitated comprehensive and focused analyses on the mutation status of cancer-related genes. We have used these databases to analyze the CTNNB1 mutations assembled from different tumor types. High incidences of CTNNB1 mutations were detected in endometrial, liver, and colorectal cancers. This finding agrees with the oncogenic role of aberrantly activated β-catenin in epithelial cells. Elevated frequencies of missense mutations were found in the exon 3 of CTNNB1, which is responsible for encoding the regulatory amino acids at the N-terminal region of the protein. In the case of metastatic colorectal cancers, inframe deletions were revealed in the region spanning exon 3. Thus, exon 3 of CTNNB1 can be considered to be a mutation hotspot in these cancers. Since the N-terminal region of the β-catenin protein forms a flexible structure, many questions arise regarding the structural and functional impacts of hotspot mutations. Clinical identification of hotspot mutations could provide the mechanistic basis for an oncogenic role of mutant β-catenin proteins in cancer cells. Furthermore, a systematic understanding of tumor-driving hotspot mutations could open new avenues for precision oncology.

CCAAT/enhancer-binding protein-β functions as a negative regulator of Wnt/β-catenin signaling through activation of AXIN1 gene expression

Axin1, a concentration-limiting component of the β-catenin destruction complex, negatively regulates the Wnt/β-catenin pathway. Axin1 concentration is reported to be regulated by proteasomal degradation; however, its transcriptional regulation has not yet been reported. Here, we demonstrated that CCAAT/enhancer-binding protein-β (C/EBP-β) activates axis inhibition protein 1 (AXIN1) gene expression, thereby attenuating Wnt/β-catenin signaling. C/EBP-β interacted with cis-regulatory element for C/EBP-β in the 5′-upstream sequences of the AXIN1 gene and increased AXIN1 promoter activity. Functional analysis using Drosophila and zebrafish models established that C/EBP-β negatively regulates the Wnt/β-catenin pathway. Small-molecule-based up-regulation of C/EBP-β induces AXIN1 gene expression and down-regulates the intracellular β-catenin level, thereby inhibiting hepatoma cell growth. Thus, our findings provide a unique mechanistic insight into the regulation of Axin homeostasis and present a novel strategy for the development of anticancer therapeutics targeting Wnt/β-catenin signaling.

A Dominant Negative Antisense Approach Targeting β-Catenin

There have been many attempts to unveil the therapeutic potential of antisense molecules during the last decade. Due to its specific role in canonical Wnt signalling, β-catenin is a potential target for an antisense-based antitumour therapy. In order to establish such a strategy with peptide nucleic acids, we developed a reporter assay for quantification of antisense effects. The luciferase-based assay detects splice blocking with high sensitivity. Using this assay, we show that the splice donor of exon 13 of β-catenin is particularly suitable for an antisense strategy, as it results in a truncated protein which lacks transactivating functions. Since the truncated proteins retain the interactions with Tcf/Lef proteins, they act in a dominant negative fashion competing with wild-type proteins and thus blocking the transcriptional activity of β-catenin. Furthermore, we show that the truncation does not interfere with binding of cadherin and α-catenin, both essential for its function in cell adhesion. Therefore, the antisense strategy blocks Wnt signalling with high efficiency but retains other important functions of β-catenin.

Role of neutral ceramidase in colon cancer

Alterations in sphingolipid metabolism, especially ceramide and sphingosine 1-phosphate, have been linked to colon cancer, suggesting that enzymes of sphingolipid metabolism may emerge as novel regulators and targets in colon cancer. Neutral ceramidase (nCDase), a key enzyme in sphingolipid metabolism that hydrolyzes ceramide into sphingosine, is highly expressed in the intestine; however, its role in colon cancer has not been defined. Here we show that molecular and pharmacological inhibition of nCDase in colon cancer cells increases ceramide, and this is accompanied by decreased cell survival and increased apoptosis and autophagy, with minimal effects on noncancerous cells. Inhibition of nCDase resulted in loss of β-catenin and inhibition of ERK, components of pathways relevant for colon cancer development. Furthermore, inhibition of nCDase in a xenograft model delayed tumor growth and increased ceramide while decreasing proliferation. It is noteworthy that mice lacking nCDase treated with azoxymethane were protected from tumor formation. Taken together, these studies show that nCDase is pivotal for regulating initiation and development of colon cancer, and these data suggest that this enzyme is a suitable and novel target for colon cancer therapy.-García-Barros, M., Coant, N., Kawamori, T., Wada, M., Snider, A. J., Truman, J.-P., Wu, B. X., Furuya, H., Clarke, C. J., Bialkowska, A. B., Ghaleb, A., Yang, V. W., Obeid, L. M., Hannun, Y. A. Role of neutral ceramidase in colon cancer.

Crosstalk between Wnt/β-catenin and Hedgehog/Gli signaling pathways in colon cancer and implications for therapy

Wnt/β-catenin and Hedgehog/Gli signalings play key roles in multiple biogenesis such as embryonic development and tissue homeostasis. Dysregulations of these 2 pathways are frequently found in most cancers, particularly in colon cancer. Their crosstalk has been increasingly appreciated as an important mechanism in regulating colon cancer progression. Our studies into the link between Wnt/β-catenin and Hedgehog/Gli signalings in colon cancer revealed several possible crosstalk points and suggested potential therapeutic strategies for colon cancer.

A novel ent-kaurane diterpenoid executes antitumor function in colorectal cancer cells by inhibiting Wnt/β-catenin signaling

Aberrant activation of Wnt signaling pathway is crucial for the onset and progression of human colorectal cancer (CRC). Owing to the persistent dependence on Wnt signaling for growth and survival, inhibition of this pathway is an attractive approach for new therapies. 11α, 12α-epoxyleukamenin E (EPLE) is a novel ent-kaurane diterpenoid that we previously isolated from Salvia cavaleriei, exhibiting antitumor activities in a variety of cancer cells. Herein, we found that whereas sparing normal human colon mucosal epithelial cells, EPLE selectively inhibited the proliferation of CRC cell lines as well as primary tumor cells. Mechanistically, we demonstrated EPLE exerted its function through suppressing Wnt signaling pathway, as evidenced by EPLE-mediated downregulation of Wnt target genes such as c-Myc, Axin2 and Survivin. Consistently, luciferase reporter assays showed that the EPLE directly blocked Wnt/β-catenin-mediated transcriptional activation. In combination of co-immunoprecipitation and protein structure-based analyses, we determined that the EPLE entered the interface of β-catenin/TCF4 complexes and blocked their interaction that is required for β-catenin-mediated transcriptional activation. Moreover, overexpression of β-catenin alleviated the cytotoxicity of EPLE in CRC cells, supporting Wnt signaling is a major and specific target of EPLE. Combined treatments of EPLE and 5-fluorouracil, the first-line chemotherapy for CRC patients, achieved a synergistic effect. More importantly, EPLE hampered tumor development in a CRC xenograft model. Our data thus establish EPLE as a novel inhibitor of Wnt signaling that holds great promise as a potential candidate for further preclinical evaluation for CRC treatments.

Ilimaquinone and ethylsmenoquinone, marine sponge metabolites, suppress the proliferation of multiple myeloma cells by down-regulating the level of β-catenin

Deregulation of Wnt/β-catenin signaling promotes the development of a broad range of human cancers, including multiple myeloma, and is thus a potential target for the development of therapeutics for this disease. Here, we used a cell-based reporter system to demonstrate that ilimaquinone and ethylsmenoquinone (formerly smenorthoquinone), sesquiterpene-quinones from a marine sponge, inhibited β-catenin response transcription induced with Wnt3a-conditioned medium, by down-regulating the level of intracellular β-catenin. Pharmacological inhibition of glycogen synthase kinase-3β did not abolish the ilimaquinone and ethylsmenoquinone-mediated β-catenin down-regulation. Degradation of β-catenin was consistently found in RPMI-8226 multiple myeloma cells after ilimaquinone and ethylsmenoquinone treatment. Ilimaquinone and ethylsmenoquinone repressed the expression of cyclin D1, c-myc, and axin-2, which are β-catenin/T-cell factor-dependent genes, and inhibited the proliferation of multiple myeloma cells. In addition, ilimaquinone and ethylsmenoquinone significantly induced G₀/G₁ cell cycle arrest and apoptosis in RPMI-8266 cells. These findings suggest that ilimaquinone and ethylsmenoquinone exert their anti-cancer activity by blocking the Wnt/β-catenin pathway and have significant potential as therapies for multiple myeloma.

c-Src antisense complexed with PAMAM denderimes decreases of c-Src expression and EGFR-dependent downstream genes in the human HT-29 colon cancer cell line

c-Src is one member of non-receptor tyrosine kinase protein family that has over expression and activation in many human cancer cells. It has been shown that c-Src is implicated in various downstream signaling pathways associated with EGFR-dependent signaling such as MAPK and STAT5 pathways. Transactivation of EGFR by c-Src is more effective than EGFR ligands. To inhibit the c-Src expression, we used c-Src antisense oligonucleotide complexed with PAMAM Denderimes. The effect of c-Src antisense oligonucleotide on HT29 cell proliferation was determined by MTT assay. Then, the expression of c-Src, EGFR and the genes related to EGFR-depended signaling with P53 was applied by real time PCR. We used western blot analysis to elucidate the effect of antisense on the level of c-Src protein expression. The results showed, c-Src antisense complexed with PAMAM denderimers has an effective role in decrease of c-Src expression and EGFR-dependent downstream genes.

Drugging Wnt signalling in cancer

Aberrant regulation of the Wnt signalling pathway has emerged as a prevalent theme in cancer biology. This chapter summarizes the research that provides a proof of concept for inhibiting Wnt signalling in cancer, the potential means by which this could be achieved, and some recent advances towards this goal. A brief discussion of molecular diagnostics and possible safety concerns is also provided.

Wnt signaling in cancer

Aberrant regulation of the Wnt signaling pathway is a prevalent theme in cancer biology. From the earliest observation that Wnt overexpression could lead to malignant transformation of mouse mammary tissue to the most recent genetic discoveries gleaned from tumor genome sequencing, the Wnt pathway continues to evolve as a central mechanism in cancer biology. This article summarizes the evidence supporting a role for Wnt signaling in human cancer. This includes a review of the genetic mutations affecting Wnt pathway components, as well as some of epigenetic mechanisms that alter expression of genes relevant to Wnt. I also highlight some research on the cooperativity of Wnt with other signaling pathways in cancer. Finally, some emphasis is placed on laboratory research that provides a proof of concept for the therapeutic inhibition of Wnt signaling in cancer.

cGMP-dependent protein kinases as potential targets for colon cancer prevention and treatment

In recent years, several antitumor signaling pathways mediated by the cGMP-dependent protein kinases have been identified in colon cancer cells. This review aims to present the mounting evidence in favor of cGMP/protein kinase G (PKG) signaling as a therapeutic strategy in colon cancer. The homeostatic and tumor suppressive effects of cGMP in the intestine are uncontested, but the signaling details are not understood. PKG is the central cGMP effector, and can block proliferation and tumor angiogenesis by inhibiting β-catenin/TCF and SOX9 signaling. Therapeutic activation of cGMP/PKG offers a promising avenue for the prevention and treatment of colon cancer, but additional preclinical studies are needed to fully understand the potential of this system.

Galangin suppresses the proliferation of β-catenin response transcription-positive cancer cells by promoting adenomatous polyposis coli/Axin/glycogen synthase kinase-3β-independent β-catenin degradation

Galangin is a naturally occurring bioflavonoid with anticancer activity against certain human cancers, yet little is known about its mechanism of action. Here, we used a chemical biology approach to reveal that galangin suppresses β-catenin response transcription (CRT), which is aberrantly up-regulated in colorectal and liver cancers, by promoting the degradation of intracellular β-catenin. Inhibition of glycogen synthase kinase-3β (GSK-3β) activity or mutation of the GSK-3β-targeted sequence from β-catenin was unable to abrogate the galangin-mediated degradation of β-catenin. In addition, galangin down-regulated the intracellular β-catenin levels in cancer cells with inactivating mutations of adenomatous polyposis coli (APC) or Axin, which are components of the β-catenin destruction complex. Galangin repressed the expression of β-catenin/T-cell factor-dependent genes, such as cyclin D1 and c-myc, and thus inhibited the proliferation of CRT-positive cancer cells. Structure-activity data indicated that the major structural requirements for galangin-mediated β-catenin degradation are hydroxyl groups at positions 3, 5, and 7. Our findings suggest that galangin exerts its anticancer activity by promoting APC/Axin/GSK-3β-independent proteasomal degradation of β-catenin.

Postgenomic technologies targeting the Wnt signaling network

The recent development of high-throughput sequencing technologies and the availability of whole genome sequences of a variety of living organisms, including that of humans, have led to an enormous push in the quest for a comprehensive inquiry for the function of each and every gene discovered in different model organisms. A major conclusion from the sequencing projects was that while forward genetics had been extremely successful in identifying key genes/components of many biological processes, such as signal transduction cascades, the function(s) of the majority of genes in the genome remains a mystery. In this article, we discuss the use of a variety of high-throughput postgenomic tools, including functional genomics, proteomics, and chemical genetics that are being implemented in an exhaustive molecular dissection of a key evolutionarily conserved signal transduction pathway, namely the Wnt/wingless (wg) pathway and its associated signaling network.

Development of small molecules targeting the Wnt pathway for the treatment of colon cancer: a high-throughput screening approach

Wnt proteins play major roles in development and differentiation, and abnormalities in their regulation are believed to contribute to the formation of many cancers, including colorectal malignancies. As a result, there has been an interest in identifying small molecule inhibitors of Wnt signaling as tool compounds for research or as precursors to new generations of anticancer drugs. Advancements in robotic technology along with reductions in the costs of equipment, chemical libraries, and information handling have made high-throughput drug discovery programs possible in an academic setting. In this minireview we discuss the most plausible protein targets for inhibiting Wnt signaling in colon cancer therapy, list small molecule Wnt inhibitors that have been identified through recent drug discovery efforts, and provide our laboratory's strategy for identifying novel Wnt signaling antagonists using high-throughput screening. In particular, we summarize the results of a screen of over 1,200 drug and druglike compounds we recently completed in which niclosamide was identified as a Wnt pathway antagonist.

Murrayafoline A attenuates the Wnt/beta-catenin pathway by promoting the degradation of intracellular beta-catenin proteins

Molecular lesions in Wnt/beta-catenin signaling and subsequent up-regulation of beta-catenin response transcription (CRT) occur frequently during the development of colon cancer. To identify small molecules that suppress CRT, we screened natural compounds in a cell-based assay for detection of TOPFalsh reporter activity. Murrayafoline A, a carbazole alkaloid isolated from Glycosmis stenocarpa, antagonized CRT that was stimulated by Wnt3a-conditioned medium (Wnt3a-CM) or LiCl, an inhibitor of glycogen synthase kinase-3beta (GSK-3beta), and promoted the degradation of intracellular beta-catenin without altering its N-terminal phosphorylation at the Ser33/37 residues, marking it for proteasomal degradation, or the expression of Siah-1, an E3 ubiquitin ligase. Murrayafoline A repressed the expression of cyclin D1 and c-myc, which is known beta-catenin/T cell factor (TCF)-dependent genes and thus inhibited the proliferation of various colon cancer cells. These findings indicate that murrayafoline A may be a potential chemotherapeutic agent for use in the treatment of colon cancer.

Isoreserpine promotes beta-catenin degradation via Siah-1 up-regulation in HCT116 colon cancer cells

Aberrant accumulation of intracellular beta-catenin in intestinal epithelial cells is a frequent early event during the development of colon cancer. To identify small molecules that decrease the level of intracellular beta-catenin, we performed cell-based chemical screening using genetically engineered HEK293 reporter cells to detect compounds that inhibit TOPFlash reporter activity, which was stimulated by Wnt3a-conditioned medium. We found that isoreserpine promoted the degradation of intracellular beta-catenin by up-regulation of Siah-1 in HEK293 and HCT116 colon cancer cells. Moreover, isoreserpine repressed the expression of beta-catenin/T-cell factor (TCF)-dependent genes, such as cyclin D1 and c-myc, resulting in the suppression of HCT116 cell proliferation. Our findings suggest that isoreserpine can potentially be used as a chemotherapeutic agent against colon cancer.

New mechanisms and therapeutic potential of curcumin for colorectal cancer

Curcumin is a polyphenol derived from Curcuma longa. Over the last few years, a number of studies have provided evidence of its main pharmacological properties including chemosensitizing, radiosensitizing, wound healing activities, antimicrobial, antiviral, antifungical, immunomodulatory, antioxidant and anti-inflammatory. More recent data provide interesting insights into the effect of this compound on cancer chemoprevention and chemotherapy. In fact, preclinical studies have shown its ability to inhibit carcinogenesis in various types of cancer including colorectal cancer (CRC). Curcumin has the capacity of interact with multiple molecular targets affecting the multistep process of carcinogenesis. Also, curcumin is able to arrest the cell cycle, to inhibit the inflammatory response and the oxidative stress and to induce apoptosis in cancer cells. Likewise, it has been shown to possess marked antiangiogenic properties. Furthermore, curcumin potentiates the growth inhibitory effect of cyclo-oxygenase (COX)-2 inhibitors and traditional chemotherapy agents implicating another promising therapy regimen in the future treatment of CRC. However, its clinical advance has been hindered by its short biological half-life and low bioavailability after oral administration. This review is intended to provide the reader an update of the bioavailability and pharmacokinetics of curcumin and describes the recently identified molecular pathways responsible of its anticancer potential in CRC.

Targeted suppression of beta-catenin blocks intestinal adenoma formation in APC Min mice

Mutations involving the adenomatous polyposis coli (APC) tumor suppressor gene leading to activation of beta-catenin have been identified in the majority of sporadic colonic adenocarcinomas and in essentially all colonic tumors from patients with Familial Adenomatous Polyposis. The C57BL/6J-APC(min) (Min) mouse, which carries a germ line mutation in the murine homolog of the APC gene is a useful model for intestinal adenoma formation linked to loss of APC activity. One of the critical downstream molecules regulated by APC is beta-catenin; molecular targeting of beta-catenin is, thus, an attractive chemopreventative strategy in colon cancer. Antisense oligodeoxynucleotides (AODNs) capable of downregulating murine beta-catenin have been identified. ANALYSIS OF beta-CATENIN PROTEIN EXPRESSION IN LIVER TISSUE AND INTESTINAL ADENOMAS: Adenomas harvested from mice treated for 7 days with beta-catenin AODNs demonstrated clear downregulation of beta-catenin expression, which was accompanied by a significant reduction in proliferation. There was no effect on proliferation in normal intestinal epithelium. Min mice treated systemically with beta-catenin AODNs over a 6-week period had a statistically significant reduction in the number of intestinal adenomas. These studies provide direct evidence that targeted suppression of beta-catenin inhibits the formation of intestinal adenomas in APC-mutant mice. Furthermore, these studies suggest that molecular targeting of beta-catenin holds significant promise as a chemopreventative strategy in colon cancer.

Drug development against metastasis-related genes and their pathways: a rationale for cancer therapy

It is well recognized that the majority of cancer related deaths is caused by metastatic diseases. Therefore, there is an urgent need for the development of therapeutic intervention specifically targeted to the metastatic process. In the last decade, significant progress has been made in this research field, and many new concepts have emerged that shed light on the molecular mechanism of metastasis cascade which is often portrayed as a succession of six distinct steps; localized invasion, intravasation, translocation, extravasation, micrometastasis and colonization. Successful metastasis is dependent on the balance and complex interplay of both the metastasis promoters and suppressors in each step. Therefore, the basic strategy of our interventions is aimed at either blocking the promoters or potentiating the suppressors in this disease process. Toward this goal, various kinds of antibodies and small molecules have been designed. These include agents that block the ligand-recepter interaction of metastasis promoters (HGF/c-Met), antagonize the metastasis-promoting enzymes (AMF, uPA and MMP) and inhibit the transcriptional activity of metastasis promoter (beta-Catenin). On the other hand, the intriguing roles of metastasis suppressors and their signal pathways have been extensively studied and various attempts have been made to potentiate these factors. Small molecules have been developed to restore the expression or mimic the function of metastasis-suppressor genes such as NM23, E-cadherin, Kiss-1, MKK4 and NDRG1, and some of them are under clinical trials. This review summarizes our current understanding of the molecular pathway of tumor metastasis and discusses strategies and recent development of anti-metastatic drugs.

Nuclear β-catenin expression as a prognostic factor in advanced colorectal carcinoma

AIM: To investigate the changing pattern of β-catenin expression and its prognostic value in advanced colorectal cancer (CRC).

METHODS: Archival tumor samples were analyzed for β-catenin using immunohistochemistry (IHC) in 95 patients with advanced CRC.

RESULTS: Membranous β-catenin expression was found in the normal colorectal epithelium. Almost 100% of CRC cases showed membranous and cytoplasmic expression, and 55 (58%) cases showed nuclear expression. In univariate (Kaplan-Meier) survival analysis, only the nuclear index (NI) was a significant predictor of disease-free survival (DFS) (P = 0.023; n = 35), with a NI above the median associated with longer DFS (34.2 mo) than those with a NI below the median (15.5 mo) (P = 0.045, ANOVA). The other indices were not significant predictors of DFS, and none of the three tested indices (for membranous, cytoplasmic, or nuclear expression) predicted disease-specific survival (DSS). However, when dichotomized as positive or negative nuclear expression, the former was a significant predictor of more favorable DFS (P = 0.041) and DSS (P = 0.046).

CONCLUSION: Nuclear β-catenin expression provides additional information in predicting patient outcome in advanced CRC.

Protein kinase G as a therapeutic target for the treatment of metastatic colorectal cancer

Colorectal cancer is a leading cause of cancer-related death in the world and there is an urgent need for new strategies to combat this disease. Findings from several independent laboratories have converged on cGMP signaling as an exciting new therapeutic target, but the mechanisms remain controversial. A key intracellular effector of cGMP is protein kinase G (PKG). This article reviews the scientific literature concerning PKG effects on tumor development and progression, and discusses possible strategies for its exploitation in future cancer therapies. Studies from several independent laboratories have described novel anti-tumor effects of PKG in colon cancer cells that include inhibition of tumor growth and angiogenesis. While more preclinical research is warranted to better understand signaling mechanisms, these properties support the notion that PKG is a novel cancer target.

An oncogenic hub: beta-catenin as a molecular target for cancer therapeutics

The Wnt/beta-catenin signaling pathway plays diverse roles in embryonic development and in maintenance of organs and tissues in adults. Activation of this signaling cascade inhibits degradation of the pivotal component beta-catenin, which in turn stimulates transcription of downstream target genes. Over the past two decades, intensive worldwide investigations have yielded considerable progress toward understanding the cellular and molecular mechanisms of Wnt signaling and its involvement in the pathogenesis of a range of human diseases. Remarkably, beta-catenin signaling is aberrantly activated in greater than 70% of colorectal cancers and to a lesser extent in other tumor types, promoting cancer cell proliferation, survival and migration. Accordingly, beta-catenin has gained recognition as an enticing molecular target for cancer therapeutics. Disruption of protein-protein interactions essential for beta-catenin activity holds immense promise for the development of novel anti-cancer drugs. In this review, we focus on the regulation of beta-catenin-dependent transcriptional activation and discuss potential therapeutic opportunities to block this signaling pathway in cancer.

Derivation of sarcomas from mesenchymal stem cells via inactivation of the Wnt pathway

Malignant fibrous histiocytoma (MFH), now termed high-grade undifferentiated pleomorphic sarcoma, is a commonly diagnosed mesenchymal tumor, yet both the underlying molecular mechanisms of tumorigenesis and cell of origin remain unidentified. We present evidence demonstrating that human mesenchymal stem cells (hMSCs) are the progenitors of MFH. DKK1, a Wnt inhibitor and mediator of hMSC proliferation, is overexpressed in MFH. Using recombinant proteins, antibody depletion, and siRNA knockdown strategies of specific Wnt elements, we show that DKK1 inhibits hMSC commitment to differentiation via Wnt2/beta-catenin canonical signaling and that Wnt5a/JNK noncanonical signaling regulates a viability checkpoint independent of Dkk1. Finally, we illustrate that hMSCs can be transformed via inhibition of Wnt signaling to form MFH-like tumors in nude mice, and conversely, MFH cells in which Wnt signaling is appropriately reestablished can differentiate along mature connective tissue lineages. Our results provide mechanistic insights regarding the cell of origin of MFH, establish what we believe is a novel tumor suppressor role for Wnt signaling, and identify a potential therapeutic differentiation strategy for sarcomas.

Small-molecule modulators of Hh and Wnt signaling pathways

Hedgehog (Hh) and Wnt signaling pathways play key roles in growth and patterning during embryonic development and in the postembryonic regulation of stem cell number in the epithelia. Numerous studies link aberrant modulation of these pathways to specific human diseases. This article focuses on general aspects of Hh and Wnt signal transduction and biologic molecules involved in the respective signaling cascades. Specifically, the authors summarize small-molecule modulators of both pathways that show promise as therapeutic modalities.

Expression level of beta-catenin is associated with prognosis of esophageal carcinoma

AIM: To examine the association of beta-catenin with the clinicopathologic features and prognosis of esophageal squamous cell carcinoma (ESCC).

METHODS: Beta-catenin mRNA expression level in 40 ESCC patients (28 males and 12 females, age range 38-82 years, median 60 years) was analyzed by real-time PCR. Beta-catenin mRNA expression levels in tumor cells were categorized as weaker (level 1) or equal to or stronger (level 2) than those in endothelial cells. We examined the correlation between the beta-catenin expression and the clinicopathological factors and prognosis of ESCC patients.

RESULTS: Level 2 beta-catenin expression was found in 29 patients. ESCC with level 2 expression had a higher rate of lymphnode metastasis (0.0776 ± 0.0369 vs 0.3413 ± 0.1803, P < 0.001) and deeper tumor invasion (0.0751 ± 0.0356 vs 0.3667 ± 0.1928, P < 0.001), and a poorer survival rate (P = 0.0024) than ESCC with level 1 expression.

CONCLUSION: Beta-catenin expression in ESCC is of great importance.

Targeting the Wnt signaling pathway to treat Barrett’s esophagus

Barrett's esophagus (BE) is an acquired condition in which the normal squamous epithelium in the distal esophagus is replaced by a metaplastic columnar epithelium, as a complication of chronic gastroesophageal reflux. The clinical significance of this disease is its associated predisposition to esophageal adenocarcinoma (EAC). Recently, and similarly to other human malignancies, the Wnt signaling pathway and its key component beta-catenin have been implicated in the carcinogenesis of BE. Although mutations in adenomatous polyposis coli (APC) or beta-catenin are rare in EAC, alterations of upstream components, such as overexpression of Wnt2 ligand or downregulation of Wnt antagonists may play dominant roles in the activation of the Wnt pathway. Increasing evidence suggests that inhibiting the Wnt pathway may be a new targeted therapy for the treatment of cancers and could, therefore, be promising for the cure of EAC, which remains a highly lethal disease.

Wnt signaling in stem cells and lung cancer

The Wnt signal transduction pathway plays important roles during embryo development, regulating cell proliferation and survival of immature cells. However, its improper function can lead to harmful consequences for humans, such as aberrant cell proliferation and, therefore, cancer. Increasing evidence suggests that stem cells may be the source of mutant cells that cause cancers to develop and proliferate. Wnt signaling has been shown to promote self-renewal in both gut epithelial and hematopoietic stem cells (HSCs) and to trigger critical pathways in carcinogenesis. Although the function of stem cells in solid tumor development is unclear, the Wnt pathway's role in determining the fate and self-renewal potential of cancer stem cells suggests a critical role in carcinogenesis. The development of new inhibitors, such as antibodies or small molecules, to inhibit this pathway may be of great therapeutic utility against cancer.

Truncated APC regulates the transcriptional activity of beta-catenin in a cell cycle dependent manner

Most colon cancer cells express truncated versions of the tumour suppressor Adenomatous Polyposis Coli (APC). These molecules are selected during tumourigenesis for impaired beta-catenin degrading activity. In this study, we describe that truncated APC can still control the activity of beta-catenin in colon cancer cell lines via its first 20 amino acid repeat. First, we show that both endogenous and ectopically expressed truncated APC molecules can bind to beta-catenin. Second, reduction of the levels of truncated APC by RNA interference increases the activity of a beta-catenin-dependent reporter gene and stimulates the expression of the beta-catenin target gene AXIN2/conductin. This occurs without alterations of the amounts of cytosolic beta-catenin. Conversely, ectopic expression of truncated APC decreases beta-catenin-dependent transcription without affecting the intensity of immunofluorescence staining of beta-catenin in transfected cells. Third, we reveal that the APC level increases when cells reach the G1-S boundary during cell cycle progression. Simultaneously, the amount of beta-catenin bound to APC increases and the transcriptional activity of beta-catenin drops in an APC-dependent manner. Again, this occurs independently of the amounts of either total or phosphorylated cytosolic beta-catenin. Together, these results indicate that truncated APC controls the ability of beta-catenin to activate transcription. As we also show that the inhibition involves the first 20 amino acid repeat of APC, our data suggest that colon cancer cells retain a truncated APC molecule containing at least the first 20 amino acid repeat to modulate the transcriptional activity of beta-catenin in a cell cycle-dependent manner.

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Effect of aspirin on the Wnt/beta-catenin pathway is mediated via protein phosphatase 2A

Nonsteroidal anti-inflammatory drugs show chemopreventive efficacy in colon cancer, but the mechanism behind this remains unclear. Elucidating this mechanism is seen as vital to the development of new chemopreventive agents. We studied the effects of aspirin on the oncogenic Wnt/beta-catenin pathway activity in colorectal cancer cell lines and observed that aspirin dose-dependently decreased the activity of this pathway, as judged by TCF-driven luciferase activity, reduced Wnt target gene expression and increased phosphorylation of beta-catenin by immunoblotting. Furthermore, the ubiquitination and cytoplasmic levels of beta-catenin were assessed by immunoblotting, and also the localization of beta-catenin was shown by green fluorescent protein-tagged beta-catenin and time-lapse fluorescent imaging. Importantly, aspirin treatment caused increased phosphorylation of protein phosphatase 2A (PP2A), an event associated with inhibition of PP2A enzymatic activity, which was confirmed by a reduction in enzymatic PP2A activity. Moreover, this inhibition of PP2A enzymatic activity was essential for the effects of aspirin on the Wnt/beta-catenin pathway as shown by transient transfection with PP2A constructs. The findings in this article provide a molecular explanation for the efficacy of aspirin in chemoprevention of colorectal cancer and shows biochemical evidence that PP2A is an important regulator of Wnt/beta-catenin pathway activity in these cells.

Notch and Wnt inhibitors as potential new drugs for intestinal neoplastic disease

Colorectal cancer is a major cause of death in the western world. Recent advances in treatment comprise variations on the classical themes of surgical resection combined with chemotherapy using cytotoxic drugs and radiation therapy. Because this therapy is only moderately successful, novel approaches to the treatment of colorectal cancer are required. Our rapidly increasing knowledge of molecular signalling pathways that are deregulated in colorectal cancer might provide a platform from which to develop new rational cancer therapies. Here, we give an update on the roles of the Wnt and Notch signalling pathways in the self renewal of the intestinal epithelium and the consequences of Wnt deregulation in colorectal cancer. We focus on the potential of recently identified small-molecule inhibitors of the Wnt pathway and gamma-secretase inhibitors of the Notch pathway as novel colon cancer therapeutics.

Changes in the Wnt signalling pathway in gastrointestinal cancers and their prognostic significance

Many steps in the Wnt signalling pathway may be altered during the process of carcinogenesis. This Review focuses on the changes observed in gastrointestinal cancers. A literature search was undertaken and the currently available data summarised. Understanding the alterations to this signalling pathway may help to reveal future targets for therapeutic agents. In addition, since in some tumours, levels of components of the Wnt pathway have been found to correlate with clinical stage, their potential use as prognostic indicators is highlighted.

Curcumin, a multi-functional chemopreventive agent, blocks growth of colon cancer cells by targeting beta-catenin-mediated transactivation and cell-cell adhesion pathways

Colorectal cancer, the second most frequent diagnosed cancer in the US, causes significant morbidity and mortality in humans. Over the past several years, the molecular and biochemical pathways that influence the development of colon cancer have been extensively characterized. Since the development of colon cancer involves multi-step events, the available drug therapies for colorectal cancer are largely ineffective. The radiotherapy, photodynamic therapy, and chemotherapy are associated with severe side effects and offer no firm expectation for a cure. Thus, there is a constant need for the investigation of other potentially useful options. One of the widely sought approaches is cancer chemoprevention that uses natural agents to reverse or inhibit the malignant transformation of colon cancer cells and to prevent invasion and metastasis. Curcumin (diferuloylmethane), a natural plant product, possesses such chemopreventive activity that targets multiple signalling pathways in the prevention of colon cancer development.

Expression level of Wnt signaling components possibly influences the biological behavior of colorectal cancer in different age groups

Advancing of age apparently influences the behavior of colorectal cancer (CRC). The pattern of activation and expression of Wnt target genes may influence the behavior of the cancer. In the present study, the level of activation of some elements of Wnt signaling was evaluated and correlated with the patient's age and clinicopathological characteristics of the tumor. Beta-catenin and c-Myc mRNA expressions were evaluated by semiquantitative real-time PCR, and subcellular localization of the beta-catenin protein was evaluated by immunohistochemistry. Patients aged 70-84 tended to have locally advanced disease more frequently than younger patients. The same group of patients also more frequently had high nuclear expression of beta-catenin protein and higher expression of c-Myc mRNA. Beta-catenin mRNA had a rather constant expression with advancing of age. High nuclear expression of beta-catenin and high expression of c-Myc were apparently also correlated with locally advanced disease. We concluded that the level of Wnt signaling activation might influence the behavior of the disease in different age groups.

Down-regulation of beta catenin inhibits the growth of esophageal carcinoma cells

INTRODUCTION

Esophageal cancer remains a highly lethal malignancy, with therapeutic options of limited efficacy in the majority of patients. Understanding the molecular events involved in the pathogenesis of esophageal cancer offers insight into potential targets for treatment. Beta catenin and Wnt signaling abnormalities are involved in the development of both adenocarcinoma and squamous carcinoma of the esophagus. We hypothesized that down-regulation of beta catenin would inhibit the growth of human esophageal cancer.

METHODS

A human esophageal squamous cell carcinoma cell line (TE10) was treated with phosphorothioate antisense oligonucleotides to beta catenin. The cells were subsequently assayed for beta catenin mRNA and protein by real-time polymerase chain reaction and Western blot. Beta catenin transcriptional activity was determined by TOPFlash assay. Cell viability and growth was assessed by methyl-thiazol-diphenyl-tetrazolium assay and trypan blue exclusion. A colorimetric assay was employed to assess caspase 3 activity, and flow cytometry was done to determine percentage of cells in a given phase of the cell cycle.

RESULTS

Following antisense treatment, beta catenin mRNA and protein concentration were decreased. There was corresponding decrease in beta catenin-transcription factor-dependent transcription. Treatment with beta catenin antisense resulted in significantly decreased cell viability and proliferation. The mechanism appears to be increased induction of apoptosis.

CONCLUSIONS

These data suggest a potential role for the targeting of beta catenin in the treatment of esophageal cancer.

Small-molecule antagonists of the oncogenic Tcf/beta-catenin protein complex

Key molecular lesions in colorectal and other cancers cause beta-catenin-dependent transactivation of T cell factor (Tcf)-dependent genes. Disruption of this signal represents an opportunity for rational cancer therapy. To identify compounds that inhibit association between Tcf4 and beta-catenin, we screened libraries of natural compounds in a high-throughput assay for immunoenzymatic detection of the protein-protein interaction. Selected compounds disrupt Tcf/beta-catenin complexes in several independent in vitro assays and potently antagonize cellular effects of beta-catenin-dependent activities, including reporter gene activation, c-myc or cyclin D1 expression, cell proliferation, and duplication of the Xenopus embryonic dorsal axis. These compounds thus meet predicted criteria for disrupting Tcf/beta-catenin complexes and define a general standard to establish mechanism-based activity of small molecule inhibitors of this pathogenic protein-protein interaction.