Development of TGF-beta signalling inhibitors for cancer therapy

The transforming growth factor-beta (TGF-beta) superfamily of ligands has a pivotal role in the regulation of a wide variety of physiological processes from development to pathogenesis. Since the discovery of the prototypic member, TGF-beta, almost 20 years ago, there have been tremendous advances in our understanding of the complex biology of this superfamily. Deregulation of TGF-beta has been implicated in the pathogenesis of a variety of diseases, including cancer and fibrosis. Here we present the rationale for evaluating TGF-beta signalling inhibitors as cancer therapeutics, the structures of small-molecule inhibitors that are in development and the targeted drug discovery model that is being applied to their development.

Early changes in protein expression detected by mass spectrometry predict tumor response to molecular therapeutics

Biomarkers that predict therapeutic response are essential for the development of anticancer therapies. We have used matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to directly analyze protein profiles in mouse mammary tumor virus/HER2 transgenic mouse frozen tumor sections after treatment with the erbB receptor inhibitors OSI-774 and Herceptin. Inhibition of tumor cell proliferation and induction of apoptosis and tumor reduction were predicted by a >80% reduction in thymosin beta4 and ubiquitin levels that were detectable after 16 hours of a single drug dose before any evidence of in situ cellular activity. These effects were time- and dose-dependent, and their spatial distribution in the tumor correlated with that of the small-molecule inhibitor OSI-774. In addition, they predicted for therapeutic synergy of OSI-774 and Herceptin as well as for drug resistance. These results suggest that drug-induced early proteomic changes as measured by MALDI-MS can be used to predict the therapeutic response to established and novel therapies.

Dual Role of Transforming Growth Factor β in Mammary Tumorigenesis and Metastatic Progression

It is generally accepted that transforming growth factor β (TGFβ) is both a tumor suppressor and tumor promoter. Whereas loss or attenuation of TGFβ signal transduction is permissive for transformation, introduction of dominant-negative TGFβ receptors into metastatic breast cancer cells has been shown to inhibit epithelial-to-mesenchymal transition, motility, invasiveness, survival, and metastases. In addition, there is evidence that excess production and/or activation of TGFβ by cancer cells can contribute to tumor progression by paracrine mechanisms involving neoangiogenesis, production of stroma and proteases, and subversion of immune surveillance mechanisms in tumor hosts. These data provide a rationale in favor of blockade of autocrine/paracrine TGFβ signaling in human mammary tumors with therapeutic intent. Several treatment approaches are currently in early clinical development and have been the focus of our laboratory. These include (1) ligand antibodies or receptor-containing fusion proteins aimed at blocking ligand binding to cognate receptors and (2) small-molecule inhibitors of the type I TGFβ receptor serine/threonine kinase. Many questions remain about the viability of anti-TGFβ treatment strategies, the best molecular approach (or combinations) for inhibition of TGFβ function in vivo, the biochemical surrogate markers of tumor response, the molecular profiles in tumors for selection into clinical trials, and potential toxicities, among others.

Transforming growth factor (TGF)-β in conjunction with H-ras activation promotes malignant progression of MCF10A breast epithelial cells

To address how transforming growth factor (TGF)-beta and oncogenic H-ras signal transduction pathways interact with each other in the malignant progression of breast epithelial cells, we investigated the role of TGF-beta signaling pathway in invasive and migrative properties of H-ras-transformed MCF10A human breast epithelial cells in this study. Here we show that TGF-beta treatment significantly enhanced invasion and migration of H-ras MCF10A cells. H-ras-mediated activation of p38 MAPK and ERK-1/2 was stimulated by TGF-beta. TGF-beta increased expression of matrix metalloproteinase (MMP)-2 through transcriptional activation while TGF-beta-stimulated MMP-9 up-regulation did not occur at transcription level. Activation of p38 MAPK pathway was required for TGF-beta-induced cell migration, invasion and MMP-2/-9 up-regulation, indicating a critical role of p38 MAPK signaling in TGF-beta-promoted tumor progression of H-ras-activated cells. ERKs signaling was also crucial for TGF-beta-enhanced invasive and migrative phenotypes but the up-regulation of MMP-2/-9 was not dependent on ERKs activity. Taken together, we show that TGF-beta promotes H-ras-mediated cell migration and invasive phenotypes in which p38 MAPK and ERKs signaling pathways are involved. Our findings revealing how H-ras and TGF-beta signal pathways interact with each other in MCF10A human breast cells may provide an insight into molecular mechanisms for contribution of TGF-beta to a malignant progression of breast cancer in collaboration with activated H-ras.

Oncogenes as Novel Targets for Cancer Therapy (Part I)

In the past 10 years, progress made in cancer biology, genetics, and biotechnology has led to a major transition in cancer drug design and development. There has been a change from an emphasis on non-specific, cytotoxic agents to specific, molecular-based therapeutics. Mechanism-based therapy is designed to act on cellular and molecular targets that are causally involved in the formation, growth, and progression of human cancers. These agents, which may have greater selectivity for cancer versus normal cells, and which may produce better anti-tumor efficacy and lower host toxicity, can be small molecules, natural or engineered peptides, proteins, antibodies, or synthetic nucleic acids (e.g. antisense oligonucleotides, ribozymes, and siRNAs). Novel targets are identified and validated by state-of-the-art approaches, including high-throughput screening, combinatorial chemistry, and gene expression arrays, which increase the speed and efficiency of drug discovery and development. Examples of oncogene-based, molecular therapeutics that show promising clinical activity include trastuzumab (Herceptin), imatinib (Gleevec), and gefitinib (Iressa). However, the full potential of oncogenes as novel targets for cancer therapy has not been realized and many challenges remain, from the validation of novel targets, to the design of specific agents, to the evaluation of these agents in both preclinical and clinical settings. In maximizing the benefits of molecular therapeutics in monotherapy or combination therapy of cancer, it is necessary to have an understanding of the underlying molecular abnormalities and mechanisms involved. This is the first part of a four-part review in which we discuss progress made in the last decade as it relates to the discovery of novel oncogenes and signal transduction pathways, in the context of their potential as targets for cancer therapy. This part delineates the latest discoveries about the potential use of growth factors and protein tyrosine kinases as targets for therapy. Later parts focus on intermediate signaling pathways, transcription factors, and proteins involved in cell cycle, DNA damage, and apoptotic pathways.

Integrin-linked kinase: a cancer therapeutic target unique among its ILK

Cancer development requires the acquisition of several capabilities that include increased replicative potential, anchorage and growth-factor independence, evasion of apoptosis, angiogenesis, invasion of surrounding tissues and metastasis. One protein that has emerged as promoting many of these phenotypes when dysregulated is integrin-linked kinase (ILK), a unique intracellular adaptor and kinase that links the cell-adhesion receptors, integrins and growth factors to the actin cytoskeleton and to a range of signalling pathways. The recent findings of increased levels of ILK in various cancers, and that inhibition of ILK expression and activity is antitumorigenic, makes ILK an attractive target for cancer therapeutics.

Convergence of p53 and TGF-beta signaling networks

p53 is a protein with many talents. One of the most fundamental is the ability to act as essential growth checkpoint that protects cells against cellular transformation. p53 does so through the induction of genes leading to growth arrest or apoptosis. Most of the studies focusing on the mechanisms of p53 activity have been performed in cultured cells upon treatment with well-established p53-activating inputs, such as high doses of radiations, DNA-damaging drugs and activated oncogenes. However, how the tumor suppressive functions of p53 become concerted with the extracellular cues arriving at the cell surface during tissue homeostasis, remains largely unknown. Intriguingly, two recent papers have shed new light into this unexplored field, indicating that p53 plays a key role in TGF-beta-induced growth arrest and, unexpectedly, in the developmental effects of TGF-beta in early embryos. Here we review and comment on these findings and on their implications for cancer biology.

Prognostic significance of transforming growth factor beta receptor II in estrogen receptor-negative breast cancer patients

PURPOSE

The role of transforming growth factor beta (TGF-beta) in breast cancer is ambiguous; it can display both tumor suppressing and enhancing effects. Activation of the TGF-beta signal transduction system is subject to hormonal regulation. This study was conducted to further analyze the role of TGF-beta receptors in breast cancer and to evaluate their significance as prognostic markers.

EXPERIMENTAL DESIGN

Expression of TGF-beta receptor I (TbetaRI) and TGFbeta receptor II (TbetaRII) was retrospectively analyzed by immunohistochemistry in 246 breast cancer patients.

RESULTS

Expression of TbetaRI was strongly correlated with tumor size (P < 0.001) and nodal status (P = 0.012) but only weakly with overall survival (P = 0.056). In contrast, TbetaRII was prognostic for overall survival in univariate analysis (P = 0.0370). In estrogen receptor (ER) -negative patients TbetaRII expression was correlated with highly reduced overall survival (P = 0.0083). In multivariate analysis TbetaRII proved to be an independent and highly significant prognostic marker with a hazard ratio of 6.8. Simultaneous loss of both ER and TbetaRII was associated with longer overall survival times comparable with those of ER-positive patients.

CONCLUSIONS

The results of this exploratory study show that TbetaRII is an independent, highly significant prognostic indicator for overall survival in ER-negative patients. In addition our results are supportive of a mechanism of breast cancer progression in which a selective loss of the tumor inhibitory action of TGFbeta takes place, whereas tumor- promoting aspects remain intact.

α2HS-glycoprotein, an Antagonist of Transforming Growth Factor β In vivo, Inhibits Intestinal Tumor Progression

Transforming growth factor (TGF)-beta1 is associated with tumor progression and resistance to chemotherapy in established cancers, as well as host immune suppression. Here, we show that the serum glycoprotein alpha2-HS-glycoprotein (AHSG) blocks TGF-beta1 binding to cell surface receptors, suppresses TGF-beta signal transduction, and inhibits TGF-beta-induced epithelial-mesenchymal transition, suggesting that AHSG may play a role in tumor progression. In 66 consecutive sporadic human colorectal cancer specimens, we observed a 3-fold depletion of ASHG in tumor compared with normal tissue, whereas levels of other abundant plasma proteins, albumin and transferrin, were equivalent. Using the Multiple intestinal neoplasia/+ (Min/+) mouse model of intestinal tumorigenesis, we found twice as many intestinal polyps overall, twice as many large polyps (>3 mm diameter), and more progression to invasive adenocarcinoma in Min/+ Ahsg-/- mice than in littermates expressing Ahsg. Phosphorylated Smad2 was more abundant in the intestinal mucosa and tumors of Min/+ mice lacking Ahsg, demonstrating increased TGF-beta signaling in vivo. Furthermore, TGF-beta-mediated suppression of immune cell function was exaggerated in Ahsg-/- animals, as shown by inhibition of macrophage activation and reduction in 12-O-tetradecanoylphorbol 13-acetate-induced cutaneous inflammation. Reconstitution of Ahsg-/- mice with bovine Ahsg suppressed endogenous TGF-beta-dependent signaling to wild-type levels, suggesting that therapeutic enhancement of AHSG levels may benefit patients whose tumors are driven by TGF-beta.

Chronic exposure of transforming growth factor beta 1 confers a more aggressive tumor phenotype through downregulation of p21(WAF1/CIP1) in conditionally immortalized pancreatic epithelial cells

BACKGROUND

Recent studies have demonstrated that transforming growth factor beta 1 (TGF-beta1) expression is markedly enhanced in invasive ductal pancreatic adenocarcinomas, although the precise role of TGF-beta1 in pancreatic carcinogenesis remains unclear. We analyzed TGF-beta1 expression in pancreatic intraepithelial neoplasias (PanINs) and the effects of chronic TGF-beta1 exposure on conditionally immortalized pancreatic epithelial (IMPE) cells.

METHODS

Sixty-one PanIN lesions were immunohistochemically stained with a polyclonal rabbit antibody against human TGF-beta1. Growth-inhibitory effects of short-term exposure to TGF-beta1 were examined in IMPE cells. IMPE cells resistant to TGF-beta1 (IMPE-Tr cells) were generated by continuous exposure to 1 ng/mL of TGF-beta1 for more than 50 days. Phenotypic alterations of IMPE-Tr cells were examined by soft agar and Matrigel assay and Western blot analysis. IMPE and IMPE-Tr cells were injected subcutaneously into nude mice for an in vivo tumorigenicity assay.

RESULTS

Forty-six percent of PanINs (28/61) were positive for TGF-beta1 expression, whereas all the epithelia of normal pancreatic ducts were negative. TGF-beta1 treatment showed the marked growth-inhibitory effects (>75%) in IMPE cells, whereas its effects were not observed in IMPE-Tr cells. IMPE-Tr cells were more spindle shaped compared with IMPE cells. In soft agar and Matrigel, formations of many colonies were observed in IMPE-Tr cells, but not in IMPE cells. Interestingly, the expression of p21(WAF1/CIP1) was induced by short-term exposure to TGF-beta1 in IMPE cells, whereas the induction was decreased in IMPE-Tr cells. All of the IMPE-Tr cell-injected mice (5/5) had subcutaneous tumors, although no tumor was found in the IMPE cell-injected mice.

CONCLUSIONS

TGF-beta1 expression in PanINs and neoplastic transformation of IMPE cells by long-term exposure to TGF-beta1 suggest that TGF-beta1 may act as a tumor promoter in the early stage of pancreatic carcinogenesis.

Antitumor activity of Soamsan, a traditional Korean medicine, via suppressing angiogenesis and growth factor transcription

Antiangiogenic and antitumor activities of Soamsan known as an anticancer remedy in traditional Korean medicine were examined. In contrast to the normal branching of vascular vessels in chorioallantoic membrane (CAM), blood vessels in CAM treated with Soamsan (50 microg per egg) were run parallel to each other with less branching. Oral administration of Soamsan (20 mg/kg per day) for 4 weeks significantly inhibited the rat corneal neovascularization induced by suture, and the length of blood vessels in Soamsan-treated rat cornea was conspicuously low compared to control. When HT1080 cells, human fibrosarcoma, were treated with 2.18 mg/ml of Soamsan up to 24 h, mRNA transcription of VEGF, TGF-beta and bFGF genes was dramatically reduced in a time-dependent manner. Soamsan showed a prolongation of life span and a reduction of tumor volume in CT-26 cell (colon adenocarcinoma)-bearing mice. These results suggest that antitumor activity of Soamsan may be mediated, at least in part, by antiangiogenic mechanism.

The role of Fas ligand and transforming growth factor beta in tumor progression: molecular mechanisms of immune privilege via Fas-mediated apoptosis and potential targets for cancer therapy

Despite the fact that expression of Fas ligand (FasL) in cytotoxic T lymphocytes (CTLs) and in natural killer (NK) cells plays an important role in Fas-mediated tumor killing, During tumor progression FasL-expressing tumor cells are involved in counterattacking to kill tumor-infiltrating lymphocytes (TILs). Soluble FasL levels also increase with tumor progression in solid tumors, and this increase inhibits Fas-mediated tumor killing by CTLs and NK cells. The increased expression of FasL in tumor cells is associated with decreased expression of Fas; and the promoter region of the FASL gene is regulated by transcription factors, such as neuronal factor kappaB (NF-kappaB) and AP-1, in the tumor microenvironment. Although the ratio of FasL expression to Fas expression in tumor cells is not strongly related to the induction of apoptosis in TILs, increased expression of FasL is associated with decreased Fas levels in tumor cells that can escape immune surveillance and facilitate tumor progression and metastasis. Transforming growth factor beta (TGF-beta) is a potent growth inhibitor and has tumor-suppressing activity in the early phases of carcinogenesis. During subsequent tumor progression, the increased secretion of TGF-beta by both tumor cells and, in a paracrine fashion, stromal cells, is involved in the enhancement of tumor invasion and metastasis accompanied by immunosuppression. Herein, the authors review the clinical significance of FasL and TGF-beta expression patterns as features of immune privilege accompanying tumor progression in the tumor microenvironment. Potential strategies for identifying which molecules can serve as targets for effective antitumor therapy also are discussed.

Investigation of three new mouse mammary tumor cell lines as models for transforming growth factor (TGF)-beta and Neu pathway signaling studies: identification of a novel model for TGF-beta-induced epithelial-to-mesenchymal transition

Introduction

This report describes the isolation and characterization of three new murine mammary epithelial cell lines derived from mammary tumors from MMTV (mouse mammary tumor virus)/activated Neu + TβRII-AS (transforming growth factor [TGF]-β type II receptor antisense RNA) bigenic mice (BRI-JM01 and BRI-JM05 cell lines) and MMTV/activated Neu transgenic mice (BRI-JM04 cell line).

Methods

The BRI-JM01, BRI-JM04, and BRI-JM05 cell lines were analyzed for transgene expression, their general growth characteristics, and their sensitivities to several growth factors from the epidermal growth factor (EGF) and TGF-β families (recombinant human EGF, heregulin-β₁ and TGF-β₁). The BRI-JM01 cells were observed to undergo a striking morphologic change in response to TGF-β₁, and they were therefore further investigated for their ability to undergo a TGF-β-induced epithelial-to-mesenchymal transition (EMT) using motility assays and immunofluorescence microscopy.

Results

We found that two of the three cell lines (BRI-JM04 and BRI-JM05) express the Neu transgene, whereas, unexpectedly, both of the cell lines that were established from MMTV/activated Neu + TβRII-AS bigenic tumors (BRI-JM01 and BRI-JM05) do not express the TβRII-AS transgene. The cuboidal BRI-JM01 cells exhibit a short doubling time and are able to form confluent monolayers. The BRI-JM04 and BRI-JM05 cell lines are morphologically much less uniform, grow at a much slower rate, and do not form confluent monolayers. Only the BRI-JM05 cells can form colonies in soft agar. In contrast, all three cell lines form colonies in Matrigel, although the BRI-JM04 and BRI-JM05 cell lines do so more efficiently than the BRI-JM01 cell line. All three cell lines express the cell surface marker E-cadherin, confirming their epithelial character. Proliferation assays showed that the three cell lines respond differently to recombinant human EGF and heregulin-β₁, and that all are growth inhibited by TGF-β₁, but that only the BRI-JM01 cell line undergoes an EMT and exhibits increased motility upon TGF-β₁ treatment.

Conclusion

We suggest that the BRI-JM04 and BRI-JM05 cell lines can be used to investigate Neu oncogene driven mammary tumorigenesis, whereas the BRI-JM01 cell line will be useful for studying TGF-β₁-induced EMT.

Selective inhibitors of type I receptor kinase block cellular transforming growth factor-β signaling

Transforming growth factor (TGFbeta) is a 25-kDa dimeric polypeptide that plays a key role in a variety of physiological processes and disease states. Blocking TGFbeta signaling represents a potentially powerful and conceptually novel approach to the treatment of disorders in which the signaling pathway is constitutively activated, such as cancer, chronic inflammation with fibrosis and select immune disorders. In this paper, we describe the biological properties of a novel series of quinazoline-derived inhibitors of the type I transforming growth factor receptor kinase (TbetaKIs) that bind to the ATP-binding site and keep the kinase in its inactive conformation. These compounds effectively inhibited TGFbeta-induced Smad2 phosphorylation in cultured cells in vitro with an IC(50) between 20 and 300 nM. Moreover, TbetaKIs were able to broadly block TGFbeta-induced reporter gene activation. Finally, TbetaKIs inhibited TGFbeta-mediated growth inhibition of normal murine mammary epithelial cells (NMuMG) and mink lung epithelial cells (Mv1Lu), and TGFbeta-induced epithelial-mesenchymal transdifferentiation (EMT) of NMuMG cells. Thus, these chemical TbetaKIs have the potential to be further developed as anti-cancer and -fibrosis agents. In addition, they represent valuable new tools for dissecting the biochemical mechanisms of TGFbeta signal transduction and understanding the role of TGFbeta signaling pathways in different physiological and disease processes.

Extracellular glycosaminoglycan changes in healthy and overgrown gingiva fibroblasts after cyclosporin A and cytokine treatments

BACKGROUND

It has been demonstrated that cyclosporin A (CyA) blocks the immune system, acts on cytoskeleton and stimulates the production of extracellular matrix (ECM) and transforming growth factor-beta1 (TGF-beta1). This cytokine, such as transforming growth factor-alpha (TGF-alpha), induces deposition of glycosaminoglycans (GAG), proteoglycans and collagen fibres in the ECM.

METHODS

In this work, we examined the effect induced by CyA, TGF-beta1 and TGF-alpha on cultures of healthy and overgrown human gingival fibroblasts in order to evaluate the glycosaminoglycan, cytoskeletal changes and the behaviour of fibroblasts after concanavalin A (Con A) treatment. Moreover, we examined gingival biopsies by Alcian blue histochemical staining and electron transmission microscopy.

RESULTS

Total and extracellular sulphated GAG in overgrown gingiva specimens and in derived fibroblast cultures treated with CyA and cytokines were significantly higher than controls. The action of cytokines was increased (P < or = 0.01) compared with CyA with a greater effect of TGF-alpha in comparison with TGF-beta1; the electron microscopy showed ECM accumulation. The agglutinations showed the heterogeneity of fibroblast populations.

CONCLUSIONS

Stimulation with Con A showed that the fibroblast population had cell surface heterogeneity, and could respond in a different way to both CyA and cytokine stimulus. Moreover, increased synthesis of GAG in overgrown gingiva compared with synthesis in normal fibroblasts before CyA treatment suggests a possible genetic origin of damage. As not all CyA-treated patients develop gingival overgrowth, a genetic predisposition may explain the different responses of gingival fibroblast populations.

Overexpression of HER2 (erbB2) in Human Breast Epithelial Cells Unmasks Transforming Growth Factor β-induced Cell Motility

We have examined overexpression of the human epidermal growth factor receptor 2 (HER2) to determine if it modifies the anti-proliferative effect of transforming growth factor (TGF)-beta against MCF-10A human mammary epithelial cells. Exogenous TGF-beta inhibited cell proliferation and induced Smad-dependent transcriptional reporter activity in both MCF-10A/HER2 and MCF-10A/vector control cells. Ligand-induced reporter activity was 7-fold higher in HER2-overexpressing cells. In wound closure and transwell assays, TGF-beta induced motility of HER2-transduced, but not control cells. The HER2-blocking antibody trastuzumab (Herceptin) prevented TGF-beta-induced cell motility. Expression of a constitutively active TGF-beta type I receptor (ALK5(T204D)) induced motility of MCF-10A/HER2 but not MCF-10A/vector cells. TGF-beta-induced motility was blocked by coincubation with either the phosphatidylinositol 3-kinase inhibitor LY294002, the mitogen-activated protein kinase (MAPK) inhibitor U0126, the p38 MAPK inhibitor SB202190, and an integrin beta(1) blocking antibody. Rac1 activity was higher in HER2-overexpressing cells, where both Rac1 and Pak1 proteins were constitutively associated with HER2. Both exogenous TGF-beta and transduction with constitutively active ALK5 enhanced this association. TGF-beta induced actin stress fibers as well as lamellipodia within the leading edge of wounds. Herceptin blocked basal and TGF-beta-stimulated Rac1 activity but did not repress TGF-beta-stimulated transcriptional reporter activity. These data suggest that 1) overexpression of HER2 in nontumorigenic mammary epithelial is permissive for the ability of TGF-beta to induce cell motility and Rac1 activity, and 2) HER2 and TGF-beta signaling cooperate in the induction of cellular events associated with tumor progression.

Enhanced tenascin-C expression and matrix deposition during Ras/TGF-beta-induced progression of mammary tumor cells

Overexpression of tenascin-C (TN-C) in breast carcinomas has been associated with a migratory or even invasive tumor cell phenotype. The mechanisms regulating expression and matrix deposition of TN-C in normal and cancerous breast tissues are, however, little understood. Here, we demonstrate that mouse mammary epithelial cells (EpH4) transformed by oncogenic Ha-Ras (EpRas) overexpress TN-C, which accumulates in the cytoplasm. When EpRas cells undergo epithelial-mesenchymal transition (EMT) in response to TGFbeta1, they secrete TN-C into the culture medium. In EpRas cells undergoing TGFbeta1-induced EMT in three-dimensional (3D)-collagen gel cultures, TN-C was deposited into an extracellular matrix (ECM) already containing fibronectin and perlecan. Under less physiological 2D plastic cultures, EpRas cells undergoing EMT failed to deposit TN-C into an (apparently incomplete) ECM. Ras-downstream signaling was dissected by pharmacological inhibitors and effector-specific Ras mutants (V12S35, V12C40), specifically inhibiting or activating ERK/MAPK or PI3K signaling, respectively. We showed that TN-C overexpression required a hyperactive ERK/MAPK-signaling pathway, while elevated PI3K signaling did not enhance TN-C expression. Similarly, tumors induced by cells exhibiting hyperactive ERK/MAPK signaling showed expression of TN-C in the tumor cells themselves, while only endothelial cells expressed TN-C in tumors caused by the V12C40 mutant (incapable of EMT in vivo). Taken together, our data indicate that hyperactive ERK/MAPK signaling causes enhanced expression of TN-C, while its secretion is induced by TGFbeta1 and both signals cooperate in TN-C matrix deposition. Importantly, both signals also cooperate to induce EMT in vitro and tumor progression/metastasis in vivo.

Spontaneous and genetically engineered animal models; use in preclinical cancer drug development

The preclinical development of anticancer drugs has been based primarily on the transplantation of murine or human cancers into mice. Alternatives to these transplantation models are animals that naturally develop cancers with features relevant to the human disease. The first group of these models arises in mice that are genetically engineered to develop cancer. The second group includes pet dogs and cats that naturally develop cancer. This review will discuss the use and integration of these spontaneous cancer models into a comprehensive and comparative approach to preclinical drug development. Examples of their successful use and an outline of their relative strengths and weaknesses will be provided.

ARK5 is a tumor invasion-associated factor downstream of Akt signaling

AMP-activated protein kinases (AMPKs) are a class of serine/threonine protein kinases that are activated by an increase in intracellular AMP concentration. They are a sensitive indicator of cellular energy status and have been found to promote tumor cell survival during nutrient starvation. We recently identified a novel AMPK catalytic subunit family member, ARK5, whose activation is directly regulated by Akt, which, in turn, has been reported to be a key player in tumor malignancy. In this study, we attempted to determine whether ARK5 is involved in tumor malignancy under regulation by Akt. Matrigel invasion assays demonstrated that both overexpressed and endogenous ARK5 showed strong activity dependent on Akt. In addition, ARK5 expression induced activation of matrix metalloproteinase 2 (MMP-2) and MMP-9 following new expression of membrane type 1 MMP (MT1-MMP), and the MT1-MMP expression induced by ARK5 was initiated by rapamycin-sensitive signaling. In nude mice, ARK5 expression was associated with a significant increase in tumor growth and significant suppression of necrosis in tumor tissue. Interestingly, only the ARK5-overexpressing PANC-1 cell line (P/ARK) tumor showed invasion and metastasis in nude mice, although Akt was activated in tumors derived from both P/ARK and its parental cell line. We report that a novel AMPK catalytic subunit family member, ARK5, plays a key role in tumor malignancy downstream of Akt.

Regulation of interleukin-12 gene expression and its anti-tumor activities by prostaglandin E2 derived from mammary carcinomas

Interleukin-12 (IL-12)-mediated immune responses are critical for the control of malignant development. Tumors can actively resist detrimental immunity of the host via many routes. Prostaglandin E2 (PGE2) is one of the major immune-suppressive factors derived from many types of tumors. Here, we show that systemic administration of recombinant IL-12 could therapeutically control the growth of aggressive TS/A and 4T1 mouse mammary carcinomas. However, PGE2 produced by tumors potently inhibits the production of endogenous IL-12 at the level of protein secretion, mRNA synthesis, and transcription of the constituent p40 and p35 genes. The inhibition can be reversed by NS-398, a selective inhibitor of the enzymatic activity of cyclooxygenase 2 in PGE2 synthesis. Moreover, PGE2-mediated inhibition of IL-12 production requires the functional cooperation of AP-1 and AP-1 strongly suppresses IL-12 p40 transcription. Blocking PGE2 production in vivo results in a marked reduction in lung metastasis of 4T1 tumors, accompanied by enhanced ability of peritoneal macrophages to produce IL-12 and spleen lymphocytes to produce interferon-gamma. This study contributes to the elucidation of the molecular mechanisms underlying the interaction between a progressive malignancy and the immune defense apparatus.

Collaborative activities of macrophage-stimulating protein and transforming growth factor-beta1 in induction of epithelial to mesenchymal transition: roles of the RON receptor tyrosine kinase

Epithelial to mesenchymal transition (EMT) is a process occurring during embryonic development and cancer progression. Using recepteur d'origine nantais (RON)-expressing epithelial cells as a model, we showed that RON activation causes spindle-shaped morphology with increased cell motilities. These activities resemble those observed in EMT induced by transforming growth factor (TGF)-beta1 or by Ras-Raf signaling. By immunofluorescent and Western blot analyses, we found that constitutive RON expression results in diminished expression of E-cadherin, redistribution of beta-catenin, reorganization of actin cytoskeleton, and increased expression of vimentin, a mesenchymal filament. RON expression is also essential for TGF-beta1-induced expression of alpha-smooth muscle actin (alpha-SMA), a specialized mesenchymal marker. In the study of signaling pathways responsible for RON-mediated EMT, it was found that PD98059, a MAP kinase inhibitor, blocks the collaborative activities of RON and TGF-beta1 in induction of alpha-SMA expression and restores epithelial cells to their original morphology. Moreover, we showed that RON expression increases Smad2 gene promoter activities and protein expression, which significantly lowers TGF-beta1 threshold for EMT induction. These results suggest that persistent RON expression and activation cause the loss of epithelial phenotypes. These changes, collaborating with TGF-beta1 signaling, could play a critical role in epithelial transdifferentiation towards invasiveness and metastasis of certain cancers.

Enhancement of the antagonistic potency of transforming growth factor-beta receptor extracellular domains by coiled coil-induced homo- and heterodimerization

Transforming growth factor-beta (TGF-beta) plays a causal role in several human pathologies including fibrotic diseases and metastasis. TGF-beta signaling is mediated through its interaction with three types of cell surface receptors, RI, RII, and RIII. The soluble ectodomains of RII and RIII bind to TGF-beta, making them attractive candidates to sequester TGF-beta and inhibit its activity. To optimize the activity of the ectodomains, we studied the effect of artificially dimerizing them upon their kinetics of binding to TGF-beta using an optical biosensor and studied their antagonistic potencies using an in vitro signaling assay. We fused the RII ectodomain and the membrane-proximal ligand-binding domain of the RIII ectodomain to de novo designed heterodimerizing coil strands and demonstrated that the coil strands within the fusion proteins were capable of promoting the dimerization of the coil-tagged ectodomains. Our results indicate that coiled coil-induced dimerization of the ectodomains stabilized their interaction with TGF-beta as compared with the monomeric ectodomains. Also, in contrast to the monomeric ectodomains, which did not block signaling, the coiled coil-induced dimers were characterized by antagonistic potencies in the low nanomolar range.

Induction by transforming growth factor-beta1 of epithelial to mesenchymal transition is a rare event in vitro

INTRODUCTION

Transforming growth factor (TGF)-beta1 is proposed to inhibit the growth of epithelial cells in early tumorigenesis, and to promote tumor cell motility and invasion in the later stages of carcinogenesis through the induction of an epithelial to mesenchymal transition (EMT). EMT is a multistep process that is characterized by changes in cell morphology and dissociation of cell-cell contacts. Although there is growing interest in TGF-beta1-mediated EMT, the phenotype is limited to only a few murine cell lines and mouse models.

METHODS

To identify alternative cell systems in which to study TGF-beta1-induced EMT, 18 human and mouse established cell lines and cultures of two human primary epithelial cell types were screened for TGF-beta1-induced EMT by analysis of cell morphology, and localization of zonula occludens-1, E-cadherin, and F-actin. Sensitivity to TGF-beta1 was also determined by [3H]thymidine incorporation, flow cytometry, phosphorylation of Smad2, and total levels of Smad2 and Smad3 in these cell lines and in six additional cancer cell lines.

RESULTS

TGF-beta1 inhibited the growth of most nontransformed cells screened, but many of the cancer cell lines were insensitive to the growth inhibitory effects of TGF-beta1. In contrast, TGF-beta1 induced Smad2 phosphorylation in the majority of cell lines, including cell lines resistant to TGF-beta1-mediated cell cycle arrest. Of the cell lines screened only two underwent TGF-beta1-induced EMT.

CONCLUSION

The results presented herein show that, although many cancer cell lines have lost sensitivity to the growth inhibitory effect of TGF-beta1, most show evidence of TGF-beta1 signal transduction, but only a few cell lines undergo TGF-beta1-mediated EMT.

Genetic Polymorphisms in the TGF-β1 Gene and Breast Cancer Survival

The effect of genetic polymorphisms in the TGF-beta1 gene at codon 10 (T+29C), codon 25 (G+74C), and the promoter region [C --> T at -509 from the transcription site, (C-509T)] on breast cancer survival was evaluated among a cohort of 1111 patients. The median follow-up time for the cohort was 5.17 years after cancer diagnosis. No DNA sequence variation at codon 25 of the TGF-beta1 gene was found, whereas polymorphisms in C-509T and T+29C were in strong linkage disequilibrium. Patients who carried the C allele of T+29C polymorphism had a reduced 5-year disease-free survival rate (75.6% for T/C, and 78.2% for C/C) compared with the T/T genotype (85.1%; P, 0.04); the age-adjusted hazard ratio was 1.5 (95% confidence interval, 1.1-2.2). Adjustment for clinical prognostic factors slightly attenuated the association (hazard ratio, 1.4, 95% confidence interval, 1.0-1.9). Our study suggests that genetic polymorphisms in the TGF-beta1 gene may play a role in breast cancer progression.

IL-3 affects endothelial cell-mediated smooth muscle cell recruitment by increasing TGFβ activity: potential role in tumor vessel stabilization

Interleukin-3 (IL-3) expression by tumor-infiltrating lymphocytes (TILs) and its effects on vessel assembly were evaluated. TILs from 'in situ' human breast cancers expressed CD4/CD25 antigens and IL-3. An injection of Matrigel containing SMC and IL-3 or basic-fibroblast growth factor (bFGF) into SCID mice confirmed the neoangiogenetic effect of both factors. However, in response to IL-3, but not to bFGF, only few SMC became incorporated into the nascent vessels. To evaluate the possibility that signals emanated by the nascent vasculature in the presence of IL-3 may negatively regulate SMC recruitment, conditioned media (CM) from IL-3-treated endothelial cells (EC) or SMC were tested for their biological effects on SMC and EC. CM from IL-3-treated SMC stimulated the migration of EC. In contrast, the migration of SMC was not affected by CM from IL-3-stimulated EC; however, it was greatly enhanced by blocking transforming growth factor beta (TGF beta) activity. TGF beta immunoenzymatic assay demonstrated the following: (i) the absence of TGF beta activity in CM from IL-3-stimulated EC; (ii) a barely detectable TGF beta activity in CM from IL-3-stimulated SMC; and (iii) the presence of TGF beta activity in the supernatants of SMC stimulated with CM from IL-3-, but not from bFGF-stimulated EC. Increased TGF beta mRNA expression was only detected in SMC stimulated with CM from IL-3-treated EC. Finally, the inhibitory signals induced by IL-3 in vivo were abrogated by the addition of the neutralizing TGF beta antibody. Thus, the positive immunostaining for IL-3 by TILs in 'in situ' breast cancers sustains the possibility that early in tumor development, IL-3 can contribute to the chronic immaturity of these vessels.

Cooperation of the ErbB2 receptor and transforming growth factor beta in induction of migration and invasion in mammary epithelial cells

MCF10A mammary epithelial cells form growth-arrested structures when cultured in three-dimensional basement membrane gels. Activation of the receptor tyrosine kinase ErbB2 induces formation of proliferative structures that share properties with noninvasive early stage lesions. We conducted a genetic screen to identify cDNAs that can cooperate with ErbB2 to induce migration in these cells, with the hypothesis that they would represent candidate "second hits" in the development of invasive breast carcinomas. We found that expression of transforming growth factor (TGF)beta1 and TGFbeta3 in cells expressing activated ErbB2 induces migration in transwell chambers and invasive behavior in both basement membrane cultures and invasion chambers. The ability of ErbB2 to cooperate with TGFbeta correlated with sustained, elevated activation of extracellular signal-regulated kinase (Erk)-mitogen-activated protein kinase. Pharmacological reduction of Erk activity inhibited the cooperative effect of TGFbeta and ErbB2 on migration and expression of activated Erk kinase was sufficient to cooperate with TGFbeta to induce migration and invasion, suggesting that sustained Erk activation is critical for ErbB2/TGFbeta cooperation. In addition, we show that costimulation of ErbB2 and TGFbeta induces autocrine secretion of factors that are sufficient to induce migration, but not invasion, by means of both epidermal growth factor receptor-dependent and -independent processes. These results support the role of TGFbeta as a pro-invasion factor in the progression of breast cancers with activated ErbB2 and suggest that activation of the Erk and epidermal growth factor receptor pathways are key in mediating these events.

Cripto-1 overexpression leads to enhanced invasiveness and resistance to anoikis in human MCF-7 breast cancer cells

Cripto-1 (CR-1) is an epidermal growth factor (EGF)-CFC protein that has been shown to signal through nodal/Alk-4, PI3K/Akt, and/or ras/raf/MEK/MAPK pathways in mammalian cells, and that is frequently expressed in human primary breast carcinomas. In the present study, the human estrogen receptor positive, MCF-7 breast cancer cell line, that expresses low levels of endogenous CR-1, was transfected with a CR-1 expression vector. MCF-7 CR-1 cells expressed high levels of a 25 kDa recombinant CR-1 protein that was not detected in MCF-7 cells transfected with a control vector (MCF-7 neo). Overexpression of CR-1 did not induce an estrogen independent phenotype in MCF-7 cells. In fact, MCF-7 CR-1 cells showed a response to exogenous estrogens that was similar to MCF-7 neo cells, and failed to grow in immunosuppressed mice in absence of estrogen stimulation. However, MCF-7 CR-1 cells showed a rate of proliferation in serum free conditions, and an ability to form colonies in soft-agar that were higher as compared with MCF-7 neo cells. More importantly, overexpression of CR-1 enhanced the resistance to anoikis and the invasion ability of MCF-7 cells. MCF-7 CR-1 cells showed levels of activation of both Akt and Smad-2 that were significantly higher as compared with MCF-7 neo. These findings suggest that CR-1 overexpression might be associated with the progression towards a more aggressive phenotype in breast carcinoma, through the activation of both Akt and Smad-2 signalling pathways.

Transforming growth factor-beta production and myeloid cells are an effector mechanism through which CD1d-restricted T cells block cytotoxic T lymphocyte-mediated tumor immunosurveillance: abrogation prevents tumor recurrence

Our previous work demonstrated that cytotoxic T lymphocyte (CTL)-mediated tumor immunosurveillance of the 15-12RM tumor could be suppressed by a CD1d-restricted lymphocyte, most likely a natural killer (NK) T cell, which produces interleukin (IL)-13. Here we present evidence for the effector elements in this suppressive pathway. T cell–reconstituted recombination activating gene (RAG)2 knockout (KO) and RAG2/IL-4 receptor α double KO mice showed that inhibition of immunosurveillance requires IL-13 responsiveness by a non–T non–B cell. Such nonlymphoid splenocytes from tumor-bearing mice produced more transforming growth factor (TGF)-β, a potent inhibitor of CTL, ex vivo than such cells from naive mice, and this TGF-β production was dependent on the presence in vivo of both IL-13 and CD1d-restricted T cells. Ex vivo TGF-β production was also abrogated by depleting either CD11b⁺ or Gr-1⁺ cells from the nonlymphoid cells of tumor-bearing mice. Further, blocking TGF-β or depleting Gr-1⁺ cells in vivo prevented the tumor recurrence, implying that TGF-β made by a CD11b⁺ Gr-1⁺ myeloid cell, in an IL-13 and CD1d-restricted T cell–dependent mechanism, is necessary for down-regulation of tumor immunosurveillance. Identification of this stepwise regulation of immunosurveillance, involving CD1-restricted T cells, IL-13, myeloid cells, and TGF-β, explains previous observations on myeloid suppressor cells or TGF-β and provides insights for targeted approaches for cancer immunotherapy, including synergistic blockade of TGF-β and IL-13.

Interaction with Smad4 is indispensable for suppression of BMP signaling by c-Ski

c-Ski is a transcriptional corepressor that interacts strongly with Smad2, Smad3, and Smad4 but only weakly with Smad1 and Smad5. Through binding to Smad proteins, c-Ski suppresses signaling of transforming growth factor-beta (TGF-beta) as well as bone morphogenetic proteins (BMPs). In the present study, we found that a mutant of c-Ski, termed c-Ski (ARPG) inhibited TGF-beta/activin signaling but not BMP signaling. Selectivity was confirmed in luciferase reporter assays and by determination of cellular responses in mammalian cells (BMP-induced osteoblastic differentiation of C2C12 cells and TGF-beta-induced epithelial-to-mesenchymal transdifferentiation of NMuMG cells) and Xenopus embryos. The ARPG mutant recruited histone deacetylases 1 (HDAC1) to the Smad3-Smad4 complex but not to the Smad1/5-Smad4 complex. c-Ski (ARPG) was unable to interact with Smad4, and the selective loss of suppression of BMP signaling by c-Ski (ARPG) was attributed to the lack of Smad4 binding. We also found that c-Ski interacted with Smad3 or Smad4 without disrupting Smad3-Smad4 heteromer formation. c-Ski (ARPG) would be useful for selectively suppressing TGF-beta/activin signaling.

Increased malignancy of Neu-induced mammary tumors overexpressing active transforming growth factor beta1

To determine if Neu is dominant over transforming growth factor beta (TGF-beta), we crossed mouse mammary tumor virus (MMTV)-Neu mice with MMTV-TGF-beta1(S223/225) mice expressing active TGF-beta1 in the mammary gland. Bigenic (NT) and Neu-induced mammary tumors developed with a similar latency. The bigenic tumors and their metastases were less proliferative than those occurring in MMTV-Neu mice. However, NT tumors exhibited less apoptosis and were more locally invasive and of higher histological grade. NT mice exhibited more circulating tumor cells and lung metastases than Neu mice, while NT tumors contained higher levels of phosphorylated (active) Smad2, Akt, mitogen-activated protein kinase (MAPK), and p38, as well as vimentin content and Rac1 activity in situ than tumors expressing Neu alone. Ex vivo, NT cells exhibited higher levels of P-Akt and P-MAPK than Neu cells. These were inhibited by the TGF-beta inhibitor-soluble TGF-beta type II receptor (TbetaRII:Fc), suggesting they were activated by autocrine TGF-beta. TGF-beta stimulated migration of Neu cells into surrounding matrix, while the soluble TGF-beta inhibitor abrogated motility and invasiveness of NT cells. These data suggest that (i) the antimitogenic and prometastatic effects of TGF-beta can exist simultaneously and (ii) Neu does not abrogate TGF-beta-mediated antiproliferative action but can synergize with TGF-beta in accelerating metastatic tumor progression.

Squamous cell carcinoma and mammary abscess formation through squamous metaplasia inSmad4/Dpc4conditional knockout mice

Smad4 is a central mediator for TGFβ signals, which play important functions in many biological processes. To study the role of Smad4 in mammary gland development and neoplasia, we disrupted this gene in mammary epithelium using a Cre-loxP approach. Smad4 is expressed in the mammary gland throughout development; however, its inactivation did not cause abnormal development of the gland during the first three pregnancies. Instead, lack of Smad4 gradually induced cell proliferation, alveolar hyperplasia and transdifferentiation of mammary epithelial cells into squamous epithelial cells. Consequently, all mutant mice developed squamous cell carcinoma and/or mammary abscesses between 5 and 16 months of age. We demonstrated that absence of Smad4 resulted in β-catenin accumulation at onset and throughout the process of transdifferentiation, implicating β-catenin, a key component of the Wnt signaling pathway, in the development of squamous metaplasia in Smad4-null mammary glands. We further demonstrated that TGFβ1 treatment degraded β-catenin and induced epithelial-mesenchymal transformation in cultured mammary epithelial cells. However, such actions were blocked in the absence of Smad4. These findings indicate that TGFβ/Smad4 signals play a role in cell fate maintenance during mammary gland development and neoplasia.

Expression profiling of epithelial plasticity in tumor progression

Epithelial-to-mesenchymal transition (EMT), a switch of polarized epithelial cells to a migratory, fibroblastoid phenotype, is increasingly considered as an important event during malignant tumor progression and metastasis. To identify molecular players involved in EMT and metastasis, we performed expression profiling of a set of combined in vitro/in vivo cellular models, based on clonal, fully polarized mammary epithelial cells. Seven closely related cell pairs were used, which were modified by defined oncogenes and/or external factors and showed specific aspects of epithelial plasticity relevant to cell migration, local invasion and metastasis. Since mRNA levels do not necessarily reflect protein levels in cells, we used an improved expression profiling method based on polysome-bound RNA, suitable to analyse global gene expression on Affymetrix chips. A substantial fraction of all regulated genes was found to be exclusively controlled at the translational level. Furthermore, profiling of the above multiple cell pairs allowed one to identify small numbers of genes by cluster analysis, specifically correlating gene expression with EMT, metastasis, scattering and/or oncogene function. A small set of genes specifically regulated during EMT was identified, including key regulators and signaling pathways involved in cell proliferation, epithelial polarity, survival and trans-differentiation to mesenchymal-like cells with invasive behavior.

TGF-β-induced apoptosis in human thyrocytes is mediated by p27kip1 reduction and is overridden in neoplastic thyrocytes by NF-κB activation

Millions of people worldwide suffer goiter, a proliferative disease of the follicular cells of the thyroid that may become neoplastic. Thyroid neoplasms have low proliferative index, low apoptotic index and a high incidence of metastasis. TGF-beta is overexpressed in thyroid follicular tumor cells. To investigate the role of TGF-beta in thyroid tumor progression, we established cultures of human thyrocytes from different proliferative pathologies (Grave's disease, multinodular goiter, follicular adenoma, papillary carcinoma), lymph node metastasis, and a normal thyroid sample. All cultures maintained the thyrocyte phenotype. TGF-beta induced cell-cycle arrest in all cultures, in contrast with results reported for other epithelial tumors. In deprived medium, TGF-beta induced apoptosis in normal thyrocyte cultures and all neoplastic cultures except the metastatic cultures. This apoptosis was mediated by a reduction in p27kip1 levels, inducing cell-cycle initiation. Antisense p27 expression induced apoptosis in the absence of TGF-beta. By contrast, in cells in which p27 was overexpressed, TGF-beta had a survival effect. In growth medium, a net survival effect occurs in neoplastic thyrocytes only, not normal thyrocytes, due to activation of the NF-kappaB survival program. Together, these findings suggest that (a) thyroid neoplasms are due to reduced apoptosis, not increased division, in line with the low proliferative index of these pathologies, and (b) TGF-beta induces apoptosis in normal thyrocytes via p27 reduction, but that in neoplastic thyrocytes this effect is overridden by activation of the NF-kappaB program.

Transgenic mice expressing a dominant-negative mutant type II transforming growth factor-beta receptor exhibit impaired mammary development and enhanced mammary tumor formation

We have previously shown that expression of a dominant-negative type II transforming growth factor-beta receptor (DNIIR) in mammary epithelium under control of the MMTV promoter/enhancer causes alveolar hyperplasia and differentiation in virgin mice. Here we show that MMTV-DNIIR female mice have accelerated mammary gland differentiation during early pregnancy with impaired development during late pregnancy and lactation followed by delayed postlactational involution. Mammary tumors, mostly carcinoma in situ, developed spontaneously in the MMTV-DNIIR mice with a long median latency (27.5 months). Crossbreeding to MMTV-transforming growth factor (TGF)-alpha mice to obtain mice expressing both transgenes resulted in mammary tumor formation with a much shorter latency more similar to those expressing only the MMTV-TGF-alpha transgene (<10 months median latency). The major difference in mammary tumors arising in MMTV-TGF-alpha compared to bigenic MMTV-DNIIR/MMTV-TGF-alpha was the marked suppression of tumor invasion by DNIIR transgene expression. Invading carcinoma cells in both MMTV-DNIIR and bigenic animals showed loss of DNIIR transgene expression as determined by in situ hybridization. The data indicate that signaling from endogenous TGF-betas not only plays an important role in normal mammary gland physiology but also can also suppress the early stage of tumor formation and contribute to tumor invasion once carcinomas have developed.

Transforming growth factor-beta in osteolytic breast cancer bone metastases

Breast cancers frequently metastasize to the skeleton and cause bone destruction. Tumor cells secrete factors that stimulate osteoclasts. The consequent osteolytic resorption releases active factors from the bone matrix, in particular transforming growth factor-beta (TGF-beta). The released factors then stimulate tumor cell signaling, which causes breast cancer cells to make increased amounts of osteolytic factors, such as parathyroid hormone-related protein (PTHrP), interleukin-11 (IL-11), and vascular endothelial growth factor (VEGF). Therefore, tumor cell-bone cell interactions cause a vicious cycle in which tumor cells stimulate bone cells to cause bone destruction. As a consequence, the local microenvironment is enriched with factors that fuel tumor growth in bone. Transforming growth factor-beta is of particular importance because it increases breast cancer production of PTHrP. Parathyroid hormone-related protein then stimulates osteoblasts to express RANK (receptor activator of nuclear factor kappa B) ligand, which in turns enhances osteoclast formation and activity. Breast cancer osteolytic metastasis can be interrupted at four points in the vicious cycle: by neutralizing PTHrP biologic activity, by blocking the TGF-beta signaling pathway in the tumor cells, by inhibiting PTHrP gene transcription, and by inhibiting bone resorption.

Antibody blockade of the Cripto CFC domain suppresses tumor cell growth in vivo

Cripto, a cell surface-associated protein belonging to the EGF-CFC family of growth factor-like molecules, is overexpressed in many human solid tumors, including 70-80% of breast and colon tumors, yet how it promotes cell transformation is unclear. During embryogenesis, Cripto complexes with Alk4 via its unique cysteine-rich CFC domain to facilitate signaling by the TGF-beta ligand Nodal. We report, for the first time to our knowledge, that Cripto can directly bind to another TGF-beta ligand, Activin B, and that Cripto overexpression blocks Activin B growth inhibition of breast cancer cells. This result suggests a novel mechanism for antagonizing Activin signaling that could promote tumorigenesis by deregulating growth homeostasis. We show that an anti-CFC domain antibody, A8.G3.5, both disrupts Cripto-Nodal signaling and reverses Cripto blockade of Activin B-induced growth suppression by blocking Cripto's association with either Alk4 or Activin B. In two xenograft models, testicular and colon cancer, A8.G3.5 inhibited tumor cell growth by up to 70%. Both Nodal and Activin B expression was found in the xenograft tumor, suggesting that either ligand could be promoting tumorigenesis. These data validate that functional blockade of Cripto inhibits tumor growth and highlight antibodies that block Cripto signaling mediated through its CFC domain as an important class of antibodies for further therapeutic development.

Diverse cellular and molecular mechanisms contribute to epithelial plasticity and metastasis

In contrast to the aberrant control of proliferation, apoptosis, angiogenesis and lifespan, the cellular mechanisms that cause local invasion and metastasis of tumour cells are still poorly understood. New experimental approaches have identified different types of epithelial-plasticity changes in tumour cells towards fibroblastoid phenotypes as crucial events that occur during metastasis, and many molecules and signalling pathways cooperate to trigger these processes.

Transforming growth factor beta signaling impairs Neu-induced mammary tumorigenesis while promoting pulmonary metastasis

The influence of transforming growth factor beta (TGF-beta) signaling on Neu-induced mammary tumorigenesis and metastasis was examined with transgenic mouse models. We generated mice expressing an activated TGF-beta type I receptor or dominant negative TGF-beta type II receptor under control of the mouse mammary tumor virus promoter. When crossed with mice expressing activated forms of the Neu receptor tyrosine kinase that selectively couple to the Grb2 or Shc signaling pathways the activated type I receptor increased the latency of mammary tumor formation but also enhanced the frequency of extravascular lung metastasis. Conversely, expression of the dominant negative type II receptor decreased the latency of Neu-induced mammary tumor formation while significantly reducing the incidence of extravascular lung metastases. These observations argue that TGF-beta can promote the formation of lung metastases while impairing Neu-induced tumor growth and suggest that extravasation of breast cancer cells from pulmonary vessels is a point of action of TGF-beta in the metastatic process.

Fibroblast-specific expression of a kinase-deficient type II transforming growth factor beta (TGFbeta) receptor leads to paradoxical activation of TGFbeta signaling pathways with fibrosis in transgenic mice

To better understand the role of disrupted transforming growth factor beta (TGFbeta) signaling in fibrosis, we have selectively expressed a kinase-deficient human type II TGFbeta receptor (TbetaRIIDeltak) in fibroblasts of transgenic mice, using a lineage-specific expression cassette subcloned from the pro-alpha2(I) collagen gene. Surprisingly, despite previous studies that characterized TbetaRIIDeltak as a dominant negative inhibitor of TGFbeta signaling, adult mice expressing this construct demonstrated TGFbeta overactivity and developed dermal and pulmonary fibrosis. Compared with wild type cells, transgenic fibroblasts proliferated more rapidly, produced more extracellular matrix, and showed increased expression of key markers of TGFbeta activation, including plasminogen activator inhibitor-1, connective tissue growth factor, Smad3, Smad4, and Smad7. Smad2/3 phosphorylation was increased in transgenic fibroblasts. Overall, the gene expression profile of explanted transgenic fibroblasts using cDNA microarrays was very similar to that of littermate wild type cells treated with recombinant TGFbeta1. Despite basal up-regulation of TGFbeta signaling pathways, transgenic fibroblasts were relatively refractory to further stimulation with TGFbeta1. Thus, responsiveness of endogenous genes to TGFbeta was reduced, and TGFbeta-regulated promoter-reporter constructs transiently transfected into transgenic fibroblasts showed little activation by recombinant TGFbeta1. Responsiveness was partially restored by overexpression of wild type type II TGFbeta receptors. Activation of MAPK pathways by recombinant TGFbeta1 appeared to be less perturbed than Smad-dependent signaling. Our results show that expression of TbetaRIIDeltak selectively in fibroblasts leads to paradoxical ligand-dependent activation of downstream signaling pathways and causes skin and lung fibrosis. As well as confirming the potential for nonsignaling receptors to regulate TGFbeta activity, these findings support a direct role for perturbed TGFbeta signaling in fibrosis and provide a novel genetically determined animal model of fibrotic disease.

Role of tissue stroma in cancer cell invasion

Maintenance of epithelial tissues needs the stroma. When the epithelium changes, the stroma inevitably follows. In cancer, changes in the stroma drive invasion and metastasis, the hallmarks of malignancy. Stromal changes at the invasion front include the appearance of myofibroblasts, cells sharing characteristics with fibroblasts and smooth muscle cells. The main precursors of myofibroblasts are fibroblasts. The transdifferentiation of fibroblasts into myofibroblasts is modulated by cancer cell-derived cytokines, such as transforming growth factor-beta (TGF-beta). TGF-beta causes cancer progression through paracrine and autocrine effects. Paracrine effects of TGF-beta implicate stimulation of angiogenesis, escape from immunosurveillance and recruitment of myofibroblasts. Autocrine effects of TGF-beta in cancer cells with a functional TGF-beta receptor complex may be caused by a convergence between TGF-beta signalling and beta-catenin or activating Ras mutations. Experimental and clinical observations indicate that myofibroblasts produce pro-invasive signals. Such signals may also be implicated in cancer pain. N-Cadherin and its soluble form act as invasion-promoters. N-Cadherin is expressed in invasive cancer cells and in host cells such as myofibroblasts, neurons, smooth muscle cells, and endothelial cells. N-Cadherin-dependent heterotypic contacts may promote matrix invasion, perineural invasion, muscular invasion, and transendothelial migration; the extracellular, the juxtamembrane and the beta-catenin binding domain of N-cadherin are implicated in positive invasion signalling pathways. A better understanding of stromal contributions to cancer progression will likely increase our awareness of the importance of the combinatorial signals that support and promote growth, dedifferentiation, invasion, and ectopic survival and eventually result in the identification of new therapeutics targeting the stroma.

A multigenic program mediating breast cancer metastasis to bone

We investigated the molecular basis for osteolytic bone metastasis by selecting human breast cancer cell line subpopulations with elevated metastatic activity and functionally validating genes that are overexpressed in these cells. These genes act cooperatively to cause osteolytic metastasis, and most of them encode secreted and cell surface proteins. Two of these genes, interleukin-11 and CTGF, encode osteolytic and angiogenic factors whose expression is further increased by the prometastatic cytokine TGF beta. Overexpression of this bone metastasis gene set is superimposed on a poor-prognosis gene expression signature already present in the parental breast cancer population, suggesting that metastasis requires a set of functions beyond those underlying the emergence of the primary tumor.

Effect of glutamine on glutathione, IGF-I, and TGF-beta 1

BACKGROUND

Our previous results have showed that oral glutamine (GLN) supplementation decreased carcinogenesis in 7,12-dimethylbenz[a]antracene (DMBA) breast cancer model. We also have found that GLN raises blood glutathione (GSH) levels in an implantable breast cancer model. The process of tumor growth was accompanied by depressed GSH production and increased levels of insulin-like growth factor-I (IGF-I) and transforming growth factor beta1 (TGF-beta 1). GSH is counter-regulatory to IGF-I. We therefore hypothesized that in DMBA model of breast cancer, the increased GSH levels seen with oral GLN would be associated with lowered levels of IGF-I &TGF-beta(1).

METHODS

Time-dated pubertal Sprague-Dawley rats were gavaged at time 0 with 1 g/kg/day glutamine (GLN) (n = 18), isonitrogenous Freamine (FA) (n = 18), or water (H(2)O) (n = 18). Rats were further randomized on day 7 to 100 mg/kg DMBA or oil. After 14 days, the animals were sacrificed and blood GSH, IGF-1, TGF-beta 1, breast tissue, and gut mucosa GSH levels were measured.

RESULTS

Oral GLN increased significantly blood, breast tissue, and gut mucosa levels of GSH in both DMBA and control groups in comparison with the control groups not treated with GLN. At the same time, the levels of blood IGF-I and TGF-beta 1 decreased significantly in both DMBA-treated and control groups. DMBA did not significantly affect any of these levels. CONCLUSIONS ;Oral GLN increased GSH levels and lowered IGF-I and TGF-beta 1 in a range that is considered clinically significant. However, the effect of GLN in maintaining normal gut GSH production in the presence of DMBA was much more significant. Inconsistent with our hypothesis, reduction in IGF and TGF-beta 1 levels did not correlate with DMBA's effect on gut GSH production.

Cellular response to hypoxia involves signaling via Smad proteins

The transforming growth factor-beta (TGF-beta) family of cytokines regulates vascular development and inflammatory responses. We have recently shown that exposure of human umbilical vein endothelial cells (HUVECs) to hypoxia (1% O(2)) increases gene expression and bioactivation of TGF-beta2 and induces its downstream effectors, Smad proteins (Smads), to associate with DNA. In the present study, we show that hypoxia-induced TGF-beta2 gene expression is dependent on thrombospondin-1-mediated bioactivation of latent TGF-beta. Blocking TGF-beta2 but not TGF-beta1 in hypoxic endothelial cell cultures inhibited induction of the TGF-beta2 gene, indicating that an autocrine mechanism driven by bioactivation of TGF-beta2 leads to its gene expression in hypoxic HUVECs. Exposure of HUVECs to hypoxia resulted in phosphorylation and nuclear transportation of Smad2 and Smad3 proteins as well as stimulation of transcriptional activities of Smad3 and the transcription factor hypoxia-inducible factor-1alpha and culminated in up-regulation of TGF-beta2 gene expression. Autocrine regulation of TGF-beta2 production in hypoxia may involve cross-talk between Smad3 and HIF-1alpha signaling pathways, and could be an important mechanism by which endothelial cells respond to hypoxic stress.

The not-so innocent bystander: the microenvironment as a therapeutic target in cancer

The microenvironment in which cancer arises is often regarded as a bystander to the clonal expansion and acquisition of malignant characteristics of the tumour. However, a major function of the microenvironment is to suppress cancer, and its disruption is required for the establishment of cancer. In addition, tumour cells can further distort the microenvironment to promote growth, recruit non-malignant cells that provide physiological resources, and facilitate invasion. In this review, the authors discuss the contribution of the microenvironment, i.e., the stroma and its resident vasculature, inflammatory cells, growth factors and the extracellular matrix (ECM), in the development of cancer, and focus on two components as potential therapeutic targets in breast cancer. First, the ECM, which imparts crucial signalling via integrins and other receptors, is a first-line barrier to invasion, modulates aggressive behaviour and may be manipulated to provide novel impediments to tumour growth. Second, the authors discuss the involvement of TGF-beta1 as an example of one of many growth factors that can regulate ECM composition and degradation and that play complex roles in cancer. Compared to the variable routes taken by cells to become cancers, the response of tissues to cancer is relatively consistent. Therefore, controlling and eliminating cancer may be more readily achieved indirectly via the tissue microenvironment.