Histone deacetylases, Mbd3/NuRD, and Tet2 hydroxylase are crucial regulators of epithelial-mesenchymal plasticity and tumor metastasis.

An epithelial-mesenchymal transition (EMT) represents a basic morphogenetic process of high cell plasticity underlying embryogenesis, wound healing, cancer metastasis and drug resistance. It involves a profound transcriptional and epigenetic reprogramming of cells. A critical role of epigenetic modifiers and their specific chromatin modifications has been demonstrated during EMT. However, it has remained elusive whether epigenetic control differs between the dynamic cell state transitions of reversible EMT and the fixed differentiation status of irreversible EMT. We have employed varying EMT models of murine breast cancer cells to identify the key players establishing epithelial-mesenchymal cell plasticity during reversible and irreversible EMT. We demonstrate that the Mbd3/NuRD complex and the activities of histone deacetylases (HDACs), and Tet2 hydroxylase play a critical role in keeping cancer cells in a highly metastatic mesenchymal state. Combinatorial interference with their functions leads to mesenchymal-epithelial transition (MET) and efficiently represses metastasis formation by invasive murine and human breast cancer cells in vivo.

Nintedanib Is a Highly Effective Therapeutic for Neuroendocrine Carcinoma of the Pancreas (PNET) in the Rip1Tag2 Transgenic Mouse Model.

PURPOSE: Pancreatic neuroendocrine tumors (PNET) represent a rare but challenging heterogeneous group of cancers with an increasing incidence over the last number of decades. Herein, we report an in-depth evaluation of the new antiangiogenic small-molecule tyrosine kinase inhibitor (TKI) nintedanib in the preclinical Rip1Tag2 transgenic mouse model of neuroendocrine carcinoma of the pancreas (insulinoma). EXPERIMENTAL DESIGN: We have assessed the antiangiogenic and antitumor activity of nintedanib, in comparison with other antiangiogenic TKI, by treating Rip1Tag2 transgenic mice with different treatment schedules complemented with histopathologic, cell biologic, and biochemical analyses. RESULTS: Prolonged nintedanib treatment of Rip1Tag2 mice has led to a strong suppression of angiogenesis, accompanied by a reduced tumor burden, which translated into a significant prolongation of survival. Despite nintedanib's inhibitory action on perivascular cells, the blood vessels remaining after therapy displayed a considerably mature phenotype with tight perivascular cell coverage and preserved perfusion. Nintedanib treatment did not increase local tumor invasiveness or metastasis to the liver and pancreatic lymph nodes--a phenomenon that has been observed with antiangiogenic treatments of Rip1Tag2 transgenic mice in other laboratories. In contrast with the strong reduction in blood microvessel densities, nintedanib did not have any impact on tumor lymphangiogenesis. CONCLUSIONS: Based on our findings, we propose the clinical evaluation of the antiangiogenic drug nintedanib as a new treatment modality for PNET patients, notably in a direct comparison with already established therapeutic regimens, such as sunitinib.

Klf4 is a transcriptional regulator of genes critical for EMT, including Jnk1 (Mapk8).

We have identified the zinc-finger transcription factor Kruppel-like factor 4 (Klf4) among the transcription factors that are significantly downregulated in their expression during epithelial-mesenchymal transition (EMT) in mammary epithelial cells and in breast cancer cells. Loss and gain of function experiments demonstrate that the down-regulation of Klf4 expression is required for the induction of EMT in vitro and for metastasis in vivo. In addition, reduced Klf4 expression correlates with shorter disease-free survival of subsets of breast cancer patients. Yet, reduced expression of Klf4 also induces apoptosis in cells undergoing TGFß-induced EMT. Chromatin immunoprecipitation/deep-sequencing in combination with gene expression profiling reveals direct Klf4 target genes, including E-cadherin (Cdh1), N-cadherin (Cdh2), vimentin (Vim), ß-catenin (Ctnnb1), VEGF-A (Vegfa), endothelin-1 (Edn1) and Jnk1 (Mapk8). Thereby, Klf4 acts as a transcriptional activator of epithelial genes and as a repressor of mesenchymal genes. Specifically, increased expression of Jnk1 (Mapk8) upon down-regulation of its transcriptional repressor Klf4 is required for EMT cell migration and for the induction of apoptosis. The data demonstrate a central role of Klf4 in the maintenance of epithelial cell differentiation and the prevention of EMT and metastasis.

A bioluminescent mouse model of pancreatic {beta}-cell carcinogenesis.

The Rip1Tag2 transgenic mouse model of pancreatic beta-cell carcinogenesis has been instrumental in identifying several hallmarks of cancer, including tumor cell evasion from apoptosis, tumor angiogenesis and tumor invasion. Moreover, Rip1Tag2 mice have been helpful in the development and testing of innovative cancer therapies and tumor imaging protocols. However, based on tumor localization in the mouse, primary tumor growth and metastatic dissemination cannot be easily monitored in a longitudinal axis by non-invasive and low-technology approaches. Here, we report the generation of a new transgenic mouse line as a versatile tool to study beta-cell carcinogenesis. Transgenic expression of a bicistronic messenger RNA encoding simian virus large T antigen and firefly luciferase in pancreatic beta-cells recapitulates insulinoma development in a reproducible multistage process. In the mouse line called RipTag-IRES-Luciferase line (RTL) 1, the beta-cell-specific expression of luciferase allows the non-invasive monitoring of primary tumor growth over time in vivo and the detection and quantification of disseminated tumor cells and micrometastases in distant organs ex vivo. When crossed to mouse lines in which the expression of cancer 'modifier' genes has been manipulated, tumor initiation and tumor progression are similarly affected as previously reported for Rip1Tag2 mice, indicating a robust tumor progression pathway shared between the two different transgenic mouse lines. Together, the data indicate that the RTL1 mouse line will be of great value to study anti-tumoral therapeutic approaches as well as to define the functional roles of cancer- and metastasis-related genes when crossed to appropriate transgenic or gene-targeted mouse lines.

Differential effects of the vascular endothelial growth factor receptor inhibitor PTK787/ZK222584 on tumor angiogenesis and tumor lymphangiogenesis.

Halting tumor growth by interfering with tumor-induced angiogenesis is an attractive therapeutic approach. Such treatments include humanized antibodies blocking the activity of vascular endothelial growth factor (VEGF)-A (bevacizumab), soluble VEGF receptor (VEGFR) constructs (VEGF-Trap), or small-molecule inhibitors of VEGFR signaling, including PTK787/ZK222584 (PTK/ZK), sorafenib, and sunitinib. PTK/ZK has been shown previously to specifically block VEGF-induced phosphorylation of VEGFR-1, -2 and -3 and thereby to inhibit endothelial cell proliferation, differentiation, and tumor angiogenesis. We have investigated the effect of PTK/ZK on tumor angiogenesis and tumor lymphangiogenesis using the Rip1Tag2 transgenic mouse model of pancreatic beta cell carcinogenesis. In Rip1Tag2 mice, tumor angiogenesis is predominantly mediated by VEGF-A, and as expected, PTK/ZK efficiently impaired tumor blood vessel angiogenesis and tumor growth. Double-transgenic Rip1Tag2;Rip1VEGF-C and Rip1Tag2;Rip1VEGF-D mice not only exhibit VEGF-A-dependent blood vessel angiogenesis but also tumor lymphangiogenesis induced by the transgenic expression of VEGF-C or -D. In these mouse models, PTK/ZK also repressed tumor blood vessel angiogenesis and tumor growth yet failed to affect tumor lymphangiogenesis and lymphogenic metastasis. Adenoviral delivery of soluble VEGFR-3 also did not prevent tumor lymphangiogenesis in these mice. In contrast, spontaneous tumor lymphangiogenesis, as observed by the stochastic expression of VEGF-C and -D in tumors of neural cell adhesion molecule-deficient Rip1Tag2 mice, was repressed by PTK/ZK and soluble VEGFR-3. The results indicate that the time of onset and the levels of VEGF-C/D expression may be critical variables in efficiently repressing tumor lymphangiogenesis and that pathways other than VEGFR signaling may be involved in tumor lymphangiogenesis.

Increased tumor cell dissemination and cellular senescence in the absence of beta1-integrin function.

Integrins are transmembrane receptors that bind extracellular matrix proteins and enable cell adhesion and cytoskeletal organization, as well as transduction of signals into cells, to promote various aspects of cellular behavior, such as proliferation or survival. Integrins participate in many aspects of tumor biology. Here, we have employed the Rip1Tag2 transgenic mouse model of pancreatic beta cell carcinogenesis to investigate the role of beta(1)-integrin in tumor progression. Specific ablation of beta(1)-integrin function in pancreatic beta cells resulted in a defect in sorting between insulin-expressing beta cells and glucagon-expressing alpha cells in islets of Langerhans. Ablation of beta(1)-integrin in beta tumor cells of Rip1Tag2 mice led to the dissemination of tumor cell emboli into lymphatic blood vessels in the absence of ongoing lymphangiogenesis. Yet, disseminating beta(1)-integrin-deficient beta tumor cells did not elicit metastasis. Rather, primary tumor growth was significantly impaired by reduced tumor cell proliferation and the acquisition of cellular senescence by beta(1)-integrin-deficient beta tumor cells. The results indicate a critical role of beta(1)-integrin function in mediating metastatic dissemination and preventing tumor cell senescence.

Moderate antiangiogenic activity by local, transgenic expression of endostatin in Rip1Tag2 transgenic mice.

Many previous reports have demonstrated that systemic administration of endostatin (ES), a proteolytic cleavage product of collagen type XVIII and an endogenous angiogenesis inhibitor, represses tumor angiogenesis in different preclinical tumor models with varying efficacy. For example, systemic delivery of recombinant ES to rat insulin promoter 1 (Rip1)T-antigen 2 (Tag2)-transgenic mice, a mouse model of pancreatic beta-cell carcinogenesis, has repressed tumor angiogenesis efficiently and with it, tumor growth. Here, we report that the transgenic expression of ES in Rip1ES-transgenic mice only interferes moderately with tumor growth in Rip1Tag2;Rip1ES double-transgenic mice. Tumor incidence is not reduced by the local expression of ES, and tumor outgrowth and progression to tumor malignancy are only retarded slightly. A significant effect of local ES expression on tumor angiogenesis is only apparent during the early stages of tumor development, where less angiogenic hyperplastic lesions are observed. Although efficiently produced and secreted by transgenic beta cells, locally expressed ES appears to be sequestered in the microenvironment, and its systemic levels are not increased. The results indicate that the antiangiogenic functions of ES critically depend on the mode of delivery and the site of expression: although its systemic application represses tumor angiogenesis and tumor growth efficiently, locally expressed ES appears to be less effective, and hence, additional mechanisms of solubilization or activation of latent ES seem to be required. These results have important implications about the modes of delivery used in antiangiogenic, therapeutic strategies, which are based on the antiangiogenic activities of ES.