Angiopoietin-4 promotes glioblastoma progression by enhancing tumor cell viability and angiogenesis

Angiopoietin4 (ANGPT4) expression and potential mechanisms in carcinogenesis: current achievements and perspectives

Angiopoietin4(ANGPT4) which plays a significant role in endothelial cell proliferation, survival, angiogenesis and expansion in tumors and other pathological states is a significant regulator of tumor angiogenesis. ANGPT4 expression is enhanced in many cancer cells. For example, the overexpression of ANGPT4 promotes the formation, development and progress of lung adenocarcinoma, glioblastoma and ovarian cancer. Related studies show that ANGPT4 encourages the proliferation, survival and invasion of tumor cells, while promoting the expansion of the tumor vascular system and affecting the tumor immune microenvironment. ANGPT4 can also promote carcinogenesis by affecting the ERK1/2, PI3K/AKT and other signal pathways downstream of tyrosine kinase with immunoglobulin-like and EGF-like domains 2(TIE2) and TIE2. Therefore, ANGPT4 may be a potential and significant biomarker for predicting malignant tumor progression and adverse outcomes. In addition, inhibition of ANGPT4 may be a meaningful cancer treatment. This paper reviews the latest research results of ANGPT4 in preclinical research, and emphasizes its role in carcinogenesis. Additional research on the carcinogenic function of ANGPT4 could provide new insights into cancer biology and novel methods for cancer diagnosis and treatment.

The role of angiogenic growth factors in the immune microenvironment of glioma

Angiogenic growth factors (AGFs) are a class of secreted cytokines related to angiogenesis that mainly include vascular endothelial growth factors (VEGFs), stromal-derived factor-1 (SDF-1), platelet-derived growth factors (PDGFs), fibroblast growth factors (FGFs), transforming growth factor-beta (TGF-β) and angiopoietins (ANGs). Accumulating evidence indicates that the role of AGFs is not only limited to tumor angiogenesis but also participating in tumor progression by other mechanisms that go beyond their angiogenic role. AGFs were shown to be upregulated in the glioma microenvironment characterized by extensive angiogenesis and high immunosuppression. AGFs produced by tumor and stromal cells can exert an immunomodulatory role in the glioma microenvironment by interacting with immune cells. This review aims to sum up the interactions among AGFs, immune cells and cancer cells with a particular emphasis on glioma and tries to provide new perspectives for understanding the glioma immune microenvironment and in-depth explorations for anti-glioma therapy.

Double Immunohistochemical Staining on Formalin-Fixed Paraffin-Embedded Tissue Samples to Study Vascular Co-option

Vascular co-option is a non-angiogenic mechanism whereby tumor growth and progression move on by hijacking the pre-existing and nonmalignant blood vessels and is employed by various tumors to grow and metastasize.The histopathological identification of co-opted blood vessels is complex, and no specific markers were defined, but it is critical to develop new and possibly more effective therapeutic strategies. Here, in glioblastoma, we show that the co-opted blood vessels can be identified, by double immunohistochemical staining, as weak CD31⁺ vessels with reduced P-gp expression and proliferation and surrounded by highly proliferating and P-gp- or S100A10-expressing tumor cells. Results can be quantified by the Aperio Colocalization algorithm, which is a valid and robust method to handle and investigate large data sets.

The Vascular Microenvironment in Glioblastoma: A Comprehensive Review

Glioblastoma multiforme, the deadliest primary brain tumor, is characterized by an excessive and aberrant neovascularization. The initial expectations raised by anti-angiogenic drugs were soon tempered due to their limited efficacy in improving the overall survival. Intrinsic resistance and escape mechanisms against anti-VEGF therapies evidenced that tumor angiogenesis is an intricate multifaceted phenomenon and that vessels not only support the tumor but exert indispensable interactions for resistance and spreading. This holistic review covers the essentials of the vascular microenvironment of glioblastoma, including the perivascular niche components, the vascular generation patterns and the implicated signaling pathways, the endothelial–tumor interrelation, and the interconnection between vessel aberrancies and immune disarrangement. The revised concepts provide novel insights into the preclinical models and the potential explanations for the failure of conventional anti-angiogenic therapies, leading to an era of new and combined anti-angiogenic-based approaches.

Targeting Tie2 in the Tumor Microenvironment: From Angiogenesis to Dissemination

Simple Summary

The dissemination of cancer cells from their original location to distant organs where they grow, a process called metastasis, causes more than 90% of cancer deaths. The identification of the molecular mechanisms of metastasis and the development of anti-metastatic therapies are essential to increase patient survival. In recent years, targeting the tumor microenvironment has become a promising avenue to prevent both tumor growth and metastasis. As the tumor microenvironment contains not only cancer cells but also blood vessels, immune cells, and other non-cancerous cells, it is naïve to think that therapy only affects a single cell type in this complex environment. Here we review the importance, and ways to inhibit the function, of one therapeutic target: the receptor Tie2. Tie2 is a receptor present on the cell surface of several cell types within the tumor microenvironment and regulates tumor angiogenesis, growth, and metastasis to distant organs.

Abstract

The Tie2 receptor tyrosine kinase is expressed in vascular endothelial cells, tumor-associated macrophages, and tumor cells and has been a major focus of research in therapies targeting the tumor microenvironment. The most extensively studied Tie2 ligands are Angiopoietin 1 and 2 (Ang1, Ang2). Ang1 plays a critical role in vessel maturation, endothelial cell migration, and survival. Ang2, depending on the context, may function to disrupt connections between the endothelial cells and perivascular cells, promoting vascular regression. However, in the presence of VEGF-A, Ang2 instead promotes angiogenesis. Tie2-expressing macrophages play a critical role in both tumor angiogenesis and the dissemination of tumor cells from the primary tumor to secondary sites. Therefore, Ang-Tie2 signaling functions as an angiogenic switch during tumor progression and metastasis. Here we review the recent advances and complexities of targeting Tie2 signaling in the tumor microenvironment as a possible anti-angiogenic, and anti-metastatic, therapy and describe its use in combination with chemotherapy.

Angiopoietins as Potential Targets in Management of Retinal Disease

The Ang/Tie2 pathway complements VEGF-mediated activity in retinal vascular diseases such as DME, AMD, and RVO by decreasing vascular integrity, increasing neovascularization, and increasing inflammatory signaling. Faricimab is a bispecific antibody that has been developed as an inhibitor of both VEGF and Ang2 that has shown positive results in phase I, II and III trials. Recent Year 1 data from phase III clinical trials YOSEMITE, RHINE, TENAYA, and LUCERNE have confirmed the efficacy, safety, durability, and superiority of faricimab in patients with DME and nAMD. Faricimab, if approved, may significantly decrease treatment burden in patients with retinal vascular diseases to a greater extent than would current standard of care anti-VEGF injections.

Tumor Vessels Fuel the Fire in Glioblastoma

Glioblastoma, a subset of aggressive brain tumors, deploy several means to increase blood vessel supply dedicated to the tumor mass. This includes typical program borrowed from embryonic development, such as vasculogenesis and sprouting angiogenesis, as well as unconventional processes, including co-option, vascular mimicry, and transdifferentiation, in which tumor cells are pro-actively engaged. However, these neo-generated vascular networks are morphologically and functionally abnormal, suggesting that the vascularization processes are rather inefficient in the tumor ecosystem. In this review, we reiterate the specificities of each neovascularization modality in glioblastoma, and, how they can be hampered mechanistically in the perspective of anti-cancer therapies.

ΔNp73/ETS2 complex drives glioblastoma pathogenesis- targeting downstream mediators by rebastinib prolongs survival in preclinical models of glioblastoma

BACKGROUND

Glioblastoma (GBM) remains one of the least successfully treated cancers. It is essential to understand the basic biology of this lethal disease and investigate novel pharmacological targets to treat GBM. The aims of this study were to determine the biological consequences of elevated expression of ΔNp73, an N-terminal truncated isoform of TP73, and to evaluate targeting of its downstream mediators, the angiopoietin 1 (ANGPT1)/tunica interna endothelial cell kinase 2 (Tie2) axis, by using a highly potent, orally available small-molecule inhibitor (rebastinib) in GBM.

METHODS

ΔNp73 expression was assessed in glioma sphere cultures, xenograft glioblastoma tumors, and glioblastoma patients by western blot, quantitative reverse transcription PCR, and immunohistochemistry. Immunoprecipitation, chromatin immunoprecipitation (ChiP) and sequential ChIP were performed to determine the interaction between ΔNp73 and E26 transformation-specific (ETS) proto-oncogene 2 (ETS2) proteins. The oncogenic consequences of ΔNp73 expression in glioblastomas were examined by in vitro and in vivo experiments, including orthotopic zebrafish and mouse intracranial-injection models. Effects of rebastinib on growth of established tumors and survival were examined in an intracranial-injection mouse model.

RESULTS

ΔNp73 upregulates both ANGPT1 and Tie2 transcriptionally through ETS conserved binding sites on the promoters by interacting with ETS2. Elevated expression of ΔNp73 promotes tumor progression by mediating angiogenesis and survival. Therapeutic targeting of downstream ΔNp73 signaling pathways by rebastinib inhibits growth of established tumors and extends survival in preclinical models of glioblastoma.

CONCLUSION

Aberrant expression of ΔNp73 in GBM promotes tumor progression through autocrine and paracrine signaling dependent on Tie2 activation by ANGPT1. Disruption of this signaling by rebastinib improves tumor response to treatment in glioblastoma.

Long non-coding RNA linc00665 interacts with YB-1 and promotes angiogenesis in lung adenocarcinoma

Angiogenesis is a core hallmark of advanced cancers, especially in lung adenocarcinoma (LUAD). However, the underlying functions and mechanisms of lncRNAs in tumor angiogenesis remain largely unknown. Here we found that linc00665 depletion could markedly depressed proliferation and capillary tube formation of HUVECs in vitro. Mechanistically, linc00665 directly interacted with YB-1 protein, enhanced its stability through inhibiting ubiquitination-dependent proteolysis and stimulated its nuclear translocation in LUAD cells. The accumulated nuclear YB-1 activated expression of ANGPT4, ANGPTL3 and VEGFA by binding to their promoters, contributing to tumor-related angiogenesis in vitro and in vivo. Collectively, we conclude that linc00665 induces tumor-related angiogenesis in LUAD by directly interacting with YB-1 and activating YB-1-ANGPT4/ANGPTL3/VEGFA axis, which provides promising anti-angiogenic targets for cancer therapy.

Tumor Development and Angiogenesis in Adult Brain Tumor: Glioblastoma

Angiogenesis is the growth of new capillaries from the preexisting blood vessels. Glioblastoma (GBM) tumors are highly vascularized tumors, and glioma growth depends on the formation of new blood vessels. Angiogenesis is a complex process involving proliferation, migration, and differentiation of vascular endothelial cells (ECs) under the stimulation of specific signals. It is controlled by the balance between its promoting and inhibiting factors. Various angiogenic factors and genes have been identified that stimulate glioma angiogenesis. Therefore, attention has been directed to anti-angiogenesis therapy in which glioma proliferation is inhibited by inhibiting the formation of new tumor vessels using angiogenesis inhibitory factors and drugs. Here, in this review, we highlight and summarize the various molecular mediators that regulate GBM angiogenesis with focus on recent clinical research on the potential of exploiting angiogenic pathways as a strategy in the treatment of GBM patients.

Receptor Tyrosine Kinases: Principles and Functions in Glioma Invasion

Protein tyrosine kinases are enzymes that are capable of adding a phosphate group to specific tyrosines on target proteins. A receptor tyrosine kinase (RTK) is a tyrosine kinase located at the cellular membrane and is activated by binding of a ligand via its extracellular domain. Protein phosphorylation by kinases is an important mechanism for communicating signals within a cell and regulating cellular activity; furthermore, this mechanism functions as an "on" or "off" switch in many cellular functions. Ninety unique tyrosine kinase genes, including 58 RTKs, were identified in the human genome; the products of these genes regulate cellular proliferation, survival, differentiation, function, and motility. Tyrosine kinases play a critical role in the development and progression of many types of cancer, in addition to their roles as key regulators of normal cellular processes. Recent studies have revealed that RTKs such as epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), c-Met, Tie, Axl, discoidin domain receptor 1 (DDR1), and erythropoietin-producing human hepatocellular carcinoma (Eph) play a major role in glioma invasion. Herein, we summarize recent advances in understanding the role of RTKs in glioma pathobiology, especially the invasive phenotype, and present the perspective that RTKs are a potential target of glioma therapy.

PROGNOSTIC ROLE OF CD44 EXPRESSION AND NEOVASCULARIZATION DETERMINED BY ENDOGLIN (CD105) IN GLIOBLASTOMA PATIENTS

Glioblastoma multiforme (GBM) is the most common and most aggressive malignant primary brain tumor in humans. Clinically useful molecular markers that help predict response to therapy and prognosis are still rare. The research was conducted in 55 patients with GBM, 26 (47.3%) women and 29 (52.7%) men, mean age 62.58 years. On immunohistochemical analysis, primary antibody to CD44 (dilution 1:50) and primary antibody to endoglin (CD105) (dilution 1:250) were used to evaluate neovascularization. Statistical analysis showed negative correlation between CD44 and survival (p=0.023) (higher expression of CD44 was correlated with shorter survival), but there was no correlation between neovascularization determined by CD105 in GBM and patient survival. Thus, significant individual predictors of longer survival were lower expression of CD44 (p=0.004), higher Karnofsky score (p=0.045), and female gender (p=0.017). The results obtained suggested the possible role of CD44 in the progression and tumor neovascularization of GBM.

Angiopoietins in Diabetic Retinopathy: Current Understanding and Therapeutic Potential

Diabetic retinopathy (DR) is the commonest cause of blindness in the working-age population of the developed world. The molecular pathophysiology of DR is complex, and a complete spatiotemporal model of the disease is still being elucidated. Recently, a role for angiopoietin (Ang) proteins in the pathophysiology of DR has been proposed by several research groups, and several aspects of Ang signalling are being explored as novel therapeutic strategies. Here, we review the role of the Ang proteins in two important forms of DR, diabetic macular oedema and proliferative diabetic retinopathy. The function of the Ang proteins in regulating blood vessel permeability and neovascularisation is discussed, and we also evaluate recent preclinical and clinical studies highlighting the potential benefits of modulating Ang signalling as a treatment for DR.

Angiopoietin-4-dependent venous maturation and fluid drainage in the peripheral retina

The maintenance of fluid homeostasis is necessary for function of the neural retina; however, little is known about the significance of potential fluid management mechanisms. Here, we investigated angiopoietin-4 (Angpt4, also known as Ang3), a poorly characterized ligand for endothelial receptor tyrosine kinase Tie2, in mouse retina model. By using genetic reporter, fate mapping, and in situ hybridization, we found Angpt4 expression in a specific sub-population of astrocytes at the site where venous morphogenesis occurs and that lower oxygen tension, which distinguishes peripheral and venous locations, enhances Angpt4 expression. Correlating with its spatiotemporal expression, deletion of Angpt4 resulted in defective venous development causing impaired venous drainage and defects in neuronal cells. In vitro characterization of angiopoietin-4 proteins revealed both ligand-specific and redundant functions among the angiopoietins. Our study identifies Angpt4 as the first growth factor for venous-specific development and its importance in venous remodeling, retinal fluid clearance and neuronal function.

Prognostic value of NUSAP1 in progression and expansion of glioblastoma multiforme

Nucleolar and spindle-associated protein (NUSAP1) is a microtubule and chromatin-binding protein that stabilizes microtubules to prevent depolymerization, maintains spindle integrity. NUSAP1 could cross-link spindles into aster-like structures, networks and fibers. It has also been found to play roles in progression of several cancers. However, the potential correlation between NUSAP1 and clinical outcome in patients with glioblastoma multiforme (GBM) remains largely unknown. In the current study, we demonstrated that NUSAP1 was significantly up-regulated in GBM tissues compared with adult non-tumor brain tissues both in a validated cohort and a TCGA cohort. In addition, Kaplan-Meier analysis indicated that patients with high NUSAP1 expression had significantly lower OS (P = 0.0027). Additionally, in the TCGA cohort, NUSAP1 expression was relatively lower in GBM patients within the neural and mesenchymal subtypes compared to other subtypes, and associated with the status of several genetic aberrations such as PTEN deletion and wild type IDH1. The present study provides new insights and evidence that NUSAP1 over-expression was significantly correlated with progression and prognosis of GBM. Furthermore, knockdown of NUSAP1 revealed its regulation on G2/M progression and cell proliferation (both in vitro and in vivo). These data demonstrate that NUSAP1 could serve as a novel prognostic biomarker and a potential therapeutic target for GBM.

UniPR1331, a small molecule targeting Eph/ephrin interaction, prolongs survival in glioblastoma and potentiates the effect of antiangiogenic therapy in mice

Glioblastoma multiforme (GBM) is the most malignant brain tumor, showing high resistance to standard therapeutic approaches that combine surgery, radiotherapy, and chemotherapy. As opposed to healthy tissues, EphA2 has been found highly expressed in specimens of glioblastoma, and increased expression of EphA2 has been shown to correlate with poor survival rates. Accordingly, agents blocking Eph receptor activity could represent a new therapeutic approach. Herein, we demonstrate that UniPR1331, a pan Eph receptor antagonist, possesses significant in vivo anti-angiogenic and anti-vasculogenic properties which lead to a significant anti-tumor activity in xenograft and orthotopic models of GBM. UniPR1331 halved the final volume of tumors when tested in xenografts (p<0.01) and enhanced the disease-free survival of treated animals in the orthotopic models of GBM both by using U87MG cells (40 vs 24 days of control, p<0.05) or TPC8 cells (52 vs 16 days, p<0.01). Further, the association of UniPR1331 with the anti-VEGF antibody Bevacizumab significantly increased the efficacy of both monotherapies in all tested models. Overall, our data promote UniPR1331 as a novel tool for tackling GBM.

FRMD6 inhibits human glioblastoma growth and progression by negatively regulating activity of receptor tyrosine kinases

FRMD6 is an Ezrin/Radixin/Moesin (ERM) family protein and a human homologue of Drosophila expanded (ex). Ex functions in parallel of Drosophila merlin at upstream of the Hippo signaling pathway that controls proliferation, apoptosis, tissue regeneration, and tumorigenesis. Even though the core kinase cascade (MST1/2-Lats1/2-YAP/TAZ) of the Hippo pathway has been well established, its upstream regulators are not well understood. Merlin promotes activation of the Hippo pathway. However, the effect of FRMD6 on the Hippo pathway is controversial. Little is known about how FRMD6 functions and the potential role of FRMD in gliomagenesis and glioblastoma (GBM) progression. We demonstrate for the first time that FRMD6 is down-regulated in human GBM cells and tissues and that increased FRMD6 expression inhibits whereas FRMD6 knockdown promotes GBM cell proliferation/invasion in vitro and GBM growth/progression in vivo. Furthermore, we demonstrate that unlike increased expression of merlin, which enhances the stress induced activation of the Hippo pathway, increased FRMD6 expression displays little effect on the pathway. In contrast, we show that FRMD6 inhibits activation of a couple of receptor tyrosine kinases (RTKs) including c-Met and PDGFR and their downstream Erk and AKT kinases. Moreover, we show that expression of constitutively active c-Met, the TPR-Met fusion protein, largely reverses the anti-GBM effect of FRMD6 in vivo, suggesting that FRMD6 functions at least partially through inhibiting activity of RTKs especially c-Met. These results establish a novel function of FRMD6 in inhibiting human GBM growth and progression and uncover a novel mechanism by which FRMD6 exerts its anti-GBM activity.

Radiogenomic analysis of hypoxia pathway is predictive of overall survival in Glioblastoma

Hypoxia, a characteristic trait of Glioblastoma (GBM), is known to cause resistance to chemo-radiation treatment and is linked with poor survival. There is hence an urgent need to non-invasively characterize tumor hypoxia to improve GBM management. We hypothesized that (a) radiomic texture descriptors can capture tumor heterogeneity manifested as a result of molecular variations in tumor hypoxia, on routine treatment naïve MRI, and (b) these imaging based texture surrogate markers of hypoxia can discriminate GBM patients as short-term (STS), mid-term (MTS), and long-term survivors (LTS). 115 studies (33 STS, 41 MTS, 41 LTS) with gadolinium-enhanced T1-weighted MRI (Gd-T1w) and T2-weighted (T2w) and FLAIR MRI protocols and the corresponding RNA sequences were obtained. After expert segmentation of necrotic, enhancing, and edematous/nonenhancing tumor regions for every study, 30 radiomic texture descriptors were extracted from every region across every MRI protocol. Using the expression profile of 21 hypoxia-associated genes, a hypoxia enrichment score (HES) was obtained for the training cohort of 85 cases. Mutual information score was used to identify a subset of radiomic features that were most informative of HES within 3-fold cross-validation to categorize studies as STS, MTS, and LTS. When validated on an additional cohort of 30 studies (11 STS, 9 MTS, 10 LTS), our results revealed that the most discriminative features of HES were also able to distinguish STS from LTS (p = 0.003).

The Selective Tie2 Inhibitor Rebastinib Blocks Recruitment and Function of Tie2Hi Macrophages in Breast Cancer and Pancreatic Neuroendocrine Tumors

Tumor-infiltrating myeloid cells promote tumor progression by mediating angiogenesis, tumor cell intravasation, and metastasis, which can offset the effects of chemotherapy, radiation, and antiangiogenic therapy. Here, we show that the kinase switch control inhibitor rebastinib inhibits Tie2, a tyrosine kinase receptor expressed on endothelial cells and protumoral Tie2-expressing macrophages in mouse models of metastatic cancer. Rebastinib reduces tumor growth and metastasis in an orthotopic mouse model of metastatic mammary carcinoma through reduction of Tie2⁺ myeloid cell infiltration, antiangiogenic effects, and blockade of tumor cell intravasation mediated by perivascular Tie2^Hi/Vegf-A^Hi macrophages in the tumor microenvironment of metastasis (TMEM). The antitumor effects of rebastinib enhance the efficacy of microtubule inhibiting chemotherapeutic agents, either eribulin or paclitaxel, by reducing tumor volume, metastasis, and improving overall survival. Rebastinib inhibition of angiopoietin/Tie2 signaling impairs multiple pathways in tumor progression mediated by protumoral Tie2⁺ macrophages, including TMEM-dependent dissemination and angiopoietin/Tie2-dependent angiogenesis. Rebastinib is a promising therapy for achieving Tie2 inhibition in cancer patients. Mol Cancer Ther; 16(11); 2486-501. ©2017 AACR.

Dimerization of Tie2 mediated by its membrane-proximal FNIII domains

Tie1 and Tie2, members of the tyrosine kinase family with immunoglobulin and EGF homology domains, are receptor tyrosine kinases found primarily in endothelial cells with key roles in development and maintenance of the vasculature and in angiogenesis. They are attractive targets for therapeutic intervention in tumor angiogenesis, inflammation, and sepsis. Tie2 is regulated directly by the multimeric angiopoietin (Ang) ligands, with Ang1 being its primary activator. Structural studies have shown how Angs bind to the Tie2 ligand-binding region, but do not explain Tie2 activation and suggest a passive role for the Tie2 extracellular region (ECR) in ligand-induced receptor dimerization. Here we show that the Tie2 ECR forms strong dimers even in the absence of bound ligand. Dimerization is mediated by membrane-proximal fibronectin type III (FNIII) domains that were omitted in previous structural studies. We describe a 2.5-Å resolution X-ray crystal structure of the membrane-proximal three Tie2 FNIII domains, Tie2(FNIIIa-c), revealing two possible dimerization modes that primarily involve the third FNIII domain, FNIIIc. Mutating these dimer interfaces implicates one of them (dimer 1) in soluble Tie2 (sTie2) dimerization in solution but suggests that both could play a role in Ang1-induced Tie2 activation, possibly modulated by Tie1. Through small-angle X-ray scattering studies of sTie2 dimers in solution and modeling based on crystal structures, we suggest that Ang1 binding may cross-link Tie2 dimers into higher-order oligomers, potentially explaining how Tie2 is differentially clustered following ligand engagement in different cellular contexts. Our results also firmly implicate FNIII domain-mediated interactions in Tie2 activation, identifying a potential Achilles' heel for therapeutic inhibition.

Novel TIE-2 inhibitor BAY-826 displays in vivo efficacy in experimental syngeneic murine glioma models

Targeting the vascular endothelial growth factor signaling axis in glioblastoma inevitably leads to tumor recurrence and a more aggressive phenotype. Therefore, other angiogenic pathways, like the angiopoietin/tunica interna endothelial cell kinase (TIE) signaling axis, have become additional targets for therapeutic intervention. Here, we explored whether targeting the receptor tyrosine kinase TIE-2 using a novel, highly potent, orally available small molecule TIE-2 inhibitor (BAY-826) improves tumor control in syngeneic mouse glioma models. BAY-826 inhibits TIE-2 phosphorylation in vitro and in vivo as demonstrated by suppression of Angiopoietin-1- or Na₃ VO₄ -induced TIE-2 phosphorylation in glioma cells or extracts of lungs from BAY-826-treated mice. There was a trend toward prolonged survival upon single-agent treatment in two of four models (SMA-497 and SMA-540) and there was a significant survival benefit in one model (SMA-560). Co-treatment with BAY-826 and irradiation was ineffective in one model (SMA-497), but provided synergistic prolongation of survival in another (SMA-560). Decreased vessel densities and increased leukocyte infiltration were observed, but might be independent processes as the effect was also observed in single treatment modalities. These data demonstrate that TIE-2 inhibition may improve tumor response to treatment in highly vascularized tumors such as glioblastoma.

Single-cell RNA-seq reveals cell type-specific transcriptional signatures at the maternal-foetal interface during pregnancy

Growth and survival of the mammalian embryo within the uterine environment depends on the placenta, a highly complex vascularized organ comprised of both maternal and foetal tissues. Recent experiments demonstrate that the zinc finger transcriptional repressor Prdm1/Blimp1 is essential for specification of spiral artery trophoblast giant cells (SpA-TGCs) that invade and remodel maternal blood vessels. To learn more about functional contributions made by Blimp1+ cell lineages here we perform the first single-cell RNA-seq analysis of the placenta. Cell types of both foetal and maternal origin are profiled. Comparisons with microarray datasets from mutant placenta and in vitro differentiated trophoblast stem cells allow us to identify Blimp1-dependent transcripts enriched in SpA-TGCs. Our experiments provide new insights into the functionally distinct cell types present at the maternal–foetal interface and advance our knowledge of dynamic gene expression patterns controlling placental morphogenesis and vascular mimicry.

The zinc finger transcriptional repressor Prdm1/Blimp1 is essential for remodelling maternal blood vessels in a subset of trophoblast cells. Here, the authors perform single-cell RNA-seq analysis on this Blimp1+ lineage, identifying functionally distinct cell types present at the maternal–foetal interface.

High expression of N-myc (and STAT) interactor predicts poor prognosis and promotes tumor growth in human glioblastoma

Glioma is the most malignant brain tumor and glioblastoma (GBM) is the most aggressive type. The involvement of N-myc (and STAT) interactor (NMI) in tumorigenesis was sporadically reported but far from elucidation. This study aims to investigate roles of NMI in human glioma. Three independent cohorts, the Chinese tissue microarray (TMA) cohort (N = 209), the Repository for Molecular Brain Neoplasia Data (Rembrandt) cohort (N = 371) and The Cancer Genome Atlas (TCGA) cohort (N = 528 or 396) were employed. Transcriptional or protein levels of NMI expression were significantly increased according to tumor grade in all three cohorts. High expression of NMI predicted significantly unfavorable clinical outcome for GBM patients, which was further determined as an independent prognostic factor. Additionally, expression and prognostic value of NMI were associated with molecular features of GBM including PTEN deletion and EGFR amplification in TCGA cohort. Furthermore, overexpression or depletion of NMI revealed its regulation on G1/S progression and cell proliferation (both in vitro and in vivo), and this effect was partially dependent on STAT1, which interacted with and was regulated by NMI. These data demonstrate that NMI may serve as a novel prognostic biomarker and a potential therapeutic target for glioblastoma.

Pro-apoptotic and anti-angiogenic properties of the α /β-thujone fraction from Thuja occidentalis on glioblastoma cells

The most aggressive type of brain tumor is glioblastoma multiforme, which to date remains incurable. Thuja occidentalis is used in homeopathy for the treatment of cancer, however, its mechanism of action remains unknown. We set out to study the effects of thujone fractions of Thuja on glioblastoma using in vitro and in vivo models. We found that the α/ β-thujone fraction decrease the cell viability and exhibit a potent anti-proliferative, pro-apoptotic and anti-angiogenic effects in vitro. In vivo assays showed that α /β-thujone promotes the regression of neoplasia and inhibits the angiogenic markers VEGF, Ang-4 and CD31 into the tumor.

Tie-1: A potential target for anti-angiogenesis therapy

The tyrosine kinase system angiopoietin (Ang)/Tie interacts with vascular endothelial growth factor pathway and regulates vessel quiescence in adults as well as later steps of the angiogenic cascade related to vessel maturation. Since all Angs are able to bind to Tie-2 but none binds to Tie-1, the function of Tie-2 and its ligands have captured attention. However, emerging evidence indicates unique roles of the orphan receptor Tie-1 in angiogenesis under physiological and pathological conditions. It is required for maintaining vascular endothelial cell integrity and survival during murine embryo development and in adult and may be involved in modulating differentiation of hematopoietic cells in adult. Tie-1 exhibits poor tyrosine kinase activity and signals via forming heterodimers with Tie-2, inhibiting Tie-2 signaling mediated by Angs. This inhibition can be relieved by Tie-1 ectodomain cleavage mediated by tumor- and inflammatory-related factors, which causes destabilization of vessels and initiates vessel remodeling. Up-regulated Tie-1 expression has been found not only in some leukemia cells and tumor related endothelial cells but also in cytoplasm of carcinoma cells of a variety of human solid tumors, which is associated with tumor progression. In addition, it has pro-inflammatory functions in endothelial cells and is involved in some inflammatory diseases associated with angiogenesis. Recent research indicated that Tie-1 gene ablation exhibited significant effects on tumor blood- and lymph-angiogenesis and improved anti-Ang therapy, suggesting Tie-1 may be a potential target for tumor anti-angiogenesis treatment.

Altiratinib Inhibits Tumor Growth, Invasion, Angiogenesis, and Microenvironment-Mediated Drug Resistance via Balanced Inhibition of MET, TIE2, and VEGFR2

Altiratinib (DCC-2701) was designed based on the rationale of engineering a single therapeutic agent able to address multiple hallmarks of cancer (1). Specifically, altiratinib inhibits not only mechanisms of tumor initiation and progression, but also drug resistance mechanisms in the tumor and microenvironment through balanced inhibition of MET, TIE2 (TEK), and VEGFR2 (KDR) kinases. This profile was achieved by optimizing binding into the switch control pocket of all three kinases, inducing type II inactive conformations. Altiratinib durably inhibits MET, both wild-type and mutated forms, in vitro and in vivo. Through its balanced inhibitory potency versus MET, TIE2, and VEGFR2, altiratinib provides an agent that inhibits three major evasive (re)vascularization and resistance pathways (HGF, ANG, and VEGF) and blocks tumor invasion and metastasis. Altiratinib exhibits properties amenable to oral administration and exhibits substantial blood-brain barrier penetration, an attribute of significance for eventual treatment of brain cancers and brain metastases.

Angiopoietin-4 increases permeability of blood vessels and promotes lymphatic dilation

The angiopoietin (Ang) ligands are potential therapeutic targets for lymphatic related diseases, which include lymphedema and cancer. Ang-1 and Ang-2 functions are established, but those of Ang-4 are poorly understood. We used intravital fluorescence microscopy to characterize Ang-4 actions on T241 murine fibrosarcoma-associated vessels in mice. The diameters of lymphatic vessels draining Ang-4- or VEGF-C (positive control)-expressing tumors increased to 123 and 135 μm, respectively, and parental, mock-transduced (negative controls) and tumors expressing Ang-1 or Ang-2 remained at baseline (∼60 μm). Ang-4 decreased human dermal lymphatic endothelial cell (LEC) monolayer permeability by 27% while increasing human dermal blood endothelial cell (BEC) monolayer permeability by 200%. In vivo, Ang-4 stimulated a 4.5-fold increase in tumor-associated blood vessel permeability compared with control when measured using intravital quantitative multiphoton microscopy. Ang-4 activated receptor signaling in both LECs and BECs, evidenced by tyrosine kinase with Ig and endothelial growth factor homology domains-2 (TIE2) receptor, protein kinase B, and Erk1,2 phosphorylation detectable by immunoblotting. These data suggest that Ang-4 actions are mediated through cell-type-specific networks and that lymphatic vessel dilation occurs secondarily to increased vascular leakage. Ang-4 also promoted survival of LECs. Thus, blocking Ang-4 may prune the draining lymphatic vasculature and decrease interstitial fluid pressure (IFP) by reducing vascular permeability.

Angiopoietins promote ovarian cancer progression by establishing a procancer microenvironment

Despite decades of research, the survival rate of ovarian cancer patients is largely unchanged. Current chemotherapeutic drugs are effective only transiently because patients with advanced disease eventually develop resistance. Thus, there is a pressing need for identifying novel therapeutic targets in ovarian cancer. Mounting evidence suggests that angiopoietins (Angpts) may play an essential role in cancer progression; however, the expression profiles and biological effects of Angpts on ovarian cancer remain largely unknown. Here, we show that, compared with their normal counterparts, expressions of Angpt1, Angpt2, and Angpt4 are increased in ovarian cancer cells and tissues and that human ovarian cancer cells also express the Angpt receptor Tie-2-receptor tyrosine kinase. We show that increased expression of Angpt1, Angpt2, or Angpt4 promotes intraperitoneal growth of ovarian cancers and shortens survival of the experimental mice. We further show, for the first time, that Angpts promote accumulation of cancer-associated fibroblasts and tumor angiogenesis in the ovarian cancer microenvironment, as well as enhance ovarian cancer cell proliferation and invasion in vivo. In addition, we establish a novel function of Angpts in promoting proliferation and invasion and inducing Tie-2 and extracellular signal-regulated kinase 1/2 activation in ovarian cancer-associated fibroblasts. Taken together, these data suggest that the Angpt-Tie-2 functional axis is an important player in ovarian cancer progression and an attractive target for ovarian cancer therapy.

VAMP8 facilitates cellular proliferation and temozolomide resistance in human glioma cells

BACKGROUND

Malignant glioma is a common and lethal primary brain tumor in adults. Here we identified a novel oncoprotein, vesicle-associated membrane protein 8 (VAMP8), and investigated its roles in tumorigenisis and chemoresistance in glioma.

METHODS

The expression of gene and protein were determined by quantitative PCR and Western blot, respectively. Histological analysis of 282 glioma samples and 12 normal controls was performed by Pearson's chi-squared test. Survival analysis was performed using the log-rank test and Cox proportional hazards regression. Cell proliferation and cytotoxicity assay were conducted using Cell Counting Kit-8. Autophagy was detected by confocal microscopy and Western blot.

RESULTS

VAMP8 was significantly overexpressed in human glioma specimens and could become a potential novel prognostic and treatment-predictive marker for glioma patients. Overexpression of VAMP8 promoted cell proliferation in vitro and in vivo, whereas knockdown of VAMP8 attenuated glioma growth by arresting cell cycle in the G0/G1 phase. Moreover, VAMP8 contributed to temozolomide (TMZ) resistance by elevating the expression levels of autophagy proteins and the number of autophagosomes. Further inhibition of autophagy via siRNA-mediated knockdown of autophagy-related gene 5 (ATG5) or syntaxin 17 (STX17) reversed TMZ resistance in VAMP8-overexpressing cells, while silencing of VAMP8 impaired the autophagic flux and alleviated TMZ resistance in glioma cells.

CONCLUSION

Our findings identified VAMP8 as a novel oncogene by promoting cell proliferation and therapeutic resistance in glioma. Targeting VAMP8 may serve as a potential therapeutic regimen for the treatment of glioma.

Glioblastoma-associated stromal cells (GASCs) from histologically normal surgical margins have a myofibroblast phenotype and angiogenic properties

Glioblastoma (GB) displays diffusely infiltrative growth patterns. Dispersive cells escape surgical resection and contribute to tumour recurrence within a few centimeters of the resection cavity in 90% of cases. We know that the non-neoplastic stromal compartment, in addition to infiltrative tumour cells, plays an active role in tumour recurrence. We isolated a new stromal cell population from the histologically normal surgical margins of GB by computer-guided stereotaxic biopsies and primary culture. These GB-associated stromal cells (GASCs) share phenotypic and functional properties with the cancer-associated fibroblasts (CAFs) described in the stroma of carcinomas. In particular, GASCs have tumour-promoting effects on glioma cells in vitro and in vivo. Here, we describe a quantitative proteomic analysis, using iTRAQ labelling and mass spectrometry, to compare GASCs with control stromal cells derived from non-GB peripheral brain tissues. A total of 1077 proteins were quantified and 67 proteins were found to differ between GASCs and control stromal cells. Several proteins changed in GASCs are related to a highly motile myofibroblast phenotype, and to wound healing and angiogenesis. The results for several selected proteins were validated by western blotting or flow cytometry. Furthermore, the effect of GASCs on angiogenesis was confirmed using the orthotopic U87MG glioma model. In conclusion, GASCs, isolated from GB histologically normal surgical margins and found mostly near blood vessels, could be a vascular niche constituent establishing a permissive environment, facilitating angiogenesis and possibly colonization of recurrence-initiating cells. We identify various proteins as being expressed in GASCs: some of these proteins may serve as prognostic factors for GB and/or targets for anti-glioma treatment.

The effect of gestational age on angiogenic gene expression in the rat placenta

The placenta plays a central role in determining the outcome of pregnancy. It undergoes changes during gestation as the fetus develops and as demands for energy substrate transfer and gas exchange increase. The molecular mechanisms that coordinate these changes have yet to be fully elucidated. The study performed a large scale screen of the transcriptome of the rat placenta throughout mid-late gestation (E14.25–E20) with emphasis on characterizing gestational age associated changes in the expression of genes invoved in angiogenic pathways. Sprague Dawley dams were sacrificed at E14.25, E15.25, E17.25 and E20 (n = 6 per group) and RNA was isolated from one placenta per dam. Changes in placental gene expression were identifed using Illumina Rat Ref-12 Expression BeadChip Microarrays. Differentially expressed genes (>2-fold change, <1% false discovery rate, FDR) were functionally categorised by gene ontology pathway analysis. A subset of differentially expressed genes identified by microarrays were confirmed using Real-Time qPCR. The expression of thirty one genes involved in the angiogenic pathway was shown to change over time, using microarray analysis (22 genes displayed increased and 9 gene decreased expression). Five genes (4 up regulated: Cd36, Mmp14, Rhob and Angpt4 and 1 down regulated: Foxm1) involved in angiogenesis and blood vessel morphogenesis were subjected to further validation. qPCR confirmed late gestational increased expression of Cd36, Mmp14, Rhob and Angpt4 and a decrease in expression of Foxm1 before labour onset (P<0.0001). The observed acute, pre-labour changes in the expression of the 31 genes during gestation warrant further investigation to elucidate their role in pregnancy.

Stromal-epithelial crosstalk provides a suitable microenvironment for the progression of ovarian cancer cells in vitro

The tumor microenvironment plays an important role in the progression of cancer. This study focused on carcinoma-associated fibroblasts (CAFs) and stromal–epithelial interaction between CAFs and epithelial ovarian carcinoma (EOC) cells. We isolated and established primary cultures of CAFs and co-cultured CAFs and EOC cells in vitro. The co-culture conditioned medium (CC-CM) was harvested and its influence on EOC cells was examined. Cytokine, chemokine, and growth factor levels were screened using a biotin label-based human antibody array system. We found that the stromal–epithelial crosstalk provided a suitable microenvironment for the progression of ovarian cancer cells in vitro.

TIMP-1 promotes accumulation of cancer associated fibroblasts and cancer progression

Treatment options for late stage prostate and colon cancer are limited and there is an urgent need to develop more effective and targeted novel therapies, which starts with identification and validation of novel therapeutic targets. Recent clinical studies have demonstrated that tissue inhibitor matrix metalloproteinase-1 (TIMP-1) levels are elevated in cancer patient plasma and elevated TIMP-1 levels are associated with worse clinical outcomes. However, it is unknown whether TIMP-1 serves merely as a biomarker of cancer progression or has a functional role in promoting cancer progression and can serve as a cancer therapeutic target, which is the main objective of this study. Here, we show that stroma of human prostate and colon cancer express higher levels of TIMP-1 compared to their normal counterparts and increased expression of TIMP-1 promotes in vivo growth of both cancer types. We demonstrate for the first time that increased TIMP-1 expression stimulates accumulation of cancer associated fibroblasts (CAFs) within prostate and colon cancer tissues and that TIMP-1 enhances prostate CAF proliferation and migration in vitro and promotes ERK1/2 kinase activation in these CAF cells. Our results establish the novel promotive effects of TIMP-1 on cancer progression and on accumulation of CAFs that in turn provides a pro-tumor microenvironment. Together, these results establish the potential of TIMP-1 as a novel target for cancer therapy and the mechanism underlying the pro-tumor activity of TIMP-1.

Effect of intracavernous administration of angiopoietin-4 on erectile function in the streptozotocin-induced diabetic mouse

INTRODUCTION

Erectile dysfunction (ED) is a highly prevalent complication of diabetes, and the severity of endothelial dysfunction is one of the most important factors in reduced responsiveness to oral phosphodiesterase type 5 inhibitors.

AIM

To study the effects of human angiopoietin-4 (Ang-4) protein on erectile function in diabetic mice.

METHODS

Diabetes was induced by intraperitoneal injection of streptozotocin into 8-week-old C57BL/6J male mice. At 8 weeks after the induction of diabetes, the animals were divided into four groups: control nondiabetic mice and diabetic mice receiving two successive intracavernous injections of phosphate buffered saline (days -3 and 0), a single intracavernous injection of Ang-4 protein (day 0), or two successive intracavernous injections of Ang-4 protein (days -3 and 0).

MAIN OUTCOME MEASURES

One week after treatment, we measured erectile function by electrical stimulation of the cavernous nerve. The penis was harvested and stained with hydroethidine or antibodies to Ang-4, platelet/endothelial cell adhesion molecule-1, and phosphorylated endothelial nitric oxide synthase (eNOS). We also determined the differential expression of Ang-4 in cavernous tissue in the control and diabetic mice. The effect of Ang-4 protein on the phosphorylation of Tie-2, Akt, and eNOS was determined in human umbilical vein endothelial cells (HUVECs) by Western blot.

RESULTS

The cavernous expression of Ang-4 was downregulated in diabetic mice; Ang-4 was mainly expressed in endothelial cells. Local delivery of Ang-4 protein significantly increased cavernous endothelial content, induced eNOS phosphorylation, and decreased the generation of superoxide anion and apoptosis in diabetic mice. Ang-4 protein strongly increased the phosphorylation of Tie-2, Akt, and eNOS in HUVECs. Repeated intracavernous injections of Ang-4 induced significant restoration of erectile function in diabetic mice (87% of control values), whereas a single intracavernous injection of Ang-4 protein elicited modest improvement.

CONCLUSIONS

Cavernous endothelial regeneration by use of Ang-4 protein may have potential for the treatment of vascular disease-induced ED, such as diabetic ED.

Effect of angiopoietin-like protein 4 on rat pulmonary microvascular endothelial cells exposed to LPS

Pulmonary microvascular endothelial cells (PMVECs) possess highly proliferative and angiogenic capacities and are localized at the critical interface between the blood and microvessel wall; they are the primary targets of inflammatory cytokines during lung inflammation. Angiopoietin-like protein 4 (Angptl4) is a circulating protein that has recently been im-plicated in the regulation of angiogenesis and metastasis. This study aimed to investigate the effect of Angptl4 on rat PMVECs (RPMVECs) exposed to lipopolysaccharide (LPS). The cell culture was stimulated with LPS. Total Angptl4 cDNA was obtained from Source BioScience. The PCR product was cloned into the pcDNA3.1-eGFP or the pcDNA3.1‑eGFP‑Angptl4 vector, which were then transfected into the RPMVECs using SuperFect transfection reagent. The Angptl4 mRNA levels, protein levels and cell morphology of the RPMVECs in the experimental groups were detected using real time-PCR, western blot analysis, MTT assay, ELISA and confocal microscopy methods, respective-ly. The Angptl4 expression vector, pcDNA3.1‑eGFP-Angptl4, was successfully constructed. The Angptl4 mRNA level in the LPS-pcDNA3.1-eGFP-transfected group (blank control) was slightly increased and was significantly higher in the experimental group compared with the empty vector and blank control group with significant differences. Pro-apoptotic caspase-8, -9 and Bax protein were inhibited, while p-AKT/AKT and p-Mek1/2 protein expression was also decreased. The rosiglitazone group had significantly decreased levels of the inflammatory cytokine, tumor necrosis factor (TNF)-α (P<0.01). The overexpression of Angptl4 inhibited the LPS-induced increase in the permeability of the RPMVECs, which was associated with the depolymerization of central F-actin in the RPMVECs. In conclusion, our study demonstrates that the overexpression of Angptl4 exerts protective, anti-inflammatory and anti-angiogenic effects. It re-presents a novel therapeutic target gene for the treatment of acute lung injury induced by LPS.

EGFR wild-type amplification and activation promote invasion and development of glioblastoma independent of angiogenesis

Angiogenesis is regarded as a hallmark of cancer progression and it has been postulated that solid tumor growth depends on angiogenesis. At present, however, it is clear that tumor cell invasion can occur without angiogenesis, a phenomenon that is particularly evident by the infiltrative growth of malignant brain tumors, such as glioblastomas (GBMs). In these tumors, amplification or overexpression of wild-type (wt) or truncated and constitutively activated epidermal growth factor receptor (EGFR) are regarded as important events in GBM development, where the complex downstream signaling events have been implicated in tumor cell invasion, angiogenesis and proliferation. Here, we show that amplification and in particular activation of wild-type EGFR represents an underlying mechanism for non-angiogenic, invasive tumor growth. Using a clinically relevant human GBM xenograft model, we show that tumor cells with EGFR gene amplification and activation diffusely infiltrate normal brain tissue independent of angiogenesis and that transient inhibition of EGFR activity by cetuximab inhibits the invasive tumor growth. Moreover, stable, long-term expression of a dominant-negative EGFR leads to a mesenchymal to epithelial-like transition and induction of angiogenic tumor growth. Analysis of human GBM biopsies confirmed that EGFR activation correlated with invasive/non-angiogenic tumor growth. In conclusion, our results indicate that activation of wild-type EGFR promotes invasion and glioblastoma development independent of angiogenesis, whereas loss of its activity results in angiogenic tumor growth.

Receptor tyrosine kinases: principles and functions in glioma invasion

Protein tyrosine kinases are enzymes that are capable of adding a phosphate group to specific tyrosines on target proteins. A receptor tyrosine kinase (RTK) is a tyrosine kinase located at the cellular membrane and is activated by binding of a ligand via its extracellular domain. Protein phosphorylation by kinases is an important mechanism for communicating signals within a cell and regulating cellular activity; furthermore, this mechanism functions as an "on" or "off" switch in many cellular functions. Ninety unique tyrosine kinase genes, including 58 RTKs, were identified in the human genome; the products of these genes regulate cellular proliferation, survival, differentiation, function, and motility. Tyrosine kinases play a critical role in the development and progression of many types of cancer, in addition to their roles as key regulators of normal cellular processes. Recent studies have revealed that RTKs such as epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), c-Met, Tie, Axl, discoidin domain receptor 1 (DDR1), and erythropoietin-producing human hepatocellular carcinoma (Eph) play a major role in glioma invasion. Herein, we summarize recent advances in understanding the role of RTKs in glioma pathobiology, especially the invasive phenotype, and present the perspective that RTKs are a potential target of glioma therapy.

Angiopoietins in angiogenesis

Tie-1 and Tie-2 tyrosine kinase receptors are expressed specifically on vascular endothelial cells and on a certain subtype of macrophages implicated in angiogenesis, thus, they have been a major focus of angiogenesis research. Tie-1 and Tie-2 are essential for vascular maturation during developmental, physiological and pathological angiogenesis. Angiopoietin 1-4 (Ang-1-4) have been identified as bona fide ligands of the Tie-2 receptor, while Tie-1 remains an orphan receptor which is able to heterodimerize with Tie-2 and to modulate Tie-2 signal transduction. The most exhaustively studied angiopoietins are Ang-1 and Ang-2. Ang-1 is a critical player in vessel maturation and it mediates migration, adhesion and survival of endothelial cells. Ang-2 disrupts the connections between the endothelium and perivascular cells and promotes cell death and vascular regression. Yet, in conjunction with VEGF, Ang-2 promotes neo-vascularization. Hence, angiopoietins exert crucial roles in the angiogenic switch during tumor progression, and increased expression of Ang-2 relative to Ang-1 in tumors correlates with poor prognosis. Its central role in the regulation of physiological and pathological angiogenesis makes the angiopoietin/Tie signaling pathway a therapeutically attractive target for the treatment of vascular disease and cancer.

Merlin is a negative regulator of human melanoma growth

Merlin is encoded by the neurofibromatosis type 2 (NF2) gene and is a member of the Band 4.1 protein family. This protein acts as a linker that connects cell surface proteins to the actin cytoskeleton. Defects caused by mutations of the NF2 gene give rise to NF2 disease, which is generally characterized by the formation of bilateral vestibular schwannomas and, to a lesser extent, meningiomas and ependymomas. In addition to these tumor types, NF2 is mutated and/or merlin expression is reduced or lost in numerous non-NF2 associated tumors, including melanoma. However, the role of merlin in human melanoma growth and the mechanism underlying its effect are currently unknown. In the present study, we show that merlin knockdown enhances melanoma cell proliferation, migration, and invasion in vitro and that decreased merlin expression promotes subcutaneous melanoma growth in immunocompromised mice. Concordantly, we find that increased expression of merlin in a metastatic melanoma cell line reduced their in vitro migration and proliferation, and diminished their ability to grow in an anchorage independent manner. Increased merlin expression also inhibits in vivo growth of these melanoma cells. Lastly, we demonstrate that higher merlin levels in human melanoma cells promote the H₂O₂-induced activation of MST1/2 Ser/Thr kinases, which are known tumor suppressors in the Hippo signaling pathway. Taken together, these results provide for the first time evidence that merlin negatively regulates human melanoma growth, and that loss of merlin, or impaired merlin function, results in an opposite effect. In addition, we show that increased merlin expression leads to enhanced activation of the MTS1/2 kinases, implying the potential roles of MST1/2 in mediating the anti-melanoma effects of merlin.

AT-406, an orally active antagonist of multiple inhibitor of apoptosis proteins, inhibits progression of human ovarian cancer

Ovarian carcinoma is the most deadly gynecological malignancy. Current chemotherapeutic drugs are only transiently effective and patients with advance disease often develop resistance despite significant initial responses. Mounting evidence suggests that anti-apoptotic proteins, including those of the inhibitor of apoptosis protein (IAP) family, play important roles in the chemoresistance. There has been a recent emergence of compounds that block the IAP functions. Here, we evaluated AT-406, a novel and orally active antagonist of multiple IAP proteins, in ovarian cancer cells as a single agent and in the combination with carboplatin for therapeutic efficacy and mechanism of action. We demonstrate that AT-406 has significant single agent activity in 60% of human ovarian cancer cell lines examined in vitro and inhibits ovarian cancer progression in vivo and that 3 out of 5 carboplatin-resistant cell lines are sensitive to AT-406, highlighting the therapeutic potential of AT-406 for patients with inherent or acquired platinum resistance. Additionally, our in vivo studies show that AT-406 enhances the carboplatin-induced ovarian cancer cell death and increases survival of the experimental mice, suggesting that AT-406 sensitizes the response of these cells to carboplatin. Mechanistically, we demonstrate that AT-406 induced apoptosis is correlated with its ability to down-regulate XIAP whereas AT-406 induces cIAP1 degradation in both AT-406 sensitive and resistance cell lines. Together, these results demonstrate, for the first time, the anti-ovarian cancer efficacy of AT-406 as a single agent and in the combination with carboplatin, suggesting that AT-406 has potential as a novel therapy for ovarian cancer patients, especially for patients exhibiting resistance to the platinum-based therapies.

Modulation of tumor tolerance in primary central nervous system malignancies

Central nervous system tumors take advantage of the unique immunology of the CNS and develop exquisitely complex stromal networks that promote growth despite the presence of antigen-presenting cells and tumor-infiltrating lymphocytes. It is precisely this immunological paradox that is essential to the survival of the tumor. We review the evidence for functional CNS immune privilege and the impact it has on tumor tolerance. In this paper, we place an emphasis on the role of tumor-infiltrating myeloid cells in maintaining stromal and vascular quiescence, and we underscore the importance of indoleamine 2,3-dioxygenase activity as a myeloid-driven tumor tolerance mechanism. Much remains to be discovered regarding the tolerogenic mechanisms by which CNS tumors avoid immune clearance. Thus, it is an open question whether tumor tolerance in the brain is fundamentally different from that of peripheral sites of tumorigenesis or whether it simply stands as a particularly strong example of such tolerance.

Continuous local delivery of interferon-β stabilizes tumor vasculature in an orthotopic glioblastoma xenograft resection model

BACKGROUND

High-grade glioblastomas have immature, leaky tumor blood vessels that impede the efficacy of adjuvant therapy. We assessed the ability of human interferon (hIFN)-β delivered locally via gene transfer to effect vascular stabilization in an orthotopic model of glioblastoma xenograft resection.

METHODS

Xenografts were established by injecting 3 grade IV glioblastoma cell lines (GBM6-luc, MT330-luc, and SJG2-luc) into the cerebral cortex of nude rats. Tumors underwent subtotal resection, and then had gel foam containing an adeno-associated virus vector encoding either hIFN-β or green fluorescence protein (control) placed in the resection cavity. The primary endpoint was stabilization of tumor vasculature, as evidenced by CD34, α-SMA, and CA IX staining. Overall survival was a secondary endpoint.

RESULTS

hIFN-β treatment altered the tumor vasculature of GBM6-luc and SJG2-luc xenografts, decreasing the density of endothelial cells, stabilizing vessels with pericytes, and decreasing tumor hypoxia. The mean survival for rats with these neoplasms was not improved, however. In rats with MT330-luc xenografts, hIFN-β resulted in tumor regression with a 6-month survival of 55% (INF-β group) and 9% (control group).

CONCLUSION

The use of AAV hIFN-β in our orthotopic model of glioblastoma resection stabilized tumor vasculature and improved survival in rats with MT330 xenografts.

Prognostic impacts of angiopoietins in NSCLC tumor cells and stroma: VEGF-A impact is strongly associated with Ang-2

Introduction

Angiopoietins and their receptor Tie-2 are, in concert with VEGF-A, key mediators in angiogenesis. This study evaluates the prognostic impact of all known human angiopoietins (Ang-1, Ang-2 and Ang-4) and their receptor Tie-2, as well as their relation to the prognostic expression of VEGF-A.

Methods

335 unselected stage I-IIIA NSCLC-patients were included and tissue samples of respective tumor cells and stroma were collected in tissue microarrays (TMAs). Immunohistochemistry (IHC) was used to semiquantitatively evaluate the expression of markers in duplicate tumor and stroma cores.

Principal Findings

In univariate analyses, low tumor cell expression of Ang-4 (P = 0.046) and low stromal expressions of Ang-4 (P = 0.009) and Ang-2 (P = 0.017) were individually associated with a poor survival. In the multivariate analysis, low stromal Ang-2 (HR 1.88; CI 95% 1.15-3.08) and Ang-4 (HR 1.47, CI 95% 1.02–2.11, P = 0.04) expressions were independently associated with a poor prognosis. In patients with high tumor cell expression of Ang-2, a concomitantly high tumor VEGF-A expression mediated a dramatic survival reduction (P<0.001). In the multivariate analysis of patients with high Ang-2 expression, high tumor VEGF-A expression appeared an independent poor prognosticator (HR 6.43; CI 95% 2.46–16.8; P<0.001).

Conclusions

In tumor cells, only Ang-4 expression has prognostic impact in NSCLC. In tumor stroma, Ang-4 and Ang-2 are independently associated with survival. The prognostic impact of tumor cell VEGF-A in NSCLC appears strongly associated with a concomitantly high tumor cell expression of Ang-2.