Signal transducer and activator of transcription-3: a molecular hub for signaling pathways in gliomas

Cytomegalovirus contributes to glioblastoma in the context of tumor suppressor mutations

To study the controversial role of cytomegalovirus (CMV) in glioblastoma, we assessed the effects of murine CMV (MCMV) perinatal infection in a GFAP-cre; Nf1(loxP/+); Trp53(-/+) genetic mouse model of glioma (Mut3 mice). Early on after infection, MCMV antigen was predominantly localized in CD45+ lymphocytes in the brain with active viral replication and local areas of inflammation, but, by 7 weeks, there was a generalized loss of MCMV in brain, confirmed by bioluminescent imaging. MCMV-infected Mut3 mice exhibited a shorter survival time from their gliomas than control Mut3 mice perinatally infected with mock or with a different neurotropic virus. Animal survival was also significantly shortened when orthotopic gliomas were implanted in mice perinatally infected with MCMV versus controls. MCMV infection increased phosphorylated STAT3 (p-STAT3) levels in neural stem cells (NSC) harvested from Mut3 mice subventricular zone, and, in vivo, there was increased p-STAT3 in NSCs in MCMV-infected compared with control mice. Of relevance, human CMV (HCMV) also increased p-STAT3 and proliferation of patient-derived glioblastoma neurospheres, whereas a STAT3 inhibitor reversed this effect in vitro and in vivo. These findings thus associate CMV infection to a STAT3-dependent modulatory role in glioma formation/progression in the context of tumor suppressor mutations in mice and possibly in humans.

NF-κB-induced IL-6 ensures STAT3 activation and tumor aggressiveness in glioblastoma

Glioblastoma (GBM) is the most aggressive, neurologically destructive and deadly tumor of the central nervous system (CNS). In GBM, the transcription factors NF-κB and STAT3 are aberrantly activated and associated with tumor cell proliferation, survival, invasion and chemoresistance. In addition, common activators of NF-κB and STAT3, including TNF-α and IL-6, respectively, are abundantly expressed in GBM tumors. Herein, we sought to elucidate the signaling crosstalk that occurs between the NF-κB and STAT3 pathways in GBM tumors. Using cultured GBM cell lines as well as primary human GBM xenografts, we elucidated the signaling crosstalk between the NF-κB and STAT3 pathways utilizing approaches that either a) reduce NF-κB p65 expression, b) inhibit NF-κB activation, c) interfere with IL-6 signaling, or d) inhibit STAT3 activation. Using the clinically relevant human GBM xenograft model, we assessed the efficacy of inhibiting NF-κB and/or STAT3 alone or in combination in mice bearing intracranial xenograft tumors in vivo. We demonstrate that TNF-α-induced activation of NF-κB is sufficient to induce IL-6 expression, activate STAT3, and elevate STAT3 target gene expression in GBM cell lines and human GBM xenografts in vitro. Moreover, the combined inhibition of NF-κB and STAT3 signaling significantly increases survival of mice bearing intracranial tumors. We propose that in GBM, the activation of NF-κB ensures subsequent STAT3 activation through the expression of IL-6. These data verify that pharmacological interventions to effectively inhibit the activity of both NF-κB and STAT3 transcription factors must be used in order to reduce glioma size and aggressiveness.

CXCR4 negatively regulates keratinocyte proliferation in IL-23-mediated psoriasiform dermatitis

CXCR4 is expressed by basal keratinocytes (KCs), but little is known about its function in inflamed skin. We crossed K14-Cre and CXCR4(flox/flox (f/f)) transgenic mice, resulting in mice with specific loss of the CXCR4 gene in K14-expressing cells (K14-CXCR4KO), including basal KCs. K14-CXCR4KO pups had no obvious skin defects. We compared K14-CXCR4KO and CXCR4(f/f) control mice in an IL-23-mediated psoriasiform dermatitis model and measured skin edema, and histologic and immunohistological changes. IL-23-treated K14-CXCR4KO mice showed a 1.3-fold increase in mean ear swelling, a 2-fold increase in epidermal thickness, and greater parakeratosis. IL-23-treated wild-type (WT) mice showed weak CXCR4 expression in areas of severe epidermal hyperplasia, but strong CXCR4 expression in nonhyperplastic regions, suggesting that CXCR4 may regulate KC proliferation. To test this hypothesis, we overexpressed CXCR4 in HaCaT KC cells and treated them with IL-22 and/or CXCL12 (chemokine (C-X-C motif) ligand 12). CXCL12 blocked IL-22-mediated HaCaT cell proliferation in vitro and synergized with IL-22 in upregulating SOCS3 (suppressor of cytokine signaling 3), a key regulator of STAT3 (signal transducer and activator of transcription 3). SOCS3 was required for CXCR4-mediated growth inhibition. In human psoriatic skin, both CXCR4 and SOCS3 were upregulated in the junctional region at the border of psoriatic plaques. Thus, CXCR4 has an unexpected role in inhibiting KC proliferation and mitigating the effects of proliferative T helper type 17 cytokines.

Prosapogenin A induces apoptosis in human cancer cells in vitro via inhibition of the STAT3 signaling pathway and glycolysis

Signal transducer and activator of transcription 3 (STAT3) is considered to be an oncogene. Blocking STAT3 signaling may induce growth arrest and apoptosis in different types of tumors. Cancer cells utilize the glycolytic pathway to maintain cell growth even when adequate oxygen is present. Glycolysis inhibition is a potential therapeutic modality. In the present study, the effects of Prosapogenin A (PSA) from the traditional Chinese medicine, Veratrum, on apoptosis, the STAT3 signaling pathway and glycometabolism in cancer cells were investigated. The results indicated that PSA induced growth inhibition and apoptosis in HeLa, HepG2 and MCF-7 cells. PSA inhibited the STAT3 signaling pathway and modulated the expression of glycometabolism-related genes. The results indicate that the inhibition of the STAT3 signaling and glycometabolism pathways contributes to the PSA-mediated apoptosis of HeLa, HepG2 and MCF-7 cells.

Mutations in glioblastoma oncosuppressive pathways pave the way for oncomodulatory activity of cytomegalovirus

Over the last decade, cytomegalovirus (CMV) has been suggested to promote the development of glioblastoma multiforme (GBM). Recent evidence demonstrates that CMV contributes to the progression of GBM in the context of oncosuppressor gene mutations. This finding provides further insights into the mechanisms whereby CMV exacerbates the malignancy of GBM.

The expression of cytoglobin as a prognostic factor in gliomas: a retrospective analysis of 88 patients

BACKGROUND

Evidence suggests that cytoglobin (Cygb) may function as a tumor suppressor gene.

METHODS

We immunohistochemically evaluated the expression of Cygb, phosphatidylinositol-3 kinase (PI-3K), phosphorylated (p)-Akt, Interleukin-6 (IL-6), tumor necrosis factor-α (TNFα) and vascular endothelial growth factor (VEGF) in 88 patients with 41 high-grade gliomas and 47 low-grade gliomas. Intratumoral microvessel density (IMD) was also determined and associated with clinicopathological factors.

RESULTS

Low expression of Cygb was significantly associated with the higher histological grading and tumor recurrence. A significant negative correlation emerged between Cygb expression and PI3K, p-Akt, IL-6, TNFα or VEGF expression. Cygb expression was negatively correlated with IMD. There was a positive correlation between PI3K, p-Akt, IL-6, TNFα and VEGF expression with IMD.High histologic grade, tumor recurrence, decreased Cygb expression, increased PI3K expression, increased p-Akt expression and increased VEGF expression correlated with patients' overall survival in univariate analysis. However, only histological grading and Cygb expression exhibited a relationship with survival of patients as independent prognostic factors of glioma by multivariate analysis.

CONCLUSIONS

Cygb loss may contribute to tumor recurrence and a worse prognosis in gliomas. Cygb may serve as an independent predictive factor for prognosis of glioma patients.

The role of Stat3 in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common brain tumor and has the worst prognosis. Several signaling molecules have been clearly implicated in the development, progression, and aggressiveness of GBM. Here we review the role of signal transducer and activator of transcription-3 (Stat3) in GBM. We particularly focus on its expression in clinical GBM samples, its role in brain tumorigenicity in cell lines and animal models, and discuss possible therapeutic strategies targeting Stat3. This review also summarizes the current knowledge regarding the role of Stat3 regulation by upstream activators and repressors in promoting GBM progression in both translational and clinical studies.

Glioma stem cells and immunotherapy for the treatment of malignant gliomas

Stem cell research has led to the discovery of glioma stem cells (GSCs), and because these cells are resistant to chemotherapy and radiotherapy, analysis of their properties has been rapidly pursued for targeted treatment of malignant glioma. Recent studies have also revealed complex crosstalk between GSCs and their specialized environment (niche). Therefore, targeting not only GSCs but also their niche may be a principle for novel therapies of malignant glioma. One possible novel strategy for targeting GSCs and their niches is immunotherapy with different antitumor mechanism(s) from those of conventional therapy. Recent clinical studies of immunotherapy using peptide vaccines and antibodies have shown promising results. This review describes the recent findings related to GSCs and their niches, as well as immunotherapies for glioma, followed by discussion of immunotherapies that target GSCs for the treatment of malignant glioma.

Tumor-associated macrophages in glioma: friend or foe?

Tumor-associated macrophages (TAMs) contribute substantially to the tumor mass of gliomas and have been shown to play a major role in the creation of a tumor microenvironment that promotes tumor progression. Shortcomings of attempts at antiglioma immunotherapy may result from a failure to adequately address these effects. Emerging evidence supports an independent categorization of glioma TAMs as alternatively activated M2-type macrophages, in contrast to classically activated proinflammatory M1-type macrophages. These M2-type macrophages exert glioma-supportive effects through reduced anti-tumor functions, increased expression of immunosuppressive mediators, and nonimmune tumor promotion through expression of trophic and invasion-facilitating substances. Much of our work has demonstrated these features of glioma TAMs, and together with the supporting literature will be reviewed here. Additionally, the dynamics of glioma cell-TAM interaction over the course of tumor development remain poorly understood; our efforts to elucidate glioma cell-TAM dynamics are summarized. Finally, the molecular pathways which underlie M2-type TAM polarization and gene expression similarly require further investigation, and may present the most potent targets for immunotherapeutic intervention. Highlighting recent evidence implicating the transcription factor STAT3 in immunosuppressive tumorigenic glioma TAMs, we advocate for gene array-based approaches to identify yet unappreciated expression regulators and effector molecules important to M2-type glioma TAMs polarization and function within the glioma tumor microenvironment.

STAT3 silencing inhibits glioma single cell infiltration and tumor growth

BACKGROUND

Diffuse infiltration remains the fulcrum of glioblastoma's incurability, leading inevitably to recurrence. Therefore, uncovering the pathological mechanism is imperative. Because signal transducer and activator of transcription 3 (STAT3) correlates with glioma malignancy and predicts poor clinical outcome, we determined its role in glioma single cell infiltration and tumor growth.

METHODS

STAT3 was silenced in Tu-2449 glioma cells via lentiviral gene transfer. Target gene expression was measured by real-time reverse transcription PCR, Western blotting, and immunohistochemistry. Microvilli were visualized by staining with wheat germ agglutinin. Migration and invasion were measured by Scratch and Matrigel chamber assays. Diffuse infiltration was studied in 350-μm-thick organotypic tissue cultures over 14 days using cells tagged with enhanced green fluorescent protein and live confocal laser scanning microscopy. Survival of tumor-bearing syngeneic, immunocompetent B6C3F1 mice was analyzed by Kaplan-Meier plots.

RESULTS

STAT3 silencing reduced cell migration and invasion in vitro and stopped single cell infiltration ex vivo, while STAT3-expressing cells disseminated through the neuropil at ∼100 µm/day. STAT3 silencing reduced transcription of several tumor progression genes. Mice with intracranial STAT3 knockdown tumors had a significant (P< .0007) survival advantage over controls, yielding 27% long-term survival. STAT3 knockdown reduced podoplanin expression 50-fold and inhibited concurrent microvilli formation. STAT3 knockdown tumors exhibited a weaker podoplanin immunoreactivity compared with controls. Podoplanin staining was diffuse, preferentially at tumor margins, and absent in normal brain.

CONCLUSIONS

Our results show compelling evidence that STAT3 is a key driver of diffuse infiltration and glioma growth and might therefore represent a promising target for an anti-invasive therapy.

Cancer immunoediting in malignant glioma

Significant work from many laboratories over the last decade in the study of cancer immunology has resulted in the development of the cancer immunoediting hypothesis. This contemporary framework of the naturally arising immune system-tumor interaction is thought to comprise 3 phases: elimination, wherein immunity subserves an extrinsic tumor suppressor function and destroys nascent tumor cells; equilibrium, wherein tumor cells are constrained in a period of latency under immune control; and escape, wherein tumor cells outpace immunity and progress clinically. In this review, we address in detail the relevance of the cancer immunoediting concept to neurosurgeons and neuro-oncologists treating and studying malignant glioma by exploring the de novo immune response to these tumors, how these tumors may persist in vivo, the mechanisms by which these cells may escape/attenuate immunity, and ultimately how this concept may influence our immunotherapeutic approaches.

Modeling microRNA-transcription factor networks in cancer

An increasing number of transcription factors (TFs) and microRNAs (miRNAs) is known to form feedback loops (FBLs) of interactions where a TF positively or negatively regulates the expression of a miRNA, and the miRNA suppresses the translation of the TF messenger RNA. FBLs are potential sources of instability in a gene regulatory network. Positive FBLs can give rise to switching behaviors while negative FBLs can generate periodic oscillations. This chapter presents documented examples of FBLs and their relevance to stem cell renewal and differentiation in gliomas. Feed-forward loops (FFLs) are only discussed briefly because they do not affect network stability unless they are members of cycles. A primer on qualitative network stability analysis is given and then used to demonstrate the network destabilizing role of FBLs. Steps in model formulation and computer simulations are illustrated using the miR-17-92/Myc/E2F network as an example. This example possesses both negative and positive FBLs.

DARPP32, STAT5 and STAT3 mRNA expression ratios in glioblastomas are associated with patient outcome

Based on recent developments in glioblastoma subtyping, we examined DARPP32 (PPP1R1B), a neuronal marker against STAT5 and STAT3 that are pro-oncogenic in glioblastoma. mRNA ratios of DARPP32, STAT1, STAT3, STAT5A and STAT5B were assessed in routinely diagnosed gliomas s including a series of glioblastomas from patients (n = 67) treated with chemoradiotherapy (temozolomide), out of which 88 % had sequencing validated IDH-negative disease. DARPP32/STAT1 (p = 0.0007), DARPP32/STAT3 (p = 0.0004) and DARPP32/STAT5B (p = 0.0039) ratios were significantly higher in grade II and III as compared to grade IV tumours. The same high ratios were also associated with absence of immunohistochemically assessed AKT/PKB phosphorylation and survivin protein expression. High DARPP32/STAT3, DARPP32/STAT5B, and STAT5B/STAT3 ratios were associated with longer patient progression free (PFS) and overall survival (OS). Upon multivariate analysis, total/subtotal removal of the tumour (HR:0.431; 95%CI:0.241-0.771, Wald p = 0.005), high DARPP32/STAT5B (HR:0.341; 95%CI:0.169-0.690; Wald p = 0.003) and STAT5B/STAT3 mRNA ratios (HR:0.480; 95%CI:0.280-0.824; Wald p = 0.008) were independent favorable parameters for prolonged PFS. Extent of surgery (HR:0.198; 95%CI:0.101-0.390; p < 0.001) and high DARPP32/STAT5A ratios (HR:0.320; 95%CI:0.160-0.638, p = 0.001) were independently predictive for longer OS. The presented approach is applicable for prospective validation and appears promising towards an effective glioblastoma patient stratification in addition to IDH mutations. These data may contribute to understanding the biology of gliomas with respect to their potential neuronal characteristics and justify STAT-inhibiting therapeutic interventions in the same tumour system.

Essential role of cooperative NF-κB and Stat3 recruitment to ICAM-1 intronic consensus elements in the regulation of radiation-induced invasion and migration in glioma

Although radiotherapy improves survival in patients, glioblastoma multiformes (GBMs) tend to relapse with augmented tumor migration and invasion even after ionizing radiation (IR). Aberrant nuclear factor-κB (NF-κB) and signal transducer and activator of transcription factor 3 (Stat3) activation and interaction have been suggested in several human tumors. However, possible NF-κB/Stat3 interaction and the role of Stat3 in maintenance of NF-κB nuclear retention in GBM still remain unknown. Stat3 and NF-κB (p65) physically interact with one another in the nucleus in glioma tumors. Most importantly, glutathione S-transferase pull-down assays identified that Stat3 binds to the p65 transactivation domain and is present in the NF-κB DNA-binding complex. Irradiation significantly elevated nuclear phospho-p65/phospho-Stat3 interaction in correlation with increased intercellular adhesion molecule-1 (ICAM-1) and soluble-ICAM-1 levels, migration and invasion in human glioma xenograft cell lines 4910 and 5310. Chromatin immunopreicipitation and promoter luciferase activity assays confirmed the critical role of adjacent NF-κB (+399) and Stat3 (+479) binding motifs in the proximal intron-1 in elevating IR-induced ICAM-1 expression. Specific inhibition of Stat3 or NF-κB with Stat3.siRNA or JSH-23 severely inhibited IR-induced p65 recruitment onto ICAM-1 intron-1 and suppressed migratory properties in both the cell lines. On the other hand, Stat3C- or IR-induced Stat3 promoter recruitment was significantly decreased in p65-knockdown cells, thereby suggesting the reciprocal regulation between p65 and Stat3. We also observed a significant increase in NF-κB enrichment on ICAM-1 intron-1 and ICAM-1 transactivation in Stat3C overexpressing cells. In in vivo orthotopic experiments, suppression of tumor growth in Stat3.si+IR-treated mice was associated with the inhibition of IR-induced p-p65/p-Stat3 nuclear colocalization and ICAM-1 levels. To our knowledge, this is the first study showing the crucial role of NF-κB/Stat3 nuclear association in IR-induced ICAM-1 regulation and implies that targeting NF-κB/Stat3 interaction may have future therapeutic significance in glioma treatment.

Potential for statins in the chemoprevention and management of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common, treatment-resistant malignancy with a complex molecular pathogenesis. Statins are a widely used class of cholesterol-lowering drugs with potential anticancer activity. We reviewed the evidence for a role of statins in primary and secondary chemoprevention of HCC and slowing the course of otherwise incurable primary or recurrent disease. A literature search (key words: Statins, hepatocellular carcinoma) conducted to this end, retrieved 119 references. Here we summarize the history, mechanism of action and cardiovascular use of statins and highlight that statins can affect several pathways implicated in the development of HCC. In vitro and animal studies provide strong evidence for a favorable effect of statins on HCC. However, evidence in humans is conflicting. We discuss in full detail the methodological strengths and pitfalls of published data including three cohort studies suggesting that the use of statins may protect from the development of HCC and of a single trial reporting increased survival in those with advanced HCC randomized to receive statins. A remarkably hepato-safe class of drugs acting on both hepatocyte and endothelial cells, statins also have potentially beneficial effects in lowering portal hypertension. In conclusion, there is strong experimental evidence that statins are beneficial in chemopreventing and slowing the growth of HCC. However, randomized controlled trials are necessary in order to investigate the role of statins in the chemoprevention of HCC and in slowing the course of otherwise incurable disease in humans.

Hypoxia-induced decreases in SOCS3 increase STAT3 activation and upregulate VEGF gene expression

Signal transducer and activator of transcription (STAT) 3 has been described as a master regulator of the signaling pathways that are involved in the mesenchymal transition of glioblastomas, which are the most aggressive type of tumors and which result in poor prognoses. Hypoxia, which is a strong inducer of vascular endothelial growth factor (VEGF), results in angiogenesis and the bulky growth of tumors. Here, we show that hypoxia induces VEGF gene expression through a STAT3 signaling cascade. Hypoxia increases the levels of aberrantly activated STAT3 by decreasing the levels of the suppressor of cytokine signaling (SOCS) 3, which is a negative regulator of the STAT3 signaling cascade. Activated STAT3 binds to the hypoxia-responsible element that is located -914 to -905 bp upstream of the transcription initiation site in the VEGF promoter and that transcriptionally regulates VEGF gene expression. This sequence closely resembled the previously defined sis-inducible element in the STAT3-binding sequences. The enforced overexpression of SOCS3 abolished the hypoxia-induced STAT3 activation and the STAT3-mediated transcriptional upregulation of the VEGF gene. In addition, activated STAT3 was found around necrotic foci in surgical specimens. These observations suggest that STAT3 is a molecular target of antiangiogenesis.

APE1/Ref-1 regulates STAT3 transcriptional activity and APE1/Ref-1-STAT3 dual-targeting effectively inhibits pancreatic cancer cell survival

Pancreatic cancer is a largely incurable disease, and increasing evidence supports strategies targeting multiple molecular mediators of critical functions of pancreatic ductal adenocarcinoma cells. Intracellular redox state modulates the activity of various signal transduction pathways and biological processes, including cell survival, drug resistance and responsiveness to microenvironmental factors. Recently, it has been shown that the transcription factor STAT3 is under redox control, but the mechanisms involved in its regulation are unknown. Here, we demonstrate for the first time that STAT3 DNA binding and transcriptional activity is directly regulated by the redox function of the APE1/Ref-1 endonuclease, using overexpression and redox-specific mutational strategies, and gene knockdown. Also, pharmacological blockade of APE1/Ref-1 by the redox-selective inhibitor E3330 abrogates STAT3 DNA binding. Since APE1/Ref-1 also exerts redox control on other cancer-associated transcription factors, we assessed the impact of dual-targeting of STAT3 signaling and APE1/Ref-1 redox on pancreatic cancer cell functions. We observed that disruption of APE1/Ref-1 redox activity synergizes with STAT3 blockade to potently inhibit the proliferation and viability of human PDAC cells. Mechanistically, we show that STAT3–APE1/Ref-1 dual targeting promotes marked tumor cell apoptosis, with engagement of caspase-3 signaling, which are significantly increased in comparison to the effects triggered by single target blockade. Also, we show that STAT3–APE1/Ref-1 dual blockade results in significant inhibition of tumor cell migration. Overall, this work demonstrates that the transcriptional activity of STAT3 is directly regulated by the redox function of APE1/Ref-1, and that concurrent blockade of STAT3 and APE1/Ref-1 redox synergize effectively inhibit critical PDAC cell functions.

Novel synthetic derivatives of the natural product berbamine inhibit Jak2/Stat3 signaling and induce apoptosis of human melanoma cells

Persistent Jak/Stat3 signal transduction plays a crucial role in tumorigenesis and immune development. Activated Jak/Stat3 signaling has been validated as a promising molecular target for cancer therapeutics discovery and development. Berbamine (BBM), a natural bis-benzylisoquinoline alkaloid, was identified from the traditional Chinese herbal medicine Berberis amurensis used for treatment of cancer patients. While BBM has been shown to have potent antitumor activities with low toxicity in various cancer types, the molecular mechanism of action of BBM remains largely unknown. Here, we determine the antitumor activities of 13 synthetic berbamine derivatives (BBMDs) against human solid tumor cells. BBMD3, which is the most potent in this series of novel BBMDs, exhibits over 6-fold increase in biological activity compared to natural BBM. Moreover, BBMD3, directly inhibits Jak2 autophosphorylation kinase activity in vitro with IC(50)0.69 μM. Autophosphorylation of Jak2 kinase at Tyr1007/1008 sites also was strongly inhibited in the range of 15 μM of BBMD3 in human melanoma cells at 4h after treatment. Following inhibition of autophosphorylation of Jak2, BBMD3 blocked constitutive activation of downstream Stat3 signaling in melanoma cells. BBMD3 also down-regulated expression of the Stat3 target proteins Mcl-1and Bcl-x(L), associated with induction of apoptosis. In sum, our findings demonstrate that the novel berbamine derivative BBMD3 is an inhibitor of the Jak2/Stat3 signaling pathway, providing evidence for a molecular mechanism whereby BBMD3 exerts at least in part the apoptosis of human melanoma cells. In addition, BBMD3 represents a promising lead compound for development of new therapeutics for cancer treatment.

The molecular profile of microglia under the influence of glioma

Microglia, which contribute substantially to the tumor mass of glioblastoma, have been shown to play an important role in glioma growth and invasion. While a large number of experimental studies on functional attributes of microglia in glioma provide evidence for their tumor-supporting roles, there also exist hints in support of their anti-tumor properties. Microglial activities during glioma progression seem multifaceted. They have been attributed to the receptors expressed on the microglia surface, to glioma-derived molecules that have an effect on microglia, and to the molecules released by microglia in response to their environment under glioma control, which can have autocrine effects. In this paper, the microglia and glioma literature is reviewed. We provide a synopsis of the molecular profile of microglia under the influence of glioma in order to help establish a rational basis for their potential therapeutic use. The ability of microglia precursors to cross the blood-brain barrier makes them an attractive target for the development of novel cell-based treatments of malignant glioma.

Recent developments on immunotherapy for brain cancer

INTRODUCTION

Brain tumors are a unique class of cancers since they are anatomically shielded from normal immunosurveillance by the blood-brain barrier, lack a normal lymphatic drainage system and reside in a potently immunosuppressive environment. Of the primary brain cancers, glioblastoma multiforme (GBM) is the most common and aggressive in adults. Although treatment options include surgery, radiation and chemotherapy, the average lifespan of GBM patients remains at only 14.6 months post-diagnosis.

AREAS COVERED

A review of key cellular and molecular immune system mediators in the context of brain tumors including TGF-β, cytotoxic T cells, Tregs, CTLA-4, PD-1 and IDO is discussed. In addition, prognostic factors, currently utilized immunotherapeutic strategies, ongoing clinical trials and a discussion of new or potential immunotherapies for brain tumor patients are considered.

EXPERT OPINION

Current drugs that improve the quality of life and overall survival in patients with brain tumors, especially for GBM, are poorly effective. This disease requires a reanalysis of currently accepted treatment strategies, as well as newly designed approaches. Here, we review the fundamental aspects of immunosuppression in brain tumors, new and promising immunotherapeutic drugs as well as combinatorial strategies that focus on the simultaneous inhibition of immunosuppressive hubs, both in immune and brain tumor cells, which is critical to consider for achieving future success for the treatment of this devastating disease.

Resveratrol suppresses tumorigenicity and enhances radiosensitivity in primary glioblastoma tumor initiating cells by inhibiting the STAT3 axis

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor. Patients diagnosed with GBM have a poor prognosis, and it has been reported that tumor malignancy and GBM recurrence are promoted by STAT3 signaling. As resveratrol (RV), a polyphenol in grapes, is reported to be a potent and non-toxic cancer-preventive compound, the aim of this study was to investigate the therapeutic effect and molecular mechanisms of RV on GBM-derived radioresistant tumor initiating cells (TIC). Firstly, our results showed that primary GBM-CD133(+) TIC presented high tumorigenic and radiochemoresistant properties as well as increased protein levels of phosphorylated STAT3. We consistently observed that treatment with shRNA-STAT3 (sh-STAT3) or AG490, a STAT3 inhibitor, significantly inhibited the cancer stem-like cell properties and radioresistance of GBM-CD133(+) in vitro and in vivo. Furthermore, treatment of GBM-CD133(+) with 100 µM RV induced apoptosis and enhanced radiosensitivity by suppressing STAT3 signaling. Microarray results suggested that RV or AG490 inhibited the stemness gene signatures of GBM-CD133(+) and facilitated the differentiation of GBM-CD133(+) into GBM-CD133(-) or astrocytoma cells. Finally, xenotransplant experiments indicated that RV or sh-STAT3 therapy could significantly improve the survival rate and synergistically enhance the radiosensitivity of radiation-treated GBM-TIC. In summary, RV can reduce in vivo tumorigenicity and enhance the sensitivity of GBM-TIC to radiotherapies through the STAT3 pathway.

Signal transducer and activator of transcription 1 (Stat1) maintains basal mRNA expression of pro-survival stat3-target genes in glioma C6 cells

The STAT proteins (signal transducers and activators of transcription) are transcription factors mediating cytokine/growth factor signaling, which play important role in controlling cell cycle progression and apoptosis. In many cancer cell lines and tumors (including gliomas) the STAT proteins (in particular Stats 1, 3, and 5) are persistently activated. In this study, we employed DNA decoys, siRNAs, and protein overexpression, to elucidate the role of Stat1 and Stat3 in regulation of expression of endogenous Stat3-target genes (Bcl2l1, Myc, Ccnd1) and a Stat-driven reporter plasmid, in rat C6 glioma cells. The results obtained with the decoys and siRNA suggest that in proliferating C6 cells, Stat1 supports the basal expression of Bcl2l1, while the decoy and chromatin immunoprecipitation results suggest it also plays a similar role for Myc. In the Stat-driven reporter system, overexpression of Stat1 stimulated, while overexpression of Stat3 inhibited the reporter gene expression. The level of Stat1 phosphorylation observed under basal conditions in proliferating glioma C6 cells is very low. Therefore, we speculate that it is the activity of the unphosphorylated Stat1 that is inhibited by Stat1 decoy or Stat1 siRNA. Taken together, our results demonstrate that it is Stat1 not Stat3 that maintains the expression of Bcl2l1 and possibly Myc in proliferating glioma C6 cells. An established paradigm is that Stat3 exerts a pro-survival and potentially oncogenic effects, while Stat1 is mainly associated with the immune response. Our results add to a number of reports that challenge this paradigm.

Biologically targeted therapeutics in pediatric brain tumors

Pediatric brain tumors are often difficult to cure and involve significant morbidity when treated with traditional treatment modalities, including neurosurgery, conventional chemotherapy, and radiotherapy. During the past two decades, a clearer understanding of tumorigenesis, molecular growth pathways, and immune mechanisms in the pathogenesis of cancer has opened up promising avenues for therapy. Pediatric clinical trials with novel biologic agents are underway to treat various pediatric brain tumors, including high and low grade gliomas and embryonal tumors. As the therapeutic potential of these agents undergoes evaluation, their toxicity profiles are also becoming better understood. These agents have potentially better central nervous system penetration and lower toxicity profiles compared with conventional chemotherapy. In infants and younger children, biologic agents may prove to be of equal or greater efficacy compared with traditional chemotherapy and radiation therapy, and may reduce the deleterious side effects of traditional therapeutics on the developing brain. Molecular pathways implicated in pediatric brain tumors, agents that target these pathways, and current clinical trials are reviewed. Associated neurologic toxicities will be discussed subsequently. Considerable work is needed to establish the efficacy of these agents alone and in combination, but pediatric neurologists should be aware of these agents and their rationale.

Highly malignant behavior of a murine oligodendrocyte precursor cell line following transplantation into the demyelinated and nondemyelinated central nervous system

Understanding the basic mechanisms that control CNS remyelination is of direct clinical relevance. Suitable model systems include the analysis of naturally occurring and genetically generated mouse mutants and the transplantation of oligodendrocyte precursor cells (OPCs) following experimental demyelination. However, aforementioned studies were exclusively carried out in rats and little is known about the in vivo behavior of transplanted murine OPCs. Therefore in the present study, we (i) established a model of ethidium bromide-induced demyelination of the caudal cerebellar peduncle (CCP) in the adult mouse and (ii) studied the distribution and marker expression of the murine OPC line BO-1 expressing the enhanced green fluorescent protein (eGFP) 10 and 17 days after stereotaxic implantation. Injection of ethidium bromide (0.025%) in the CCP resulted in a severe loss of myelin, marked astrogliosis, and mild to moderate axonal alterations. Transplanted cells formed an invasive and liquorogenic metastasizing tumor, classified as murine giant cell glioblastoma. Transplanted BO-1 cells displayed substantially reduced CNPase expression as compared to their in vitro phenotype, low levels of MBP and GFAP, prominent upregulation of NG2, PDGFRα, nuclear p53, and an unaltered expression of signal transducer and activator of transcription (STAT)-3. Summarized environmental signaling in the brain stem was not sufficient to trigger oligodendrocytic differentiation of BO-1 cells and seemed to block CNPase expression. Moreover, the lack of the remyelinating capacity was associated with tumor formation indicating that BO-1 cells may serve as a versatile experimental model to study tumorigenesis of glial tumors.

Inhibition of phosphorylated STAT3 by cucurbitacin I enhances chemoradiosensitivity in medulloblastoma-derived cancer stem cells

INTRODUCTION

CD133 (PROM1) is a potential marker for cancer stem cells (CSCs), including those found in brain tumors. Recently, medulloblastoma (MB)-derived CD133-positive cells were found to have CSC-like properties and were proposed to be important contributors to tumorigenicity, cancer progression, and chemoradioresistance. However, the biomolecular pathways and therapeutic targets specific to MB-derived CSCs remain unresolved.

MATERIALS AND METHODS

In the present study, we isolated CD133(+) cells from MB cell lines and determined that they showed increased tumorigenicity, radioresistance, and higher expression of both embryonic stem cell-related and drug resistance-related genes compared to CD133(-) cells. Bioinformatics analysis suggested that the STAT3 pathway might be important in MB and CD133(+) cells. To evaluate the effects of inhibiting the STAT3 pathway, MB-derived CD133(+/-) cells were treated with the potent STAT3 inhibitor, cucurbitacin I. Treatment with cucurbitacin I significantly suppressed the CSC-like properties and stemness gene signature of MB-derived CD133(+) cells. Furthermore, cucurbitacin I treatment increased the apoptotic sensitivity of MB-derived CD133(+) cells to radiation and chemotherapeutic drugs. Notably, cucurbitacin I demonstrated synergistic effects with ionizing radiation to inhibit tumorigenicity in MB-CD133(+)-inoculated mice.

RESULTS

These results indicate that the STAT3 pathway plays a key role in mediating CSC properties in MB-derived CD133(+) cells. Targeting STAT3 with cucurbitacin I may therefore represent a novel therapeutic approach for treating malignant brain tumors.

Quercetin abrogates IL-6/STAT3 signaling and inhibits glioblastoma cell line growth and migration

Evidence has suggested that STAT3 functions as an oncogene in gliomagenesis. As a consequence, changes in the inflammatory microenvironment are thought to promote tumor development. Regardless of its origin, cancer-related inflammation has many tumor-promoting effects, such as the promotion of cell cycle progression, cell proliferation, cell migration and cell survival. Given that IL-6, a major cancer-related inflammatory cytokine, regulates STAT3 activation and is upregulated in glioblastoma, we sought to investigate the inhibitory effects of the chemopreventive flavonoid quercetin on glioblastoma cell proliferation and migration triggered by IL-6, and to determine the underlying mechanisms of action. In this study, we show that quercetin is a potent inhibitor of the IL-6-induced STAT3 signaling pathway in T98G and U87 glioblastoma cells. Exposure to quercetin resulted in the reduction of GP130, JAK1 and STAT3 activation by IL-6, as well as a marked decrease of the proliferative and migratory properties of glioblastoma cells induced by IL-6. Interestingly, quercetin also modulated the expression of two target genes regulated by STAT3, i.e. cyclin D1 and matrix metalloproteinase-2 (MMP-2). Moreover, quercetin reduced the recruitment of STAT3 at the cyclin D1 promoter and inhibited Rb phosphorylation in the presence of IL-6. Overall, these results provide new insight into the role of quercetin as a blocker of the STAT3 activation pathway stimulated by IL-6, with a potential role in the prevention and treatment of glioblastoma.

STAT3 silencing enhances the efficacy of the HSV.tk suicide gene in gastrointestinal cancer therapy

Aberrant activation of Signal Transducer and Activator of Transcription 3 (STAT3) signaling has been shown to be associated with uncontrolled cell proliferation and suppression of host-immune surveillance. Conversely, silencing STAT3 can have the dual effects of inhibiting cancer cell proliferation and inducing anti-tumor immune responses. Here, we report on the effects of STAT3 silencing on suicide gene therapy with thymidine kinase (tk). STAT3 silencing by siRNA inhibited the proliferation of AGS human gastric cancer cells through G1 cell cycle arrest, decreased levels of immune-suppressive cytokines, and increased levels of immune-activating cytokines. CT26 mouse colon adenocarcinoma cells, in which STAT3 expression was knocked-down by a STAT3 shRNA-containing lentivirus, grew more slowly in syngenic model Balb/c mice than control CT26 cells. Moreover, we found that STAT3 silencing augmented the efficacy of suicide gene therapy in CT26 cell xenografted mice. When we administrated adenoviruses harboring the herpes simplex virus thymidine kinase gene (Ad5.CMV.HSV.tk) into STAT3-silenced CT26 cell tumors, extensive apoptosis was observed and there was a significant reduction in the size of CT26 cell tumors. STAT3 silencing also enhanced the recruitment and cytotoxic activity of CD3(+)CD8(+) T-cells, and changed the cytokine expression pattern of CT26 cell tumors, reflecting augmentation of anti-cancer immune responses. We conclude that combining suicide gene therapy with STAT3 silencing can result in enhanced anti-cancer effects.

Glioma cell migration on three-dimensional nanofiber scaffolds is regulated by substrate topography and abolished by inhibition of STAT3 signaling

A hallmark of malignant gliomas is their ability to disperse through neural tissue, leading to long-term failure of all known therapies. Identifying new antimigratory targets could reduce glioma recurrence and improve therapeutic efficacy, but screens based on conventional migration assays are hampered by the limited ability of these assays to reproduce native cell motility. Here, we have analyzed the motility, gene expression, and sensitivity to migration inhibitors of glioma cells cultured on scaffolds formed by submicron-sized fibers (nanofibers) mimicking the neural topography. Glioma cells cultured on aligned nanofiber scaffolds reproduced the elongated morphology of cells migrating in white matter tissue and were highly sensitive to myosin II inhibition but only moderately affected by stress fiber disruption. In contrast, the same cells displayed a flat morphology and opposite sensitivity to myosin II and actin inhibition when cultured on conventional tissue culture polystyrene. Gene expression analysis indicated a correlation between migration on aligned nanofibers and increased STAT3 signaling, a known driver of glioma progression. Accordingly, cell migration out of glioblastoma-derived neurospheres and tumor explants was reduced by STAT3 inhibitors at subtoxic concentrations. Remarkably, these inhibitors were ineffective when tested at the same concentrations in a conventional two-dimensional migration assay. We conclude that migration of glioma cells is regulated by topographical cues that affect cell adhesion and gene expression. Cell migration analysis using nanofiber scaffolds could be used to reproduce native mechanisms of migration and to identify antimigratory strategies not disclosed by other in vitro models.

Consensus on the role of human cytomegalovirus in glioblastoma

The human cytomegalovirus (HCMV) and glioma symposium was convened on April 17, 2011 in Washington, DC, and was attended by oncologists and virologists involved in studying the relationship between HCMV and gliomas. The purpose of the meeting was to reach a consensus on the role of HCMV in the pathology of gliomas and to clarify directions for future research. First, the group summarized data that describe how HCMV biology overlaps with the key pathways of cancer. Then, on the basis of published data and ongoing research, a consensus was reached that there is sufficient evidence to conclude that HCMV sequences and viral gene expression exist in most, if not all, malignant gliomas, that HCMV could modulate the malignant phenotype in glioblastomas by interacting with key signaling pathways; and that HCMV could serve as a novel target for a variety of therapeutic strategies. In summary, existing evidence supports an oncomodulatory role for HCMV in malignant gliomas, but future studies need to focus on determining the role of HCMV as a glioma-initiating event.

STAT3 signaling after traumatic brain injury

Astrocytes respond to trauma by stimulating inflammatory signaling. In studies of cerebral ischemia and spinal cord injury, astrocytic signaling is mediated by the cytokine receptor glycoprotein 130 (gp130) and Janus kinase (Jak) which phosphorylates the transcription factor signal transducer and activator of transcription-3 (STAT3). To determine if STAT3 is activated after traumatic brain injury (TBI), adult male Sprague-Dawley rats received moderate parasagittal fluid-percussion brain injury or sham surgery, and then the ipsilateral cortex and hippocampus were analyzed at various post-traumatic time periods for up to 7 days. Western blot analyses indicated that STAT3 phosphorylation significantly increased at 30 min and lasted for 24 h post-TBI. A significant increase in gp130 and Jak2 phosphorylation was also observed. Confocal microscopy revealed that STAT3 was localized primarily within astrocytic nuclei. At 6 and 24 h post-TBI, there was also an increased expression of STAT3 pathway-related genes: suppressor of cytokine signaling 3, nitric oxide synthase 2, colony stimulating factor 2 receptor β, oncostatin M, matrix metalloproteinase 3, cyclin-dependent kinase inhibitor 1A, CCAAT/enhancer-binding protein β, interleukin-2 receptor γ, interleukin-4 receptor α, and α-2-macroglobulin. These results clarify some of the signaling pathways operative in astrocytes after TBI and demonstrate that the gp130-Jak2-STAT3 signaling pathway is activated after TBI in astrocytes.

Induction of cell-cycle arrest and apoptosis in glioblastoma stem-like cells by WP1193, a novel small molecule inhibitor of the JAK2/STAT3 pathway

Glioma stem-like cells (GSCs) may be the initiating cells in glioblastoma (GBM) and contribute to the resistance of these tumors to conventional therapies. Development of novel chemotherapeutic agents and treatment approaches against GBM, especially those specifically targeting GSCs are thus necessary. In the present study, we found that a novel Janus kinase 2/Signal Transducer and Activator of Transcription 3 (JAK2/STAT3) pathway inhibitor (WP1193) significantly decreased the proliferation of established glioma cell lines in vitro and inhibit the growth of glioma in vivo. To test the efficacy of WP1193 against GSCs, we then administrated WP1193 to GSCs isolated and expanded from multiple human GBM tumors. We revealed that WP1193 suppressed phosphorylation of JAK2 and STAT3 with high potency and demonstrated a dose-dependent inhibition of proliferation and neurosphere formation of GSCs. These effects were at least due in part to G1 arrest associated with down-regulation of cyclin D1 and up-regulation of p21( Cip1/Waf-1 ). Furthermore, WP1193 exposure decreased expression of stem cell markers including CD133 and c-myc, and induced cell death in GSCs through apoptosis. Taken together, our data indicate that WP1193 is a potent small molecule inhibitor of the JAK2/STAT3 pathway that shows promise as a therapeutic agent against GBM by targeting GSCs.

Challenges in immunotherapy presented by the glioblastoma multiforme microenvironment

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in adults. Despite intensive treatment, the prognosis for patients with GBM remains grim with a median survival of only 14.6 months. Immunotherapy has emerged as a promising approach for treating many cancers and affords the advantages of cellular-level specificity and the potential to generate durable immune surveillance. The complexity of the tumor microenvironment poses a significant challenge to the development of immunotherapy for GBM, as multiple signaling pathways, cytokines, and cell types are intricately coordinated to generate an immunosuppressive milieu. The development of new immunotherapy approaches frequently uncovers new mechanisms of tumor-mediated immunosuppression. In this review, we discuss many of the current approaches to immunotherapy and focus on the challenges presented by the tumor microenvironment.

Metabolic patterns and biotransformation activities of resveratrol in human glioblastoma cells: relevance with therapeutic efficacies

Background

Trans-resveratrol rather than its biotransformed monosulfate metabolite exerts anti-medulloblastoma effects by suppressing STAT3 activation. Nevertheless, its effects on human glioblastoma cells are variable due to certain unknown reason(s).

Methodology/Principal Findings

Citing resveratrol-sensitive UW228-3 medulloblastoma cell line and primarily cultured rat brain cells/PBCs as controls, the effect of resveratrol on LN-18 human glioblastoma cells and its relevance with metabolic pattern(s), brain-associated sulfotransferase/SULT expression and the statuses of STAT3 signaling and protein inhibitor of activated STAT3 (PIAS3) were elucidated by multiple experimental approaches. Meanwhile, the expression patterns of three SULTs (SULT1A1, 1C2 and 4A1) in human glioblastoma tumors were profiled immunohistochemically. The results revealed that 100 µM resveratrol-treated LN-18 generated the same metabolites as UW228-3 cells, while additional metabolite in molecular weight of 403.0992 in negative ion mode was found in PBCs. Neither growth arrest nor apoptosis was found in resveratrol-treated LN-18 and PBC cells. Upon resveratrol treatment, the levels of SULT1A1, 1C2 and 4A1 expression in LN-18 cells were more up-regulated than that expressed in UW228-3 cells and close to the levels in PBCs. Immunohistochemical staining showed that 42.0%, 27.1% and 19.6% of 149 glioblastoma cases produced similar SULT1A1, 1C2 and 4A1 levels as that of tumor-surrounding tissues. Unlike the situation in UW228-3 cells, STAT3 signaling remained activated and its protein inhibitor PIAS3 was restricted in the cytosol of resveratrol-treated LN-18 cells. No nuclear translocation of STAT3 and PIAS3 was observed in resveratrol-treated PBCs. Treatment with STAT3 chemical inhibitor, AG490, committed majority of LN-18 and UW228-3 cells but not PBCs to apoptosis within 48 hours.

Conclusions/Significance

LN-18 glioblastoma cells are insensitive to resveratrol due to the more inducible brain-associated SULT expression, insufficiency of resveratrol to suppress activated STAT3 signaling and the lack of PIAS3 nuclear translocation. The findings from PBCs suggest that an effective anticancer dose of resveratrol exerts little side effect on normal brain cells.

Therapeutic potential of AZD1480 for the treatment of human glioblastoma

Aberrant activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway has been implicated in glioblastoma (GBM) progression. To develop a therapeutic strategy to inhibit STAT-3 signaling, we have evaluated the effects of AZD1480, a pharmacologic inhibitor of JAK1 and JAK2. In this study, the in vitro efficacy of AZD1480 was tested in human and murine glioma cell lines. AZD1480 treatment effectively blocks constitutive and stimulus-induced JAK1, JAK2, and STAT-3 phosphorylation in both human and murine glioma cells, and leads to a decrease in cell proliferation and induction of apoptosis. Furthermore, we used human xenograft GBM samples as models for the study of JAK/STAT-3 signaling in vivo, because human GBM samples propagated as xenografts in nude mice retain both the hallmark genetic alterations and the invasive phenotype seen in vivo. In these xenograft tumors, JAK2 and STAT-3 are constitutively active, but levels vary among tumors, which is consistent with the heterogeneity of GBMs. AZD1480 inhibits constitutive and stimulus-induced phosphorylation of JAK2 and STAT-3 in these GBM xenograft tumors in vitro, downstream gene expression, and inhibits cell proliferation. Furthermore, AZD1480 suppresses STAT-3 activation in the glioma-initiating cell population in GBM tumors. In vivo, AZD1480 inhibits the growth of subcutaneous tumors and increases survival of mice bearing intracranial GBM tumors by inhibiting STAT-3 activity, indicating that pharmacologic inhibition of the JAK/STAT-3 pathway by AZD1480 should be considered for study in the treatment of patients with GBM tumors.

Cetuximab induces mitochondrial translocalization of EGFRvIII, but not EGFR: involvement of mitochondria in tumor drug resistance?

Dysregulation of growth factor receptors such as the epidermal growth factor receptor (EGFR) and of its truncated form EGFRvIII is frequently found in human tumors. EGFRvIII is a promising target for selective molecular tumor therapy because it is exclusively expressed by tumor cells. Cetuximab/Erbitux is a monoclonal antibody which targets EGFR and EGFRvIII. The effects of cetuximab on EGFRvIII but still the exact function and mechanism of cetuximab in relation to EGFR and EGFRvIII are incompletely understood. Therefore, we investigated the influence of cetuximab on EGFRvIII signaling and cellular survival. We found that cetuximab leads to increased internalization of EGFRvIII in NR6M cells but is unable to inhibit neither the activation of EGFRvIII nor its downstream signaling pathways. Incubation with cetuximab also did not alter the survival and proliferation of EGFRvIII-expressing cells. However, it caused increased mitochondrial activity and an increase in co-localization of EGFRvIII with mitochondria. These results demonstrate that interaction of EGFRvIII with mitochondria could play a role in survival of cetuximab-treated NR6M cells. Thus, a role of mitochondria in resistance to cetuximab has to be considered.

Downregulation of GRIM-19 promotes growth and migration of human glioma cells

It has become increasingly clear that there are notable parallels between normal development and tumorigenesis. Glioma is a classic model that links between tumorigenesis and development. We evaluated the expression of GRIM-19, a novel gene essential for normal development, in various grades of gliomas and several human glioma cell lines. We showed that GRIM-19 mRNA and protein expression were markedly lower in gliomas than in control brain tissues and negatively correlated with the malignancy of gliomas. Downregulation of GRIM-19 in glioma cells significantly enhanced cell proliferation and migration, whereas overexpression of GRIM-19 showed the opposite effects. We also showed that the activation of signal transducer and activator of transcription 3 (STAT3) and the expression of many STAT3-dependent genes were regulated by the expression of GRIM-19. In addition, GRIM-19 exerted its role probably through the non-STAT3 signaling pathway. Collectively, our data suggest that most gliomas expressed GRIM-19 at low levels, which may play a major role in tumorigenesis in the brain.

Adenovirus-mediated delivery of bFGF small interfering RNA reduces STAT3 phosphorylation and induces the depolarization of mitochondria and apoptosis in glioma cells U251

Glioblastoma multiforme (GBM) carries a dismal prognosis primarily due to its aggressive proliferation in the brain regulated by complex molecular mechanisms. One promising molecular target in GBM is over-expressed basic fibroblast growth factor (bFGF), which has been correlated with growth, progression, and vascularity of human malignant gliomas. Previously, we reported significant antitumor effects of an adenovirus-vector carrying bFGF small interfering RNA (Ad-bFGF-siRNA) in glioma in vivo and in vitro. However, its mechanisms are unknown. Signal transducer and activator of transcription 3 (STAT3) is constitutively active in GBM and correlates positively with the glioma grades. In addition, as a specific transcription factor, STAT3 serves as the convergent point of various signaling pathways activated by multiple growth factors and/or cytokines. Therefore, we hypothesized that the proliferation inhibition and apoptosis induction by Ad-bFGF-siRNA may result from the interruption of STAT3 phosphorylation. In the current study, we found that in glioma cells U251, Ad-bFGF-siRNA impedes the activation of ERK1/2 and JAK2, but not Src, decreases IL-6 secretion, reduces STAT3 phosphorylation, decreases the levels of downstream molecules CyclinD1 and Bcl-xl, and ultimately results in the collapse of mitochondrial membrane potentials as well as the induction of mitochondrial-related apoptosis. Our results offer a potential mechanism for using Ad-bFGF-siRNA as a gene therapy for glioma. To our knowledge, it is the first time that the bFGF knockdown using adenovirus-mediated delivery of bFGF siRNA and its potential underlying mechanisms are reported. Therefore, this finding may open new avenues for developing novel treatments against GBM.

The pro-migratory and pro-invasive role of the procoagulant tissue factor in malignant gliomas

During the infiltration process, glioma cells are known to migrate along preexisting anatomical structures such as blood vessels, axonal fiber tracts and the subependymal space, thereby widely invading surrounding CNS tissue. This phenomenon represents a major obstacle for the clinical treatment of these tumours. Several extracellular key factors and intracellular signaling pathways have been previously linked to the highly aggressive, invasive phenotype observed in malignant gliomas. The glioblastoma (GBM) which is the most malignant form of these tumors, is histologically characterized by areas of tumor necroses and pseudopalisading cells, the latter likely representing tumor cells actively migrating away from the hypoxic-ischemic core of the tumor. It is believed that intravascular thromboses play a major role in the emergence of hypoxia and intratumoral necroses in GBMs. One of the most highly upregulated prothrombotic factor in malignant gliomas is tissue factor (TF), a 47 kDa type I transmembrane protein belonging to the cytokine receptor superfamily. In a recent study, we provided evidence that TF/FVIIa signaling via the protease-activated receptor 2 (PAR-2) promotes cell growth, migration and invasion of glioma cells. In this point of view article we outline the key molecular players involved in migration and invasion of gliomas, highlight the potential role of TF for the pro-migratory and pro-invasive phenotype of these tumors and discuss the underlying mechanisms on the cellular level and in the tumor microenvironment.

Intronic microRNA suppresses endothelial nitric oxide synthase expression and endothelial cell proliferation via inhibition of STAT3 signaling

Intronic microRNA (miRNAs) suppressed the expression of endothelial nitric oxide synthase (eNOS) gene in endothelial cells (ECs). This study was to investigate the role of signal transducer and activator of transcription 3 (STAT3) in the regulation of eNOS expression and vascular EC proliferation by the intronic 27-nucleotide (nt) miRNA derived from the 27-base pair repeats in intron 4 of eNOS gene. A detectable level of the 27-nt miRNA was present in the control ECs. Overexpression of the 27-nt miRNA dramatically suppressed the expression of eNOS and STAT3 at both transcription and translation levels in ECs in association with significant inhibition of EC proliferation. Mutation of the 27-nt miRNA at the 3'-terminal region resulted in substantial reduction of the inhibitory effect of miRNA on eNOS and STAT3 expression, and EC proliferation. Overexpression of active STAT3 significantly reversed the inhibitory effect of the 27-nt miRNA on eNOS expression and EC proliferation. In summary, we demonstrated that the 27-nt intronic miRNA functioned as a negative regulator for the expression of its host gene eNOS and cell proliferation in ECs. The sequence in 3'-terminal region played a key role in the function of the 27-nt miRNA. The regulatory effect of the intronic miRNA on eNOS gene expression was associated with miRNA polymorphisms, and mediated through inhibition of STAT3 signaling in ECs.

STAT6 expression in glioblastoma promotes invasive growth

BACKGROUND

Glioblastoma (GBM) is a highly aggressive malignant primary brain tumor, characterized by rapid growth, diffuse infiltration of cells into both adjacent and remote brain regions, and a generalized resistance to currently available treatment modalities. Recent reports in the literature suggest that Signal Transducers and Activators of Transcription (STATs) play important roles in the regulation of GBM pathophysiology.

METHODS

STAT6 protein expression was analyzed by Western blotting in GBM cell lines and by immunohistochemistry in a tissue microarray (TMA) of glioma patient tissues. We utilized shRNA against STAT6 to investigate the effects of prolonged STAT6 depletion on the growth and invasion of two STAT6-positive GBM cell lines. Cell proliferation was assessed by measuring (3)H-Thymidine uptake over time. Invasion was measured using an in vitro transwell assay in which cells invade through a type IV collagen matrix toward a chemoattractant (Fetal Bovine Serum). Cells were then stained and counted. Kaplan-Meyer survival curves were generated to show the correlation between STAT6 gene expression and patient survival in 343 glioma patients and in a subset of patients with only GBM. Gene expression microarray and clinical data were acquired from the Rembrandt 1 public data depository (https://caintegrator.nci.nih.gov/rembrandt/). Lastly, a genome-wide expression microarray analysis was performed to compare gene expression in wild-type GBM cells to expression in stable STAT6 knockdown clones.

RESULTS

STAT6 was expressed in 2 GBM cell lines, U-1242MG and U-87MG, and in normal astrocytes (NHA) but not in the U-251MG GBM cell line. In our TMA study, STAT6 immunostaining was visible in the majority of astrocytomas of all grades (I-IV) but not in normal brain tissue. In positive cells, STAT6 was localized exclusively in the nuclei over 95% of the time. STAT6-deficient GBM cells showed a reduction in (3)H-Thymidine uptake compared to the wild-type. There was some variation among the different shRNA- silenced clones, but all had a reduction in (3)H-Thymidine uptake ranging from 35%- 70% in U-1242MG and 40- 50% in U-87MG cells. Additionally, STAT6- depleted cells were less invasive than controls in our in vitro transmembrane invasion assay. Invasiveness was decreased by 25-40% and 30-75% in U-1242MG and U-87MG cells, respectively. The microarray analysis identified matrix metalloproteinase 1 (MMP-1) and urokinase Plasminogen activator (uPA) as potential STA6 target genes involved in the promotion of GBM cell invasion. In a Kaplan-Meier survival curve based on Rembrandt 1 gene expression microarray and clinical data, there was a significant difference in survival (P < 0.05) between glioma patients with up- and down-regulated STAT6. Decreased STAT6 expression correlated with longer survival times. In two subsets of patients with either grade IV tumors (GBM) or Grade II/III astrocytomas, there was a similar trend that however did not reach statistical significance.

CONCLUSIONS

Taken together, these findings suggest a role for STAT6 in enhancing cell proliferation and invasion in GBM, which may explain why up-regulation of STAT6 correlates with shorter survival times in glioma patients. This report thus identifies STAT6 as a new and potentially promising therapeutic target.

Glioma-associated cytomegalovirus mediates subversion of the monocyte lineage to a tumor propagating phenotype

PURPOSE

Cytomegalovirus (CMV) has been ubiquitously detected within high-grade gliomas, but its role in gliomagenesis has not been fully elicited.

EXPERIMENTAL DESIGN

Glioblastoma multiforme (GBM) tumors were analyzed by flow cytometry to determine CMV antigen expression within various glioma-associated immune populations. The glioma cancer stem cell (gCSC) CMV interleukin (IL)-10 production was determined by ELISA. Human monocytes were stimulated with recombinant CMV IL-10 and levels of expression of p-STAT3, VEGF (vascular endothelial growth factor), TGF-β, viral IE1, and pp65 were determined by flow cytometry. The influence of CMV IL-10-treated monocytes on gCSC biology was ascertained by functional assays.

RESULTS

CMV showed a tropism for macrophages (MΦ)/microglia and CD133+ gCSCs within GBMs. The gCSCs produce CMV IL-10, which induces human monocytes (the precursor to the central nervous system MΦs/microglia) to assume an M2 immunosuppressive phenotype (as manifested by downmodulation of the major histocompatibility complex and costimulatory molecules) while upregulating immunoinhibitory B7-H1. CMV IL-10 also induces expression of viral IE1, a modulator of viral replication and transcription in the monocytes. Finally, the CMV IL-10-treated monocytes produced angiogenic VEGF, immunosuppressive TGF-β, and enhanced migration of gCSCs.

CONCLUSIONS

CMV triggers a feedforward mechanism of gliomagenesis by inducing tumor-supportive monocytes.

Short hairpin RNA-mediated fibronectin knockdown delays tumor growth in a mouse glioma model

Glioblastoma multiforme is the most common and lethal primary brain tumor. Glioma progression depends on the rapid proliferation of tumor cells accompanied by an acute immunosuppressive environment, facilitated mainly by tumor infiltration of regulatory T cells (Tregs). In this study, we characterize the role of fibronectin, a high-molecular weight extracellular matrix glycoprotein secreted by tumor cells, in controlling glioma progression and in mediating immunosuppression. Fibronectin binds to membrane-spanning integrin receptors and plays an important role in cell signaling, in defining cellular shape, in mobility, and in regulating the cell cycle. We found that inhibition of fibronectin expression in glioma cells, using short hairpin RNA-mediated silencing of gene expression, delayed cell proliferation in vitro. This delayed growth is explained, in part, by the observed reduced expression of integrin β(1) fibronectin receptor, which was restored by the inhibition of proteosomal activity. In our analysis of the downstream signaling targets of integrin β(1), we demonstrated reduced phosphorylation of Src kinase and STAT-3. We also observed reduced survivin expression that induced a three-fold increased accumulation of fibronectin-knockdown cells in the G(2)/M phase. In an experimental animal model, the fibronectin knockdown tumors had a mean survival advantage of 23 days over wild-type tumors. Moreover, brain samples of animals bearing fibronectin-knockdown tumors showed delayed Treg recruitment. Collectively, we propose that fibronectin is a key mediator of glioma progression because its inhibition delays both tumor progression and immunosuppression.

Glioblastoma chemotherapy adjunct via potent serotonin receptor-7 inhibition using currently marketed high-affinity antipsychotic medicines

Glioblastoma treatment as now constituted offers increased survival measured in months over untreated patients. Because glioblastomas are active in synthesizing a bewildering variety of growth factors, a systematic approach to inhibiting these is being undertaken as treatment adjunct. The serotonin 7 receptor is commonly overexpressed in glioblastoma. Research documentation showing agonists at serotonin receptor 7 cause increased extracellular regulated kinase 1/2 activation, increased interleukin-6 synthesis, increased signal transducer and activator of transcription-3 activation, increased resistance to apoptosis and other growth enhancing changes in glioblastoma is reviewed in this paper. Because three drugs in wide use to treat thought disorders - paliperidone, pimozide and risperidone - are also potent and well-tolerated inhibitors at serotonin receptor 7, these drugs should be studied for growth factor deprivation in an adjunctive role in glioblastoma treatment.