Association of increased phosphatidylinositol 3-kinase signaling with increased invasiveness and gelatinase activity in malignant gliomas

Farnesoid X receptor induction decreases invasion and tumor progression by JAK2/occludin signaling in human glioblastoma cells

Glioblastoma multiforme (GBM) is a brain cancer characterized by low survival and high recurrence rates. Farnesoid X receptor (FXR), a nuclear receptor for bile acids, is expressed at low levels in GBM. This study explores the impact of FXR regulation on GBM cell migration and invasion. Higher FXR expression correlated with increased survival in GBM patients, based on TCGA data. FXR overexpression inhibited cell viability, migration and invasion as well as matrix metalloproteinase 2 (MMP2) activity, while knockdown of FXR exerted the opposite effects. The expression of the tight junction proteins occludin and ZO-1 was enhanced after FXR overexpression. Moreover, a JAK2 activator reversed the migration and invasion of FXR-overexpressing GBM cells. In an animal study, FXR overexpression combined with temozolomide treatment decreased tumor mass, and MMP2 expression and elevated occludin expression in mice. In conclusion, FXR overexpression inhibits the progression of GBM, which may be mediated by inhibiting JAK2 and enhancing tight junction protein expression.

Interrogating glioma-M2 macrophage interactions identifies Gal-9/Tim-3 as a viable target against PTEN-null glioblastoma

Genomic alteration can reshape tumor microenvironment to drive tumor malignancy. However, how PTEN deficiency influences microenvironment-mediated cell-cell interactions in glioblastoma (GBM) remains unclear. Here, we show that PTEN deficiency induces a symbiotic glioma-M2 macrophage interaction to support glioma progression. Mechanistically, PTEN-deficient GBM cells secrete high levels of galectin-9 (Gal-9) via the AKT-GSK3β-IRF1 pathway. The secreted Gal-9 drives macrophage M2 polarization by activating its receptor Tim-3 and downstream pathways in macrophages. These macrophages, in turn, secrete VEGFA to stimulate angiogenesis and support glioma growth. Furthermore, enhanced Gal-9/Tim-3 expression predicts poor outcome in glioma patients. In GBM models, blockade of Gal-9/Tim-3 signaling inhibits macrophage M2 polarization and suppresses tumor growth. Moreover, α-lactose attenuates glioma angiogenesis by down-regulating macrophage-derived VEGFA, providing a novel antivascularization strategy. Therefore, our study suggests that blockade of Gal-9/Tim-3 signaling is effective to impair glioma progression by inhibiting macrophage M2 polarization, specifically for PTEN-null GBM.

Drug Delivery Systems in the Development of Novel Strategies for Glioblastoma Treatment

Glioblastoma multiforme (GBM) is a grade IV glioma considered the most fatal cancer of the central nervous system (CNS), with less than a 5% survival rate after five years. The tumor heterogeneity, the high infiltrative behavior of its cells, and the blood-brain barrier (BBB) that limits the access of therapeutic drugs to the brain are the main reasons hampering the current standard treatment efficiency. Following the tumor resection, the infiltrative remaining GBM cells, which are resistant to chemotherapy and radiotherapy, can further invade the surrounding brain parenchyma. Consequently, the development of new strategies to treat parenchyma-infiltrating GBM cells, such as vaccines, nanotherapies, and tumor cells traps including drug delivery systems, is required. For example, the chemoattractant CXCL12, by binding to its CXCR4 receptor, activates signaling pathways that play a critical role in tumor progression and invasion, making it an interesting therapeutic target to properly control the direction of GBM cell migration for treatment proposes. Moreover, the interstitial fluid flow (IFF) is also implicated in increasing the GBM cell migration through the activation of the CXCL12-CXCR4 signaling pathway. However, due to its complex and variable nature, the influence of the IFF on the efficiency of drug delivery systems is not well understood yet. Therefore, this review discusses novel drug delivery strategies to overcome the GBM treatment limitations, focusing on chemokines such as CXCL12 as an innovative approach to reverse the migration of infiltrated GBM. Furthermore, recent developments regarding in vitro 3D culture systems aiming to mimic the dynamic peritumoral environment for the optimization of new drug delivery technologies are highlighted.

Molecular signatures associated with diuron exposure on rat urothelial mitochondria

Diuron, 3- (3,4-dichlorophenyl)-1,1-dimethylurea, is a worldwide used herbicide whose biotransformation gives rise to the metabolites, 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and 3,4-dichloroaniline (DCA). Previous studies indicate that diuron and/or its metabolites are toxic to the bladder urothelium of the Wistar rats where, under certain conditions of exposure, they may induce successively urothelial cell degeneration, necrosis, hyperplasia and eventually tumors. The hypothesis was raised that the molecular initiating event (MIE) of this Adverse Outcome Pathway (AOP) is the mitochondrial toxicity of those compounds. Therefore, this study aimed to investigate in vitro the metabolic alterations resulting from urothelial mitochondria isolated from male Wistar rats exposure to diuron, DCPMU and DCA at 10 and 100 µM. A non-targeted metabolomic analysis using mass spectrometry showed discriminative clustering among groups and alterations in the intensity abundance of membrane-associated molecules phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidylserine (PS), in addition to methylhexanoyl-CoA and, particularly for diuron 100 µM, dehydro-L-gulonate, all of them involved in critical mitochondrial metabolism. Collectively, these data indicate the mitochondrial dysfunction as a MIE that triggers cellular damage and death observed in previous studies.

How do phosphodiesterase-5 inhibitors affect cancer? A focus on glioblastoma multiforme

Since the discovery of phosphodiesterase-5 (PDE5) enzyme overexpression in the central nervous system (CNS) malignancies, investigations have explored the potential capacity of current PDE5 inhibitor drugs for repositioning in the treatment of brain tumors, notably glioblastoma multiforme (GBM). It has now been recognized that these drugs increase brain tumors permeability and enhance standard chemotherapeutics effectiveness. More importantly, studies have highlighted the promising antitumor functions of PDE5 inhibitors, e.g., triggering apoptosis, suppressing tumor cell growth and invasion, and reversing tumor microenvironment (TME) immunosuppression in the brain. However, contradictory reports have suggested a pro-oncogenic role for neuronal cyclic guanosine monophosphate (cGMP), indicating the beneficial function of PDE5 in the brain of GBM patients. Unfortunately, due to the inconsistent preclinical findings, only a few clinical trials are evaluating the therapeutic value of PDE5 inhibitors in GBM treatment. Accordingly, additional studies should be conducted to shed light on the precise effect of PDE5 inhibitors in GBM biology regarding the existing molecular heterogeneities among individuals. Here, we highlighted and discussed the previously investigated mechanisms underlying the impacts of PDE5 inhibitors in cancers, focusing on GBM to provide an overview of current knowledge necessary for future studies.

Effect of PACAP on Hypoxia-Induced Angiogenesis and Epithelial-Mesenchymal Transition in Glioblastoma

Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts different effects in various human cancer. In glioblastoma (GBM), PACAP has been shown to interfere with the hypoxic micro-environment through the modulation of hypoxia-inducible factors via PI3K/AKT and MAPK/ERK pathways inhibition. Considering that hypoxic tumor micro-environment is strictly linked to angiogenesis and Epithelial–Mesenchymal transition (EMT), in the present study, we have investigated the ability of PACAP to regulate these events. Results have demonstrated that PACAP and its related receptor, PAC1R, are expressed in hypoxic area of human GBM colocalizing either in epithelial or mesenchymal cells. By using an in vitro model of GBM cells, we have observed that PACAP interferes with hypoxic/angiogenic pathway by reducing vascular-endothelial growth factor (VEGF) release and inhibiting formation of vessel-like structures in H5V endothelial cells cultured with GBM-conditioned medium. Moreover, PACAP treatment decreased the expression of mesenchymal markers such as vimentin, matrix metalloproteinase 2 (MMP-2) and matrix metalloproteinase 9 (MMP-9) as well as CD44 in GBM cells by affecting their invasiveness. In conclusion, our study provides new insights regarding the multimodal role of PACAP in GBM malignancy.

Multimodal Role of PACAP in Glioblastoma

Glioblastoma multiforme (GBM) is the deadliest form of brain tumors. To date, the GBM therapeutical approach consists of surgery, radiation-therapy and chemotherapy combined with molecules improving cancer responsiveness to treatments. In this review, we will present a brief overview of the GBM classification and pathogenesis, as well as the therapeutic approach currently used. Then, we will focus on the modulatory role exerted by pituitary adenylate cyclase-activating peptide, known as PACAP, on GBM malignancy. Specifically, we will describe PACAP ability to interfere with GBM cell proliferation, as well as the tumoral microenvironment. Considering its anti-oncogenic role in GBM, synthesis of PACAP agonist molecules may open new perspectives for combined therapy to existing gold standard treatment.

Lack of GD3 synthase (St8sia1) attenuates malignant properties of gliomas in genetically engineered mouse model

High expression of gangliosides GD3 and GD2 is observed in human gliomas. The functions of GD3 and GD2 in malignant properties have been reported in glioma cells in vitro, but those functions have not yet been investigated in vivo. In this study, we showed that deficiency of GD3 synthase (GD3S, St8sia1) attenuated glioma progression and clinical and pathological features in a platelet-derived growth factor B-driven murine glioma model. Lack of GD3S resulted in the prolonged lifespan of glioma-bearing mice and low-grade pathology in generated gliomas. Correspondingly, they showed reduced phosphorylation levels of Akt, Erks, and Src family kinases in glioma tissues. A DNA microarray study revealed marked alteration in the expression of various genes, particularly in MMP family genes, in GD3S-deficient gliomas. Re-expression of GD3S restored expression of MMP9 in primary-cultured glioma cells. We also identified a transcription factor, Ap2α, expressed in parallel with GD3S expression, and showed that Ap2α was critical for the induction of MMP9 by transfection of its cDNA and luciferase reporter genes, and a ChIP assay. These findings suggest that GD3S enhances the progression of gliomas by enhancement of the Ap2α-MMP9 axis. This is the first report to describe the tumor-enhancing functions of GD3S in vivo.

High levels of ubidecarenone (oxidized CoQ10) delivered using a drug-lipid conjugate nanodispersion (BPM31510) differentially affect redox status and growth in malignant glioma versus non-tumor cells

Metabolic reprogramming in cancer cells, vs. non-cancer cells, elevates levels of reactive oxygen species (ROS) leading to higher oxidative stress. The elevated ROS levels suggest a vulnerability to excess prooxidant loads leading to selective cell death, a therapeutically exploitable difference. Co-enzyme Q₁₀ (CoQ₁₀) an endogenous mitochondrial resident molecule, plays an important role in mitochondrial redox homeostasis, membrane integrity, and energy production. BPM31510 is a lipid-drug conjugate nanodispersion specifically formulated for delivery of supraphysiological concentrations of ubidecarenone (oxidized CoQ₁₀) to the cell and mitochondria, in both in vitro and in vivo model systems. In this study, we sought to investigate the therapeutic potential of ubidecarenone in the highly treatment-refractory glioblastoma. Rodent (C6) and human (U251) glioma cell lines, and non-tumor human astrocytes (HA) and rodent NIH3T3 fibroblast cell lines were utilized for experiments. Tumor cell lines exhibited a marked increase in sensitivity to ubidecarenone vs. non-tumor cell lines. Further, elevated mitochondrial superoxide production was noted in tumor cells vs. non-tumor cells hours before any changes in proliferation or the cell cycle could be detected. In vitro co-culture experiments show ubidecarenone differentially affecting tumor cells vs. non-tumor cells, resulting in an equilibrated culture. In vivo activity in a highly aggressive orthotopic C6 glioma model demonstrated a greater than 25% long-term survival rate. Based on these findings we conclude that high levels of ubidecarenone delivered using BPM31510 provide an effective therapeutic modality targeting cancer-specific modulation of redox mechanisms for anti-cancer effects.

Knockdown of Tousled‑like kinase 1 inhibits survival of glioblastoma multiforme cells

Glioblastoma multiforme (GBM) is an aggressive type of brain tumour that commonly exhibits resistance to treatment. The tumour is highly heterogenous and complex kinomic alterations have been reported leading to dysregulation of signalling pathways. The present study aimed to investigate the novel kinome pathways and to identify potential therapeutic targets in GBM. Meta‑analysis using Oncomine identified 113 upregulated kinases in GBM. RNAi screening was performed on identified kinases using ON‑TARGETplus siRNA library on LN18 and U87MG. Tousled‑like kinase 1 (TLK1), which is a serine/threonine kinase was identified as a potential hit. In vitro functional validation was performed as the role of TLK1 in GBM is unknown. TLK1 knockdown in GBM cells significantly decreased cell viability, clonogenicity, proliferation and induced apoptosis. TLK1 knockdown also chemosensitised the GBM cells to the sublethal dose of temozolomide. The downstream pathways of TLK1 were examined using microarray analysis, which identified the involvement of DNA replication, cell cycle and focal adhesion signalling pathways. In vivo validation of the subcutaneous xenografts of stably transfected sh‑TLK1 U87MG cells demonstrated significantly decreased tumour growth in female BALB/c nude mice. Together, these results suggested that TLK1 may serve a role in GBM survival and may serve as a potential target for glioma.

Cross-Talk in Nucleotide Signaling in Glioma C6 Cells

The chapter is focused on the mechanism of action of metabotropic P2Y nucleotide receptors: P2Y₁, P2Y₂, P2Y₁₂, P2Y₁₄ and the ionotropic P2X₇ receptor in glioma C6 cells. P2Y₁ and P2Y₁₂ both respond to ADP, but while P2Y₁ links to PLC and elevates cytosolic Ca²⁺ concentration, P2Y₁₂ negatively couples to adenylate cyclase, maintaining cAMP at low level. In glioma C6, these two P2Y receptors modulate activities of ERK1/2 and PI3K/Akt signaling and the effects depend on physiological conditions of the cells. During prolonged serum deprivation, cell growth is arrested, the expression of the P2Y₁ receptor strongly decreases and P2Y₁₂ becomes a major player responsible for ADP-evoked signal transduction. The P2Y₁₂ receptor activates ERK1/2 kinase phosphorylation (a known cell proliferation regulator) and stimulates Akt activity, contributing to glioma invasiveness. In contrast, P2Y₁ has an inhibitory effect on Akt pathway signaling. Furthermore, the P2X₇ receptor, often responsible for apoptotic fate, is not involved in Ca²⁺elevation in C6 cells. The shift in nucleotide receptor expression from P2Y₁ to P2Y₁₂ during serum withdrawal, the cross talk between both receptors and the lack of P2X₇ activity shows the precise self-regulating mechanism, enhancing survival and preserving the neoplastic features of C6 cells.

Extracellular Vesicles in Glioblastoma Tumor Microenvironment

Glioblastomas (GBM) are highly aggressive primary brain tumors. Complex and dynamic tumor microenvironment (TME) plays a crucial role in the sustained growth, proliferation, and invasion of GBM. Several means of intercellular communication have been documented between glioma cells and the TME, including growth factors, cytokines, chemokines as well as extracellular vesicles (EVs). EVs carry functional genomic and proteomic cargo from their parental cells and deliver that information to surrounding and distant recipient cells to modulate their behavior. EVs are emerging as crucial mediators of establishment and maintenance of the tumor by modulating the TME into a tumor promoting system. Herein we review recent literature in the context of GBM TME and the means by which EVs modulate tumor proliferation, reprogram metabolic activity, induce angiogenesis, escape immune surveillance, acquire drug resistance and undergo invasion. Understanding the multifaceted roles of EVs in the niche of GBM TME will provide invaluable insights into understanding the biology of GBM and provide functional insights into the dynamic EV-mediated intercellular communication during gliomagenesis, creating new opportunities for GBM diagnostics and therapeutics.

PI3K activation in neural stem cells drives tumorigenesis which can be ameliorated by targeting the cAMP response element binding protein

Background

Hyperactivation of phosphoinositide 3-kinase (PI3K) signaling is common in cancers, but the precise role of the pathway in glioma biology remains to be determined. Some understanding of PI3K signaling mechanisms in brain cancer comes from studies on neural stem/progenitor cells (NSPCs), where signals transmitted via the PI3K pathway cooperate with other intracellular pathways and downstream transcription factors to regulate critical cell functions.

Methods

To investigate the role of the PI3K pathway in glioma initiation and development, we generated a mouse model targeting the inducible expression of a PIK3CAH1047A oncogenic mutant and deletion of the PI3K negative regulator, phosphatase and tensin homolog (PTEN), to NSPCs.

Results

Expression of a Pik3caH1047A was sufficient to generate tumors with oligodendroglial features, but simultaneous loss of PTEN was required for the development of invasive, high-grade glioma. Pik3caH1047A-PTEN mutant NSPCs exhibited enhanced neurosphere formation which correlated with increased Wnt signaling, while loss of cAMP response element binding protein (CREB) in Pik3caH1047A-Pten mutant tumors led to longer symptom-free survival in mice.

Conclusion

Taken together, our findings present a novel mouse model for glioma demonstrating that the PI3K pathway is important for initiation of tumorigenesis and that disruption of downstream CREB signaling attenuates tumor expansion.

The Copper(II)-Assisted Connection between NGF and BDNF by Means of Nerve Growth Factor-Mimicking Short Peptides

Nerve growth factor (NGF) is a protein necessary for development and maintenance of the sympathetic and sensory nervous systems. We have previously shown that the NGF N-terminus peptide NGF(1-14) is sufficient to activate TrkA signaling pathways essential for neuronal survival and to induce an increase in brain-derived neurotrophic factor (BDNF) expression. Cu2+ ions played a critical role in the modulation of the biological activity of NGF(1-14). Using computational, spectroscopic, and biochemical techniques, here we report on the ability of a newly synthesized peptide named d-NGF(1-15), which is the dimeric form of NGF(1-14), to interact with TrkA. We found that d-NGF(1-15) interacts with the TrkA-D5 domain and induces the activation of its signaling pathways. Copper binding to d-NGF(1-15) stabilizes the secondary structure of the peptides, suggesting a strengthening of the noncovalent interactions that allow for the molecular recognition of D5 domain of TrkA and the activation of the signaling pathways. Intriguingly, the signaling cascade induced by the NGF peptides ultimately involves cAMP response element-binding protein (CREB) activation and an increase in BDNF protein level, in keeping with our previous result showing an increase of BDNF mRNA. All these promising connections can pave the way for developing interesting novel drugs for neurodegenerative diseases.

Correlation of OGR1 with proliferation and apoptosis of breast cancer cells

Effects of ovarian cancer G-protein-coupled receptor 1 (OGR1) protein on proliferation and apoptosis of breast cancer cells, as well as its molecular mechanism were investigated. The MCF-7 cell line highly expressed OGR1 was constructed by transient transfection of eukaryotic expression vector using breast cancer cells. At the same time, cells were transfected with empty vector as controls. The effects of highly expressed OGR1 on cell growth, proliferation, apoptosis and other abilities were identified. In addition, the effects of highly expressed OGR1 on serine-threonine kinase (AKT), p53 and other genes were studied. It was proved in apoptosis experiment that highly expressed OGR1 protein in breast cancer cells could effectively increase the proportion of apoptosis of cells. Cell proliferation experiment revealed that the growth and proliferation abilities of breast cancer cells with highly expressed OGR1 were inhibited to some extent, compared with those of breast cancer cells with low expression of OGR1. Results of western blotting showed that the gene and protein expression levels of p53 in breast cancer cells with highly expressed OGR1 were increased. There was no significant difference in protein expression of AKT between breast cancer cells with low expression of OGR1 and those with highly expressed OGR1. However, the protein content of phosphorylated-AKT (p-AKT) in breast cancer cells with highly expressed OGR1 was lower than that in breast cancer cells with low expression of OGR1. The proliferation and apoptosis of breast cancer cells are influenced by the changes of OGR1 expression, which are correlated with the gene expression levels of AKT and p53 to some extent, but the detailed molecular mechanism requires additional study.

Regulation of glioma cell invasion by 3q26 gene products PIK3CA, SOX2 and OPA1

Diffuse gliomas progress by invading neighboring brain tissue to promote postoperative relapse. Transcription factor SOX2 is highly expressed in invasive gliomas and maps to chromosome region 3q26 together with the genes for PI3K/AKT signaling activator PIK3CA and effector molecules of mitochondria fusion and cell invasion, MFN1 and OPA1. Gene copy number analysis at 3q26 from 129 glioma patient biopsies revealed mutually exclusive SOX2 amplifications (26%) and OPA1 losses (19%). Both forced SOX2 expression and OPA1 inactivation increased LN319 glioma cell invasion in vitro and promoted cell dispersion in vivo in xenotransplanted D. rerio embryos. While PI3 kinase activity sustained SOX2 expression, pharmacological PI3K/AKT pathway inhibition decreased invasion and resulted in SOX2 nucleus-to-cytoplasm translocation in an mTORC1-independent manner. Chromatin immunoprecipitation and luciferase reporter gene assays together demonstrated that SOX2 trans-activates PIK3CA and OPA1. Thus, SOX2 activates PI3K/AKT signaling in a positive feedback loop, while OPA1 deletion is interpreted to counteract OPA1 trans-activation. Remarkably, neuroimaging of human gliomas with high SOX2 or low OPA1 genomic imbalances revealed significantly larger necrotic tumor zone volumes, corresponding to higher invasive capacities of tumors, while autologous necrotic cells are capable of inducing higher invasion in SOX2 overexpressing or OPA1 knocked-down relative to parental LN319. We thus propose necrosis volume as a surrogate marker for the assessment of glioma invasive potential. Whereas glioma invasion is activated by a PI3K/AKT-SOX2 loop, it is reduced by a cryptic invasion suppressor SOX2-OPA1 pathway. Thus, PI3K/AKT-SOX2 and mitochondria fission represent connected signaling networks regulating glioma invasion.

Identification of expression quantitative trait loci of MTOR associated with the progression of glioma

Mechanistic target of rapamycin (MTOR) encodes a key modulator of cell growth, proliferation, and apoptosis. Previous studies have demonstrated that the dysregulation of MTOR is involved in the development and progression of several types of cancer, including glioma. In the present study, a comprehensive analysis was conducted to examine whether the expression quantitative trait loci (eQTLs) of MTOR are associated with the progression of glioma. Candidate eQTLs of MTOR were obtained from the Genotype-Tissue Expression eQTL Browser. The Kaplan-Meier method and multivariate Cox model were used to analyze the progression-free survival time of glioma patients. Based on the analysis of 138 glioma patients, one eQTL of MTOR, rs4845964, was demonstrated to be significantly associated with the progression of glioma in a dominant manner. The adjusted hazard ratios (HRs) for patients with the AG or AA genotype at rs4845964 were 2.82 [95% confidence interval (CI), 1.27-6.27; P=0.0111] and 2.79 (95% CI, 1.10-7.07; P=0.0312), respectively, compared with those with the GG genotype. When the rs4845964 AG and AA genotypes were combined for analysis, the HR was 2.70 (95% CI, 1.25-5.82; P=0.0114) vs. the GG genotype. Stratified analyses revealed similar associations between the rs4845964 genotypes and the progression of glioma in all subgroups (following stratification by age, sex and tumor grade). These results demonstrate for the first time that the MTOR eQTL rs4845964 is associated with the progression of glioma.

Concurrent activation of β2-adrenergic receptor and blockage of GPR55 disrupts pro-oncogenic signaling in glioma cells

Activation of β₂-adrenergic receptor (β₂AR) and deorphanized GPR55 has been shown to modulate cancer growth in diverse tumor types in vitro and in xenograft models in vivo. (R,R')-4'-methoxy-1-naphthylfenoterol [(R,R')-MNF] is a bivalent compound that agonizes β₂AR but inhibits GPR55-mediated pro-oncogenic responses. Here, we investigated the molecular mechanisms underlying the anti-tumorigenic effects of concurrent β₂AR activation and GPR55 blockade in C6 glioma cells using (R,R')-MNF as a marker ligand. Our data show that (R,R')-MNF elicited G1-phase cell cycle arrest and apoptosis, reduced serum-inducible cell motility, promoted the phosphorylation of PKA target proteins, and inhibited constitutive activation of ERK and AKT in the low nanomolar range, whereas high nanomolar levels of (R,R')-MNF were required to block GPR55-mediated cell motility. siRNA knockdown and pharmacological inhibition of β₂AR activity were accompanied by significant upregulation of AKT and ERK phosphorylation, and selective alteration in (R,R')-MNF responsiveness. The effects of agonist stimulation of GPR55 on various readouts, including cell motility assays, were suppressed by (R,R')-MNF. Lastly, a significant increase in phosphorylation-mediated inactivation of β-catenin occurred with (R,R')-MNF, and we provided new evidence of (R,R')-MNF-mediated inhibition of oncogenic β-catenin signaling in a C6 xenograft tumor model. Thus, simultaneous activation of β₂AR and blockade of GPR55 may represent a novel therapeutic approach to combat the progression of glioblastoma cancer.

Blockade of CCR5 receptor prevents M2 microglia phenotype in a microglia-glioma paradigm

Microglia express chemokines and their cognate receptors that were found to play important roles in many processes required for tumor development, such as tumor growth, proliferation, invasion, and angiogenesis. Among the chemokine receptor, CCR5 have been documented in different cancer models; in particular, CCR5 is highly expressed in human glioblastoma, where it is associated to poor prognosis. In the present study, we investigated the effect of CCR5 receptor blockade on a paradigm of microglia-glioma interaction; the CCR5 blocker maraviroc (MRV) was used as a pharmacological tool. We found that MVR is able to reduce the gene expression and function of the M2 markers ARG1 and IL-10 in presence of both basal glioma-released factors (C-CM) and activated glioma-released factors (LI-CM), but it up-regulates the M1 markers NO and IL-1β only if microglia is stimulated by LI-CM; the latter effect appears to be mediated by the inhibition of mTOR pathway. In addition, CCR5 blockade was associated to a significant reduction in microglia migration, an effect mediated through the inhibition of AKT pathway.

P2Y1 Receptors - Properties and Functional Activities

In this chapter we try to show a comprehensive image of current knowledge of structure, activity and physiological role of the P2Y₁ purinergic receptor. The structure, distribution and changes in the expression of this receptor are summarized, as well as the mechanism of its signaling activity by the intracellular calcium mobilization. We try to show the connection between the components of its G protein activation and cellular or physiological effects, starting from changes in protein phosphorylation patterns and ending with such remote effects as receptor-mediated apoptosis. The special emphasis is put on the role of the P2Y₁ receptor in cancer cells and neuronal plasticity. We concentrate on the P2Y₁ receptor, it is though impossible to completely abstract from other aspects of nucleotide signaling and cross-talk with other nucleotide receptors is here discussed. Especially, the balance between P2Y₁ and P2Y₁₂ receptors, sharing the same ligand but signaling through different pathways, is presented.

Developing a Novel Embryo-Larval Zebrafish Xenograft Assay to Prioritize Human Glioblastoma Therapeutics

Glioblastoma is an aggressive brain cancer requiring improved treatments. Existing methods of drug discovery and development require years before new therapeutics become available to patients. Zebrafish xenograft models hold promise for prioritizing drug development. We have developed an embryo-larval zebrafish xenograft assay in which cancer cells are implanted in a brain microenvironment to discover and prioritize compounds that impact glioblastoma proliferation, migration, and invasion. We illustrate the utility of our assay by evaluating the well-studied, phosphatidylinositide 3-kinase inhibitor LY294002 and zinc oxide nanoparticles (ZnO NPs), which demonstrate selective cancer cytotoxicity in cell culture, but the in vivo effectiveness has not been established. Exposures of 3.125-6.25 μM LY294002 significantly decreased proliferation up to 34% with concentration-dependent trends. Exposure to 6.25 μM LY294002 significantly inhibited migration/invasion by ∼27% within the glioblastoma cell mass (0-80 μm) and by ∼32% in the next distance region (81-160 μm). Unexpectedly, ZnO enhanced glioblastoma proliferation by ∼19% and migration/invasion by ∼35% at the periphery of the cell mass (161+ μm); however, dissolution of these NPs make it difficult to discern whether this was a nano or ionic effect. These results demonstrate that we have a short, relevant, and sensitive zebrafish-based assay to aid glioblastoma therapeutic development.

Analysis of caveolin-1 and phosphoinositol-3 kinase expression in primary uveal melanomas

BACKGROUND

To evaluate the regulation of blood supply in primary uveal melanomas through caveolin-1 (Cav-1)/phosphoinositol-3 kinase (PI3K).

METHODS

The expression of Cav-1 and PI3K was analysed in 51 paraffin sections of metastatic (n = 30) and non-metastastic uveal melanomas (n = 21). Two trained observers quantified Cav-1 and PI3K immunofluorescensce expression by determining intensity of staining and percentage of positive cells. The expression was correlated with known prognostic factors. Besides angiogenesis by means of endoglin expression, the normal vasculature (von Willebrand Factor expression) was evaluated semi-quantitatively. Vasculogenic mimicry (VM) was analysed by CD31/PAS staining.

RESULTS

All examined specimens expressed Cav-1 with a mean of 90.34% Cav-1 positive cells (range, 3.23-100%). Metastatic disease was associated with a higher Cav-1 expression. The correlation of Cav-1 with well-established prognostic factors showed a significant association between Cav-1 expression and largest tumour diameter (P = 0.022), tumour node metastasis classification (P = 0.008) and invasion of optic nerve head (P = 0.048). PI3K was expressed by all uveal melanomas with a mean of 87.28% cells showing PI3K expression. A higher level of PI3K was significantly associated with larger height (P = 0.042) and progressed tumour node metastasis stage (P = 0.016). The percentage of PI3K and Cav-1 positive cells were significantly associated (P = 0.034). For PI3K and Cav-1 expression a non-significant association with VM was shown (P = 0.064 and P = 0.072, respectively). No correlation of PI3K or Cav-1 with angiogenesis or mature vasculature was seen (P > 0.05).

CONCLUSIONS

Cav-1 expression may be especially up-regulated in larger uveal melanomas. As it was correlated with PI3K expression and VM in this series of uveal melanoma, Cav-1 might induce the formation of VM via the PI3K-signalling cascade.

Proteomic analysis of human glioblastoma cell lines differently resistant to a nitric oxide releasing agent

Glioblastoma multiforme is the most aggressive astrocytoma characterized by the development of resistant cells to various cytotoxic stimuli. Nitric oxide (NO) is able to overcome tumor resistance in PTEN mutated rat C6 glioma cells due to its ability to inhibit cell growth by influencing the intracellular distribution of ceramide. The aim of this study is to monitor the effects of NO donor PAPANONOate on ceramide trafficking in human glioma cell lines, CCF-STTG1 (PTEN-mutated, p53-wt) and T98G (PTEN-harboring, p53-mutated), together with the assessment of their differential molecular signature by 2D-DIGE and MALDI mass spectrometry. In the CCF-STTG1 cell line, the results indicate that treatment with PAPANONOate decreased cell proliferation (<50%) and intracellular trafficking of ceramide, assessed by BODIPY-C5Cer, while these events were not observed in the T98G cell line. Proteomic results suggest that CCF-STTG1 cells are characterized by an increased expression of proteins involved in NO-associated ER stress (i.e. protein disulfide-isomerase A3, calreticulin, 78 kDa glucose-regulated protein), which could compromise ceramide delivery from ER to Golgi, leading to ceramide accumulation in ER and partial growth arrest. Conversely, T98G cell lines, resistant to NO exposure, are characterized by increased levels of cytosolic antioxidant proteins (i.e. glutathione-S-transferase P, peroxiredoxin 1), which might buffer intracellular NO. By providing differential ceramide distribution after NO exposure and differential protein expression of two high grade glioma cell lines, this study highlights specific proteins as possible markers for tumor aggressiveness. This study demonstrates that, in two different high grade glioma cell lines, NO exposure results in a different ceramide distribution and protein expression. Furthermore, this study highlights specific proteins as possible markers for tumor aggressiveness.

Dihydroartemisinin inhibits the Raf/ERK/MEK and PI3K/AKT pathways in glioma cells

It has previously been reported that dihydroartemisinin (DHA) is an effective novel anticancer compound in a number of types of tumor cells. Previous studies have demonstrated the anticancer activity of DHA in gioma cells. However, its underlining mechanism remains unclear. In the present study, the anticancer activity of DHA was examined in the glioma cell lines BT325 and C6. Western blot analysis was also employed to determine the signaling pathway changes. It was demonstrated that DHA effectively inhibited cell growth and induced apoptosis in glioma cells. Moreover, western blot analysis indicated that DHA-induced apoptosis was accompanied by inactivation of the Raf/MEK/ERK and PI3K/AKT signaling pathways, in addition to the downregulation of anti-apoptotic proteins Mcl-1 and Bcl-2 expression levels.

Identification of expression quantitative trait loci of RPTOR for susceptibility to glioma

Expression quantitative trait loci (eQTLs) have been recognized to be more likely to associate with complex diseases including cancer. As an essential scaffold for MTOR complex 1, RPTOR is necessary for the MTOR-catalyzed phosphorylation. This study examined the associations between the eQTLs of RPTOR and glioma susceptibility. The eQTLs of RPTOR were obtained from GTEx eQTL Browser. Associations were estimated by logistic regression models. On the basis of analysis of 138 cases with glioma and 327 cancer-free population controls, we demonstrated that the eQTL of RPTOR, rs7502563, was significantly associated with a decreased glioma risk [odds ratio (OR) = 0.59, 95 % confidence interval (CI) = 0.38-0.89, P = 0.0123] in a dominant manner. Stratified analyses indicated that the association between rs7502563 and glioma was more pronounced in females (OR = 0.40, 95 % CI = 0.20-0.80, P = 0.0091), older subjects (OR = 0.47, 95 % CI = 0.26-0.86, P = 0.0135), and subjects with high-grade glioma (OR = 0.45, 95 % CI = 0.27-0.77, P = 0.0031). Moreover, an interest gradual decrease in OR with higher grade glioma was observed. Further analysis of the extracted data from GTEx eQTL Browser found that rs7502563 G allele was associated with significantly higher expression of RPTOR in all HapMap populations. Our results demonstrate for the first time that the eQTL of RPTOR, rs7502563, is susceptible to glioma.

CRM197 in Combination With shRNA Interference of VCAM-1 Displays Enhanced Inhibitory Effects on Human Glioblastoma Cells

CRM197 is a naturally nontoxic diphtheria toxin mutant that binds and inhibits heparin-binding epidermal growth factor-like growth factor. CRM197 serves as carrier protein for vaccine and other therapeutic agents. CRM197 also inhibits the growth, migration, invasion, and induces apoptosis in various tumors. Vascular cell adhesion molecule-1 (VCAM-1) is an important cell surface adhesion molecule associated with malignancy of gliomas. In this work, we aimed to investigate the role and mechanism of CRM197 combined with shRNA interference of VCAM-1 (shRNA-VCAM-1) on the migration, invasion, and apoptosis of glioblastoma cells. U87 and U251 human glioblastoma cells were treated with CRM197 (10 µg/ml) and shRNA interfering technology was employed to silence VCAM-1 expression. Cell viability, migration, invasiveness, and apoptosis were assessed with CCK8, Transwell and Annexin V-PE/7-AAD staining. Activation of cleaved caspase-3, 8, and 9, activity of matrix metalloproteinase-2/9 (MMP-2/9), and expression of phosphorylated Akt (p-Akt) were also checked. Results showed that CRM197 and shRNA-VCAM-1 not only significantly inhibited the cell proliferation, migration, invasion, but also promoted the apoptosis of U87 and U251 cells. Combined treatment of both displayed enhanced inhibitory effects on the malignant biological behavior of glioma cells. The activation of cleaved caspase-3, 8, 9 was promoted, activity of MMP-2 and MMP-9 and expression of p-Akt were inhibited significantly by the treatment of CRM197 and shRNA-VCAM-1 alone or in combination, indicating that the combination of CRM197 with shRNA-VCAM-1 additively inhibited the malignant behavior of human glioblastoma cells via activating caspase-3, 8, 9 as well as inhibiting MMP-2, MMP-9, and Akt pathway.

Mechanisms regulating glioma invasion

Glioblastoma (GBM) is the most aggressive, deadliest, and most common brain malignancy in adults. Despite the advances made in surgical techniques, radiotherapy and chemotherapy, the median survival for GBM patients has remained at a mere 14 months. GBM poses several unique challenges to currently available treatments for the disease. For example, GBM cells have the propensity to aggressively infiltrate/invade into the normal brain tissues and along the vascular tracks, which prevents complete resection of all malignant cells and limits the effect of localized radiotherapy while sparing normal tissue. Although anti-angiogenic treatment exerts anti-edematic effect in GBM, unfortunately, tumors progress with acquired increased invasiveness. Therefore, it is an important task to gain a deeper understanding of the intrinsic and post-treatment invasive phenotypes of GBM in hopes that the gained knowledge would lead to novel GBM treatments that are more effective and less toxic. This review will give an overview of some of the signaling pathways that have been shown to positively and negatively regulate GBM invasion, including, the PI3K/Akt, Wnt, sonic hedgehog-GLI1, and microRNAs. The review will also discuss several approaches to cancer therapies potentially altering GBM invasiveness.

Tetraarsenic oxide-induced inhibition of malignant glioma cell invasion in vitro via a decrease in matrix metalloproteinase secretion and protein kinase B phosphorylation

OBJECT

Local invasiveness of malignant glioma is a major reason for the failure of current treatments including surgery and radiation therapy. Tetraarsenic oxide (As4O6 [TAO]) is a trivalent arsenic compound that has potential anticancer and antiangiogenic effects in selected cancer cell lines at a lower concentration than arsenic trioxide (As2O3 [ATO]), which has been more widely tested in vitro and in vivo. The authors tried to determine the cytotoxic concentration of TAO in malignant glioma cell lines and whether TAO would show anti-invasive effects under conditions independent of cell death or apoptosis.

METHODS

The human phosphatase and tensin homolog (PTEN)-deficient malignant glioma cell lines U87MG, U251MG, and U373MG together with PTEN-functional LN428 were cultured with a range of micromolar concentrations of TAO. The invasiveness of the glioma cell lines was analyzed. The effect of TAO on matrix metalloproteinase (MMP) secretion and membrane type 1 (MT1)-MMP expression was measured using gelatin zymography and Western blot, respectively. Akt, or protein kinase B, activity, which is a downstream effector of PTEN, was assessed with a kinase assay using glycogen synthesis kinase-3β (GSK-3β) as a substrate and Western blotting of phosphorylated Akt.

RESULTS

Tetraarsenic oxide inhibited 50% of glioma cell proliferation at 6.3-12.2 μM. Subsequent experiments were performed under the same TAO concentrations and exposure times, avoiding the direct tumoricidal effect of TAO, which was confirmed with apoptosis markers. An invasion assay revealed a dose-dependent decrease in invasiveness under the influence of TAO. Both the gelatinolytic activity of MMP-2 and MT1-MMP expression decreased in a dose-dependent manner in all cell lines, which was in accordance with the invasion assay results. The TAO decreased kinase activity of Akt on GSK-3β assay and inhibited Akt phosphorylation in a dose-dependent manner in all cell lines regardless of their PTEN status.

CONCLUSIONS

These results showed that TAO effectively inhibits proliferation of glioblastoma cell lines and also exerts an anti-invasive effect via decreased MMP-2 secretion, decreased MT1-MMP expression, and the inhibition of Akt phosphorylation under conditions devoid of cytotoxicity. Further investigations using an in vivo model are needed to evaluate the potential role of TAO as an anti-invasive agent.

Inhibition of CXCR7 extends survival following irradiation of brain tumours in mice and rats

Background:

In experimental models of glioblastoma multiforme (GBM), irradiation (IR) induces local expression of the chemokine CXCL12/SDF-1, which promotes tumour recurrence. The role of CXCR7, the high-affinity receptor for CXCL12, in the tumour's response to IR has not been addressed.

Methods:

We tested CXCR7 inhibitors for their effects on tumour growth and/or animal survival post IR in three rodent GBM models. We used immunohistochemistry to determine where CXCR7 protein is expressed in the tumours and in human GBM samples. We used neurosphere formation assays with human GBM xenografts to determine whether CXCR7 is required for cancer stem cell (CSC) activity in vitro.

Results:

CXCR7 was detected on tumour cells and/or tumour-associated vasculature in the rodent models and in human GBM. In human GBM, CXCR7 expression increased with glioma grade and was spatially associated with CXCL12 and CXCL11/I-TAC. In the rodent GBM models, pharmacological inhibition of CXCR7 post IR caused tumour regression, blocked tumour recurrence, and/or substantially prolonged survival. CXCR7 expression levels on human GBM xenograft cells correlated with neurosphere-forming activity, and a CXCR7 inhibitor blocked sphere formation by sorted CSCs.

Conclusions:

These results indicate that CXCR7 inhibitors could block GBM tumour recurrence after IR, perhaps by interfering with CSCs.

Targeting the PI3K/AKT/mTOR signaling pathway in glioblastoma: novel therapeutic agents and advances in understanding

Glioblastoma multiforme (GBM) is a grade IV astrocytoma with a median survival of 12 months despite current multi-modal treatment options. GBM is distinguished clinicopathologically into primary and secondary subtypes. Mutations of phosphatase and tensin homolog, and subsequent upregulation of the downstream protein kinase B/mammalian target of rapamycin (mTOR) signaling pathway, are commonly seen in primary GBM and less predominantly in secondary GBM. While investigations into targeted treatments of mTOR have been attempted, feedback regulation within the mTOR signaling pathway may account for therapeutic resistance. Currently, rapamycin analogs, dual-targeted mTOR complex 1 and 2 agents as well as dual mTOR and phosphatidylinositol-3 kinase-targeted agents are being investigated experimentally and in clinical trials. This review will discuss the experimental potential of these agents in the treatment of GBM and their current stage in the GBM drug pipeline. Knowledge obtained from the application of these agents can help in understanding the pathogenesis of GBM as well as delineating subsequent treatment strategies.

Artemether combined with shRNA interference of vascular cell adhesion molecule-1 significantly inhibited the malignant biological behavior of human glioma cells

Artemether is the derivative extracted from Chinese traditional herb and originally used for malaria. Artemether also has potential therapeutic effects against tumors. Vascular cell adhesion molecule-1 (VCAM-1) is an important cell surface adhesion molecule associated with malignancy of gliomas. In this work, we investigated the role and mechanism of artemether combined with shRNA interference of VCAM-1 (shRNA-VCAM-1) on the migration, invasion and apoptosis of glioma cells. U87 human glioma cells were treated with artemether at various concentrations and shRNA interfering technology was employed to silence the expression of VCAM-1. Cell viability, migration, invasiveness and apoptosis were assessed with MTT, wound healing, Transwell and Annexin V-FITC/PI staining. The expression of matrix metalloproteinase-2 (MMP-2), matrix metalloproteinase-9 (MMP-9) and phosphorylated Akt (p-Akt) was checked by Western blot assay. Results showed that artemether and shRNA-VCAM-1 not only significantly inhibited the migration, invasiveness and expression of MMP-2/9 and p-Akt, but also promoted the apoptosis of U87 cells. Combined treatment of both displayed the maximum inhibitory effects on the malignant biological behavior of glioma cells. Our work revealed the potential therapeutic effects of artemether and antiVCAM-1 in the treatments of gliomas.

Metabolic response of glioma to dichloroacetate measured in vivo by hyperpolarized (13)C magnetic resonance spectroscopic imaging

BACKGROUND

The metabolic phenotype that derives disproportionate energy via glycolysis in solid tumors, including glioma, leads to elevated lactate labeling in metabolic imaging using hyperpolarized [1-(13)C]pyruvate. Although the pyruvate dehydrogenase (PDH)-mediated flux from pyruvate to acetyl coenzyme A can be indirectly measured through the detection of carbon-13 ((13)C)-labeled bicarbonate, it has proven difficult to visualize (13)C-bicarbonate at high enough levels from injected [1-(13)C]pyruvate for quantitative analysis in brain. The aim of this study is to improve the detection of (13)C-labeled metabolites, in particular bicarbonate, in glioma and normal brain in vivo and to measure the metabolic response to dichloroacetate, which upregulates PDH activity.

METHODS

An optimized protocol for chemical shift imaging and high concentration of hyperpolarized [1-(13)C]pyruvate were used to improve measurements of lactate and bicarbonate in C6 glioma-transplanted rat brains. Hyperpolarized [1-(13)C]pyruvate was injected before and 45 min after dichloroacetate infusion. Metabolite ratios of lactate to bicarbonate were calculated to provide improved metrics for characterizing tumor metabolism.

RESULTS

Glioma and normal brain were well differentiated by lactate-to-bicarbonate ratio (P = .002, n = 5) as well as bicarbonate (P = .0002) and lactate (P = .001), and a stronger response to dichloroacetate was observed in glioma than in normal brain.

CONCLUSION

Our results clearly demonstrate for the first time the feasibility of quantitatively detecting (13)C-bicarbonate in tumor-bearing rat brain in vivo, permitting the measurement of dichloroacetate-modulated changes in PDH flux. The simultaneous detection of lactate and bicarbonate provides a tool for a more comprehensive analysis of glioma metabolism and the assessment of metabolic agents as anti-brain cancer drugs.

Cross-talk in nucleotide signaling in glioma C6 cells

The chapter is focused on the mechanism of action of metabotropic P2Y nucleotide receptors: P2Y(1), P2Y(2), P2Y(12), P2Y(14) and the ionotropic P2X(7) receptor in glioma C6 cells. P2Y(1) and P2Y(12) both respond to ADP, but while P2Y(1) links to PLC and elevates cytosolic Ca(2+) concentration, P2Y(12) negatively couples to adenylate cyclase, maintaining cAMP at low level. In glioma C6, these two P2Y receptors modulate activities of ERK1/2 and PI3K/Akt signaling and the effects depend on physiological conditions of the cells. During prolonged serum deprivation, cell growth is arrested, the expression of the P2Y(1) receptor strongly decreases and P2Y(12) becomes a major player responsible for ADP-evoked signal transduction. The P2Y(12) receptor activates ERK1/2 kinase phosphorylation (a known cell proliferation regulator) and stimulates Akt activity, contributing to glioma invasiveness. In contrast, P2Y(1) has an inhibitory effect on Akt pathway signaling. Furthermore, the P2X(7) receptor, often responsible for apoptotic fate, is not involved in Ca(2+)elevation in C6 cells. The shift in nucleotide receptor expression from P2Y(1) to P2Y(12) during serum withdrawal, the cross talk between both receptors and the lack of P2X(7) activity shows the precise self-regulating mechanism, enhancing survival and preserving the neoplastic features of C6 cells.

Metabolite kinetics in C6 rat glioma model using magnetic resonance spectroscopic imaging of hyperpolarized [1-(13)C]pyruvate

In addition to an increased lactate-to-pyruvate ratio, altered metabolism of a malignant glioma can be further characterized by its kinetics. Spatially resolved dynamic data of pyruvate and lactate from C6-implanted female Sprague-Dawley rat brain were acquired using a spiral chemical shift imaging sequence after a bolus injection of a hyperpolarized [1-(13)C]pyruvate. Apparent rate constants for the conversion of pyruvate to lactate in three different regions (glioma, normal appearing brain, and vasculature) were estimated based on a two-site exchange model. The apparent conversion rate constant was 0.018 ± 0.004 s(-1) (mean ± standard deviation, n = 6) for glioma, 0.009 ± 0.003 s(-1) for normal brain, and 0.005 ± 0.001 s(-1) for vasculature, whereas the lactate-to-pyruvate ratio, the metabolic marker used to date to identify tumor regions, was 0.36 ± 0.07 (mean ± SD), 0.24 ± 0.07, and 0.12 ± 0.02 for glioma, normal brain, and vasculature, respectively. The data suggest that the apparent conversion rate better differentiate glioma from normal brain (P = 0.001, n = 6) than the lactate-to-pyruvate ratio (P = 0.02).

Cabozantinib (XL184), a novel MET and VEGFR2 inhibitor, simultaneously suppresses metastasis, angiogenesis, and tumor growth

The signaling pathway of the receptor tyrosine kinase MET and its ligand hepatocyte growth factor (HGF) is important for cell growth, survival, and motility and is functionally linked to the signaling pathway of VEGF, which is widely recognized as a key effector in angiogenesis and cancer progression. Dysregulation of the MET/VEGF axis is found in a number of human malignancies and has been associated with tumorigenesis. Cabozantinib (XL184) is a small-molecule kinase inhibitor with potent activity toward MET and VEGF receptor 2 (VEGFR2), as well as a number of other receptor tyrosine kinases that have also been implicated in tumor pathobiology, including RET, KIT, AXL, and FLT3. Treatment with cabozantinib inhibited MET and VEGFR2 phosphorylation in vitro and in tumor models in vivo and led to significant reductions in cell invasion in vitro. In mouse models, cabozantinib dramatically altered tumor pathology, resulting in decreased tumor and endothelial cell proliferation coupled with increased apoptosis and dose-dependent inhibition of tumor growth in breast, lung, and glioma tumor models. Importantly, treatment with cabozantinib did not increase lung tumor burden in an experimental model of metastasis, which has been observed with inhibitors of VEGF signaling that do not target MET. Collectively, these data suggest that cabozantinib is a promising agent for inhibiting tumor angiogenesis and metastasis in cancers with dysregulated MET and VEGFR signaling.

Calpain 2 is required for glioblastoma cell invasion: regulation of matrix metalloproteinase 2

Invasion of glioblastoma cells significantly reduces the effectiveness of current treatments, highlighting the importance of understanding dispersal mechanisms and characteristics of the invasive population. Induction of calcium fluxes into glioblastoma cells by autocrine glutamate is critical for invasion. However, the target(s) by which calcium acts to stimulate the dispersal of glioblastoma cells is not clear. In this study, we tested the hypothesis that the calcium-activated protease calpain 2 is required for glioblastoma cell invasion. Knockdown of calpain 2 expression using shRNA or chemical inhibition of calpain activity reduced glioblastoma cell invasion by 90%. Interestingly, decreased expression of calpain 2 did not influence morphology or migration, suggesting regulation of invasion specific mechanisms. Consistent with this idea, 39% less extracellular MMP2 was measured from knockdown cells identifying one mechanism by which calpain 2 mediates glioblastoma cell invasion. This is the first report demonstrating that calpain 2 is required for glioblastoma cell invasion.

Inhibition of Necl-5 (CD155/PVR) reduces glioblastoma dispersal and decreases MMP-2 expression and activity

Patients afflicted with glioblastoma (GBM) have poor survival due to dispersive invasion throughout the brain. Necl-5, a cell surface receptor for vitronectin, is expressed in GBM but not normal brain. In several GBM cell lines Necl-5 promotes migration and invasion but the mechanism is poorly understood. In this study, we show that knockdown of Necl-5 by RNAi results in markedly decreased invasion of A172 GBM cells in a 3-dimensional matrix. There is a concomitant decrease in the expression and activity of matrix metalloproteinase-2 (MMP-2), a known factor in GBM invasion and disease severity. Knockdown of Necl-5 diminishes basal activation of Akt, an established mediator of MMP-2 expression in gliomas. Knockdown of Necl-5 also limits the maximal Akt activation in response to vitronectin, which requires the activity of Integrin-linked kinase (ILK). During migration, Necl-5, Akt and ILK co-localize at focal contacts at the leading edge of the plasma membrane, suggesting that these molecules may act to integrate Akt signaling at the leading edge to induce MMP-2 expression. By virtue of its restricted expression in GBM and its role in invasion, Necl-5 may be an attractive target for limiting MMP-2 production in glioblastoma, and therefore limiting dispersal.

CXCL12-induced glioblastoma cell migration requires intermediate conductance Ca2+-activated K+ channel activity

The activation of ion channels is crucial during cell movement, including glioblastoma cell invasion in the brain parenchyma. In this context, we describe for the first time the contribution of intermediate conductance Ca2+-activated K (IKCa) channel activity in the chemotactic response of human glioblastoma cell lines, primary cultures, and freshly dissociated tissues to CXC chemokine ligand 12 (CXCL12), a chemokine whose expression in glioblastoma has been correlated with its invasive capacity. We show that blockade of the IKCa channel with its specific inhibitor 1-[(2-chlorophenyl) diphenylmethyl]-1 H-pyrazole (TRAM-34) or IKCa channel silencing by short hairpin RNA (shRNA) completely abolished CXCL12-induced cell migration. We further demonstrate that this is not a general mechanism in glioblastoma cell migration since epidermal growth factor (EGF), which also activates IKCa channels in the glioblastoma-derived cell line GL15, stimulate cell chemotaxis even if the IKCa channels have been blocked or silenced. Furthermore, we demonstrate that both CXCL12 and EGF induce Ca2+ mobilization and IKCa channel activation but only CXCL12 induces a long-term upregulation of the IKCa channel activity. Furthermore, the Ca2+-chelating agent BAPTA-AM abolished the CXCL12-induced, but not the EGF-induced, glioblastoma cell chemotaxis. In addition, we demonstrate that the extracellular signal-regulated kinase (ERK)1/2 pathway is only partially implicated in the modulation of CXCL12-induced glioblastoma cell movement, whereas the phosphoinositol-3 kinase (PI3K) pathway is not involved. In contrast, EGF-induced glioblastoma migration requires both ERK1/2 and PI3K activity. All together these findings suggest that the efficacy of glioblastoma invasiveness might be related to an array of nonoverlapping mechanisms activated by different chemotactic agents.

Delayed growth of glioma by Scutellaria flavonoids involve inhibition of Akt, GSK-3 and NF-κB signaling

Plants of the genus Scutellaria constitute one of the common components of Eastern as well as traditional American medicine against various human diseases, including cancer. In this study, we examined the in vivo anti-glioma activity of a leaf extract of Scutellaria ocmulgee (SocL) while also exploring their potential molecular mechanisms of action. Oral administration of SocL extract delayed the growth of F98 glioma in F344 rats, both in intracranial and subcutaneous tumor models. Immunohistochemistry revealed inhibition of Akt, GSK-3α/β and NF-κB phosphorylation in the subcutaneous tumors following treatment with Scutellaria. The SocL extract as well as the constituent flavonoid wogonin also showed dose- and time-dependent inhibition of Akt, GSK-3α/β and NF-κB in F98 cell cultures in vitro, as determined by western blot analysis. Pharmacologic inhibitors of PI3K and NF-κB also significantly inhibited the in vitro proliferation of F98 glioma cells, indicating the key role of these signaling molecules in the growth of malignant gliomas. Transfection of F98 cells with constitutively active mutant of AKT (AKT/CA), however, did not significantly reverse Scutellaria-mediated inhibition of proliferation, indicating that Scutellaria flavonoids either directly inhibited Akt kinase activity or acted downstream of Akt. In vitro Akt kinase assay demonstrated that the SocL extract or wogonin could indeed bind to Akt and inhibit its kinase activity. This study provides the first in vivo evidence and mechanistic support for anti-glioma activity of Scutellaria flavonoids and has implications in potential usage of Scutellaria flavonoids in adjuvant therapy for malignant tumors, including gliomas.

The role of matrix metalloproteinases in the pathophysiology and progression of human nervous system malignancies: a chance for the development of targeted therapeutic approaches?

BACKGROUND

Matrix metalloproteinases (MMPs) are a group of zinc- dependent endopeptidases involved in the degradation of extracellular matrix components. MMPs have been implicated in a wide variety of physiological processes, such as angiogenesis, wound healing and tissue remodeling. However, recent studies have revealed a significant role for MMPs in tumorigenesis pathophysiology and prediction of patients' clinical outcome. Alterations in the regulation of MMP expression are thought to play an important role in the development and progression of central nervous system (CNS) malignancies.

OBJECTIVE/METHODS

This study provides an up-to-date review of the literature on the pathophysiologic involvement of MMPs in the development and progression of human CNS malignancies, as well as the potential use of natural and/or synthetic MMP-inhibitors (MMPIs) as a targeted therapeutic approach to this group of neoplasms.

RESULTS/CONCLUSIONS

The currently available data provide clear evidence for the involvement of MMPs in the pathophysiology of astrocytomas, glioblastomas, meningiomas, medulloblastomas/primitive neuroectodermal tumors and pituitary tumors. The use of MMPIs in the treatment of CNS malignancies has, until now, reached controversial (but mainly disappointing) results that can nevertheless provide the basis for further investigation. The co-administration of other agents, the use of surgery and/or radiation, and elimination of the MMPIs-induced adverse effects, as well as the use of antisense technology, might be the tools by which the natural and synthetic MMPIs could find their place in everyday clinical practice for the management of CNS malignancies.

Phosphatidylinositol 3-kinase/AKT pathway regulates the endoplasmic reticulum to golgi traffic of ceramide in glioma cells: a link between lipid signaling pathways involved in the control of cell survival

Different lines of evidence indicate that both aberrant activation of the phosphatidylinositol 3-OH kinase (PI3K)/Akt survival pathway and down-regulation of the death mediator ceramide play a critical role in the aggressive behavior, apoptosis resistance, and adverse clinical outcome of glioblastoma multiforme. Furthermore, the inhibition of the PI3K/Akt pathway and the up-regulation of ceramide have been found functional to the activity of many cytotoxic treatments against glioma cell lines and glioblastomas as well. A reciprocal control between PI3K/Akt and ceramide signaling in glioma cell survival/death is suggested by data demonstrating a protective role of PI3K/Akt on ceramide-induced cell death in glial cells. In this study we investigated the role of the PI3K/Akt pathway in the regulation of the ceramide metabolism in C6 glioma cells, a cell line in which the PI3K/Akt pathway is constitutively activated. Metabolic experiments performed with different radioactive metabolic precursors of sphingolipids and microscopy studies with fluorescent ceramides demonstrated that the chemical inhibition of PI3K and the transfection with a dominant negative Akt strongly inhibited ceramide utilization for the biosynthesis of complex sphingolipids by controlling the endoplasmic reticulum (ER) to Golgi vesicular transport of ceramide. These findings constitute the first evidence for a PI3K/Akt-dependent regulation of vesicle-mediated movements of ceramide in the ER-Golgi district. Moreover, the findings also suggest the activation of the PI3K/Akt pathway as crucial to coordinate the biosynthesis of membrane complex sphingolipids with cell proliferation and growth and/or to maintain low ceramide levels, especially as concerns those treatments that promote ceramide biosynthesis in the ER.

Inhibition of angiogenesis and invasion in malignant gliomas

Malignant gliomas confer a dismal prognosis. As the molecular events that underlie tumor angiogenesis are elucidated, angiogenesis inhibition is emerging as a promising therapy for recurrent and newly diagnosed tumors. Data from animal studies suggest that angiogenesis inhibition may promote an invasive phenotype in tumor cells. This may represent an important mechanism of resistance to antiangiogenic therapies. Recent studies have begun to clarify the mechanisms by which glioma cells detach from the tumor mass, remodel the extracellular matrix and infiltrate normal brain. An array of potential therapeutic targets exists. Combination therapy with antiangiogenic and novel anti-invasion agents is a promising approach that may produce a synergistic antitumor effect and a survival benefit for patients with these devastating tumors.

The combination of novel low molecular weight inhibitors of RAF (LBT613) and target of rapamycin (RAD001) decreases glioma proliferation and invasion

Monotherapies have proven largely ineffective for the treatment of glioblastomas, suggesting that increased patient benefit may be achieved by combining therapies. Two protumorigenic pathways known to be active in glioblastoma include RAS/RAF/mitogen-activated protein kinase and phosphatidylinositol 3-kinase/AKT/target of rapamycin (TOR). We investigated the efficacy of a combination of novel low molecular weight inhibitors LBT613 and RAD001 (everolimus), which were designed to target RAF and TOR, respectively. LBT613 decreased phosphorylation of extracellular signal-regulated kinase 1 and 2, downstream effectors of RAF, in a human glioma cell line. RAD001 resulted in decreased phosphorylation of the TOR effector S6. To determine if targeting RAF and TOR activities could result in decreased protumorigenic glioma cellular behaviors, we evaluated the abilities of LBT613 and RAD001 to affect the proliferation, migration, and invasion of human glioma cells. Treatment with either LBT613 or RAD001 alone significantly decreased the proliferation of multiple human glioma cell lines. Furthermore, LBT613 and RAD001 in combination synergized to decrease glioma cell proliferation in association with G(1) cell cycle arrest. Glioma invasion is a critical contributor to tumor malignancy. The combination of LBT613 and RAD001 inhibited the invasion of human glioma cells through Matrigel to a greater degree than treatment with either drug alone. These data suggest that the combination of LBT613 and RAD001 reduces glioma cell proliferation and invasion and support examination of the combination of RAF and TOR inhibitors for the treatment of human glioblastoma patients.