Novel animal glioma models that separately exhibit two different invasive and angiogenic phenotypes of human glioblastomas

Potential therapeutic efficiency of pan-ERBB inhibitors for canine glioma

Canine glioma is one of the most common brain tumors with poor prognosis, making effective chemotherapy highly desirable. Previous studies have suggested that ERBB4, a signaling molecule involving one of the epidermal growth factor receptors (EGFR), may be a promising therapeutic target. In this study, the anti-tumor effects of pan-ERBB inhibitors, which can inhibit the phosphorylation of ERBB4, were evaluated both in vitro and in vivo using a canine glioblastoma cell line. The results demonstrated that both afatinib and dacomitinib effectively reduced the expression of phosphorylated ERBB4, and significantly decreased the number of viable cells, ultimately prolonging the survival time of orthotopically xenografted mice. Further downstream of ERBB4, afatinib was found to suppress the expression of phosphorylated Akt and phosphorylated Extracellular signal-related kinases1 and 2 (ERK1/2) and induced apoptotic cell death. Thus, pan-ERBB inhibition is a promising therapeutic strategy for the treatment of canine gliomas.

Evaluation of in vitro intrinsic radiosensitivity and characterization of five canine high-grade glioma cell lines

Glioma is the most common primary brain tumor in dogs and predominantly affects brachycephalic breeds. Diagnosis relies on CT or MRI imaging, and the proposed treatments include surgical resection, chemotherapy, and radiotherapy depending on the tumor's location. Canine glioma from domestic dogs could be used as a more powerful model to study radiotherapy for human glioma than the murine model. Indeed, (i) contrary to mice, immunocompetent dogs develop spontaneous glioma, (ii) the canine brain structure is closer to human than mice, and (iii) domestic dogs are exposed to the same environmental factors than humans. Moreover, imaging techniques and radiation therapy used in human medicine can be applied to dogs, facilitating the direct transposition of results. The objective of this study is to fully characterize 5 canine glioma cell lines and to evaluate their intrinsic radiosensitivity. Canine cell lines present numerous analogies between the data obtained during this study on different glioma cell lines in dogs. Cell morphology is identical, such as doubling time, clonality test and karyotype. Immunohistochemical study of surface proteins, directly on cell lines and after stereotaxic injection in mice also reveals close similarity. Radiosensitivity profile of canine glial cells present high profile of radioresistance.

Effect of the NFL-TBS.40-63 peptide on canine glioblastoma cells

Glioblastomas are the most frequent and aggressive cancer of the nervous system. The standard treatment is composed of neurosurgery followed by radiotherapy and chemotherapy, but the median survival remains very low. The NFL-TBS.40-63 peptide, also known as NFL-peptide, is capable to specifically penetrating all glioblastoma cell lines tested so far (rat, mouse and human), where it alters their microtubule network. Consequently, the peptide inhibits selectively the in vitro cell division of glioblastoma cells and their tumor development in vivo. When lipid nanocapsules are functionalized with the NFL-peptide, their uptake is targeted into glioblastoma cells both in vitro and in vivo. Here, we evaluated the impact of the NFL-peptide on J3T cells derived from a canine spontaneous glioblastoma, and its activity when functionalized to nanocapsules. Both flow cytometry and confocal microscopy experiments indicate that the NFL-peptide interacts with these cells and affects their biology, but it cannot enter in cells. By functionalizing lipid nanoparticles with the NFL-peptide, their uptake is also increased, while the peptide stays outside. This investigation reveals similarities and major differences between these canine cells and other glioblastoma cells, which are important aspects to consider when using this type of drug delivery system or performing pre-clinical studies with this animal model.

The NRG3/ERBB4 signaling cascade as a novel therapeutic target for canine glioma

Canine glioma is a common brain tumor with poor prognosis despite surgery and/or radiation therapy. Therefore, newer and more effective treatment modalities are needed. Neuregulin 3 (NRG3) has known to be a ligand of ERBB4. This study aimed to investigate the usefulness of the NRG3/ERBB4 signaling cascade as a novel therapeutic target in canine glioma. We found out that microRNA (miR)-190a was downregulated in canine brain tumor tissues, including glioma and meningioma. miR-190a directly targeted NRG3 and inhibited the growth of canine glioma cells. The level of p-Akt, which is a downstream target of ERBB4 signaling, was decreased by transfection with miR-190a. NRG3 silencing also suppressed cell growth and decreased the levels of p-Akt and p-ERK1/2, and NRG3 overexpression exhibited opposed effects in canine glioma J3T-1 cells. The mRNA level of erbb4 was significantly upregulated in glioma tissues compared with that in normal brain tissues and meningioma tissues. Furthermore, compared with gefitinib and lapatinib, afatinib exerted a greater inhibitory effect on the growth of canine glioma cells. In conclusion, NRG3/ERBB4 signaling is negatively regulated by miR-190a and contributes to the growth of canine glioma cells, indicating that it may be a promising therapeutic target in canine glioma.

Annexin A2-STAT3-Oncostatin M receptor axis drives phenotypic and mesenchymal changes in glioblastoma

Glioblastoma (GBM) is characterized by extensive tumor cell invasion, angiogenesis, and proliferation. We previously established subclones of GBM cells with distinct invasive phenotypes and identified annexin A2 (ANXA2) as an activator of angiogenesis and perivascular invasion. Here, we further explored the role of ANXA2 in regulating phenotypic transition in GBM. We identified oncostatin M receptor (OSMR) as a key ANXA2 target gene in GBM utilizing microarray analysis and hierarchical clustering analysis of the Ivy Glioblastoma Atlas Project and The Cancer Genome Atlas datasets. Overexpression of ANXA2 in GBM cells increased the expression of OSMR and phosphorylated signal transducer and activator of transcription 3 (STAT3) and enhanced cell invasion, angiogenesis, proliferation, and mesenchymal transition. Silencing of OSMR reversed the ANXA2-induced phenotype, and STAT3 knockdown reduced OSMR protein expression. Exposure of GBM cells to hypoxic conditions activated the ANXA2–STAT3–OSMR signaling axis. Mice bearing ANXA2-overexpressing GBM exhibited shorter survival times compared with control tumor-bearing mice, whereas OSMR knockdown increased the survival time and diminished ANXA2-mediated tumor invasion, angiogenesis, and growth. Further, we uncovered a significant relationship between ANXA2 and OSMR expression in clinical GBM specimens, and demonstrated their correlation with tumor histopathology and patient prognosis. Our results indicate that the ANXA2–STAT3–OSMR axis regulates malignant phenotypic changes and mesenchymal transition in GBM, suggesting that this axis is a promising therapeutic target to treat GBM aggressiveness.

Methods for in vitro modeling of glioma invasion: Choosing tools to meet the need

Widespread tumor cell invasion is a fundamental property of diffuse gliomas and is ultimately responsible for their poor prognosis. A greater understanding of basic mechanisms underlying glioma invasion is needed to provide insights into therapies that could potentially counteract them. While none of the currently available in vitro models can fully recapitulate the complex interactions of glioma cells within the brain tumor microenvironment, if chosen and developed appropriately, these models can provide controlled experimental settings to study molecular and cellular phenomena that are challenging or impossible to model in vivo. Therefore, selecting the most appropriate in vitro model, together with its inherent advantages and limitations, for specific hypotheses and experimental questions achieves primary significance. In this review, we describe and discuss commonly used methods for modeling and studying glioma invasion in vitro, including platforms, matrices, cell culture, and visualization techniques, so that choices for experimental approach are informed and optimal.

Flexible, sticky, and biodegradable wireless device for drug delivery to brain tumors

Implantation of biodegradable wafers near the brain surgery site to deliver anti-cancer agents which target residual tumor cells by bypassing the blood-brain barrier has been a promising method for brain tumor treatment. However, further improvement in the prognosis is still necessary. We herein present novel materials and device technologies for drug delivery to brain tumors, i.e., a flexible, sticky, and biodegradable drug-loaded patch integrated with wireless electronics for controlled intracranial drug delivery through mild-thermic actuation. The flexible and bifacially-designed sticky/hydrophobic device allows conformal adhesion on the brain surgery site and provides spatially-controlled and temporarily-extended drug delivery to brain tumors while minimizing unintended drug leakage to the cerebrospinal fluid. Biodegradation of the entire device minimizes potential neurological side-effects. Application of the device to the mouse model confirms tumor volume suppression and improved survival rate. Demonstration in a large animal model (canine model) exhibited its potential for human application.

There is a need to further improve the efficacy of biodegradable wafers used in surgically treated brain tumors. Here, the authors report a flexible, biodegradable wireless device capable of adhesion to surgical site for optimal drug delivery upon mild-thermic actuation and report therapeutic efficacy in mouse and canine tumor models.

Visualization of spatiotemporal dynamics of human glioma stem cell invasion

Glioblastoma exhibits phenotypic and genetic heterogeneity, aggressive invasiveness, therapeutic resistance, and tumor recurrence, which can be explained by the existence of glioma stem cells (GSCs). In this study, we visualized the spatiotemporal dynamics of invasion of human GSCs in an orthotopic xenograft mouse model using time-lapse imaging of organotypic brain slice cultures and three-dimensional imaging of optically cleared whole brains. GSCs implanted in the striatum exhibited directional migration toward axon bundles, perivascular area, and the subventricular zone around the inferior horn of the lateral ventricle. GSCs migrated in a helical pattern around axon bundles in the striatum and invaded broadly in both the rostral and caudal directions. GSCs in the corpus callosum migrated more rapidly and unidirectionally toward the contralateral side with pseudopod extension. These characteristics of GSC invasion shared histological features observed in glioblastoma patients. Spatiotemporal visualization techniques can contribute to the elucidation of the mechanisms underlying GSC invasion that may lead to the development of effective therapy for glioblastoma.

Investigation of hypoxia conditions using oxygen-enhanced magnetic resonance imaging measurements in glioma models

The objective of this study was to determine whether using oxygen-enhanced magnetic resonance imaging (OE-MRI) to assess hypoxia is feasible and whether historical measurements, pO2 changes, and percentage of signal intensity changes (PSIC) are correlated in an animal model of glioma. A total of 25 Sprague-Dawley rats were used to establish C6 brain or subcutaneous glioma model. Nine rats with brain gliomas underwent OE-MRI followed by histopathologic analysis to assess microvessel density and hypoxia. Another 11 rats were underwent OE-MRI and were followed for a survival analysis. Time-T1-weighted MR signal intensity (SI) curves and PSIC maps were derived from the OE-MRI data. High-regions of interests (ROI-h; PSIC > 10%) and low-ROIs (ROI-l; PSIC < 10%) were defined on the PSIC maps. To validate the PSIC map for identifying tumor hypoxia, we subjected an additional 5 rats with subcutaneous glioma to OE-MRI and pO2 measurements. All tumors showed regional heterogeneity on the PSIC maps. For the brain tumors, the time-SI curves for the ROIs-h showed a greater increase in SI than those for the ROIs-l did. The percentage of tumor area with a low PSIC was significantly correlated with the percentage of hypoxia staining and necrosis (r =0.71; P<0.05). ROIs with a higher PSIC typically had more vessels (r=0.88; P<0.05). A significant difference in survival was shown (log-rank P = 0.035). The time-pO2 curves of the subcutaneous tumors were similar to the time-SI curves. PSIC was significantly correlated with pO2 changes (r =0.82; P<0.05). These findings suggest that OE-MRI measurements can be used to assess hypoxia in C6 glioma models. In these models, the PSIC value was correlated with survival, indicating that PSIC could serve as a prognostic marker for glioma.

Molecular crosstalk between tumour and brain parenchyma instructs histopathological features in glioblastoma

The histopathological and molecular heterogeneity of glioblastomas represents a major obstacle for effective therapies. Glioblastomas do not develop autonomously, but evolve in a unique environment that adapts to the growing tumour mass and contributes to the malignancy of these neoplasms. Here, we show that patient-derived glioblastoma xenografts generated in the mouse brain from organotypic spheroids reproducibly give rise to three different histological phenotypes: (i) a highly invasive phenotype with an apparent normal brain vasculature, (ii) a highly angiogenic phenotype displaying microvascular proliferation and necrosis and (iii) an intermediate phenotype combining features of invasion and vessel abnormalities. These phenotypic differences were visible during early phases of tumour development suggesting an early instructive role of tumour cells on the brain parenchyma. Conversely, we found that tumour-instructed stromal cells differentially influenced tumour cell proliferation and migration in vitro, indicating a reciprocal crosstalk between neoplastic and non-neoplastic cells. We did not detect any transdifferentiation of tumour cells into endothelial cells. Cell type-specific transcriptomic analysis of tumour and endothelial cells revealed a strong phenotype-specific molecular conversion between the two cell types, suggesting co-evolution of tumour and endothelial cells. Integrative bioinformatic analysis confirmed the reciprocal crosstalk between tumour and microenvironment and suggested a key role for TGFβ1 and extracellular matrix proteins as major interaction modules that shape glioblastoma progression. These data provide novel insight into tumour-host interactions and identify novel stroma-specific targets that may play a role in combinatorial treatment strategies against glioblastoma.

Fibroblast growth factor 13 regulates glioma cell invasion and is important for bevacizumab-induced glioma invasion

Glioblastoma has the poorest prognosis, and is characterized by excessive invasion and angiogenesis. To determine the invasive mechanisms, we previously used two glioma cell lines (J3T-1 and J3T-2) with different invasive phenotypes. The J3T-1 showed abundant angiogenesis and tumor cell invasion around neovasculature, while J3T-2 showed diffuse cell infiltration into surrounding healthy parenchyma. Microarray analyses were used to identify invasion-related genes in J3T-2 cells, and the expressed genes and their intracellular and intratumoral distribution patterns were evaluated in J3T-2 cell lines, human glioma cell lines, human glioblastoma stem cells and human glioblastoma specimens. To determine the role of the invasion-related genes, invasive activities were evaluated in vitro and in vivo. Fibroblast growth factor 13 (FGF13) was overexpressed in J3T-2 cells compared to J3T-1 cells, and in human glioma cell lines, human glioblastoma stem cells and human glioblastoma specimens, when compared to that of normal human astrocytes. Immunohistochemical staining and the RNA-seq (sequencing) data from the IVY Glioblastoma Atlas Project showed FGF13 expression in glioma cells in the invasive edges of tumor specimens. Also, the intracellular distribution was mainly in the cytoplasm of tumor cells and colocalized with tubulin. Overexpression of FGF13 stabilized tubulin dynamics in vitro and knockdown of FGF13 decreased glioma invasion both in vitro and in vivo and prolonged overall survival of several xenograft models. FGF13 was negatively regulated by hypoxic condition. Silencing of FGF13 also decreased in vivo bevacizumab-induced glioma invasion. In conclusion, FGF13 regulated glioma cell invasion and bevacizumab-induced glioma invasion, and could be a novel target for glioma treatment.

Dogs are man's best friend: in sickness and in health

With the median survival of 14.6 months following best available standard of care, malignant gliomas (MGs) remain one of the biggest therapeutic challenges of the modern time. Although the last several decades have witnessed tremendous advancement in our understanding of MG and evolution of many successful preclinical therapeutic strategies, even the most successful preclinical therapeutic strategies often fail to cross the phase I/II clinical trial threshold. One of the significant, but less commonly discussed, barriers in developing effective glioma therapy is the lack of a robust preclinical model. For the last 30 years, rodent orthotopic xenograft models have been extensively used in the preclinical setting. Although they provide a good basic model for understanding tumor biology, their value in successfully translating preclinical therapeutic triumph into clinical success is extremely poor. Companion dogs, which share the same environmental stress as their human counterparts, also spontaneously develop MGs. Dog gliomas that develop spontaneously in an immunocompetent host are very similar to human gliomas and potentially provide a stronger platform for validating the efficacy of therapeutic strategies proven successful in preclinical mouse models. Integrating this model can accelerate development of effective therapeutic options that will benefit both human subjects and pet dogs.

Epidermal growth factor receptor activity is elevated in glioma cancer stem cells and is required to maintain chemotherapy and radiation resistance

Glioblastoma remains among the most aggressive of all human and canine malignancies, displaying high mortality rates and limited treatment options. We propose that given the similarities between canine and human gliomas, such as incidence of occurrence, histopathology, molecular characteristics, and response to therapy, that canine gliomas are a natural model of the human disease. A range of human and canine tumours have been shown to harbor specific subpopulations of cells with stem cell-like properties that initiate and maintain neoplasticity while resisting conventional therapies. Here, we show that both canine and human glioma cell lines contain a small population of cancer stem cells (CSCs), and by molecular profiling highlight the important role of the epidermal growth factor receptor (EGFR) pathway in canine CSCs. EGFR signaling is crucial in the regulation of cancer cell proliferation, migration and survival. To date EGFR-targeted interventions alone have been largely ineffective. Our findings confirm that specifically inhibiting EGFR signaling alone has no significant effect on the viability of CSCs. However inhibition of EGFR did enhance the chemo- and radio-sensitivity of both canine and human glioma CSCs, enabling this resistant, tumourigenic population of cells to be effectively targeted by conventional therapies.

Microscopic DTI accurately identifies early glioma cell migration: correlation with multimodal imaging in a new glioma stem cell model

Monitoring glioma cell infiltration in the brain is critical for diagnosis and therapy. Using a new glioma Glio6 mouse model derived from human stem cells we show how diffusion tensor imaging (DTI) may predict glioma cell migration/invasion. In vivo multiparametric MRI was performed at one, two and three months of Glio6 glioma growth (Glio6 (n = 6), sham (n = 3)). This longitudinal study reveals the existence of a time window to study glioma cell/migration/invasion selectively. Indeed, at two months only Glio6 cell invasion was detected, while tumor mass formation, edema, blood-brain barrier leakage and tumor angiogenesis were detected later, at three months. To robustly confirm the potential of DTI for detecting glioma cell migration/invasion, a microscopic 3D-DTI (80 μm isotropic spatial resolution) technique was developed and applied to fixed mouse brains (Glio6 (n = 6), sham (n = 3)). DTI changes were predominant in the corpus callosum (CC), a known path of cell migration. Fractional anisotropy (FA) and perpendicular diffusivity (D_⊥ ) changes derived from ex vivo microscopic 3D-DTI were significant at two months of tumor growth. In the caudate putamen an FA increase of +38% (p < 0.001) was observed, while in the CC a - 28% decrease in FA (p < 0.005) and a + 95% increase in D_⊥ (p < 0.005) were observed. In the CC, DTI changes and fluorescent Glio6 cell density obtained by two-photon microscopy in the same brains were correlated (p < 0.001, r = 0.69), validating FA and D_⊥ as early quantitative biomarkers to detect glioma cell migration/invasion. The origin of DTI changes was assessed by electron microscopy of the same tract, showing axon bundle disorganization. During the first two months, Glio6 cells display a migratory phenotype without being associated with the constitution of a brain tumor mass. This offers a unique opportunity to apply microscopic 3D-DTI and to validate DTI parameters FA and D_⊥ as biomarkers for glioma cell invasion.

Phenotypic Transition as a Survival Strategy of Glioma

Malignant glioma is characterized by rapid proliferation, invasion into surrounding central nervous system tissues, and aberrant vascularization. There is increasing evidence that shows gliomas are more complex than previously thought, as each tumor comprises considerable intratumoral heterogeneity with mixtures of genetically and phenotypically distinct subclones. Heterogeneity within and across tumors is recognized as a critical factor that limits therapeutic progress for malignant glioma. Recent genotyping and expression profiling of gliomas has allowed for the creation of classification schemes that assign tumors to subtypes based on similarity to defined expression signatures. Also, malignant gliomas frequently shift their biological features upon recurrence and progression. The ability of glioma cells to resist adverse conditions such as hypoxia and metabolic stress is necessary for sustained tumor growth and strongly influences tumor behaviors. In general, glioma cells are in one of two phenotypic categories: higher proliferative activity with angiogenesis, or higher migratory activity with attenuated proliferative ability. Further, they switch phenotypic categories depending on the situation. To date, a multidimensional approach has been employed to clarify the mechanisms of phenotypic shift of glioma. Various molecular and signaling pathways are involved in phenotypic shifts of glioma, possibly with crosstalk between them. In this review, we discuss molecular and phenotypic heterogeneity of glioma cells and mechanisms of phenotypic shifts in regard to the glioma proliferation, angiogenesis, and invasion. A better understanding of the molecular mechanisms that underlie phenotypic shifts of glioma may provide new insights into targeted therapeutic strategies.

Annexin A2 regulates angiogenesis and invasion phenotypes of malignant glioma

We have established a pair of animal models (J3T-1 and J3T-2) with different invasive and angiogenic phenotypes, and demonstrated that annexin A2 is expressed at higher levels in J3T-1 than J3T-2 cells. The function of annexin A2 in relation to angiogenesis and invasion was investigated using these models. Stable silencing or overexpression of annexin A2 in J3T-1 and J3T-2 cells (J3T-1shA and J3T-2A cells) was established and used. Thirty human glioblastoma samples were evaluated for expression of annexin A2, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF). Immunohistochemical and quantitative reverse-transcription polymerase chain reaction analyses revealed higher expression of annexin A2, VEGF and PDGF in J3T-1 and J3T-2A cells. Cultured J3T-1 and J3T-2A cells exhibited higher adhesive ability to endothelial cells. Histopathological analysis of animal brain tumors revealed that J3T-1 and J3T-2A tumors displayed marked angiogenesis and invasion along the neovasculature, whereas J3T-2 and J3T-1shA tumors exhibited diffuse, infiltrative invasion without angiogenesis. Positive expression of annexin A2 was observed in tumor cells surrounding dilated vessels in 25/30 human glioblastoma specimens. Our results reveal that the phenotype of glioma invasion is closely related to angiogenesis. We identify annexin A2 as a factor regulating angiogenesis and invasion of malignant gliomas.

Bevacizumab in Japanese patients with malignant glioma: from basic research to clinical trial

An antiangiogenic approach is especially suitable for the treatment of malignant gliomas. Recently, two large clinical trials in newly diagnosed glioblastoma (the Avastin in Glioblastoma study and Radiation Therapy Oncology Group 0825 study) showed a 3- to 4-month prolongation of progression-free survival (PFS) with bevacizumab, but no significant effect on overall survival (OS). Japan is the first, and so far only, country to approve the use of bevacizumab in newly diagnosed glioblastoma in combination with radiotherapy and temozolomide chemotherapy. The drug is also approved for use as monotherapy for recurrent glioblastoma and certain other types of high-grade glioma after previous therapy. The effectiveness of bevacizumab on Japanese malignant glioma patients was reviewed. The Phase II clinical trial demonstrated that the PFS with bevacizumab alone was 34% at 6 months and 3.3 months at median for 32 patients with recurrent malignant gliomas. In the Avastin in Glioblastoma study, 44 Japanese patients were registered from Japan. PFS and OS for bevacizumab combined with standard temozolomide and radiotherapy were 12.2 months and 29.2 months at median, respectively, for the patients with newly diagnosed glioblastoma. PFS and OS tended to be longer for those treated with bevacizumab than for those not treated with the drug. In addition, biomarkers of bevacizumab effectiveness were investigated in Japanese patients. Vascular endothelial growth factor concentration, matrix metalloproteinase 9 activities in urine, and apparent diffusion coefficient values on magnetic resonance imaging may be biomarkers that predict patient prognosis. Finally, novel experiments for vascular endothelial growth factor antibody action were described; these include the induction of glioma cell apoptosis, an antibody treatment failure model, and a study of the synergistic effect with chemotherapeutic agents.

Integrin inhibitor suppresses bevacizumab-induced glioma invasion

Glioblastoma is known to secrete high levels of vascular endothelial growth factor (VEGF), and clinical studies with bevacizumab, a monoclonal antibody to VEGF, have demonstrated convincing therapeutic benefits in glioblastoma patients. However, its induction of invasive proliferation has also been reported. We examined the effects of treatment with cilengitide, an integrin inhibitor, on bevacizumab-induced invasive changes in glioma. U87ΔEGFR cells were stereotactically injected into the brain of nude mice or rats. Five days after tumor implantation, cilengitide and bevacizumab were administered intraperitoneally three times a week. At 18 days after tumor implantation, the brains were removed and observed histopathologically. Next, the bevacizumab and cilengitide combination group was compared to the bevacizumab monotherapy group using microarray analysis. Bevacizumab treatment led to increased cell invasion in spite of decreased angiogenesis. When the rats were treated with a combination of bevacizumab and cilengitide, the depth of tumor invasion was significantly less than with only bevacizumab. Pathway analysis demonstrated the inhibition of invasion-associated genes such as the integrin-mediated cell adhesion pathway in the combination group. This study showed that the combination of bevacizumab with cilengitide exerted its anti-invasive effect. The elucidation of this mechanism might contribute to the treatment of bevacizumab-refractory glioma.

Mechanisms of tumor development and anti-angiogenic therapy in glioblastoma multiforme

Despite advances in surgical and medical therapy, glioblastoma multiforme (GBM) remains a fatal disease. There has been no significant increase in survival for patients with this disease over the last 20 years. Tumor vasculature formation and glioma cell invasion along the white matter tracts both play a pivotal role in glioma development. Angiogenesis and invasion are the major factors believed to be responsible for treatment resistance in tumors, and a better understanding of the glioma invasion and angiogenesis mechanisms will lead to the development of potential new treatments. In this review, we focus on the molecular characteristics of angiogenesis and invasion in human malignant glioma. We discuss bevacizumab and cilengitide, which are used to inhibit angiogenesis in GBM.

Cilengitide treatment for malignant glioma: current status and future direction

Malignant glioma is the most common primary brain tumor and accounts for the majority of diagnoses. Treatment has involved a combination of surgery, radiation, and chemotherapy, yet these modalities rarely extend the life of the patient to more than one year from diagnosis. Integrins are expressed in tumor cells and tumor endothelial cells, and are important in angiogenesis and invasion in glioma. αvβ3 and αvβ5 integrins regulate cell adhesion, and inhibitors of these integrins suppress tumor growth in certain pre-clinical models. Several integrin-targeted drugs are in clinical trials as potential compounds for the treatment of cancer. Among them, cilengitide is a novel integrin antagonist for the treatment of glioblastoma. The multimodal anti-glioma effects are based on its cytotoxic, anti-angiogenic, anti-invasive, and synergetic effects. Preclinical studies showed a promising synergy between cilengitide and radiochemotherapy in order to normalize tumor vasculature and attenuate tumor invasion. Cilengitide is currently being assessed in phase III trials for patients with glioblastoma multiforme and in phase II trials for other types of cancers, demonstrating promising therapeutic outcomes to date. The results of these and other clinical studies are expected with great hope and interest. A more clear understanding of the benefits and pitfalls of each approach can then lead to the design of strategies to derive maximal benefit from these therapies.

Proteomics-based analysis of invasion-related proteins in malignant gliomas

One of the insidious biological features of gliomas is their potential to extensively invade normal brain tissue, yet molecular mechanisms that dictate this locally invasive behavior remain poorly understood. To investigate the molecular basis of invasion by malignant gliomas, proteomic analysis was performed using a pair of canine glioma subclones - J3T-1 and J3T-2 - that show different invasion phenotypes in rat brains but have similar genetic backgrounds. Two-dimensional protein electrophoresis of whole-cell lysates of J3T-1 (angiogenesis-dependent invasion phenotype) and J3T-2 (angiogenesis-independent invasion phenotype) was performed. Twenty-two distinct spots were recognized when significant alteration was defined as more than 1.5-fold change in spot intensity between J3T-1 and J3T-2. Four proteins that demonstrated increased expression in J3T-1, and 14 proteins that demonstrated increased expression in J3T-2 were identified using liquid chromatography-mass spectrometry analysis. One of the proteins identified was annexin A2, which was expressed at higher levels in J3T-1 than in J3T-2. The higher expression of annexin A2 in J3T-1 was corroborated by quantitative RT-PCR of the cultured cells and immunohistochemical staining of the rat brain tumors. Moreover, immunohistochemical analysis of human glioblastoma specimens showed that annexin A2 was expressed at high levels in the tumor cells that formed clusters around dilated vessels. These results reveal differences in the proteomic profiles between these two cell lines that might correlate with their different invasion profiles. Thus, annexin A2 may be related to angiogenesis-dependent invasion.

Bimodal anti-glioma mechanisms of cilengitide demonstrated by novel invasive glioma models

Integrins are expressed in tumor cells and tumor endothelial cells, and likely play important roles in glioma angiogenesis and invasion. We investigated the anti-glioma mechanisms of cilengitide (EMD121974), an αvβ3 integrin inhibitor, utilizing the novel invasive glioma models, J3T-1 and J3T-2. Immunohistochemical staining of cells in culture and brain tumors in rats revealed positive αvβ3 integrin expression in J3T-2 cells and tumor endothelial cells, but not in J3T-1 cells. Established J3T-1 and J3T-2 orthotopic gliomas in athymic rats were treated with cilengitide or solvent. J3T-1 gliomas showed perivascular tumor cluster formation and angiogenesis, while J3T-2 gliomas showed diffuse single-cell infiltration without obvious angiogenesis. Cilengitide treatment resulted in a significantly decreased diameter of the J3T-1 tumor vessel clusters and its core vessels when compared with controls, while an anti-invasive effect was shown in the J3T-2 glioma with a significant reduction of diffuse cell infiltration around the tumor center. The survival of cilengitide-treated mice harboring J3T-1 tumors was significantly longer than that of control animals (median survival: 57.5 days and 31.8 days, respectively, P < 0.005), while cilengitide had no effect on the survival of mice with J3T-2 tumors (median survival: 48.9 days and 48.5, P = 0.69). Our results indicate that cilengitide exerts a phenotypic anti-tumor effect by inhibiting angiogenesis and glioma cell invasion. These two mechanisms are clearly shown by the experimental treatment of two different animal invasive glioma models.

Antiangiogenic therapy for glioma

Currently, antiangiogenic agents are routinely used for the treatment of patients with glioma. However, despite advances in pharmacological and surgical therapy, glioma remains an incurable disease. Indeed, the formation of an abnormal tumor vasculature and the invasion of glioma cells along neuronal tracts are proposed to comprise the major factors that are attributed to the therapeutic resistance of these tumors. The development of curative therapeutic modalities for the treatment of glioma requires further investigation of the molecular mechanisms regulating angiogenesis and invasion. In this review, we discuss the molecular characteristics of angiogenesis and invasion in human malignant glioma, we present several available drugs that are used or can potentially be utilized for the inhibition of angiogenesis in glioma, and we focus our attention on the key mediators of the molecular mechanisms underlying the resistance of glioma to antiangiogenic therapy.