Invasion of experimental rat brain tumor: early morphological changes following microinjection of C6 glioma cells

In vivo C6 glioma models: an update and a guide toward a more effective preclinical evaluation of potential anti-glioblastoma drugs

Glioblastoma multiform (GBM) is the most common primary brain tumor with a poor prognosis and few therapeutic choices. In vivo, tumor models are useful for enhancing knowledge of underlying GBM pathology and developing more effective therapies/agents at the preclinical level, as they recapitulate human brain tumors. The C6 glioma cell line has been one of the most widely used cell lines in neuro-oncology research as they produce tumors that share the most similarities with human GBM regarding genetic, invasion, and expansion profiles and characteristics. This review provides an overview of the distinctive features and the different animal models produced by the C6 cell line. We also highlight specific applications of various C6 in vivo models according to the purpose of the study and offer some technical notes for more convenient/repeatable modeling. This work also includes novel findings discovered in our laboratory, which would further enhance the feasibility of the model in preclinical GBM investigations.

Tumor-specific migration routes of xenotransplanted human glioblastoma cells in mouse brain

The migration of neural progenitor cells (NPCs) to their final destination during development follows well-defined pathways, such as along blood vessels. Cells originating from the highly malignant tumor glioblastoma (GBM) seem to exploit similar routes for infiltrating the brain parenchyma. In this report, we have examined the migration of GBM cells using three-dimensional high-resolution confocal microscopy in brain tumors derived from eight different human GBM cell lines xenografted into immunodeficient mice. The primary invasion routes identified were long-distance migration along white matter tracts and local migration along blood vessels. We found that GBM cells in the majority of tumors (6 out of 8) did not exhibit association with blood vessels. These tumors, derived from low lamin A/C expressing GBM cells, were comparatively highly diffusive and invasive. Conversely, in 2 out of 8 tumors, we noted perivascular invasion and displacement of astrocyte end-feet. These tumors exhibited less diffusive migration, grew as solid tumors, and were distinguished by elevated expression of lamin A/C. We conclude that the migration pattern of glioblastoma is distinctly tumor cell-specific. Furthermore, the ability to invade the confined spaces within white matter tracts may necessitate low expression of lamin A/C, contributing to increased nuclear plasticity. This study highlights the role of GBM heterogeneity in driving the aggressive growth of glioblastoma.

Glucose Infusion Induced Change in Intracellular pH and Its Relationship with Tumor Glycolysis in a C6 Rat Model of Glioblastoma

INTRODUCTION

The reliance on glycolytic metabolism is a hallmark of tumor metabolism. Excess acid and protons are produced, leading to an acidic tumor environment. Therefore, we explored the relationship between the tumor glycolytic metabolism and tissue pH by comparing ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) and hyperpolarized [1-¹³C]pyruvate MR spectroscopy imaging (MRSI) to chemical exchange saturation transfer (CEST) MRI measurements of tumor pH.

METHODS

10⁶ C6 glioma cells were implanted in the brains of male Wistar rats (N = 11) using stereotactic surgery. A 60-min PET acquisition after a bolus of FDG was performed at 11-13 days post implantation, and standardized uptake value (SUV) was calculated. CEST measurements were acquired the following day before and during constant infusion of glucose solution. Tumor intracellular pH (pHi) was evaluated using amine and amide concentration-independent detection (AACID) CEST MRI. The change of pH_i (∆pH_i) was calculated as the difference between pH_i pre- and during glucose infusion. Rats were imaged immediately with hyperpolarized [1-¹³C]pyruvate MRSI. Regional maps of the ratio of Lac:Pyr were acquired. The correlations between SUV, Lac:Pyr ratio, and ∆pH_i were evaluated using Pearson's correlation.

RESULTS

A decrease of 0.14 in pH_i was found after glucose infusion in tumor region. Significant correlations between tumor glycolysis measurements of Lac:Pyr and ∆pH_i within the tumor (ρ = 0.83, P = 0.01) and peritumoral region (ρ = 0.76, P = 0.028) were observed. No significant correlations were found between tumor SUV and ∆pH_i within the tumor (ρ =  - 0.45, P = 0.17) and peritumor regions (ρ =  - 0.6, P = 0.051).

CONCLUSION

AACID detected the changes in pH_i induced by glucose infusion. Significant correlations between tumor glycolytic measurement of Lac:Pyr and tumoral and peritumoral pH_i and ∆pH_i suggest the intrinsic relationship between tumor glycolytic metabolism and the tumor pH environment as well as the peritumor pH environment.

Pioneering models of pediatric brain tumors

Among children and adolescents in the United States (0 to 19 years old), brain and other central nervous system tumors are the second most common types of cancers, surpassed in incidence only by leukemias. Despite significant progress in the diagnosis and treatment modalities, brain cancer remains the leading cause of death in the pediatric population. There is an obvious unfulfilled need to streamline the therapeutic strategies and improve survival for these patients. For that purpose, preclinical models play a pivotal role. Numerous models are currently used in pediatric brain tumor research, including genetically engineered mouse models, patient-derived xenografts and cell lines, and newer models that utilize novel technologies such as genome engineering and organoids. Furthermore, extensive studies by the Children's Brain Tumor Network (CBTN) researchers and others have revealed multiomic landscapes of variable pediatric brain tumors. Combined with such integrative data, these novel technologies have enabled numerous applicable models. Genome engineering, including CRISPR/Cas9, expanded the flexibility of modeling. Models generated through genome engineering enabled studying particular genetic alterations in clean isogenic backgrounds, facilitating the dissection of functional mechanisms of those mutations in tumor biology. Organoids have been applied to study tumor-to-tumor-microenvironment interactions and to address developmental aspects of tumorigenesis, which is essential in some pediatric brain tumors. Other modalities, such as humanized mouse models, could potentially be applied to pediatric brain tumors. In addition to current valuable models, such novel models are anticipated to expedite functional tumor biology study and establish effective therapeutics for pediatric brain tumors.

Vascular Co-Option and Other Alternative Modalities of Growth of Tumor Vasculature in Glioblastoma

Non-angiogenic tumors grow in the absence of angiogenesis by two main mechanisms: cancer cells infiltrating and occupying the normal tissues to exploit pre-existing vessels (vascular co-option); the cancer cells themselves forms channels able to provide blood flow (the so called vasculogenic mimicry). In the original work on vascular co-option initiated by Francesco Pezzella, the non-angiogenic cancer cells were described as “exploiting” pre-existing vessels. Vascular co-option has been described in primary and secondary (metastatic) sites. Vascular co-option is defined as a process in which tumor cells interact with and exploit the pre-existing vasculature of the normal tissue in which they grow. As part of this process, cancer cells first migrate toward vessels of the primary tumor, or extravasate at a metastatic site and rest along the ab-luminal vascular surface. The second hallmark of vascular co-option is the interaction of cancer cells with the ab-luminal vascular surface. The first evidence for this was provided in a rat C6 glioblastoma model, showing that the initial tumor growth phase was not always avascular as these initial tumors can be vascularized by pre-existing vessels. The aim of this review article is to analyze together with vascular co-option, other alternative mode of vascularization occurring in glioblastoma multiforme (GBM), including vasculogenic mimicry, angiotropism and trans-differentiation of glioblastoma stem cells.

Breaking barriers: Neurodegenerative repercussions of radiotherapy induced damage on the blood-brain and blood-tumor barrier

Exposure to radiation during the treatment of CNS tumors leads to detrimental damage of the blood brain barrier (BBB) in normal tissue. Effects are characterized by leakage of the vasculature which exposes the brain to a host of neurotoxic agents potentially leading to white matter necrosis, parenchymal calcification, and an increased chance of stroke. Vasculature of the blood tumor barrier (BTB) is irregular leading to poorly perfused and hypoxic tissue throughout the tumor that becomes resistant to radiation. While current clinical applications of cranial radiotherapy use dose fractionation to reduce normal tissue damage, these treatments still cause significant alterations to the cells that make up the neurovascular unit of the BBB and BTB. Damage to the vasculature manifests as reduction in tight junction proteins, alterations to membrane transporters, impaired cell signaling, apoptosis, and cellular senescence. While radiotherapy treatments are detrimental to normal tissue, adapting combined strategies with radiation targeted to damage the BTB could aid in drug delivery. Understanding differences between the BBB and the BTB may provide valuable insight allowing clinicians to improve treatment outcomes. Leveraging this information should allow advances in the development of therapeutic modalities that will protect the normal tissue while simultaneously improving CNS tumor treatments.

Adaptive mechanoproperties mediated by the formin FMN1 characterize glioblastoma fitness for invasion

Glioblastoma are heterogeneous tumors composed of highly invasive and highly proliferative clones. Heterogeneity in invasiveness could emerge from discrete biophysical properties linked to specific molecular expression. We identified clones of patient-derived glioma propagating cells that were either highly proliferative or highly invasive and compared their cellular architecture, migratory, and biophysical properties. We discovered that invasiveness was linked to cellular fitness. The most invasive cells were stiffer, developed higher mechanical forces on the substrate, and moved stochastically. The mechano-chemical-induced expression of the formin FMN1 conferred invasive strength that was confirmed in patient samples. Moreover, FMN1 expression was also linked to motility in other cancer and normal cell lines, and its ectopic expression increased fitness parameters. Mechanistically, FMN1 acts from the microtubule lattice and promotes a robust mechanical cohesion, leading to highly invasive motility.

C6 Cell Injection into the Optic Nerve of Long-Evans Rats: A Short-Term Model of Optic Pathway Gliomas

The optic pathway glioma (OPG) is a slow-growing brain tumor that arises along the optic nerve or its downstream connections and causing vision to gradually worsen with time. This tumor forms in children with a genetic condition called neurofibromatosis type 1 (NF1), causing tumors to grow on nerves. In normal conditions, glial cells are there to support and protect nerve cells but, in NF1-OPG, glial cells have a genetic defect and grow out of control forming a tumor called a glioma. There are no rat models of NF1-OPG that can be used to explore various treatment options, and mouse models make interventional studies difficult due to their small eye size. We have created a model in which to study the progression of tumor growth in the optic nerve and establish the anatomical and functional consequences of the model and determine its suitability to serve as a surrogate for human disease. C6 rat glioma cells were injected into the optic nerve of Long-Evans rats and allowed to proliferate for 2 weeks. The eye clearly showed proptosis and lens opacity was observed, likely due to increased intraocular pressure caused by growing tumors. Hematoxylin–eosin staining showed marked cellularity, with hyperchromatism and pleomorphism. There was prominent area of necrosis with neoplastic cells palisading around the penumbra. Immunostaining with markers such as S100, β-tubulin III, Foxp3, CD45, Vimentin, and Ki67 confirmed low-grade tumor formation, with a mild immune response. Our results show the utility of a surgically induced rat model of OPG that may be used for exploring various treatment options for NF1 ocular tumors.

AVNP2 protects against cognitive impairments induced by C6 glioma by suppressing tumour associated inflammation in rats

Glioblastoma is a kind of malignant tumour and originates from the central nervous system. In the last century, some researchers and clinician have noticed that the psychosocial and neurocognitive functioning of patients with malignant gliomas can be impaired. Many clinical studies have demonstrated that part of patients, adults or children, diagnosed with glioblastoma will suffer from cognitive deficiency during their clinical course, especially in long-term survivors. Many nanoparticles (NPs) can inhibit the biological functions of tumours by modulating tumour-associated inflammation, which provokes angiogenesis and tumour growth. As one of the best antiviral nanoparticles (AVNPs), AVNP2 is the 2nd generation of AVNP2 that have been conjugated to graphite-graphene for improving physiochemical performance and reducing toxicity. AVNP2 inactivates viruses, such as the H1N1 and H5N1influenza viruses and even the SARS coronavirus, while it inhibits bacteria, such as MRSA and E. coli. As antimicrobials, nanoparticles are considered to be one of the vectors for the administration of therapeutic compounds. Yet, little is known about their potential functionalities and toxicities to the neurotoxic effects of cancer. Herein, we explored the functionality of AVNP2 on inhibiting C6 in glioma-bearing rats. The novel object-recognition test and open-field test showed that AVNP2 significantly improved the neuro-behaviour affected by C6 glioma. AVNP2 also alleviated the decline of long-term potentiation (LTP) and the decreased density of dendritic spines in the CA1 region induced by C6. Western blot assay and immunofluorescence staining showed that the expressions of synaptic-related proteins (PSD-95 and SYP) were increased, and these findings were in accordance with the results mentioned above. It revealed that the sizes of tumours in C6 glioma-bearing rats were smaller after treatment with AVNP2. The decreased expression of inflammatory factors (IL-1β, IL-6 and TNF-α) by Western blotting assay and ELISA, angiogenesis protein (VEGF) by Western blotting assay and other related proteins (BDNF, NF-ĸB, iNOS and COX-2) by Western blotting assay in peri-tumour tissue indicated that AVNP2 could control tumour-associated inflammation, thus efficiently ameliorating the local inflammatory condition and, to some extent, inhibiting angiogenesis in C6-bearing rats. In conclusion, our results suggested that AVNP2 could have an effect on the peri-tumor environment, obviously restraining the growth progress of gliomas, and eventually improving cognitive levels in C6-bearing rats.

Models and molecular mechanisms of blood vessel co-option by cancer cells

Cancer cells have diverse mechanisms for utilizing the vasculature; they can initiate the formation of new blood vessels from preexisting ones (sprouting angiogenesis) or they can form cohesive interactions with the abluminal surface of preexisting vasculature in the absence of sprouting (co-option). The later process has received renewed attention due to the suggested role of blood vessel co-option in resistance to antiangiogenic therapies and the reported perivascular positioning and migratory patterns of cancer cells during tumor dormancy and invasion, respectively. However, only a few molecular mechanisms have been identified that contribute to the process of co-option and there has not been a formal survey of cell lines and laboratory models that can be used to study co-option in different organ microenvironments; thus, we have carried out a comprehensive literature review on this topic and have identified cell lines and described the laboratory models that are used to study blood vessel co-option in cancer. Put into practice, these models may help to shed new light on the molecular mechanisms that drive blood vessel co-option during tumor dormancy, invasion, and responses to different therapies.

Signaling Determinants of Glioma Cell Invasion

Tumor cell invasiveness is a critical challenge in the clinical management of glioma patients. In addition, there is accumulating evidence that current therapeutic modalities, including anti-angiogenic therapy and radiotherapy, can enhance glioma invasiveness. Glioma cell invasion is stimulated by both autocrine and paracrine factors that act on a large array of cell surface-bound receptors. Key signaling elements that mediate receptor-initiated signaling in the regulation of glioblastoma invasion are Rho family GTPases, including Rac, RhoA and Cdc42. These GTPases regulate cell morphology and actin dynamics and stimulate cell squeezing through the narrow extracellular spaces that are typical of the brain parenchyma. Transient attachment of cells to the extracellular matrix is also necessary for glioblastoma cell invasion. Interactions with extracellular matrix components are mediated by integrins that initiate diverse intracellular signalling pathways. Key signaling elements stimulated by integrins include PI3K, Akt, mTOR and MAP kinases. In order to detach from the tumor mass, glioma cells secrete proteolytic enzymes that cleave cell surface adhesion molecules, including CD44 and L1. Key proteases produced by glioma cells include uPA, ADAMs and MMPs. Increased understanding of the molecular mechanisms that control glioma cell invasion has led to the identification of molecular targets for therapeutic intervention in this devastating disease.

Brain Invasion along Perivascular Spaces by Glioma Cells: Relationship with Blood-Brain Barrier

The question whether perivascular glioma cells invading the brain far from the tumor bulk may disrupt the blood-brain barrier (BBB) represents a crucial issue because under this condition tumor cells would be no more protected from the reach of chemotherapeutic drugs. A recent in vivo study that used human xenolines, demonstrated that single glioma cells migrating away from the tumor bulk are sufficient to breach the BBB. Here, we used brain xenografts of patient-derived glioma stem-like cells (GSCs) to show by immunostaining that in spite of massive perivascular invasion, BBB integrity was preserved in the majority of vessels located outside the tumor bulk. Interestingly, the tumor cells that invaded the brain for the longest distances traveled along vessels with retained BBB integrity. In surgical specimens of malignant glioma, the area of brain invasion showed several vessels with preserved BBB that were surrounded by tumor cells. On transmission electron microscopy, the cell inter-junctions and basal lamina of the brain endothelium were preserved even in conditions in which the tumor cells lay adjacently to blood vessels. In conclusion, BBB integrity associates with extensive perivascular invasion of glioma cells.

Vessel co-option in cancer

All solid tumours require a vascular supply in order to progress. Although the ability to induce angiogenesis (new blood vessel growth) has long been regarded as essential to this purpose, thus far, anti-angiogenic therapies have shown only modest efficacy in patients. Importantly, overshadowed by the literature on tumour angiogenesis is a long-standing, but continually emerging, body of research indicating that tumours can grow instead by hijacking pre-existing blood vessels of the surrounding nonmalignant tissue. This process, termed vessel co-option, is a frequently overlooked mechanism of tumour vascularization that can influence disease progression, metastasis and response to treatment. In this Review, we describe the evidence that tumours located at numerous anatomical sites can exploit vessel co-option. We also discuss the proposed molecular mechanisms involved and the multifaceted implications of vessel co-option for patient outcomes.

Tumor growth under rhGM-CSF application in an orthotopic rodent glioma model

Regulation of the host immune response serves a pivotal role in the persistence and progression of malignant glioma. To date, cytotoxic cluster of differentiation (CD)-8+ T and natural killer cells are considered the main cellular components of host tumor control. The influence of macrophages in an orthotropic C6 tumor implantation model was investigated and the aim of the present study was to characterize the effects of systemic macrophage-activation on glioma growth by using the granulocyte macrophage colony stimulating factor (rhGM-CSF). A total of 20 male Sprague-Dawley rats were orthotopically implanted with C6 glioma spheroids and treated subcutaneously with 10 µg/kg rhGM-CSF every other day; 9 animals served as controls. Serial magnetic resonance imaging was performed on days 7, 14, 21, 28, 32 and 42 post-implantation to monitor tumor volume. Histological work-up included hematoxylin and eosin, CD68/ED-1 macrophage, CD8 T-cell and Ki-67 MIB1 proliferation staining in gliomas and spleen. Experimental C6-gliomas developed in 15/20 (75%) animals. In rhGM-CSF treated rats, tumors developed significantly later and reached a smaller size (median, 134 mm³) compared with the controls (median, 262 mm³). On day 14, solid tumors presented in 11/17 (65%) rhGM-CSF-treated animals; in control animals tumor growth was detected in 3/9 animals on day 7 and in all animals on day 14. The mean survival time was 35 days in the rhGM-CSF group and significantly longer when compared with the control group (24 days). Immunohistochemistry exhibited significantly more macrophages in tumors, particularly in the perivascular zone of the rhGM-CSF group when compared with untreated animals; intratumoral CD8+ counts were equal in both groups. A systemic stimulation of macrophages by rhGM-CSF resulted in significantly reduced and delayed tumor growth in the rodent C6 glioma model. The present data suggested a significant role of macrophages in host control of experimental gliomas on the innate immune response. Until now, the role of macrophages may have been underestimated in host glioma control.

Mechanical Durotactic Environment Enhances Specific Glioblastoma Cell Responses

Background: A hallmark of glioblastoma is represented by their ability to widely disperse throughout the brain parenchyma. The importance of developing new anti-migratory targets is critical to reduce recurrence and improve therapeutic efficacy. Methods: Polydimethylsiloxane substrates, either mechanically uniform or presenting durotactic cues, were fabricated to assess GBM cell morphological and dynamical response with and without pharmacological inhibition of NNMII contractility, of its upstream regulator ROCK and actin polymerization. Results: Glioma cells mechanotactic efficiency varied depending on the rigidity compliance of substrates. Morphologically, glioma cells on highly rigid and soft bulk substrates displayed bigger and elongated aggregates whereas on durotactic substrates the same cells were homogeneously dispersed with a less elongated morphology. The durotactic cues also induced a motility change, cell phenotype dependent, and with cells being more invasive on stiffer substrates. Pharmacological inhibition of myosin or ROCK revealed a rigidity-insensitivity, unlike inhibition of microfilament contraction and polymerization of F-actin, suggesting that alternative signalling is used to respond to durotactic cues. Conclusions: The presence of a distinct mechanical cue is an important factor in cell migration. Together, our results provide support for a durotactic role of glioma cells that acts through actomyosin contractility to regulate the aggressive properties of GBM cells.

Human astrocytes secrete IL-6 to promote glioma migration and invasion through upregulation of cytomembrane MMP14

The brain microenvironment has emerged as an important component in malignant progression of human glioma. However, astrocytes, the most abundant glial cells in the glioma microenvironment, have as yet a poorly defined role in the development of this disease, particularly with regard to invasion. Here, we co-cultured human astrocytes with human glioma cell lines, U251 and A172, in an in vitro transwell system in order to ascertain their influence on migration and invasion of gliomas. mRNA and protein expression assays were subsequently used to identify candidate proteins mediating this activity. Astrocytes significantly increased migration and invasion of both U251 and A172 cells in migration and invasion (plus matrigel) assays. Membrane type 1 matrix metalloproteinase (MMP14) originating from glioma cells was identified in qRT-PCR as the most highly up-regulated member of the MMP family of genes (~ 3 fold, p < 0.05) in this system. A cytokine array and ELISA were used to identify interleukin-6 (IL-6) as a highly increased factor in media collected from astrocytes, especially under co-culture conditions. IL-6 was also the key cytokine inducing cytomembrane MMP14 expression, the active form of MMP14, in glioma cells. Knockdown of MMP14 with siRNA led to decreased migration and invasion. Taken together, our results indicated that cytomembrane MMP14 was induced by IL-6 secreted from astrocytes, thereby enhancing the migration and invasion of glioma cells through activation of MMP2. Therefore, this IL-6 and MMP14 axis between astrocytes and glioma cells may become a potential target for treatment of glioma patients.

Engraftment of C6-2B Cells into the Striatum of Aci Nude Rats as a Tool for Comparison of the in Vitro and in Vivo Phenotype of a Glioma Cell Line

The C6-2B is a well-characterized glioma cell line used extensively in the study of malignant glial biology. While the C6-2B cell line has traditionally been thought of as a homogenous cell line, the in vitro phenotype of the C6-2B cell line can vary considerably depending on the culture technique used and the stratum on which the cells are grown. Thus, we asked whether the in vitro phenotype of the C6-2B cell line was significantly different than the in vivo phenotype of the cell line once it was engrafted into the striatum of nude rats. Under culture conditions used in our laboratory, 100% of the C6 cells were found to express p75, the low-affinity nerve growth factor (NGF) receptor, and Major Histocompatability Class I (MHC Class I), while only 10-15% demonstrated vimentin reactivity. Immunohistochemistry was consistently negative for GFAP, trkA (the high-affinity receptor for NGF), CD4, CD8, and a macrophage specific marker (Ox-41). Once engrafted into the striatum of nude rats, the cells remained 100% p75 and MHC Class I positive, and again, only 15% of the cells demonstrated vimentin reactivity. The grafted cells retained this characteristic for 28 days in vivo. Although an immunoincompetent host was selected to minimize the effects an inflammatory response would have on the graft, a transient inflammatory response was detected. During the first week of engraftment, numerous MHC class II cells, some of which were macrophages, were seen infiltrating the graft. However, by 4 weeks postengraftment, no inflammatory cells were appreciated in the graft and surprisingly little reactive gliosis was seen in the penumbra of the tumor mass. Thus, the limited number of in vitro phe-notypic characteristics we examined in the C6-2B cell line remained constant once the cells were engrafted into the striatum of athymic nude rats.

Implanting Glioblastoma Spheroids into Rat Brains and Monitoring Tumor Growth by MRI Volumetry

The outcome of patients suffering from glioblastoma multiforme (GBM) remains poor with a median survival of less than 15 months. To establish innovative therapeutical approaches or to analyze the effect of protein overexpression or protein knockdown by RNA interference in vivo, animal models are mandatory. Here, we describe the implantation of C6 glioma spheroids into the rats' brain and how to follow tumor growth by MRI scans. We show that C6 cells grown in Sprague-Dawley rats share several morphologic features of human glioblastoma like pleomorphic cells, areas of necrosis, vascular proliferation, and tumor cell invasion into the surrounding brain tissue. In addition, we describe a method for tumor volumetry utilizing the CISS 3D- or contrast-enhanced T1-weighted 3D sequence and freely available post-processing software.

EphrinB2 drives perivascular invasion and proliferation of glioblastoma stem-like cells

Glioblastomas (GBM) are aggressive and therapy-resistant brain tumours, which contain a subpopulation of tumour-propagating glioblastoma stem-like cells (GSC) thought to drive progression and recurrence. Diffuse invasion of the brain parenchyma, including along preexisting blood vessels, is a leading cause of therapeutic resistance, but the mechanisms remain unclear. Here, we show that ephrin-B2 mediates GSC perivascular invasion. Intravital imaging, coupled with mechanistic studies in murine GBM models and patient-derived GSC, revealed that endothelial ephrin-B2 compartmentalises non-tumourigenic cells. In contrast, upregulation of the same ephrin-B2 ligand in GSC enabled perivascular migration through homotypic forward signalling. Surprisingly, ephrin-B2 reverse signalling also promoted tumourigenesis cell-autonomously, by mediating anchorage-independent cytokinesis via RhoA. In human GSC-derived orthotopic xenografts, EFNB2 knock-down blocked tumour initiation and treatment of established tumours with ephrin-B2-blocking antibodies suppressed progression. Thus, our results indicate that targeting ephrin-B2 may be an effective strategy for the simultaneous inhibition of invasion and proliferation in GBM.

Mechanical confinement triggers glioma linear migration dependent on formin FHOD3

Glioblastomas are extremely aggressive brain tumors with highly invasive properties. Brain linear tracks such as blood vessel walls constitute their main invasive routes. Here we analyze rat C6 and patient-derived glioma cell motility in vitro using micropatterned linear tracks to mimic blood vessels. On laminin-coated tracks (3-10 μm), these cells used an efficient saltatory mode of migration similar to their in vivo migration. This saltatory migration was also observed on larger tracks (50-400 μm in width) at high cell densities. In these cases, the mechanical constraints imposed by neighboring cells triggered this efficient mode of migration, resulting in the formation of remarkable antiparallel streams of cells along the tracks. This motility involved microtubule-dependent polarization, contractile actin bundles and dynamic paxillin-containing adhesions in the leading process and in the tail. Glioma linear migration was dramatically reduced by inhibiting formins but, surprisingly, accelerated by inhibiting Arp2/3. Protein expression and phenotypic analysis indicated that the formin FHOD3 played a role in this motility but not mDia1 or mDia2. We propose that glioma migration under confinement on laminin relies on formins, including FHOD3, but not Arp2/3 and that the low level of adhesion allows rapid antiparallel migration.

Induction of neural differentiation in rat C6 glioma cells with taxol

BACKGROUND

Glioblastoma is a common and aggressive type of primary brain tumor. Several anticancer drugs affect GBM (glioblastoma multiforme) cells on cell growth and morphology. Taxol is one of the widely used antineoplastic drugs against many types of solid tumors, such as breast, ovarian, and prostate cancers. However, the effect of taxol on GBM cells remains unclear and requires further investigation.

METHODS

Survival rate of C6 glioma cells under different taxol concentrations was quantified. To clarify the differentiation patterns of rat C6 glioma cells under taxol challenge, survived glioma cells were characterized by immunocytochemical, molecular biological, and cell biological approaches.

RESULTS

After taxol treatment, not only cell death but also morphological changes, including cell elongation, cellular processes thinning, irregular shapes, and fragmented nucleation or micronuclei, occurred in the survived C6 cells. Neural differentiation markers NFL (for neurons), β III-tubulin (for neurons), GFAP (for astrocytes), and CNPase (for oligodendrocytes) were detected in the taxol-treated C6 cells. Quantitative analysis suggested a significant increase in the percentage of neural differentiated cells. The results exhibited that taxol may trigger neural differentiation in C6 glioma cells. Increased expression of neural differentiation markers in C6 cells after taxol treatment suggest that some anticancer drugs could be applied to elimination of the malignant cancer cells as well as changing proliferation and differentiation status of tumor cells.

Characterization of highly proliferative secondary tumor clusters along host blood vessels in malignant glioma

The aim of the present study was to investigate the extensive invasion of tumor cells into normal brain tissue, a life‑threatening feature of malignant gliomas. How invasive tumor cells migrate into normal brain tissue and form a secondary tumor structure remains to be elucidated. In the present study, the morphological and phenotypic changes of glioma cells during invasion in a C6 glioma model were investigated. C6 glioma cells were stereotactically injected into the right putamen region of adult Sprague‑Dawley rats. The brain tissue sections were then subjected to hematoxylin and eosin, immunohistochemical or immunofluorescent staining. High magnification views of the tissue sections revealed that C6 cells formed tumor spheroids following implantation and marked invasion was observed shortly after spheroid formation. In the later stages of invasion, certain tumor cells invaded the perivascular space and formed small tumor clusters. These small tumor clusters exhibited certain common features, including tumor cell multilayers surrounding an arteriole, which occurred up to several millimeters away from the primary tumor mass; a high proliferation rate; and similar gene expression profiles to the primary tumor. In conclusion, the present study revealed that invading tumor cells are capable of forming highly proliferative cell clusters along arterioles near the tumor margin, which may be a possible cause of the recurrence of malignant glioma.

γ-H2AX as a marker for dose deposition in the brain of wistar rats after synchrotron microbeam radiation

Objective

Synchrotron radiation has shown high therapeutic potential in small animal models of malignant brain tumours. However, more studies are needed to understand the radiobiological effects caused by the delivery of high doses of spatially fractionated x-rays in tissue. The purpose of this study was to explore the use of the γ-H2AX antibody as a marker for dose deposition in the brain of rats after synchrotron microbeam radiation therapy (MRT).

Methods

Normal and tumour-bearing Wistar rats were exposed to 35, 70 or 350 Gy of MRT to their right cerebral hemisphere. The brains were extracted either at 4 or 8 hours after irradiation and immediately placed in formalin. Sections of paraffin-embedded tissue were incubated with anti γ-H2AX primary antibody.

Results

While the presence of the C6 glioma does not seem to modulate the formation of γ-H2AX in normal tissue, the irradiation dose and the recovery versus time are the most important factors affecting the development of γ-H2AX foci. Our results also suggest that doses of 350 Gy can trigger the release of bystander signals that significantly amplify the DNA damage caused by radiation and that the γ-H2AX biomarker does not only represent DNA damage produced by radiation, but also damage caused by bystander effects.

Conclusion

In conclusion, we suggest that the γ-H2AX foci should be used as biomarker for targeted and non-targeted DNA damage after synchrotron radiation rather than a tool to measure the actual physical doses.

The role of microRNA-30c in the self-renewal and differentiation of C6 glioma cells

BACKGROUND

Sphere formation, one method for identifying self-renewal ability, has been used to report that cancer stem-like cells exist in rat C6 glioma cells. Recent studies suggested that cancer stem-like cells share the stem cell properties of self-renewal and multipotent ability of neural stem cells and might be regulated by microRNAs (miRNAs). However, the mechanism of miRNA involvement in the sphere formation and neural differentiation abilities of cancer stem-like cells is poorly understood.

RESULTS

We found that miRNA-30c could assist in sphere formation of C6 cells under defined conditions in neural stem cell medium DMEM/F12-bFGF-EGF-B27. Moreover, overexpression of miRNA-30c might reduce 3-isobutyl-1-methylxanthine (IBMX)-induced neural differentiation, as the expression of neural markers, especially glial fibrillary acidic protein (GFAP), decreased. Further experiments revealed that miRNA-30c inhibited the IBMX-induced astrocyte differentiation via targeting the upstream genes and inactivating phosphorylation of STAT3 of the JAK-STAT3 pathway. Subsequently, the expression of GFAP was reduced and the number of astrocyte differentiation from C6 cells decreased.

CONCLUSIONS

Our findings suggest that miRNA-30c could play a regulatory role in self-renewal and neural differentiation in C6 glioma cells.

Glioma cells escaped from cytotoxicity of temozolomide and vincristine by communicating with human astrocytes

Resistance to chemotherapeutic drugs remains a great obstacle to successful treatment of gliomas. Understanding the mechanism of glioma chemoresistance is conducive to develop effective strategies to overcome resistance. Astrocytes are the major stromal cells in the brain and have been demonstrated to play a key role in the malignant phenotype of gliomas. However, little is known regarding its role in glioma chemoresistance. In our study, we established a co-culture system of human astrocytes and glioma in vitro to simulate tumor microenvironment. Our results showed that astrocytes significantly reduced glioma cell apoptosis induced by the chemotherapeutic drugs temozolomide and vincristine. This protective effect was dependent on direct contact between astrocytes and glioma cells through Cx43-GJC. Moreover, in human glioma specimens, we found astrocytes infiltrating around the tumor, with a reactive appearance, suggesting that these astrocytes would play the same chemoprotective effect on gliomas in vivo. Our results expand the understanding of the interaction between astrocytes and glioma cells and provide a possible explanation for unsatisfactory clinical outcomes of chemotherapeutic drugs. Cx43-GJC between astrocytes and glioma cells may be a potential target for overcoming chemoresistance in gliomas clinically.

The complete mitochondrial genome sequence of the rat C6 glioma cell line

In this article we have reported the complete mitochondrial genome sequence of rat C6 glioma cell line for the first time. The total length of the mitogenome was 16,314 bp, with coding 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes. This sequence was deposited in the GenBank (Accession No. KM820837).

A neurocentric perspective on glioma invasion

Malignant gliomas are devastating tumours that frequently kill patients within 1 year of diagnosis. The major obstacle to a cure is diffuse invasion, which enables tumours to escape complete surgical resection and chemo- and radiation therapy. Gliomas use the same tortuous extracellular routes of migration that are travelled by immature neurons and stem cells, frequently using blood vessels as guides. They repurpose ion channels to dynamically adjust their cell volume to accommodate to narrow spaces and breach the blood-brain barrier through disruption of astrocytic endfeet, which envelop blood vessels. The unique biology of glioma invasion provides hitherto unexplored brain-specific therapeutic targets for this devastating disease.

Disruption of astrocyte-vascular coupling and the blood-brain barrier by invading glioma cells

Astrocytic endfeet cover the entire cerebral vasculature and serve as exchange sites for ions, metabolites, and energy substrates from the blood to the brain. They maintain endothelial tight junctions that form the blood-brain barrier (BBB) and release vasoactive molecules that regulate vascular tone. Malignant gliomas are highly invasive tumors that use the perivascular space for invasion and co-opt existing vessels as satellite tumors form. Here we use a clinically relevant mouse model of glioma and find that glioma cells, as they populate the perivascular space of pre-existing vessels, displace astrocytic endfeet from endothelial or vascular smooth muscle cells. This causes a focal breach in the BBB. Furthermore, astrocyte-mediated gliovascular coupling is lost, and glioma cells seize control over regulation of vascular tone through Ca²⁺-dependent release of K⁺. These findings have important clinical implications regarding blood flow in the tumor-associated brain and the ability to locally deliver chemotherapeutic drugs in disease.

Signaling determinants of glioma cell invasion

Tumor cell invasiveness is a critical challenge in the clinical management of glioma patients. In addition, there is accumulating evidence that current therapeutic modalities, including anti-angiogenic therapy and radiotherapy, can enhance glioma invasiveness. Glioma cell invasion is stimulated by both autocrine and paracrine factors that act on a large array of cell surface-bound receptors. Key signaling elements that mediate receptor-initiated signaling in the regulation of glioblastoma invasion are Rho family GTPases, including Rac, RhoA and Cdc42. These GTPases regulate cell morphology and actin dynamics and stimulate cell squeezing through the narrow extracellular spaces that are typical of the brain parenchyma. Transient attachment of cells to the extracellular matrix is also necessary for glioblastoma cell invasion. Interactions with extracellular matrix components are mediated by integrins that initiate diverse intracellular signalling pathways. Key signaling elements stimulated by integrins include PI3K, Akt, mTOR and MAP kinases. In order to detach from the tumor mass, glioma cells secrete proteolytic enzymes that cleave cell surface adhesion molecules, including CD44 and L1. Key proteases produced by glioma cells include uPA, ADAMs and MMPs. Increased understanding of the molecular mechanisms that control glioma cell invasion has led to the identification of molecular targets for therapeutic intervention in this devastating disease.

Plausible role of naringenin against cerebrally implanted C6 glioma cells in rats

Gliomas encompass a significant percentage of intrinsic neoplasms of the central nervous system in both adults and children. The constitutive activation of phosphatidylinositol 3-kinase (PI3K) and protein kinase B is the hallmark of glioma. The up-regulated protein kinase B could influence the expression of cyclooxygenase-2, an indicator of aggressive glioma. The present study was embarked to demonstrate the effect of naringenin (50 mg/kg bw for 30 days administrated orally) on PI3K, protein kinase B, and cyclooxygenase-2 in cerebrally implanted rat C6 glioma model. After the experimental period of 30 days, the animals were sacrificed and excised brain tissues were subjected to study the expressions of PI3K, protein kinase B, and cyclooxygenase-2 by reverse transcriptase polymerase chain reaction followed Western blot analysis. The activity of COX-2 (production of prostaglandin-E(2)) was also determined by high pressure liquid chromatography. The results showed that the naringenin could down-regulate the expressions of PI3K and protein kinase B along with activity and expression of cyclooxygenase-2 in C6 glioma cells implanted rat brain. In conclusion, it can be argued that the reduced expressions of phosphatidylinositol 3-kinase and protein kinase B in naringenin-treated glioma-induced rat brain might be involved in the down-regulation of cyclooxygenase-2 expression and activity. Thus, fine-tuned investigation of which will be helpful for targeted drug discovery against glioma.

Calpain 2 is required for the invasion of glioblastoma cells in the zebrafish brain microenvironment

Glioblastoma is an aggressive primary brain tumor with a 5-year survival rate of less than 5%. The ability of glioblastoma cells to invade surrounding brain tissue presents the primary challenge for the success of focal therapeutic approaches. We previously reported that the calcium-activated protease calpain 2 is critical for glioblastoma cell invasion in vitro. Here, we show that expression of calpain 2 is required for the dispersal of glioblastoma cells in a living brain microenvironment. Knockdown of calpain 2 resulted in a 2.9-fold decrease in the invasion of human glioblastoma cells in zebrafish brain. Control cells diffusely migrated up to 450 μm from the site of injection, whereas knockdown cells remained confined in clusters. The invasion study was repeated in organotypic mouse brain tissues, and calpain 2 knockdown cells demonstrated a 2.3-fold lower area of dispersal compared with control cells. In zebrafish brain, glioblastoma cells appeared to migrate in part along the blood vessels of the host. Furthermore, angiogenesis was detected in 27% of zebrafish injected with control cells, whereas only 12.5% of fish receiving knockdown cells showed the formation of new vessels, suggesting a role for calpain 2 in tumor cell angiogenesis. Consistent with the progression of glioblastoma in humans, transplanted tumor cells were not observed to metastasize outside the brain of zebrafish. This study demonstrates that calpain 2 expression is required for the dispersal of glioblastoma cells within the dynamic microenvironment of the brain, identifying zebrafish as a valuable orthotopic system for studying glioblastoma cell invasion.

Effect of Naringenin on metabolic markers, lipid profile and expression of GFAP in C6 glioma cells implanted rat's brain

BACKGROUND

Naringenin, a flavanone, has been reported to exhibit a wide range of pharmacological properties including antitumor activity.

PURPOSE

We wanted to test the efficacy of Naringenin on C6 glioma cells-implanted into rats was investigated.

METHODS

Biochemical and immunohistochemical methods were used for analyzing various markers.

RESULTS

Injection of C6 glioma cells into rat brain resulted in increased metabolic markers {Lactatate Dehydrogenase (LDH), 5' Nucleotidase 5'ND), creatine kinase (CK), Hexokinase (HK) and Glucose 6-phosphate dehydrogenase (G6PD)} and lipid profile (triglycerides, free fatty acids, phos-pholipids, total cholesterol and free cholesterol). Oral administration of Naringenin (50 mg /kg of BW for 30 days) significantly altered this biochemical profile. Further, the immuno fluorescence expression of Glial fibrilary acidic protein (GFAP) was also studied.

CONCLUSION

In C6 glioma cells-implanted rats, increased expression of GFAP was noted on treatment with Naringenin. These observations suggest that Naringenin may participate by inhibiting glial cell tumorigenesis.

Current review of in vivo GBM rodent models: emphasis on the CNS-1 tumour model

GBM (glioblastoma multiforme) is a highly aggressive brain tumour with very poor prognosis despite multi-modalities of treatment. Furthermore, recent failure of targeted therapy for these tumours highlights the need of appropriate rodent models for preclinical studies. In this review, we highlight the most commonly used rodent models (U251, U86, GL261, C6, 9L and CNS-1) with a focus on the pathological and genetic similarities to the human disease. We end with a comprehensive review of the CNS-1 rodent model.

The variability of stimulus thresholds in electrophysiologic cortical language mapping

The aim of this study was to investigate the variability of electrical stimulation threshold in cortical language mapping in relationship to the lobar location of the mapped eloquent cortex and the distance between the latter and the location of the cortical lesion. A multivariate linear regression analysis was performed in a sample of 39 patients who underwent standardized successful language cortical mapping. Estimated stimulus threshold for temporal language cortex was 1.45 times higher than the estimated threshold for frontal language cortex, after adjusting for the other variables (P = 0.017). Stimulation of the mapped cortex in close proximity to the lesion or to the lesional edema increased the estimated threshold 2.6 or 1.8 times, respectively, compared with stimulation in other areas, after adjusting for the other variables (P < 0.0001, P = 0.0017). In concordance with prior findings, our results show that stimulus threshold in cortical language mapping is dependent on the lobar location of the mapped cortex. In addition, stimulus threshold is increased when the mapped cortex is in close proximity to the location of the lesion or perilesional edema.

Accumulation of CD133-positive glioma cells after high-dose irradiation by Gamma Knife surgery plus external beam radiation

OBJECT

Recent evidence suggests that a glioma stem cell subpopulation might contribute to radioresistance in malignant gliomas. To investigate this hypothesis, the authors examined recurrent malignant gliomas for histopathological changes after high-dose irradiation with Gamma Knife surgery (GKS) and external beam radiation therapy (EBRT).

METHODS

Thirty-two patients with malignant gliomas (Grade 3 in 8 patients, Grade 4 in 24) underwent GKS in combination with EBRT. Serial MR and L-[methyl-(11)C] methionine PET images were employed to assess remnant or recurrent tumors after GKS. Twelve patients underwent surgical removal after GKS and EBRT. Histological sections were subjected to immunohistochemistry for MIB-1, factor VIII, and stem cell markers, nestin and CD133.

RESULTS

The site of GKS treatment failure was local in 16 (76.2%) of 21 patients with glioblastomas showing progression; in 9 of these 16 patients, the recurrence clearly arose within the target lesion of GKS. Histopathological examination after GKS and EBRT showed variable mixtures of viable tumor tissues and necrosis. Viable tumor tissues exhibited high MIB-1 indices but reduced numbers of tumor blood vessels. There was marked accumulation of CD133-positive glioma cells, particularly in remnant tumors within the necrotic areas, in sections obtained after GKS plus EBRT, whereas CD133-positive cells appeared very infrequently in primary sections prior to adjuvant treatment.

CONCLUSIONS

The results indicate that CD133-positive glioma stemlike cells can survive high-dose irradiation, leading to recurrence, despite prolonged damage to tumor blood vessels. This could be an essential factor limiting the effectiveness of GKS plus EBRT for malignant gliomas.

Glioma surgery using a multimodal navigation system with integrated metabolic images

Object

A multimodal neuronavigation system using metabolic images with PET and anatomical images from MR images is described here for glioma surgery. The efficacy of the multimodal neuronavigation system was evaluated by comparing the results with that of the conventional navigation system, which routinely uses anatomical images from MR and CT imaging as guides.

Methods

Thirty-three patients with cerebral glioma underwent 36 operations with the aid of either a multimodal or conventional navigation system. All of the patients were preliminarily examined using PET with l-methyl-[11C] methionine (MET) for surgical planning. Seventeen of the operations were performed with the multimodal navigation system by integrating the MET-PET images with anatomical MR images. The other 19 operations were performed using a conventional navigation system based solely on MR imaging.

Results

The multimodal navigation system proved to be more useful than the conventional navigation system in determining the area to be resected by providing a clearer tumor boundary, especially in cases of recurrent tumor that had lost a normal gyral pattern. The multimodal navigation system was therefore more effective than the conventional navigation system in decreasing the mass of the tumor remnant in the resectable portion. A multivariate regression analysis revealed that the multimodal navigation system–guided surgery benefited patient survival significantly more than the conventional navigation–guided surgery (p = 0.016, odds ratio 0.52 [95% confidence interval 0.29–0.88]).

Conclusions

The authors' preliminary intrainstitutional comparison between the 2 navigation systems suggested the possible premise of multimodal navigation. The multimodal navigation system using MET-PET fusion imaging is an interesting technique that may prove to be valuable in the future.

Experimental nodel of C6 brain tumors in athymic rats

Malignant brain tumor experimental models tend to employ cells that are immunologically compatible with the receptor animal. In this study, we have proposed an experimental model of encephalic tumor development by injecting C6 cells into athymic Rowett rats, aiming at reaching a model which more closely resembles to the human glioma tumor. In our model, we observed micro-infiltration of tumor cell clusters in the vicinity of the main tumor mass, and of more distal isolated tumor cells immersed in normal encephalic parenchyma. This degree of infiltration is superior to that usually observed in other C6 models.

Modeling and immunohistochemical analysis of C6 glioma in vivo

A reproducible in vivo model of C6 glioma was developed in Wistar rats. Analysis of histological preparations showed similar morphology of rat C6 glioma and human glioblastoma. The formation of a glial border at the periphery of the glioma, consisting of GFAP-positive reactive astrocytes, was shown by the immunohistochemical method. The border appeared on day 8 after implantation, astrogliosis was observed until animal death (day 28). Reactive astrocytes with branched processes surrounded not only the primary glioma focus, but also all sites of tumor invasion in the nervous tissue. Expression of EBA (blood-brain barrier marker) was disturbed and synthesis of AMVB1 (endothelial antigen) increased in neoplastic endotheliocytes, which suggested pronounced functional restructuring of the blood-tumor barrier in comparison with the blood-brain barrier. The phenomenon of predominant expression of GFAP and AMVB in the tumor tissue can be used for the development of systems for targeted drug transport into the tumor by means of appropriate antibodies.

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.