Invading C6 glioma cells maintaining tumorigenicity

Arbutin: Occurrence in Plants, and Its Potential as an Anticancer Agent

Arbutin, a hydroquinone glucoside, has been detected in ca. 50 plant families, especially in the plants of the Asteraceae, Ericaceae, Proteaceae and Rosaceae families. It is one of the most widely used natural skin-whitening agents. In addition to its skin whitening property, arbutin possesses other therapeutically relevant biological properties, e.g., antioxidant, antimicrobial and anti-inflammatory, as well as anticancer potential. This review presents, for the first time, a comprehensive overview of the distribution of arbutin in the plant kingdom and critically appraises its therapeutic potential as an anticancer agent based on the literature published until the end of August 2022, accessed via several databases, e.g., Web of Science, Science Direct, Dictionary of Natural Products, PubMed and Google Scholar. The keywords used in the search were arbutin, cancer, anticancer, distribution and hydroquinone. Published outputs suggest that arbutin has potential anticancer properties against bladder, bone, brain, breast, cervix, colon, liver, prostate and skin cancers and a low level of acute or chronic toxicity.

Use of multimodality imaging, histology, and treatment feasibility to characterize a transgenic Rag2-null rat model of glioblastoma

Many drugs that show potential in animal models of glioblastoma (GBM) fail to translate to the clinic, contributing to a paucity of new therapeutic options. In addition, animal model development often includes histologic assessment, but multiparametric/multimodality imaging is rarely included despite increasing utilization in patient cancer management. This study developed an intracranial recurrent, drug-resistant, human-derived glioblastoma tumor in Sprague-Dawley Rag2-Rag2 ^tm1Hera knockout rat and was characterized both histologically and using multiparametric/multimodality neuroimaging. Hybrid ¹⁸F-fluoroethyltyrosine positron emission tomography and magnetic resonance imaging, including chemical exchange saturation transfer (¹⁸F-FET PET/CEST MRI), was performed for full tumor viability determination and characterization. Histological analysis demonstrated human-like GBM features of the intracranially implanted tumor, with rapid tumor cell proliferation (Ki67 positivity: 30.5 ± 7.8%) and neovascular heterogeneity (von Willebrand factor VIII:1.8 to 5.0% positivity). Early serial MRI followed by simultaneous ¹⁸F-FET PET/CEST MRI demonstrated consistent, predictable tumor growth, with exponential tumor growth most evident between days 35 and 49 post-implantation. In a second, larger cohort of rats, ¹⁸F-FET PET/CEST MRI was performed in mature tumors (day 49 post-implantation) for biomarker determination, followed by evaluation of single and combination therapy as part of the model development and validation. The mean percentage of the injected dose per mL of ¹⁸F-FET PET correlated with the mean %CEST (r = 0.67, P < 0.05), but there was also a qualitative difference in hot spot location within the tumor, indicating complementary information regarding the tumor cell demand for amino acids and tumor intracellular mobile phase protein levels. Finally, the use of this glioblastoma animal model for therapy assessment was validated by its increased overall survival after treatment with combination therapy (temozolomide and idasanutlin) (P < 0.001). Our findings hold promise for a more accurate tumor viability determination and novel therapy assessment in vivo in a recently developed, reproducible, intracranial, PDX GBM.

Preclinical models of glioblastoma: limitations of current models and the promise of new developments

Glioblastoma (GBM) is the most common and aggressive primary brain tumour, yet little progress has been made towards providing better treatment options for patients diagnosed with this devastating condition over the last few decades. The complex nature of the disease, heterogeneity, highly invasive potential of GBM tumours and until recently, reduced investment in research funding compared with other cancer types, are contributing factors to few advancements in disease management. Survival rates remain low with less than 5% of patients surviving 5 years. Another important contributing factor is the use of preclinical models that fail to fully recapitulate GBM pathophysiology, preventing efficient translation from the lab into successful therapies in the clinic. This review critically evaluates current preclinical GBM models, highlighting advantages and disadvantages of using such models, and outlines several emerging techniques in GBM modelling using animal-free approaches. These novel approaches to a highly complex disease such as GBM show evidence of a more truthful recapitulation of GBM pathobiology with high reproducibility. The resulting advancements in this field will offer new biological insights into GBM and its aetiology with potential to contribute towards the development of much needed improved treatments for GBM in future.

A practical method for multimodal registration and assessment of whole-brain disease burden using PET, MRI, and optical imaging

Many neurological diseases present with substantial genetic and phenotypic heterogeneity, making assessment of these diseases challenging. This has led to ineffective treatments, significant morbidity, and high mortality rates for patients with neurological diseases, including brain cancers and neurodegenerative disorders. Improved understanding of this heterogeneity is necessary if more effective treatments are to be developed. We describe a new method to measure phenotypic heterogeneity across the whole rodent brain at multiple spatial scales. The method involves co-registration and localized comparison of in vivo radiologic images (e.g. MRI, PET) with ex vivo optical reporter images (e.g. labeled cells, molecular targets, microvasculature) of optically cleared tissue slices. Ex vivo fluorescent images of optically cleared pathology slices are acquired with a preclinical in vivo optical imaging system across the entire rodent brain in under five minutes, making this methodology practical and feasible for most preclinical imaging labs. The methodology is applied in various examples demonstrating how it might be used to cross-validate and compare in vivo radiologic imaging with ex vivo optical imaging techniques for assessing hypoxia, microvasculature, and tumor growth.

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.

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.

Next-Generation in vivo Modeling of Human Cancers

Animal models of human cancers played a major role in our current understanding of tumor biology. In pre-clinical oncology, animal models empowered drug target and biomarker discovery and validation. In turn, this resulted in improved care for cancer patients. In the quest for understanding and treating a diverse spectrum of cancer types, technological breakthroughs in genetic engineering and single cell "omics" offer tremendous potential to enhance the informative value of pre-clinical models. Here, I review the state-of-the-art in modeling human cancers with focus on animal models for human malignant gliomas. The review highlights the use of glioma models in dissecting mechanisms of tumor initiation, in the retrospective identification of tumor cell-of-origin, in understanding tumor heterogeneity and in testing the potential of immuno-oncology. I build on the deep review of glioma models as a basis for a more general discussion of the potential ways in which transformative technologies may shape the next-generation of pre-clinical models. I argue that refining animal models along the proposed lines will benefit the success rate of translation for pre-clinical research in oncology.

Characterization of an Orthotopic Rat Model of Glioblastoma Using Multiparametric Magnetic Resonance Imaging and Bioluminescence Imaging

Glioblastoma multiforme (GBM) is the most common primary brain tumor, with most patients dying within 15–18 months of diagnosis despite aggressive therapy. Preclinical GBM models are valuable for exploring GBM progression and for evaluating new therapeutics or imaging approaches. The rat C6 glioma model shares similarities with human GBM, and application of noninvasive imaging enables better study of disease progression. Here, multiparametric magnetic resonance imaging (mpMRI) and bioluminescence imaging (BLI) were applied to characterize longitudinal development of orthotopic luciferase-expressing C6 tumors. Across all rats (n = 11), a large variability was seen for BLI signal, a relative measure of C6 cell viability, but in most individuals, BLI signal peaked at day 11 and decreased thereafter. T2 and contrast-enhanced T1 tumor volumes significantly increased over time (P < .05), and volume measures did not correlate with BLI signal. After day 11, tumor regions of noncontrast enhancement appeared in postcontrast T1-weighted magnetic resonance imaging, and had significantly higher apparent diffusion coefficient values compared with contrast-enhanced regions (P < .05). This suggests formation of ill-perfused, necrotic regions beyond day 11, which were apparent at end-point–matched tissue sections. Our study represents the first combined use of BLI and mpMRI to characterize the progression of disease in the orthotopic C6 rat model, and it highlights the variability in tumor growth, the complementary information from BLI and mpMRI, and the value of multimodality imaging to better characterize tumor development. Future application of these imaging tools will be useful for evaluation of treatment response, and should be pertinent for other preclinical models.

Antitumor activity of 7-O-succinyl macrolactin A tromethamine salt in the mouse glioma model

Chemoradiotherapy with temozolomide is the current standard treatment option for patients with glioblastoma. However, the majority of patients with glioblastoma survive for <2 years. Therefore, it is necessary to develop more effective therapeutic strategies for the treatment of glioblastoma. 7-O-succinyl macrolactin A tromethamine salt (SMA salt), a macrolactin compound, is known to possess an antiangiogenic activity. The present study investigated the antitumor effects of SMA salt in the treatment of glioblastoma by evaluating in vitro and in vivo antitumor effects of SMA salt in an experimental glioblastoma model. The antitumor effects of the drug on human glioblastoma U87MG, U251MG and LN229 cell lines were assessed using in vitro cell viability, migration and invasion assays. Nude mice with established U87MG glioblastoma were assigned to either the control or SMA salt treatment group. The volume of tumors and the duration of survival were also measured. SMA salt affected cell viability and caused a concentration-dependent inhibition effect on the migration and invasion of glioblastoma cell lines. Animals in the SMA salt treatment group demonstrated a significant reduction in tumor volume and an increase in survival (P<0.05). Treatment with SMA salt presented more cytotoxic effects as well as anti-migration and anti-invasion activity compared with the control group in vitro and in vivo. These results suggest that SMA salt has significant antitumor effects on glioblastoma.

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.

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.

Spatial profiles of markers of glycolysis, mitochondria, and proton pumps in a rat glioma suggest coordinated programming for proliferation

Background

In cancer cells in vitro, the glycolytic pathway and the mitochondrial tricarboxylic acid (TCA) cycle are programmed to produce more precursor molecules, and relatively less ATP, than in differentiated cells. We address the questions of whether and where these changes occur in vivo in glioblastomas grown from C6 cells in rat brain. These gliomas show some spatial organization, notably in the upregulation of membrane proton transporters near the rim.

Results

We immunolabeled pairs of proteins (as well as DNA) on sections of rat brains containing gliomas, measured the profiles of fluorescence intensity on strips 200 µm wide and at least 3 mm long running perpendicular to the tumor rim, and expressed the intensity in the glioma relative to that outside. On averaged profiles, labeling of a marker of the glycolytic pathway, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), was, as expected, greater in the glioma. Over distances up to 2.5 mm into the glioma, expression of a marker of the TCA cycle, Tom20, a pre-protein receptor on the translocation complex of the mitochondrial outer membrane, was also upregulated. The ratio of upregulation of Tom20 to upregulation of GAPDH was, on average, slightly greater than one. Near the rim (0.4–0.8 mm), GAPDH was expressed less and there was a peak in the mean ratio of 1.16, SEM = 0.001, N = 16 pairs of profiles. An antibody to V-ATPase, which, by pumping protons into vacuoles contributes to cell growth, also indicated upregulation by about 40%. When compared directly with GAPDH, upregulation of V-ATPase was only 0.764, SD = 0.016 of GAPDH upregulation.

Conclusions

Although there was considerable variation between individual measured profiles, on average, markers of the glycolytic pathway, of mitochondria, and of cell proliferation showed coherent upregulation in C6 gliomas. There is a zone, close to the rim, where mitochondrial presence is upregulated more than the glycolytic pathway, in agreement with earlier suggestions that lactate is taken up by cells near the rim.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1191-z) contains supplementary material, which is available to authorized users.

Laboratory models for central nervous system tumor stem cell research

Central nervous system (CNS) tumors are complex organ systems comprising of a neoplastic component with associated vasculature, inflammatory cells, and reactive cellular and extracellular components. Research has identified a subset of cells in CNS tumors that portray defining properties of neural stem cells, namely, that of self-renewal and multi-potency. Growing evidence suggests that these tumor stem cells (TSC) play an important role in the maintenance and growth of the tumor. Furthermore, these cells have also been shown to be refractory to conventional therapy and may be crucial for tumor recurrence and metastasis. Current investigations are focusing on isolating these TSC from CNS tumors to investigate their unique biological processes. This understanding will help identify and develop more effective and comprehensive treatment strategies. This chapter provides an overview of some of the most commonly used laboratory models for CNSTSC research.

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.

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).

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.

Fast bound pool fraction imaging of the in vivo rat brain: association with myelin content and validation in the C6 glioma model

Cross-relaxation imaging (CRI) is a quantitative magnetic resonance technique that measures the kinetic parameters of magnetization transfer between protons bound to water and protons bound to macromolecules. In this study, in vivo, four-parameter CRI of normal rat brains (N=5) at 3.0 T was first directly compared to histology. The bound pool fraction, f, was strongly associated with myelin density (Pearson's r=0.99, p<0.001). The correlation persisted in separate analyses of gray matter (GM; r=0.89, p=0.046) and white matter (WM; r=0.97, p=0.029). Subsequently, a new time-efficient approach for solely capturing the whole-brain parametric map of f was proposed, validated with histology, and used to estimate myelin density. Since the described approach for the rapid acquisition of f applied constraints to other CRI parameters, a theoretical analysis of error was performed. Estimates of f in normal and pathologic tissue were expected to have <10% error. A comparison of values for f obtained from the traditional four-parameter fit of CRI data versus the proposed rapid acquisition of f was within this expected margin for in vivo rat brain gliomas (N=4; mean±SE; 3.9±0.2% vs. 4.0±0.2%, respectively). In both whole-brain f maps and myelin density maps, replacement of normal GM and WM by proliferating and invading tumor cells could be readily identified. The rapid, whole-brain acquisition of the bound pool fraction may provide a reliable method for detection of glioma invasion in both GM and WM during animal and human imaging.

An extensive invasive intracranial human glioblastoma xenograft model: role of high level matrix metalloproteinase 9

The lack of an intracranial human glioma model that recapitulates the extensive invasive and hypervascular features of glioblastoma (GBM) is a major hurdle for testing novel therapeutic approaches against GBM and studying the mechanism of GBM invasive growth. We characterized a high matrix metalloproteinase-9 (MMP-9) expressing U1242 MG intracranial xenograft mouse model that exhibited extensive individual cells and cell clusters in a perivascular and subpial cellular infiltrative pattern, geographic necrosis and infiltrating tumor-induced vascular proliferation closely resembling the human GBM phenotype. MMP-9 silencing cells with short hairpin RNA dramatically blocked the cellular infiltrative pattern, hypervascularity, and cell proliferation in vivo, and decreased cell invasion, colony formation, and cell motility in vitro, indicating that a high level of MMP-9 plays an essential role in extensive infiltration and hypervascularity in the xenograft model. Moreover, epidermal growth factor (EGF) failed to stimulate MMP-9 expression, cell invasion, and colony formation in MMP-9-silenced clones. An EGF receptor (EGFR) kinase inhibitor, a RasN17 dominant-negative construct, MEK and PI3K inhibitors significantly blocked EGF/EGFR-stimulated MMP-9, cell invasion, and colony formation in U1242 MG cells, suggesting that MMP-9 is involved in EGFR/Ras/MEK and PI3K/AKT signaling pathway-mediated cell invasion and anchorage-independent growth in U1242 MG cells. Our data indicate that the U1242 MG xenograft model is valuable for studying GBM extensive invasion and angiogenesis as well as testing anti-invasive and anti-angiogenic therapeutic approaches.

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.

In vivo imaging in a murine model of glioblastoma

OBJECTIVE

To use in vivo imaging methods in mice to quantify intracranial glioma growth, to correlate images and histopathological findings, to explore tumor marker specificity, to assess effects on cortical function, and to monitor effects of chemotherapy.

METHODS

Mice with DBT glioma cell tumors implanted intracranially were imaged serially with a 4.7-T small-animal magnetic resonance imaging (MRI) scanner. MRI tumor volumes were measured and correlated with postmortem histological findings. Different nonspecific and specific positron emission tomography radiopharmaceuticals, [18F]2-fluoro-2-deoxy-d-glucose, [18F]3'-deoxy-3'-fluorothymidine, or [11C]RHM-I, a sigma2-receptor ligand, were visualized with microPET (CTI-Concorde MicroSystems LLC, Knoxville, TN). Intrinsic optical signals were imaged serially during contralateral whisker stimulation to study the impact of tumor growth on cortical function. Other groups of mice were imaged serially with MRI after one or two doses of the antimitotic N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU).

RESULTS

MRI and histological tumor volumes were highly correlated (r2 = 0.85). Significant binding of [11C]RHM-I was observed in growing tumors. Over time, tumors reduced and displaced (P # 0.001) whisker-activated intrinsic optical signals but did not change intrinsic optical signals in the contralateral hemisphere. Tumor growth was delayed 7 days after a single dose of BCNU and 18 days after two doses of BCNU. Mean tumor volume 15 days after DBT implantation was significantly smaller for treated mice (1- and 2-dose BCNU) compared with controls (P = 0.0026).

CONCLUSION

Mouse MRI, positron emission tomography, and optical imaging provide quantitative and qualitative in vivo assessments of intracranial tumors that correlate directly with tumor histological findings. The combined imaging approach provides powerful multimodality assessments of tumor progression, effects on brain function, and responses to therapy.

Fluorescent nanoparticle uptake for brain tumor visualization

Accurate delineation of tumor margins is vital to the successful surgical resection of brain tumors. We have previously developed a multimodal nanoparticle CLIO-Cy5.5, which is detectable by both magnetic resonance imaging and fluorescence, to assist in intraoperatively visualizing tumor boundaries. Here we examined the accuracy of tumor margin determination of orthotopic tumors implanted in hosts with differing immune responses to the tumor. Using a nonuser-based signal intensity method applied to fluorescent micrographs of 9L gliosarcoma green fluorescent protein (GFP) tumors, mean overestimations of 2 and 24 microm were obtained using Cy5.5 fluorescence, compared to the true tumor margin determined by GFP fluorescence, in nude mice and rats, respectively. To resolve which cells internalized the nanoparticle and to quantitate degree of uptake, tumors were disaggregated and cells were analyzed by flow cytometry and fluorescence microscopy. Nanoparticle uptake was seen in both CD11b+ cells (representing activated microglia and macrophages) and tumor cells in both animal models by both methods. CD11b+ cells were predominantly found at the tumor margin in both hosts, but were more pronounced at the margin in the rat model. Additional metastatic (CT26 colon) and primary (Gli36 glioma) brain tumor models likewise demonstrated that the nanoparticle was internalized both by tumor cells and by host cells. Together, these observations suggest that fluorescent nanoparticles provide an accurate method of tumor margin estimation based on a combination of tumor cell and host cell uptake for primary and metastatic tumors in animal model systems and offer potential for clinical translation.

The role of thrombin in gliomas

BACKGROUND

In a previous study we found that intracerebral infusion of argatroban, a specific thrombin inhibitor, reduces brain edema and neurologic deficits in a C6 glioma model.

OBJECTIVES

To examine the role of thrombin in gliomas and whether systemic argatroban administration can reduce glioma mass and neurologic deficits and extend survival time in C6 and F98 gliomas.

METHODS

The presence of thrombin in human glioblastoma samples and rat C6 glioma cells (in vitro and in vivo) was assessed using immunohistochemistry. The effect of thrombin on C6 cell proliferation in vitro was assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay. The role of thrombin in vivo was assessed in rat C6 and F98 glioma cell models using argatroban, a thrombin inhibitor. The effects of argatroban on tumor mass, neurologic deficits and survival time were investigated.

RESULTS

Thrombin immunoreactivity was found in cultured rat C6 glioma cells and human glioblastomas. Thrombin induced C6 cell proliferation in vitro. In C6 glioma, argatroban reduced glioma mass (P < 0.05) and neurologic deficits (P < 0.05) at day 9. In F98 glioma, argatroban prolonged survival time (P < 0.05).

CONCLUSION

These results suggest that thrombin plays an important role in glioma growth. Thrombin may be a new therapeutic target for gliomas.

Why are systemic glioblastoma metastases rare? Systemic and cerebral growth of mouse glioblastoma

BACKGROUND

Systemic metastasis of glioblastoma multiforme (GBM) in the form of bulk tumor is rare. This could be because of patient death before clinically detectable systemic metastasis, impediments to systemic egress, or the inability of GBM to grow outside the central nervous system (CNS). In the present paper, we tested this last hypothesis.

METHODS

The delayed brain tumor (DBT) cell was characterized with respect to in vitro and in vivo morphology, growth rate, anchorage-independent growth, glial fibrillary acidic protein expression and cytogenetic analysis, and major histocompatibility complex (MHC) typing. We then assayed implantation-induced intracerebral and systemic GBM growth using 3 rodent models with increasing relative immunologic differences between implanted DBT cells and hosts (Balb/c mice, an isograft, MHC I H2, class type D; C3H mice, an allograft; Wistar rats, a xenograft).

RESULTS

After implantation in the brain, DBT cells generated tumors that were similar to human GBM. Intracerebral DBT implantation as an isograft or allograft produced only intracranial tumors, whereas intracerebral and systemic implantation as a xenograft produced no tumors. Systemic isograft implantation yielded only systemic tumors. Systemic implantation as allografts produced only transient subcutaneous masses.

CONCLUSIONS

Delayed brain tumor cells implanted outside the CNS formed tumors unless there was a significant difference between the immunotype of the implanted cells and host. These results support the hypothesis that the rarity of systemic GBM tumors lies in the presence of physical barriers and/or systemic hurdles that prevent their timely growth. These results also demonstrate that GBMs are antigenic, although not immunogenic, with their syngeneic host. Therefore, GBM may be amenable to targeted immunotherapy given successful artificial priming of the immune system.

Polysialic acid facilitates tumor invasion by glioma cells

Polysialic acid (PSA) is thought to attenuate neural cell adhesion molecule (NCAM) adhesion, thereby facilitating neural cell migration and regeneration. Although the expression of PSA has been shown to correlate with the progression of certain tumors such as small cell lung carcinoma, there have been no studies to determine the roles of PSA in gliomas, the most common type of primary brain tumor in humans. In this study, we first revealed that among patients with glioma, PSA was detected more frequently in diffuse astrocytoma cells, which spread extensively. To determine directly the role of PSA in glioma cell invasion, we transfected C6 glioma cells with polysialyltransferases to express PSA. In those transfected cells, PSA is attached mainly to NCAM-140, whereas the mock-transfected C6 cells express equivalent amounts of PSA-free NCAM-140. Both PSA negative and positive C6 cell lines exhibited almost identical growth rates measured in vitro. However, PSA positive C6 cells exhibited increased invasion to the corpus callosum, where the mock-transfected C6 glioma cells rarely invaded when inoculated into the brain. By contrast, the invasion to the corpus callosum by both the mock-transfected and PSA positive C6 cells was observed in NCAM-deficient mice. These results combined indicate that PSA facilitates tumor invasion of glioma in the brain, and that NCAM-NCAM interaction is likely attenuated in the PSA-mediated tumor invasion.

Cancer Cell Invasion of Brain Tissue: Guided by a Prepattern?

The malignant brain tumourGlioblastoma multiforme(GBM) displays a highly invasive behaviour. Spreading of the malignant cells appears to be guided by the white matter fibre tracts within the brain. In order to understand the global growth process we introduce a lattice-gas cellular automaton model which describes the local interaction between individual malignant cells and their neighbourhood. We consider interactions between cells (brain cells and tumour cells) and between malignant cells and the fibre tracts in the brain, which are considered as a prepattern. The prepattern implies persistent individual cell motion along the fibre structure. Simulations with the model show that only the inclusion of the prepattern results in invading tumour and growing tumour islets in front of the expanding tumour bulk (i.e. the growth pattern observed in clinical practice). Our results imply that the infiltrative growth of GBMs is, in part, determined by the physical structure of the surrounding brain rather than by intrinsic properties of the tumour cells.

Evidence for a secreted chemorepellent that directs glioma cell invasion

Secreted chemotropic cues guide the migration of neuronal and glial cell precursors during neural development. It is not known if chemotropism contributes to directing the invasion of brain tissue by glioma cells. A model system has been developed that allows quantification of invasive behavior using gliomas spheroids embedded in collagen gels. Here we provide evidence that glioma spheroids secrete a chemorepellent factor(s) that directs cells away from the spheroid and into the collagen matrix. The relationship between total invasion, cell number, and implantation distance suggests that glioma cells respond to a gradient of the chemorepellent cue(s) that is well established at 48 h. C6 astrocytoma cells normally invade the collagen at an angle perpendicular to the spheroid edge. In contrast, an adjacent spheroid causes cells to turn away from their normal trajectory and slow their rate of invasion. Astrocytoma cells are repelled by an adjacent glioma spheroid but rapidly infiltrate astrocyte aggregates, indicating that astrocytes do not express the repellent cue. Uniform concentrations of repellent factor(s) in spheroid conditioned medium overwhelm endogenous gradients and render glioma cells less able to exhibit this chemotropic response. Concentration gradients of spheroid conditioned medium in cell migration assays also demonstrate the chemorepellent cue(s)'s tropic effect. Our findings indicate that glioma spheroids produce a secreted diffusible cue(s) that promotes glioma cell invasion. Identification of this factor(s) may advance current therapies that aim to limit tumor cell invasion.

Metastasis and angiogenesis

Angiogenesis and the development of metastases are intrinsically connected. Experimental data suggest that establishment and growth of metastases are influenced by soluble factors secreted from the originating solid tumor. Among these factors are so-called endogenous inhibitors of angiogenesis which keep metastasis in a non-proliferating quiescent state. For a number of tumors it has been shown that this dormant state is mediated through inhibition of angiogenesis. This dormant state is characterized by normal proliferation, increased apoptosis, and insufficient neovascularization. Removal of inhibiting antiangiogenic factors leads to growth of dormant metastases. Several endogenous inhibitors have been identified so far and some of them have already been successfully applied in experimental therapeutic trials. This might be of special interest for the treatment of cerebral metastases which are the most common type of malignant brain tumors. Similar to the spread of metastases, it is known that single glioma cells can be found in distant parts of the brain. While local recurrence is a common phenomenon in glioma, formation of clinical apparent distant metastasis occurs rarely. Several lines of evidence suggest that growth inhibition of remote glioma cells may be mediated by an endogenous inhibitory mechanism.

Analysis of the antitumoral mechanisms of lipopolysaccharide against glioblastoma multiforme

Our objective was to analyze the lipopolysaccharide (LPS) antitumoral effect upon glioblastoma, including whether the lipid A subunit alone can elicit glioblastoma regression, whether dexamethasone suppresses this response to LPS, whether B and T lymphocytes factor in this response, and whether this antitumoral effect of LPS provides resistance against subsequent challenge with glioblastoma. Mice (BALB/c, nude or SCID) implanted with s.c. DBT glioblastomas were treated with LPS (with or without dexamethasone) or with lipid A. A subset of BALB/c mice in which s.c. DBT glioblastomas had previously been eradicated using LPS were re-implanted with s.c. or intracranial (i.c.) DBT cells. For mice with s.c. tumors, mean tumor masses (MTM) were compared between groups. Survival was compared for mice with i.c. tumors. Lipid A caused near complete tumor regression of DBT glioblastomas in BALB/c mice (p<0.0001). Dexamethasone did not alter the antitumoral effect of LPS (p=0.48). LPS reduced the MTM of s.c. glioblastomas in T lymphocyte-deficient nude mice, but not as effectively as in immunocompetent mice. The antitumoral response to LPS for T and B lymphocyte-deficient SCID mice bearing DBT glioblastomas was similar to that for nude mice. Eradication of s.c. DBT glioblastoma in BALB/c provided partial resistance to subsequent challenge with s.c. or i.c. glioblastoma. We conclude that the LPS-mediated antitumoral response against glioblastoma is dependent upon the lipid A subunit of LPS, partially dependent upon T lymphocytes, independent of B lymphocytes, unaffected by dexamethasone and provides partial protection against subsequent challenges with glioblastoma.

Characterization of gastrin-induced cytostatic effect on cell proliferation in experimental malignant gliomas

OBJECTIVE

Growth patterns of astrocytic tumors can be modulated in vitro by gastrin. In this study, the influence of gastrin on the in vitro cell cycle kinetics and the in vivo growth features of three experimental malignant gliomas was investigated.

METHODS

Gastrin-induced influence on overall growth was assayed in vitro by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium colorimetric assay for human U373 and rat C6 gliomas and for rat 9L gliosarcoma. Although cell cycle analyses were performed by means of computer-assisted microscope analyses of Feulgen-stained nuclei, the gastrin-induced effects of the levels of expression of cyclins D3 and E, CDK2, CDK4, CDK5, CDK7, p15, p16, E2F1, and E2F2 were assayed by means of quantitative Western blot test. The presence of ribonucleic acids for the CCK(B) and CCK(C) gastrin receptors in the U373, C6, and 9L models was assayed by means of quantitative reverse transcriptase-polymerase chain reaction, and the presence or absence of ribonucleic acids for CCK(A) receptor was checked by means of conventional polymerase chain reaction. The influence of gastrin was also characterized in vivo in terms of the survival periods of conventional rats orthotopically grafted with the C6 and 9L models and nude rats with the U373 model.

RESULTS

Gastrin significantly decreased the overall growth rate in the rat C6 and the human U373 high-grade astrocytic tumor models with either CCK(B) or CCK(C) gastrin receptor but not in the 9L rat gliosarcoma, which had no CCK(B) gastrin receptor (but had CCK(A) receptor) and only weak amounts of CCK(C) receptor. This effect seems to occur via a cytostatic effect; that is, an accumulation of tumor astrocytes occurs in the G(1) cell cycle phase. The cytostatic effect could relate to a gastrin-induced decrease in the amounts of the cyclin D3-CDK4 complex in both C6 and U373 glioma cells. In vivo, gastrin significantly increased the survival periods of C6 and U373 glioma-bearing rats, but not of 9L gliosarcoma-bearing rats.

CONCLUSION

Gastrin is able to significantly modify the growth levels of a number of experimental gliomas.

GABA(A)-receptor expression in glioma cells is triggered by contact with neuronal cells

The expression of functional GABA(A)-receptors in glioma cells correlates with low malignancy of tumours and cell lines from glioma lack these receptors. Here we show that contact with neurons induces the expression of functional GABA(A)-receptors. C6 and F98 glioma cell lines were labelled by recombinant expression of enhanced green fluorescent protein injected into rat brain and studied in acute slices after two to three weeks of tumour growth. The cells responded to GABA or the specific agonist, muscimol with a current typical for GABA(A)-receptors, as studied with the patch-clamp technique. To get insight into the mechanism of GABA(A) receptor induction, the C6 or F98 cells were co-cultured with neurons, astrocytes, oligodendrocytes and microglia. Glioma cells expressed functional GABA(A) receptors within 24 h only in cultures where physical contact to neurons occurred. Activation of GABA(A)-receptors in the co-cultures attenuated glioma cell metabolism while blockade of the receptors increased metabolism. We conclude that with this form of interaction, neurons can influence tumour behaviour in the brain.

Migration pathways of human glioblastoma cells xenografted into the immunosuppressed rat brain

Diffuse invasion of the brain by tumor cells is a hallmark of human glioblastomas and a major cause for the poor prognosis of these tumors. This phenomenon is only partially reproduced by rodent models of gliomas that display a very high rate of proliferation and limited cell migration. We have analyzed the development of human glioblastoma cells (GL15) xenografted into the brain of immunosuppressed rats, in order to define the characteristics of tumor cell invasion. As identified by the specific immunolabeling of the tumor cells for the human HLA-ABC antigen, GL15 tumors reproduced the three types of intraparenchymal invasion observed in patients. First, a majority of multipolar tumor cells intermingled rapidly and profusely with host neural cells in the margin of the injection site. This progressively enlarging area was principally responsible for the tumor growth over time. Second, in the gray matter, columns of thin bipolar tumor cells aligned along capillary walls. Third, in the white matter, elongated bipolar isolated tumor cells were observed scattered between axonal fibers. The maximum migration distances along white matter fibers remained significantly higher than the maximum migration distances along blood vessels, up to two months after injection. Development of the tumor was associated with a significant increase of vascularization in the area of tumor spread. Xenografting of human GL15 glioblastoma cells into the immunosuppressed rat brain allowed to differentiate between the three classical types of invasion identified in the clinic, to quantify precisely the distances of migration, and to evaluate cell morphology for each of these routes. The present results support the existence of host/tumor cells interactions with specific characteristics for each type of invasion.

Intratumoral injection of lipopolysaccharide causes regression of subcutaneously implanted mouse glioblastoma multiforme

OBJECTIVE

Anecdotal reports documented extended survival times for patients who developed infections at the site of resection of malignant gliomas. Hypothesized mechanisms for this phenomenon include immune responses triggered by lipopolysaccharide (LPS). This investigation assessed whether LPS could produce tumor regression in an in vivo model of malignant glioma.

METHODS

Delayed brain tumor cells (2 x 10(6)) were injected subcutaneously into female BALB/c mice. LPS (300-500 microg) was injected intratumorally or subcutaneously at a contralateral site on Days 10, 17, and 24. Control animals received phosphate-buffered saline intratumorally or subcutaneously. Mice were killed on Day 28, and tumors were removed. Mean tumor masses for control animals and the two LPS-treated groups (intratumoral or contralateral subcutaneous treatment) were compared. Histological assessments of treated and control tumors were performed.

RESULTS

Complete or nearly total tumor regression was achieved in all 20 mice with subcutaneous delayed brain tumor cell tumors treated intratumorally with 400 microg of LPS (mean tumor mass of 0.09 +/- 0.38 g versus 2.42 +/- 2.46 g for control animals, P < 0.0001). Intratumoral administration of 300 microg of LPS or subcutaneous injection of 300 or 400 microg of LPS at a contralateral site resulted in less consistent regression of subcutaneous tumors. Administration of 500 microg of LPS resulted in tumor regression similar to that observed with lower doses but was limited by treatment-related deaths in 40% of animals. Histological assessment revealed lymphocytic infiltration of LPS-treated tumors.

CONCLUSION

Intratumoral injections of LPS caused dramatic regression of subcutaneously implanted delayed brain tumor cell mouse gliomas. Investigation of this antitumoral effect may improve treatment responses for patients with malignant gliomas.

The expression and activation of matrix metalloproteinase-2 in rat brain after implantation of C6 rat glioma cells

It has been reported that matrix metalloproteinases (MMPs) are highly expressed in malignant glioma cells and that this increased expression may facilitate the invasiveness of tumor cells. The authors investigated the expression and enzymatic activity of MMPs in rat brain during the growth of malignant gliomas at different time intervals. C6 rat glioma cells were unilaterally implanted into rat cerebral hemispheres. After 7 or 14 days, these brain tissues were prepared for SDS-PAGE zymography, Western blotting, immunohistochemistry, and in situ zymography. SDS-PAGE zymography and Western blotting revealed that the expression of proMMP-2 in rat brains with C6 glioma cells was significantly higher than that in normal or the sham-operated rat brains, and that the activated form of MMP-2 was detected only in the former but not in the latter. On immunohistochemistry, C6 glioma cells presenting invasive growth into the rat brain parenchyma and vessels demonstrated MMP-2 immunoreactivity. On in situ zymography, foci of invasive C6 glioma cells in rat brain tissue showed gelatinolytic activity. These results suggest that expression and activation of MMP-2 may be one of the crucial steps for glioma cell invasion into the brain parenchyma in vivo.

Tracking the invasiveness of human astrocytoma cells by using green fluorescent protein in an organotypical brain slice model

OBJECT

Although it is known that malignant astrocytomas infiltrate diffusely into regions of normal brain, it is frequently difficult to identify unequivocally the solitary, invading astrocytoma cell in histopathological preparations or experimental astrocytoma models. The authors describe an experimental system that facilitates the tracking of astrocytoma cells by using nonneoplastic cerebral tissue as the substrate for invasion.

METHODS

Cerebral tissue was cut into 1-mm-thick slices and cultured in the upper chamber of a Transwell culture dish on top of a polyester membrane (0.4-mm pore size) that was bathed in medium supplied by the lower chamber. Two astrocytoma cell lines, U-87 MG (U87) and U343 MG-A (U343), were selected because of their differing basal cell motilities in monolayer cultures. The astrocytoma cells were stably transfected with vectors that expressed green fluorescent protein (GFP), either alone or as a fusion protein with the receptor for hyaluronic acid-mediated motility (RHAMM) in either sense or antisense orientations. Stably transfected clones that had high levels of GFP expression were selected using the direct visualization provided by fluorescence microscopy and fluorescence-activated cell-sorter analysis. The GFP-expressing astrocytoma cell clones were implanted into the center of the brain slice and the degree of astrocytoma invasion into brain tissue was measured at different time points by using the optical sectioning provided by the confocal laser microscope. The authors observed that GFP-expressing astrocytoma cells could be readily tracked and followed in this model system. Individual astrocytoma cells that exhibited green fluorescence could be readily identified following their migration through the brain slices. The GFP-labeled U87 astrocytoma cells migrated farther into the brain slice than the U343 astrocytoma cells. The RHAMM-transfected GFP-labeled astrocytoma cells also infiltrated farther than the GFP-labeled astrocytoma cells themselves. The expression of antisense RHAMM virtually abrogated the invasion of the brain slices by both astrocytoma cell lines.

CONCLUSIONS

The authors believe that this organotypical culture system may be of considerable utility in studying the process of astrocytoma invasion, not only because it provides a better representation of the extracellular matrix molecules normally encountered by invading astrocytoma cells, but also because the GFP tag enables tracking of highly migratory and invasive astrocytoma cells under direct vision.

Limitations of the C6/Wistar rat intracerebral glioma model: implications for evaluating immunotherapy

OBJECTIVE

Intracranial rat glioma models are a useful method for evaluating the efficacy and toxicity of novel therapies for malignant glioma. The C6/Wistar model has been used extensively as a reproducible in vivo model for studying primary brain tumors including anti-glioma immune responses. The objective of the present study is to provide in vivo evidence that the C6 rat glioma model is allogeneic within Wistar rats and is therefore inappropriate for evaluating immune responses.

METHODS

Growth patterns and immune responses of C6 cells implanted into the brain and flank of Wistar rats were analyzed and compared to an immunogenic syngeneic model (9L/Fischer).

RESULTS

Wistar rats with C6 tumors developed a potent humoral and cellular immune response to the tumor. Wistar rats given simultaneous flank and intracerebral tumors had a survival rate of 100% compared to an 11% survival rate in control animals receiving only intracranial C6 cells.

CONCLUSION

The C6 rat glioma induces a vigorous immune reaction that may mimic a specific anti-tumor response in Wistar rats. Efficacy of immunotherapy within this model must be cautiously interpreted.

Angiogenesis, metastasis, and endogenous inhibition

Angiogenesis and the development of metastases are intrinsically connected. Experimental data suggest that establishment and growth of metastases are influenced by soluble factors secreted from the originating solid tumor. Among these factors are so-called endogenous inhibitors of angiogenesis which keep metastasis in a non-proliferating quiescent state. For a number of tumors it has been shown that this dormant state is mediated through inhibition of angiogenesis. This dormant state is characterized by normal proliferation, increased apoptosis, and insufficient neo-vascularization. Removal of inhibiting anti-angiogenic factors led to growth of dormant metastases. A number of endogenous inhibitors have been identified and have shown success in experimental therapeutic trials. This might be of special interest for the treatment of cerebral metastases which are the most common type of malignant brain tumors. Similar to the spread of metastases, it is known that single glioma cells can be found in distant parts of the brain. While local recurrence is a common phenomenon in glioma, formation of clinical apparent distant metastasis occurs rarely. Several lines of evidence suggest that growth inhibition of remote glioma cells may be mediated by an endogenous inhibitory mechanism.

Gliomas in rodent whisker barrel cortex: a new tumor model

OBJECT

Surgical treatment of gliomas is difficult because they are invasive. Invasion of essential cortex often limits or precludes surgical resection. A tumor model was developed in which the rodent whisker barrel cortex was used to examine how gliomas affect cortical function and structure.

METHODS

Both DBT (mouse) and C6 (rat) glioma cell lines were grown in culture and labeled with the fluorescent marker Dil in vitro. Labeled tumor cells were then injected into the whisker barrel cortex of adult mice and rats. Neurological assessments were made daily and magnetic resonance (MR) images were obtained. Animals were killed by perfusion 6 to 14 days after injection, and histological sections were prepared and studied. Tumors were found in all 20 rats and 10 mice that had been injected with the C6 and DBT cell lines, respectively. The animal cells had been labeled with Dil in vitro, and all in vivo tumors proved to be Dil positive. The MR images revealed the tumor locations and serial MR images demonstrated tumor growth. Histological evaluation confirmed the location of the tumor and the disruption of barrel cortex architecture.

CONCLUSIONS

Both DBT and C6 glioma cell lines can be used to generate malignant glial tumors reproducibly in the whisker barrel cortex. Fluorescent labeling and cytochrome oxidase staining permit visualization of tumor growth patterns, which disrupt the barrel cortex by microscopic invasion and by gross tissue deformation. Magnetic resonance imaging demonstrates the anatomical extension of these tumors in live rodents. Using this model for further studies on the effects of malignant glioma growth on functional cerebral cortex should advance our understanding of the neurological issues and management of patients with these tumors.

Inhibition of tumor growth, angiogenesis, and microcirculation by the novel Flk-1 inhibitor SU5416 as assessed by intravital multi-fluorescence videomicroscopy

Vascular endothelial growth factor (VEGF) plays a fundamental role in mediating tumor angiogenesis and tumor growth. Here we investigate the direct effect of a novel small molecule inhibitor of the Flk-1-mediated signal transduction pathway of VEGF, SU5416, on tumor angiogenesis and microhemodynamics of an experimental glioblastoma by using intravital multifluorescence videomicroscopy. SU5416 treatment significantly suppressed tumor growth. In parallel, SU5416 demonstrated a potent antiangiogenic activity, resulting in a significant reduction of both the total and functional vascular density of the tumor microvasculature, which indicates an impaired vascularization as well as significant perfusion failure in treated tumors. This malperfusion was not compensated for by changes in vessel diameter or recruitment of nonperfused vessels. Analyses of the tumor microcirculation revealed significant microhemodynamic changes after angiogenesis blockage such as a higher red blood cell velocity and blood flow in remnant tumor vessels when compared with controls. Our results demonstrate that the novel antiangiogenic concept of targeting the tyrosine kinase of Flk-1/KDR by means of a small molecule inhibitor represents an efficient strategy to control growth and progression of angiogenesis-dependent tumors. This study provides insight into microvascular consequences of Flk-1/KDR targeting in vivo and may have important implications for the future treatment of angiogenesis-dependent neoplasms.

Uptake and kinetics of 14C-labelled meta-tetrahydroxyphenylchlorin and 5-aminolaevulinic acid in the C6 rat glioma model

Meta-tetrahydroxyphenylchlorin (m-THPC) and 5-aminolaevulinic acid (5-ALA) are two second-generation photosensitizers which are currently under investigation for photodynamic therapy (PDT) and photodynamic diagnosis (PDD). So far, the experience with these photosensitizers for use within brain tumours is limited. We examined the distribution and retention of 14C-labelled m-THPC and [14C]5-ALA in the rat C6 glioma brain tumour model. After intraperitoneal injection of m-THPC (71,909 d.p.m. microl(-1); 0.16 mg ml(-1) m-THPC; 0.3 mg kg(-1)), the following activities were found after 36 h: brain tumour 223,664 d.p.m. g(-1), brain contralateral to the tumour side 2567 d.p.m. g(-1), liver 369,959 d.p.m. g(-1) and skin 55,197 d.p.m. g(-1); 100,000 d.p.m. corresponding to 0.22 microg of m-THPC. After 7 days, the concentration of m-THPC decreased to 76,277 d.p.m. g(-1) in tumour and 635 d.p.m. g(-1) in brain. The radioactivity after intravenous administration of [14C]5-ALA (23,079 d.p.m. microl(-1); 40 mg ml(-1); 120 mg kg(-1)) increased within 15 min (59,634 d.p.m. g(-1) in tumour, 17,427 d.p.m. g(-1) in brain); after 8 h only a small amount (3653 d.p.m. g(-1) in tumour) remained. Brain adjacent to the tumour was also found to have a higher uptake of 5-ALA. This study provides basic information for the use of m-THPC and 5-ALA in brain tumours. Because of the different pharmacokinetic and toxicological profile, we recommend m-THPC for PDT and 5-ALA for PDD. Clinical trials now have to prove the superior phototoxic properties of these second-generation photosensitizers.

Mitogens as motogens

Numerous in vivo methodologies have documented the invasive behavior of glioma cells through normal brain parenchyma. Glioma cell locomotion has also been assessed with a number of in vitro assays including the Boyden chamber and other chemotaxis assays, colloidal gold cell tracking, analysis of migration of cells tumor cells from spheroids, confrontation cultures of glioma cells with aggregates of non-neoplastic tissue, time-lapse video microscopy, electron microscopic examination of the cytomorphologic correlates of cell motility, the radial dish assay, and quantitative enzyme immunoassay of proteins associated with invasion (e.g. laminin). Several of these techniques have been specifically modified to assess the effects of cytokines on glioma cell motility in vitro. Cytokines studied utilizing these methods include: epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), the bb dimer of platelet-derived growth factor (PDGFbb), nerve growth factor (NGF), interleukin 2 (IL-2), transforming growth factors alpha and beta 1 (TGF alpha and TGFstraat1), and tumor necrosis factor alpha (TNF alpha). This review summarizes the investigational methods used to evaluate random and directional glioma cell motility and invasion in vivo and in vitro. The roles of specific mitogens as motogens, as evaluated with these methods are then presented.

Rat brain tumor models in experimental neuro-oncology: the 9L, C6, T9, F98, RG2 (D74), RT-2 and CNS-1 gliomas

Rat brain tumor models have been widely used in experimental neuro-oncology for almost three decades. The present review, which will be selective rather than comprehensive, will focus entirely on seven rat brain tumor models and their utility in evaluating the efficacy of various therapeutic modalities. Although no currently available animal brain tumor model exactly simulates human high grade brain tumors, the rat models that are currently available have provided a wealth of information on in vitro and in vivo biochemical and biological properties of brain tumors and their in vivo responses to various therapeutic modalities. Ideally, valid brain tumor models should be derived from glial cells, grow in vitro and in vivo with predictable and reproducible growth patterns that simulate human gliomas, be weakly or non-immunogenic, and their response to therapy, or lack thereof, should resemble human brain tumors. The following tumors will be discussed. The 9L gliosarcoma, which was chemically induced in an inbred Fischer rat, has been one of the most widely used of all rat brain tumor models and has provided much useful information relating to brain tumor biology and therapy. The T9 glioma, although generally unrecognized, was and probably still is the same as the 9L. Both of these tumors can be immunogenic under the appropriate circumstances, and this must be taken into consideration when using either of them for studies of therapeutic efficacy, especially if survival is used as an endpoint. The C6 glioma, which was chemically induced in an outbred Wistar rat, has been extensively used for a variety of studies, but is not syngeneic to any inbred strain. Its potential to evoke an alloimmune response is a serious limitation, if it is being used in survival studies. The F98 and RG2 (D74) gliomas were both chemically induced tumors that appear to be either weakly or non-immunogenic. These tumors have been refractory to a variety of therapeutic modalities and their invasive pattern of growth and uniform lethality following an innoculum of as few as 10 tumor cells make them particularly attractive models to test new therapeutic modalities. The Avian Sarcoma Virus induced tumors and a continuous cell line derived from one of them, designated RT-2, have been useful for studies in which de novo tumor induction is an important requirement. These tumors, however, are immunogenic and this may limit their usefulness for survival studies. Finally, a new chemically induced tumor recently has been described, the CNS-1, and it appears to have a number of properties that should make it useful in experimental neuro-oncology. It is essential to recognize, however, the limitations of each of the models that have been described, and depending upon the nature of the study to be conducted, it is important that the appropriate model be selected.

Mitogens as motogens

Numerous in vivo methodologies have documented the invasive behavior of glioma cells through normal brain parenchyma. Glioma cell locomotion has also been assessed with a number of in vitro assays including the Boyden chamber and other chemotaxis assays, colloidal gold cell tracking, analysis of migration of cells tumor cells from spheroids, confrontation cultures of glioma cells with aggregates of non-neoplastic tissue, time-lapse video microscopy, electron microscopic examination of the cytomorphologic correlates of cell motility, the radial dish assay, and quantitative enzyme immunoassay of proteins associated with invasion (e.g. laminin). Several of these techniques have been specifically modified to assess the effects of cytokines on glioma cell motility in vitro. Cytokines studied utilizing these methods include: epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), the bb dimer of platelet-derived growth factor (PDGFbb), nerve growth factor (NGF), interleukin 2 (IL-2), transforming growth factors alpha and beta 1 (TGF alpha and TGFstraat1), and tumor necrosis factor alpha (TNF alpha). This review summarizes the investigational methods used to evaluate random and directional glioma cell motility and invasion in vivo and in vitro. The roles of specific mitogens as motogens, as evaluated with these methods are then presented.

Fast blue, a fluorescent tracer in glioma cell culture, affects cell proliferation and motility

The azo-dye, Fast Blue (FB), initially employed for retrograde neuronal tracing is increasingly used in cell invasion and migration studies to detect living cells in monolayer and glioma tumor cell spheroid models. As yet, it is assumed that a cell stained with a tracker dye retains the characteristics of the original cell. The following experiments compared the adhesion, migration and proliferation properties of the cell lines U373 and GaMG with and without FB staining. FB staining reduced cell adhesion (P < 0.01) and proliferative activity (P < 0.01) and also had a significant inhibitory effect on cell migration (P < 0.001). From the results presented it follows that FB staining markedly influences basic cell characteristics.

Isolation and characterization of human malignant glioma cells from histologically normal brain

Brain invasion prevents complete surgical extirpation of malignant gliomas; however, invasive cells from distant, histologically normal brain previously have not been isolated, cultured, and characterized. To evaluate invasive human malignant glioma cells, the authors established cultures from gross tumor and histologically normal brain. Three men and one woman, with a mean age of 67 years, underwent two frontal and two temporal lobectomies for tumors, which yielded specimens of both gross tumor and histologically normal brain. Each specimen was acquired a minimum of 4 cm from the gross tumor. The specimens were split: a portion was sent for neuropathological evaluation (three glioblastomas multiforme and one oligodendroglioma) and a portion was used to establish cell lines. Morphologically, the specimens of gross tumor and histologically normal brain were identical in three of the four cell culture pairs. Histochemical staining characteristics were consistent both within each pair and when compared with the specimens sent for neuropathological evaluation. Cultures demonstrated anchorage-independent growth in soft agarose and neoplastic karyotypes. Growth rates in culture were greater for histologically normal brain than for gross tumor in three of the four culture pairs. Although the observed increases in growth rates of histologically normal brain cultures do not correlate with in vivo behavior, these findings corroborate the previously reported stem cell potential of invasive glioma cells. Using the radial dish assay, no significant differences in motility between cultures of gross tumor and histologically normal brain were found. In summary, tumor cells were cultured from histologically normal brain acquired from a distance greater than 4 cm from the gross tumor, indicating the relative insensitivity of standard histopathological identification of invasive glioma cells (and hence the inadequacy of frozen-section evaluation of resection margins). Cell lines derived from gross tumor and histologically normal brain were usually histologically identical and demonstrated equivalent motility, but had different growth rates.