Tumour cell migration in the central nervous system

Chondroitin Sulphate Proteoglycans in the Tumour Microenvironment

Proteoglycans are macromolecules that are essential for the development of cells, human diseases and malignancies. In particular, chondroitin sulphate proteoglycans (CSPGs) accumulate in tumour stroma and play a key role in tumour growth and invasion by driving multiple oncogenic pathways in tumour cells and promoting crucial interactions in the tumour microenvironment (TME). These pathways involve receptor tyrosine kinase (RTK) signalling via the mitogen-activated protein kinase (MAPK) cascade and integrin signalling via the activation of focal adhesion kinase (FAK), which sustains the activation of extracellular signal-regulated kinases 1/2 (ERK1/2).Human CSPG4 is a type I transmembrane protein that is associated with the growth and progression of human brain tumours. It regulates cell signalling and migration by interacting with components of the extracellular matrix, extracellular ligands, growth factor receptors, intracellular enzymes and structural proteins. Its overexpression by tumour cells, perivascular cells and precursor/progenitor cells in gliomas suggests that it plays a role in their origin, progression and neo-angiogenesis and its aberrant expression in tumour cells may be a promising biomarker to monitor malignant progression and patient survival.The aim of this chapter is to review and discuss the role of CSPG4 in the TME of human gliomas, including its potential as a druggable therapeutic target.

Evaluation of Poly (Glycerol-Adipate) Nanoparticle Uptake in an In Vitro 3-D Brain Tumor Co-Culture Model

Despite the inherent problems associated with in vivo animal models of tumor growth and metastases, many of the current in vitro brain tumor models also do not accurately mimic tumor-host brain interactions. Therefore, there is a need to develop such co-culture models to study tumor biology and, importantly, the efficacy of drug delivery systems targeting the brain. So far, few investigations of this nature have been published. In this paper we describe the development of a new model system and its application to drug delivery assessment. For our new model, a co-culture of DAOY cell brain tumor aggregates and organo-typic brain slices was developed. Initially, the DAOY aggregates attached to cerebellum slices and invaded as a unit. Single cells in the periphery of the aggregate detached from the DAOY aggregates and gradually replaced normal brain cells. This invasive behavior of DAOY cells toward organotypic cerebellum slices shows a similar pattern to that seen in vivo. After validation of the co-culture model using transmission electron microscopy, nanoparticle (NP) uptake was then evaluated. Confocal micrographs illustrated that DAOY cells in this co-culture model took up most of the NPs, but few NPs were distributed into brain cells. This finding corresponded with results of NP uptake in DAOY and brain aggregates reported elsewhere.

Time-lapse phenotyping of invasive glioma cells ex vivo reveals subtype-specific movement patterns guided by tumor core signaling

The biology of glioblastoma invasion and its mechanisms are poorly understood. We demonstrate using time-lapse microscopy that grafting of glioblastoma (GBM) tumorspheres into rodent brain slices results in experimental ex vivo tumors with invasive properties that recapitulate the invasion observed after orthotopic transplantation into the rodent brain. The migratory movements and mitotic patterns were clearly modified by signals extrinsic to the invading cells. The cells migrated away from the tumorspheres, and removal of the spheres reduced the directed invasive movement. The cell cultures contained different populations of invasive cells that had distinct morphology and invasive behavior patterns. Grafts of the most invasive GBM culture contained 91±8% cells with an invasive phenotype, characterized by small soma with a distinct leading process. Conversely, the majority of cells in less invasive GBM grafts were phenotypically heterogeneous: only 6.3±4.1% of the cells had the invasive phenotype. Grafts of highly and moderately invasive cultures had different proportions of cells that advanced into the brain slice parenchyma during the observation period: 89.2±2.2% and 23.1±6.8%, respectively. In grafts with moderately invasive properties, most of the cells (76.8±6.8%) invading the surrounding brain tissue returned to the tumor bulk or stopped centrifugal migration. Our data suggest that the invasion of individual GBM tumors can be conditioned by the prevalence of a cell fraction with particular invasive morphology and by signaling between the tumor core and invasive cells. These findings can be important for the development of new therapeutic strategies that target the invasive GBM cells.

Opposing signaling of ROCK1 and ROCK2 determines the switching of substrate specificity and the mode of migration of glioblastoma cells

Despite current advances in therapy, the prognosis of patients with glioblastoma has not improved sufficiently in recent decades. This is due mainly to the highly invasive capacity of glioma cells. Little is known about the mechanisms underlying this particular characteristic. While the Rho-kinase (ROCK)-dependent signaling pathways involved in glioma migration have yet to be determined, they show promise as one of the candidates in targeted glioblastoma therapy. There are two ROCK isoforms: ROCK1, which is upregulated in glioblastoma tissue compared to normal brain tissue, and ROCK2, which is also expressed in normal brain tissue. Blockage of both of these ROCK isoforms with pharmacologic inhibitors regulates the migration process. We examined the activities of ROCK1 and ROCK2 using knockdown cell lines and the newly developed stripe assay. Selective knockdown of either ROCK1 or ROCK2 exerted antidromic effects on glioma migration: while ROCK1 deletion altered the substrate-dependent migration, deletion of ROCK2 did not. Furthermore, ROCK1 knockdown reduced cell proliferation, whereas ROCK2 knockdown enhanced it. Along the signaling pathways, key regulators of the ROCK pathway are differentially affected by ROCK1 and ROCK2. These data suggest that the balanced activation of ROCKs is responsible for the substrate-specific migration and the proliferation of glioblastoma cells.

Dissecting the inter-substrate navigation of migrating glioblastoma cells with the stripe assay reveals a causative role of ROCK

A hallmark of gliomas is the growth and migration of cells over long distances within the brain and proliferation within selected niches, indicating that the migrating cells navigate between complex substrates. We demonstrate in the present study a differential preference for migration that depends on Rho-associated coil kinase (ROCK) signaling, using the alternating Bonhoeffer stripe assay. Membrane fractions from nonmyelinated and myelinated brain areas from female rats, purified myelin also from female rats, and commercial extracellular matrix were used as substrates, with each substrate being tested against the others. The human tumor cell lines exhibited a clear preference for extracellular matrix over all other substrates and for myelinated over nonmyelinated tissue. ROCK signaling was different when cells were cultured on either substrate. The ROCK inhibitor Y27632 significantly attenuated and neutralized the preference for extracellular matrix and myelin, indicating that ROCK controls the substrate selectivity. The findings of this study pave the way for navigation-targeted therapeutics.

CD133: holy of grail of neuro-oncology or promiscuous red-herring?

The CD133 glycoprotein is a controversial cancer stem cell marker in the field of neuro-oncology, based largely on the now considerable experimental evidence for the existence of both CD133+ve and CD133-ve populations as tumour-initiating cells. It is thought that decreasing oxygen tension enhances the complex regulation and phenotype of CD133 in glioma. In light of these ideologies, establishing the precise functional role of CD133 is becoming increasingly critical. In this article, we review the complex regulation of CD133 and its extracellular epitope AC133, and associated alterations, to tumour cell behaviour by hypoxia. Furthermore, its role in functional modulation of tumours, rather than determination of a specific stem cell type is therefore alluded to, while evidence for and against its ability as a cancer stem cell marker in primary brain tumours, is critically evaluated. Thus, the suggestion that CD133 may be a central 'holy grail' in identifying core cells for propagation of malignant glial neoplasms seems increasingly less convincing. It remains to be seen, however, whether CD133 is randomly expressed on such brain tumour cell populations or whether it is of major significance to brain biological behaviour.

Probing the mechanical properties of brain cancer cells using a microfluidic cell squeezer device

Despite being invasive within surrounding brain tissues and the central nervous system, little is known about the mechanical properties of brain tumor cells in comparison with benign cells. Here, we present the first measurements of the peak pressure drop due to the passage of benign and cancerous brain cells through confined microchannels in a "microfluidic cell squeezer" device, as well as the elongation, speed, and entry time of the cells in confined channels. We find that cancerous and benign brain cells cannot be differentiated based on speeds or elongation. We have found that the entry time into a narrow constriction is a more sensitive indicator of the differences between malignant and healthy glial cells than pressure drops. Importantly, we also find that brain tumor cells take a longer time to squeeze through a constriction and migrate more slowly than benign cells in two dimensional wound healing assays. Based on these observations, we arrive at the surprising conclusion that the prevailing notion of extraneural cancer cells being more mechanically compliant than benign cells may not apply to brain cancer cells.

A Prominin-1-Rich Pediatric Glioblastoma: Biologic Behavior Is Determined by Oxygen Tension-Modulated CD133 Expression but Not Accompanied by Underlying Molecular Profiles

Few studies on the biologic and molecular properties of pediatric glioblastoma have been performed. Until now, differential genomic analysis of CD133(+)ve and CD133(-)ve fractions has not been described in pediatric glioma. We hypothesize not only that the presence of CD133 could be the source of tumor resistance but also that maintenance of this molecule by hypoxia dictates cellular and molecular behavior. From a series of human glioblastoma biopsies investigated, only one, IN699 (from a pediatric glioblastoma), generated greater than 4% of the total cell volume as CD133(+)ve cells. Using this pediatric glioblastoma, containing unprecedented high levels of the putative brain tumor stem cell marker CD133, as a study model, we report biologic and molecular characteristics of the parent culture and of CD133(+)ve and CD133(-)ve populations derived therefrom under atmospheric and hypoxic culture conditions. Immunocytochemistry and flow cytometry were performed with antigenic markers known to characterize neural stem cells and associated glioma behavior. Behavioral analysis was carried out using proliferation, adhesion, migration, and invasion assays. Cell cycle analysis and array comparative genomic hybridization were used to assess copy number profiles for parental cells and CD133(+)ve and CD133(-)ve fractions, respectively. With regard to invasion and proliferation, CD133(+)ve and CD133(-)ve fractions were inversely proportional, with a significant increase in invasive propensity within the CD133(-)ve cells (P < .005) and a significant increase in proliferation within CD133(+)ve cells (P < .005). Our observations indicate identical genomic imbalances between CD133(+)ve and CD133(-)ve fractions. Furthermore, our research documents a direct link between decreasing oxygen tension and CD133 expression.

Receptors for hyaluronic acid and poliovirus: a combinatorial role in glioma invasion?

Background

CD44 has long been associated with glioma invasion while, more recently, CD155 has been implicated in playing a similar role. Notably, these two receptors have been shown closely positioned on monocytes.

Methods and Findings

In this study, an up-regulation of CD44 and CD155 was demonstrated in established and early-passage cultures of glioblastoma. Total internal reflected fluorescence (TIRF) microscopy revealed close proximity of CD44 and CD155. CD44 antibody blocking and gene silencing (via siRNA) resulted in greater inhibition of invasion than that for CD155. Combined interference resulted in 86% inhibition of invasion, although in these investigations no obvious evidence of synergy between CD44 and CD155 in curbing invasion was shown. Both siRNA-CD44 and siRNA-CD155 treated cells lacked processes and were rounder, while live cell imaging showed reduced motility rate compared to wild type cells. Adhesion assay demonstrated that wild type cells adhered most efficiently to laminin, whereas siRNA-treated cells (p<0.0001 for both CD44 and CD155 expression) showed decreased adhesion on several ECMs investigated. BrdU assay showed a higher proliferation of siRNA-CD44 and siRNA-CD155 cells, inversely correlated with reduced invasion. Confocal microscopy revealed overlapping of CD155 and integrins (β₁, α_vβ₁ and α_vβ₃) on glioblastoma cell processes whereas siRNA-transfected cells showed consequent reduction in integrin expression with no specific staining patterns. Reduced expression of Rho GTPases, Cdc42, Rac1/2/3, RhoA and RhoB, was seen in siRNA-CD44 and siRNA-CD155 cells. In contrast to CD44-knockdown and ‘double’-knockdown cells, no obvious decrease in RhoC expression was observed in CD155-knockdown cells.

Conclusions

This investigation has enhanced our understanding of cell invasion and confirmed CD44 to play a more significant role in this biological process than CD155. Joint CD44/CD155 approaches may, however, merit further study in therapeutic targeting of infiltrating glioma cells.

Predictive factors for overall and progression-free survival, and dissemination in oligodendroglial tumors

The pattern of recurrence and predictive factors for tumor progression, dissemination and survival in oligodendroglial tumors were investigated. 56 consecutive patients with oligodendroglial tumors were retrospectively analyzed to determine the predictive significance of various factors, including World Health Organization grade, loss of chromosomes 1p and 19q, and immunohistochemical features of TP53, O(6)-methylguanine-deoxyribonucleic-acid-methyltransferase, CD44H, nestin, and Ki-67. Eleven patients developed dissemination, and had significantly shorter post-progression survival compared to ten patients with local recurrence. Univariate analysis showed that retention of chromosome 1p or 19q, Ki-67 labeling index > or = 25%, diffuse expression of nestin, and p53 labeling index > or = 10% were unfavorable factors for overall, progression-free, and dissemination-free survival. Multivariate analysis showed that Ki-67 labeling index > or = 25% and diffuse expression of nestin were significant for dissemination-free survival. In conclusion, post-progression survival shows significant differences between patients with local and disseminated recurrence. Ki-67 labeling index and nestin expression pattern are useful markers to predict dissemination.

Approaches to mitochondrially mediated cancer therapy

For some malignant cancers even combined surgical, radiotherapeutic and chemotherapeutic approaches are not curative, indeed, in certain tumour types even a modest survival benefit is difficult to achieve. There are various biological reasons which underlie this profound resistance but the propensity of cancer cells to repair breaks caused by DNA-damaging radiation and cytotoxic drugs is of major significance in this context. Such highly resistant tumours include the malignant gliomas which are intrinsic to and directly affect the brain and spinal cord. In evaluating approaches which do not elicit tumour cell death directly by DNA damage, it is intriguing to consider mitochondrially mediated apoptosis as a potentially effective alternative. Since the mitochondrial membrane potentials in cancer cells are frequently reduced in comparison with those of non-neoplastic cells this allows a window of opportunity for small molecule agents to enter the tumour cell mitochondria and reduce oxygen consumption with subsequent release of cytochrome c and activation of a caspase pathway to apoptosis which is cancer cell specific. In the quest for agents which can selectively destroy neoplastic cells in this manner, whilst leaving normal adjacent cells intact, various tricyclic drugs have come under scrutiny. In a range of laboratory assays we, and others, have established that certain cancers and, in particular, malignant glioma, are intrinsically sensitive to this approach. We have also established the cellular, molecular and biochemical mechanisms underlying this process. While such archival tricyclics as the antidepressants, clomipramine and amitriptyline, have been used in these experiments their commercial development in cancer therapy has not been forthcoming and their clinical use in glioma has been confined to anecdotal cases. In addition, the dose-dependant role of agents such as anticonvulsants and steroids commonly used in glioma patients in modulating efficacy of the tricyclics is a matter for continued investigation. Other ways of targeting the mitochondrion for cancer therapy include exploitation of the 18kDa translocator protein (peripheral-type benzodiazepine receptor) within the mitochondrial permeability transition pore and enzymatic or molecular modification of a species of ganglioside (GD3/GD3(A)) expressed on the surface of neoplastic cells which are determinants of mitochondrially mediated apoptosis. It is hoped that such approaches may lead to clinical programmes which will improve the prognosis for patients suffering from highly resistant neoplasms.

Cancer stem cells in the mammalian central nervous system

Malignant tumours intrinsic to the central nervous system (CNS) are among the most difficult of neoplasms to treat effectively. The major biological features of these tumours that preclude successful therapy include their cellular heterogeneity, which renders them highly resistant to both chemotherapy and radiotherapy, and the propensity of the component tumour cells to invade, diffusely, the contiguous nervous tissues. The tumours are classified according to perceived cell of origin, gliomas being the most common generic group. In the 1970s transplacental administration of the potent neurocarcinogen, N-ethyl-N-nitrosourea (ENU), enabled investigation of the sequential development of brain and spinal neoplasms by electron microscopy and immunohistochemistry. The significance of the primitive cells of the subependymal plate in cellular origin and evolution of a variety of glial tumours was thereby established. Since then, the development of new cell culture methods, including the in vitro growth of neurospheres and multicellular tumour spheroids, and new antigenic markers of stem cells and glial/neuronal cell precursor cells, including nestin, Mushashi-1 and CD133, have led to a reappraisal of the histological classification and origins of CNS tumours. Moreover, neural stem cells may also provide new vectors in exciting novel therapeutic strategies for these tumours. In addition to the gliomas, stem cells may have been identified in paediatric tumours including cerebellar medulloblastoma, thought to be of external granule cell neuronal derivation. Interestingly, while the stem cell marker CD133 is expressed in these primitive neuroectodermal tumours (PNETs), the chondroitin sulphate proteoglycan neuronal/glial 2 (NG2), which appears to denote increased proliferative, but reduced migratory activity in adult gliomas, is rarely expressed. This is in contrast to the situation in the histologically similar supratentorial PNETs. A possible functional 'switch' between proliferation and migration in developing neural tumour cells may exist between NG2 and ganglioside GD3. The divergent pathways of differentiation of CNS tumours and the possibility of stem cell origin, for some, if not all, such neoplasms remain a matter for debate and continued research, but the presence of self-renewing neural stem cells in the CNS of both children and adults strongly suggests a role for these cells in tumour initiation and resistance to current therapeutic strategies.

The Tumor Necrosis Factor-like Weak Inducer of Apoptosis (TWEAK)-Fibroblast Growth Factor-inducible 14 (Fn14) Signaling System Regulates Glioma Cell Survival via NFκB Pathway Activation and BCL-XL/BCL-W Expression

The Fn14 gene encodes a type Ia transmembrane protein that belongs to the tumor necrosis factor receptor superfamily. We recently showed that fibroblast growth factor-inducible 14 (Fn14) is overexpressed in migrating glioma cells in vitro and in glioblastoma multiforme clinical specimens in vivo. To determine the biological role of Fn14 in brain cancer progression, we examined the activity of Fn14 as a potential mediator of cell survival. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK)-stimulated glioma cells had increased cellular resistance to cytotoxic therapy-induced apoptosis. Either TWEAK treatment or Fn14 overexpression in glioma cells resulted in the activation of NFkappaB and subsequently the translocation of NFkappaB from the cytoplasm to the nucleus. In addition, Fn14 activation induced BCL-XL and BCL-W mRNA and protein levels, and this effect was dependent upon NFkappaB transcriptional activity. Substitution of a putative NFkappaB binding site identified in the BCL-X promoter significantly decreased Fn14-induced transactivation. Furthermore Fn14-induced transactivation of the BCL-X promoter was also diminished by the super-repressor IkappaBalpha mutant, which specifically inhibits NFkappaB activity, and by mutations in the NFkappaB binding motif of the BCL-X promoter. Additionally small interfering RNA-mediated depletion of either BCL-XL or BCL-W antagonized the TWEAK protective effect on glioma cells. Our results suggest that NFkappaB-mediated up-regulation of BCL-XL and BCL-W expression in glioma cells increases cellular resistance to cytotoxic therapy-induced apoptosis. We propose that the Fn14 protein functions, in part, through the NFkappaB signaling pathway to up-regulate BCL-XL and BCL-W expression to foster malignant glioblastoma cell survival. Targeted therapy against Fn14 as an adjuvant to surgery may improve management of invasive glioma cells and advance the outcome of this devastating cancer.

Expression of Cathepsin B and microvascular density increases with higher grade of astrocytomas

Samples were taken from supratentorial gliomas border and normal brain autopsy which were divided into four groups, these including eight cases normal brain tissues, 30 cases of astrocytomas, 25 cases of anaplastic astrocytomas and 22 cases of glioblastomas. Cathepin B (CB) expression and microvessel density (MVD) were determined with immunohistochemical studies. Staining results of CB was scored according to the percentage of positive cells, graded as negative (-), weak (+), moderate (++), and strong (+ + +). MVD was analyzed by Weidner's revised technique. CB positive staining was negative in eight cases of normal brain tissue. Only 9 out of 30 cases of astrocytomas showed a low percentage of positive cells that were stained in a light, diffuse cytoplasmic pattern (score +). Twenty-two out of 35 cases of anaplastic astrocytomas showed positive light, granular staining pattern, it including five samples (score +), and 17 samples (score + +). In contrast, all 22 cases of glioblastomas were stained all, and it was present in a course, granular staining pattern with an intensity of score (+ +) of two sample, and score (+ + +) of 20 samples. Positive staining tumor cells were found in extracellular matrix (ECM), basement membrane (BM), and the endothelial cells of blood vessels were also positive stained. Along with elevating glioma grade, CB expression and MVD value were both increased. Therefore, it showed MVD value was positive correlated with expression of CB. It highly suggested that CB and angiogenesis plays an important role in glioma progression.

Cathepsin B, D and K expression in adamantinomatous craniopharyngiomas relates to their levels of differentiation as determined by the patterns of retinoic acid receptor expression

AIMS

To investigate the potential predictive value of cathepsins B, D and K in a series of 51 adamantinomatous craniopharyngiomas. While almost always benign, craniopharyngiomas exhibit a high propensity to recur postsurgically and biological markers are therefore needed to predict their recurrence. We have previously demonstrated the potential predictive value of retinoic acid receptors (RARs) (Lefranc et al., J. Neurosurg. 2003; 98; 145-153).

METHODS AND RESULTS

Computer-assisted microscopy was used to determine quantitatively the immunohistochemical levels of expression of the alpha, beta and gamma RAR subtypes and cathepsins B, D and K. The levels of expression of cathepsin D and of cathepsin B correlated significantly with the levels of expression of RARbeta. The levels of expression of cathepsin K correlated significantly with the levels of expression of RARgamma.

CONCLUSIONS

Recurrent adamantinomatous craniopharyngiomas are characterized by low levels of RARbeta and high levels of RARgamma. The tendency to recurrence seems, at least partly, to relate to the fact that (i) craniopharyngiomas with low levels of RARbeta express low levels of cathepsin D, and (ii) craniopharyngiomas with high levels of RARgamma express high levels of cathepsin K.

Matrix metalloproteinase-2 and-9 expression in astrocytic tumors

In this study, we investigated whether the expression of matrix metalloproteinase (MMP)-2 and MMP-9 correlated with invasiveness, proliferative potential, or prognosis in astrocytic tumors. Thirty-seven astrocytic tumors (8 diffuse astrocytomas, 15 anaplastic astrocytomas, and 14 glioblastomas) and three gliomatosis cerebri were investigated immunohistochemically. The invasive glioma group included three cases of gliomatosis cerebri and two of glioblastoma associated with cerebrospinal fluid dissemination. The expression of MMP-2 and MMP-9 was evaluated by assigning an immunohistochemical (IHC) score defined as the sum of expression frequency and intensity. mRNA expression patterns for the MMPs were also evaluated in a reverse transcription-polymerase chain reaction assay. Neither the MMP-2 nor MMP-9 IHC score was related to histological malignancy. The MMP-2 IHC score of the invasive glioma group was significantly higher than those of other kinds of astrocytic tumors. However, the MMP-9 IHC score did not correlate with dissemination among astrocytic tumors. An inverse correlation was observed between the MIB-1 labeling index and the IHC scores of MMP-2, but it was not significant. A Kaplan-Meyer survival analysis revealed no significant relationship between the survival rate and MMP-2 or MMP-9 expression. Our study showed that MMP-2 expression, but not MMP-9 expression, may be associated with invasion in astrocytic tumors.

AMOG/beta2 and glioma invasion: does loss of AMOG make tumour cells run amok?

The beta2 subunit of Na,K-ATPase, initially described as adhesion molecule on glia (AMOG), has been shown to mediate neurone-astrocyte adhesion as well as neural cell migration in vitro. We have investigated the expression of AMOG/beta2 in human gliomas and its effect on glioma cell adhesion and migration. Compared to normal astrocytes of human brain, AMOG/beta2 expression levels of neoplastic astrocytes were down-regulated in biopsy specimens and inversely related to the grade of malignancy. One rat and four human glioma cell lines showed complete loss of AMOG. To investigate the function of AMOG/beta2, its expression was re-established by transfecting an expression plasmid into AMOG/beta2-negative C6 rat glioma cells. In vitro assays revealed increased adhesion and decreased migration on matrigel of AMOG/beta2-positive cells as compared to their AMOG/beta2-negative counterparts. We conclude that increasing loss of AMOG/beta2 during malignant progression parallels and may underlie the extensive invasion pattern of malignant gliomas.

Extraneural metastases of paediatric brain tumours

A survey of published cases of extraneural metastases of primary brain tumours in children under the age of 18 years revealed 245 cases; 60.7% occurred in boys and 27.3% were directly related to the placing of a shunt. The most common entities leading to extraneural metastases were medulloblastomas (56.3%), germinomas (9.8%), glioblastomas (6.9%), ependymomas (3.7%) and pilocytic astrocytomas (2.9%). While medulloblastomas were frequent among non-shunt-related metastases (69.4%), germ cell tumours were most common among shunt-related metastases (33.3%). Metastases were encountered equally often in bone (56.3%) and visceral organs (55.5%) but were markedly rarer in lymph nodes (25.3%). Medulloblastomas showed a preference for bones (88.3% of cases), germinomas for bones (77.8%) and visceral organs (66.7%), whereas ependymomas and ependymoblastomas were more frequently found in lymph nodes and visceral organs (71.5-100%). The most frequent sites of bone metastases were the pelvis (59.3% of cases with osseous lesions), femur (54%) and vertebrae (46%). Medulloblastomas preferentially spread into pelvis, femur and vertebrae, whereas germ cell tumours mainly involved pelvis, femur and ribs and glioblastomas vertebrae and pelvis. Most frequent sites of lymph node metastases were cervical (45.8% of cases with nodular lesions) and thoracic (31.3%) with 54% of children suffering from medulloblastomas and 7.9% from germ cell tumours. The most frequent organ involved in non-shunt-related metastases were the lungs (56.5% of children with visceral lesions) followed by muscle/soft tissue (26.9%), pleura (16.4%), skin (14.9%) and liver (13.4%). Among shunt-related cases, the peritoneum was the most frequent site (86.6% of children). The mean interval between primary brain tumour and occurrence of metastasis was 22.1 months with particularly grave outcomes among medulloblastomas, non-germinomatous germ cell tumours and glioblastomas (85.5-100% deceased children), whereas 60% of children suffering from germinomas were still alive at the time of reporting.

The human Fn14 receptor gene is up-regulated in migrating glioma cells in vitro and overexpressed in advanced glial tumors

Glioblastoma multiforme comprises the majority of human brain tumors. Patients with glioblastoma multiforme have poor survival rates, with an average life expectancy of <1 year. To assess possible mechanisms and to potentially target invasive glioma cells, we previously measured the gene expression profiles of glioma cells under migration-activated or passive states. One of the genes identified was Fn14, which encodes a cell surface receptor for the tumor necrosis factor superfamily member named TWEAK. In this study, we show that Fn14 gene expression is induced in migration-activated glioma cells in vitro and significantly increases according to tumor grade in vivo (P < 0.01), with highest levels in glioblastoma tissue specimens. The in situ expression pattern of Fn14 mRNA and protein was confined to primary glioma cells and the vascular endothelium, with no detection in adjacent normal brain. Conversely, TWEAK mRNA levels are low in glioblastoma samples relative to normal brain tissue. In addition, activation of the Fn14 receptor by addition of recombinant TWEAK resulted in increased glioma cell migration in vitro. These results suggest a positive role for TWEAK and Fn14 in glioma progression and indicate that Fn14 gene expression may serve as a marker for invasive glioma cells.

Selective suppression of cathepsin L by antisense cDNA impairs human brain tumor cell invasion in vitro and promotes apoptosis

Invasion and metastasis of certain tumors are accompanied by increased mRNA protein levels and enzymatic activity of cathepsin L. Cathepsin L has also been suggested to play a role in the proteolytic cascades associated with apoptosis. To investigate the role of cathepsin L in brain tumor invasion and apoptosis, the human glioma cell line, IPTP, was stably transfected with full-length antisense and sense cDNA of cathepsin L. Down-regulation of cathepsin L by antisense cDNA significantly impaired (up to 70%) glioma cell invasion in vitro and markedly increased glioma cell apoptosis induced by staurosporine. Compared to control and parental cell lines, antisense down-regulation of cathepsin L was associated with an earlier induction of caspase-3 activity. Up-regulation of cathepsin L activity by sense cDNA was associated with reduced apoptosis and later induction of caspase-3 activity. Moreover, down-regulation of cathepsin L lowered the expression of antiapoptotic protein Bcl-2, whereas up-regulation increased the expression of Bcl-2, indicating that cathepsin L acts upstream of caspase-3. These data show that cathepsin L is an important protein mediating the malignancy of gliomas and its inhibition may diminish their invasion and lead to increased tumor cell apoptosis by reducing apoptotic threshold.

CD44H is expressed by cells of the oligodendrocyte lineage and by oligodendrogliomas in humans

CD44, a family of cell surface glycoproteins involved in cell-cell and cell-extracellular matrix adhesion, is widely expressed in the white matter of the normal brain and in astrocytic gliomas under its standard form (CD44s also called CD44H). On the other hand, several variants have been found in brain metastases and rarely found in gliomas. We have investigated by immunohistochemistry CD44H and CD44v6 expression in 28 oligodendrogliomas. All tumors were CD44v6 negative whereas nearly all tumors were immunolabelled with anti-CD44H antibody. Immunostaining increased in parallel with grade and was particulary strong around vessels and in tumoral subpial nodules. Western blot analysis showed that oligodendrogliomas expressed the same 80-kDa CD44 isoform as normal brain. Since gliomas may arise from a dividing progenitor cell, we also studied CD44H expression during the oligodendrocyte lineage in vitro in parallel with specific markers of the O-2A cells. Precursor cells (PSA-NCAM positive), O-2A progenitor cells, as well as preoligodendrocytes (A2B5 positive cells) and immature oligodendrocytes (O4 positive cells), coexpressed CD44H. Our data showed that CD44H is expressed by cells of the oligodendrocyte lineage in vitro and by oligodendrogliomas in vivo especially in sites of dissemination such as subpial spaces. This suggests that CD44H could play a role in migration of tumor cells in oligodendrocytic tumors.

The role of matrix metalloproteinase genes in glioma invasion: co-dependent and interactive proteolysis

Matrix metalloproteinases (MMPs) are cation-dependent endopeptidases which have been implicated in the malignancy of gliomas. It is thought that the MMPs play a critical role in both metastasis and angiogenesis, and that interference with proteases might therefore deter local tumor dissemination and neovascularization. However, the attempt to control tumor-associated proteolysis will rely on better definition of the normal tissue function of MMPs, an area of study still in its infancy in the central nervous system (CNS). Understanding the role of MMP-mediated proteolysis in the brain relies heavily on advances in other areas of molecular neuroscience, most notably an understanding of extracellular matrix (ECM) composition and the function of cell adhesion molecules such as integrins, which communicate knowledge of ECM composition intracellularly. Recently, protease expression and function has been shown to be strongly influenced by the functional state and signaling properties of integrins. Here we review MMP function and expression in gliomas and present examples of MMP profiling studies in glioma tissues and cell lines by RT-PCR and Western blotting. Co-expression of MMPs and certain integrins substantiates the gathering evidence of a functional intersection between the two, and inhibition studies using recombinant TIMP-1 and integrin antisera demonstrate significant inhibition of glioma invasion in vitro. Use of promising new therapeutic compounds with anti-MMP and anti-invasion effects are discussed. These data underline the importance of functional interaction of MMPs with accessory proteins such as integrins during invasion, and the need for further studies to elucidate the molecular underpinnings of this process.

Migratory activity of human glioma cell lines in vitro assessed by continuous single cell observation

A new migration assay, the time-lapse individual cell migration assay (TIM-assay), was developed, which allows the observation of cells over 24 h under controlled conditions. Using this technique, the migratory behavior of 8 human glioblastoma cell lines in vitro was studied. Special features are simultaneous documentation of migratory parameters of individual cells, i.e., migration velocities and migration paths of individual cells. Migration velocity for cell populations of the same cell line ranged from 0 to 24 microm/h. The migration paths were examined for being directional. Two thirds of all cells showed directional migration. Migration paths were further classified according to visual judgements for being linear, oscillating or mixed. The migration index had a mean of 91%. The presented TIM-assay allows the assessment of several new parameters. that may be useful to identify subgroups of gliomas with different biological characteristics.

The role of matrix metalloproteinase genes in glioma invasion: co-dependent and interactive proteolysis

Matrix metalloproteinases (MMPs) are cation-dependent endopeptidases which have been implicated in the malignancy of gliomas. It is thought that the MMPs play a critical role in both metastasis and angiogenesis, and that interference with proteases might therefore deter local tumor dissemination and neovascularization. However, the attempt to control tumor-associated proteolysis will rely on better definition of the normal tissue function of MMPs, an area of study still in its infancy in the central nervous system (CNS). Understanding the role of MMP-mediated proteolysis in the brain relies heavily on advances in other areas of molecular neuroscience, most notably an understanding of extracellular matrix (ECM) composition and the function of cell adhesion molecules such as integrins, which communicate knowledge of ECM composition intracellularly. Recently, protease expression and function has been shown to be strongly influenced by the functional state and signaling properties of integrins. Here we review MMP function and expression in gliomas and present examples of MMP profiling studies in glioma tissues and cell lines by RT-PCR and Western blotting. Co-expression of MMPs and certain integrins substantiates the gathering evidence of a functional intersection between the two, and inhibition studies using recombinant TIMP-1 and integrin antisera demonstrate significant inhibition of glioma invasion in vitro. Use of promising new therapeutic compounds with anti-MMP and anti-invasion effects are discussed. These data underline the importance of functional interaction of MMPs with accessory proteins such as integrins during invasion, and the need for further studies to elucidate the molecular underpinnings of this process.

Migration and invasion in brain neoplasms

Local invasion of the brain by neoplastic glial cells is a major obstacle to effective treatment of intrinsic brain tumors. Invasion is directly related to histologic malignancy, but occurs to some extent irrespective of tumor grade. Because the brain-to-tumor interface is not well demarcated, total surgical removal is rarely possible; moreover, as invading cells transiently arrest from cell division they are refractory to radiotherapeutic intervention. Invading cells may also be protected from the action of cytotoxic drugs by the presence of an intact blood-brain barrier. The invading cells, having migrated several millimeters or even centimeters from the main focus of the tumor, return to cycle phase under the control of some as yet unknown microenvironmental cue to form a recurrent tumor adjacent to the original site of presentation. Recent cellular and genetic information concerning factors underlying invasion may not only yield suitable targets for adaptation of existing therapies, but may also lead to novel approaches in glioma management.

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.

Evaluation of the effects of swainsonine, captopril, tangeretin and nobiletin on the biological behaviour of brain tumour cells in vitro

Although intrinsic tumours of the brain seldom metastasize to distant sites, their diffuse, infiltrative-invasive growth within the brain generally precludes successful surgical and adjuvant therapy. Hence, attention has now focused on novel therapeutic approaches to combat brain tumours that include the use of anti-invasive and anti-proliferative agents. The effect of four anti-invasive agents, swainsonine (a locoweed alkaloid), captopril (an anti-hypertensive drug), tangeretin and nobiletin (both citrus flavonoids), were investigated on various parameters of brain tumour invasion such as matrix metalloproteinase (MMP) secretion, migration, invasion and adhesion. A standard cytotoxicity assay was used to optimize working concentrations of the drugs on seven human brain tumour-derived cell lines of various histological type and grade of malignancy. A qualitative assessment by gelatin zymography revealed that the effect of these agents varied between the seven cell lines such that the low grade pilocytic astrocytoma was unaffected by three of the agents. In contrast, downregulation of the two gelatinases, MMP-2 and MMP-9 was seen in the grade 3 astrocytoma irrespective of which agent was used. Generally, swainsonine was the least effective whereas the citrus flavonoids, particularly nobiletin, showed the greatest downregulation of secretion of the MMPs. Furthermore, captopril and nobiletin were most efficient at inhibiting invasion, migration and adhesion in four representative cell lines (an ependymoma, a grade II oligoastrocytoma, an anaplastic astrocytoma and a glioblastoma multiforme). Yet again, the effects of the four agents varied between the four cell lines. Nobiletin was, nevertheless, the most effective agent used in these assays. In conclusion, the differential effects seen on the various parameters studied by these putative anti-invasive agents may be the result of interference with MMPs and other mechanisms underlying the invasive phenotype. From these pilot studies, it is possible that these agents, especially the citrus flavonoids, could be of future therapeutic value. However, further work is needed to validate this in a larger study.

Expression of matrix metalloproteinase-2 in glial and neuronal tumor cell lines: inverse correlation with proliferation rate

The expression of matrix metalloproteinases (MMPs) has been found to be positively correlated to the degree of malignancy in gliomas, indicating that poorly differentiated brain tumor cells produce more MMPs than differentiated ones. We determined the production of active MMP-2 in five glial (U138MG, U373MG, A172, C6, GOS-3), two neuronal (SK-N-SH, SK-N-MC), and two pluripotent cell lines with facultative neuronal and glial differentiation (P19 and NT2) by gelatin zymography. The MMP-2 activity profiles were compared to the proliferative activities of the cell lines. MMP-2 expression varied from barely existent (P19 cells) to strong (U138MG and SK-N-SH). Interestingly, for the cell lines with high MMP-2 expression levels, low proliferative activities were recorded, and vice versa. Retinoic acid induced neuronal differentiation and a reduction of proliferation of P19 cells; the differentiated cells produced significantly more MMP-2 than untreated cells. Upon confluency, GOS-3 cells showed reduced proliferation, but increased MMP expression. Thus, proliferative activity was inversely correlated to MMP-2 expression in the tumor cell lines analyzed.

The NG2 chondroitin sulfate proteoglycan: role in malignant progression of human brain tumours

The expression and function of NG2, a transmembrane chondroitin sulfate proteoglycan was studied in human gliomas of various histological types in culture using immunocytochemistry and flow cytometry. NG2 was differentially expressed in the neoplasms, with higher expression in high compared to low-grade gliomas. In acutely isolated cells from human biopsies, NG2 +ve and NG2 -ve populations were morphologically distinct from each other, and NG2 +ve cells were more proliferative than NG2 -ve cells. The mitogens platelet derived growth factor (PDGF-AA) and basic fibroblast growth factor (bFGF) added in combination to serum-free medium (SFM) upregulated NG2 expression on glioblastoma multiforme cells in culture but had little effect on NG2 expression on the anaplastic astrocytoma cells. Furthermore, NG2 was colocalised with the platelet derived growth factor alpha receptor (PDGFalphaR) and antibody blockade of the PDGF-alphaR ablated NG2 expression on the glioblastoma multiforme cells, suggesting that increased NG2 expression in the presence of PDGF-AA is mediated via the PDGF-alphaR. Assays of migration and invasion indicate that NG2 +ve glioma cells migrated more efficiently on collagen IV and that NG2 -ve cells were more invasive than their NG2 +ve counterparts. The results indicate that NG2 may be, respectively, positively and negatively related to the proliferative and invasive capacity of glioma cells. Thus, expression of the NG2 proteoglycan may have major implications for malignant progression in glial neoplasms and may prove a useful target for future therapeutic regimens.

CD44 expression in primary and recurrent oligodendrogliomas and in adjacent gliotic brain tissue

CD44 expression was evaluated in 114 primary and recurrent oligodendrogliomas (46 primary oligodendrogliomas grade II and 15 recurrences grade II; 17 primary anaplastic oligodendrogliomas and nine recurrent oligodendrogliomas grade III; 14 glioblastomas with oligodendroglial growth pattern and 13 tumour recurrences grade IV). CD44 expression was found to correlate with tumour grading (P<0.001) and with survival (Kaplan-Meier Log Rank P<0.01, median survival 28 months in oligodendrogliomas with CD44 expression vs. 108 months in CD44-negative tumours). However, multivariate Cox regression analysis of grading and CD44 expression revealed that CD44 expression had no prognostic relevance independent of histological grading. Characterization of CD44 positive cells by double labelling with GFAP revealed that in addition to oligodendroglioma cells, reactive astrocytes within the tumour, at the invasive margin and along the pathways of oligodendroglioma invasion in the subpial matrix, and in the vicinity of vessels, frequently expressed CD44. It is suggested that in analogy to carcinoma invasion where a tumour-induced production of hyaluronan was found in fibroblasts at the invasive margin of the tumour, in the brain reactive astrocytes may produce hyaluronan which would facilitate the adhesion of new CD44-positive astrocytic processes but which would also promote tumour invasion.

CD44 expression and hyaluronic acid binding of malignant glioma cells

The mechanisms leading to rapid invasive growth of malignant gliomas are poorly understood. Expression of the hyaluronic acid (HA) receptor CD44 and adhesion to HA are involved in invasive properties. Our previous studies have shown that malignant glioma cells are able to adhere to extracellular HA. Here we investigated expression of the hyaluronic acid receptor CD44 protein in five human (T98G, A172, U87MG, 86HG39, 85HG66) and two rat (C6, 9L) glioma cell lines. Influence of anti-CD44 antibody and hyaluronidase-preincubation on the HA-binding was determined using HA/BSA (bovine serum albumin)-coated culture plates. While all gliomas were highly positive for CD44 with no differences in the number of positive staining cells, median fluorescence intensity decreased as follows: C6>T98G>9L>85HG66> 86HG39>A172>U87MG. Using HA/BSA coated culture plates the relative levels of specific adhesion to HA were determined as T98G>A172>9L>86HG39>U87MG> 85HG66. C6 cells failed to bind HA specifically. Incubation with anti-human-CD44 MAb significantly decreased HA-adhesion of T98G, A172, 85HG66 and U87MG human glioma cells. However the binding capacity was completely blocked only in 85HG66 cells. The three other cell lines kept a specific HA-adhesion after saturation of the receptor. Hyaluronidase pretreatment markedly enhanced HA-adhesion of C6 and 9L rat glioma cells. These results suggest that (i) HA-adhesion of malignant glioma cells is mainly, but not only, mediated by CD44, (ii) expression of CD44 does not correspond with adhesion capacity and (iii) cell-bound glycosaminoglycans may influence glioma cell adhesion to extracellular HA.

Membrane-type 1 matrix metalloprotease (MT1-MMP) enables invasive migration of glioma cells in central nervous system white matter

Invasive glioma cells migrate preferentially along central nervous system (CNS) white matter fiber tracts irrespective of the fact that CNS myelin contains proteins that inhibit cell migration and neurite outgrowth. Previous work has demonstrated that to migrate on a myelin substrate and to overcome its inhibitory effect, rat C6 and human glioblastoma cells require a membrane-bound metalloproteolytic activity (C6-MP) which shares several biochemical and pharmacological characteristics with MT1-MMP. We show now that MT1-MMP is expressed on the surface of rat C6 glioblastoma cells and is coenriched with C6-MP activity. Immunodepletion of C6-MP activity is achieved with an anti-MT1-MMP antibody. These data suggest that MT1-MMP and the C6-MP are closely related or identical. When mouse 3T3 fibroblasts were transfected with MT1-MMP they acquired the ability to spread and migrate on the nonpermissive myelin substrate and to infiltrate into adult rat optic nerve explants. MT1-MMP-transfected fibroblasts and C6 glioma cells were able to digest bNI-220, one of the most potent CNS myelin inhibitory proteins. Plasma membranes of both MT1-MMP-transfected fibroblasts and C6 glioma cells inactivated inhibitory myelin extracts, and this activity was sensitive to the same protease inhibitors. Interestingly, pretreatment of CNS myelin with gelatinase A/MMP-2 could not inactivate its inhibitory property. These data imply an important role of MT1-MMP in spreading and migration of glioma cells on white matter constituents in vitro and point to a function of MT1-MMP in the invasive behavior of malignant gliomas in the CNS in vivo.

Quantitative analysis of microvascular changes in diffuse astrocytic neoplasms with increasing grade of malignancy

Because glioblastoma multiforme (GBM) frequently shows striking, glomeruloid microvascular proliferation (MVP), this tumor has become a strong candidate for anti-angiogenic therapy. However, the efficacy of anti-angiogenic treatment may rather be determined by the extent of classic angiogenesis with the formation of delicate microvascular sprouts. Therefore, this study differentially quantifies the microvascular changes in supratentorial diffuse astrocytic neoplasms by computerized image analysis of histological sections in which the microvessels were highlighted by a combined anti-collagen IV/MIB-1 staining. Four microvascular parameters (number, area, perimeter, diameter), the cellularity of the glial tissue, and the MIB-1 labeling index were assessed in biopsies of astrocytoma (A, n = 13), anaplastic astrocytoma (AA, n = 14), and GBM (n = 20), and in normal cerebral cortex (n = 7) and white matter (n = 7). In As and AAs, the microvascular parameters were not significantly different from each other, and the microvascular changes were generally limited compared with WM and CX. In contrast, in GBMs the microvascular parameters were highly variable, and their overall mean value was significantly increased compared with As and AAs (ranging from 1.3x for vessel diameter to 3.3x for vessel area). Our study indicates that not only glomeruloid MVP, but also classic angiogenesis, occurs mainly and only locally in GBMs. Thus, this study provides evidence that As and AAs are not good candidates for anti-angiogenic therapy. The efficacy of such therapy for GBMs awaits further evaluation.

Angiogenesis in brain tumors; pathobiological and clinical aspects

Angiogenesis is the outgrowth of new blood vessels from the preexistent vasculature. In 1971, Folkman hypothesized that solid tumors are dependent on angiogenesis for sustained growth and that anti-angiogenic treatment is a potential antineoplastic therapy. Because glioblastoma multiforma (GBM) frequently shows florid microvascular proliferation (MVP), this tumor has been considered since then as a suitable candidate for such treatment that attempts to eradicate or control a neoplasm by interfering with its blood supply. Indeed, in animal models the growth of glioma xenografts can be inhibited by targeting the angiogenic process. However, unlike many glioma xenografts, human infiltrating gliomas such as GBMs have a diffuse infiltrative growth pattern, and preexistent vessels may suffice to provide many tumor cells with much of their blood supply, particularly in the critical peripheral infiltrative margins. Thus, while attractive in concept, anti-angiogenic therapy of GBM must address the anatomic vascular realities of this neoplasm. Even if anti-angiogenic therapy ultimately has a role in infiltrative neoplasms, there are a host of other intracranial neoplasms whose discrete architecture might make them attractive candidates for anti-angiogenic therapy. This review summarizes the angiogenic process in GBM and suggests other types of tumors for which the efficacy of anti-angiogenic therapy might be studied.

A molecular genetic model of astrocytoma histopathology

As the molecular events responsible for astrocytoma formation and progression are being clarified, it is becoming possible to correlate these alterations with the specific histopathological and biological features of astrocytoma, anaplastic astrocytoma and glioblastoma multiforme. In WHO grade II astrocytomas, autocrine stimulation by the plateletderived growth factor system coupled with inactivation of the p53 gene may lead to a growth stimulus in the face of decreased cell death with slow net growth ensuing. Such cells would also have defective responses to DNA damage and impaired DNA repair, setting the stage for future malignant change. Such biological scenarios recapitulate many of the clinicopathological features of WHO grade II astrocytomas. Anaplastic astrocytomas further display release of a critical cell cycle brake that involves the CDKN2/p16, RB and CDK4 genes. This results in mitoses seen histologically; clinically, there is more conspicuous, rapid growth. Finally, glioblastomas may emerge from the microenvironmental outgrowth of more malignant clones in a complex vicious cycle that involves necrosis, hypoxia, growth factor release, angiogenesis and clonal selection; growth signals mediated by activation of epidermal growth factor receptors may precipitate glioblastomas. It is clear as well that glioblastoma multiforme can arise via a number of independent genetic pathways, although the clinical significance of these distinctions remains unclear.

Glioma invasion in vitro is mediated by CD44-hyaluronan interactions

Invasion is a clinically important problem contributing to mortality and morbidity in patients with gliomas, but the mechanism(s) by which glioma cells invade surrounding brain structures is poorly understood. Various experimental models have been used in attempts to elucidate the process of glioma invasion. An in vitro model which is increasingly being employed involves measurement of the rate of invasion of tumour cells through Matrigel-a complex mixture of extracellular matrix components derived from the Engelbroth-Holm-Swarm (EHS) sarcoma. This model has been used to examine the possibility that extracellular hyaluronan (HA) might facilitate the invasive behaviour of human glioma cells. The major component of Matrigel is laminin, with smaller amounts of collagen IV, heparan sulphate proteoglycans, entactin, and nidogen but it lacks HA. In our experiments, we have incorporated HA into Matrigel and have measured its effect on the rate of invasion of human glioma cells in a modified Boyden chamber assay system. The incorporation of HA (50-800 mg/cm2) resulted in a dose-dependent increase in invasion. Invasion was enhanced by up to 70 per cent in comparison with HA-free Matrigel. Since CD44 is a major HA receptor expressed on gliomas, it might have a role in the HA-mediated facilitation of invasion. This was tested by blocking CD44 with specific antibody, which resulted in a 43 per cent reduction in invasion rate. We conclude that in an in vitro model system, HA enhances invasion of glioma cells and that the mechanism involves a CD44-HA interaction.

Dynamic characterization of glioblastoma cell motility

The cell motility dynamic of two glioblastoma cell lines (U373 and U87) was studied by means of an automatic video-cell-tracking-system enabling each cell in a colony to be tracked for several hours. Twenty-five experiments were performed on both models growing on three different supports (glass, plastic and Matrigel). Cell motility was significantly different in each cell line and also for different growth support in a given cell line. We observed that U87 cells are significantly (p < 0.00001) less motile than U373 cells. The most favorable growth supports for cell motility studies were Matrigel and glass. A significant (p < 0.001) correlation between cell colony density and cell motility was highlighted, with isolated cells exhibiting a motility level distinct from the one observed for colonies. The present methodology, which enabled cell motility to be quantified in human glioblastoma cells, represents an original tool for identifying new classes of compounds able to reduce glioblastoma cell motility and cell migration potential into the brain.

Local spread of malignant neuroepithelial tumors

A short review of invasiveness of primary malignant neoplasms in the nervous system is given. Invasiveness implies progressive spread and destruction locally, which eventually leads to a fatal outcome in the patient. In particular, the malignant cells are able to rapidly migrate over large parts of the brain. This process includes the capacity to adhere to a substratum, usually constituted by the various components of the extracellular matrix, followed by detachment and migration. Anatomical structures and local regulatory factors in the brain influence the direction and extent of this migration. Several model systems are now available for monitoring the aggressiveness of such tumours both in vivo and in vitro, and different phenotypic properties characteristic of invasive cells have been elucidated. Although still in its infancy, and currently as an experimental approach, anti-invasive therapy may in the future be an interesting alternative to conventional chemotherapy of brain tumours.

The standard isoform of CD44 is preferentially expressed in atypical papillomas and carcinomas of the choroid plexus

Isoforms of the CD44 adhesion molecule have been assigned a pivotal role in tumor invasion and metastasis. CD44 splice variants may be selectively expressed in various normal and neoplastic tissues. We investigated immunohistochemically the presence of the standard (H) and two variant (v3, v6) isoforms of the CD44 molecule in a series comprising 13 choroid plexus papillomas (WHO grade I) and 8 carcinomas (WHO grade III). In the papilloma group, 5 tumors showed variable cellular pleomorphism and foci of infiltrative growth, and were tentatively classified as atypical papillomas. Autopsy specimens of normal pediatric and adult choroid plexus were used as control. Western-blot analysis of CD44H was carried out on 4 carcinomas, 1 papilloma and on normal choroid plexus. The proliferation rate was assessed by MIB-1 immunoreactivity. The normal choroid plexuses and 9 papillomas were negative for the standard as well as the variant CD44 molecules investigated. Four atypical papillomas and 5 carcinomas expressed CD44H. CD44v3 and CD44v6 were only detected in one of the atypical papillomas also positive for CD44H. These data indicate that CD44H is preferentially expressed on atypical papillomas and carcinomas and may correlate with the infiltrative growth of these tumors.

Role of CD44 in the invasiveness of glioblastoma multiforme and the noninvasiveness of meningioma: an immunohistochemistry study

CD44 is a polymorphic family of cell adhesion molecules that seems to be instrumental in the mechanism of tumor invasion and metastasis. Tumor cell expression of CD44, or lack thereof, may be one of the factors conditioning the highly disparate ability to penetrate the brain extracellular matrix (ECM) exhibited by glioblastoma multiforme (GM) and conventional meningioma. To assess the presence of CD44 in these two tumor types we have immunohistochemically investigated the expression of CD44 standard form (CD44s) and the variant isoforms containing the domain encoded by variant exon 3 (CD44v3) and variant exon 6 (CD44v6) in paraffin-embedded tissue from 10 conventional meningiomas and 10 GMs. A CD44s-/CD44v-phenotype was discerned in the meningioma cases, whereas GMs featured a CD44s+/CD44v- expression profile. Consequently, the growth patterns of meningioma and GM seem to be, at least in part, a reflection of their CD44 expression status. Paucity of CD44 in meningioma cells would render them unable to infiltrate the brain ECM, whereas CD44-rich glioma cells would successfully migrate through it. Conversely, lack of CD44v expression would contribute to explain the lack of metastatic potential characterizing both conventional meningioma and GM.

Growth factors and gangliosides stimulate laminin production by human glioma cells in vitro

Neoplastic cells from intrinsic, neuroectodermal tumours may migrate up to several millimeters away from the original tumour mass into normal nervous tissue. The biological mechanisms underlying this local invasive behaviour of gliomas are poorly understood. We have demonstrated recently that growth factors and cell surface gangliosides are positively involved in human glioma cell adhesion, migration and invasion in vitro. In order to study the mechanism of action of gangliosides and growth factors in this process, their role in the production of laminin, the major component of glioma vascular basal lamina, was investigated. Both growth factors and gangliosides stimulated laminin production in vitro suggesting that these factors increase laminin production in order to enable glioma cells to adhere and then migrate and invade in vivo.

Interactions of glioma cells and extracellular matrix

The communication between tumor cells and extracellular matrix (ECM) is responsible for clinically important features of malignant gliomas, such as cerebral invasion and leptomeningeal spread. The synthesis of ECM components, ECM-degrading activities and ECM receptors as well as the interaction between ECM components and their receptors represents the molecular basis for these processes. Recent studies have shown that proteases and integrins, the major group of ECM receptors, may be over-expressed by astrocytic tumor cells. Furthermore, integrins and the hyaluronate receptor CD44 have been found to be involved in adhesion and basement membrane invasion of glioma cells. Critical issues which are poorly understood so far include the ECM composition of the normal human brain and of brain tumors, the function of individual ECM components and receptors in a neuro-oncological context, and the molecular processes mediating the diffuse invasion of glioma cells into the brain.