The role of growth factors in the malignant and invasive progression of intrinsic brain tumours

Although growth factors are acknowledged for their mitogenic activity, a number of other functions are fulfilled by such peptides. These include control of motile and invasive behaviour, angiogenesis and phenotype. Various growth factors including epidermal growth factor, fibroblast growth factor, platelet derived growth factor, transforming growth factor and vascular endothelial growth factor have been described in human glial tumours. These factors may act in either autocrine or paracrine loop systems to determine the malignant potential of intrinsic brain tumours. This review examines each of these factors and their various isoforms and outlines the influence they may exert on the behaviour of neoplastic glia. Moreover, the role of growth factors in the control of the various mechanisms which underlie diffuse infiltrative invasion, neovascularisation and proliferation are explored. Finally, the potential of growth factors and their receptors as therapeutic targets is considered.

Adenovirus-mediated p16/CDKN2 gene transfer suppresses glioma invasion in vitro

Malignant gliomas extensively infiltrate the surrounding normal brain, and their diffuse invasion is one of the most important barriers to successful therapy. Recent studies indicate that the progression of gliomas from low-grade to high-grade may depend on the acquisition of a new phenotype and the subsequent addition of genetic defects. One of the most frequent abnormalities in the progression of gliomas is the inactivation of tumor-suppressor gene p16, suggesting that loss of p16 is associated with acquisition of malignant characteristics. Consistent with this hypothesis, our previous studies showed that restoring wild-type p16 activity into p16-null malignant glioma cells modified their phenotype. In order to understand whether the biological consequences of p16 inactivation in high-grade gliomas included facilitating invasiveness, we used a recombinant replication-deficient adenovirus carrying the cDNA of the p16/CDKN2 gene to infect and express high levels of p16 protein in p16-null SNB19 glioma cells. Invasion of SNB19 glioma cells was tested into two models: invasion of glioma cells through Matrigel-coated transwell inserts and invasion of tumor-cell spheroids into fetal rat-brain aggregates in a co-culture system. Matrigel invasion assays showed that the SNB19 cells expressing exogenous p16 exhibited significantly reduced invasion. Similarly, invasion of p16-treated SNB19 cells into fetal rat-brain aggregates was reduced during a 72 h time period compared to invasion of the adenovirus-control and mock-infected cells. Expression of matrix metalloproteinase-2 (MMP-2), an enzyme involved in tumor-cell invasion, in SNB19 cells expressing p16 was significantly reduced compared to that of parental SNB19 and vector-infected cells. Our results show that restoring wild-type p16 activity into p16-null SNB19 glioma cells significantly inhibits tumor-cell invasion, thus suggesting a novel function of the p16 gene.

Inhibition of in vivo tumorigenicity and invasiveness of a human glioblastoma cell line transfected with antisense uPAR vectors

Our previous studies showed that glioblastomas express increased urokinase-type plasminogen activator receptors (uPARs) in comparison to low-grade gliomas (Yamamoto et al., Cancer Res., 54, 5016-5020, 1994). To explore whether downregulation of uPAR inhibits tumor formation and invasiveness, a human glioblastoma cell line was transfected with a cDNA construct corresponding to 300 bp of the human uPAR's 5' end in an antisense orientation, resulting in a reduced number of uPA receptors. Co-culture studies with tumor spheroids and fetal rat brain aggregates showed that antisense SNB19-AS1 cells expressing reduced uPAR failed to invade fetal rat brain aggregates. Intracerebral injection of SNB19-AS1 stable transfectants failed to form tumors and were negative for uPAR expression in nude mice. Thus uPAR appears in this model to be essential for tumorigenicity and invasion of glioblastomas in vivo.

Effects of photodynamic therapy on glioma spheroids

The present study describes the sensitivity of glioma cells to a haematoporphyrin derivative (Photosan-3) under laser activation (argon-pumped dye laser). The effects of photodynamic therapy (PDT) on cell growth, directional migration and cell invasion were investigated on two human glioma cell lines (GaMg and U-251 Mg). The directional cell migration and spheroid growth was determined for both cell lines exposed to increasing laser energy output (15-35J/cm2) with concentrations of 5 and 7 micrograms/ml of Photosan-3. Both cell lines showed a dose-dependent migratory response to increasing laser irradiation, that was more prominent in the 7 micrograms/ml treatment group. This effect occurred during the first 4 days after drug exposure. Also, spheroids from both cell lines showed a drug and laser output energy dose-dependent inhibition of growth which became apparent after a lag period of 6 days. The lag period was characterized by a decreased growth rate as compared with the control group. During this period the outer cell layers of the spheroids fell apart. The remaining spheroid tissue was not able to migrate and to regrow when exposed to the highest laser energy outputs (30-35J/cm2, 5 and 7 micrograms/ml Photosan-3). These spheroids showed, however, the ability for invasion when confronted with normal brain cell aggregated in vivo. Light microscopic observations of co-cultures between tumour tissue and brain cell aggregates revealed a normal tumour morphology. This indicates that the remaining tumour cells were not dead and could be stimulated to invade the normal tissue when exposed to a normal brain microenvironment.

Release of replication-deficient retroviruses from a packaging cell line: interaction with glioma tumor spheroids in vitro

The present study describes how various growth conditions affect gene expression and virus production from a retroviral packaging cell line (Liz 9), grown as monolayers and as multicellular spheroids. In addition, to study the direct interaction between packaging cells and tumor tissue of glioma origin, Liz 9 spheroids were confronted with tumor spheroids derived from a human glioma cell line, GaMg. The results show a progressive gene transfer into the tumor tissue, with 9% transfection efficacy after 5 days of co-culture. In comparison, no gene transfer was observed when the Liz 9 spheroids were confronted with normal brain-cell aggregates. The Liz 9 spheroids established from early-passage cultures (passages 7-14) showed limited growth during 28 days, whereas those initiated from late-passage monolayer cultures (passages 39-49) showed extensive growth. Flow-cytometric DNA profiles of monolayers and of spheroids indicated no difference in cell-cycle distribution or ploidy between early and late passages. A cell-viability assay using scanning confocal microscopy revealed mostly viable cells in the Liz 9 spheroids, with only a few dead cells scattered within the structures. The lacZ-gene expression was maintained in early- and in late-passage cultures. In comparison, in Liz 9 early-passage monolayers, the virus titer was 3.1 x 10(4) +/- 0.4 x 10(4) CFU/ml, whereas no virus titer was found in late-passage cultures. The virus titer from the Liz 9 spheroids was found to be between 10(3) and 10(4) CFU/ml. It is concluded that the virus production from packaging cells may vary, depending on passage number and tissue-culture conditions. In the present study, this is demonstrated by a complete loss in virus titer during prolonged culture of packaging cells. In addition, the 3-dimensional confrontation system described allows direct visualization of how packaging cells interact with tumor tissue. Thus, the co-culture system represents a model for studying the efficiency of packaging cells in transfecting heterogeneous tumor tissue in vitro.

Tumor cell invasion and angiogenesis in the central nervous system

Tumor cell growth and invasion within the CNS imply complex interactions among malignant cells, neural cells, and endothelial cells. Various in vitro assays have been developed to study tumor cell invasion that includes the use of cocultures between tumor spheroids and organotypic cultures of normal brain tissue. Furthermore, various animal models have been developed to study biologic characteristics of brain tumors. At present, there is evidence that several growth factors are involved in both endothelial and tumor cell proliferation, whereas the interrelationship between glioma growth and invasion is less well established. It is also emerging that the process of invasion is characterized by dynamic interactions between the extracellular matrix, proteases, and specific cell surface receptors. The dissemination of tumor cells within the CNS also involves a passive component where single tumor cells may follow specific pathways mediated by the constant flow of cerebrospinal fluid.

Role of high molecular weight extracellular matrix proteins in glioma cell migration

Malignant human gliomas are characterized by an uncontrolled cell proliferation and infiltrative growth within the brain. Complete surgical removal is difficult due to disseminated tumour cells, and the fundamental mechanisms responsible for this spread are poorly understood. An extensive tumour cell movement along blood vessels is frequently observed and this may be due to specific interactions between tumour cell surface receptors and specific extracellular matrix (ECM) components present in conjunction with vascular elements. In order to investigate the influence of ECM on glioma cell migration, three different human glioma cell lines (U-373 MG, A-172 MG and HF-66) were exposed to known ECM components of the basement membrane (laminin, fibronectin and collagen type IV). Cell migration from multicellular spheroids was studied, using a custom-made medium which was prepared by removing the high molecular weight protein fraction (>100 kDa) from newborn calf serum by ultrafiltration. To this medium, the specific ECM components were added. For two of the cell lines (A-172 MG and U-373 MG), laminin was the most potent stimulator of glioma cell migration; the effect of laminin exceeded that evoked by ordinary serum-supplemented medium. For the HF-66 cell line, fibronectin was the most potent stimulator of migration. Western blot analysis showed that the A-172 MG and HF-66 cell lines expressed low amounts of laminin compared with U-373 MG, which showed extensive intrinsic synthesis of this ligand. U-373 MG was the only cell line that migrated in pure filtered medium. The cells stimulated by fibronectin expressed a different morphology from those stimulated by laminin suggesting that specific ECM-receptor binding may activate different cytoskeletal components within the cells. Furthermore, it was shown that there was no difference in the amount of protein synthesis between cells grown in filtered medium and in filtered medium supplemented with different ECM components. This suggests that ECM-induced cell migration is not dependent on a high level of protein synthesis. It is also shown that alpha3 integrin, which is a receptor-subunit for laminin, fibronectin and collagen type IV, was highly expressed in all cell lines. This study indicates that glioma cells need serum proteins with a molecular weight >100 kDa to migrate in vitro, and that laminin and fibronectin play an important role in this process.

Proliferation, migration and invasion of human glioma cells exposed to paclitaxel (Taxol) in vitro

Paclitaxel (Taxol), an anti-cancer drug derived from Taxus species, was tested for its anti-migrational, anti-invasive and anti-proliferative effect on two human glioma cell lines (GaMg and D-54Mg) grown as multicellular tumour spheroids. In addition, the direct effect of paclitaxel on glioma cells was studied using flow cytometry and scanning confocal microscopy. Both cell lines showed a dose-dependent growth and migratory response to paclitaxel. The GaMg cells were found to be 5-10 times more sensitive to paclitaxel than D-54Mg cells. Paclitaxel also proved to be remarkably effective in preventing invasion in a co-culture system in which tumour spheroids were confronted with fetal rat brain cell aggregates. Control experiments with Cremophor EL (the solvent of paclitaxel for clinical use) in this study showed no effect on tumour cell migration, cell proliferation or cell invasion. Scanning confocal microscopy of both cell lines showed an extensive random organization of the microtubules in the cytoplasm. After paclitaxel exposure, the GaMg and the D-54Mg cells exhibited a fragmentation of the nuclear material, indicating a possible induction of apoptosis. In line with this, flow cytometric DNA histograms showed an accumulation of cells in the G2/M phase of the cell cycle after 24 h of paclitaxel exposure. After 48 h, a deterioration of the DNA histograms was observed indicating nuclear fragmentation.

Stimulation of glioma-cell migration by laminin and inhibition by anti-alpha3 and anti-beta1 integrin antibodies

An induction of laminin in the confrontation zone between tumor cells and normal brain tissue has been observed in our model systems in vivo and in vitro. In order to study the effects of ECM components on glioma-cell migration and invasion, we have used 2 lacZ-transfected glioma cell lines, AN1/lacZ and U-251 /lacZ. Cell migration from multicellular spheroids was studied using different types of media: DMEM with 10% serum, Ultra Culture medium, and filtrated DMEM with serum in which the protein fraction > 100 kDa had been removed by ultrafiltration. Laminin, fibronectin and collagen type-IV were individually added to the different media, and cell migration from the spheroids was studied. The results show that cell migration in both cell lines, was stimulated by laminin and fibronectin. Collagen type-IV stimulated only cell migration of U-251/lacZ cells. Scanning electron microscopy revealed an extensive change in cell shape as a result of laminin stimulation. Flowcytometric studies showed that both AN1/lacZ and U-251/lacZ strongly express the alpha3 beta1 integrin receptor, which can bind to several ECM components (laminin, fibronectin, collagen). Immunofluorescence microscopy demonstrated that the same integrin sub-units were expressed in multicellular spheroids. When monoclonal antibodies to alpha3 and beta1 were added to the laminin-stimulated cultures, cell migration was significantly reduced. This indicates that the alpha3 beta1 integrin receptor plays an important role during glioma-cell migration.

Nonadhesive stationary organ culture of human bronchial mucosa

The supply of fresh bronchial tissue from human donors for in vitro culture is limited. Routine fiberoptic bronchoscopy offers a safe and easy procedure for obtaining minor biopsies and we wanted to see if the material provided could be used for organ culture by using a simple liquid overlay technique. Bronchial biopsies were cut into fragments 400-500 microns and kept immersed in a standard serum-supplemented medium for 40 days. An agar base prevented adhesion of the tissue. By light and electron microscopy it was shown that the tissue fragments had a differentiated epithelium at their surface throughout the culture period. An outgrowth of epithelial cells on the scaffold of the exposed stroma, covering the surface of the whole fragment, occurred within the first 5 days of culture. This epithelium was partly ciliated, 2-4 cell layers thick with squamous and cuboidal cells and expressed epithelial markers (cytokeratin and Ber-Ep4). The amount of cilia increased during the first 15 days of culture. The epithelium rested on a neosynthesized basement membrane as visualized by electron microscopy and immunohistochemistry with antibodies directed against collagen IV, laminin, and fibronectin. The central stroma consisted of loose connective tissue with fibroblasts. This simple tissue culture model combines maintenance and neoformation of bronchial epithelium on top of a living natural substrate, thus enabling direct biological studies on clinical biopsy material under perfectly viable conditions.

The lac-z reporter gene: a tool for in vitro studies of malignant glioma cell invasion

A reporter gene (lac-z) was introduced into rat (BT4C) and human (D-54 MG) proliferating glioma cell lines by means of liposomal transfection. Lac-z-transfected glioma cells were first cultured as multicellular spheroids and then confronted with fetal brain aggregates. After various intervals the lac-z reporter gene product, bacterial beta-galactosidase, was histochemically detected in the cocultures. beta-Galactosidase was only detected in the glioma cells which showed an intense blue staining, which made them easily distinguishable from fetal tissue. Both glioma cell lines showed a clear pattern of migration and increasing invasion with time as the tumor cells infiltrated and destroyed the brain aggregates. Spheroid growth curves showed no significant differences between transfected and nontransfected cell lines. Likewise, flow cytometry measurements revealed no significant changes in ploidy between transfected and nontransfected rat glioma cells. In comparison, a shift in ploidy was observed in the human glioma cells after lac-z transfection. Stable integration of the lac-z gene into tumor cells was verified by Southern blot analysis. The results indicate that transfection of the lac-z reporter gene into glioma cells lines does not affect their growth or invasion potential in vitro. The lac-z reporter gene can thus be exploited to facilitate visualization of single migrating tumor cells and quantification of tumor invasion in in vitro coculture systems.

Migratory patterns of lac-z transfected human glioma cells in the rat brain

Malignant brain tumors are characterized by extensive tumor-cell infiltration into the normal brain tissue. The present work describes the migratory behavior of human glioma cells transplanted into the adult rat brain with the aim of exploiting the extent of active cell migration and passive cell displacement within the central nervous system. To detect every transplanted tumor cell, a stably bacterial beta-galactosidase (lac-z) transfected human glioma cell line was used. To distinguish between an active cell migration process and passive cell displacement, rat brains were also implanted with inert fluorescent polystyrene microspheres and the distribution of tumor cells and microspheres was studied 1 hr and 3 days after implantation. One hour after implantation the tumor cells were strictly localized at the implantation site. However, 3 days after implantation, both tumor cells and microspheres showed an extensive distribution within the brain. Confirming earlier neuropathological and experimental studies, it is shown that the lac-z-transfected glioma cells had the capacity to move within the Virchow-Robin and subarachnoid spaces. However, since fluorescent microspheres were also found in these areas, this spread of tumor cells may be primarily mediated by the extensive cerebrospinal fluid flow that exists within the brain. Three days after implantation, the glioma cells also showed an active migration over the corpus callosum. In comparison, the fluorescent microspheres showed only limited spread along the callosal body. It is concluded that the bacterial lac-z gene can be stably transfected into human glioma cells and, since every tumor cell can be visualized within the brain, this model provides a tool for studying the mechanisms behind tumor-cell invasion of the brain.

Sensitive and rapid detection of beta-galactosidase expression in intact cells by microinjection of fluorescent substrate

Bacterial beta-galactosidase, coded by lacZ, is a widely used reporter for studies of transcriptional activity of eukaryotic promoters at the single cell level. Unfortunately, current detection methods, like X-gal cytochemistry, are slow, have suboptimal sensitivity, and are incompatible with cell survival. By a novel approach based on microinjection into cells of the fluorogenic substrate 5-chloromethylfluorescein di-beta-D-galactopyranoside lacZ gene expression was detected without affecting cell viability or proliferative capacity. The method was far more sensitive than the conventional X-gal cytochemistry in all cell systems tested (primary hepatocytes, fibroblasts, and glioma cells). Results were obtained within seconds to minutes after injection, and cells remained fluorescent for hours.

Primary organ-culture of nonneoplastic and neoplastic thyroid-tissue as multicellular spheroids

Biopsy specimens from 5 papillary thyroid carcinomas (PC), 2 lymph node metastases (LM) from PC, 3 colloid goitres (CG) and 7 normal (N) thyroid tissue were maintained as three-dimensional structures in agar overlay culture for up to 6 weeks. This organ culture method provides a system that maintains the cellular complexity present in the original tissue, including the stromal elements. Organotypic cultures with a well defined surface architecture were obtained. Follicles present in the spheroids maintained a polarized epithelial cell layer. Immunohistochemical staining showed thyroglobulin expression in most spheroids after two weeks of culture. Proliferating cells were also observed after the same time period evaluated by proliferation cell nuclear antigen (PCNA) immunostaining. The spheroids obtained from one of the papillary carcinomas and the corresponding lymph node metastasis increased in volume size during the first three weeks of culture while in the other cases volume decreased. The proportion of connective tissue increased in most of the spheroids during the culture period and a partial collapse of follicles was observed in parallel. Papillary structures were observed in spheroids from papillary carcinomas and lymph node metastases. Our data indicate that viable organotypic spheroid cultures can be obtained and propagated in vitro from thyroid tissue. Such a system has a potential use for studying normal biological functions of thyroid tissue in vitro and this method may be of special value in studying mechanisms of invasive growth as well as effects of therapy on normal and neoplastic tissue taken from individual patients.

Tumour fragment spheroids from human non-small-cell lung cancer maintained in organ culture

Biopsy material from 17 human non-small-cell lung carcinomas (NSCLC) was maintained in agar overlay culture as tumour fragment spheroids for 40 days. A practical procedure for the formation of spheroids and organ culture is described. The mechanically dissociated tumour specimens showed a variation in their ability to generate spheroids that was not related to the ploidy or the histological differentiation of the biopsies. Light microscopic observations revealed a heterogeneous spheroid population with a mixture of tumour cells and stromal elements. Most of the histological elements normally found in human NSCLC could be seen in the spheroids. The cellular components in the spheroids varied between highly cellular to sparsely cellular, dominated by stromal elements. The squamous carcinomas were in general found to generate highly cellular spheroids more often than the adenocarcinomas. Spheroids with a different cellular content could be selected in vitro by using a morphometric technique. Diameter measurements showed a large variability in spheroid growth. Most of the spheroids decreased in size although bromodeoxyuridine labelling indicated active cell proliferation in the specimens. Frequent changes of medium did not affect spheroid growth. The culture system presented provides a model for studying the cellular heterogeneity as well as the biological characteristics of tumour tissue from individual patients in vitro.

Human microglial cells have phenotypic and functional characteristics in common with both macrophages and dendritic antigen-presenting cells

Resting microglia comprise up to 13% of the cells in human central nervous system (CNS) white matter. Their large number and dendritic morphology make them ideally suited to survey the CNS for noxious stimuli. Upon activation microglia gradually lose dendritic processes and transform into typical phagocytic macrophages. Microglia have been implicated as the main antigen presenting cell within the CNS, and appear to be of central importance as effectors and regulators of demyelination. To further characterize the capacity for immune reactivity within the human CNS, we have studied several characteristics of microglia, both in situ and in vitro. We find that human microglia have ultrastructural, phenotypic (CD11c, CD68, acid phosphatase), and functional (FcR and CR mediated phagocytosis) properties typical for cells of the monocyte lineage. Our data indicate that microglia also have properties in common with dendritic antigen-presenting cells. Electron microscopy studies show extended dendritic cell processes on cultured microglia, and microglia are, like dendritic cells, negative for the monocyte markers nonspecific esterase, endogenous peroxidase, CD14, and RFD7. Microglia constitutively express HLA-DR in situ, and express the dendritic cell marker RFD1 upon activation. Coculturing of microglia with CD4+ T cells results in clustering of T cells around microglia and initiation of a mixed lymphocyte reaction, both distinguishing features of dendritic cells. These functional properties of microglia may be of importance for the maintenance of an immunologic response in the CNS, an organ where dendritic cells, in contrast to other organs, have not previously been identified.

Leptomeningeal tissue: a barrier against brain tumor cell invasion

BACKGROUND

Primary brain tumors are characterized by an extensive infiltrative growth into the surrounding brain tissue. This process is confined to the central nervous system, and tumor cell metastasis to other organs is rare. However, other tumors of non-neural origin may frequently metastasize to the central nervous system.

PURPOSE

The purpose of the present study was to examine the invasive behavior of different glioma cells into tissues of neural (brain aggregates) as well as non-neural origin (leptomeningeal tissue). Using the same target tissues, the invasive characteristics of two neural metastatic tumors (one malignant melanoma and one small-cell lung carcinoma) were also studied. This direct comparison of the invasive behavior between tumors of neural and non-neural origin provides valuable information regarding the mechanisms of glioma cell dissemination in the central nervous system.

METHODS

The in vitro invasive behavior of human tumors of the central nervous system into human leptomeningeal tissue as well as into normal rat brain tissue was studied. For this purpose, a co-culture system consisting of tumor biopsy specimens, human leptomeningeal cell aggregates, and brain cell aggregates was established. Three glioblastomas, one oligodendroglioma, one meningioma, one small-cell lung carcinoma, and one malignant melanoma were studied.

RESULTS

In co-cultures of gliomas and leptomeningeal cell aggregates, a well-defined border between the two tissues was observed. The brain cell aggregates, in contrast, were consistently invaded by the glioma cells. The brain metastases showed a different invasion pattern. The metastatic cells invaded and progressively destroyed leptomeningeal cell aggregates, whereas they did not invade the brain cell aggregates. Upon confrontation of the leptomeningeal tissue with the meningioma, a fusion of the two tissues was observed. Immunostaining of the leptomeningeal tissue showed a strong expression of the basement membrane components fibronectin, collagen type IV, and laminin with no expression of glial fibrillary acidic protein, neuron-specific enolase, or S-100 protein.

CONCLUSIONS

The present study indicates that there may be important biologic differences between the invasive behavior of gliomas and non-neuroepithelial tumors. Our co-culture experiments suggest that leptomeningeal cells and associated acellular components may constitute a barrier against glioma cell invasion. However, this barrier may not be functional for metastatic tumors to the brain. The presence of glioma cells within the leptomeninges should not necessarily be taken as evidence of aggressive growth or as an indicator of malignancy.

Three-dimensional growth of glial cell lines affects growth factor and growth factor receptor mRNA levels

We have studied, at the mRNA level, the influence of various defined growth conditions on the expression of TGF-alpha, PDGF-BB, EGF-R, PDGF-R alpha, and PDGF-R beta in five different glioma cell lines (D-37MG, D-54MG, D-263MG, GaMG, and U-251MG). RNA isolated from logarithmically growing, confluent monolayer cells or multicellular spheroids was analyzed. Northern blot experiments show that with a few exceptions, specific mRNA steady-state levels were considerably higher in cells grown in a three-dimensional organization relative to cells in the logarithmic growth phase.

Organ culture of a glioblastoma from a patient with an unusually long survival

Multicellular tumor spheroids were directly initiated in vitro from the biopsy specimens of a patient who is alive and who has had no neurological changes in 7 years after the gross removal of a glioblastoma. The spheroids were studied alone and in confrontation with aggregates of fetal rat brain tissue. Both in the biopsy and in the tumor spheroids, a very high proportion of cells were proliferating, as flow cytometric deoxyribonucleic acid measurements showed that 40% of the cells in the biopsy specimens and in the tumor spheroids were in the S and G2M phases of the cell cycle. Despite this high proliferation rate, the volume of the spheroids decreased, indicating an even greater cell loss. Light and scanning electron microscopic studies also indicated cell death in the spheroids. This behavior may be related to the long-time survival.

Transfection of glioma cells with the neural-cell adhesion molecule NCAM: effect on glioma-cell invasion and growth in vivo

The tumor growth and the invasive capacity of a rat glioma cell line (BT4Cn) were studied after transfection with the human transmembrane 140-kDa isoform of the neural-cell adhesion molecule, NCAM. After s.c. injection, the NCAM-transfected cells showed a slower growth rate than the parent cell line (BT4Cn). Upon intracerebral implantation with BT4Cn cells and different clones of NCAM-transfected cells, all animals developed neurological symptoms within 13-16 days. However, the tumors showed different growth characteristics. The NCAM-transfected BT4Cn cells were localized in the region of the injection site, with a sharply demarcated border between the tumor and brain tissue. In contrast, the parental cell line showed single-cell infiltration and more pronounced destruction of normal brain tissue. Using a 51Cr-release assay, spleen cells from rats transplanted with BT4Cn tumor cells generally showed a lower cytotoxic response than the spleen cells from rats transplanted with the transfected variants of BT4Cn cells, indicating that the transfection procedure in itself mediated an activation of the immune system. The present data suggest that NCAM may influence the malignant behavior of rat glioma cells in vivo.

Laminin: a potential inhibitor of rat glioma cell invasion in vitro

The lack of metastatic behaviour of primary glioma is poorly understood. A possible natural barrier accounting for this phenomenon may be the proteins of the extracellular matrix which are found in the basement membranes of the blood vascular system. This hypothesis is reinforced by the finding that glioma invasion in vitro using a syngeneic model system results in a lack of invasion of areas of target tissue which contain extracellular matrix proteins. The study was extended by examining the effect of the incorporation of these proteins during the formation of fetal rat brain cell aggregates and glioma spheroids and on the invasion of aggregates by tumour spheroids. Laminin was shown to reduce the size of the aggregates and spheroids during their formation while fibronectin and type IV collagen had no effect. Laminin also prevented the invasion of the tumour spheroid into the target aggregate and appeared to inhibit migration of glioma cells on laminin coated tissue culture plastic.