Adhesion molecules and malignant gliomas: implications for tumorigenesis

Communication of Glioma cells with neuronal plasticity: What is the underlying mechanism?

There has been a significantly rising discussion on how neuronal plasticity communicates with the glioma growth and invasion. This literature review aims to determine which neurotransmitters, ion channels and signaling pathways are involved in this context, how information is transferred from synaptic sites to the glioma cells and how glioma cells apply established mechanics of synaptic plasticity for their own increment. This work is a compilation of some outstanding findings related to the influence of the glutamate, calcium, potassium, chloride and sodium channels and other important brain plasticity molecules over the glioma progression. These topics also include the relevant molecular signaling data which could prove to be helpful for an effective clinical management of brain tumors in the future.

Glioma malignancy is linked to interdependent and inverse AMOG and L1 adhesion molecule expression

BACKGROUND

Gliomas account for the majority of primary human brain tumors and remain a challenging neoplasm for cure due to limited therapeutic options. Cell adhesion molecules play pivotal roles in the growth and progression of glial tumors. Roles of the adhesion molecules on glia (AMOG) and L1CAM (L1) in glioma cells have been shown to correlate with tumorigenesis: Increased expression of L1 and decreased expression of AMOG correlate with degree of malignancy.

METHODS

We evaluated the interdependence in expression of these molecules by investigating the role of AMOG in vitro via modulation of L1 expression and analyzing apoptosis and cell senescence of glioma cells.

RESULTS

Immunohistochemical staining of normal human cortical and glioma tissue microarrays demonstrated that AMOG expression was lower in human gliomas compared to normal tissue and is inversely correlated with the degree of malignancy. Moreover, reduction of AMOG expression in human glioblastoma cells elevated L1 expression, which is accompanied by decreased cell apoptosis as well as senescence.

CONCLUSION

AMOG and L1 interdependently regulate their expression levels not only in U-87 MG cells but also in U251 and SHG44 human glioma cell lines. The capacity of AMOG to reduce L1 expression suggests that methods for increasing AMOG expression may provide a therapeutic choice for the management of glial tumors with high expression of L1.

Adhesion molecules and the extracellular matrix as drug targets for glioma

The formation of tumor vasculature and cell invasion along white matter tracts have pivotal roles in the development and progression of glioma. A better understanding of the mechanisms of angiogenesis and invasion in glioma will aid the development of novel therapeutic strategies. The processes of angiogenesis and invasion cause the production of an array of adhesion molecules and extracellular matrix (ECM) components. This review focuses on the role of adhesion molecules and the ECM in malignant glioma. The results of clinical trials using drugs targeted against adhesion molecules and the ECM for glioma are also discussed.

Epirubicin inhibits growth and alters the malignant phenotype of the U‑87 glioma cell line

Epirubicin, an anthracycline derivative, is one of the main line treatments for brain tumors. The aim of the present study was to verify that epirubicin alters the growth and morphological characteristics of U‑87 glioma cells. In the present study, the effects of epirubicin were tested using cellular and biochemical assays, which demonstrated its anti‑proliferative and cytotoxic effects, with an IC50 of 6.3 µM for the U‑87 cell line, while rat normal neuronal cells were resistant to epirubicin. Epirubicin also reduced the secretion of matrix metalloproteinase‑9 by 48 and 56% at concentrations of 2.5 and 5 µM, respectively. Exposure to epirubicin also diminished levels of vascular endothelial growth factor in U‑87 cells. Furthermore, a cell migration assay showed a significant decrease in cell migration from 28 to 59% following exposure to 1 µM epirubicin. The present study demonstrated the cytotoxic, anti‑proliferative and anti‑migrative potential of epirubicin against glioma cells in vitro.

Molecular neuro-oncology and development of targeted therapeutic strategies for brain tumors. Part 2: PI3K/Akt/PTEN, mTOR, SHH/PTCH and angiogenesis

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that might be amenable to targeted therapy. Activity of the phosphoinositide 3; kinase (PI3K)/Akt pathway is often upregulated in brain tumors due to excessive stimulation by growth factor receptors and Ras. Loss of function of the tumor suppressor gene PTEN also frequently contributes to upregulation of PI3K/Akt. Several compounds, such as wortmannin and LY-294002, can target PI3K and inhibit activity of this pathway. The mammalian target of rapamycin (mTOR) is an important regulator of cell growth and metabolism and is often upregulated by Akt. Clinical trials of CCI-779, an inhibitor of mTOR, are ongoing in recurrent malignant glioma patients. The sonic hedgehog/PTCH pathway is involved in the tumorigenesis of some familial and sporadic medulloblastomas. This pathway can be targeted by cyclopamine, which is under evaluation in preclinical studies. Angiogenesis is a critical process for development and progression of brain tumors. Targeted approaches to inhibit angiogenesis include monoclonal antibodies, receptor tyrosine kinase inhibitors, antisense oligonucleotides and gene therapy. Clinical trials are ongoing for numerous angiogenesis inhibitors, including thalidomide, CC-5103 and PTK 787/ZK 222584. Further development of targeted therapies and evaluation of these new agents in clinical trials will be needed to improve survival and quality of life of patients with brain tumors.

Immunobiology of malignant gliomas

The immune system of patients with malignant gliomas is profoundly suppressed. The suppression involves both the cellular and humoral immunity and it is mainly attributable to selective depletion and malfunction of helper T cells. Malignant glioma cells express potent immunosuppressive factors such as transforming growth factor-beta(2), inteleukin-10 and prostaglandin E(2). Malignant glioma cells also produce chemoattractants and immunostimulatory cytokines which may activate the immune cells. However, the production of these stimulatory cytokines is not self-destructive to glioma cells because of the immunosuppression. Rather, the tumour cells use them to gain a growth advantage. Indeed the cytokines may act as a growth stimulator of the tumour cells themselves (autocrine mechanism), they may act as angiogenic factors to endothelial cells (paracrine mechanism) or induce the attracted immune cells to secrete angiogenic factors. Some cytokines produced by malignant glioma cells are known to be growth inhibitory to normal astrocytes. Recent studies on tumour suppressor genes suggest a close link between the aberrant genes and the immunobiologic features of malignant glioma cells.

Cadherin-dependent adhesion of human U373MG glioblastoma cells promotes neurite outgrowth and increases migratory capacity. Laboratory investigation

OBJECT

The current management of primary CNS tumors involves a multimodal approach, incorporating cytoreductive techniques including resection, radiotherapy, and antiproliferative chemotherapeutic agents. Despite these attempts, the majority of patients with a diagnosis of a high-grade glioma have a dismal prognosis, with the leading cause of treatment failure and tumor recurrence attributable to local invasion of adjacent brain parenchyma. The current study examines the capacity of glioma tumor cells to undergo neurite outgrowth and local migration, specifically focusing on the role of the cadherin cell adhesion system.

METHODS

Using a recombinant cadherin ectodomain protein, U373MG human glioblastoma cells were assessed for their ability to adhere and migrate in a cadherin-dependent manner in culture. Adhesion was evaluated via growth assessment and neurite length at 72 hours growth on an immobilized cadherin substrate and compared with other matrix adhesion proteins, such as Type IV collagen and vitronectin. Migratory capacity was measured via modified transwell assays, also using recombinant cadherin ectodomain in comparison with collagen and vitronectin. Results Cadherin adherent cells adopt a fasciculated morphology, with a significant increase in neurite extension, measuring 104 ± 13.3 μm in length, compared with background adhesion on bovine serum albumin and nonfunctional cadherin ectodomain controls measuring 55 ± 4.4 and 47 ± 3.84 μm, respectively (p = 0.029). Significant increases in neurite length compared with controls were also observed in the vitronectin (81 ± 4.69 μm) and Type IV collagen (91 ± 7.7 μm) groups (p = 0.017 and 0.025, respectively). With respect to migration, U373 cells demonstrate increased invasion in response to cadherin ectodomain exposure, whereas vitronectin and Type IV collagen were not potent initiators of migration through the transwell barrier. Both adhesion and migration outcomes were noted in the absence of any relative changes in cell proliferation, indicating a primary role for the cadherin-based adhesion system in tumor invasion.

CONCLUSIONS

Cadherin-based adhesion promotes increased adhesion, neurite outgrowth, and migration in human U373MG glioblastoma cells, providing a novel area of research for the development of therapeutic targets addressing local tumor invasion.

Molecular neuro-oncology and the development of targeted therapeutic strategies for brain tumors. Part 3: brain tumor invasiveness

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that might be amenable to targeted therapy. Cellular invasion of surrounding brain is one of the key features of brain tumor behavior and is currently under evaluation for potential therapeutic targets. Tumor invasion occurs in the context of the extracellular matrix (ECM) of the brain and involves the interaction between cell-surface adhesion molecules, such as integrins and proteins embedded within the ECM. The overexpression of integrins is often associated with invasive behavior and can be inhibited by targeted approaches such as antibodies, antisense constructs and cyclic peptides. Tumor cell-secreted matrix metalloproteinases and serine proteinases degrade ECM proteins and provide space for movement and infiltration. The expression of proteinases positively correlates with tumor grade and infiltrative capacity. Proteinase activity can be reduced by several methods, including antibodies and small-molecule inhibitors such as marimastat. Early clinical trials suggest that marimastat may have activity in combination with traditional chemotherapy regimens. Further development of targeted therapies designed to inhibit tumor infiltration, and evaluation of these new agents in clinical trials, will be needed to improve survival and quality of life for patients with brain tumors.

Serum matrix metalloproteinase-3 levels correlate with disease activity in relapsing-remitting multiple sclerosis

BACKGROUND

Adhesion molecules and matrix metalloproteinases (MMPs) are known to be relevant to the ongoing development and disappearance of areas of demyelination in the white matter of the CNS of multiple sclerosis (MS) patients. This study examined whether serum matrix metalloproteinase-3 (MMP-3) levels correlate with disease activity in MS.

METHODS

Serum MMP-3 levels in 47 consecutive patients with relapsing-remitting MS were measured by immunoassay every 4 weeks over a 15 month period.

RESULTS

During the study period, 48 clinical relapses occurred. Serum MMP-3 levels within 1 month of relapse were significantly higher than during the remission phase. Sequential analysis showed that serum MMP-3 levels had increased transiently at the time of clinical relapse but returned to the normal range within a month.

CONCLUSIONS

Circulatory MMP-3 levels are correlated with disease activity in relapsing-remitting MS. This may contribute to the breakdown of the blood-brain barrier at the time of relapse.

Increased ability of peripheral blood lymphocytes to degrade laminin in multiple sclerosis

T lymphocytes and macrophages probably play a role in the pathogenesis of multiple sclerosis (MS), and migration of these cells into the central nervous system is facilitated by disruption of the capillary basement membrane. Laminin is a major extracellular matrix of the basement membrane. To investigate whether ability of lymphocytes to degrade laminin correlates with disease activity in MS, we conducted a prospective study in consecutive 24 MS patients. A novel quantitative assay was developed to estimate the ability of peripheral blood mononuclear cells (PBMCs) to degrade laminin. The assay was performed every four weeks over a period of 12 months. During the study period, a total of 41 relapses were observed. The ability to degrade laminin was significantly higher in MS patients, even during clinical remission, than in normal and neurological controls, and was transiently increased further within 4 weeks before relapse (p=0.076). In MS, the ability of peripheral blood lymphocytes to degrade laminin increases, and may correlate with disease activity.

Mechanisms of glioma cell invasion

Invasive growth is one of the characteristics of gliomas--local infiltration into the surrounding nerve tissue decisively restricts all treatment strategies. Particularly the merit of all local treatment modalities is queried. The question whether a glioma represents a diffuse disease of the CNS or a local disturbance with unrestrained expansion tendency is still at issue. Understanding of the invasion mechanisms is of importance inasmuch as biologically reasonable and effective strategies of limiting and suppressing glioma invasion can only hence be derived. The affinity of glioma cells towards certain structures of the extracellular matrix as well as taking advantage of tumour vascularisation with regard to extension play a decisive role. Still not fully understood are tumour host interactions. Future thinking will have to take into account these interactions as well as evidence to be derived from development neurobiology and regeneration capacity of the CNS. The present review is meant to give a short overview and disclose many questions.

Effects of IFN-gamma and interleukin-1beta on major histocompatibility complex antigen and intercellular adhesion molecule-1 expression by 9L gliosarcoma: relevance to its cytolysis by alloreactive cytotoxic T lymphocytes

To enhance the efficacy of cellular immunotherapy for gliomas, we tested the concept of using proinflammatory cytokine treatment with interferon-gamma (IFN-gamma) or interleukin-1beta (IL-1beta) or both to render glioma cells more susceptible to cytolysis by alloreactive cytotoxic T lymphocytes (aCTL). The cytokines, separately or in combination, were able to upregulate major histocompatibility complex (MHC) class I antigen or intercellular adhesion molecule-1 (ICAM-1) on Fischer rat 9L gliosarcoma cells. 9L cells were incubated in vitro for 24, 48, or 72 h with varying concentrations of rat IFN-gamma (0-2000 U/ml) or recombinant human IL-1 (rHUIL-1) (0-1000 U/ml) or both. By 48 h, IFN-gamma (500 U/ml) maximally induced the percentage of positive expressing cells and the relative antigen density of MHC class I and ICAM-1 on 9L cells, whereas IL-1 induced only ICAM-1 expression. Simultaneous incubation of IL-1 with IFN-gamma did not further affect the induction of class I on 9L cells more than that achieved with IFN-gamma alone. 9L cells with upregulated MHC class I and ICAM-1 expression were more sensitive to lysis by aCTL in in vitro cytotoxicity assays, regardless of whether the precursor aCTL came from naive or from 9L-immunized rats. Furthermore, inhibition of 9L cytotoxicity in assays that included blocking antibodies to MHC class I or to ICAM-1 revealed that T cell receptor (TCR) interactions with MHC class I and that ICAM-1 interactions with lymphocyte function-associated-1 (LFA-1) antigen account for a portion of the glioma lysis by aCTL.

Hyaluronate receptors mediating glioma cell migration and proliferation

The extracellular matrix (ECM) of the central nervous system (CNS) is enriched in hyaluronate (HA). Ubiquitous receptors for HA are CD44 and the Receptor for HA-Mediated Motility known as RHAMM. In the present study, we have investigated the potential role of CD44 and RHAMM in the migration and proliferation of human astrocytoma cells. HA-receptor expression in brain tumor cell lines and surgical specimens was determined by immunocytochemistry and western blot analyses. The ability of RHAMM to bind ligand was determined through cetylpyridinium chloride (CPC) precipitations of brain tumor lysates in HA-binding assays. The effects of HA, CD44 blocking antibodies, and RHAMM soluble peptide on astrocytoma cell growth and migration was determined using MTT and migration assays. Our results show that the expression of the HA-receptors, CD44, and RHAMM, is virtually ubiquitous amongst glioma cell lines, and glioma tumor specimens. There was a gradient of expression amongst gliomas with high grade gliomas expressing more RHAMM and CD44 than did lower grade lesions or did normal human astrocytes or non-neoplastic specimens of human brain. Specific RHAMM variants of 85- and 58-kDa size were shown to bind avidly to HA following CPC precipitations. RHAMM soluble peptide inhibited glioma cell line proliferation in a dose-dependent fashion. Finally, while anti-CD44 antibodies did not inhibit the migration of human glioma cells, soluble peptides directed at the HA-binding domain of RHAMM inhibited glioma migration both on and off an HA-based ECM. These data support the notion that HA-receptors contribute to brain tumor adhesion, proliferation, and migration, biological features which must be better understood before more effective treatment strategies for these tumors can be found.

Novel chemotherapeutic agents for the treatment of brain cancer

Brain cancer encompasses both primary and metastatic brain tumours and accounts for over 120,000 new patients each year. Despite aggressive therapy, the majority of patients with brain cancer have poor prognosis and have brief survival intervals. Current chemotherapy drugs, used alone or in combination, have minimal or only modest activity. Novel agents that have recently been applied to brain cancer include temozolomide, irinotecan and paclitaxel. Temozolomide is a DNA alkylating agent, irinotecan inhibits DNA topoisomerase I and paclitaxel binds to microtubules and induces polymerisation. Neoplastic angiogenesis and brain tumour invasion are also targets for therapeutic intervention with new agents such as thalidomide, suramin and marimastat. All of these agents have demonstrated activity against brain cancer in vitro. Several of the drugs, in particular temozolomide, paclitaxel and irinotecan, have entered preliminary clinical trials and have demonstrated some efficacy. However, chemotherapy for primary brain tumours remains rather non-specific and mostly ineffective. The use of chemotherapy may be more effective against selected metastatic brain tumours. Continued basic research is needed to further elucidate the genetic basis of transformation, tumour invasion and angiogenesis. It is hoped that this research will lead to new therapeutic targets for drug design and development. In addition, new strategies must be developed to overcome the problem of chemotherapy resistance.

Circulating intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and plasma thrombomodulin levels in glioblastoma patients

Cellular adhesion molecules have been implicated in tumor progression and metastasis. Serum samples from 22 patients with glioblastoma (GBM), before surgery, and 19 sex and age matched healthy controls were analyzed for circulating levels of ICAM-1 and VCAM-1. At the same time also soluble plasma thrombomodulin, a marker of endothelial cell damage and activation, was detected. Soluble ICAM-1 and VCAM-1 levels were comparable in glioblastoma patients and healthy controls, while plasma thrombomodulin (TM) was significantly increased in cancer patients. There was no correlation between thrombomodulin levels and the presence of an intratumoral hemorrhage detected by CT scan, while entity of post-contrast enhacemement at CT correlated with higher TM levels. Further study with serial sampling of GBM patients and correlation with enhancement at CT will allow to ascertain the value of serum TM as a marker of disease recurrence or angiogenesis in those tumors.

The role of protein kinase Calpha in U-87 glioma invasion

To investigate the hypothesis that protein kinase Calpha (PKCalpha) is functional glial tumor cell invasion, stable PKCalpha sense and antisense transfected U-87 cell lines were established and PKCalpha expression characterized by Western blot and PKC activity assays. Invasion assays including barrier migration (Koochekpour et al., Extracellular matrix proteins inhibit proliferation, upregulate migration and induce morphological changes in human glioma lines. Eur. J. Cancer, 1995, 31, 375-380; Merzak et al., CD44 mediates human glioma cell adhesion and invasion in vitro. Cancer Res., 1994, 54, 3988-3992; Merzak et al., Cell surface gangliosides are involved in the control of human glioma cell invasion in vitro. Neurosci. Lett., 1994, 177, 11-16), and spheroid confrontation were used to study the relationship between PKCalpha expression and invasiveness. PKCalpha overexpressing clones show increased barrier migration (1.5x) relative to the control transfected clones. PKCalpha inhibited clones exhibited reduced invasiveness, to < 50%. In coculture with PKCalpha overexpressing clones, the remaining normal fetal rat brain aggregate volume was significantly decreased (up to 200%) but 90% of the initial brain volume was left in PKCalpha inhibited clone in the rat brain aggregate tumor spheroid confrontation. This effect was not associated with significant growth inhibition. We conclude that expression of PKCalpha in glioma-derived cell lines appears to be central to glioma invasion in vitro.

Paucity of retinoic acid receptor alpha (RAR alpha) nuclear immunostaining in gliomas and inability of retinoic acid to influence neural cell adhesion molecule (NCAM) expression

Neural cell adhesion molecule (NCAM) is down-regulated during periods of embryological cell migration and may be important in local tumor migration or metastases. Conflicting information exists in the literature about NCAM expression in human glial tumors and little is known about its expression in human brain metastases. We immunohistochemically stained a panel of 43 primary human brain tumors and their cultured counterparts for NCAM including glioblastoma multiformes, anaplastic astrocytomas, oligodendrogliomas, and contrasted their staining with a panel of 3 meningiomas, 11 brain metastases, and 5 normal brain samples utilizing the monoclonal antibody NKH-1. Most gliomas and metastatic melanomas and lung carcinomas showed a high percentage of cells positive for NCAM expression while NCAM staining was negative for other carcinomas. No difference was seen between intensity or percentage of cells that were NCAM positive, based on tumor grade or type. In glioma cell lines, NCAM expression was lost upon passage. In 15 glioma cell lines we also determined NCAM isoform expression by reverse transcription/polymerase chain reaction (RT/PCR) and found that 6 of 15 had message for NCAM 180, 8 of 15 for NCAM 140, and only 3 of 15 had message for NCAM 120. Normal brains always contained message for the 180 isoform and usually had mRNA for all 3 isoforms. Using monoclonal antibodies for retinoic acid receptor alpha (RAR alpha), we found nuclear staining in melanomas and lung carcinomas metastatic to brain and only rarely in gliomas. Neither the relative antigen density of NCAM nor the percent of NCAM-positive cells appreciably changed upon incubation with retinoic acid (RA), as measured by flow cytometry. RAR alpha was not found at a level measurable by immunohistochemistry in nuclei of most glial tumors, providing an explanation for why RA might not induce NCAM expression. Whether paucity of RAR alpha on primary gliomas might also correlate with results from clinical trials showing limited efficacy of RA in treatment of human gliomas awaits further study.

ECM-mediated glioma cell invasion

Cell adhesion receptors of the integrin superfamily, CD44, and adhesion receptors of the immunoglobulin superfamily are expressed by high-grade astrocytic tumors of the central nervous system. These receptors are critical for the invasion of these tumors in the nervous system. Glioma cells utilize these receptors to adhere to and migrate along the components of the extracellular matrix, which is uniquely distributed and regulated within the brain and the spinal cord. For this reason, glioma cell invasion into the adjacent brain tissue is dependent on the interaction of glioma cells with the extracellular matrix. The receptor-ECM component interaction is discussed, focusing on the role of cell adhesion molecules of the integrin family and CD44 in glioma cell adhesion and invasion.

Induction of matrix metalloproteinase-9 requires a polymerized actin cytoskeleton in human malignant glioma cells

Alterations in cytoskeleton and subsequent cell shape changes exert specific effects on the expression of various genes. Our previous results suggested that malignant human gliomas express elevated levels of matrix metalloproteinases compared with normal brain tissue and low grade gliomas. To understand the role of cell shape changes on matrix metalloproteinase expression in human glioma cells, we treated SNB19 cells with cytochalasin-D, an inhibitor of actin polymerization, and colchicine-B, a tubulin inhibitor, in the presence of phorbol 12-myristate 13-acetate. Cytochalasin-D treatment of SNB19 cells resulted in the loss of phorbol 12-myristate 13-acetate-induced matrix metalloproteinase-9 (also known as gelatinase-B) expression and coincided with inhibition of actin polymerization, resulting in cell rounding. Moreover, compared with monolayers, cells grown as spheroids or cell aggregates failed to express matrix metalloproteinase-9 in the presence of phorbol 12-myristate 13-acetate. Matrix metalloproteinase-9 expression was also inhibited by calphostin-C, a protein kinase inhibitor, suggesting the involvement of protein kinase C in matrix metalloproteinase-9 expression. Phorbol 12-myristate 13-acetate-induced invasion of SNB19 cells through Matrigel was inhibited by cytochalasin-D and calphostin-C. These results suggest that the actin polymerization transduces signals that modulate the expression of matrix metalloproteinase-9 expression and the subsequent invasion of human glioma cells.

Inhibition of human malignant glioma cell motility and invasion in vitro by hypericin, a potent protein kinase C inhibitor

The effect of hypericin, an antiviral drug and a potent protein kinase C (PKC) inhibitor, on glioma cell invasion was investigated in vitro. Treatment of the established human glioblastoma cell line, T98G, with 1 microM hypericin for 24 h resulted in a significant inhibition of the cell invasion through an artificial basement membrane, but not cell attachment or proliferation. Furthermore, tamoxifen and staurosporine, both PKC inhibitors, also inhibited T98G cell invasion, suggesting that PKC may be the cellular target for hypericin-inhibited glioma cell migration. Similarly, hypericin decreased cell motility significantly in established lines, T98G and U87-MG, and also in a low-passage human malignant glioma cell line. Thus, hypericin may prove useful for studying mechanisms of glioma invasion, and may represent a new agent in malignant glioma therapy.

Expression of LFA-1alpha and ICAM-1 in the developing rat brain: a potential mechanism for the recruitment of microglial cell precursors

Several studies agree that microglial cells derive from monocytes that infiltrate the central nervous system during development, but the precise mechanism by which these cells enter into the nervous tissue is still unknown. In this way, the aim of the present study was to analyze the expression of two cell adhesion molecules involved in the recruitment of blood leukocytes into tissues, the lymphocyte function-associated antigen-1alpha (LFA-1alpha) and the intercellular adhesion molecule-1 (ICAM-1) in the developing rat brain (from E16 to P18). By means of immunohistochemistry, our observations showed that LFA-1alpha and ICAM-1 were expressed in the developing rat brain with a definite distribution pattern and a characteristic time course of appearance. In the embryonic period, LFA-1alpha immunoreactivity was displayed not only by intravascular blood cells but also by intraparenchymal round cells with a horseshoe-shaped nucleus, showing the typical morphological features of monocytes. Monocyte-like cells present in the embryonic brain parenchyma often displayed mitotic profiles. LFA-1alpha immunohistochemistry also revealed the presence of some LFA-1alpha-positive cells belonging to the ameboid microglial population (mostly in the white matter from E18). In the postnatal period, LFA-1alpha immunoreactivity was displayed by some ameboid microglial cells (P0-P9) and also by some ramified microglia. LFA-1alpha immunoreactivity observed in ramified microglia was weaker when compared to LFA-1alpha stained ameboid microglia. In contrast, ICAM-1 immunolabeling during the embryonic period was mainly located in endothelial cells of parenchymal brain blood vessels (principally from day E18). Blood vessels in choroid plexus and meninges also expressed ICAM-1 during the embryonic time. In postnatal animals, ICAM-1 immunoreactivity was found in relation to endothelial cells of blood vessels, but the density of ICAM-1-positive blood vessels was lower than that during the embryonic period. The gradual regulation in the expression of LFA-1alpha by monocyte-like cells and cells of the microglial lineage, and the expression of ICAM-1 by the brain vasculature strongly suggest that the LFA-1/ICAM-1 system may be a mechanism involved in the entry of microglial cell precursors into the developing rat brain.

Cellular adhesion molecules in neurology

The study of cellular adhesion molecules offers crucial understanding of cellular interactions. Their name implies an underestimation of their function, as intercellular glue. In fact, they play vital roles in tissue development and intra- and intercellular signaling. In neurology, cellular adhesion molecules are already providing welcome new insight into neurodevelopmental anomalies, autoimmune demyelination, and invasive tumours. Cellular adhesion molecule manipulation has led to several therapeutic options which are the subject of ongoing clinical investigation.

Mechanisms of glioma invasion: role of matrix-metalloproteinases

One of the most lethal properties of high grade gliomas is their ability to invade the surrounding normal brain tissue, as infiltrated cells often escape surgical resection and inevitably lead to tumour recurrence. The consequent poor prognosis and survival rate underscore the need to further understand and target the cellular mechanisms that underly tumour invasiveness. Proteases which degrade the surrounding stromal cells and extracellular matrix proteins have been demonstrated to be critical effectors of invasion for tumours of both central and peripheral origin. Within the nervous system, the role of metalloproteinases as well as other classes of proteases in mediating the invasive phenotype of high grade gliomas has been an intense area of research. We present in this article a review of this literature and address the possibility that these proteases and the biochemical pathways that regulate their expression, such as protein kinase C, may represent potential targets in the therapy of high grade gliomas.

Glioma invasion in vitro: regulation by matrix metalloprotease-2 and protein kinase C

A hallmark of invasive tumors is their ability to effect degradation of the surrounding extracellular matrix (ECM) by the local production of proteolytic enzymes, such as the matrix metalloproteases (MMPs). In this paper, we demonstrate that the invasion of human gliomas is mediated by a 72 kDa MMP, referred to as MMP-2, and provide further evidence that the activity of MMP-2 is regulated by protein kinase C (PKC). The invasiveness of five human glioma cell lines (A172, U87, U118, U251, U563) was assessed in an in vitro invasion assay and was found to correlate with the level of MMP-2 activity (r2 = 0.95); in contrast, the activity of this 72 kDa metalloprotease was barely detectable in non-invasive control glial cells (non-transformed human astrocytes and oligodendrocytes). Treatment with 1,10-phenanthroline, a metalloprotease inhibitor, or with a synthetic dipeptide, containing a blocking sequence (ala-phe) specific for MMPs, resulted in a > 90% reduction in glioma invasion. Furthermore, this MMP-2 activity could be inhibited by the treatment of tumor cells with calphostin C, a specific inhibitor of PKC. Glioma cell lines treated with calphostin C demonstrated a dose-dependent decrease (IC50 = 30 nM) in tumor invasiveness with a concomitant reduction in the activity of the MMP-2. Conversely, treatment of non-invasive control astrocytes with a PKC activator (phorbol ester) led to a corresponding increase in their invasiveness and metalloprotease activity. These findings support the postulate that MMP-2 activity constitutes an important effector of human glioma invasion and that the regulation of this proteolytic activity can be modulated by PKC.

Modulation of matrix metalloprotease-2 and invasion in human glioma cells by alpha 3 beta 1 integrin

We have investigated the effect of integrin antibodies to a well-characterized alpha 5 beta 1 (fibronectin receptor) and to a multi-specific alpha 3 beta 1 (laminin, collagen, and fibronectin receptor), on the expression of matrix metalloproteases and the invasion ability of two human glioblastoma cell lines, SNB19 and U251. Cell adhesion assays indicated that both cell lines adhere to fibronectin, type IV collagen and laminin. Adhesion of cells to fibronectin was inhibited by a RGD peptide. Cells treated with anti-alpha 3 beta 1 or anti-alpha 5 beta 1 antibodies expressed increased levels of MMP-2. An in vitro matrigel assay also showed that the alpha 3 beta 1 antibody-treated cells had greater invasive ability than the controls. Immunofluorescence data showed that glioma cells treated with either anti-alpha 3 beta 1 or anti-alpha 5 beta 1 antibodies expressed diminished alpha 3 beta-1 and alpha 5 beta 1 integrins relative to the controls. The data show that treatment of cells with alpha 3 beta 1 antibody diminishes the integrin expression on the cell surface and increases the MMP-2 activity and invasiveness.

Organization of F-actin filaments in human glioma cell lines cultured on extracellular matrix proteins

Extracellular matrix (ECM) constituents likely play an important role in cell proliferation and the invasion of malignant human gliomas. We examined the formation of stress fibers and the growth of the human glioblastoma cell lines A172 and T98G cultured on collagen types I, IV, and V, laminin (LN), and fibronectin (FN). A172 cells cultured on LN and FN formed complete F-actin filaments after 24 h of culture and grew logarithmically after 48 h. In contrast, T98G cells on LN and FN reorganized only short F-actin filaments after 24 h of culture and grew rapidly after 72 h. However, on the collagen preparations, neither cell line formed definite stress fibers and both showed lower rates of cellular proliferation. Significantly positive correlation was observed between the relative intensity of F-actin filaments and the cell proliferation. The results indicate that the ability of ECM components to modulate the growth and differentiation of malignant glioma cells may be mediated, in part, by the assembly and disassembly of F-actin filaments.

Characterization of perivascular cells in astrocytic tumours and peritumoral oedematous brain

Perivascular cells (PVCs) form an immunophenotypically defined population that plays an important scavenging role in the perivascular fluid drainage pathways in the rat brain; such cells may also act as antigen-presenting cells. The present study tests the hypotheses that (a) PVCs in human brain are distinct from microglia and haematogenous macrophages, and (b) PVCs within astrocytic tumours and peritumoral oedematous brain tissue react in a similar way to PVCs in the rat brain. Paraffin sections of formalin-fixed tissue from 10 astrocytomas, 10 anaplastic astrocytomas, 10 glioblastoma multiforme, peritumoral oedematous brain and from normal human brain were examined immunocytochemically using antibodies HLA-DR beta-chain for MHC class II antigen, PGM1 and MAC 387 directed against macrophage components, MT1 for T lymphocytes and GFAP for astrocytes. No PVCs, microglia or macrophages were labelled by these techniques in paraffin sections of normal brain. Microglia, macrophages recently derived from haematogenous monocytes and PVCs were labelled by immunocytochemistry in all tumours but were more numerous in glioblastomas than in astrocytomas or anaplastic astrocytomas. Perivascular cells were distinguished by their perivascular position, their expression of MHC class II antigen and were labelled by PGM1 antibody but not by MAC 387 antibody. Microglia and monocyte/macrophages, remote from blood vessels, on the other hand, were strongly labelled by MAC 387, moderately by PGM1 and showed weak expression of MHC class II antigen. A similar pattern of staining was seen in peritumoral oedematous tissue. These findings suggest that PVCs form a defined population of resident cells in the human brain and that they are distinct from microglia, monocytes and macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Neural cell adhesion molecule expression in human pituitary adenomas

Neural cell adhesion molecule (NCAM) is a cell surface glycoprotein whose expression may be important in metastatic or local growth of neoplasms. Expression of NCAM in human pituitary adenomas was assessed on snap-frozen and Bouin's and/or formalin-fixed, paraffin-embedded archival tissue using a sensitive alkaline phosphatase-antialkaline phosphatase method of immunostaining with the monoclonal antibody, NKH-1. The 20 pituitary adenoma patients consisted of 13 males and 7 females, ages 19-78 years, with null cell macroadenomas (3), plurihormonal macroadenomas (4), weak gonadotropic macroadenomas (5), growth hormone-prolactin adenomas (2), and prolactinomas (6). Eight of the adenomas were clinically invasive. The snap-frozen material from 14 pituitary tumors showed immunostaining for NCAM in either a cytoplasmic, peripheral membranous, or mixed pattern; 2 of 3 prolactinomas showed patchy immunostaining. The Bouin's and/or formalin-fixed pituitary adenoma specimens from 6 clinically invasive cases showed less distinct NCAM localization but 4 out of 6 showed diffusely positive NCAM immunostaining, with greatest intensity appreciated on the Bouin's-fixed tissue. There was no correlation between NCAM staining pattern and invasive characteristics of the tumors. These results suggest that NCAM expressivity is not a useful marker for assessing pituitary adenoma tumor invasiveness.

Cell adhesion molecules acting between C6 glioma and endothelial cells

The interactions between tumor cells and endothelium play a key role in the process of tumor growth, local invasion, and distant metastasis. In the present study, we examined the adhesion of C6 glioma cells to bovine endothelial cell (EC) monolayers and defined the cell adhesion molecules acting between these cells. Pretreatment of the EC monolayer with cytokines, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta, and interferon (INF)-gamma, significantly increased the adhesion of C6 glioma cells to the EC monolayer. The effect lasted more than 24 hours and was protein-synthesis dependent. The adhesion of C6 glioma cells to TNF-activated ECs was blocked by the monoclonal antibody to the intercellular adhesion molecule-1 (ICAM-1) or beta 2 integrin, whereas that of melanoma cells was not. These findings provide evidence that ICAM-1 and beta 2 integrin function as inducible cell surface molecules that can support the adhesion of C6 glioma cells to ECs, and may contribute to the characteristic growth of glial tumors in vivo.

T cell-mediated cytotoxicity of human gliomas: a tumor necrosis factor-independent mechanism

Cellular immune effector mechanisms are implicated as potential therapies for malignant gliomas. We have examined the potential for anti-CD3-activated human peripheral blood-derived CD4+ and CD8+ T cells to induce lysis of human glioma cell lines in vitro, the mechanism of action of these cells, and the capacity of the glioma to inhibit the effect. We found that activated CD4+ and CD8+ T cell preparations containing less than 5% natural killer cells could induce significant lysis of the glioma cell line U251, as measured by an 18-hour, but not 5-hour, chromium-51 or lactate dehydrogenase release assay. This effect was not reproduced using recombinant tumor necrosis factor or inhibited with antitumor necrosis factor antibody. Anti-lymphocyte functional antigen-1 and anti-intercellular adhesion molecule antibodies also did not inhibit the effect. Glioma-derived supernatant could inhibit the proliferation of the T cells but not the cytotoxic effect. Human fetal astrocytes were also susceptible to the cytotoxic effect of the activated T cells. These results indicate that activated T cells can induce glioma cytotoxicity via a mechanism independent of tumor necrosis factor. The therapeutic potential of this effector mechanism will depend on its capacity to deliver these cells or their specific effector molecules to the tumor site or to augment the activity of such cells, which accumulate naturally in gliomas.

CD44 plays a role in adhesive interactions between glioma cells and extracellular matrix components

Glioma invasion is a complex process involving interactions of tumour cells with host cells and extracellular matrix (ECM). The initial event in the process is recognition and attachment of glioma cells to specific ECM molecules prior to migration into proteolytically modified matrix. In comparison with other tissues, brain ECM is a relatively amorphous matrix which contains glycosaminoglycans including hyaluronan (HA). Recently CD44 which is a transmembrane adhesion molecule found on a wide variety of cells, has been suggested as the principal cell surface receptor for HA. In the present in vitro investigation we have analysed the role of CD44 in adhesive interactions between human gliomas and ECM. Our experimental procedures included immunocytochemistry, immunoblotting, in vitro adhesion assay and flow cytometry. CD44 was expressed on the surface of all gliomas analysed (9) and the level of expression showed no correlation with tumour grade. Eighty, 95 and 120 kDa isoforms were demonstrated by immunoblotting. In an adhesion blocking assay it was found that ligation of CD44 with specific antibody resulted in reduced adhesion to hyaluronan, chondroitin sulphate, fibronectin, laminin, collagen IV and Matrigel. We conclude that CD44 is involved in adhesion of glioma cells to a wide range of ECM components.

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.

Extracellular matrix-degrading proteinases in the nervous system

The proteolytic activities of matrix metalloproteinases and plasminogen activators as well as their inhibitors are important in maintaining the integrity of the extracellular matrix (ECM). Cell-ECM interactions influence cell proliferation, differentiation, adhesion and migration. In the nervous system, proteolysis of the ECM is involved in neuronal cell migration in the developing cerebellum and in neurite outgrowth. Likewise, in pathological conditions such as brain tumour growth and invasion, leukocyte infiltration into brain tumours, leukocyte trafficking in the central nervous system in inflammatory diseases such as multiple sclerosis and viral encephalitis, and in nerve demyelination, matrix-degrading proteinases and their inhibitors have been implicated. An understanding of cell-ECM interactions and ECM degradation in diseases of the nervous system would provide new insight for drug design and other forms of therapy.

Basement membrane invasion of glioma cells mediated by integrin receptors

Basement membrane invasion precedes meningeal dissemination and systemic metastasis of glioma cells. In order to investigate the invasive ability of glioblastomas and the functional role of extracellular matrix receptors, the authors performed in vitro invasion assays where the number of cells was determined from freshly resected tumors (primary cultures and fifth passages) and from cell lines (U-138 MG, U-373 MG, and GaMg) that had migrated through a filter coated with a reconstituted basement membrane (Matrigel). The involvement of integrin adhesion molecules was examined by preincubation of glioma cells with blocking antibodies to specific integrin chains. Cells from all of the glioblastomas had migrated through the Matrigel after 4 to 24 hours; the number of invasive cells was highest in the cell lines. Invasion of U-138 MG cells was reduced with antibodies to alpha 7, alpha v, beta 1, and beta 3 integrin chains and markedly increased by anti-alpha 5, while invasion of U-373 MG cells was reduced by antibodies to alpha 3, alpha v, beta 1, and beta 3 and increased by anti-alpha 6. It is concluded that: 1) glioma cells are able to penetrate Matrigel, indicating that the basement membrane is not a resistant barrier for infiltrating cells; and 2) basement membrane invasion is mediated by integrins in a complex manner. Some integrins promote while others inhibit basement membrane invasion. Furthermore, the integrins involved may differ between various glioma cells.

Interferon effect on glycosaminoglycans in mouse glioma in vitro

The effect of mouse interferon alpha/beta (MuIFN alpha/beta) on the production of glycosaminoglycans (GAGs) by mouse glioma G-26 in vitro was evaluated. Two GAG species secreted extracellularly by the mouse glioma G-26 were isolated using cellulose acetate electrophoresis. They were identified as hyaluronic acid (HA) and chondroitin sulfate (CS) following enzymatic digestion with enzymes: hyaluronidase and chondroitinase ABC. Further characterization of CS by enzymatic digestion with specific chondroitinases for chondroitin 4-sulfate (CSA) and chondroitin 6-sulfate (CSC), revealed that the isolated CS was neither CSA nor CSC. Therefore, it may be either chondroitin sulfate B (CSB) (dermatan sulfate) or one of the 'chondroitin sulfate isomers' (D-H). The three day incubation of glioma G-26 cells with 8 x 10-8 x 10(4) U/ml of MuIFN alpha/beta resulted in a dose dependent inhibition of cell proliferation measured by 3H-thymidine incorporation and the MTT assay. The significant decrease of the CS (p < 0.008) but not the HA level, (measured densitometrically), was observed following 72 hours (hrs) incubation of G-26 cells with 8 x 10(3) U/ml of MuIFN alpha/beta (IFN treated cells: 0.03 +/- 0.007 integrated optical density (IOD); control cells: 0.07 +/- 0.01 IOD). The decreased CS production may be the underlying cause of IFN mediated inhibition of glioma cell proliferation.

Rapid detection of transferrin receptor expression on glioma cell lines by using magnetic microspheres

A rapid method for detecting the presence of transferrin receptors (TR) on human glioblastoma-derived cell lines is presented. The development of new treatment modalities, such as immunotoxins for central nervous system cancer, requires the identification of appropriate surface antigens on tumor cells. Seven established human glioblastoma-derived cell lines were assayed for the presence of TR with antibody-coated magnetic microspheres (immunobeads). The immunobeads bound to glioblastoma cells in the presence of human anti-TR monoclonal antibodies to a significantly greater degree than to control cell lines (P < 0.0001). The expression of TR was confirmed by standard immunocytochemical techniques. A 9L rat gliosarcoma cell line was used as a nonhuman control and did not demonstrate TR expression by either the immunobead assay or immunocytochemistry. This assay represents a simple, sensitive way to detect TR expression on malignant cells, which may be useful for the identification of other cell surface antigens that can be exploited by targeted therapies.

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

We present morphological data of the early stage of tumor invasion in the central nervous system. C6 rat glioma cells were injected into the caudate-putamen of rat brain using glass micropipettes to minimize traumatic reactions. Four days after the inoculation, we examined the tumor-brain interface using light and electron microscopy. Ultrastructurally the tumor processes were attached to the perivascular basement membrane instead of the astroglial end-feet. At the tumor periphery, the vessel walls were in contact with both tumor processes and astroglial end-feet. Astrocytes withdrew their processes from the vascular walls and changed into a reactive phenotype, while the neuronal cells remained virtually intact, even when surrounded by tumor cells. Immunohistochemical study using C6 cells labeled with bromodeoxyuridine showed migration of the cells toward the perivascular space that was distant from the site of injection. These observations represent the earliest morphologically detectable changes of the tumor-brain interface, and suggest that the C6 cells possess the characteristics of high affinity to the endothelial basement membrane and invade along the preexisting blood vessels with brain parenchymal infiltration.