Factors influencing tumor cell traffic in the central nervous system

The brain slice chamber, a novel variation of the Boyden Chamber Assay, allows time-dependent quantification of glioma invasion into mammalian brain in vitro

Glioma cell invasion occurs in a complex micromilieu consisting of neural and glial cells, myelinated fiber tracts, blood vessels and extracellular matrix proteins. The present work describes the brain slice chamber (BSC) as a novel experimental model for assessing invasion of glioma cells into adult mammalian white and gray matter on the basis of the well known Boyden chamber system. As a matrix for invasive tumor cells we used freshly prepared brain tissue from adult pigs. The tissue was sectioned into 40 mum slices that were mechanically fixed to a millipore filter. The neural structures and the three-dimensional architecture of the slice was preserved as verified by immunohistochemistry, light- and electron microscopy. Human U-373 and U87 astrocytoma cells stably transfected with green fluorescent protein (GFP) were assessed for their invasiveness into the brain-slices during a 24 h period. Invasion of U-87 GFP cells was quantified at different time intervals by confocal laser scanning microscopy showing more intense invasion into white compared to gray matter. Two cytostatics (vincristin and paclitaxel) which both are known to affect the cytoskeleton, inhibited glioma cell invasion in a dose dependent manner, which makes the presented model system suitable for functional experiments. In conclusion, the BSC represents a valid and rapid experimental model that may be used to describe the invasive behavior of glioma cells within the preserved three-dimensional structure of mammalian brain tissue in vitro.

Modulation of motility and proliferation of glioma cells by hepatocyte growth factor

Invasive proliferation is a critical biological characteristic of gliomas. We evaluated the activities of hepatocyte growth factor (HGF) on proliferation and motility of glioma cells, comparing them with the effects of other growth factors (EGF, bFGF, PDGF-BB, TGF-beta 1). Seven primary culture lines all expressed c-met and HGF mRNA, and secreted HGF. HGF stimulated 3H-thymidine uptake of every glioma cell line (30 to 70% upregulation). Boyden chamber assay and scattering assay revealed that HGF promoted cell motility with chemokinetic and strong chemotactic activities. Concentric circle assay showed that HGF promoted two-dimensional expansion (proliferation and motility) most strongly among the growth factors studied. Further, we analyzed 23 paraffin-embedded sections of surgically resected gliomas (7 grade II, 8 grade III, and 8 grade IV) by immunohistochemistry. Expression of HGF and Met increased with malignant progression of gliomas, suggesting that gliomas stimulated their invasive proliferation by autocrine HGF production. Neurons and vasculature were HGF-positive, and Met-positive glioma cells gathered around them. The data indicate that neurons and vasculature, which are the main tracks of glioma invasion, augment chemotactic invasion and proliferation of gliomas by paracrine HGF secretion. Clearly HGF plays a critical role in invasive proliferation of glioma cells and it is therefore a candidate target of therapeutic intervention.

Proliferation and motility responses of primary and recurrent gliomas related to changes in epidermal growth factor receptor expression

Astrocytic neoplasms show a high incidence of elevated or mutated epidermal growth factor receptor (EGFR) expression. Although proliferative effects from EGFR activation are well described, the role that changes in this receptor play in glioma growth and migration remain poorly addressed. This report characterizes changes in the levels of EGFR expression in three glial tumors at initial presentation (resection) and at the time of recurrence. By quantitative flow cytometry the mean level of EGFR expression increased, decreased, or remained the same in different recurrent astrocytomas relative to their primary tumor cells. Immunocytochemistry for EGFR on monolayer cells corroborated the level of expression in the recurrent tumors relative to their matched primary specimen. Immunoprecipitation indicated that 170 kd EGFR was expressed in each of the tumors, and showed normal down regulation following treatment with EGF. Proliferation response to EGF was seen in only 1/6 instances, but was concentration-dependent when observed. Stimulated migration of the cells was frequently seen and was also concentration-dependent on EGF; the magnitude of response was related to the relative level of 170 kd EGFR expression in the cells. EGFR immunostaining of tissue sections from the tumors confirmed the levels of EGFR expressed in primary and recurrent astrocytomas as was seen in the cultured cells. These results indicate that the relative levels of EGFR in early passage cell cultures from glioma specimens concurs with the measured tissue levels of expression. Human glioma cells are more responsive to migration induction than proliferation induction by EGF.

Substrates for astrocytoma invasion

A better understanding of the influences of specific extracellular substrates, including proteins, glycosaminoglycans, and parenchymal cells, on the invasive behavior of glioma cells would potentially lead to novel forms of treatment aimed at confining the tumor. A monolayer, microliter scale assay was used to investigate how different substrates influenced glioma migration. Basal or unspecific movement (range, 10-260 microns/d) was determined by observing a panel of seven established human glioma cell lines. Migration rates two to five times higher than this basal activity were referred to as preferential and specific glioma migration; these rates generally occurred on merosin and tenascin. Collagen, fibronectin, or vitronectin were less supportive of migration. The glioma cells migrated on hyaluronic acid, but they did not migrate to the extent generally found on the extracellular matrix proteins. Glioma-derived extracellular matrix also served to promote cell migration. This finding implicates a role for either glioma remodeling or synthesis of a permissive environment for local dissemination that may be independent of the constitutive matrix proteins normally found in the brain. Although the glioma cells were able to migrate over monolayers of other glioma cells, they were unable to migrate over astrocytes and fibroblasts. Our findings indicate that the invasive behavior of glioma cells in situ is most likely a consequence of the interplay between the cells' manipulation of the environment and the constitutive ligands associated with specific regions or structures of the brain.

The in vitro motility of human gliomas increases with increasing grade of malignancy

BACKGROUND

Malignant gliomas are a highly invasive disease with a dismal prognosis despite aggressive therapeutic interventions.

METHODS

The authors tested the hypothesis that increasing in vitro motility of human glial tumors correlates with increasing grade of malignancy. A radial dish assay was used to quantitatively assess the brain tumor cell motility of 14 low passage cell lines derived from human glial tumors of varied malignancy, and 3 cell lines derived from human glia. The egress of cells from a central region of high tumor cell density to a region of lower tumor cell density was determined at various time points. A motility coefficient (MC), the slope of distance traveled against time, was generated by simple linear regression analysis.

RESULTS

The MC increased with the increased histologic grade of malignancy. Generation of a t-statistic was used to determine the significance of differences in motility among 5 histopathologic groups: 10 glioblastoma (World Health Organization Grade IV) cell lines (mean MC, 0.00396), 2 mixed anaplastic oligoastrocytoma (Grade III) cell lines (mean MC, 0.00382), 1 anaplastic astrocytoma (Grade III) cell line (mean MC, 0.00295), 1 Grade I glioma cell line (mean MC, 0.00206), and 3 human glial cell lines (mean MC, 0.00110).

CONCLUSIONS

The radial dish assay provided a reproducible method for quantitatively assessing brain tumor cell motility. The higher MC observed with the malignant human glioma cell lines correlated with the tendency of these tumors to invade into adjacent brain tissue. The potential to inhibit glial tumor motility may provide an important therapeutic avenue in the future.

Differential effects of vincristine and phenytoin on the proliferation, migration, and invasion of human glioma cell lines

The aim of this study was to investigate the antimigratory and antiinvasive potential of vincristine sulfate (VCR) on human glioma cells and to analyze whether phenytoin (5,5-diphenylhydantoin; DPH) might act synergistically with VCR. Vincristine affects the cytoplasmic microtubules; DPH has been reported to enhance VCR cytotoxicity in murine cells. In two human glioma cell lines, GaMG and D-37MG, we found VCR to reduce monolayer growth and colony formation in a dose-dependent fashion at concentrations of 10 ng/ml and above. Phenytoin increased the cytotoxic and cytostatic effects of VCR in monolayer cells but not in spheroids. Multicellular spheroids were used to investigate directional migration. A coculture system of GaMG and D-37MG spheroids with fetal rat brain aggregates was used to analyze and quantify tumor cell invasion. A dose-dependent inhibition of migration and invasion by VCR was observed in both cell lines without further enhancement by DPH. Immunofluorescence microscopy with antibodies against alpha-tubulin revealed dose-dependent morphological alterations in the microtubules when the cells were exposed to VCR but not after incubation with DPH. Based on the combination of standardized in vitro model systems currently in use and the present data, the authors strongly suggest that VCR inhibits migration and invasion of human glioma cells. This is not altered by DPH, which inhibits cell proliferation in combination with VCR.