UMLS:C0017638 - FACTA Search

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Query: UMLS:C0017638 (glioma)
30,880 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

VEGF (vascular endothelial growth factor), one of the most potent angiogenic factors, has recently been identified as an inducer of neoangiogenesis in many tumors including gliomas. VEGF itself appears to be regulated through different pathways. Since malignant gliomas frequently show EGF receptor amplification and express IL-1, a pivotal regulatory cytokine involved in angiogenesis, we analyzed interactions between EGF/EGF receptor and IL-1/IL-1 receptor and VEGF in the established glioblastoma cell lines U-87 MG and A-172. Basal VEGF expression was an order of magnitude higher in U-87 MG compared to A-172. IL-1 caused a fast and strong increase of VEGF secretion in U-87 MG which appeared to harbor an intracellular VEGF pool for enhanced exocytosis. The IL-1 receptor antagonist (IL-1-ra) reversed this effect suggesting an IL-1 receptor-associated mechanism. In contrast, VEGF secretion could not be increased by exogenous IL-1 exposure in A-172, which apparently lacked an intracellular VEGF pool for augmented exocytosis. However, IL-1-ra treatment alone caused a significant reduction of basal VEGF secretion in both U-87 MG and A-172. This suggests that baseline secretion of VEGF involves IL-1 receptor activation by endogenously produced IL-1. EGF also stimulated the secretion of VEGF into the cell supernatant. However, this effect, observed in both U-87 MG and A-172, was delayed and only occurred following replenishment of the intracellular VEGF pool. EGF upregulated the amount of VEGF mRNA. In general, the effects of IL-1 and EGF on VEGF were additive, suggesting independent mechanisms. Since IL-1 appears to be involved in VEGF secretion in glial tumors through an autocrine/paracrine mechanism, recombinant human IL-1-ra may evolve as a new agent for anti-angiogenic glioma therapy.
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PMID:Differential control of VEGF synthesis and secretion in human glioma cells by IL-1 and EGF. 1057 18

We recently showed that severe hypoxia was not universally present adjacent to necrosis in human glioma xenografts and spheroids established from the M059K, M006, M006X, M006XLo and M010b cell lines. Using these glioma models, we wished to test whether oxygen serves as a regulator of cellular VEGF expression in situ. In situ hybridization (ISH) and immunohistochemistry (IHC) were used to detect vascular endothelial growth factor (VEGF) mRNA and protein expression in sections of glioma xenografts and spheroids in which hypoxic regions and regions with well-oxygenated necrosis were identified on contiguous sections by use of the hypoxia-specific marker, 3H-misonidazole. Independent validation of the presence of radiobiologically hypoxic cells in M006 xenografts was undertaken using the comet assay. Northern blotting analyses of monolayer cells demonstrated significant up-regulation of VEGF mRNA in the M006X line at oxygen concentrations of 6% and below. ISH analysis of VEGF mRNA showed unexpectedly strong staining for VEGF mRNA across the entire viable rim of M006X and M006XLo glioma spheroids. Similarly, in virtually all xenograft tumours of the M059K, M006 and M010b lines, VEGF ISH showed similar staining across all regions of healthy cells up to the border of necrosis. Only in one M006X tumour was there a suggestion of increased VEGF expression in cells adjacent to necrosis. IHC for VEGF showed good concordance with the ISH results. IHC analysis of the VEGF receptor flt-1 showed strong tumour cell staining in M006XLo glioma cells. In human glioma spheroids and xenograft tumours, regions of severe hypoxia do not correspond to areas of up-regulated VEGF expression; in fact, VEGF expression is quite uniform. Furthermore, this and our previous study demonstrate that levels of VEGF expression vary among sublines (M006, M006X and M006XLo) derived from a single human glioma specimen.
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PMID:Vascular endothelial growth factor expression is independent of hypoxia in human malignant glioma spheroids and tumours. 1068 77

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor in human gliomas. VEGF-induced proteins in endothelial cells, tissue factor (TF), osteopontin (OPN) and alphavbeta3 integrin have been implicated as important molecules by which VEGF promotes angiogenesis in vivo. Sixty-eight gliomas were immunohistochemically stained with TF, VEGF, OPN and alphavbeta3 integrin antibody. Twenty-three tumours, six normal brains and nine glioma cell lines were evaluated for their mRNA expression of VEGF and TF by reverse transcription polymerase chain reaction analysis. The data indicated that TF as well as VEGF was a strong regulator of human glioma angiogenesis. First, TF expression in endothelial cells which was observed in 74% of glioblastomas, 54% of anaplastic astrocytomas and none of low-grade astrocytomas, correlated with the microvascular density of the tumours. Double staining for VEGF and TF demonstrated co-localization of these two proteins in the glioblastoma tissues. Second, there was a correlation between TF and VEGF mRNA expression in the glioma tissues. Third, glioma cell conditioned medium containing a large amount of VEGF up-regulated the TF mRNA expression in human umbilical vein endothelial cells. OPN and alphavbeta3 integrin, were also predominantly observed in the microvasculature of glioblastomas associated with VEGF expression. Microvascular expression of these molecules could be an effective antiangiogenesis target for human gliomas.
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PMID:Tissue factor, osteopontin, alphavbeta3 integrin expression in microvasculature of gliomas associated with vascular endothelial growth factor expression. 1086 5

Biotherapy including interleukin-2 (IL-2) treatment seems to be more effective outside the central nervous system when compared to the effects obtained when the same tumour is located intracerebrally. Recently published studies suggest that reduced activity of NK cells in tumour tissue can be increased by histamine. The present study was designed to determine whether IL-2 and histamine, alone or in combination, can induce anti-tumour effects in an orthotopic rat glioma model. One group of rats was treated with histamine alone (4 mg kg(-1)s.c. as daily injections from day 6 after intracranial tumour implantation), another group with IL-2 alone as a continuous subcutaneous infusion and a third group with both histamine and IL-2. The animals were sacrificed at day 24 after tumour implantation. IL-2 and histamine in combination significantly reduced tumour growth. The microvessel density was significantly reduced, an effect mainly affecting the small vessels. No obvious alteration in the pattern of VEGF mRNA expression was evident and no significant changes in apoptosis were observed. Neither IL-2 nor histamine alone caused any detectable effects on tumour growth. Histamine caused an early and pronounced decline in tumour blood flow compared to normal brain. The results indicate that the novel combination of IL-2 and histamine can be of value in reducing intracerebral tumour growth and, thus, it might be of interest to re-evaluate the therapeutic potential of biotherapy in malignant glioma.
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PMID:Interleukin-2 and histamine in combination inhibit tumour growth and angiogenesis in malignant glioma. 1095 89

Overexpression of vascular endothelial growth factor (VEGF) is associated with disease progression in human glioblastomas. We recently showed that VEGF promoter activity is inversely correlated with tumor extracellular pH (pH(o)) in vivo in the human glioma (U87 MG) xenografts. Here we show that substitution of the neutral culture medium (pH 7.3) with acidic pH medium (pH 6.6) up-regulates VEGF mRNA and protein production in human glioblastoma cells as reflected by Northern blot analysis and enzyme-linked immunosorbent assay. Functional analysis of the VEGF promoter reveals that the sequence between -961 bp and -683 bp upstream of the transcription start site is responsible for the transcriptional activation of the VEGF gene by acidic pH. This region contains the binding site for AP-1. Consequently, AP-1 luciferase reporter gene was activated by acidic pH. Gel-shift analysis confirmed that AP-1 DNA binding activity is induced under acidic pH. While investigating the upstream signaling pathways, we found that ERK1/2 MAPK is activated and translocates to the nucleus to activate Elk-1, and inhibition of the activation of ERK by specific inhibitors of MEK1 blocks the up-regulation of VEGF by low pH. Dominant negative forms of Ras and Raf abolished the activation of VEGF promoter by acidic pH. These results show that acidic pH activates Ras and the ERK1/2 MAPK pathway to enhance VEGF transcription via AP-1, leading to increased VEGF production.
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PMID:Acidic extracellular pH induces vascular endothelial growth factor (VEGF) in human glioblastoma cells via ERK1/2 MAPK signaling pathway: mechanism of low pH-induced VEGF. 1174 77

Hypoxia regulates expression of vascular endothelial growth factor (VEGF) by increasing its transcription and by stabilizing its mRNA. Despite the pivotal role of hypoxia-inducible factor 1 (HIF-1) in transcriptional activation of hypoxia-responsive genes, it is not known whether HIF-1 mediates hypoxia-induced stabilization of VEGF mRNA. We constructed adenoviral vectors expressing either the wild-type HIF-1 alpha (Ad2/HIF-1 alpha/FL), a constitutively stable hybrid form of HIF-1 alpha (Ad2/HIF-1 alpha/VP16), or no transgene (Ad2/CMVEV). In rat glioma (C6) cells and human cardiac, vascular smooth muscle, and endothelial cells, infection with Ad2/HIF-1 alpha/VP16 or Ad2/HIF-1 alpha/FL increased VEGF expression at both the mRNA and protein levels. Under normoxic conditions, the half-life of VEGF mRNA was 42 min in C6 cells. Hypoxia and Ad2/HIF-1 alpha/VP16 increased the half-life of VEGF mRNA to 3.3 and 2.7 h, respectively, while Ad2/CMVEV had no effect. These studies are the first to demonstrate that overexpression of HIF-1 alpha increases VEGF mRNA stability. Our results also suggest that stabilization of VEGF mRNA by hypoxia is mediated, at least in part, by HIF-1.
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PMID:Stabilization of vascular endothelial growth factor mRNA by hypoxia-inducible factor 1. 1186 51

Vascular endothelial growth factor (VEGF) is a multifunctional cytokine with important roles in angiogenesis. VEGF is overexpressed in human cancers, including highly vascularized and infiltrative brain tumors. In our previous study of seven glioma cell lines, VEGF expression levels correlated with blood vessel density and tumorigenicity, and U251 MG and NG-1 cells were recognized as low-tumorigenic glioma cell lines. We hypothesized that low-tumorigenic cells can become highly tumorigenic when high levels of VEGF are expressed. To test this hypothesis, we constructed VEGF expression vectors containing 564 bp or 696 bp of VEGF(121) or VEGF(165) cDNA, respectively, and transfected them into U251 MG and NG-1 cells. In comparison to parental cells, the 20 VEGF-expressing clones examined had on average 8-10-fold more VEGF mRNA and 12-88-fold more secreted VEGF proteins. Four VEGF-overexpressing clones (U251 MG/V121-C2, U251 MG/V165-C3, NG-1/V121-C6, and NG-1/V165-C3) were selected for additional study. As VEGF production increased with population growth, U251 MG/V121-C2 and U251 MG/V165-C3 cells accumulated 47.9 and 22.0 ng of VEGF during a 5-day culture of 10(4) cells, a 313- and 144-fold overexpression when compared with that in parental U251 MG cells. NG-1/V121-C6 and NG-1/V165-C3 cells secreted 30.4 and 9.4 ng of VEGF, respectively, or 138- and 43-fold more than did the parental NG-1 cells. Subcutaneous implantation of the VEGF-overexpressing U251 MG cells into nude mice caused huge, soft hemorrhagic tumors to form, whereas controls maintained very small tumors. Intracranial implantation of the VEGF-overexpressing cell lines significantly shortened survival of the mice when compared with controls, and it caused formation of solid brain tumors with variable sized hemorrhages, whereas the controls had no apparent brain tumors. Tumorigenicity of U251 MG cells was synergized by co-overexpression of VEGF(121) and VEGF(165). In addition, VEGF(165) seemed to be more potent to the brain endothelium than was VEGF(121). More interestingly, except when an admixture of cells was implanted s.c., VEGF overexpression in NG-1 cells did not promote hemorrhagic tumor formation. These data suggested that a switch from a phenotype of low tumorigenicity to one of high tumorigenicity is possible when VEGF overexpression occurs, although other factors may also be required.
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PMID:VEGF(121), VEGF(165) overexpression enhances tumorigenicity in U251 MG but not in NG-1 glioma cells. 1191 65

Thrombin is a key enzyme in the blood coagulation system where it converts fibrinogen to fibrin. It participates in a variety of biological processes such as the induction of mitogenesis and of morphological changes, the production of cytokines and growth factors, and apoptosis. To clarify the role of thrombin in the proliferation of human malignant gliomas, we investigated its effect on the expression of vascular endothelial growth factor (VEGF) in vitro and determined its intrinsic expression in human glioma tissues. In 3 human glioma cell lines tested, U-87 MG, U-251 MG, and U-105 MG, thrombin induced the VEGF mRNA expression and protein in a dose- and time-dependent manner. The thrombin receptor expression was detectable by RT-PCR and immunoblot. The secretion of VEGF protein in glioma cells was stimulated by the thrombin receptor agonist peptide and the induction of VEGF was significantly blocked by the thrombin inhibitor hirudin, indicating that the up-regulation of VEGF was mediated by the thrombin/thrombin receptor pathway. Immunoblot analysis demonstrated that prothrombin, the precursor of thrombin, was distributed in all 10 glioma tissues examined. In situ hybridization and immunohistochemical analysis revealed the co-localization of prothrombin mRNA-positive and GFAP-positive cells in the glioma tissues. Although various factors may be involved in the up-regulation of VEGF, our results suggest that human gliomas per se express prothrombin, and that thrombin, converted from prothrombin in glioma tissues, substantially stimulates angiogenesis in an autocrine fashion.
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PMID:The role of thrombin in the neo-vascularization of malignant gliomas: an intrinsic modulator for the up-regulation of vascular endothelial growth factor. 1195 84

Hypoxia-inducible factor 1 (HIF-1) is a master regulator of the transcriptional response to oxygen deprivation. HIF-1 has been implicated in the regulation of genes involved in angiogenesis [e.g., vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase] and anaerobic metabolism (e.g., glycolytic enzymes). HIF-1 is essential for angiogenesis and is associated with tumor progression. In addition, overexpression of HIF-1 alpha has been demonstrated in many common human cancers. Therefore, HIF-1 is an attractive molecular target for development of novel cancer therapeutics. We have developed a cell-based high-throughput screen for the identification of small molecule inhibitors of the HIF-1 pathway. We have genetically engineered U251 human glioma cells to stably express a recombinant vector in which the luciferase reporter gene is under control of three copies of a canonical hypoxia-responsive element (U251-HRE). U251-HRE cells consistently expressed luciferase in a hypoxia- and HIF-1-dependent fashion. We now report the results of a pilot screen of the National Cancer Institute "Diversity Set," a collection of approximately 2000 compounds selected to represent the greater chemical diversity of the National Cancer Institute chemical repository. We found four compounds that specifically inhibited HIF-1-dependent induction of luciferase but not luciferase expression driven by a constitutive promoter. In addition, these compounds inhibited hypoxic induction of VEGF mRNA and protein expression in U251 cells. Interestingly, three compounds are closely related camptothecin analogues and topoisomerase (Topo)-I inhibitors. We show that concomitant with HIF-1 and VEGF inhibition, the activity of the Topo-I inhibitors tested is associated with induction of cyclooxygenase 2 mRNA expression. The luciferase-based high-throughput screen is a feasible tool for the identification of small molecule inhibitors of HIF-1 transcriptional activation. In addition, our results suggest that altered Topo-I function may be associated with repression of HIF-1-dependent induction of gene expression.
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PMID:Identification of small molecule inhibitors of hypoxia-inducible factor 1 transcriptional activation pathway. 1215 35

Brain specific angiogenesis inhibitor (BAI)-1 is a novel p53-inducible anti-angiogenic molecule. We examined the expression of BAI-1 in glial tumors and its association with patient survival. The expression of BAI-1 was evaluated in 20 brain tumors (meningiomas, pituitary adenomas, hemangiopericytomas, hemangioblastomas), 2 normal brain samples, 5 benign gliomas, and 26 glioblastomas. In the 26 glioblastoma tumors, we also evaluated the expression of VEGF, p53, p53 mutations, and MIB-1 to determine their association with survival. BAI-1 mRNA was expressed in all benign gliomas, normal brain, and 9 out of 26 glioblastomas, but not in the other tumors. Low VEGF and aberrant high expression of p53 were associated with a favorable outcome in univariate survival analysis, but they were not independent factors in multivariate analysis. For the treatment response, BAI-1 expression was associated with better response to radiation therapy (p=0.014). When we divided the patients into groups according to the expression patterns of BAI-1 and VEGF mRNA, the median survival of 9 patients with high VEGF expression and no expression of BAI-1 was just 6 months, while the median survival of the other 17 patients was 14 months (p=0.013). Glioblastomas with no BAI-1 and high VEGF mRNA expression are more often associated with poor clinical outcome. These findings suggest that the balance between the angiogenic and anti-angiogenic factors is important in the progression of glioblastoma and its response to treatment.
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PMID:Expression of VEGF and brain specific angiogenesis inhibitor-1 in glioblastoma: prognostic significance. 1501 Aug 86

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