Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0017636 (glioblastoma)
 18,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aim of this study was to identify targets for rational chemotherapy of glioblastoma. In order to elucidate differences in the biochemistry of tumor and normal human brain, in vivo pool sizes of purine nucleotides, nucleosides, and nucleobases and of purine metabolizing enzymes in biopsy material from 14 grade IV astrocytomas and 4 normal temporal lobe samples were analyzed. Specimens were collected during surgery using the freeze-clamp sampling technique and analyzed by high pressure liquid chromatography. Total purine nucleotides, adenylates, and guanylates in the tumors were 2186, 1865, and 310 nmol/g (wet weight), respectively, which corresponds to 61, 60, and 71% of normal brain tissue concentrations. Relative to normal brain the tumors had significantly lower ATP and GTP levels, essentially normal pool sizes of purine nucleosides and bases, unchanged activities of the salvage enzymes hypoxanthine-guanine phosphoribosyltransferase, adenine phosphoribosyltransferase, and adenosine kinase (659, 456, and 98 nmol/h/mg protein, respectively) and 4-fold higher activities of IMP dehydrogenase (11.6 nmol/h/mg protein); the latter is the rate limiting enzyme for guanylate de novo synthesis. IMP pools in the tumors were 64% of values in normal brain. Modulation of the guanylate pathway in glioblastoma by inhibition of IMP dehydrogenase with tumor specific agents such as tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide) appears to be a rational therapeutic approach. Preliminary in vitro experiments with normal and malignant tissue specimens from 2 additional patients revealed that significant amounts of the active metabolite thiazole-4-carboxamide adenine dinucleotide are formed from tiazofurin. At a concentration of 200 microM this drug was able to deplete guanylate pools in the tumors to a median of 54% of phosphate buffered saline treated controls. Flux studies with [14C]formate showed that tiazofurin strongly inhibited de novo synthesis of guanylates in glioblastoma to an average of 10% of controls. This effect was more pronounced in the tumors as compared to normal brain. No inhibition of salvage of [14C]guanine by tiazofurin could be observed in normal and malignant tissues. Supportive measures have to be considered to inhibit the highly active salvage enzyme hypoxanthine-guanine phosphoribosyltransferase that can partly antagonize a tiazofurin induced decrease in guanine nucleotides.
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PMID:Purine metabolism of human glioblastoma in vivo. 215 28

The cyclin kinase inhibitor WAF1/CIP1, also termed CDKN1, mediates p53-induced cell cycle arrest in response to DNA damage. This property makes it an attractive tumour-suppressor candidate for a p53-associated tumour-suppressor gene. In order to investigate the role of WAF1/CIP1 in the pathogenesis of primary human brain tumours we performed single-stranded conformation polymorphism (SSCP) analysis and direct sequencing of exon 2 of the gene in a representative series of 158 brain tumours and corresponding blood samples. In addition, all tumours were examined for mutations in exons 5-8 of the p53 gene. Analysis of WAF1/CIP1 revealed multiple polymorphisms, the most abundant being AGC-->AGA (Ser-->Arg) at codon 31 with an allele frequency of 8.5%. Less common polymorphisms included GTG-->GGG (Val-->Gly) at codon 25, GCC-->ACC (Ala-->Thr) at codon 64, CGC-->CTC (Arg-->Leu) at codon 32, GGC-->AGC (Gly-->Ser) at codon 14 and GCG-->GTG (Ala-->Val) at codon 39 each with an allele frequency of 0.3%. These polymorphisms were all located in a conserved region of exon 2. Two of the polymorphisms were also seen in a group of 157 healthy controls indicating that WAF1/CIP1 polymorphisms do not predispose to cancer. None of the tumours included in our series showed a somatic mutation in WAF1/CIP1. All samples were also analysed for loss of heterozygosity on the short arm of chromosome 6 in the region of the WAF1/CIP1 locus. Allelic loss was observed in only one patient with a glioblastoma. Mutations in the p53 gene were found in 22 of 158 tumours. No association was found between any polymorphism of the WAF1/CIP1 gene, p53 mutations and histopathological tumour type. Our data indicate that WAF1/CIP1 mutations are probably not involved in the formation of primary human brain tumours.
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PMID:Multiple polymorphisms, but no mutations, in the WAF1/CIP1 gene in human brain tumours. 757 73

The activity of IMP dehydrogenase (EC 1.2.1.14), the key enzyme of de novo guanylate biosynthesis, was shown to be increased in tumor cells. Tiazofurin (TR), a potent and specific inhibitor of this enzyme, proved to be effective in the treatment of refractory granulocytic leukemia in blast crisis. We examined the effects of tiazofurin as a single agent and in combination with hypoxanthine and allopurinol in six different neuroectodermal tumor cell lines, the STA-BT-3 and 146-18 human glioblastoma cell lines, the SK-N-SH, LA-N-1 and LA-N-5 human neuroblastoma cell lines, and the STA-ET-1 Ewing tumor cell line. Tiazofurin inhibited tumor cell growth with IC50 values between 2.2 microM (LA-N-1 cell line) and 550 microM (LA-N-5 cells) and caused a significant decrease of intracellular GTP pools (GTP concentrations decreased to 39-79% of control). Incorporation of [8-14C]guanine into GTP pools was determined as a measure of guanylate salvage activity; incubation with 100 microM hypoxanthine caused a 62-96% inhibition of the salvage pathway. Incubation with tiazofurin (100 microM) and hypoxanthine (100 microM) synergistically inhibited tumor cell growth, and the addition of allopurinol (100 microM) strengthened these effects. Therefore, this drug combination, inhibiting guanylate de novo and salvage pathways, may prove useful in the treatment of human neuroectodermal tumors.
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PMID:Synergistic action of tiazofurin with hypoxanthine and allopurinol in human neuroectodermal tumor cell lines. 790 33

A mutant epidermal growth factor receptor (DeltaEGFR) containing a deletion of 267 amino acids from the extracellular domain is common in human glioblastomas. We have previously shown that the mutant receptor fails to bind EGF, is constitutively phosphorylated, and confers upon U87MG glioblastoma cells expressing it (U87MG. DeltaEGFR), an increased ability to form tumors in mice. Here we demonstrate that the constitutively phosphorylated DeltaEGFR enhances growth of glioblastoma cells through increased activity of Ras: 1) there was an increase in the proportion of Ras present in the GTP-bound form, and 2) introduction of neutralizing anti-Ras 259 antibodies into U87MG and U87MG.DeltaEGFR cells by microinjection inhibited DNA synthesis to the same low level in both cell populations. We also show that the truncated EGF receptor constitutively associates with the adapter proteins Shc and Grb2 which are involved in the recruitment of Ras to activated receptors. Several derivatives of DeltaEGFR containing single, or multiple mutations at critical autophosphorylation sites were constructed and used to demonstrate that the major Shc binding site is Tyr-1148, and that Grb2 association occurs primarily through Tyr-1068. We conclude that the increased tumorigenic potential of glioblastoma cells expressing the truncated EGF receptor is due at least in part to Ras activation presumably involving the Shc and Grb2 adapter proteins.
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PMID:Enhanced tumorigenic behavior of glioblastoma cells expressing a truncated epidermal growth factor receptor is mediated through the Ras-Shc-Grb2 pathway. 881 Mar 40

A fundamental issue in neuronal and glial cells is how intracellular rises in Ca2+ are coupled to signaling cascades and changes in subcellular morphology. We studied the expression and localization of annexin VII (synexin), a Ca(2+)-/GTP-dependent membrane fusion protein, in the human CNS. Here, we demonstrate the presence of two annexin VII isoforms (47 and 51 kDa) in human brain tissue as well as its exclusive expression in astroglial cells. An in vitro study of astrocyte-derived C6 rat glioblastoma cells expressing a GFP tagged annexin VII fusion protein demonstrates a sequential redistribution of the fusion protein in response to rising intracellular Ca2+ concentrations. Our findings indicate a role of annexin VII in the regulation of intracellular Ca(2+)-dependent processes in astroglial cells.
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PMID:Annexin VII: an astroglial protein exhibiting a Ca2+-dependent subcellular distribution. 1133 80

Agents that interact with cytoskeletal elements such as tubulin include synthetic spiroketal pyrans (SPIKET), targeting the spongistatin binding site of beta-tubulin, and monotetrahydrofuran compounds (COBRA compounds), targeting a unique binding cavity on alpha-tubulin. At nanomolar concentrations, the SPIKET compound SPIKET-P caused tubulin depolymerization and demonstrated potent cytotoxic activity against cancer cells. COBRA-1 inhibited GTP-induced tubulin polymerization. Treatment of human breast cancer and brain tumor cells with COBRA-1 caused destruction of microtubule organization and apoptosis. Other agents that have shown promise for cancer treatment include phorboxazoles, natural products that are extremely cytostatic towards the National Cancer Institute's panel of 60 tumor cell lines. In standard MTT assays, synthetic phorboxazole A exhibited potent cytotoxicity against NALM-6 acute lymphoblastic leukemia cells (IC50 = 1.7 nM), BT-20 breast cancer cells (IC50 = 3.4 nM), and U373 glioblastoma cells (IC50 = 6.7 nM). Structure-activity studies were reported for seven synthetic analogs of phorboxazole A. Out of these, two showed potent anti-cancer activity. Phorboxazole analog 2 was active against NALM-6 cells (IC50 = 4.8 nM), BT-20 cells (IC50 = 12.6 nM) and U373 cells (IC50 = 27.4 nM), as was analog 3 (NALM-6 IC50 = 5.2 nM, BT-20 IC50 = 11.3 nM, and U373 IC50 = 29.2 nM). Anticancer activity of the phorboxazole analogs was correlated to the presence of certain structural moieties such as portions of the macrolide group, the central oxazole group, and the polyene side chain. The requirement of more than one structural element for activity suggested that at least bimodal interactions of the natural product with key cellular components may occur. Promising anti-mitotic agents with pro-apoptotic activity include inhibitors of the tyrosine kinase BTK. The leflunomide metabolite analog LFM-A13 inhibited BTK in leukemia and lymphoma cells (IC50 = 17 microM). Consistent with the anti-apoptotic function of BTK, treatment of leukemic cells with LFM-A13 enhanced their sensitivity to chemotherapy-induced apoptosis.
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PMID:Rationally designed anti-mitotic agents with pro-apoptotic activity. 1156 3

p53 protein is a transcription factor involved in multiple tumor-suppressor activities including cell cycle control and apoptosis. TP53 gene is frequently mutated in glioblastoma, suggesting the importance of inactivation of this gene product in gliomagenesis. Restoration of p53 function in glioblastoma cell lines deficient for p53 has shown that p53 induces growth arrest or apoptosis depending on the cell line and vector used to transduce wild-type TP53 alleles. Considering that astrocytes grow and express p53, it is not clear whether these results reflect physiologic responses or the result of p53 overexpression in combination with cellular responses to viral vector infection. Here, we reassessed this issue using a glioblastoma cell line (LN382) that expresses an endogenous temperature-sensitive mutant p53. This cell line expresses TP53 alleles (100% as determined by a p53 transcriptional assay in yeast) mutated at codon 197 GTG (Val) > CTG (Leu). We found that the p53 protein in these cells acted as an inactive mutant at 37 degrees C and as a functional wild-type p53 below 34 degrees C as demonstrated by several lines of evidence, including (i) restoration of transactivating ability in yeast, (ii) induction of p53-modulated genes such as CDKN1(p21) and transforming growth factor-alpha, (iii) disappearance of accumulated p53 protein in the nucleus and (iv) decrease in steady state p53 protein levels. This temperature switch allowed p53 levels, which were close to physiological levels to dramatically reduce LN382 cell proliferation by inducing a G(1)/S cell cycle block, but not to induce apoptosis. The lack of apoptosis was considered to be a result of the low level p53 expression, because increasing wild-type p53 levels by adenoviral-mediated gene transfer caused apoptosis in these cells. The LN382 cell line will be extremely useful for investigations into the roles of p53 in cellular responses to a variety of stimuli or damages.
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PMID:Restoration of endogenous wild-type p53 activity in a glioblastoma cell line with intrinsic temperature-sensitive p53 induces growth arrest but not apoptosis. 1166 76

Primary glioblastomas (GBMs) commonly overexpress the oncogene epidermal growth factor receptor (EGFR), which leads to increased Ras activity. FTA, a novel Ras inhibitor, produced both time- and dose-dependent caspase-mediated apoptosis in GBM cell lines. EGFR-mediated increase in 3H-thymidine uptake was inhibited by FTA. FACS analysis was performed to determine the percent of apoptotic cells. The sub-Go population of GBM cells was increased from 4.5 to 13.8% (control) to over 45-53.6% in FTA-treated cells within 24 h. Furthermore, FTA also increased the activities of both caspase-3 and -9, and PARP cleavage. Treatment of GBMs with FTA before or after EGF addition to the cultures blocked phosphorylation of Akt and mitogen-activated protein kinases (MAPK). FTA also significantly reduced the amount of EGF-induced Ras-GTP as reflected by a decrease in the level of Ras bound to Raf-RBD-GST. This study demonstrates that inhibition of Ras methylation may provide a therapeutic target for the treatment of GBMs overexpressing EGFR.
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PMID:Farnesylthiosalicylic acid induces caspase activation and apoptosis in glioblastoma cells. 1623 32

Eph receptor tyrosine kinases are involved in nervous system development. Eph ligands, termed ephrins, are transmembrane proteins that bind to Eph receptors, the mutual activation of which causes repulsive effects in reciprocally contacting cells. Previously, we showed that overexpression of EphB2 in glioma cells increases cell invasion. Here, expression profiles of ephrin-B family members were determined in four glioma cell lines and in invading glioblastoma cells collected by laser capture microdissection. Ephrin-B3 mRNA was up-regulated in migrating cells of four of four glioma cell lines (1.3- to 1.7-fold) and in invading tumor cells of eight of eight biopsy specimens (1.2- to 10.0-fold). Forced expression of ephrin-B3 in low expressor cell lines (U87, T98G) stimulated cell migration and invasion in vitro and ex vivo, concomitant with tyrosine phosphorylation of ephrin-B3. In high expressor cell lines (U251, SNB19), ephrin-B3 colocalized with Rac1 to lamellipodia of motile wild-type cells. Cells transfected with ephrin-B3 small interfering RNA (siRNA) showed significant morphologic change and decreased invasion in vitro and ex vivo. Depletion of endogenous ephrin-B3 expression abrogated the increase of migration and invasion induced by EphB2/Fc, indicating increased invasion is dependent on ephrin-B3 activation. Furthermore, using a Rac1-GTP pull-down assay, we showed that ephrin-B3 is associated with Rac1 activation. Reduction of Rac1 by siRNA negated the increased invasion by addition of EphB2/Fc. In human glioma specimens, ephrin-B3 expression and phosphorylation correlated with increasing tumor grade. Immunohistochemistry revealed robust staining for phosphorylated ephrin-B and ephrin-B3 in invading glioblastoma cells. These data show that ephrin-B3 expression and signaling through Rac1 are critically important to glioma invasion.
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PMID:Ephrin-B3 ligand promotes glioma invasion through activation of Rac1. 1695 Nov 61

Neurofibromin contains several domains, most notably a GAP-related domain (GRD), that down-regulates Ras pathways. The functions of the non-GRD neurofibromin domains are largely known. Here we show that the pre-GRD region of neurofibromin alters the expression of genes involved in cell adhesion and migration and acts as a negative regulator of the Rac1/Pak1/LIMK1/cofilin pathway. Thus, neurofibromin-deficient glioblastoma and mouse fibroblasts are enriched in Rac1-GTP, p-Pak1, p-LIMK1 and p-cofilin, with all proteins exhibiting decreased expression upon expression of NF1(1-1163) polypeptide. Concomitantly, actin stress fibers and focal adhesion were disassembled and cell migration was halted. These effects were independent of the Ras signaling pathways. It seems that NF1(1-1163), through negative regulation of Rac-1, shifts the balance from a state of inactive phospho-cofilin to active unphosphorylated cofilin, resulting in severing of F-actin. Impairment of these cellular functions of neurofibromin provides novel insights into the invasiveness/progression of NF1-associated tumors.
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PMID:The pre-GAP-related domain of neurofibromin regulates cell migration through the LIM kinase/cofilin pathway. 1966 24


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