Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

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

There is considerable interest in identifying factors responsible for expression of the O-6-methylguanine DNA methyltransferase (MGMT) gene, as MGMT is a major determinant in the response of glioma cells to the chemotherapeutic agent 1,3 bis(2-chloroethyl)-1-nitrosourea. Recently we have shown that MGMT expression is correlated in a direct, graded fashion with methylation in the body of the MGMT gene and in an inverse, graded fashion with promoter methylation in human glioma cell lines. To determine if promoter methylation is an important component of MGMT expression, this study addressed the complex interactions between methylation, chromatin structure, and in vivo transcription factor occupancy in the MGMT promoter of glioma cell lines with different levels of MGMT expression. Our results show that the basal promoter in MGMT-expressing glioma cell lines, which is 100% unmethylated, was very accessible to restriction enzymes at all sites tested, suggesting that this region may be nucleosome free. The basal promoter in glioma cells with minimal MGMT expression, however, which is 75% unmethylated, was much less accessible, and the basal promoter in nonexpressing cells, which is 50% unmethylated, was entirely inaccessible to restriction enzymes. Despite the presence of the relevant transcription factors in all cell lines examined, in vivo footprinting showed DNA-protein interactions at six Sp1 binding sites and one novel binding site in MGMT-expressing cell lines but no such interactions in nonexpressors. We conclude that in contrast to findings of previous in vitro studies, Sp1 is an important component of MGMT transcription. These correlations also strongly suggest that methylation and chromatin structure, by determining whether Sp1 and other transcription factors can access the MGMT promoter, set the transcriptional state of the MGMT gene.
...
PMID:Methylation-related chromatin structure is associated with exclusion of transcription factors from and suppressed expression of the O-6-methylguanine DNA methyltransferase gene in human glioma cell lines. 752 53

The purpose of this study was to evaluate the anti-tumor activity of sequenced administration of O6-benzylguanine (BG), streptozotocin (STZ), and 1,3-bis(2-chloroethyl)-1- nitrosourea (BCNU) in vitro and in vivo. We measured the recovery of O6-methylguanine DNA methyltransferase (MGMT) and BCNU cytotoxicity in the human glioma SF767 cell line, and anti-tumor activity against xenografts following exposure to BG, STZ or the combination of BG + STZ combined with BCNU. In SF767 cells, the combination of BG (10 microM) + STZ (0.05 mM) produced sustained inhibition of MGMT activity for at least 24 hr, and a greater potentiation of BCNU cytotoxicity than either agent alone. The combined treatment of BG + STZ increased BCNU-induced cell kill by 0.5 to 1.0 log over BG or STZ alone. The maximally tolerated doses of the combination of BG + STZ + BCNU administered to nude mice i.p. were the following: BG (80 mg/kg), STZ (100 mg/kg), and BCNU (15 mg/kg). Utilizing these doses of BG and STZ, the depletion and repletion profile of MGMT activity in SF767 xenografts was measured. STZ at 100 mg/kg did not affect xenograft MGMT activity. Subsequent to BG treatment, xenograft MGMT activity was inactivated completely for 12 hr, and the tumors gradually recovered approximately 40% of control activity by 24 hr. The combination of BG + STZ produced sustained inhibition of MGMT activity for 24 hr in the xenografts with complete recovery of MGMT activity by 48 hr. Administration of the combination of BG + BCNU to nude mice bearing SF767 tumor resulted in significant inhibition of tumor growth for 23 days. However, the addition of STZ to this combination provided no greater anti-tumor activity than that observed with BG + BCNU. The three-drug combination of BG, STZ, and BCNU produced no more than 2.4 to 13.0% weight loss with occasional lethal toxicity. Collectively, these data suggest that prolonged depletion of MGMT might be required for optimal reversal of BCNU resistance both in vitro and in vivo.
...
PMID:Anti-neoplastic activity of sequenced administration of O6-benzylguanine, streptozotocin, and 1,3-bis(2-chloroethyl)-1-nitrosourea in vitro and in vivo. 780 3

Expression of the O6-methylguanine DNA methyltransferase (MGMT) gene in human glioma cell lines is strongly associated with resistance to the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea. To examine the possibility that methylation of the body and promoter regions of the MGMT gene is associated with MGMT expression in a graded, rather than a completely on/off fashion, the present study analyzed the methylation status of the MGMT gene in human glioma cell lines exhibiting a wide range of MGMT expression. Methylation in the body of the gene was uniform within each cell line and correlated directly with MGMT expression. The level of MGMT promoter methylation was also graded across the cell lines, at 21 of 25 CpGs tested, but correlated inversely with MGMT expression. Two sites in the MGMT promoter were also much more accessible to restriction enzyme digestion, and thus in a more open chromatin conformation, in nuclei from high MGMT expressors relative to nuclei from cells with little or no MGMT expression. We conclude that the level of methylation, in both the body and promoter of the MGMT gene, is associated with MGMT expression in a graded fashion and may be important in setting the transcriptional state of the MGMT promoter through changes in chromatin structure.
...
PMID:Graded methylation in the promoter and body of the O6-methylguanine DNA methyltransferase (MGMT) gene correlates with MGMT expression in human glioma cells. 800 31

Aberrant transcriptional inactivation of the non-X-linked human O-6-methylguanine DNA methyltransferase (MGMT) gene has been associated with loss of open chromatin structure and increases in cytosine methylation in the Sp1-binding region of the 5'-CpG island of the gene. To examine the necessity of these events for gene silencing, we have isolated and characterized a subline of human MGMT+ T98G glioma cells. The subline, T98Gs, does not express MGMT activity or MGMT mRNA, and exhibits no in vivo DNA-protein interactions at Sp1-like binding sites in the MGMT 5'-CpG island. While the MGMT CpG island is less accessible to exogenously added restriction enzymes in T98Gs nuclei than in T98G nuclei, it is similarly methylated in both T98G and T98Gs cell lines 5' and 3' to the transcription factor binding sites, and similarly unmethylated in the region encompassing the binding sites. Inappropriate transcriptional inactivation of MGMT, therefore, does not require methylation of transcription factor binding sites within the 5'-CpG island. Rather, MGMT gene silencing and transcription factor exclusion from T98Gs MGMT CpG island binding sites is most closely associated with condensed chromatin structure, which is in turn indirectly influenced by distant sites of methylation.
...
PMID:Methylation of CpG island transcription factor binding sites is unnecessary for aberrant silencing of the human MGMT gene. 866 60

Tumor-associated aberrant silencing of CpG island-containing genes has been correlated with increased cytosine methylation, a "closed" chromatin structure, and exclusion of transcription factor binding in the CpG island/promoter regions of affected genes. Given the lack of understanding of what constitutes a closed chromatin structure in CpG islands, however, it has been difficult to assess the relationship among cytosine methylation, chromatin structure, and inappropriate gene silencing. In this study, nuclease accessibility analysis was used to more clearly define the chromatin structure in the CpG island of the human O6-methylguanine DNA methyltransferase (MGMT) gene. Chromatin structure was then related to in vivo DNA-protein interactions and cytosine methylation status of the MGMT CpG island in human glioma cells varying in MGMT expression. The results of these studies indicated that the "open" chromatin structure associated with the MGMT CpG island in MGMT+ cells consisted of an approximately 250-bp transcription factor-binding, nuclease-accessible, nucleosome-free region of DNA, whose formation was associated with at least four flanking, precisely positioned nucleosome-like structures. In MGMT- cells, this precise nucleosomal array was lost and was replaced by randomly positioned nucleosomes (i.e., the closed chromatin structure), regardless of whether methylation of the CpG island was spread over the entire island or limited to regions outside the transcription factor binding region. These results suggest that CpG islands facilitate the expression of housekeeping genes by facilitating nucleosomal positioning and that the conditions that alter the formation of this array (such as perhaps methylation) may indirectly affect CpG island-containing gene expression.
...
PMID:Aberrant silencing of the CpG island-containing human O6-methylguanine DNA methyltransferase gene is associated with the loss of nucleosome-like positioning. 931 39

New adjuvant therapy individualized by the results of reverse transcription-polymerase chain reaction (RT-PCR) for drug-resistance genes has been used to treat malignant gliomas. Protocol studies for malignant gliomas were not so encouraging in their therapeutic results because of heterogeneity and the various drug-sensitivities of the tumors. Individualization of glioma therapy is recommended. Drug-resistance genes messenger ribonucleic acid (mRNA) expressions were investigated in drug-resistant human glioma cell lines derived from U87MG and 46 frozen samples of retrospectively examined neuroepithelial tumors (12 low grade neuroepithelial tumors, 16 Grade III gliomas, 11 glioblastomas, and 7 other malignant neuroepithelial tumors such as medulloblastomas and primitive neuroectodermal tumors) by RT-PCR with the specific primers for O6-methylguanine DNA methyltransferase (MGMT), multidrug-resistance gene 1 (MDR1), multidrug-resistance-associated protein (MRP), and glutathione-S-transferase-pi (GST-pi). Thirty-seven preliminary individual adjuvant therapies (IAT) based on RT-PCR results, mainly in MGMT expression, were performed on 30 consecutive patients with neuroepithelial tumors. In the retrospectively examined series, the initial response to 1-(4-amino-2-methyl-5-pyrimidynyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU) was correlated most significantly to the MGMT mRNA expression among 11 independent prognostic factors (p = 0.0037) in multivariate logistic regression analysis. In the preliminary IAT, 17 of 32 evaluable therapies had a partial or complete response (53.1% response rate). Our IAT based on RT-PCR seemed to be more effective than conventional therapies for malignant gliomas.
...
PMID:Preliminary individual adjuvant therapy for gliomas based on the results of molecular biological analyses for drug-resistance genes. 1089 69

Previous studies have demonstrated that optimal reversal of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) resistance requires complete inactivation of the DNA repair protein O(6)-methylguanine DNA methyltransferase (MGMT) for at least 24 h following BCNU administration. In preparation for clinical trials at this institution, this study was undertaken to compare the efficacy of a conventional single-bolus dose versus double-bolus dose treatments with O(6)-benzylguanine (BG) in depleting MGMT activity in vivo. In xenograft human glioma SF767 tumors, a single 30-mg/kg bolus dose of BG completely inhibited MGMT activity for at least 8 h, but approximately 50% of the basal MGMT activity recovered within 24 h. To sustain the MGMT depletion for 24 h, a second bolus injection of BG at escalating doses was administered 8 h after the first dose. Second bolus doses of 5, 10, and 15 mg/kg BG attenuated the MGMT recovery in a dose-dependent manner compared with the single 30-mg/kg BG dose alone. When the 15-mg/kg BG dose was administered 8 h after the 30-mg/kg initial dose, MGMT activity was completely inactivated in the tumor xenografts for 24 h. This double-bolus BG treatment also depleted MGMT activity in normal murine tissues, including the liver, kidney, lung, brain, spleen, and bone marrow; and the kinetics of MGMT recovery varied among these tissues. When combined with BCNU treatment, the double-bolus BG treatment would be expected to produce greater antitumor activity in future trials than the conventional single-bolus BG treatment.
...
PMID:Comparison of single- versus double-bolus treatments of O(6)-benzylguanine for depletion of O(6)-methylguanine DNA methyltransferase (MGMT) activity in vivo: development of a novel fluorometric oligonucleotide assay for measurement of MGMT activity. 1130 39

We have shown previously that the tissue factor pathway inhibitor-2 (TFPI-2), a broad range proteinase inhibitor, is highly expressed in low-grade gliomas, but, minimally expressed or undetectable in glioblastomas, and that enforced expression of this gene reduces the invasive properties of brain tumor cells. Here, we examined the role of promoter methylation as a mechanism of TFPI-2 gene silencing. In SNB19 glioblastoma cells, which have no detectable TFPI-2 expression, 5-aza-2'-deoxycytidine (5aC), an inhibitor of DNA methyltransferase, induced TFPI-2 mRNA in a dose-dependent manner. Trichostatin A (TSA), the histone deacetylase (HDAC) inhibitor, by itself, was more efficient than 5aC in inducing TFPI-2 transcripts, and the 5aC+TSA combination resulted in highly synergistic reactivation of the gene, both at the transcript and protein levels. In Hs683 glioma cells, which express the TFPI-2 gene at high levels, transfection of the in vitro methylated TFPI-2 promoter constructs resulted in a drastic decrease of promoter activity compared to the unmethylated promoter. Further, the methylation-specific PCR in SNB19 and Hs683 cells showed that TFPI-2 gene repression was closely linked with methylation of the CpG islands in the promoter. Finally, the chromatin immunoprecipitation assays in SNB19 cells showed that the methylated and repressed TFPI-2 promoter was associated with the methyl-CpG binding protein 2 (MeCP2), and that gene reactivation resulted in the loss of MeCP2 from this site. These studies establish that TFPI-2 is transcriptionally silenced through promoter methylation in SNB19 cells.
...
PMID:Promoter methylation and silencing of the tissue factor pathway inhibitor-2 (TFPI-2), a gene encoding an inhibitor of matrix metalloproteinases in human glioma cells. 1288 7

Effective therapies for primary brain tumors continue to be elusive. Successful adjuvant therapies for CNS tumors will require a better understanding of their basic biology. Hepatocyte growth factor activator inhibitor type-2/placental bikunin (HAI-2/PB) is a serine proteinase inhibitor that has a broad inhibitory spectra against various serine proteinases. HAI-2/PB has anti-invasive effects thought to be mediated primarily by the inhibitory activity against serine proteinase-dependent matrix degradation. It has been previously demonstrated that the expression of HAI-2/PB is inversely related to degree of malignancy and possibly involved in the progression and invasion of human gliomas. Aberrant methylation patterns are an early change in glioma tumorigenesis, earlier than genetic changes. Methylation within 5' regulatory CpG islands by DNA methyltransferase is one of the most common epigenetic modifications. 5-Aza-2'-deoxycytidine (azacytidine) inhibits DNA methyltransferase and has been used in vitro to induce the expression of genes silenced by methylation. We have utilized azacytidine treatment and a micro-array system to investigate methylation influenced gene expression across several tumor cell lines of different lineage (brain, breast, prostate, liver). Using this system we have demonstrated that the expression of HAI-2/PB is under methylation control to a variable extent in glioma cell lines, in comparison to the other tested cell lines. Because the expression of HAI-2/B is inversely related to glioma invasiveness and degree of malignancy, this finding may provide insight into glioma initiation and progression as well as potentially providing new therapeutic targets.
...
PMID:Differential expression of bikunin (HAI-2/PB), a proposed mediator of glioma invasion, by demethylation treatment. 1455 97

The major mechanism of tumor cell resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) is the DNA repair protein O(6)-methylguanine DNA methyltransferase (MGMT). This repair system can be temporarily inhibited by the free base O(6)-benzylguanine (BG), which depletes cellular MGMT activity and sensitizes tumor cells and xenografts to BCNU. In clinical studies, the combination of BG and BCNU enhanced the myeloid toxicity of BCNU, thereby reducing the maximum tolerated dose. We have shown previously that retroviral expression of the P140K mutant of MGMT (MGMT-P140K) in murine and human hematopoietic cells produces significant resistance of bone marrow cells to low-dose, combination BG and BCNU treatment in vivo. In the current study, we investigated the ability of bone marrow transplantation with MGMT-P140K-transduced hematopoietic cells to protect against an intensive antitumor treatment regimen of combination BG and BCNU in non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice. The donor marrow cells underwent in vivo BG and BCNU selection before transplantation, allowing infusion of a highly selected population of transduced cells. Tolerance to the intensive BG and BCNU treatment was markedly improved in secondary MGMT-P140K-transplanted mice (n = 19) compared to untransplanted mice (n = 15), as indicated by blood counts and survival rate. The dose-intensified BG and BCNU therapy produced significant growth delays of glioma xenografts in MGMT-P140K-transplanted mice, extending the tumor doubling time by >40 days. These results demonstrate that MGMT-P140K-transduced bone marrow protects against BG and BCNU combination therapy in vivo and allows dose-intensified treatment of tumor xenografts.
...
PMID:Hematopoietic expression of O(6)-methylguanine DNA methyltransferase-P140K allows intensive treatment of human glioma xenografts with combination O(6)-benzylguanine and 1,3-bis-(2-chloroethyl)-1-nitrosourea. 1470 73


1 2 3 4 5 6 7 8 Next >>

---