Human malignant gliomas (glioblastomas and anaplastic astrocytomas) are the most frequent brain tumors and are associated with a variety of genetic alterations including retinoblastoma (RB) and p53 gene mutations, loss of interferon alpha and beta (IFNA, IFNB) genes and lack of O6-methylguanine-DNA methyltransferase (MGMT) expression.
The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) removes mutagenic adducts from the O6 position of guanine, thereby protecting the genome against guanine : cytosine to adenine : thymine transition and, meanwhile, conferring tumor resistance to many anti-cancer alkylating agents commonly used in the treatment of malignant gliomas.
The DNA repair enzyme O(6)-methylguanine DNA methyltransferase (MGMT) may cause resistance to DNA-alkylating drugs commonly used in the treatment of anaplastic oligodendrogliomas and other malignant gliomas.
These results indicate that dexamethasone-mediated upregulation of MGMT limits the efficiency of alkylating agents in the treatment of malignant gliomas.
Prognostic significance of O6-methylguanine-DNA methyltransferase determined by promoter hypermethylation and immunohistochemical expression in anaplastic gliomas.
LOH of 1p in the heterogeneous population of malignant gliomas may be one of the important factors besides MGMT methylation that predict better outcome in patients treated with TMZ.
Currently, the most efficacious treatment for malignant gliomas is temozolomide; however, gliomas expressing the DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT) are resistant to this drug.
Immediately after the operation, mRNA expression for drug-resistance genes was investigated in frozen samples of malignant gliomas from 55 patients (30 glioblastoma multiformes, 20 anaplastic astrocytomas and 5 anaplastic oligodendroglial tumors) by real-time quantitative RT-PCR with specific primers for MGMT.
Aberrant methylation of the MGMT (O6-methylguanine-DNA methyltransferase) DNA-repair gene is a predictive marker for the response to chemotherapy with alkylating agents (e.g., temozolomide) in malignant gliomas.
These results suggest that the clinical therapeutic efficacy of TMZ might be improved by a combination with IFN-beta in malignant gliomas unmethylated at the MGMT gene.
We investigated the impact of MGMT methylation and expression on survival of children with high-grade glioma (HGG) registered into the German HIT-GBM database receiving temozolomide (TMZ) as part of their treatment (n = 21 relapsed, n = 4 primary).
According to pathological examination, the tumor was a high-grade glioma that was positive for methylated O-6-methylguanine-DNA methyltransferase promoter.
Our findings indicate that, in pHGG, (a) MGMT promoter methylation is less frequent than in adult malignant gliomas, (b) there is a high correlation between MGMT MSP and MGMT IHC, and (c) as in adults, MGMT status is associated with prognosis, although this observation has to be statistically validated on larger series of patients.
The O6-methylguanine-DNA-methyltransferase (MGMT) promoter methylation status is a predictive parameter for the response of malignant gliomas to alkylating agents such as temozolomide.
Different molecular biomarkers were identified by genetic studies and some of these are used in neuro-oncology for the evaluation of glioma patients, in particular combined deletions of the chromosome arms 1p and 19q in oligodendroglial tumors, methylation status of the O-6 methylguanine- DNA methyltransferase gene promoter and alterations in the epidermal growth factor receptor pathway in adult malignant gliomas, isocitrate dehydrogenase 1 (IDH1) and IDH2 gene mutations in diffuse gliomas, as well as BRAF status in pilocytic astrocytomas.
Recently published results of trials on elderly patients with malignant gliomas have revived the call for routine MGMT testing for clinical decision making.
MGMT promoter methylation is a predictive biomarker for benefit from alkylating agent chemotherapy in patients with IDH1-wild-type, but not IDH1-mutant, malignant gliomas of World Health Organization grades III/IV.