Promoter methylation and expression analysis of MGMT in advanced pediatric brain tumors

Abstract

Abstract. Insufficient response to oral temozolomide (TMZ) in children with brain tumor may depend on the repair-action of inducible O 6 -methylguanine-DNA methyltransferase (MGMT). To investigate the clinical relevance of MGMT expression, we analyzed MGMT levels by qRT-PCR and immunohistochemistry, and the methylation of gene promoter in patients with relapsed or refractory brain tumor, enrolled in an off-label trial with oral temozolomide. The drug was administered at the dose of 200 mg/m 2 /day in patients with no prior cranio-spinal irradiation, and 180 mg/m 2 /day in those with previous radiotherapy and/or high-dose chemotherapy followed by autologous hematopoietic stem cell rescue. Nine patients with recurrent ependymoma (n=3), low grade glioma (n=3), glioblastoma (n=1), relapsed medulloblastoma (n=2) were enrolled in the study. Median absolute MGMT mRNA expression level standardized for GAPDH was 1.06 (range -0.453 to 3.932). The median relative expression level (RQ=2 -ddC ) was 4.29 (range 1.585 to 12.228). By immunohistochemistry, the score was 2+ in 6 of the 9 tumor samples, and 1+ in 3, while none was MGMT negative. Methylation of MGMT promoter was detected in only one ependymoma sample. The heterogeneous PFS in our patients treated with second line TMZ, indicates that MGMT expression alone is insufficient to predict the response to TMZ, presumably because of the DNA repair mechanisms involved.

Aberrant Methylation of Different DNA Repair Genes Demonstrates Distinct Prognostic Value for Esophageal Cancer

“…Recently, great progress has been made regarding MGMT silencing because of the methylation of its promoter. On one hand, MGMT gene silencing could lead to the accumulation of tumorrelated transition mutations; on the other hand, hypermethylation of MGMT is closely associated with the tumor's increased drug sensitivity to alkylating drugs [32][33][34][35]. Therefore, MGMT methylation is a potential predictor of the tumor's response to alkylating chemotherapy [36].…”

“…This is a suicidal reaction, wherein the methylated MGMT is inactivated, released from the DNA, and subsequently degraded in the ubiquitination pathway, instead of being recovered by demethylation. In this case, the biological effects of the cells to overcome the O 6 -AG alkylation damage are directly dependent on the concentration of molecular MGMT [29][30][31][32][33]. Studies have shown that the abnormal methylation of MGMT gene promoter was closely correlated with MGMT protein deficiency, mRNA expression deficiency, and lack of MGMT activity.…”

“…The methylation of MGMT gene promoter regulates its protein expression; therefore, it can be considered as a potential molecular marker to predict the drug resistance of tumors to alkylating agents [23,24,[29][30][31][32][33][34][35][36]. The KaplanMeier survival analysis of the follow-up clinical information of the patients and the corresponding MGMT gene methylation status showed that the survival periods of patients with MGMT methylation were significantly longer than those without MGMT methylation.…”

The Transcription Factor Evi-1 Is Overexpressed, Promotes Proliferation, and Is Prognostically Unfavorable in Infratentorial Ependymomas

“…The MDS1/EVI1 fusion transcript contains a putative methyltransferase domain (21) and has been associated with differential promoter methylation in acute myeloid leukemia (28), suggesting that the observed correlation of MDS1/EVI1 fusion transcript status and MGMT promoter methylation might represent more than an epiphenomenon. Because MGMT promoter methylation status is less frequently encountered in ependymomas as compared with malignant astrocytic tumors (22) and has no proven prognostic role (29), the clinical implications of these findings remain uncertain.…”

Multiplexed methylation profiles of tumor suppressor genes and clinical outcome in oligodendroglial tumors

“…Recent studies found that the methylation of the promoter of the AGT gene at 10q26, which encodes the MGMT protein, leads to transcriptional inactivation of the gene, thereby increasing chemosensitivity in gliomas, especially glioblastomas. Although methylation of tumor‐related genes, such as MGMT has been detected in other types of brain tumors, including oligodendroglial tumors, meningiomas and ependymomas, the association between methylation status of these genes and progression‐free or overall survival has not been completely examined 7, 8, 9. Nevertheless, detection of gene methylation may prove essential in not only diagnosis but also therapeutic response and prognostic prediction.…”