O6-Methylguanine-DNA Methyltransferase Expression Strongly Correlates With Outcome in Childhood Malignant Gliomas: Results From the CCG-945 Cohort

The Ohio State University, Columbus, Ohio, United States
Journal of Clinical Oncology (Impact Factor: 18.43). 08/2006; 24(21):3431-7. DOI: 10.1200/JCO.2006.05.7265
Source: PubMed


O6-methylguanine-DNA methyltransferase (MGMT) functions to counteract the cytotoxic effects of alkylating agents, such as nitrosoureas, which play a central role in the treatment of childhood malignant gliomas. Epigenetic silencing of MGMT has been associated with prolonged survival in adults with malignant gliomas, although the association between MGMT expression status and outcome in pediatric malignant gliomas has not been defined.
We examined the association between MGMT expression and survival duration using tumor samples from the Children's Cancer Group 945 study, the largest randomized trial for childhood malignant gliomas completed to date. All patients received alkylator-based chemotherapy as a component of adjuvant therapy. Archival histopathologic material yielded tissue of sufficient quality for immunohistochemical assessment of MGMT expression status in 109 specimens.
Twelve of the 109 samples demonstrated overexpression of MGMT compared with normal brain. Five-year progression-free survival was 42.1% +/- 5% in the 97 patients whose tumors had low levels of MGMT expression versus 8.3% +/- 8% in the 12 patients whose tumors overexpressed MGMT (P = .017, exact log-rank test). The association between MGMT overexpression and adverse outcome remained significant after stratifying for institutional histologic diagnosis (eg, anaplastic astrocytoma or glioblastoma multiforme), as well as age, amount of residual tumor, and tumor location.
Overexpression of MGMT in childhood malignant gliomas is strongly associated with an adverse outcome in children treated with alkylator-based chemotherapy, independently of a variety of clinical prognostic factors.

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Available from: Robert W Sobol, Feb 01, 2016
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    • "Without MGMT repair, O6-methylguanine initiates activation of mismatch repair-deficient (MMR) proteins or Rad3-related protein kinase that ultimately leads to apoptotic cell death (Caporali et al., 2004; Wang and Edelmann, 2006; Roos et al., 2007). High expression of MGMT or loss of MMR contributes significantly to TMZ resistance in many clinical cases (Pollack et al., 2006; Hegi et al., 2008; Sarkaria et al., 2008). The initiation of apoptotic signaling fails in the absence of the MMR system. "
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    • "Abnormalities of p53 were most commonly seen in WHO grade IV tumors; however, p53 was shown to be an independent prognostic factor regardless of histologic grade (Pollack et al., 2002). A follow-up analysis of O6-methylguanine- DNA methyltransferase (MGMT) status in this same group of patients revealed a statistically worse outcome in children with overexpression of MGMT (Pollack et al., 2006). "
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    • "However, if the O6meG is not repaired before the re-synthesis step, it is believed that the repetitive cycle of futile MMR will generate tertiary lesions, most likely DSBs, eliciting a cell death response (Branch et al., 1993). Whereas a significant percentage of gliomas lack expression of MGMT, due to hypermethylation of the MGMT promoter, whereas at least half of glioblastomas multiforme (GBM) express MGMT, its expression being associated with resistance to chemotherapy and poor prognosis (Hegi et al., 2005; Pollack et al., 2006). Strategies to target the MMR pathway and to improve the efficacy of TMZ to overcome resistance resulting from MGMT activity have been implemented. "

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