Correlation of MGMT promoter methylation status with gene and protein expression levels in glioblastoma.
OBJECTIVE
1) To correlate the methylation status of the O6-methylguanine-DNA-methyltransferase (MGMT) promoter to its gene and protein expression levels in glioblastoma and 2) to determine the most reliable method for using MGMT to predict the response to adjuvant therapy in patients with glioblastoma.


BACKGROUND
The MGMT gene is epigenetically silenced by promoter hypermethylation in gliomas, and this modification has emerged as a relevant predictor of therapeutic response.


METHODS
Fifty-one cases of glioblastoma were analyzed for MGMT promoter methylation by methylation-specific PCR and pyrosequencing, gene expression by real time polymerase chain reaction, and protein expression by immunohistochemistry.


RESULTS
MGMT promoter methylation was found in 43.1% of glioblastoma by methylation-specific PCR and 38.8% by pyrosequencing. A low level of MGMT gene expression was correlated with positive MGMT promoter methylation (p = 0.001). However, no correlation was found between promoter methylation and MGMT protein expression (p = 0.297). The mean survival time of glioblastoma patients submitted to adjuvant therapy was significantly higher among patients with MGMT promoter methylation (log rank = 0.025 by methylation-specific PCR and 0.004 by pyrosequencing), and methylation was an independent predictive factor that was associated with improved prognosis by multivariate analysis.


CONCLUSIONS
MGMT promoter methylation status was a more reliable predictor of susceptibility to adjuvant therapy and prognosis of glioblastoma than were MGMT protein or gene expression levels. Methylation-specific polymerase chain reaction and pyrosequencing methods were both sensitive methods for determining MGMT promoter methylation status using DNA extracted from frozen tissue.
Department of Neurology, Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil. unomiyuki@lim15.fm.usp.br
Miyuki
M
Uno
Sueli Mieko
SM
Oba-Shinjo
Anamaria Aranha
AA
Camargo
Ricardo Pereira
RP
Moura
Paulo Henrique de
PH
Aguiar
Hector Navarro
HN
Cabrera
Marcos
M
Begnami
Sérgio
S
Rosemberg
Manoel Jacobsen
MJ
Teixeira
Suely Kazue Nagahashi
SK
Marie
D000293:Adolescent; D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics* / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D005909:Glioblastoma / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011237:Predictive Value of Tests; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000235:genetics*; D018709:Statistics, Nonparametric; D013997:Time Factors; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes