title: O-methylguanine-DNA methyltransferase (MGMT) mRNA expression predicts outcome in malignant glioma independent of MGMT promoter methylation.
abstract: BACKGROUND
  We analyzed prospectively whether MGMT (O(6)-methylguanine-DNA methyltransferase) mRNA expression gains prognostic/predictive impact independent of MGMT promoter methylation in malignant glioma patients undergoing radiotherapy with concomitant and adjuvant temozolomide or temozolomide alone. As DNA-methyltransferases (DNMTs) are the enzymes responsible for setting up and maintaining DNA methylation patterns in eukaryotic cells, we analyzed further, whether MGMT promoter methylation is associated with upregulation of DNMT expression.
  
  
  RESULTS
  ADULT PATIENTS WITH A HISTOLOGICALLY PROVEN MALIGNANT ASTROCYTOMA (GLIOBLASTOMA: N = 53, anaplastic astrocytoma: N = 10) were included. MGMT promoter methylation was determined by methylation-specific PCR (MSP) and sequencing analysis. Expression of MGMT and DNMTs mRNA were analysed by real-time qPCR. Prognostic factors were obtained from proportional hazards models. Correlation between MGMT mRNA expression and MGMT methylation status was validated using data from the Cancer Genome Atlas (TCGA) database (N = 229 glioblastomas). Low MGMT mRNA expression was strongly predictive for prolonged time to progression, treatment response, and length of survival in univariate and multivariate models (p<0.0001); the degree of MGMT mRNA expression was highly correlated with the MGMT promoter methylation status (p<0.0001); however, discordant findings were seen in 12 glioblastoma patients: Patients with methylated tumors with high MGMT mRNA expression (N = 6) did significantly worse than those with low transcriptional activity (p<0.01). Conversely, unmethylated tumors with low MGMT mRNA expression (N = 6) did better than their counterparts. A nearly identical frequency of concordant and discordant findings was obtained by analyzing the TCGA database (p<0.0001). Expression of DNMT1 and DNMT3b was strongly upregulated in tumor tissue, but not correlated with MGMT promoter methylation and MGMT mRNA expression.
  
  
  CONCLUSIONS
  MGMT mRNA expression plays a direct role for mediating tumor sensitivity to alkylating agents. Discordant findings indicate methylation-independent pathways of MGMT expression regulation. DNMT1 and DNMT3b are likely to be involved in CGI methylation. However, their exact role yet has to be defined.
authors.affiliation: Department of Anaesthesiology, Ludwig Maximilians University, Munich, Germany. fkreth@med.uni-muenchen.de
authors.forename: Simone
authors.initials: S
authors.lastname: Kreth
authors.forename: Niklas
authors.initials: N
authors.lastname: Thon
authors.forename: Sabina
authors.initials: S
authors.lastname: Eigenbrod
authors.forename: Juergen
authors.initials: J
authors.lastname: Lutz
authors.forename: Carola
authors.initials: C
authors.lastname: Ledderose
authors.forename: Rupert
authors.initials: R
authors.lastname: Egensperger
authors.forename: Joerg C
authors.initials: JC
authors.lastname: Tonn
authors.forename: Hans A
authors.initials: HA
authors.lastname: Kretzschmar
authors.forename: Ludwig C
authors.initials: LC
authors.lastname: Hinske
authors.forename: Friedrich W
authors.initials: FW
authors.lastname: Kreth
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000235:genetics* / Q000378:metabolism / Q000628:therapy; D017024:Chemotherapy, Adjuvant; D019175:DNA Methylation / Q000187:drug effects / Q000502:physiology*; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000627:therapeutic use; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005910:Glioma / Q000175:diagnosis* / Q000235:genetics* / Q000378:metabolism / Q000628:therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics* / Q000378:metabolism; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D018714:Radiotherapy, Adjuvant; D000077204:Temozolomide; D016896:Treatment Outcome
chemical_list: D018906:Antineoplastic Agents, Alkylating; D012333:RNA, Messenger; D003606:Dacarbazine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000077204:Temozolomide