Careful exclusion of non-neoplastic brain components is required for an appropriate evaluation of O6-methylguanine-DNA methyltransferase status in glioma: relationship between immunohistochemistry and methylation analysis.
Evaluation of O6-methylguanine-DNA methyltransferase (MGMT) expression is important for antiglioma therapy as many clinical trials have demonstrated that promoter hypermethylation and low level expression of MGMT are associated with an enhanced response to alkylating agents. However, here we report that the current strategies used to evaluate MGMT status in gliomas are unreliable. We observed discordance in the MGMT expression status when immunohistochemical evaluation and polymerase chain reaction-based methylation assessments were used: 73% of gliomas with methylated MGMT promoter had substantial numbers of MGMT-immunopositive tumor cells. Furthermore, when MGMT expression was tested in tumor homogenates using reverse transcription-polymerase chain reaction, 43% of tumors were found positive, in comparison to only 24%, when histologic samples were assayed immunohistochemically. To explain these inconsistencies we undertook a detailed immunohistochemical evaluation of tumor samples and found that some gliomas demonstrated remarkably high expression of MGMT in the entire tumor whereas others contained only a small immunopositive area. Additionally, we found that gliomas contained various types of non-neoplastic cells expressing MGMT, including lymphocytes, vascular endothelial cells, and macrophages/microglias, which contribute to overall MGMT expression detected in tumor homogenates, and thus result in overestimation of tumor MGMT expression. Therefore, to correctly establish MGMT expression in the tumor, which could be informative of glioma sensitivity to alkylating agents, exclusion of non-neoplastic brain components from analysis is required.
Sasai
Ken
K
Laboratory of Molecular and Cellular Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
Nodagashira
Miho
M
Nishihara
Hiroshi
H
Aoyanagi
Eiko
E
Wang
Lei
L
Katoh
Masahito
M
Murata
Junichi
J
Ozaki
Yoshimaru
Y
Ito
Tamio
T
Fujimoto
Shin
S
Kaneko
Sadao
S
Nagashima
Kazuo
K
Tanaka
Shinya
S
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use; D001921:Brain / Q000201:enzymology* / Q000473:pathology; D001932:Brain Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000032:analysis* / Q000235:genetics; D045643:DNA Repair Enzymes / Q000032:analysis* / Q000235:genetics; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D005910:Glioma / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D007564:Japan; D008297:Male; D008875:Middle Aged; D018579:Patient Selection; D011401:Promoter Regions, Genetic; D015203:Reproducibility of Results; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013048:Specimen Handling; D025521:Tumor Suppressor Proteins / Q000032:analysis* / Q000235:genetics
D018906:Antineoplastic Agents, Alkylating; D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes