Abstract
BackgroundThe CD133 antigen is a marker of radio- and chemo-resistant stem cell populations in glioblastoma (GBM). The O6-methylguanine DNA methyltransferase (MGMT) enzyme is related with temozolomide (TMZ) resistance. Our propose is to analyze the prognostic significance of the CD133 antigen and promoter methylation and protein expression of MGMT in a homogenous group of GBM patients uniformly treated with radiotherapy and TMZ. The possible connection between these GBM markers was also investigated.MethodsSeventy-eight patients with GBM treated with radiotherapy combined with concomitant and adjuvant TMZ were analyzed for MGMT and CD133. MGMT gene promoter methylation was determined by methylation-specific polymerase chain reaction after bisulfite treatment. MGMT and CD133 expression was assessed immunohistochemically using an automatic quantification system. Overall and progression-free survival was calculated according to the Kaplan–Meier method.ResultsThe MGMT gene promoter was found to be methylated in 34 patients (44.7%) and unmethylated in 42 patients (55.3%). A significant correlation was observed between MGMT promoter methylation and patients’ survival. Among the unmethylated tumors, 52.4% showed low expression of MGMT and 47.6% showed high-expression. Among methylated tumors, 58.8% showed low-expression of MGMT and 41.2% showed high-expression. No correlation was found between MGMT promoter methylation and MGMT expression, or MGMT expression and survival. In contrast with recent results, CD133 expression was not a predictive marker in GBM patients. Analyses of possible correlation between CD133 expression and MGMT protein expression or MGMT promoter methylation were negative.ConclusionsOur results support the hypothesis that MGMT promoter methylation status but not MGMT expression may be a predictive biomarker in the treatment of patients with GBM. In addition, CD133 should not be used for prognostic evaluation of these patients. Future studies will be necessary to determine its clinical utility.
Highlights
The CD133 antigen is a marker of radio- and chemo-resistant stem cell populations in glioblastoma (GBM)
methylguanine DNA methyltransferase (MGMT) promoter methylation was detected in 44.7% (34/76) of the GBM samples analyzed by Methylation-specific PCR (MSP) (Figure 1)
Criniere et al [22] showed that while the MGMT promoter methylation status had no impact on the Overall survival (OS) of GBM patients treated with alkylating agents, it did have an impact on those treated with chemo-radiotherapy, suggesting that the prognostic impact of this methylation is dependent on therapeutic modalities
Summary
The CD133 antigen is a marker of radio- and chemo-resistant stem cell populations in glioblastoma (GBM). Our propose is to analyze the prognostic significance of the CD133 antigen and promoter methylation and protein expression of MGMT in a homogenous group of GBM patients uniformly treated with radiotherapy and TMZ. Glioblastoma (GBM), the most common primary brain tumor in adults, is a rapidly progressive and fatal disease with a low median overall survival [1]. The treatment of these tumors with temozolomide (TMZ) introduces alkyl groups into DNA preventing its replication.This structural modification induces cell death. These inconsistencies may be caused by intratumoral heterogeneity, different evaluation methods, and different cut-off values
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