MGMT Gene Promoter Research Articles

CpG Island Methylation of the MLH1, MGMT, DAPK, and CASP8 Genes in Cancerous and Adjacent Noncancerous Stomach Tissues

BACKGROUND AND OBJECTIVE. Many factors are involved in the development of gastric adenocarcinoma. The CpG island methylation of apoptosis and mismatch repair genes by the loss of their function is important in gastric adenocarcinoma. The aim of this study was to determine the methylation frequency of MLH1, MGMT, CASP8, and DAPK in cancerous and adjacent noncancerous stomach tissues, to determine possible associations with the selected clinicopathological characteristics, and to identify possible correlation between the methylation of individual genes. MATERIAL AND METHODS. The methylation status of MLH1, MGMT, DAPK, and CASP8 was investigated in 69 patients with gastric adenocarcinoma by using methylation-specific polymerase chain reaction. The associations between patients' clinical characteristics and methylation status were assessed. RESULTS. The methylation frequency of the MLH1, DAPK, MGMT, and CASP8 gene promoters in cancerous and adjacent noncancerous tissues was 31.9% and 27.5%; 47.8% and 46.4%; 36.2% and 44.9%; and 5.8% and 5.8%, respectively, but the differences were not significant. There was no significant association between the methylation status of the mentioned genes and clinicopathological characteristics, such as age, sex, tumor type by the Lauren classification, degree of differentiation G, and TNM staging. An inverse correlation between the methylation of the DAPK and MLH1 gene promoters in cancerous and surrounding noncancerous tissues was found. CONCLUSIONS. The methylation of the MLH1, MGMT, DAPK, and CASP8 genes was found to occur both in cancerous and noncancerous stomach tissues. These findings provide additional insights into gene methylation patterns in gastric adenocarcinoma.

Personalized treatment strategies in glioblastoma: MGMT promoter methylation status

The identification of molecular genetic biomarkers considerably increased our current understanding of glioma genesis, prognostic evaluation, and treatment planning. In glioblastoma, the most malignant intrinsic brain tumor entity in adults, the promoter methylation status of the gene encoding for the repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) indicates increased efficacy of current standard of care, which is concomitant and adjuvant chemoradiotherapy with the alkylating agent temozolomide. In the elderly, MGMT promoter methylation status has recently been introduced to be a predictive biomarker that can be used for stratification of treatment regimes. This review gives a short summery of epidemiological, clinical, diagnostic, and treatment aspects of patients who are currently diagnosed with glioblastoma. The most important molecular genetic markers and epigenetic alterations in glioblastoma are summarized. Special focus is given to the physiological function of DNA methylation–in particular, of the MGMT gene promoter, its clinical relevance, technical aspects of status assessment, its correlation with MGMT mRNA and protein expressions, and its place within the management cascade of glioblastoma patients.

Bayesian inference supports a location and neighbour-dependent model of DNA methylation propagation at the MGMT gene promoter in lung tumours

We exploit model-based Bayesian inference methodologies to analyse lung tumour-derived methylation data from a CpG island in the O6-methylguanine-DNA methyltransferase (MGMT) promoter. Interest is in modelling the changes in methylation patterns in a CpG island in the first exon of the promoter during lung tumour development. We propose four competils of methylation state propagation based on two mechanisms. The first is the location-dependence mechanism in which the probability of a gain or loss of methylation at a CpG within the promoter depends upon its location in the CpG sequence. The second mechanism is that of neighbour-dependence in which gain or loss of methylation at a CpG depends upon the methylation status of the immediately preceding CpG. Our data comprises the methylation status at 12 CpGs near the 5′ end of the CpG island in two lung tumour samples for both alleles of a nearby polymorphism. We use approximate Bayesian computation, a computationally intensive rejection-sampling algorithm to infer model parameters and compare models without the need to evaluate the likelihood function. We compare the four proposed models using two criteria: the approximate Bayes factors and the distribution of the Euclidean distance between the summary statistics of the observed and simulated datasets. Our model-based analysis demonstrates compelling evidence for both location and neighbour dependence in the process of aberrant DNA methylation of this MGMT promoter CpG island in lung tumours. We find equivocal evidence to support the hypothesis that the methylation patterns of the two alleles evolve independently.

Cilengitide combined with standard treatment for patients with newly diagnosed glioblastoma and methylated O6-methylguanine-DNA methyltransferase (MGMT) gene promoter: Key results of the multicenter, randomized, open-label, controlled, phase III CENTRIC study.

LBA2009 Background: Cilengitide (CIL) is a selective αvβ3 and αvβ5 integrin inhibitor. In a phase II study in patients with newly diagnosed glioblastoma, CIL added to standard temozolomide (TMZ) and radiotherapy (RT) was well tolerated and appeared to confer improved survival in patients with glioblastoma and methylated MGMT gene promoter (Stupp et al. J Clin Oncol. 2010;28:2712-8). Methods: This multicenter, randomized, controlled, open-label, phase III study randomized (1:1) patients (≥ 18 years) with newly diagnosed, histologically proven supratentorial glioblastoma (WHO Grade IV) and centrally determined MGMT gene promoter methylation. Treatment consisted of CIL 2000 mg twice weekly i.v. plus standard TMZ/RT→TMZ (concomitant and adjuvant temozolomide and radiotherapy; Stupp et al. N Engl J Med. 2005;352:987-96) or standard TMZ/RT→TMZ alone. CIL was to be administered for ≥ 18 months, or until disease progression or unacceptable toxicity. Primary endpoint was overall survival (OS); secondary endpoints included progression-free survival (PFS) per investigator read and safety. Results: 272 patients received CIL plus TMZ/RT→TMZ, and 273 were treated with TMZ/RT→TMZ alone (intention-to-treat population). 54% and 52% of patients were male, and 42% and 44% had ECOG-PS ≥ 1, respectively. 75% of patients of both arms were ≥ 50 years old. Overall, baseline characteristics were well balanced across treatment arms. Median OS was 26.3 months in both arms (Hazard Ratio [HR] = 1.02 [95%CI: 0.81-1.29], p = 0.86). Median PFS per investigator read was 13.5 months in the CIL arm and 10.7 months in the control arm (HR = 0.93 [95%CI: 0.76-1.14], p = 0.48). Treatment was generally well tolerated and the known safety profile of CIL was confirmed. Conclusions: CIL failed to prolong PFS or OS in patients with newly diagnosed glioblastoma and methylated MGMT gene promoter. The previously reported safety profile of CIL in addition to standard therapy was confirmed. Clinical trial information: NCT00689221.

Evaluation of Methylation of MGMT (O6-Methylguanine-DNA Methyltransferase) Gene Promoter in Sporadic Colorectal Cancer

The DNA repair gene O⁶-methylguanine-DNA methyltransferase (MGMT) is frequently methylated in colorectal cancer (CRC). The aim of this study was to demonstrate that MGMT methylation may be one of the candidate mediators of field cancerization in the colon mucosa. Therefore, quantitative methylation-specific polymerase chain reaction was performed on tumor itself and additional samples of 5 and 10 cm away from the tumor in 40 CRC patients. Moreover, colon mucosa was examined from 30 cases with no evidence of cancer as a control. MGMT promoter methylation was present in 27.5% of colorectal tumor specimens. Tumors that showed MGMT promoter methylation had substantial MGMT promoter methylation in their normal adjacent mucosa. The methylation was also observed in 36.36% (4/11) of normal samples with MGMT promoter methylation in the adjacent tumors, in 20.79% (6/29) of samples without MGMT methylation in the adjacent tumors, and in 6.66% (2/30) of control samples (p<0.006 and p<0.001 respectively). Finally, the mean of MGMT methylation levels was significantly higher in the cancerous group than in the control group (6.25±1.702 vs. 0.086±0.036, p<0.001). Some CRCs arise from a field defect defined by epigenetic inactivation of MGMT. Detection of such abnormality may ultimately be useful in risk assessment for CRCs.

Dose-intensified rechallenge with temozolomide: One week on/one week off versus 3 weeks on/one week off in patients with progressive or recurrent glioblastoma (DIRECTOR).

TPS2103 Background: No standard of care has been defined for patients with glioblastoma who relapse or progress on or after standard temozolomide (TMZ)-based radiochemotherapy. Rechallenge with TMZ using various dose-intensified regimens is a common approach for recurrent glioblastoma. O6-methylguanylmethyltransferase (MGMT) promoter methylation is a strong prognostic marker in newly diagnosed glioblastoma. However, in recurrent glioblastoma, the prognostic value of the MGMT status has remained unclear. Methods: The DIRECTOR trial is an open-label prospectively randomized phase II trial investigating 2 different TMZ rechallenge regimens, i.e. 1 week on/1 week off (Arm A, 120-150 mg/m2 per day for 7 days) versus 3 weeks on/1 week off (Arm B, 80-100 mg/m2 per day for 21 days) in recurrent glioblastoma. Patients were enrolled at first progression after having completed the first-line TMZ radiochemotherapy and at least 2 adjuvant TMZ cycles. At randomization, MGMT gene promoter methylation status from the primary or recurrent tumor was mandatory. The study treatment was monitored every 2 months by MRI using MacDonald criteria. Translational studies included blood biomarker (e.g. regulatory T cell counts, MGMT activity in peripheral blood). In addition, quality-of-life was evaluated by QLQ-C30 and QLQ-BN20 EORTC scores. Neurocognitive testing using the NeuroCogFx was optional. The primary endpoint is median time-to-treatment failure that was defined as progression, toxicity or death from any cause. Secondary endpoints are progression-free survival, overall survival, response and MGMT correlations. The trial was performed in 16 sites in Austria, Germany, and Switzerland. 105 of 166 patients have been enrolled (53 patients in Arm A and 52 patients in Arm B) before the enrollment was prematurely stopped on 30 June 2012. The database will be closed on 30 June 2013. Clinical trial information: NCT00941460.

Abstract 653: Gliomas: methylation status of MGMT gene monitoring in plasma DNA of patients receiving chemotherapy with alkylating agents.

Abstract The protein MGMT (O6-methylguanine-DNA-methyltransferase) is responsible for the DNA repair from damage in O6 position of guanine induced by alkylating agent such as temozolomide, which represent the conventional treatment of gliomas. Silencing of the MGMT gene by epigenetic methylation of its promoter may disable this repair mechanism, thus increasing the cytotoxicity of chemotherapy. Previous studies showed that glioblastama patients, with a methylated MGMT gene promoter in tumour tissue, are more sensitive to the action of alkylating agents and experience higher survival. The aim of the study was to verify the feasibility and the utility of monitoring the state of methylation of MGMT in circulating DNA as a predictive marker of prognosis and response to treatment. Fiftyeight patients with glioma (12 with low and 46 with high grade) who underwent surgical resection and who were eligible for therapy with temozolomide, were enrolled in the study. Blood samples for the analysis of MGMT methylation status were collected before any treatment (T0) and during the treatment at the time of each magnetic resonance imaging (about every 3 months). The methylation status of the MGMT gene promoter in circulating DNA was investigated using PCR with a specific probe for the methylated sequence. The MGMT promoter methylation status in tumour tissue and in plasma was highly concordant: in the 79% of the patients the MGMT promoter was methylated both in tumour tissue and plasma, while in the 21% of patients MGMT promoter was methylated in tissue but not in plasma (Cohen's kappa coefficient = 0.75, p &amp;lt;0.001). The overall survivals (OS) was higher in methylated versus unmethylated MGMT promoter patients both in tumour tissue and plasma, even if with a borderline statistically significance (p = 0.06 by the log-rank test for plasma). The risk of death increased in patients with unmethylated MGMT promoter both in tumour tissue (Adjusted HR=2.23; 95%CI 0.99-5.04) and in plasma (Adjusted HR1.73; 95%CI 0.92-3.22) Finally, in all patients after one year from diagnosis we noticed a decrease of the state of methylation of MGMT promoter in plasma. At the end of follow up in the 98% of patients who presented the methylation of the MGMT promoter at T0, a complete unmethylation was observed. In conclusion the results of this study confirm the feasibility of monitoring the state of methylation of MGMT in circulating DNA in glioma patients. MGMT promoter methylation status may be a prognostic marker of clinical interest in tissue and in plasma. Furthermore the complete unmethylation of MGMT promoter in the 98% of the glioma patients after one year from diagnosis, is a potentially important finding for future researches on biological history and treatment of gliomas. Citation Format: Valentina Fiano, Morena Trevisan, Carlotta Sacerdote, Anna Castiglione, Elisa Trevisan, Rebecca Senetta, Anna Gillio Tos, Laura De Marco, Paola Cassoni, Riccardo Soffietti, Franco Merletti. Gliomas: methylation status of MGMT gene monitoring in plasma DNA of patients receiving chemotherapy with alkylating agents. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 653. doi:10.1158/1538-7445.AM2013-653

Abstract 1808: Gene expression signature of malignant astrocytomas and its association with MGMT promoter methylation status.

Abstract Background: MGMT promoter methylation has been reported as a predictive marker, not only for response to temozolomide (TMZ), but also for the longer survival of the patients with malignant astrocytomas (MAs) regardless of treatment with TMZ. This led us to hypothesize that methylation status of MGMT in MAs could somehow associate with epigenetic modification of other cancer-related gene promoters resulting in alterations of gene expression profiles and acquisition of therapy- sensitive characters. In this study, to elucidate the molecular characteristics that contribute to chemosensitivity and prognosis in MAs, we conducted gene expression profiling of the tumors with or without MGMT promoter methylation. Materials and Methods: Forty-seven MAs including 5 anaplastic astrocytomas and 42 glioblastomas were enrolled in this study. Methylation status of MGMT gene promoter was evaluated by methylation-specific PCR and subsequent pyrosequencing. Gene expression profile was analyzed using 13,000 genes-cDNA microarray which was developed in our institute. Differentially expressed genes between MGMT-methylated and -unmethylated cases were picked up by statistical analysis (Wilcoxon test). Results: MGMT promoter methylation was found in 26 out of 47 cases. Among the 13,000 genes examined, 163 genes demonstrated statistically significant difference in expression between MGMT-methylated and -unmethylated cases. 22 genes demonstrated lower expression in MGMT-methylated cases, while the remaining 141 genes showed higher expression in methylated cases. When we classify the cases into two groups according to the expression profiles of these 163 genes, survival of the patients were clearly divided (median survival: 18.9m vs. 9.7m, p=0.039). Annotation analysis indicated that the 22 genes with lower expression in MGMT-methylated tumors include those which actively participate in tumor progression, invasion and metastasis, and one of these showed a significant prognostic power in 47 MAs examined (p=0.049). Validation of methylation status of these gene promoters is underway. Conclusion: We identified a gene expression signature strongly correlated with MGMT methylation in MAs, which might contribute to predict chemosensitivity of tumors as well as prognosis of the patients with MA in combination of MGMT methylation. Citation Format: Toshihiko Iuchi, Miki Ohira, Sana Yokoi, Hajime Kageyama, Yuzo Hasegawa, Koichiro Kawasaki, Tsukasa Sakaida, Akira Nakagawara. Gene expression signature of malignant astrocytomas and its association with MGMT promoter methylation status. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1808. doi:10.1158/1538-7445.AM2013-1808

Kras Gene Mutation and RASSF1A, FHIT and MGMT Gene Promoter Hypermethylation: Indicators of Tumor Staging and Metastasis in Adenocarcinomatous Sporadic Colorectal Cancer in Indian Population

ObjectiveColorectal cancer (CRC) development involves underlying modifications at genetic/epigenetic level. This study evaluated the role of Kras gene mutation and RASSF1A, FHIT and MGMT gene promoter hypermethylation together/independently in sporadic CRC in Indian population and correlation with clinicopathological variables of the disease.MethodsOne hundred and twenty four consecutive surgically resected tissues (62 tumor and equal number of normal adjacent controls) of primary sporadic CRC were included and patient details including demographic characteristics, lifestyle/food or drinking habits, clinical and histopathological profiles were recorded. Polymerase chain reaction - Restriction fragment length polymorphism and direct sequencing for Kras gene mutation and Methylation Specific-PCR for RASSF1A, FHIT and MGMT genes was performed.ResultsKras gene mutation at codon 12 & 13 and methylated RASSF1A, FHIT and MGMT gene was observed in 47%, 19%, 47%, 37% and 47% cases, respectively. Alcohol intake and smoking were significantly associated with presence of Kras mutation (codon 12) and MGMT methylation (p-value <0.049). Tumor stage and metastasis correlated with presence of mutant Kras codon 12 (p-values 0.018, 0.044) and methylated RASSF1A (p-values 0.034, 0.044), FHIT (p-values 0.001, 0.047) and MGMT (p-values 0.018, 0.044) genes. Combinatorial effect of gene mutation/methylation was also observed (p-value <0.025). Overall, tumor stage 3, moderately differentiated tumors, presence of lymphatic invasion and absence of metastasis was more frequently observed in tumors with mutated Kras and/or methylated RASSF1A, FHIT and MGMT genes.ConclusionSynergistic interrelationship between these genes in sporadic CRC may be used as diagnostic/prognostic markers in assessing the overall pathological status of CRC.

IDH/MGMT-driven molecular classification of low-grade glioma is a strong predictor for long-term survival

Low-grade gliomas (LGGs) are rare brain neoplasms, with survival spanning up to a few decades. Thus, accurate evaluations on how biomarkers impact survival among patients with LGG require long-term studies on samples prospectively collected over a long period. The 210 adult LGGs collected in our databank were screened for IDH1 and IDH2 mutations (IDHmut), MGMT gene promoter methylation (MGMTmet), 1p/19q loss of heterozygosity (1p19qloh), and nuclear TP53 immunopositivity (TP53pos). Multivariate survival analyses with multiple imputation of missing data were performed using either histopathology or molecular markers. Both models were compared using Akaike's information criterion (AIC). The molecular model was reduced by stepwise model selection to filter out the most critical predictors. A third model was generated to assess for various marker combinations. Molecular parameters were better survival predictors than histology (ΔAIC = 12.5, P< .001). Forty-five percent of studied patients died. MGMTmet was positively associated with IDHmut (P< .001). In the molecular model with marker combinations, IDHmut/MGMTmet combined status had a favorable impact on overall survival, compared with IDHwt (hazard ratio [HR] = 0.33, P< .01), and even more so the triple combination, IDHmut/MGMTmet/1p19qloh (HR = 0.18, P< .001). Furthermore, IDHmut/MGMTmet/TP53pos triple combination was a significant risk factor for malignant transformation (HR = 2.75, P< .05). By integrating networks of activated molecular glioma pathways, the model based on genotype better predicts prognosis than histology and, therefore, provides a more reliable tool for standardizing future treatment strategies.

A pilot study of glioblastoma multiforme in elderly patients: Treatments, O-6-methylguanine-DNA methyltransferase (MGMT) methylation status and survival

ObjectivesElderly Glioblastoma multiforme (GBM) patients have a worse prognosis and receive variable treatments. MGMT gene promoter methylation is linked with improved survival in GBM. We examined treatments administered and survival including in relation to MGMT methylation status in elderly GBM patients. Patients and methodsPatients ≥65 years with diagnosed GBM between 1/01/2007 and 30/04/2009 and undergoing either a biopsy, subtotal (STR) or gross total resection (GTR) were included. The collected information included MGMT status [methylated (ME) vs. unmethylated (UN)] and survival data. p<0.05 was considered significant. Results59 patients were identified with median age at diagnosis being 72.68 years (65.72–85.04). Treatment included surgery (25 GTR, 8 STR, 26 biopsy), chemoradiation (22) and radiotherapy alone (20). Overall median overall survival (MOS) was 219 days. MOS with chemoradiation was 316 days vs. 143 days without it (p=0.011). 47 patients had definite MGMT status (28 ME, 19 UN). In ME patients, 9/28 received temozolamide compared to 10/19 in UN category. Temozolamide administration in patients with definite MGMT status was based on WHO performance status (p=0.007). MOS in UN group was 308 days vs. 167 days in ME group (p=0.068). In a multivariate Cox model including use of temozolamide, WHO score and methylation status, only temozolamide use was significantly associated with a reduced risk for death (HR 0.443, 95% CI 0.200–0.982, p=0.045). ConclusionsIn this small cohort of patients, chemoradiation in suitable elderly GBM patients seemed to afford a survival benefit. MGMT methylation was not associated with an improved survival with temozolamide being the only factor leading to a better survival. Temozolamide use should be considered irrespective of MGMT status in this population with future large prospective studies needed to elucidate this further.

Changes in Gene Methylation Following Chemotherapy in Breast Cancer Cell Lines

Objective: Epigenetic modulation of gene expression by DNA promoter methylation may contribute to acquired resistance to chemotherapy in cancer cells. Decitabine (5-aza-2'- deoxycytidine), a demethylating agent, may act synergistically with standard chemotherapy regimens to activate epigenetically silenced genes. In the present in vitro study, it was investigated the effect of gene methylation level after treatment with decitabine and combination of decitabine with anthracycline-based therapeutics (5-fluorouracil plus epirubicine plus cyclophosphamide; FEC) on breast cancer cells (MCF-7 and MDA-MB-231). Methods: The effect of decitabine and its combination with FEC on different genes methylation level has been tested in MDA-MB-231 and MCF-7 human breast cancer cell lines. The effect of decitabine on the cell viability was assayed by MTT assay. Methylight real-time PCR and methylation specific PCR were carried out to determine the methylation status of certain genes: DAPK, TMS1, MGMT and the global methylation marker LINE-1. Results: The LINE-1 methylation status significantly decreased in both cell lines after treatment with the combination of decitabine with FEC. In MDA-MB-231 cells, methylation of the TMS1 and the MGMT gene promoter was significantly reduced by FEC plus decitabine while no effect was observed in MCF-7 cells. Conclusion: Anthracycline-based therapy regimens in combination with demethylating agents such as decitabine may affect chemotherapy outcome by modulation of apoptosis- relevant genes by methylation. More importantly, this modulation seems to be dependent on

Toward a Molecular Classification of Colorectal Cancer: The Role of MGMT

O6-methylguanine DNA methyltransferase (MGMT) is a DNA repair enzyme with the ability to protect cells from DNA mutations by removing alkyl groups from the O6 position of guanine. Colon mucosa is exposed to the direct effects of environmental carcinogens and therefore maintaining a proficient DNA repair system is very important to stay protected against DNA mutagenesis. Loss of MGMT expression is almost exclusively associated with methylation of CpG islands in the MGMT gene promoter region which is found in approximately 40% of colorectal cancers. The role of MGMT loss in colorectal tumorigenesis is complex but numerous studies have documented methylation of this gene even in the normal appearing mucosa as well as in aberrant crypt foci, suggesting that MGMT methylation can be regarded as an early event or “field defect” in colon cancer neoplasia. The focus of this perspective is the role of MGMT in different pathways of colorectal carcinogenesis as well as the implication of this molecule in treatment decisions in colorectal cancer patients.

Expression of O&amp;lt;sup&amp;gt;6&amp;lt;/sup&amp;gt;-Methylguanine-DNA Methyltransferase Examined by Alkyl-Transfer Assays, Methylation-Specific PCR and Western Blots in Tumors and Matched Normal Tissue

The tumor selectivity of alkylating agents that produce guanine O6-chloroethyl (laromustine and carmustine) and O6-methyl (temozolomide) lesions, depends upon O6-methylguanine-DNA methyltransferase (MGMT) activity being lower in tumor than in host tissue. Despite the established role of MGMT as a tumor resistance factor, consensus on how to assess MGMT expression in clinical samples is unsettled. The aim of this study is to examine the relationship between the values derived from distinctive MGMT measurements in 13, 12, 6 and 2 pairs of human tumors and matched normal adjacent tissue from the colon, kidney, lung and liver, respectively, and in human cell lines. The MGMT measurements included (a) alkyl-transfer assays using [benzene-3H]O6-benzylguanine as a substrate to assess functional MGMT activity, (b) methylation-specific PCR (MSP) to probe MGMT gene promoter CpG methylations as a measure of gene silencing, and (c) western immunoblots to analyze the MGMT protein. In human cell lines, a strict negative correlation existed between MGMT activity and the extent of promoter methylation. In tissue specimens, by contrast, the correlation between these two variables was low. Moreover, alkyl-transfer assays identified 3 pairs of tumors and normal tissue with tumor-selective reduction in MGMT activity in the absence of promoter methylation. Cell line MGMT migrated as a single band in western analyses, whereas tissue MGMT was heterogeneous around its molecular size and at much higher molecular masses, indicative of multi-layered post-translational modifications. Malignancy is occasionally associated with a mobility shift in MGMT. Contrary to the prevalent expectation that MGMT expression is governed at the level of gene silencing, these data suggest that other mechanisms that can lead to tumor-selective reduction in MGMT activity exist in human tissue.

Different patterns of DNA methylation of the two distinct O6-methylguanine-DNA methyltransferase (O6-MGMT) promoter regions in colorectal cancer

Colorectal cancer (CRC) is the third most common cancer worldwide. Colorectal cancer incidence differs widely among different geographic regions. In addition to mutational changes, epigenetic mechanisms also play important roles in the pathogenesis of CRCs. O6-methylguanine-DNA methyltransferase (O(6)-MGMT) is a DNA repair protein and in the absence of MGMT activity, G-to-A transition may accumulate in the specific genes such as K-ras and p53. To identify which CpG sites are critical for its downregulation, we analyzed the methylation status of the MGMT gene promoter in two sites in CRC patients. Then we compared the frequency of their methylation changes with the results of our previously reported K-ras gene mutation, APC2 and p16 methylation. MGMT methylation was examined in 92 tumor samples. A methylation specific PCR (MSP) method was performed for two loci of MGMT gene which described as MGMT-A and MGMT-B. The prevalence of MGMT-A, and MGMT-B methylation was 49/91 (53.8%), and 83/92 (90.2%), respectively. We detected high frequency of MGMT-B but not MGMT-A methylation in tumor tissues with APC2 methylation. Our results showed that MGMT-B methylation is significantly associated with K-ras gene mutation rather than MGMT-A (p = 0.04). Simultaneously, an inverse correlation was found between p16 and MGMT-B methylation simultaneously (p = 0.02). Our study indicated that hypermethylation of the specific locus near the MGMT start codon is critical for cancer progression. MGMT-B assessment that is associated with K-ras mutation can have a prognostic value in patients with CRC.

MGMT promoter methylation status and MGMT and CD133 immunohistochemical expression as prognostic markers in glioblastoma patients treated with temozolomide plus radiotherapy.

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.

Survival in Patients with Newly Diagnosed Conventional Glioblastoma: A Modified Prognostic Score Based on a Single-Institution Series

Recursive partioning analysis (RPA) is commonly used to define the stratification of patients with glioblastoma. Epigenetic silencing of the O6-methylguanine methyltransferase (MGMT) gene by promoter methylation plays an important role in regulating MGMT expression in gliomas and this is an established independent prognostic factor. We tested a prognostic scoring system including all clinical variables used by RPA classification (age, ECOG performance status and type of surgery) and MGMT gene promoter methylation status. Seventy-eight consecutive patients with newly diagnosed, histopathologically confirmed conventional glioblastoma were included. Information about MGMT promoter methylation status was available for all of them. Based on the patients' age (<50 vs ≥50 years), ECOG performance status (0 vs ≥1), type of surgery (gross tumor resection versus partial resection/biopsy) and MGMT promoter methylation status (methylated versus unmethylated), three classes of risk were generated where the prognostic score was defined assigning 1 point to every favorable parameter (Class I: ≥3; Class II: 2; Class III: 0-1). All classes were correlated with overall survival. The median survival times were 32.4, 8.6 and 8.8 months for Class I, II and III, respectively, corresponding to 2-year survival rates of 69%, 13.5% and <1%. The same analysis was performed on 54 patients treated with postoperative concomitant chemoradiotherapy. The median survival times were 32.5, 13.4 and 8.9 months for Class I, II and III, respectively, corresponding to 2-year survival rates of 68.6%, 26.9% and <1%. In both groups of 78 and 54 patients the differences in survival between Class I and III were statistically significant ( P <0.0001). The proposed prognostic scoring system including clinical variables and MGMT promoter methylation status proved valuable in patients with primary conventional glioblastoma, especially those treated with postoperative chemoradiotherapy.

Methylation of MGMT in paired primary and recurrent GBMs.

65 Background: Epigenetic sliencing of the MGMT gene promoter in primary glioblastomas of patients subsequently treated with TMZ is associated with prolonged survival. Further, several studies have observed a change in MGMT silencing in paired primary and recurrent glioblastoma. However, the relationship between this “MGMT switch” and patients outcome is largely unknown. Methods: The study involved primary and recurrent tumor tissue samples from 53 glioblastoma patients diagnosed and treated within the First Hospital of Jilin University from January 2003 to November 2010. After surgical treatment, all patients were subjected to radiotherapy with concomitant administration of TMZ. Patients that experienced recurrent tumors received TMZ. 53 patients underwent 58 further operations after recurrence (5 pats received a third surgery). MGMT promoter methylation levels were determined using qMSP. The relationship between “MGMT switch” and clinical outcome was investigated. Results: 53 (M/F=33/20; median age: 49.2±3.6, 19.5-72.3 ys) underwent a first operation for GBM. qMSP analysis revealed MGMT promoter methylation in 19 pats (35.8%, A, OS 31.5 ms); no methylation in 34 pats (64.2%, B, OS 7.9 ms). In the recurrent tumors, MGMT promoter methylation was detected in 25 pats (47.2%); and no methylation in 28 pats (52.8%). Comparison of individual pairs of primary and recurrent GBMs revealed a changed methylation status in 10 (18.9%), including 8 changed from unmethylated to methylated tumors (15.1%, C, OS 29.4 ms), 2 changed from methylated to unmethylated tumors (3.8%, D, OS 10.5 ms). Median overall survival (OS) was 12.1 months. MGMT promoter methylation was significantly associated with a favorable clinical outcome (A vs B, p=0.0027). The outcome of patients were not significant different between group A and group C (p&gt;0.01). Conclusions: The methylation status of the MGMT promoter was altered in 10 (18.9%) of 53 recurrent GBM after chemoradiotherapy. 8 patients the promoter changed from unmethylated to methylated and these patients had a median overall survival similar to the better prognosis of patients who had a methylated promoter in their primary tumor. 2 pats where a change from methylated to unmethylated was observed had a poorer outcome.

Neuroonkologie - neue Therapiestrategien

Over the last decade, understanding of gliomas on a molecular level has greatly expanded This update briefly reviews the potential utility of molecular markers in refining diagnosis, prognosis, and treatment decisions, focussing on 1p/19q co-deletion, MGMT promoter methylation, EGFR mutations, and IDH 1/2 mutation. In the past, clinicians relied primarily on clinical factors such as age, Karnofsky performance status and extent of resection to inform prognosis. These para-meters and others have been used to identify prognostically distinct classes using recursive partitioning analysis (RPA) for patients with anaplastic astrocytomas and glioblastomas. They have been proven useful and were validated by subsequent glioma trials both at dia-gnosis and recurrence. Today clinical trials incorporate molecular information, either as stratification factors to balance treatment arms in randomized studies, or as eligibility criteria. Currently two markers are recommended to guide a clinician in deciding treatment: LOH 1p 19q in WHO III glioma defines a subgroup which should be treated with postoperative chemotherapy and radiation therapy and the methylation of the MGMT gene promoter is predictive for chemotherapy in elderly patients with a glioblastoma. Neuroimaging as the basic tool to diagnose a glioma and monitor treatment response during the course of the disease has markedly evolved. Conventional T1 sequences with and without contrast and T2/FLAIR sequences still remain the gold standard to delineate a new lesion and inform about criteria of malignancy. During treatment, advanced MRI techniques and PET imaging are being incorporated and explored to reflect metabolic activity of a lesion.

Glioneuronal Tumor with Neuropil-Like Islands: Clinical, Morphologic, Immunohistochemical, and Molecular Features of Three Pediatric Cases

Glioneuronal tumors with neuropil-like islands are rare. The 1st reported cases were localized in the cerebral hemispheres of adults, showed homogeneous histopathologic features (infiltrating astrocytic growth and neuropil-like islands rimmed by neuronal cells), and had an unfavorable behavior. We report 3 pediatric cases (1 boy and 2 girls, ages 4, 6, and 8 years, respectively). The boy had a cerebral tumor, and the girls had a spinal tumor. The younger girl also had multiple posterior fossa lesions. The boy and older girl underwent a gross total resection. The younger girl underwent a subtotal resection of the spinal tumor; posterior fossa lesions were not surgically treated. The boy and younger girl are in complete remission at 33 and 24 months, respectively, after surgery and subsequent high-dose chemoradiotherapy. The older girl had a recurrence that was partially resected. Afterward, she started high-dose chemoradiotherapy and had an optimal radiologic response at 4 months follow up. Microscopically, the common denominator was the presence of synaptophysin-positive neuropil-like islands. One tumor showed ependymal features (pseudorosettes and punctate epithelial membrane antigen immunopositivity). Two tumors had 1p deletion. 19q deletion, MGMT gene promoter methylation, EGFR amplifications or polysomy, and EGFR, IDH1, IDH2, and TP53 genes mutation analyses yielded negative results. In conclusion, glioneuronal tumor with neuropil-like islands can affect children, arise in the spinal cord, and show ependymal features in its glial component. A high-dose chemoradiotherapy program is effective.