methylguanine-DNA Methyltransferase Expression Research Articles

O6-Methylguanine-DNA Methyltransferase (MGMT) Promoter Methylation and Low MGMT-Encoded Protein Expression as Prognostic Markers in Glioblastoma Patients Treated with Biodegradable Carmustine Wafer Implants after Initial Surgery Followed by Radiotherapy with Concomitant and Adjuvant Temozolomide (P06.004)

Objective: To study the prognostic impact of O 6 -methylguanine-DNA methyltransferase (MGMT) on newly diagnosed glioblastoma patients being treated with carmustine-releasing wafers (Gliadel®) along with temozolomide (TMZ). Background MGMT promoter methylation status was proposed as a prognostic biomarker for glioblastoma patients. However, the prognostic impact of MGMT on newly diagnosed glioblastoma patients treated using surgical resection and Gliadel® implants followed by Stupp9s protocol is still unknown. Design/Methods: MGMT promoter methylation status and protein expression were analyzed in formalin-fixed, paraffin-embedded tumor specimens obtained from 111 French patients with newly diagnosed glioblastoma. Patients received Gliadel® followed by radiotherapy plus concomitant and adjuvant TMZ chemotherapy, while being enrolled in a French multicenter prospective study. Results: For the whole cohort, median overall survival (OS) and progression-free survival (PFS) were 17.5 and 10.3 months, respectively. Patients with tumors harboring MGMT methylation displayed a significantly longer OS compared to those with wild-type MGMT (21.7 vs . 15.1 months, p=0.025). Similarly, patients with low MGMT protein expression (≤15%) exhibited significantly improved OS compared to those with high MGMT expression (27.0 vs. 15.1 months, p=0.021). The extent of resection was the strongest clinical outcome predictor. In multivariate Cox models adjusted for gender, performance status, and extent of surgery, both MGMT methylation and protein expression were found to be independent prognosticators, which was internally validated using bootstrap resampling techniques. However, no significant correlation was found between protein expression and MGMT methylation status, thus suggesting that the two assays probably assess different biological features. Conclusions: MGMT promoter methylation status and low MGMT expression were both found to be positive prognosticators in newly diagnosed glioblastoma patients treated using surgical resection and Gliadel® implants followed by Stupp9s protocol. Disclosure: Dr. Guillamo has nothing to disclose. Dr. Levallet has nothing to disclose. Dr. Dugue has nothing to disclose. Dr. Vital has nothing to disclose. Dr. Diebold has nothing to disclose. Dr. Menei has nothing to disclose. Dr. Colin has nothing to disclose. Dr. Peruzzy has nothing to disclose. Dr. Emery has nothing to disclose. Dr. Bernaudin has nothing to disclose. Dr. Chapon has nothing to disclose. Dr. Lechapt-Zalcman has nothing to disclose.

Expression of O6‐methylguanine DNA methyltransferase (MGMT) and immunohistochemical analysis of 12 pineal parenchymal tumors

Pineal parenchymal tumors (PPTs) are rare neoplasms which occupy less than 1% of primary CNS tumors. Because of their rare incidence, previous reports on PPTs are limited in number and the useful molecular markers for deciding histological grading and even selecting chemotherapy are undetermined. In this study, we conducted immunohistochemical analysis of 12 PPT specimens, especially for expression of O⁶-methylguanine DNA methyltransferase (MGMT) to assess whether temozolomide (TMZ) could serve as a possible alternative therapy for PPTs. We analyzed 12 PPTs, consisting of three pineocytomas, six PPTs of intermediate differentiation (PPTIDs), and three pineoblastomas. Immunohistochemical analysis was performed using antibodies against MGMT, synaptophysin, neurofilament protein (NF), p53, and neuronal nuclear antigen (NeuN). Immunohistochemically, 11 out of 12 cases were positive for MGMT. The mean MIB-1 labeling index was less than 1% in pineocytoma, 3.5% in PPTID, and 10.5% in pineoblastoma. All 12 cases were positive for synaptophysin and 11 cases, except one PPTID case, showed positive for NF. Nuclear staining of NeuN was negative in all cases although cytoplasmic staining of NeuN was observed in five cases. No case was positive for p53. Eleven out of 12 cases of PPTs demonstrated MGMT expression, suggesting chemoresistancy to TMZ treatment. This is the first report showing MGMT expression in PPTs. In addition, MIB-1 labeling index correlated with WHO grade, although the immunoreactivity of synaptophysin, NF, NeuN and p53 did not correlate with the histological grade.

O6‐methylguanine‐DNA methyltransferase (MGMT) promoter methylation and low MGMT‐encoded protein expression as prognostic markers in glioblastoma patients treated with biodegradable carmustine wafer implants after initial surgery followed by radiotherapy with concomitant and adjuvant temozolomide

O(6) -methylguanine-DNA methyltransferase (MGMT) promoter methylation status was proposed as a prognostic biomarker for patients with glioblastoma. However, the prognostic impact of MGMT in patients with newly diagnosed glioblastoma who receive carmustine-releasing wafers (Gliadel) along with temozolomide (TMZ) is still unknown. MGMT promoter methylation status and protein expression were analyzed in formalin-fixed, paraffin-embedded tumor specimens obtained from 111 French patients with newly diagnosed glioblastoma. Patients received the Gliadel wafers followed by radiotherapy plus concomitant and adjuvant TMZ chemotherapy while they were enrolled in a French multicenter prospective study. For the whole cohort, the median overall survival (OS) was 17.5 months, and the progression-free survival was 10.3 months. Patients with tumors that harbored MGMT methylation had a significantly longer OS compared with patients who had wild-type MGMT (21.7 months vs 15.1 months; P = .025). Similarly, patients who had low MGMT protein expression (≤15%) had a significantly improved OS compared with patients who had high MGMT expression (27.0 months vs 15.1 months; P = .021). The extent of resection was the strongest clinical predictor of outcome. In multivariate Cox models that were adjusted for sex, performance status, and extent of surgery, both MGMT methylation and protein expression were identified as independent prognosticators, and the finding was validated internally using a bootstrap resampling technique. Discrepancies were identified between protein expression and MGMT methylation status, thus suggesting that the 2 assays probably assess different biologic features. MGMT promoter methylation status and low MGMT expression both were identified as positive prognosticators in patients with newly diagnosed glioblastoma who underwent surgical resection and received Gliadel wafer implants followed by adjuvant radiotherapy and concomitant oral TMZ chemotherapy (the Stupp protocol).

The strategy for enhancing temozolomide against malignant glioma

A combined therapy of the alkylating agent temozolomide (TMZ) and radiotherapy is standard treatment, and it improves the survival of patients with newly diagnosed glioblastoma (GBM). The DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) removes the most cytotoxic lesions generated by TMZ, O6-methylguanine, establishing MGMT as one of the most important DNA repair mechanisms of TMZ-induced DNA damage. Thus, the expression of MGMT, its activity, and its promoter methylation status are associated with the response of GBM to TMZ, confirming that MGMT promotes clinical resistance to TMZ. Previous studies have shown that a variety of drugs such as interferon-β (IFN-β), levetiracetam (LEV), resveratrol, and valproic acid (VAP) increased the sensitivity of TMZ through MGMT-dependent or MGMT-independent mechanisms. In this review, we describe drugs and promising molecules that influence the responsiveness of GBM to TMZ and discuss their putative mechanism of action. In MGMT-positive GBMs, drugs that modulate MGMT activity could enhance the therapeutic activity of TMZ. Thus, administration of these drugs as an adjunct to TMZ chemotherapy may have clinical applications in patients with malignant gliomas to improve the outcome.

Altered Methylation of the DNA Repair Gene MGMT Is Associated with Neural Tube Defects

DNA repair is critical for proper embryogenesis, and altered expression of DNA repair genes has been associated with neural tube defects (NTDs). The expression of DNA repair enzymes may be controlled, in part, by methylation of the promoter region. To assess whether disturbed promoter methylation pattern increases the incidence of NTDs, we employed methylation specific-multiplex ligation-dependent probe amplification (MS-MLPA) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) to quantify the methylation levels of multiple promoter CpG sites in normal human embryos and embryos with NTDs. Of the total seven DNA repair genes, two genes (MGMT, MSH6) were examined as having disturbed methylation levels by MS-MLPA kit, while only one gene was confirmed with a significant alternated methylation pattern by MALDI-TOF MS. In our research, methylation profiling of the DNA repair gene O (6)-methylguanine-DNA methyltransferase (MGMT) showed gender difference in embryogenesis. Comparison of MGMT promoter methylation revealed that hypomethylation was associated with an increased risk for cephalic malformations, especially with female embryos (Adjusted Odds Ratio = 8.250). The majority of individual CpG units within the promoter demonstrated hypomethylation. Meanwhile, the expression of MGMT was proven to increase significant in female cases. These results underscore the role of stable promoter methylation in the DNA repair enzymes MGMT for proper embryogenesis.

Pre-Screening for Low Methyl Guanine Methyltransferase (MGMT) Expression Results in High Response Rates to Temozolomide (TMZ) Therapy in AML and MDS Patients.

Abstract 422 Introduction:Many patients with acute myeloid leukemia (AML) and high-risk myelodysplasia (MDS) are not suitable candidates for standard induction therapy, and newer treatment approaches are needed. TMZ anti-tumor activity is attributed to methylation of DNA, leading to the formation of O6-methylguanine that eventually leads to apoptosis. Expression of MethylGuanine DNA MethylTransferase (MGMT) restores normal guanine, decreasing DNA alkylation and thus anti-tumor activity of TMZ. Brandwein et al. (Leukemia 2007;21:821–4) previously demonstrated that response to TMZ in AML patients could be correlated with low MGMT expression. Thus MGMT expression prescreening could be used to identify patients more likely to respond to TMZ and provide an alternative for patients who are not candidates for standard induction therapy. Methods:We conducted a prospective multicenter study of patients with previously untreated AML and high risk MDS who were not candidates for standard induction therapy. Patient selection was based on MGMT expression as determined by Western blot in bone marrow or peripheral blood. Screening was performed by comparing the expression ratio between MGMT and b-actin protein levels. Patients with a ratio <0.25 were eligible to receive TMZ therapy 200 mg/m2/day × 7 days. Patients achieving a complete response (CR) could receive up to 12 monthly cycles of temozolomide 200 mg/m2/day × 5 days. Partial responders received a modified schedule of temozolomide 100 mg/m2/day × 21 days. Results:MGMT expression was tested in 188 patients; median age was 75 years old (range 46–94 years);62% were male. Primary diagnoses were AML (86%) and MDS (14%). Low or weak MGMT expression was detected in 46% of patient that were therefore potential candidates for TMZ therapy. Responses were evaluated in 42 patients, and were divided into 4 categories: Complete (CR/CRp), Morphologic Leukemia-Free State (MLFS), Partial (PR) Minimal (MR). Response was observed in 74% of cases including 29% CR, 10% MLFS, 19% PR and 17% MR. Prognostic factors associated with a higher response rate to temozolomide included MDS presentation, ECOG PS 0 and favorable/standard cytogenetic risk group. Induction and post-remission cycles were well-tolerated and most patients could be successfully treated on an outpatient basis.Patient who reached CR/CRp had a significantly longer median survival (>18 months) compared to those who reached MLFS, PR and MR (5.6 months). Median duration of therapy for patients reaching CR/CRp was 255 days and a majority (80%) became transfusion independent. Grade 3 and 4 toxicities were rare with the most common being fatigue (17%) and diarrhea (6%). Discussion:Pre-selection of patients based on MGMT expression level was associated with a higher response rate to TMZ as compared to previously reported unselected patients. Complete response was associated with increased survival and treatment had a favorable toxicity profile even in frail elderly patients. Targeted therapy with TMZ is feasible in patients with low MGMT expression and represents a new option for AML and MDS patients who are not candidate for standard induction therapy. Disclosures:Brandwein:Merck: Research Funding. Off Label Use: Temozolomide therapy for AML and MDS. Kassis:Merck: Research Funding. Leber:Merck: Research Funding. Howson-Jan:Merck: Research Funding. Minden:Merck: Research Funding. Galarneau:Merck: Employment. Pouliot:Merck: Employment.

Molecular prognostic factors of anaplastic oligodendroglial tumors and its relationship: a single institutional review of 77 patients from China

The increased chemosensitivity of oligodendroglial tumors has been associated with loss of heterozygosity (LOH) on chromosomes 1p and 19q. Other clinical and molecular factors have also been identified as being prognostic and predictive for treatment outcome. Seventy-seven patients with anaplastic oligodendroglioma (AO) or anaplastic oligoastrocytoma (AOA), treated in Beijing Tiantan Hospital from 2006 through 2008, were reviewed. LOH 1p, LOH 19q, IDH1 mutation, O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation, and protein expression level of MGMT, P53, EGFR, and Ki-67 were evaluated. Age at diagnosis, LOH 1p and 19q, IDH1 mutation, P53 expression level, reoperation when progression, and adjuvant chemotherapy were statistically significant factors for overall survival (OS) in univariate analysis. Further multivariate analysis showed that age at diagnosis (P = .010), LOH 1p and 19q (P = .016), IDH1 mutation (P = .011), and reoperation after progression (P = .048) were independent predictors for longer survival in these patients. Nonrandom associations were found between LOH 1p and LOH 19q, MGMT promoter methylation and LOH 1p or 19q, IDH1 mutation and LOH 1p and 19q, IDH1 mutation and MGMT promoter methylation, whereas mutual exclusion was found between MGMT promoter methylation and MGMT expression level. The present study confirmed that age at diagnosis, LOH 1p and 19q, IDH1 mutation, and reoperation after progression were independent significant prognostic factors for patients with anaplastic oligodendroglial tumors. Inter-relationship between LOH 1p, LOH 19q, IDH1 mutation, MGMT promoter methylation, and MGMT expression level were also revealed. Future clinical trials for AO and AOA should consider the molecular alterations of patients.

Chemoresistance to Temozolomide in Human Glioma Cell Line U251 is Associated with Increased Activity of O 6-methylguanine-DNA Methyltransferase and Can be Overcome by Metronomic Temozolomide Regimen

Temozolomide (TMZ) is a novel cytotoxic alkylating agent for chemotherapy of malignant gliomas. However, intrinsic or acquired resistance to TMZ often defines poor efficacy of chemotherapy in malignant gliomas. A growing number of studies indicate that expression of O(6)-methylguanine-DNA methyltransferase (MGMT) is one of the principal mechanisms responsible for this chemoresistance. In the present study, we evaluated the relationship between expression of MGMT and resistance to TMZ. We generated a TMZ-resistant cell line, U251/TR, by stepwise (8 months) exposure of parental U251 cells to TMZ. The resistance to TMZ was quantified using SRB assay. MGMT expression was evaluated at mRNA (RT-PCR) and protein (Western blot) levels. U251/TR cells showed increased (~ sevenfold) resistance to TMZ. The MGMT expression (both mRNA and protein) was significantly (P < 0.01) increased in U251/TR cells compared with parental U251 cells. Further, MGMT expression fluctuated during exposure of U251/TR cells to TMZ. The resistance of U251/TR cells to TMZ could be overcome by application of elevated doses of TMZ when MGMT expression was at the lowest level. In conclusion, our results demonstrate that the primary mechanism responsible for resistance of U251/TR cells to TMZ is associated with increased expression of MGMT. Resistance of malignant gliomas to TMZ can be overcome by synchronizing metronomic TMZ regimen with MGMT expression.

Relationship between magnetic resonance imaging and molecular pathology in patients with glioblastoma multiforme.

Glioblastoma multiforme (GBM) is the most common and lethal primary brain tumor in adults. Magnetic resonance imaging (MRI) is routinely used in the diagnosis, characterization and clinical management of GBM. The diagnosis and treatment of GBM is largely guided by histopathology and immunohistochemistry. This study aimed to identify the relationship between magnetic resonance features and molecular pathology of GBM. MRI images of 43 glioblastoma patients were collected. Four imaging features, degree of edema, contrast tumor enhanced/T2 ratio, multiple lesions and tumor across the midline, were selected to identify their relationship with P53, Ki-67 and O(6)-methylguanine-DNA methyltransferase (MGMT) expression in patients with GBM. The relationship between imaging features and molecular pathology was studied by chi-square test using the software SPSS 13.0. High expression of P53 was found correlated with low contrast tumor enhanced/T2 ratio, low expression of Ki-67 was correlated with multiple lesions and high expression of KI-67 may be related with tumor across the midline, low expression of MGMT was correlated with edema. Some MRI features such as the degree of edema, contrast tumor enhanced/T2 ratio, multiple lesions and tumor acrossing the midline are correlated with P53, Ki-67 and MGMT of GBM.

MGMT expression and promoter methylation status may depend on the site of surgical sample collection within glioblastoma: a possible pitfall in stratification of patients?

We recently described a three-layer concentric model of a glioblastoma (GBM) related to a specific distribution of molecular and phenotypic characteristics driven by the intratumoral hypoxic gradient in which the cancer stem cells niche is located in the hypoxic necrotic core of the tumour. The purpose of this study was to investigate the relationship between O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation status and MGMT expression in GBM samples collected according to the three-layer concentric model. Multiple tissue samples were obtained, by means of image-guided surgery, from the three concentric layers of newly diagnosed GBM. Two samples from each layer were collected from 12 patients (total 72 samples). Immunohistochemical analysis was performed on formalin-fixed paraffin-embedded tissue samples. The methylation status of the MGMT promoter was determined by methylation-specific polymerase-chain-reaction analysis. In all tumours, MGMT protein expression decreased progressively from the inner to the outer layer, and methylation of the MGMT promoter was unrelated to tumour layer. In particular, the MGMT promoter was unmethylated in all layers in 41.7% of tumours, methylated in all layers in 25%, and variably methylated in the three layers in 33.3%. We recorded concordance between MGMT expression and MGMT promoter methylation status within the GBM in only 58.8% of the samples collected. Our data suggest that both MGMT expression and promoter methylation data may be variable throughout GBM and that they may, consequently, depend on the site of surgical sample collection, even in the same patient. However, whereas MGMT expression is pre-operatively predictable when sampling is performed according to the three-layer concentric model, MGMT promoter methylation is not. These results must be considered when sample collection is performed for assessment of MGMT data.

Promoter methylation and expression of MGMT and the DNA mismatch repair genes MLH1, MSH2, MSH6 and PMS2 in paired primary and recurrent glioblastomas

Epigenetic silencing of the O(6) -methylguanine-DNA methyltransferase (MGMT) gene promoter is associated with prolonged survival in glioblastoma patients treated with temozolomide (TMZ). We investigated whether glioblastoma recurrence is associated with changes in the promoter methylation status and the expression of MGMT and the DNA mismatch repair (MMR) genes MLH1, MSH2, MSH6 and PMS2 in pairs of primary and recurrent glioblastomas of 80 patients, including 64 patients treated with radiotherapy and TMZ after the first operation. Among the primary tumors, the MGMT promoter was methylated in 31 patients and unmethylated in 49 patients. In 71 patients (89%), the MGMT promoter methylation status of the primary tumor was retained at recurrence. MGMT promoter methylation, but not MGMT protein expression, was associated with longer progression-free survival, overall survival and postrecurrence survival (PRS). Moreover, PRS was increased under salvage chemotherapy. Investigation of primary and recurrent glioblastomas of 43 patients did not identify promoter methylation in any of the four MMR genes. However, recurrent glioblastomas demonstrated significantly lower MSH2, MSH6 and PMS2 protein expression as detected by immunohistochemistry. In conclusion, reduced expression of MMR proteins, but not changes in MGMT promoter methylation, is characteristic of glioblastomas recurring after the current standards of care.

O(6)-methylguanine DNA-methyltransferase (MGMT) in glioblastoma: Analysis on first and following surgeries.

2097 Background: Glioblastoma (GBM) is the most common malignant primary brain tumor in adults. Outcome has recently improved with the introduction of post-operative concomitant chemoradiotherapy (CRT) followed by 6 cycles of temozolomide (TMZ). MGMT expression has already been encoded as an independent prognostic factor and predictive for TMZ sensitivity, but few data are available on the modifications of MGMT status after CRT. Methods: From January 2005 to November 2010 at Modena University Hospital and Nuovo Ospedale Civile S. Agostino-Estense, 15 consecutive patients (pts) with GBM and treated with at least 2 subsequent surgeries were included in this retrospective study. Aim of the present analysis is to evaluate if methylation status may change between first and following determinations. Results: Fifteen pts (M/F=10/5; median age: 48, range: 40-67 years) underwent a first surgery for GBM. MGMT status was: methylated in 5 (33%); unmethylated in 10 pts (77%). Two unmethylated pts presented an early relapse and underwent a second surgery after 41 and 46 days, respectively. MGMT analysis confirmed the absence of methylation. One pt with multifocal GBM was treated after the first surgery on right frontal lobe with TMZ, operated on left frontal lobe, submitted to CRT, then re-operated for a relapse in the first site of surgery (right frontal lobe). In this case MGMT status evaluated in the site of relapse (right frontal lobe) changed from unmethylated to methylated. MGMT on the lesion of left frontal lobe was unmethylated. The remaining 12 pts underwent post-operative concomitant CRT followed by monthly TMZ (median number of cycles: 8.5; range: 2-24). MGMT status on second surgery was: 5 methylated (42%) and 7 unmethylated (58%), with a 100% concordance. Two pts received a third surgery: in one case MGMT status changed from unmethylated to methylated. Overall median survival was 15.8 months. The two patients with “MGMT switch” have a median survival of 35.8 months. Conclusions: in 2 on 13 cases (15%) after CRT, MGMT status changed from unmethylated to methylated and these pts have a median overall survival similar to methylated pts. This observation may be confirmed on larger series.

O6-Methylguanine DNA methyltransferase expression in tumor cells predicts outcome of radiotherapy plus concomitant and adjuvant temozolomide therapy in patients with primary glioblastoma

Expression of the O(6)-methylguanine-DNA methyltransferase (MGMT) gene has been shown to correlate with clinical outcomes in patients with glioblastoma multiforme treated with alkylating agents. We evaluated MGMT protein expression in 53 primary glioblastomas by the immunohistochemistry (IHC) and analyzed the correlation between results of immunostaining and patient outcomes. There were 28 MGMT-immunopositive and 25 negative glioblastomas. Patients with MGMT-immunonegative glioblastomas showed significantly longer progression-free survival (PFS) (P = 0.0032), but no statistically significant benefits on overall survival (OS) (P = 0.0825) were shown. In 41 glioblastomas treated with temozolomide (TMZ) therapy (MGMT-immunopositive: n = 22, negative: n = 19), both PFS and OS were significantly better in MGMT-immunonegative glioblastomas. (PFS: P = 0.0015, OS: P = 0.0384). We conclude that MGMT expression on immunohistochemistry (IHC) correlates with outcomes in patients with primary glioblastoma receiving TMZ and suggest the use of MGMT-IHC as a surrogate marker for predicting tumor chemosensitivity.

A distinct region of the MGMT CpG island critical for transcriptional regulation is preferentially methylated in glioblastoma cells and xenografts

O(6)-Methylguanine-DNA methyltransferase (MGMT) is a DNA repair protein that removes alkyl DNA adducts such as those induced by alkylating agents. Loss of MGMT expression through transcriptional silencing by hypermethylation of its CpG island (CGI) is found in diverse human cancers including glioblastomas. Glioblastomas that have MGMT methylation respond to temozolomide, an alkylating agent, resulting in improved survival. Consequently, assessment of MGMT methylation has become a therapy response and prognostic indicator. However, it is not clear whether the region of the MGMT CGI commonly analysed is the critical region involved in transcriptional control. We measured methylation levels at each CpG site for the entire MGMT CGI using bisulfite modification and pyrosequencing, and compared them with MGMT mRNA expression in glioblastoma cell lines, xenografts and normal brain tissues (41 samples). Two critical regions were identified (DMR1 and DMR2). DMR2 encompasses the commonly analysed region and was always methylated when DMR1 was methylated. A luciferase reporter assay showed that substitutions of several specific CpG sites within DMR2 significantly attenuated the promoter activity of the MGMT CGI. Our results indicate that several CpG sites within DMR2 play a critical role in the transcriptional control of MGMT, making DMR2 the optimal target for methylation testing. However, given the highly variable patterns of MGMT methylation associated with transcriptional silencing observed in this region among the tumours in this study, methylation levels need to be measured at a number of individual CpGs within DMR2 to confidently predict transcriptional silencing and thus sensitivity to alkylating agents.

Role of heterogeneous nuclear ribonucleoprotein A2/B1 protein in the pathogenesis of non-small cell lung cancer

To study the expression of heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) in non-small cell lung cancer (NSCLC), and the interaction between hnRNP A2/B1 protein and mRNA of DNA repair enzymes O(6)-methylguanine DNA-methyltransferase (MGMT), 8-oxoguanine DNA glycosylase (OGG1), redox factor 1(Ref-1), DNA-dependent protein kinase (including DNA-PKcs and ku). The expression and distribution of hnRNP A2/B1 were detected by immunohistochemistry and Western blot on 50 NSCLC samples from patients who underwent resection in Zhongshan Hospital. The hnRNP A2/B1 mRNA expression was tested by real-time PCR. Co-immunoprecipitation (co-IP) combined RT-PCR was used to investigate whether hnRNP A2/B1 could be bound with the mRNA of the above mentioned 5 DNA repair enzymes in human lung cancer cell line (HTB-182). Then immunohistochemistry and real-time PCR were used to detect the expression of MGMT in the same group of patients. HnRNP A2/B1 protein and mRNA expressions were increased in the NSCLC tissues than that in the corresponding normal lung tissues. HnRNP A2/B1 was expressed predominantly in the nuclei of tumor cells. The positive rate and immunohistochemistry score of hnRNP A2/B1 in tumor tissue were significantly higher than that in normal tissue (P < 0.01). In stage III-IV NSCLC, hnRNP A2/B1 expression was higher than that in stage I-II. There was no significant differences of hnRNP A2/B1 expression among patients of different age, sex, histological type, and smoking history. The results of co-IP combined RT-PCR suggested that hnRNP A2/B1 is bound with MGMT mRNA, and MGMT expression is decreased in tumor tissue of NSCLC. The results of this study show that hnRNP A2/B1 protein and mRNA are highly expressed in NSCLC, and hnRNP A2/B1 is bound with MGMT mRNA, which indicate that it might be one of the mechanisms of hnRNP A2/B1 participating in the pathogenesis of NSCLC.

Metronomic treatment of temozolomide increases anti-angiogenicity accompanied by down-regulated O6-methylguanine-DNA methyltransferase expression in endothelial cells

Metronomic chemotherapy is a continuous low-dose administration of chemotherapeutic agents to minimize toxicity and target tumor-associated endothelial cells. This therapy is beneficial to anti-angiogenic efficacy which is linked to the inhibition of tumor growth. In the present study, we compared the anti-angiogenicity of temozolomide in human umbilical vein endothelial cells (HUVECs) between conventional and metronomic treatment. Metronomic treatment of temozolomide (TMZ) (6.25 and 12.5 μM) showed increased inhibition of the proliferation of HUVECs compared to an equivalent conventional treatment of TMZ. The differential effects between conventional and metronomic treatment of TMZ were also noted in cell migration and angiogenic tube formation. Notably, the expression level of O(6)-methylguanine-DNA methyltransferase (MGMT) was markedly reduced in the HUVECs treated with metronomic TMZ (12.5 and 25 μM) compared to cells treated with conventional treatment of TMZ. Accordingly, HUVECs treated with metronomic treatment of TMZ were more sensitive to TMZ treatment. Taken together, metronomic chemotherapy with TMZ enhances the inhibition of angiogenesis accompanied by the down-regulation of MGMT expression in endothelial cells when compared to conventional chemotherapy.

Nijmegen Breakage Syndrome Protein (NBN) Causes Resistance to Methylating Anticancer Drugs Such as Temozolomide

Methylating agents are first-line therapeutics for gliomas and malignant melanomas. They attack DNA at various sites, and both O(6)-methylguanine and N-methylated base adducts contribute to the killing response. The mechanism of cellular defense against these agents primarily involves O(6)-methylguanine-DNA methyltransferase (MGMT) and base excision repair (BER). Here, we determined whether a key protein involved in DNA double-strand break (DSB) recognition and signaling, nibrin (NBN alias NBS-1), plays a role in the cellular defense against methylating agents. Comparing NBN mutated fibroblasts and lymphoblastoid cells from patients suffering from Nijmegen breakage syndrome, we show that NBN mutants are clearly more sensitive to N-methyl-N'-nitro-N-nitrosoguanidine and temozolomide than the corresponding wild-type cells. Hypersensitivity was due to the induction of both apoptosis and necrosis. The mismatch repair proteins MSH2, MSH6, MLH1, and PMS2 were expressed at a similar level in the cell lines and BER was not affected by NBN mutation. Because MGMT expression abrogated the hypersensitivity of NBN mutated cells, we conclude that O(6)-methylguanine-derived lesions are responsible for triggering the response. Down-regulation of NBN in melanoma cells by small interfering RNA rendered them more sensitive to temozolomide, suggesting that NBN is a novel modulator of temozolomide sensitivity. Because NBN is part of the MRN complex, which recognizes DSBs, the data strongly indicate that MRN is critically involved in DSB processing after O(6)-methylguanine induction. The data provide first evidence that NBN is involved in the cellular defense against O(6)-methylguanine-inducing agents such as temozolomide and identify NBN as a critical target of methylating anticancer drug resistance.

Levetiracetam enhances p53-mediated MGMT inhibition and sensitizes glioblastoma cells to temozolomide

Antiepileptic drugs (AEDs) are frequently used to treat seizures in glioma patients. AEDs may have an unrecognized impact in modulating O(6)-methylguanine-DNA methyltransferase (MGMT), a DNA repair protein that has an important role in tumor cell resistance to alkylating agents. We report that levetiracetam (LEV) is the most potent MGMT inhibitor among several AEDs with diverse MGMT regulatory actions. In vitro, when used at concentrations within the human therapeutic range for seizure prophylaxis, LEV decreases MGMT protein and mRNA expression levels. Chromatin immunoprecipitation analysis reveals that LEV enhances p53 binding on the MGMT promoter by recruiting the mSin3A/histone deacetylase 1 (HDAC1) corepressor complex. However, LEV does not exert any MGMT inhibitory activity when the expression of either p53, mSin3A, or HDAC1 is abrogated. LEV inhibits malignant glioma cell proliferation and increases glioma cell sensitivity to the monofunctional alkylating agent temozolomide. In 4 newly diagnosed patients who had 2 craniotomies 7-14 days apart, prior to the initiation of any tumor-specific treatment, samples obtained before and after LEV treatment showed the inhibition of MGMT expression. Our results suggest that the choice of AED in patients with malignant gliomas may have an unrecognized impact in clinical practice and research trial design.

MGMT Immunoexpression in Silent Subtype 3 Pituitary Adenomas: Possible Therapeutic Implications

The objective of the study was to assess O(6)-methylguanine-DNA methyltransferase (MGMT) immunoreactivity in pituitary adenomas of silent subtype 3 as a potential indicator of temozolomide susceptibility. The Mayo Clinic Anatomic Pathology Database was searched for all cases of silent subtype 3 pituitary adenoma. Each of the 23 cases identified had been confirmed on the basis of histology, immunohistochemical staining for pituitary hormones, as well as on diagnostic ultrastructural criteria. Unstained microscopic sections were immunostained for MGMT and were semiquantitatively assessed. Of the 23 tumors examined, 18 (78%) showed no MGMT immunoreactivity. The remaining five (22%) showed immunoreactivity in < or =50% of tumor cells. Among eight of the most clinically aggressive tumors in this study, six (75%) lacked MGMT immunoreactivity. The observed lack of or low-level expression of MGMT by this distinctive, clinically aggressive form of pituitary adenoma suggests potential efficacy of treatment with the alkylating agent temozolomide.

Loss expression of O6-methylguanine DNA methyltransferase by promoter hypermethylation and its relationship to betel quid chewing in oral squamous cell carcinoma

O(6)-methylguanine-DNA methyltransferase (MGMT) ameliorates mutagenic, carcinogenic, and cytotoxic adducts from O(6)-methylguanine in DNA through a direct reversal mechanism. Decreased expression of MGMT has been reported in a variety of human malignant tumors. The purpose of this study was to clarify the correlation of MGMT expression levels in oral squamous cell carcinoma (OSCC) with promoter hypermethylation and with betel quid chewing and cigarette smoking. MGMT protein expression in 63 cases of oral squamous cell carcinoma by immunohistochemistry was investigated. Methylation status of the MGMT was analyzed by methylation-specific PCR. Correlation with clinicopathologic parameters was then tested by statistical analysis. MGMT immunohistochemistry revealed nuclear staining in normal epithelium, whereas 47 (75%) of 63 OSCC tumors were devoid of MGMT expression and this was related to tumor cell differentiation. Furthermore, the association between loss of MGMT expression and promoter hypermethylation was significant. Lacking protein expression for MGMT in OSCC was also associated with the use of betel quid. The results suggest that the absence of MGMT expression, which would seem to be associated with promoter hypermethylation, is related to betel quid chewing and, thus, in turn, might be a significant event in oral carcinogenesis.