Predictive MGMT status in a homogeneous cohort of IDH wildtype glioblastoma patients

Methylation of the O(6)-Methylguanine-DNA methyltransferase (MGMT) promoter is predictive for treatment response in glioblastoma patients. However, precise predictive cutoff values to distinguish "MGMT methylated" from "MGMT unmethylated" patients remain highly debated in terms of pyrosequencing (PSQ) analysis. We retrospectively analyzed a clinically and molecularly very well-characterized cohort of 111 IDH wildtype glioblastoma patients, who underwent gross total tumor resection and received standard Stupp treatment. Detailed clinical parameters were obtained. Predictive cutoff values for MGMT promoter methylation were determined using ROC curve analysis and survival curve comparison using Log-rank (Mantel-Cox) test. MGMT status was analyzed using pyrosequencing (PSQ), semi-quantitative methylation specific PCR (sqMSP) and direct bisulfite sequencing (dBiSeq). Highly methylated (> 20%) MGMT correlated with significantly improved progression-free survival (PFS) and overall survival (OS) in our cohort. Median PFS was 7.2 months in the unmethylated group (UM, 20% mean methylation). Median OS was 13.4 months for UM, 17.9 months for LM and 29.93 months for HM. Within the LM group, correlation of PSQ and sqMSP or dBiSeq was only conclusive in 51.5% of our cases. ROC curve analysis revealed superior test precision for survival if additional sqMSP results were considered (AUC = 0.76) compared to PSQ (cutoff 10%) alone (AUC = 0.67). We therefore challenge the widely used, strict PSQ cutoff at 10% which might not fully reflect the clinical response to alkylating agents and suggest applying a second method for MGMT testing (e.g. MSP) to confirm PSQ results for patients with LM MGMT levels if therapeutically relevant

Synthesis and Quantitative Structure–Activity Relationship of Imidazotetrazine Prodrugs with Activity Independent of O6-Methylguanine-DNA-methyltransferase, DNA Mismatch Repair and p53.

The antitumor prodrug Temozolomide is compromised by its dependence for activity on DNA mismatch repair (MMR) and the repair of the chemosensitive DNA lesion, O6-methylguanine (O6-MeG), by O6-methylguanine-DNA-methyltransferase (EC 2.1.1.63, MGMT). Tumor response is also dependent on wild-type p53. Novel 3-(2-anilinoethyl)-substituted imidazotetrazines are reported that have activity independent of MGMT, MMR and p53. This is achieved through a switch of mechanism so that bioactivity derives from imidazotetrazine-generated arylaziridinium ions that principally modify guanine-N7 sites on DNA. Mono- and bi-functional analogs are reported and a quantitative structure-activity relationship (QSAR) study identified the p-tolyl-substituted bi-functional congener as optimized for potency, MGMT-independence and MMR-independence. NCI60 data show the tumor cell response is distinct from other imidazotetrazines and DNA-guanine-N7 active agents such as nitrogen mustards and cisplatin. The new imidazotetrazine compounds are promising agents for further development and their improved in vitro activity validates the principles on which they were designed

O6-methylguanine-DNA methyltransferase (MGMT) Promoter methylation is a rare event in soft tissue sarcoma

BACKGROUND: Gene silencing of O6-methylguanine–DNA methyltransferase (MGMT) by promoter methylation improves the outcome of glioblastoma patients after combined therapy of alkylating chemotherapeutic agents and radiation. The purpose of this study was to assess the frequency of MGMT promoter methylation in soft tissue sarcoma to identify patients eligible for alkylating agent chemotherapy such as temozolomide. FINDINGS: Paraffin tumor blocks of 75 patients with representative STS subtypes were evaluated. The methylation status of the MGMT promoter was assessed by methylation-specific polymerase-chain-reaction analysis (PCR). Furthermore, immunohistochemistry was applied to verify expression of MGMT. MGMT gene silencing was assumed if MGMT promoter methylation was present and the fraction of tumor cells expressing MGMT was 20% or less. Methylation specific PCR detected methylated MGMT promoter in 10/75 cases. Immunohistochemical staining of nuclear MGMT was negative in 15/75 cases. 6/75 tumor samples showed MGMT promoter methylation and negative immunohistochemical nuclear staining of MGMT. In none of the tested STS subtypes we found a fraction of tumors with MGMT silencing exceeding 22%. CONCLUSION: MGMT gene silencing is a rare event in soft tissue sarcoma and cannot be recommended as a selection criterion for the therapy of STS patients with alkylating agents such as temozolomide

The first-in-class alkylating deacetylase inhibitor molecule tinostamustine shows antitumor effects and is synergistic with radiotherapy in preclinical models of glioblastoma

Background: The use of alkylating agents such as temozolomide in association with radiotherapy (RT) is the therapeutic standard of glioblastoma (GBM). This regimen modestly prolongs overall survival, also if, in light of the still dismal prognosis, further improvements are desperately needed, especially in the patients with O6- methylguanine-DNA-methyltransferase (MGMT) unmethylated tumors, in which the benefit of standard treatment is less. Tinostamustine (EDO-S101) is a first-in-class alkylating deacetylase inhibitor (AK-DACi) molecule that fuses the DNA damaging effect of bendamustine with the fully functional pan-histone deacetylase (HDAC) inhibitor, vorinostat, in a completely new chemical entity. Methods: Tinostamustine has been tested in models of GBM by using 13 GBM cell lines and seven patient-derived GBM proliferating/stem cell lines in vitro. U87MG and U251MG (MGMT negative), as well as T98G (MGMT positive), were subcutaneously injected in nude mice, whereas luciferase positive U251MG cells and patient-derived GBM stem cell line (CSCs-5) were evaluated the orthotopic intra-brain in vivo experiments. Results: We demonstrated that tinostamustine possesses stronger antiproliferative and pro-apoptotic effects than those observed for vorinostat and bendamustine alone and similar to their combination and irrespective of MGMT expression. In addition, we observed a stronger radio-sensitization of single treatment and temozolomide used as control due to reduced expression and increased time of disappearance of γH2AX indicative of reduced signal and DNA repair. This was associated with higher caspase-3 activation and reduction of RT-mediated autophagy. In vivo, tinostamustine increased time-to-progression (TTP) and this was additive/synergistic to RT. Tinostamustine had significant therapeutic activity with suppression of tumor growth and prolongation of DFS (disease-free survival) and OS (overall survival) in orthotopic intra-brain models that was superior to bendamustine, RT and temozolomide and showing stronger radio sensitivity. Conclusions: Our data suggest that tinostamustine deserves further investigation in patients with glioblastoma

Expression of O6-methylguanine-DNA methyltransferase in childhood medulloblastoma

Medulloblastomas (MB) are the most common malignant brain tumors in childhood. Alkylator-based drugs are effective agents in the treatment of patients with MB. In several tumors, including malignant glioma, elevated O6-methylguanine-DNA methyltransferase (MGMT) expression levels or lack of MGMT promoter methylation have been found to be associated with resistance to alkylating chemotherapeutic agents such as temozolomide (TMZ). In this study, we examined the MGMT status of MB and central nervous system primitive neuroectodermal tumor (PNET) cells and two large sets of primary MB. In sevenMB/PNET cell lines investigated, MGMT promoter methylation was detected only in D425 human MB cells as assayed by the qualitative methylation-specific PCR and the more quantitative pyrosequencing assay. In D425 human MB cells, MGMT mRNA and protein expression was clearly lower when compared with the MGMT expression in the other MB/PNET cell lines. In MB/PNET cells, sensitivity towards TMZ and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) correlated with MGMT methylation and MGMT mRNA expression. Pyrosequencing in 67 primary MB samples revealed a mean percentage of MGMT methylation of 3.7-92% (mean: 13.25%, median: 10.67%). Percentage of MGMT methylation and MGMT mRNA expression as determined by quantitative RT-PCR correlated inversely (n=46; Pearson correlation r 2=0.14, P=0.01). We then analyzed MGMT mRNA expression in a second set of 47 formalin-fixed paraffin-embedded primary MB samples from clinically well-documented patients treated within the prospective randomized multicenter trial HIT'91. No association was found between MGMT mRNA expression and progression-free or overall survival. Therefore, it is not currently recommended to use MGMT mRNA expression analysis to determine who should receive alkylating agents and who should no

The tumoral A genotype of the MGMT rs34180180 single-nucleotide polymorphism in aggressive gliomas is associated with shorter patients' survival

Malignant gliomas are the most common primary brain tumors. Grade III and IV gliomas harboring wild-type IDH1/2 are the most aggressive. In addition to surgery and radiotherapy, concomitant and adjuvant chemotherapy with temozolomide (TMZ) significantly improves overall survival (OS). The methylation status of the O-6-methylguanine-DNA methyltransferase (MGMT) promoter is predictive of TMZ response and a prognostic marker of cancer outcome. However, the promoter regions the methylation of which correlates best with survival in aggressive glioma and whether the promoter methylation status predictive value could be refined or improved by other MGMT-associated molecular markers are not precisely known. In a cohort of 87 malignant gliomas treated with radiotherapy and TMZ-based chemotherapy, we retrospectively determined the MGMT promoter methylation status, genotyped single nucleotide polymorphisms (SNPs) in the promoter region and quantified MGMT mRNA expression level. Each of these variables was correlated with each other and with the patients' OS. We found that methylation of the CpG sites within MGMT exon 1 best correlated with OS and MGMT expression levels, and confirmed MGMT methylation as a stronger independent prognostic factor compared to MGMT transcription levels. Our main finding is that the presence of only the A allele at the rs34180180 SNP in the tumor was significantly associated with shorter OS, independently of the MGMT methylation status. In conclusion, in the clinic, rs34180180 SNP genotyping could improve the prognostic value of the MGMT promoter methylation assay in patients with aggressive glioma treated with TMZ.ARC -Fondation ARC pour la Recherche sur le Cancer(EML20120904843

MGMT methylation analysis of glioblastoma on the Infinium methylation BeadChip identifies two distinct CpG regions associated with gene silencing and outcome, yielding a prediction model for comparisons across datasets, tumor grades, and CIMP-status

The methylation status of the O6-methylguanine-DNA methyltransferase (MGMT) gene is an important predictive biomarker for benefit from alkylating agent therapy in glioblastoma. Recent studies in anaplastic glioma suggest a prognostic value for MGMT methylation. Investigation of pathogenetic and epigenetic features of this intriguingly distinct behavior requires accurate MGMT classification to assess high throughput molecular databases. Promoter methylation-mediated gene silencing is strongly dependent on the location of the methylated CpGs, complicating classification. Using the HumanMethylation450 (HM-450K) BeadChip interrogating 176 CpGs annotated for the MGMT gene, with 14 located in the promoter, two distinct regions in the CpG island of the promoter were identified with high importance for gene silencing and outcome prediction. A logistic regression model (MGMT-STP27) comprising probes cg1243587 and cg12981137 provided good classification properties and prognostic value (kappa=0.85; log-rank p<0.001) using a training-set of 63 glioblastomas from homogenously treated patients, for whom MGMT methylation was previously shown to be predictive for outcome based on classification by methylation-specific PCR. MGMT-STP27 was successfully validated in an independent cohort of chemo-radiotherapy-treated glioblastoma patients (n=50; kappa=0.88; outcome, log-rank p<0.001). Lower prevalence of MGMT methylation among CpG island methylator phenotype (CIMP) positive tumors was found in glioblastomas from The Cancer Genome Atlas than in low grade and anaplastic glioma cohorts, while in CIMP-negative gliomas MGMT was classified as methylated in approximately 50% regardless of tumor grade. The proposed MGMT-STP27 prediction model allows mining of datasets derived on the HM-450K or HM-27K BeadChip to explore effects of distinct epigenetic context of MGMT methylation suspected to modulate treatment resistance in different tumor type

Изменение экспрессии гена MGMT под действием экзогенных цитокинов в клетках человека in vitro

Исследовано влияние цитокинов LIF, SCF, IL-3, EMAP II и препарата Лаферобион (IFN-a2b) на экспрессию гена репаративного энзима MGMT в культурах клеток человека. Показано, что экзогенные цитокины модулируют экспрессию гена MGMT на уровне белка. EMAP II способен повышать или понижать уровень экспрессии гена MGMT в зависимости от условий эксперимента. Цитокины LIF, SCF, IL-3 и Лаферобион, как правило, вызывали снижение экспрессии гена MGMT в исследуемых клетках человека. Определены условия, которые способствуют разрушению белкового комплекса MGMT.Досліджено вплив цитокінів LIF, SCF, IL-3, EMAP II і препарату Лаферобіон (IFN-a2b) на експресію гена репаративного ензиму MGMT в культурах клітин людини. Встановлено, що екзогенні цитокіни здатні модулювати експресію гена MGMT на рівні білка. EMAP II підвищував або знижував рівень експресії гена MGMT в залежності від умов експерименту. Цитокіни LIF, SCF, IL-3 і Лаферобіон, як правило, спричиняли зниження експресії гена MGMT в досліджуваних клітинах людини. Визначено умови, які сприяють руйнуванню білкового комплексу MGMT.The influence of cytokines LIF, SCF, IL-3, and EMAP II and the Laferobion (IFN-a2b) drug on the MGMT gene expression in human cell cultures has been studied. It was shown that exogenous cytokines can modulate the MGMT gene expression at the protein level. EMAP II is able to increase or decrease the MGMT level, depending on the experimental conditions. Cytokines LIF, SCF, IL-3 and Laferobion decreased the MGMT expression level in human cells in vitro. Some conditions leading to the destruction of the MGMT protein complex were identified

Alkylation-induced colon tumorigenesis in mice deficient in the Mgmt and Msh6 proteins

O[superscript 6]-methylguanine DNA methyltransferase (MGMT) suppresses mutations and cell death that result from alkylation damage. MGMT expression is lost by epigenetic silencing in a variety of human cancers including nearly half of sporadic colorectal cancers, suggesting that this loss maybe causal. Using mice with a targeted disruption of the Mgmt gene, we tested whether Mgmt protects against azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF), against AOM and dextran sulfate sodium (DSS)-induced colorectal adenomas and against spontaneous intestinal adenomas in Apc[superscript Min] mice. We also examined the genetic interaction of the Mgmt null gene with a DNA mismatch repair null gene, namely Msh6. Both Mgmt and Msh6 independently suppress AOM-induced ACF, and combination of the two mutant alleles had a multiplicative effect. This synergism can be explained entirely by the suppression of alkylation-induced apoptosis when Msh6 is absent. In addition, following AOM+DSS treatment Mgmt protected against adenoma formation to the same degree as it protected against AOM-induced ACF formation. Finally, Mgmt deficiency did not affect spontaneous intestinal adenoma development in Apc[superscript Min/+] mice, suggesting that Mgmt suppresses intestinal cancer associated with exogenous alkylating agents, and that endogenous alkylation does not contribute to the rapid tumor development seen in Apc[superscript Min/+] mice.National Institutes of Health (U.S.) (grant ES02109)National Institutes of Health (U.S.) (grant CA75576)American Cancer Society (Research Professor