MGMT Unmethylated Tumors Research Articles

Clinical, radiological, and genomic features of BRAF V600E-mutated adult glioblastoma.

2554 Background: Although uncommon, detection of a BRAF V600E mutation in adult patients with glioblastoma has become relevant given the increased availability of NGS and encouraging therapeutic activity of BRAF/MEK inhibitors. The clinical course, radiological characteristics and genetic mutations in this patient population has, however, not been well described. Methods: Adult patients treated at Dana-Farber Cancer Institute or Massachusetts General Hospital with glioblastoma diagnosed from 2013-2019 and an identified BRAF V600E mutation on immunohistochemistry staining or institutional NGS platform were included. Patient demographics, treatments and outcomes were collected retrospectively. Molecular diagnostics (Oncopanel or SNaPSHOT) and cytogenetics (array CGH) were reviewed for relevant mutations or copy number variants (CNV). Qualitative MRI data was analyzed using Visually Accessible Rembrandt Images (VASARI) feature set. Response assessment was performed using the RANO criteria. Results: Nineteen glioblastoma patients had a BRAF V600E mutation (16 on NGS and 19 on IHC). The median age at diagnosis was 41 (22-69) years; 13/19 were female, 12/19 were Caucasian. Only 1/19 had an IDH mutation; 10 of the 17 with known methylation status had MGMT unmethylated tumors. The most frequent mutations on NGS or CNV on array-CGH were TERT (12/16), CDKN2A (10/16), EGFR (7/16), PIK3R1 (6/16) and CKDN2B (6/16). Most tumors were well circumscribed (12/19) and all were contrast-enhancing on MRI. While no patient had clear leptomeningeal involvement at diagnosis, 11/19 eventually developed subependymal or leptomeningeal dissemination. Six patients were treated with BRAF/MEK inhibition following progression after standard of care therapy, with 3/6 patients showing partial response and 2 showing stable disease as their best response. PFS after BRAF/MEK inhibition ranged from 1.9 to 19 months. Grade 1 skin rash was present in 1 patient, but no other adverse events were reported. Median OS for the patients with confirmed deaths (15/19) was 22.6 (14.5 – 39.0) months. Conclusions: Compared to the general glioblastoma population, adult patients with BRAF V600E mutations are younger, more frequently female, and have a higher median OS despite a much higher incidence of leptomeningeal dissemination. Outcome following BRAF/MEK targeted therapy was encouraging. Understanding the natural history and features of these tumors may help better screen patients for BRAF/MEK inhibition and identify novel therapeutic strategies.

Epigenetic preconditioning with decitabine sensitizes glioblastoma to temozolomide via induction of MLH1

IntroductionTo improve the standard treatment paradigm for glioblastoma (GBM), efforts have been made to explore the efficacy of epigenetic agents as chemosensitizers. Recent data suggest possible synergy between decitabine (DAC), a DNA hypomethylating agent, and temozolomide (TMZ) in GBM, but the mechanism remains unclear. The objective of this study was to determine the effects of DAC on TMZ sensitization in a consecutively derived set of primary GBM cultures, with a focus on mismatch repair (MMR) proteins.MethodsHalf maximal inhibitory concentrations (IC50) of TMZ were calculated in eleven consecutive patient-derived GBM cell lines before and after preconditioning with DAC. MMR protein expression changes were determined by quantitative immunoblots and qPCR arrays. Single-molecule real-time (SMRT) sequencing of bisulfite (BS)-converted PCR amplicons of the MLH1 promoter was performed to determine methylation status.ResultsTMZ IC50 significantly changed in 6 of 11 GBM lines of varying MGMT promoter methylation status in response to DAC preconditioning. Knockdown of MLH1 after preconditioning reversed TMZ sensitization. SMRT-BS sequencing of the MLH1 promoter region revealed higher levels of baseline methylation at proximal CpGs in desensitized lines compared to sensitized lines.ConclusionsDAC enhances TMZ cytotoxicity in a subset of GBM cell lines, comprising lines both MGMT methylated and unmethylated tumors. This effect may be driven by levels of MLH1 via E2F1 transcription factor binding. Using unbiased long-range next-generation bisulfite-sequencing, we identified a region of the proximal MLH1 promoter with differential methylation patterns that has potential utility as a clinical biomarker for TMZ sensitization.

TMOD-40. IN VIVO EVALUATION OF O6-METHYLGUANINE-DNA-METHYLTRANSFERASE (MGMT) PROMOTER METHYLATION STATUS FOR DE NOVO GLIOBLASTOMA PATIENTS USING DEEP LEARNING FEATURES

Abstract BACKGROUND High expression of O6-methylguanine-DNA methyltransferase (MGMT) in glioblastoma is associated with resistance to temozolomide, as tumor cells lacking MGMT activity are significantly more sensitive to the cytotoxic effects of temozolomide. The MGMT promoter methylation status (MGMTpms) is typically determined as MGMT-methylated or MGMT-unmethylated. Some single-center studies have reported results ranging from 70–95% detection rates using MRI. We aim to further validate these findings using a multi-institutional data set. We hypothesize that transfer learning based features when integrated via machine learning may lead to non-invasive determination of MGMTpms. METHODS A total of 270 patients were included across the 3 institutions (Hospital of the University of Pennsylvania (HUP), Jefferson University Hospital (JUH); the TCIA). JUH and TCIA datasets comprised conventional modalities (T1,T2,T2-FLAIR,T1-Gd), whereas HUP dataset had additional modalities (DSC,DTI) as well. We used transfer learning and adapted a convolutional neural network (CNN) model pre-trained on 1.2 million 3-channel images of the ImageNet to extract deep learning features from the given images. A support vector machine multivariately integrated these features towards a non-invasive marker of MGMTpms. RESULTS The cross-validated accuracy of our MGMT marker in classifying the mutation status in individual patients was 86.95%, 81.56%, and 82.43%, respectively, in HUP, JUH, and TCIA. Our marker revealed MGMT-methylated tumors with lower neovascularization and cell density, when compared with MGMT-unmethylated tumors. MGMT-unmethylated tumors were found to be more lateralized to the right hemisphere, when compared with MGMT-methylated tumors. CONCLUSION Our findings suggest that transfer learning features when integrated via machine learning allow robust prediction of MGMTpms on mpMRI acquired within multiple institutions. The proposed non-invasive MGMT marker may contribute to (i) MGMTpms determination for patients with inadequate tissue/inoperable tumors, (ii) stratification of patients into clinical trials, (iii) patient selection for targeted therapy, and (iv) personalized treatment planning.

P14.124 EORTC 1709/CCTG CE.8: A phase III trial of marizomib in combination with standard temozolomide-based radiochemotherapy versus standard temozolomide-based radiochemotherapy alone in patients with newly diagnosed glioblastoma

Abstract BACKGROUND The standard of care for patients with newly diagnosed glioblastoma includes maximal debulking surgery followed by radiotherapy (RT), and concomitant as well as maintenance therapy with the alkylating agent, temozolomide (TMZ). However, the prognosis remains poor and novel treatment strategies are urgently needed. Targeting the proteasome has been considered a promising anti-cancer approach for several years. Marizomib is a novel, irreversible and pan-proteasome inhibitor, which crosses the blood-brain barrier and has been assessed in phase I trials in patients with newly diagnosed or recurrent glioblastoma. MATERIAL AND METHODS EORTC 1709/CCTG CE.8 is a randomized, controlled, open label phase III superiority trial. Patients with histologically confirmed newly diagnosed glioblastoma and a performance status >70 are eligible. Patients are randomized in a 1:1 ratio to receive standard of care (TMZ/RT→TMZ) alone or TMZ/RT→TMZ plus marizomib. The study aims at enrolling 750 patients. Stratification factors include study site, age, performance status and extent of resection. The primary objective of this trial is to compare overall survival in patients receiving marizomib in addition to standard of care with those receiving standard treatment only. The testing strategy specifies the determination of this objective in the intent-to-treat population as well as the subgroup of patients with MGMT-unmethylated tumors. Secondary endpoints include progression-free survival, safety, neurocognitive function and quality of life. A translational research program has been set up. The study will be activated at approximately 50 EORTC sites across Europe, 25 sites in Canada and additional sites in the US. Patient recruitment started in June 2018 and as of April 29, 2019, a total of 164 patients have been randomized. An update on the enrolment status will be provided at the EANO meeting. ClinicalTrials.gov Identifier: NCT03345095

Abstract CT168: Phase I/II study of dianhydrogalactitol (VAL-083) with radiation therapy in patients with newly diagnosed glioblastoma, MGMT-unmethylated

Abstract Glioblastoma (GBM) is the most common and aggressive primary brain cancer. Current standard-of-care includes surgery followed by concomitant chemo-radiation and adjuvant temozolomide (TMZ). Unmethylated promoter status for O6-methylguanine-DNA-methyltransferase (MGMT), a validated biomarker for TMZ-resistance, is strongly correlated with TMZ-resistance. In addition, defective DNA mismatch repair (MMR) has been identified as a secondary mechanism of TMZ resistance. MGMT-unmethylated tumors represent a majority of newly diagnosed GBM patients demonstrating significantly inferior progression free and overall survival compared to MGMT-methylated GBM patients. VAL-083 is a first-in-class bi-functional DNA-targeting agent that has shown activity against GBM in NCI-sponsored clinical trials both as a single agent and in combination with radiotherapy. VAL-083 rapidly induces interstrand DNA cross-links at N7-guanine, leading to persistent DNA double-strand breaks and cell death in GBM cell lines and GBM cancer stem cells (CSCs). VAL-083's unique cytotoxic mechanism circumvents MGMT-mediated chemoresistance and maintains cytotoxic activity in cancer cells deficient in MMR. Furthermore, VAL-083 acts as a radiosensitizer in GBM CSCs and non-CSCs, in vitro. We completed a 3:3 dose-escalation trial of VAL-083 in temozolomide- and bevacizumab-refractory rGBM. 40mg/m2/day given on days 1, 2, and 3 of a 21-day cycle was well-tolerated with 6% grade 3 or 4 thrombocytopenia. This dose was selected for further clinical development in a pivotal Phase 3 study in bevacizumab refractory rGBM. The present trial is an ongoing open-label, biomarker-driven, Phase 1/2 study to evaluate the tolerability and efficacy of VAL-083 in combination with radiotherapy in newly diagnosed MGMT-unmethylated GBM patients. A treatment regimen, consisting of a 6-week induction period of VAL-083 and concurrent radiation (2 Gy given daily, 5 days/week) followed by up to 24 weeks of adjuvant maintenance therapy with single-agent VAL-083, is being evaluated as an alternative to standard-of-care in MGMT-unmethylated GBM. The study is being conducted in two parts: 1) a dose-escalation part (20, 30, and 40 mg/m2/day IV infusion on days 1, 2, and 3 of a 21-day cycle) in up to 10 patients, to assess safety and activity of VAL-083 when administered concurrently with radiation therapy; 2) an expansion phase, in which VAL-083 will be studied in up to 20 additional patients at the determined well-tolerated dose. Tumor response will be assessed by MRI, according to RANO criteria. Efficacy endpoints include progression-free survival (PFS) and overall survival (OS). Additional endpoints include safety evaluations and pharmacokinetic assessments of plasma and CSF samples (when available). Enrollment and safety data update will be provided at the meeting. Clinicaltrials.gov identifier: NCT03050736. Citation Format: Zhong-ping Chen, Chengcheng Guo, Jeffrey Bacha, Anne Steino, John Langlands, Claire Kwan, Sarath Kanekal, Richard Schwartz, Lorena Lopez, Dennis M. Brown. Phase I/II study of dianhydrogalactitol (VAL-083) with radiation therapy in patients with newly diagnosed glioblastoma, MGMT-unmethylated [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT168.

Analysis of immunobiologic markers in primary and recurrent glioblastoma.

Glioblastoma (GBM) generates a varied immune response and understanding the immune microenvironment may lead to novel immunotherapy treatments modalities. The goal of this study was to evaluate the expression of immunologic markers of potential clinical significance in primary versus recurrent GBM and assess the relationship between these markers and molecular characteristics of GBM. Human GBM samples were evaluated and analyzed with immunohistochemistry for multiple immunobiologic markers (CD3, CD8, FoxP3, CD68, CD163, PD1, PDL1, CTLA4, CD70). Immunoreactivity was analyzed using Aperio software. Degree of strong positive immunoreactivity within the tumor was compared to patient and tumor characteristics including age, gender, MGMT promoter methylation status, and ATRX, p53, and IDH1 mutation status. Additionally, the TCGA database was used to perform similar analysis of these factors in GBM using RNA-seq by expectation-maximization. Using odds ratios, IDH1 mutated GBM had statistically significant decreased expression of CD163 and CD70 and a trend for decreased PD1, CTLA4, and Foxp3. ATRX-mutated GBMs exhibited statistically significant increased CD3 immunoreactivity, while those with p53 mutations were found to have significantly increased CTLA4 immunoreactivity. The odds of having strong CD8 and CD68 reactivity was significantly less in MGMT methylated tumors. No significant difference was identified in any immune marker between the primary and recurrent GBM, nor was a significant change in immunoreactivity identified among age intervals. TCGA analysis corroborated findings related to the differential immune profile of IDH1 mutant, p53 mutant, and MGMT unmethylated tumors. Immunobiologic markers have greater association with the molecular characteristics of the tumor than with primary/recurrent status or age.

Frontal glioblastoma multiforme may be biologically distinct from non-frontal and multilobar tumors

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and carries a grim prognosis. Lobar GBM, notably those localized to the frontal lobe, are generally more amenable to complete surgical resection, and may carry a better prognosis. The biology of differently localized GBM has been reported scarcely in terms of prognostic markers, including isocitrate dehydrogenase 1 (IDH1) mutation and O(6)-methylguanine-methyltransferase (MGMT) methylation. To our knowledge, there has been no evaluation in the literature of different proliferation indexes in different GBM locations in the brain. We performed a retrospective evaluation of our prospectively collected database to assess the rate of IDH1 positivity, MGMT methylation and Ki67 index for GBM located in the frontal lobes alone, lobar GBM in other supra-tentorial lobes and multilobar GBM. IDH1 mutated tumors were localized in the frontal lobes in 50.0%, whereas only 20.3% of IDH1 wild-type tumors were localized in the frontal lobe (p=0.006); MGMT methylated tumors were localized in the frontal lobe in 32.0% of the cases. Only 13.75% of the MGMT unmethylated tumors were localized to the frontal lobe (p=0.005); Tumors with higher Ki67 proliferation index were more likely to be localized in the frontal lobe (40.6% vs. 19.5%, p=0.019). This is the largest cohort of GBM assessed for these purposes in the literature. Frontal lobe GBMs may be intrinsically biologically distinct from GBM in other lobes and from multilobar tumors.

3. Characteristics of Glioblastoma in Latino Americans

Latino Americans are a rapidly growing ethnic group in the United States. The characteristics of glioblastoma in this population is poorly studied. We have evaluated the data of 47,540 glioblastoma patients from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute. This SEER data from 1973-2000 includes up to 13 cancer registries. For 2001 to 2011, the data has improved geographic coverage with 18 registries encompassing 28% of the U.S. population.Latinos have a lower incidence of GBM than non-Latino Whites. Gender distribution is similar. The total SEER data show that Latinos present slightly younger and have a higher incidence of giant cell glioblastoma and gliosarcoma than non-Latino Whites. Despite higher rates of radiation therapy, the one year survival rate (34.7%) for non-Latino White populations is less than for Latinos (39.0%, p <0.001). Subset analyses (2001-2011) of all the above parameters show similar results except for gliosarcoma incidence. A literature search does not identify MGMT or IDH1 data regarding Latino Americans.We have assessed 2 prognostic markers in 30 Latino glioblastoma patients. MGMT methylation is present in 24% and IDH1 mutation is found in 12.5%. Our preliminary data suggests that Latinos may have a greater incidence of MGMT unmethylated tumors. Younger age may possibly contribute to improved survival in Latinos but the underlying molecular basis is unresolved.

O10.06 * A PHASE II STUDY OF AINO (ITALIAN ASSOCIATION OF NEURO-ONCOLOGY) ON BEVACIZUMAB AND FOTEMUSTINE FOR RECURRENT GLIOBLASTOMA: OUTCOME, PATTERNS OF RELAPSE AND SALVAGE TREATMENTS

BACKGROUND: Information on outcome after the combination of bevacizumab and nitrosoureas in recurrent glioblastomas are lacking. PATIENTS AND METHODS: We have performed a phase 2 trial of combined bevacizumab (BEV) and fotemustine (FTM)(a higly lipophilic nitrosourea) for patients with GBM at first relapse after radiotherapy and concomitant and adjuvant temozolomide. Treatment consisted of BEV at 10 mg/kg on day 1, 15 and FTM at 75 mg/m2/die on day 1, 8 and, after 3 weeks interval, followed by BEV at 10 mg/kg and FTM at 75mg/m2 every 3 weeks as a maintenance treatment, until tumor progression or unacceptable toxicity. MRI was performed at baseline, after 6 weeks from the start of therapy, and thereafter every 2 months. Response on MRI was evaluated according to RANO. RESULTS: Between May 2007 and December 2010, 54 patients were enrolled. The median age was 57 years. Forty-six patients had unifocal tumors, while 8 multifocal tumors. At study entry 41/54 of patients were on steroids, with a median dosage of 4mg. Twenty patients had MGMT unmethylated tumors while 18 had MGMT methylated tumors (in 16 patients data were not available). Median PFS was 5.2 months, and PFS-6 rate was 42.6%. Median OS was 9.1 months and OS-6 and OS-12 were 75.9% and 29.7% respectively. The overall RR was 52% (4% CR, 48% PR) with 37% of SD and 11% of PD. The median time to maximum response was 4 weeks (range 4-12 weeks). Among the 41 patients who were on steroids at study initiation, 32 were able to taper, including 17 who completely stopped. MGMT methylation was not associated with response, PFS or OS. Patterns of tumor failure on MRI after study treatment were available in 50/54 patients. All 8 tumors, that were multifocal before treatment, had a multifocal progression. Forty-two patients had unifocal tumors before treatment, and patterns of progression were as follows: local (enhancing) in 76%, distant (enhancing) in 7%, multifocal (local + distant enhancing) in 4.5%, diffuse (nonenhancing) in 9.5% and isolated leptomeningeal spread in 2%. The pattern of tumor failure was not associated with previous response to treatment. Overall survival after failure was not significantly different according to patterns of tumor progression. Following progression on BEV + FTM, 21/50 patients received salvage chemotherapy and in 1 of these patients BEV was maintained beyond progression in association with chemotherapy. Twenty-nine out of 50 patients received supportive care alone. Patients who received salvage chemotherapy had a median survival of 4.53 months, while patients who received supportive care alone had a median survival of 2.2 months. CONCLUSIONS: This study failed to demonstrate a superiority of the combination of BEV and FTM over either BEV or FTM alone as historical controls. Patterns of tumor progression after treatment did not influence the outcome while the prognosis was poor regardless of salvage chemotherapy or palliative care.

Treatment options and outcomes for glioblastoma in the elderly patient.

Age remains the most powerful prognostic factor among glioblastoma (GBM) patients. Half of all patients with GBM are aged 65 years or older at the time of diagnosis, and the incidence rate of GBM in patients aged over 65 years is increasing rapidly. Median survival for elderly GBM patients is less than 6 months and reflects less favorable tumor biologic factors, receipt of less aggressive care, and comorbid disease. The standard of care for elderly GBM patients remains controversial. Based on limited data, extensive resection appears to be more beneficial than biopsy. For patients with favorable Karnofsky performance status (KPS), adjuvant radiotherapy (RT) has a demonstrated survival benefit with no observed decrement in quality of life. Concurrent and adjuvant temozolomide (TMZ) along with RT to 60 Gy have not been prospectively studied among patients aged over 70 years but should be considered for patients aged 65–70 years with excellent KPS. Based on the recent NOA-08 and Nordic randomized trials, testing for O6-methylguanine-DNA-methyltransferase (MGMT) promoter methylation should be performed routinely immediately after surgery to aid in adjuvant treatment decisions. Patients aged over 70 years with favorable KPS, or patients aged 60–70 years with borderline KPS, should be considered for monotherapy utilizing standard TMZ dosing for patients with MGMT-methylated tumors, and hypofractionated RT (34 Gy in ten fractions or 40 Gy in 15 fractions) for patients with MGMT-unmethylated tumors. The ongoing European Organisation for Research and Treatment of Cancer/National Cancer Institute of Canada trial will help clarify the role for concurrent TMZ with hypofractionated RT. For elderly patients with poor KPS, reasonable options include best supportive care, TMZ alone, hypofractionated RT alone, or whole brain RT for symptomatic patients needing to start treatment urgently. Given the balance between short survival and quality of life in this patient population, optimal management of elderly GBM patients must be made individually according to patient age, MGMT methylation status, performance score, and patient preferences.

Efficacy of protracted temozolomide dosing is limited in MGMT unmethylated GBM xenograft models

Temozolomide (TMZ) is important chemotherapy for glioblastoma multiforme (GBM), but the optimal dosing schedule is unclear. The efficacies of different clinically relevant dosing regimens were compared in a panel of 7 primary GBM xenografts in an intracranial therapy evaluation model. Protracted TMZ therapy (TMZ daily M-F, 3 wk every 4) provided superior survival to a placebo-treated group in 1 of 4 O(6)-DNA methylguanine-methyltransferase (MGMT) promoter hypermethylated lines (GBM12) and none of the 3 MGMT unmethylated lines, while standard therapy (TMZ daily M-F, 1 wk every 4) provided superior survival to the placebo-treated group in 2 of 3 MGMT unmethylated lines (GBM14 and GBM43) and none of the methylated lines. In comparing GBM12, GBM14, and GBM43 intracranial specimens, both GBM14 and GBM43 mice treated with protracted TMZ had a significant elevation in MGMT levels compared with placebo. Similarly, high MGMT was found in a second model of acquired TMZ resistance in GBM14 flank xenografts, and resistance was reversed in vitro by treatment with the MGMT inhibitor O(6)-benzylguanine, demonstrating a mechanistic link between MGMT overexpression and TMZ resistance in this line. Additionally, in an analysis of gene expression data, comparison of parental and TMZ-resistant GBM14 demonstrated enrichment of functional ontologies for cell cycle control within the S, G2, and M phases of the cell cycle and DNA damage checkpoints. Across the 7 tumor models studied, there was no consistent difference between protracted and standard TMZ regimens. The efficacy of protracted TMZ regimens may be limited in a subset of MGMT unmethylated tumors by induction of MGMT expression.

Toxicity and survival in primary glioblastoma patients treated with concomitant plus adjuvant temozolomide versus adjuvant temozolomide: results of a single-institution, retrospective, matched-pair analysis

To compare survival and hematological toxicity rates between two postoperative therapy regimens in patients with primary glioblastoma (GBM), namely temozolomide (TMZ) concomitant to radiation, followed by adjuvant TMZ, versus adjuvant TMZ after radiation only. A total of 191 patients with primary GBM were postoperatively treated with either radiation and concomitant TMZ, followed by adjuvant TMZ (Stupp protocol) (n = 154), or radiation followed by adjuvant TMZ (n = 37). The incidence of hematological adverse effects (AE) was recorded for all patients. From both treatment groups, 26 patients were matched according to age, Karnofsky performance scale (KPS) score, and O6-methylguanine-DNA-methyltransferase (MGMT) promoter methylation. Hematological AEs were mild in both unmatched groups, but were significantly more frequent in the concomitant plus adjuvant TMZ group (p < 0.001). Matched-pair analysis confirmed significantly more frequent hematological AEs in the concomitant and adjuvant group compared to the sequential (adjuvant) TMZ group (p = 0,012). Patients treated with concomitant plus adjuvant TMZ showed significantly longer progression-free survival (PFS) (10.6 versus 6.6 months; p = 0.014), but no prolonged overall survival (OS) (16.9 vs. 15.6 months; p = 0.717) compared to patients who received the sequential treatment regimen. In this retrospective study, the OS in patients with primary GBM treated with sequential TMZ following radiation appeared to be similar to that in patients treated with concomitant plus adjuvant TMZ. Given the significantly higher risk of hematological AE for concomitant treatment, the role of concomitant plus adjuvant TMZ use compared to sequential administration of TMZ, especially for patients with MGMT-unmethylated tumors, should be further evaluated.

Predictive impact of MGMT promoter methylation in glioblastoma of the elderly

O(6)-methylguanine-DNA-methyltransferase (MGMT) promoter methylation identifies a subpopulation of glioblastoma patients with more favorable prognosis and predicts a benefit from alkylating agent chemotherapy (CT). Little is known about its prevalence and clinical significance in older glioblastoma patients. We studied 233 glioblastoma patients aged 70 years or more (144 males, 89 females, median age: 74 years, range: 70.0-86.6 years), who were prospectively enrolled in the German Glioma Network, for MGMT promoter methylation by methylation-specific PCR (MSP) in all patients and DNA pyrosequencing in 166 patients. MGMT data were correlated with patient outcome. Median progression-free survival (PFS) was 4.8 months (95% CI: 4.3-5.3) and median overall survival (OS) was 7.7 months (95% CI: 6.3-9.0). MGMT promoter methylation was detected by MSP in 134 patients (57.5%). For the whole cohort, PFS was 5.2 versus 4.7 months (p = 0.207) and OS was 8.4 versus 6.4 months (p = 0.031) in patients with versus without MGMT promoter methylation. Patients with MGMT methylated tumors had longer PFS when treated with radiotherapy (RT) plus CT or CT alone compared to patients treated with RT alone. Patients with MGMT unmethylated tumors appeared to derive no survival benefit from CT, regardless of whether given at diagnosis together with RT or as a salvage treatment. Patients treated with RT plus CT or CT alone demonstrated longer OS when pyrosequencing revealed >25% MGMT methylated alleles. Taken together, MGMT promoter methylation may be a useful biomarker to stratify elderly glioblastoma patients for treatment with versus without alkylating agent CT.

Radiosensitizing Effects of Temozolomide Observed in vivo only in a Subset of O6-Methylguanine-DNA Methyltransferase Methylated Glioblastoma Multiforme Xenografts

Concurrent temozolomide (TMZ) and radiation therapy (RT) followed by adjuvant TMZ is standard treatment for patients with glioblastoma multiforme (GBM), although the relative contribution of concurrent versus adjuvant TMZ is unknown. In this study, the efficacy of TMZ/RT was tested with a panel of 20 primary GBM xenografts.Mice with intracranial xenografts were treated with TMZ, RT, TMZ/RT, or placebo. Survival ratio for a given treatment/line was defined as the ratio of median survival for treatment vs. placebo.The median survival ratio was significantly higher for O6-methylguanine-DNA methyltransferase (MGMT) methylated tumors versus unmethylated tumors following treatment with TMZ (median survival ratio, 3.6 vs. 1.5, respectively; p = 0.008) or TMZ/RT (5.7 vs. 2.3, respectively; p = 0.001) but not RT alone (1.7 vs. 1.6; p = 0.47). In an analysis of variance, MGMT methylation status and p53 mutation status were significantly associated with treatment response. When we analyzed the additional survival benefit conferred specifically by combined therapy, only a subset (5 of 11) of MGMT methylated tumors derived substantial additional benefit from combined therapy, while none of the MGMT unmethylated tumors did. Consistent with a true radiosensitizing effect of TMZ, sequential treatment in which RT (week 1) was followed by TMZ (week 2) proved significantly less effective than TMZ followed by RT or concurrent TMZ/RT (survival ratios of 4.0, 9.6 and 12.9, respectively; p < 0.0001).Concurrent treatment with TMZ and RT provides significant survival benefit only in a subset of MGMT methylated tumors and provides superior antitumor activity relative to sequential administration of RT and TMZ.

Induction of MGMT expression is associated with temozolomide resistance in glioblastoma xenografts

Temozolomide (TMZ)-based therapy is the standard of care for patients with glioblastoma multiforme (GBM), and resistance to this drug in GBM is modulated by the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT). Expression of MGMT is silenced by promoter methylation in approximately half of GBM tumors, and clinical studies have shown that elevated MGMT protein levels or lack of MGMT promoter methylation is associated with TMZ resistance in some, but not all, GBM tumors. In this study, the relationship between MGMT protein expression and tumor response to TMZ was evaluated in four GBM xenograft lines that had been established from patient specimens and maintained by serial subcutaneous passaging in nude mice. Three MGMT unmethylated tumors displayed elevated basal MGMT protein expression, but only two of these were resistant to TMZ therapy (tumors GBM43 and GBM44), while the other (GBM14) displayed a level of TMZ sensitivity that was similar in extent to that seen in a single MGMT hypermethylated line (GBM12). In tissue culture and animal studies, TMZ treatment resulted in robust and prolonged induction of MGMT expression in the resistant GBM43 and GBM44 xenograft lines, while MGMT induction was blunted and abbreviated in GBM14. Consistent with a functional significance of MGMT induction, treatment of GBM43 with a protracted low-dose TMZ regimen was significantly less effective than a shorter high-dose regimen, while survival for GBM14 was improved with the protracted dosing regimen. In conclusion, MGMT expression is dynamically regulated in some MGMT nonmethylated tumors, and in these tumors, protracted dosing regimens may not be effective.

Preliminary Individualized Chemotherapy for Malignant Astrocytomas Based on O6-Methylguanine-Deoxyribonucleic Acid Methyltransferase Methylation Analysis

O(6)-methylguanine-deoxyribonucleic acid methyltransferase gene (MGMT) methylation is apparently correlated with responsiveness to nitrosourea chemotherapy, suggesting this alkylating agent should be effective against MGMT-methylated tumors. MGMT appears not to be linked to platinum resistance, so platinum chemotherapy should be used for MGMT-unmethylated tumors. This study was a preliminary trial of individualized chemotherapy based on MGMT methylation status in a total of 20 patients with newly diagnosed malignant astrocytomas (9 anaplastic astrocytomas and 11 glioblastomas multiforme). The procarbazine, 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-2(2-chloroethyl)-3-nitrosourea, and vincristine (PAV) regimen was administered to seven patients with MGMT-methylated tumors, and the carboplatin and etoposide (CE) regimen was administered to 13 patients with MGMT-unmethylated tumors. Objective response to the PAV therapy was noted in all three patients with measurable residual tumor (2 complete responses and 1 partial response). Five of the seven patients continued to be disease-free after initiation of the PAV therapy. Objective response to the CE therapy was seen in only one of seven patients with measurable residual tumor (1 partial response). Three of the 13 patients were free from progression, whereas the remaining 10 patients showed early progression. The PAV regimen is effective against MGMT-methylated malignant astrocytomas, but the CE regimen is not useful at the given dose and schedule in MGMT-unmethylated tumors.