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  • Weller, Michael  (18)
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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 07 January 2014, Vol.111(1), pp.409-14
    Description: A hypoxic microenvironment induces resistance to alkylating agents by activating targets in the mammalian target of rapamycin (mTOR) pathway. The molecular mechanisms involved in this mTOR-mediated hypoxia-induced chemoresistance, however, are unclear. Here we identify the mTOR target N-myc downstream regulated gene 1 (NDRG1) as a key determinant of resistance toward alkylating chemotherapy, driven by hypoxia but also by therapeutic measures such as irradiation, corticosteroids, and chronic exposure to alkylating agents via distinct molecular routes involving hypoxia-inducible factor (HIF)-1alpha, p53, and the mTOR complex 2 (mTORC2)/serum glucocorticoid-induced protein kinase 1 (SGK1) pathway. Resistance toward alkylating chemotherapy but not radiotherapy was dependent on NDRG1 expression and activity. In posttreatment tumor tissue of patients with malignant gliomas, NDRG1 was induced and predictive of poor response to alkylating chemotherapy. On a molecular level, NDRG1 bound and stabilized methyltransferases, chiefly O(6)-methylguanine-DNA methyltransferase (MGMT), a key enzyme for resistance to alkylating agents in glioblastoma patients. In patients with glioblastoma, MGMT promoter methylation in tumor tissue was not more predictive for response to alkylating chemotherapy in patients who received concomitant corticosteroids.
    Keywords: Drug Resistance, Neoplasm ; Gene Expression Regulation, Neoplastic ; Antineoplastic Agents, Alkylating -- Pharmacology ; Brain Neoplasms -- Drug Therapy ; Cell Cycle Proteins -- Metabolism ; Glioblastoma -- Drug Therapy ; Glioma -- Drug Therapy ; Intracellular Signaling Peptides and Proteins -- Metabolism ; O(6)-Methylguanine-DNA Methyltransferase -- Pharmacology ; Tor Serine-Threonine Kinases -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    Language: English
    In: PLoS ONE, 2012, Vol.7(3), p.e33449
    Description: Hypermethylation in the promoter region of the MGMT gene encoding the DNA repair protein O 6 -methylguanine-DNA methyltransferase is among the most important prognostic factors for patients with glioblastoma and predicts response to treatment with alkylating agents like temozolomide. Hence, the MGMT status is widely determined in most clinical trials and frequently requested in routine diagnostics of glioblastoma. Since various different techniques are available for MGMT promoter methylation analysis, a generally accepted consensus as to the most suitable diagnostic method remains an unmet need. Here, we assessed methylation-specific polymerase chain reaction (MSP) as a qualitative and semi-quantitative method, pyrosequencing (PSQ) as a quantitative method, and methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) as a semi-quantitative method in a series of 35 formalin-fixed, paraffin-embedded glioblastoma tissues derived from patients treated in a prospective clinical phase II trial that tested up-front chemoradiotherapy with dose-intensified temozolomide (UKT-05). Our goal was to determine which of these three diagnostic methods provides the most accurate prediction of progression-free survival (PFS). The MGMT promoter methylation status was assessable by each method in almost all cases ( n  = 33/35 for MSP; n  = 35/35 for PSQ; n  = 34/35 for MS-MLPA). We were able to calculate significant cut-points for the continuous methylation signals at each CpG site analysed by PSQ (range, 11.5 to 44.9%) and at one CpG site assessed by MS-MLPA (3.6%) indicating that a dichotomisation of continuous methylation data as a prerequisite for comparative survival analyses is feasible. Our results show that, unlike MS-MLPA, MSP and PSQ provide a significant improvement of predicting PFS compared with established clinical prognostic factors alone (likelihood ratio tests: p 〈0.001). Conclusively, taking into consideration prognostic value, cost effectiveness and ease of use, we recommend pyrosequencing for analyses of MGMT promoter methylation in high-throughput settings and MSP for clinical routine diagnostics with low sample numbers.
    Keywords: Research Article ; Medicine ; Oncology ; Pathology
    E-ISSN: 1932-6203
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  • 3
    Language: English
    In: Current Neurology and Neuroscience Reports, 2011, Vol.11(3), pp.305-312
    Description: Antiangiogenic treatment has recently become an integral part of modern cancer therapy targeting the vasculature of numerous aggressive malignancies including glioblastoma. There is preclinical evidence that antiangiogenic therapies promote glioma cell invasiveness. In clinical series, upon progression on antiangiogenic therapy with the vascular endothelial growth factor–directed antibody bevacizumab (BEV), glioblastoma has been reported to display a more infiltrative pattern of recurrence. This distant spread at recurrence or progression and a gliomatosis cerebri-like growth pattern is best detectable on fluid-attenuated inversion recovery MRI. The frequency of up to 20% to 30% of such a pattern in BEV-treated patients is higher than expected to occur without BEV. Older reports and common clinical knowledge estimate the frequency of diffuse or distant spread in recurrent glioblastoma at 10%. This observation stimulated two streams of research. One is to overcome this often insidious adverse effect of antiangiogenic treatment, to optimize antiangiogenic therapies and to face this major challenge, integrating antiangiogenic with anti-invasive mechanisms into one combined treatment concept. The second is questioning a specific property of antiangiogenic therapy to induce diffuse or distant spread. Here, alternative hypotheses of increased awareness and better imaging as well as invasiveness being part of the natural course of the disease have been tested. Without doubt, migration and invasiveness are major obstacles to successful glioma therapy, notably local therapies, both in the natural course of the disease and in the concept of “evasive resistance.” However, clinical analyses of case series, matched pairs analyses, and follow-up on the BRAIN trial (A Study to Evaluate Bevacizumab Alone or in Combination with Irinotecan for Treatment of Glioblastoma Multiforme), which led to accelerated approval of BEV for recurrent glioblastoma in the United States, have not supported a specific propensity of BEV to induce diffuse growth or distant spread at recurrence.
    Keywords: Evasive resistance ; Recurrence pattern ; MRI ; Bevacizumab
    ISSN: 1528-4042
    E-ISSN: 1534-6293
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  • 4
    In: Journal of Neurochemistry, October 2014, Vol.131(2), pp.251-264
    Description: Human glioblastomas may be hierarchically organized. Within this hierarchy, glioblastoma‐initiating cells have been proposed to be more resistant to radiochemotherapy and responsible for recurrence. Here, established stem cell markers and stem cell attributed characteristics such as self‐renewal capacity and tumorigenicity have been profiled in primary glioblastoma cultures to predict radiosensitivity. Furthermore, the sensitivity to radiotherapy of different subpopulations within a single primary glioblastoma culture was analyzed by a flow cytometric approach using Nestin, SRY (sex‐determining region Y)‐box 2 (SOX2) and glial fibrillary acidic protein. The protein expression of Nestin and SOX2 as well as the mRNA levels of Musashi1, L1 cell adhesion molecule, CD133, Nestin, and pleiomorphic adenoma gene‐like 2 inversely correlated with radioresistance in regard to the clonogenic potential. Only CD44 protein expression correlated positively with radioresistance. In terms of proliferation, Nestin protein expression and Musashi1, pleiomorphic adenoma gene‐like 2, and CD133 mRNA levels are inversely correlated with radioresistance. Higher expression of stem cell markers does not correlate with resistance to radiochemotherapy in the cancer genome atlas glioblastoma collective. SOX2 expressing subpopulations exist within single primary glioblastoma cultures. These subpopulations predominantly form the proliferative pool of the primary cultures and are sensitive to irradiation. Thus, profiling of established stem cell markers revealed a surprising result. Except CD44, the tested stem cell markers showed an inverse correlation between expression and radioresistance. Markers used to define glioma‐initiating cells (GIC) are generally not defining a more resistant, but rather a more sensitive group of glioma cells. An exemption is CD44 expression. Also proliferation of the GIC culture itself was not systematically associated with radiosensitivity or – resistance, but a SOX‐2 positive, proliferative subgroup within a GIC culture is showing the highest radiosensitivity. Markers used to define glioma‐initiating cells (GIC) are generally not defining a more resistant, but rather a more sensitive group of glioma cells. An exemption is CD44 expression. Also proliferation of the GIC culture itself was not systematically associated with radiosensitivity or – resistance, but a SOX‐2 positive, proliferative subgroup within a GIC culture is showing the highest radiosensitivity.
    Keywords: Cd133 ; Glioma‐Initiating Cells ; Profiling ; Radiotherapy Sensitivity ; Sox2 ; Stem Cell Markers
    ISSN: 0022-3042
    E-ISSN: 1471-4159
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  • 5
    Language: English
    In: Cancer Research, 04/15/2012, Vol.72(8 Supplement), pp.4736-4736
    ISSN: 0008-5472
    E-ISSN: 1538-7445
    Source: CrossRef
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  • 6
    Language: English
    In: International Journal of Radiation Oncology, Biology, Physics, 01 July 2010, Vol.77(3), pp.670-676
    Description: To evaluate the toxicity and efficacy of chemoradiotherapy with temozolomide (TMZ) administered in an intensified 1-week on/1-week off schedule plus indomethacin in patients with newly diagnosed glioblastoma. A total of 41 adult patients (median Karnofsky performance status, 90%; median age, 56 years) were treated with preirradiation TMZ at 150 mg/m (1 week on/1 week off), involved-field radiotherapy combined with concomitant low-dose TMZ (50 mg/m ), maintenance TMZ starting at 150 mg/m using a 1-week on/1-week off schedule, plus maintenance indomethacin (25 mg twice daily). The median follow-up interval was 21.7 months. Grade 4 hematologic toxicity was observed in 15 patients (36.6%). Treatment-related nonhematologic Grade 4-5 toxicity was reported for 2 patients (4.9%). The median progression-free survival was 7.6 months (95% confidence interval, 6.2–10.4). The 1-year survival rate was 73.2% (95% confidence interval, 56.8–84.2%). The presence of gene promoter methylation in the tumor tissue was associated with significantly superior progression-free survival. The dose-dense regimen of TMZ administered in a 1-week on/1-week off schedule resulted in acceptable nonhematologic toxicity. Compared with data from the European Organization for Research and Treatment of Cancer/National Cancer Institute of Canada trial 26981-22981/CE.3, patients with an unmethylated gene promoter appeared not to benefit from intensifying the TMZ schedule regarding the median progression-free survival and overall survival. In contrast, data are promising for patients with a methylated promoter.
    Keywords: Glioblastoma ; Indomethacin ; O6-Methylguanine-DNA Methyltransferase ; Mgmt ; Radiotherapy ; Temozolomide ; Medicine
    ISSN: 0360-3016
    E-ISSN: 1879-355X
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  • 7
    In: Neuro-Oncology, 2011, Vol. 13(6), pp.566-579
    Description: Insights into the molecular pathogenesis of glioblastoma have not yet resulted in relevant clinical improvement. With standard therapy, which consists of surgical resection with concomitant temozolomide in addition to radiotherapy followed by adjuvant temozolomide, the median duration of survival is 12–14 months. Therefore, the identification of novel molecular targets and inhibitory agents has become a focus of research for glioblastoma treatment. Recent results of bevacizumab may represent a proof of principle that treatment with targeted agents can result in clinical benefits for patients with glioblastoma. This review discusses limitations in the existing therapy for glioblastoma and provides an overview of current efforts to identify molecular targets using large-scale screening of glioblastoma cell lines and tumor samples. We discuss preclinical and clinical data for several novel molecular targets, including growth factor receptors, phosphatidylinositol-3 kinase, SRC-family kinases, integrins, and CD95 ligand and agents that inhibit these targets, including erlotinib, enzastaurin, dasatinib, sorafenib, cilengitide, AMG102, and APG101. By combining advances in tumor screening with novel targeted therapies, it is hoped that new treatment options will emerge for this challenging tumor type.
    Keywords: Integrins ; Pi3 Kinase ; Receptor Tyrosine Kinase ; Src - Family Kinases ; Vegf Signaling
    ISSN: 1522-8517
    E-ISSN: 1523-5866
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  • 8
    In: Nature Reviews Neurology, 2014
    Description: Many patients with malignant gliomas do not respond to alkylating agent chemotherapy. Alkylator resistance of glioma cells is mainly mediated by the DNA repair enzyme 06-methylguanine-DNA methyltransferase (MGMT). Epigenetic silencing of the MGMT gene by promoter methylation in glioma cells compromises this DNA repair mechanism and increases chemosensitivity. MGMT promoter methylation is, therefore, a strong prognostic biomarker in paediatric and adult patients with glioblastoma treated with temozolomide. Notably, elderly patients (〉65-70 years) with glioblastoma whose tumours lack MGMT promoter methylation derive minimal benefit from such chemotherapy. Thus, MGMT promoter methylation status has become a frequently requested laboratory test in neuro-oncology. This Review presents current data on the prognostic and predictive relevance of MGMT testing, discusses clinical trials that have used MGMT status to select participants, evaluates known issues concerning the molecular testing procedure, and addresses the necessity for molecular-contextdependent interpretation of MGMT test results. Whether MGMT promoter methylation testing should be offered to all individuals with glioblastoma, or only to elderly patients and those in clinical trials, is also discussed. Justifications for withholding alkylating agent chemotherapy in patients with MGMT-unmethylated glioblastomas outside clinical trials, and the potential role for MGMT testing in other gliomas, are also discussed. published online 10 June 2014; doi: 10.1038/nrneurol.2014.100
    Keywords: Methyltransferases – Properties ; Gliomas – Genetic Aspects ; Gliomas – Care and Treatment ; Molecular Targeted Therapy – Research;
    ISSN: 1759-4758
    E-ISSN: 17594766
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  • 9
  • 10
    In: Neuro-Oncology, 2010, Vol. 12(9), pp.894-907
    Description: Previous findings suggest an angiogenesis-regulating function of the p53 tumor suppressor protein in various malignancies. With several antiangiogenic agents entering the clinic, we assessed the value of the TP53 status in predicting angiogenesis in glioblastoma in vivo and examined underlying angiogenic-signaling pathways in vitro. We identified 26 TP53 wild-type and 9 TP53 mutated treatment-naïve, primary, isocitrate dehydrogenase 1 (IDH1) wild-type glioblastoma specimens by sequence analysis and quantified vascularization. P53 responsiveness of the angiogenesis-related target genes, such as vascular endothelial growth factor ( VEGF ), basic fibroblast growth factor ( bFGF ), thrombospondin 1 ( TSP-1 ), brain-specific angiogenesis inhibitor 1 ( BAI1 ), and collagen prolyl-4-hydroxylase alpha 2 ( P4HA2 ), was evaluated by (i) overexpression of wild-type p53 in homozygously TP53 -deleted LN-308 cells; (ii) shRNA-mediated p53 knockdown in the TP53 wild-type LNT-229 cells; and (iii) chemical induction of wild-type p53 expression in LNT-229 cells by camptothecin. Irrespective of the TP53 status, vascularization did not differ significantly between the two groups of glioblastoma specimens. Of all target genes, only P4HA2 mRNA was upregulated through wild-type p53. As opposed to several nonglial tumors, in glioblastoma cells, p53-mediated transcriptional induction of P4HA2 mRNA neither resulted in increased levels of P4HA2 protein or antiangiogenic endostatin nor did it influence endothelial cell sprouting, viability, or transmigration in vitro. Moreover, p53-uncoupled stable overexpression of P4HA2 in LN-308 cells did not affect endothelial cell viability. These data challenge the view of p53 as an angiogenesis-regulator in glioblastoma in that relevant signaling pathways are silenced, potentially contributing to the angiogenic switch during malignant progression.
    Keywords: Angiogenesis ; Collagen Prolyl Hydroxylase ; Glioblastoma ; P53
    ISSN: 1522-8517
    E-ISSN: 1523-5866
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