Cancer Biology and Signal Transduction Interferon-b Induces Loss of Spherogenicity and Overcomes Therapy Resistance of Glioblastoma Stem Cells

Abstract

Glioblastoma is the most common malignant brain tumor in adults and characterized by a poor prognosis. Glioma cells expressing O-methylguanine DNA methyltransferase (MGMT) exhibit a higher level of resistance toward alkylating agents, including the standard of care chemotherapeutic agent temozolomide. Here, we demonstrate that long-term glioma cell lines (LTL) as well as glioma-initiating cell lines (GIC) express receptors for the immune modulatory cytokine IFN-b and respond to IFN-b with induction of STAT-3 phosphorylation. Exposure to IFN-b induces a minor loss of viability, but strongly interferes with sphere formation in GIC cultures. Furthermore, IFN-b sensitizes LTL andGIC to temozolomide and irradiation. RNA interference confirmed that both IFN-b receptors, R1 and R2, are required for IFN-b–mediated sensitization, but that sensitization is independent of MGMT or TP53. Most GIC lines are highly temozolomide-resistant, mediated byMGMT expression, but nevertheless susceptible to IFN-b sensitization. Gene expression profiling following IFN-b treatment revealed strong upregulation of IFN-b–associated genes, including a proapoptotic gene cluster, but did not alter stemness-associated expression signatures. Caspase activity and inhibition studies revealed the proapoptotic genes to mediate glioma cell sensitization to exogenous death ligands by IFN-b, but not to temozolomide or irradiation, indicating distinct pathways of death sensitizationmediated by IFN-b. Thus, IFN-b is a potential adjunct to glioblastoma treatment that may target the GIC population. IFN-b operates independently of MGMT-mediated resistance, classical apoptosis-regulatory networks, and stemness-associated gene clusters. Mol Cancer Ther; 13(4); 948–61. 2014 AACR. Introduction Glioblastomas are characterized by infiltrative growth and resistance to cell death induction.Despitemultimodal therapy, tumor progression occurs inevitably and survival remains in the range of months (1–3). Early therapy failure is associatedwith the expression of O-methylguanine-DNA-methyltransferase (MGMT), a DNA repair protein that accounts for glioma cell resistance by counteracting the effects of alkylating chemotherapy (4). MGMT has become an important molecular marker and is now implemented in clinical diagnostics as predictive biomarker for benefit from alkylating chemotherapy and clinical outcome (5–7). Patients with a nonmethylated MGMT promoter are prone to therapy failure with standard alkylating chemotherapy, and to date, effective approaches for this large group of patients, comprising more than half of all the patients with glioblastoma, are still lacking, including dose intensification of temozolomide (8). Recently, a subfraction of glioma cells exhibiting stem cell–like properties (stem-like glioma cells), referred to as glioma-initiating cells (GIC), has been identified (9, 10). GICs are thought to have the ability of self-renewal, tumor initiation, and pluripotency and have been proposed to account for the ultimately lethal nature of glioblastoma. They may contribute to therapy resistance in vivo and therefore promote tumor progression. The value of GIC cultures and their MGMT status as a model to study resistance to temozolomide in glioblastoma has remained controversial. Among a panel of 20 GIC lines, some were sensitive to temozolomide, which was associated with lowMGMT protein levels, but notMGMT promoter methylation, and the MGMT promoter status was thus not strongly predictive of response to temozolomide (11). High temozolomide sensitivity of GIC cultures lacking MGMTexpressionhasbeendescribed in vitro (12). Finally, the frequency of MGMT promoter-methylated alleles in glioblastomas may range from 10% to 90%, but Authors' Affiliations: Laboratory of Molecular Neuro-Oncology, Department of Neurology, and Department of Neurosurgery, University Hospital Zurich and Neuroscience Center Zurich, Zurich, Switzerland; Laboratory for Brain Tumor Biology, Department of Neurosurgery, University Hospital Hamburg-Eppendorf, Hamburg; Department of Neuropathology and Center for Biological and Medical Research, Heinrich Heine University, D€ usseldorf; and German Cancer Consortium (DKTK), German Cancer Research Center (DKFZ), Heidelberg, Germany Corresponding Author: Michael Weller, Department of Neurology, University Hospital Zurich, Frauenklinikstrasse 26, 8091 Zurich, Switzerland. Phone: 410-44255-5500; Fax: 410-44255-4507; E-mail: Michael.Weller@usz.ch doi: 10.1158/1535-7163.MCT-13-0772 2014 American Association for Cancer Research. Molecular Cancer Therapeutics Mol Cancer Ther; 13(4) April 2014 948 on June 24, 2017. © 2014 American Association for Cancer Research. mct.aacrjournals.org Downloaded from Published OnlineFirst February 13, 2014; DOI: 10.1158/1535-7163.MCT-13-0772

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@inproceedings{Happold2014CancerBA, title={Cancer Biology and Signal Transduction Interferon-b Induces Loss of Spherogenicity and Overcomes Therapy Resistance of Glioblastoma Stem Cells}, author={Caroline J Happold and Patrick Roth and Manuela Silginer and Ana-Maria Florea and Katrin Lamszus and Karl Frei and Ren{\'e} Deenen and Guido Reifenberger and Michael Weller}, year={2014} }