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      Reactive oxygen species-mediated therapeutic response and resistance in glioblastoma

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          Abstract

          Glioblastoma (GBM) resistance to therapy is the most common cause of tumor recurrence, which is ultimately fatal in 90% of the patients 5 years after initial diagnosis. A sub-population of tumor cells with stem-like properties, glioma stem cells (GSCs), is specifically endowed to resist or adapt to the standard therapies, leading to therapeutic resistance. Several anticancer agents, collectively termed redox therapeutics, act by increasing intracellular levels of reactive oxygen species (ROS). In this study, we investigated mechanisms underlying GSC response and resistance to cannabidiol (CBD), a non-toxic, non-psychoactive cannabinoid and redox modulator. Using primary GSCs, we showed that CBD induced a robust increase in ROS, which led to the inhibition of cell survival, phosphorylated (p)-AKT, self-renewal and a significant increase in the survival of GSC-bearing mice. Inhibition of self-renewal was mediated by the activation of the p-p38 pathway and downregulation of key stem cell regulators Sox2, Id1 and p-STAT3. Following CBD treatment, a subset of GSC successfully adapted, leading to tumor regrowth. Microarray, Taqman and functional assays revealed that therapeutic resistance was mediated by enhanced expression of the antioxidant response system Xc catalytic subunit xCT (SLC7A11 (solute carrier family 7 (anionic amino-acid transporter light chain), member 11)) and ROS-dependent upregulation of mesenchymal (MES) markers with concomitant downregulation of proneural (PN) markers, also known as PN–MES transition. This ‘reprogramming' of GSCs occurred in culture and in vivo and was partially due to activation of the NFE2L2 (NRF2 (nuclear factor, erythroid 2-like)) transcriptional network. Using genetic knockdown and pharmacological inhibitors of SLC7A11, we demonstrated that combining CBD treatment with the inhibition of system Xc resulted in synergistic ROS increase leading to robust antitumor effects, that is, decreased GSC survival, self-renewal, and invasion. Our investigation provides novel mechanistic insights into the antitumor activity of redox therapeutics and suggests that combinatorial approaches using small molecule modulators of ROS offer therapeutic benefits in GBM.

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          Most cited references18

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          Molecular subclasses of high-grade glioma predict prognosis, delineate a pattern of disease progression, and resemble stages in neurogenesis.

          Previously undescribed prognostic subclasses of high-grade astrocytoma are identified and discovered to resemble stages in neurogenesis. One tumor class displaying neuronal lineage markers shows longer survival, while two tumor classes enriched for neural stem cell markers display equally short survival. Poor prognosis subclasses exhibit markers either of proliferation or of angiogenesis and mesenchyme. Upon recurrence, tumors frequently shift toward the mesenchymal subclass. Chromosomal locations of genes distinguishing tumor subclass parallel DNA copy number differences between subclasses. Functional relevance of tumor subtype molecular signatures is suggested by the ability of cell line signatures to predict neurosphere growth. A robust two-gene prognostic model utilizing PTEN and DLL3 expression suggests that Akt and Notch signaling are hallmarks of poor prognosis versus better prognosis gliomas, respectively.
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            Mesenchymal differentiation mediated by NF-κB promotes radiation resistance in glioblastoma.

            Despite extensive study, few therapeutic targets have been identified for glioblastoma (GBM). Here we show that patient-derived glioma sphere cultures (GSCs) that resemble either the proneural (PN) or mesenchymal (MES) transcriptomal subtypes differ significantly in their biological characteristics. Moreover, we found that a subset of the PN GSCs undergoes differentiation to a MES state in a TNF-α/NF-κB-dependent manner with an associated enrichment of CD44 subpopulations and radioresistant phenotypes. We present data to suggest that the tumor microenvironment cell types such as macrophages/microglia may play an integral role in this process. We further show that the MES signature, CD44 expression, and NF-κB activation correlate with poor radiation response and shorter survival in patients with GBM. Copyright © 2013 Elsevier Inc. All rights reserved.
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              Glutamine sensitivity analysis identifies the xCT antiporter as a common triple-negative breast tumor therapeutic target.

              A handful of tumor-derived cell lines form the mainstay of cancer therapeutic development, yielding drugs with an impact typically measured as months to disease progression. To develop more effective breast cancer therapeutics and more readily understand their clinical impact, we constructed a functional metabolic portrait of 46 independently derived breast cell lines. Our analysis of glutamine uptake and dependence identified a subset of triple-negative samples that are glutamine auxotrophs. Ambient glutamine indirectly supports environmental cystine acquisition via the xCT antiporter, which is expressed on one-third of triple-negative tumors in vivo. xCT inhibition with the clinically approved anti-inflammatory sulfasalazine decreases tumor growth, revealing a therapeutic target in breast tumors of poorest prognosis and a lead compound for rapid, effective drug development. Copyright © 2013 Elsevier Inc. All rights reserved.
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                Author and article information

                Journal
                Cell Death Dis
                Cell Death Dis
                Cell Death & Disease
                Nature Publishing Group
                2041-4889
                January 2015
                15 January 2015
                1 January 2015
                : 6
                : 1
                : e1601
                Affiliations
                [1 ]California Pacific Medical Center Research Institute , San Francisco, CA, USA
                [2 ]Cincinnati Children's Hospital Medical Center , Cincinnati, OH, USA
                [3 ]Center for Applied Genomics, UMDNJ , Newark, NJ, USA
                Author notes
                [* ]California Pacific Medical Center Research Institute , 475 Brannan Street, Suite 220, San Francisco, CA 94107, USA. Tel: +1 415 600 1770; Fax: +1 415 600 1725; E-mail: McAllis@ 123456cpmcri.org (SM) or sorocel@ 123456cpmcri.org (LS)
                Article
                cddis2014566
                10.1038/cddis.2014.566
                4669764
                25590811
                1f507b57-5378-4454-9ce7-d8453366d86e
                Copyright © 2015 Macmillan Publishers Limited

                Cell Death and Disease is an open-access journal published by Nature Publishing Group. This work is licensed under a Creative Commons Attribution 4.0 International Licence. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons licence, users will need to obtain permission from the licence holder to reproduce the material. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0

                History
                : 04 November 2014
                : 27 November 2014
                Categories
                Original Article

                Cell biology
                Cell biology

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