Sensitivity of Glioblastomas to Clinically Available MEK Inhibitors Is Defined by Neurofibromin 1 Deficiency
ABSTRACT Loss of neurofibromin 1 (NF1) leads to hyperactivation of RAS, which in turn signals through the RAF/MEK/ERK and phosphoinositide 3-kinase (PI3K)/mTOR pathways to regulate cell growth and survival. Because NF1-deficient acute myeloid leukemias are sensitive to MEK inhibitors, we investigated here whether NF1-deficient glioblastoma multiforme (GBM) would respond to MEK inhibition. In 19 GBM cell lines, we found that treatment with the clinically available MEK inhibitors PD0325901 or AZD6244 decreased levels of phospho-ERK, the downstream effector of MEK, regardless of NF1 status. However, growth inhibition occurred only in a subset of NF1-deficient cells, in association with decreased levels of cyclin D1, increased levels of p27, and G1 arrest. As a single agent, PD0325901 suppressed the growth of NF1-deficient, MEK inhibitor-sensitive cells in vivo as well. Mechanistically, NF1-deficient, MEK inhibitor-sensitive cells were dependent upon the RAF/MEK/ERK pathway for growth and did not activate the PI3K pathway as a mechanism of acquired resistance. Importantly, NF1-deficient cells intrinsically resistant to MEK inhibition were sensitized by the addition of the dual PI3K/mTOR inhibitor PI-103. Taken together, our findings indicate that a subset of NF1-deficient GBMs may respond to MEK inhibitors currently being tested in clinical trials.
- SourceAvailable from: Aleksei Stepanenko[Show abstract] [Hide abstract]
ABSTRACT: •Karyotypically distinct U251, U373, and SNB19 cell lines are of the same origin.•Changes in karyotype result in the alterations of transcriptome and proteome.•Isogenic cell lines with different karyotypes have individual drug sensitivity.•Chromosome instability should be emphasized in the evaluation of multidrug resistance.Gene 02/2014; 540(2). DOI:10.1016/j.gene.2014.02.053 · 2.08 Impact Factor
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ABSTRACT: The availability of adult malignant glioma stem cells (GSCs) has provided unprecedented opportunities to identify the mechanisms underlying treatment resistance. Unfortunately, there is a lack of comparable reagents for the study of pediatric low-grade glioma (LGG). Leveraging a neurofibromatosis 1 (Nf1) genetically engineered mouse LGG model, we report the isolation of CD133(+) multi-potent low-grade glioma stem cells (LG-GSCs), which generate glioma-like lesions histologically similar to the parent tumor following injection into immunocompetent hosts. In addition, we demonstrate that these LG-GSCs harbor selective resistance to currently employed conventional and biologically targeted anti-cancer agents, which reflect the acquisition of new targetable signaling pathway abnormalities. Using transcriptomic analysis to identify additional molecular properties, we discovered that mouse and human LG-GSCs harbor high levels of Abcg1 expression critical for protecting against ER-stress-induced mouse LG-GSC apoptosis. Collectively, these findings establish that LGG cancer stem cells have unique molecular and functional properties relevant to brain cancer treatment. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
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ABSTRACT: Hypoxia-inducible factor 1α (HIF-1α) activity is one of the major players in hypoxia-mediated glioma progression and resistance to therapies, and therefore the focus of this study was the evaluation of HIF-1α modulation in relation to tumour response with the purpose of identifying imaging biomarkers able to document tumour response to treatment in a murine glioma model. U251-HRE-mCherry cells expressing Luciferase under the control of a hypoxia responsive element (HRE) and mCherry under the control of a constitutive promoter were used to assess HIF-1α activity and cell survival after treatment, both in vitro and in vivo, by optical, MRI and positron emission tomography imaging. This cell model can be used to monitor HIF-1α activity after treatment with different drugs modulating transduction pathways involved in its regulation. After temozolomide (TMZ) treatment, HIF-1α activity is early reduced, preceding cell cytotoxicity. Optical imaging allowed monitoring of this process in vivo, and carbonic anhydrase IX (CAIX) expression was identified as a translatable non-invasive biomarker with potential clinical significance. A preliminary in vitro evaluation showed that reduction of HIF-1α activity after TMZ treatment was comparable to the effect of an Hsp90 inhibitor, opening the way for further elucidation of its mechanism of action. The results of this study suggest that the U251-HRE-mCherry cell model can be used for the monitoring of HIF-1α activity through luciferase and CAIX expression. These cells can become a useful tool for the assessment and improvement of new targeted tracers for potential theranostic procedures.European Journal of Nuclear Medicine 03/2015; 42(7). DOI:10.1007/s00259-015-3040-7 · 5.22 Impact Factor