Search

Mutations in the isocitrate dehydrogenase gene IDH1 are common in low-grade glioma, where they result in the production of 2-hydroxyglutarate (2HG), disrupted patterns of histone methylation, and gliomagenesis. IDH1 mutations also cosegregate with mutations in the ATRX gene and the TERT promoter, suggesting that IDH mutation may drive the creation or selection of telomere-stabilizing events as part of immortalization/transformation process. To determine whether and how this may occur, we investigated the phenotype of pRb-/p53-deficient human astrocytes engineered with IDH1 wild-type (WT) or R132H-mutant (IDH1mut) genes as they progressed through their lifespan. IDH1mut expression promoted 2HG production and altered histone methylation within 20 population doublings (PD) but had no effect on telomerase expression or telomere length. Accordingly, cells expressing either IDH1WT or IDH1mut entered a telomere-induced crisis at PD 70. In contrast, only IDH1mut cells emerged from crisis, grew indefinitely in culture, and formed colonies in soft agar and tumors in vivo. Clonal populations of postcrisis IDH1mut cells displayed shared genetic alterations, but no mutations in ATRX or the TERT promoter were detected. Instead, these cells reactivated telomerase and stabilized their telomeres in association with increased histone lysine methylation (H3K4me3) and c-Myc/Max binding at the TERT promoter. Overall, these results show that although IDH1mut does not create or select for ATRX or TERT promoter mutations, it can indirectly reactivate TERT, and in doing so contribute to astrocytic immortalization and transformation. Cancer Res; 76(22); 6680–9. ©2016 AACR.

Mutant IDH1 expression is associated with down- regulation of RAP1 and XRCC1

Schematics of ATRX CRISPR vector, verification of different cell lines for ALT associated characteristics, in-vivo growth and screening of off-target CRISPR effect

Supplementary Figures S1-S9 and tables S1-S6

Purpose:The immunosuppressive tumor microenvironment present in the majority of diffuse glioma limits therapeutic response to immunotherapy. As the determinants of the glioma-associated immune response are relatively poorly understood, the study of glioma with more robust tumor-associated immune responses may be particularly useful to identify novel immunomodulatory factors that can promote T-cell effector function in glioma.Experimental Design:We used multiplex immune-profiling, proteomic profiling, and gene expression analysis to define the tumor-associated immune response in two molecular subtypes of glioma and identify factors that may modulate this response. We then used patient-derived glioma cultures and an immunocompetent murine model for malignant glioma to analyze the ability of tumor-intrinsic factors to promote a CD8+ T-cell response.Results:As compared with isocitrate dehydrogenase (IDH)-mutant astrocytoma, MAPK-activated pleomorphic xanthoastrocytoma (PXA) harbored increased numbers of activated cytotoxic CD8+ T cells and Iba1+ microglia/macrophages, increased MHC class I expression, enrichment of genes associated with antigen presentation and processing, and increased tumor cell secretion of the chemokine CXCL14. CXCL14 promoted activated CD8+ T-cell chemotaxis in vitro, recruited tumor-infiltrating CD8+ T cells in vivo, and prolonged overall survival in a cytotoxic T-cell–dependent manner. The immunomodulatory molecule B7-H3 was also highly expressed in PXA.Conclusions:We identify the MAPK-activated lower grade astrocytoma PXA as having an immune-rich tumor microenvironment and suggest this tumor may be particularly vulnerable to immunotherapeutic modulation. We also identify CXCL14 as an important determinant of the glioma-associated immune microenvironment, sufficient to promote an antitumor CD8+ T-cell response.

CQ and BAF do not affect ER area or phospholipid levels in IDHwt glioma cells.

CQ and BAF restore phospholipid levels and inhibit clonogenicity of IDHmut glioma cells.

2-HG induces a reduction in ER area in IDHmut glioma cells.

Multiple telomere signals, change in cell viability and chromosome fusion in IDH1mut, ATRX-KO ALT astrocytes with and without XRCC1 overexpression.

siRNA-mediated suppression of RAP1 and/or XRCC1 substitutes for mutant IDH1 in driving the ALT phenotype.

Tumor metabolism is reprogrammed to meet the demands of proliferating cancer cells. In particular, cancer cells upregulate synthesis of the membrane phospholipids phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdE) in order to allow for rapid membrane turnover. Nonetheless, we show here that, in mutant isocitrate dehydrogenase 1 (IDHmut) gliomas, which produce the oncometabolite 2-hydroxyglutarate (2-HG), PtdCho and PtdE biosynthesis is downregulated and results in lower levels of both phospholipids when compared with wild-type IDH1 cells. 2-HG inhibited collagen-4-prolyl hydroxylase activity, leading to accumulation of misfolded procollagen-IV in the endoplasmic reticulum (ER) of both genetically engineered and patient-derived IDHmut glioma models. The resulting ER stress triggered increased expression of FAM134b, which mediated autophagic degradation of the ER (ER-phagy) and a reduction in the ER area. Because the ER is the site of phospholipid synthesis, ER-phagy led to reduced PtdCho and PtdE biosynthesis. Inhibition of ER-phagy via pharmacological or molecular approaches restored phospholipid biosynthesis in IDHmut glioma cells, triggered apoptotic cell death, inhibited tumor growth, and prolonged the survival of orthotopic IDHmut glioma-bearing mice, pointing to a potential therapeutic opportunity. Glioma patient biopsies also exhibited increased ER-phagy and downregulation of PtdCho and PtdE levels in IDHmut samples compared with wild-type, clinically validating our observations. Collectively, this study provides detailed and clinically relevant insights into the functional link between oncometabolite-driven ER-phagy and phospholipid biosynthesis in IDHmut gliomas.Significance: Downregulation of phospholipid biosynthesis via ER-phagy is essential for proliferation and clonogenicity of mutant IDH1 gliomas, a finding with immediate therapeutic implications. Cancer Res; 78(9); 2290–304. ©2018 AACR.

2-HG inhibits PtdCho and PtdE biosynthesis.

SNVs identified by exome-sequencing.

Supplementary Figure from CXCL14 Promotes a Robust Brain Tumor-Associated Immune Response in Glioma

A subset of tumors use a recombination-based alternative lengthening of telomere (ALT) pathway to resolve telomeric dysfunction in the absence of TERT. Loss-of-function mutations in the chromatin remodeling factor ATRX are associated with ALT but are insufficient to drive the process. Because many ALT tumors express the mutant isocitrate dehydrogenase IDH1 R132H, including all lower grade astrocytomas and secondary glioblastoma, we examined a hypothesized role for IDH1 R132H in driving the ALT phenotype during gliomagenesis. In p53/pRb–deficient human astrocytes, combined deletion of ATRX and expression of mutant IDH1 were sufficient to create tumorigenic cells with ALT characteristics. The telomere capping complex component RAP1 and the nonhomologous DNA end joining repair factor XRCC1 were each downregulated consistently in these tumorigenic cells, where their coordinate reexpression was sufficient to suppress the ALT phenotype. RAP1 or XRCC1 downregulation cooperated with ATRX loss in driving the ALT phenotype. RAP1 silencing caused telomere dysfunction in ATRX-deficient cells, whereas XRCC1 silencing suppressed lethal fusion of dysfunctional telomeres by allowing IDH1-mutant ATRX-deficient cells to use homologous recombination and ALT to resolve telomeric dysfunction and escape cell death. Overall, our studies show how expression of mutant IDH1 initiates telomeric dysfunction and alters DNA repair pathway preferences at telomeres, cooperating with ATRX loss to defeat a key barrier to gliomagenesis.Significance: Studies show how expression of mutant IDH1 initiates telomeric dysfunction and alters DNA repair pathway preferences at telomeres, cooperating with ATRX loss to defeat a key barrier to gliomagenesis and suggesting new therapeutic options to treat low-grade gliomas. Cancer Res; 78(11); 2966–77. ©2018 AACR.

Phospholipid biosynthesis is down-regulated in IDHmut glioma cells.

Silencing FAM134b, Atg5 or Atg7 restores phospholipid biosynthesis in IDHmut glioma cells.

2-HG induces ER-phagy in IDHmut glioma cells.

Supplementary Data from CXCL14 Promotes a Robust Brain Tumor-Associated Immune Response in Glioma

Although lower grade gliomas are driven by mutations in the isocitrate dehydrogenase 1 (IDH1) gene and are less aggressive than primary glioblastoma, they nonetheless generally recur. IDH1-mutant patients are increasingly being treated with temozolomide, but early detection of response remains a challenge and there is a need for complementary imaging methods to assess response to therapy prior to tumor shrinkage. The goal of this study was to determine the value of magnetic resonance spectroscopy (MRS)–based metabolic changes for detection of response to temozolomide in both genetically engineered and patient-derived mutant IDH1 models. Using 1H MRS in combination with chemometrics identified several metabolic alterations in temozolomide-treated cells, including a significant increase in steady-state glutamate levels. This was confirmed in vivo, where the observed 1H MRS increase in glutamate/glutamine occurred prior to tumor shrinkage. Cells labeled with [1–13C]glucose and [3–13C]glutamine, the principal sources of cellular glutamate, showed that flux to glutamate both from glucose via the tricarboxylic acid cycle and from glutamine were increased following temozolomide treatment. In line with these results, hyperpolarized [5–13C]glutamate produced from [2–13C]pyruvate and hyperpolarized [1–13C]glutamate produced from [1–13C]α-ketoglutarate were significantly higher in temozolomide-treated cells compared with controls. Collectively, our findings identify 1H MRS-detectable elevation of glutamate and hyperpolarized 13C MRS-detectable glutamate production from either pyruvate or α-ketoglutarate as potential translatable metabolic biomarkers of response to temozolomide treatment in mutant IDH1 glioma.Significance:These findings show that glutamate can be used as a noninvasive, imageable metabolic marker for early assessment of tumor response to temozolomide, with the potential to improve treatment strategies for mutant IDH1 patients.

ER-phagy is linked to phospholipid biosynthesis in BT54 neurospheres (A-C), orthotopic IDHmut tumor xenografts (D-J) and IDHmut patient biopsies (K-Q).

Forced overexpression of RAP1 and/or XRCC1 suppresses mutant IDH1-mediated ALT phenotype in genetically modified human astrocytes.

Effect of 2-HG on cell proliferation of IDH1 wild-type cells for the U87 (A) and NHA (B) models.

Supplementary Table 1 from Dose-Dependent Effects of Focal Fractionated Irradiation on Secondary Malignant Neoplasms in Nf1 Mutant Mice

Nuclear factor-κB (NF-κB) activation may play an important role in the pathogenesis of cancer and also in resistance to treatment. Inactivation of the p53 tumor suppressor is a key component of the multistep evolution of most cancers. Links between the NF-κB and p53 pathways are under intense investigation. In this study, we show that the receptor interacting protein 1 (RIP1), a central component of the NF-κB signaling network, negatively regulates p53 tumor suppressor signaling. Loss of RIP1 from cells results in augmented induction of p53 in response to DNA damage, whereas increased RIP1 level leads to a complete shutdown of DNA damage–induced p53 induction by enhancing levels of cellular mdm2. The key signal generated by RIP1 to up-regulate mdm2 and inhibit p53 is activation of NF-κB. The clinical implication of this finding is shown in glioblastoma, the most common primary malignant brain tumor in adults. We show that RIP1 is commonly overexpressed in glioblastoma, but not in grades II and III glioma, and increased expression of RIP1 confers a worse prognosis in glioblastoma. Importantly, RIP1 levels correlate strongly with mdm2 levels in glioblastoma. Our results show a key interaction between the NF-κB and p53 pathways that may have implications for the targeted treatment of glioblastoma. [Cancer Res 2009;69(7):2809–16]

Supplementary Figure 3 from The PTEN/Akt Pathway Dictates the Direct αVβ3-Dependent Growth-Inhibitory Action of an Active Fragment of Tumstatin in Glioma Cells In vitro and In vivo

Supplementary Figures 1-4 from p53 Small-Molecule Inhibitor Enhances Temozolomide Cytotoxic Activity against Intracranial Glioblastoma Xenografts

PDF file - 738K, Immunoblot and sub-G1 FACs analysis of NF1-deficient GBM cells treated with PD0325901 and/or PI-103

Supplementary Figure 3 from Dose-Dependent Effects of Focal Fractionated Irradiation on Secondary Malignant Neoplasms in Nf1 Mutant Mice

SuppFigure3. Stable suppression of PKM2 expression in G55 cells significantly alters intra-cellular concentrations of pyruvate and lactate. (*, p

Supplementary Table 2 from Dose-Dependent Effects of Focal Fractionated Irradiation on Secondary Malignant Neoplasms in Nf1 Mutant Mice

Supplementary Figure 2 from The PTEN/Akt Pathway Dictates the Direct αVβ3-Dependent Growth-Inhibitory Action of an Active Fragment of Tumstatin in Glioma Cells In vitro and In vivo

Comparison of PDH activity in the various models used in this study.

Supplementary Legends for Figures 1-3, Tables 1-2 from Dose-Dependent Effects of Focal Fractionated Irradiation on Secondary Malignant Neoplasms in Nf1 Mutant Mice

The collagen type IV cleavage fragment tumstatin and its active subfragments bind to integrin αVβ3 and inhibit activation of focal adhesion kinase, phophoinositol-3 kinase, Akt, and mammalian target of rapamycin (mTOR) in what is thought to be an endothelial cell–specific manner. The resultant endothelial cell apoptosis accounts for the ability of tumstatin to function as an endogenous inhibitor of angiogenesis and an indirect suppressor of tumor growth. We hypothesized that the inability of tumstatin to directly suppress tumor cell growth might be the result of the constitutive activation of the Akt/mTOR pathway commonly seen in tumors. Consistent with this idea, several integrin αVβ3–expressing glioma cell lines with PTEN mutations and high levels of phospho-Akt (pAkt) were unaffected by exposure to an active fragment of tumstatin (T3), whereas αVβ3-expressing glioma cell lines with a functional PTEN/low levels of pAkt exhibited T3-induced growth suppression that could be bypassed by small interfering RNA–mediated suppression of PTEN, introduction of a constitutively expressed Akt, or introduction of the Akt and mTOR target eukaryotic translation initiation factor 4E. The direct tumor-suppressive actions of T3 were further shown in an αVβ3-deficient in vivo mouse model in which T3, while unable to alter the tumstatin-insensitive vasculature contributed by the αVβ3-deficient host, nonetheless suppressed the growth and proliferative index of i.c. implanted αVβ3-expressing PTEN-proficient glioma cells. These results show that tumstatin, previously considered to be only an endogenous inhibitor of angiogenesis, also directly inhibits the growth of tumors in a manner dependent on Akt/mTOR activation. (Cancer Res 2006; 66(23): 11331-40)

Supplementary Figure 1 from The PTEN/Akt Pathway Dictates the Direct αVβ3-Dependent Growth-Inhibitory Action of an Active Fragment of Tumstatin in Glioma Cells In vitro and In vivo

Supplementary Figure 2 from Dose-Dependent Effects of Focal Fractionated Irradiation on Secondary Malignant Neoplasms in Nf1 Mutant Mice

PDF file - 44K

PDF file - 809K, Immunoblot analysis of NF1-deficient GBM cells treated with AZD6244

Purpose: The immunosuppressive tumor microenvironment present in the majority of diffuse glioma limits therapeutic response to immunotherapy. As the determinants of the glioma-associated immune response are relatively poorly understood, the study of glioma with more robust tumor-associated immune responses may be particularly useful to identify novel immunomodulatory factors that can promote T-cell effector function in glioma. Experimental Design: We used multiplex immune-profiling, proteomic profiling, and gene expression analysis to define the tumor-associated immune response in two molecular subtypes of glioma and identify factors that may modulate this response. We then used patient-derived glioma cultures and an immunocompetent murine model for malignant glioma to analyze the ability of tumor-intrinsic factors to promote a CD8+ T-cell response. Results: As compared with isocitrate dehydrogenase (IDH)-mutant astrocytoma, MAPK-activated pleomorphic xanthoastrocytoma (PXA) harbored increased numbers of activated cytotoxic CD8+ T cells and Iba1+ microglia/macrophages, increased MHC class I expression, enrichment of genes associated with antigen presentation and processing, and increased tumor cell secretion of the chemokine CXCL14. CXCL14 promoted activated CD8+ T-cell chemotaxis in vitro, recruited tumor-infiltrating CD8+ T cells in vivo, and prolonged overall survival in a cytotoxic T-cell–dependent manner. The immunomodulatory molecule B7-H3 was also highly expressed in PXA. Conclusions: We identify the MAPK-activated lower grade astrocytoma PXA as having an immune-rich tumor microenvironment and suggest this tumor may be particularly vulnerable to immunotherapeutic modulation. We also identify CXCL14 as an important determinant of the glioma-associated immune microenvironment, sufficient to promote an antitumor CD8+ T-cell response.

Background The alternative lengthening of telomeres (ALT) pathway is essential for tumor proliferation in astrocytomas. The goal of this study was to identify metabolic alterations linked to the ALT pathway that can be exploited for noninvasive magnetic resonance spectroscopy (MRS)-based imaging of astrocytomas in vivo. Methods Genetic and pharmacological methods were used to dissect the association between the ALT pathway and glucose metabolism in genetically engineered and patient-derived astrocytoma models. 2H-MRS was used for noninvasive imaging of ALT-linked modulation of glycolytic flux in mice bearing orthotopic astrocytomas in vivo. Results The ALT pathway was associated with higher activity of the rate-limiting glycolytic enzyme phosphofructokinase-1 and concomitantly elevated flux of glucose to lactate in astrocytoma cells. Silencing the ALT pathway or treating with the poly(ADP-ribose) polymerase inhibitor niraparib that induces telomeric fusion in ALT-dependent astrocytoma cells abrogated glycolytic flux. Importantly, this metabolic reprogramming could be non-invasively visualized by 2H-MRS. Lactate production from [6,6′-2H]-glucose was higher in ALT-dependent astrocytoma tumors relative to the normal brain in vivo. Furthermore, treatment of orthotopic astrocytoma-bearing mice with niraparib reduced lactate production from [6,6′-2H]-glucose at early timepoints when alterations in tumor volume could not be detected by anatomical imaging, pointing to the ability of [6,6′-2H]-glucose to report on pseudoprogression in vivo. Conclusions We have mechanistically linked the ALT pathway to elevated glycolytic flux and demonstrated the ability of [6,6′-2H]-glucose to non-invasively assess tumor burden and response to therapy in astrocytomas. Our findings point to a novel, clinically translatable method for metabolic imaging of astrocytoma patients.

Telomere maintenance is a universal hallmark of cancer. Most tumors including low-grade oligodendrogliomas use telomerase reverse transcriptase (TERT) expression for telomere maintenance while astrocytomas use the alternative lengthening of telomeres (ALT) pathway. Although TERT and ALT are hallmarks of tumor proliferation and attractive therapeutic targets, translational methods of imaging TERT and ALT are lacking. Here we show that TERT and ALT are associated with unique 1H-magnetic resonance spectroscopy (MRS)-detectable metabolic signatures in genetically-engineered and patient-derived glioma models and patient biopsies. Importantly, we have leveraged this information to mechanistically validate hyperpolarized [1-13C]-alanine flux to pyruvate as an imaging biomarker of ALT status and hyperpolarized [1-13C]-alanine flux to lactate as an imaging biomarker of TERT status in low-grade gliomas. Collectively, we have identified metabolic biomarkers of TERT and ALT status that provide a way of integrating critical oncogenic information into non-invasive imaging modalities that can improve tumor diagnosis and treatment response monitoring., Telomerase expression and the alternative lengthening of telomeres pathway are hallmarks of cancer. Here, the authors show that, in primary brain tumors, these features are correlated with metabolic signatures detectable by metabolic imaging, suggesting that they can be used to non-invasively monitor telomere maintenance in brain tumours.

Author(s): Molloy, Abigail R; Najac, Chloe; Viswanath, Pavithra; Lakhani, Aliya; Subramani, Elavarasan; Batsios, Georgios; Radoul, Marina; Gillespie, Anne Marie; Pieper, Russell O; Ronen, Sabrina M | Abstract: Mutations in isocitrate dehydrogenase 1 (IDH1mut) are reported in 70-90% of low-grade gliomas and secondary glioblastomas. IDH1mut catalyzes the reduction of α-ketoglutarate (α-KG) to 2-hydroxyglutarate (2-HG), an oncometabolite which drives tumorigenesis. Inhibition of IDH1mut is therefore an emerging therapeutic approach, and inhibitors such as AG-120 and AG-881 have shown promising results in phase 1 and 2 clinical studies. However, detection of response to these therapies prior to changes in tumor growth can be challenging. The goal of this study was to identify non-invasive clinically translatable metabolic imaging biomarkers of IDH1mut inhibition that can serve to assess response. Methods: IDH1mut inhibition was confirmed using an enzyme assay and 1H- and 13C- magnetic resonance spectroscopy (MRS) were used to investigate the metabolic effects of AG-120 and AG-881 on two genetically engineered IDH1mut-expressing cell lines, NHAIDH1mut and U87IDH1mut. Results: 1H-MRS indicated a significant decrease in steady-state 2-HG following treatment, as expected. This was accompanied by a significant 1H-MRS-detectable increase in glutamate. However, other metabolites previously linked to 2-HG were not altered. 13C-MRS also showed that the steady-state changes in glutamate were associated with a modulation in the flux of glutamine to both glutamate and 2-HG. Finally, hyperpolarized 13C-MRS was used to show that the flux of α-KG to both glutamate and 2-HG was modulated by treatment. Conclusion: In this study, we identified potential 1H- and 13C-MRS-detectable biomarkers of response to IDH1mut inhibition in gliomas. Although further studies are needed to evaluate the utility of these biomarkers in vivo, we expect that in addition to a 1H-MRS-detectable drop in 2-HG, a 1H-MRS-detectable increase in glutamate, as well as a hyperpolarized 13C-MRS-detectable change in [1-13C] α-KG flux, could serve as metabolic imaging biomarkers of response to treatment.