bims-malgli Biomed News
on Biology of malignant gliomas
Issue of 2021‒02‒07
fourteen papers selected by
Oltea Sampetrean
Keio University
  1. Theranostic Design of Angiopep-2 Conjugated Hyaluronic Acid Nanoparticles (Thera-ANG-cHANPs) for Dual Targeting and Boosted Imaging of Glioma Cells.
  2. OLIG2 maintenance is not essential for diffuse intrinsic pontine glioma cell line growth but regulates tumor phenotypes.
  3. PRMT6 methylation of RCC1 regulates mitosis, tumorigenicity, and radiation response of glioblastoma stem cells.
  4. The Role of Hypoxia in Glioblastoma Radiotherapy Resistance.
  5. Molecular and Metabolic Mechanisms Underlying Selective 5-Aminolevulinic Acid-Induced Fluorescence in Gliomas.
  6. Adult precision medicine: learning from the past to enhance the future.
  7. Differentiation of recurrent glioblastoma from radiation necrosis using diffusion radiomics with machine learning model development and external validation.
  8. H3.3-K27M drives neural stem cell-specific gliomagenesis in a human iPSC-derived model.
  9. Neuronavigation-guided focused ultrasound for transcranial blood-brain barrier opening and immunostimulation in brain tumors.
  10. Pediatric High-Grade Glioma: Moving Toward Subtype-Specific Multimodal Therapy.
  11. Immunostimulant hydrogel for the inhibition of malignant glioma relapse post-resection.
  12. Preclinical modeling of surgery and steroid therapy for glioblastoma reveals changes in immunophenotype that are associated with tumor growth and outcome.
  13. Intranasal delivery of experimental compounds in orthotopic brain tumor mouse models.
  14. Premalignant oligodendrocyte precursor cells stall in a heterogeneous state of replication stress prior to gliomagenesis.
  1. Cancers (Basel). 2021 Jan 28. pii: 503. [Epub ahead of print]13(3):
    Theranostic Design of Angiopep-2 Conjugated Hyaluronic Acid Nanoparticles (Thera-ANG-cHANPs) for Dual Targeting and Boosted Imaging of Glioma Cells.
    Angela Costagliola di Polidoro, Giorgia Zambito, Joost Haeck, Laura Mezzanotte, Martine Lamfers, Paolo Antonio Netti, Enza Torino.
      Glioblastoma multiforme (GBM) has a mean survival of only 15 months. Tumour heterogeneity and blood-brain barrier (BBB) mainly hinder the transport of active agents, leading to late diagnosis, ineffective therapy and inaccurate follow-up. The use of hydrogel nanoparticles, particularly hyaluronic acid as naturally occurring polymer of the extracellular matrix (ECM), has great potential in improving the transport of drug molecules and, furthermore, in facilitatating the early diagnosis by the effect of hydrodenticity enabling the T1 boosting of Gadolinium chelates for MRI. Here, crosslinked hyaluronic acid nanoparticles encapsulating gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) and the chemotherapeutic agent irinotecan (Thera-cHANPs) are proposed as theranostic nanovectors, with improved MRI capacities. Irinotecan was selected since currently repurposed as an alternative compound to the poorly effective temozolomide (TMZ), generally approved as the gold standard in GBM clinical care. Also, active crossing and targeting are achieved by theranostic cHANPs decorated with angiopep-2 (Thera-ANG-cHANPs), a dual-targeting peptide interacting with low density lipoprotein receptor related protein-1(LRP-1) receptors overexpressed by both endothelial cells of the BBB and glioma cells. Results showed preserving the hydrodenticity effect in the advanced formulation and internalization by the active peptide-mediated uptake of Thera-cHANPs in U87 and GS-102 cells. Moreover, Thera-ANG-cHANPs proved to reduce ironotecan time response, showing a significant cytotoxic effect in 24 h instead of 48 h.
    Keywords:  BBB; MRI; active targeting; angiopep-2; glioblastoma; hyaluronic acid; hydrodenticity; irinotecan; nanomedicine; precision medicine; theranostics
    DOI:  https://doi.org/10.3390/cancers13030503
  2. Neuro Oncol. 2021 Feb 04. pii: noab016. [Epub ahead of print]
    OLIG2 maintenance is not essential for diffuse intrinsic pontine glioma cell line growth but regulates tumor phenotypes.
    Yunfei Liao, Zaili Luo, Yaqi Deng, Feng Zhang, Rohit Rao, Jiajia Wang, Lingli Xu, Shiva Senthil Kumar, Satarupa Sengupta, Mariko DeWire -Schottmiller, Kalen Berry, Matthew Garrett, Maryam Fouladi, Rachid Drissi, Q Richard Lu.
      BACKGROUND: Diffuse intrinsic pontine glioma (DIPG) is a pediatric lethal high-grade brainstem glioma with no effective therapies. OLIG2 was reported to be critical for the growth of a DIPG cell line CCHMC-DIPG-1. Surprisingly, we found that the CCHMC-DIPG-1 cells express little OLIG2 and exhibit a mesenchymal phenotype, which raised a question regarding the role of OLIG2 in the growth of DIPG cells.METHODS: We evaluated the function of OLIG2 in different DIPG cell lines through molecular and genetic approaches and performed transcriptomic and genomic landscape profiling including whole-genome bisulfite-sequencing, RNA-seq, ATAC-seq, and ChIP-seq. shRNA-mediated knockdown and CRISPR-Cas9-mediated knockout approaches were utilized to assess OLIG2 functions in DIPG cell growth.
    RESULTS: We found that DIPG cells are phenotypically heterogeneous and exhibit the characteristics of distinct malignant gliomas including proneural, classical, and mesenchymal subtypes. OLIG2 knockdown did not impact the growth of CCHMC-DIPG-1 cells, wherein OLIG2 is epigenetically silenced. Moreover, OLIG2 deletion did not substantially impair OLIG2-expressing proneural-like DIPG growth but led to an upregulation of HIPPO-YAP1 and EGFR signaling and a tumor phenotype shift. Targeting HIPPO-YAP1 and EGFR signaling in OLIG2-deficient DIPG cells inhibited tumor cell growth.
    CONCLUSIONS: Our data indicate that OLIG2 is dispensable for DIPG growth but regulates the phenotypic switch of DIPG tumor cells. OLIG2 downregulation leads to deregulation of adaptive YAP1 and EGFR signaling. Targeting YAP1 and EGFR pathways inhibits the growth of OLIG2-deficient DIPG cells, pointing to a therapeutic potential by targeting adaptive signaling to treat DIPG tumors with nominal OLIG2 expression.
    Keywords:  Diffuse intrinsic pontine glioma (DIPG); OLIG2; YAP1 and EGFR signaling; distinct DIPG tumor phenotypes; genomic landscapes
    DOI:  https://doi.org/10.1093/neuonc/noab016
  3. Mol Cell. 2021 Jan 30. pii: S1097-2765(21)00015-0. [Epub ahead of print]
    PRMT6 methylation of RCC1 regulates mitosis, tumorigenicity, and radiation response of glioblastoma stem cells.
    Tianzhi Huang, Yongyong Yang, Xiao Song, Xuechao Wan, Bingli Wu, Namratha Sastry, Craig M Horbinski, Chang Zeng, Deanna Tiek, Anshika Goenka, Fabao Liu, Cameron W Brennan, John A Kessler, Roger Stupp, Ichiro Nakano, Erik P Sulman, Ryo Nishikawa, Charles David James, Wei Zhang, Wei Xu, Bo Hu, Shi-Yuan Cheng.
      Aberrant cell proliferation is a hallmark of cancer, including glioblastoma (GBM). Here we report that protein arginine methyltransferase (PRMT) 6 activity is required for the proliferation, stem-like properties, and tumorigenicity of glioblastoma stem cells (GSCs), a subpopulation in GBM critical for malignancy. We identified a casein kinase 2 (CK2)-PRMT6-regulator of chromatin condensation 1 (RCC1) signaling axis whose activity is an important contributor to the stem-like properties and tumor biology of GSCs. CK2 phosphorylates and stabilizes PRMT6 through deubiquitylation, which promotes PRMT6 methylation of RCC1, which in turn is required for RCC1 association with chromatin and activation of RAN. Disruption of this pathway results in defects in mitosis. EPZ020411, a specific small-molecule inhibitor for PRMT6, suppresses RCC1 arginine methylation and improves the cytotoxic activity of radiotherapy against GSC brain tumor xenografts. This study identifies a CK2α-PRMT6-RCC1 signaling axis that can be therapeutically targeted in the treatment of GBM.
    Keywords:  CK2; GBM; GSC; PRMT; RCC1; arginine methylation; mitosis; phosphorylation; therapy response; tumorigenicity
    DOI:  https://doi.org/10.1016/j.molcel.2021.01.015
  4. Cancers (Basel). 2021 Feb 01. pii: 542. [Epub ahead of print]13(3):
    The Role of Hypoxia in Glioblastoma Radiotherapy Resistance.
    Agathe L Chédeville, Patricia A Madureira.
      Glioblastoma (GB) (grade IV astrocytoma) is the most malignant type of primary brain tumor with a 16 months median survival time following diagnosis. Despite increasing attention regarding the development of targeted therapies for GB that resulted in around 450 clinical trials currently undergoing, radiotherapy still remains the most clinically effective treatment for these patients. Nevertheless, radiotherapy resistance (radioresistance) is commonly observed in GB patients leading to tumor recurrence and eventually patient death. It is therefore essential to unravel the molecular mechanisms underpinning GB cell radioresistance in order to develop novel strategies and combinational therapies focused on enhancing tumor cell sensitivity to radiotherapy. In this review, we present a comprehensive examination of the current literature regarding the role of hypoxia (O2 partial pressure less than 10 mmHg), a main GB microenvironmental factor, in radioresistance with the ultimate goal of identifying potential molecular markers and therapeutic targets to overcome this issue in the future.
    Keywords:  Hypoxia Inducible Factor (HIF); glioblastoma (GB); glioma stem cells (GSC); hypoxia; radioresistance; radiotherapy
    DOI:  https://doi.org/10.3390/cancers13030542
  5. Cancers (Basel). 2021 Feb 02. pii: 580. [Epub ahead of print]13(3):
    Molecular and Metabolic Mechanisms Underlying Selective 5-Aminolevulinic Acid-Induced Fluorescence in Gliomas.
    Jeffrey I Traylor, Mark N Pernik, Alex C Sternisha, Samuel K McBrayer, Kalil G Abdullah.
      5-aminolevulinic acid (5-ALA) is a porphyrin precursor in the heme synthesis pathway. When supplied exogenously, certain cancers consume 5-ALA and convert it to the fluorogenic metabolite protoporphyrin IX (PpIX), causing tumor-specific tissue fluorescence. Preoperative administration of 5-ALA is used to aid neurosurgical resection of high-grade gliomas such as glioblastoma, allowing for increased extent of resection and progression free survival for these patients. A subset of gliomas, especially low-grade tumors, do not accumulate PpIX intracellularly or readily fluoresce upon 5-ALA administration, making gross total resection difficult to achieve in diffuse lesions. We review existing literature on 5-ALA metabolism and PpIX accumulation to explore potential mechanisms of 5-ALA-induced glioma tissue fluorescence. Targeting the heme synthesis pathway and understanding its dysregulation in malignant tissues could aid the development of adjunct therapies to increase intraoperative fluorescence after 5-ALA treatment.
    Keywords:  5-ALA; high-grade glioma; intraoperative fluorescence; low-grade glioma; protoporphyrin IX
    DOI:  https://doi.org/10.3390/cancers13030580
  6. Neurooncol Adv. 2021 Jan-Dec;3(1):3(1): vdaa145
    Adult precision medicine: learning from the past to enhance the future.
    Ashley Ghiaseddin, Lan B Hoang Minh, Michalina Janiszewska, David Shin, Wolfgang Wick, Duane A Mitchell, Patrick Y Wen, Stuart A Grossman.
      Despite therapeutic advances for other malignancies, gliomas remain challenging solid tumors to treat. Complete surgical resection is nearly impossible due to gliomas' diffuse infiltrative nature, and treatment is hampered by restricted access to the tumors due to limited transport across the blood-brain barrier. Recent advances in genomic studies and next-generation sequencing techniques have led to a better understanding of gliomas and identification of potential aberrant signaling pathways. Targeting the specific genomic abnormalities via novel molecular therapies has opened a new avenue in the management of gliomas, with encouraging results in preclinical studies and early clinical trials. However, molecular characterization of gliomas revealed significant heterogeneity, which poses a challenge for targeted therapeutic approaches. In this context, leading neuro-oncology researchers and clinicians, industry innovators, and patient advocates convened at the inaugural annual Remission Summit held in Orlando, FL in February 2019 to discuss the latest advances in immunotherapy and precision medicine approaches for the treatment of adult and pediatric brain tumors and outline the unanswered questions, challenges, and opportunities that lay ahead for advancing the duration and quality of life for patients with brain tumors. Here, we provide historical context for precision medicine in other cancers, present emerging approaches for gliomas, discuss their limitations, and outline the steps necessary for future success. We focus on the advances in small molecule targeted therapy, as the use of immunotherapy as an emerging precision medicine modality for glioma treatment has recently been reviewed by our colleagues.
    Keywords:  blood–brain barrier (BBB); glioma; next-generation sequencing (NGS); precision medicine; tumor heterogeneity
    DOI:  https://doi.org/10.1093/noajnl/vdaa145
  7. Sci Rep. 2021 Feb 03. 11(1): 2913
    Differentiation of recurrent glioblastoma from radiation necrosis using diffusion radiomics with machine learning model development and external validation.
    Yae Won Park, Dongmin Choi, Ji Eun Park, Sung Soo Ahn, Hwiyoung Kim, Jong Hee Chang, Se Hoon Kim, Ho Sung Kim, Seung-Koo Lee.
      The purpose of this study was to establish a high-performing radiomics strategy with machine learning from conventional and diffusion MRI to differentiate recurrent glioblastoma (GBM) from radiation necrosis (RN) after concurrent chemoradiotherapy (CCRT) or radiotherapy. Eighty-six patients with GBM were enrolled in the training set after they underwent CCRT or radiotherapy and presented with new or enlarging contrast enhancement within the radiation field on follow-up MRI. A diagnosis was established either pathologically or clinicoradiologically (63 recurrent GBM and 23 RN). Another 41 patients (23 recurrent GBM and 18 RN) from a different institution were enrolled in the test set. Conventional MRI sequences (T2-weighted and postcontrast T1-weighted images) and ADC were analyzed to extract 263 radiomic features. After feature selection, various machine learning models with oversampling methods were trained with combinations of MRI sequences and subsequently validated in the test set. In the independent test set, the model using ADC sequence showed the best diagnostic performance, with an AUC, accuracy, sensitivity, specificity of 0.80, 78%, 66.7%, and 87%, respectively. In conclusion, the radiomics models models using other MRI sequences showed AUCs ranging from 0.65 to 0.66 in the test set. The diffusion radiomics may be helpful in differentiating recurrent GBM from RN..
    DOI:  https://doi.org/10.1038/s41598-021-82467-y
  8. Cancer Cell. 2021 Jan 29. pii: S1535-6108(21)00049-0. [Epub ahead of print]
    H3.3-K27M drives neural stem cell-specific gliomagenesis in a human iPSC-derived model.
    Daniel Haag, Norman Mack, Patricia Benites Goncalves da Silva, Britta Statz, Jessica Clark, Koji Tanabe, Tanvi Sharma, Natalie Jäger, David T W Jones, Daisuke Kawauchi, Marius Wernig, Stefan M Pfister.
      Diffuse intrinsic pontine glioma (DIPG) is an aggressive childhood tumor of the brainstem with currently no curative treatment available. The vast majority of DIPGs carry a histone H3 mutation leading to a lysine 27-to-methionine exchange (H3K27M). We engineered human induced pluripotent stem cells (iPSCs) to carry an inducible H3.3-K27M allele in the endogenous locus and studied the effects of the mutation in different disease-relevant neural cell types. H3.3-K27M upregulated bivalent promoter-associated developmental genes, producing diverse outcomes in different cell types. While being fatal for iPSCs, H3.3-K27M increased proliferation in neural stem cells (NSCs) and to a lesser extent in oligodendrocyte progenitor cells (OPCs). Only NSCs gave rise to tumors upon induction of H3.3-K27M and TP53 inactivation in an orthotopic xenograft model recapitulating human DIPGs. In NSCs, H3.3-K27M leads to maintained expression of stemness and proliferative genes and a premature activation of OPC programs that together may cause tumor initiation.
    Keywords:  DIPG; H3.3-K27M; H3K27me3; H3K4me3; NSC; OPC; bivalent chromatin; glioma; iPSC; orthotopic xenograft
    DOI:  https://doi.org/10.1016/j.ccell.2021.01.005
  9. Sci Adv. 2021 Feb;pii: eabd0772. [Epub ahead of print]7(6):
    Neuronavigation-guided focused ultrasound for transcranial blood-brain barrier opening and immunostimulation in brain tumors.
    Ko-Ting Chen, Wen-Yen Chai, Ya-Jui Lin, Chia-Jung Lin, Pin-Yuan Chen, Hong-Chieh Tsai, Chiung-Yin Huang, John S Kuo, Hao-Li Liu, Kuo-Chen Wei.
      Focused ultrasound (FUS) in the presence of microbubbles can transiently open the blood-brain barrier (BBB) to increase therapeutic agent penetration at the targeted brain site to benefit recurrent glioblastoma (rGBM) treatment. This study is a dose-escalating pilot trial using a device combining neuronavigation and a manually operated frameless FUS system to treat rGBM patients. The safety and feasibility were established, while a dose-dependent BBB-opening effect was observed, which reverted to baseline within 24 hours after treatment. No immunological response was observed clinically under the applied FUS level in humans; however, selecting a higher level in animals resulted in prolonged immunostimulation, as confirmed preclinically by the recruitment of lymphocytes into the tumor microenvironment (TME) in a rat glioma model. Our findings provide preliminary evidence of FUS-induced immune modulation as an additional therapeutic benefit by converting the immunosuppressive TME into an immunostimulatory TME via a higher but safe FUS dosage.
    DOI:  https://doi.org/10.1126/sciadv.abd0772
  10. FEBS J. 2021 Feb 01.
    Pediatric High-Grade Glioma: Moving Toward Subtype-Specific Multimodal Therapy.
    Hannah V Chatwin, Joselyn Cruz Cruz, Adam L Green.
      Pediatric high grade gliomas (pHGG) comprise a deadly, heterogenous category of pediatric gliomas with a clear need for more effective treatment options. Advances in high-throughput molecular techniques have enhanced molecular understanding of these tumors, but outcomes are still poor, and treatments beyond resection and radiation have not yet been clearly established as standard of care. In this review, we first discuss the history of treatment approaches to pHGG to this point. We then review four distinct categories of pHGG, including histone 3-mutant, IDH-mutant, histone 3/IDH-wildtype, and radiation-induced pHGG. We discuss the molecular understanding of each subgroup and targeted treatment options in development. Finally, we look at the development and current status of two novel approaches to pHGG as a whole: localized convection-enhanced chemotherapy delivery, and immunotherapy, including checkpoint inhibitors, vaccine therapy, and CAR-T cells. Through this review, we demonstrate the potential for rational, molecularly driven, subtype-specific therapy to be used with other novel approaches in combinations that could meaningfully improve the prognosis in pHGG.
    Keywords:  convection-enhanced delivery; immunotherapy; pediatric high-grade glioma; radiation-induced glioma
    DOI:  https://doi.org/10.1111/febs.15739
  11. Nat Nanotechnol. 2021 Feb 01.
    Immunostimulant hydrogel for the inhibition of malignant glioma relapse post-resection.
    Jing Zhang, Chen Chen, Anning Li, Weiqiang Jing, Peng Sun, Xueyang Huang, Yingchao Liu, Shengchang Zhang, Wei Du, Rui Zhang, Ying Liu, Aihua Gong, Jibiao Wu, Xinyi Jiang.
      Immunotherapies have revolutionized intervention strategies for many primary cancers, but have not improved the outcomes of glioblastoma multiforme (GBM), which remains one of the most lethal malignant cerebral tumours. Here we present an injectable hydrogel system that stimulates tumoricidal immunity after GBM surgical resection, which mitigates its relapse. The hydrogel comprises a tumour-homing immune nanoregulator, which induces immunogenic cell death and suppression of indoleamine 2,3-dioxygenase-1, and chemotactic CXC chemokine ligand 10, for a sustained T-cell infiltration. When delivered in the resected tumour cavity, the hydrogel system mimics a 'hot' tumour-immunity niche for attacking residual tumour cells and significantly suppresses postoperative GBM recurrence. Our work provides an alternative strategy for conferring effective tumoricidal immunity in GBM patients, which may have a broad impact in the immunotherapy of 'cold' tumours after surgical intervention.
    DOI:  https://doi.org/10.1038/s41565-020-00843-7
  12. Clin Cancer Res. 2021 Feb 04. pii: clincanres.3262.2020. [Epub ahead of print]
    Preclinical modeling of surgery and steroid therapy for glioblastoma reveals changes in immunophenotype that are associated with tumor growth and outcome.
    Balint Otvos, Tyler J Alban, Matthew M Grabowski, Defne Bayik, Erin E Mulkearns-Hubert, Tomas Radivoyevitch, Anja Rabljenovic, Sarah Johnson, Charlie Androjna, Alireza M Mohammadi, Gene H Barnett, Manmeet S Ahluwalia, Michael A Vogelbaum, Peter E Fecci, Justin D Lathia.
      PURPOSE: Glioblastoma (GBM) immunotherapy clinical trials are generally initiated after standard-of-care treatment, including surgical resection, perioperative high-dose steroid therapy, chemotherapy, and radiation treatment, has either begun or failed. However, the impact of these interventions on the anti-tumoral immune response is not well studied. While discoveries regarding the impact of chemotherapy and radiation on immune response have been made and translated into clinical trial design, the impact of surgical resection and steroids on the anti-tumor immune response has yet to be determined.EXPERIMENTAL DESIGN: We developed a murine model integrating tumor resection and steroid treatment and used flow cytometry to analyze systemic and local immune changes. These mouse model findings were validated in a cohort of 95 primary GBM patients.
    RESULTS: Using our murine resection model, we observed a systemic reduction in lymphocytes corresponding to increased tumor volume and decreased circulating lymphocytes that was masked by dexamethasone treatment. The reduction in circulating T cells was due to reduced CCR7 expression, resulting in T-cell sequestration in lymphoid organs and the bone marrow. We confirmed these findings in a cohort of primary GBM patients and found that prior to steroid treatment, circulating lymphocytes inversely correlated with tumor volume. Lastly, we demonstrated that peripheral lymphocyte content varies with progression-free and overall survival, independent of tumor volume, steroid use, or molecular profiles.
    CONCLUSIONS: These data reveal that prior to intervention, increased tumor volume corresponds with reduced systemic immune function and that peripheral lymphocyte counts are prognostic when steroid treatment is taken into account.
    DOI:  https://doi.org/10.1158/1078-0432.CCR-20-3262
  13. STAR Protoc. 2021 Mar 19. 2(1): 100290
    Intranasal delivery of experimental compounds in orthotopic brain tumor mouse models.
    Katharina M Eyme, Litia Carvalho, Christian E Badr.
      Effective therapeutics for malignant primary brain tumors, such as glioblastomas (GBMs), are urgently needed. To facilitate and expedite early-phase GBM therapeutic development, we describe a protocol that allows the intranasal delivery of experimental compounds in GBM orthotopic mouse models. Compounds delivered through this route can bypass the blood-brain barrier and thus help validate effective therapeutic targets for GBMs. For complete details on the use and execution of this protocol, please refer to Pinkham et al. (2019).
    Keywords:  Cancer; Model organisms; Neuroscience
    DOI:  https://doi.org/10.1016/j.xpro.2020.100290
  14. Cancer Res. 2021 Feb 02. pii: canres.1037.2020. [Epub ahead of print]
    Premalignant oligodendrocyte precursor cells stall in a heterogeneous state of replication stress prior to gliomagenesis.
    Matthew D Sutcliffe, Rui P Galvao, Lixin Wang, Jungeun Kim, Lauren K Rosenfeld, Shambhavi Singh, Hui Zong, Kevin A Janes.
      Cancer evolves from premalignant clones that accumulate mutations and adopt unusual cell states to achieve transformation. We previously pinpointed the oligodendrocyte precursor cell (OPC) as a cell-of-origin for glioma, but the early changes of mutant OPCs during premalignancy remained unknown. Using mice engineered for inducible Nf1-Trp53 loss in OPCs, we acutely isolated labeled mutant OPCs by laser-capture microdissection and determined gene expression changes by bulk RNA sequencing and a fluctuation analysis called stochastic profiling, which uses RNA-sequencing measurements from random pools of 10 mutant cells. At 12 days after Nf1-Trp53 deletion, bulk differences were mostly limited to mitotic hallmarks and genes for ribosome biosynthesis, and stochastic profiling revealed a spectrum of stem-progenitor (Axl, Aldh1a1), proneural, and mesenchymal states as potential starting points for gliomagenesis. At 90 days, bulk sequencing detected few differentially expressed transcripts, whereas stochastic profiling revealed cell states for neurons and mural cells that do not give rise to glial tumors, suggesting cellular dead-ends for gliomagenesis. Importantly, mutant OPCs that strongly expressed key effectors of nonsense-mediated decay (Upf3b) and homology-dependent DNA repair (Rad51c, Slx1b, Ercc4) were identified along with DNA-damage markers, suggesting transcription-associated replication stress. Analysis of 10-cell transcriptomes at 90 days identified a locus of elevated gene expression containing an additional repair endonuclease (Mus81) and Rin1, a Ras-Raf antagonist and possible counterbalance to Nf1 loss. At 150 days, Rin1 was microdeleted in some gliomas and downregulated in all others. In summary, replication stress may pose a considerable bottleneck that must be resolved for glioma initiation.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-20-1037
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