Chemoresistance in High-Grade Gliomas: Relevance of Adenosine Signalling in Stem-Like Cells of Glioblastoma Multiforme

Investigative needle core biopsies for multi-omics in Glioblastoma

Glioblastoma (GBM) is a primary brain cancer with an abysmal prognosis and few effective therapies. The ability to investigate the tumor microenvironment before and during treatment would greatly enhance both understanding of disease response and progression, as well as the delivery and impact of therapeutics. Stereotactic biopsies are a routine surgical procedure performed primarily for diagnostic histopathologic purposes. The role of investigative biopsies - tissue sampling for the purpose of understanding tumor microenvironmental responses to treatment using integrated multi-modal molecular analyses ('Multi-omics") has yet to be defined. Secondly, it is unknown whether comparatively small tissue samples from brain biopsies can yield sufficient information with such methods. Here we adapt stereotactic needle core biopsy tissue in two separate patients. In the first patient with recurrent GBM we performed highly resolved multi-omics analysis methods including single cell RNA sequencing, spatial-transcriptomics, metabolomics, proteomics, phosphoproteomics, T-cell clonotype analysis, and MHC Class I immunopeptidomics from biopsy tissue that was obtained from a single procedure. In a second patient we analyzed multi-regional core biopsies to decipher spatial and genomic variance. We also investigated the utility of stereotactic biopsies as a method for generating patient derived xenograft models in a separate patient cohort. Dataset integration across modalities showed good correspondence between spatial modalities, highlighted immune cell associated metabolic pathways and revealed poor correlation between RNA expression and the tumor MHC Class I immunopeptidome. In conclusion, stereotactic needle biopsy cores are of sufficient quality to generate multi-omics data, provide data rich insight into a patient's disease process and tumor immune microenvironment and can be of value in evaluating treatment responses.

One sentence summary

Integrative multi-omics analysis of stereotactic needle core biopsies in glioblastoma.

STAT3 mediated upregulation of C-MET signaling acts as a compensatory survival mechanism upon EGFR family inhibition in chemoresistant breast cancer cells

Chemotherapy remains the most common treatment for all types of breast cancer. Chemoresistance in tumors is still a major obstacle for treating late-stage breast cancer. In the process of acquiring resistance, tumor cells dynamically evolve to adapt to the challenge of anti-cancer drugs. Besides the upregulation of drug-pumps, signal pathways related to proliferation and survival undergo adaptive evolution. Thus, these drug-resistant cells are more conducive to proliferation, even in stressful conditions. Nevertheless, the detailed mechanism that drives cancer cells to sustain their proliferation ability is unclear. Herein, we reported that the upregulated C-MET signaling acts as a compensatory mechanism that sustains the proliferation of chemoresistant cells in which EGFR family signaling was attenuated. Both C-MET and EGFR family are essential for cell proliferation due to their activation of the STAT3 signaling. Different from other cell models in which C-MET interacts with and phosphorylates EGFR family members, our cell model showed no direct interaction between C-MET and EGFR family members. Therefore, C-MET and EGFR family signaling pathways function independently to sustain the proliferation of resistant cells. Moreover, chemoresistant cells have evolved a novel, STAT3-C-MET feed-forward loop that plays a vital role in sustaining cell proliferation. The activated STAT3 interacts with the MET gene promoter to upregulate its transcription. Most importantly, the combined inhibition of C-MET and EGFR family synergistically inhibits the proliferation of drug-resistant cells in vitro and in xenograft tumor models. This work provides a new strategy for treating drug-resistant breast cancer.

Autophagy Induction by Trichodermic Acid Attenuates Endoplasmic Reticulum Stress-Mediated Apoptosis in Colon Cancer Cells

Colorectal cancer (CRC) is the third leading malignant tumor in the world, which has high morbidity and mortality. In this study we found that trichodermic acid (TDA), a secondary metabolite isolated from the plant endophytic fungus Penicillium ochrochloronthe with a variety of biological and pharmacological activities, exhibited the antitumor effects on colorectal cancer cells in vitro and in vivo. Our results showed that TDA inhibited the proliferation of colon cancer cells in a dose-dependent manner. TDA induces sustained endoplasmic reticulum stress, which triggers apoptosis through IRE1α/XBP1 and PERK/ATF4/CHOP pathways. In addition, we found that TDA mediated endoplasmic reticulum stress also induces autophagy as a protective mechanism. Moreover, combined treatment of TDA with autophagy inhibitors significantly enhanced its anticancer effect. In conclusion, our results indicated that TDA can induce ER stress and autophagy mediated apoptosis, suggesting that targeting ER stress and autophagy may be an effective strategy for the treatment of CRC.

A Systematic Review of Glioblastoma-Targeted Therapies in Phases II, III, IV Clinical Trials

Glioblastoma (GBM), the most frequent and aggressive glial tumor, is currently treated as first line by the Stupp protocol, which combines, after surgery, radiotherapy and chemotherapy. For recurrent GBM, in absence of standard treatment or available clinical trials, various protocols including cytotoxic drugs and/or bevacizumab are currently applied. Despite these heavy treatments, the mean overall survival of patients is under 18 months. Many clinical studies are underway. Based on clinicaltrials.org and conducted up to 1 April 2020, this review lists, not only main, but all targeted therapies in phases II-IV of 257 clinical trials on adults with newly diagnosed or recurrent GBMs for the last twenty years. It does not involve targeted immunotherapies and therapies targeting tumor cell metabolism, that are well documented in other reviews. Without surprise, the most frequently reported drugs are those targeting (i) EGFR (40 clinical trials), and more generally tyrosine kinase receptors (85 clinical trials) and (ii) VEGF/VEGFR (75 clinical trials of which 53 involving bevacizumab). But many other targets and drugs are of interest. They are all listed and thoroughly described, on an one-on-one basis, in four sections related to targeting (i) GBM stem cells and stem cell pathways, (ii) the growth autonomy and migration, (iii) the cell cycle and the escape to cell death, (iv) and angiogenesis.

In vitro biomimetic models for glioblastoma-a promising tool for drug response studies

The poor response of glioblastoma to current treatment protocols is a consequence of its intrinsic drug resistance. Resistance to chemotherapy is primarily associated with considerable cellular heterogeneity, and plasticity of glioblastoma cells, alterations in gene expression, presence of specific tumor microenvironment conditions and blood-brain barrier. In an attempt to successfully overcome chemoresistance and better understand the biological behavior of glioblastoma, numerous tri-dimensional (3D) biomimetic models were developed in the past decade. These novel advanced models are able to better recapitulate the spatial organization of glioblastoma in a real time, therefore providing more realistic and reliable evidence to the response of glioblastoma to therapy. Moreover, these models enable the fine-tuning of different tumor microenvironment conditions and facilitate studies on the effects of the tumor microenvironment on glioblastoma chemoresistance. This review outlines current knowledge on the essence of glioblastoma chemoresistance and describes the progress achieved by 3D biomimetic models. Moreover, comprehensive literature assessment regarding the influence of 3D culturing and microenvironment mimicking on glioblastoma gene expression and biological behavior is also provided. The contribution of the blood-brain barrier as well as the blood-tumor barrier to glioblastoma chemoresistance is also reviewed from the perspective of 3D biomimetic models. Finally, the role of mathematical models in predicting 3D glioblastoma behavior and drug response is elaborated. In the future, technological innovations along with mathematical simulations should create reliable 3D biomimetic systems for glioblastoma research that should facilitate the identification and possibly application in preclinical drug testing and precision medicine.

The Selective Acetamidine-Based iNOS Inhibitor CM544 Reduces Glioma Cell Proliferation by Enhancing PARP-1 Cleavage In Vitro

Gliomas are the most aggressive adult primary brain tumors. Expression of inducible Nitric Oxide Synthase has been reported as a hallmark of chemoresistance in gliomas and several studies have reported that inhibition of inducible Nitric Oxide Synthase could be related to a decreased proliferation of glioma cells. The present work was to analyze the molecular effects of the acetamidine derivative compound 39 (formally CM544, N-(3-{[(1-iminioethyl)amino]methyl}benzyl) prolinamide dihydrochloride), a newly synthetized iNOS inhibitor, in a C6 rat glioma cell model. There is evidence of CM544 selective binding to the iNOS, an event that triggers the accumulation of ROS/RNS, the expression of Nrf-2 and the phosphorylation of MAPKs after 3 h of treatment. In the long run, CM544 leads to the dephosphorylation of p38 and to a massive cleavage of PARP-1, confirming the block of C6 rat glioma cell proliferation in the G1/S checkpoint and the occurrence of necrotic cell death.

Extracellular adenosine promotes cell migration/invasion of Glioblastoma Stem-like Cells through A3 Adenosine Receptor activation under hypoxia

Glioblastoma (GBM) is the brain tumor with the worst prognosis composed of a cell subpopulation called Glioblastoma Stem-like Cells (GSCs) responsible for tumor recurrence mediated by cell invasion. GSCs persist in a hypoxic microenvironment which promotes extracellular adenosine production and activation of the A₃ Adenosine Receptor (A₃AR), therefore, the aim of this study was to determine the role of extracellular adenosine and A₃AR on GSCs invasion under hypoxia. GSCs were obtained from a U87MG cell line and primary cultures of GBM patients, and then incubated under normoxia or hypoxia. Gene expression was evaluated by RNAseq, RT-qPCR, and western blot. Cell migration was measured by spreading and transwell boyden chamber assays; cell invasion was evaluated by Matrigel-coated transwell, ex vivo brain slice, and in vivo xenograft assays. The contribution of A₃AR on cell migration/invasion was evaluated using the A₃AR antagonist, MRS1220. Extracellular adenosine production was higher under hypoxia than normoxia, mainly by the catalytic action of the prostatic acid phosphatase (PAP), promoting cell migration/invasion in a HIF-2-dependent process. A₃AR blockade decreased cell migration/invasion and the expression of Epithelial-Mesenchymal Transition markers. In conclusion, high levels of extracellular adenosine production enhance cell migration/invasion of GSCs, through HIF-2/PAP-dependent activation of A₃AR under hypoxia.

Zinc-doped copper oxide nanocomposites reverse temozolomide resistance in glioblastoma by inhibiting AKT and ERK1/2

AIM

To assess the effect of zinc-doped copper oxide nanocomposites (nZn-CuO NPs) on glioblastoma therapy.

MATERIALS & METHODS

nZn-CuO NPs were synthesized by sonochemical method and its antitumor effects and underlying molecular mechanisms were investigated both in vitro and in vivo.

RESULTS

After nZn-CuO NPs treatment, cell proliferation was significantly inhibited in dividing cancer cells but less toxicity was observed in normal cells. In vivo studies show that nZn-CuO NPs inhibited tumor growth in a dose-dependent manner. Further study found that nZn-CuO NPs trigger cell reactive oxygen species (ROS) generation and intrinsic apoptotic pathway. In temozolomide resistance glioblastoma, nZn-CuO NPs disturb cell growth and sphere formation by inhibiting AKT and ERK1/2 activation.

CONCLUSION

nZn-CuO NPs possess the potential to be developed as a novel anti-tumor agent, especially to treat temozolomide resistance glioblastoma.

Decane-1,2-diol derivatives as potential antitumor agents for the treatment of glioblastoma

Glioblastoma remains the most common and aggressive type of malignant brain tumor among adults thus, considerable attention has been given to discovery of novel anti-tumor drugs for its treatment. This study reports the synthesis of a series of twelve novel decane-1,2-diol derivatives and evaluation of its anti-tumor activity in mammalian glioblastoma cell lines, U87 and LN229. Starting from decane-1,2-diol, several derivatives were prepared using a diversity oriented synthesis approach through which a small library composed of esters, silyl ethers, sulfonates, sulfites, sulfates, ketals, and phosphonates was built. The decane-1,2-diol ditosylated derivative, DBT, found to have higher cytotoxicity than the standard drug cisplatin, has IC₅₀ value of 52 µM in U87 and 270 µM in LN229. Migration analysis of U87 cell line treated with the DBT indicated its ability to effectively suppress proliferation during initial hours of treatment and decrease anti-proliferative property over time. Additionally, DBT was assessed for its role in apoptosis, oxidative stress and caspase 3/7 activation in U87. Interestingly, our experiments indicated that its cytotoxicity is independent of Reactive oxygen species induced caspase 3/7 activity. The compound also exhibited caspase independent apoptosis activity in U87. DBT treatment led to G1/S cell cycle arrest and apoptosis induction of glioma cell lines. In addition, we identified 1533 genes with significant changes at the transcriptional level, in response to DBT. A molecular docking study accounting for the interaction of DBT with NMDA receptor disclosed several hydrogen bonds and charged residue interactions with 17 amino acids, which might be the basis of the DBT cytotoxicity observed. We conclude that this molecule exerts its cytotoxicity via caspase 3/7 independent pathways in glioblastoma cells. Concisely, simple decane-1,2-diol derivatives might serve as scaffolds for the development of effective anti-glioblastoma agents.

Inhibition of glioma growth by flavokawain B is mediated through endoplasmic reticulum stress induced autophagy

Flavokawain B (FKB), a natural kava chalcone, displays potent antitumor activity in various types of cancer. The mechanism of action, however, remains unclear. Here, we evaluated the efficacy of FKB in the treatment of human glioblastoma multiforme (GBM) as well as the molecular basis for its inhibitory effects in cancer. Approximately 60% of GBM cells became senescent after treatment with FKB as assessed in the senescence-associated (SA)-GLB1/SA-β-galactosidase assay. The cellular process of autophagy potentially contributed to the establishment of senescence. Transmission electron microscopy revealed the formation of autophagic vesicles under FKB treatment, and MAP1LC3B (microtubule associated protein 1 light chain 3 beta)-II was increased. Transfection of ATG5 or ATG7 small interfering RNAs (siRNAs) inhibited FKB-induced autophagy in U251 cells. Western blot revealed that molecular components of the endoplasmic reticulum stress pathway were activated, including ATF4 (activating transcription factor 4) and DDIT3 (DNA damage inducible transcript 3), while levels of TRIB3 (tribbles pseudokinase 3) increased. In addition, based on the phosphorylation status, the AKT-MTOR-RPS6KB1 pathway was inhibited, which induced autophagy in GBM cells. Inhibition of autophagy by autophagy inhibitors 3-methyladenine and chloroquine or knockdown of ATG5 or ATG7 caused FKB-treated U251 cells to switch from senescence to apoptosis. Finally, knockdown of ATG5 or treatment with chloroquine in combination with FKB, significantly inhibited tumor growth in vivo. Our results demonstrated that FKB induced protective autophagy through the ATF4-DDIT3-TRIB3-AKT-MTOR-RPS6KB1 signaling pathway in GBM cells, indicating that the combination treatment of FKB with autophagy inhibitors may potentially be an effective therapeutic strategy for GBM.

ABBREVIATIONS

3-MA: 3-methyladenine; 4-PBA: 4-phenylbutyrate; AKT: AKT serine/threonine kinase; ATF4: activating transcription factor 4; ATG: autophagy related; CASP3: caspase 3; CCK-8: cell counting kit-8; CDKN1A: cyclin-dependent kinase inhibitor 1A; CQ: chloroquine; DDIT3: DNA damage inducible transcript 3; DMEM: Dulbecco's modified Eagle's medium; EIF2A: eukaryotic translation initiation factor 2A; EIF2AK3: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; FKB: flavokawain B; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GBM: glioblastoma multiforme; GFP: green fluorescent protein; HSPA5: heat shock protein family A (Hsp70) member 5; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; PARP1: poly(ADP-ribose) polymerase; 1RPS6KB1: ribosomal protein S6 kinase B1; SA-GLB1: senescence-associated galactosidase beta 1; siRNA: short interfering RNA; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TRIB3: tribbles pseudokinase 3; TUNEL: deoxynucleotidyl transferase-mediated dUTP nick-end labeling.

PARP1 expression and its correlation with survival is tumour molecular subtype dependent in glioblastoma

Overexpression of PARP1 exists in various cancers, including glioblastoma (GBM). Although PARP1 inhibition is a promising therapeutic target, no comprehensive study has addressed PARP1's expression characteristics and prognostic role regarding molecular heterogeneity in astrocytomas including GBM. Our aim was to evaluate PARP1's associations with survival, WHO grade, lineage specific markers, and GBM transcriptomic subtypes. We collected genomic and clinical data from the latest glioma datasets of The Cancer Genome Atlas and performed PARP1, ATRX, IDH1, and p53 immunohistochemistry on GBM tissue samples. We demonstrated that PARP1 gain and increased mRNA expression are characteristics of high-grade astrocytomas, particularly of Proneural and Classical GBM subtypes. Additionally, higher PARP1 levels exhibited an inverse correlation with patient survival (p<0.005) in the Classical subgroup. ATRX (p=0.006), and TP53 (p=0.015) mutations were associated with increased PARP1 expression and PARP1 protein level correlated with ATRX loss and p53 overexpression. Furthermore, higher PARP1 expression together with wildtype TP53 indicated shorter survival (p=0.039). Therefore, due to subtype specificity, PARP1 expression level and TP53 mutation status are reliable marker candidates to distinguish Proneural and Classical subtypes, with prognostic and therapeutic implications in GBM.

ABC Transporters in Cancer Stem Cells: Beyond Chemoresistance

The efficacy of chemotherapy is one of the main challenges in cancer treatment and one of the major obstacles to overcome in achieving lasting remission and a definitive cure in patients with cancer is the emergence of cancer resistance. Indeed, drug resistance is ultimately accountable for poor treatment outcomes and tumour relapse. There are various molecular mechanisms involved in multidrug resistance, such as the change in the activity of membrane transporters primarily belonging to the ATP binding cassette (ABC) transporter family. In addition, it has been proposed that this common feature could be attributed to a subpopulation of slow-cycling cancer stem cells (CSCs), endowed with enhanced tumorigenic potential and multidrug resistance. CSCs are characterized by the overexpression of specific surface markers that vary in different cancer cell types. Overexpression of ABC transporters has been reported in several cancers and more predominantly in CSCs. While the major focus on the role played by ABC transporters in cancer is polarized by their involvement in chemoresistance, emerging evidence supports a more active role of these proteins, in which they release specific bioactive molecules in the extracellular milieu. This review will outline our current understanding of the role played by ABC transporters in CSCs, how their expression is regulated and how they support the malignant metabolic phenotype. To summarize, we suggest that the increased expression of ABC transporters in CSCs may have precise functional roles and provide the opportunity to target, particularly these cells, by using specific ABC transporter inhibitors.

Multidrug resistance in glioblastoma stem-like cells: Role of the hypoxic microenvironment and adenosine signaling

Glioblastoma multiforme (GBM) is considered the most common and aggressive tumour of the central nervous system and is characterized for being highly chemoresistant. This property is mainly due to the activation of Multiple Drug Resistance (MDR) mechanisms that protect cancer cells from structurally and morphologically different drugs. Overexpression and increased ABC transporters activity is one of the most important MDR mechanisms at the clinical level, and both its expression and activity are elevated in GBM cells. Within the tumour, there is a subpopulation called glioblastoma stem-like cells (GSCs), which due to its high tumourigenic capacity and chemoresistance, have been postulated as the main responsible for tumour recurrence. The GSCs inhabit hypoxic tumour zones, niches that apart from maintaining and promoting stem phenotype have also been correlated with high chemoresistance. Of the signalling pathways activated during hypoxia, purinergic signalling has been highly associated to the induction of MDR mechanisms. Through its receptors, the nucleoside adenosine has been shown to promotes the chemoresistance mediated by ABC transporters. Therefore, targeting its components is a promising alternative for GBM treatment. In this review, we will discuss chemoresistance in GSCs and the effect of the hypoxic microenvironment and adenosine on MDR mechanisms.

VB-111: a novel anti-vascular therapeutic for glioblastoma multiforme

Glioblastoma multiforme (GBM) is among the most highly vascularized of solid tumors, contributing to the infiltrative nature of the disease, and conferring poor outcome. Due to the critical dependency of GBM on growth of new endothelial vasculature, we evaluated the preclinical activity of a novel adenoviral gene therapy that targets the endothelium within newly formed blood vessels for apoptosis. VB-111, currently in phase II clinical trials, consists of a non-replicating Adenovirus 5 (El deleted) carrying a proapoptotic human Fas-chimera (transgene) under the control of a modified murine promoter (PPE-1-3×) which specifically targets endothelial cells within the tumor vasculature. Here we report that a single intravenous dose of 2.5 × 10(11) or 1 × 10(11) VPs was sufficient to extend survival in nude rats bearing U87MG-luc2 or nude mice bearing U251-luc, respectively. Bioluminescence imaging of nude rats showed that VB-111 effectively inhibited tumor growth within four weeks of treatment. This was confirmed in a select group of animals by MRI. In our mouse model we observed that 3 of 10 nude mice treated with VB-111 completely lost U251 luciferase signal and were considered long term survivors. To assess the antiangiogenic effects of VB-111, we evaluated the tumor-associated microvaculature by CD31, a common marker of neovascularization, and found a significant decrease in the microvessel density by IHC. We further assessed the neovasculature by confocal microscopy and found that VB-111 inhibits vascular density in two separate mouse models bearing U251-RFP xenografts. Collectively, this study supports the clinical development of VB-111 as a treatment for GBM.

Convection-enhanced delivery for glioblastoma: targeted delivery of antitumor therapeutics

Glioblastoma is the most common primary brain tumor in adults and carries a dismal prognosis despite advancements in treatment. Diffuse tumor infiltration precludes curative surgical resection and necessitates advancements in drug delivery mechanisms. Convection-enhanced delivery (CED) enables continuous local drug delivery for a diverse population of antitumor agents. Importantly, CED circumvents therapeutic challenges posed by the blood-brain barrier by facilitating concentrated local therapeutic drug delivery with limited systemic effects. Here, we present a concise review of properties essential for safe and efficient convection-enhanced drug delivery, as well as a focused review of clinical studies evaluating CED in the treatment of glioblastoma.

Proton pump inhibitors while belonging to the same family of generic drugs show different anti-tumor effect

CONTEXT

Tumor acidity represents a major cause of chemoresistance. Proton pump inhibitors (PPIs) can neutralize tumor acidity, sensitizing cancer cells to chemotherapy.

OBJECTIVE

To compare the anti-tumor efficacy of different PPIs in vitro and in vivo.

MATERIALS AND METHODS

In vitro experiments PPIs anti-tumor efficacy in terms of cell proliferation and cell death/apoptosis/necrosis evaluation were performed. In vivo PPIs efficacy experiments were carried out using melanoma xenograft model in SCID mice.

RESULTS

Lansoprazole showed higher anti-tumor effect when compared to the other PPIs. The lansoprazole effect lasted even upon drug removal from the cell culture medium and it was independent from the lipophilicity of the PPIs formulation.

DISCUSSION

These PPIs have shown different anti-tumoral efficacy, and the most effective at low dose was lansoprazole.

CONCLUSION

The possibility to contrast tumor acidity by off-label using PPIs opens a new field of oncology investigation.

Biomarkers for glioma immunotherapy: the next generation

The term "biomarker" historically refers to a single parameter, such as the expression level of a gene or a radiographic pattern, used to indicate a broader biological state. Molecular indicators have been applied to several aspects of cancer therapy: to describe the genotypic and phenotypic state of neoplastic tissue for prognosis, to predict susceptibility to anti-proliferative agents, to validate the presence of specific drug targets, and to evaluate responsiveness to therapy. For glioblastoma (GBM), immunohistochemical and radiographic biomarkers accessible to the clinical lab have informed traditional regimens, but while immunotherapies have emerged as potentially disruptive weapons against this diffusely infiltrating, heterogeneous tumor, biomarkers with strong predictive power have not been fully established. The cancer immunotherapy field, through the recently accelerated expansion of trials, is currently leveraging this wealth of clinical and biological data to define and revise the use of biomarkers for improving prognostic accuracy, personalization of therapy, and evaluation of responses across the wide variety of tumors. Technological advancements in DNA sequencing, cytometry, and microscopy have facilitated the exploration of more integrated, high-dimensional profiling of the disease system-incorporating both immune and tumor parameters-rather than single metrics, as biomarkers for therapeutic sensitivity. Here we discuss the utility of traditional GBM biomarkers in immunotherapy and how the impending transformation of the biomarker paradigm-from single markers to integrated profiles-may offer the key to bringing predictive, personalized immunotherapy to GBM patients.

Prognostic microRNAs in high-grade glioma reveal a link to oligodendrocyte precursor differentiation

MicroRNA expression can be exploited to define tumor prognosis and stratification for precision medicine. It remains unclear whether prognostic microRNA signatures are exclusively tumor grade and/or molecular subtype-specific, or whether common signatures of aggressive clinical behavior can be identified. Here, we defined microRNAs that are associated with good and poor prognosis in grade III and IV gliomas using data from The Cancer Genome Atlas. Pathway analysis of microRNA targets that are differentially expressed in good and poor prognosis glioma identified a link to oligodendrocyte development. Notably, a microRNA expression profile that is characteristic of a specific oligodendrocyte precursor cell type (OP1) correlates with microRNA expression from 597 of these tumors and is consistently associated with poor patient outcome in grade III and IV gliomas. Our study reveals grade-independent and subtype-independent prognostic molecular signatures in high-grade glioma and provides a framework for investigating the mechanisms of brain tumor aggressiveness.