Glioblastoma Stem Research Articles

Lactate reprograms glioblastoma immunity through CBX3-regulated histone lactylation.

Glioblastoma (GBM), an aggressive brain malignancy with a cellular hierarchy dominated by GBM stem cells (GSCs), evades antitumor immunity through mechanisms that remain incompletely understood. Like most cancers, GBMs undergo metabolic reprogramming toward glycolysis to generate lactate. Here, we show that lactate production by patient-derived GSCs and microglia/macrophages induces tumor cell epigenetic reprogramming through histone lactylation, an activating modification that leads to immunosuppressive transcriptional programs and suppression of phagocytosis via transcriptional upregulation of CD47, a "don't eat me" signal, in GBM cells. Leveraging these findings, pharmacologic targeting of lactate production augments efficacy of anti-CD47 therapy. Mechanistically, lactylated histone interacts with the heterochromatin component chromobox protein homolog 3 (CBX3). Although CBX3 does not possess direct lactyltransferase activity, CBX3 binds histone acetyltransferase (HAT) EP300 to induce increased EP300 substrate specificity toward lactyl-CoA and a transcriptional shift toward an immunosuppressive cytokine profile. Targeting CBX3 inhibits tumor growth by both tumor cell-intrinsic mechanisms and increased tumor cell phagocytosis. Collectively, these results suggest that lactate mediates metabolism-induced epigenetic reprogramming in GBM that contributes to CD47-dependent immune evasion, which can be leveraged to augment efficacy of immuno-oncology therapies.

IMMU-36. MULTI-OMIC CHARACTERIZATION OF A SYNGENEIC MOUSE CANCER STEM CELL MODEL OF GBM FOR PRECLINICAL APPLICATIONS

Abstract Glioblastoma (GBM) is resistant to many therapies including immunotherapies. There is an urgent need to explore the role of the microenvironment in resistance to therapy with tailored pre-clinical models. Using multi-omic approaches we describe a syngeneic cancer stem cell mouse model of GBM, with a spontaneous amplification of Igf2. We investigate whether Igf2 influences tumour and microenvironment cells to promote immunosuppression in GBM. Three cell lines were previously established from spontaneous brain tumours in C57Bl/6 Trp53+/-/Nf1+/- mice and maintained under neural stem cell culture conditions. Whole genome sequencing (WGS) was used to determine single nucleotide, copy number, and structural variation, revealing loss of both copies of Trp53 and Nf1 in all three cell lines. However only one cell line, mBT0309, developed tumors when orthotopically allografted. Analysis of genomic alterations and transcriptomics revealed that mBT309 exhibits amplification of the Igf2 loci and overexpression was confirmed at the RNA and protein level. Spatial and single cell transcriptomics showed that Igf2 is overexpressed in mBT0309 allografted tumours and correlated with specific transcriptomic programs. A high-parameter Imaging Mass Cytometry (IMCTM) panel was used for spatial proteomic analysis, to monitor the development of tumours in a time-course experiment. In vitro growth characteristics and stem marker expression in both transcriptomic and spatial IMC data suggest that high levels of Igf2 may regulate GBM stemness features. Analysis of human GBM datasets revealed that Igf2 amplified tumours have reduced CXCL11 expression. These findings suggest that high levels of Igf2 may influence immunosuppression by reducing T-cell recruitment. This syngeneic immunocompetent GBM stem cell model harbouring Igf2 amplification adds to the suite of models to study the GBM microenvironment and its role in immunosuppression and resistance to therapy.

DDDR-41. A GENOME-WIDE CRISPR/CAS9 SCREEN IN GLIOBLASTOMA STEM CELLS UNVEILS SYNTHETIC LETHAL INTERACTIONS AND RESISTANCE MECHANISMS OF JIN001, A BLOOD-BRAIN BARRIER-PENETRANT HSP90 INHIBITOR

Abstract Glioblastomas (GBMs) are aggressive brain tumors characterized by extensive genetic heterogeneity and therapeutic resistance. Heat shock protein 90 (Hsp90) is a molecular chaperone that stabilizes and facilitates the proper folding of numerous proteins, including oncogenic drivers and is overexpressed in cancers. Hsp90 inhibitors can disrupt multiple oncogenic signaling pathways by degrading various client proteins essential for tumor growth and survival, making them attractive therapeutic candidates for GBMs. We have previously reported on the efficacy of Hsp90 inhibitors against gliomas. However, cancer cells develop resistance to Hsp90 inhibitors by upregulating compensatory chaperones (e.g., Hsp70), mutating client proteins, or activating alternative survival pathways, reducing the long-term efficacy of these agents. Combination approaches overcoming such resistance mechanisms are needed. JIN001, a novel Hsp90 inhibitor, demonstrates superior blood-brain barrier (BBB) penetration, and high potential for clinical translation. we performed a genome-wide CRISPR/Cas9 knockout screen using the Toronto Knockout Library v3 (TKOv3) with screen selection pressure from JIN001 in GBM stem cells (GSC272) to identify synthetic lethal interactions and resistance mechanisms associated with JIN001 treatment. Experiments were performed in triplicate with two time points, T22 and T37. Quality control analysis of the NGS data indicated excellent quality and consistency between different replicates. DrugZ analysis revealed a set of sensitive and resistant genes, informing potential combination therapies and further elucidating JIN001’s mechanism of action. Validation studies for the top synthetic lethal targets are underway to confirm the identified interactions and will be presented. This CRISPR-Cas9 screen offers valuable insights into JIN001’s therapeutic potential, reveals new combination strategies to overcome resistance to Hsp90 inhibitors and for use of these agents in other cancers, and paves the way for the development of more effective GBM combination treatment strategies.

DDDR-38. TRANSLATIONAL STEPS OF THE ANTITUMOR PEPTIDE TAT-CX43266-283 AS A TREATMENT FOR GLIOBLASTOMA: EGFR AS A TREATMENT RESPONSE BIOMARKER AND RESULTS OF COMBINATION THERAPY IN A PRECLINICAL RESECTION MODEL

Abstract Glioblastomas (GBM) are the most malignant primary brain tumors, and they remain incurable. Despite the current standard of care (surgical resection of the tumor and administration of chemotherapy and radiotherapy) some GBM stem cells (GSCs) remain in the brain parenchyma causing tumor recurrence. The Src-inhibitory peptide TAT-Cx43266-283 has shown promising antitumor results in GBM preclinical models, reducing GSC viability and increasing survival in GBM-bearing mice. Here we have investigated some of the main gaps to overcome when translating preclinical results to the clinic, to promote the progress of TAT-Cx43266-283 as a clinical therapy to fight GBM. First, we investigated biomarkers of treatment response to design a more targeted therapy. We assessed cell viability after treatment with TAT-Cx43266-283 in 13 patient-derived GSC lines and we found a stronger treatment response in those GSCs that had alterations in the Epidermal Growth Factor Receptor (EGFR). This was further confirmed in several murine GBM lines. Importantly, we found that treatment with TAT-Cx43266-283 was more effective in vitro than temozolomide or the classical EGFR inhibitor, erlotinib. Moreover, we showed that EGFR participates in TAT-Cx43266-283 response together with Src, by decreasing EGFR and EGFRvIII activity in some GSCs and increasing survival in mice bearing tumors with EGFR alterations. Next, we studied the effect of TAT-Cx43266-283 in a clinical context by administering it in a murine model of tumor resection. We analyzed the histopathology of this GBM model, uncovering histological features typical of human GBM. We found that resection alone improved, although not significantly, GBM-bearing mice survival. However, tumors that regrew after resection exhibited more aggressive features. Importantly, the combination of tumor resection and TAT-Cx43266-283 achieved better survival outcomes and showed reduced invasive features. Altogether, these results serve as a base for future clinical investigations and support the therapeutic potential of TAT-Cx43266-283 as a treatment for GBM.

DDDR-23. DECODING GLIOBLASTOMA DRUG RESISTANCE DYNAMICS USING NOVEL MICROFLUIDIC EX VIVO MODELS

Abstract Glioblastoma (GBM) is clinically challenging due to its aggressive nature and limited treatment options. Current standard of care involves surgical resection and chemoradiation with temozolomide (TMZ). GBM, however, often returns post-treatment fueled by its complex biology and the presence of resilient GBM stem cells. Compounding the issue is the blood-brain barrier, which poses a formidable obstacle to drug delivery into the brain. Understanding the molecular dynamics post-therapy within the brain, influenced by the tissue microenvironment, is key for developing more effective therapeutic strategies. Unfortunately, existing research models have fallen short in capturing the complexity of GBM and its response to treatment. While animal models have been a mainstay in GBM research, their ability to predict human responses has been called into question, highlighted by the disappointing results seen in clinical trials. We are therefore advancing bioprinting-based approaches for modeling various components of the tumor microenvironment to gain insight into mechanisms of drug resistance. We report on the development of three novel microfluidic platforms to investigate and interrogate GBM biology. First, we have developed a novel microfluidic model of GBM, termed GlioFlow-3D, produced through a combination of 3D printing methods. GlioFlow-3D mimics specific aspects of the perivascular niche, including protection from circulating TMZ. Second, we have adapted GlioFlow-3D as part of a platform to investigate advanced ultrasound techniques for delivering novel therapeutics into the human brain. Third, we are developing a novel approach aimed at exploring the relationship between the brain extracellular matrix and tumoral cells using bioprinting of living tumor organoids obtained from patients with a history of recurrence. By integrating bioprinting technologies with patient-derived models to create novel ex vivo platforms, we aim to obtain new insights into the intricate dynamics of drug resistance in GBM, ultimately paving the way for more effective therapeutic strategies. Funding: The Brain Tumor Center Research Award (UCGNI) The ARC Project - CCHMC and UC joint Research Award

TMIC-54. OHSV-MEDIATED NOTCH BLOCKADE FOR BRAIN TUMORS

Abstract Primary brain tumors such as glioblastoma (GBM) are refractory to current standard-of-care, and so there is an urgent need to develop novel therapies to treat brain tumors. NOTCH is a cell-cell communication pathway that is exploited by GBM stem cells to bypass treatment. The role of NOTCH signaling in tumor growth and resistance is well studied, but the significance of this pathway for immunotherapy of GBM is not very well understood. We have recently shown that NOTCH activation with viro-immunotherapy contributes to tumor regrowth and induces recruitment of monocytic MDSC cells into the tumor, which limit optimal immune activation to kill tumor cells. Herein, we evaluated the impact of blocking NOTCH signaling using two different peptides: NIX1 and NIX2 that can interfere with NOTCH ligand binding with their receptors. Both NIX1 and NIX2 could effectively block the ligation of NOTCH ligands with Notch receptors in the tumor microenvironment. Secretion of both NIX1 and NIX2 was confirmed by western blot (WB) and ELISA. Functionality of NIX1 and NIX2 to block NOTCH signaling was assessed by western blot analysis for NOTCH cleaved intracellular domain (NICD). RNA sequencing and PCR based assays were utilized to evaluate the impact of NIX1 and NIX2 on global pathways that were enriched. Gene therapy using oncolytic immunotherapy vectors revealed that both NIX1 and NIX2 could suppress NOTCH signaling. In vitro, NIX1 and NIX2 did not increase the benefit of viro-immunotherapy. Treatment of mice bearing intracranial tumors with NIX1 or NIX2 armed viro-immunotherapy revealed a significant increase in therapeutic benefit with some long-term survivors. Both NIX1 and NIX2-expressing viruses induced macrophage migration relative to unarmed viro-immunotherapy in two different glioma models. Role of macrophages in guiding therapeutic benefit is currently being explored.

MiR-124-3p inhibits cell stemness in glioblastoma via targeting EPHA2 through ALKBH5-mediated m6A modification.

Glioblastoma (GBM) is the most aggressive form of glioma, characterized by high mortality and poor prognosis. Dysregulation of microRNAs (miRNAs) plays a critical role in the progression and metastasis of GBM. This study aimed to investigate the role and molecular mechanism of miR-124-3p in GBM. Levels of miR-124-3p, EPHA2, and ALKBH5 were measured using quantitative real-time polymerase chain reaction (qRT-PCR). Cell proliferation, migration, invasion, and stemness were assessed using the Cell Counting Kit-8 (CCK-8), colony formation, Transwell, and sphere formation assays, respectively. Bioinformatics prediction, dual-luciferase reporter assays, and RNA pull-down experiments were employed to validate the target of miR-124-3p. RNA binding protein immunoprecipitation (RIP) and methylated RNA immunoprecipitation (Me-RIP) were utilized to evaluate the regulation of miR-124-3p maturation by ALKBH5. The results indicated that overexpression of miR-124-3p inhibited the proliferation, migration, invasion, and stemness of GBM cells. EPHA2 was identified as a direct downstream target of miR-124-3p, and its overexpression reversed the inhibitory effects of miR-124-3p on cellular functions. Furthermore, miR-124-3p targeted EPHA2 to inactivate the Wnt/β-catenin pathway. Additionally, ALKBH5 negatively regulated miR-124-3p by impeding its processing. In conclusion, knockdown of ALKBH5 promoted the processing of pri-miR-124-3p, increasing mature miR-124-3p levels, which inhibited the malignant behaviors of GBM cells by targeting EPHA2. These findings highlight the importance of the ALKBH5/miR-124-3p/EPHA2 axis in GBM.

Transcription factor YY1-activated GNG5 facilitates glioblastoma cell growth, invasion, stemness and glycolysis through Wnt/β-catenin pathway

G protein subunit Gamma 5 (GNG5) has been found to be involved in regulating glioma progression. However, its function and mechanism in glioblastoma (GBM) progression need to be further elucidated. GBM cell proliferation, apoptosis, invasion and stemness were assessed by cell counting kit 8 assay, EdU assay, flow cytometry, transwell assay and sphere formation assay. The mRNA and protein levels of GNG5 and Yin Yang 1 (YY1) were determined by quantitative real-time PCR and western blot (WB). Detection of the glucose consumption, lactate production and ATP/ADP ratios were used to assess cell glycolysis. Besides, Wnt/β-catenin pathway-related protein levels were examined by WB. Mice xenograft model was also constructed to explore GNG5 roles in vivo. GNG5 was highly expressed in GBM, and its silencing inhibited GBM cell proliferation, invasion, stemness and glycolysis, while promoted apoptosis. Transcription factor YY1 could bind to the GNG5 promoter region and induce its expression. GNG5 overexpression reversed the inhibitory effects of YY1 silencing on GBM cell growth, invasion, stemness and glycolysis. YY1/GNG5 axis could activate the Wnt/β-catenin pathway, and Wnt/β-catenin pathway agonists SKL2001 could revert the effects of GNG5 silencing on GBM cell progression. Furthermore, GNG5 facilitated GBM tumor growth by mediating the Wnt/β-catenin pathway. YY1-mediated GNG5 promoted GBM progression through the Wnt/β-catenin pathway.

Muscarinic receptor drug trihexyphenidyl can alter growth of mesenchymal glioblastoma in vivo.

Glioblastoma (GBM) is the most commonly occurring and most aggressive primary brain tumor. Transcriptomics-based tumor subtype classification has established the mesenchymal lineage of GBM (MES-GBM) as cancers with particular aggressive behavior and high levels of therapy resistance. Previously it was show that Trihexyphenidyl (THP), a market approved M1 muscarinic receptor-targeting oral drug can suppress proliferation and survival of GBM stem cells from the classical transcriptomic subtype. In a series of in vitro experiments, this study confirms the therapeutic potential of THP, by effectively suppressing the growth, proliferation and survival of MES-GBM cells with limited effects on non-tumor cells. Transcriptomic profiling of treated cancer cells identified genes and associated metabolic signaling pathways as possible underlying molecular mechanisms responsible for THP-induced effects. In vivo trials of THP in immunocompromised mice carry orthotopic MES-GBMs showed moderate response to the drug. This study further highlights the potential of THP repurposing as an anti-cancer treatment regimen but mode of action and d optimal treatment procedures for in vivo regimens need to be investigated further.

BMP4 and Temozolomide Synergize in the Majority of Patient-Derived Glioblastoma Cultures.

One of the main causes of poor prognoses in patient with glioblastoma (GBM) is drug resistance to current standard treatment, which includes chemoradiation and adjuvant temozolomide (TMZ). In addition, the concept of cancer stem cells provides new insights into therapy resistance and management also in GBM and glioblastoma stem cell-like cells (GSCs), which might contribute to therapy resistance. Bone morphogenetic protein-4 (BMP4) stimulates astroglial differentiation of GSCs and thereby reduces their self-renewal capacity. Exposure of GSCs to BMP4 may also sensitize these cells to TMZ. A recent phase I trial has shown that local delivery of BMP4 is safe, but a large variation in survival is seen in these treated patients and in features of their cultured tumors. We wanted to combine TMZ and BMP4 (TMZ + BMP4) therapy and assess the inter-tumoral variability in response to TMZ + BMP4 in patient-derived GBM cultures. A phase II trial could then benefit a larger group of patients than those treated with BMP4 only. We first show that simultaneous treatment with TMZ + BMP4 is more effective than sequential treatment. Second, when applying our optimized treatment protocol, 70% of a total of 20 GBM cultures displayed TMZ + BMP4 synergy. This combination induces cellular apoptosis and does not inhibit cell proliferation. Comparative bulk RNA-sequencing indicates that treatment with TMZ + BMP4 eventually results in decreased MAPK signaling, in line with previous evidence that increased MAPK signaling is associated with resistance to TMZ. Based on these results, we advocate further clinical trial research to test patient benefit and validate pathophysiological hypothesis.

An ILK/STAT3 pathway controls glioblastoma stem cell plasticity.

Glioblastoma (GBM) is driven by malignant neural stem-like cells that display extensive heterogeneity and phenotypic plasticity, which drive tumor progression and therapeutic resistance. Here, we show that the extracellular matrix-cell adhesion protein integrin-linked kinase (ILK) stimulates phenotypic plasticity and mesenchymal-like, invasive behavior in a murine GBM stem cell model. ILK is required for the interconversion of GBM stem cells between malignancy-associated glial-like states, and its loss produces cells that are unresponsive to multiple cell state transition cues. We further show that an ILK/STAT3 signaling pathway controls the plasticity that enables transition of GBM stem cells to an astrocyte-like state invitro and invivo. Finally, we find that ILK expression correlates with expression of STAT3-regulated proteins and protein signatures describing astrocyte-like and mesenchymal states in patient tumors. This work identifies ILK as a pivotal regulator of multiple malignancy-associated GBM phenotypes, including phenotypic plasticity and mesenchymal state.

Microenvironment T-Type calcium channels regulate neuronal and glial processes to promote glioblastoma growth.

Background Glioblastoma (GBM) is the most common primary malignant brain tumor. The aim of this study was to elucidate the role of microenvironment and intrinsic T-type calcium channels (Cav3) in regulating tumor growth and progression. Methods We grafted syngeneic GBM cells into Cav3.2 knockout mice to assess the role of microenvironment T-Type calcium channels on GBM tumor growth. We performed single-cell RNA-seq (scRNA-seq) of tumors from WT and Cav3.2 KO mice to elucidate the regulation of tumors by the microenvironment. We used neurons from WT and Cav3.2 KO mice in co-culture with GBM stem cells (GSC) to assess the effects of Cav3.2 on neuron/GSC synaptic connections and tumor cell growth. Results Cav3.2 KO in the microenvironment led to significant reduction of GBM growth and prolongation of animal survival. scRNA-seq showed that microenvironment Cav3.2 regulates neuronal and glial biological processes. Microenvironment Cav3.2 downregulated numerous genes associated with regulating the OPC cell state in GBM tumors such as SOX10 and Olig2. Neuronal Cav3.2 promoted neuron/GSC synaptic connections and GSC growth. Treatment of GSCs with the Cav3 blocker mibefradil downregulated genes associated with neuronal processes. The Cav3 blocker drug mibefradil synergized with temozolomide (TMZ) and radiation to reduce in vivo tumor growth and prolong animal survival. Conclusions Together these data reveal a role for microenvironment Cav3 in promoting GBM tumor progression through regulating neuronal and glial processes particularly associated with the OPC-cell state. Targeting both intrinsic and microenvironment Cav3 with the inhibitor mibefradil significantly enhanced the anti-GBM effects of TMZ and radiation.

Hypoxia-driven heterogeneous expression of α5 integrin in glioblastoma stem cells is linked to HIF-2α

Despite numerous molecular targeted therapies tested in glioblastoma (GBM), no significant progress in patient survival has been achieved in the last 20 years in the overall population of GBM patients except with TTfield setup associated with the standard of care chemoradiotherapy. Therapy resistance is associated with target expression heterogeneity and plasticity between tumors and in tumor niches. We focused on α5 integrin implicated in aggressive GBM in preclinical and clinical samples. To address the characteristics of α5 integrin heterogeneity we started with patient data indicating that elevated levels of its mRNA are related to hypoxia pathways. We turned on glioma stem cells which are considered at the apex of tumor formation and recurrence but also as they localize in hypoxic niches. We demonstrated that α5 integrin expression is stem cell line dependent and is modulated positively by hypoxia in vitro. Importantly, heterogeneity of expression is conserved in in vivo stem cell-derived mice xenografts. In hypoxic niches, HIF-2α is preferentially implicated in α5 integrin expression which confers migratory capacity to GBM stem cells. Hence combining HIF-2α and α5 integrin inhibitors resulted in proliferation and migration impairment of α5 integrin expressing cells. Stabilization of HIF-2α is however not sufficient to control integrin α5 expression. Our results show that AHR (aryl hydrocarbon receptor) expression is inversely related to HIF-2α and α5 integrin expressions suggesting a functional competition between the two transcription factors. Collectively, data confirm the high heterogeneity of a GBM therapeutic target, its induction in hypoxic niches by HIF-2α and suggest a new way to attack molecularly defined GBM stem cells.

Stepwise-targeting and hypoxia-responsive liposome AMVY@NPs carrying siYAP and verteporfin for glioblastoma therapy

BackgroundThe Hippo pathway is a conserved tumour suppressor signalling pathway, and its dysregulation is often associated with abnormal cell growth and tumorigenesis. We previously revealed that the transcriptional coactivator Yes-associated protein (YAP), the key effector of the Hippo pathway, is a molecular target for glioblastoma (GBM), the most common malignant brain tumour. Inhibiting YAP with small interfering RNA (siYAP) or the specific inhibitor verteporfin (VP) can diminish GBM growth to a certain degree.ResultsIn this study, to enhance the anti-GBM effect of siYAP and VP, we designed stepwise-targeting and hypoxia-responsive liposomes (AMVY@NPs), which encapsulate hypoxia-responsive polymetronidazole-coated VP and DOTAP adsorbed siYAP, with angiopep-2 (A2) modification on the surface. AMVY@NPs exhibited excellent blood‒brain barrier crossing, GBM targeting, and hypoxia-responsive and efficient siYAP and VP release properties. By inhibiting the expression and function of YAP, AMVY@NPs synergistically inhibited both the growth and stemness of GBM in vitro. Moreover, AMVY@NPs strongly inhibited the growth of orthotopic U87 xenografts and improved the survival of tumour-bearing mice without adverse effects.ConclusionSpecific targeting of YAP with stepwise-targeting and hypoxia-responsive liposome AMVY@NPs carrying siYAP and VP efficiently inhibited GBM progression. This study provides a valuable drug delivery platform and creative insights for molecular targeted treatment of GBM in the future.

A novel TAp73-inhibitory compound counteracts stemness features of glioblastoma stem cells.

Glioblastoma (GB) is the most common and fatal type of primary malignant brain tumor for which effective therapeutics are still lacking. GB stem cells, with tumor-initiating and self-renewal capacity, are mostly responsible for GB malignancy, representing a crucial target for therapies. The TP73 gene, which is highly expressed in GB, gives rise to the TAp73 isoform, a pleiotropic protein that regulates neural stem cell biology; however, its role in cancer has been highly controversial. We inactivated TP73 in human GB stem cells and revealed that TAp73 is required for their stemness potential, acting as a regulator of the transcriptional stemness signatures, highlighting TAp73 as a possible therapeutic target. As proof of concept, we identified a novel natural compound with TAp73-inhibitory capacity, which was highly effective against GB stem cells. The treatment reduced GB stem cell-invasion capacity and stem features, at least in part by TAp73 repression. Our data are consistent with a novel paradigm in which hijacking of p73-regulated neurodevelopmental programs, including neural stemness, might sustain tumor progression, pointing out TAp73 as a therapeutic strategy for GB.

AB045. E2F6 promotes temozolomide resistance in glioblastoma by enrichment in CARD6 and POSTN promoter region.

Glioblastoma (GBM) is the most aggressive primary malignant brain tumor. Temozolomide (TMZ) is the most used first-line chemotherapeutic agent for GBM after surgery, but acquired resistance to TMZ frequently leads to treatment failure and is a major challenge in the clinical treatment of GBM. Increasing evidence suggests that E2F transcription factor 6 (E2F6) is associated with a variety of tumor malignant biological behaviors and drug resistance, but its biological function and underlying molecular mechanisms in GBM are unknown. The study investigated the levels of E2F6 in both TMZ-sensitive and TMZ-resistant GBM cells and tissues using Western blotting and immunofluorescence assays. In vitro experiments were conducted to explore the impact of E2F6 on TMZ resistance and glioma stem cell stemness. These experiments included Western blotting, colony formation assay, flow cytometry assay, and TdT-mediated dUTP nick-end labeling (TUNEL) assay. Bioinformatic analyses were conducted to investigate the mechanism behind the high expression of E2F6 in TMZ-resistant cells and its correlation with caspase recruitment domain 6 (CARD6) and disulfide-linked cell adhesion protein (POSTN). The study employed bioinformatic analyses, messenger RNA (mRNA) sequencing, chromatin immunoprecipitation sequencing assay, immunofluorescence, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting. To examine the function of E2F6, an intracranial xenograft tumor mouse model was used for in vivo experiments. It was found that CARD6 and POSTN were significantly associated with TMZ resistance and survival of GBM patients. E2F6 was up-regulated in TMZ-resistant cells and tissues. Knockdown of E2F6 down-regulated the expression of CARD6, promoted TMZ-induced apoptosis, and enhanced chemo-sensitivity, whereas its overexpression significantly increased TMZ resistance in vitro and in vivo. In addition, E2F6 can promote TMZ resistance through stem-like properties acquisition. We identified a signaling pathway related to E2F6 and POSTN, which maintains the self-renewal of GBM stem cells (GSCs). E2F6 concentrates in the promoter region of POSTN, thereby regulating the expression of GSCs-related genes cluster of differentiation 133 (CD133), Nestin, and sex-determining region Y-box 2 (SOX2), which may be involved in tumor metabolism and drug resistance processes. Down-regulation of E2F6 down-regulated the expression of POSTN and inhibited tumor growth in nude mice. These results suggest that the E2F6-CARD6/POSTN signaling axis regulates the malignant biological behaviors of GBM and TMZ resistance. These findings are expected to provide promising therapeutic targets for CARD6 overcoming GBM TMZ resistance.

AB046. Dual role of POSTN in maintaining glioblastoma stem cells and immune-suppressive microglia in glioblastoma.

Glioblastoma (GBM) is an immunosuppressive, universally lethal cancer driven by GBM stem cells (GSCs). The interplay between GSCs and the immunosuppressive microglia plays crucial roles in promoting malignant growth of GBM, however, the molecular mechanisms underlying this crosstalk are incompletely understood. We performed RNA sequencing to explore the mechanism by which periostin (POSTN) regulates GSCs and microglia. The biological function of POSTN in GBM development was confirmed in vitro and in vivo. Specifically, tumorsphere formation assay, proliferation analysis, migration assays, enzyme-linked immunosorbent assay, immunoblotting, and intracranial mouse model were performed. We identified POSTN secreted from GSCs promotes GSC self-renewal and tumor growth via activation of the αVβ3/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/β-catenin/FOS like antigen 1 (FOSL1) pathway. In addition to its GSC intrinsic effects, POSTN is able to recruit microglia and upregulate cluster of differentiation 70 (CD70) expression through PI3K/AKT/nuclear factor-kappa B (NFκB) pathway in microglial cells, which in turn promotes the Treg development and functionality, and generates an immunosuppressive tumor microenvironment. Inhibition POSTN disrupts the GSC maintenance, inhibits recruitment of immunosuppressive microglial, reduces Treg development and function, and suppresses GBM growth, suggesting that targeting POSTN may effectively improve GBM treatment. In conclusion, our study defined POSTN as a key regulator in mediating the molecular crosstalk between GSCs and immune-suppressive Microglia in the tumor microenvironment in GBM. POSTN activates the PI3K/AKT/β-catenin/FOSL1 pathway in an autocrine manner to promote GSC self-renewal and tumor growth. At the same time, POSTN recruits microglia in a paracrine manner and upregulates the expression of CD70 in microglia through the PI3K/AKT/NFκB pathway, thereby promoting the development and function of Treg and generating an immunosuppressive tumor microenvironment. Our findings indicate that targeting the POSTN gene may be a promising approach to ablating GSCs, breaking the immunosuppressive environment and overcoming treatment resistance in GBM.

Phosphocreatine Promotes Epigenetic Reprogramming to Facilitate Glioblastoma Growth Through Stabilizing BRD2.

Glioblastoma (GBM) exhibits profound metabolic plasticity for survival and therapeutic resistance, while the underlying mechanisms remain unclear. Here, we show that GBM stem cells reprogram the epigenetic landscape by producing substantial amounts of phosphocreatine (PCr). This production is attributed to the elevated transcription of brain-type creatine kinase, mediated by Zinc finger E-box binding homeobox 1. PCr inhibits the poly-ubiquitination of the chromatin regulator bromodomain containing protein 2 (BRD2) by outcompeting the E3 ubiquitin ligase SPOP for BRD2 binding. Pharmacological disruption of PCr biosynthesis by cyclocreatine (cCr) leads to BRD2 degradation and a decrease in its targets' transcription, which inhibits chromosome segregation and cell proliferation. Notably, cyclocreatine treatment significantly impedes tumor growth and sensitizes tumors to a BRD2 inhibitor in mouse GBM models without detectable side effects. These findings highlight that high production of PCr is a druggable metabolic feature of GBM and a promising therapeutic target for GBM treatment. Significance: Glioblastoma (GBM) exhibits an adaptable metabolism crucial for survival and therapy resistance. We demonstrate that GBM stem cells modify their epigenetics by producing phosphocreatine (PCr), which prevents bromodomain containing protein 2 (BRD2) degradation and promotes accurate chromosome segregation. Disrupting PCr biosynthesis impedes tumor growth and improves the efficacy of BRD2 inhibitors in mouse GBM models.

The unfolded protein response machinery in glioblastoma genesis, chemoresistance and as a druggable target.

The role of the unfolded protein response (UPR) has been progressively unveiled over the last decade and several studies have investigated its implication in glioblastoma (GB) development. The UPR restores cellular homeostasis by triggering the folding and clearance of accumulated misfolded proteins in the ER consecutive to endoplasmic reticulum stress. In case it is overwhelmed, it induces apoptotic cell death. Thus, holding a critical role in cell fate decisions. This article, reviews how the UPR is implicated in cell homeostasis maintenance, then surveils the evidence supporting the UPR involvement in GB genesis, progression, angiogenesis, GB stem cell biology, tumor microenvironment modulation, extracellular matrix remodeling, cell fate decision, invasiveness, and grading. Next, it concurs the evidence showing how the UPR mediates GB chemoresistance-related mechanisms. The UPR stress sensors IRE1, PERK, and ATF6 with their regulator GRP78 are upregulated in GB compared to lower grade gliomas and normal brain tissue. They are activated in response to oncogenes and are implicated at different stages of GB progression, from its genesis to chemoresistance and relapse. The UPR arms can be effectors of apoptosis as mediators or targets. Recent research has established the role of the UPR in GB pathophysiology and chemoresistance. Targeting its different sensors have shown promising in overcoming GB chomo- and radioresistance and inducing apoptosis.

Transcriptional mechanisms of phenotypic plasticity in glioblastoma.

e14027 Background: Primary glioblastoma (GBM) tumor cells exhibit plasticity and can adopt different cellular states that exhibit dynamic transitions between states. This could be one of the mechanisms for treatment escape and leads to poor prognosis in GBM. In this regard, we sought to uncover transcriptional regulatory mechanisms responsible for this phenotypic plasticity in GBM. Methods: Standard of care (SOC) treatment (radiation and temozolomide) modulates transcriptional regulatory networks (TRNs) of the tumor cells and drives treatment resistance. Since TRNs could be key mechanistic drivers for state transitions, integrated single-cell RNA sequencing (scRNAseq) data of primary and relapse patient samples (11) were analyzed with scMINER. Our method uses a systems biology framework to identify cell states (St_1 to St_n) in terms of regulatory networks and their activities. Clustering of co-regulated gene modules (regulons), enabled the identification of transcriptional programs and regulatory mechanisms that specify tumor cell states. Results: Activity patterns of 38 transcriptional programs clustered tumor cells from the patients into 21 states. Preliminarily, we observed common regulatory network cell states (St_1, St_2, St_5, St_6) across patient tumors. Additionally, primary tumor cells of a patient (UW14) transitioned from initial cell state(s) observed across multiple patients (e.g., St_1) to a recurrent state (e.g., St_9) through a trajectory driven by transcription factors (TFs). Herein, scMINER regulatory network inference method also defines master TFs (TFs that regulate the majority of the other TFs in the network) that were used to characterize initial (St_1) or recurrent (St_9) cell states. Moreover, certain transcription factors (22) and their co-expressed target genes (regulons) also exhibit variation in expression across the pseudotime trajectory (from St_1 to St_9) including masterTFs such as SOX9 and MECOM. Conclusions: Therefore, we observed that shared cell states may exist across patients (primary and relapse) although in different proportions. Our analysis suggests a de-differentiation trajectory from neuronal cells to developing GBM stem cells and predicts transcription factors that could be playing an important role therein. Moreover, similar transcriptional regulatory mechanisms may promote transitions between primary and recurrent tumor cell states that exhibit phenotypic plasticity.