Human Glioblastoma Research Articles

EXTH-14. IRREVERSIBLE TARGETING OF THE C-MYC/TOPOISOMERASE I AXIS IN GLIOBLASTOMA: DUAL INHIBITION USING A NOVEL INDENOISOQUINOLINE INHIBITOR

Abstract Glioblastoma–the most common primary CNS malignancy–is notorious for its cellular and molecular complexity and uniform fatality. Overexpression of the c-MYC and TOPOISOMERASE 1 (TOP1) oncogenes is implicated in more than 50% of human cancers. They are involved in the pathogenesis of glioblastomas with overexpression correlating with decreased overall median survival in glioblastoma patients. LMP744 is a non-camptothecin indenoisoquinoline small molecule inhibitor designed to target the C-MYC/TOP1 axis. The compound is inherently stable, has high brain penetrance, and irreversibly binds to its target providing several advantages over the camptothecin class of drugs. Human glioblastoma cells treated with LMP744 show a dose-dependent decrease in viability with LD50 ranging between 50 and 100 nM compared to 100-200µM following treatment with temozolomide in the same cell lines. Treatment results in a pro-apoptotic effect in exposed cells as well as S-phase arrest. Protein arrays and confirmatory western blots demonstrate increased CHK2 and decreased p53 and GSK-a/ß in treated cells. Orthotopic xenotransplantation via stereotactic injection of human glioblastoma cells (7×105 cells/4 µL) in nude mice showed exquisite sensitivity to LMP744 without adverse events. Administration of 20 mg/kg of LMP744 via tail vein injection resulted in total eradication of tumor signal on bioluminescent imaging. These preliminary findings suggest that LMP744–and perhaps the class of non-camptothecin indenoisoquinolones–is a promising novel candidate for glioblastoma pharmacotherapy.

IMMU-39. CAR T CELLS TARGETING ICAM-1 SHOW A SURVIVAL BENEFIT IN BOTH SYNGENEIC AND XENOGRAFT GLIOMA MOUSE MODELS

Abstract BACKGROUND Chimeric antigen receptor (CAR) T-cell therapy, while effective against hematological malignancies, has faced significant hurdles in its application to solid tumors. Challenges in CAR T-cell therapy for glioblastoma include the immunosuppressive tumor microenvironment, the limited infiltration of CAR T-cells into the tumor, heterogeneous target expression and antigen escape. In this study, we focused on targeting Intracellular adhesion molecule-1 (ICAM-1), a protein expressed on both glioma cells and tumor-associated cells like macrophages and endothelial cells. METHODS Glioblastoma and normal brain tissue microarray sections (TMA) were immunohistochemically analyzed for ICAM-1 expression. Second-generation human and murine ICAM-1-targeting CAR T cells were generated by lentiviral or retroviral transduction of T cells from healthy human donors or murine splenocytes. Their efficacy was evaluated in co- culture assays with human and murine glioma and endothelial cell lines. Syngeneic and xenograft orthotopic glioma mouse models were used to assess the in vivo activity of CAR T cells. Ex vivo analysis of these tumors included examination of changes in the tumor microenvironment using high-dimensional flow cytometry. RESULTS Immunohistochemical staining of TMA revealed a significant upregulation of ICAM-1 in human glioblastoma tissue compared to normal brain tissue. Single-cell RNA sequencing data from glioblastoma specimens showed a high level of ICAM-1 expression in tumor- associated macrophages. Human and murine ICAM-1-targeting CAR T cells displayed strong lysis of ICAM-1-expressing glioma and endothelial cells in vitro. Intratumoral application of CAR T cells resulted in a survival benefit in both syngeneic and xenograft glioma mouse models. Ex vivo analysis of the tumor microenvironment revealed treatment-induced changes from our CAR T cell therapy and indicates potential for further enhancements. CONCLUSION Our study demonstrates that ICAM-1-targeting CAR T cells improve survival in human and murine glioma mouse models. Flow cytometry of the tumor microenvironment reveals therapy-induced changes, for future improvements of the CAR T cell therapy.

BIOM-14. TRANSMEMBRANE WATER EFFLUX RATE (KIO) IS AN MRI-DETECTABLE BIOMARKER TO EVALUATE THE EFFICIENCY OF TTFIELDS TREATMENT ON GLIOBLASTOMA

Abstract BACKGROUND Tumor Treating Fields (TTFields) has emerged as an effective treatment modality for Glioblastoma, shown to improve both OS and PFS. Yet how to monitor response to TTFields remains unclear. In this study, we proposed using transmembrane water efflux rate (kio), a non-invasive biomarker detectable in conventional MRI and reflecting cell membrane permeability, to assess the treatment efficiency of TTFields. METHODS U-87 MG human glioblastoma cell line were treated with TTFields at frequency of 200 kHz and varying field strengths of 0 V/cm, 0.8 V/cm, 1.2 V/cm and 1.6 V/cm using the inovitro system from Novocure. The measurement of kio was performed on a 0.5 T benchtop MRI system (Pure Devices GmbH) using a home-developed filter-exchange imaging (FEXI) sequence. Cell membrane morphology were quantitatively analysed using scanning electron microscopy. Patients with newly diagnosed glioblastoma (ndGBM) who underwent DCE-MRI before and after TTFields treatment were identified and the change of FEXI-kio value were analysed. RESULTS In the same frequency, the effect of TTFields on cancer cell proliferation is dependent on intensity, manifested a decrease in cell growth rate under high electric field intensity. As the TTFields electric field intensity increased, the cell membrane permeability (kio) also increased, exhibits a significant negative correlation with glioblastoma cell growth rate (p=0.031). Scanning electron microscopy reveals that TTFields can induce significant cell membrane pores, and the total surface area of membrane pores correlates significantly positively with FEXSY-kio index. DCE-MRI data obtained from 4 ndGBM before and after TTFields therapy showed that the FEXI-kio value is increased after TTFields treatment. CONCLUSION This study demonstrated that TTFields increases membrane permeability by inducing cell membrane holes, and kio is a promising non-invasive MRI biomarker to evaluate the efficiency of TTFields treatment.

CNSC-67. ANATOMICAL ORGANIZATION AND ELECTRICAL PROPERTIES OF GLIOMA-INNERVATING NEURONS

Abstract Gliomas are the most common malignant primary brain tumors and are often associated with severe neurological deficits and mortality. Unlike many cancers, gliomas rarely metastasize outside the brain, indicating a possible dependency on the brain’s unique microenvironment. Recent discoveries have highlighted the existence of neuron-glioma synapses, suggesting that glioma cells depend on neuronal inputs and AMPA-receptor-mediated glutamate signaling for their proliferation. Yet, the specific locations and properties of the neurons that innervate gliomas remain elusive. In this study, we utilized transsynaptic tracing with a pseudotyped, glycoprotein-deleted rabies virus to specifically infect TVA and glycoprotein-expressing human glioblastoma cells in an orthotopic xenograft model. This approach allowed us to identify the presynaptic neuronal inputs to the glioma. Comprehensive whole-brain mapping and quantification revealed that these glioma-innervating neurons, predominantly glutamatergic, exhibit a consistent input pattern influenced by the tumor’s locations and engage selective neuromodulatory pathways. Notably, the electrophysiological properties of these neurons mirror those innervating the cortex in vivo. Our study introduces a novel method for investigating glioma-innervating neurons and reveals that these neurons are consistently integrated into the glioma network, displaying distinctive location-dependent neuromodulatory patterns. Our findings offer a promising scaffold for future interventions aimed at disrupting these critical neuronal inputs, potentially redefining therapeutic strategies against brain tumors.

TMIC-87. ICAM-1 REGULATE EXTRACELLULAR VESICLE-MEDIATED IMMUNOSUPPRESSIVE MONOCYTE IN HUMAN GLIOBLASTOMA CELL

Abstract Glioblastoma is the most common malignant primary brain tumor and is universally fatal. Treatment involves maximal safe resection with adjuvant chemoradiation. Poor prognosis in glioblastoma is multifactorial, and local and systemic immunosuppression is an important factor. Extracellular vesicles (EVs) are small, membrane-bound particles released by cells into the external environment. They play a key role in intercellular communication. In glioblastomas, EVs regulate immunosuppression through induction of myeloid-derived suppressor cells (MDSCs) in a process dependent on the PD-1/PD-L1 and IL-6 axes. Primary cilia are microtubule-based organelles that play crucial roles in various cellular processes and signal transduction cascades. We recently showed that primary cilia modulate IL-6 expression and consequently, MDSC induction. Comparative proteomic analysis of EVs derived from human glioblastoma cells devoid of cilia showed loss of ICAM-1 expression compared to control glioblastoma cells. ICAM-1 (Intercellular Adhesion Molecule-1) is a cell surface glycoprotein that mediates cell-cell adhesion and immune responses. In this study, we showed that depletion of primary cilia in human glioblastoma cells result in increased PD-L1 but loss of IL-6 and ICAM-1. RNAi-meidated loss of ICAM-1 was synergistic with primary cilia depletion in preventing MDSC inductionn normal human monocytes exposed to glioblastoma-derived EVs. Exogenous IFN-g was sufficient to restore IL-6 levels and MDSC induction despite loss of primary cilia and ICAM-1 suggesting that primary cilia act upstream of IFN-g, IL-6 and ICAM-1 in glioblastoma-mediated MDSC induction. This study is the first to connect primary cilia signal transduction to IL-6 and ICAM-1 expression and to MDSC induction. The evidence suggests a potential parallel primary cilia regulatory cascade independent of the PD-L1 axis that controls tumor-mediated immunosuppression. These results may inform novel therapeutic strategies aimed at increasing efficacy of immunotherapy in the glioblastoma and other neoplastic processes.

TMIC-69. HUMAN ORGANOID TUMOR TRANSPLANTATION IDENTIFIES FUNCTIONAL GLIOBLASTOMA MICROENVIRONMENTAL COMMUNICATION MEDIATED BY PTPRZ1

Abstract Glioblastoma, the most aggressive form of primary brain cancer, is driven by both intrinsic cellular properties and extrinsic factors from the tumor microenvironment (TME). Here, we leverage our novel human organoid tumor transplantation (HOTT) system to explore how external cues modulate glioblastoma cell type specification, heterogeneity, and migration. Comparing the single-cell transcriptomes of HOTT and matched primary tumors, we found that HOTT recapitulates not only core features of major patient tumor cell types but also those of peritumor non-neoplastic cell types. This enables us to explore tumor-TME interactions and identify PTPRZ1, a receptor tyrosine phosphatase implicated in brain tumor migration, as a key mediator in intercellular communication. This finding was further confirmed by interrogation of published datasets from patients containing non-neoplastic microenvironmental cells. PTPRZ1 activation, resulting from the reactivation of developmental programs in both the tumor and its TME, highlights the relevance of the organoid system for modeling the GBM microenvironment. Moreover, HOTT uniquely allows for perturbations in either patient tumors or their microenvironments, or both, to verify PTPRZ1 function. Tumor knockdown of PTPRZ1 confirmed its role in promoting tumor migration and maintaining progenitor identity. Surprisingly, environmental PTPRZ1 knockdown in human cortical organoids before tumor transplantation inhibited tumor migration and promoted differentiation, even without direct tumor manipulation. Overall, this fundamental result demonstrates that a single treatment delivered to the tumor and its TME can exert opposite effects on the tumor. Consequently, it underscores the necessity of studying human glioblastoma within a human microenvironment context, such as HOTT, especially when evaluating therapeutic efficacy in GBM, as effective treatments must address both the tumor and its complex TME, rather than the tumor alone.

IMMU-08. PRECLINICAL EVALUATION OF GAL-1-SPECIFIC CAR-T CELL FUNCTION IN AN IN VITRO AND EX VIVO MODEL OF GLIOBLASTOMA

Abstract BACKGROUND Human glioblastoma (GBM), especially those exhibiting anti-VEGF resistance, overexpress the carbohydrate-binding protein galectin-1 (Gal-1). To develop novel anti-GBM approaches, we developed Gal-1 targeted CAR-T cells to investigate potential antitumor effect with in vitro and ex vivo slice culture models. METHODS Uniform GBM brain slice cultures were collected using NICO’s Myriad resection tool and their Automated Preservation System (APS), designed to obtain fresh brain tumor samples maintaining tumor cytoarchitecture and microenvironment. To prepare Gal-1 CAR-T cells, we used creative laboratory to utilize a third-generation Gal-1-CAR construct with high binding and codon optimized scFv-Gal-1 fragment fused with CD3ζ and co-stimulatory cytoplasmic domains of CD28 and 4-1BB (Gal-1 scFv-CD28-4-1BB-CD3ζ). We then transfected into the T cells, from peripheral blood, mononuclear cells using a lentiviral system. The anti-tumor capabilities of CAR-T cells were evaluated by co-culturing with GBM cells and ex vivo APS-GBM slices. RESULTS The collected APS- GBM slices samples were clear of debris and blood product, not requiring post-surgical mechanical slices, and exhibited viability up to 12 days over traditionally prepared ex vivo cultures. With this, we found Gal-1-CAR-T cells grew exponentially in the presence of cytokines and maintained phenotypic and biological attributes such as cell viability, potency, migration, and T cell activation. Gal-1 scFv-CD28-4-1BB-CD3ζ -CAR-T cells killed more than 80% of GBM tumor cells within 24 hours in Gal-1+ve, but not Gal-1-ve GBM cells in vitro. Additionally, these CAR-T cells selectively caused significant release of IL-2, IFN-γ and TNF-α only from Gal-1+ve co-cultures and induced significant Gal-1+ve GBM cell death in an ex vivo model without any general toxicity. CONCLUSION Based on in vitro cell culture and ex vivo APS-brain slice culture results, we conclude that the novel Gal-1 scFv-CD28-4-1BB-CD3ζ CAR-T cell therapy may offer an effective therapeutic option. Further pre-clinical and clinical studies need to be performed to validate this novel approach

EPCO-33. OMICON: A CLOUD PLATFORM FOR FAIR RESEARCH ON GENE COEXPRESSION NETWORKS IN NORMAL HUMAN BRAIN AND BRAIN TUMORS

Abstract Genome-wide coexpression analysis of bulk human brain samples is a powerful approach for identifying highly reproducible transcriptional signatures of cell types and cell states, since it can survey huge numbers of individuals, cells, and transcripts. However, it is difficult to optimize gene coexpression network construction, compare gene coexpression modules from independent datasets, or even locate gene expression datasets with similar attributes. To address these challenges, we have developed the OMICON platform (theomicon.ucsf.edu) to promote FAIR (Findable, Accessible, Interoperable, Reusable) research practices involving human brain gene coexpression networks. OMICON contains structured gene expression data for >17K bulk human brain samples (~10K normal and ~7K malignant glioma), which were collected from diverse public repositories and consortia (e.g., GEO, TCGA, CGGA, CPTAC, REMBRANDT, IvyGAP, GTEx, NABEC, the Allen Institute). To promote interoperability, we have standardized metadata for hundreds of dataset and sample attributes, including single-nucleotide and copy-number mutations. For each dataset, we have used the FindModules R function to construct dozens of gene coexpression networks by iterating over module detection parameters. These efforts have identified ~100K gene coexpression modules, which have been extensively characterized via enrichment analysis with thousands of curated gene sets. All datasets, metadata, gene coexpression networks, enrichment results, and analysis steps can be browsed with an interactive workflow visualization tool, which promotes accessibility, reusability, and reproducibility by maintaining complete data provenance with unique identifiers. To promote findability, we have built an advanced search engine to identify datasets, samples, modules, and more, by filtering standardized metadata (e.g., find gene coexpression modules in human glioblastoma datasets that are significantly enriched with markers of T-cells). A detailed description of OMICON’s functionality is described on our Help page: theomicon.ucsf.edu/home/help. Through this functionality, OMICON seeks to build community and focus therapeutic efforts around reproducible analyses of transcriptional variation in normal human brain and brain tumors.

CSIG-09. BEYOND SINGLE AGENTS: EXPLORING THE POTENTIAL OF ABEMACICLIB IN COMBINATION WITH PANOBINOSTAT FOR IMPROVED GLIOMA TREATMENT

Abstract BACKGROUND Glioblastoma is the most common primary central nervous system tumour with a median survival of less than 15 months. Addressing the underlying redundant, and converging signaling pathways necessitates the utilization of small molecule inhibitors capable of simultaneous targeting and inhibition. In glioma, the aberrant CDK4/6-Rb pathway dysregulation resulting in disruption of cell cycle checkpoint progression can lead to uncontrolled cell division, a hallmark of cancer. The neuro-pharmacokinetics of abemaciclib, a Cyclin-dependent kinase inhibitor, is being currently investigated in phase 1 clinical trials by National Cancer Institue, [NCT05413304]. The importance of panobinostat as a Histone deacetylase inhibitor and potentiating the effects of various small molecular inhibitors in published literature is paramount. This study is based on investigating ways to overcome resistance by exploring the synergistic cytotoxic effects of abemaciclib in combination with panobinostat in glioma. METHODS We investigated the antiproliferative effects of abemaciclib and panobinostat on glioma cells using an MTS cell proliferation assay. Inhibitor combination analysis was done using, SYNERGYFINDER via zip-model. Flow cytometry with Annexin V staining further assessed cell death and apoptosis induced. RESULTS The antiproliferative effects of abemaciclib, alone and in combination with panobinostat, in pediatric lines (KNS 42, SJG2), and adult human glioblastoma line, SF188 exhibited lower IC50 as compared to adult high grade glioma lines (LN 18, LNZ 308). Synergy analysis revealed a strong cytotoxic effect in KNS 42 and SF 188 cells treated with the combination. Flow cytometric analysis indicated that the combination therapy induced significant cell death only in a subset of cell lines- KNS 42 and SF 188, suggesting underlying genetic heterogeneity influences treatment response, warranting further mechanistic studies. CONCLUSION Combination therapies using abemaciclib and panobinostat, targeting CDK4/6 and histone deacetylation pathways, show promise against aggressive and treatment-resistant gliomas. Further investigation into these combination approaches is crucial to understand resistant mechanisms, optimize efficacy, and establish their clinical efficacy for improving glioma patient outcomes.

EXTH-44. ENHANCING THERAPEUTIC APPROACHES IN HIGH-GRADE GLIOMAS: SYNERGISTIC EFFECTS OF LSD1 AND KINASE INHIBITION

Abstract BACKGROUND Glioblastoma (GBM) and Diffuse Intrinsic Pontine Glioma (DIPG) are devastating high-grade gliomas (HGGs) with poor prognoses. Lysine-specific demethylase 1 (LSD1) is a promising therapeutic target and a key regulator in tumor initiation and recurrence. Crosstalk between LSD1 and other signaling pathways, such as the MAPK pathway, frequently hyperactivated in HGG, offers an opportunity to enhance the efficacy of LSD1 inhibitors. This study investigates the combined inhibition of LSD1 and kinase signaling to improve therapeutic outcomes in HGG. METHODS Transcriptional changes following LSD1 knockdown in human GBM cells were analyzed using RNA-seq and GSEA. RPPA and western blotting assessed the impact of LSD1 inhibition on kinase signaling. Pharmacological LSD1 inhibition was tested using NCD38 or bomedemstat in HGG models and normal human astrocytes (NHA). The effects of combining LSD1 inhibitors with kinase inhibitors (osimertinib, afatinib, and ulixertinib) on cell viability were evaluated. Combination treatment was also assessed in orthotopic xenograft models of GBM. RESULTS GSEA revealed LSD1 expression was enriched for gene sets involved in kinase signaling processes. Increased phosphorylated ERK1/2 levels were observed following NCD38 treatment in MDA-GSC17, as shown by RPPA and western blot analyses. The LSD1 inhibitor, NCD38, increased phospho-ERK1/2 levels (72% increase from baseline), while co-treatment with osimertinib mitigated this effect. Combined LSD1 and kinase inhibition (EGFR and ERK inhibition) showed synergistic effects in vitro in GBM and DIPG models but not in the NHA. DISCUSSION Our results demonstrate that kinase activity can be modulated by inhibiting LSD1, potentially leading to a resistant subpopulation. This study underscores the potential of combining LSD1 and kinase inhibition to enhance therapeutic efficacy in HGG, including GBM and DIPG. Future research will focus on elucidating the mechanisms by which LSD1 regulates kinase signaling, aiming to optimize combination therapies.

CNSC-26. INVESTIGATING THE ROLE OF QUAKING IN REGULATING MHC II ANTIGEN PRESENTATION IN TUMOR-ASSOCIATED MACROPHAGES OF GBM

Abstract Glioblastoma (GBM) is the most common and malignant primary brain tumor with a median survival rate of 14 months. Despite the success of immunotherapy in treating various cancer types, its efficacy remains poor in GBM. Such limitation can be attributed to the profound immunosuppressive tumor microenvironment of GBM enriched with the tumor-associated macrophages (TAMs). Quaking (Qki) is an RNA-binding protein that is mutated or deleted in more than 35% of GBM patients. Decreased levels of Qki in TAMs associates with worsened survival rates and responsiveness to immunotherapy in GBM mouse and patients. Moreover, Qki is a tumor suppressor gene in GBM and a major regulator in phagocytosis, a fundamental biological process in delivering antigens to major histocompatibility complex class II (MHC II). MHC II-restricted antigen presentation in macrophages of GBM is important in maintaining the fitness of cytotoxic and helper T cells required in anti-tumor response. However, the mechanism through which Qki regulates MHCII expression and presentation has yet to be elucidated. I hypothesize that Qki promotes MHC II expression in TAMs, thereby constraining the development and progression of GBM. In vitro assays like immunofluorescent staining, qRT-PCR, cell co-culture system, and flow cytometry will be performed involving QPP (Qk-/-Trp53-/-; Pten-/-) mouse brains, QPP cells, and mouse macrophage cell lines. A positive correlation between transcriptomic and protein expression levels of Qki, MHC II, and CIITA (a master regulator of MHC II) was confirmed in both mouse QPP and human GBM samples. Moreover, bone-marrow-derived macrophages activated by QPP cell supernatant shows upregulated levels of Qki and thus MHC II genes. A preliminary conclusion is that Qki plays a permissive role in MHCII expression in TAMs of GBM. Further downstream impact of Qki in TAMs will be evaluated in T cell activity and in transcription of MHC II in TAMs.

CNSC-20. MONOSYNAPTIC TRACING DEFINES BRAIN-WIDE CIRCUIT CONNECTIVITY OF HUMAN GLIOBLASTOMA

Abstract Glioblastoma (GBM), a deadly brain cancer, infiltrates the brain and can be synaptically innervated by neurons. Synaptic inputs onto GBM cells identified so far are largely short-range and glutamatergic in nature. The extent of integration of GBM cells into the brain-wide neuronal circuitry is therefore not well understood. We report the application of transsynaptic viral tracing approaches to study the neuronal connectome of GBM. We applied rabies virus-mediated retrograde tracing and herpes simplex virus (HSV)-mediated anterograde tracing approaches to characterize presynaptic partners in vivo in the adult mouse brain and ex vivo with iPSC-derived neurons, cortical organoid-GBM assembloids, and human surgical specimens. After transplantation into adult mice, GBM cells derived from multiple patients rapidly integrated into brain-wide neuronal circuits. GBM exhibited increased connectivity rates compared to transplanted neural progenitor cells, highlighting functional connectivity as a hallmark of malignant cells. Beyond glutamatergic inputs, we identified neuromodulatory inputs across the brain, including cholinergic inputs from the basal forebrain. We validated these long-range cholinergic neuron-to-glioma synapses signaling through the metabotropic CHRM3 receptor by high-resolution microscopy, anterograde monosynaptic HSV tracing, calcium imaging, and patch-clamp electrophysiology. To interrogate the functional effects of acetylcholine (ACh) on GBM, we performed calcium imaging and RNA sequencing analyses, which showed that ACh stimulation induced sustained calcium oscillations and long-lasting transcriptional reprogramming of GBM cells into a more invasive state via CHRM3. Importantly, CHRM3 activation promoted GBM cell invasion, whereas CHRM3 downregulation suppressed GBM cell invasion in vitro and in vivo, suggesting CHRM3 as a potential therapeutic target for this disease. Together, these results reveal the capacity of human GBM cells to robustly integrate into anatomically and molecularly diverse neuronal circuitry in the adult brain. They also support a model wherein rapid synapse formation onto GBM cells may promote a long-lasting increase in tumor cell fitness.

STEM-13. NUCLEAR LOCALIZATION OF ALPHA-1-ANTICHYMOTRYPSIN INCREASES IN GLIOBLASTOMA FOLLOWING STANDARD OF CARE TREATMENT

Abstract Glioblastoma (GBM) is the most common malignant primary brain tumor in adults with a median survival of 8-14 months and 5-year survival rate of 6.9%. Its aggressive nature arises mostly from molecular heterogeneity and resistance to standard of care (SOC), including radiation and temozolomide (TMZ). Recurrence is nearly inevitable, driven by highly invasive brain tumor initiating cells (BTICs). Our previous studies revealed that exposing BTICs to cerebrospinal fluid (CSF) from GBM patients increases cell migration and proliferation compared to non-cancer CSF. Transcriptomic analysis identified the upregulation of the SERPINA3 gene, which encodes alpha-1-antichymotrypsin (ACT). Silencing of SERPINA3 reduces BTIC migration and proliferation and abolishes the promigratory response to GBM-derived CSF, highlighting SERPINA3 as a potential therapeutic target. ACT has been reported to bind to DNA, although the implications of this interaction are unknown. We have previously observed higher levels of intranuclear ACT in human GBM compared to non-cancer brain tissues. We hypothesize that the nuclear localization of SERPINA3 in GBM contributes to increased malignancy, opening the possibility of therapeutically targeting its intranuclear transport. Here, we determined the intracellular localization of ACT in BTICs and GBM and compared it to non-cancer tissues. Additionally, we evaluated whether SOC affected intranuclear localization of ACT. Patient-derived BTICs were treated with TMZ, radiation, and a combination of both, to assess changes in ACT expression via Western Blot, PCR, and ICC. A decrease in cell confluency was correlated with a significant decrease (p<0.05) in SERPINA3 mRNA and overall protein expression when BTICs were treated with TMZ alone or in combination. Interestingly, confocal microscopy revealed a significant increase (p<0.05) in its nuclear localization, particularly with TMZ treatment, indicating a change in its intracellular distribution. Overall, nuclear translocation of SERPINA3 increases in response to SOC with potential implications as a treatment resistance mechanism.

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.

EXTH-69. DEVELOPMENT OF A NOVEL, HUMAN ANTIBODY TO IMPROVE ONCOLYTIC VIRUS THERAPY FOR GLIOBLASTOMA

Abstract Glioblastoma (GBM) is the most aggressive, malignant, primary brain tumor with abysmal overall survival. GBM is regarded as an “immune cold” tumor due to poor immune cell infiltration and immunosuppressive signaling in the tumor microenvironment (TME). Oncolytic herpes virus (oHSV) therapy has emerged as a possible therapeutic avenue for solid tumors such as GBM. We have observed that oHSV-treated tumor cells release extracellular ATP (eATP) which functions as immunostimulatory signaling molecule. In the TME, eATP is rapidly hydrolyzed into immunosuppressive adenosine by ectoenzymes CD39 and CD73. Using global CD73 knock out (CD73KO) mice or a function-blocking murine antibody, we found that blocking CD73 activity improves oHSV therapy in vivo. Intracranial tumor-bearing CD73KO mice respond significantly better to oHSV therapy than wild type (WT). These long-term survivors also rejected a subsequent tumor challenge, demonstrating development of a memory response. scRNA-seq revealed significantly increased immune cell infiltration in CD73KO mice compared to WT. We evaluated cellular crosstalk using CellChat and uncovered a major CCL-directed signaling pathway in the CD73KO mice. Furthermore, we identified a novel, human CD73 antibody from panning an scFv phage display library derived from human tonsils. This antibody, Ab6, demonstrated functional inhibition of purified CD73 and very high binding affinity for CD73. Co-culture of human GBM cells treated with OV and Ab6 and donor PBMCs resulted in increased tumor cell death. Additionally, human DCs exposed to Ab6 and OV-treated conditioned media were better able to activate T cells. To evaluate in vivo efficacy of this novel antibody, we have generated custom humanized CD73 knock-in mice wherein human CD73 has replaced murine CD73. We are currently evaluating the efficacy of Ab6 and oHSV in these mice against intracranial glioma. These results will support the translation of Ab6 as a potential immune therapeutic to add to the arsenal against brain tumors.

EXTH-51. ENHANCING GLIOBLASTOMA TREATMENT: ALLOGENEIC CAR-T CELLS OVERCOMES FUNCTIONAL DEFICITS OF PATIENT-DERIVED AUTOLOGOUS PRODUCTS

Abstract Glioblastoma (GBM) is the most common primary brain malignancy in adults, with a dismal prognosis despite an intensive standard of care. Recently, chimeric antigen receptor T-cell (CAR-T) therapy has shown promising outcomes in treating liquid malignancies. However, clinical trials targeting various tumor antigens in GBM failed to show durable clinical benefit. Though this may stem from various tumor-intrinsic immune evasion strategies typical of GBM, there has been little work investigating whether the problem lies in the quality of the CAR-T products treatment itself. Currently, CAR-T cells for clinical studies are produced in an autologous setting, where T-cells are extracted from patients, engineered ex-vivo, and then re-infused. However, peripheral T-cells taken from GBM patients have shown qualitative and functional deficits, which may contribute to suboptimal treatment outcomes. Thus, we aimed to explore whether CAR-Ts generated from GBM patients had any functional deficits in comparison to healthy donors, utilizing our previously validated CD133 CAR-T. In this study, we show pre-treatment exhaustion, poor tumor control, and reduced survival advantage in autologous, patient-derived CD133-targeting CAR-T cell products using an orthotopic xenograft model of human GBM. To address the functional and logistical considerations of autologous therapy, we also sought to generate an “off-the-shelf” allogeneic CD133 CAR-T. Using CRISPR gene editing technology, we generated TCR-knockout CAR-T cells with comparable pre-clinical efficacy to our healthy donor derived autologous models. Ultimately, this work highlights the need to reevaluate autologous CAR-T therapy for GBM and consider allogeneic approaches as biologically-informed therapeutic alternatives.

TMIC-67. EMERGING ROLE OF EXTRACELLULAR MATRIX STIFFNESS AS A HALLMARK OF GLIOBLASTOMA: INSIGHT TO MECHANICAL MEMORY FORMATION AND PROLONGED INVASION IN THE TUMOR PERIPHERY

Abstract The extracellular matrix (ECM) plays a critical role in cancer progression, with its biophysical properties influencing cancer behavior. ECM stiffness can induce long-lasting adaptations in cancer cells, promoting sustained invasion through a process known as “mechanical memory” (MM). Glioblastoma (GBM) exhibits spatial heterogeneity in stiffness, with stiffer ECM found at the tumor periphery where invasive cells reside and promote recurrence. We hypothesize that increased stiffness at the tumor periphery primes GBM cells for sustained invasion through MM. METHODS Cell lines were established from image-guided human GBM samples from tumor margin and core (n=10 patients, 20 cell lines). Cells from random locations were conditioned in physiologically relevant extracellular matrices for two weeks. Human organotypic assay (n=3), Migration Assays, Atomic Force Microscopy (AFM), Immunocytochemistry, Western Blot, and RNA-sequencing (n=6) were performed. RESULTS GBM cells at higher stiff surfaces displayed increased migration (p<0.01). Magnetic Resonance Elastography (n=9) confirmed GBM heterogeneity, with softer cores (0.2-0.5kPa) transitioning to stiffer margins (>2kPa). Organotypic scaffolds mimicking the tumor margin promoted enhanced migration of GFP-labeled GBM cells. Margin cells and cells conditioned on stiffer matrices demonstrated higher migratory potential compared to their core and soft-conditioned counterparts (p<0.05). These trends persist over time and across multiple passages. ECM stiffness exposure causes nanomechanical, cytoskeletal, and transcriptional adaptations. AFM shows that cells from the margin (n=6) are softer (p<0.01) and more deformable (p<0.01). RNAseq identified upregulation of MM-specific genes in GBM margin cells. The mechanosensitive transcription factor YAP1 emerged as a key driver of MM. Notably, YAP1 is targetable by the FDA-approved drug Verteporfin. YAP1 expression was elevated in margin and stiff-conditioned cells (p<0.05). Stiff-conditioned cells and margin cells displayed increased sensitivity to Verteporfin treatment (p<0.05), with treatment significantly reducing margin migration compared to the core (p<0.001). CONCLUSION Stiffer GBM margins promote the formation of aggressive phenotypes through MM. Targeting YAP1 with Verteporfin, a readily available drug, presents a promising strategy to halt GBM invasion and improve patient outcomes.

EPCO-17. CARM1 METHYLATES GLIOBLASTOMA TUMOR SUPPRESSOR QUAKING TO REGULATE ITS TRANSCRIPTIONAL COACTIVATOR FUNCTION

Abstract Glioblastoma (GBM) represents the most prevalent and deadly primary brain tumor in adults, and it remains highly refractory to current therapeutic interventions. Significant intratumor heterogeneity drives rapid invasion, immune escape, and therapeutic resistance. Therapeutic paradigms based on deconvoluting key molecular mechanisms driving gliomagenesis are urgently needed. Quaking (Qki, encoded by Qk) is frequently altered in GBM patients; Qk mutations or deletions occur in 35% percent of cases, and the Qki protein is absent in 50-60% of cases. Our lab has characterized Qki as important tumor suppressor in GBM, where deletion of Qk enables pre-malignant neural stem cells to expand outside their niche and develop into tumors that recapitulate human GBM. We discovered that Qki functions as a transcriptional coactivator of lipid metabolism genes, whereby Qki loss disrupts lipid homeostasis and compromises the integrity of various membrane structures. Several downstream processes governed by Qki have been delineated; however, upstream regulators of Qki have yet to be identified. Recurrent cancer mutations to specific Qki arginine sites implicate the dysregulation of arginine methylation, a common post-translational modification catalyzed by protein arginine methyltransferases (PRMTs). Leveraging in vitro methylation assays, we demonstrate that Qki is selectively methylated by the PRMT coactivator-associated arginine methyltransferase 1 (CARM1), specifically in the Quaking regulatory domain where cancer mutations are reported. We observe that Qki interacts with known CARM1 substrates, functioning in the transcriptional complex assembled by CARM1. Through mutagenesis studies, we identified arginine 242 (R242) and arginine 256 (R256) as specific CARM1-mediated methylation sites on Qki. Importantly, mutations to these sites compromise Qki’s activity as a transcriptional coactivator. Moreover, brain-specific deletion of CARM1 in vivo results in neurological phenotypes reminiscent of Qki deletion. Altogether, we provide evidence that CARM1 represents a novel tumor suppressor in GBM that functions through the arginine methylation of Qki.

EPCO-44. SPATIAL TRANSCRIPTOMICS ENABLES STATISTICAL MODELING OF SEX DIFFERENCE IN GENE CO-EXPRESSION NETWORK AND IMMUNE LANDSCAPE OF GLIOBLASTOMA

Abstract Glioblastoma (GBM) is characterized by inter- and intra-tumor molecular heterogeneity and demonstrated cell plasticity. Sex differences have been observed in various aspects: a male:female GBM incidence ratio is 1.6:1; standard of care treatments (debulking, radiation, and temozolomide) benefit females more than males. 14 human GBM samples from two study sites were subject to spatial profiling on the Vizgen Merscope platform to examine whether distinct biological and therapeutic niches in GBM were evident, to understand how the tumor microenvironments (TME) contributed to the heterogeneity of GBM, and to interrogate sex difference in the immune landscape of GBM. Multiple sets of spatial probes were designed to capture the cell identities (cancer stem cells, astrocytes, oligodendrocytes, microglia, macrophages, etc.) and the spatially-resolved expression patterns of genes with different functions. Two of the 14 GBM samples were also profiled on another FISH-based spatial platform (Veranome). The data from the two platforms exhibited a linear correlation. We explored the gene-gene co-expression network, and calculated the interaction probabilities between genes which were then compared for sex difference. We found that female samples showed significantly lower (two-fold) CD4+/CD8A+ T-cell count ratios than male samples. We also observed sample-specific spatial niches of different GBM cell subtypes and immune cell populations. Our large-scale spatial transcriptomics study revealed intrinsic sex-based differences in immune response to tumor and illuminated microenvironmental influences on GBM.

DDEL-17. INTRA-TUMORAL CONVECTION ENHANCED DELIVERY OF DEXAMETHASONE REDUCES INFLAMMATORY SIGNATURES AND EXTENDS SURVIVAL IN GBM MODEL

Abstract Dexamethasone is the most widely utilized drug for glioblastoma (GBM). However, systemic delivery of dexamethasone in GBM patients is associated with significant side effects and increasing doses with worse survival. Convection-enhanced delivery (CED) can deliver high doses of immunotherapy directly into the tumor microenvironment (TME) while avoiding systemic toxicity. Here, we report that high doses of dexamethasone can be delivered locally by CED without side effects and increase survival in a GBM model along with reduced inflammatory myeloid signatures. We investigated CED of dexamethasone treatment on survival(n=40), adverse side effects, and the immunological TME through peripheral analyses, liquid chromatography–mass spectrometry, and histology in a preclinical syngeneic mouse model. Additionally, we assessed the transcriptional responses of human GBM slices and stem-cell-derived human microglia after steroid treatment through bulk and single-cell RNA sequencing. We found that 7-day treatment with CED of dexamethasone produced a significant survival advantage in glioma-bearing mice compared to non-treated control(p=0.03). Systemic dexamethasone achieved low levels of drug in the TME and caused dysregulated blood glucose, blood counts, and peripheral organ weights, while high CED doses avoided these side effects(p< 0.05 each). Steroid treatment of acute GBM slices and lipopolysaccharide-activated microglia in-vitro both reversed inflammatory myeloid signatures associated with poor survival and recurrence on RNA sequencing analyses. We demonstrate the preclinical efficacy of delivering high local doses of dexamethasone in a GBM model through CED and observed prolonged survival along with reduced adverse inflammatory myeloid signatures. No side effects were demonstrated after chronic CED treatment of dexamethasone while systemic delivery achieved poor tumor penetration and caused known hematologic and metabolic side effects supporting the potential to optimize the clinical use of this therapy. CED of dexamethasone provides us a new treatment paradigm to locally control inflammatory signatures in the glioma TME in a controlled fashion.