Patient-derived Glioblastoma Multiforme Research Articles

Isoform balance of the long noncoding RNA NEAT1 is regulated by the RNA-binding protein QKI, governs the glioma transcriptome, and impacts cell migration

The long noncoding RNA nuclear paraspeckle assembly transcript 1 (NEAT1) is involved in a variety of human cancers. Two overlapping NEAT1 isoforms, NEAT1_1 and NEAT1_2, are produced through mutually exclusive alternative 3' end formation. Previous studies extensively investigated NEAT1 dysregulation in tumors, but often failed to achieve distinct quantification of the two NEAT1 isoforms. Moreover, molecular mechanisms governing the biogenesis of NEAT1 isoforms and the functional impacts of their dysregulation in tumorigenesis remain poorly understood. In this study, we employed an isoform-specific quantification assay and found differential dysregulation of NEAT1 isoforms in patient-derived glioblastoma multiforme cells. We further showed usage of the NEAT1 proximal polyadenylation site (PAS) is a critical mechanism that controls glioma NEAT1 isoform production. CRISPR-Cas9-mediated PAS deletion reduced NEAT1_1 and reciprocally increased NEAT1_2, which enhanced nuclear paraspeckle formation in human glioma cells. Moreover, the utilization of the NEAT1 PAS is facilitated by the RNA-binding protein quaking (QKI), which binds to the proximal QKI recognition elements. Functionally, we identified transcriptomic changes and altered biological pathways caused by NEAT1 isoform imbalance in glioma cells, including the pathway for the regulation of cell migration. Finally, we demonstrated the forced increase of NEAT1_2 upon NEAT1 PAS deletion is responsible for driving glioma cell migration and promoting the expression of genes implicated in the regulation of cell migration. Together, our studies uncovered a novel mechanism that regulates NEAT1 isoforms and their functional impacts on the glioma transcriptome, which affects pathological pathways of glioma, represented by migration.

Suppressing PD-L1 Expression via AURKA Kinase Inhibition Enhances Natural Killer Cell-Mediated Cytotoxicity against Glioblastoma.

Immunotherapies have shown significant promise as an impactful strategy in cancer treatment. However, in glioblastoma multiforme (GBM), the most prevalent primary brain tumor in adults, these therapies have demonstrated lower efficacy than initially anticipated. Consequently, there is an urgent need for strategies to enhance the effectiveness of immune treatments. AURKA has been identified as a potential drug target for GBM treatment. An analysis of the GBM cell transcriptome following AURKA inhibition revealed a potential influence on the immune system. Our research revealed that AURKA influenced PD-L1 levels in various GBM model systems in vitro and in vivo. Disrupting AURKA function genetically led to reduced PD-L1 levels and increased MHC-I expression in both established and patient-derived xenograft GBM cultures. This process involved both transcriptional and non-transcriptional pathways, partly implicating GSK3β. Interfering with AURKA also enhanced NK-cell-mediated elimination of GBM by reducing PD-L1 expression, as evidenced in rescue experiments. Furthermore, using a mouse model that mimics GBM with patient-derived cells demonstrated that Alisertib decreased PD-L1 expression in living organisms. Combination therapy involving anti-PD-1 treatment and Alisertib significantly prolonged overall survival compared to vehicle treatment. These findings suggest that targeting AURKA could have therapeutic implications for modulating the immune environment within GBM cells.

Reprogramming Glioblastoma Cells into Non-Cancerous Neuronal Cells as a Novel Anti-Cancer Strategy.

Glioblastoma Multiforme (GBM) is an aggressive brain tumor with a high mortality rate. Direct reprogramming of glial cells to different cell lineages, such as induced neural stem cells (iNSCs) and induced neurons (iNeurons), provides genetic tools to manipulate a cell's fate as a potential therapy for neurological diseases. NeuroD1 (ND1) is a master transcriptional factor for neurogenesis and it promotes neuronal differentiation. In the present study, we tested the hypothesis that the expression of ND1 in GBM cells can force them to differentiate toward post-mitotic neurons and halt GBM tumor progression. In cultured human GBM cell lines, including LN229, U87, and U373 as temozolomide (TMZ)-sensitive and T98G as TMZ-resistant cells, the neuronal lineage conversion was induced by an adeno-associated virus (AAV) package carrying ND1. Twenty-one days after AAV-ND1 transduction, ND1-expressing cells displayed neuronal markers MAP2, TUJ1, and NeuN. The ND1-induced transdifferentiation was regulated by Wnt signaling and markedly enhanced under a hypoxic condition (2% O2 vs. 21% O2). ND1-expressing GBM cultures had fewer BrdU-positive proliferating cells compared to vector control cultures. Increased cell death was visualized by TUNEL staining, and reduced migrative activity was demonstrated in the wound-healing test after ND1 reprogramming in both TMZ-sensitive and -resistant GBM cells. In a striking contrast to cancer cells, converted cells expressed the anti-tumor gene p53. In an orthotopical GBM mouse model, AAV-ND1-reprogrammed U373 cells were transplanted into the fornix of the cyclosporine-immunocompromised C57BL/6 mouse brain. Compared to control GBM cell-formed tumors, cells from ND1-reprogrammed cultures formed smaller tumors and expressed neuronal markers such as TUJ1 in the brain. Thus, reprogramming using a single-factor ND1 overcame drug resistance, converting malignant cells of heterogeneous GBM cells to normal neuron-like cells in vitro and in vivo. These novel observations warrant further research using patient-derived GBM cells and patient-derived xenograft (PDX) models as a potentially effective treatment for a deadly brain cancer and likely other astrocytoma tumors.

Subtype-Selective Peptide and Protein Neurotoxic Inhibitors of Nicotinic Acetylcholine Receptors Enhance Proliferation of Patient-Derived Glioblastoma Cell Lines.

Glioblastoma multiforme (GBM) is the most aggressive type of brain cancer, with a poor prognosis. GBM cells, which develop in the environment of neural tissue, often exploit neurotransmitters and their receptors to promote their own growth and invasion. Nicotinic acetylcholine receptors (nAChRs), which play a crucial role in central nervous system signal transmission, are widely represented in the brain, and GBM cells express several subtypes of nAChRs that are suggested to transmit signals from neurons, promoting tumor invasion and growth. Analysis of published GBM transcriptomes revealed spatial heterogeneity in nAChR subtype expression, and functional nAChRs of α1*, α7, and α9 subtypes are demonstrated in our work on several patient-derived GBM microsphere cultures and on the U87MG GBM cell line using subtype-selective neurotoxins and fluorescent calcium mobilization assay. The U87MG cell line shows reactions to nicotinic agonists similar to those of GBM patient-derived culture. Selective α1*, α7, and α9 nAChR neurotoxins stimulated cell growth in the presence of nicotinic agonists. Several cultivating conditions with varying growth factor content have been proposed and tested. The use of selective neurotoxins confirmed that cell cultures obtained from patients are representative GBM models, but the use of media containing fetal bovine serum can lead to alterations in nAChR expression and functioning.

MODL-38. DEFINING THE ROLE OF DAAM2 R414W MUTATION IN GLIOMAGENESIS AND GBM GROWTH

Abstract Each year in the United States, more than 13,000 people are diagnosed with glioblastoma multiforme (GBM), and more than 10,000 are estimated to succumb to the disease, making GBM the most common and lethal primary adult brain tumor. Despite advancing therapies, GBM patient survival has not improved over the decades, so it is critical to better understand glioma etiology. The majority of GBM cases arise from a sporadic accumulation of somatic mutations, but approximately 5-10% of gliomas are classified as “familial”, occurring clustered with hereditary cancer predispositions. These familial gliomas are caused by germline mutations inherited from parent to offspring, and only a few of these mutations have been directly linked to the development of GBM. We recently discovered five germline mutations in Daam2 (Dishevelled associated activator of morphogenesis 2) from GBM patients with a history of familial glioma. To examine the role of these mutations in GBM, we overexpressed these mutations in patient-derived GBM cells, which were then orthotopically xenografted into immunodeficient mice. We identified that one of these mutations, Daam2-R414W, promotes tumor cell proliferation both in vitro and in vivo. To further understand the role of the Daam2-R414W mutation in GBM, we generated a knock-in immunocompetent mouse model that harbors the Daam2-R414W mutation. In these mutant mice, we found increased proliferation of glial progenitor cells in the subventricular zone compared to Daam2 wildtype mice, suggesting the potential of the Daam2-R414W mutation to influence glial progenitor expansion to stimulate glioma initiation. Future experiments aim to answer whether this mutation promotes GBM growth in an immunocompetent model and to decipher the mechanism relating the Daam2-R414W mutation to GBM pathology. These studies will shed light on the repercussions of a human developmental gene variant and its potential to disrupt normal cellular machinery to promote malignancy and GBM development.

EPCO-41. MICRORNA-MEDIATED DIRECT NEURONAL REPROGRAMMING OF GLIOBLASTOMAS

Abstract Neuron-specific microRNAs miR-9/9* and miR-124 (miR-9/9*-124) are potent neurogenic molecules whose ectopic expression in non-neuronal somatic cells effectively induces direct cell fate conversion into a neuronal fate. Our recent work indicates that the fate transition occurs in distinct steps where miR-9/9*-124 first represses core gene regulatory networks to erase the original non-neuronal cell identity and subsequently activates the neuronal program to confer neuronal fate. Extending these findings, we reason that repression of similar gene regulatory networks by miR-9/9*-124 can also induce fate erasure in cancerous cells using glioblastoma as a paradigm. Glioblastoma multiforme (GBM) is a type of aggressive brain tumor with poor prognosis. Instead of having specific mutation profiles, GBMs present a global genetic network dysregulation which gives rise to a neural stem cell or progenitor cell-like state resembling embryonic neural development. Whereas miR-9/9*-124 plays a key role in inducing mitotic exit and orchestrating neurogenesis during development and neuronal reprogramming, we hypothesize that miR-9/9*-124 will instruct neuronal reprogramming of GBMs. Our results so far demonstrate that miR-9/9*-124 indeed exerts reprogramming activities in patient-derived GBM cell lines. Ectopic expression of miR-9/9*-124 in vitro readily induces GBM cells to exit cell cycle and promotes neuronal identity over time. In GBM intracerebral xenograft mouse model, mice receiving GBM cells overexpressing miR-9/9*-124 were able to survive longer than those with GBMs overexpressing non-specific microRNAs. We are currently carrying out transcriptomic and chromatin accessibility analyses to infer the epigenetic switch as GBM cells are reprogrammed to neurons. Based on these studies, we will further examine whether the GBM cells undergo irreversible fate erasure and are reprogrammed into a stable post-mitotic neuronal state. Our studies will provide insights into the plasticity of GBM fate that can be controlled by microRNAs and the key downstream regulatory nodes underlying fate transition of GBM to permanent post-mitotic state.

Establishment of a 3D Model to Characterize the Radioresponse of Patient-Derived Glioblastoma Cells.

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor in adults. Despite modern, multimodal therapeutic options of surgery, chemotherapy, tumor-treating fields (TTF), and radiotherapy, the 5-year survival is below 10%. In order to develop new therapies, better preclinical models are needed that mimic the complexity of a tumor. In this work, we established a novel three-dimensional (3D) model for patient-derived GBM cell lines. To analyze the volume and growth pattern of primary GBM cells in 3D culture, a CoSeedisTM culture system was used, and radiation sensitivity in comparison to conventional 2D colony formation assay (CFA) was analyzed. Both culture systems revealed a dose-dependent reduction in survival, but the high variance in colony size and shape prevented reliable evaluation of the 2D cultures. In contrast, the size of 3D spheroids could be measured accurately. Immunostaining of spheroids grown in the 3D culture system showed an increase in the DNA double-strand-break marker γH2AX one hour after irradiation. After 24 h, a decrease in DNA damage was observed, indicating active repair mechanisms. In summary, this new translational 3D model may better reflect the tumor complexity and be useful for analyzing the growth, radiosensitivity, and DNA repair of patient-derived GBM cells.

α-Solanine Suppresses Glioblastoma Multiforme Growth and Metastatic Properties by Modulating the Apoptosis-autophagy Axis

Introduction: Glioblastoma multiforme (GBM) has a poor prognosis despite optimal treatment. Recent studies have shown the potential of phytochemicals as anti-cancer agents. α-solanine, derived from plants of the Solanum genus, is a promising molecule in this regard. This study investigated the efficacy of α-solanine compared to temozolomide (TMZ) against GBM cell lines (U87MG, U251, and T98G) in vitro.
 Methods: In-vitro assays were conducted to assess the viability, migration, invasion, and mode of cell death of U87MG, U251 and T98G GBM cell lines following α-solanine treatment in comparison to TMZ. Rt-qPCR and proteome profiling were conducted to investigate the changes induced by α-solanine on a molecular level.
 Results: α-solanine demonstrated potent cytotoxicity on all GBM lines, with IC50 values ranging from 19.66 µM to 22.87 µM between cell lines tested, and significantly inhibited GBM cell migration compared to TMZ treatment. RNA and protein level assays indicated upregulation of both apoptotic and autophagy proteins, suggesting the involvement of BECN1 and BNIP3L in α-solanine-induced cell death.
 Discussion and Conclusion: These findings contribute to the search for effective GBM treatments. Future studies should increase the number of biological replicates, employ alternative methods to strengthen the findings, and conduct in vivo experiments and testing using patient-derived GBM tissue to better evaluate any therapeutic suitability of and fully understand the mode of action of α-solanine on GBM.

A Novel Patient-Personalized Nanovector Based on Homotypic Recognition and Magnetic Hyperthermia for an Efficient Treatment of Glioblastoma Multiforme.

Glioblastoma multiforme (GBM) is the deadliest brain tumor, characterized by an extreme genotypic and phenotypic variability, besides a high infiltrative nature in healthy tissues. Apart from very invasive surgical procedures, to date, there are no effective treatments, and life expectancy is very limited. In this work, an innovative therapeutic approach based on lipid-based magnetic nanovectors is proposed, owning a dual therapeutic function: chemotherapy, thanks to an antineoplastic drug (regorafenib) loaded in the core, and localized magnetic hyperthermia, thanks to the presence of iron oxide nanoparticles, remotely activated by an alternating magnetic field. The drug is selected based on ad hoc patient-specific screenings; moreover, the nanovector is decorated with cell membranes derived from patients' cells, aiming at increasing homotypic and personalized targeting. It is demonstrated that this functionalization not only enhances the selectivity of the nanovectors toward patient-derived GBM cells, but also their blood-brain barrier in vitro crossing ability. The localized magnetic hyperthermia induces both thermal and oxidative intracellular stress that lead to lysosomal membrane permeabilization and to the release of proteolytic enzymes into the cytosol. Collected results show that hyperthermia and chemotherapy work in synergy to reduce GBM cell invasion properties, to induce intracellular damage and, eventually, to prompt cellular death.

The addition of arginine deiminase potentiates Mithramycin A-induced cell death in patient-derived glioblastoma cells via ATF4 and cytochrome C

BackgroundArginine auxotrophy constitutes a shortcoming for ~ 30% of glioblastoma multiforme (GBM). Indeed, arginine-depleting therapy using arginine deiminase from Streptococcus pyogenes (SpyADI) has proven activity against GBM in preclinical studies. The good safety profile of SpyADI renders this agent an ideal combination partner for cytostatic therapy.MethodsIn this study, we combined the antineoplastic antibiotic Mithramycin A (MitA) with SpyADI to boost single-agent activity and analyzed underlying response mechanisms in-depth.ResultsMitA monotherapy induced a time- and dose-dependent cytotoxicity in eight patient-derived GBM cell lines and had a radiosensitizing effect in all but one cell line. Combination treatment boosted the effects of the monotherapy in 2D- and 3D models. The simultaneous approach was superior to the sequential application and significantly impaired colony formation after repetitive treatment. MitA monotherapy significantly inhibited GBM invasiveness. However, this effect was not enhanced in the combination. Functional analysis identified SpyADI-triggered senescence induction accompanied by increased mitochondrial membrane polarization upon mono- and combination therapy. In HROG63, induction of lysosomes was seen after both monotherapies, indicative of autophagy. These cells seemed swollen and had a more pronounced cortically formed cytoskeleton. Also, cytochrome C and endoplasmatic reticulum-stress-associated proteins ATF4 and Calnexin were enhanced in the combination, contributing to apoptosis. Notably, no significant increases in glioma-stemness marker were seen.ConclusionsTherapeutic utilization of a metabolic defect in GBM along with cytostatic therapy provides a novel combination approach. Whether this SpyADI/MitA regimen will provide a safe alternative to combat GBM, will have to be addressed in subsequent (pre-)clinical trials.Graphical

Identification of Dysregulated microRNAs in Glioblastoma Stem-like Cells.

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor in adults. Despite multimodal therapy, median survival is poor at 12-15 months. At the molecular level, radio-/chemoresistance and resulting tumor progression are attributed to a small fraction of tumor cells, termed glioblastoma stem-like cells (GSCs). These CD133-expressing, self-renewing cells display the properties of multi-lineage differentiation, resulting in the heterogenous composition of GBM. MicroRNAs (miRNAs) as regulators of gene expression at the post-transcriptional level can alter many pathways pivotal to cancer stem cell fate. This study explored changes in the miRNA expression profiles in patient-derived GSCs altered on differentiation into glial fiber acid protein (GFAP)-expressing, astrocytic tumor cells using a polymerase chain reaction (PCR) array. Initially, 22 miRNAs showed higher expression in GSCs and 9 miRNAs in differentiated cells. The two most downregulated miRNAs in differentiated GSCs were miR-17-5p and miR-425-5p, whilst the most upregulated miRNAs were miR-223-3p and let-7-5p. Among those, miR-425-5p showed the highest consistency in an upregulation in all three GSCs. By transfection of a 425-5p miRNA mimic, we demonstrated downregulation of the GFAP protein in differentiated patient-derived GBM cells, providing potential evidence for direct regulation of miRNAs in the GSC/GBM cell transition.

The CDK inhibitor AT7519 inhibits human glioblastoma cell growth by inducing apoptosis, pyroptosis and cell cycle arrest

Glioblastoma multiforme (GBM) is the most lethal primary brain tumor with a poor median survival of less than 15 months. However, clinical strategies and effective therapies are limited. Here, we found that the second-generation small molecule multi-CDK inhibitor AT7519 is a potential drug for GBM treatment according to high-throughput screening via the Approved Drug Library and Clinical Compound Library (2718 compounds). We found that AT7519 significantly inhibited the cell viability and proliferation of U87MG, U251, and patient-derived primary GBM cells in a dose-dependent manner. Furthermore, AT7519 also inhibited the phosphorylation of CDK1/2 and arrested the cell cycle at the G1-S and G2-M phases. More importantly, AT7519 induced intrinsic apoptosis and pyroptosis via caspase-3-mediated cleavage of gasdermin E (GSDME). In the glioblastoma intracranial and subcutaneous xenograft assays, tumor volume was significantly reduced after treatment with AT7519. In summary, AT7519 induces cell death through multiple pathways and inhibits glioblastoma growth, indicating that AT7519 is a potential chemical available for GBM treatment.

Inhibition of MZF1/c-MYC Axis by Cantharidin Impairs Cell Proliferation in Glioblastoma

Myeloid zinc finger 1 (MZF1), also known as zinc finger protein 42, is a zinc finger transcription factor, belonging to the Krüppel-like family that has been implicated in several types of malignancies, including glioblastoma multiforme (GBM). MZF1 is reportedly an oncogenic gene that promotes tumor progression. Moreover, higher expression of MZF1 has been associated with a worse overall survival rate among patients with GBM. Thus, MZF1 may be a promising target for therapeutic interventions. Cantharidin (CTD) has been traditionally used in Chinese medicine to induce apoptosis and inhibit cancer cell proliferation; however, the mechanism by which CTD inhibits cell proliferation remains unclear. In this study, we found that the expression of MZF1 was higher in GBM tissues than in adjacent normal tissues and low-grade gliomas. Additionally, the patient-derived GBM cells and GBM cell lines presented higher levels of MZF1 than normal human astrocytes. We demonstrated that CTD had greater anti-proliferative effects on GBM than a derivative of CTD, norcantharidin (NCTD). MZF1 expression was strongly suppressed by CTD treatment. Furthermore, MZF1 enhanced the proliferation of GBM cells and upregulated the expression of c-MYC, whereas these effects were reversed by CTD treatment. The results of our study suggest that CTD may be a promising therapeutic agent for patients with GBM and suggest a promising direction for further investigation.

The IAP antagonist birinapant enhances chimeric antigen receptor T cell therapy for glioblastoma by overcoming antigen heterogeneity

Antigen heterogeneity that results in tumor antigenic escape is one of the major obstacles to successful chimeric antigen receptor (CAR) Tcell therapies in solid tumors including glioblastoma multiforme (GBM). To address this issue and improve the efficacy of CAR Tcell therapy for GBM, we developed an approach that combines CAR Tcells with inhibitor of apoptosis protein (IAP) antagonists, a new class of small molecules that mediate the degradation of IAPs, to treat GBM. Here, we demonstrated that the IAP antagonist birinapant could sensitize GBM cell lines and patient-derived primary GBM organoids to apoptosis induced by CAR Tcell-derived cytokines, such as tumor necrosis factor. Therefore, birinapant could enhance CAR Tcell-mediated bystander death of antigen-negative GBM cells, thus preventing tumor antigenic escape in antigen-heterogeneous tumor models invitro and invivo. In addition, birinapant could promote the activation of NF-κB signaling pathways in antigen-stimulated CAR Tcells, and with a birinapant-resistant tumor model we showed that birinapant had no deleterious effect on CAR Tcell functions invitro and invivo. Overall, we demonstrated the potential of combining the IAP antagonist birinapant with CAR Tcells as a novel and feasible approach to overcoming tumor antigen heterogeneity and enhancing CAR Tcell therapy forGBM.

MicroRNA and mRNA Expression Changes in Glioblastoma Cells Cultivated under Conditions of Neurosphere Formation.

Glioblastoma multiforme (GBM) is one of the most highly metastatic cancers. The study of the pathogenesis of GBM, as well as the development of targeted oncolytic drugs, require the use of actual cell models, in particular, the use of 3D cultures or neurospheres (NS). During the formation of NS, the adaptive molecular landscape of the transcriptome, which includes various regulatory RNAs, changes. The aim of this study was to reveal changes in the expression of microRNAs (miRNAs) and their target mRNAs in GBM cells under conditions of NS formation. Neurospheres were obtained from both immortalized U87 MG and patient-derived BR3 GBM cell cultures. Next generation sequencing analysis of small and long RNAs of adherent and NS cultures of GBM cells was carried out. It was found that the formation of NS proceeds with an increase in the level of seven and a decrease in the level of 11 miRNAs common to U87 MG and BR3, as well as an increase in the level of 38 and a decrease in the level of 12 mRNA/lncRNA. Upregulation of miRNAs hsa-miR: -139-5p; -148a-3p; -192-5p; -218-5p; -34a-5p; and -381-3p are accompanied by decreased levels of their target mRNAs: RTN4, FLNA, SH3BP4, DNPEP, ETS2, MICALL1, and GREM1. Downregulation of hsa-miR: -130b-5p, -25-5p, -335-3p and -339-5p occurs with increased levels of mRNA-targets BDKRB2, SPRY4, ERRFI1 and TGM2. The involvement of SPRY4, ERRFI1, and MICALL1 mRNAs in the regulation of EGFR/FGFR signaling highlights the role of hsa-miR: -130b-5p, -25-5p, -335-3p, and -34a-5p not only in the formation of NS, but also in the regulation of malignant growth and invasion of GBM. Our data provide the basis for the development of new approaches to the diagnosis and treatment of GBM.

Abstract 6058: The serine synthesis pathway contributes to the radiation-induced metabolic plasticity in glioblastoma multiforme

Abstract Purpose: Glioblastoma multiforme (GBM) remains a fatal disease despite aggressive treatment approaches. Post-surgical radiation therapy (RT) is the only treatment that significantly improves survival of GBM patients but recurrence is inevitable. Elucidating the mechanisms of resistance to RT could transform GBM patient outcomes. The purpose of this study was to elucidate the effect of radiation on the serine synthesis pathway (SSP) and the role of SSP in boosting antioxidant defenses in irradiated GBM cells and promoting radioresistance. Methods: We compared copy number alterations (CNA) and amplification of SSP enzymes (PHGDH, PSAT1, PSPH, SHMT1/2) in low-grade gliomas (LGG, n = 511) and GBM (n = 575) via TCGA pan-cancer analysis. In vitro HPLC/MS-based metabolomics assays were used to study the changes in overall metabolite levels induced by radiation in patient-derived GBM specimens. Targeted metabolomics with 13C-labeled glucose was used for tracking the fate of glucose towards SSP intermediates and antioxidant species. Gene expression levels after radiation were measured via molecular biology approaches. De novo SSP was targeted via pharmacological inhibition of PHGDH. Modified clonogenic, sphere forming assays (SFA) on gliomasphere cultures were used to determine radiosensitivity. Dependence on extracellular serine/glycine was determined via serine/glycine depletion experiments. Results: The TCGA analysis revealed increased CNAs in all the de novo SSP enzymes in GBM tumors relative to the LGGs. 82% of GBM tumors had CNAs or amplification of the PSPH gene, which codes for the ultimate enzyme in serine synthesis. In vitro metabolomics assays revealed that radiation increases the levels of serine, glycine and cystine in gliomaspheres, and this is accompanied by elevated levels of reduced glutathione (GSH). Targeted glucose metabolomics revealed radiation-induced upregulation of the de novoSSP, with a concomitant increase in gene expression of SSP enzymes. Downstream of the SSP, metabolomics data show that irradiated GBM cells elevate nucleotide and precursor levels, likely to support DNA damage repair mechanisms after radiation. The inhibition of PHGDH, the first rate-limiting enzyme in de novo SSP, significantly reduced GBM cell survival in vitro. Extracellular serine/glycine appeared to also be important contributors to radiation survival. Gene expression of SLC1A4, an amino acid transporter, was upregulated by radiation, while depletion of extracellular serine/glycine led to significant decreased survival in in vitro SFAs. Conclusion: Here we provide evidence that the de novo serine synthesis pathway is an important contributor to the metabolic reprogramming of GBM cells after radiation that promotes radiation resistance. These data call for further investigations to evaluate the radiosensitizing potential of targeting de novo SSP in GBM. Citation Format: Justine Bailleul, Yangjingyi Ruan, Erina Vlashi. The serine synthesis pathway contributes to the radiation-induced metabolic plasticity in glioblastoma multiforme [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6058.

Implementation of a combined CDK inhibition and arginine-deprivation approach to target arginine-auxotrophic glioblastoma multiforme cells

Constitutive activation of cyclin-dependent kinases (CDKs) or arginine auxotrophy are hallmarks of Glioblastoma multiforme (GBM). The latter metabolic defect renders tumor cells vulnerable to arginine-depleting substances, such as arginine deiminase from Streptococcus pyogenes (SpyADI). Previously, we confirmed the susceptibility of patient-derived GBM cells towards SpyADI as well as CDK inhibitors (CDKis). To improve therapeutic effects, we here applied a combined approach based on SpyADI and CDKis (dinaciclib, abemaciclib). Three arginine-auxotrophic patient-derived GBM lines with different molecular characteristics were cultured in 2D and 3D and effects of this combined SpyADI/CDKi approach were analyzed in-depth. All CDKi/SpyADI combinations yielded synergistic antitumoral effects, especially when given sequentially (SEQ), i.e., CDKi in first-line and most pronounced in the 3D models. SEQ application demonstrated impaired cell proliferation, invasiveness, and viability. Mitochondrial impairment was demonstrated by increasing mitochondrial membrane potential and decreasing oxygen consumption rate and extracellular acidification rate after SpyADI/abemaciclib monotherapy or its combination regimens. The combined treatment even induced autophagy in target cells (abemaciclib/SpyADI > dinaciclib/SpyADI). By contrast, the unfolded protein response and p53/p21 induced senescence played a minor role. Transmission electron microscopy confirmed damaged mitochondria and endoplasmic reticulum together with increased vacuolization under CDKi mono- and combination therapy. SEQ-abemaciclib/SpyADI treatment suppressed the DSB repair system via NHEJ and HR, whereas SEQ-dinaciclib/SpyADI treatment increased γ-H2AX accumulation and induced Rad51/Ku80. The latter combination also activated the stress sensor GADD45 and β-catenin antagonist AXIN2 and induced expression changes of genes involved in cellular/cytoskeletal integrity. This study highlights the strong antitumoral potential of a combined arginine deprivation and CDK inhibition approach via complex effects on mitochondrial dysfunction, invasiveness as well as DNA-damage response. This provides a good starting point for further in vitro and in vivo proof-of-concept studies to move forward with this strategy.

Gas Plasma Exposure of Glioblastoma Is Cytotoxic and Immunomodulatory in Patient-Derived GBM Tissue.

Simple SummaryDespite treatment advances, glioblastoma multiforme (GBM) remains an often-fatal disease, motivating novel therapeutic avenues. Gas plasma is a technology that has been recently employed in preclinical oncology research and acts primarily via reactive oxygen-species-induced cell death. In addition, the modulation of immune processes and inflammation have been ascribed to gas plasma exposure. This is the first study that extends those observations from in vitro investigations to a set of 16 patient-derived GBM tumor biopsies analyzed after gas plasma treatment ex vivo. Besides cell culture results showing cell cycle arrest and apoptosis induction, an immunomodulatory potential was identified for gas plasma exposure in vitro and cultured GBM tissues. The proapoptotic action shown in this study might be an important step forward to the first clinical observational studies on the future discovery of gas plasma technology’s potential in neurosurgery and neuro-oncology.Glioblastoma multiforme (GBM) is the most common primary malignant adult brain tumor. Therapeutic options for glioblastoma are maximal surgical resection, chemotherapy, and radiotherapy. Therapy resistance and tumor recurrence demand, however, new strategies. Several experimental studies have suggested gas plasma technology, a partially ionized gas that generates a potent mixture of reactive oxygen species (ROS), as a future complement to the existing treatment arsenal. However, aspects such as immunomodulation, inflammatory consequences, and feasibility studies using GBM tissue have not been addressed so far. In vitro, gas plasma generated ROS that oxidized cells and led to a treatment time-dependent metabolic activity decline and G2 cell cycle arrest. In addition, peripheral blood-derived monocytes were co-cultured with glioblastoma cells, and immunomodulatory surface expression markers and cytokine release were screened. Gas plasma treatment of either cell type, for instance, decreased the expression of the M2-macrophage marker CD163 and the tolerogenic molecule SIGLEC1 (CD169). In patient-derived GBM tissue samples exposed to the plasma jet kINPen ex vivo, apoptosis was significantly increased. Quantitative chemokine/cytokine release screening revealed gas plasma exposure to significantly decrease 5 out of 11 tested chemokines and cytokines, namely IL-6, TGF-β, sTREM-2, b-NGF, and TNF-α involved in GBM apoptosis and immunomodulation. In summary, the immuno-modulatory and proapoptotic action shown in this study might be an important step forward to first clinical observational studies on the future discovery of gas plasma technology’s potential in neurosurgery and neuro-oncology especially in putative adjuvant or combinatory GBM treatment settings.

PEGylation increases antitumoral activity of arginine deiminase of Streptococcus pyogenes

Arginine auxotrophy is a metabolic defect that renders tumor cells vulnerable towards arginine-depleting substances, such as arginine deiminase (ADI) from Streptococcus pyogenes (SpyADI). Previously, we confirmed SpyADI susceptibility on patient-derived glioblastoma multiforme (GBM) models in vitro and in vivo. For application in patients, serum half-life of the enzyme has to be increased and immunogenicity needs to be reduced. For this purpose, we conjugated the S. pyogenes-derived SpyADI with 20 kDa polyethylene glycol (PEG20) moieties, achieving a PEGylation of seven to eight of the 26 accessible primary amines of the SpyADI. The PEGylation reduced the overall activity of the enzyme by about 50% without affecting the Michaelis constant for arginine. PEGylation did not increase serum stability of SpyADI in vitro, but led to a longer-lasting reduction of plasma arginine levels in mice. Furthermore, SpyADI-PEG20 showed a higher antitumoral capacity towards GBM cells in vitro than the native enzyme.Key points• PEGylation has no effect on the affinity of SpyADI for arginine• PEGylation increases the antitumoral effects of SpyADI on GBM in vitro• PEGylation prolongs plasma arginine depletion by SpyADI in mice

EXTH-52. SYSTEMIC AND BRAIN PHARMACOKINETICS OF THE AMP-ACTIVATED PROTEIN KINASE SELECTIVE INHIBITOR SBI-0206965 AS A POTENTIAL THERAPEUTIC AGENT FOR THE TREATMENT OF GLIOBLASTOMA MULTIFORME

Abstract PURPOSE AMP-activated protein kinase (AMPK) is a molecular hub for cellular metabolic control. Recent evidence suggests that AMPK is a “druggable” novel target for the treatment of Glioblastoma Multiforme (GBM). However, AMPK-inhibitory compounds are largely limited to compound C, which has a poor selectivity profile. SBI-0206965 is a diaminopyrimidine derivative that directly inhibits AMPK with 40-fold greater potency and markedly lower kinase promiscuity than compound C. The current studies provide insights into systemic pharmacokinetics and plasma to brain partitioning of SBI-0206965. METHODS We conducted an intracerebral microdialysis study employing jugular vein-cannulated Sprague Dawley rats (males, 6- 8 weeks). Serial brain extracellular fluid (ECF) and venous blood samples were collected up to 10 hrs following intraperitoneal administration of SBI-0206965 (25 mg/kg). These samples were then quantitated for SBI-0206965 levels using a LC/MS method (Thermo Scientific LTQ-FT™, Ionization: Electrospray Ionization; positive ion). PK analysis was performed using the Non–Compartmental Analysis (Phoenix® WinNonlin 8.2 Certara USA, Inc.). RESULTS Plasma and ECF peak concentrations (Cmax) were 7.15 µM and 0.68 µM, whereas the time to peak (Tmax) were 0.5 and 1 hr, respectively. The plasma and brain ECF elimination half-lives were 1.5 and 3 hours, respectively. Plasma protein binding of SBI-0206965 was 82%. A comparison of the brain ECF Cmax and area under the curve (AUC) to corresponding plasma values suggested that the brain partitioning of the compound was 10-18%. When corrected for unbound fraction in plasma the AUC ratio was 0.86. Thus, these studies show that SBI-0206965 has adequate brain penetration. Further studies are now in progress to assess selectivity of SBI-0206965 for AMPK expressing cell lines, efficacy against patient-derived GBM and PK in tumor-bearing mice. CONCLUSION Results from this study will help to design optimal dosing regimen of SBI-0206965 in our efforts to explore AMPK as a GBM-specific drug target.