Glioma Stem-like Cells Research Articles

Abstract 3281: DNMT targeting enhances vulnerability of glioblastoma cells to MNK inhibition

Abstract Many factors complicate therapeutic strategies for glioblastoma (GBM), including the existence of the blood brain barrier and a heterogenous population of difficult to treat glioma stem cells. Innovative strategies targeting novel pathways alone or in combination are needed for sustainable therapeutic improvements. The MAPK pathway has been implicated in many cancers. MAPK interacting kinases (MNK1 and MNK2) are downstream of MAPKs and phosphorylate the eukaryotic translation initiation factor 4E (eIF4E), a protein involved in translation of oncogenic mRNAs. We have previously established pharmacological MNK inhibition as a promising strategy for GBM. However, most currently available MNK inhibitors lack specificity and exhibit off-target effects. We developed novel selective MNK inhibitors that show MNK inhibition specificity in GBM established cell lines as well as patient-derived cell lines propagated under stem cell permissive conditions as 3-D neurospheres. MNK inhibitors reduced cell viability and neurosphere growth. Our previous work with MNK inhibitors showed involvement in negative feedback loops activated with treatment of other pharmacological agents, so we conducted a high-throughput screening to identify potential targets for combination treatment. One of the top hits was a DNA methyltransferase (DNMT) inhibitor that enhanced MNK inhibitor antineoplastic effects in GBM cells. Dual MNK and DNMT inhibition synergistically reduced neurosphere growth in 3-D glioma stem-like cells. The combination promoted apoptosis in the mesenchymal glioma stem-like cells as shown through flow cytometry and increased expression of cleaved PARP, cleaved caspase 3, and Bax. Also, DNMT targeting enhanced the viability reduction effects of siRNA mediated MNK1 knockdown in GBM cells. This combination of our novel MNK inhibitor with DNMT inhibition elicited antineoplastic benefits in both 2-D cultures and 3-D glioma stem cell-like populations, demonstrating a potential novel therapeutic strategy in GBM. Citation Format: Candice Mazewski, Frank Eckerdt, Aneta Baran, Mariafausta Fischietti, Purav P. Vagadia, Ricardo E. Perez, Charles D. James, Gary E. Schiltz, Leonidas C. Platanias. DNMT targeting enhances vulnerability of glioblastoma cells to MNK inhibition [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 3281.

Abstract 905: Targeting muscarinic acetylcholine receptors in glioma stem like cells

Abstract Primary gliomas arising within the brain remain the deadliest form of brain cancer and account for 78% of all malignant brain tumors. Glioblastoma patients have a 5 percent five-year survival rate and drug-resistant tumors often recur following surgical resection and treatment with radiation or chemotherapy. The cancer stem cell hypothesis suggests the presence of a subset of undifferentiated cells, namely glioma stem cells (GSCs), in the heterogenous tumor mass that are likely responsible for tumor initiation and recurrence of tumors post resection and give rise to drug resistant tumors. Determining a way to suppress these malignant characteristics and/or depleting the GSC population could improve current cancer treatments and the survival of glioma patients. Some GSCs are similar to oligodendrocyte precursor cells (OPCs), found during neural development and also residing in the adult brain. OPCs are prone to malignant transformation and believed to be a cellular origin for glioma. Recent findings indicate that the well-characterized neurotransmitter acetylcholine (ACh) maintains the primitive state of normal OPCs via muscarinic ACh receptors (mAChRs) preventing maturation and cell cycle exit. We investigated the functional characterization of ACh and mAChRs in modulating malignancy in OPC-like cells. We studied cultures of primary mouse OPC-like GSCs. We used the primary cells to culture three-dimensional tumor organoids in vitro to better represent tumor heterogeneity. We also used patient derived xenografts (PDX) of glioma to grow flank xenografts in NSG mice for an in vivo model. Publicly available data and studies in our lab show high levels of expression of CHRM3 (M3mAChR) in glioma patients and in primary OPC like GSCs. A drug screen conducted in the context of multiple sclerosis determined that benztropine (BZT), an anti muscarinic drug targeting M3mAChR, causes normal OPCs to exit the cell cycle, lose stem cell like characteristics, and differentiate. In our lab, electrophysiological studies demonstrated that activation of mAChRs in OPC-like cells from mouse and patient tumors generates rapid (< 1 second) increases in cytosolic calcium. Pharmacologic studies indicated that treatment with FDA approved anti muscarinic benztropine suppresses proliferation in cultured glioma cells. We also observed that serially passaging flank tumors treated with BZT into new host mice slowed down recurrence of new tumors. In order to determine key receptors mediating cholinergic responses in OPC-like cells we performed protein quantification, which displayed lowered phosphorylation of ERK. Electrophysiological studies are being conducted to dissect the mechanisms by which ACh evokes calcium release. These studies improve understanding of how cholinergic microenvironment influences stem-like glioma cells, providing a platform for repositioning available small molecule modifiers for treatment of glioma. Citation Format: Sumyuktha V. Anand, Alexander G. Skorput, Allan T. Gulledge, Isabella B. Fox, Damian A. Bonnin, Alison L. Young, Matthew C. Havrda. Targeting muscarinic acetylcholine receptors in glioma stem like cells [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 905.

Integrative analysis of cell adhesion molecules in glioblastoma identified prostaglandin F2 receptor inhibitor (PTGFRN) as an essential gene

BackgroundGlioblastoma (GBM) is the most common primary malignant brain tumor in adults exhibiting infiltration into surrounding tissues, recurrence, and resistance to therapy. GBM infiltration is accomplished by many deregulated factors such as cell adhesion molecules (CAMs), which are membrane proteins that participate in cell-cell and cell-ECM interactions to regulate survival, proliferation, migration, and stemness.MethodsA comprehensive bioinformatics analysis of CAMs (n = 518) in multiple available datasets revealed genetic and epigenetic alterations among CAMs in GBM. Univariate Cox regression analysis using TCGA dataset identified 127 CAMs to be significantly correlated with survival. The poor prognostic indicator PTGFRN was chosen to study its role in glioma. Silencing of PTGFRN in glioma cell lines was achieved by the stable expression of short hairpin RNA (shRNA) against the PTGFRN gene. PTGFRN was silenced and performed cell growth, migration, invasion, cell cycle, and apoptosis assays. Neurosphere and limiting dilution assays were also performed after silencing of PTGFRN in GSCs.ResultsAmong the differentially regulated CAMs (n = 181, 34.9%), major proportion of them were found to be regulated by miRNAs (n = 95, 49.7%) followed by DNA methylation (n = 32, 16.7%), and gene copy number variation (n = 12, 6.2%). We found that PTGFRN to be upregulated in GBM tumor samples and cell lines with a significant poor prognostic correlation with patient survival. Silencing PTGFRN diminished cell growth, colony formation, anchorage-independent growth, migration, and invasion and led to cell cycle arrest and induction of apoptosis. At the mechanistic level, silencing of PTGFRN reduced pro-proliferative and promigratory signaling pathways such as ERK, AKT, and mTOR. PTGFRN upregulation was found to be due to the loss of its promoter methylation and downregulation of miR-137 in GBM. PTGFRN was also found to be higher in glioma stem-like cells (GSCs) than the matched differentiated glioma cells (DGCs) and is required for GSC growth and survival. Silencing of PTGFRN in GSCs reduced transcript levels of reprogramming factors (Olig2, Pou3f2, Sall2, and Sox2).ConclusionIn this study, we provide a comprehensive overview of the differential regulation of CAMs and the probable causes for their deregulation in GBM. We also establish an oncogenic role of PTGFRN and its regulation by miR-137 in GBM, thus signifying it as a potential therapeutic target.

IMMU-05. Integrative transcriptomic analysis of pilocytic astrocytomas reveals CNS region-associated characteristics

BACKGROUND: Recent insights highlight how the initiation and growth of gliomas is governed by interactions between glioma stem-like cells and stromal and immune cells in the tumor microenvironment. For pilocytic astrocytomas, the most common pediatric CNS tumor, this relationship is so far less explored. To this end, we used transcriptomic methods to investigate inter-patient heterogeneity, and the stromal and immune microenvironment of pilocytic astrocytomas. MATERIALS AND METHODS: In this study, we collected clinical data and tissue of 90 pre-treatment pilocytic astrocytomas from different CNS compartments: posterior fossa (n=57), supratentorial (n=23), and spinal (n=10). The median age at primary resection was 8 (0-16) years, and 66% (n=59) of our cohort was male. From 10 of these patients, we collected post-treatment samples after re-growth of the tumor as well. We characterized all samples by bulk RNA-sequencing and DNA methylation profiling, and selected a subset (n=10) samples for single-nucleus RNA-sequencing. RESULTS: Principal component analysis and unsupervised clustering of bulk sequencing data revealed gene expression patterns correlating to the CNS location of the tumor, consistent with prior reports. Using differential expression and functional pathway analysis, we found CNS region-associated enrichment of cell-cycle, developmental, and inflammatory-related pathways. With respect to the glioma immune microenvironment, supratentorial tumors were enriched in gene-sets related to T-cell activation and cytotoxicity, while spinal tumors had lowest expression of immune-related genes. Moreover, spinal tumors were enriched in pathways related to cell division, nucleotide synthesis, and neurodevelopment. To resolve cell-type expression programs of glioma and immune cells in the microenvironment, we collected and analyzed snRNA-seq data of 10 pilocytic astrocytomas, as well as harmonized our findings with a pre-existing dataset from Vladoiu, 2019. CONCLUSION: Our integrative transcriptomic analysis of pilocytic astrocytomas highlights CNS region-associated differences in expression programs of the glioma cells and in the immune cell composition of the tumor microenvironment.

HGG-13. Combined CDK inhibition and arginine-deprivation as targeted therapy for arginine-auxotrophic glioblastoma multiforme cells

INTRODUCTION/BACKGROUND: Glioblastoma multiforme show constitutive activation of cyclin-dependent kinases (CDKs) or arginine auxotrophy. This renders tumor cells vulnerable towards arginine-depleting substances, such as arginine deiminase from Streptococcus pyogenes (SpyADI). Previously, we confirmed the susceptibility of patient-derived GBM cells towards administration of SpyADI as well as CDK inhibitors (CDKis). To improve effects, we applied a sequential (SEQ) CDKi/SpyADI approach to examine mechanistic insights and drug susceptibility. MATERIALS AND METHODS: Three arginine-auxotrophic patient-derived GBM lines with different molecular characteristics were cultured in 2D and 3D (spheres and glioma stem-like cells (GSC)) and effects of this combined CDKi/SpyADI approach were analyzed. This included viability staining via Calcein AM in 2D and 3D-Glo in 3D culture and cell death analysis via flow cytometry. Therapy-induced morphological changes were identified with transmission electron microscopy (TEM). Besides, 3D-invasiveness, cellular stress, and DNA damage responses were measured. RESULTS: All SEQ-CDKi/SpyADI combinations yielded synergistic antitumoral effects, characterized by impaired cell proliferation, invasiveness, and viability. Notably, this SEQ-CDKi/SpyADI approach was most effective in 3D models. Mitochondrial impairment was demonstrated by increasing mitochondrial membrane potential and decreasing oxygen consumption rate along with extracellular acidification rate after abemaciclib/SpyADI monotherapy or its combination regimens. TEM confirmed damaged mitochondria and endoplasmic reticulum together with increased vacuolization under CDKi mono- and SEQ- CDKi/SpyADI 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. CONCLUSION: This study highlights the antitumoral potential of a combined SpyADI/CDKi approach. We show that sequential application of these substances has complex effects on mitochondrial dysfunction, invasiveness, and DNA-damage response. This provides a good starting point for further proof-of-concept studies to move forward with this strategy.

Differentiated glioma cell-derived fibromodulin activates integrin-dependent Notch signaling in endothelial cells to promote tumor angiogenesis and growth.

Cancer stem cells (CSCs) alone can initiate and maintain tumors, but the function of non-cancer stem cells (non-CSCs) that form the tumor bulk remains poorly understood. Proteomic analysis showed a higher abundance of the extracellular matrix small leucine-rich proteoglycan fibromodulin (FMOD) in the conditioned medium of differentiated glioma cells (DGCs), the equivalent of glioma non-CSCs, compared to that of glioma stem-like cells (GSCs). DGCs silenced for FMOD fail to cooperate with co-implanted GSCs to promote tumor growth. FMOD downregulation neither affects GSC growth and differentiation nor DGC growth and reprogramming in vitro. DGC-secreted FMOD promotes angiogenesis by activating integrin-dependent Notch signaling in endothelial cells. Furthermore, conditional silencing of FMOD in newly generated DGCs in vivo inhibits the growth of GSC-initiated tumors due to poorly developed vasculature and increases mouse survival. Collectively, these findings demonstrate that DGC-secreted FMOD promotes glioma tumor angiogenesis and growth through paracrine signaling in endothelial cells and identifies a DGC-produced protein as a potential therapeutic target in glioma.

Targeting nuclear pore complex and therapeutic response in glioblastoma stem cells.

e14000 Background: Glioblastoma is the most prevalent and lethal primary intrinsic tumor in the central nervous system. Glioblastoma stem cells (GSCs) reprogram the transcriptional and metabolic machinery to survive in a dynamic microenvironment. Understanding the regulatory mechanism of GSCs may inform novel therapeutic approaches to improve the clinical outcome for glioblastoma patients. Nuclear pore complex (NPC) is an evolutionarily conserved structure that maintains the traffic between the nucleus and cytoplasm. In current study, we aim to interrogate the aberrant regulation of NPC in GSCs and develop novel targeted approach to sensitize GSC to conventional therapy. Methods: Patient-derived GSCs were validated using functional assays. Transcriptional analysis of GSCs and matched differentiated glioblastoma cells (DGCs) were performed using RNA sequencing to identify aberrant regulatory pathways upregulated in GSCs. The clinical impact of target genes on patient survival was assessed using the glioblastoma dataset from The Cancer Genome Atlas (TCGA). Quantitative RT-PCR and Western blotting were performed to assess the relative expression between GSCs and DGCs. Radiation sensitivity was measured using Cs-137 irradiator. Validation of the stem-like function of target genes was performed using RNA interference followed by in vitro neurosphere formation assay and in vivo tumorigenesis with xenograft mouse model. Results: 27 of the total 31 NPC genes were found to be upregulated in the primary glioblastoma patient specimens compared to non-tumor brain tissue in the TCGA dataset. Among them, a systemic approach combining transcriptional profiling and clinical validation linked nucleoporin 98 (NUP98) to a nexus between GSC phenotype and therapeutic resistance. GSCs preferentially express NUP98, which is essential for GSC maintenance and tumorigenesis in vitro and in vivo. RNA sequencing demonstrated that NUP98 regulates the expression of key DNA repair genes, including BRCA1, BRCA2, and RAD51. NUP98 forms a complex with the transcription factor P65, and directly stimulates the active transcription of genes involved in homologous recombination. Attenuation of NUP98 or P65 expression leads to the accumulation of unrepaired intrinsic DNA damage and sensitizes GSC to the treatment of ionizing radiation. Clinically, overexpression of NUP98 informs poor clinical outcome among patients with glioblastoma. Conclusions: Combining transcriptional discovery and clinical validation, we discovered that NUP98, an essential NPC component, maintains GSC proliferation and tumorigenesis through modulating the transcriptional control of homologous recombination pathway. Our results demonstrated a novel therapeutic approach of sensitizing GSC to conventional treatment through targeting the nexus between aberrant transcriptional regulation and therapeutic resistance in stem-like glioma cells.

Retraction: Secreted Frizzled-Related Protein 4 Inhibits Glioma Stem-Like Cells by Reversing Epithelial to Mesenchymal Transition, Inducing Apoptosis and Decreasing Cancer Stem Cell Properties.

Retraction: Secreted Frizzled-Related Protein 4 Inhibits Glioma Stem-Like Cells by Reversing Epithelial to Mesenchymal Transition, Inducing Apoptosis and Decreasing Cancer Stem Cell Properties.

Lucanthone Targets Lysosomes to Perturb Glioma Proliferation, Chemoresistance and Stemness, and Slows Tumor Growth In Vivo.

Glioblastoma is the most common and aggressive primary brain tumor in adults. Median survival time remains at 16-20 months despite multimodal treatment with surgical resection, radiation, temozolomide and tumor-treating fields therapy. After genotoxic stress glioma cells initiate cytoprotective autophagy, which contributes to treatment resistance, limiting the efficacy of these therapies and providing an avenue for glioma recurrence. Antagonism of autophagy steps has recently gained attention as it may enhance the efficacy of classical chemotherapies and newer immune-stimulating therapies. The modulation of autophagy in the clinic is limited by the low potency of common autophagy inhibitors and the inability of newer ones to cross the blood-brain barrier. Herein, we leverage lucanthone, an anti-schistosomal agent which crosses the blood-brain barrier and was recently reported to act as an autophagy inhibitor in breast cancer cells. Our studies show that lucanthone was toxic to glioma cells by inhibiting autophagy. It enhanced anti-glioma temozolomide (TMZ) efficacy at sub-cytotoxic concentrations, and suppressed the growth of stem-like glioma cells and temozolomide-resistant glioma stem cells. In vivo lucanthone slowed tumor growth: reduced numbers of Olig2+ glioma cells, normalized tumor vasculature, and reduced tumor hypoxia. We propose that lucanthone may serve to perturb a mechanism of temozolomide resistance and allow for successful treatment of TMZ-resistant glioblastoma.

Phenotypic and molecular states of IDH1 mutation-induced CD24-positive glioma stem-like cells

Mutations in IDH1 and IDH2 drive the development of gliomas. These genetic alterations promote tumor cell renewal, disrupt differentiation states, and induce stem-like properties. Understanding how this phenotypic reprogramming occurs remains an area of high interest in glioma research. Previously, we showed that IDH mutation results in the development of a CD24-positive cell population in gliomas. Here, we demonstrate that this CD24-positive population possesses striking stem-like properties at the molecular and phenotypic levels. We found that CD24 expression is associated with stem-like features in IDH-mutant tumors, a patient-derived gliomasphere model, and a neural stem cell model of IDH1-mutant glioma. In orthotopic models, CD24-positive cells display enhanced tumor initiating potency compared to CD24-negative cells. Furthermore, CD24 knockdown results in changes in cell viability, proliferation rate, and gene expression that closely resemble a CD24-negative phenotype. Our data demonstrate that induction of a CD24-positive population is one mechanism by which IDH-mutant tumors acquire stem-like properties. These findings have significant implications for our understanding of the molecular underpinnings of IDH-mutant gliomas.

HIF1α/HIF2α induces glioma cell dedifferentiation into cancer stem cells through Sox2 under hypoxic conditions.

Objective: Our previous study showed that glioma stem-like cells could be induced to undergo dedifferentiation under hypoxic conditions, but the mechanism requires further study. HIF1α and HIF2α are the main molecules involved in the response to hypoxia, and Sox2, as a retroelement, plays an important role in the formation of induced pluripotent stem cells, especially in hypoxic microenvironments. Therefore, we performed a series of experiments to verify whether HIF1α, HIF2α and Sox2 regulated glioma cell dedifferentiation under hypoxic conditions.Materials and methods: Sphere formation by single glioma cells was observed, and CD133 and CD15 expression was compared between the normoxic and hypoxic groups. HIF1α, HIF2α, and Sox2 expression was detected using the CGGA database, and the correlation among HIF1α, HIF2α and Sox2 levels was analyzed. We knocked out HIF1α, HIF2α and Sox2 in glioma cells and cultured them under hypoxic conditions to detect CD133 and CD15 expression. The above cells were implanted into mouse brains to analyze tumor volume and survival time.Results: New spheres were formed from single glioma cells in 1% O2, but no spheres were formed in 21% O2. The cells cultured in 1% O2 highly expressed CD133 and CD15 and had a lower apoptosis rate. The CGGA database showed HIF1α and HIF2α expression in glioma. Knocking out HIF1α or HIF2α led to a decrease in CD133 and CD15 expression and inhibited sphere formation under hypoxic conditions. Moreover, tumor volume and weight decreased after HIF1α or HIF2α knockout with the same temozolomide treatment. Sox2 was also highly expressed in glioma, and there was a positive correlation between the HIF1α/HIF2α and Sox2 expression levels. Sox2 was expressed at lower levels after HIF1α or HIF2α was knocked out. Then, Sox2 was knocked out, and we found that CD133 and CD15 expression was decreased. Moreover, a lower sphere formation rate, higher apoptosis rate, lower tumor formation rate and longer survival time after temozolomide treatment were detected in the Sox2 knockout cells.Conclusion: In a hypoxic microenvironment, the HIF1α/HIF2α-Sox2 network induced the formation of glioma stem cells through the dedifferentiation of differentiated glioma cells, thus promoting glioma cell chemoresistance. This study demonstrates that both HIF1α and HIF2α, as genes upstream of Sox2, regulate the malignant progression of glioma through dedifferentiation.

ANGI-2 Identification and functions of CD44 as a predictor for bevacizumab-resistant glioblastoma to optimally treat the tumor with bevacizumab

Anti-angiogenic therapy with bevacizumab (Bev), a monoclonal antibody targeting vascular endothelial growth factor (VEGF), is a common treatment for recurrent glioblastoma (GBM), but its survival benefit is limited. Resistance to Bev is thought to be a major cause of ineffectiveness on Bev therapy. To optimize Bev therapy, identification of a predictive biomarker for responsiveness to Bev is required. Based on our previous study, we focused on the expression and functions of CD44 and VEGF in the Bev therapy. Here, we analyze a relationship between CD44 expression and responsiveness to Bev and elucidate the role of CD44 in anti-VEGF therapy. CD44 and VEGF expression in the tumor core and periphery of 22 GBMs was examined, and the relationship between expression of these molecules and progression-free time on Bev therapy was analyzed. The degree of CD44 expression in the tumor periphery was evaluated by the ratio of the mRNA expression in the tumor periphery to that in the tumor core (P/C ratio). VEGF expression was evaluated by the amount of the mRNA expression in the tumor periphery. To elucidate the roles of CD44 in the Bev therapy, in vitro and in vivo studies were performed using glioma stem-like cells (GSCs) and a GSC-transplanted mouse xenograft model, respectively. GBMs expressing high P/C ratio of CD44 were much more refractory to Bev than those expressing low P/C ratio of CD44, and the survival time of the former was much shorter than that of the latter. In vitro inhibition of VEGF with siRNA or Bev activated CD44 expression and increased invasion of GSCs. Bev showed no anti-tumor effects in mice transplanted with CD44-overexpressing GSCs. The P/C ratio of CD44 expression may become a useful biomarker predicting responsiveness to Bev in GBM. CD44 reduces the anti-tumor effect of Bev, resulting in much more highly invasive tumors.

IM-6 HVJ-E containing PD-L1 siRNA inhibits immunosuppressive activities and elicits antitumor immune responses in glioma

Inactivated Sendai virus particle, hemagglutinating virus of Japan-envelope (HVJ-E), is a non-replicating virus-derived vector, in which the genomic RNA of Sendai virus (HVJ) has been destroyed. HVJ-E is a promising vector that enables the highly efficient and safe introduction of enclosed molecules such as RNA into target cells. Moreover, HVJ-E provokes robust antitumoral immunity by activating natural killer (NK) cells and CD8+ T lymphocytes and their induction into the tumor periphery, and by suppressing regulatory T lymphocytes (Treg) locally in the tumor. In the present study, we investigated a novel combination of antitumor immunotherapy by the antitumor immune-activating effect of HVJ-E itself with the inhibition of tumor PD-L1 molecule expression. We confirmed that intratumoral injection of HVJ-E containing siRNA targeting PD-L1 (siPDL1/HVJ-E) inhibited tumor PD-L1 protein expression in a mouse subcutaneous tumor model using TS, a mouse glioma stem-like cell. We conducted treatment experiments in the mouse brain tumor model in three groups: control group (PBS), siNC/HVJ-E group (negative control siRNA + HVJ-E), and siPDL1/HVJ-E group. We obtained a significant prolongation of overall survival in the siPDL1/HVJ-E group. Flow cytometric analyses of brain tumor models showed that the proportions of brain-infiltrating CD8+ T lymphocytes and NK cells were significantly increased after giving siPDL1/HVJ-E; in contrast, the rate of Treg/CD4+ lymphocytes was significantly decreased in HVJ-E-treated tumors (siNC/HVJ-E and siPDL1/HVJ-E). No difference was observed in the proportions of macrophages or M2 macrophages. CD8 depletion abrogated the therapeutic effect of siPDL1/HVJ-E, indicating that CD8+ T lymphocytes mainly mediated this therapeutic effect. We believe that this non-replicating immunovirotherapy may be a novel therapeutic alternative to treat patients with glioblastoma. The full article has been published (Cancer Science. 2021 Jan;112(1):81–90).

WITHDRAWN: Long non-coding RNA RP5-821D11.7 promotes proliferation, migration, and epithelial-mesenchymal transition in glioma and glioma stem-like cells

Long noncoding RNA (lncRNA) has been recently revealed as a main regulatory molecule, which implicates many cellular functions. Studies showed that lncRNA abnormally expressed and involved in the progression and tumorigenesis of glioma. Present study identified a novel lncRNA associated with glioma, glioma stem-like cells (GSCs), and then revealed their potential functions. During the screening of lncRNAs, we investigated overexpression of lncRNA RP5-821D11.7 (lncRNA-RP5) in GSCs compared to glioma cells. Lentivirus-mediated shRNA for lncRNA-RP5 was constructed and transfected into glioma cells. Transfected stable glioma cells were transplanted into nude mice and tumor growth was observed. Knockdown of lncRNA-RP5 significantly inhibits proliferation, colony formation, migration and reduces epithelial-mesenchymal transition (EMT) by activating the Wnt/β-catenin pathway. Additionally, the results showed that lncRNA RP5 knockdown enhances cell apoptosis through endoplasmic reticulum stress. Therefore, this study may provide a better understanding about lncRNA-RP5 which revealed that it might be a potential therapeutic target in case of glioma progression and recurrence.

Targeting alpha2,3-sialylated glycan in glioma stem-like cells by Maackia amurensis lectin-II: A promising strategy for glioma treatment

Glioma stem/initiating cells have been considered a major cause of tumor recurrence and therapeutic resistance. In this study, we have established a new glioma stem-like cell (GSC), named U373-GSC, from the U373 glioma cell line. The cells exhibited stemness properties, e.g., expression of stem cell markers, self-renewal activity, multi-lineage differentiating abilities, and drug resistance. Using U373-GSC and GSC-03A–a GSC clone previously established from patient tissue, we have identified a novel GSC-associated sialic acid-modified glycan commonly expressed in both cell lines. Lectin fluorescence staining showed that Maackia amurensis lectin II (MAL–II)–binding alpha2,3-sialylated glycan (MAL-SG) was highly expressed in GSCs, and drastically decreased during FBS induced differentiation to glioma cells or little in the parental cells. Treatment of GSCs by MAL-II, compared with other lectins, showed that MAL-II significantly suppresses cell viability and sphere formation via induction of cell cycle arrest and apoptosis of the GSCs. Similar effects were observed when the cells were treated with a sialyltransferase inhibitor or sialidase. Taken together, we demonstrate for the first time that MAL-SGs/alpha-2,3 sialylations are upregulated and control survival/maintenances of GSCs, and their functional inhibitions lead to apoptosis of GSCs. MAL-SG could be a potential marker and therapeutic target of GSCs; its inhibitors, such as MAL-II, may be useful for glioma treatment in the future.

MEOX2 Transcription Factor Is Involved in Survival and Adhesion of Glioma Stem-like Cells.

Simple SummaryGlioblastoma is the most common and lethal primary brain tumor for which no curative treatment currently exists. In our previous work, we showed that MEOX2 was associated with a poor patient prognosis but its biological involvement in tumor development remains ill defined. To this purpose, the aim of our study was to investigate the role of MEOX2 in patient-derived glioblastoma cell cultures. We unraveled the MEOX2 contribution to cell viability and growth and its potential involvement in phenotype and adhesion properties of glioblastoma cells. This work paves the way toward a better understanding of the role of MEOX2 in the pathophysiology of primary brain tumors.The high expression of MEOX2 transcription factor is closely associated with poor overall survival in glioma. MEOX2 has recently been described as an interesting prognostic biomarker, especially for lower grade glioma. MEOX2 has never been studied in glioma stem-like cells (GSC), responsible for glioma recurrence. The aim of our study was to investigate the role of MEOX2 in GSC. Loss of function approach using siRNA was used to assess the impact of MEOX2 on GSC viability and stemness phenotype. MEOX2 was localized in the nucleus and its expression was heterogeneous between GSCs. MEOX2 expression depends on the methylation state of its promoter and is strongly associated with IDH mutations. MEOX2 is involved in cell proliferation and viability regulation through ERK/MAPK and PI3K/AKT pathways. MEOX2 loss of function correlated with GSC differentiation and acquisition of neuronal lineage characteristics. Besides, inhibition of MEOX2 is correlated with increased expression of CDH10 and decreased pFAK. In this study, we unraveled, for the first time, MEOX2 contribution to cell viability and proliferation through AKT/ERK pathway and its potential involvement in phenotype and adhesion properties of GSC.

Suppression of Ribosome Biogenesis by Targeting WD Repeat Domain 12 (WDR12) Inhibits Glioma Stem-Like Cell Growth.

Glioma stem-like cells (GSCs) are a subset of tumor cells that initiate malignant growth and promote the therapeutic resistance of glioblastoma, the most lethal primary brain tumor. Ribosome biogenesis is an essential cellular process to maintain cell growth, but its regulatory mechanism in GSCs remains largely unknown. Here, we show that WD repeat domain 12 (WDR12), a component of the Pes1-Bop1 complex (PeBoW), is required for ribosome biogenesis in GSCs. WDR12 is preferentially expressed in GSCs compared to non-stem tumor cells and normal brain cells. High levels of WDR12 are associated with glioblastoma progression and poor prognosis. Silencing WDR12 results in the degradation of PeBoW complex components and prevents the maturation of 28S rRNA, thereby inhibiting ribosome biogenesis in GSCs. Subsequently, WDR12 depletion compromises GSC proliferation, inhibits GSC-derived orthotopic tumor growth, and extends animal survival. Together, our results suggest that WDR12 is crucial for ribosome biogenesis in GSCs, and is thus a potential target for GSC-directed therapy of glioblastoma.

DDRE-33. PRECLINICAL THERAPEUTIC EFFICACY OF THE NOVEL BLOOD BRAIN BARRIER PENETRANT ATR INHIBITOR LR02 IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) remains an incurable tumor with median overall survival of 15 months despite radiation and alkylating temozolomide (TMZ) chemotherapy. DNA damage response (DDR) pathways are among the most important key players of oncogenic mutations associated with resistance to both chemotherapy and radiation in GBM. The high frequency of alterations in DDR pathways in GBM suggests that its inhibition by DDR inhibitors may render GBM cells more susceptible to DNA damaging interventions. Here, we report the preclinical in vitro and in vivo activity of a novel, orally bioavailable Ataxia-telangiectasia mutated serine/threonine protein kinase and Rad3-related (ATR) inhibitor LR02 (Laevoroc Oncology) in a panel of 15 well-characterized glioma stem-like cells (GSCs). Effects on cell proliferation, survival and tumor formation were analyzed following treatment with LR02. Growth inhibition was time- and dose-dependent with a 3-day exposure resulting in a growth inhibitory IC50 (gIC50) in the low nM range in all the glioblastoma cell lines tested. LR02 inhibited growth of GSCs at IC50 values ranging from 500nmol/L to-~2umol/L. Additional studies showed that temozolomide sensitized GSC to LR02. Importantly, we demonstrate that MGMT promotor methylation status was associated with cellular response to LR02 treatment with preferential inhibition of cell growth in MGMT promotor methylated (MGMT deficient) cell lines. LR02 showed efficacy and survival benefit in a GSC262 (MGMT methylated) orthotopic model of GBM. Further administration of LR02 further enhanced the in vivo antitumor efficacy of temozolomide (TMZ) against GBM using the GSC262 model demonstrating that ATR inhibitor LR02 may enhance alkylating agent-mediated cytotoxicity and provide a novel treatment combination for GBM patients. Our present findings establish that the ATR inhibitor LR02 can specifically be used in tumors with MGMT deficiency when combined with alkylating chemotherapy. Further studies are ongoing to evaluate the potential of LR02 to overcome radiation and chemotherapy resistance in glioblastoma.

TAMI-71. EFFECTS OF THE TREATED MICROENVIRONMENT ON GLIOMA CELL PROPERTIES IN AN ORGANOTYPIC BRAIN SLICE MODEL

Abstract Glioblastoma is the most aggressive primary brain tumor. Despite treatment all patients invariably recur. Treatment resistance is attributed to the presence of glioma stem-like cells. Initially thought to be a distinct and static cell population, it is becoming increasingly clear that the glioma stem-like cell phenotype represents one of many cellular states and that glioma cells show plasticity between stem-like and non-stem like states. These plastic cell states are affected by the tumor microenvironment. In our lab we have shown that irradiated and hypoxic astrocytes increase the stem-like cell properties of glioma cells. In this study, we aim to evaluate how the treated microenvironment alters glioma cell properties and use ex vivo organotypic brain slices generated from tumor bearing and tumor naïve mice to assess all aspects of the microenvironment. We first characterized organotypic brain slices cultured in different oxygen tensions. We saw that tumor-bearing slices survive for at least 14 days in culture at 21%, 5% or 1% oxygen tension (O2). Tumor cells were more viable in all culture conditions and timepoints compared to non-tumor cells. Moreover, we found that astrocytes seem to be attracted to tumor areas in both 5% and 1% O2 cultures. We then used the organotypic glioma slice culture system to address how preconditioning the microenvironment using radiation or temozolomide affects the properties of glioma cells that are seeded in these pretreated, tumor naïve slices. We saw that fluorescently labelled glioma cells seeded in treated slices can be isolated after two days of culture in the slices and can be used for downstream analyses, such as temozolomide or radiation treatment and colony formation. This study will elucidate the effect of the treated microenvironment on glioma cell properties by using the medium throughput method of organotypic slice cultures.

DDRE-27. METABOLIC SWITCHING AS A MECHANISM OF DRUG RESISTANCE AGAINST NAMPT INHIBITION IN GLIOMAS

Abstract BACKGROUND Gliomas exhibit significant heterogeneity in treatment response and characteristically deploy resistance mechanisms that render conventional therapies ineffective. Recently, novel agents have been developed that target regulators of differential energy pathways specifically utilized by gliomas. We previously reported on the targeting of Nicotinamide Phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD+ salvage pathway and its essential role in glioma cell energy metabolism. Here, we determined the mechanisms by which glioma cells bypass blockade of energy metabolism and develop resistance to NAMPT inhibitors. METHODS Using isogenic parental and drug-resistant patient-derived glioma stem-like cells (GSCs), we examined adaptive changes after NAMPT inhibition in glycolysis, mitochondrial function (oxidative state, basal respiration rate, spare respiratory capacity, maximum respiration capacity and proton leak) and metabolite levels using Agilent Seahorse assay and targeted metabolomics. Cross reactivity across various NAMPT inhibitors was measured using Cell Titer Glo assay. RESULTS GSCs exposed for an extended period to sub-lethal doses of FK866, a potent NAMPT inhibitor, acquired drug resistance to the agent which were also cross-resistant to other NAMPT inhibitors. Drug-resistant GSCs showed a decrease in extracellular acidification rate and oxygen consumption rate compared to isogenic parental lines. Further, metabolomic analysis showed a high accumulation of glutamate, creatine and histidine metabolites in these cells. These results indicate a shift in metabolism of drug-resistant GSCs from carbon metabolism to nitrogen metabolism. CONCLUSIONS GSCs resistant to the NAMPT inhibitor, FK866 showed cross resistance to other NAMPT inhibitors indicating specificity of this effect. The resistance mechanism involves a shift of preferential energy generation from glycolysis to amino acid metabolism which allows the cells to use alternative methods to generate NAD. Additional results from ongoing studies to delineate the mechanisms of metabolic switch in the drug resistance lines will be presented that will help develop strategies to combat resistance to NAMPT inhibitors.