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The ATP6V1G1 subunit (V1G1) of the vacuolar proton ATPase (V-ATPase) pump is crucial for glioma stem cells (GSC) maintenance and in vivo tumorigenicity. Moreover, V-ATPase reprograms the tumor microenvironment through acidification and release of extracellular vesicles (EV). Therefore, we investigated the role of V1G1 in GSC small EVs and their effects on primary brain cultures. To this end, small EVs were isolated from patients-derived GSCs grown as neurospheres (NS) with high (V1G1HIGH-NS) or low (V1G1LOW-NS) V1G1 expression and analyzed for V-ATPase subunits presence, miRNA contents, and cellular responses in recipient cultures. Our results show that NS-derived small EVs stimulate proliferation and motility of recipient cells, with small EV derived from V1G1HIGH-NS showing the most pronounced activity. This involved activation of ERK1/2 signaling, in a response reversed by V-ATPase inhibition in NS-producing small EV. The miRNA profile of V1G1HIGH-NS–derived small EVs differed significantly from that of V1G1LOW-NS, which included miRNAs predicted to target MAPK/ERK signaling. Mechanistically, forced expression of a MAPK-targeting pool of miRNAs in recipient cells suppressed MAPK/ERK pathway activation and blunted the prooncogenic effects of V1G1HIGH small EV. These findings propose that the GSC influences the brain milieu through a V1G1-coordinated EVs release of MAPK/ERK-targeting miRNAs. Interfering with V-ATPase activity could prevent ERK-dependent oncogenic reprogramming of the microenvironment, potentially hampering local GBM infiltration. Implications: Our data identify a novel molecular mechanism of gliomagenesis specific of the GBM stem cell niche, which coordinates a V-ATPase–dependent reprogramming of the brain microenvironment through the release of specialized EVs.

PTEN deletion or mutation occurs in 30% to 60% of patients with glioblastoma (GBM) and is associated with poor prognosis. Efficacious therapy for this subgroup of patients is currently lacking. To identify potential target(s) to selectively suppress PTEN-deficient GBM growth, we performed a three-step synthetic lethal screen on LN18 PTEN wild-type (WT) and knockout (KO) isogeneic GBM cell lines using a library containing 606 target-selective inhibitors. A MCL1 inhibitor UMI-77 identified in the screen exhibited excellent suppression on the proliferation, colony formation, 3D spheroid, and neurosphere formation of PTEN-deficient GBM cells. Mechanistically, loss of PTEN in GBM cells led to upregulation of MCL1 in posttranslational level via inhibition of GSK3β, and consequently confer cells resistance to apoptosis. Pharmacologic inhibition or knockdown of MCL1 blocked this PI3K–GSK3β–MCL1 axis and caused reduction of several antiapoptotic proteins, finally induced massive caspase-3 cleavage and apoptosis. In both subcutaneous and orthotopic GBM models, knockdown of MCL1 significantly impaired the in vivo growth of PTEN-deficient xenografts. Moreover, the combination of UMI-77 and temozolomide synergistically killed PTEN-deficient GBM cells. Collectively, our work identified MCL1 as a promising target for PTEN-deficient GBM. For future clinical investigations, priority should be given to the development of a selective MCL1 inhibitor with efficient brain delivery and minimal in vivo toxicity.

Purpose: Diffuse intrinsic pontine glioma (DIPG) bears a dismal prognosis. A genetically engineered brainstem glioma model harboring the recurrent DIPG mutation, Activin A receptor type I (ACVR1)-G328V (mACVR1), was developed for testing an immune-stimulatory gene therapy. Experimental Design: We utilized the Sleeping Beauty transposase system to generate an endogenous mouse model of mACVR1 brainstem glioma. Histology was used to characterize and validate the model. We performed RNA-sequencing analysis on neurospheres harboring mACVR1. mACVR1 neurospheres were implanted into the pons of immune-competent mice to test the therapeutic efficacy and toxicity of immune-stimulatory gene therapy using adenoviruses expressing thymidine kinase (TK) and fms-like tyrosine kinase 3 ligand (Flt3L). mACVR1 neurospheres expressing the surrogate tumor antigen ovalbumin were generated to investigate whether TK/Flt3L treatment induces the recruitment of tumor antigen–specific T cells. Results: Histologic analysis of mACVR1 tumors indicates that they are localized in the brainstem and have increased downstream signaling of bone morphogenetic pathway as demonstrated by increased phospho-smad1/5 and Id1 levels. Transcriptome analysis of mACVR1 neurosphere identified an increase in the TGFβ signaling pathway and the regulation of cell differentiation. Adenoviral delivery of TK/Flt3L in mice bearing brainstem gliomas resulted in antitumor immunity, recruitment of antitumor-specific T cells, and increased median survival (MS). Conclusions: This study provides insights into the phenotype and function of the tumor immune microenvironment in a mouse model of brainstem glioma harboring mACVR1. Immune-stimulatory gene therapy targeting the hosts' antitumor immune response inhibits tumor progression and increases MS of mice bearing mACVR1 tumors.

Background. Breast cancer brain metastases (BCBM) represents a terminal diagnosis accompanied by neurological decline and diminished quality of life. Average survival is less than a year following detection of neural lesions, due in part to an absence of targeted therapeutics. BCBM affects 12-17% of all breast cancer patients and over 25% of triple negative breast cancer (TNBC) patients. In the search for improved therapies, there is a focus increasingly on the role of the unique microenvironment of the brain in tumour progression. Few studies have investigated the establishment of an in vitro breast cancer brain microenvironment model that could enable the high-throughput identification and modulation of potential targets. In order to address this issue, a novel co-culture model was developed utilising the human neural progenitor cell (NPC) line ReNcell VM and MDA-MB-468 TNBC cells. Methods. ReNcell VM were differentiated as monolayers or neurospheres for four or ten days and stained for the glial marker glial fibrillary acidic protein (GFAP) and the neuronal marker β3-tubulin. Cultures were imaged via automated epi-fluorescence microscopy (ImageXpress Micro, Molecular Devices) and proportions of cell types were calculated with MetaXpress image analysis software. Differentiation characteristics of neurospheres and monolayers were compared. Functionality of neural cultures was determined using calcium assays with the muscarinic agonist carbachol as a validation tool. MDA-MB-468 cells loaded with a Cell Tracker Green dye were assessed for viability on the neural matrix via bright field and epi-fluorescence microscopy. Results. ReNcell VM cultured and differentiated for four days as neurospheres displayed a higher expression of β3-tubulin and GFAP than those cultured as monolayers (β3-tubulin 10.4% vs 7.7%, GFAP 53.6% vs 48.8%, respectively). Expression of β3 tubulin was higher after four days of differentiation than after ten days for neurosphere cultures (10.4% vs 4.4%, respectively). Carbachol elicited oscillatory calcium responses from ReNcell VM differentiated as neurospheres or monolayers, indicating functionality of both populations. MDA-MB-468 and ReNcell VM stained after four days of co-culture displayed successful integration of neoplastic cells on the neural matrix. Conclusions. Human NPCs provide a reproducible model of prominent cell types within the brain milieu and are suited to high-throughput automated epi-fluorescence microscopy applications. Co-culture models of TNBC and differentiated ReNcell VM represent a powerful platform for mechanistic studies and drug screening. Citation Format: Chalmers SB, Dalley AJ, Kalita-de Croft P, Saunus J, Bassett JJ, Sadras F, Roberts-Thomson SJ, Monteith GR. Establishment of a human neural progenitor cell microenvironment model to investigate signalling events in triple negative breast cancer brain metastases in a high-throughput setting [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-19-05.

Glioblastoma (GBM) is the most common and lethal form of primary brain tumor with dismal median and 2-year survivals of 14.5 months and 18%, respectively. The paucity of new therapeutic agents stems from the complex biology of a highly adaptable tumor that uses multiple survival and proliferation mechanisms to circumvent current treatment approaches. Here, we investigated the potency of a new generation of siRNAs to silence gene expression in orthotopic brain tumors generated by transplantation of human glioma stem-like cells in athymic nude mice. We demonstrate that cholesterol-conjugated, nuclease-resistant siRNAs (Chol-hsiRNAs) decrease mRNA and silence luciferase expression by 90% in vitro in GBM neurospheres. Furthermore, Chol-hsiRNAs distribute broadly in brain tumors after a single intratumoral injection, achieving sustained and potent (>45% mRNA and >90% protein) tumor-specific gene silencing. This readily available platform is sequence-independent and can be adapted to target one or more candidate GBM driver genes, providing a straightforward means of modulating GBM biology in vivo. Mol Cancer Ther; 17(6); 1251–8. ©2018 AACR.

Purpose: Pediatric glioblastoma multiforme (pGBM) is a highly aggressive tumor in need of novel therapies. Our objective was to demonstrate the therapeutic efficacy of MLN8237 (alisertib), an orally available selective inhibitor of Aurora A kinase (AURKA), and to evaluate which in vitro model system (monolayer or neurosphere) can predict therapeutic efficacy in vivo. Experimental Design: AURKA mRNA expressions were screened with qRT-PCR. In vitro antitumor effects were examined in three matching pairs of monolayer and neurosphere lines established from patient-derived orthotopic xenograft (PDOX) models of the untreated (IC-4687GBM), recurrent (IC-3752GBM), and terminal (IC-R0315GBM) tumors, and in vivo therapeutic efficacy through log rank analysis of survival times in two models (IC-4687GBM and IC-R0315GBM) following MLN8237 treatment (30 mg/kg/day, orally, 12 days). Drug concentrations in vivo and mechanism of action and resistance were also investigated. Results: AURKA mRNA overexpression was detected in 14 pGBM tumors, 10 PDOX models, and 6 cultured pGBM lines as compared with 11 low-grade gliomas and normal brains. MLN8237 penetrated into pGBM xenografts in mouse brains. Significant extension of survival times were achieved in IC-4687GBM of which both neurosphere and monolayer were inhibited in vitro, but not in IC-R0315GBM of which only neurosphere cells responded (similar to IC-3752GBM). Apoptosis-mediated MLN8237 induced cell death, and the presence of AURKA-negative and CD133+ cells appears to have contributed to in vivo therapy resistance. Conclusions: MLN8237 successfully targeted AURKA in a subset of pGBMs. Our data suggest that combination therapy should aim at AURKA-negative and/or CD133+ pGBM cells to prevent tumor recurrence. Clin Cancer Res; 24(9); 2159–70. ©2018 AACR.

Purpose: Despite significant advances in the understanding of the biology, the prognosis of glioblastoma (GBM) remains dismal. The objective was to carry out whole-exome sequencing (WES) of Indian glioma and integrate with that of TCGA to find clinically relevant mutated pathways. Experimental Design: WES of different astrocytoma samples (n = 42; Indian cohort) was carried out and compared with that of TCGA cohort. An integrated analysis of mutated genes from Indian and TCGA cohorts was carried out to identify survival association of pathways with genetic alterations. Patient-derived glioma stem-like cells, glioma cell lines, and mouse xenograft models were used for functional characterization of calcitonin receptor (CALCR) and establish it as a therapeutic target. Results: A similar mutation spectrum between the Indian cohort and TCGA cohort was demonstrated. An integrated analysis identified GBMs with defective “neuroactive ligand–receptor interaction” pathway (n = 23; 9.54%) that have significantly poor prognosis (P < 0.0001). Furthermore, GBMs with mutated calcitonin receptor (CALCR) or reduced transcript levels predicted poor prognosis. Exogenously added calcitonin (CT) inhibited various properties of glioma cells and pro-oncogenic signaling pathways in a CALCR-dependent manner. Patient-derived mutations in CALCR abolished these functions with the degree of loss of function negatively correlating with patient survival. WT CALCR, but not the mutant versions, inhibited Ras-mediated transformation of immortalized astrocytes in vitro. Furthermore, calcitonin inhibited patient-derived neurosphere growth and in vivo glioma tumor growth in a mouse model. Conclusions: We demonstrate CT–CALCR signaling axis is an important tumor suppressor pathway in glioma and establish CALCR as a novel therapeutic target for GBM. Clin Cancer Res; 24(6); 1448–58. ©2017 AACR.

Background: Glioblastoma Multiforme (GBM-Grade IV) is the most aggressive form of glioma in the USA carrying only a 15 month median survival time. IDH1R132H is an early onset mutation present in 70-80% of low grade gliomas (LGG-Grade I and II) and secondary GBM patients that causes intracellular oxidative stress and impairment of post-radiation DNA damage repair (DDR) via Homologous Recombination (HR). Although IDH1R132H is associated with improved patient survival and clinical response to chemotherapy, astrocytoma (LGG) patients specifically also harbor ATRXLoss, a genetic alteration that inactivates the ATRX chromatin remodeling protein and impairs DDR via non-homologous end joining (NHEJ). Importantly, the recent discovery of glioma stem cells (GSCs), a subpopulation of chemoradioresistant, self-renewable, tumor initiating cells known to promote tumor recurrence, presents a new target for therapeutic intervention. However, the mechanisms by which IDH1R132H and ATRXLoss contribute to GSC sensitivity to proton radiotherapy (PRT), a more tumor specific and cytotoxic form of radiation therapy than conventional X-rays (XRT), is not well understood. We hypothesize that both IDH1R132H and ATRXLoss contribute to the impairment of GSC self-renewal after PRT, but not after XRT. Methods: Isogenic MGG18-IDH1WT, MGG18-IDH1R132H, TS543-ATRXWT, and TS543-ATRXLoss patient derived glioma cells were cultured as neurospheres and treated with 3-6 Gy of XRT or PRT. GSC self-renewal, based on neurosphere formation frequency, was quantified using extreme limiting dilution analysis (ELDA). Results: TS543-ATRXLoss significantly inhibited GSC self-renewal over TS543-ATRXWT when subject to PRT (Pairwise Testing Pr(>χ2)χ2)χ2)χ2) Conclusions: We conclude that ATRXLoss and IDH1R132H both substantially contribute to PRT sensitivity in GSCs, thereby supporting the benefits of PRT for astrocytoma patients. Our future experiments will further elucidate the biological mechanisms by which ATRXLoss and IDH1R132H confer PRT sensitivity, especially via dsDNA damage and apoptosis. Citation Format: Ángel Adrian Garcés, Lawrence Bronk, Krishna P. Bhat, David R. Grosshans. ATRXLoss and IDH1R132H impair self-renewal of glioma stem cells after proton radiotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3077.

Invasive motility limits treatment efficacy and is a significant contributor to poor outcomes in glioblastoma (GBM). GBM tumor microtubes are actin- and microtubule-enriched membrane tubes that facilitate invasive motility and underlie many components of GBM pathophysiology. Rho-GTPases mediate GBM invasion through localized activation of cytoskeletal effector proteins, such as mammalian Diaphanous-related formins (mDia) and Rho-associated protein kinase (ROCK). Active mDia nucleates and polymerizes F-actin and independently stabilizes microtubules, while active ROCK phosphorylates myosin phosphatase and myosin light chain to induce the actomyosin crosslinking required for contractility. GBM invasion depends on a delicate balance between mDia-mediated extension of leading-edge structures (such as tumor microtubes) and ROCK-mediated contraction of trailing cell bodies. In this study, we assessed the roles of ROCK and mDia in tumor microtube-associated GBM invasion using a 3D patient-derived neurosphere model of GBM invasion. Neurospheres were embedded in 3D matrices and treated with the small molecule inhibitor of ROCK (Y-27632) and the small molecule agonist of mDia (IMM-02). Treatment with Y-27632 alone reduced the total distance of cell body migration and increased tumor microtube length without effecting the total area of neurosphere invasion. Tumor microtubes extending from Y-27632 treated neurospheres displayed an atypical undulant morphology, further suggesting that ROCK inhibition modifies primary invasion programs. Treatment with IMM-02 alone profoundly reduced total area of neurosphere invasion, distance of cell body migration, and length of tumor microtubes. Combination treatment effects (Y-27632 + IMM-02) were time dependent. At 24 hours, combination treatment did not significantly reduce total area of invasion over either individual treatment. However, tumor microtubes were shorter with combination treatment than Y-27632 alone and longer than IMM-02 alone. At 96 hours, combination treatment reduced total area invaded and length of tumor microtubes in comparison to Y-27632 alone, but no significant difference was observed in comparison to IMM-02 alone. Western blot analysis of both free-floating patient-derived 3D neurospheres and semi-adherent “2.5D” monolayer cultures demonstrated that agonism of mDia formins with IMM-02 (96-hrs) results in the progressive loss of mDia1 and mDia2 protein expression. Therefore, endogenous mDia regulatory mechanisms triggered in response to continuous agonist-mediated mDia activation may inhibit mDia function more effectively than direct antagonism strategies in GBM. Conclusively, both IMM-02 and Y-27632 treatment disrupt the tumor microtube mechanism of GBM neurosphere invasion. Further studies are warranted to evaluate these small molecule compounds for potential anti-tumor microtube therapeutic effect in vivo. Citation Format: Kathryn N. Becker, Krista M. Pettee, Amanda Sugrue, Kevin A. Reinard, Jason L. Schroeder, Kathryn M. Eisenmann. ROCK and mDia have dynamic roles in glioblastoma tumor microtube invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2887.

Glioblastoma (GBM) is the most common primary brain malignancy. Brain fatty acid binding protein (B-FABP, FABP7) promotes glioblastoma (GBM) migration and correlates to dismal prognosis in GBM patients. Long chain polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and arachidonic acid (AA) are abundant in brain cell membranes. DHA and AA are preferred ligands of FABP7, with DHA having the stronger affinity for FABP7. Previous studies have shown that DHA inhibits GBM migration in an FABP7-dependent manner. In the current study, we have demonstrated that DHA dramatically altered membrane FABP7 nanoscale distribution pattern, which resulting from plasma membrane lipid ordered domain disruption in GBM cells and neurosphere cultures. We used quantitative membrane order assay to show that FABP7-expressing cells has increased membrane lipid order which is tightly correlated with higher GBM migration property. Using stimulated emission depletion (STED) microscopy, we observed lipid ordered domain was associated with FABP7 nanoscale domain formation. Interestingly, super-resolution microscopy quantitative image analysis revealed that FABP7 membrane nanodomains distribution was dramatically altered upon DHA treatment, which is associated with DHA inhibitory effect on membrane lipid order. Furthermore, STED microscopy has also revealed that reduced FABP7 nanodomain formation in slow migrating GBM cells are similar as FABP7-expressing GBM cells upon DHA treatment. Therefore, we hypothesize that these alterations are likely to be the mechanism of FABP7-mediated DHA inhibitory role in GBM migration. Citation Format: Xia Xu, Yixiong Wang, Wonshik Choi, Roseline Godbout. The mechanistic effect of DHA on FABP7 associated membrane lipid order & nanodomain distribution in glioblastoma migration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2886.

Glioblastoma multiforme is a common malignant brain tumor that portends extremely poor patient survival. Recent studies reveal that glioma stem-like cells (GSC) are responsible for glioblastoma multiforme escape from chemo-radiotherapy and mediators of tumor relapse. Previous studies suggest that AEG-1 (MTDH), an oncogene upregulated in most types of cancers, including glioblastoma multiforme, plays a focal role linking multiple signaling pathways in tumorigenesis. We now report a crucial role of AEG-1 in glioma stem cell biology. Primary glioblastoma multiforme cells were isolated from tumor specimens and cultured as neurospheres. Using the surface marker CD133, negative and positive cells were separated as nonstem and stem populations by cell sorting. Tissue samples and low passage cells were characterized and compared with normal controls. Functional biological assays were performed to measure stemness, self-renewal, differentiation, adhesion, protein–protein interactions, and cell signaling. AEG-1 was upregulated in all glioblastoma multiforme neurospheres compared with normal neural stem cells. Expression of AEG-1 was strongly associated with stem cell markers CD133 and SOX2. AEG-1 facilitated β-catenin translocation into the nucleus by forming a complex with LEF1 and β-catenin, subsequently activating Wnt signaling downstream genes. Through an AEG-1/Akt/GSK3β signaling axis, AEG-1 controlled phosphorylation levels of β-catenin that stabilized the protein. Implications: This study discovers a previously unrecognized role of AEG-1 in GSC biology and supports the significance of this gene as a potential therapeutic target for glioblastoma multiforme. Mol Cancer Res; 15(2); 225–33. ©2016 AACR.

While radiotherapy (RT) is fundamental for the treatment of brain tumors, irradiation of the brain frequently causes devastating effects on cognitive function and quality of life. DNA damage within neural stem cells (NSC) is a key factor in the pathogenesis of radiation-induced cognitive dysfunction. The ataxia telangiectasia mutated (ATM) kinase is a central protein in the DNA damage response and a critical determinant of tumor cell survival after radiation. ATM inhibition potently radiosensitizes preclinical models of GBM in vitro and in vivo. A novel, brain penetrant ATM inhibitor AZD1390, which is predicted to achieve brain tumor concentrations in the range of 1-5nM, is currently in early phase clinical evaluation in combination with RT. In marked contrast to observations in tumor models, genetic knockdown of ATM has radioprotective effects on NSC in vitro; the proposed mechanism is via suppression of p53 mediated apoptosis. The purpose of this study was to investigate the impact of AZD1390 on survival responses and mode of death in NSCs exposed to RT in vitro and in vivo. NSCs were derived from the telencephalon of E13 mouse embryos. Cells were treated with AZD1390 (0.1-10nM) 1 hour prior to ionizing radiation (IR; 0-5 Gy). Mode and timing of cell death was interrogated using IncuCyte live cell analysis to measure proliferation, cytotoxicity and apoptosis up to 72 hours post-IR. Cell viability and neurosphere formation assays were also used to measure radiation sensitivity in vitro. C57BL/6 mice received 20Gy hemibrain irradiation +/- 7-day treatment with AZD1390 (10mg/kg). Immunohistochemistry for Ki67 and Sox2 was used to assess effects on NSC in the subventricular zone (SVZ) 50 days post-irradiation. In vitro AZD1390 (1-10nM) inhibited ATM kinase function within 1 hour, evidenced by abrogation of KAP1 and p53 phosphorylation. NSCs primarily undergo apoptosis in response to IR. AZD1390 at 1 and 3nM significantly reduced apoptosis in irradiated NSCs (ratios of annexin V area under the curve 1.95 and 2 respectively); 10 nM had no effect on this parameter. Proliferation rates and cell viability after radiation were preserved at all drug concentrations. AZD1390 at 1nM did not modulate radiation effects on neurosphere formation whereas at 10nM a radiosensitizing effect was observed (ratio of SF[3Gy]=0.25). In vivo, IR decreased the number of Ki67 positive proliferating cells (92% reduction) and Sox2-positive cells (24% reduction) in the SVZ after 50 days; these effects were not exacerbated by addition of AZD1390. Acute effects (24 hours post-IR) are under investigation. We demonstrate in vitro that AZD1390 has radioprotective effects on NSCs at clinically achievable concentrations. In vivo, treatment with AZD1390 did not enhance the effects of radiation on NSCs in the SVZ. In the context of its profound radiosensitizing effects on GBM models, the absence of radiosensitization of NSCs both in vitro and in vivo strengthens the rationale for evaluating AZD1390 in combination with RT in GBM patients. Citation Format: Rodrigo Guttierez-Quintana, David J. Walker, Mark R. Jackson, Natividad Gomez-Roman, Sandeep Chahal, Stephen T. Durant, Anthony J. Chalmers. Radiotherapy in combination with the brain penetrant ATM inhibitor AZD1390 does not exacerbate radiation toxicity of neural stem cells in vitro or in vivo [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-017.

Glioblastoma multiforme remains the deadliest malignant brain tumor, with glioma stem cells (GSC) contributing to treatment resistance and tumor recurrence. We have identified MAPK-interacting kinases (MNK) as potential targets for the GSC population in glioblastoma multiforme. Isoform-level subtyping using The Cancer Genome Atlas revealed that both MNK genes (MKNK1 and MKNK2) are upregulated in mesenchymal glioblastoma multiforme as compared with other subtypes. Expression of MKNK1 is associated with increased glioma grade and correlated with the mesenchymal GSC marker, CD44, and coexpression of MKNK1 and CD44 predicts poor survival in glioblastoma multiforme. In established and patient-derived cell lines, pharmacologic MNK inhibition using LY2801653 (merestinib) inhibited phosphorylation of the eukaryotic translation initiation factor 4E, a crucial effector for MNK-induced mRNA translation in cancer cells and a marker of transformation. Importantly, merestinib inhibited growth of GSCs grown as neurospheres as determined by extreme limiting dilution analysis. When the effects of merestinib were assessed in vivo using an intracranial xenograft mouse model, improved overall survival was observed in merestinib-treated mice. Taken together, these data provide strong preclinical evidence that pharmacologic MNK inhibition targets mesenchymal glioblastoma multiforme and its GSC population. Implications: These findings raise the possibility of MNK inhibition as a viable therapeutic approach to target the mesenchymal subtype of glioblastoma multiforme. Mol Cancer Res; 14(10); 984–93. ©2016 AACR.

Intra-tumor heterogeneity presents one of the biggest challenges in the development of solid cancer therapeutics. Cells within the same tumor display distinct phenotypes that affect their growth rate, survival, migration, therapy-response, and tumor-propagating capacity. We now understand cancer stem cells (CSCs) play critical roles in driving intra-tumor cellular heterogeneity by establishing dynamic cellular transitions within tumors. GBM are highly aggressive tumors that display a poorly differentiated cell phenotype characterized by high expression of genes enriched in embryonic stem cells (ESCs). Lineage-tracing experiments show that stem-like cells are responsible for GBM re-growth after therapy and this process is in part mediated by known drivers of stemness (e.g. Sox2). There is a strong correlation between the expression of stem cell drivers and markers and tumor recurrence in multiple cancers, including GBM. We and others have established that reprogramming transcription factors Oct4 and Sox2 are important drivers of the stem-cell, tumor and therapy-resistant phenotype in GBM. We present data showing that GBM cells expressing transgenic Oct4 and Sox2 are more resistant to ionizing radiation (IR) treatment and exposing GBM neurospheres to temozolomide (TMZ) and IR gives rise to a cell sub-set with higher gene expression levels of Oct4 and Sox2 compared to untreated cells. The clinical and potential therapeutic relevance of this phenotype is supported by multi-dimensional transcriptome analyses that identifies a group of genes induced by Oct4 and Sox2 enriched in recurrent GBM. The promiscuous quality of miRNAs is an underexploited characteristic that could allow the targeting of multiple parallel oncogenic pathways using a single agent, enhancing therapeutic efficacy and reducing chances of tumor recurrence. To explore this untapped potential, we predicted miRNAs likely to target the transcripts induced by Oct4/Sox2 in recurrent GBM and identified miR-149-3p as a high-priority candidate. Importantly, transient expression of miR-149-3p simultaneously repressed these transcripts in GSCs as measured by qRT-PCR, concurrent with a decrease in the capacity of both parental and GSCs expressing transgenic Oct4/Sox2 to self-renew as spheres, a biomarker of cell stemness and tumor-propagating potential. Additionally, transient expression of miR-149-3p also re-sensitized therapy-resistant GBM neurospheres to TMZ treatment. These results show this resistant phenotype is reversible and support our hypothesis that GSC-driving mechanisms induce a subset of genes that give rise to therapy-resistant GBM cells and suggests that miR-149-3p can be developed as a therapeutic for recurrent GBM. Citation Format: Hernando Lopez-Bertoni. miR-149-3p inhibits the glioma stem cell phenotype and re-sensitizes therapy-resistant GBM cells [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-112.

Introduction: Glioblastoma (GBM) is the most aggressive neurological cancer with a very poor prognosis due to its propensity to regenerate after medical interventions. Our experimental model is U87-MG cells, which contain subsets of cancer stem cells (CSC) and have the unusual property of spontaneously forming neurospheres in culture. We are investigating the origins of these stem cells. Materials and Methods: We employ recently developed time label-free, time-lapse quantitative phase imaging (QPI) technology that allows precise quantification of the refractive index (RI) distributions on a sub-cellular level. These measurements are stored in 2D or 3D arrays which can be presented as images or videos at various resolutions. Cells were seeded into sealable culture Petrie dishes and imaged while maintaining appropriate environmental controls. Results: We first noted CSCs in late stage cultures in exploratory experiments, where they presented as small cells (10-15 um) compared to the 50-100 um range of mature U8-MR cells. Their refractive index (RI) is 1.42, compared to about 1.40 for the cytoplasm of mature cells. QPI technology sensitivity enables almost complete separation between the two cell types in RI histograms. We exemplify a grouping of cells in an 80 um2 field of view, tracked in multiple time segments ranging from 20 minutes to 12 hours over a period of about 18 hours, containing a mature U87 which serves as a reference marker. Around this cell, there are 3 distinct pro-stem (PS) cells 12 to 16 um in size: PS-1 with numerous 0.5 um particles in the size range of mitochondria, PS-2 with a nucleus with nucleoli but no nuclear membrane, and PS-3 with a distinct nucleus, nucleoli, and cytosol. The cells are all connected in a network of nanotubes and tunnels. PS-1 and PS-2 are not very active in the early analysis, but they eventually move together and appear to fuse while still maintaining their individual shapes. PS-3 is very actively interacting with another cell on the border of the analysis window. It is extending and retracting a tube and is apparently moving materials both to and away from the other cell in a very regular and linear fashion, suggesting a primitive form of transcription. Discussion: The processes we observed are consistent with tumor stem cell generation by autophagy, mitophagy, and catabolization followed by reprograming of the remnants and formation of neoplastic stem cells. The novelty of our approach is determined by technical capabilities of our QPI platforms, which is non-invasive label-free approach coupled with ultra-high-resolution analysis, previously unobtainable in traditional time-lapse imaging systems. Citation Format: Ed Luther, Livia P. Mendes, Vladimir P. Torchilin. Identification of the neo-genesis of glioblastoma stem cells using label-free quantitative phase imaging [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6019.

Diffuse Intrinsic Pontine Glioma (DIPG) is a lethal pediatric brain cancer with a five-year survival rate of less than 1%. This is reflective of a 100% tumor reoccurrence emphasizing the need for efficacious therapies. Previous studies have identified Aldehyde dehydrogenase expression (ALDH) as a marker for stemness and an indicator of tumor aggression and therapeutic resistance in many malignancies including adult glioma. Understanding the role of cancer stem-cells in gliomagenesis of DIPG is critical for developing therapies targeting resistance and averting 200-400 pediatric deaths in the US per year. We identified a subpopulation of cells expressing the ALDH cancer stem-cell marker in patient-derived DIPG cell lines with high variability in ALDH expression among the cell lines likely indicating previous treatment and resistance. As expected, proliferation and neurosphere formation as well as neurosphere size were dramatically increased in ALDH+ CSC compared to ALDH- CSC supporting our hypothesis of a tumor initiating, aggressive subpopulation likely conferring therapeutic resistance. To evaluate tumor initiation properties of ALDH+ CSC subpopulation in vivo, implantation of SU-DIPG-7 luciferase expressing cells into the pons of immunocompromised mice (NSG) was performed after sorting for ALDH by FACS. Our results demonstrate tumor initiation and tumor growth in ALDH+ mice as assessed by Bioluminescence imaging (BLI) as well as histological analysis. Furthermore, survival of mice implanted with ALDH+ CSCs was significantly reduced compared to mice implanted with ALDH- cells indicating tumor initiating and ‘stem cell' properties of this subpopulation. In summary, we have identified and characterized ALDH+ cancer stem-cells in DIPG which are more aggressive than the non-cancer stem-cell population (ALDH-). These results highlight the need to develop therapies targeting this highly aggressive cancer stem-cell population. Future studies investigating the gene regulation response to treatment in these stem-cell subpopulations could provide valuable insight to co-targeted therapies to address treatment resistance in DIPG. Citation Format: Sarah F. Ferris, Rachel K. Surowiec, Carlos Espinoza, Stefanie Galban. Characterizing cancer stem cells in diffuse intrinsic pontine glioma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6152.

Glioblastoma multiforme (GBM), the most common and aggressive form of brain tumor, has been associated with the dysregulation of G-protein coupled receptors signaling. Data from The Cancer Genome Atlas demonstrated remarkable upregulation of mRNA for the Gα12 protein, which is elevated in 26% of GBM patient tumors (the highest rate of tumor samples surveyed). The Gα12 protein couples GPCRs to guanine nucleotide exchange factors (GEFs) for RhoA and was originally isolated as an oncogene. Furthermore, the subset of GPCRs that couples to Gα12 to activate RhoA includes S1P, LPA, and thrombin. These are generated, respectively, through sphingosine kinase, autotaxin, and tissue factor, all of which are elevated in glioblastoma tumors or cell lines. Signaling to RhoA leads to activation of the transcriptional co-activator YAP (Yes-associated protein 1). The role of YAP in growth of glioblastoma cells and in vivo GBM tumor development was explored in our previous studies (Yu et al., Oncogene 2018) using human glioblastoma cell lines and GBM stem cells (GSCs) derived from patient-derived xenografts (PDX). We showed that shRNA mediated knockdown of YAP in GSC-23 PDX cells significantly attenuated in vitro self-renewal capability assessed by limiting dilution, neurosphere formation, and stem cell gene expression. Orthotopic xenografts of the YAP knockdown PDX cells formed significantly smaller tumors and were of lower morbidity than wild-type cells. Our current work examines the effects of Gα12 since it transduces effects of multiple GPCRs upstream to RhoA that could be activated in the tumor environment. Targeting Gα12 using shRNA in two GBM cancer stem cell lines, GSC-23 and HK-281, decreased Gα12 mRNA levels by 80% without compensatory upregulation in the expression of the homologous Gα13 protein. Loss of Gα12 attenuated GSC-23 stemness as determined by limiting dilution assay and reduced mRNA expression levels of canonical stem cells genes (CCND1, NANONG, OCT4, SOX2, and NESTIN by approximately 50%). We are currently examining tumor growth of GSC-23 control and Gα12 knockdown cells as orthotopic xenografts. We are also examining the role of specific YAP-regulated target genes identified by RNA-sequencing of S1P-treated control and YAP knockout glioblastoma cells. In particular, one of the genes highly dependent on YAP is F3, which encodes the protein for tissue factor (TF) which is involved not only in coagulation but also in generation of thrombin, a ligand for PAR1, a GPCR that is upregulated in GBM and regulates RhoA signaling. Expression of TF was also selectively decreased in tumors from PDX cells lacking YAP, indicating that this transcriptional pathway is regulated in preclinical GBM models. Thus, Gα12/RhoA-mediated YAP signaling pathway appears to play a pivotal role in GBM tumor growth and progression. Citation Format: Olga M. Chaim, Jinhui Ma, Jacqueline Lara, Frank Furnari, Shigeki Myamoto, Joan H. Brown. Regulation of glioblastoma tumor growth and stem cell properties through Gα12 and tissue factor, upstream and downstream players in YAP signaling [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr A19.

Long-term cognitive impairments are common in pediatric brain cancer survivors. While these impairments are thought to arise following radiation treatment, recent reports suggest a link to tumor-specific mechanisms. We therefore hypothesized that pediatric brain tumors, more specifically medulloblastoma (MB), can directly affect neural stem and precursor cell function in the forebrain stem cell niche—the subventricular zone (V-SVZ) —by secreting bioactive factors. Mice harboring subcutaneous flank MB tumors had fewer proliferating neural precursor cells in the V-SVZ than controls as well as decreased olfactory bulb neurogenesis and white matter oligodendrogenesis. To assess the effects of the MB secretome in the brain, concentrated conditioned media from MB cell lines (MB-CM) was injected intracerebroventricular (ICV) into mouse pups. ICV injection of MB-CM decreased neural precursor cell proliferation as well as decreased numbers of V-SVZ neurospheres in culture. MB-CM from multiple cell lines decreased V-SVZ neurosphere number and promoted astrocyte differentiation in culture. To identify the ligands contributing to the phenotype, an interaction model was developed extracting ligands from MB microarray data, networking them to receptors on NSCs. Of the predicted ligands, IL6-family cytokine expression and secretion was validated in MB cells. When added in culture, recombinant IL6, IL11, and CT1 decreased neurosphere number and ICV injection of IL11 into mouse pups decreased V-SVZ neural precursor cell proliferation. Overall, this work demonstrates that medulloblastoma secretes bioactive compounds that perturb neural stem cell function and the circuity involved in normal cognitive function. This abstract is also being presented as Poster B64. Citation Format: Alexander Gont, Jaclin V. Simonetta, Jenna Park, Alice R. Shan, Michael J. Borrett, Michael D. Taylor, Freda D. Miller, David R. Kaplan. Acting at a distance: Medulloblastoma-secreted ligands disrupt normal neural stem cell function [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr PR15.

Objective: To determine the biological and signaling effects of dual-pathway inhibition with mTORC1/2 and MEK inhibitors in glioblastoma neurosphere cell lines. Background: The PI3K/mTOR signaling pathway is frequently dysregulated in glioblastoma (GBM), making it the focus of active scientific and drug development efforts in brain tumors. Unfortunately, small molecule targeted therapies against EGFR and its downstream effector pathways, while promising in the pre-clinical setting, have been disappointing in glioma clinical trials. The mTOR pathway target ribosomal protein S6 (RPS6) can also be activated by the ERK pathway target p90-RSK. We therefore tested the hypothesis that small molecule inhibition of both ERK and mTOR signaling pathways would result in enhanced anti-tumor activity. Methods: Seven glioblastoma neurosphere lines were tested for sensitivity to the ATP-competitive mTORC1/2 inhibitor sapanisertib (MLN0128) alone or in combination with the allosteric MEK1/2 inhibitor trametinib (GSK1120212) using cell growth assays and immunoblots as indicated. Results: The dual mTORC1/2 inhibitor sapanisertib inhibits mTOR signaling and cell growth in all GBM neurosphere lines, but only partially inhibits phosphorylation of the downstream target ribosomal protein S6 (phospho-RPS6) in these models. The MEK inhibitor, trametinib, inhibited ERK phosphorylation in all neurosphere lines, though phosphorylation of downstream targets and cell growth were inhibited to varying degrees. Inhibition of RPS6 activation was dose-dependent and correlated with cell line sensitivity when treated with trametinib but not with sapanisertib. In combination, sapanisertib plus trametinib showed more profound inhibition of phospho-RPS6, as well as enhanced growth inhibition and induction of apoptosis in sensitive neurosphere lines. Conclusions: The combination of sapanisertib and trametinib may have significant antitumor activity in glioblastoma neurospheres by enhanced inhibition of S6, which serves as the convergence point between these effector pathways. Citation Format: Karisa C Schreck, Amy Allen, Jiawan Wang, Christine A Pratilas. Sapanisertib in combination with trametinib in glioblastoma models enhances target inhibition and antitumor activity [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B074. doi:10.1158/1535-7163.TARG-19-B074

Glioblastoma (GBM) is the most aggressive type of primary brain tumor, characterized by the intrinsic resistance to chemotherapy due to the presence of a highly aggressive Cancer Stem Cell (CSC) sub-population. The coexistence in the same mass of bulk and CSCs stuck at different stages of differentiation and genetic backgrounds prevents counteracting all cells with single treatments. Through the application of a Dielectrophoretic force (DEP) we provide a successful CSC isolation from a mixed cell population, exploiting their physical properties. Using FACS, the expression of specific stem cell and differentiation markers (CD133, Nestin, Sox1, Sox2, GFAP, Doublecortin (DCX) and Ki67) were analyzed in 17 primary cell lines of GBM. CD133 expression was also exploited as a reliable marker for the identification of the CSC subpopulation and thus used for sorting CD133+ and CD133- GBM primary cells by flow cytometry techniques. CD133+ and CD133- cells were characterized for their ability to self-renew and form neurospheres. In all experiments, CD133+ cells have shown a significant increased efficiency of neurosphere generation that was accompanied by a higher self-renewal potential as measured by the limiting dilution assay (LDA) in vitro. The characterization and isolation of patient-derived GBM cells by FACS allowed constituting a cell library with three distinct cell subpopulation types: CD133+/CD133-/Total population, that have been characterized for their specific Electromagnetic (EM) signature. Determination of EM signature was performed using a sensor that applies electromagnetic fields in the MHz regime to selectively electromanipulate cells with dielectrophoresis (DEP) and allows the monitoring of the induced cell motion generated by the field. By scanning the frequency range of interest, the cell DEP signature and the cross over frequency (frequency for which the DEP force becomes null) were identified. We found that CD133+ and CD133- cell display a significantly different crossover frequency. In particular, CD133+ cells are characterized by a lower cross over frequency than both CD133- and total population. This data suggest a non obvious correlation between crossover frequency and CSCs phenotype which would be potentially exploited to set up a label free system able to efficiently identify and physically separate subpopulation of cells enriched for CSC characteristics. Citation Format: Roberta Bortolozzi, Elena Mariotto, Elena Rampazzo, Elena Porcù, Sofiane Saada, Thomas Provent, Fabrice Lalloué, Arnaud Pothier, Giampietro Viola, Luca Persano. Dielectric characterization of glioblastoma cancer stem cells [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A058. doi:10.1158/1535-7163.TARG-19-A058

Cancer stem cells, capable of self-renewal and multipotent differentiation, influence tumor behavior through a complex balance of symmetric and asymmetric cell divisions. Mechanisms regulating the dynamics of stem cells and their progeny in human cancer are poorly understood. In Drosophila, mutation of brain tumor (brat) leads to loss of normal asymmetric cell division by developing neural cells and results in a massively enlarged brain composed of neuroblasts with neoplastic properties. Brat promotes asymmetric cell division and directs neural differentiation at least partially through its suppression on Myc. We identified TRIM3 (11p15.5) as a human ortholog of Drosophila brat and demonstrate its regulation of asymmetric cell division and stem cell properties of glioblastoma (GBM), a highly malignant human brain tumor. TRIM3 gene expression is markedly reduced in human GBM samples, neurosphere cultures, and cell lines and its reconstitution impairs growth properties in vitro and in vivo. TRIM3 expression attenuates stem-like qualities of primary GBM cultures, including neurosphere formation and the expression of stem cell markers CD133, Nestin, and Nanog. In GBM stem cells, TRIM3 expression leads to a greater percentage dividing asymmetrically rather than symmetrically. As with Brat in Drosophila, TRIM3 suppresses c-Myc expression and activity in human glioma cell lines. We also demonstrate a strong regulation of Musashi–Notch signaling by TRIM3 in GBM neurospheres and neural stem cells that may better explain its effect on stem cell dynamics. We conclude that TRIM3 acts as a tumor suppressor in GBM by restoring asymmetric cell division. Cancer Res; 74(16); 4536–48. ©2014 AACR.

Great interest persists in useful prognostic and therapeutic targets in glioblastoma. In this study, we report the definition of miRNA (miR)-148a as a novel prognostic oncomiR in glioblastoma. miR-148a expression was elevated in human glioblastoma specimens, cell lines, and stem cells (GSC) compared with normal human brain and astrocytes. High levels were a risk indicator for glioblastoma patient survival. Functionally, miR-148a expression increased cell growth, survival, migration, and invasion in glioblastoma cells and GSCs and promoted GSC neurosphere formation. Two direct targets of miR-148a were identified, the EGF receptor (EGFR) regulator MIG6 and the apoptosis regulator BIM, which rescue experiments showed were essential to mediate the oncogenic activity of miR-148a. By inhibiting MIG6 expression, miR-148a reduced EGFR trafficking to Rab7-expressing compartments, which includes late endosomes and lysosomes. This process coincided with reduced degradation and elevated expression and activation of EGFR. Finally, inhibition of miR-148a strongly suppressed GSC and glioblastoma xenograft growth in vivo. Taken together, our findings provide a comprehensive analysis of the prognostic value and oncogenic function of miR-148a in glioblastoma, further defining it as a potential target for glioblastoma therapy. Cancer Res; 74(5); 1541–53. ©2014 AACR.

Glioblastoma (GBM) is a highly malignant and lethal cancer of the central nervous system for which there has been limited progress in improving patient outcomes despite intensive research efforts. The current multimodal therapy for newly diagnosed GBM patients includes surgical resection, radiotherapy and cytotoxic chemotherapy with temozolomide (TMZ), conferring a median survival time of just 14.6 months. Failure to generate more effective treatment strategies is due to 1) the infiltrative nature of GBM tumor cells preventing complete surgical resection, and 2) the cellular heterogeneity within GBM tumors, which often comprise a sub-population of GBM cancer stem cells (GSCs) characterized by self-renewal characteristics and resistance to chemotherapeutic alkylating agents including TMZ. Multiple signaling pathways, including Notch, participate to the formation and maintenance of GSCs. Recent studies, including our research, have shown that increased levels of gap junction protein Connexin43 (Cx43) correlate with TMZ resistance in GBM cells and inversely correlated with GBM patient survival. Importantly, Cx43 has also been associated with anti-proliferative effects in glioma, and reduced levels of Cx43 protein occur in high-grade gliomas. Therefore, we hypothesized that altering Cx43 localization and/or activity rather than Cx43 expression represents a potent strategy for GBM treatment. Regulating Cx43 function is primarily associated with the multiple sites for post-translational modifications and protein-protein interactions within the Cx43 carboxy-terminus. Our research identifies crosstalk between Cx43 and Notch signaling in GSCs. Using a Cx43 carboxy-terminus mimetic peptide that modulates non-junctional functions of Cx43, we observe a decrease in Notch1 protein expression and reduced transcription of its downstream targets Hes1 and Hey1 in GSCs derived from patient tumors. Most importantly, our Cx43 mimetic peptide decreases cell survival in TMZ-resistant GSCs, limits GSC neurosphere formation in vitro, and inhibits GSC-derived tumor growth in vivo. Our current research aims at dissecting the molecular mechanisms of Cx43 functions on Notch signaling in GSCs using this Cx43 mimetic peptide. In conclusion, we have identified a novel therapeutic opportunity to decrease the tumorigenic potential of GSCs through altering Cx43 activity and Notch signaling to target chemoresistant GSCs in GBM treatment. Citation Format: Michael Lunski, James Smyth, Jennifer Vaughn, Zhi Sheng, Robert Gourdie, Benjamin Purow, Samy Lamouille. Targeting notch signaling in glioblastoma cancer stem cells through modulation of Connexin43 function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4284.

Glioblastoma (GBM) is the most lethal brain tumor; it is characterized by poor response to standard post-resection radiation and cytotoxic therapy, resulting in a dismal prognosis with a five-year survival rate of 10%. Recurrence after therapy for GBM is unavoidable. There are substantial differences among the cells of GBM tumors in the abundance and types of genetic material. This heterogeneity likely is the major cause of therapy failure, the development of treatment resistance, and ultimately recurrence. A recent study has suggested that the majority of GBM activate oncogenes through amplification extrachromosomal DNA (ecDNA). Despite the speculation that ecDNA is a key factor of tumor heterogeneity, how ecDNA is propagated and distributed among—and how it behaves within—cancer cells is completely unknown. To address this gap in knowledge, this study focused on developing a novel cytogenetic tool that enables visualization and tracking ecDNA behavior in live GBM cells. We found breakpoint sequences resulting from genome rearrangements during ecDNA formation by performing computational analysis whole genome sequencing data from a pair of primary/recurrent GBM neurospheres. Each breakpoint represents a unique target sequence for ecDNA-specific labeling. Breakpoint were validated by breakpoint-PCR, focusing on breakpoints shared by the primary and recurrent neurosphere. We determined location and quantity of all ecDNA breakpoints through breakpoint-FISH (BP-FISH) analysis, which showed that all signal was found outside of the conventional chromosomes in the metaphase spread, validating the extrachromosomal nature of the ecDNA breakpoints. The breakpoint quantities, reflecting the number of ecDNA elements per cell, varied between primary and recurrent neurosphere suggesting that ecDNAs quantitatively changed during GBM evolution. These results emphasize the necessity of tracking ecDNA dynamics to answer the question of how ecDNA is distributed into the daughter cells. Our findings will be strong evidence to make ecDNA-specific CRISPR system in further research. Tracing ecDNA dynamics will provide new insight into the impact of ecDNA on cancer evolution. Citation Format: Eunhee Yi, Roel Verhaak. Tracing extrachromosomal DNA inheritance patterns in glioblastoma using CRISPR [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2564.

A molecular subtype of low grade gliomas (LGG) is characterized by mutations in Alpha-Thalassemia Mental Retardation X-linked (ATRX), TP53 and isocitrate dehydrogenase 1 (IDH1R132H, mIDH1). Our lab has generated a genetically engineered mouse model that harbors the characteristic genetic lesions found in this molecular subtype of LGG. We determined that mouse neurospheres (NS) bearing these mutations showed downregulation of signaling pathways involved in oligodendrocyte differentiation. The production of 2-hydroxyglutarate (2HG) by mIDH1 induces histone and DNA hypermethylation, which has been shown to impair neural precursor cells’ differentiation. We aim to investigate how the presence of mIDH1 impacts the epigenetic regulation of long non-coding RNAs (lncRNAs), microRNAs (miRNAs) and mRNAs in human mutant IDH1 glioma cell cultures obtained from patients at the time of surgery. We hypothesize that the dysregulation/remodeling of lncRNAs, miRNAs and mRNAs contributes to the invasiveness, differentiation status and stemness of glioma cells. Only a handful of lncRNAs have been studied in relation to their role in neural cells’ lineage commitment and glioma stem cells’ biology. We identified 127 differentially expressed (DE) lncRNA (FDR SC is supported by the T32 Cancer Biology Training Grant, the work is supported by grants from NIH/NINDS to MGC and PRL. Citation Format: Stephen Carney, Felipe Nuñez, Pedro R. Lowenstein, Maria G. Castro. Identifying dysregulated lncRNAs and miRNAs in low grade glioma: Uncovering signaling pathways and novel therapeutic targets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3414.

Purpose: In malignant gliomas, invasive phenotype and cancer stemness promoting resurgence of residual tumor cells, render treatment very difficult. Hence, identification of epithelial-mesenchymal transition (EMT) factors associated with invasion and stemness of glioma cells is critical. Methods: To address the issue, we investigated several EMT factors in hypermotile U87MG and U251 cells, mouse xenograft model, and human glioma samples. Of several EMT markers, SLUG expression was notably increased at the invasive fronts of gliomas, both in mouse tumor xenografts and human glioma samples. The biological role played by SLUG was investigated using a colony-forming assay after chemotherapy and irradiation, and by employing a neurosphere culture assay. The effect of SLUG on glioma progression was examined in our patient cohort and samples, and compared to large public data from the REMBRANDT and TCGA. Results: Genetic upregulation of SLUG was associated with increased levels of stemness factors and enhanced resistance to radiation and temozolomide. In our cohort, patients exhibiting lower-level SLUG expression evidenced longer progression-free survival (P=0.042). Also, in the REMBRANDT dataset, a group in which SLUG was downregulated exhibited a significant survival benefit (P Conclusion: SLUG may contribute to glioma progression by controlling invasion at infiltrating margins, associated with increased stemness and therapeutic resistance. Citation Format: Kyung-Hwa Lee, Se-Jeong Oh, Eun-Jung Ahn, Shin Jung, Jae-Hyuk Lee, Kyung-Keun Kim, Hangun Kim, Kyung-Sub Moon. The role played by SLUG, an epithelial-mesenchymal transition factor, in invasion and therapeutic resistance of malignant glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1877.

Glioblastomas (GBM) are the most common primary malignant brain tumor in adults and are recognized as one of the deadliest forms of cancer. Despite aggressive therapy consisting of maximal surgical resection followed by concomitant radiation and temozolomide (TMZ) chemotherapy, GBM remains to have a median survival time of ~ 15 months. Glioblastoma stem cells (GSCs) are suggested to play a critical role in the GBM phenotype; GSC have tumor initiation ability, propagation ability, and have been shown to be a driver in promoting GBM resistance to current therapeutic interventions. Due to these poor clinical outcomes and resistance to current treatments, more potent and preferably more specific pharmacological therapies are needed in order to target cellular-molecular pathways to eradicate GSCs and effectively treat GBM. In an effort to identify agents that specifically inhibit GSC growth, we recently conducted a drug screen of over 3,000 small molecules. HSR020913 patient derived neurospheres were treated for 72 hours with library agents at a concentration of 10 µM and cell growth was observed for a period of 5 days. We identified twelve highly potent compounds in the primary screen that inhibited the growth of HSR020913 neurospheres by over 50%. Subsequently, the potency of these compounds was tested on five additional GBM patient derived neurosphere lines (HSR040622, HSR040822, CCF3691, CCF3832, and CCF08-387) at even lower concentrations. We next sought to determine the specificity of these compounds in killing GSCs but not normal cells. To this aim we tested these compounds against immortalized human neural stem cells (v-Myc hNSCs) and normal human astrocytes (NHA). Of the twelve potent compounds identified in the primary screen, three compounds (AGSC9, AGSC11, AGSC12) showed to have negligible to minimal effect, only at higher doses, on normal neural stem cells. The respective half maximal inhibitory concentration (IC50) was determined for all the neurosphere lines utilized. Subsequent studies determined the inhibitory effect of these compounds on clonogenic capacity and enzymatic activity. Future studies are warranted to identify molecular pathways targeted by these compounds and determine their effect on tumor progression and survival in vivo. Citation Format: Anthony R. Sloan, Raffaella Spina, Dillon M. Voss, Sophie Laye, Eli E. Bar. Identifying small molecules that specifically inhibit glioma stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1171.

Glioblastoma (GBM) is the most common type of primary brain tumor, with the standard therapy only modestly improving the prognosis, highlighting the necessity to develop advanced treatments. We and others have established the platform to potentiate immune response against GBMs using chimeric antigen receptor (CAR) engineered T-cells. Specifically, we have shown that intracranial administration of CAR T-cells can be well tolerated in patients with recurrent GBMs, together with some early clinical evidence of antitumor response. However, CAR T-cell therapy against GBMs is complicated by the inter- and intratumoral heterogeneity, while the single-targeting therapies only respond to a subset of tumor cells. The development of new CAR therapy would thus aim for targeting a wider range of tumor cells and bypassing antigen escape. Here, we took an approach different from conventional strategies of tumor antigen discovery, exploiting the tumor-binding potential of a natural peptide to develop CAR T-cells that broadly target GBMs. Chlorotoxin (CLTX) is a 36-amino acid peptide with demonstrated GBM-binding capability. Inspired by the utilization of CLTX in GBM tumor imaging, we used a fluorescence-conjugated CLTX to screen the freshly-dispersed primary GBM cells and patient-derived GBM neurospheres, and found that CLTX binding was more homogeneous than the expression of other GBM-associated antigens including EGFR, HER2 and IL13Rα2. Although CLTX has limited inhibitory effect on GBM growth, its broad binding to GBM cells illustrates the potential to be conjugated with a cytotoxic agent. Therefore, we generated CAR T-cells bearing CLTX as the antigen targeting domain. CLTX-CAR T-cells were able to get activated after stimulating with GBM cells, as indicated by their degranulation, cytokine production and immuno-synapse formation. Modification of CAR constructs revealed that CLTX-CAR T-cells with CD28 costimulatory signal exhibited potent effector activity, while the 4-1BB costimulation resulted in inadequate CAR activation. In both in vitro and in vivo models, CLTX-CAR T-cells effectively eliminated GBM cells and tumors, including the ones with no/low expression of EGFR, HER2 and IL13Rα2. Importantly, CLTX peptide exhibited negligible binding to a panel of normal cells from neural and other tissues, and CLTX-CAR T-cells showed no off-target effect against normal organs in tumor-bearing mouse models. Screening on patient-derived GBM neurospheres, we discovered that the expression of metalloproteinase (MMP)-2 on targeT-cells was correlated with the effector function of CLTX-CAR T-cells. Further, the antitumor function of CLTX-CAR T-cells was severely diminished against GBMs with MMP-2 knockdown. Consistent with the cytotoxicity of CLTX-CAR T-cells, MMP-2 expression was also present in a subgroup of GBM cells with undetectable levels of EGFR, HER2 and IL13Rα2 expression. Our results demonstrate for the first time that a peptide toxin can be successfully used as the tumor targeting domain of a CAR, which eliminates GBMs with high efficiency and selectivity. The CLTX-CAR has the potential to limit GBM heterogeneity and compensate current CAR T-cell therapies against solid tumors. Citation Format: Dongrui Wang, Vanessa Jonsson, Sarah Wright, Wen-Chung Chang, Xin Yang, Renate Starr, Alfonso Brito, Brenda Aguilar, Aniee Sarkissian, Lihong Weng, Stephen J Forman, Michael E Barish, Christine E. Brown. Chlorotoxin redirects T-cells for specific and effective targeting against glioblastomas [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A045.

Purpose: To examine the effects of clinically relevant pharmacologic Notch inhibition on glioblastoma xenografts. Experimental Design: Murine orthotopic xenografts generated from temozolomide-sensitive and -resistant glioblastoma neurosphere lines were treated with the γ-secretase inhibitor MRK003. Tumor growth was tracked by weekly imaging, and the effects on animal survival and tumor proliferation were assessed, along with the expression of Notch targets, stem cell, and differentiation markers, and the biology of neurospheres isolated from previously treated xenografts and controls. Results: Weekly MRK003 therapy resulted in significant reductions in growth as measured by imaging, as well as prolongation of survival. Microscopic examination confirmed a statistically significant reduction in cross-sectional tumor area and mitotic index in a MRK003-treated cohort as compared with controls. Expression of multiple Notch targets was reduced in the xenografts, along with neural stem/progenitor cell markers, whereas glial differentiation was induced. Neurospheres derived from MRK003-treated xenografts exhibited reduced clonogenicity and formed less aggressive secondary xenografts. Neurospheres isolated from treated xenografts remained sensitive to MRK003, suggesting that therapeutic resistance does not rapidly arise during in vivo Notch blockade. Conclusions: Weekly oral delivery of MRK003 results in significant in vivo inhibition of Notch pathway activity, tumor growth, stem cell marker expression, and clonogenicity, providing preclinical support for the use of such compounds in patients with malignant brain tumors. Some of these effects can persist for some time after in vivo therapy is complete. Clin Cancer Res; 19(12); 3224–33. ©2013 AACR.

The existence of treatment-resistant cancer stem cells contributes to the aggressive phenotype of glioblastoma. However, the molecular alterations that drive stem cell proliferation in these tumors remain unknown. In this study, we found that expression of the MET oncogene was associated with neurospheres expressing the gene signature of mesenchymal and proneural subtypes of glioblastoma. Met expression was almost absent from neurospheres expressing the signature of the classical subtype and was mutually exclusive with amplification and expression of the EGF receptor (EGFR) gene. Met-positive and Met-negative neurospheres displayed distinct growth factor requirements, differentiated along divergent pathways, and generated tumors with distinctive features. The Methigh subpopulation within Met-pos neurospheres displayed clonogenic potential and long-term self-renewal ability in vitro and enhanced growth kinetics in vivo. In Methigh cells, the Met ligand HGF further sustained proliferation, clonogenicity, expression of self-renewal markers, migration, and invasion in vitro. Together, our findings suggest that Met is a functional marker of glioblastoma stem cells and a candidate target for identification and therapy of a subset of glioblastomas. Cancer Res; 72(17); 4537–50. ©2012 AACR.

Malignant neuroblastomas contain stem-like cells. These tumors also overexpress the Forkhead box transcription factor FoxM1. In this study, we investigated the roles of FoxM1 in the tumorigenicity of neuroblastoma. We showed that depletion of FoxM1 inhibits anchorage-independent growth and tumorigenicity in mouse xenografts. Moreover, knockdown of FoxM1 induces differentiation in neuroblastoma cells, suggesting that FoxM1 plays a role in the maintenance of the undifferentiated progenitor population. We showed that inhibition of FoxM1 in malignant neuroblastoma cells leads to the downregulation of the pluripotency genes sex determining region Y box 2 (Sox2) and Bmi1. We provided evidence that FoxM1 directly activates expression of Sox2 in neuroblastoma cells. By using a conditional deletion system and neurosphere cultures, we showed that FoxM1 is important for expression of Sox2 and Bmi1 in the mouse neural stem/progenitor cells and is critical for its self-renewal. Together, our observations suggested that FoxM1 plays an important role in the tumorigenicity of the aggressive neuroblastoma cells through maintenance of the undifferentiated state. Cancer Res; 71(12); 4292–302. ©2011 AACR.

Diffuse intrinsic pontine glioma (DIPG), the most common pediatric brainstem tumor, is associated with a dismal prognosis with almost no survivors within two years of diagnosis. It is unamenable to surgical resection, is not responsive to conventional chemotherapy, and responds only temporarily to radiation therapy (XRT). Recent publications identified carboxy (C)-terminal truncating mutations of PPM1D, which encodes the protein WIP1, in up to 25% of DIPGs. WIP1 is a serine/threonine protein phosphatase that plays an important role in DNA damage response (DDR). Prior publications show that most, but not all, PPM1D C-terminal mutants function in a dominant negative fashion to promote tumor growth in cancer models. We hypothesized that PPM1D mutation promotes DIPG growth, and WIP1 inhibition suppresses tumor proliferation. We further hypothesized that, due to its key role in DDR, WIP1 inhibition enhances the antitumor effects of XRT. Using Sanger sequencing, we identified de novo mutation of PPM1D in the C-terminus of multiple patient-derived DIPG cell lines. We also stably introduced clinically relevant PPM1D mutations, which we identified in DIPGs resected from patients, into a PPM1D wild-type DIPG cell line, DIPG VI, as well as into DIPG cells derived from a DIPG mouse model. Using trypan blue exclusion, bioluminescence, and immunofluorescence detection of markers of proliferation and cell death, in the presence or absence of PPM1D knockdown or pharmacologic WIP1 inhibition, and/or following XRT exposure, we measured proliferation of DIPG VI, DIPG VI L513X, a cell line with stable expression of a mutant PPM1D, and DIPG7, a cell line with a de novo PPM1D mutation. We also assayed proliferation in organotypic brain slice cultures derived from symptomatic immunocompromised mice orthotopically xenografted with DIPG cells and of DIPG cells embedded within the brainstem of organotypic brain slices derived from immunocompetent mice. Finally, we orthotopically xenografted DIPG cells into the early post-natal (P0-2) brainstem of immunodeficient mice, treated mice with vehicle or with a small-molecule WIP1 inhibitor, and measured effects on survival, as well as proliferation in tumor cells post-necropsy. Under cell culture conditions, expression of PPM1D mutants promoted tumor cell proliferation in wild-type PPM1D murine and human DIPG cells. Conversely, PPM1D knockdown significantly suppressed DIPG cell proliferation, especially in PPM1D mutated DIPG cells. Similarly, treatment with a small-molecule WIP1 inhibitor suppressed the growth of PPM1D-mutated, but not PPM1D wild-type DIPG cells, in neurosphere cultures, on immunocompetent organotypic brain slices, and on organotypic brain slices derived from symptomatic, orthotopic, xenografted mice. WIP1 inhibition had similar effects on growth inhibition to XRT alone and augmented the antiproliferative and proapoptotic effects of XRT in vitro. Mice bearing an orthotopic xenograft of PPM1D-mutated human DIPG cells, DIPG7, died of disease earlier than mice xenografted with PPM1D wild-type human DIPG cells, DIPG VI. Treatment of mice bearing orthotopically, xenografted DIPG7 cells with a WIP1 inhibitor via a continuous 14-day infusion into the lateral ventricles resulted in a significant reduction in proliferation of tumor cells. In summary, our results show that C-terminal mutated PPM1D is oncogenic in DIPG, promoting proliferation and reduced survival in vivo. WIP1 inhibition suppresses growth and increases the radiosensitivity of PPM1D-mutated DIPG. These results suggest that WIP1 is a druggable target alone and in combination with XRT in DIPG. Further studies will examine the PPM1D-mediated mechanisms of tumorigenesis and treatment responsiveness in DIPG in order to develop clinically viable treatment paradigms that target PPM1D-mutated tumors. Citation Format: Mwangala P. Akamandisa, Kai Nie, Jing Wen, Rita Nahta, Dolores Hambardzumyan, Robert C. Castellino. Mechanisms of PPM1D-mediated tumorigenesis in diffuse intrinsic pontine glioma (DIPG) [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr B05.

Background: Glioblastoma (GBM) is associated with poor survival (1 year-34.6% and 5 year-4.75%) and affects approximately 13,000 patients per year. Standard treatment consists of surgical resection, external beam radiation therapy, adjuvant chemotherapy with temozolomide and tumor treating fields. Nonetheless, despite a heavy investment in therapy, all patients eventually succumb to their disease. Hypoxic regions are common in GBM and are implicated in maintenance of glioma stem cells (GSCs), promoting angiogenesis and therapeutic resistance. Recently, we and others have shown that lysine-specific histone demethylase 1A (KDM1A) is overexpressed in GBM and GSCs. However, the role of KDM1A and its functions in hypoxic response remains unknown. The objective of this study is to elucidate the functional role of KDM1A in hypoxia and test the efficacy of novel KDM1A inhibitors on hypoxia-mediated functions in GBM. Methods: The expression of KDM1A following hypoxia induction was determined in vitro by Western blotting and qRT-PCR. The expression of KDM1A in GBM tissue was examined by immunohistochemistry (IHC). KDM1A knockout cells were generated using CRISPR/Cas9 system and knockdown cells were generated using KDM1A shRNA lentiviral particles. The effect of KDM1A knockdown or treatment with KDM1A inhibitors NCL-1 and NCD-38 on stemness and self-renewal of primary patient-derived GBM cells was examined using neurosphere formation and extreme limiting dilution assays. Interaction of KDM1A with hypoxia inducible factor 1α (HIF-1α) was examined by immunoprecipitation (IP). The role of KDM1A on HIF target genes was determined using qRT-PCR and HRE-reporter activity. Mouse orthotopic xenografts models were used for preclinical evaluation of KDM1A inhibitors. Results: Western blot analysis revealed that KDM1A expression is induced in primary GBM cells following hypoxia. IHC analysis demonstrated elevated expression of KDM1A in hypoxic regions in human GBM tissues as well as mouse GBM xenografts. IP analysis demonstrated that KDM1A interacts with HIF-1α. Cell viability assays revealed that NCD-38 is more potent in reducing the cell viability of primary GBM cells compared to other KDM1A inhibitors. KDM1A knockdown or KDM1A inhibitor treatment significantly reduced the HIF- target gene expression including VEGF, PGK, CAIX, and HRE-Luc reporter activity in GBM cells. Further, hypoxia mediated cell proliferation and self-renewal ability of GSCs was compromised in KDM1A knockdown and KDM1A inhibitor-treated cells. Further, knockdown of KDM1A or treatment with KDM1A inhibitor significantly reduced the in vivo tumor growth and improved survival in orthotopic models. Conclusions: Our results demonstrate that KDM1A plays a critical role in hypoxia response and inhibition of KDM1A is a novel therapeutic approach for the treatment of GBM. Citation Format: Gangadhara R. Sareddy, Suryavathi Viswanadhapalli, Mei Zhou, Yiliao Luo, Xiaonan Li, Jinyou Liu, Aleksandra Gruslova, Takayoshi Suzuki, Andrew Brenner. The lysine demethylase KDM1A inhibition attenuates hypoxic responses in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2422.

Objective: Glioblastoma and Medulloblastoma are deadliest brain tumors both in adults and children. While next-generation sequencing rapidly identifies whole exome/genome gene mutations, the efficacy of targeting mutated genes/pathways has not been systematically analyzed. Additionally, it remains unknown if neurospheres (enriched with cancer stem cells) and non-stem monolayer tumor cells will respond equally to the same target therapies. Methods: Matching pairs of neurosphere and monolayer cell cultures from 4 molecularly characterized PDOX mouse models established from distinct clinical stages of pediatric GBM and MB were treated with 7,913 drugs (mostly in clinical use or trials) at 4 doses (0-10 uM) for 3 and 7 days. Dose-response curves and active area under the curve were constructed to identify active drugs and correlate with model-specific gene mutations. Results: Relatively long-term treatment (7 day screening) was achieved for high-throughput drug screening and revealed time- and dose-dependent effects in most of the 4,629 compounds that were active in at least one culture at one time point. When gene mutations were druggable, not all inhibitors of the same family were active. In IC-4687GBM (a treatment-naïve GBM), high NF1 mutation (>76-99% allele) frequency was found in patient tumor, xenografts, and cultured cells, but only 3/17 MEK inhibitors were active in neurospheres and 2/17 in monolayer cells (GDC0980 and PI-103 were active in both) on day 7. In IC-R0315GBM (from an autopsied terminal GBM) that carried PI3KCA mutation (allele frequency 22-27%), 5/33 PI3K inhibitors were active in neurospheres and 8/33 in monolayer cells (only Tremetinib was active in both) after 7 days. In IC-3752GBM (recurrent GBM) and ICb-1127AA (radiation-induced anaplastic astrocytoma), no druggable mutations were detected. The number of active drugs on day 7 was 366 in IC-4768GBM, 406 in IC-3752GBM, 284 in IC-R0315GBM, and 305 in ICb-1277AA. When the 4 matching pairs of neurospheres and monolayers were compared, the agents active in both cultures ranged from 36% to 60%, active only in neurosphere from 10.3% to 25%, and active only in monolayer cells from 14.8% to 53%. The response of MB to the drugs is on the way for analysis. Conclusion: We showed that long-term treatment is feasible for high-throughput drug screening. Targeting druggable mutations can be achieved but only by a fraction of specific agents. Neurospheres and monolayer cells do not always respond equally toward the same drugs, and effective targeting of both subpopulations is needed to generate prolonged animal survival times. Citation Format: Lin Qi, Yuchen Du, Goeun Bae, Mari Mari, Frank Braun, Holly Lindsay, Huiyuan Zhang, Sibo Zhao, Sarah Injac, Patricia Baxter, Jack Su, Michael Mancini, Oliver Hampton, William Parsons, Mural Chintagumpala, Clifford Stephan, Peter Davies, Xiaonan Li. Identification of personalized active agents in pediatric medulloblastoma through high-throughput drug screening in matching pairs of patient derived orthotopic xenograft neurosphere and monolayer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-069.

Nuclear Respiratory Factor 1 (NRF1), a transcription factor historically known to regulate several mitochondrial genes, has been recently implicated in human cancers. We have previously demonstrated the importance of NRF1 in estrogen driven breast cancer. The NRF1 motif exhibits some of the strongest pioneer activity (pioneer index indicates an increase in chromatin opening activity during developmental process) in mouse embryonic stem cells. Both neurogenesis and synaptogenesis are controlled by NRF1 regulated genes. There is a strong association of NRF1 with human fetal brain and neural development. To begin our study of the effect of NRF1 on glioblastoma pathogenesis, we examined whether NRF1 contributes to the acquisition of multipotent neural stem/progenitor cell (NSPC) properties in adult human brain cells. We generated NRF1 overexpressing stable human brain cerebral cortex astrocytes. Both 17β-estradiol (E2, 100 pg/ml) and NRF1 overexpression increased the percentage of cells co-expressing SOX2 and Nestin by 8 and 20%, respectively as shown by flow cytometry. Nestin is an intermediate filament protein important for guaranteeing neural stem pluripotent stem cell (NSPC) self-renewal while SOX2 is expressed at the earliest development stage of the brain and functions as a marker of neural development. SOX2 also plays a key role in the maintenance of neural stem cell (NSC) properties, including proliferation/survival, self-renewal, and neurogenesis. Multipotency allows NSPCs to differentiate into the neurons, astrocytes or oligodendrocytes. NRF1-induced SOX2+Nestin+ NSPCs expressed the neuronal marker β-III-tubulin, the neural phenotype, and neurosphere formation. NRF1 induced NSPCs were subjected to FACS analysis after FITC Annexin V and Propidium Iodide staining. Dead cells stained positive for both FITC Annexin V and PI and these cells are lowest in NRF1+ (0.42%) compared to vector control (4%). In summary, overexpression of NRF1 suppresses cellular senescence and increases resistance to apoptosis. Both are major barriers to cell reprogramming that may contribute in the generation of glioblastoma stem cells. To investigate the role of NRF1 gene network in glioblastoma, we used Bayesian network (BN) analysis on TCGA based RNA-seq data of 154 glioblastoma patients samples. NRF1 based gene association networks were significantly different in low overall survival (OS) patients compared with high OS patients. Specifically, TNFRSF10B, HGF, EBF4, and PAX5 showed up consistently as first degree Markov Blanket genes of NRF1 in low OS ( Citation Format: Kaumudi Bhawe, Jayanta Das, Changwon Yoo, Deodutta Roy. Role of NRF1 regulatory gene-networks in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1127.

Glioblastoma (GBM) has a median survival of less than 2 years due to intra-tumoral heterogeneity, diffuse infiltrations of adjacent brain tissue, and a lack of effective therapies. Development of more efficacious therapies will require better GBM models for the testing and identification of novel agents. Towards this end, we have successfully developed a GBM 3D tissue model that can provide in vitro, patient-specific compound screening. Stable populations of glioma stem cells (GSC) from 24 of 41 patient samples have been successfully established and cultured long-term with minimal changes. To confirm stemness of the GSC population, we have successfully established a limiting-dilution series within SCID/Bg mice and characterized the resultant tumors. 4 of these lines have been used to establish patient-derived xenograft (PDX) models in mice. The original, primary patient tissue established GSC populations, and the resultant PDX tissues have been characterized by flow cytometry, IHC, RNA expression, NGS, and MGMT methylation status. With the goal of better modeling the patient tumor tissue in vitro, our GSC populations have also been used to establish complex microtumors within the KIYATEC 3DKUBE™ perfusion system, consisting of monoculture GSCs, GSCs co-cultured with human brain endothelial cells (HBECs), and GSCs co-cultured with HBECs and CD14+ peripheral blood mononuclear cells. Our monoculture microtumors consisting of only GSCs show a maintenance of GSC markers Nestin and Sox2 by both IHC and mRNA. Interestingly, when these cells are used to produce PDX, they up-regulate GFAP as a marker of differentiation that is not observed in the neurosphere or monoculture microtumor cultures. We have shown these 3D models to be viable for more than 1 month in perfusion and to be effective models for drug compound screening by dosing the microtumors on a weekly basis with temozolomide (TMZ). We have correlated TMZ response to MGMT methylation as reported both clinically and measured in vitro. Finally, In vitro drug response has been compared to both matched PDX in vivo drug response and the patient's clinical response to TMZ and MGMT methylation. Our data supports that this complex, 3D, patient-derived GBM model can be used to effectively screen, identify and characterize novel treatments of GBM. Citation Format: Ashley M. Smith, Melissa Millard, Lillia Holmes, Michael T. Lewis, Lacey E. Dobrolecki, Charles Kanos, Stephen Gardner, Philip Hodge, Fred Nelson, Michael Lynn, Jeff Edenfield, Christopher Corless, David Schammel, Howland E. Crosswell, Teresa M. DesRochers. Profiling patient-specific glioblastoma drug response in vitro using complex 3D microtumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1121.

The magnetic nanoparticle has emerged as a potential multifunctional clinical tool that can provide cancer cell detection by magnetic resonance imaging (MRI) contrast enhancement as well as targeted cancer cell therapy. A major barrier in the use of nanotechnology for brain tumor applications is the difficulty in delivering nanoparticles to intracranial tumors. Iron oxide nanoparticles (IONP; 10 nm in core size) conjugated to a purified antibody that selectively binds to the epidermal growth factor receptor (EGFR) deletion mutant (EGFRvIII) present on human glioblastoma multiforme (GBM) cells were used for therapeutic targeting and MRI contrast enhancement of experimental glioblastoma, both in vitro and in vivo, after convection-enhanced delivery (CED). A significant decrease in glioblastoma cell survival was observed after nanoparticle treatment and no toxicity was observed with treatment of human astrocytes (P < 0.001). Lower EGFR phosphorylation was found in glioblastoma cells after EGFRvIIIAb-IONP treatment. Apoptosis was determined to be the mode of cell death after treatment of GBM cells and glioblastoma stem cell–containing neurospheres with EGFRvIIIAb-IONPs. MRI-guided CED of EGFRvIIIAb-IONPs allowed for the initial distribution of magnetic nanoparticles within or adjacent to intracranial human xenograft tumors and continued dispersion days later. A significant increase in animal survival was found after CED of magnetic nanoparticles (P < 0.01) in mice implanted with highly tumorigenic glioblastoma xenografts (U87ΔEGFRvIII). IONPs conjugated to an antibody specific to the EGFRvIII deletion mutant constitutively expressed by human glioblastoma tumors can provide selective MRI contrast enhancement of tumor cells and targeted therapy of infiltrative glioblastoma cells after CED. Cancer Res; 70(15); 6303–12. ©2010 AACR.

Purpose: Telomerase activity is one of the hallmarks of cancer and is a highly relevant therapeutic target. The effects of a novel human telomerase antagonist, imetelstat, on primary human glioblastoma (GBM) tumor-initiating cells were investigated in vitro and in vivo. Experimental Design: Tumor-initiating cells were isolated from primary GBM tumors and expanded as neurospheres in vitro. The GBM tumor-initiating cells were treated with imetelstat and examined for the effects on telomerase activity levels, telomere length, proliferation, clonogenicity, and differentiation. Subsequently, mouse orthotopic and subcutaneous xenografts were used to assess the in vivo efficacy of imetelstat. Results: Imetelstat treatment produced a dose-dependent inhibition of telomerase (IC50 0.45 μmol/L). Long-term imetelstat treatment led to progressive telomere shortening, reduced rates of proliferation, and eventually cell death in GBM tumor-initiating cells. Imetelstat in combination with radiation and temozolomide had a dramatic effect on cell survival and activated the DNA damage response pathway. Imetelstat is able to cross the blood-brain barrier in orthotopic GBM xenograft tumors. Fluorescently labeled GBM tumor cells isolated from orthotopic tumors, following systemic administration of imetelstat (30 mg/kg every day for three days), showed ∼70% inhibition of telomerase activity. Chronic systemic treatment produced a marked decrease in the rate of xenograft subcutaneous tumor growth. Conclusion: This preclinical study supports the feasibility of testing imetelstat in the treatment of GBM patients, alone or in combination with standard therapies. Clin Cancer Res; 16(1); 154–63

Glioblastoma, the most malignant type of primary brain tumor, is one of the solid cancers where cancer stem cells have been isolated, and studies have suggested resistance of those cells to chemotherapy and radiotherapy. Here, we report the establishment of CSC-enriched cultures derived from human glioblastoma specimens. They grew as neurospheres in serum-free medium with epidermal growth factor and fibroblast growth factor 2, varied in the level of CD133 expression and very efficiently formed highly invasive and/or vascular tumors upon intracerebral implantation into immunodeficient mice. As a novel therapeutic strategy for glioblastoma-derived cancer stem–like cells (GBM-SC), we have tested oncolytic herpes simplex virus (oHSV) vectors. We show that although ICP6 (UL39)–deleted mutants kill GBM-SCs as efficiently as wild-type HSV, the deletion of γ34.5 significantly attenuated the vectors due to poor replication. However, this was significantly reversed by the additional deletion of α47. Infection with oHSV G47Δ (ICP6−, γ34.5−, α47−) not only killed GBM-SCs but also inhibited their self-renewal as evidenced by the inability of viable cells to form secondary tumor spheres. Importantly, despite the highly invasive nature of the intracerebral tumors generated by GBM-SCs, intratumoral injection of G47Δ significantly prolonged survival. These results for the first time show the efficacy of oHSV against human GBM-SCs, and correlate this cytotoxic property with specific oHSV mutations. This is important for designing new oHSV vectors and clinical trials. Moreover, the new glioma models described in this study provide powerful tools for testing experimental therapeutics and studying invasion and angiogenesis. [Cancer Res 2009;69(8):3472–81]

In vitro investigations of tumor stem-like cells (TSC) isolated from human glioblastoma (GB) surgical specimens have been done primarily at an atmospheric oxygen level of 20%. To determine whether an oxygen level more consistent with in situ conditions affects their stem cell–like characteristics, we compared GB TSCs grown under conditions of 20% and 7% oxygen. Growing CD133+ cells sorted from three GB neurosphere cultures at 7% O2 reduced their doubling time and increased the self-renewal potential as reflected by clonogenicity. Furthermore, at 7% oxygen, the cultures exhibited an enhanced capacity to differentiate along both the glial and neuronal pathways. As compared with 20%, growth at 7% oxygen resulted in an increase in the expression levels of the neural stem cell markers CD133 and nestin as well as the stem cell markers Oct4 and Sox2. In addition, whereas hypoxia inducible factor 1α was not affected in CD133+ TSCs grown at 7% O2, hypoxia-inducible factor 2α was expressed at higher levels as compared with 20% oxygen. Gene expression profiles generated by microarray analysis revealed that reducing oxygen level to 7% resulted in the up-regulation and down-regulation of a significant number of genes, with more than 140 being commonly affected among the three CD133+ cultures. Furthermore, Gene Ontology categories up-regulated at 7% oxygen included those associated with stem cells or GB TSCs. Thus, the data presented indicate that growth at the more physiologically relevant oxygen level of 7% enhances the stem cell–like phenotype of CD133+ GB cells. (Mol Cancer Res 2009;7(4):489–97)

MicroRNAs (miR) show characteristic expression signatures in various cancers and can profoundly affect cancer cell behavior. We carried out miR expression profiling of human glioblastoma specimens versus adjacent brain devoid of tumor. This revealed several significant alterations, including a pronounced reduction of miR-128 in tumor samples. miR-128 expression significantly reduced glioma cell proliferation in vitro and glioma xenograft growth in vivo. miR-128 caused a striking decrease in expression of the Bmi-1 oncogene, by direct regulation of the Bmi-1 mRNA 3′-untranslated region, through a single miR-128 binding site. In a panel of patient glioblastoma specimens, Bmi-1 expression was significantly up-regulated and miR-128 was down-regulated compared with normal brain. Bmi-1 functions in epigenetic silencing of certain genes through epigenetic chromatin modification. We found that miR-128 expression caused a decrease in histone methylation (H3K27me3) and Akt phosphorylation, and up-regulation of p21CIP1 levels, consistent with Bmi-1 down-regulation. Bmi-1 has also been shown to promote stem cell self-renewal; therefore, we investigated the effects of miR-128 overexpression in human glioma neurosphere cultures, possessing features of glioma “stem-like” cells. This showed that miR-128 specifically blocked glioma self-renewal consistent with Bmi-1 down-regulation. This is the first example of specific regulation by a miR of a neural stem cell self-renewal factor, implicating miRs that may normally regulate brain development as important biological and therapeutic targets against the “stem cell–like” characteristics of glioma. [Cancer Res 2008;68(22):9125–30]

Gli signaling is critical for central nervous system development and is implicated in tumorigenesis. To monitor Gli signaling in gliomas in vivo, we created platelet-derived growth factor–induced gliomas in a Gli-luciferase reporter mouse. We find that Gli activation is found in gliomas and correlates with grade. In addition, we find that sonic hedgehog (SHH) is expressed in these tumors and also correlates with grade. We identify microvascular proliferation and pseudopalisades, elements that define high-grade gliomas as SHH-producing microenvironments. We describe two populations of SHH-producing stromal cells that reside in perivascular niche (PVN), namely low-cycling astrocytes and endothelial cells. Using the Ptc-LacZ knock-in mouse as a second Gli responsive reporter, we show β-galactosidase activity in the PVN and in some tumors diffusely throughout the tumor. Lastly, we observe that SHH is similarly expressed in human gliomas and note that an intact tumor microenvironment or neurosphere conditions in vitro are required for Gli activity. [Cancer Res 2008;68(7):2241–49]

Although glioblastomas show the same histologic phenotype, biological hallmarks such as growth and differentiation properties vary considerably between individual cases. To investigate whether different subtypes of glioblastomas might originate from different cells of origin, we cultured tumor cells from 22 glioblastomas under medium conditions favoring the growth of neural and cancer stem cells (CSC). Secondary glioblastoma (n = 7)–derived cells did not show any growth in the medium used, suggesting the absence of neural stem cell–like tumor cells. In contrast, 11/15 primary glioblastomas contained a significant CD133+ subpopulation that displayed neurosphere-like, nonadherent growth and asymmetrical cell divisions yielding cells expressing markers characteristic for all three neural lineages. Four of 15 cell lines derived from primary glioblastomas grew adherently in vitro and were driven by CD133− tumor cells that fulfilled stem cell criteria. Both subtypes were similarly tumorigenic in nude mice in vivo. Clinically, CD133− glioblastomas were characterized by a lower proliferation index, whereas glial fibrillary acidic protein staining was similar. GeneArray analysis revealed 117 genes to be differentially expressed by these two subtypes. Together, our data provide first evidence that CD133+ CSC maintain only a subset of primary glioblastomas. The remainder stems from previously unknown CD133− tumor cells with apparent stem cell–like properties but distinct molecular profiles and growth characteristics in vitro and in vivo. [Cancer Res 2007;67(9):4010–5]

Recent studies suggest that cancer can arise from a cancer stem cell (CSC), a tumor-initiating cell that has properties similar to those of stem cells. CSCs have been identified in several malignancies, including those of blood, brain, and breast. Here, we test whether stem cell–like populations exist in human melanomas. In ∼20% of the metastatic melanomas cultured in growth medium suitable for human embryonic stem cells, we found a subpopulation of cells propagating as nonadherent spheres, whereas in standard medium, adherent monolayer cultures were established. Individual cells from melanoma spheres (melanoma spheroid cells) could differentiate under appropriate conditions into multiple cell lineages, such as melanocytic, adipocytic, osteocytic, and chondrocytic lineages, which recapitulates the plasticity of neural crest stem cells. Multipotent melanoma spheroid cells persisted after serial cloning in vitro and transplantation in vivo, indicating their ability to self-renew. Furthermore, they were more tumorigenic than adherent cells when grafted to mice. We identified similar multipotent spheroid cells in melanoma cell lines and found that the stem cell population was enriched in a CD20+ fraction of melanoma cells. Based on these findings, we propose that melanomas can contain a subpopulation of stem cells that contribute to heterogeneity and tumorigenesis. Targeting this population may lead to effective treatments for melanomas.

Current therapies for gliomas often fail to address their infiltrative nature. Conventional treatments leave behind small clusters of neoplastic cells, resulting in eventual tumor recurrence. In the present study, we have evaluated the antitumor activity of neural progenitor cells against gliomas when stereotactically injected into nucleus Caudatus of Fisher rats. We show that the rat neural progenitor cell lines HiB5 and ST14A, from embryonic hippocampus and striatum primordium, respectively, are able to prolong animal survival and, in 25% of the cases, completely inhibit the outgrowth of N29 glioma compared with control animals. Delayed tumor outgrowth was also seen when HiB5 cells were inoculated at the site of tumor growth 1 week after tumor inoculation or when a mixture of tumor cells and HiB5 cells were injected s.c. into Fisher rats. HiB5 cells were additionally coinoculated together with two alternative rat gliomas, N32 and N25. N32 was growth inhibited, but rats inoculated with N25 cells did not show a prolonged survival. To evaluate the possibility of the involvement of the immune system in the tumor outgrowth inhibition, we show that HiB5 cells do not evoke an immune response when injected into Fisher rats. Furthermore, the rat neural progenitor cells produce all transforming growth factor β isotypes, which could explain the observed immunosuppressive nature of these cells. Hence, some neural progenitor cells have the ability to inhibit tumor outgrowth when implanted into rats. These results indicate the usefulness of neural stem cells as therapeutically effective cells for the treatment of intracranial tumors.

Glioblastoma Multiforme (GBM, WHO Grade IV glioma) is one of the deadliest adult CNS tumors with a median survival of less than two years. It is largely resistant to aggressive therapeutic regimes, which combine radiation, chemotherapy and surgery. Thus, it is imperative to identify the molecular players and pathways that facilitate GBM resistance and recurrence. Nuclear co-repressor protein NCoR2 is upregulated in GBM and its increased expression correlates with poor prognosis in GBM patients (Alrfaei. Plos one. 2013). NCoR2, through its binding to the histone deacetylase protein HDAC3, mediates transcriptional repression (Zhu et al. Brain Res. 2013). NCoR2 is also involved in maintenance of neural stem cells (Jepson et al. Nature. 2007), which contribute to treatment resistance. Our study employs two distinct lineages of glioma - the less aggressive proneural and the highly aggressive mesenchymal subtypes. We show that NCoR2 is differentially expressed across these subtypes, suggesting a role for NCoR2-mediated transcriptional reprogramming in GBM progression. Moreover, knockdown of NCoR2 leads to phenotypic changes both in vitro and in vivo - including effects on neurosphere formation and proliferation, differential expression of stem-like markers as well as regulation of tumor growth and progression in mice. We also demonstrate that NCoR2 expression is increased upon treatment with temozolomide (used for GBM therapy), indicating a protective pro-tumor role for NCoR2. Finally, we explore the contribution of the GBM microenvironment to GBM progression by varying the three-dimensional properties as well as the rigidity of the extracellular matrix and investigating changes in NCoR2 expression and its regulation of tumor progression. We conclude that NCoR2 regulates GBM progression and resistance to therapy potentially via inducing a stem-like phenotype as well as responding to the tumor-promoting mechanical cues within the GBM microenvironment. Citation Format: Shelly Kaushik, Joanna J. Phillips, Valerie M. Weaver. NCoR2 regulates glioblastoma progression and treatment resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3985. doi:10.1158/1538-7445.AM2017-3985

Introduction: Patient-derived xenograft (PDX) models for glioblastoma (GBM) from resected tumor tissues replicate several features of the original tumor. They are considered to be representative models to study tumor progression, and to test responses to putative therapies. Longitudinal noninvasive imaging can be useful in such investigations. To that end, we employed magnetic resonance imaging (MRI) to visualize and measure tumor burden in four different PDX models of GBM. Experimental procedures: Four orthotopic mouse PDX models, HF2587, HF2927, HF3077 and HF3253, developed from neurosphere cultures of four different human glioblastoma samples were used in the study. The neurosphere cells were implanted into the right striatum in immunocompromised nude mice (n=5-8 per model) and allowed to grow for 2-8 weeks, depending on their known growth rates from previous studies. They were imaged in a Varian 7T MRI system with the following weightings: T2, T1, magnetization transfer (MT), and contrast enhanced MRI (CE-MRI) with Magnevist as the contrast agent (CA). Following imaging, all the mice were sacrificed and their brains processed for hematoxylin and eosin (H&E) histology and human major histocompatibility complex (MHC) immunohistochemistry. Results: Tumor masses were visible as hyperintense regions on MT and T2-weighted images. The extent of such masses matched the H&E and MHC staining patterns. Ventricle enlargements seen on MRI in several mice were also confirmed by histology. Necrotic cores, when present, were observed on both imaging and on histopathology with good spatial correlations. Surprisingly, post-contrast T1 imaging did not enhance in the tumor mass or peritumorally, except in one mouse in which some intra-tumoral enhancement was observed. In all other instances from the four PDX models tested, enhancement was observed only when the tumor tissue or parts of it were contiguous with pial or dural vasculature. Conclusions: At 7 Tesla, MT-MRI and T2-weighted imaging, rather than CE-MRI, appear to be of better utility in visualizing these PDX models of GBM if MRI is chosen as the imaging modality. Since the parent tumors imaged at lower field strengths showed contrast enhancement, absence of a similar feature in these models needs additional studies to understand their vascular characteristics. Such properties may include low level of vascularization and/or relatively less leaky tumor vasculature. Another possible reason may be that the models tested represent the invasive features of GBM better than the vascular features, e.g. peritumoral ring enhancement, of larger clinical tumors with increased exposure to hypoxia. Citation Format: Tavarekere N. Nagaraja, Rasha Elmghirbi, Susan Irtenkauf, Laura Hasselbach, Baruch Tawil, Stephen L. Brown, Swayamprava Panda, Glauber Cabral, Tom Mikkelsen, James R. Ewing, Ana deCarvalho. Magnetization transfer and T2-weighted MRI studies are useful for visualizing phenotypic presentations of orthotopic, patient-derived xenograft mouse models of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3860. doi:10.1158/1538-7445.AM2017-3860

Development of effective novel anti-tumor treatments will require improved in vitro models that incorporate physiologic microenvironments and maintain intratumoral heterogeneity including tumor initiating cells. Brain tumor initiating cells (BTIC) are a target for cancer therapy because they are highly tumorigenic and contribute to tumor angiogenesis, invasion, and therapeutic resistance. Current leading studies rely on BTIC isolation from patient-derived xenografts followed by propagation as neurospheres. As this process is expensive and time-consuming, we determined whether three-dimensional microtumors were an alternative in vitro method for modeling tumor growth via BITC maintenance and/or enrichment. Brain tumor cells were grown as neurospheres or as microtumors produced using a human-derived biomatrix HuBiogelTM and maintained with physiologically relevant microenvironments. Percentages of BITCs were determined based on cell surface marker expression (CD133), label retention (carboxyfluorescein succinimidyl ester; CFSE), and tumorsphere formation capacity. Our data demonstrate that expansion of brain tumor cells as hypoxic and nutrient restricted microtumors significantly increased the percentage of both CD133+ and CFSE+ cells. We further demonstrate that BTIC-marker positive cells isolated from microtumors maintain neurosphere formation capacity in the in vitro limiting dilution assay and tumorigenic potential in vivo. These data demonstrate that microtumors can be a useful three-dimensional biological model for the study of BTIC maintenance and targeting. Citation Format: Ashley Gilbert, Kiera Walker, Anh Tran, Yancey Gillespie, Raj Singh, Anita B. Hjelmeland. Modeling physiologic microenvironments in three-dimensional microtumors facilitates brain tumor initiating cell maintenance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1925. doi:10.1158/1538-7445.AM2017-1925

Background: Recent evidences highlighted that GBM secreted microvesicles (EVs), particularly exosomes (Exo) and large oncosomes (LO), play a major role in the cross-talk between tumor cell and non-neoplastic parenchyma. How GBMs manage to thrive in a highly unfavorable, acidic microenvironment is still unclear, but recent work from our group has identified the vacuolar pump H+-ATPase (V-ATPase) as an important effector of GBM growth and glioma stem cells (GSC) maintenance. Additionally, in ExoCarta database V-ATPase subunits have been described in Exo from different cancer cell types. Taken together, these data identify V-ATPase as an important driver of gliomagenesis, and a novel, actionable therapeutic target for disease intervention. However, the role of V-ATPase in reprogramming the GBM microenvironment has not been previously investigated. Methods: Exo and LO were isolated by an Invitrogen kit and serial centrifugation, respectively, from media of patients’ derived GBM neurospheres, enriched in GSC (NS, n=12) or differentiated cultures (n=8). For EVs internalization studies, Exo or LO were stained using FM 1-43 FX dye and the process was followed live for 30’ and at selected time points (30’-4h-24h), using a confocal microscopy or flow cytometry (FACS). Electron microscopy, FACS (of Exo stained with CellTrace and SytoRNA in combination with CD63 coated beads), Nanosight and immunoblotting (for CD63, CD9 and Clathrin) analyses were used to confirm EVs subtypes. Cultures from patients’ derived brain tumor margins or primary GBM (differentiated and not) were used as EVs-recipient cells. miRNA profiling was performed using Taqman Low density arrays and analyzed by R packages. Gene Ontology analysis was performed by DAVID. The study was approved by the Institutional Ethical Committee. Results: NS are able to produce different EVs, which are internalized by recipient cells after 4 and up to 24 hours of co-culture. Both Exo than LO from NS are able to significantly increase cell growth in recipient cells (brain tumor margins and primary GMB differentiated monolayers), and this effect is stronger with EVs produced by NS with higher V-ATPase expression (V-ATPaseHIGH NS). Primary GBM cells after co-culture with EVs are able to produce a higher number of NS and V-ATPase activity block by BafilomycinA1 in NS-producing EVs completely revert this effect. Finally, the co-culture of V-ATPaseLOW NS with EVs from V-ATPaseHIGH NS increases their motility in collagen matrixes. At molecular level, profiling of Exo-derived miRNAs distinguishes differentiated cultures from NS and, among NS, V-ATPaseHIGH cultures. In silico analysis and annotation of miRNA target genes from V-ATPaseHIGH–derived Exo showed an enrichment of cancer, cell cycle and PI3K/Akt pathways. Conclusions: Altogether, these data point toward the central role of different EV types in GBM communication and suggest a role of the V-ATPase proton pump in regulating EV’s contents. Citation Format: Irene Bertolini, Andrea Terrasi, Andrea Di Cristofori, Silvano Bosari, Valentina Vaira. V-ATPase control of EV signaling in glioma stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2889. doi:10.1158/1538-7445.AM2017-2889

Objective: Glioblastoma (GBM) is one of the deadliest brain tumors both in adults and children. While next-generation sequencing rapidly identifies whole exome/genome gene mutations, the efficacy of targeting mutated genes/pathways has not been systematically analyzed. Additionally, it remains unknown if neurospheres (enriched with cancer stem cells) and non-stem monolayer tumor cells will respond equally to the same target therapies. Methods: Matching pairs of neurosphere and monolayer cell cultures from 4 molecularly characterized PDOX mouse models established from distinct clinical stages of pediatric glioma (treatment-naïve, early recurrent, terminal, and radiation-induced) were treated with 7,913 drugs (mostly in clinical use or trials) at 4 doses (0-10 uM) for 3 and 7 days. Dose-response curves and active area under the curve (AAUC) were constructed to identify active drugs and correlate with model-specific gene mutations. Results: Relatively long-term treatment (7 day screening) was achieved for high-throughput drug screening and revealed time- and dose-dependent effects in most of the 4,629 compounds that were active in at least one culture at one time point. When gene mutations were druggable, not all inhibitors of the same family were active. In IC-4687GBM (a treatment-naïve GBM), high NF1 mutation (>76-99% allele) frequency was found in patient tumor, xenografts, and cultured cells, but only 3/17 MEK inhibitors were active in neurospheres and 2/17 in monolayer cells (GDC0980 and PI-103 were active in both) on day 7. In IC-R0315GBM (from an autopsied terminal GBM) that carried PI3KCA mutation (allele frequency 22-27%), 5/33 PI3K inhibitors were active in neurospheres and 8/33 in monolayer cells (only Tremetinib was active in both) after 7 days. In IC-3752GBM (recurrent GBM) and ICb-1127AA (radiation-induced anaplastic astrocytoma), no druggable mutations were detected. The number of active drugs on day 7 was 366 in IC-4768GBM, 406 in IC-3752GBM, 284 in IC-R0315GBM, and 305 in ICb-1277AA. When the 4 matching pairs of neurospheres and monolayers were compared, the agents active in both cultures ranged from 36% to 60%, active only in neurosphere from 10.3% to 25%, and active only in monolayer cells from 14.8% to 53%. Subsequent in vivo validation using MLN8327 in IC-4687GBM and IC-R0315GBM showed that effective targeting of both neurosphere and monolayer was required for significantly-improved animal survival times. Conclusion: We showed that long-term treatment is feasible for high-throughput drug screening. Targeting druggable mutations can be achieved but only by a fraction of specific agents. Neurospheres and monolayer cells do not always respond equally toward the same drugs, and effective targeting of both subpopulations is needed to generate prolonged animal survival times. Citation Format: Lin Qi, Yuchen Du, Mari Kogiso, Goeun Bae, Frank Braun, Holly Lindsay, Huiyuan Zhang, Sibo Zhao, Sarah Injac, Patricia Baxter, Jack Su, Michael Mancini, Oliver Hampton, William Parsons, Murali Chintagumpala, Clifford Stephan, Peter Davies, Xiao-Nan Li, Xiao-Nan Li. Identification of personalized active agents in pediatric gliomas through high-throughput drug screening in matching pairs of patient derived orthotopic xenograft (PDOX) neurosphere and monolayer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4214. doi:10.1158/1538-7445.AM2017-4214