Response Of Glioblastoma Cells Research Articles

EXTH-39. A BENCH-TOP MODEL FOR THE OPTIMIZATION OF ULTRASOUND PARAMETERS FOR SONODYNAMIC THERAPY OF GLIOBLASTOMA

Abstract BACKGROUND In-vitro studies have demonstrated that low frequency sound waves can interact with hemo-porphyrin molecule to induce the production of reactive oxygen species. This biophysical phenomenon can induce tumour cell death in glioblastoma cells in-vitro. The purpose of this study was to evaluate the production of reactive oxygen species and expression of apoptotic markers in glioblastoma cells in response to varying total treatment time and ultrasound power using a bench-top focused ultrasound (FUS) device. METHODS U251 cells were exposed to 5-Aminolevulenic Acid (5-ALA) at varying concentrations for up to 24 hours. The time point with peak proto-porphyrin IX (PPIX) fluorescence was established using fluorescence activated cell sorting (FACS). A transducer utilized at 0.91MHz was placed on an inverted stage with the focus targeted to the bottom of a standard 96-well cell culture plate. Pressure wave delivery was confirmed using a hydrophone. GBM cells were treated with 5-ALA alone, FUS alone, or 5-ALA + FUS and the cells were incubated for 24 hours prior to measuring ROS induction and cell death. ROS was measured using FACS with the CellROX Green Kit for Oxidative Stress Detection and Annexin-V was measured using the Dead Cell Stain Kit. RESULTS Peak fluorescence intensity for PPIX in the U251 cell line was found to be induced through incubation with 5-ALA for 24 hours with a concentration 200mg/mL. The fluorescence intensity of PPIX was found to be 313% greater in the treated group compared to the control group. Peak ROS was observed using a 0.91MHz transducer frequency for a total time of 120s with 6W average power. ROS was 61% and 66% greater in the SDT group compared to the FUS and 5-ALA group respectively. CONCLUSION Using this bench-top set up we successfully induced ROS and apoptosis in U251 cells. Establishing a reliable in-vitro model will allow us to further investigate the effects of other sonication parameters such as burst length.

Triggering of endoplasmic reticulum stress via ATF4-SPHK1 signaling promotes glioblastoma invasion and chemoresistance

Despite advances in therapies, glioblastoma (GBM) recurrence is almost inevitable due to the aggressive growth behavior of GBM cells and drug resistance. Temozolomide (TMZ) is the preferred drug for GBM chemotherapy, however, development of TMZ resistance is over 50% cases in GBM patients. To investigate the mechanism of TMZ resistance and invasive characteristics of GBM, analysis of combined RNA-seq and ChIP-seq was performed in GBM cells in response to TMZ treatment. We found that the PERK/eIF2α/ATF4 signaling was significantly upregulated in the GBM cells with TMZ treatment, while blockage of ATF4 effectively inhibited cell migration and invasion. SPHK1 expression was transcriptionally upregulated by ATF4 in GBM cells in response to TMZ treatment. Blockage of ATF4-SPHK1 signaling attenuated the cellular and molecular events in terms of invasive characteristics and TMZ resistance. In conclusion, GBM cells acquired chemoresistance in response to TMZ treatment via constant ER stress. ATF4 transcriptionally upregulated SPHK1 expression to promote GBM cell aggression and TMZ resistance. The ATF4-SPHK1 signaling in the regulation of the transcription factors of EMT-related genes could be the underlying mechanism contributing to the invasion ability of GBM cells and TMZ resistance. ATF4-SPHK1-targeted therapy could be a potential strategy against TMZ resistance in GBM patients.

Metabolic Plasticity of Glioblastoma Cells in Response to DHODH Inhibitor BAY2402234 Treatment.

Glioblastoma (IDH-wildtype) represents a formidable challenge in oncology, lacking effective chemotherapeutic or biological interventions. The metabolic reprogramming of cancer cells is a hallmark of tumor progression and drug resistance, yet the role of metabolic reprogramming in glioblastoma during drug treatment remains poorly understood. The dihydroorotate dehydrogenase (DHODH) inhibitor BAY2402234 is a blood-brain barrier penetrant drug showing efficiency in in vivo models of many brain cancers. In this study, we investigated the effect of BAY2402234 in regulating the metabolic phenotype of EGFRWT and EGFRvIII patient-derived glioblastoma cell lines. Our findings reveal the selective cytotoxicity of BAY2402234 toward EGFRWT glioblastoma subtypes with minimal effect on EGFRvIII patient cells. At sublethal doses, BAY2402234 induces triglyceride synthesis at the expense of membrane lipid synthesis and fatty acid oxidation in EGFRWT glioblastoma cells, while these effects are not observed in EGFRvIII glioblastoma cells. Furthermore, BAY2402234 reduced the abundance of signaling lipid species in EGFRWT glioblastoma. This study elucidates genetic mutation-specific metabolic plasticity and efficacy in glioblastoma cells in response to drug treatment, offering insights into therapeutic avenues for precision medicine approaches.

Cadherin-6 is a novel mediator for the migration of mesenchymal stem cells to glioblastoma cells in response to stromal cell-derived factor-1.

Glioblastoma recruits various nontransformed cells from distant tissues. Although bone marrow-derived mesenchymal stem cells (MSCs) have been observed migrating to glioblastoma, the underlying mechanism driving MSC migration toward glioblastoma remains unclear. Tumor vascularity is critical in the context of recurrent glioblastoma and is closely linked to the expression of stromal cell-derived factor-1 (SDF-1). We demonstrated that cadherin-6 mediated MSC migration both toward SDF-1 and toward glioblastoma cells. Cadherin-6 knockdown resulted in the downregulation of MSCs capacity to migrate in response to SDF-1. Furthermore, MSCs with cadherin-6 knockdown exhibited impaired migration in response to conditioned media derived from glioblastoma cell lines (U87 and U373) expressing SDF-1, thus simulating the glioblastoma microenvironment. Moreover, MSCs enhanced the vasculogenic capacity of U87 cells without increasing the proliferation, cancer stem cell characteristics, or migration of U87. These results suggest that the current strategy of utilizing MSCs as carriers for antiglioblastoma drugs requires careful examination. Furthermore, cadherin-6 may represent a novel potential target for controlling the recruitment of MSCs toward glioblastoma.

Acetylation of mtHSP70 at Lys595/653 affecting its interaction between GrpEL1 regulates glioblastoma progression via UPRmt

BackgroundThe mitochondrial unfolded protein response (UPRmt) is a vital biological process that regulates mitochondrial protein homeostasis and enables glioblastoma cells to cope with mitochondrial oxidative stress in the tumor microenvironment. We previously reported that the binding of mitochondrial stress-70 protein (mtHSP70) to GrpE protein homolog 1 (GrpEL1) is involved in the regulation of the UPRmt. However, the mechanisms regulating their binding remain unclear. Herein, we examined the UPRmt in glioblastoma and explored whether modulating the interaction between mtHSP70 and GrpEL1 affects the UPRmt. MethodsWestern blot analysis, aggresome staining, and transmission electron microscopy were used to detect the activation of the UPRmt and protein aggregates within mitochondria. Molecular dynamics simulations were performed to investigate the impact of different mutations in mtHSP70 on its binding to GrpEL1. Endogenous site-specific mutations were introduced into mtHSP70 in glioblastoma cells using CRISPR/Cas9. In vitro and in vivo experiments were conducted to assess mitochondrial function and glioblastoma progression. ResultsThe UPRmt was activated in glioblastoma cells in response to oxidative stress. mtHSP70 regulated mitochondrial protein homeostasis by facilitating UPRmt-progress protein import into the mitochondria. Acetylation of mtHSP70 at Lys595/653 enhanced its binding to GrpEL1. Missense mutations at Lys595/653 increased mitochondrial protein aggregates and inhibited glioblastoma progression in vitro and in vivo. ConclusionsWe identified an innovative mechanism in glioblastoma progression by which acetylation of mtHSP70 at Lys595/653 influences its interaction with GrpEL1 to regulate the UPRmt. Mutations at Lys595/653 in mtHSP70 could potentially serve as therapeutic targets and prognostic indicators of glioblastoma.

ERN1 knockdown modifies the hypoxic regulation of homeobox gene expression in U87MG glioblastoma cells.

Homeobox genes play an important role in health and disease including oncogenesis. The present investigation aimed to study ERN1-dependent hypoxic regulation of the expression of genes encoding homeobox proteins MEIS (zinc finger E-box binding homeobox 2) and LIM homeobox 1 family, SPAG4 (sperm associated antigen 4) and NKX3-1 (NK3 homeobox 1) in U87MG glioblastoma cells in response to inhibition of ERN1 (endoplasmic reticulum to nucleus signaling 1) for evaluation of their possible significance in the control of glioblastoma growth. The expression level of homeobox genes was studied in control (transfected by vector) and ERN1 knockdown U87MG glioblastoma cells under hypoxia induced by dimethyloxalylglycine (0.5 mM for 4 h) by quantitative polymerase chain reaction and normalized to ACTB. It was found that hypoxia down-regulated the expression level of LHX2, LHX6, MEIS2, and NKX3-1 genes but up-regulated the expression level of MEIS1, LHX1, MEIS3, and SPAG4 genes in control glioblastoma cells. At the same time, ERN1 knockdown of glioblastoma cells significantly modified the sensitivity of all studied genes to a hypoxic condition. Thus, ERN1 knockdown of glioblastoma cells removed the effect of hypoxia on the expression of MEIS1 and LHX1 genes, but increased the sensitivity of MEIS2, LHX2, and LHX6 genes to hypoxia. However, the expression of MEIS3, NKX3-1, and SPAG4 genes had decreased sensitivity to hypoxia in ERN1 knockdown glioblastoma cells. Moreover, more pronounced changes under the conditions of ERN1 inhibition were detected for the pro-oncogenic gene SPAG4. The results of the present study demonstrate that hypoxia affected the expression of homeobox genes MEIS1, MEIS2, MEIS3, LHX1, LHX2, LHX6, SPAG4, and NKX3-1 in U87MG glioblastoma cells in gene-specific manner and that the sensitivity of all studied genes to hypoxia condition is mediated by ERN1, the major pathway of the endoplasmic reticulum stress signaling, and possibly contributed to the control of glioblastoma growth. A fundamentally new results of this work is the establishment of the fact regarding the dependence of hypoxic regulation of SPAG4 gene expression on ER stress, in particular ERN1, which is associated with suppression of cell proliferation and tumor growth.

GFAP serves as a structural element of tunneling nanotubes between glioblastoma cells and could play a role in the intercellular transfer of mitochondria.

Tunneling nanotubes (TNTs) are long F-actin-positive plasma membrane bridges connecting distant cells, allowing the intercellular transfer of cellular cargoes, and are found to be involved in glioblastoma (GBM) intercellular crosstalk. Glial fibrillary acid protein (GFAP) is a key intermediate filament protein of glial cells involved in cytoskeleton remodeling and linked to GBM progression. Whether GFAP plays a role in TNT structure and function in GBM is unknown. Here, analyzing F-actin and GFAP localization by laser-scan confocal microscopy followed by 3D reconstruction (3D-LSCM) and mitochondria dynamic by live-cell time-lapse fluorescence microscopy, we show the presence of GFAP in TNTs containing functional mitochondria connecting distant human GBM cells. Taking advantage of super-resolution 3D-LSCM, we show the presence of GFAP-positive TNT-like structures in resected human GBM as well. Using H2O2 or the pro-apoptotic toxin staurosporine (STS), we show that GFAP-positive TNTs strongly increase during oxidative stress and apoptosis in the GBM cell line. Culturing GBM cells with STS-treated GBM cells, we show that STS triggers the formation of GFAP-positive TNTs between them. Finally, we provide evidence that mitochondria co-localize with GFAP at the tip of close-ended GFAP-positive TNTs and inside receiving STS-GBM cells. Summarizing, here we found that GFAP is a structural component of TNTs generated by GBM cells, that GFAP-positive TNTs are upregulated in response to oxidative stress and pro-apoptotic stress, and that GFAP interacts with mitochondria during the intercellular transfer. These findings contribute to elucidate the molecular structure of TNTs generated by GBM cells, highlighting the structural role of GFAP in TNTs and suggesting a functional role of this intermediate filament component in the intercellular mitochondria transfer between GBM cells in response to pro-apoptotic stimuli.

MiR-200c-based metabolic modulation in glioblastoma cells as a strategy to overcome tumor chemoresistance.

Glioblastoma (GB) is the most aggressive and common form of primary brain tumor characterized by fast proliferation, high invasion and resistance to current standard treatment. The average survival rate post-diagnosis is 14.6months, despite the aggressive standard post-surgery radiotherapy concomitant with chemotherapy with temozolomide (TMZ). Currently, efforts are being endowed to develop new and more efficient therapeutic approaches capable to overcome chemoresistance, inhibit tumor progression and improve overall patient survival rate. Abnormal microRNA (miRNA) expression has been correlated with chemoresistance, proliferation and resistance to apoptosis, which result from their master regulatory role of gene expression. Altered cell metabolism, favoring glycolysis, was identified as an emerging cancer hallmark and has been described in GB, thus offering a new target for innovative GB therapies. In this work, we hypothesized that a gene therapy-based strategy consisting of the overexpression of a miRNA downregulated in GB and predicted to target crucial metabolic enzymes might promote a shift of GB cell metabolism, decreasing the glycolytic dependence of tumor cells and contributing to their sensitization to chemotherapy with TMZ. The increase of miR-200c levels in DBTRG cells resulted in downregulation of messenger RNA of enzymes involved in bioenergetics pathways and impaired cell metabolism and mobility. In addition, miR-200c overexpression prior to DBTRG cell exposure to TMZ resulted in cell cycle arrest. Overall, our results show that miR-200c overexpression could offer a way to overcome chemoresistance developed by GB cells in response to current standard chemotherapy, providing an improvement to current GB standard treatment, with benefit for patient outcome.

Abstract PO035: Engineered glioblastoma tumor models reveal extracellular matrix signals influence the efficacy of targeted inhibitors

Abstract Biomaterial-based ex vivo models of healthy and diseased brain tissue are among those tools that may help study the complexity of cerebral tissue to better diagnose, prevent, and treat brain diseases. We have established engineered brain tumor biomaterials based on methacrylamide-functionalized gelatin hydrogels and used microfluidic-forming techniques to generate platforms that combine transitions of biophysical and biomolecular properties found in the glioblastoma tumor microenvironment, from the core to the tumor margins (1). Moreover, this biomaterial approach is able to monitor the response of patient-derived xenograft (PDX) cell populations with different molecular signatures; in particular, we have analyzed the amplified and the constitutively activated vIII mutant EGF receptor. We have also characterized PDX response to targeted inhibitors, such as erlotinib, a tyrosine kinase inhibitor that specifically blocks EGFR (2). Patients with glioblastoma (GBM) exhibit poor survival rates, tied both to the significant intra and interpatient heterogeneity of the tumor as well as the complex signaling pathways underlying malignancy. Spatial and temporal gradients regulate cell proliferation, migration, and differentiation during cancer. Therefore, the use of a microfluidic approach to fabricate patterned biomaterials, have the ability to examine transitions between defined environments (e.g., glioma core, periphery and neural tissue). Cells within these structured materials can be fully analyzed by imaging, secretomic and gene expression analyses. Cell morphology evolved to a more spread shape from low to high crosslinking density of gelatin and hypoxic levels depended on cell concentration. Using patient derived GBM tumor samples we are able to generate a miniaturized tumor tissue analog to examine how the heterogeneities within the tumor microenvironment impact glioma malignant phenotype, growth, and therapeutic efficacy. The ability to manipulate tumor extracellular matrix (ECM) can improve therapeutic outcomes and restrict glioma infiltration. Our in vitro tumor model is able to analyze the relationship between HA and the invasive phenotype of GBM tumor cells. We show that cell growth, motility and proteomic responses of GBM cells within our platform were significantly altered by HA molecular weight in response to a tyrosine kinase inhibitor. These results provide additional insights regarding the importance of extracellular microenvironment in the invasive potential of GBM tumors. We have demonstrated that repeated dosing of erlotinib promotes expression of PDGFRb in EGFR vIII mutant cells and that extracellular HA plays a favorable role in the inhibition of EGFR, through STAT3 deactivation (3). (1) Pedron S et al. (2015), Adv. Mater., 27: 1567; (2) Pedron S. et al. (2017), Adv. Healthcare Mater., 6: 1700529; (3) Pedron S, et al. (2019), Biomaterials, 219: 119371. Citation Format: Sara Pedron, Jann N. Sarkaria, Brendan A.C. Harley. Engineered glioblastoma tumor models reveal extracellular matrix signals influence the efficacy of targeted inhibitors [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PO035.

Abstract 4769: Mapping cellular metabolic activity within U87MR glioblastoma cells in response to chemical and environmental insult using label-free quantitative phase imaging

Abstract Introduction: One of our drug development target diseases is Glioblastoma multiforme (GBM), a serious neurological disease with a very poor prognosis for the patients due, in part, to the large number of metabolic pathways it can follow. Materials and Methods: We are using U87-MR cells as a model. We employ time-lapse quantitative phase imaging technology that quantifies the refractive index (RI) of cells via light interference. There is no need for labeling of the cells. The RI is an intrinsic physical property of the cells which lends itself to highly precise and accurate quantitative analysis. Our basic protocol involves seeding cells, providing atmosphere and temperature control. Time-lapse images are automatically obtained at intervals ranging from 10 seconds up to 5 minutes and over time periods from minutes to days. Cells are unlabeled, and can be untreated, or treated with drugs or components of multi-drug formulations. We used drugs that have known effects on the cell cycle, mitochondria and induce apoptosis. We also tested drugs such as temozolomide (TMZ) the first line regimen in GBM therapy protocols. Results: Our first notable finding relates to U87-MR motility. The cells self-assemble into a pattern of well separated cell clusters with tubular connections. These connections are initiated by mitochondrial tunneling and are stable over time. The tunnels are reinforced with actin, and mitochondrial fusion occurs at substrate contact foci. These connections between cells also are conduits for intercellular communication and the transport of objects such as mitochondria (MT). Many drugs that have nuclear targets, including demecolcine, topoisomerase inhibitors, present effects in the cytoplasm of the cells, including vacuoles and possible the remnants of DNA repair. MT contain their DNA. The necessary genes are needed to control their own replication to replace damaged MT and to initiate alternative energy sources, such as mitophagy where cellular protein digestion is utilized as a source of energy. There are numerous factors that cause a wide range of textures within cells, including MT fission, lipid droplets, and autophagy. In many treatments, we see a definite region forming with very active textural changes. Due to its proximity to the nuclear membrane as well as the endoplasmic reticulum, we hypothesize that this may be where mTOR1 and mTOR2C activities originate. In the TMZ studies, we found a strong correlation between the dosage, and the morphology of the cells with a transformation to mesenchymal morphologies at the higher dosages. Discussion: GBM cells adapt to and control a number of different metabolic pathways which are primarily characterized by biochemical analysis. We have vastly improved-time lapse imaging capabilities. We produced first evidence of successful characterization of the metabolic changes based on RI quantifications and visual effects. Citation Format: Ed Luther, Livia P. Mendes, Vladimir P. Torchilin. Mapping cellular metabolic activity within U87MR glioblastoma cells in response to chemical and environmental insult 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 4769.

Conventional Treatment of Glioblastoma Reveals Persistent CD44+ Subpopulations.

Glioblastoma (GBM) is the most frequent and devastating primary tumor of the central nervous system with a median survival of 12 to 15months after diagnosis. GBM is highly difficult to treat due to its delicate location, inter- and intra-tumoral heterogeneity, and high plasticity in response to treatment. In this study, we intracranially implanted primary GBM cells into mice which underwent conventional GBM treatments, including irradiation, temozolomide, and a combination. We obtained single cell suspensions through a combination of mechanical and enzymatic dissociation of brain tissue and investigated in detail the changes in GBM cells in response to conventional treatments in vivo using multi-color flow cytometry and cluster analysis. CD44 expression was elevated in all treatment groups, which was confirmed by subsequent immunohistochemistry. High CD44 expression was furthermore shown to correlate with poor prognosis of GBM and low-grade glioma (LGG) patients. Together, these results indicate a key role for CD44 in glioma pathogenesis.

A role for caveola-forming proteins caveolin-1 and CAVIN1 in the pro-invasive response of glioblastoma to osmotic and hydrostatic pressure.

In solid tumours, elevated interstitial fluid pressure (osmotic and hydrostatic pressure) is a barrier to drug delivery and correlates with poor prognosis. Glioblastoma (GBM) further experience compressive force when growing within a space limited by the skull. Caveolae are proposed to play mechanosensing roles, and caveola‐forming proteins are overexpressed in GBM. We asked whether caveolae mediate the GBM response to osmotic pressure. We evaluated in vitro the influence of spontaneous or experimental down‐regulation of caveola‐forming proteins (caveolin‐1, CAVIN1) on the proteolytic profile and invasiveness of GBM cells in response to osmotic pressure. In response to osmotic pressure, GBM cell lines expressing caveola‐forming proteins up‐regulated plasminogen activator (uPA) and/or matrix metalloproteinases (MMPs), some EMT markers and increased their in vitro invasion potential. Down‐regulation of caveola‐forming proteins impaired this response and prevented hyperosmolarity‐induced mRNA expression of the water channel aquaporin 1. CRISPR ablation of caveola‐forming proteins further lowered expression of matrix proteases and EMT markers in response to hydrostatic pressure, as a model of mechanical force. GBM respond to pressure by increasing matrix‐degrading enzyme production, mesenchymal phenotype and invasion. Caveola‐forming proteins mediate, at least in part, the pro‐invasive response of GBM to pressure. This may represent a novel target in GBM treatment.

Matrix protease production, epithelial-to-mesenchymal transition marker expression and invasion of glioblastoma cells in response to osmotic or hydrostatic pressure

Both hydrostatic and osmotic pressures are altered in the tumour microenvironment. Glioblastoma (GBM) is a brain tumour with high invasiveness and poor prognosis. We hypothesized that physical and osmotic forces regulate glioblastoma (GBM) invasiveness. The osmotic pressure of GBM cell culture medium was adjusted using sodium chloride or water. Alternatively, cells were subjected to increased hydrostatic force. The proteolytic profile and epithelial–mesenchymal transition (EMT) were investigated using zymography and real-time qPCR. The EMT markers assessed were Snail-1, Snail-2, N-cadherin, Twist and vimentin. Invasion was investigated in vitro using extracellular matrix-coated Transwell inserts. In response to osmotic and mechanical pressure, GBM cell lines U87 and U251 and patient-derived neural oncospheres upregulated the expression of urokinase-type plasminogen activator (uPA) and/or matrix metalloproteinases (MMPs) as well as some of the EMT markers tested. The adherent cell lines invaded more when placed in media of increased osmolality. Therefore, GBM respond to osmotic or mechanical pressure by increasing matrix degrading enzyme production, and adopting a phenotype reminiscent of EMT. Better understanding the molecular and cellular mechanisms by which increased pressure promotes GBM invasiveness may help to develop innovative therapeutic approaches.

MicroRNA-93 acts as an "anti-inflammatory tumor suppressor" in glioblastoma.

BackgroundInflammation is an important driver of malignant glioma disease. Inflammatory mediators are not only produced by immune cells in the tumor microenvironment, but also by glioblastoma (GBM) cells themselves creating a mutually reinforcing loop. We here aimed at identifying an “anti-inflammatory switch” that allows to dampen inflammation in GBM.MethodsWe used human GBM specimens, primary cultures, and cell lines. The response of GBM cells toward inflammatory stimuli was tested by incubation with supernatant of stimulated human immune cells. Expression levels were measured by whole transcriptome microarrays and qRT-PCR, and protein was quantified by LUMINEX and SDS-PAGE. MicroRNA binding to 3′UTRs was analyzed by luciferase assays. Proliferation rates were determined by flow cytometry, and invasion and angiogenesis were studied using migration and endothelial tube formation assays.ResultsWe demonstrated GBM cells to secrete high amounts of proinflammatory mediators in an inflammatory microenvironment. We found miR-93 as a potential “anti-inflammatory tumor suppressor” dramatically downregulated in GBM. Concordantly, cytokine secretion dropped after miR-93 re-expression. Transfection of miR-93 in GBM cells led to down-regulation of hubs of the inflammatory networks, namely, HIF-1α and MAP3K2 as well as IL-6, G-CSF, IL-8, LIF, IL-1β, COX2, and CXCL5. We showed only COX2 and CXCL5 to be indirectly regulated by miR-93 while all other genes are true targets. Phenotypically, re-expression of miR-93 in GBM cells substantially suppressed proliferation, migration, and angiogenesis.ConclusionsAlleviating GBM-derived inflammation by re-expression of miR-93 may be a powerful tool to mitigate these tumors’ aggressiveness and holds promise for new clinical approaches.

Survival of glioblastoma cells in response to endogenous and exogenous oxidative challenges: possible implication of NMDA receptor-mediated regulation of redox homeostasis.

Cancer cells are highly metabolically active and produce high levels of reactive oxygen species (ROS). Drug resistance in cancer cells is closely related to their redox status. The role of ROS and its impact on cancer cell survival seems far from elucidation. The mechanisms through which glioblastoma cells overcome aberrant ROS and oxidative stress in a milieu of hypermetabolic state is still elusive. We hypothesize that the formidable growth potential of glioma cells is through manipulation of tumor microenvironment for its survival and growth, which can be attributed to an astute redox regulation through a nexus between activation of N-methyl-d-aspartate receptor (NMDAR) and glutathione (GSH)-based antioxidant prowess. Hence, we examined the NMDAR activation on intracellular ROS level, and cell viability on exposure to hydrogen peroxide (H2 O2 ), and antioxidants in glutamate-rich microenvironment of glioblastoma. The activation of NMDAR attenuated the intracellular ROS production in LN18 and U251MG glioma cells. MK-801 significantly reversed this effect. On evaluation of GSH redox cycle in these cells, the level of reduced GSH and glutathione reductase (GR) activity were significantly increased. NMDAR significantly enhanced the cell viability in LN18 and U251MG glioblastoma cells, by attenuating exogenous H2 O2 -induced oxidative stress, and significantly increased catalase activity, the key antioxidant that detoxifies H2 O2 . We hereby report an unexplored role of NMDAR activation induced protection of the rapidly multiplying glioblastoma cells against both endogenous ROS as well as exogenous oxidative challenges. We propose potentiation of reduced GSH, GR, and catalase in glioblastoma cells through NMDAR as a novel rationale of chemoresistance in glioblastoma.

Mechano-biological model of glioblastoma cells in response to osmotic stress.

This work investigates the mechano-biological features of cells cultured in monolayers in response to different osmotic conditions. In-vitro experiments have been performed to quantify the long-term effects of prolonged osmotic stresses on the morphology and proliferation capacity of glioblastoma cells. The experimental results highlight that both hypotonic and hypertonic conditions affect the proliferative rate of glioblastoma cells on different cell cycle phases. Moreover, glioblastoma cells in hypertonic conditions display a flattened and elongated shape. The latter effect is explained using a nonlinear elastic model for the single cell. Due to a crossover between the free energy contributions related to the cytosol and the cytoskeletal fibers, a critical osmotic stress determines a morphological transition from a uniformly compressed to an elongated shape.

Abstract 5776: Glioblastoma tumor model to analyze the mechanisms of resistance to tyrosine kinase inhibitors

Abstract The extracellular matrix (ECM) is increasingly recognized as having a key role in cancer development. We have developed a biomaterial tumor mimic that recapitulates systematically the main characteristics and heterogeneities of glioblastoma ECM. With the use of these 3D in vitro platforms we seek to understand the key features that make this cancer so challenging to treat. We are using this device in three different ways: (1) to further understand how particularities of brain tumor ECM affect cancer cells and assist in the diagnostic of different glioblastoma (GBM) tumor types, (2) provide new models for drug screening to afford more personalized therapies and (3) study the mechanisms of resistance to current therapies in order to identify more effective combinatorial treatments and new therapeutic targets. Hyaluronic acid (HA), is the main component of the brain ECM and GBM is associated with aberrant HA secretion and overexpression of receptors associated with HA, such as CD44 and EGFR. We cultured GBM patient-derived xenograft (PDX) cells within gelatin based hydrogels that contained variable concentrations of HA. Cell proliferation and gene expression analyses demonstrate that biomimetic hydrogels support xenograft culture and cells upregulate matrix remodeling genes and others related to tumor growth in response to matrix biophysical properties. We also used these platforms to evaluate the mechanisms of cell resistance to tyrosine kinase inhibitors. For this purpose, we first focused on the epidermal growth factor receptor (EGFR), which has been identified as a molecular target and associated with worse clinical outcomes. We characterized the 3D in vitro behavior of 3 PDX that represent these EGFR variants: GBM10 (EGFR, wild type), GBM12 (EGFR+) and GBM6 (EGFRvIII). We studied the relationship between the HA contained in the surrounding matrix and response of GBM cells to a tyrosine kinase inhibitor (TKI), erlotinib. Results indicate that while EGFR+ cells are sensitive to TKI in HA hydrogels, HA seems to collaborate with EGFRvIII signaling to stir cell activity. Immunoblots demonstrate that this enhanced cell activity is related to a significant increase in PDGFR concentration. Blockade of the CD44 receptor, in combination with erlotinib treatment, does not affect phosphorylation rates of PI3K or ERK, however, it leads to a significant decrease of STAT3 phosphorylation. This is translated into a lower tumor cell metabolic activity in HA matrices. Finally, we show that, patient-derived xenograft cells resistant to erlotinib in vivo (GBM10), become sensitive when CD44 is blocked in HA-containing matrices, as demonstrated by a decrease of phosphorylated PI3K. In summary, we highlight the importance of extracellular HA in EGFR inhibition efficiency. We demonstrate that this biomaterial tumor model can be used as a valuable tool in the mechanistic studies of tumor development and prediction of tyrosine kinase inhibitors efficacy. Citation Format: Sara Pedron, Gabrielle L. Wolter, Emily Chen, Jann N. Sarkaria, Brendan A. Harley. Glioblastoma tumor model to analyze the mechanisms of resistance to tyrosine kinase inhibitors [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 5776. doi:10.1158/1538-7445.AM2017-5776

Abstract B05: Engineered biomaterials as essential tools to determine the mechanisms of resistance to tyrosine kinase inhibitors in glioblastoma

Abstract The extracellular matrix (ECM) is increasingly recognized as having a key role in cancer development. Advances in biomaterials design and preparation have led to highly defined sophisticated platforms that can recapitulate key features of the complex tumor microenvironment. We have developed a biomaterial tumor mimic that recapitulates systematically the main characteristics and heterogeneities of glioblastoma ECM. With the use of these 3D in vitro platforms we seek to understand the key features that make this cancer so challenging to treat. We are using this device in three different ways: (1) to further understand how particularities of brain tumor ECM affect cancer cells and assist in the diagnostic of different GBM tumor types, (2) provide new models for drug screening to afford more personalized therapies and (3) study the mechanisms of resistance to current therapies in order to identify more effective combinatorial treatments and new therapeutic targets. Glioblastoma (GBM) tumors are highly heterogeneous, both cell composition and ECM biophysical properties are key factors in cancer cell malignancy and treatment outcomes. Hyaluronic acid (HA), is the main component of the brain extracellular matrix and GBM is associated with aberrant HA secretion and overexpression of receptors associated with HA, such as CD44 and EGFR. We use a microfluidic system to culture GBM patient-derived cells within gelatin based hydrogels that contained gradually increasing concentrations of HA, in order to recreate the heterogeneity of the tumor mass. Cell proliferation and gene expression analyses demonstrate that biomimetic hydrogels support xenograft culture; cells remain viable, active, and upregulate matrix remodeling genes and others related to tumor growth. More importantly, we found that GBM cells respond to changes in the ECM composition presenting different gene expression profiles (VEGF, IL6, MMP2, MMP9, HAS3, CD44) depending on the particularities of every tumor, such as EGFR overexpression or PTEN suppression. These findings pave the way for new clinical tools that allow a more precise cataloging of GBM tumor types and tailoring treatments to individual patients. We have also used these platforms to evaluate potential therapeutic strategies for different GBM xenograft cells and to study the mechanisms of cell resistance. For this purpose, we first focused on the epidermal growth factor receptor (EGFR), which has been identified as a molecular target and associated with worse clinical outcomes. Amplification, overexpression and mutation of the EGFR tyrosine kinase has been identified in 50% of GBM patients. The genetic aberration of EGFR (EGFR+) often comes with the overexpression of the mutant EGFR variant III (EGFRvIII). We characterized the 3D in vitro behavior of 3 patient-derived xenografts that represent these EGFR variants: GBM10 (EGFR, wild type), GBM12 (EGFR+) and GBM6 (EGFRvIII). We studied the relationship between the HA contained in the surrounding matrix and response of GBM cells to a tyrosine kinase inhibitor (TKI), erlotinib. We demonstrate that an interaction exists between CD44 and EGF receptors. Results indicate that while EGFR+ cells are sensitive to TKI in HA hydrogels, HA seems to collaborate with EGFRvIII signaling to stir cell activity. Our results indicate that a combination of both bound and cell secreted soluble HA may influence GBM sensitivity and resistance to erlotinib. Moreover, immunoblots that analyze PI3K pathway support the hypothesis that matrix-bound HA is a key factor in the negative response of vIII tumors to EGFR inhibitors, and that the benefits of EGFR inhibition in GBMs may be found in combination to other inhibitors of ECM signaling. In summary, we demonstrate that engineered tumor avatar biomaterials can be used to reproduce some of the main characteristics of brain tumor microenvironment and become a valuable tool in the mechanistic studies of tumor development and treatment efficacy. Citation Format: Sara Pedron, Amanda M. Pritchard, Jann N. Sarkaria, Mark A. Schroeder, Brendan A. Harley. Engineered biomaterials as essential tools to determine the mechanisms of resistance to tyrosine kinase inhibitors in glioblastoma. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr B05.

Response of glioblastoma cells to activation of the G-protein coupled estrogen receptor, GPER1/GPR30, and possible crosstalk with the aryl hydrocarbon receptor.

Glioblastomas are almost invariably fatal brain tumors. Glioblastoma incidence in men is 1.5 times that of pre-menopausal women and this difference decreases post-menopause. Therefore estrogen is thought to play a protective role, although the mechanism is not well understood. Glioblastomas produce and respond to a tryptophan derivative, kynurenine, that binds and activates the aryl hydrocarbon receptor (AHR). Promiscuity of ligand binding can result in cross talk between AHR and nuclear estrogen receptors and both receptor types are known to use the p300 acetyltransferase as a cofactor. We demonstrated that inhibition of p300 resulted in a reduction of proliferation of CH157-MN meningioma cells. Treatment with β-estradiol or kynurenine partially abrogated this effect, suggesting both ligands may act through another receptor that we hypothesize to be the G-protein linked estrogen receptor, GPER1/GPR30. We verified the expression of GPER1, estrogen receptor β; some estrogen receptor β isoforms and AHR by CH157-MN cells and U-87 and A-172 glioblastoma cells. Inhibition of p300 with C646 reduced proliferation of both U87 and A172 cells. In U87 cells, this effect was abrogated by co-treatment with β-estradiol, the xenobiotic AHR agonist 2’,3’,7,8’-tetrachlorodibenzo-p-dioxin, and the GPER1 agonist G-1. Exogenous kynurenine did not abrogate the effect of p300 inhibition. However, in A172 cells, none of the agonists abrogated the effect of p300 inhibition, possibly due to the higher kynurenine production in A172 cells. Treatment of A172 and U87 cells with G-1 resulted in decreased cell proliferation which was abrogated by co-treatment with the GPER1 antagonist G-36.

Abstract 4559: Sprouty2 differentially regulates signaling and phenotypic responses of glioblastoma cells to DNA damaging agents and receptor kinase inhibitors

Abstract Key to improving glioblastoma patient survival is the exploration of the signaling mechanisms that regulate cellular response to approved and investigational therapeutics, including DNA damaging agents and targeted therapeutics such as EGFR and MET kinase inhibitors. Previous work from our group demonstrated that Sprouty2 (SPRY2) surprisingly acted more as a tumor promoter than tumor suppressor in glioblastoma cell lines and tumor xenografts, with SPRY2 knockdown reducing proliferation of human glioblastoma cells and antagonizing the growth of subcutaneous tumor xenografts in mice. We hypothesized here that these effects may result from a perturbation in the cell cycle and that such effects may augment cell cycle shifts induced by DNA damaging agents or kinase inhibitors. Flow cytometry measurements indicated shifts in DNA content distribution in glioblastoma cell lines consistent with cell cycle arrest in response to SPRY2 knockdown alone, and that these shifts were substantially augmented by carboplatin or to a lesser degree by a combination of EGFR and MET inhibitors, but not by temozolomide. Western blotting indicated that SPRY2 knockdown resulted in increased phosphorylation of Ataxia Telangiectasia Mutated (ATM), a kinase involved in the DNA damage response pathway, at a serine residue (1981) that regulates the dissociation of inactivate ATM homodimers into activated monomers. In response to carboplatin, but not the other therapeutics tested, a robust increase was observed in Checkpoint kinase 1 (CHK1) phosphorylation at serine 345, which has been reported to cause cell cycle arrest. This effect was further enhanced by SPRY2 knockdown, which may help explain why the largest cell cycle perturbations were observed in SPRY2-deficient cells treated with carboplatin. Increased phosphorylation of p38 was also observed in response to carboplatin or EGFR and MET inhibitors. This may have contributed to cell cycle arrest, but may also have cooperated with the inhibition of AKT phosphorylation that occurred only in response to EGFR and MET inhibition to drive cell death, an effect that was also augmented by SPRY2 knockdown. Overall, this work has identified a small network of SPRY2-regulated signaling processes that control phenotypic responses of glioblastoma cells to different clinically relevant therapeutics and provides motivation for further study of the role of SPRY2 in glioblastoma. Citation Format: Nisha G. Sosale, Sally Shin, Matthew J. Lazzara. Sprouty2 differentially regulates signaling and phenotypic responses of glioblastoma cells to DNA damaging agents and receptor kinase inhibitors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4559.