Primary Glioblastoma Cell Cultures Research Articles

Targeting the Leloir Pathway with Galactose-Based Antimetabolites in Glioblastoma.

Glioblastoma (GBM) uses Glut3 and/or Glut14 and the Leloir pathway to catabolize D-Galactose (Gal). UDP-4-deoxy-4-fluorogalactose (UDP-4DFG) is a potent inhibitor of the two key enzymes, UDP-galactose-4-epimerase (GALE) and UDP-Glucose 6-dehydrogenase (UGDH), involved in Gal metabolism and in glycan synthesis. The Gal antimetabolite 4-deoxy-4-fluorogalactose (4DFG) is a good substrate for Glut3/Glut14 and acts as a potent glioma chemotherapeutic. Primary GBM cell cultures were used to examine toxicity and alterations in glycan composition via lectin binding in fixed cells and by Western blots. Toxicity/efficacy in vivo data was performed in mouse flank and intracranial models. The effect of 4DFG on D-glucose (Glc) metabolism in GBM cells was assessed by using 13C NMR-based tracer studies. 4DFG is moderately potent against GBM cells (IC50: 125-300 µM). GBM glycosylation is disrupted by 4DFG. Survival analysis in an intracranial mouse model showed that treatment with 4DFG (6 × 25 mg/kg of 4DFG, intravenously) improved outcomes by three-fold (p < 0.01). Metabolic flux analysis revealed that both glycolytic and mitochondrial metabolic fluxes of [U-13C]Glc were significantly decreased in the presence of 4DFG in GBM cells. A functional Gal-scavenging pathway in GBM allows Gal-based antimetabolites to act as chemotherapeutics. 4DFG is metabolized by GBM in vitro and in vivo, is lethal to GBM tumors, and is well tolerated in mice.

Transduction Efficiency of Zika Virus E Protein Pseudotyped HIV-1gfp and Its Oncolytic Activity Tested in Primary Glioblastoma Cell Cultures.

The development of new tools against glioblastoma multiforme (GBM), the most aggressive and common cancer originating in the brain, remains of utmost importance. Lentiviral vectors (LVs) are among the tools of future concepts, and pseudotyping offers the possibility of tailoring LVs to efficiently transduce and inactivate GBM tumor cells. Zika virus (ZIKV) has a specificity for GBM cells, leaving healthy brain cells unharmed, which makes it a prime candidate for the development of LVs with a ZIKV coat. Here, primary GBM cell cultures were transduced with different LVs encased with ZIKV envelope variants. LVs were generated by using the pNLgfpAM plasmid, which produces the lentiviral, HIV-1-based, core particle with GFP (green fluorescent protein) as a reporter (HIVgfp). Using five different GBM primary cell cultures and three laboratory-adapted GBM cell lines, we showed that ZIKV/HIVgfp achieved a 4-6 times higher transduction efficiency compared to the commonly used VSV/HIVgfp. Transduced GBM cell cultures were monitored over a period of 9 days to identify GFP+ cells to study the oncolytic effect due to ZIKV/HIVgfp entry. Tests of GBM tumor specificity by transduction of GBM tumor and normal brain cells showed a high specificity for GBM cells.

Retraction Note: Dissecting the role of novel EZH2 inhibitors in primary glioblastoma cell cultures: effects on proliferation, epithelialmesenchymal transition, migration, and on the pro-inflammatory phenotype

Retraction Note: Dissecting the role of novel EZH2 inhibitors in primary glioblastoma cell cultures: effects on proliferation, epithelialmesenchymal transition, migration, and on the pro-inflammatory phenotype

The possible effects of sodium fluoroscein to primary cell culture sampling in glioblastoma surgery

IntroductionPrimary glioblastoma (GBM) cell cultures have become a very important tool for future research due to the patient-specific genetic makeup of GBM cells and different treatment response variations. In sodium fluorescein-guided surgeries, regions sampled for primary cell culture are also stained with FL. However, the effects of FL on GBM cell cultures are unknown. In our study, the effect of FL on GBM cell cultures after a possible contamination was investigated. Resarch QuestionDoes sodium fluorescein have an effect on glioblastoma cell cultures? If there is, should sodium fluorescein be used after primary cell culture sampling when performing sodium fluorescein-guided glioblastoma surgery? MethodsStandard cell culture techniques were used to generate GBM cell lines, which were then split into control and FL treated groups. Cell counts, cell viability, cellular aging, and beta-galactosidase analyses were compared between these groups. Cells' microscopic pictures were also assessed. ResultsOur study reveals that FL-applied cultures had fewer cells overall and more s beta-galactosidase activity than control groups. The notion that FL may have an impact on the environment of GBM cell cultures is thus raised by our main findings regarding the use of FL and its effects on cell cultures. ConclusionTo prevent adverse effects on the growth of primary GBM cell cultures, neurosurgeons might think about using FL after sampling the tumor tissue during operations.

EXTH-48. INHIBITION OF SREBP-1 IS SYNTHETICALLY LETHAL WITH BCL-XL/BCL-2 INHIBITION IN GLIOBLASTOMA IN VITRO

Abstract OBJECTIVE A cellular homeostasis that is shifted away from apoptosis and a reprogramming of the lipid metabolism are both, features that are frequently encountered in glioblastoma. This study aimed at investigating whether interference with the lipid metabolism is synthetically lethal with inhibition of anti-apoptotic Bcl-2 family proteins in glioblastoma in vitro. METHODS Established (U251) and primary-cultured glioblastoma cells (PC38, PC40 and PC128) as well as glioblastoma stem-like cells (SC38 and SC40) were treated with the Bcl-xL/Bcl-2 inhibitor ABT-263 (navitoclax) and/or the SREBP-1 inhibitor Fatostatin. MTT-assays were performed to assess effects of the combination therapy on the cell viability. Isobolograms were calculated to characterize the drug-drug interaction. Spheroids were used to determine anti-proliferative effects in a 3-dimensional setting. Staining with annexin V/propidium iodide and flowcytometric analysis were performed to assess pro-apoptotic effects. For molecular analyses, Western blots and specific knock-down experiments with siRNA were performed. RESULTS Combined targeting of SREBP-1 and Bcl-xL/Bcl-2 led to a synergistic inhibitory effect on the cellular viability of established, primary-cultured and glioblastoma stem-like cells as well as spheroids. This effect was shown to be at least in part mediated by enhanced apoptosis and to occur in a caspase-dependent manner. On the molecular level, treatment with increasing concentrations of Fatostatin led to a downregulation of Mcl-1. CONCLUSION Our study indicates that combined inhibition of Bcl-xL/Bcl-2 and interference with the lipid metabolism targeting SREBP-1 synergistically induces caspase-dependent apoptosis in glioblastoma cells. This effect can also be observed in more complex 3-dimensional glioblastoma cell formations. Further studies will focus on deciphering the drug-induced alterations of the metabolic pathways that are responsible for the synergistic effect of this therapeutic strategy.

EXTH-15. DRUG SCREENING ON PATIENT GBM CELL CULTURES IDENTIFIES OMACETAXINE MEPESUCCINATE AS A POTENT ANTI-GLIOMA AGENT WITH THE ABILITY TO CROSS THE BLOOD-BRAIN-BARRIER

Abstract INTRODUCTION Little progress has been made in the development of effective new therapies for glioblastoma (GBM) the past decades. Fresh patient-derived GBM cell culture models have become the gold standard for GBM drug discovery and development. One of the major obstacles in identifying novel candidate drugs against GBM remains the blood-brain barrier (BBB). Therefore, it is crucial to select drugs with favourable physicochemical properties to cross BBB and reach the tumour tissue in therapeutically effective concentrations. In current drug repurposing approach, we evaluated available anti-cancer agents in our patient-derived drug screening platform against GBM. METHODS The FDA-approved Oncology Drug Set II library was tested on 45 primary GBM cell cultures. We developed a drug shortlisting pipeline combining efficacy data with pharmacodynamic and pharmacokinetic characteristics of each compound. The therapeutic efficacy of the selected agent was assessed in an orthotopic mouse PDX model, while penetration into the CNS by LC/MS/MS. RESULTS Omacetaxine mepesuccinate (OMA) was ranked as one of the most promising candidates applying our drug selection approach. In vitro, OMA revealed anti-tumour activity at IC50 values well-below reported Cmax plasma values in approximately 80% of GBM cultures. NanoString nCounter analysis, revealed DNA damage repair as the main pathway involved in OMA’s anti-tumour effect. Activation of caspase 3/7 activity and decrease of glioma cell invasiveness were also linked to its anti-tumour effect. In vivo, 1mg/kg dose of OMA was found to reach the brain tumour tissue in concentrations similar to the reported IC50 values in vitro. No adverse reactions were noted and a survival benefit was observed in a proportion of the treated mice. CONCLUSIONS At 1 mg/kg, OMA reaches the tumour brain tissue in therapeutically effective concentrations in mice while a moderate therapeutic benefit was observed. Additional in vivo experiments are ongoing investigating higher dosages of OMA and longer exposure.

Establishing a Standardized Method for the Effective Intraoperative Collection and Biological Preservation of Brain Tumor Tissue Samples Using a Novel Tissue Preservation System: A Pilot Study

Glioblastoma (GB) is an aggressive tumor showing extensive intertumoral and intratumoral heterogeneity. Several possible reasons contribute to the historical inability to develop effective therapeutic strategies for treatment of GB. One such challenge is the inability to consistently procure high-quality biologically preserved specimens for use in molecular research and patient-derived xenograft model development. No scientifically derived standardized method exists for intraoperative tissue collection specifically designed with the fragility of RNA in mind. In this investigation, we set out to characterize matched specimens from 6 GB patients comparing the traditional handling and collection processes of intraoperative tissue used in most neurosurgical operating rooms versus an automated resection, collection, and biological preservation system (APS) which captures, preserves, and biologically maintains tissue in a prescribed and controlled microenvironment. Matched specimens were processed in parallel at various time points and temperatures, evaluating viability, RNA and protein concentrations, and isolation of GB cell lines. We found that APS-derived GB slices stored in an APS modified medium remained viable and maintained high-quality RNA and protein concentration for up to 24 hours. Our results showed that primary GB cell cultures derived in this manner had improved growth over widely used collection and preservation methods. By implementing an automated intraoperative system, we also eliminated inconsistencies in methodology of tissue collection, handling and biological preservation, establishing a repeatable and standardized practice that does not require additional staff or a laboratory technician to manage it.

HLA-E and HLA-F Are Overexpressed in Glioblastoma and HLA-E Increased After Exposure to Ionizing Radiation.

Glioblastoma (GBM) is one of the deadliest human cancers responding very poorly to therapy. Although the central nervous system has been traditionally considered an immunologically privileged site with an enhanced immune response, GBM appears to benefit from this immunosuppressive milieu. Immunomodulatory molecules play an important role in immune tumor-host interactions. Non-classical human leukocyte antigens (HLA) class Ib molecules HLA-E, HLA-F, and HLA-G have been previously described to be involved in protecting semi-allogeneic fetal allografts from the maternal immune response and in transplant tolerance as well as tumoral immune escape. Unfortunately, their role in GBM remains poorly understood. Our study, therefore, aimed to characterize the relationship between the expression of these molecules in GBM on the transcriptional level and clinicopathological and molecular features of GBM as well as the effect of ionizing radiation. We performed the analysis of HLA-E, HLA-F, and HLA-G mRNA expression in 69 GBM tissue samples and 21 non-tumor brain tissue samples (controls) by reverse transcription polymerase chain reaction. Furthermore, two primary GBM cell cultures had been irradiated to identify the effect of ionizing radiation on the expression of non-classical HLA molecules. Analyses revealed that both HLA-E and HLA-F are significantly up-regulated in GBM samples. Subsequent survival analysis showed a significant association between low expression of HLA-E and shorter survival of GBM patients. The dysregulated expression of both molecules was also observed between patients with methylated and unmethylated O-6-methylguanine-DNA methyltransferase (MGMT) promoter. Finally, we showed that ionizing radiation increased HLA-E expression level in GBM cells in vitro. HLA-E and HLA-F play an important role in GBM biology and could be used as diagnostic biomarkers, and in the case of HLA-E also as a prognostic biomarker.

Exploring the efficacy of tumor electric field therapy against glioblastoma: An in vivo and in vitro study.

AimsTumor electric fields therapy (TTFields) is emerging as a novel anti‐cancer physiotherapy. Despite recent breakthroughs of TTFields in glioma treatment, the average survival time for glioblastoma patients with TTFields is <2 years, even when used in conjugation with traditional anti‐cancer therapies. To optimize TTFields‐afforded efficacy against glioblastoma, we investigated the cancer cell‐killing effects of various TTFields paradigms using in vitro and in vivo models of glioblastoma.MethodsFor in vitro studies, the U251 glioma cell line or primary cell cultures prepared from 20 glioblastoma patients were treated with the tumor electric field treatment (TEFT) system. Cell number, volume, and proliferation were measured after TEFT at different frequencies (100, 150, 180, 200, or 220 kHz), durations (24, 48, or 72 h), field strengths (1.0, 1.5, or 2.2V/cm), and output modes (fixed or random sequence output). A transwell system was used to evaluate the influence of TEFT on the invasiveness of primary glioblastoma cells. For in vivo studies, the therapeutic effect and safety profiles of random sequence electric field therapy in glioblastoma‐transplanted rats were assessed by calculating tumor size and survival time and evaluating peripheral immunobiological and blood parameters, respectively.ResultsIn the in vitro settings, TEFT was robustly effective in suppressing cell proliferation of both the U251 glioma cell line and primary glioblastoma cell cultures. The anti‐proliferation effects of TEFT were frequency‐ and “dose” (field strength and duration)‐dependent, and contingent on the field sequence output mode, with the random sequence mode (TEFT‐R) being more effective than the fixed sequence mode (TEFT‐F). Genetic tests were performed in 11 of 20 primary glioblastoma cultures, and 6 different genetic traits were identified them. However, TEFT exhibited comparable anti‐proliferation effects in all primary cultures regardless of their genetic traits. TEFT also inhibited the invasiveness of primary glioblastoma cells in transwell experiments. In the in vivo rat model of glioblastoma brain transplantation, treatment with TEFT‐F or TEFT‐R at frequency of 200 kHz and field strength of 2.2V/cm for 14 days significantly reduced tumor volume by 42.63% (TEFT‐F vs. control, p = 0.0002) and 63.60% (TEFT‐R vs. control, p < 0.0001), and prolonged animal survival time by 30.15% (TEFT‐F vs. control, p = 0.0415) and 69.85% (TEFT‐R vs. control, p = 0.0064), respectively. The tumor‐bearing rats appeared to be well tolerable to TEFT therapies, showing only moderate increases in blood levels of creatine and red blood cells. Adverse skin reactions were common for TEFT‐treated rats; however, skin reactions were curable by local treatment.ConclusionTumor electric field treatment at optimal frequency, strength, and output mode markedly inhibits the cell viability, proliferation, and invasiveness of primary glioblastoma cells in vitro independent of different genetic traits of the cells. Moreover, a random sequence electric field output confers considerable anti‐cancer effects against glioblastoma in vivo. Thus, TTFields are a promising physiotherapy for glioblastoma and warrants further investigation.

Photodynamic Therapy Combined with Bcl-2/Bcl-xL Inhibition Increases the Noxa/Mcl-1 Ratio Independent of Usp9X and Synergistically Enhances Apoptosis in Glioblastoma.

Simple SummaryGlioblastoma represents one of the most common malignant brain tumors in adults and is associated with a poor clinical outcome despite current therapeutic measures. Therefore, novel strategies for the treatment of this disease are urgently needed. In this work, we examined the antineoplastic effects of a combined treatment with photodynamic therapy and ABT-263 on different glioblastoma cells. Photodynamic therapy uses the selective uptake of a photosensitive molecule followed by activation by light of a specific wavelength to kill cancer cells. ABT-263 is a small molecule inhibitor that targets cancer cells by facilitating programmed cell death. This novel combinatorial therapeutic strategy synergistically killed glioblastoma cells. These results indicate that a combination of the two treatment modalities may be of benefit for the treatment of glioblastoma supporting further studies.The purpose of this study was to assess in vitro whether the biological effects of 5-aminolevulinic acid (5-ALA)-based photodynamic therapy are enhanced by inhibition of the anti-apoptotic Bcl-2 family proteins Bcl-2 and Bcl-xL in different glioblastoma models. Pre-clinical testing of a microcontroller-based device emitting light of 405 nm wavelength in combination with exposure to 5-ALA (PDT) and the Bcl-2/Bcl-xL inhibitor ABT-263 (navitoclax) was performed in human established and primary cultured glioblastoma cells as well as glioma stem-like cells. We applied cell count analyses to assess cellular proliferation and Annexin V/PI staining to examine pro-apoptotic effects. Western blot analyses and specific knockdown experiments using siRNA were used to examine molecular mechanisms of action. Bcl-2/Bcl-xL inhibition synergistically enhanced apoptosis in combination with PDT. This effect was caspase-dependent. On the molecular level, PDT caused an increased Noxa/Mcl-1 ratio, which was even more pronounced when combined with ABT-263 in a Usp9X-independent manner. Our data showed that Bcl-2/Bcl-xL inhibition increases the response of glioblastoma cells toward photodynamic therapy. This effect can be partly attributed to cytotoxicity and is likely related to a pro-apoptotic shift because of an increased Noxa/Mcl-1 ratio. The results of this study warrant further investigation.

Src Inhibitors Pyrazolo[3,4-d]pyrimidines, Si306 and Pro-Si306, Inhibit Focal Adhesion Kinase and Suppress Human Glioblastoma Invasion In Vitro and In Vivo.

Glioblastoma (GBM), as the most aggressive brain tumor, displays a high expression of Src tyrosine kinase, which is involved in the survival, migration, and invasiveness of tumor cells. Thus, Src emerged as a potential target for GBM therapy. The effects of Src inhibitors pyrazolo[3,4-d]pyrimidines, Si306 and its prodrug pro-Si306 were investigated in human GBM cell lines (U87 and U87-TxR) and three primary GBM cell cultures. Primary GBM cells were more resistant to Si306 and pro-Si306 according to the 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. However, the ability of all GBM cells to degrade the extracellular matrix was considerably compromised after Si306 and pro-Si306 applications. Besides reducing the phosphorylation of Src and its downstream signaling pathway components, both compounds decreased the phosphorylated form of focal adhesion kinase (FAK) and epidermal growth factor receptor (EGFR) expression, showing the potential to suppress the aggressiveness of GBM. In vivo, Si306 and pro-Si306 displayed an anti-invasive effect against U87 xenografts in the zebrafish embryo model. Considering that Si306 and pro-Si306 are able to cross the blood–brain barrier and suppress the spread of GBM cells, we anticipate their clinical testing in the near future. Moreover, the prodrug showed similar efficacy to the drug, implying the rationality of its use in clinical settings.

Dual metabolic reprogramming by ONC201/TIC10 and 2-Deoxyglucose induces energy depletion and synergistic anti-cancer activity in glioblastoma

BackgroundDysregulation of the metabolome is a hallmark of primary brain malignancies. In this work we examined whether metabolic reprogramming through a multi-targeting approach causes enhanced anti-cancer activity in glioblastoma.MethodsPreclinical testing of a combined treatment with ONC201/TIC10 and 2-Deoxyglucose was performed in established and primary-cultured glioblastoma cells. Extracellular flux analysis was used to determine real-time effects on OXPHOS and glycolysis. Respiratory chain complexes were analysed by western blotting. Biological effects on tumour formation were tested on the chorioallantoic membrane (CAM).ResultsONC201/TIC10 impairs mitochondrial respiration accompanied by an increase of glycolysis. When combined with 2-Deoxyglucose, ONC201/TIC10 induces a state of energy depletion as outlined by a significant decrease in ATP levels and a hypo-phosphorylative state. As a result, synergistic anti-proliferative and anti-migratory effects were observed among a broad panel of different glioblastoma cells. In addition, this combinatorial approach significantly impaired tumour formation on the CAM.ConclusionTreatment with ONC201/TIC10 and 2-Deoxyglucose results in a dual metabolic reprogramming of glioblastoma cells resulting in a synergistic anti-neoplastic activity. Given, that both agents penetrate the blood–brain barrier and have been used in clinical trials with a good safety profile warrants further clinical evaluation of this therapeutic strategy.

RETRACTED ARTICLE: Dissecting the role of novel EZH2 inhibitors in primary glioblastoma cell cultures: effects on proliferation, epithelial-mesenchymal transition, migration, and on the pro-inflammatory phenotype

BackgroundGlioblastoma (GBM) is the most lethal and aggressive malignant primary brain tumor in adults. After surgical resection of the tumor, the patient typically should be subjected to chemotherapy (temozolomide, TMZ) and concomitant radiotherapy. Since the TMZ treatment does not lead to complete remission and often develops resistance, the identification of efficacious therapeutics is strongly to pursue. Among the epigenetic players, the H3K27 methyltransferase (MT) EZH2 (enhancer of zeste homologue 2) has been found overexpressed or mutated in several human cancers including gliomas, and its overexpression is associated with poor outcome in GBM. Two EZH2 inhibitors (EZH2i), UNC1999 and GSK343, suppressed GBM growth in vitro and in vivo indicating that EZH2i can be potential drugs against GBM.ResultsTwo new EZH2i, MC4040 and MC4041, were designed, prepared, and tested by us to determine their effects in primary GBM cell cultures. MC4040 and MC4041 displayed single-digit micromolar inhibition of EZH2, 10-fold less potency against EZH1, and no activity towards other MTs. In primary GBM cells as well as in U-87 GBM cells, the two compounds reduced H3K27me3 levels, and dose- and time-dependently impaired GBM cell viability without inducing apoptosis and arresting the cell cycle in the G0/G1 phase, with increased p21 and p27 levels. In combination with TMZ, MC4040 and MC4041 displayed stronger, but not additive, effects on cell viability. The potent clinical candidate as EZH2i tazemetostat, alone or in combination with TMZ, exhibited a similar potency of inhibition of GBM cell growth when compared to MC4040 and MC4041. At the molecular level, MC4040 and MC4041 reduced the VEGFR1/VEGF expression, reversed the epithelial-mesenchymal transition (EMT), and hampered cell migration and invasion attenuating the cancer malignant phenotype. Treatment of GBM cells with MC4040 and MC4041 also impaired the GBM pro-inflammatory phenotype, with a significant decrease of TGF-β, TNF-α, and IL-6, joined to an increase of the anti-inflammatory cytokine IL-10.ConclusionsThe two novel EZH2i MC4040 and MC4041 impaired primary GBM cell viability, showing even stronger effects in combination with TMZ. They also weakened the aggressive malignant phenotype by reducing angiogenesis, EMT, cell migration/invasion and inflammation, thus they may be considered potential candidates against GBM also for combination therapies.

CBMT-35. METABOLIC REWIRING BY ONC201/TIC10 AND 2-DEOXYGLUCOSE HAS SYNERGISTIC ANTI-GLIOBLASTOMA ACTIVITY

Abstract BACKGROUND Metabolic dysregulation is a common feature of cancers such as primary brain malignancies. In this work we examined whether a rewiring of the metabolome by a multi-targeting approach would induce enhanced anti-neoplastic activity in glioblastoma. METHODS Preclinical testing of a combined treatment with ONC201/TIC10 and 2-Deoxyglucose was performed in established and primary cultured glioblastoma cells. Extracellular flux analysis was used to determine real-time effects on OXPHOS (OCR) and glycolysis (ECAR). Expression of respiratory chain complexes was analysed by Western blotting. Biological effects on tumor formation were tested in patient-derived model systems on the chorion allantoic membrane (CAM). Protein array analyses were performed to determine effects on phospho protein kinase expression. RESULTS Treatment with ONC201/TIC10 leads to impaired mitochondrial respiration and a dose-dependent increase of glycolysis. ONC201/TIC10 combined with 2-Deoxyglucose, induces a state of energy deprivation characterized by a significant decrease in ATP levels. On the molecular level, pAMPK α1 was significantly up-regulated while a hypo-phosphorylation signature was noted including mTOR signaling, src family kinases and receptor tyrosine kinases such as EGFR and PDGFR-β. As a result, synergistic anti-proliferative and anti-migratory effects were observed among established and primary cultured glioblastoma cells. In addition, tumor formation on the CAM was significantly impaired following the combination treatment. CONCLUSIONS Simultaneous treatment with ONC201/TIC10 and 2-Deoxyglucose causes a reprogramming of the metabolic circuitry and results in a synergistic anti-glioblastoma activity. Since both agents were tested in clinical trials with good tolerability, and they both penetrate the blood-brain barrier, further clinical evaluation of this therapeutic strategy seems promising.

Negative regulation of miR-1275 by H3K27me3 is critical for glial induction of glioblastoma cells.

Activation of the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) pathway induces glial differentiation of glioblastoma (GBM) cells, but the mechanism by which microRNA (miRNA) regulate this process remains poorly understood. In this study, by performing miRNA genomics and loss‐ and gain‐of‐function assays in dibutyryl‐cAMP‐treated GBM cells, we identified a critical negative regulator, hsa‐miR‐1275, that modulates a set of genes involved in cancer progression, stem cell maintenance, and cell maturation and differentiation. Additionally, we confirmed that miR‐1275 directly and negatively regulates the protein expression of glial fibrillary acidic protein (GFAP), a marker of mature astrocytes. Of note, tri‐methyl‐histone H3 (Lys27) (H3K27me3), downstream of the PKA/polycomb repressive complex 2 (PRC2) pathway, accounts for the downregulation of miR‐1275. Furthermore, decreased miR‐1275 expression and induction of GFAP expression were also observed in dibutyryl‐cAMP‐treated primary cultured GBM cells. In a patient‐derived glioma stem cell tumor model, a cAMP elevator and an inhibitor of H3K27me3 methyltransferase inhibited tumor growth, induced differentiation, and reduced expression of miR‐1275. In summary, our study shows that epigenetic inhibition of miR‐1275 by the cAMP/PKA/PRC2/H3K27me3 pathway mediates glial induction of GBM cells, providing a new mechanism and novel targets for differentiation‐inducing therapy.

Disruption of peroxisome proliferator–activated receptor γ coactivator (PGC)-1α reverts key features of the neoplastic phenotype of glioma cells

The peroxisome proliferator-activated receptor γ coactivator (PGC)-1α is a master regulator of mitochondrial biogenesis and controls metabolism by coordinating transcriptional events. Here, we interrogated whether PGC-1α is involved in tumor growth and the metabolic flexibility of glioblastoma cells. PGC-1α was expressed in a subset of established glioma cell lines and primary glioblastoma cell cultures. Furthermore, a higher PGC-1α expression was associated with an adverse outcome in the TCGA glioblastoma dataset. Suppression of PGC-1α expression by shRNA in the PGC-1α-positive U343MG glioblastoma line suppressed mitochondrial gene expression, reduced mitochondrial membrane potential, and diminished oxygen as well as glucose consumption, and lactate production. Compatible with the known PGC-1α functions in reactive oxygen species (ROS) metabolism, glioblastoma cells deficient in PGC-1α displayed ROS accumulation, had reduced RNA levels of proteins involved in ROS detoxification, and were more susceptible to death induction by H2O2 compared with control cells. PGC-1αsh cells also had impaired proliferation and migration rates in vitro and displayed less stem cell characteristics. Complementary effects were observed in PGC-1α-low LNT-229 cells engineered to overexpress PGC-1α. In an in vivo xenograft experiment, tumors formed by U343MG PGC-1αsh glioblastoma cells grew much slower than control tumors and were less invasive. Interestingly, the PGC-1α knockdown conferred protection against hypoxia-induced cell death, probably as a result of less active anabolic pathways, and this effect was associated with reduced epidermal growth factor expression and mammalian target of rapamycin signaling. In summary, PGC-1α modifies the neoplastic phenotype of glioblastoma cells toward more aggressive behavior and therefore makes PGC-1α a potential target for anti-glioblastoma therapies.

VEGF-C sustains VEGFR2 activation under bevacizumab therapy and promotes glioblastoma maintenance.

BackgroundGlioblastoma ranks among the most lethal cancers, with current therapies offering only palliation. Paracrine vascular endothelial growth factor (VEGF) signaling has been targeted using anti-angiogenic agents, whereas autocrine VEGF/VEGF receptor 2 (VEGFR2) signaling is poorly understood. Bevacizumab resistance of VEGFR2-expressing glioblastoma cells prompted interrogation of autocrine VEGF-C/VEGFR2 signaling in glioblastoma.MethodsAutocrine VEGF-C/VEGFR2 signaling was functionally investigated using RNA interference and exogenous ligands in patient-derived xenograft lines and primary glioblastoma cell cultures in vitro and in vivo. VEGF-C expression and interaction with VEGFR2 in a matched pre- and post-bevacizumab treatment cohort were analyzed by immunohistochemistry and proximity ligation assay.ResultsVEGF-C was expressed by patient-derived xenograft glioblastoma lines, primary cells, and matched surgical specimens before and after bevacizumab treatment. VEGF-C activated autocrine VEGFR2 signaling to promote cell survival, whereas targeting VEGF-C expression reprogrammed cellular transcription to attenuate survival and cell cycle progression. Supporting potential translational significance, targeting VEGF-C impaired tumor growth in vivo, with superiority to bevacizumab treatment.ConclusionsOur results demonstrate VEGF-C serves as both a paracrine and an autocrine pro-survival cytokine in glioblastoma, promoting tumor cell survival and tumorigenesis. VEGF-C permits sustained VEGFR2 activation and tumor growth, where its inhibition appears superior to bevacizumab therapy in improving tumor control.

P08.69 A lentiviral-based system for targeting the regulatory subunit R2A of protein kinase A in human glioblastoma

Introduction: Glioblastoma (GBM) is the most frequent and lethal primary brain tumor, associated with a median survival of 12-15 months after first diagnosis. The identification of new therapeutic approaches is required for the development of effective treatments. The cAMP-activated protein kinase (PKA) pathway is dysregulated in many pathological conditions, including cancer, and could potentially provide new therapeutic targets for GBM treatment. In rodent and human GBM cells the regulatory subunit R2A of PKA presents a specific localization on Golgi apparatus, that is not detectable in the healthy brain parenchyma. Moreover, downregulation of PKA R2A expression induces a reduction of GBM cell viability. In order to deeply investigate the effects of stable PKA R2A downregulation, a lentiviral-based system was developed for delivery of short hairpin RNA (shRNA) targeting PKA R2A gene to human GBM cells. The 3rd generation lentiviral vector cPPT.hCMV.EGFP was first tested for transduction of U87 human GBM cell line and primary GBM cell cultures. Then, recombinant lentiviral vectors were generated for expression of shRNA targeting PKA R2A gene. This lentiviral system represents an efficient strategy for shRNA delivery and downregulation of PKA R2A expression. Material and method: U87 human GBM cell line and primary GBM cell cultures were grown respectively as adherent cells in serum-supplemented medium and as spheres in serum-free medium. 293T cells were used for production and titration of lentiviral vectors. EGFP expression was monitored at epifluorescence microscope and western blot analysis was performed to evaluate R2A expression. Results and discussion: The lentiviral cPPT.hCMV.EGFP vector is able to efficiently transduce U87 cells and primary GBM spheres. Transduced U87 cells maintain the expression of the EGFP reporter gene for more than two weeks and no apparent influence on cell growth was observed. Expression of EGFP is detected from most, but not all, cells forming the transduced primary GBM spheres. Moreover, transduced primary GBM cells are able to form spheres and maintain the expression of the reporter gene after dissociation. Recombinant lentiviral cPPT.hCMV.EGFP-based vectors were generated for expression of shRNA.Temp1 or shRNA.Temp2, targeting different exons of PKA R2A gene, and for their co-expression with EGFP. Western blot analysis demonstrated an efficient reduction of R2A expression in cells transfected with the cis-elements of recombinant vectors and in cells transduced with the recombinant lentiviral particles. Conclusion: The 3rd generation lentiviral cPPT.hCMV.EGFP vector proved to efficiently transduce human GBM cells and primary GBM spheres. This lentiviral system allows efficient delivery of shRNA for downregulation of PKA R2A expression, thus representing a new strategy for targeting protein kinase A in human GBM cells.

Simultaneous Interference with HER1/EGFR and RAC1 Signaling Drives Cytostasis and Suppression of Survivin in Human Glioma Cells in Vitro.

We have previously reported that combined inhibition of the epidermal growth factor receptor by erlotinib and of RAC1 by NSC23766 yielded a synergistic antiproliferative effect on established and primary cultured glioblastoma cells. The current study aimed at identifying the molecular mechanism. Staining for annexin V/PI or carboxyfluorescein succinimidyl ester was performed in order to determine the induction of apoptosis, necrosis or cytostasis in established and primary cultured glioblastoma cells. Moreover, expression of Ki-67 was determined by immunofluorescence, and the expression of cell cycle proteins was analysed by Western blot. Our data show that combined treatment with erlotinib and NSC23766 resulted in a reduced number of cell divisions, a significantly decreased Ki-67 expression, increased apoptosis and autophagy when compared to single agent treatments. On the molecular level, concomitant treatment with both agents resulted in a pronounced downregulation of cyclin D1, cyclin-dependent kinases 2, 4 and 6, as well as of survivin when compared to treatments with either agent alone. In conclusion, we demonstrate that combined treatment of human glioma cell lines in vitro with erlotinib and NSC23766 markedly inhibits cell division, induces apoptosis independent of caspase-3 activation and induces autophagy concomitant with suppression of survivin.

Inhibition of histone deacetylases sensitizes glioblastoma cells to lomustine.

Glioblastoma (GBM) ranks among the deadliest solid cancers worldwide and its prognosis has remained dismal, despite the use of aggressive chemo-irradiation treatment regimens. Limited drug delivery into the brain parenchyma and frequent resistance to currently available therapies are problems that call for a prompt development of novel therapeutic strategies. While only displaying modest efficacies as mono-therapy in pre-clinical settings, histone deacetylase inhibitors (HDACi) have shown promising sensitizing effects to a number of cytotoxic agents. Here, we sought to investigate the sensitizing effect of the HDACi trichostatin A (TSA) to the alkylating agent lomustine (CCNU), which is used in the clinic for the treatment of GBM. Twelve primary GBM cell cultures grown as neurospheres were used in this study, as well as one established GBM-derived cell line (U87 MG). Histone deacetylase (HDAC) expression levels were determined using quantitative real-time PCR and Western blotting. The efficacy of either CCNU alone or its combination with TSA was assessed using various assays, i.e., cell viability assays (MTT), cell cycle assays (flow cytometry, FACS), double-strand DNA break (DSB) quantification assays (microscopy/immunofluorescence) and expression profiling assays of proteins involved in apoptosis and cell stress (Western blotting and protein array). We found that the HDAC1, 3 and 6 expression levels were significantly increased in GBM samples compared to non-neoplastic brain control samples. Additionally, we found that pre-treatment of GBM cells with TSA resulted in an enhancement of their sensitivity to CCNU, possibly via the accumulation of DSBs, decreased cell proliferation and viability rates, and an increased apoptotic rate. From our data we conclude that the combined administration of TSA and CCNU eradicates GBM cells with a higher efficacy than either drug alone, thereby opening a novel avenue for the treatment of GBM.