Riluzole Reverses a Number of Undesirable Effects of Dexamethasone in Glioblastoma Cells

BACKGROUND/AIM

Glioblastoma multiforme (GBM)-induced oedema is a major cause of morbidity and mortality among patients with GBM. Dexamethasone (Dex) is the most common corticosteroid used pre-operatively to control cerebral oedema in patients with GBM. Dex is associated with many side effects, and shorter overall survival and progression-free survival of patients with GBM. These negative effects of Dex highlight the need for combinational therapy. Riluzole (Ril), a drug used to treat amyotrophic lateral sclerosis (ALS), is thought to have potential as a treatment for various cancers, with clinical trials underway. Here, we investigated whether Ril could reverse some of the undesirable effects of Dex.

MATERIALS AND METHODS

The effect of Dex, Ril, and Ril-Dex treatment on cell migration was monitored using the xCELLigence system. Cell viability assays were performed using 3-(4, 5-dimethylthiazol)-2, 5-diphenyltetrazolium bromide (MTT). The expression of genes involved in migration, glucose metabolism, and stemness was examined using real-time polymerase chain reaction (PCR).

RESULTS

Pre-treating GBM cells with Ril reduced Dex-induced cell migration and altered Dex-induced effects on cell invasion, stem cell, and glucose metabolism markers. Furthermore, Ril remained effective in killing GBM cells in combination with Dex.

CONCLUSION

Ril, which acts as an anti-tumorigenic drug, mediates some of the negative effects of Dex; therefore, it could be a potential drug to manage the side effects of Dex therapy in GBM.

Novel hybrids of sclareol and 1,2,4-triazolo[1,5-a]pyrimidine show collateral sensitivity in multidrug-resistant glioblastoma cells

The synthesis of 24 hybrid molecules, consisting of naturally occurring sclareol (SCL) and synthetic 1,2,4-triazolo[1,5-a]pyrimidines (TPs), is described. New compounds were designed with the aim of improving the cytotoxic properties, activity, and selectivity of the parent compounds. Six analogs (12a-f) contained 4-benzylpiperazine linkage, while 4-benzyldiamine linkage was present in eighteen derivatives (12g-r and 13a-f). Hybrids 13a-f consist of two TP units. After purification, all hybrids (12a-r and 13a-f), as well as their precursors (9a-e and 11a-c), were tested on human glioblastoma U87 cells. More than half of the tested synthesized molecules, 16 out of 31, caused a significant reduction of U87 cell viability (more than 75% reduction) at 30 µM. The concentration-dependent cytotoxicity of these 16 compounds was also examined on U87 cells, corresponding multidrug-resistant (MDR) U87-TxR cells with increased P-glycoprotein (P-gp) expression and activity, and normal lung fibroblasts MRC-5. Importantly, 12l and 12r were active in the nanomolar range, while seven compounds (11b, 11c, 12i, 12l, 12n, 12q, and 12r) were more selective towards glioblastoma cells than SCL. All compounds except 12r evaded MDR, showing even better cytotoxicity in U87-TxR cells. In particular, 11c, 12a, 12g, 12j, 12k, 12m, 12n, and SCL showed collateral sensitivity. Hybrid compounds 12l, 12q, and 12r decreased P-gp activity to the same extent as a well-known P-gp inhibitor - tariquidar (TQ). Hybrid compound 12l and its precursor 11c affected different cellular processes including the cell cycle, cell death, and mitochondrial membrane potential, and changed the levels of reactive oxygen and nitrogen species (ROS/RNS) in glioblastoma cells. Collateral sensitivity towards MDR glioblastoma cells was caused by the modulation of oxidative stress accompanied by inhibition of mitochondria.

Combined effects of vitamin C and cold atmospheric plasma-conditioned media against glioblastoma via hydrogen peroxide

Glioblastoma is the most lethal intracranial malignant tumor, for which the five-year overall survival rate is approximately 5%. Here we explored the therapeutic combination of vitamin C and plasma-conditioned medium on glioblastoma cells in culture and as subcutaneous or intracranial xenografts in mice. The combination treatment reduced cell viability and proliferation while promoting apoptosis, and the effects were significantly stronger than with either treatment on its own. Similar results were obtained in the two xenograft models. Vitamin C appeared to upregulate aquaporin-3 and enhance the uptake of extracellular H₂O₂, while the combination treatment increased intracellular levels of reactive oxygen species including H₂O₂ and activated the JNK signaling pathway. The cytotoxic effects of the combination treatment were partially reversed by the specific JNK signaling inhibitor SP600125. Our results suggest that the combination of vitamin C and plasma-conditioned medium has therapeutic potential against glioblastoma, and they provide mechanistic insights that may help investigate this and other potential therapies in greater depth.

The autophagy inducer trehalose stimulates macropinocytosis in NF1-deficient glioblastoma cells

Background

Glioblastoma is a highly aggressive brain tumor. A big effort is required to find novel molecules which can cross the blood–brain barrier and efficiently kill these tumor cells. In this perspective, trehalose (α-glucopyranosyl‐[1→1]‐α‐d‐glucopyranoside), found in various dietary sources and used as a safe nutrient supplement, attracted our attention for its pleiotropic effects against tumor cells.

Methods

Human glioblastoma cell lines U373-MG and T98G were exposed to trehalose and analyzed at different time points. Cell proliferation was evaluated at medium term, and clonogenic capacity and cell morphology were evaluated at long term. Western blot was used to evaluate biochemical markers of autophagy (also measured in cells co-treated with EIPA or chloroquine), and mTOR, AMPK and ERK 1/2 signalling. Macropinocytosis was evaluated morphologically by bright-field microscopy; in cells loaded with the fluorescein-conjugated fluid-phase tracer dextran, macropinocytic vacuoles were also visualized by fluorescence microscopy, and the extent of macropinocytosis was quantified by flow cytometry.

Results

The long-term effect of trehalose on U373-MG and T98G cell lines was impressive, as indicated by a dramatic reduction in clonogenic efficiency. Mechanistically, trehalose proved to be an efficient autophagy inducer in macropinocytosis-deficient T98G cells and an efficient inducer of macropinocytosis and eventual cell death by methuosis in U373-MG glioblastoma cells, proved to be poorly responsive to induction of autophagy. These two processes appeared to act in a mutually exclusive manner; indeed, co-treatment of U373-MG cells with the macropinocytosis inhibitor, EIPA, significantly increased the autophagic response. mTOR activation and AMPK inhibition occurred in a similar way in the two trehalose-treated cell lines. Interestingly, ERK 1/2 was activated only in macropinocytosis-proficient U373-MG cells harbouring loss-of-function mutations in the negative RAS regulator, NF1, suggesting a key role of RAS signalling.

Conclusions

Our results indicate that trehalose is worthy of further study as a candidate molecule for glioblastoma therapy, due to its capacity to induce a sustained autophagic response, ultimately leading to loss of clonogenic potential, and more interestingly, to force macropinocytosis, eventually leading to cell death by methuosis, particularly in tumor cells with RAS hyperactivity. As a further anticancer strategy, stimulation of macropinocytosis may be exploited to increase intracellular delivery of anticancer drugs.

Unique combinations of epigenetic modifiers synergistically impair the viability of the U87 glioblastoma cell line while exhibiting minor or moderate effects on normal stem cell growth

Discoveries made over the last decade have shown that critical changes in cancer cells, such as activation of oncogenes and silencing of tumor suppressor genes are caused not only by genetic but also by epigenetic mechanisms. While epigenetic alterations are somatically heritable, in contrast to genetic changes, they are potentially reversible, making them perfect targets for therapeutic intervention. Covalent modifications of chromatin, such as methylation of DNA and acetylation and methylation of histones, are important components of epigenetic machinery. Multiple recent studies have shown that epigenetic modifiers are candidates for potent new drugs in multiple cancers' therapies, including gliomas, and several clinical trials are ongoing. However, as with other chemotherapeutic drugs, toxicity is one of the main concerns with some of the potent epigenetic drugs. Synergistic combinations of these agents are one approach to overcoming toxicity issues while enhancing efficacy. In this study, we demonstrated that while individually BIX01294, an inhibitor of histone methyltransferase G9a, DZNep, an inhibitor of lysine methyltransferase EZH2, and Trichostatin A (TSA), an inhibitor of histone deacetylase at their low concentrations showed a moderate effect on the viability of U87 glioblastoma cells, in combinations they exhibited a synergistic effect. Importantly, these combinations exhibited minimal effect on adipose mesenchymal stem cells (AD-MSCs) growth. Thus, unique combinations and concentrations of epigenetic modifiers, that synergistically attenuated the U87 glioblastoma cells while exhibiting minor or moderate effects on normal stem cell growth, have been discovered.

2-Deoxy-D-glucose increases the sensitivity of glioblastoma cells to BCNU through the regulation of glycolysis, ROS and ERS pathways: In vitro and in vivo validation

Chloroethylnitrosoureas (CENUs) exert antitumor activity via producing dG-dC interstrand crosslinks (ICLs). However, tumor resistance make it necessary to find novel strategies to improve the therapeutic effect of CENUs. 2-Deoxy-D-glucose (2-DG) is a well-known glycolytic inhibitor, which can reprogram tumor energy metabolism closely related to tumor resistance. Here, we investigated the chemosensitization effect of 2-DG on l,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) against glioblastoma cells and the underlying mechanisms. We found that 2-DG significantly increased the inhibitory effects of BCNU on tumor cells compared with BCNU alone, while 2-DG showed no obvious enhancing effect on the BCNU-induced cytotoxicity for normal HaCaT and HA1800 cells. Proliferation, migration and invasion determinations presented the same trend as survival on tumor cells. 2-DG plus BCNU increased the energy deficiency through a more effective inhibition of glycolytic pathway. Notably, the combination of 2-DG and BCNU aggravated oxidative stress in glioblastoma cells, along with a significant decrease in glutathione (GSH) levels, and an increase in intracellular reactive oxygen species (ROS). Subsequently, we demonstrated that the combination treatment led to increased apoptosis via activating mitochondria and endoplasmic reticulum stress (ERS) related apoptosis pathways. Finally, we found that the dG-dC level was significantly increased after 2-DG pretreatment compared to BCNU alone by HPLC-ESI-MS/MS analysis. Finally, in vivo, 2-DG plus BCNU significantly suppressed tumor growth with lower side effects compared with BCNU alone in tumor-bearing mice. In summary, we proposed that 2-DG may have potential to increase the sensitivity of glioblastoma cells to BCNU by regulating glycolysis, ROS and ERS pathways in clinical setting.

The effect of iodine-131 beta-particles in combination with A-966492 and Topotecan on radio-sensitization of glioblastoma: An in-vitro study

Glioblastoma tumors are resistant to radiotherapy, and the need for drugs to induce radio-sensitization in tumor cells has always been a challenge. Besides, radiotherapy using targeted radionuclide would be effective even for resistant tumors. It has been shown topoisomerase I and poly (ADP-ribose) polymerase (PARP) enzymes have critical roles in the repair process of DNA injury in cells. Therefore, the inhibition of the activity of these enzymes can halt this process and result in the accumulation of damaged DNA in cells and the induction of cell death in tumors. In the present research, the impact of beta-particles of iodine-131 in combination with Topotecan (TPT), as the inhibitor of topoisomerase I, and A-966492, as the inhibitor of the PARP enzyme on the possible increase of radio-sensitivity of glioblastoma cells was assessed. For this purpose, a human glioblastoma cell line, U87MG, was cultured in flasks coated with Poly-Hema to achieve 300 μm-diameter spheroids. Then, nontoxic concentrations of A-966492 and TPT were applied in the cell culture media. The viability of the cells treated with iodine131 in combination with A-966492 and TPT was determined by the clonogenic assay. The expression rate of gamma-H2AX, as a biomarker of DNA double-strand breaks, was analyzed using immunofluorescence microscopy to unravel the effect of TPT, A-966492 (1 μM), and radiation on the cell death induction. The combination of each TPT or A-966492 with radiation resulted in the increased rate of cell death, and the ratios of sensitizer enhancement at 50% survival (SER50) were elevated by 1.45 and 1.25, respectively. Chemo- and radio-sensitization were promoted when iodine-131 was combined with A-966492 and TPT, with the SER50 of 1.68. Also, the expression of γ-H2AX was significantly increased in cells treated with A-966492 and TPT combined with radiation. The results demonstrated that iodine-131, in combination with A-966492 and TPT, had marked effects on radio-sensitizing and can be used as a targeted radionuclide for targeting radiotherapy in combination with topoisomerase I and PARP inhibitors to enhance radiotherapy in clinics.

Tat-NTS Suppresses the Proliferation, Migration and Invasion of Glioblastoma Cells by Inhibiting Annexin-A1 Nuclear Translocation

Prevention of the nuclear translocation of ANXA1 with Tat-NTS was recently reported to alleviate neuronal injury and protect against cerebral stroke. However, the role that Tat-NTS plays in the occurrence and development of gliomas still needs to be elucidated. Therefore, human glioblastoma (GB) cells were treated with various concentrations of Tat-NTS for 24 h, and cell proliferation, migration and invasion were assessed with CCK-8 and Transwell assays. The nuclear translocation of ANXA1 was evaluated by subcellular extraction and immunofluorescence, and protein expression levels were detected by Western blot analysis. In addition, the activity of MMP-2/9 was measured by gelatin zymography. The results revealed that Tat-NTS significantly inhibited the nuclear translocation of ANXA1 in U87 cells and inhibited the proliferation, migration and invasion of GB cells. Tat-NTS also suppressed cell cycle regulatory proteins and MMP-2/-9 activity and expression. Moreover, Tat-NTS reduced the level of p-p65 NF-κB in U87 cells. These results suggest that the Tat-NTS-induced inhibition of GB cell proliferation, migration and invasion is closely associated with the induction of cell cycle arrest, downregulation of MMP-2/-9 expression and activity and suppression of the NF-κB signaling pathway. Thus, Tat-NTS may be a potential chemotherapeutic agent for the treatment of GB.

Cyproheptadine causes apoptosis and decreases inflammation by disrupting thiol/disulfide balance and enhancing the levels of SIRT1 in C6 glioblastoma cells

Cyproheptadine is first-generation antihistamine drug, that is, H₁ receptor antagonist, with a drug being anesthetic, anti-serotonergic and anti-cholinergic and started to be used clinically in the 1960s. As firstly utilized as an anti-allergic drug, usage of cyproheptadine was expanded to other cases including serotonin syndrome, appetite increasing, migraines and insomnia. However, there are almost few studies seeking to explore the association between cyproheptadine and cancer in general. In the present study, we sought to determine the impact of cyproheptadine on C6 glioblastoma cells by morphological, biochemical and cytotoxic analyzes. We searched the effective doses of cyproheptadine for C6 glioblastoma cells and examined the cells under an inverted microscope. Next, we determined the protein levels of SIRT1, NFκB and IL-6 protein. Then, we measured and calculated the levels of thiols, disulfide bonds and related parameters. After that, we evaluated apoptotic activity by Annexin V and caspase 3 assays. As a result, we detected a dose-dependent increase in apoptosis and SIRT 1 protein levels, and a decrease in inflammatory proteins. Furthermore, we have detected a drop in thiol and disulfide content. Our study suggests that Cyproheptadine causes apoptosis and decreases inflammation by disrupting thiol/disulfide balance and enhancing the levels of SIRT1, offering the potential for being an anti-cancer drug. Therefore, it might be further investigated in future studies.

The efficacy of the anticancer 3-bromopyruvate is potentiated by antimycin and menadione by unbalancing mitochondrial ROS production and disposal in U118 glioblastoma cells

Metabolic reprogramming of tumour cells sustains cancer progression. Similar to other cancer cells, glioblastoma cells exhibit an increased glycolytic flow, which encourages the use of antiglycolytics as an effective complementary therapy. We used the antiglycolytic 3-bromopyruvate (3BP) as a metabolic modifier to treat U118 glioblastoma cells and investigated the toxic effects and the conditions to increase drug effectiveness at the lowest concentration. Cellular vitality was not affected by 3BP concentrations lower than 40 μM, although p-Akt dephosphorylation, p53 degradation, and ATP reduction occurred already at 30 μM 3BP. ROS generated in mitochondria were enhanced at 30 μM 3BP, possibly by unbalancing their generation and their disposal because of glutathione peroxidase inhibition. ROS triggered JNK and ERK phosphorylation, and cyt c release outside mitochondria, not accompanied by caspases-9 and -3 activation, probably due to 3BP-dependent alkylation of cysteine residues at caspase-9 catalytic site. To explore the possibility of sensitizing cells to 3BP treatment, we exploited 3BP effects on mitochondria by using 30 μM 3BP in association with antimycin A or menadione concentrations that in themselves exhibit poor toxicity. 3BP effect on cyt c release and cell vitality loss was potentiated due the greater oxidative stress induced by antimycin or menadione association with 3BP, supporting a preeminent role of mitochondrial ROS in 3BP toxicity. Indeed, the scavenger of mitochondrial superoxide MitoTEMPO counteracted 3BP-induced cyt c release and weakened the potentiating effect of 3BP/antimycin association. In conclusion, the biochemical mechanisms leading U118 glioblastoma cells to viability loss following 3BP treatment rely on mitochondrial ROS-dependent pathways. Their potentiation at low 3BP concentrations is consistent with the goal to minimize the toxic effect of the drug towards non-cancer cells.

Zn phthalocyanines loaded into liposomes: Characterization and enhanced performance of photodynamic activity on glioblastoma cells

Photodynamic therapy (PDT) is considered a promising strategy for cancer treatment. PDT utilizes light in combination with a photosensitizer (PS) to induce several phototoxic reactions. Phthalocyanines (Pcs), a second generation of photosensitizers, have been studied in several cancer models. Among these, Pcs, have become of interest for the treatment of glioblastomas which are one of the most common and aggressive forms of tumors of the central nervous system. Due to the lipophilic nature of Pcs and their limited solubility in water, Pcs can be loaded in liposomes. In this work, we characterized liposomes of ZnPc and TAZnPc and their effectiveness to photoinactivate glioblastoma cells, was evaluated. Both Pcs show an increase in their photosensitizing activity when they were administrated in Dipalmitoylphosphatidylcholine-cholesterol liposomes compared to Pcs administrated in dimethylformamide.

Design, synthesis and cytotoxicity of the antitumor agent 1-azabicycles for chemoresistant glioblastoma cells

Twelve multi-functional pyrrolizidinones, indolizidinones and pyrroliazepinones were prepared from formal aza-[3 + 2] and aza-[3 + 3] cycloadditions of five- to seven-membered heterocyclic enaminones as diverse ambident electrophiles. The antitumor activity of these alkaloid-like compounds was investigated through an initial screening performed on human glioblastoma multiform (GBM) cell lines (GL-15, U251), on murine glioma cells line (C6) and on normal glial cells. Of the compounds tested, the new pyrrolo[1,2a]azepinone, [ethyl (3-oxo-1,2-diphenyl-6,7,8,9-tetrahydro-3H-pyrrolo[1,2a]azepin-9a(5H)-yl)acetate] or (Compound-13) exhibited selective cytotoxic effects on GBM-temozolomide resistant cells. Compound-13 exerted dose-dependent cytotoxic activity by promoting arrest of cells in the G0/G1 phase of the cell cycle in the first 24 h. The apoptotic effect observed was in a time-dependent manner. Anti-migratory effect promoted by the treatment with compound-13 was also observed. Moreover, healthy mixed glial cell cultures from rat brain exhibited no cytotoxicity effect upon exposure to compound-13. Thus, the present study paves the way for the use of compound-13 as novel antitumor scaffold candidate for glioma cell therapy.

Cytotoxic effect of crude and purified pectins from Campomanesia xanthocarpa Berg on human glioblastoma cells

A new source of pectin with a cytotoxic effect on glioblastoma cells is presented. A homogeneous GWP-FP-S fraction (M_w of 29,170 g mol^-1) was obtained by fractionating the crude pectin extract (GW) from Campomanesia xanthocarpa pulp. According to the monosaccharide composition, the GWP-FP-S was composed of galacturonic acid (58.8%), arabinose (28.5%), galactose (11.3%) and rhamnose (1.1%), comprising 57.7% of homogalacturonans (HG) and 42.0% of type I rhamnogalacturonans (RG-I). These structures were characterized by chromatographic and spectroscopic methods; GW and GWP-FP-S fractions were evaluated by MTT and crystal violet assays for their cytotoxic effects. Both fractions induced cytotoxicity (15.55-37.65%) with concomitant increase in the cellular ROS levels in human glioblastoma cells at 25-400 μg mL^-1, after 48 h of treatment, whereas no cytotoxicity was observed for normal NIH 3T3 cells. This is the first report of in vitro bioactivity and the first investigation of the antitumor potential of gabiroba pectins.

Combined Applications of Repurposed Drugs and Their Detrimental Effects on Glioblastoma Cells

BACKGROUND/AIM

Glioblastoma multiforme (GBM) is a malignant primary brain tumor with high rates of recurrence. This study aimed to investigate the effect of repurposed drug combinations on GBM.

MATERIALS AND METHODS

Viability of U87 MG and 11ST patient-derived GMB cell lines, after valproic acid, tranylcypromine or riluzole alone, in different combinations, as well as combined with standard temozolomide chemotherapy was examined using the MTT assay. Proliferation, mRNA level of tissue factor pathway inhibitor 2 (TFPI2), and cell invasion were evaluated using anti-Ki-67 antibody staining, reverse transcriptase-polymerase chain reaction and xCELLigence system.

RESULTS

The strongest effect on cell viability was achieved by the combination of riluzole with valproic acid (U87MG: 27.2%, 11ST: 25.99%). Tranylcypromine significantly enhanced the effect of temozolomide when used in combination, as did valproic acid. The normally high proliferation of GBM significantly declined under treatment with valproic acid with tranylcypromine (p=0.01). Finally, we observed reduction of invasion comparing single tranylcypromine to its combination with valproic acid or riluzole.

CONCLUSION

These results support the idea that combinations of drugs could increase the treatment efficiency of GBM.

Alpha lipoic acid attenuates hypoxia-induced apoptosis, inflammation and mitochondrial oxidative stress via inhibition of TRPA1 channel in human glioblastoma cell line

Apoptosis, overload Ca²⁺ entry and oxidative stress are induced in neurons by hypoxia. Drug-resistant cancer cells are killed by hypoxic conditions. α-Lipoic acid (ALA) has antioxidant and pro-oxidant functions. The TRPA1 channel is activated by oxidative stress and pro-oxidant ALA may have a regulator role in the TRPA1 activity in the human glioblastoma (DBTRG) cells. The aim of this study was to evaluate if a combination therapy of ALA with a hypoxia can alter the effect of this hypoxia through TRPA1 activation in the DBTRG cells. The DBTRG cells were divided into four treatment groups as control, ALA (50 μM), and hypoxia and hypoxia + ALA. Hypoxia in the cells was induced by CoCl₂ (200 μM). Apoptosis, Annexin V, mitochondrial membrane depolarization (JC-1), reactive oxygen species (ROS) production, IL-1β, IL-18, caspase 3 and 9 values were increased through activation of TRPA1 (cinnamaldehyde) in the cells by the hypoxia induction, although cell viability, reduced glutathione and glutathione peroxidase values were decreased by the treatments. The values were modulated in the cells by TRPA1 blocker (AP18) and ALA treatments. Involvements of TRPA1 activity on values in the cells were also confirmed by patch-clamp and laser confocal microscopy analyses. In conclusion, apoptotic, inflammatory and oxidant effects of hypoxia were increased by activation of TRPA1, but its action on the values was decreased by the ALA treatment. ALA treatment could be used as an effective strategy in the treatment of hypoxia-induced oxidative stress, apoptosis and inflammation in the neurons.

Mechanosensitivity of the BK Channels in Human Glioblastoma Cells: Kinetics and Dynamical Complexity

BK channels are potassium selective and exhibit large single-channel conductance. They play an important physiological role in glioma cells: they are involved in cell growth and extensive migrating behavior. Due to the fact that these processes are accompanied by changes in membrane stress, here, we examine mechanosensitive properties of BK channels from human glioblastoma cells (gBK channels). Experiments were performed by the use of patch-clamp method on excised patches under membrane suction (0-40 mmHg) at membrane hyper- and depolarization. We have also checked whether channel's activity is affected by possible changes of membrane morphology after a series of long impulses of suction. Unconventionally, we also analyzed internal structure of the experimental signal to make inferences about conformational dynamics of the channel in stressed membranes. We examined the fractal long-range memory effect (by R/S Hurst analysis), the rate of changes in information by sample entropy, or correlation dimension, and characterize its complexity over a range of scales by the use of Multiscale Entropy method. The obtained results indicate that gBK channels are mechanosensitive at membrane depolarization and hyperpolarization. Prolonged suction of membrane also influences open-closed fluctuations-it decreases channel's activity at membrane hyperpolarization and, in contrary, increases channel's activity at high voltages. Both membrane strain and its "fatigue" reduce dynamical complexity of channel gating, which suggest decrease in the number of available open conformations of channel protein in stressed membranes.

A bidirectional crosstalk between glioblastoma and brain endothelial cells potentiates the angiogenic and proliferative signaling of sphingosine-1-phosphate in the glioblastoma microenvironment

Glioblastoma is one of the most malignant, angiogenic, and incurable tumors in humans. The aberrant communication between glioblastoma cells and tumor microenvironment represents one of the major factors regulating glioblastoma malignancy and angiogenic properties. Emerging evidence implicates sphingosine-1-phosphate signaling in the pathobiology of glioblastoma and angiogenesis, but its role in glioblastoma-endothelial crosstalk remains largely unknown. In this study, we sought to determine whether the crosstalk between glioblastoma cells and brain endothelial cells regulates sphingosine-1-phosphate signaling in the tumor microenvironment. Using human glioblastoma and brain endothelial cell lines, as well as primary brain endothelial cells derived from human glioblastoma, we report that glioblastoma-co-culture promotes the expression, activity, and plasma membrane enrichment of sphingosine kinase 2 in brain endothelial cells, leading to increased cellular level of sphingosine-1-phosphate, and significant potentiation of its secretion. In turn, extracellular sphingosine-1-phosphate stimulates glioblastoma cell proliferation, and brain endothelial cells migration and angiogenesis. We also show that, after co-culture, glioblastoma cells exhibit enhanced expression of S1P₁ and S1P₃, the sphingosine-1-phosphate receptors that are of paramount importance for cell growth and invasivity. Collectively, our results envision glioblastoma-endothelial crosstalk as a multi-compartmental strategy to enforce pro-tumoral sphingosine-1-phosphate signaling in the glioblastoma microenvironment.

The effect of quercetin on the electrical properties of model lipid membranes and human glioblastoma cells

Quercetin is a naturally-occurring flavonoid claimed to exert many beneficial health effects. In this report, the influence of quercetin on the surface charge of phosphatidylcholine liposomes and human glioblastoma LN-229 and LN-18 cells was studied using microelectrophoretic mobility measurements. The effect of quercetin on the electrical resistance and capacitance of bilayer lipid membranes was analyzed via electrochemical impedance spectroscopy. The results showed that after flavonoid treatment, the cell lines demonstrated changes in surface charge only in alkaline pH solutions, whereas there were no significant alterations in quercetin-treated vs. control cells in acidic pH solutions. The same tendency was found for liposomal membranes proving that quercetin insertion into membranes is strongly pH-dependent. Capacitance and resistance measurements conducted in acidic electrolyte solutions demonstrated an increase in both electrical parameters, indicating an increased amount of quercetin inserted into the bilayers. Moreover, the cytotoxic effect of quercetin confirms that the flavonoid enters the cells and perturbs the proliferation of LN-229 and LN-18 glioblastoma cell lines. As such, our results indicate that the specific localization of quercetin, membrane-bound or cell-entering, might be crucial for its pharmacological activity. However, further studies are necessary prior to applying these physicochemical measurements as standard methods of evaluating drug activity.

A cell-autonomous positive-signaling circuit associated with the PDGF-NO-ID4-regulatory axis in glioblastoma cells

Most cancer-related signaling pathways sustain their active or inactive status via genetic mutations or various regulatory mechanisms. Previously, we demonstrated that platelet-derived growth factor (PDGF) activates Notch signaling through nitric oxide (NO)-signaling-driven activation of inhibitor of differentiation 4 (ID4) in glioblastoma (GBM) stem cells (GSCs) and endothelial cells in the vascular niche of GBM, leading to maintenance of GSC traits and GBM progression. Here, we determined that the PDGF-NO-ID4-signaling axis is constantly activated through a positive regulatory circuit. ID4 expression significantly increased PDGF subunit B expression in both in vitro cultures and in vivo tumor xenografts and regulated NO synthase 2 (NOS2) expression and NO production by activating PDGF signaling, as well as that of its receptor (PDGFR). Additionally, ectopic expression of PDGFRα, NOS2, or ID4 activated the PDGF-NO-ID4-signaling circuit and enhanced the self-renewal of GBM cell lines. These results suggested that the positive regulatory circuit associated with PDGF-NO-ID4 signaling plays a pivotal role in regulating the self-renewal and tumor-initiating capacity of GSCs and might provide a promising therapeutic target for GBM.

ER-α36, a novel variant of ERα, is involved in the regulation of Tamoxifen-sensitivity of glioblastoma cells

Although accumulating evidence has confirmed that adjuvant Tamoxifen (TAM) treatment is able to sensitize glioblastoma cells to radiotherapy and inhibit their proliferation, TAM is not a suitable treatment for all types of glioblastoma cells; furthermore, long-term TAM usage may lead to TAM resistance. Therefore, understanding the underlying molecular mechanism of TAM resistance is necessary in order to improve TAM clinical therapy and the quality of life of patients suffering from glioblastomas. In this study, the significance of ER-α36 to TAM resistance in glioblastoma cells was examined. First, an analysis of ER-α36 expression in two glioblastoma cell lines U87-MG and U251, showed that ER-α36 was anchored to the cytoplasmic membrane of these cells via Caveolin-1. Subsequent experiments investigating the mechanism of TAM-induced inhibition of U87-MG cell growth showed that TAM exerts its effect by inducing apoptosis via a down-regulation of Survivin expression and an up-regulation of Caspase-3 expression. Furthermore, TAM also arrested the cell cycle at S-phase. However, when U87-MG cells were preconditioned with an ER-α36-specific agonist, IC162, this neutralized TAM-induced inhibition of cell growth. This contrasted with the effect of ER-α36 depletion by RNAi, which enhanced TAM-induced inhibition of cell growth. These findings suggest that resistance to TAM involves ER-α36, which probably acts as a negative regulator of TAM-induced inhibition of glioblastoma cell growth. These findings provide a novel insight into the basis of TAM resistance during glioblastoma therapy and a further study is underway to reveal more about the specific molecular mechanisms associated with ER-α36-mediated TAM resistance.

Epigenetic silencing of miR-181c by DNA methylation in glioblastoma cell lines

Background

Post-transcriptional regulation by microRNAs is recognized as one of the major pathways for the control of cellular homeostasis. Less well understood is the transcriptional and epigenetic regulation of genes encoding microRNAs. In the present study we addressed the epigenetic regulation of the miR-181c in normal and malignant brain cells.

Methods

To explore the epigenetic regulation of the miR-181c we evaluated its expression using RT-qPCR and the in vivo binding of the CCCTC-binding factor (CTCF) to its regulatory region in different glioblastoma cell lines. DNA methylation survey, chromatin immunoprecipitation and RNA interference assays were used to assess the role of CTCF in the miR-181c epigenetic silencing.

Results

We found that miR-181c is downregulated in glioblastoma cell lines, as compared to normal brain tissues. Loss of expression correlated with a notorious gain of DNA methylation at the miR-181c promoter region and the dissociation of the multifunctional nuclear factor CTCF. Taking advantage of the genomic distribution of CTCF in different cell types we propose that CTCF has a local and cell type specific regulatory role over the miR-181c and not an architectural one through chromatin loop formation. This is supported by the depletion of CTCF in glioblastoma cells affecting the expression levels of NOTCH2 as a target of miR-181c.

Conclusion

Together, our results point to the epigenetic role of CTCF in the regulation of microRNAs implicated in tumorigenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2273-6) contains supplementary material, which is available to authorized users.

Autophagic flux in glioblastoma cells

To establish metabolic context for radiation sensitivity by measuring autophagic flux in two different glioblastoma (GBM) cell lines. Clonogenic survival curve analysis of U87 or U251 cells exposed to γ radiation, fast neutrons, a mixed energy neutron beam (METNB) or Auger electrons from a gadolinium neutron capture (GdNC) reaction suggested other factors, beyond a defective DNA damage response, contribute to cell death of U251 cells. Altered tumor metabolism (autophagy) was hypothesized as a factor in U251 cells' clonogenic response. Each of the four different radiation modalities induced an increase in the number of autophagosomes in both U87 and U251 cells. Changes in the number of autophagosomes can be explained by either induction of autophagy or alterations in autophagic flux so autophagic flux was assayed by p62 immunoblotting or in engineered GBM cells that stably express an autophagy marker protein, LC3B-eGFP-mCherry. Perturbations in later stages of autophagy in U251 cells corresponded with radiation sensitivity of U251 cells irradiated with 10 Gy γ rays. Establishment of altered autophagic flux is a useful biomarker for metabolic stress and provided metabolic context for radiation sensitization to 10 Gy γ rays. These results provide strong evidence for the usefulness of managing tumor cell metabolism as a tool for the enhancement of radiation therapy.

Genome-wide transcriptional profiling of human glioblastoma cells in response to ITE treatment

A ligand-activated transcription factor aryl hydrocarbon receptor (AhR) is recently revealed to play a key role in embryogenesis and tumorigenesis (Feng et al. [1], Safe et al. [2]) and 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) (Song et al. [3]) is an endogenous AhR ligand that possesses anti-tumor activity. In order to gain insights into how ITE acts via the AhR in embryogenesis and tumorigenesis, we analyzed the genome-wide transcriptional profiles of the following three groups of cells: the human glioblastoma U87 parental cells, U87 tumor sphere cells treated with vehicle (DMSO) and U87 tumor sphere cells treated with ITE. Here, we provide the details of the sample gathering strategy and show the quality controls and the analyses associated with our gene array data deposited into the Gene Expression Omnibus (GEO) under the accession code of GSE67986.

miR-20a mediates temozolomide-resistance in glioblastoma cells via negatively regulating LRIG1 expression

AIMS

Resistance to temozolomide (TMZ) is a major obstacle in the treatment of glioblastoma multiforme (GBM). MiRNAs is considered as an important modulator of drug resistance in many cancers. Here, we aimed to elucidate the relationship between miR-20a, its predicted target genes leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) and TMZ resistance in GBM.

MAIN METHODS

Real-time PCR or western blot was used to measure the levels of miR-20a and LRIG1. The cell viability was obtained to investigate the sensitivity of U251 cells and TMZ-resistant U251 (U251/TMZ) cells to TMZ. MiR-20a inhibitor or miR-20a mimic was used to down-regulate or up-regulate miR-20a expression. The interaction between miR-20a and its predicted target gene LRIG1 was confirmed by 3'-UTR dual-luciferase reporter assay. pcDNA-LRIG1 was used to overexpress LRIG1 [corrected]. A xenograft tumor model was used to investigate the in vivo antitumor activity.

KEY FINDINGS

MiR-20a was highly expressed and LRIG1 lowly expressed in U251/TMZ cells. Knockdown of miR-20a by treatment with miR-20a inhibitor restored sensitivity of U251/TM cells to TMZ in vivo and in vitro, whereas overexpression of miR-20a by treatment with miR-20a mimic resulted in increased TMZ resistance. The levels of LRIG1 were inversely related to miR-20a levels. And the luciferase reporter assays showed that miR-20a directly targeted the 3'UTR of LRIG1. In addition, functional knock-down of LRIG1 by gene specific siRNA reversed the effect of miR-20a inhibitor.

SIGNIFICANCE

MiR-20a mediated TMZ-resistance in glioblastoma cells through negatively regulating LRIG1 expression, which suggesting that miR-20a and LRIG1 would be potential therapeutic targets for glioma therapy.

The G-quadruplex-stabilising agent RHPS4 induces telomeric dysfunction and enhances radiosensitivity in glioblastoma cells

G-quadruplex (G4) interacting agents are a class of ligands that can bind to and stabilise secondary structures located in genomic G-rich regions such as telomeres. Stabilisation of G4 leads to telomere architecture disruption with a consequent detrimental effect on cell proliferation, which makes these agents good candidates for chemotherapeutic purposes. RHPS4 is one of the most effective and well-studied G4 ligands with a very high specificity for telomeric G4. In this work, we tested the in vitro efficacy of RHPS4 in astrocytoma cell lines, and we evaluated whether RHPS4 can act as a radiosensitising agent by destabilising telomeres. In the first part of the study, the response to RHPS4 was investigated in four human astrocytoma cell lines (U251MG, U87MG, T67 and T70) and in two normal primary fibroblast strains (AG01522 and MRC5). Cell growth reduction, histone H2AX phosphorylation and telomere-induced dysfunctional foci (TIF) formation were markedly higher in astrocytoma cells than in normal fibroblasts, despite the absence of telomere shortening. In the second part of the study, the combined effect of submicromolar concentrations of RHPS4 and X-rays was assessed in the U251MG glioblastoma radioresistant cell line. Long-term growth curves, cell cycle analysis and cell survival experiments, clearly showed the synergistic effect of the combined treatment. Interestingly the effect was greater in cells bearing a higher number of dysfunctional telomeres. DNA double-strand breaks rejoining after irradiation revealed delayed repair kinetics in cells pre-treated with the drug and a synergistic increase in chromosome-type exchanges and telomeric fusions. These findings provide the first evidence that exposure to RHPS4 radiosensitizes astrocytoma cells, suggesting the potential for future therapeutic applications.

High resistance to X-rays and therapeutic carbon ions in glioblastoma cells bearing dysfunctional ATM associates with intrinsic chromosomal instability

PURPOSE

To investigate chromosomal instability and radiation response mechanisms in glioblastoma cells.

METHODS AND MATERIALS

We undertook a comparative analysis of two patient-derived glioblastoma cell lines. Their resistance to low and high linear energy transfer (LET) radiation was assessed using clonogenic survival assay and their intrinsic chromosome instability status using fluorescence in situ hybridization. DNA damage was analyzed by pulsed-field gel electrophoresis and by γ-H2AX foci quantification. Expression of DNA damage response proteins was assessed by immunoblot.

RESULTS

Increased radioresistance to X-rays as well as carbon ions was observed in glioblastoma cells exhibiting high levels of naturally occurring chromosomal instability and impaired Ataxia-telangiectasia mutated (ATM) signaling, as reflected by lack of phosphorylation of ATM, CHK2 and p53 after double-strand breaks induction.

CONCLUSION

Our results indicate the existence of highly radioresistant glioblastoma cells, characterized by dysfunctional ATM signaling and high levels of intrinsic chromosomal instability.

Carbon ion beam is more effective to induce cell death in sphere-type A172 human glioblastoma cells compared with X-rays

PURPOSE

To obtain human glioblastoma cells A172 expressing stem cell-related protein and comparison of radiosensitivity in these cells with X-rays and carbon beam.

METHODS

Human monolayer-type A172 glioblastoma cells were maintained in normal medium with 10% bovine serum. In order to obtain sphere-type A172 cells the medium was replaced with serum-free medium supplemented with growth factors. Both types of A172 cells were irradiated with either X-rays or carbon ion beams and their radiosensitivity was evaluated.

RESULTS

Serum-free medium induced expression of stem cell-related proteins in A172 cells along with the neurosphere-like appearance. These sphere-type cells were found resistant to both X-rays and carbon ion beams. Phosphorylation of histone H2A family member X persisted for a longer period in the cells exposed to carbon ion beams than in those exposed to X-rays and it disappeared quicker in the sphere type than in the monolayer type. Relative radioresistance of the sphere type cells was smaller for carbon ion beams than for X-rays.

CONCLUSIONS

We demonstrated that glioblastoma A172 cells with induced stem cell-related proteins turned resistant to irradiation. Accelerated heavy ion particles may have advantage over X-rays in overcoming the tumor resistance due to cell stemness.

Functional analysis of [methyl-(3)H]choline uptake in glioblastoma cells: Influence of anti-cancer and central nervous system drugs

Positron emission tomography (PET) and PET/computed tomography (PET-CT) studies with (11)C- or (18)F-labeled choline derivatives are used for PET imaging in glioblastoma patients. However, the nature of the choline transport system in glioblastoma is poorly understood. In this study, we performed a functional characterization of [methyl-(3)H]choline uptake and sought to identify the transporters that mediate choline uptake in the human glioblastoma cell lines A-172 and U-251MG. In addition, we examined the influence of anti-cancer drugs and central nervous system drugs on the transport of [methyl-(3)H]choline. High- and low-affinity choline transport systems were present in A-172 cells, U-251MG cells and astrocytes, and these were Na(+)-independent and pH-dependent. Cell viability in A-172 cells was not affected by choline deficiency. However, cell viability in U-251MG cells was significantly inhibited by choline deficiency. Both A-172 and U-251MG cells have two different choline transporters, choline transporter-like protein 1 (CTL1) and CTL2. In A-172 cells, CTL1 is predominantly expressed, whereas in U-251MG cells, CTL2 is predominantly expressed. Treatment with anti-cancer drugs such as cisplatin, etoposide and vincristine influenced [methyl-(3)H]choline uptake in U-251MG cells, but not A-172 cells. Central nervous system drugs such as imipramine, fluvoxamine, paroxetine, reboxetine, citalopram and donepezil did not affect cell viability or [methyl-(3)H]choline uptake. The data presented here suggest that CTL1 and CTL2 are functionally expressed in A-172 and U-251MG cells and are responsible for [methyl-(3)H]choline uptake that relies on a directed H(+) gradient as a driving force. Furthermore, while anti-cancer drugs altered [methyl-(3)H]choline uptake, central nervous system drugs did not affect [methyl-(3)H]choline uptake.

Protein kinase CK2 is required for the recruitment of 53BP1 to sites of DNA double-strand break induced by radiomimetic drugs

The ataxia telangiectasia mutated (ATM) signaling pathway responds rapidly to DNA double-strand breaks (DSBs) and it is characterized by recruitment of sensor, mediator, transducer and repair proteins to sites of DNA damage. Data suggest that CK2 is implicated in the early cellular response to DSBs. We demonstrate that CK2 binds constitutively the adaptor protein 53BP1 through the tandem Tudor domains and that the interaction is disrupted upon induction of DNA damage. Down-regulation of CK2 results in significant reduction of (i) 53BP1 foci formation, (ii) binding to dimethylated histone H4 and (iii) ATM autophosphorylation. Our data suggest that CK2 is required for 53BP1 accumulation at sites of DSBs which is a prerequisite for efficient activation of the ATM-mediated signaling pathway.