Conoidin A, a Covalent Inhibitor of Peroxiredoxin 2, Reduces Growth of Glioblastoma Cells by Triggering ROS Production

Compounds that cause oxidative stress have recently gained considerable interest as potential anticancer treatment modalities. Nevertheless, their efficiency may be diminished by the antioxidant systems often upregulated in cancer cells. Peroxiredoxins (PRDXs) are antioxidant enzymes that scavenge peroxides and contribute to redox homeostasis. They play a role in carcinogenesis and are upregulated in several cancer types. Here, we assessed the expression pattern of PRDX1 and PRDX2 in glioblastoma (GBM) and examined the efficacy of their inhibitors in GBM cell lines and patient-derived GBM cells. Both PRDX1 and PRDX2 were upregulated in GBM compared to non-tumor brain tissues and their considerable amounts were observed in GBM cells. Adenanthin, a compound inhibiting PRDX1 activity, slightly decreased GBM cell viability, while conoidin A (CONA), a covalent PRDX2 inhibitor, displayed high toxicity in GBM cells. CONA elevated the intracellular reactive oxygen species (ROS) level. Pre-treatment with an ROS scavenger protected cells from CONA-induced death, indicating that ROS accumulation plays a crucial role in this phenomenon. Menadione or celecoxib, both of which are ROS-inducing agents, potentiated the anticancer activity of CONA. Collectively, our results unveil PRDX1 and PRDX2 as potential targets for GBM therapy, and substantiate the further exploration of their inhibitors.

Menadione Potentiates Auranofin-Induced Glioblastoma Cell Death

Glioblastoma (GBM) is the most aggressive primary brain tumor. Recently, agents increasing the level of oxidative stress have been proposed as anticancer drugs. However, their efficacy may be lowered by the cytoprotective activity of antioxidant enzymes, often upregulated in neoplastic cells. Here, we assessed the mRNA and protein expression of thioredoxin reductase 1 (TrxR1), a master regulator of cellular redox homeostasis, in GBM and non-tumor brain tissues. Next, we examined the influence of an inhibitor of TrxR1, auranofin (AF), alone or in combination with a prooxidant menadione (MEN), on growth of GBM cell lines, patient-derived GBM cells and normal human astrocytes. We detected considerable amount of TrxR1 in the majority of GBM tissues. Treatment with AF decreased viability of GBM cells and their potential to form colonies and neurospheres. Moreover, it increased the intracellular level of reactive oxygen species (ROS). Pre-treatment with ROS scavenger prevented the AF-induced cell death, pointing to the important role of ROS in the reduction of cell viability. The cytotoxic effect of AF was potentiated by treatment with MEN. In conclusion, our results identify TrxR1 as an attractive drug target and highlights AF as an off-patent drug candidate in GBM therapy.

Comprehensive analysis of the expression levels and prognostic values of PRDX family genes in glioma

Gliomas are a histologically and molecularly heterogeneous group of neoplasms accounting for 80% of malignant primary brain tumors. Growing evidence suggests that production of reactive oxygen species (ROS) is linked to glioma pathogenesis, although it is still unclear whether it is a cause or an effect of this process. Peroxiredoxins (PRDXs), a family of six antioxidant proteins, may promote or inhibit carcinogenesis, depending on the tumor type and stage. The current knowledge on their expression, regulation and functions in glioma is scarce. In this study, a comprehensive analysis of PRDXs expression in distinct glioma subtypes and non-tumor brain tissues was conducted using gene expression data from The Cancer Genome Atlas (TCGA), REpository for Molecular BRAin NeoplasiaDaTa (REMBRANDT), The Chinese Glioma Atlas (CGGA) and Gene Expression Omnibus (GEO) datasets. The association between gene expression and patient survival was investigated. DNA methylation, mutations, copy number alterations of deregulated PRDXs as well as the correlation between gene expression and tumor-infiltrating immune cells were assessed. The analysis revealed overexpression of PRDX1, PRDX4, and PRDX6 in most histological glioma types compared to the non-tumor tissues, while PRDX2, PRDX3 and PRDX5 expression remained unaltered. The expression of PRDX4 and PRDX6 was higher in mesenchymal than proneural and classical glioma subtypes. Moreover, lower expression of PRDX1, PRDX4 and PRDX6 was observed in tumors with a glioma CpG island methylator phenotype (G-CIMP) compared to non-G-CIMP tumors, as well as in isocitrate dehydrogenase (IDH) mutant and 1p/19q co-deleted gliomas compared to the wild-type counterparts. High expression of PRDX1, PRDX4 or PRDX6 correlated with poor survival of glioma patients. PRDX1 and PRDX6 displayed a positive correlation with different immune cell population in low grade gliomas and, to a lesser extent, in glioblastoma. PRDX1 expression exhibited negative correlation with DNA methylation. These results indicate that high expression of PRDX1, PRDX4 and PRDX6 is associated with poor outcome in gliomas.

Peptide Dendrimers with Non-Symmetric Bola Structure Exert Long Term Effect on Glioblastoma and Neuroblastoma Cell Lines

BACKGROUND

Glioblastoma (GBM) is the most common malignant tumor of the central nervous system (CNS). Neuroblastoma (NB) is one of the most common cancers of childhood derived from the neural crest cells. The survival rate for patients with GBM and high-risk NB is poor; therefore, novel therapeutic approaches are needed. Increasing evidence suggests a dual role of redox-active compounds in both tumorigenesis and cancer treatment. Therefore, in this study, polyfunctional peptide-based dendrimeric molecules of the bola structure carrying residues with antiproliferative potential on one side and the antioxidant residues on the other side were designed.

METHODS

We synthesized non-symmetric bola dendrimers and assessed their radical scavenging potency as well as redox capability. The influence of dendrimers on viability of rat primary cerebellar neurons (CGC) and normal human astrocytes (NHA) was determined by propidium iodide staining and cell counting. Cytotoxicity against human GBM cell lines, T98G and LN229, and NB cell line SH-SY5Y was assessed by cell counting and colony forming assay.

RESULTS

Testing of CGC and NHA viability allowed to establish a range of optimal dendrimers structure and concentration for further evaluation of their impact on two human GBM and one human NB cell lines. According to ABTS, DPPH, FRAP, and CUPRAC antioxidant tests, the most toxic for normal cells were dendrimers with high charge and an excess of antioxidant residues (Trp and PABA) on both sides of the bola structure. At 5 μM concentration, most of the tested dendrimers neither reduced rat CGC viability below 50-40%, nor harmed human neurons (NHA). The same dose of compounds 16 or 22, after 30 min treatment decreased the number of SH-SY5Y and LN229 cells, but did not affect the number of T98G cells 48 h post treatment. However, either compound significantly reduced the number of colonies formed by SH-SY5Y, LN229, and T98G cells measured 14 days after treatment.

CONCLUSIONS

Peptide dendrimers with non-symmetric bola structure are excellent scaffolds for design of molecules with pro/antioxidant functionality. Design of molecules with an excess of positive charges and antioxidant residues rendered molecules with high neurotoxicity. Single, 30 min exposition of the GBM and NB cell lines to the selected bola dendrimers significantly suppressed their clonogenic potential.

Roles of nitric oxide and polyamines in brain tumor growth

Nitric oxide (NO) and polyamines: putrescine, spermidine and spermine, are key arginine metabolites in mammalian tissues that play critical roles i.a. in regulation of vascular tone (NO), and cell cycle regulation (polyamines). In the brain, both classes of molecules additionally have neuromodulatory and neuroprotective potential, and NO also a neurotoxic potential. Here we review evidence that brain tumors use the NO- and polyamine-synthesizing machineries to the benefit of their differentiation and growth from healthy glia and neurons. With a few exceptions, brain tumors show increased activities of one or all of the three arginine (Arg) to NO-converting nitric oxide synthase (NOS) isoforms (iNOS, eNOS, nNOS), but also elevated activities of polyamines-generating and modifying enzymes: arginase I/II, ornithine decarboxylase and spermidine/spermine N¹-acetyltransferase. The degree of stimulation of NO- and polyamine synthesis often correlates with brain tumor malignancy. Excess NO, but also spermine, spermidine and their N¹-acetylated forms, are tumor- and context-dependently involved in angiogenesis, tumor initiation and growth, and resistance to chemo- or radiotherapy. Hypothetically, increased demand for NO and/or polyamines is likely to contribute to Arg auxotrophy of malignant brain tumors, albeit the causal nexus awaits experimental verification.

Peroxiredoxins in Neurodegenerative Diseases

Substantial evidence indicates that oxidative/nitrosative stress contributes to the neurodegenerative diseases. Peroxiredoxins (PRDXs) are one of the enzymatic antioxidant mechanisms neutralizing reactive oxygen/nitrogen species. Since mammalian PRDXs were identified 30 years ago, their significance was long overshadowed by the other well-studied ROS/RNS defense systems. An increasing number of studies suggests that these enzymes may be involved in the neurodegenerative process. This article reviews the current knowledge on the expression and putative roles of PRDXs in neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and dementia with Lewy bodies, multiple sclerosis, amyotrophic lateral sclerosis and Huntington's disease.

Design, synthesis and biological evaluation of novel 1,3,4-thiadiazole derivatives as anti-glioblastoma agents targeting the AKT pathway

In spite of progress in understanding biology of glioblastoma (GBM), this tumor remains incurable with a median survival rate of 15 months. Previous studies have shown that 2-(4-fluorophenyloamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole (FPDT) and 2-(3-chlorophenyloamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole (CPDT) diminished viability of cancer cell lines of different origin. In the current study, we have examined activity of these compounds in several GBM cell lines and patient-derived GBM cells. We have also designed, synthesized and evaluated anti-GBM activity of novel 1,3,4-thiadiazole derivatives containing additional Cl or CH₂CH₃ substitute at C5-position of 2,4-dihydroxyphenyl. The tested compounds presented a considerable cytotoxicity against all GBM cell lines examined as well as patient-derived GBM cells. They were 15-110 times more potent than temozolomide, the first-line chemotherapeutic agent for GBM. Notably, in anticancer concentrations three of the derivatives were not toxic to human astrocytes. FPDT appeared to be the most promising compound with IC₅₀ values between 45 μM and 68 μM for GBM cells and >100 μM for astrocytes. It augmented activity of temozolomide and inhibited proliferation migration and invasion of GBM cells. Treatment with FPDT diminished phosphorylation level of GSK3β and AKT. Pretreatment with PDGF-BB, an AKT activator, partially protected cells from death caused by FPDT, indicating that FPDT-mediated decrease in cell viability is causatively related to the inhibition of the AKT pathway.

Thiadiazole derivatives as anticancer agents

In spite of substantial progress made toward understanding cancer pathogenesis, this disease remains one of the leading causes of mortality. Thus, there is an urgent need to develop novel, more effective anticancer therapeutics. Thiadiazole ring is a versatile scaffold widely studied in medicinal chemistry. Mesoionic character of this ring allows thiadiazole-containing compounds to cross cellular membrane and interact strongly with biological targets. Consequently, these compounds exert a broad spectrum of biological activities. This review presents the current state of knowledge on thiadiazole derivatives that demonstrate in vitro and/or in vivo efficacy across the cancer models with an emphasis on targets of action. The influence of the substituent on the compounds' activity is depicted. Furthermore, the results from clinical trials assessing thiadiazole-containing drugs in cancer patients are summarized.

Targeting Glutamine Addiction in Gliomas

The most common malignant brain tumors are those of astrocytic origin, gliomas, with the most aggressive glioblastoma (WHO grade IV) among them. Despite efforts, medicine has not made progress in terms of the prognosis and life expectancy of glioma patients. Behind the malignant phenotype of gliomas lies multiple genetic mutations leading to reprogramming of their metabolism, which gives those highly proliferating cells an advantage over healthy ones. The so-called glutamine addiction is a metabolic adaptation that supplements oxidative glycolysis in order to secure neoplastic cells with nutrients and energy in unfavorable conditions of hypoxia. The present review aims at presenting the research and clinical attempts targeting the different metabolic pathways involved in glutamine metabolism in gliomas. A brief description of the biochemistry of glutamine transport, synthesis, and glutaminolysis, etc. will forego a detailed comparison of the therapeutic strategies undertaken to inhibit glutamine utilization by gliomas.

Transcription factor GATA3 expression is induced by GLS2 overexpression in a glioblastoma cell line but is GLS2-independent in patient-derived glioblastoma

Phosphate-activated glutaminase (GA), a ubiquitous glutamine-metabolizing enzyme, is encoded by two genes, GLS and GLS2. In mammalian cancers, GLS isoforms are perceived as molecules promoting cell proliferation and invasion, whereas the role of GLS2 isoforms seems to be more complex and cell type-specific. Previous studies have shown abundance of GLS and lack of GLS2 transcripts in T98G human glioblastoma (GBM) cell line and patient-derived GBM. Transfection with GAB sequence, the whole GLS2 cDNA transcript, suppressed malignant phenotype of T98G cells. Microarray analysis revealed upregulation of GATA3, the product of which has been implicated in suppressing growth of some peripheral cancers. In this study we confirmed a significant upregulation of GATA3 expression in the transfected cells both at mRNA and protein level. Considerable expression of GATA3 was also observed in GBM tissues (previously shown as not expressing GLS2), while only traces or no GATA3 was detected in (GLS2-expressing) non-tumorigenic brain samples. In conclusion, while mechanistic relation between GAB and GATA3 expression is evident following in vitro manipulation of GBM cell line, it does not appear to be an intrinsic property of GBM nor non-tumorigenic brain tissue.

Expression of prophage-encoded endolysins contributes to autolysis of Lactococcus lactis

Analysis of autolysis of derivatives of Lactococcus lactis subsp. cremoris MG1363 and subsp. lactis IL1403, both lacking the major autolysin AcmA, showed that L. lactis IL1403 still lysed during growth while L. lactis MG1363 did not. Zymographic analysis revealed that a peptidoglycan hydrolase activity of around 30 kDa is present in cell extracts of L. lactis IL1403 that could not be detected in strain MG1363. A comparison of all genes encoding putative peptidoglycan hydrolases of IL1403 and MG1363 led to the assumption that one or more of the 99 % homologous 27.9-kDa endolysins encoded by the prophages bIL285, bIL286 and bIL309 could account for the autolysis phenotype of IL1403. Induced expression of the endolysins from bIL285, bIL286 or bIL309 in L. lactis MG1363 resulted in detectable lysis or lytic activity. Prophage deletion and insertion derivatives of L. lactis IL1403 had a reduced cell lysis phenotype. RT-qPCR and zymogram analysis showed that each of these strains still expressed one or more of the three phage lysins. A homologous gene and an endolysin activity were also identified in the natural starter culture L. lactis subsp. cremoris strains E8, Wg2 and HP, and the lytic activity could be detected under growth conditions that were identical as those used for IL1403. The results presented here show that these endolysins of L. lactis are expressed during normal growth and contribute to autolysis without production of (lytic) phages. Screening for natural strains expressing homologous endolysins could help in the selection of strains with enhanced autolysis and, thus, cheese ripening properties.

Glutamine Metabolism in Gliomas

By histological, morphological criteria, and malignancy, brain tumors are classified by WHO into grades I (most benign) to IV (highly malignant), and gliomas are the most frequently occurring class throughout the grades. Similar to peripheral tumors, the growth of glia-derived tumor cells largely depends on glutamine (Gln), which is vividly taken up by the cells, using mostly ASCT2 and SN1 as Gln carriers. Tumor growth-promoting effects of Gln are associated with its phosphate-activated glutaminase (GA) (specifically KGA)-mediated degradation to glutamate (Glu) and/or with its entry to the energy- and intermediate metabolite-generating pathways related to the tricarboxylic acid cycle. However, a subclass of liver-type GA are absent in glioma cells, a circumstance which allows phenotype manipulations upon their transfection to the cells. Gln-derived Glu plays a major role in promoting tumor proliferation and invasion. Glu is relatively inefficiently recycled to Gln and readily leaves the cells by exchange with the extracellular pool of the glutathione (GSH) precursor Cys mediated by xc- transporter. This results in (a) cell invasion-fostering interaction of Glu with ionotropic Glu receptors in the surrounding tissue, (b) intracellular accumulation of GSH which increases tumor resistance to radio- and chemotherapy.

Expression of RNAs Coding for Metal Transporters in Blood of Patients with Huntington's Disease

Recent studies have demonstrated elevated levels of iron (Fe) in brains of patients with Huntington's disease (HD). Striatal cells carrying mutated Huntingtin presented increased sensitivity to cadmium (Cd) toxicity, decreased sensitivity to manganese (Mn) toxicity and deficits in Mn uptake. The hypothesis arose that the observed alterations result from the altered expression and/or activity of proteins engaged in the transport of these metals, that is: transferrin (TF), transferrin receptor (TFR), divalent metal transporter 1 (DMT1) and ZIP8 protein. Here we examined the expression levels of genes encoding these proteins in blood of HD patients and control subjects. A decreasing tendency in the level of TF transcript and increasing tendency of SLC11A2 mRNA encoding DMT1 was observed in the blood of HD patients compared to the control subjects, but neither attained statistical significance. No changes were found in the levels of TFRC coding for TFR and SLC39A8 coding for ZIP8 between HD patients and controls. The results indicate that HD-associated changes in metal homeostasis occur are not related to mechanisms other than the expression level of the here analyzed metal transporters.

Downregulation of GLS2 in glioblastoma cells is related to DNA hypermethylation but not to the p53 status

Human phosphate-activated glutaminase (GA) is encoded by two genes: GLS and GLS2. Glioblastomas (GB) usually lack GLS2 transcripts, and their reintroduction inhibits GB growth. The GLS2 gene in peripheral tumors may be i) methylation- controlled and ii) a target of tumor suppressor p53 often mutated in gliomas. Here we assessed the relation of GLS2 downregulation in GB to its methylation and TP53 status. DNA demethylation with 5-aza-2'-deoxycytidine restored GLS2 mRNA and protein content in human GB cell lines with both mutated (T98G) and wild-type (U87MG) p53 and reduced the methylation of CpG1 (promoter region island), and CpG2 (first intron island) in both cell lines. In cell lines and clinical GB samples alike, methylated CpG islands were detected both in the GLS2 promoter (as reported earlier) and in the first intron of this gene. CpG methylation of either island was absent in GLS2-expressing non-tumoros brain tissues. Screening for mutation in the exons 5-8 of TP53 revealed a point mutation in only one out of seven GB examined. In conclusion, aberrant methylation of CpG islands, appear to contribute to silencing of GLS2 in GB by a mechanism bypassing TP53 mutations. © 2015 Wiley Periodicals, Inc.

Opposing roles of glutaminase isoforms in determining glioblastoma cell phenotype

Glutamine (Gln) and glutamate (Glu) play pivotal roles in the malignant phenotype of brain tumors via multiple mechanisms. Glutaminase (GA, EC 3.5.1.2) metabolizes Gln to Glu and ammonia. Human GA isoforms are encoded by two genes: GLS gene codes for kidney-type isoforms, KGA and GAC, whereas GLS2 codes for liver-type isoforms, GAB and LGA. The expression pattern of both genes in different neoplastic cell lines and tissues implicated that the kidney-type isoforms are associated with cell proliferation, while the liver-type isoforms dominate in, and contribute to the phenotype of quiescent cells. GLS gene has been demonstrated to be regulated by oncogene c-Myc, whereas GLS2 gene was identified as a target gene of p53 tumor suppressor. In glioblastomas (GBM, WHO grade IV), the most aggressive brain tumors, high levels of GLS and only traces or lack of GLS2 transcripts were found. Ectopic overexpression of GLS2 in human glioblastoma T98G cells decreased their proliferation and migration and sensitized them to the alkylating agents often used in the chemotherapy of gliomas. GLS silencing reduced proliferation of glioblastoma T98G cells and strengthen the antiproliferative effect evoked by previous GLS2 overexpression.

Both GLS silencing and GLS2 overexpression synergize with oxidative stress against proliferation of glioma cells

Mitochondrial glutaminase (GA) plays an essential role in cancer cell metabolism, contributing to biosynthesis, bioenergetics, and redox balance. Humans contain several GA isozymes encoded by the GLS and GLS2 genes, but the specific roles of each in cancer metabolism are still unclear. In this study, glioma SFxL and LN229 cells with silenced isoenzyme glutaminase KGA (encoded by GLS) showed lower survival ratios and a reduced GSH-dependent antioxidant capacity. These GLS-silenced cells also demonstrated induction of apoptosis indicated by enhanced annexin V binding capacity and caspase 3 activity. GLS silencing was associated with decreased mitochondrial membrane potential (ΔΨm) (JC-1 dye test), indicating that apoptosis was mediated by mitochondrial dysfunction. Similar observations were made in T98 glioma cells overexpressing glutaminase isoenzyme GAB, encoded by GLS2, though some characteristics (GSH/GSSG ratio) were different in the differently treated cell lines. Thus, control of GA isoenzyme expression may prove to be a key tool to alter both metabolic and oxidative stress in cancer therapy. Interestingly, reactive oxygen species (ROS) generation by treatment with oxidizing agents: arsenic trioxide or hydrogen peroxide, synergizes with either KGA silencing or GAB overexpression to suppress malignant properties of glioma cells, including the reduction of cellular motility. Of note, negative modulation of GLS isoforms or GAB overexpression evoked lower c-myc and bcl-2 expression, as well as higher pro-apoptotic bid expression. Combination of modulation of GA expression and treatment with oxidizing agents may become a therapeutic strategy for intractable cancers and provides a multi-angle evaluation system for anti-glioma pre-clinical investigations.

KEY MESSAGE

Silencing GLS or overexpressing GLS2 induces growth inhibition in glioma cell lines. Inhibition is synergistically enhanced after arsenic trioxide (ATO) or H2O2 treatment. Glutatione levels decrease in GLS-silenced cells but augment if GLS2 is overexpressed. ROS synergistically inhibit cell migration by GLS silencing or GLS2 overexpression. c-myc, bid, and bcl-2 mediate apoptosis resulting from GLS silencing or GLS2 overexpression.

Silencing of GLS and overexpression of GLS2 genes cooperate in decreasing the proliferation and viability of glioblastoma cells

Glutamine (Gln) metabolism, initiated by its degradation by glutaminases (GA), is elevated in neoplastic cells and tissues. In malignant glia-derived tumors, GA isoforms, KGA and GAC, coded by the GLS gene, are overexpressed, whereas the GLS2-coded GAB and LGA isoforms, are hardly detectable in there. Our previous study revealed that transfection of T98G glioblastoma cells with GAB reduced cell proliferation and migration, by a yet unknown mechanism not related to Gln degradation. The question arose how simultaneous overexpression of GAB and inhibition of KGA would affect glioblastoma cell growth. Here, we used siRNA to silence the expression of Gls in T98G cells which were or were not stably transfected with GAB (TGAB cells). In both T98G and TGAB cell lines, silencing of Gls with siRNAs targeted at different sequences decreased cell viability and proliferation in a different, sequence-dependent degree, and the observed decreases were in either cell line highly correlated with increase of intracellular Gln (r > 0.9), a parameter manifesting decreased Gln degradation. The results show that combination of negative modulation of GA isoforms arising from GLS gene with the introduction of the GLS2 gene product, GAB, may in the future provide a useful means to curb glioblastoma growth in situ. At the same time, the results underscore the critical role of Gln degradation mediated by KGA in the manifestations of aggressive glial tumor phenotype.

AcmD, a homolog of the major autolysin AcmA of Lactococcus lactis, binds to the cell wall and contributes to cell separation and autolysis

Lactococcus lactis expresses the homologous glucosaminidases AcmB, AcmC, AcmA and AcmD. The latter two have three C-terminal LysM repeats for peptidoglycan binding. AcmD has much shorter intervening sequences separating the LysM repeats and a lower iso-electric point (4.3) than AcmA (10.3). Under standard laboratory conditions AcmD was mainly secreted into the culture supernatant. An L. lactis acmAacmD double mutant formed longer chains than the acmA single mutant, indicating that AcmD contributes to cell separation. This phenotype could be complemented by plasmid-encoded expression of AcmD in the double mutant. No clear difference in cellular lysis and protein secretion was observed between both mutants. Nevertheless, overexpression of AcmD resulted in increased autolysis when AcmA was present (as in the wild type strain) or when AcmA was added to the culture medium of an AcmA-minus strain. Possibly, AcmD is mainly active within the cell wall, at places where proper conditions are present for its binding and catalytic activity. Various fusion proteins carrying either the three LysM repeats of AcmA or AcmD were used to study and compare their cell wall binding characteristics. Whereas binding of the LysM domain of AcmA took place at pHs ranging from 4 to 8, LysM domain of AcmD seems to bind strongest at pH 4.

Transfection of a human glioblastoma cell line with liver-type glutaminase (LGA) down-regulates the expression of DNA-repair gene MGMT and sensitizes the cells to alkylating agents

O(6)-methylguanine-DNA methyltransferase (MGMT) is a DNA-repair protein promoting resistance of tumor cells to alkylating chemotherapeutic agents. Glioma cells are particularly resistant to this class of drugs which include temozolomide (TMZ) and carmustine (BCNU). A previous study using the RNA microarray technique showed that decrease of MGMT mRNA stands out among the alterations in gene expression caused by the cell growth-depressing transfection of a T98G glioma cell line with liver-type glutaminase (LGA) [Szeliga et al. (2009) Glia, 57, 1014]. Here, we show that stably LGA-transfected cells (TLGA) exhibit decreased MGMT protein expression and activity as compared with non-transfected or mock transfected cells (controls). However, the decrease of expression occurs in the absence of changes in the methylation of the promoter region, indicating that LGA circumvents, by an as yet unknown route, the most common mechanism of MGMT silencing. TLGA turned out to be significantly more sensitive to treatment with 100-1000 μM of TMZ and BCNU in the acute cell growth inhibition assay (MTT). In the clonogenic survival assay, TLGA cells displayed increased sensitivity even to 10 μM TMZ and BCNU. Our results indicate that enrichment with LGA, in addition to inhibiting glioma growth, may facilitate chemotherapeutic intervention.

2-Amino-1,3,4-thiadiazole derivative (FABT) inhibits the extracellular signal-regulated kinase pathway and induces cell cycle arrest in human non-small lung carcinoma cells

The anticancer potential of 2-amino-1,3,4-thiadiazole compounds has been documented by in vitro and in vivo studies. In our previous research, we described the synthesis as well as the antiproliferative and neuroprotective activities of 2-(4-fluorophenyloamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole (FABT). The aim of the present study was to investigate the molecular mechanisms involved in FABT-induced growth inhibition in A549 lung carcinoma cells. Western blotting analysis revealed that FABT inhibited the activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, and Real-time PCR analysis showed no changes in the expression of P44ERK1 and CREB1 genes. Furthermore, FABT induced cell cycle arrest in the GO/G1 phase and enhanced p27/Kip1 expression. Our results suggest that FABT acts by inhibiting ERK1/2 pathway and cell cycle progression through G1 into S phase in A549 cells. Further studies are needed to completely explain the molecular mechanisms of anticancer action of this 2-aminothiadiazole derivative.

Down-regulation of Kir4.1 in the cerebral cortex of rats with liver failure and in cultured astrocytes treated with glutamine: Implications for astrocytic dysfunction in hepatic encephalopathy

Brain edema in acute hepatic encephalopathy (HE) is due mainly to swelling of astrocytes. Efflux of potassium is implicated in the prevention of glial swelling under hypoosmotic conditions. We investigated whether pathogenic factors of HE, glutamine (Gln) and/or ammonia, induce alterations in the expression of glial potassium channels (Kir4.1, Kir2.1) and Na(+) -K(+) -2Cl(-) cotransporter-1 (NKCC1) in rat cerebral cortex and cultured rat cortical astrocytes and whether these alterations have consequences for potassium efflux and astrocytic swelling. Thioacetamide-induced acute liver failure in rats resulted in significant decreases in the Kir4.1 mRNA and protein contents of cerebral cortex, whereas expression of Kir2.1 and NKCC1 remained unaltered. Incubation of primary cortical astrocytes for 72 hr in the presence of Gln (5 mM), but not of ammonia (5 mM or 10 mM), induced a decrease in the levels of Kir4.1 mRNA and protein. Similarly to incubation with Gln, reduction of Kir4.1 mRNA expression by RNA interference caused swelling of astrocytes as shown by confocal imaging followed by 3D computational analysis. Gln reduced the astrocytic uptake of D-[(3) H]aspartate, but, in contrast to the earlier reported effect of ammonia, this reduction was not accompanied by decreased expression of the astrocytic glutamate transporter GLT-1 mRNA. Both Gln and ammonia decreased hypoosmolarity-induced (86) Rb efflux from the cells, but the effect was more pronounced with Gln. The results indicate that down-regulation of Kir4.1 may mediate distinct aspects of Gln-induced astrocytic dysfunction in HE.

Transfection with liver-type glutaminase cDNA alters gene expression and reduces survival, migration and proliferation of T98G glioma cells

Liver-type glutaminase (LGA) is a glutaminase isoform that has been implicated in transcription modulation. LGA mRNA is absent from postoperative samples of primary gliomas and is low in cultured astrocytes. In this study, stable transfection of T98G cells with a vector carrying human LGA sequence increased the expression of LGA mRNA and protein, and the ability of the cells to degrade glutamine (Gln), as manifested by a three-fold reduction of their steady-state Gln content and a 2.5-fold increase of their glutamate (Glu) content. The transfected cells (TLGA cells) showed a 40% decrease of cell survival as assessed by colony formation, well correlated with significant reduction of mitochondrial activity as demonstrated with MTT test. Also, a 45% reduction of cell migration and a 47% decrease of proliferation index (Ki67 immunostaining) were found as compared with sham-transfected cells. Microarray analysis, which included over 47,000 transcripts, revealed a significantly altered expression of 85 genes in TLGA, but not in sham-transfected or control cells (P < 0.005). Microarray data were confirmed with real-time PCR analysis for eight genes potentially relevant to malignancy: S100A16, CAPN2, FNDC3B, DYNC1LI1, TIMP4, MGMT, ADM, and TIMP1. Of these changes, decreased expression of S100A16 and MGMT can be best reconciled with the current views on the role of their protein products in glioma malignancy. Malignancy-reducing effect of newly inserted LGA mRNA in glioblastoma cells can be reconciled with a hypothesis that absence of such a modulatory mechanism in glia-derived tumors deprived of LGA mRNA may facilitate some aspects of their progression.

Regulation of pH in the mammalian central nervous system under normal and pathological conditions: facts and hypotheses

The maintenance of pH homeostasis in the CNS is of key importance for proper execution and regulation of neurotransmission, and deviations from this homeostasis are a crucial factor in the mechanism underlying a spectrum of pathological conditions. The first few sections of the review are devoted to the brain operating under normal conditions. The article commences with an overview of how extrinsic factors modelling the brain at work: neurotransmitters, depolarising stimuli (potassium and voltage changes) and cyclic nucleotides as major signal transducing vehicles affect pH in the CNS. Further, consequences of pH alterations on the major aspects of CNS function and metabolism are outlined. Next, the major cellular events involved in the transport, sequestration, metabolic production and buffering of protons that are common to all the mammalian cells, including the CNS cells. Since CNS function reflects tight interaction between astrocytes and neurons, the pH regulatory events pertinent to either cell type are discussed: overwhelming evidence implicates astrocytes as a key player in pH homeostasis in the brain. The different classes of membrane proteins involved in proton shuttling are listed and their mechanisms of action are given. These include: the Na+/H+ exchanger, different classes of bicarbonate transporters acting in a sodium-dependent- or -independent mode, monocarboxylic acid transporters and the vacuolar-type proton ATPase. A separate section is devoted to carbonic anhydrase, which is represented by multiple isoenzymes capable of pH buffering both in the cell interior and in the extracellular space. Next, impairment of pH regulation and compensatory responses occurring in brain affected by different pathologies: hypoxia/ischemia, epilepsy, hyperammonemic encephalopathies, cerebral tumours and HIV will be described. The review is limited to facts and plausible hypotheses pertaining to phenomena directly involved in pH regulation: changes in pH that accompany metabolic stress but have no distinct implications for the pH regulatory mechanisms are not dealt with. In most cases, the vast body of knowledge derived from in vitro studies remains to be verified in in vivo settings.

Lack of expression of the liver-type glutaminase (LGA) mRNA in human malignant gliomas

In the central nervous system (CNS), liver-type glutaminase (LGA) shows a unique nuclear localization suggesting its role in the regulation of transcription rather than in the cellular glutamine metabolism. RT-PCR analysis of RNA derived from postoperative tissue samples revealed the absence or only traces of LGA mRNA in all (9) cases of malignant gliomas (astrocytoma anaplasticum, AA, WHO grade III; glioblastoma multiforme, WHO grade IV) examined. The RNA was strongly expressed in the non-neoplastic tissue derived from the same patients (6 cases), and in most of the brain metastases from different organs (5 out of 7 cases). By contrast, the mRNAs coding for the kidney-type glutaminase (KGA) and its less ubiquitous isoform GAC, which catalyze degradation of the cytoplasmic pool of Gln, were expressed in all the tissues examined. The lack of LGA may be thus considered as a useful negative diagnostic marker of highly malignant gliomas in situ.

[Neuroblastoma: epidemiology, pathomorphological and molecular diagnosis, prognosis]

Neuroblastoma is the third most common neoplasm of childhood. About 70% of cases occurs by 5 years old and around 95% cases in the patients younger than 10 years old. Neuroblastoma is part of the spectrum of the family neuroblastic tumors. The family consists of heterogeneous group of tumors, difficult to classify. Additionally some cases of neuroblastoma show tendency to self-maturation and regression. The family consists of neuroblastoma (NB), ganglio-neuroblastoma (GNB) and ganglineuroma (GN). In recent years there has been considerable development in the classification concepts from purely histological to clinico-pathological one. These schemes include clinical, pathological and molecular features od tumors which allow more accurate prognostication.