cyclic-gmp and Brain-Neoplasms

Since the discovery of phosphodiesterase-5 (PDE5) enzyme overexpression in the central nervous system (CNS) malignancies, investigations have explored the potential capacity of current PDE5 inhibitor drugs for repositioning in the treatment of brain tumors, notably glioblastoma multiforme (GBM). It has now been recognized that these drugs increase brain tumors permeability and enhance standard chemotherapeutics effectiveness. More importantly, studies have highlighted the promising antitumor functions of PDE5 inhibitors, e.g., triggering apoptosis, suppressing tumor cell growth and invasion, and reversing tumor microenvironment (TME) immunosuppression in the brain. However, contradictory reports have suggested a pro-oncogenic role for neuronal cyclic guanosine monophosphate (cGMP), indicating the beneficial function of PDE5 in the brain of GBM patients. Unfortunately, due to the inconsistent preclinical findings, only a few clinical trials are evaluating the therapeutic value of PDE5 inhibitors in GBM treatment. Accordingly, additional studies should be conducted to shed light on the precise effect of PDE5 inhibitors in GBM biology regarding the existing molecular heterogeneities among individuals. Here, we highlighted and discussed the previously investigated mechanisms underlying the impacts of PDE5 inhibitors in cancers, focusing on GBM to provide an overview of current knowledge necessary for future studies.

Topics: Brain Neoplasms; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 5; Glioblastoma; Humans; Phosphodiesterase 5 Inhibitors; Tumor Microenvironment

Evidence has steadily accumulated to indicate that the rapid fluctuations in cyclic nucleotides during primary and secondary stroke are more than epiphenomena of the disease. During acute phases of ischemia, anoxia or hypoxia cyclic AMP rapidly accumulates in cerebral tissue, cerebrospinal fluid (CSF) and venous plasma, while cyclic GMP either remains unchanged or declines. The massive release of transmitters (catecholamines and adenosine) or ionic fluxes (Na+ and K+) may account for these observations. If reflow is established through a previously occluded vessel cyclic AMP content rises even higher in conjunction with a sharp rise in cyclic GMP. It is during this reflow period subsequent to longer term stroke (30-60 min) that the synaptic membrane enzyme, adenylate cyclase, is especially vulnerable. Presumably the cause of injury to cell membrane systems results from excess lactic acid accumulation and/or Ca++ entry through the damaged blood-brain barrier. The latter initiates breakdown of membrane phospholipids with resultant synthesis of vasoactive prostaglandins and formation of free radicals causing further insult to membrane phospholipids. Thus drugs acting to inhibit formation of prostaglandins, scavenge free radicals, reduce lactate formation, inhibit Ca++ entry or stabilize cell membranes have been shown to possess varying degrees of protective action toward adenylate cyclase. Moreover, cyclic AMP has been found to reverse stroke-induced vasospasm in central vessels. Reduced cyclic AMP content in CSF has been used to monitor the severity of coma, whereas clinical improvement was associated with predictable increases in the cyclic nucleotide. Therefore, cyclic nucleotides and related membrane enzyme systems might be used as target molecules in which to develop future therapeutic strategies for prevention or treatment of stroke.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; 3',5'-Cyclic-GMP Phosphodiesterases; Adenosine; Adenylyl Cyclases; Animals; Brain; Brain Ischemia; Brain Neoplasms; Capillaries; Cerebrovascular Disorders; Cyclic AMP; Cyclic GMP; gamma-Aminobutyric Acid; Guanylate Cyclase; Humans; Hypoxia, Brain; In Vitro Techniques; Lactates; Lactic Acid; Norepinephrine; Phospholipids; Protein Kinases; Synaptic Membranes; Tissue Distribution

Topics: Animals; Brain Neoplasms; Calcium; Cyclic AMP; Cyclic GMP; Myosins; Peptide Hydrolases; Phospholipids; Phosphorylases; Protein Kinases; Rabbits

The high mortality associated with glioblastoma multiforme (GBM) is attributed to its invasive nature, hypoxic core, resistant cell subpopulations and a highly immunosuppressive tumor microenvironment (TME). To support adaptive immune function and establish a more robust antitumor immune response, we boosted the local innate immune compartment of GBM using an immunostimulatory mesoporous silica nanoparticle, termed immuno-MSN. The immuno-MSN was specifically designed for systemic and proficient delivery of a potent innate immune agonist to dysfunctional antigen-presenting cells (APCs) in the brain TME. The cargo of the immuno-MSN was cyclic diguanylate monophosphate (cdGMP), a Stimulator of Interferon Gene (STING) agonist. Studies showed the immuno-MSN promoted the uptake of STING agonist by APCs in vitro and the subsequent release of the pro-inflammatory cytokine interferon β, 6-fold greater than free agonist. In an orthotopic GBM mouse model, systemically administered immuno-MSN particles were taken up by APCs in the near-perivascular regions of the brain tumor with striking efficiency. The immuno-MSNs facilitated the recruitment of dendritic cells and macrophages to the TME while sparing healthy brain tissue and peripheral organs, resulting in elevated circulating CD8

Topics: Animals; Antigen-Presenting Cells; Antineoplastic Agents; Brain Neoplasms; CD8-Positive T-Lymphocytes; Cyclic GMP; Dendritic Cells; Female; Glioblastoma; Immunity, Innate; Immunologic Factors; Immunotherapy; Interferon Type I; Macrophages; Mice; Mice, Inbred C57BL; Nanoparticles; Porosity; RAW 264.7 Cells; Silicon Dioxide; Tumor Microenvironment

Cyclic nucleotides (cAMP & cGMP) are critical intracellular second messengers involved in the transduction of a diverse array of stimuli and their catabolism is mediated by phosphodiesterases (PDEs). We previously detected focal genomic amplification of PDE1C in >90 glioblastoma multiforme (GBM) cells suggesting a potential as a novel therapeutic target in these cells. In this report, we show that genomic gain of PDE1C was associated with increased expression in low passage GBM-derived cell cultures. We demonstrate that PDE1C is essential in driving cell proliferation, migration and invasion in GBM cultures since silencing of this gene significantly mitigates these functions. We also define the mechanistic basis of this functional effect through whole genome expression analysis by identifying down-stream gene effectors of PDE1C which are involved in cell cycle and cell adhesion regulation. In addition, we also demonstrate that Vinpocetine, a general PDE1 inhibitor, can also attenuate proliferation with no effect on invasion/migration. Up-regulation of at least one of this gene set (IL8, CXCL2, FOSB, NFE2L3, SUB1, SORBS2, WNT5A, and MMP1) in TCGA GBM cohorts is associated with worse outcome and PDE1C silencing down-regulated their expression, thus also indicating potential to influence patient survival. Therefore we conclude that proliferation, migration, and invasion of GBM cells could also be regulated downstream of PDE1C.

Topics: Brain; Brain Neoplasms; Cell Movement; Cell Proliferation; Cyclic AMP; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 1; Gene Expression Regulation, Neoplastic; Glioblastoma; Humans; Neoplasm Invasiveness; Up-Regulation

Nitric oxide (NO) released from NO donors can be cytotoxic in tumor cells and can enhance the transport of drugs into brain tumors by altering blood-tumor barrier permeability. The NO donor JS-K [O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate] releases NO upon enzymatic activation selectively in cells overexpressing glutathione-S-transferases (GSTs) such as gliomas. Thus, JS-K-dependent NO effects - especially on cell viability and vascular permeability - were investigated in U87 glioma cells in vitro and in an orthotopic U87 xenograft model in vivo by magnetic resonance imaging (MRI). In vitro experiments showed dose-dependent antiproliferative and cytotoxic effects in U87 cells. In addition, treatment of U87 cells with JS-K resulted in a dose-dependent activation of soluble guanylate cyclase and intracellular accumulation of cyclic guanosine monophosphate (cGMP) which was irreversibly inhibited by the selective inhibitor of soluble guanylate cyclase ODQ (1H-[1,2,4]oxadiazolo(4,3a)quinoxaline-1-one). Using dynamic contrast enhanced MRI (DCE-MRI) as a minimally invasive technique, we demonstrated for the first time a significant increase in the DCE-MRI read-out initial area under the concentration curve (iAUC60) indicating an acute increase in blood-tumor barrier permeability after i.v. treatment with JS-K. Repeated MR imaging of animals with intracranial U87 gliomas under treatment with JS-K (3.5 μmol/kg JS-K 3×/week) and of untreated controls on day 12 and 19 after tumor inoculation revealed no significant changes in tumor growth, edema formation or tumor perfusion. Immunohistochemical workup of the brains showed a significant antiproliferative effect of JS-K in the gliomas. Taken together, in vitro and in vivo data suggest that JS-K has antiproliferative effects in U87 gliomas and opens the blood-tumor barrier by activation of the NO/cGMP signaling pathway. This might be a novel approach to facilitate entry of therapeutic drugs into brain tumors. DCE-MRI is a non-invasive, repeatable imaging modality to monitor biological effects of NO donors and other experimental therapeutics in intracranial tumor models.

Topics: Animals; Azo Compounds; Brain Neoplasms; Cell Line, Tumor; Cell Proliferation; Cell Survival; Cyclic GMP; Glioma; Humans; Immunohistochemistry; Magnetic Resonance Imaging; Nitric Oxide Donors; Piperazines; Rats; Rats, Nude; Xenograft Model Antitumor Assays

The blood-brain tumor barrier (BTB) significantly limits the delivery of chemotherapeutics to brain tumors. Nitric oxide (NO) is involved in the regulation of cerebral vascular permeability. We investigated the effects of NO donors, L-arginine and hydroxyurea, on BTB permeability in 9L gliosarcoma-bearing Fischer rats.. The rats implanted with 9L gliosarcoma were dosed orally with hydroxyurea and L-arginine. BTB permeability, defined by the unidirectional transport constant, Ki, for [14C]sucrose was measured. The expression of neural and endothelial NO synthase (NOS) in tumors and normal brain tissue was examined. Further, the levels of NO, L-citrulline, and cGMP in the tumor and normal brain tissue were measured.. Oral administration of l-arginine or hydroxyurea significantly increased BTB permeability when compared with the nontreated control. The selective effects were abolished by iberiotoxin, an antagonist of calcium-dependent potassium (KCa) channel that is a cGMP pathway effector. The expression of endothelial NOS, but not neural NOS, was higher in tumor vessels than in those of normal brain. Moreover, the levels of NO, L-citrulline, a byproduct of NO formation from L-arginine, and cGMP were enhanced in the tumor tissue by oral administration of L-arginine and/or hydroxyurea.. Oral administration of L-arginine or hydroxyurea selectively increased tumor permeability, which is likely mediated by alteration in cGMP levels. The findings suggest that use of oral NO donors may be a strategy to enhance the delivery of chemotherapeutics to malignant brain tumors.

Topics: Administration, Oral; Animals; Arginine; Blood-Brain Barrier; Brain Neoplasms; Capillary Permeability; Citrulline; Cyclic GMP; Drug Delivery Systems; Drug Evaluation, Preclinical; Drug Synergism; Female; Glioma; Hydroxyurea; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Rats; Rats, Inbred F344; Tumor Cells, Cultured

The blood-brain tumor barrier (BTB) significantly limits delivery of therapeutic concentrations of chemotherapy to brain tumors. A novel approach to selectively increase drug delivery is pharmacologic modulation of signaling molecules that regulate BTB permeability, such as those in cGMP signaling. Here we show that oral administration of sildenafil (Viagra) and vardenafil (Levitra), inhibitors of cGMP-specific PDE5, selectively increased tumor capillary permeability in 9L gliosarcoma-bearing rats with no significant increase in normal brain capillaries. Tumor-bearing rats treated with the chemotherapy agent, adriamycin, in combination with vardenafil survived significantly longer than rats treated with adriamycin alone. The selective increase in tumor capillary permeability appears to be mediated by a selective increase in tumor cGMP levels and increased vesicular transport through tumor capillaries, and could be attenuated by iberiotoxin, a selective inhibitor for calcium-dependent potassium (K(Ca)) channels, that are effectors in cGMP signaling. The effect by sildenafil could be further increased by simultaneously using another BTB "opener", bradykinin. Collectively, this data demonstrates that oral administration of PDE5 inhibitors selectively increases BTB permeability and enhances anti-tumor efficacy for a chemotherapeutic agent. These findings have significant implications for improving delivery of anti-tumor agents to brain tumors.

Topics: Animals; Antineoplastic Agents; Autoradiography; Blood Pressure; Brain Chemistry; Brain Neoplasms; Capillaries; Capillary Permeability; Cyclic GMP; Female; Glioma; Imidazoles; Microscopy, Electron, Transmission; Neovascularization, Pathologic; Phosphodiesterase 5 Inhibitors; Phosphodiesterase Inhibitors; Piperazines; Purines; Rats; Rats, Inbred F344; Reverse Transcriptase Polymerase Chain Reaction; Sildenafil Citrate; Sucrose; Sulfones; Survival Analysis; Tight Junctions; Triazines; Vardenafil Dihydrochloride

Endostatin is a 20 kDa carboxyl-terminal fragment of collagen XVIII that, when added exogenously, inhibits endothelial proliferation and migration in vitro and angiogenesis and tumor growth in vivo. Previous results showed endostatin/collagen XVIII labeling in few endothelial cells in human glioblastoma multiforme. We have now observed constitutive release of endostatin from one of four endothelial cell lines. Induction of endostatin release was observed after H2O2, an in vitro model of cell stress, CoCl2, a model of hypoxia, and by IFN-gamma challenge. Endostatin expression and release was reduced by the nitric oxide synthase inhibitors aminoguanidine and L-NAME and induced by the NO synthase-independent NO donors sodium nitroprusside (SNP) and spermine-NONO-ate. SNP-mediated endostatin induction was abrogated by the soluble guanylate cyclase inhibitor 1H-(1.2.4) oxadiazolo (4,3-A) quinoxalin-1-one. Adenoviral endostatin transduction resulted in the release of endostatin from endothelial cells and in down-regulation of iNOS (NOS2) and eNOS (NOS3), and surprisingly in a 10% induction of PCNA. These results describe the modulation of endostatin release by the NO signaling cascade and provide important new pharmacological information for the systemic induction of endogenous endostatin release by common NO donor pharmacotherapy.

Topics: Adult; Aged; Animals; Brain; Brain Neoplasms; Cell Hypoxia; Cell Line; Collagen; Collagen Type XVIII; Cyclic GMP; Endostatins; Endothelium; Enzyme Inhibitors; Female; Glioblastoma; Guanylate Cyclase; Humans; Hydrogen Peroxide; Interferon-gamma; Male; Mice; Middle Aged; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Oxidants; Peptide Fragments; Rats; Signal Transduction; Tumor Cells, Cultured; Up-Regulation

Angiogenesis is a prerequisite for tumour progression and is highly regulated by growth factors and cytokines a number of which also stimulate the production of nitric oxide. Asymmetric dimethylarginine is an endogenous inhibitor of nitric oxide synthesis. Asymmetric dimethylarginine is metabolised by dimethylarginine dimethylaminohydrolase. To study the effect of dimethylarginine dimethylaminohydrolase on tumour growth and vascular development, the rat C6 glioma cell line was manipulated to overexpress the rat gene for dimethylarginine dimethylaminohydrolase I. Enhanced expression of dimethylarginine dimethylaminohydrolase I increased nitric oxide synthesis (as indicated by a two-fold increase in the production of cGMP), expression and secretion of vascular endothelial cell growth factor, and induced angiogenesis in vitro. Tumours derived from these cells grew more rapidly in vivo than cells with normal dimethylarginine dimethylaminohydrolase I expression. Immunohistochemical and magnetic resonance imaging measurements were consistent with increased tumour vascular development. Furthermore, dimethylarginine dimethylaminohydrolase activity was detected in a series of human tumours. This data demonstrates that dimethylarginine dimethylaminohydrolase plays a pivotal role in tumour growth and the development of the tumour vasculature by regulating the concentration of nitric oxide and altering vascular endothelial cell growth factor production.

Topics: Amidohydrolases; Animals; Astrocytoma; Blotting, Northern; Blotting, Western; Brain Neoplasms; Cell Division; Cell Movement; Cells, Cultured; Cyclic GMP; DNA Primers; Endothelial Growth Factors; Endothelium, Vascular; Enzyme-Linked Immunosorbent Assay; Female; Glioblastoma; Glioma; Humans; Lymphokines; Mice; Mice, Nude; Neoplasm Transplantation; Neoplasms, Experimental; Neovascularization, Pathologic; Nitric Oxide; Rats; Reverse Transcriptase Polymerase Chain Reaction; Transfection; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factors

Exisulind (sulindac sulfone) and two potent derivatives, CP248 and CP461, have been shown previously to cause growth inhibition and apoptosis in several types of human carcinoma cell lines. These and related compounds have not been previously studied with respect to glioma cell lines. In the present study, we found that these three compounds caused marked growth inhibition in four rat glioma and eight human glioma cell lines, with IC50 values of 150, 1, and 0.075 microm, respectively. When studied at these concentrations exisulind and CP461 had no significant effect on the cell cycle profile of glioma cells, but CP248 caused marked arrest in mitosis. Detailed studies of CP248 in the 9L rat gliosarcoma cell line indicated that treatment with 0.075 microM CP248 caused abnormalities in the spindle apparatus and activation of the spindle assembly check point. In interphase glioma cells, CP248 stabilized microtubules (MTs) at low concentrations (0.075 microM) and depolymerized MTs at higher concentrations (0.2-0.4 microM). In NIH 3T3 fibroblasts, 0.1 microM CP248 caused extensive MT depolymerization. CP248 also caused MT depolymerization when added to assembled MTs in vitro, which indicated that it can directly affect MTs, perhaps because it shares certain structural similarities with Colcemid. In glioma cells, the effects of CP248 on MTs were independent of the previously reported effects of this compound on activation of protein kinase G. Therefore, CP248 is a novel MT-active agent that may be useful in the treatment of glioblastoma, and possibly other types of cancer, because of its dual effects on protein kinase G and MTs.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; 3',5'-Cyclic-GMP Phosphodiesterases; 3T3 Cells; Animals; Antineoplastic Agents; Apoptosis; Brain Neoplasms; Cell Cycle Proteins; Cell Division; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Cyclic Nucleotide Phosphodiesterases, Type 2; Cyclic Nucleotide Phosphodiesterases, Type 5; Flow Cytometry; Fluorescent Antibody Technique, Indirect; Glioma; Humans; Immunoenzyme Techniques; In Vitro Techniques; Interphase; Kinesins; Mice; Microtubules; Phosphoproteins; Phosphoric Diester Hydrolases; Rats; Spindle Apparatus; Sulindac; Thymidine

Intracarotid infusion of bradykinin and its analogue, RMP-7, selectively increase the permeability of brain tumor capillaries though the nitrix oxide (NO) and cyclic GMP pathway. Maximum blood-tumor barrier (BTB) permeability induced by bradykinin is observed at 15 min after intracarotid infusion and this effect is decreased even if the infusion continues. The mechanism for this decreased effect with long term infusion has not been clearly defined. This study sought to determine the involvement of the NO-cyclic GMP pathway in this event. Regional permeability was investigated in 44 Wistar rats with implanted RG2 gliomas, using quantitative autoradiography to determine the unidirectional transfer constant (Ki) of radiolabeled 14C-dextran. Tumor bearing rats were treated by intracarotid infusion of bradykinin (10 micrograms kg-1 min-1) with or without pretreatment with bradykinin, the NO donor s-nitrosoglutathione (10 nmol kg-1 min-1), or the cyclic GMP analogue, 8Br-cyclic GMP (200 micrograms kg-1 min-1). At 30 min of bradykinin infusion, BTB permeability was significantly lower compared to 15 min of bradykinin infusion (3.79 +/- 0.99 vs. 16.20 +/- 3.43 microliters g-1 min-1, p < 0.001). Pretreatment with an NO donor significantly decreased BTB permeability in bradykinin infused rats (5.09 +/- 2.61 vs. 13.51 +/- 4.19 microliters g-1 min-1, p < 0.001), as did pretreatment with a cyclic GMP analogue (4.48 +/- 0.95 vs. 12.31 +/- 3.90 microliters g-1 min-1, p < 0.001). There was no increased permeability in nontumor brain areas. Increased tumor permeability by bradykinin appears to be regulated by NO and cyclic GMP which are second messengers involved in the bradykinin B2 receptor mediated cascade.

Topics: Animals; Bradykinin; Brain Neoplasms; Capillary Permeability; Cyclic GMP; Drug Resistance; Female; Glioma; Glutathione; Nitric Oxide; Nitroso Compounds; Rats; Rats, Wistar; S-Nitrosoglutathione

The stimulation of IP3 production by muscarinic agonists causes both intracellular Ca2+ release and activation of a voltage-independent cation current in differentiated N1E-115 cells, a neuroblastoma cell line derived from mouse sympathetic ganglia. Earlier work showed that the membrane current requires an increase in 3',5'-cyclic guanosine monophosphate (cGMP) produced through the NO-synthase/guanylyl cyclase cascade and suggested that the cells may express cyclic nucleotide-gated ion channels. This was tested using patch clamp methods. The membrane permeable cGMP analogue, 8-br-cGMP, activates Na+ permeable channels in cell attached patches. Single channel currents were recorded in excised patches bathed in symmetrical Na+ solutions. cGMP-dependent single channel activity consists of prolonged bursts of rapid openings and closings that continue without desensitization. The rate of occurrence of bursts as well as the burst length increase with cGMP concentration. The unitary conductance in symmetrical 160 mM Na+ is 47 pS and is independent of voltage in the range -50 to +50 mV. There is no apparent effect of voltage on opening probability. The dose response curve relating cGMP concentration to channel opening probability is fit by the Hill equation assuming an apparent KD of 10 microm and a Hill coefficient of 2. In contrast, cAMP failed to activate the channel at concentrations as high as 100 microm. Cyclic nucleotide gated (CNG) channels in N1E-115 cells share a number of properties with CNG channels in sensory receptors. Their presence in neuronal cells provides a mechanism by which activation of the NO/cGMP pathway by G-protein-coupled neurotransmitter receptors can directly modify Ca2+ influx and electrical excitability. In N1E-115 cells, Ca2+ entry by this pathway is necessary to refill the IP3-sensitive intracellular Ca2+ pool during repeated stimulation and CNG channels may play a similar role in other neurons.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Brain; Brain Chemistry; Brain Neoplasms; Cell Line; Cyclic GMP; Ganglia, Sympathetic; Ion Channel Gating; Membrane Potentials; Mice; Neuroblastoma; Neurons; Patch-Clamp Techniques; Sodium Channels; Sympathetic Nervous System

In the present study, we investigated the effects of chronic in vitro administration of amitriptyline, a tricyclic antidepressant, on cyclic GMP formation stimulated by 5-hydroxytryptamine (5-HT) in the neuroblastoma x glioma hybrid cell line, NG 108-15, 5-HT (0.01-100 microM)-stimulated cyclic GMP formation was concentration-dependent and was sensitive to ICS 205-930, a 5-HT3 receptor antagonist. Exposure of NG 108-15 cells to 5 microM amitriptyline for 3 days significantly reduced 5-HT-stimulated cyclic GMP formation. Acute treatment with amitriptyline had no effect on 5-HT-stimulated cyclic GMP formation. The reduction by chronic amitriptyline exposure of 10 microM 5-HT-stimulated cyclic GMP formation was concentration-dependent over the concentration range examined (0.5 to 10 microM). The IC50 of amitriptyline was 1.9 microM. In contrast, amitriptyline exposure, even at a concentration of 8 microM, failed to modify cyclic GMP formation stimulated by bradykinin, sodium nitroprusside, or atrial natriuretic peptide. Increases in intracellular Ca2+ concentration ([Ca2+]i) evoked by 10 microM 5-HT were attenuated in amitriptyline-exposed cells, while 100 nM bradykinin-induced [Ca2+]i increases were not affected. In addition, chronic exposure to 5 microM amitriptyline caused a decrease in affinity (Kd) of [3H]zacopride specific binding to 5-HT3 recognition sites. The Bmax for the labelled ligand remained unchanged. These results suggest that chronic amitriptyline exposure reduces 5-HT-stimulated cyclic GMP formation and [Ca2+]i increases, and this may reflect the functional changes of 5-HT3 receptors.

Topics: Amitriptyline; Antidepressive Agents, Tricyclic; Benzamides; Bradykinin; Brain Neoplasms; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Cyclic GMP; Fluorescent Dyes; Fura-2; Glioma; Hybrid Cells; Indoles; Kinetics; Neuroblastoma; Receptors, Serotonin; Serotonin Antagonists; Tropisetron; Tumor Cells, Cultured

Methylene blue (MB), a known inhibitor of guanylyl cyclase, induced cytotoxicity in SK-N-MC human neuroblastoma and U-373 MG human astrocytoma cells in a dose-dependent manner. MB did not significantly alter cellular levels of cGMP in both cells. 8-Br cGMP, a membrane-permeable analogue of cGMP, did not decrease MB-induced cytotoxicity, indicating that cGMP may not be a major target of the cytotoxic action of MB. However, hydroxyl radical scavengers or intracellular Ca2+ modulators effectively blocked the MB-induced cytotoxicity. These results suggest that hydroxyl radical and intracellular Ca2+ may have an important involvement in the cytotoxic action of MB. These results further suggest that the treatment with MB may be useful for the therapeutic applications of human brain tumors.

Topics: Astrocytoma; Brain Neoplasms; Calcium; Cell Division; Cyclic GMP; Humans; Intracellular Fluid; Kinetics; Methylene Blue; Neuroblastoma; Reactive Oxygen Species; Tumor Cells, Cultured

C6 glioma cells possess endothelin ETA receptor and P2 purinoceptor coupled to two signaling pathways, i.e. phosphoinositide turnover and inhibition of adenylyl cyclase. In this study, the effects of raising cyclic AMP levels on the inositol phospholipid hydrolysis and adenylyl cyclase inhibition caused by endothelin-1 and ATP in C6 glioma cells were examined. Pretreatment with cAMP generating agents (forskolin, isoproterenol and cholera toxin) or dibutyryl cAMP for 10 min-3 h did not affect the inositol phosphate accumulation caused by endothelin and ATP. Long-term (8-24 h) pretreatment with isoproterenol, forskolin, cholera toxin or dibutyryl cAMP resulted in a 40-50% inhibition of endothelin- and ATP-stimulated inositol phosphate accumulation, whereas the EC50 values of endothelin and ATP were not affected. Consistent with the effects on endothelin and ATP, NaF-induced inositol phosphate formation was also inhibited by cAMP generating agents to a similar extent. Permeabilized cells from 24 h isoproterenol-or forskolin-pretreated C6 cells also showed a diminished Ca(2+)-sensitivity of phosphoinositide-specific phospholipase C and also attenuated the potentiation response caused by GTP gamma S. The inhibitory effects on adenylyl cyclase by endothelin, ATP and 2-methylthio-ATP were unaffected by 24 h pretreatment with isoproterenol or forskolin. Long-term treatment with dibutyryl cGMP did not affect the two signaling pathways caused by ATP and endothelin. It is concluded that the phosphoinositide turnover, but not the adenylyl cyclase inhibition caused by endothelin and ATP in C6 cells, was inhibited by protein kinase A-dependent pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine Triphosphate; Adenylyl Cyclase Inhibitors; Animals; Brain Neoplasms; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Endothelins; Enzyme Activation; Glioma; Guanosine 5'-O-(3-Thiotriphosphate); Phosphatidylinositols; Rats; Signal Transduction; Stimulation, Chemical; Tumor Cells, Cultured

There is rapidly accumulating evidence that generation of nitric oxide (NO) through a Ca2+ and calmodulin-dependent pathway plays various important roles in the central nervous system. In the present study, effects of several antipsychotics on the activity of NO synthase were investigated in rat cerebellum and neuroblastoma N1E-115 cells, due to the known ability of these agents to inhibit calmodulin. In cytosolic preparations of rat cerebellum, the antipsychotic drugs inhibited the conversion of [3H]L-arginine into [3H]L-citrulline by NO synthase in a concentration-dependent manner. This inhibition was noncompetitive in nature, and it exhibited an excellent correlation with blockade of calmodulin activity. Furthermore, these drugs attenuated cyclic GMP formation induced by a calcium ionophore in N1E-115 cells, a response which takes place as a consequence of NO generation. Taken together, our data demonstrate that antipsychotic drugs inhibit NO formation in vitro. It is unlikely, however, that these actions might contribute to their therapeutic and/or side effects, since they take place at relatively high concentrations.

Topics: Amino Acid Oxidoreductases; Animals; Antipsychotic Agents; Arginine; Brain Neoplasms; Calmodulin; Cerebellum; Citrulline; Cyclic GMP; Cytosol; In Vitro Techniques; Male; Mice; Neuroblastoma; Neurons; Nitric Oxide Synthase; Phosphodiesterase Inhibitors; Rats; Rats, Sprague-Dawley; Tumor Cells, Cultured

We investigated the effects of lithium ion (Li+) on muscarinic receptor-mediated nitric oxide (NO) generation, and guanylate cyclase (GCase) activation using the mouse neuroblastoma clone, N1E-115. The levels of released NO were determined by measuring the levels of nitrite/nitrate in the incubation medium, and the activity of GCase was measured with an assay for cellular cyclic [3H] GMP levels. We determined that Li+ had no effects on muscarinic receptor-activated elevation of nitrite/nitrate levels, which were significantly inhibited by 100 microM L-NG-monomethylarginine, although it has been reported that Li+ inhibits muscarinic receptor-activated cyclic GMP formation in the cells. In addition, Li+ inhibited the cyclic GMP formation induced by an NO donor, sodium nitroprusside (SNP), in both intact cells and a crude cellular homogenate; thus, the inhibition by Li+ of muscarinic receptor-mediated cyclic GMP synthesis appeared to be at the level of GCase, but not NO synthase.

Topics: Animals; Arginine; Brain Neoplasms; Carbachol; Cyclic GMP; Guanylate Cyclase; Lithium; Mice; Muscarinic Antagonists; Neuroblastoma; Nitric Oxide; Nitroprusside; omega-N-Methylarginine; Tumor Cells, Cultured

Specific high-affinity binding sites (dissociation constant 100 pmol/l) for atrial natriuretic peptide (ANP) have been identified in the clone D384 derived from the human astrocytoma cell line G-CCM. Unrelated peptides such as angiotensin II, vasopressin and bradykinin did not compete for these sites. Of the atrial natriuretic peptides studied, both the human and rat ANP competed equally, while peptides with either C- or N-terminal residue missing or with no internal -S-S-bond either competed less effectively or did not compete at all. Human ANP stimulated the cells to increase their intracellular level of cyclic GMP in a time- and dose-dependent manner with maximum stimulation being approached but not reached at concentrations of 1 mumol/l. These results support both the notion that ANP has an important functional role within the brain and the concept of neurotransmitter/neuromodulator communication between neurones and glia.

Topics: Astrocytoma; Atrial Natriuretic Factor; Binding Sites; Brain Neoplasms; Cyclic GMP; Humans; Receptors, Atrial Natriuretic Factor; Receptors, Cell Surface; Tumor Cells, Cultured

The effects of cyclic nucleotides, dibutyryl cyclic adenosine monophosphate and dibutyryl cyclic guanosine monophosphate (db-cAMP and db-cGMP), on the growth rate of multicellular tumour spheroids were evaluated by comparing the growth delay and colony forming efficiency in vitro. Multicellular tumour spheroids were derived directly from human brain tumours. To compare the chemotherapeutic effect of cyclic nucleotides, CCNU was used as a known effective cytotoxic drug on malignant gliomas. Significant growth delay was obtained by db-cAMP (p less than 0.001) while CCNU was tumouricidal rather then producing a delay in growth of the tumour spheroids. Db-cGMP found not to be effective in decreasing the growth rate of the tumour spheroids in vitro (p greater than 0.2). The role of cyclic nucleotides in brain tumours is discussed on a review basis.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Adult; Brain Neoplasms; Bucladesine; Cell Membrane; Cell Survival; Child; Cyclic AMP; Cyclic GMP; Humans; Male; Middle Aged

It has been shown recently that astroglial cells of the mammalian CNS possess receptors for neurotransmitters. In order to analyze what sequences of cellular events occur upon activation of these glial receptors, we utilized a 5-HT receptor in a rat clonal cell of glial origin as a model system. When the C6BU-1 glioma cells were exposed to 5-HT, the cytosolic Ca2+ concentration ([Ca2+]i) was elevated and the cellular content of cGMP was increased in a dose-dependent manner. 5-HT receptor antagonists and a Ca2+ entry blocker suppressed the increases in both [Ca2+]i and cGMP. The magnitude of the cGMP increment depended on the environmental Ca2+ concentration and was totally blocked by Ca2+ depletion. Application of a Ca2+ ionophore increased [Ca2+]i and cGMP. There was a tendency for extremely high [Ca2+]i to suppress the cGMP increment. On the contrary, membrane-permeable cyclic nucleotide analogs failed to increase [Ca2+]i. These results suggest that the following sequence of events occurs in 5-HT-induced C6BU-1 cells: activation of 5-HT receptors, Ca2+ influx, a rise in [Ca2+]i, activation of guanylate cyclase, and, finally, activation of cyclic nucleotide phosphodiesterase.

Topics: Animals; Astrocytes; Brain Neoplasms; Calcium; Calcium Channel Blockers; Clone Cells; Cyclic GMP; Cytosol; Dose-Response Relationship, Drug; Ethers; Glioma; Ionomycin; Nucleotides, Cyclic; Rats; Serotonin; Serotonin Antagonists; Time Factors

It is well known that the system of cyclic nucleotides plays an important role in cell differentiation and proliferation. Cyclic AMP is capable of stimulating cell growth, and cyclic GMP is thought to control cell division and growth. The authors measured adenylcyclase activity (AC) and cGMP content in the tumor latency period and in early neoplastic proliferations in rats with brain tumors induced by transplacental ethylnitrosourea (ENU). AC activity, which is high during the first days of life, decreases until it reaches, at the 60th day, levels lower than those in control animals. Cyclic GMP, on the contrary, increases during the first month in treated animals and remains consistently higher than controls up to the 45th day. In fully developed experimental brain tumors (mixed gliomas, isomorphic and polymorphic oligodendrogliomas) the percentage of reduction in AC activity is significantly higher. AC activity was measured also in human tumoral tissue. In malignant tumors it is markedly lower than in benign tumors. In the same patients cAMP in the cerebrospinal fluid was measured with results similar to those obtained in tissues. These findings confirm that the system of cyclic nucleotides is implicated in all the developmental phases of brain tumors and therefore may reveal how research can clarify the first transformations of tumoral cells.

Topics: Adenylyl Cyclases; Animals; Brain; Brain Neoplasms; Cyclic AMP; Cyclic GMP; Humans; Norepinephrine; Rats

The mechanisms of regulation of cyclic AMP phosphodiesterases were studied using the cytoplasmic fraction of PC-12 cells sensitive to the action of nerve growth factor. The cells contain phosphodiesterases of two types. One of them possesses a high affinity for cyclic AMP (Km = 2.46 mM), whereas the other has the affinity by an order worse (Km = 37.1 mM). PC-12 cell differentiation under the action of nerve growth factor is connected with the cyclic nucleotide elevation; however, activities of both phosphodiesterases remain unchanged. This indicates that the regulation of activity of these enzymes in PC-12 cells is mediated by second messenger effects. The main object of cell regulation is phosphodiesterase with low affinity for the substrate. Its activity is modulated by the calmodulin-Ca2+ complex, cyclic GMP and NAD+ at micromolar concentrations. The effect on the phosphodiesterase system of both a "quick" messenger, Ca2+ and "slow" messengers, cyclic GMP and NAD+, has the same consequences: the turnover number of the enzymic reaction increases that is accompanied by a proportional decrease in the enzyme affinity for cyclic AMP so that the ratio Vmax/Km remains constant. A possible explanation of functional significance of such an activity modulation may be the necessity to maintain the conditions for phosphodiesterase functioning when Km much greater than [cyclic AMP] and the reaction rate are directly proportional to the substrate concentration: v = Vmax/Km [cyclic AMP]. Then the cells are transferred into such a mode when autoregulation of the cyclic nucleotide level takes place. Besides the transient effects causing changes in phosphodiesterase activity, studies of PC-12 cells revealed a chronic effect of phosphodiesterase activity change under the action of staphylococcal enterotoxin A. This protein which induces differentiation of PC-12 cells and possesses a NAD+-glycohydrolase activity is translocated into cytoplasm of cells in the presence of NAD+ and accomplishes ADP-ribosylation of phosphodiesterase. As a result, the enzyme activity falls, cyclic AMP level increases and cell differentiation starts. The activity of soluble phosphodiesterase of PC-12 cells also decreases under the effect of two neurotoxins from bee venom, melittin and tertiapin. Both the toxins at concentration of 10 microM completely block calcium regulation of the enzyme. The mechanism of tertiapin action was investigated on a model system of calmodulin-bovine brain phosphodi

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Animals; Bee Venoms; Brain Neoplasms; Calmodulin; Cell Line; Cyclic AMP; Cyclic GMP; Cytoplasm; Enzyme Activation; Models, Biological; Nerve Growth Factors; Pheochromocytoma; Rats

The biochemical characteristics of the protein kinase (PK; adenosine triphosphate-protein phosphotransferase, EC 2.7.1.37) isozymes in subcellular preparations from normal human brain cortex and glioblastoma were investigated after chromatography on diethylaminoethyl cellulose, and the following results have been obtained. Two major isozyme forms, eluted by 50 and 200 mM phosphate buffer, are present in both cytosol and membrane-derived preparations from cerebral cortex. Furthermore, these isozyme forms have properties similar to those referred to as type I and type II cyclic adenosine 3':5'-monophosphate-dependent PK. In these chromatographic isozymes, cyclic adenosine 3';5'-monophosphate is more active in stimulating the basal PK enzyme than is cyclic guanosine 3':5'-monophosphate. In glioblastoma, the PK activity from cytosol and particulate preparations is resolved by diethylaminoethyl cellulose in four peaks. In cytosol, the major portion of the enzyme is eluted with a 300 mM buffer (about 50% of the total basal PK activity) and is cyclic nucleotide dependent. On the contrary, in glioblastoma particulate, the PK enzyme is mainly eluted at 50 and 100 mM buffer; neither of these isozymes is cyclic nucleotide dependent. As for cytosol, only the particulate isozyme eluted at 300 mM buffer is strongly activated by cyclic nucleotides. Finally, in both glioblastoma subcellular preparations, only a type II cyclic adenosine 3':5'-monophosphate-dependent PK is present.

Topics: Brain; Brain Neoplasms; Chromatography, DEAE-Cellulose; Cyclic AMP; Cyclic GMP; Glioma; Humans; Isoenzymes; Protein Kinases; Subcellular Fractions

Since the cyclic nucleotides (CN) adenosine 3',5'-monophosphate (cAMP) and guanoside 3',5'-monophosphate (cGMP) are involved in the regulation of cell proliferation and tumor growth in vitro, a study was made of the levels of these compounds in the lumbar cerebrospinal fluid (CSF) of 20 patients with intracranial and spinal tumors. In the presence of benign or malignant intracranial tumors there was a slight and not significant decrease of cAMP as well as cGMP levels in the CSF, as compared to control patients. While there was no significant correlation between the levels of the two CN in controls, there was a positive correlation in tumor patients. Total protein content and cAMP were negatively correlated in malignant intracranial tumors. Possible influences of tumor growth and intracranial pressure increases on CN levels are discussed. In spinal tumor patients normal CN levels were observed. However, in a patient with meningeal sarcoma an extremely marked elevation of cAMP occurred in parallel with the extension of the tumor to the spinal meningeal space, suggesting massive secretion of cAMP from the tumor cells.

Topics: Adolescent; Adult; Aged; Brain Neoplasms; Cyclic AMP; Cyclic GMP; Female; Humans; Male; Meningeal Neoplasms; Middle Aged; Sarcoma; Spinal Neoplasms

Topics: Brain Neoplasms; Cyclic AMP; Cyclic GMP; Cysts; Humans; Isoenzymes; L-Lactate Dehydrogenase

Topics: Arginine; Brain Chemistry; Brain Neoplasms; Cyclic AMP; Cyclic GMP; Humans; Thiazoles; Thiazolidines

Recent advances indicate that cyclic nucleotides and perhaps certain adrenergic metabolites might be directly involved in contact-inhibition mechanisms and tumoral cell growth. CSF levels of 3'-5' cAMP, 3'-5' cGMP, HVA, and 5-HIAA were investigated in patients with supratentorial malignant gliomas, brain stem gliomas and posterior fossa medulloblastoma. cAMP levels were slightly decreased only in medulloblastomas, whereas no significant difference was detectable in patients with supratentorial gliomas. cGMP values turned out to be significantly higher, with a very peculiar increase in the most anaplastic neoplasms. Postoperative follow-up showed a gradual decrease of cGMP values, with progressive restoring of a normal cAMP/cGMP ratio. The possible correlation of these findings with CSF levels of HVA and 5-HIAA is discussed.

Topics: Adult; Aged; Blood-Brain Barrier; Brain Neoplasms; Brain Stem; Cranial Fossa, Posterior; Cyclic AMP; Cyclic GMP; Female; Glioma; Homovanillic Acid; Humans; Hydroxyindoleacetic Acid; Male; Medulloblastoma; Middle Aged; Phenylacetates

Topics: Astrocytoma; Brain Neoplasms; Cyclic AMP; Cyclic GMP; Glioblastoma; Glioma; Humans; Meningeal Neoplasms; Meningioma

Recent evidence indicates that cyclic nucleotides are of importance for general and neurosurgical oncology, especially with respect to the contact-inhibition mechanisms and tumour cell growth. This preliminary report deals with the CSF levels of c-AMP and c-GMP in primary neoplasms in children and to problems related to the blood-brain barrier. Some cases of medulloblastoma were studied as well as a few cases of brain stem glioma and cystic astrocytoma. The importance of some rather unusual findings seems undebatable, i.e., the marked increase in c-GMP values usually observed in medulloblastoma and the decrease of c-AMP, that is fairly common in all malignant neoplasms. The main changes in the c-AMP/c-GMP ratio are also discussed.

Topics: Astrocytoma; Blood-Brain Barrier; Brain Neoplasms; Brain Stem; Cerebellar Neoplasms; Child; Child, Preschool; Cyclic AMP; Cyclic GMP; Glioma; Humans; Infant; Medulloblastoma

Since the effects of cyclic nucleotides are mediated via protein kinases activation, we have studied the properties and regulation of these enzymes in cytosol and particulate fraction of normal cerebral tissues and of some human brain tumors. We found that distribution and activity of cyclic nucleotide-dependent protein kinases are regulated differently among various brain tumors and in comparison to normal gray and white matter. Pathological tissues show an higher cGMP-dependent protein kinase and this biochemical pattern is particularly evident in tumors with more pronounced malignancy. These data further confirm the hypothesis of a correlation between the increase of cGMP function and cellular growth and malignancy.

Topics: Astrocytoma; Brain Neoplasms; Cyclic AMP; Cyclic GMP; Cytosol; Glioma; Humans; Kinetics; Neurilemmoma; Protein Kinases

Cyclic 3-5-adenosine-monophosphate and 3-5-guanosinemonophosphate concentrations were studied in the bioptate of brain tumors, examined during neurosurgical operation and in normal brain tissues. The correlations between cyclic nucleotides in the tumors appeared to be significantly decreased in comparison to the intact tissue, being a characteristic signs for all types of tumors. There were significant fluctuations in the level of cyclic nucleotides both in the tumours and nontumorous brain tissues. There were no correlations found between the level of cyclic adenosine-monophosphate and cyclic guanosine-monophosphate on the one hand and the duration of the disease, localization of the tumor, degree of the brain oedema and the type of narcosis on the other.

Topics: Adult; Arachnoid; Astrocytoma; Brain Neoplasms; Cerebellar Neoplasms; Cyclic AMP; Cyclic GMP; Female; Frontal Lobe; Humans; Male; Meningeal Neoplasms; Meningioma; Middle Aged; Parietal Lobe

Topics: Aging; Animals; Brain; Brain Neoplasms; Cell Division; Cerebellum; Cyclic GMP; Guanylate Cyclase; Humans; In Vitro Techniques; Kinetics; Rats

Cyclic guanosine monophosphate (cGMP) levels have been measured in the cerebrospinal fluid of patients with various neurological diseases. The subjects with epilepsy or cerebrovascular diseases do not show any difference from the controls. Moreover, in the CSF of patients having cerebral tumors the levels of cGMP are markedly increased. This change is in line with previous in vitro studies on the increase of cGMP during cell growth and cell proliferation showing that the role of the nucleotide is important for the control of the life cycle of the cell.

Topics: Adolescent; Adult; Aged; Alzheimer Disease; Brain Neoplasms; Cerebrovascular Disorders; Cyclic GMP; Epilepsy; Female; Humans; Hydrocephalus, Normal Pressure; Male; Middle Aged; Multiple Sclerosis

Several reports have suggested that cylcic guanosine 3'-5' monophosphate (cGMP) and cyclic 3'-5' adenosine monophosphate (cAMP) are involved in the regulation of cellular proliferation. Following our previous reports on the cAMP system in human brain tumors, we decided to investigate the cGMP system in the same pathological tissues by studying the activity of guanylate cyclase and cGMP-phosphodiesterase (cGMP-PDE). We found that the activity of both enzymes is lower in neurinomas and glioblastomas than in meningiomas or in normal cerebral cortex. Furthermore, the subcellular distribution of guanylate cyclase in human cerebral cortex differs from that of neurinomas and glioblastomas. On the basis of such observations we have discussed the possibility that the regulatory mechanism of the enzymes related to the cyclic nucleotide metabolism is altered in brain tumors.

Topics: Brain Neoplasms; Cerebral Cortex; Cyclic GMP; Glioma; Guanosine; Guanylate Cyclase; Humans; Meningioma; Neurilemmoma; Phosphoric Diester Hydrolases