In-vitro characterization of YM872, a selective, potent and highly water-soluble alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor antagonist

Structure-Activity Relationship and Solubility Studies of N1-Substituted Quinoxaline-2,3-diones as Kainate Receptor Antagonists

Kainate receptors are a class of ionotropic glutamate receptors that respond to the excitatory neurotransmitter glutamate in the central nervous system and play an important role in the development of neurodegenerative disorders and the regulation of synaptic function. In the current study, we investigated the structure- activity relationship of the series of quinoxaline-2,3-diones substituted at N1, 6, and 7 positions, as ligands of kainate homomeric receptors GluK1-3 and GluK5. Pharmacological characterization showed that all derivatives obtained exhibited micromolar affinity at GluK3 receptors with Ki values in the range 0.1-4.4 μM range. The antagonistic properties of the selected analogues: N-(7-fluoro-6-iodo-2,3-dioxo-3,4-dihydroquinoxalin-1(2H)-yl)-3-sulfamoylbenzamide, N-(7-(1H-imidazol-1-yl)-6-iodo-2,3-dioxo-3,4-dihydroquinoxalin-1(2H)-yl)-3-sulfamoylbenzamide and N-(7-(1H-imidazol-1-yl)-2,3-dioxo-6-(phenylethynyl)-3,4-dihydroquinoxalin-1(2H)-yl)-3-sulfamoylbenzamide at GluK3 receptors, were confirmed by an intracellular calcium imaging assay. To correlate in vitro affinity data with structural features of the synthesized compounds and to understand the impact of the substituent in N1 position on ability to form additional protein-ligand interactions, molecular modeling and docking studies were carried out. Experimental solubility studies using UV spectroscopy detection have shown that 7-imidazolyl-6-iodo analogues with a sulfamoylbenzamide moiety at the N1 position are the best soluble compounds in the series, with molar solubility in TRISS buffer at pH 9 more than 3-fold higher compared to NBQX, a known AMPA/kainate antagonist.

Kainate Receptor Antagonists: Recent Advances and Therapeutic Perspective

Since the 1990s, ionotropic glutamate receptors have served as an outstanding target for drug discovery research aimed at the discovery of new neurotherapeutic agents. With the recent approval of perampanel, the first marketed non-competitive antagonist of AMPA receptors, particular interest has been directed toward 'non-NMDA' (AMPA and kainate) receptor inhibitors. Although the role of AMPA receptors in the development of neurological or psychiatric disorders has been well recognized and characterized, progress in understanding the function of kainate receptors (KARs) has been hampered, mainly due to the lack of specific and selective pharmacological tools. The latest findings in the biology of KA receptors indicate that they are involved in neurophysiological activity and play an important role in both health and disease, including conditions such as anxiety, schizophrenia, epilepsy, neuropathic pain, and migraine. Therefore, we reviewed recent advances in the field of competitive and non-competitive kainate receptor antagonists and their potential therapeutic applications. Due to the high level of structural divergence among the compounds described here, we decided to divide them into seven groups according to their overall structure, presenting a total of 72 active compounds.

Enabling dual cellular destinations of polymeric nanoparticles for treatment following partial injury to the central nervous system

Following neurotrauma, oxidative stress is spread via the astrocytic syncytium and is associated with increased aquaporin 4 (AQP4), inflammatory cell infiltration, loss of neurons and glia and functional deficits. Herein we evaluate multimodal polymeric nanoparticles functionalized with an antibody to an extracellular epitope of AQP4, for targeted delivery of an anti-oxidant as a therapeutic strategy following partial optic nerve transection. Using fluorescence microscopy, spectrophotometry, correlative nanoscale secondary ion mass spectrometry (NanoSIMS) and transmission electron microscopy, in vitro and in vivo, we demonstrate that functionalized nanoparticles are coated with serum proteins such as albumin and enter both macrophages and astrocytes when administered to the site of a partial optic nerve transection in rat. Antibody functionalized nanoparticles synthesized to deliver the antioxidant resveratrol are effective in reducing oxidative damage to DNA, AQP4 immunoreactivity and preserving visual function. Non-functionalized nanoparticles evade macrophages more effectively and are found more diffusely, including in astrocytes, however they do not preserve the optic nerve from oxidative damage or functional loss following injury. Our study highlights the need to comprehensively investigate nanoparticle location, interactions and effects, both in vitro and in vivo, in order to fully understand functional outcomes.

Synthesis, structure-activity relationships, and anticonvulsant activities of 2-amino-4H-pyrido[3,2-e][1,3]thiazin-4-one derivatives as orally active AMPA receptor antagonists

As part of a program aimed at discovering orally active 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptor antagonists, we screened our compound library and identified 2-[allyl(4-methylphenyl)amino]-4H-pyrido[3,2-e][1,3]thiazin-4-one (7) as a lead compound that inhibited kainate-induced neurotoxicity mediated by AMPA receptors in rat hippocampal cultures. Structure-activity relationship studies of a series of 2-amino-4H-pyrido[3,2-e][1,3]thiazin-4-one derivatives revealed that substituents on the phenyl ring attached to the 2-amino group and the 4H-pyrido[3,2-e][1,3]thiazin-4-one ring system play an important role in inhibitory activity against kainate-induced neurotoxicity. Several analogs bearing a phenyl group with a 4-substituent or five- or six-membered ring fused at the 3,4-positions exhibited potent inhibitory activity against kainate-induced neurotoxicity. Further, some of these compounds exhibited significant suppression of maximal electroshock seizure in mice following oral administration. Of these compounds, 2-[(4-chlorophenyl)(methyl)amino]-4H-pyrido[3,2-e][1,3]thiazin-4-one (16i) (YM928) demonstrated the most potent inhibitory effect with an ED50 value of 7.4mg/kg.

Neuroprotective effects of compounds with antioxidant and anti-inflammatory properties in a Drosophila model of Parkinson's disease

Background

Parkinson's disease (PD) is the most common movement disorder. Extrapyramidal motor symptoms stem from the degeneration of the dopaminergic pathways in patient brain. Current treatments for PD are symptomatic, alleviating disease symptoms without reversing or retarding disease progression. Although the cause of PD remains unknown, several pathogenic factors have been identified, which cause dopaminergic neuron (DN) death in the substantia nigra (SN). These include oxidative stress, mitochondrial dysfunction, inflammation and excitotoxicity. Manipulation of these factors may allow the development of disease-modifying treatment strategies to slow neuronal death. Inhibition of DJ-1A, the Drosophila homologue of the familial PD gene DJ-1, leads to oxidative stress, mitochondrial dysfunction, and DN loss, making fly DJ-1A model an excellent in vivo system to test for compounds with therapeutic potential.

Results

In the present study, a Drosophila DJ-1A model of PD was used to test potential neuroprotective drugs. The drugs applied are the Chinese herb celastrol, the antibiotic minocycline, the bioenergetic amine coenzyme Q10 (coQ10), and the glutamate antagonist 2,3-dihydroxy-6-nitro-7-sulphamoylbenzo[f]-quinoxaline (NBQX). All of these drugs target pathogenic processes implicated in PD, thus constitute mechanism-based treatment strategies. We show that celastrol and minocycline, both having antioxidant and anti-inflammatory properties, confer potent dopaminergic neuroprotection in Drosophila DJ-1A model, while coQ10 shows no protective effect. NBQX exerts differential effects on cell survival and brain dopamine content: it protects against DN loss but fails to restore brain dopamine level.

Conclusion

The present study further validates Drosophila as a valuable model for preclinical testing of drugs with therapeutic potential for neurodegenerative diseases. The lower cost and amenability to high throughput testing make Drosophila PD models effective in vivo tools for screening novel therapeutic compounds. If our findings can be further validated in mammalian PD models, they would implicate drugs combining antioxidant and anti-inflammatory properties as strong therapeutic candidates for mechanism-based PD treatment.

Antinociceptive profile of a selective metabotropic glutamate receptor 1 antagonist YM-230888 in chronic pain rodent models

Metabotropic glutamate receptor 1 (mGlu(1) receptor) has been suggested to play an important role in pain transmission. In this study, the effects of a newly-synthesized mGlu(1) receptor antagonist, (R)-N-cycloheptyl-6-({[(tetrahydro-2-furyl)methyl]amino}methyl)thieno[2,3-d]pyrimidin-4-ylamine (YM-230888), were examined in a variety of rodent chronic pain models in order to characterize the potential analgesic profile of mGlu(1) receptor blockade. YM-230888 bound an allosteric site of mGlu(1) receptor with a K(i) value of 13+/-2.5 nM and inhibited mGlu(1)-mediated inositol phosphate production in rat cerebellar granule cells with an IC(50) value of 13+/-2.4 nM. It showed selectivity for mGlu(1) versus mGlu(2)-mGlu(7) subtypes and ionotropic glutamate receptors. YM-230888 recovered mechanical allodynia with an ED(50) value of 8.4 mg/kg p.o. in L5/L6 spinal nerve ligation models. It also showed antinociceptive response at doses of 10 and 30 mg/kg p.o. in streptozotocin-induced hyperalgesia models. In addition, it significantly reduced pain parameters at a dose of 30 mg/kg p.o. in complete Freund's adjuvant-induced arthritic pain models. Although YM-230888 showed no significant effect on rotarod performance time at doses of 10 or 30 mg/kg p.o., it significantly decreased it at a dose of 100 mg/kg p.o. On the other hand, YM-230888 showed no significant sedative effect in locomotor activity measurement up to 100 mg/kg p.o. These results suggest that the blockade of mGlu(1) receptors is an attractive target for analgesics. YM-230888 has potential as a new analgesic agent for the treatment of various chronic pain conditions. In addition, YM-230888 may be a useful tool for the investigation of mGlu(1) receptors.

Ca2+-permeable AMPA receptors regulate growth of human glioblastoma via Akt activation

Evidence has been accumulated that glioblastoma cells release and exploit glutamate for proliferation and migration by autocrine or paracrine loops through Ca2+-permeable AMPA-type glutamate receptors. Here, we show that Ca2+ signaling mediated by AMPA receptor regulates the growth and motility of glioblastoma cells via activation of Akt. Ca2+ supplied through Ca2+-permeable AMPA receptor phosphorylated Akt at Ser-473, thereby facilitating proliferation and mobility. A dominant-negative form of Akt inhibited cell proliferation and migration accelerated by overexpression of Ca2+-permeable AMPA receptor. In contrast, introduction of a constitutively active form of Akt rescued tumor cells from apoptosis induced by the conversion of Ca2+-permeable AMPA receptor to Ca2+-impermeable receptors by the delivery of GluR2 cDNA. Therefore, Akt functions as downstream effectors for Ca2+-signaling mediated by AMPA receptor in glioblastoma cells. The activation of the glutamate-AMPA receptor-Akt pathway may contribute to the high degree of anaplasia and invasive growth of human glioblastoma. This novel pathway might give an alternative therapeutic target.

Water soluble RNA based antagonist of AMPA receptors

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are one of the important receptor classes involved in glutamate-mediated excitotoxicity. Although small molecule antagonists of this receptor have been shown to have neuroprotective properties, their low solubilities pose severe side effects in clinical trials. Here we have used the SELEX method to obtain water-soluble nuclease-resistant RNA ligands that bind to the agonist binding site of AMPA receptors. Using whole-cell current recordings, we have characterized the functional consequences of a representative aptamer from this class and show that it is a competitive antagonist of AMPA receptors and in the concentration range where it acts as an inhibitor of the AMPA receptor the RNA has no effect on the GluR6 homomeric kainate receptors. Additionally, using a fluorescence resonance energy transfer (FRET) probe, we show that this RNA ligand stabilizes the open cleft conformation of the ligand binding domain, consistent with the known structures of small antagonist-bound states of the soluble domain of this protein. Finally, using rat primary cortical neurons, we show that this RNA ligand significantly reduces neurotoxicity associated with oxygen glucose deprivation. The water-soluble and antagonistic properties of this aptamer coupled with its neuroprotective properties make it an excellent candidate for potential use in diseases or pathological conditions involving glutamate-mediated excitotoxicity.

Competitive AMPA receptor antagonists

Glutamic acid (Glu) is the major excitatory neurotransmitter in the mammalian central nervous system (CNS) where it is involved in the physiological regulation of different processes. It has been well established that excessive endogenous Glu is associated with many acute and chronic neurodegenerative disorders such as cerebral ischaemia, epilepsy, amiotrophic lateral sclerosis, Parkinson's, and Alzheimer's disease. These data have consequently added great impetus to the research in this field. In fact, many Glu receptor antagonists acting at the N-methyl-D-aspartic acid (NMDA), 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA), and/or kainic acid (KA) receptors have been developed as research tools and potential therapeutic agents. Ligands showing competitive antagonistic action at the AMPA type of Glu receptors were first reported in 1988, and the systemically active 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo[f]quinoxaline (NBQX) was first shown to have useful therapeutic effects in animal models of neurological disease in 1990. Since then, the quinoxaline template has represented the backbone of various competitive AMPA receptor antagonists belonging to different classes which had been developed in order to increase potency, selectivity and water solubility, but also to prolong the "in vivo" action. Compounds that present better pharmacokinetic properties and less serious adverse effects with respect to the others previously developed are undergoing clinical evaluation. In the near future, the most important clinical application for the AMPA receptor antagonists will probably be as neuroprotectant in neurodegenerative diseases, such as epilepsy, for the treatment of patients not responding to current therapies. The present review reports the history of competitive AMPA receptor antagonists from 1988 up to today, providing a systematic coverage of both the open and patent literature.

Effect of YM872, a selective and highly water-soluble AMPA receptor antagonist, in the rat kindling and rekindling model of epilepsy

We examined antiepileptogenic and anticonvulsant effects of [2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl]-acetic acid monohydrate (YM872), a potent and highly water-soluble alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptor antagonist, in the rat amygdala kindling model of epilepsy. Administration of YM872 significantly suppressed fully kindled seizures. Daily pretreatment with YM872 markedly retarded development of kindling during drug sessions. We also used the rekindling method to investigate the antiepileptogenic effect of YM872 in an attempt to differentiate between true and false effects in the conventional method of daily administration. The results using the rekindling method suggested that the effect of YM872 was truly antiepileptogenic, indicating its possible clinical usefulness as an antiepileptogenic drug. We also affirmed the importance of AMPA receptors in the seizure expression mechanism and development of kindling-induced epileptogenesis.

Ionotropic and metabotropic glutamate receptor structure and pharmacology

RATIONALE

L: -Glutamate is the major excitatory neurotransmitter in the central nervous system (CNS) and mediates its actions via activation of both ionotropic and metabotropic receptor families. The development of selective ligands, including competitive agonists and antagonists and positive and negative allosteric modulators, has enabled investigation of the functional roles of glutamate receptor family members.

OBJECTIVE

In this review we describe the subunit structure and composition of the ionotropic and metabotropic glutamate receptors and discuss their pharmacology, particularly with respect to selective tools useful for investigation of their function in the CNS.

RESULTS

A large number of ligands are now available that are selective either for glutamate receptor subfamilies or for particular receptor subtypes. Such ligands have enabled considerable advances in the elucidation of the physiological and pathophysiological roles of receptor family members. Furthermore, efficacy in animal models of neurological and psychiatric disorders has supported the progression of several glutamatergic ligands into clinical studies. These include ionotropic glutamate receptor antagonists, which have entered clinical trials for disorders including epilepsy and ischaemic stroke, alpha-amino-3-hydroxy-5-methyl-4-isoazolepropionic acid (AMPA) receptor positive allosteric modulators which are under evaluation as cognitive enhancers, and metabotropic glutamate receptor 2 (mGluR2) agonists which are undergoing clinical evaluation as anxiolytics. Furthermore, preclinical studies have illustrated therapeutic potential for ligands selective for other receptor subtypes in various disorders. These include mGluR1 antagonists in pain, mGluR5 antagonists in anxiety, pain and drug abuse and mGluR5 positive allosteric modulators in schizophrenia.

CONCLUSIONS

Selective pharmacological tools have enabled the study of glutamate receptors. However, pharmacological coverage of the family is incomplete and considerable scope remains for the development of novel ligands, particularly those with in vivo utility, and for the their use together with existing tools for the further investigation of the roles of receptor family members in CNS function and as potentially novel therapeutics.

Functional characterization of YM928, a novel moncompetitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist

The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor is thought to play an important role in the pathogenesis of several neurological disorders as well as normal brain function. The search for AMPA receptor antagonists as potential therapeutics is ongoing. Here, we describe the functional characterization of a novel noncompetitive AMPA receptor antagonist, 2-[N-(4-chlorophenyl)-N-methylamino]-4H-pyrido[3,2-e]-1,3-thiazin-4-one (YM928). This compound inhibited AMPA receptor-mediated toxicity in primary rat hippocampal cultures with an IC50 of 2 micro M. Its manner of inhibition was noncompetitive as the agonist concentration was increased. YM928 blocked AMPA-induced intracellular calcium influx with an IC50 of 3 micro M and antagonized AMPA-induced inward currents with an IC50 of 1 micro M in cultured cells. YM928 displaced neither [3H]AMPA binding nor other existing glutamate receptor-related ligand binding in rat brain membranes. In terms of in vivo activity, YM928 had an anticonvulsant effect in sound-induced seizures in DBA/2 mice 45 min after oral administration at 3 mg/kg. Thus, YM928 has potential as an oral therapeutic drug for various types of neurological disorders.

Effect of AMPA receptor antagonist YM872 on cerebral hematoma size and neurological recovery in the intracerebral hemorrhage rat model

[2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl]-acetic acid monohydrate (YM872 or zonampanel), an AMPA receptor antagonist, is in clinical development for acute ischemic cerebral infarction. Stroke patients are prone to have subsequent intracerebral hemorrhages. In order to predict potential adverse effects, YM872 was tested in a rat model with collagenase-induced intracerebral hemorrhage. The morphologically determined hematoma volumes after 24 h were compared between animal groups intravenously infused with 3600 U/kg/h heparin for 30 min, or with 20 or 40 mg/kg/h of YM872, or placebo for 4 h. Heparin enlarged hematoma volume, but neither dose of YM872 affected hematoma size. In a separate study, neurological deficits were scored at various days after intracerebral hemorrhage induction in animals with intravenous infusion for 24 h of 10 or 20 mg/kg/h YM872, or saline. The YM872 groups scored significantly better than the saline group at 14 days. These data suggest that YM872 does not exacerbate intracerebral hemorrhage and might accelerate recovery.

DOPA cyclohexyl ester potently inhibits aglycemia-induced release of glutamate in rat striatal slices

Brain ischemic insult causes glutamate release and resultant neuronal cell death. We here show that L-3,4-dihydroxyphenylalanine (DOPA) is a positive regulatory factor for glutamate release elicited by a mild brain insult using in vitro superfused rat striatal slices as a model system. Glucose deprivation for 18 min elicited release of glutamate, DOPA and dopamine (DA). Either tetrodotoxin (TTX) (1 microM) or alpha-methyl-p-tyrosine (alpha-MPT) (1 mM), a tyrosine hydroxylase inhibitor reduced markedly each of these releases. NSD-1015 (20 microM), an aromatic L-amino acid decarboxylase inhibitor restored the inhibition by alpha-MPT of glutamate and DOPA but not DA release. DOPA cyclohexyl ester (DOPA CHE) (0.3-1 microM), a competitive DOPA antagonist, concentration-dependently suppressed aglycemia-induced glutamate release, the effect which was mimicked neither by S-sulpiride nor SCH23390, a DA D(1) or D(2) receptor antagonist, respectively. Zonisamide (1-1000 microM), an anticonvulsant or YM872 (1 microM), an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) a receptor antagonist produced no effect on aglycemia-induced glutamate release. DOPA CHE thus showed a relatively potent inhibitory action on aglycemia-induced glutamate release among several neuroprotective agents tested.

The glutamate AMPA receptor antagonist, YM872, attenuates cortical tissue loss, regional cerebral edema, and neurological motor deficits after experimental brain injury in rats

A massive increase in extracellular glutamate is thought to contribute to brain damage after traumatic brain injury. We examined the neuroprotective effect of the AMPA receptor antagonist YM872 in a rat head injury model using the fluid-percussion procedure. Male Sprague-Dawley rats were subjected to right lateral (parasagittal) fluid-percussion brain injury or sham injury. At 15 min postinjury, they received either YM872 (20 mg/kg/h, 20 mg/3 mL) or normal saline (vehicle) intravenously for 4 h. The administration of YM872 significantly improved the composite neuroscore at 1 and 2 weeks postinjury (p < 0.05), and markedly reduced the volume of tissue loss in the injured cortex (p < 0.05). It also significantly reduced cerebral edema in the ipsilateral parietal cortex at 48 h postinjury (p < 0.01). These results indicate that the posttraumatic administration of YM872 may be neuroprotective by ameliorating cortical tissue loss and regional cerebral edema, and suggest the importance of AMPA receptors in traumatic brain damage involving secondary injury processes.

Neuroprotective effects of YM872 coadministered with t-PA in a rat embolic stroke model

YM872, an AMPA receptor antagonist, was administered together with t-PA to investigate the effects of coadministration on neuroprotection in a rat embolic stroke model, when administered 2 h after embolism. T-PA or YM872 alone decreased infarct volume and improved the neurological deficit score. Coadministration of YM872 and t-PA resulted in a further decrease in infarct volume and improvement of the neurological score as compared with single administration of t-PA. These data demonstrate that coadministration of YM872 and t-PA produces more potent neuroprotective effects than when t-PA is administered alone.

YM872: a selective, potent and highly water-soluble alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist

This review focuses on the in vitro and in vivo neuropharmacology of YM872, a potential neuroprotective agent currently undergoing clinical trials in the United States (trial name: AMPA Receptor Antagonist Treatment in Ischemic Stroke - ARTIST). Its neuroprotective properties in rats and cats with induced focal cerebral ischemia are described. YM872, [2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydroquinoxalin-1-yl]-acetic acid monohydrate, is a selective, potent and highly water-soluble competitive alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist. YM872 has a potent inhibitory effect on [(3)H]AMPA binding with a K(i) value of 0.096 microM. In contrast, YM872 has very low affinity for other ionotropic glutamate receptors. The solubility of YM872 is approximately 500 to 1000 times higher than that of the other competitive AMPA antagonists: YM90K, NBQX, or CNQX. The neuroprotective efficacy of YM872 was investigated in rats and cats subjected to permanent occlusion of the left middle cerebral artery. The animals were assessed either histologically or neurologically following ischemia. In rats with occluded middle cerebral artery (MCAO) YM872, by i.v. infusion, significantly reduced infarct volume measured at 24 h and 1 week after ischemia. Significant neuroprotection was maintained even when drug administration was delayed for up to 2 h after ischemia. In addition, YM872 significantly improved neurological deficit measured at 1 week after ischemia. In cats with MCAO YM872, by i.v. infusion, dose-dependently reduced infarct volume at 6 h after ischemia. YM872 produced no behavioral abnormalities and was not nephrotoxic. The evidence for the neuroprotective efficacy of YM872 suggests its therapeutic potential in the treatment of acute stroke in humans.

Blockage of Ca(2+)-permeable AMPA receptors suppresses migration and induces apoptosis in human glioblastoma cells

Glioblastoma multiforme is the most undifferentiated type of brain tumor, and its prognosis is extremely poor. Glioblastoma cells exhibit highly migratory and invasive behavior, which makes surgical intervention unsuccessful. Here, we showed that glioblastoma cells express Ca(2+)-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type glutamate receptors assembled from the GluR1 and/or GluR4 subunits, and that their conversion to Ca(2+)-impermeable receptors by adenovirus-mediated transfer of the GluR2 cDNA inhibited cell locomotion and induced apoptosis. In contrast, overexpression of Ca(2+)-permeable AMPA receptors facilitated migration and proliferation of the tumor cells. These findings indicate that Ca(2+)-permeable AMPA receptors have crucial roles in growth of glioblastoma. Blockage of these Ca(2+)-permeable receptors may be a useful therapeutic strategy for the prevention of glioblastoma invasion.

Glutamate AMPA receptor antagonist treatment for ischaemic stroke

During cerebral ischaemia, glutamate is released in supraphysiological amounts and is toxic to brain tissue. This excitotoxicity is mediated by several glutamate receptor subtypes, including the ionotropic N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors. Clinical trials of drugs that block the NMDA receptor in acute ischaemic stroke have been disappointing. No improvement in clinical outcome of stroke has been seen with competitive NMDA antagonists (selfotel) and non-competitive NMDA antagonists (dextrorphan, GV150526, aptiganel and eliprodil). The AMPA receptor differs in important ways from the NMDA receptor. It is the principal mediator of fast excitatory neurotransmission. This ligand-gated cation channel is primarily permeable to sodium rather than calcium. It is found in grey and white matter. It is expressed by oligodendrocytes. This distribution may provide neuroprotection for both grey and white matter. In a variety of animal models, reduction in infarct volume with AMPA blockade has been demonstrated. AMPA antagonists also show benefit in spinal cord ischaemia and trauma. The clinical development of safe and effective AMPA blockers has been hampered by poor water solubility and associated renal toxicity. A novel, highly water-soluble, competitive AMPA receptor antagonist, YM872 ([2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydroquinoxalin-1-yl]acetic acid monohydrate; Yamanouchi), has been identified. Phase I clinical trial data indicate that this agent can be safely administered in young and elderly subjects. Sedation and other CNS associated adverse events determine the ceiling dose and become more problematic with infusion times exceeding 24 h. Phase II studies of YM872 in acute ischaemic stroke are ongoing.

The analgesic interaction between intrathecal clonidine and glutamate receptor antagonists on thermal and formalin-induced pain in rats

Clonidine, an alpha(2) adrenergic receptor agonist, inhibits glutamate release from the spinal cord. We studied the interaction of intrathecally administered clonidine and glutamate receptor antagonists on acute thermal or formalin induced nociception. Sprague-Dawley rats with lumbar intrathecal catheters were tested for their tail withdrawal response by the tail flick test and paw flinches produced by formalin injection after intrathecal administration of saline, clonidine, AP-5 (a N-methyl-D-aspartate receptor antagonist), or YM872 (an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist). The combinations of clonidine and the other two agents were also tested by isobolographic analyses. Motor disturbance and behavioral changes were observed as side effects. The ED(50) values of clonidine decreased from 0.26 microg (tail flick), 0.12 microg (Phase 1) and 0.13 microg (Phase 2) to 0.036 microg, 0.006 microg, and 0.013 microg with AP-5, and 0.039 microg, 0.057 microg, and 0.133 microg with YM872, respectively. Side effects were attenuated in both combinations. In conclusion, spinally administered clonidine and AP-5 or YM872 exhibited potent synergistic analgesia on acute thermal and formalin-induced nociception with decreased side effects in rats.

IMPLICATIONS

Combinations of a spinally administered alpha(2) adrenergic receptor agonist and an a N-methyl-D-aspartate receptor antagonist or an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist exhibited potent synergistic analgesia in acute thermal and inflammatory-induced nociception with decreased side effects.

Synergistic analgesic effects of intrathecal midazolam and NMDA or AMPA receptor antagonists in rats

PURPOSE

To investigate the interaction of midazolam and N-methyl-D-aspartate (NMDA) receptor or -amino-3-hydroxy-5-methyl isoxazole-4-propionic acid (AMPA) receptor antagonist on the effects of persistent inflammatory nociceptive activation.

METHODS

Male Sprague-Dawley rats were implanted with lumbar intrathecal catheters and were tested for their responses to subcutaneous formalin injection into the hindpaw. Saline, midazolam (1 to 100 microg), AP-5 (I to 30 microg), a NMDA receptor antagonist, or YM872 (0.3 to 30 microg), an AMPA receptor antagonist was injected intrathecally 10 min before formalin injection. The combinations of midazolam and AP-5 or YM872 in a constant dose ratio based on the 50% effective dose (ED50) were also tested and were analysed with an isobologram.

RESULTS

Dose-dependent effects were observed with midazolam (ED50 was 1.34 microg and 1.21 microg in phase 1 and 2 of the formalin test, respectively), AP-5 (7.64 microg and 1.4 microg) and YM872 (0.24 microg and 0.21 microg). Synergistic effects in both phases were obtained when combining midazolam with AP-5 or YM872. The ED50 of midazolam decreased to 0.012 microg (phase 1) and 0.27 microg (phase 2) with AP-5 and to 0.09 microg (phase 1) and 0.35 microg (phase 2) with YM872 (P < 0.01).

CONCLUSIONS

These results suggest a functional coupling of benzodiazepine-aminobutyric acid (GABA)A receptor with NMDA and AMPA receptors in acute and persistent inflammatory nociceptive mechanisms in the spinal cord.

Neuroprotective effects of an AMPA receptor antagonist YM872 in a rat transient middle cerebral artery occlusion model

The neuroprotective effects of YM872 ([2,3-dioxo-7-(1H-imidazol-1-yl)6-nitro-1,2,3,4-tetrahydro-1-quinoxal inyl]acetic acid monohydrate), a novel alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor antagonist with high water solubility, were examined in rats with transient middle cerebral artery (MCA) occlusion. The right MCA of male SD rats was occluded for 3 h using the intraluminal suture occlusion method. YM872 significantly reduced the infarct volume 24 hours after occlusion, at dosages of 20 and 40 mg/kg/h (iv infusion) when given for 4 h immediately after occlusion. Furthermore, delayed administration of YM872 (20 mg/kg/h iv infusion for 4 h, starting 2 or 3 h after the occlusion) also reduced the infarct volume and the neurological deficits measured at 24 h. Additionally, the therapeutic efficacy of YM872 persisted for at least seven days after MCA occlusion in animals treated with YM872 for 4 h starting 2 h after MCA occlusion. These data demonstrate that AMPA receptors contribute to the development of neuronal damage after reperfusion as well as during ischemia in the focal ischemia models and that the acute effect of the blockade of AMPA receptors persists over a long time period. YM872 shows promise as an effective treatment for patients suffering from acute stroke.

Pharmacology of AMPA/kainate receptor ligands and their therapeutic potential in neurological and psychiatric disorders

It has been postulated, consistent with the ubiquitous presence of glutamatergic neurons in the brain, that defects in glutamatergic neurotransmission are associated with many human neurological and psychiatric disorders. This review evaluates the possible application of ligands acting on glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and kainate (KA) receptors to minimise the pathology and/or symptoms of various diseases. Glutamate activation of AMPA receptors is thought to mediate most fast synaptic neurotransmission in the brain, while transmission via KA receptors contributes only a minor component. Variants of the protein subunits forming these receptors greatly extend the pharmacological and electrophysiological properties of AMPA/KA receptors. Disease and drug use can differentially affect the expression of the subunits and their variants. Ligands bind to AMPA receptors by competing with glutamate at the glutamate binding site, or non-competitively at other sites on the proteins (allosteric modulators). Ligands showing selective competitive antagonist actions at the AMPA/ KA class of glutamate receptors were first reported in 1988, and the systemically active antagonist 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX) was first shown to have useful therapeutic effects on animal models of neurological diseases in 1990. Since then, newer antagonists with increased potency, higher specificity, increased water solubility, and a longer duration of action in vivo have been developed. Negative allosteric modulators such as the prototype GYKI-52466 also block AMPA receptors but have little action at KA receptors. Positive allosteric modulators enhance glutamatergic neurotransmission at AMPA receptors. Polyamines and adamantane derivatives bind within the ion channel of calcium-permeable AMPA receptors. The latest developments include ligands selective for KA receptors containing Glu-R5 subunits. Evidence for advantages of AMPA receptor antagonists over N-methyl-D-aspartate (NMDA) receptor antagonists for symptomatic treatment of neurological and psychiatric conditions, and for minimising neuronal loss occurring after acute neurological diseases, such as physical trauma, ischaemia or status epilepticus, have been shown in animal models. However, as yet AMPA receptor antagonists have not been shown to be effective in clinical trials. On the other hand, a limited number of clinical trials have been reported for AMPA receptor ligands that enhance glutamatergic neurotransmission by extending the ion channel opening time (positive allosteric modulators). These acute studies demonstrate enhanced memory capability in both young and aged humans, without any apparent serious adverse effects. The use of these allosteric modulators as antipsychotic drugs is also possible. However, the long term use of both direct agonists and positive allosteric modulators must be approached with considerable caution because of potential adverse effects.

The spinal antinociceptive effects of a novel competitive AMPA receptor antagonist, YM872, on thermal or formalin-induced pain in rats

Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonists have spinally mediated analgesic effects on acute nociception; however, their current formulations are not water-soluble and have toxic side effects. A new competitive AMPA antagonist, YM872 (2,3-dioxo-7-[1H-imidazol-1-yl]-6-nitro-1,2,3,4-tetrahydro-1-quinoxal inyl acetic acid) is water-soluble and may have fewer side effects. The purpose of this study was to investigate the analgesic effects of YM872 on both acute thermal and irritant-induced pain. Sprague-Dawley rats were implanted with chronic lumbar intrathecal catheters and were tested for their tail withdrawal response by the tail flick test and for their paw flinches by formalin injection after the intrathecal administration of YM872. The tail flick latency increased dose-dependently with a 50% effective dose (ED50) value of 1.0 microg. The number of flinches in both Phase 1 and Phase 2 of the formalin test decreased with increasing dose of YM872. ED50 values were 0.24 microg in Phase 1 and 0.21 microg in Phase 2. YM872 10 and 30 microg induced motor disturbance and flaccidity. In rats, the intrathecal administration of YM872 had analgesic effects on both acute thermal and formalin-induced nociceptions. Transient motor disturbance and flaccidity occurred only with large doses. YM872 may have potential in the clinical management of both acute and chronic pain.

IMPLICATIONS

A novel alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist, YM872, may have an analgesic effect on both acute and chronic pain when administered intrathecally.

Neuroprotective effect of the novel glutamate AMPA receptor antagonist YM872 assessed with in vivo MR imaging of rat MCA occlusion

The neuroprotective effect of post-ischemic treatment with the novel, highly water-soluble, glutamate AMPA receptor antagonist YM872 was evaluated by using MR imaging and histopathology of rats subjected to permanent MCA occlusion. Two treatment groups with continuous i.v. infusion of 20 mg kg-1 h-1 YM872 during either the first 4 h or first 24 h after MCA occlusion, called 4 h YM872 treatment group (n=9) and 24 h YM872 treatment group (n=8) respectively, were compared to a control group (n=8). The main end-point was T2 weighted MR imaging and histopathology 24 h after MCA occlusion. Also the time evolution of the ischemic tissue damage was studied by diffusion weighted MR imaging 412 and 24 h after MCA occlusion. The volume of ischemic tissue damage as assessed by diffusion weighted MR imaging 412 h after MCA occlusion was significantly smaller in both YM872 treatment groups (99+/-52 mm3 and 102+/-44 mm3 compared to 186+/-72 mm3 in the control group, +/-S.D. and p=0.008). The infarct volume as assessed by T2 weighted MR imaging 24 h after MCA occlusion was significantly smaller only in the 24 h YM872 treatment group (262+/-57 mm3 compared to 366+/-49 mm3 in the control group, +/-S.D. and p=0.01) while the infarct volume in the 4 h YM872 treatment group (357+/-88 mm3) was similar to the control group. YM872 treatment significantly reduced the infarct volume 24 h after MCA occlusion when the drug was administered as continuous infusion during the 24-h observation period.