sib-1893 and 6-methyl-2-(phenylethynyl)pyridine

Fenobam [N-(3-chlorophenyl)-N'-(4,5-dihydro-1-methyl-4-oxo-1H-imidazole-2-yl)urea], a potent metabotropic glutamate mGluR5 receptor antagonist, reported to have analgesic effects in animals and anxiolytic effects in humans, also caused adverse events, including psychostimulant-type effects and "derealization phenomena." Recent electrophysiologic, pharmacologic, and anatomic data show that the mGluR5 antagonists 2-methyl-6-(phenylethynyl)pyridine (MPEP) and (E)-2-methyl-6-styryl-pyridine (SIB-1893) can inhibit NMDA receptor-mediated activity and that mGluR5 receptors are highly expressed in limbic and forebrain regions. The present studies first evaluated the potential of mGluR5 receptor antagonists to cause PCP-like psychoactive effects in a rat drug discrimination procedure and, second, explored and characterized the selective mGluR5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) as a discriminative stimulus and compared MTEP with other drugs known to be psychoactive in humans. Additionally, the reinforcing potential of MPEP and MTEP was compared with phencyclidine (PCP) in a rat intravenous self-administration procedure. Dizocilpine [(+)-MK-801] and ketamine caused full PCP-appropriate responding. Memantine and the mGluR5 antagonists caused no or weak partial PCP-appropriate responding. In MTEP-trained rats, MTEP, MPEP, and fenobam caused full and equipotent MTEP-appropriate responding. (+)-MK-801 and memantine caused MTEP-appropriate responding below 70%, whereas PCP, chlordiazepoxide and LSD caused MTEP-appropriate responding below 50%. Δ(9)-Tetrahydrocannabinol, yohimbine, arecoline, and pentylenetetrazole all caused MTEP-appropriate responding below 20%. Rats self-administered PCP but not MPEP or MTEP, indicating a lack of reinforcing effects of the mGluR5 antagonists. These data suggest that the mGluR5 antagonists appear not to have reinforcing properties, that the discriminative effects of mGluR5 antagonists and PCP are dissimilar, and that mGluR5 antagonists may produce psychoactive effects different from NMDA-antagonists and other drugs with known psychotomimetic properties.

Topics: Animals; Behavior, Animal; Discrimination, Psychological; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Imidazoles; Male; Phencyclidine; Psychotropic Drugs; Pyridines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, N-Methyl-D-Aspartate; Reinforcement, Psychology; Self Administration; Thiazoles

To investigate the role of Group I metabotropic glutamate (mGlu) receptor subtypes on reflex-induced micturition in anaesthetized and conscious rats using selective mGlu1 (NPS 2407 and R214127) and mGlu5 (MPEP, MTEP, and SIB1893) allosteric antagonists.. The affinity of the compounds at mGlu1 and mGlu5 receptor subtypes was evaluated by displacement of tritiated R214127 and MPEP, respectively, from rat brain tissue. Effects of intravenous (i.v.) administration of the compounds on isovolumic bladder contractions were evaluated in anaesthetized rats. Effects of MPEP and NPS 2407 on bladder filling and voiding were evaluated by cystometry using saline or diluted (0.2%) acetic acid (MPEP only) infusion of bladders in conscious rats.. Binding studies confirmed the selectivity of the mGlu1 (NPS 2407 and R214127) and mGlu5 (MPEP, MTEP, and SIB1893) compounds. Isovolumic bladder contractions were blocked after i.v. administration of all compounds. However, the mGlu5 antagonists were generally more potent than mGlu1 antagonists. In conscious rats with bladders infused with saline, MPEP dose-dependently and significantly increased bladder capacity starting from oral administration of 10 mg/kg. Oral administration of NPS 2407 (up to 30 mg/kg) did not induce consistent changes in bladder capacity or micturition pressure. MPEP (10 mg/kg, orally) was also evaluated in conscious rats with bladders infused with diluted acetic acid. In this model, MPEP reduced bladder instability counteracting the decrease of bladder volume capacity induced by acetic acid. There were no consistent effects on bladder contractility.. The results indicate that i.v. and oral administration of selective mGlu5 antagonists, but not those selective for the mGlu1 subtype, have a marked inhibitory effect on reflex micturition pathways in the rat.

Topics: Animals; Female; Male; Muscle Contraction; Pyrans; Pyridines; Quinolines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Thiazoles; Urinary Bladder; Urination; Urodynamics

We combined the use of knock-out mice and subtype-selective antagonists [2-methyl-6-(phenylethynyl)pyridine (MPEP) and (E)-2-methyl-6-(2-phenylethenyl)-pyridine (SIB1893)] to examine whether endogenous activation of mGlu5 metabotropic glutamate receptors contributes to the pathophysiology of nigro-striatal damage in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of parkinsonism. High doses of MPTP (four injections of 20 mg/kg, i.p., every 2 hr) induced a high mortality rate and a nearly total degeneration of the nigro-striatal pathway in wild-type mice. mGlu5 knock-out mice were less sensitive to MPTP toxicity, as shown by a higher survival and a milder nigro-striatal damage. Protection against MPTP (80 mg/kg) toxicity was also observed after MPEP injections (four injections of 5 mg/kg, i.p., 30 min before each MPTP injection). MPEP treatment did not further increase neuroprotection against 80 mg/kg of MPTP in mGlu5 knock-out mice, indicating that the drug acted by inhibiting mGlu5 receptors. In wild-type mice, MPEP was also neuroprotective when challenged against lower doses of MPTP (either 30 mg/kg, single injection, or four of 10 mg/kg injections). The action of MPEP was mimicked by SIB1893 but not by the mGlu1 receptor antagonist 7-hydroxyiminocyclopropan[b]chromen-1a-carboxylic acid ethyl ester. MPEP did not change the kinetics of 1-methyl-4-phenylpyridinium ion formation in the striatum of mice injected with MPTP. We conclude that mGlu5 receptors act as amplifiers of MPTP toxicity and that mGlu5 receptor antagonists may limit the extent of nigro-striatal damage in experimental models of parkinsonism.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; 1-Methyl-4-phenylpyridinium; 3,4-Dihydroxyphenylacetic Acid; Animals; Corpus Striatum; Disease Models, Animal; Dopamine; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Homovanillic Acid; Mice; Mice, Knockout; MPTP Poisoning; Neuroprotective Agents; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Substantia Nigra; Survival Rate; Synaptosomes

Characterization of new chemical entities for their potential to produce drug-drug interactions is an important aspect of early drug discovery screening. In the present study, the potential for three metabotropic glutamate receptor antagonists to interact with recombinant human CYPs was investigated. 2-Methyl-6-(phenylethenyl) pyridine (SIB-1893), 2-methyl-6-(phenylethynyl) pyridine (MPEP) and 3-[2-methyl-1,3-thiazol-4-yl) ethynyl]-pyridine (MTEP) were moderate competitive inhibitors of recombinant human CYP1A2 (Ki, 0.5-1 microM). SIB-1893, but not MPEP or MTEP, was also a moderate competitive inhibitor of CYP1B1. MPEP and MTEP were weak inhibitors of CYP2C19. None of the three compounds tested were significant inhibitors (IC(50) values >50 microM) of CYP3A4, 2C9, 2D6, 2A6, 2B6 or 2E1. The results suggest that MTEP is a selective inhibitor of CYP1A2 and may prove to be a useful tool in studying drug-drug interactions involving this enzyme.

Topics: Aryl Hydrocarbon Hydroxylases; Cytochrome P-450 CYP1A2 Inhibitors; Cytochrome P-450 CYP1B1; Cytochrome P-450 Enzyme Inhibitors; Enzyme Inhibitors; Humans; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Thiazoles

We have identified 2-methyl-6-(2-phenylethenyl)pyridine (SIB-1893) and 2-methyl-6-phenylethynyl pyridine hydrochloride (MPEP) as positive allosteric modulators for the hmGluR4. SIB-1893 and MPEP enhanced the potency and efficacy of L-2-amino-4-phophonobutyrate (L-AP4) in guanosine 5'-O-(3-[(35)S]thiotriphosphate ([(35)S]GTPgammaS) binding and efficacy in cAMP studies. These effects were fully blocked by the mGluR4 competitive antagonist (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG), indicating a dependency on receptor activation. Although SIB-1893 and MPEP had no effects alone in GTPgammaS binding, effects were observed in the cell-based cAMP assay due to media-derived activation as indicated by CPPG inhibition. Positive modulation of the mGluR4 was a receptor-specific effect since SIB-1893 and MPEP had neither effects on mGluR2-expressing cells nor on the parent BHK cell line. In [(3)H]L-AP4 binding, a two-fold decrease in K(D) but not in B(max) was observed with 100 micro M SIB-1893, whereas MPEP affected neither parameter. Finally, SIB-1893 and MPEP failed to displace [(3)H]L-AP4 binding. Taken together, these data identify positive allosteric modulators for the hmGluR4.

Topics: Allosteric Regulation; Cell Culture Techniques; Humans; Pyridines; Receptors, Glutamate; Receptors, Metabotropic Glutamate

mGlu5 metabotropic glutamate receptor antagonists protect rat hepatocytes against hypoxic death. Here, we have examined whether mGlu5 receptor antagonists are protective against liver damage induced by oxidative stress.. Toxicity of isolated hepatocytes was induced by tert-butylhydroperoxide (t-BuOOH) after pretreatment with the mGlu5 receptor antagonists, MPEP, SIB-1757 and SIB-1893. The effect of these drugs was also examined in mice challenged with toxic doses of acetaminophen.. Addition of tBuOOH (0.5 mM) to isolated hepatocytes induced cell death (70+/-5% at 3 h). Addition of MPEP or SIB-1893 to hepatocytes reduced both the production of reactive oxygen species (ROS) and cell toxicity induced by t-BuOOH (tBuOOH=70+/-5%; tBuOOH+MPEP=57+/-6%; tBuOOH+SIB-1893=40+/-4%). In mice, a single injection of acetaminophen (300 mg/kg, i.p.) induced centrilobular liver necrosis, which was detectable after 24 h. MPEP (20 mg/kg, i.p.) substantially reduced liver necrosis and the production of ROS, although it did not affect the conversion of acetaminophen into the toxic metabolite, N-acetylbenzoquinoneimine. MPEP, SIB-1893 and SIB-1757 (all at 20 mg/kg, i.p.) also reduced the increased expression and activity of liver iNOS induced by acetaminophen.. We conclude that pharmacological blockade of mGlu5 receptors might represent a novel target for the treatment of drug-induced liver damage.

Topics: Acetaminophen; Analgesics, Non-Narcotic; Animals; Chemical and Drug Induced Liver Injury; Excitatory Amino Acid Antagonists; Hepatocytes; Male; Mice; Oxidative Stress; Phenazopyridine; Pyridines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; tert-Butylhydroperoxide

The synthesis of a new potent, subtype-selective radioligand [(3)H]-M-MPEP (2-methyl-6-((3-methoxyphenyl)ethynyl)-pyridine) and its in vitro pharmacological characteristics are described. Science Ltd.

Topics: Binding Sites; Binding, Competitive; Humans; Kinetics; Ligands; Pyridines; Radiopharmaceuticals; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Recombinant Proteins

Methamphetamine (MA), a widely used drug of abuse, produces oxidative damage of nigrostriatal dopaminergic terminals. We examined the effect of subtype-selective ligands of metabotropic glutamate (mGlu) receptors on MA neurotoxicity in mice. MA (5 mg/kg, i.p.; injected three times, every 2 hr) induced, 5 d later, a substantial degeneration of striatal dopaminergic terminals associated with reactive gliosis. MA toxicity was primarily attenuated by the coinjection of the noncompetitive mGlu5 receptor antagonists 2-methyl-6-(phenylethynyl)pyridine and (E)-2-methyl-6-styrylpyridine both at 10 mg/kg, i.p.). In contrast, the mGlu1 receptor antagonist 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (10 mg/kg, i.p.), and the mGlu2/3 receptor agonist (-)-2-oxa-4-aminocyclo[3.1.0]hexane-4,6-dicarboxylic acid (1 mg/kg, i.p.), failed to affect MA toxicity. mGlu5 receptor antagonists reduced the production of reactive oxygen species but did not reduce the acute stimulation of dopamine release induced by MA both in striatal synaptosomes and in the striatum of freely moving mice. We conclude that endogenous activation of mGlu5 receptors enables the development of MA neurotoxicity and that mGlu5 receptor antagonists are neuroprotective without interfering with the primary mechanism of action of MA.

Topics: 3,4-Dihydroxyphenylacetic Acid; Animals; Body Temperature; Corpus Striatum; Dopamine; Dopamine Plasma Membrane Transport Proteins; Excitatory Amino Acid Antagonists; Fever; Glial Fibrillary Acidic Protein; Homovanillic Acid; Hydroxybenzoates; Male; Membrane Glycoproteins; Membrane Transport Proteins; Methamphetamine; Mice; Mice, Inbred C57BL; Microdialysis; Nerve Tissue Proteins; Pyridines; Reactive Oxygen Species; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Tyrosine 3-Monooxygenase

The effect of selective group I metabotropic glutamate receptor subtype 5 (mGluR5) antagonists 2-methyl-6-(phenylethynyl)-pyridine (MPEP) and (E)-2-methyl-6-(2-phenylethenyl)-pyridine (SIB-1893) on neuronal cell survival and post-traumatic recovery was examined using rat in vitro and in vivo trauma models. Treatment with MPEP and SIB-1893 showed significant neuroprotective effects in rat cortical neuronal cultures subjected to mechanical injury. Application of the antagonists also attenuated glutamate- and N-methyl-D-aspartate (NMDA)-induced neuronal cell death in vitro. Intracerebroventricular administration of MPEP to rats markedly improved motor recovery and reduced deficits of spatial learning after lateral fluid percussion-induced traumatic brain injury. Lesion volumes as assessed by magnetic resonance imaging were also substantially reduced by MPEP treatment. Although we show that MPEP acts as a potent mGluR5 antagonist in our culture system, where it completely blocks agonist-induced phosphoinositide hydrolysis, electrophysiological and pharmacological studies indicate that MPEP and SIB-1893 also inhibit NMDA receptor activity at higher concentrations that are neuroprotective. Taken together, these data suggest that MPEP and SIB-1893 may have therapeutic potential in brain injury, although the mechanisms of neuroprotective action for these drugs may reflect their ability to modulate NMDA receptor activity.

Topics: Animals; Brain Injuries; Cell Survival; Cells, Cultured; Cerebral Cortex; Electrophysiology; Excitatory Amino Acid Antagonists; Glutamic Acid; Hydrolysis; Male; Maze Learning; Memory; N-Methylaspartate; Neurons; Neuroprotective Agents; Phosphatidylinositols; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate

The selective mGlu5 antagonists, MPEP, 2-methyl-6-phenylethynyl-pyridine, and SIB1893, (E)-6-methyl-2-styryl-pyridine, have been evaluated as antiepileptic drugs in DBA/2 mice and lethargic mice. Clonic seizures induced by the selective mGlu5 agonist, (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG), 3 micromol intracerebroventricularly (i.c.v.), are potently suppressed by both compounds (MPEP, ED(50)=0.42 [0.28-0.62] mg/kg intraperitoneally (i.p.); SIB 1893 ED(50)=0.19 [0.11-0.33] mg/kg i.p. ). Clonic seizures induced by the mGlu1,5 agonist, 3, 5-dihydroxyphenylglycine (DHPG), 1.5 micromol i.c.v., are less potently suppressed by both compounds (MPEP, ED(50)=22 [13-38] mg/kg i.p., 110 [67-180] nmol i.c.v.; SIB1893, ED(50)=31 [18-54] mg/kg i.p. , 95 [82-110] nmol i.c.v.). Sound-induced seizures in DBA/2 mice are suppressed at 15 min by MPEP and SIB 1893 (MPEP ED(50) clonic seizures=18 [10-32] mg/kg i.p., 93 [69-125] nmol i.c.v.; tonic seizures=6.1 [4.5-8.3] mg/kg i.p., 46 [26-80] nmol i.c.v.; SIB 1893 ED(50) clonic seizures=27 [17-44] mg/kg i.p., 825 [615-1108] nmol i. c.v., tonic seizures=5.4 [3.4-8.6] mg/kg i.p., 194 [113-332] nmol i. c.v.). The ED(50) for MPEP for impaired rotarod performance is 128 [83-193] mg/kg i.p., at 15 min, i.e. a therapeutic index for sound-induced seizures of 5-20. In lethargic mice (lh/lh), a genetic absence model, MPEP, 50 mg/kg i.p., caused a marked reduction in the incidence of spontaneous spike-and-wave discharges. These selective antagonists of mGlu5 block seizures due to activation of mGlu5 at very low systemic doses. At rather higher doses they block convulsive and non-convulsive primary generalised seizures.

Topics: Animals; Anticonvulsants; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Female; Glycine; Injections, Intraperitoneal; Injections, Intraventricular; Male; Mice; Mice, Inbred DBA; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Resorcinols; Seizures; Sound; Time Factors

1. The metabotropic glutamate receptors (mGluRs) are a family of G-protein linked receptors that can be divided into three groups (group I, II and III). A number of studies have implicated group I mGluR activation in acute neuronal injury, but until recently it was not possible to pharmacologically differentiate the roles of the two individual subunits (mGluR1 and mGluR5) in this group. 2. We investigated the role of mGluR5 in acute NMDA and glutamate mediated neurodegeneration in cultured rat cortical cells using the mGluR5 antagonists MPEP and SIB-1893, and found that they provide significant protection at concentrations of 20 or 200 microM. 3. These compounds act as effective mGluR5 antagonists in our cell culture system, as indicated by the ability of SIB-1893 to prevent phosphoinositol hydrolysis induced by the specific mGluR5 agonist, (RS)-2-chloro-5-hydroxyphenylglycine (CHPG). 4. However, they also significantly reduce NMDA evoked current recorded from whole cells voltage clamped at -60 mV, and significantly decrease the duration of opening of NMDA channels recorded in the outside out patch configuration. 5. This suggests that although MPEP and SIB-1893 are effective mGluR5 antagonists, they also act as noncompetitive NMDA receptor antagonists. Therefore, the neuroprotective effects of these compounds are most likely mediated through their NMDA receptor antagonist action, and caution should be exercised when drawing conclusions about the roles of mGluR5 based on their use.

Topics: Animals; Cell Death; Cells, Cultured; Dose-Response Relationship, Drug; Electrophysiology; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Fetus; Glutamic Acid; Glycine; Hydrolysis; Membrane Potentials; N-Methylaspartate; Neurons; Patch-Clamp Techniques; Phenylacetates; Phosphatidylinositols; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate