慢性神经痛对抑郁状态以及中枢多巴胺神经元电生理的影响

目的：探讨大鼠慢性神经痛导致抑郁症状发生后,中脑腹侧被盖区多巴胺能神经元自发放电活动的改变情况。方法：24只健康成年大鼠进行随机分组（n=12）：假手术组（Sham）大鼠仅进行坐骨神经分支暴露,坐骨神经损伤组（SNI）进行坐骨神经分支选择性损伤。在神经损伤后的第3、7、14、28、42、56天进行机械刺激计算缩足反射阈值,并进行糖水偏好、强迫游泳、旷场实验等行为学实验来评价大鼠是否发生抑郁症状;利用在体多通道电生理技术,对SNI组大鼠和假手术组大鼠中脑腹侧被盖区神经元分别进行记录分析。结果：与假手术组比较,SNI组大鼠的机械痛阈值明显降低（P<0.01）;在旷场实验、糖水偏好、强迫游泳较对照组出现显著性差异（P<0.01）;大鼠中脑腹侧被盖区多巴胺能神经元自发放电频率、簇状放电活动中动作电位的数量明显增加（P<0.01）。结论：慢性疼痛可以导致大鼠抑郁相关症状的发生,中脑腹侧被盖区多巴胺能神经元自发放电频率增加与疼痛后抑郁发生相关。     

Opposite influence of MPEP, an mGluR5 antagonist, on the locomotor hyperactivity induced by PCP and amphetamine.

Potential antipsychotic effects of a selective non-competitive antagonist of metabotropic glutamate receptor 5 (mGluR5), 2-methyl-6-phenylethynylpyridine (MPEP), was examined in two commonly used screening tests: (1) the hyperactivity induced by an NMDA receptor antagonist phencyclidine (PCP), and (2) the hyperactivity induced by an indirect dopamine agonist, D-amphetamine. PCP was administered at a dose of 2.5 mg/kg s.c. and D-amphetamine was given at a dose of 1 mg/kg s.c. MPEP (5 mg/kg i.p.) significantly enhanced the locomotor activity increased by PCP, but inhibited amphetamine-induced hyperactivity. The opposite effect of MPEP in the two above-mentioned models questions significance of the blockade of mGluR5 receptors to antipsychotic effects.     

Upregulation of tumor necrosis factor-alpha in nucleus accumbens attenuates morphine-induced rewarding in a neuropathic pain model

Treatment of neuropathic pain with opioid analgesics remains controversial and a major concern is the risk of addiction. Here, we investigated this issue with spared nerve injury (SNI) model of neuropathic pain in rats and mice. SNI prevented conditioned place preference (CPP) induced by low dose (3.5 mg/kg) of morphine (MOR), which was effective for anti-allodynia, but not by high dose (?5.0 mg/kg) of MOR. Tumor necrosis factor-alpha (TNF-α) was upregulated in nucleus accumbens (NAcc) following SNI. The inhibitory effect of SNI on MOR-induced CPP was blocked by either genetic deletion of TNF receptor 1 (TNFR1) or microinjection of anti-TNF-α into the NAcc and was mimicked by intra-NAcc injection of TNF-α in sham rats. Furthermore, SNI reduced dopamine (DA) level and upregulated dopamine transporter (DAT) in the NAcc, but did not affect total tyrosine hydroxylase (TH) or phospho-TH (p-TH), a rate-limiting enzyme of catecholamine biosynthesis, in ventral tegmental area (VTA). Accordingly, the increase in DA reuptake but not decrease in its synthesis may lead to the reduction of DA level. Finally, the upregulation of DAT in the NAcc of SNI animals was again blocked by either genetic deletion of TNFR1 or NAcc injection of anti-TNF-α, and was mimicked by NAcc injection of TNF-α in sham animals. Thus, our data provided novel evidence that upregulation of TNF-α in NAcc may attenuate MOR-induced rewarding by upregulation of DAT in NAcc under neuropathic pain condition.     

Phenyl ureas of creatinine as mGluR5 antagonists. A structure-activity relationship study of fenobam analogues

Fenobam (1) was developed by McNeil Laboratories as an anxiolytic agent with an unknown molecular target in the late 1970s. In a recent publication, it was revealed that fenobam is a non-competitive mGluR5 antagonist. Herein, we present the structure-activity relationship of fenobam and its analogues and similarities between the SAR of mGluR5 antagonism and the SAR of CNS properties originally reported by McNeil are discussed.     

Involvement of metabotropic glutamate receptors in excitatory amino acid and GABA release following spinal cord injury in rat

Spinal cord injury (SCI) leads to an increase in extracellular excitatory amino acid (EAA) concentrations resulting in glutamate receptor-mediated excitotoxic events. The glutamate receptors include ionotropic (iGluRs) and metabotropic (mGluR) receptors. Of the three groups of mGluRs, group-I activation can initiate intracellular pathways that lead to further transmitter release. Groups II and III mGluRs function mainly as autoreceptors to regulate neurotransmitter release. In an effort to examine the role of mGluRs in the increase in EAAs following SCI, we administered AIDA, a potent group-I mGluR antagonist immediately after injury. To determine subtype specific roles of the group-I mGluRs, we evaluated EAA release following LY 367385 (mGluR1 antagonist) and MPEP (mGluR5 antagonist) administration. To evaluate group-II and -III mGluRs we administered APDC (group-II agonist) and L-AP4 (group-III agonist) immediately following injury; additionally, we initiated treatment with CPPG (group-II/-III antagonist) and LY 341495 (group-II antagonist) 5 min prior to injury. Subjects were adult male Sprague-Dawley rats (225-250 g), impact injured at T10 with an NYU impactor (12.5 mm drop). Agents were injected into the epicenter of injury, amino acids where collected by microdialysis fibers inserted 0.5 mm caudal from the edge of the impact region and quantified by HPLC. Treatment with AIDA significantly decreased extracellular EAA and GABA concentrations. MPEP reduced EAA concentrations without affecting GABA. Combining LY 367385 and MPEP resulted in a decrease in EAA and GABA concentrations greater than either agent alone. L-AP4 decreased EAA levels, while treatment with LY 341495 increased EAA levels. These results suggest that mGluRs play an important role in EAA toxicity following SCI.     

Satellite glial cell P2Y12 receptor in the trigeminal ganglion is involved in lingual neuropathic pain mechanisms in rats

Background

Interstitial cystitis/painful bladder syndrome (IC/PBS), is a severely debilitating chronic condition that is frequently unresponsive to conventional pain medications. The etiology is unknown, however evidence suggests that nervous system sensitization contributes to enhanced pain in IC/PBS. In particular, central nervous system plasticity of glutamatergic signaling involving NMDA and metabotropic glutamate receptors (mGluRs) has been implicated in a variety of chronic pain conditions. Here, we test the hypothesis that mGluR5 mediates both non-inflammatory and inflammatory bladder pain or nociception in a mouse model by monitoring the visceromotor response (VMR) during graded bladder distention.

Results

Using a combination of genetic and pharmacologic approaches, we provide evidence indicating that mGluR5 is necessary for the full expression of VMR in response to bladder distention in the absence of inflammation. Furthermore, we observed that mice infected with a uropathogenic strain of Escherichia coli (UPEC) develop inflammatory hyperalgesia to bladder distention, and that the selective mGluR5 antagonist fenobam [N-(3-chlorophenyl)-N'-(4,5-dihydro-1-methyl-4-oxo-1H-imidazole-2-yl) urea], reduces the VMR to bladder distention in UPEC-infected mice.

Conclusions

Taken together, these data suggest that mGluR5 modulates both inflammatory and non-inflammatory bladder nociception, and highlight the therapeutic potential for mGluR5 antagonists in the alleviation of bladder pain.     

The Role of Metabotropic Glutamate Receptor 5 on the Stromal Cell-Derived Factor-1/CXCR4 System in Oral Cancer

We have demonstrated that blocking CXCR4 may be a potent anti-metastatic therapy for CXCR4-related oral cancer. However, as CXCR4 antagonists are currently in clinical use to induce the mobilization of hematopoietic stem cells, continuous administration as an inhibitor for the metastasis may lead to persistent leukocytosis. In this study, we investigated the novel therapeutic downstream target(s) of the SDF-1/CXCR4 system, using B88-SDF-1 cells, which have an autocrine SDF-1/CXCR4 system and exhibit distant metastatic potential in vivo. Microarray analysis revealed that 418 genes were upregulated in B88-SDF-1 cells. We identified a gene that is highly upregulated in B88-SDF-1 cells, metabotropic glutamate receptor 5 (mGluR5), which was downregulated following treatment with 1,1’ -[1,4-Phenylenebis(methylene)]bis-1,4,8,11-tetraazacyclotetradecane octahydrochloride (AMD3100), a CXCR4 antagonist. The upregulation of mGluR5 mRNA in the SDF-1/CXCR4 system was predominately regulated by the Ras-extracellular signal-regulated kinase (ERK)1/2 pathway. Additionally, the growth of B88-SDF-1 cells was not affected by the mGluR5 agonist (S)-3,5-DHPG (DHPG) or the mGluR5 antagonists 2-Methyl-6-(phenylethynyl)pyridine (MPEP) and 3-((2-Methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP). However, we observed that DHPG promoted B88-SDF-1 cell migration, whereas both MPEP and MTEP inhibited B88-SDF-1 cell migration. To assess drug toxicity, the antagonists were intraperitoneally injected into immunocompetent mice for 4 weeks. Mice injected with MPEP (5 mg/kg) and MTEP (5 mg/kg) did not exhibit any side effects, such as hematotoxicity, allergic reactions or weight loss. The administration of antagonists significantly inhibited the metastasis of B88-SDF-1 cells to the lungs of nude mice. These results suggest that blocking mGluR5 with antagonists such as MPEP and MTEP could prevent metastasis in CXCR4-related oral cancer without causing side effects.     

Regulation of increased glutamatergic input to spinal dorsal horn neurons by mGluR5 in diabetic neuropathic pain

Diabetic neuropathic pain is associated with increased glutamatergic input in the spinal dorsal horn. Group I metabotropic glutamate receptors (mGluRs) are involved in the control of neuronal excitability, but their role in the regulation of synaptic transmission in diabetic neuropathy remains poorly understood. Here we studied the role of spinal mGluR5 and mGluR1 in controlling glutamatergic input in a rat model of painful diabetic neuropathy induced by streptozotocin. Whole-cell patch-clamp recordings of lamina II neurons were performed in spinal cord slices. The amplitude of excitatory post-synaptic currents (EPSCs) evoked from the dorsal root and the frequency of spontaneous EPSCs (sEPSCs) were significantly higher in diabetic than in control rats. The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) inhibited evoked EPSCs and sEPSCs more in diabetic than in control rats. Also, the percentage of neurons in which sEPSCs and evoked EPSCs were affected by MPEP or the group I mGluR agonist was significantly higher in diabetic than in control rats. However, blocking mGluR1 had no significant effect on evoked EPSCs and sEPSCs in either groups. The mGluR5 protein level in the dorsal root ganglion, but not in the dorsal spinal cord, was significantly increased in diabetic rats compared with that in control rats. Furthermore, intrathecal administration of MPEP significantly increased the nociceptive pressure threshold only in diabetic rats. These findings suggest that increased mGluR5 expression on primary afferent neurons contributes to increased glutamatergic input to spinal dorsal horn neurons and nociceptive transmission in diabetic neuropathic pain.     

Comparison of the binding pockets of two chemically unrelated allosteric antagonists of the mGlu5 receptor and identification of crucial residues involved in the inverse agonism of MPEP

Fenobam [N-(3-chlorophenyl)-N'-(4,5-dihydro-1-methyl-4-oxo-1H-imidazole-2-yl)urea], a clinically validated non-benzodiazepine anxiolytic, has been shown to be a potent and non-competitive metabotropic glutamate (mGlu)-5 receptor antagonist. In the present study, we have used the site-directed mutagenesis coupled with three-dimensional receptor-based pharmacophore modelling to elucidate the interacting mode of fenobam within the seven-transmembrane domain (7TMD) of mGlu5 receptor and its comparison with that of 2-methyl-6-(phenylethynyl)pyridine (MPEP), the prototype antagonist. The common residues involved in the recognition of MPEP and fenobam include Pro654(3.36), Tyr658(3.40), Thr780(6.44), Trp784(6.48), Phe787(6.51), Tyr791(6.55) and Ala809(7.47). The differentiating residues between both modulators' interacting modes are Arg647(3.29), Ser657(3.39) and Leu743(5.47). Our data suggest that these chemically unrelated mGlu5 antagonists act similarly, probing a functionally unique region of the 7TMD. Using [3H]inositol phosphates accumulation assay, we have also identified the critical residues involved in the inverse agonist effect of MPEP. The mutation W784(6.48)A completely blocked the inverse agonist activity of MPEP; two mutations F787(6.51)A and Y791(6.55)A, caused a drastic decrease in the MPEP inverse agonism. Furthermore, these three mutations led to an increased efficacy of quisqualate without having any effect on its potency. The fact that the residues Trp784(6.48) and Phe787(6.51) are essential equally in antagonism and inverse agonism effects emphasizes again the key role of these residues and the involvement of a common transmembrane network in receptor inactivation by MPEP.     

The non-competitive antagonists 2-methyl-6-(phenylethynyl)pyridine and 7-hydroxyiminocyclopropan[b]chromen-1a-carboxylic acid ethyl ester interact with overlapping binding pockets in the transmembrane region of group I metabotropic glutamate receptors

We have investigated the mechanism of inhibition and site of action of the novel human metabotropic glutamate receptor 5 (hmGluR5) antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP), which is structurally unrelated to classical metabotropic glutamate receptor (mGluR) ligands. Schild analysis indicated that MPEP acts in a non-competitive manner. MPEP also inhibited to a large extent constitutive receptor activity in cells transiently overexpressing rat mGluR5, suggesting that MPEP acts as an inverse agonist. To investigate the molecular determinants that govern selective ligand binding, a mutagenesis study was performed using chimeras and single amino acid substitutions of hmGluR1 and hmGluR5. The mutants were tested for binding of the novel mGluR5 radioligand [(3)H]2-methyl-6-(3-methoxyphenyl)ethynyl pyridine (M-MPEP), a close analog of MPEP. Replacement of Ala-810 in transmembrane (TM) VII or Pro-655 and Ser-658 in TMIII with the homologous residues of hmGluR1 abolished radioligand binding. In contrast, the reciprocal hmGluR1 mutant bearing these three residues of hmGluR5 showed high affinity for [(3)H]M-MPEP. Radioligand binding to these mutants was also inhibited by 7-hydroxyiminocyclopropan[b]chromen-1a-carboxylic acid ethyl ester (CPCCOEt), a structurally unrelated non-competitive mGluR1 antagonist previously shown to interact with residues Thr-815 and Ala-818 in TMVII of hmGluR1. These results indicate that MPEP and CPCCOEt bind to overlapping binding pockets in the TM region of group I mGluRs but interact with different non-conserved residues.     

Metabotropic glutamate receptor 5 responses dictate differentiation of neural progenitors to NMDA‐responsive cells in fragile X syndrome

Disrupted metabotropic glutamate receptor 5 (mGluR5) signaling is implicated in many neuropsychiatric disorders, including autism spectrum disorder, found in fragile X syndrome (FXS). Here we report that intracellular calcium responses to the group I mGluR agonist (S)−3,5‐dihydroxyphenylglycine (DHPG) are augmented, and calcium‐dependent mGluR5‐mediated mechanisms alter the differentiation of neural progenitors in neurospheres derived from human induced pluripotent FXS stem cells and the brains of mouse model of FXS. Treatment with the mGluR5 antagonist 2‐methyl‐6‐(phenylethynyl)‐pyridine (MPEP) prevents an abnormal clustering of DHPG‐responsive cells that are responsive to activation of ionotropic receptors in mouse FXS neurospheres. MPEP also corrects morphological defects of differentiated cells and enhanced migration of neuron‐like cells in mouse FXS neurospheres. Unlike in mouse neurospheres, MPEP increases the differentiation of DHPG‐responsive radial glial cells as well as the subpopulation of cells responsive to both DHPG and activation of ionotropic receptors in human neurospheres. However, MPEP normalizes the FXS‐specific increase in the differentiation of cells responsive only to N ‐methyl‐d ‐aspartate (NMDA) present in human neurospheres. Exposure to MPEP prevents the accumulation of intermediate basal progenitors in embryonic FXS mouse brain suggesting that rescue effects of GluR5 antagonist are progenitor type‐dependent and species‐specific differences of basal progenitors may modify effects of MPEP on the cortical development. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 419–437, 2017     

mGluR5-antagonist mediated reversal of elevated stereotyped, repetitive behaviors in the VPA model of autism

Autism spectrum disorders (ASD) are highly disabling developmental disorders with a population prevalence of 1-3%. Despite a strong genetic etiology, there are no current therapeutic options that target the core symptoms of ASD. Emerging evidence suggests that dysfunction of glutamatergic signaling, in particular through metabotropic glutamate receptor 5 (mGluR5) receptors, may contribute to phenotypic deficits and may be appropriate targets for pharmacologic intervention. This study assessed the therapeutic potential of 2-methyl-6-phenylethyl-pyrididine (MPEP), an mGluR5-receptor antagonist, on repetitive and anxiety-like behaviors in the valproic acid (VPA) mouse model of autism. Mice were exposed prenatally on day E13 to VPA and assessed for repetitive self-grooming and marble burying behaviors as adults. Anxiety-like behavior and locomotor activity were measured in an open-field. VPA-exposed mice displayed increased repetitive and anxiety-like behaviors, consistent with previously published results. Across both marble burying and self-grooming assays, MPEP significantly reduced repetitive behaviors in VPA-treated mice, but had no effect on locomotor activity. These results are consistent with emerging preclinical literature that mGluR5-antagonists may have therapeutic efficacy for core symptoms of autism.     

Rational design of 7-arylquinolines as non-competitive metabotropic glutamate receptor subtype 5 antagonists

Rational replacement of the alkyne linker of mGluR5 antagonist MPEP gave 7-arylquinolines. SAR optimization gave an orally active compound with high affinity for the MPEP binding site.     

Peripheral versus central modulation of gastric vagal pathways by metabotropic glutamate receptor 5

Metabotropic glutamate receptors (mGluR) are classified into group I, II, and III mGluR. Group I (mGluR1, mGluR5) are excitatory, whereas group II and III are inhibitory. mGluR5 antagonism potently reduces triggering of transient lower esophageal sphincter relaxations and gastroesophageal reflux. Transient lower esophageal sphincter relaxations are mediated via a vagal pathway and initiated by distension of the proximal stomach. Here, we determined the site of action of mGluR5 in gastric vagal pathways by investigating peripheral responses of ferret gastroesophageal vagal afferents to graded mechanical stimuli in vitro and central responses of nucleus tractus solitarius (NTS) neurons with gastric input in vivo in the presence or absence of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP). mGluR5 were also identified immunohistochemically in the nodose ganglia and NTS after extrinsic vagal inputs had been traced from the proximal stomach. Gastroesophageal vagal afferents were classified as mucosal, tension, or tension-mucosal (TM) receptors. MPEP (1-10 microM) inhibited responses to circumferential tension of tension and TM receptors. Responses to mucosal stroking of mucosal and TM receptors were unaffected. MPEP (0.001-10 nmol icv) had no major effect on the majority of NTS neurons excited by gastric distension or on NTS neurons inhibited by distension. mGluR5 labeling was abundant in gastric vagal afferent neurons and sparse in fibers within NTS vagal subnuclei. We conclude that mGluR5 play a prominent role at gastroesophageal vagal afferent endings but a minor role in central gastric vagal pathways. Peripheral mGluR5 may prove a suitable target for reducing mechanosensory input from the periphery, for therapeutic benefit.     

Proteome of synaptosome‐associated proteins in spinal cord dorsal horn after peripheral nerve injury

Peripheral nerve injury may lead to neuroadaptive changes of cellular signals in spinal cord that are thought to contribute to central mechanisms underlying neuropathic pain. Here we used a 2‐DE‐based proteomic technique to determine the global expression changes of synaptosome‐associated proteins in spinal cord dorsal horn after unilateral fifth spinal nerve injury (SNI). The fifth lumbar dorsal horns ipsilateral to SNI or sham surgery were harvested on day 14 post‐surgery, and the total soluble and synaptosomal fractions were isolated. The proteins derived from the synaptosomal fraction were resolved by 2‐DE. We identified 27 proteins that displayed different expression levels after SNI, including proteins involved in transmission and modulation of noxious information, cellular metabolism, membrane receptor trafficking, oxidative stress, apoptosis, and degeneration. Six of the 27 proteins were chosen randomly and further validated in the synaptosomal fraction by Western blot analysis. Unexpectedly, Western blot analysis showed that only one protein in the total soluble fraction exhibited a significant expression change after SNI. The data indicate that peripheral nerve injury changes not only protein expression but also protein subcellular distribution in dorsal horn cells. These changes might participate in the central mechanism that underlies the maintenance of neuropathic pain.     

Co-localization and functional interaction between adenosine A(2A) and metabotropic group 5 receptors in glutamatergic nerve terminals of the rat striatum

The anti-Parkinsonian effect of glutamate metabotropic group 5 (mGluR5) and adenosine A(2A) receptor antagonists is believed to result from their ability to postsynaptically control the responsiveness of the indirect pathway that is hyperfunctioning in Parkinson's disease. mGluR5 and A(2A) antagonists are also neuroprotective in brain injury models involving glutamate excitotoxicity. Thus, we hypothesized that the anti-Parkinsonian and neuroprotective effects of A(2A) and mGluR5 receptors might be related to their control of striatal glutamate release that actually triggers the indirect pathway. The A(2A) agonist, CGS21680 (1-30 nM) facilitated glutamate release from striatal nerve terminals up to 57%, an effect prevented by the A(2A) antagonist, SCH58261 (50 nM). The mGluR5 agonist, CHPG (300-600 mum) also facilitated glutamate release up to 29%, an effect prevented by the mGluR5 antagonist, MPEP (10 microm). Both mGluR5 and A(2A) receptors were located in the active zone and 57 +/- 6% of striatal glutamatergic nerve terminals possessed both A(2A) and mGluR5 receptors, suggesting a presynaptic functional interaction. Indeed, submaximal concentrations of CGS21680 (1 nM) and CHPG (100 microm) synergistically facilitated glutamate release and the facilitation of glutamate release by 10 nM CGS21680 was prevented by 10 microm MPEP, whereas facilitation by 300 microm CHPG was prevented by 10 nM SCH58261. These results provide the first direct evidence that A(2A) and mGluR5 receptors are co-located in more than half of the striatal glutamatergic terminals where they facilitate glutamate release in a synergistic manner. This emphasizes the role of the modulation of glutamate release as a likely mechanism of action of these receptors both in striatal neuroprotection and in Parkinson's disease.     

The role of striatal metabotropic glutamate receptors in degeneration of dopamine neurons: review article

Summary.  Degeneration of dopaminergic nigrostriatal neurons is a primary cause of Parkinson's disease. Oxidative stress, excitotoxicity and mitochondrial failure are thought to be key mechanisms resposible for degeneration of dopaminergic cells. We found that the selective antagonist of the mGluR5 subtype MPEP in a dose of 5 mg/kg diminshed basal and veratridine (100 μM)-stimulated dopamine release in rat striatum in an in vivo model of microdialysis. In contrast, MPEP given intrastriatally in a high concentration (500 μM) enhanced the striatal extracellular concentration of dopamine. DCG-IV (100 μM), a non-selective agonist of group II mGluRs, inhibited the veratridine-stimulated striatal dopamine release. In an animal model of neuroxicity in vivo, methamphetamine (5 × 10 mg/kg, injected at 2 h intervals) produced deficits in the striatal content of dopamine and its metabolites DOPAC and HVA 72 h after the treatment. MPEP (5 × 5 mg/kg) given before each methamphetamine injection reversed the decrease in the striatal content of dopamine and diminished the methamphetamine-induced dopamine outflow from nigrostriatal terminals. It is concluded that the MPEP-produced blockade of mGluR5 situated on dopaminergic cells, or the suppression of glutamate release in the subthalamic nucleus or substantia nigra pars reticulata may directly and indirectly cause a decrease in striatal dopamine release. However, inhibitory effect of DCG-IV on dopamine release can be induced by attenuation of excitatory input from corticostriatal terminals by activation of mGluR2/3. Regulation of dopamine carriers by MPEP, an antagonist of group I mGluRs may be responsible for the reversal of toxicity induced by methamphetamine. Received July 7, 2001 Accepted August 6, 2001 Published online September 10, 2002     

AFQ056/mavoglurant,a novel clinically effective mGluR5 antagonist: Identification,SAR and pharmacological characterization

Here we describe the identification, structure–activity relationship and the initial pharmacological characterization of AFQ056/mavoglurant, a structurally novel, non-competitive mGlu5 receptor antagonist. AFQ056/mavoglurant was identified by chemical derivatization of a lead compound discovered in a HTS campaign. In vitro, AFQ056/mavoglurant had an IC₅₀ of 30 nM in a functional assay with human mGluR5 and was selective over the other mGluR subtypes, iGluRs and a panel of 238 CNS relevant receptors, transporter or enzymes. In vivo, AFQ056/mavoglurant showed an improved pharmacokinetic profile in rat and efficacy in the stress-induced hyperthermia test in mice as compared to the prototypic mGluR5 antagonist MPEP. The efficacy of AFQ056/mavoglurant in humans has been assessed in L-dopa induced dyskinesia in Parkinson’s disease and Fragile X syndrome in proof of principle clinical studies.     

Alterations in mGluR5 expression and signaling in Lewy body disease and in transgenic models of alpha-synucleinopathy--implications for excitotoxicity

Dementia with Lewy bodies (DLB) and Parkinson's Disease (PD) are neurodegenerative disorders of the aging population characterized by the abnormal accumulation of alpha-synuclein (alpha-syn). Previous studies have suggested that excitotoxicity may contribute to neurodegeneration in these disorders, however the underlying mechanisms and their relationship to alpha-syn remain unclear. For this study we proposed that accumulation of alpha-syn might result in alterations in metabotropic glutamate receptors (mGluR), particularly mGluR5 which has been linked to deficits in murine models of PD. In this context, levels of mGluR5 were analyzed in the brains of PD and DLB human cases and alpha-syn transgenic (tg) mice and compared to age-matched, unimpaired controls, we report a 40% increase in the levels of mGluR5 and beta-arrestin immunoreactivity in the frontal cortex, hippocampus and putamen in DLB cases and in the putamen in PD cases. In the hippocampus, mGluR5 was more abundant in the CA3 region and co-localized with alpha-syn aggregates. Similarly, in the hippocampus and basal ganglia of alpha-syn tg mice, levels of mGluR5 were increased and mGluR5 and alpha-syn were co-localized and co-immunoprecipitated, suggesting that alpha-syn interferes with mGluR5 trafficking. The increased levels of mGluR5 were accompanied by a concomitant increase in the activation of downstream signaling components including ERK, Elk-1 and CREB. Consistent with the increased accumulation of alpha-syn and alterations in mGluR5 in cognitive- and motor-associated brain regions, these mice displayed impaired performance in the water maze and pole test, these behavioral alterations were reversed with the mGluR5 antagonist, MPEP. Taken together the results from study suggest that mGluR5 may directly interact with alpha-syn resulting in its over activation and that this over activation may contribute to excitotoxic cell death in select neuronal regions. These results highlight the therapeutic importance of mGluR5 antagonists in alpha-synucleinopathies.     

Structure–activity relationships in a novel series of 7-substituted-aryl quinolines and 5-substituted-aryl benzothiazoles at the metabotropic glutamate receptor subtype 5

The metabotropic glutamate receptor subtype 5 (mGluR5) has been implicated in numerous neuropsychiatric disorders including addiction. We have discovered that the rigid diaryl alkyne template, derived from the potent and selective noncompetitive mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP), can serve to guide the design of novel quinoline analogues and pharmacophore optimization has resulted in potent mGluR5 noncompetitive antagonists (EC₅₀ range 60–100 nM) in the quinoline series.