Combination of the phosphodiesterase 10A inhibitor, MR1916 with risperidone shows additive antipsychotic-like effects without affecting cognitive enhancement and cataleptic effects in rats.

AIM: Phosphodiesterase 10A (PDE10A) inhibitors not only have antipsychotic-like effects but also cause cognitive enhancement without affecting extrapyramidal side effects in rodents, suggesting that PDE10A may be a novel approach for the treatment of schizophrenia. However, how a combination of PDE10A inhibitor with a currently available antipsychotic drug, risperidone contributes to the effect of each compound in rats remains unclear. The purpose of the present study was to examine the combination effects of MR1916 with a currently available antipsychotic drug, risperidone, in rats. METHODS: We examined the combination effects of the PDE10A inhibitor, MR1916 with risperidone on conditioned avoidance response (CAR) to assess antipsychotic-like effects in rats. We also examined them on catalepsy as extrapyramidal side effects and novel object recognition test in cognitive functions in rats. RESULTS: MR1916 (0.025-0.2 mg/kg, p.o.) and risperidone (0.75-6 mg/kg, p.o.) alone attenuated the CAR in a dose-dependent manner. The combination of MR1916 (0.025 mg/kg, p.o.) with risperidone (0.75 mg/kg, p.o.) significantly enhanced the attenuation of CAR without increasing the escape failure response. At the same dosage, the cataleptic effects were not enhanced by combined treatment of MR1916 with risperidone. Furthermore, the enhancement of object recognition memory induced by MR1916 (0.3 mg/kg, p.o.) was not affected by the combination with risperidone (0.75 mg/kg, p.o.). CONCLUSION: The combination of MR1916 with risperidone may have additive antipsychotic-like effects without affecting extrapyramidal side effects, and the cognitive-enhancing effect of MR1916 may not be interfered with the addition of risperidone.

Pharmacological characterization of a novel potent, selective, and orally active orexin 2 receptor antagonist, SDM-878.

AIMS: Recently, we identified a novel orexin 2 (OX2 ) receptor antagonist, SDM-878 (2-(3-(2-(1H-pyrazol-1-yl)nicotinoyl)-3,8-diazabicyclo[3.2.1]octan-8-yl)-3-methoxyisonicotinonitrile). The purpose of the present study is to characterize the in vitro and in vivo pharmacological effects of SDM-878. METHODS: The in vitro potency and selectivity of SDM-878 were examined in CHO cells that exhibit stable expression of human orexin 1 (OX1 ), human orexin 2 (OX2 ), rat OX1 , and rat OX2 receptors. Then, the plasma half-life, oral bioavailability, and brain penetration of SDM-878 were examined in rats. The in vivo effect of SDM-878 in rats was tested using electroencephalography (EEG). The target engagement of SDM-878 in the rat brain was examined using the antagonistic effect against hyperlocomotion caused by the intracerebroventricular administration of the OX2 receptor agonist, ADL-OXB ([Ala11 , d-Leu15 ]-orexin B). RESULTS: SDM-878 showed potent inhibitory activities for human and rat OX2 receptors with IC values of 10.6 and 8.8 nM, respectively, and approximately 1000-fold selectivity against the OX1 receptor. In rat studies, SDM-878 exhibited a relatively short half-life in plasma, oral bioavailability, and good brain penetration. These data indicate that SDM-878 is a potent, selective, orally active, and brain-penetrable OX2 receptor antagonist. In behavioral studies using rats, SDM-878 (100 mg/kg) antagonized hyperlocomotion caused by intracerebroventricular administration of ADL-OXB. SDM-878 exhibited a potent sleep-promoting effect at the same dose (100 mg/kg) in a rat EEG study. CONCLUSION: Our results suggest that SDM-878 is likely to be a good pharmacological tool for investigating the role of the OX2 receptor and may have therapeutic potential for the treatment of insomnia.

Ameliorative effects of a phosphodiesterase 10A inhibitor, MR1916 on L-DOPA-induced dyskinesia in parkinsonian rats.

BACKGROUND: Dopamine replacement therapy using L-3,4-dihydroxyphenylalanine (L-DOPA) is a gold standard treatment in patients with Parkinson's disease (PD); however, chronic administration of L-DOPA causes excessive involuntary movements called L-DOPA-induced dyskinesia. Therefore, the novel pharmacological treatment is needed. METHODS: We examined the antidyskinetic effect of a phosphodiesterase 10A (PDE10A) inhibitor, MR1916 and a currently available antidyskinetic drug, amantadine in unilateral 6-OHDA lesioned rats exhibited stably dyskinesia after chronic administration of L-DOPA. We also examined the influence of MR1916 and amantadine on the improvement of forelimb akinesia induced by L-DOPA using stepping test in unilateral 6-OHDA lesioned rats. RESULTS: MR1916 (0.03‒0.3 mg/kg, po) reduced L-DOPA-induced dyskinesia in a dose-dependent manner and showed significant effects at doses of 0.1 and 0.3 mg/kg, while amantadine (40 mg/kg, sc) had no remarkable effects. Neither MR1916 (0.03‒0.3 mg/kg, po) nor amantadine (40 mg/kg, sc) affected the antiparkinsonian effects induced by L-DOPA in unilateral 6-OHDA lesioned rats. CONCLUSIONS: These results indicate that MR1916 specifically reduces L-DOPA-induced dyskinesia without affecting the antiparkinsonian effect of L-DOPA in parkinsonian rats.

Pharmacological characterization of a novel, potent, selective, and orally active fatty acid amide hydrolase inhibitor, PKM-833 [(R)-N-(pyridazin-3-yl)-4-(7-(trifluoromethyl)chroman-4-yl)piperazine-1-carboxamide] in rats: Potential for the treatment of inflammatory pain.

Recently, we identified a novel fatty acid amide hydrolase (FAAH) inhibitor, PKM-833 [(R)-N-(pyridazin-3-yl)-4-(7-(trifluoromethyl)chroman-4-yl)piperazine-1-carboxamide]. The aim of the present study is to characterize the pharmacological profile of PKM-833 in vitro and in vivo. PKM-833 showed potent inhibitory activities against human and rat FAAH with IC50 values of 8.8 and 10 nmol/L, respectively, 200-fold more selectivity against other 137 molecular targets, and irreversible mode of action. In pharmacokinetic and pharmacodynamic studies, PKM-833 showed excellent brain penetration and good oral bioavailability, and elevated anandamide (AEA) concentrations in the rat brain. These data indicate that PKM-833 is a potent, selective, orally active, and brain-penetrable FAAH inhibitor. In behavioral studies using rat models, PKM-833 significantly attenuated formalin-induced pain responses (3 mg/kg) and improved mechanical allodynia in complete freund's adjuvant (CFA)-induced inflammatory pain (0.3-3 mg/kg). On the other hand, PKM-833 did not show the analgesic effects against mechanical allodynia in chronic constriction injury (CCI)-induced neuropathic pain up to 30 mg/kg. Regarding side effects, PKM-833 had no significant effects on catalepsy and motor coordination up to 30 mg/kg. These results indicate that PKM-833 is a useful pharmacological agent that can be used to investigate the role of FAAH and may have therapeutic potential for the treatment of inflammatory pain without undesirable side effects.

Orexin 2 receptor is involved in orexin A-induced hyperlocomotion in rats.

BACKGROUND: The orexin system regulates various functions, including sleep/wake cycles, feeding, and cognition. Orexin A and orexin B are endogenous neuropeptides for both orexin 1 (OX1) and orexin 2 (OX2) receptors. Orexin A has a potent agonistic activity for both the receptors and is known to increase locomotor activity in rats. However, it has not been elucidated how each receptor contributes to orexin A-induced hyperlocomotion. METHODS: We examined the effects of an OX1 receptor antagonist, SB 334867, and an OX2 receptor antagonist, EMPA, as well as an OX1 and OX2 receptor antagonist on hyperlocomotion caused by intracerebroventricular administration of orexin A or an OX2 receptor agonist, ADL-OXB ([Ala11,d-Leu15]-orexin B), in rats. RESULTS: EMPA (100 mg/kg, ip) but not SB 334867 (3-10 mg/kg, ip) showed antagonistic effects on ADL-OXB-induced hyperlocomotion without affecting the spontaneous locomotor activity. Both EMPA (100 mg/kg, ip) and the OX1 and OX2 receptor antagonist (3-30 mg/kg, po) antagonized orexin A-induced hyperlocomotion, while SB 334867 (3‒-10 mg/kg, ip) showed no effects. CONCLUSIONS: Our results suggest that orexin A-induced hyperlocomotion is mainly mediated by the activation of the OX2 receptor.

A Selective Phosphodiesterase 10A Inhibitor Reduces L-Dopa-Induced Dyskinesias in Parkinsonian Monkeys.

BACKGROUND: Phosphodiesterase 10A is a member of the phosphodiesterase family whose brain expression is restricted to the striatum. Phosphodiesterase 10A regulates cyclic adenosine monophosphate and cyclic guanosine monophosphate, which mediate responses to dopamine receptor activation, and the levels of these cyclic nucleotides are decreased in experimental models of l-dopa-induced dyskinesia. The elevation of cyclic adenosine monophosphate/cyclic guanosine monophosphate levels by phosphodiesterase 10A inhibition may thus be targeted to reduce l-dopa-induced dyskinesia. OBJECTIVES: The present study was aimed at determining the potential antidyskinetic effects of phosphodiesterase 10A inhibitors in a primate model of Parkinson's disease (PD). The experiments performed in this model were also intended to provide translational data for the design of future clinical trials. METHODS: Five MPTP-treated macaques with advanced parkinsonism and reproducible l-dopa-induced dyskinesia were used. MR1916, a selective phosphodiesterase 10A inhibitor, at doses 0.0015 to 0.05 mg/kg, subcutaneously, or its vehicle (control test) was coadministered with l-dopa methyl ester acutely (predetermined optimal and suboptimal subcutaneous doses) and oral l-dopa chronically as daily treatment for 5 weeks. Standardized scales were used to assess motor disability and l-dopa-induced dyskinesia by blinded examiners. Pharmacokinetics was also examined. RESULTS: MR1916 consistently reduced l-dopa-induced dyskinesia in acute tests of l-dopa optimal and suboptimal doses. Significant effects were present with every MR1916 dose tested, but the most effective was 0.015 mg/kg. None of the MR1916 doses tested affected the antiparkinsonian action of l-dopa at the optimal dose. The anti-l-dopa-induced dyskinesia effect of MR1916 (0.015 mg/kg, subcutaneously) was sustained with chronic administration, indicating that tolerance did not develop over the 5-week treatment. No adverse effects were observed after MR1916 administration acutely or chronically. CONCLUSIONS: Results show that regulation of striatal cyclic nucleotides by phosphodiesterase 10A inhibition could be a useful therapeutic approach for l-dopa-induced dyskinesia, and therefore data support further studies of selective phosphodiesterase 10A inhibitors for PD therapy. © 2018 International Parkinson and Movement Disorder Society.

Pharmacological characterization of a novel potent, selective, and orally active phosphodiesterase 2A inhibitor, PDM-631.

Recently, we identified a novel phosphodiesterase 2A (PDE2A) inhibitor, PDM-631 ((S)-3-cyclopropyl-6-methyl-1-(1-(4-(trifluoromethoxy)phenyl)propan-2-yl)-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one). PDM-631 showed potent inhibitory activities for human and rat PDE2A with IC50 values of 1.5 and 4.2nM, respectively and more than 2000-fold selectivity against other phosphodiesterases. In rat studies, PDM-631 showed oral bioavailability and good brain penetration, and increased the cGMP levels in the cortex. These data indicate that PDM-631 is a potent, selective, orally active, and brain-penetrable PDE2A inhibitor. In behavioral studies using rat models, PDM-631 (3-30mg/kg) resulted in better discrimination between a novel object and a familiar one 48h after the acquisition phase in the novel object recognition test, thus indicating that PDM-631 increased object recognition memory. In contrast, PDM-631 did not attenuate the conditioned avoidance response at the same dose range (3-30mg/kg) in rats, indicating that PDM-631 did not show an antipsychotic-like effect. In test for extrapyramidal side effect, PDM-631 had no effect on catalepsy at the effective doses (10 and 30mg/kg) in the novel object recognition test, while haloperidol caused catalepsy at a dose of 3mg/kg. Our results suggest that PDM-631 is a good pharmacological tool that can be used to investigate the role of PDE2A and may have therapeutic potential for the treatment of cognitive impairments associated with schizophrenia and neurodegenerative disorders, without any extrapyramidal side effects.

Dopamine D1 signaling involvement in the effects of the phosphodiesterase 10A inhibitor, PDM-042 on cognitive function and extrapyramidal side effect in rats.

Inhibition of phosphodiesterase 10A (PDE10A) results in activation of a dopamine D1 receptor-mediated direct pathway in addition to a dopamine D2 receptor-mediated indirect pathway in the striatum. Therefore, PDE10A inhibitors could be novel therapeutics for schizophrenia, which differ from the currently available antipsychotics that directly block the dopamine D2 receptor. Previously, we found that a novel PDE10A inhibitor, PDM-042, had antipsychotic-like activity similar to currently available antipsychotics and minimal cataleptic effects in rats. The purpose of the present study was to examine the pharmacological effects of PDM-042 on cognitive function and extrapyramidal side effect. In addition, we aimed to examine whether these effects were mediated by activation of dopamine D1 signaling in rats. PDM-042 (1-3mg/kg) resulted in better discrimination of a novel object from a familiar one 48h after the acquisition trial, suggesting that PDM-042 increased object recognition memory. A dopamine D1 receptor antagonist, SCH23390 (0.1mg/kg), significantly blocked the enhancement of the object recognition memory induced by PDM-042 (3mg/kg) without affecting the recognition index by itself. We also found that the cataleptic effect of PDM-042 (1mg/kg) was significantly enhanced by SCH23390 (0.01-0.03mg/kg). These results indicate that PDM-042 has the potential to increase object recognition memory and that the cognitive enhancing and cataleptic effects of PDM-042 are mediated at least by activation of dopamine D1 signaling.

Pharmacological characterization of a novel potent, selective, and orally active phosphodiesterase 10A inhibitor, PDM-042 [(E)-4-(2-(2-(5,8-dimethyl-[1,2,4]triazolo[1,5-a]pyrazin-2-yl)vinyl)-6-(pyrrolidin-1-yl)pyrimidin-4-yl)morpholine] in rats: potential for the treatment of schizophrenia.

Recently, we identified a novel phosphodiesterase 10A (PDE10A) inhibitor, PDM-042 ((E)-4-(2-(2-(5,8-dimethyl-[1,2,4]triazolo[1,5-a]pyrazin-2-yl)vinyl)-6-(pyrrolidin-1-yl)pyrimidin-4-yl)morpholine). PDM-042 showed potent inhibitory activities for human and rat PDE10A with IC 50 values of less than 1 nmol/L and more than 1000-fold selectivity against other phosphodiesterases. Tritiated PDM-042, [3H]PDM-042, had high affinity for membranes prepared from rat striatum with a Kd value of 8.5 nmol/L. The specific binding of [3H]PDM-042 was displaced in a concentration-dependent manner by PDM-042 and another structurally unrelated PDE10A inhibitor, MP-10. In rat studies, PDM-042 showed excellent brain penetration (striatum/plasma ratio = 6.3), occupancy rate (86.6% at a dose of 3 mg/kg), and good oral bioavailability (33%). These data indicate that PDM-042 is a potent, selective, orally active, and brain-penetrable PDE10A inhibitor. In behavioral studies using rat models relevant to schizophrenia, PDM-042 significantly antagonized MK-801-induced hyperlocomotion (0.1-0.3 mg/kg) without affecting spontaneous locomotor activity and attenuated the conditioned avoidance response (CAR) (0.3-1 mg/kg). In tests for adverse effects, PDM-042 had a minimal effect on catalepsy, even at a much higher dose (10 mg/kg) than the minimal effective dose (0.3 mg/kg) in the CAR. Furthermore, PDM-042 had no effect on prolactin release or glucose elevation up to 3 mg/kg, while risperidone increased prolactin release and olanzapine enhanced glucose levels at doses near their efficacious ones in the CAR. Our results suggest that PDM-042 is a good pharmacological tool that can be used to investigate the role of PDE10A and may have therapeutic potential for the treatment of schizophrenia.

Behavioral effects of N-desmethylclozapine on locomotor activity and sensorimotor gating function in mice-Possible involvement of muscarinic receptors.

N-desmethylclozapine (NDMC), a major circulating metabolite of the atypical antipsychotic drug, clozapine, and has M(1) muscarinic receptor partial agonistic property. The purpose of the present study was to examine whether in vivo behavioral effects of NDMC were elicited through the activation of muscarinic receptors. Both a non-selective muscarinic receptor agonist, oxotremorine (0.01-0.1mg/kg), and an M(1) and M(4) muscarinic receptor agonist, xanomeline (0.3-3mg/kg), decreased exploratory locomotor activity in mice. This effect was significantly antagonized by a non-selective muscarinic receptor antagonist, scopolamine, at a dose of 0.3mg/kg without affecting exploratory locomotor activity by itself. NDMC (3-30mg/kg) also decreased exploratory locomotor activity in a dose-dependent manner, and the reduced locomotor activity was significantly antagonized by scopolamine at doses of 0.1 and 0.3mg/kg. These results suggested that NDMC might decrease exploratory locomotor activity at least partly through the activation muscarinic receptors in vivo. NDMC (10-30mg/kg) and clozapine (0.3-1mg/kg) dose-dependently increased prepulse inhibition (PPI) in DBA/2J mice, as did xanomeline (1-3mg/kg). Scopolamine at a dose of 0.3mg/kg without altering PPI by itself significantly antagonized the increase of PPI caused by NDMC (30mg/kg), xanomeline (3mg/kg), and oxotremorine (0.06mg/kg). These findings suggest that the activation of muscarinic receptors may be at least partly responsible for exerting the antipsychotic-like effects of both NDMC and xanomeline in an animal model for schizophrenia.

Ameliorative effect of N-desmethylclozapine in animal models of social deficits and cognitive functions.

One of the major circulating metabolites of clozapine, N-desmethylclozapine (NDMC), has been demonstrated to exhibit partial agonistic activity at M(1) muscarinic receptors. Some of the unique therapeutic effects of clozapine might involve the pharmacological effects of this metabolite. The purpose of the present study was therefore to examine whether NDMC improved behavioral abnormalities in animal models of social deficits and cognitive deficits of schizophrenia. NDMC (3mg/kg) and clozapine (1-3mg/kg) each improved the reduction of social interaction caused by a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, 5R,10S-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) (0.1mg/kg), without affecting locomotor activity in rats. NDMC (3-10mg/kg) and clozapine (1-3mg/kg) each also resulted in better discrimination of a novel from a familiar object 24h after a training trial in a rat object recognition test. These findings suggest that NDMC can improve behavior in animal models of social deficits and cognitive deficits of schizophrenia as well as clozapine.

Antipsychotic effects of N-desmethylclozapine on sensorimotor gating function in rats--possible involvement of activation of M(1) muscarinic receptors.

N-desmethylclozapine (NDMC), one of the major metabolites of clozapine, has been demonstrated to exhibit partial agonistic activity at M(1) muscarinic receptors in vitro. Behavioral effects of NDMC were examined to determine whether NDMC contributed to the antipsychotic effects of clozapine via activation of muscarinic receptors. Both NDMC (10-30 mg/kg) and its parent compound clozapine (3-10 mg/kg) antagonized the disruption of prepulse inhibition (PPI) caused by the indirect dopamine agonist methamphetamine (3 mg/kg) in rats. However, NDMC (30 mg/kg) did not increase plasma levels of prolactin in rats. The same dose ranges of NDMC antagonized the disruption of PPI caused by the N-methyl-D-aspartate receptor antagonist ketamine (5 mg/kg) in rats. Furthermore, NDMC in the same dose ranges antagonized the disruption of PPI caused by the muscarinic receptor antagonist scopolamine (0.3 mg/kg) in rats. These findings suggest that NDMC has potent antipsychotic effects in animal models to examine sensorimotor gating function, and that NDMC may act through the activation of a muscarinic receptor for the treatment of schizophrenia.

Effects of a novel metabotropic glutamate receptor 7 negative allosteric modulator, 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazonolo[4,5-c]pyridin-4(5H)-one (MMPIP), on the central nervous system in rodents.

We recently identified 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazolo[4,5-c]pyridin-4(5H)-one (MMPIP), the first allosteric metabotropic glutamate (mGlu) 7 receptor-selective negative allosteric modulator. In this study, we examined the in vivo pharmacological effects of MMPIP on the central nervous system. MMPIP was distributed into the brain after systemic administration in both mice and rats. Pharmacokinetic study revealed that the half-life of MMPIP in circulation was about 1h in rats. Results of various behavioral studies revealed that MMPIP impaired non-spatial and spatial cognitive performances in the object recognition test and the object location test in mice, respectively. In rats, MMPIP increased time to complete the task in the 8-arm radial maze test without increasing error. In addition to impairing cognition, MMPIP decreased social interaction with reduction of line crossing in rats, while MMPIP had no effects on locomotor activity in rats and mice, rota-rod performance in mice, prepulse inhibition in rats, maternal separation-induced ultrasonic vocalization in rat pups, stress-induced hyperthermia in mice, or the tail suspension test in mice. No analgesic effects of MMPIP were detected in either the tail immersion test or formalin test in mice. MMPIP did not alter the threshold for induction of seizures by electrical shock or pentylenetetrazole in mice. These findings suggest that blockade of mGlu(7) receptors by MMPIP may modulate both non-spatial and spatial cognitive functions without non-selective inhibitory effects on the central nervous system.

Pharmacological effects of metabotropic glutamate receptor ligands on prepulse inhibition in DBA/2J mice.

Schizophrenic patients typically exhibit impairment of sensorimotor gating, which can be modeled in animals using acoustic prepulse inhibition of the startle. Both classical and atypical antipsychotics have been shown to improve prepulse inhibition in DBA/2J mice, a non-pharmacological model for impaired sensorimotor gating. The purpose of the present study was to clarify whether metabotropic glutamate receptors participate in control of sensorimotor gating. We evaluated various metabotropic glutamate receptor ligands on prepulse inhibition in DBA/2J mice. This basal level of prepulse inhibition in DBA/2J mice was increased by only the mGlu(1) receptor antagonists [2-cyclopropyl-5-[1-(2-fluoro-3-pyridinyl)-5-methyl-1H-1,2,3-triazol-4-yl]-2,3-dihydro-1H-isoindol-1-one] (CFMTI), 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-alpha]benzimidazole-2-carboxamide hydrochloride (YM-298198), and (3,4-dihydro-2H-pyrano[2,3-b]quinolin-7-yl)-(cis-4-methoxycyclohexyl)-methanone (JNJ16259685). There was no effect after treatments with the mGlu(5) receptor antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP), the mGlu(2/3) receptor agonist (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268), the mGlu(2/3) receptor antagonist (2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495), the mGlu(7) receptor agonist N,N'-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082), the mGlu(7) receptor antagonist 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazonolo[4,5-c]pyridin-4(5H)-one (MMPIP), or the mGlu(8) receptor agonist (S)-3,4-dicarboxyphenylglycine (DCPG). These findings indicate that inhibition of mGlu(1) receptor selectively increases prepulse inhibition in DBA/2J mice and suggest that mGlu(1) receptor antagonists could be a novel treatment for some aspects of schizophrenia.

Discovery and biological profile of isoindolinone derivatives as novel metabotropic glutamate receptor 1 antagonists: a potential treatment for psychotic disorders.

We describe here the discovery and biological profile of a series of isoindolinone derivatives as developed mGluR1 antagonists. Our combined strategy of rapid parallel synthesis and conventional medicinal optimization successfully led to N-cyclopropyl 22 and N-isopropyl isoindolinone analogs 21 and 23 with improved in vivo DMPK profiles. Moreover the most advanced analog 23 showed an oral antipsychotic-like effect at a dose of 1mg/kg in an animal model.

Discovery and in vitro and in vivo profiles of 4-fluoro-N-[4-[6-(isopropylamino)pyrimidin-4-yl]-1,3-thiazol-2-yl]-N-methylbenzamide as novel class of an orally active metabotropic glutamate receptor 1 (mGluR1) antagonist.

We identified 4-fluoro-N-[4-[6-(isopropylamino)pyrimidin-4-yl]-1,3-thiazol-2-yl]-N-methylbenzamide 27 as a potent mGluR1 antagonist. The compound possessed excellent subtype selectivity and good PK profile in rats. It also demonstrated relatively potent antipsychotic-like effects in several animal models. Suitable for development as a PET tracer, compound 27 would have great potential for elucidation of mGluR1 functions in human.

Correlation of receptor occupancy of metabotropic glutamate receptor subtype 1 (mGluR1) in mouse brain with in vivo activity of allosteric mGluR1 antagonists.

The aim of this study was to clarify the relationship between receptor occupancy and in vivo pharmacological activity of mGluR1 antagonists. The tritiated mGluR1-selective allosteric antagonist [(3)H]FTIDC (4-[1-(2-fluoropyridin-3-yl)-5-methyl-1H-1,2,3-triazol-4-yl]-N-isopropyl-N-methyl-3,6-dihydropyridine-1(2H)-carboxamide) was identified as a radioligand having high affinity for mGluR1-expressing CHO cells (K(D) = 2.1 nM) and mouse cerebellum (K(D) = 3.7 nM). [(3)H]FTIDC bound to mGluR1 was displaced by structurally unrelated allosteric antagonists, suggesting there is a mutual binding pocket shared with different allosteric antagonists. The binding specificity of [(3)H]FTIDC for mGluR1 in brain sections was demonstrated by the lack of significant binding to brain sections prepared from mGluR1-knockout mice. Ex vivo receptor occupancy with [(3)H]FTIDC revealed that the receptor occupancy level by FTIDC correlated well with FTIDC dosage and plasma concentration. Intracerebroventricular administration of (S)-3,5-dihydroxyphenylglycine is known to elicit face washing behavior that is mainly mediated by mGluR1. Inhibition of this behavioral change by FTIDC correlated with the receptor occupancy level of mGluR1 in the brain. A linear relationship between the receptor occupancy and in vivo activity was also demonstrated using structurally diverse mGluR1 antagonists. The receptor occupancy assays could help provide guidelines for selecting appropriate doses of allosteric mGluR1 antagonist for examining the function of mGluR1 in vivo.

Unique antipsychotic activities of the selective metabotropic glutamate receptor 1 allosteric antagonist 2-cyclopropyl-5-[1-(2-fluoro-3-pyridinyl)-5-methyl-1H-1,2,3-triazol-4-yl]-2,3-dihydro-1H-isoindol-1-one.

A newly discovered metabotropic glutamate receptor (mGluR) 1 allosteric antagonist, 2-cyclopropyl-5-[1-(2-fluoro-3-pyridinyl)-5-methyl-1H-1,2,3-triazol-4-yl]-2,3-dihydro-1H-isoindol-1-one (CFMTI), was tested both in vitro and in vivo for its pharmacological effects. CFMTI demonstrated potent and selective antagonistic activity on mGluR1 in vitro and in vivo after oral administration. CFMTI inhibited L-glutamate-induced intracellular Ca(2+) mobilization in Chinese hamster ovary cells expressing human and rat mGluR1a, with IC(50) values of 2.6 and 2.3 nM, respectively. The selectivity of CFMTI to mGluR1 over mGluR5 was >2000-fold, and CFMTI at 10 microM showed no agonistic or antagonistic activities toward other mGluR subtypes and other receptors. It antagonized face-washing behavior in mice induced by (S)-3,5-dihidroxyphenylglycine at a dose range of 3 to 30 mg/kg, for which receptor occupancy was 73 to 94%. As with the classical neuroleptic haloperidol and an atypical antipsychotic, clozapine, orally administered CFMTI reduced methamphetamine-induced hyperlocomotion and disruption of prepulse inhibition (PPI) at the same dose range as required to antagonize the face-washing behavior. CFMTI and clozapine improved ketamine-induced hyperlocomotion, PPI disruption and (5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801)-induced social withdrawal without any cataleptogenic activities, whereas haloperidol only improved ketamine-induced hyperlocomotion. CFMTI, unlike clozapine, caused neither hypolocomotion nor motor incoordination at therapeutic doses. In c-fos expression studies, CFMTI and clozapine increased the number of fos-positive neurons in the nucleus accumbens and medial prefrontal cortex but not in the dorsolateral striatum. These results suggest that the antipsychotic activities of mGluR1 antagonists are more similar to those of atypical antipsychotics than those of typical antipsychotics.

Discovery and biological profile of 4-(1-aryltriazol-4-yl)-tetrahydropyridines as an orally active new class of metabotropic glutamate receptor 1 antagonist.

We describe here the discovery and the structure-activity relationship (SAR) of a series of 4-(1-Aryltriazol-4-yl)-tetrahydropyridines as novel mGluR1 antagonists. Our extensive chemical modification of lead compound 2 successfully led to fluoropyridine analogs 7j and 1 with improved in vivo antagonistic activities. Among the evaluated compounds, chemically stable urea analog 1 showed oral antagonistic activity at dose ranges of 10-30mg/kg in an animal model.