Ryoko Yoshikawa

MGS0039: a potent and selective group II metabotropic glutamate receptor antagonist with antidepressant-like activity.

The present study describes the pharmacological profile of (1R,2R,3R,5R,6R)-2-Amino-3-(3,4-dichlorobenzyloxy)-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (MGS0039), a novel group II mGluR antagonist. MGS0039 showed high affinity for both mGluR2 (Ki = 2.2 nM) and mGluR3 (Ki = 4.5 nM), which are comparable to LY341495, another group II mGluR antagonist. MGS0039 attenuated both glutamate-induced inhibition of forskolin-evoked cyclic AMP formation in CHO cells expressing mGluR2 (IC50 = 20 nM) or mGluR3 (IC50 = 24 nM) and glutamate-increased [35S]GTPgammaS binding to mGluR2 (pA2 = 8.2), which means that MGS0039 acts as an antagonist. MGS0039 shifted the dose-response curve of glutamate-increased [35S]GTPgammaS binding rightward without altering the maximal response, and thereby indicating competitive antagonism. MGS0039 showed no significant effects on other mGluRs as well as the other receptors and transporters we studied. MGS0039 (0.3-3 mg/kg, i.p.) as well as LY341495 (0.1-3 mg/kg, i.p.) had dose-dependent antidepressant-like effects in the rat forced swim test and in the mouse tail suspension test. In contrast, MGS0039 (0.3-3 mg/kg, i.p.) had no apparent effect in the rat social interaction test and in the rat elevated plus-maze. These results indicate that MGS0039 is a potent and selective antagonist of group II mGluR, and that group II mGluR antagonists, like MGS0039, have an antidepressant-like potential in experimental animal models.

Neuropharmacological profile of peripheral benzodiazepine receptor agonists, DAA1097 and DAA1106.

Receptor binding and behavioral profiles of N-(4-chloro-2-phenoxyphenyl)-N-(2-isopropoxybenzyl)acetamide (DAA1097) and N-(2,5-dimethoxybenzyl)-N-(5-fluoro-2-phenoxyphenyl)acetamide (DAA1106), novel, selective agonists for the peripheral benzodiazepine receptor (PBR) were examined. DAA1097 and DAA1106 inhibited [3H]PK 11195 binding to crude mitochondrial preparations of rat whole brain, with IC50 values of 0.92 and 0.28 nM. Likewise, DAA1097 and DAA1106 inhibited [3H]Ro 5-4864 binding to the same mitochondrial preparation, with IC50 values of 0.64 and 0.21 nM. In contrast, DAA1097 and DAA1106 did not inhibit [3H]-flunitrazepam, the central benzodiazepine receptor (CBR) ligand, binding to membranes of rat whole brain (IC50>10,000nM). Oral administration of DAA1097 and DAA1106 had anxiolytic effects in the mouse light/dark exploration test and in the rat elevated plus- maze test. Oral administration of DAA1106, diazepam and buspirone but not DAA1097 significantly increased sleeping time in hexobarbital-induced anesthesia in mice. The order of potency of potentiation of hexobarbital anesthesia was diazepam> buspirone> DAA1106> DAA1097. Oral administration of DAA1097 and DAA1106 but not diazepam and buspirone did not affect spontaneous locomotor activity in mice. These findings indicate that DAA1097 and DAA1106 are PBR selective ligands with potent anxiolytic-like properties, in laboratory animals.

Binding characteristics of [3H]DAA1106, a novel and selective ligand for peripheral benzodiazepine receptors

Here, we investigated the binding characteristics of [3H]N-(2,5-dimethoxybenzyl)-N-(5-fluoro-2-phenoxyphenyl)acetamide ([3H]DAA1106), a potent and selective ligand for peripheral benzodiazepine receptors, in mitochondrial fractions of the rat brain. [3H]DAA1106 bound to the mitochondrial fraction of the rat brain in a saturable manner. The dissociation constant (Kd) and maximal number of binding sites (Bmax) obtained from Scatchard plot analysis of the saturation curve of [3H]DAA1106 binding were 0.12 +/- 0.03 nM and 161.03 +/- 5.80 fmol/mg protein, respectively. [3H]DAA1106 binding to mitochondrial preparations of the rat cerebral cortex was inhibited by several peripheral benzodiapine receptor ligands, and DAA1106 was the most potent inhibitor in inhibiting [3H]DAA1106 binding among the peripheral benzodiazepine receptor ligands we tested. The binding of [3H]DAA1106 was not affected by several neurotransmitter-related compounds, including adrenoceptor, gamma-aminobutyric acid (GABA), dopamine, 5-hydroxytryptamine (5-HT), acetylcholine, histamine, glutamate and central benzodiazepine receptor ligands even at a concentration of 10 microM. In the cerebral cortex of rhesus monkeys, DAA1106 and 1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoquinoline carboxamide (PK11195) potently inhibited [3H]DAA1106 binding, while 7-chloro-5-(4-chlorophenyl)-1-methyl-1,3-dihydrobenzo[e][1,4]diazepin -2-one (Ro5-4864) did not. The highest [3H]DAA1106 binding was observed in the olfactory bulb, followed by the cerebellum. In autoradiographic studies, practically the same results were obtained, in that the highest binding of [3H]DAA1106 was in the olfactory bulb. Potent labeling was also noted in ventricular structures such as the choroid plexus. Thus, [3H]DAA1106 is a potent and selective ligand for peripheral benzodiazepine receptors and should prove useful for elucidating the physiological relevance of events mediated through peripheral benzodiazepine receptors.

Nardosinone, a novel enhancer of nerve growth factor in neurite outgrowth from PC12D cells

We isolated nardosinone as a neuritogenic substance from Nardostachys chinensis. Nardosinone did not exhibit the neurotrophic activity but caused a marked enhancement of the nerve growth factor (NGF)-mediated neurite outgrowth from PC12D cells. Nardosinone-induced enhancement of the NGF-action was completely blocked by PD98059, a representative mitogen activated protein kinase (MAPK) kinase inhibitor. The microscopic observations indicated that the neurites in response to nardosinone and NGF were quite long and were generally extended to the neighboring cells. These results suggest that nardosinone enhances the NGF-induced neurite outgrowth from PC12D cells probably by amplifying an up-stream step of MAPK kinase in the NGF receptor-mediated intracellular signaling pathway.

A selective dopamine D4 receptor antagonist, NRA0160: a preclinical neuropharmacological profile.

NRA0160, 5 - [2- ( 4- ( 3 - fluorobenzylidene) piperidin-1-yl) ethyl] - 4 -(4-fluorophenyl) thiazole-2-carboxamide, has a high affinity for human cloned dopamine D4.2, D4.4 and D4.7 receptors, with Ki values of 0.5, 0.9 and 2.7 nM, respectively. NRA0160 is over 20,000fold more potent at the dopamine D4.2 receptor compared with the human cloned dopamine D2L receptor. NRA0160 has negligible affinity for the human cloned dopamine D3 receptor (Ki=39 nM), rat serotonin (5-HT)2A receptors (Ki=180 nM) and rat alpha1 adrenoceptor (Ki=237 nM). NRA0160 and clozapine antagonized locomotor hyperactivity induced by methamphetamine (MAP) in mice. NRA0160 and clozapine antagonized MAP-induced stereotyped behavior in mice, although their effects did not exceed 50% inhibition, even at the highest dose given. NRA0160 and clozapine significantly induced catalepsy in rats, although their effects did not exceed 50% induction even at the highest dose given. NRA0160 and clozapine significantly reversed the disruption of prepulse inhibition (PPI) in rats produced by apomorphine. NRA0160 and clozapine significantly shortened the phencyclidine (PCP)-induced prolonged swimming latency in rats in a water maze task. These findings suggest that NRA0160 may have unique antipsychotic activities without the liability of motor side effects typical of classical antipsychotics.

Synthesis, in vitro pharmacology, and pharmacokinetic profiles of 2-[1-amino-1-carboxy-2-(9H-xanthen-9-yl)-ethyl]-1-fluorocyclopropanecarboxylic acid and its 6-heptyl ester, a potent mGluR2 antagonist.

In this paper, we describe the synthesis of (+)-(1R( *),2R( *))-2-[(1S( *))-1-amino-1-carboxy-2-(9H-xanthen-9-yl)-ethyl]-1-fluorocyclopropanecarboxylic acid (+)-16a, a compound, that is, fluorinated at the alpha position of the carboxylic acid in the cyclopropane ring of a group II mGluRs antagonist, 1 (LY341495), using a previously reported stereoselective cyclopropanation reaction. The fluorinated compound (+)-16a exhibited almost the same affinity (IC(50)=3.49 nM) for mGluR2 as 1 but had a superior pharmacokinetic profile. Furthermore, a marked elevation of the plasma levels of (+)-16a was observed following the administration of a prodrug, (+)-17.

In vivo receptor occupancy of NRA0045, a putative atypical antipsychotic, in rats.

We have previously reported that (R)-(+)-2-amino-4-(4-fluorophenyl)-5-[1-[4-(4-fluorophenyl)-4-oxobutyl]+ ++pyrrolidin-3-yl]thiazole (NRA0045) is a novel antipsychotic agent with affinities for dopamine D4, 5-hydroxytryptamine 2A (5-HT2A) and alpha1 receptors. In the present study, in vivo receptor occupancy of 5-HT2A, alpha1, dopamine D2 and D3 receptors by NRA0045 was assessed, based on in vivo and ex vivo receptor binding, and findings were compared to reference antipsychotic drugs (haloperidol, risperidone, clozapine). Intraperitoneal administration of haloperidol highly occupied the dopamine D2 receptor in the striatum and nucleus accumbens, and alpha1 adrenoceptors in the frontal cortex. Occupation of the 5-HT2A receptor in the frontal cortex and the dopamine D3 receptor in the nucleus accumbens and islands of Cajella was moderate. By contrast, atypical antipsychotics such as risperidone and clozapine dose-dependently occupied the 5-HT2A receptor in the frontal cortex, with moderate to negligible occupancy of the D2 receptor in the striatum and the nucleus accumbens. Clozapine and risperidone also occupied the alpha1 adrenoceptor in the frontal cortex, and clozapine did not occupy the dopamine D3 receptor. As seen with other atypical antipsychotics, intraperitoneal administration of NRA0045 dose-dependently occupied the 5-HT2A receptor and the alpha1 adrenoceptor in the frontal cortex, while it was without effect on dopamine D2 and D3 receptors in the striatum, nucleus accumbens and islands of Cajella. Thus, the strong occupancy of 5-HT2A and alpha1 receptors is involved in the pharmacological action of NRA0045.

In vitro and in vivo pharmacological profile of 5-{2-[4-(6-fluoro-1H-indole-3-yl)piperidin-1-yl]ethyl}-4-(4-fluorophenyl)thiazole-2-carboxylic acid amide (NRA0562), a novel and putative atypical antipsychotic

In vitro and in vivo pharmacological properties of 5-[2-[4-(6-fluoro-1H-indole-3-yl)piperidin-1-yl]ethyl]-4-(4-fluorophenyl)thiazole-2-carboxylic acid amide (NRA0562), a novel atypical antipsychotic, were investigated. NRA0562 showed high affinities for human cloned dopamine D(1), D(2), D(3) and D(4) receptors with Ki values of 7.09, 2.49, 3.48 and 1.79 nM. In addition, NRA0562 had high affinities for the 5-HT(2A) receptor and the alpha(1) adrenoceptor with Ki values of 1.5 and 0.56 nM, and moderate affinity for the histamine H(1) receptor. Using in vivo and ex vivo receptor binding studies in rats, we showed NRA0562 occupied frontal cortical 5-HT(2A) receptors and alpha(1) adrenoceptor potently, while occupancy of striatal dopamine D(2) receptor was moderate as were other atypical antipsychotics. NRA0562 dose-dependently inhibited methamphetamine (MAP)-induced locomotor hyperactivity in rats. At higher dosage, NRA0562 dose-dependently antagonized MAP-induced stereotyped behavior and induced catalepsy dose-dependently and significantly in rats. But, the ED(50) value in inhibiting MAP-induced locomotion hyperactivity was 10 times lower than that in inhibiting MAP-induced stereotyped behavior, and 30 times lower than that in inducing catalepsy. In addition, the potency of NRA0562 in antagonizing MAP-induced hyperactivity in rats was higher than that of other antipsychotics, clozapine, risperidone and olanzapine. NRA0562 had favorable properties in view of prediction of extrapyramidal side effects. As this antipsychotic has a unique profile with affinity and occupancy for receptors, we propose that NRA0652 may have unique atypical antipsychotic activities, and a moderate liability of extrapyramidal motor side effects seen in the treatment with classical antipsychotics.