Toshihito Kumagai

The atypical antipsychotic profile of NRA0045, a novel dopamine D4 and 5-hydroxytryptamine2A receptor antagonist, in rats

The atypical antipsychotic profile of (R)‐(+)‐2‐amino‐4‐(4‐fluorophenyl)‐5‐[1‐[4‐(4‐fluorophenyl)‐4‐oxobutyl] pyrrolidin‐3‐yl] thiazole (NRA0045), a potent dopamine D4 and 5‐hydroxytryptamine (5‐HT)2A receptor antagonist, was examined in rats. Spontaneous locomotor activity was decreased dose‐dependently with i.p. administration of clozapine (ED50 3.7 mg kg−1), haloperidol (ED50 0.1 mg kg−1) and chlorpromazine (ED50 0.9 mg kg−1), whereas inhibition of this type of behaviour induced by i.p. administration of NRA0045, at doses up to 10 mg kg−1, did not exceed 50%. Locomotor hyperactivity induced by methamphetamine (MAP, 2 mg kg−1, i.p.) in rats (a model of antipsychotic activity) was dose‐dependently antagonized by NRA0045 (ED50 0.4 mg kg−1, i.p., and 0.3 mg kg−1, p.o., respectively), clozapine (ED50 0.3 mg kg−1, i.p. and 0.8 mg kg−1, p.o., respectively), haloperidol (ED50 0.02 mg kg−1, i.p. and 0.1 mg kg−1, p.o., respectively), chlorpromazine (ED50 0.3 mg kg−1, i.p. and 3.3 mg kg−1, p.o., respectively). In contrast, the MAP (3 mg kg−1, i.v.)‐induced stereotyped behaviour in rats (a model of extrapyramidal symptoms) was not affected by NRA0045 or clozapine, at the highest dose given (30 mg kg−1, i.p.). Haloperidol (ED50 0.3 mg kg−1, i.p.) and chlorpromazine (ED50 4.8 mg kg−1, i.p.) strongly blocked the MAP‐induced stereotyped behaviour. NRA0045 and clozapine selectively blocked behaviour associated with activation of the mesolimbic/mesocortical dopamine neurones rather than nigrostriatal dopamine neurones. Extracellular single‐unit recording studies demonstrated that MAP (1 mg kg−1, i.v.) decreased the firing rate in the substantia nigra (A9) and ventral tegmental area (A10) dopamine neurones in anaesthetized rats. NRA0045 completely reversed the inhibitory effects of MAP on A10 dopamine neurones (ED50 0.1 mg kg−1, i.v.), whereas the inhibitory effects of MAP on A9 dopamine neurones were not affected by NRA0045, in doses up to 1 mg kg−1 (i.v.). Clozapine completely reversed the inhibitory effects of MAP on A10 dopamine neurones (ED50 1.9 mg kg−1, i.v.) and on A9 dopamine neurones (ED50 2.5 mg kg−1, i.v.). Haloperidol completely reversed the inhibitory effects of MAP on A10 (ED50 0.03 mg kg−1, i.v.) and on A9 dopamine neurones (0.02 mg kg−1, i.v.). NRA0045, like clozapine, was more potent in reversing the effects of MAP on A10 than A9 dopamine neurones. Prepulse inhibition (PPI) is impaired markedly in humans with schizophrenia. The disruption of PPI in rats by apomorphine (0.5 mg kg−1, s.c.) was reversed significantly by NRA0045 (3 mg kg−1, i.p.), clozapine (3 mg kg−1, i.p.) and haloperidol (0.3 mg kg−1, i.p.). Phencyclidine (PCP) elicits predominantly psychotic symptoms in normal humans and in schizophrenics. NRA0045 (0.03–0.3 mg kg−1, i.p.) and clozapine (0.1–1 mg kg−1, i.p.) significantly and dose‐dependently shortened the PCP(1.25 mg kg−1, i.p.)‐induced prolonged swimming latency in rats in a water maze task, whereas haloperidol (0.01–0.1 mg kg−1, i.p.) did not significantly alter swimming latency. These findings suggest that NRA0045 may have unique antipsychotic activities without the liability of motor side effects typical of classical antipsychotics.

In vitro pharmacological profile of nonpeptide CRF1 receptor antagonists, CRA1000 and CRA1001

We investigated pharmacological properties of CRA1000 (2-(N-(2-methylthio-4-isopropylphenyl)-N-ethylamino-4-(4-(3-fluoro phenyl)-1,2,3,6-tetrahydropyridin-1-yl)-6-methylpyrimidine) and CRA1001 (2-( N-(2-bromo-4-isopropylphenyl)-N-ethylamino-4-(4-(3-fluorophenyl)-1 ,2,3,6-tetrahydropyridin-1-yl)-6-methylpyrimidine), novel and selective antagonists for the corticotropin-releasing factor1 (CRF1) receptor. Both CRA1000 and CRA1001 inhibited [125I]ovine CRF binding to membranes of COS-7 cells expressing the rat CRF1 receptor with IC50 values of 30 and 38 nM, respectively, without affecting [125I]sauvagine binding to membranes of COS-7 cells expressing the rat CRF2alpha receptor. CRF elicited intracellular cyclic AMP (cAMP) accumulation in AtT-20 cells which express the CRF1 receptor but not the CRF2 receptor, and COS-7 cells expressing CRF1 or CRF2alpha receptors. The CRF-induced cAMP accumulation was inhibited by both CRA1000 and CRA1001, concentration-dependently, in AtT-20 cells and COS-7 cells expressing the CRF1 receptor, while these compounds did not attenuate the CRF response in COS-7 cells expressing the CRF2alpha receptor. CRF increased adrenocorticotropin (ACTH) secretion from AtT-20 cells, and CRA1000 and CRA1001 inhibited CRF-induced ACTH secretion, concentration-dependently, as did other CRF1 receptor antagonists. These results show that both CRA1000 and CRA1001 are potent and selective CRF1 receptor antagonists.

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.

Design, synthesis and structure-affinity relationships of 4-methylidenepiperidine and 4-aryl-1,2,3,6-tetrahydropyridine derivatives as corticotropin-releasing factor1 receptor antagonists.

Recently, various non-peptide corticotropin-releasing factor1 (CRF1) receptor antagonists have been reported. Structure-affinity relationships (SARs) of non-peptide CRF antagonists suggest that such antagonists can be constructed of three units: a hydrophobic unit (Up-Area), a proton accepting unit (Central-Area), and an aromatic unit (Down-Area). Our interest focused on the Up-Area in deriving the novel methylidenepiperidine derivatives 8-10 and 4-aryl-1,2,3,6-tetrahydropyridine derivatives 11-13 as non-peptide CRF1 receptor antagonists. Compounds 8a and 11a had moderate affinity for CRF1 receptor, but compounds 9, 10, 12 and 13 did not exhibit CRF1 receptor affinity. Modification of derivatives 11 afforded compounds 11i (CRA1001) and 11x (CRA1000), which had high affinity and selectivity for CRF1 receptors with potent anxiolytic-like and antidepressant-like properties in some experimental animal models. These findings suggest that the hydrophonic unit (Up-Area) may be useful for design of CRF1 antagonists. We report here the design, synthesis and SARs of the derivatives 8 and 11 and isosteres 9, 10, 12 and 13.

Chemical modification of aryl-1,2,3,6-tetrahydropyridinopyrimidine derivative to discover corticotropin-releasing factor1 receptor antagonists: Aryl-1,2,3,6-tetrahydropyridino-purine, -3H-1,2,3-triazolo[4,5-d]pyrimidine, -purin-8-one, and -7H-pyrrolo[2,3-d]pyrimidine derivatives

Structure-affinity relationships (SARs) of non-peptide CRF(1) antagonists suggest that such antagonists can be constructed of three units: a hydrophobic unit (Up-Area), a proton accepting unit (Central-Area), and an aromatic unit (Down-Area). Recently, various non-peptide corticotropin-releasing factor(1) (CRF(1)) receptor antagonists obtained by modification of the Central-Area have been reported. In contrast, we modified the Up-Area and presented 4- or 5-aryl-1,2,3,6-tetrahydropyridinopyrimidine derivatives including potent CRF receptor ligands 1a-c, and proposed that the 4- or 5-aryl-1,2,3,6-tetrahydropyridino moiety might be useful as a substituent in the Up-Area. Our interest shifted to the chemical modification in which the pyrimidine ring of 1a-c was replaced by other heterocycles, purine ring of 2, 3H-1,2,3-triazolo[4,5-d]pyrimidine ring of 3, purin-8-one ring of 4 and 7H-pyrrolo[2,3-d]pyrimidine ring of 5. Among them, 5-aryl-1,2,3,6-tetrahydropyridinopurine compound 6j (CRA0186) had the highest affinity for CRF(1) receptors (IC(50)=20nM). We report here the synthesis and SARs of derivatives 6-9.

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.

In vitro and in vivo pharmacological profile of 4-(4-fluorobenzylidene)-1-[2-[5-(4-fluorophenyl)-1H-pyrazol-4-yl] ethyl] piperidine (NRA0161).

Atypical antipsychotic properties of 4-(4-fluorobenzylidene)-1-[2-[5-(4-fluorophenyl)-1H-pyrazol-4-yl]ethyl] piperidine (NRA0161) were investigated by in vitro receptor affinities, in vivo receptor occupancies and findings were compared with those of risperidone and haloperidol in rodent behavioral studies. In in vitro receptor binding studies, NRA0161 has a high affinity for human cloned dopamine D(4) and 5-HT(2A) receptor with Ki values of 1.00 and 2.52 nM, respectively. NRA0161 had a relatively high affinity for the alpha(1) adrenoceptor (Ki; 10.44 nM) and a low affinity for the dopamine D(2) receptor (Ki; 95.80 nM). In in vivo receptor binding studies, NRA0161 highly occupied the 5-HT(2A) receptor in rat frontal cortex. In contrast, NRA0161 did not occupy the striatal D(2) receptor. In behavioral studies, NRA0161, risperidone and haloperidol antagonized the locomotor hyperactivity in mice, as induced by methamphetamine (MAP). At a higher dosage, NRA0161, risperidone and haloperidol dose-dependently antagonized the MAP-induced stereotyped behavior in mice and NRA0161 dose-dependently and significantly induced catalepsy in rats. The ED(50) value in inhibiting the MAP-induced locomotor hyperactivity was 30 times lower than that inhibiting the MAP-induced stereotyped behavior and 50 times lower than that which induced catalepsy. These findings suggest that NRA0161 may have atypical antipsychotic activities yet without producing extrapyramidal side effects.