A Novel Potent and Selective Histamine H3 Receptor Antagonist Enerisant: In Vitro Profiles, In Vivo Receptor Occupancy, and Wake-Promoting and Procognitive Effects in Rodents.

Histamine H3 receptor antagonists/inverse agonists are known to enhance the activity of histaminergic neurons in the brain, thereby promoting arousal and cognition. Here, we report the in vitro and in vivo pharmacological profiles for a newly synthesized histamine H3 receptor antagonist/inverse agonist: [1-(4-{3-[(2R)-2-methylpyrrolidin-1-yl]propoxy}phenyl)-1H-pyrazol-4-yl](morpholin-4-yl)methanone monohydrochloride (enerisant hydrochloride). In vitro assays showed that enerisant was a competitive antagonist/inverse agonist with a high affinity and selectivity for human and rat histamine H3 receptors. Enerisant showed antagonist activity in vivo, as assessed using R-α-methylhistamine (a histamine H3 receptor agonist)-induced dipsogenia, and occupied the histamine H3 receptor in the frontal cortex in a dose-dependent manner. Enerisant also enhanced the extracellular levels of histamine in the posterior hypothalamus and the levels of dopamine and acetylcholine in the medial prefrontal cortex of rats. Enerisant exerted a procognitive effect or reversed scopolamine-induced cognitive impairment in a social recognition test and a novel object recognition test in rats at doses at which less than 50% of the histamine H3 receptor were occupied (0.03-0.3 mg/kg, p.o.). In contrast, higher doses (3-10 mg/kg, p.o.) at which nearly all the histamine H3 receptors were occupied were needed to exert wake-promoting effects in rats. These results indicate that enerisant is a potent and selective histamine H3 receptor antagonist/inverse agonist with the potential to promote arousal and procognition in rats. Moreover, the results also suggest that the histamine H3 receptor occupancy required to exert a pharmacological effect may vary depending on the domain that is being tested. SIGNIFICANCE STATEMENT: Enerisant is a novel histamine H3 receptor antagonist/inverse agonist that exerts wake-promoting and procognitive effects in addition to increasing the release of neurotransmitters related to these pharmacological effects in rodents. Moreover, an in vivo receptor binding study revealed that the in vivo occupancy of the histamine H3 receptor required to exert the pharmacological effects of enerisant varied, and such variations in required occupancy should be taken into account when performing dose selection in clinical studies.

Antipsychotic profiles of TASP0443294, a novel and orally active positive allosteric modulator of metabotropic glutamate 2 receptor.

Glutamatergic dysfunction has been implicated in psychiatric disorders such as schizophrenia. The stimulation of metabotropic glutamate (mGlu) 2 receptor has been shown to be effective in a number of animal models of schizophrenia. In this study, we investigated the antipsychotic profiles of (2S)-5-methyl-2-{[4-(1,1,1-trifluoro-2-methylpropan-2-yl)phenoxy]methyl}-2,3-dihydroimidazo[2,1-b][1,3]oxazole-6-carboxamide (TASP0443294), a newly synthesized positive allosteric modulator of the mGlu2 receptor. TASP0443294 potentiated the response of human mGlu2 and rat mGlu2 receptors to glutamate with EC50 values of 277 and 149 nM, respectively, without affecting the glutamate response of human mGlu3 receptor. TASP0443294 was distributed in the brain and cerebrospinal fluid after peroral administration in rats. The peroral administration of TASP0443294 inhibited methamphetamine-induced hyperlocomotion in rats, which was attenuated by an mGlu2/3 receptor antagonist, and improved social memory impairment induced by 5R,10S-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) in rats. Furthermore, TASP0443294 reduced the ketamine-induced basal gamma hyperactivity in the prefrontal cortex and suppressed rapid eye movement (REM) sleep in rats. These findings indicate that TASP0443294 is an mGlu2 receptor positive allosteric modulator with antipsychotic activity, and that the suppression of aberrant gamma oscillations and REM sleep could be considered as neurophysiological biomarkers for TASP0443294.

Neurophysiologic and antipsychotic profiles of TASP0433864, a novel positive allosteric modulator of metabotropic glutamate 2 receptor.

Excess glutamatergic neurotransmission has been implicated in the pathophysiology of schizophrenia, and the activation of metabotropic glutamate 2 (mGlu2) receptor may exert antipsychotic effects by normalizing glutamate transmission. In the present study, we investigated the neurophysiologic and antipsychotic profiles of TASP0433864 [(2S)-2-[(4-tert-butylphenoxy)methyl]-5-methyl-2,3-dihydroimidazo[2,1-b][1,3]oxazole-6-carboxamide], a newly synthesized positive allosteric modulator (PAM) of mGlu2 receptor. TASP0433864 exhibited PAM activity at human and rat mGlu2 receptors with EC50 values of 199 and 206 nM, respectively, without exerting agonist activity at rat mGlu2 receptor. TASP0433864 produced a leftward and upward shift in the concentration-response curve of glutamate-increased guanosine 5'-O-(3-[(35)S]thio)triphosphate binding to mGlu2 receptor. In contrast, TASP0433864 had negligible activities for other mGlu receptors, including mGlu3 receptor, and did not have any affinity for other receptors or transporters. In hippocampal slices, TASP0433864 potentiated an inhibitory effect of DCG-IV [(2S,2'R,3'R)-2-(2',3'-dicarboxylcyclopropyl)glycine], a mGlu2/3 receptor agonist, on the field excitatory postsynaptic potentials in the dentate gyrus, indicating that TASP0433864 potentiates the mGlu2 receptor-mediated presynaptic inhibition of glutamate release. Moreover, TASP0433864 inhibited both MK-801 [(5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate]- and ketamine-increased cortical γ band oscillation in the rat cortical electroencephalogram, which have been considered to reflect the excess activation of cortical pyramidal neurons. The inhibitory effect of TASP0433864 on cortical activation was also observed in the mouse 2-deoxy-glucose uptake study. In a behavioral study, TASP0433864 significantly inhibited both ketamine- and methamphetamine-increased locomotor activities in mice and rats, respectively. Collectively, these findings indicate that TASP0433864 is a selective mGlu2 receptor PAM with antipsychotic activity, and the attenuation of excess glutamatergic neurotransmission may be involved in the action of TASP0433864.

Imine derivatives as new potent and selective CB2 cannabinoid receptor agonists with an analgesic action.

In this study, a novel series of CB(2) receptor agonist imine derivatives, 1-6, was synthesized and evaluated for activity against the CB(2) receptor. In a previous paper we reported the synthesis and SARs of thiazole derivative 1, a potent CB(2) receptor agonist, but we had not assessed chemical modifications of the 5-membered heteroring of 1. In the present study, we therefore tried chemically modifying the 5-membered heteroring of 1 in an attempt to further improve binding affinity for the CB(2) receptor. In the course of making the structural modifications, we discovered that a novel pyrazole derivative 6b (CBS0550) had high affinity for the CB(2) receptor (IC(50)=2.9 nM, EC(50)=1.8 nM, E(max)=85%), high selectivity for CB(2) (CB(1) IC(50)/CB(2) IC(50)=1400), and good physicochemical properties (solubility in water: 5.9 mg/100mL at 25 degrees C). Oral administration of 6b to rats at a dose of 10mg/kg resulted in significant plasma concentrations, and orally administered compound 6b significantly reversed mechanical hyperalgesia in the Randall-Selitto model of inflammatory pain in rats.

N-Alkylidenearylcarboxamides as new potent and selective CB(2) cannabinoid receptor agonists with good oral bioavailability.

A novel series of N-alkylidenearylcarboxamides 4, a CB(2) receptor agonist, were synthesized and evaluated for activity against the human CB(2) receptor. In a previous paper, we reported that sulfonamide derivative 1 acted as a potent CB(2) receptor agonist (IC(50)=65 nM, EC(50)=19 nM, E(max)=90%). However, compound 1 also exhibited poor metabolic stability in human liver microsomes. During the structural modification of 1, we found that a novel series of N-alkylidenearylcarboxamide, 4-1, had a moderate affinity for the CB(2) receptor (IC(50)=260 nM, EC(50)=86 nM, E(max)=100%) and good metabolic stability in human liver microsomes. We explored its analogues to discover compounds with a high affinity for the CB(2) receptor and with good oral bioavailability. Among them, compounds 4-9 and 4-27 had high affinities for the human CB(2) receptor (CB(2) IC(50)=13 nM and 1.2 nM) and a high selectivity for CB(2) (CB(1) IC(50)/CB(2) IC(50)=270 and 1600); furthermore, significant plasma levels were observed following oral administration in rats (C(max)=233 ng/mL and 148 ng/mL, respectively, after a dose of 10 mg/kg). Furthermore, compound 4-9 had good oral bioavailability (F=52%, 3mg/kg).

Sulfonamide derivatives as new potent and selective CB2 cannabinoid receptor agonists.

A novel series of sulfonamide derivatives 3, the CB(2) receptor agonists, was synthesized and evaluated for activity against the human CB(2) receptor. We first identified sulfonamide 3a, which was obtained by random screening of our in-house chemical library as a moderately active (CB(2) IC(50)=340nM) CB(2) receptor agonist. We then attempted to test its analogues to identify compounds with a high affinity for the CB(2) receptor. One of these, compound 3f, exhibited high affinity for the human CB(2) receptor (IC(50)=16nM) and high selectivity for CB(2) over CB(1) (CB(1) IC(50)/CB(2)IC(50)=106), and behaved as a full CB(2) receptor agonist in the [(35)S]GTPgammaS binding assay (CB(2) EC(50)=7.2nM, E(max)=100%).

Design and synthesis of 1-(4-benzoylphenyl)imidazole derivatives as new potent 20-HETE synthase inhibitors.

Structural modification of the novel 20-HETE synthase inhibitor 1 (IC(50) 310nM) is described. Introduction of a side chain with a carboxylic acid at the terminal position to 1 resulted in increased ability to inhibit human renal microsomal production of 20-HETE (7c: IC(50) 7.9nM), with good selectivity toward CYP2D6 and cyclooxygenases (COX)-1 and -2.

Biological evaluation of sphingomyelin analogues as inhibitors of sphingomyelinase.

Seeking neutral sphingomyelinase inhibitors, we designed and synthesized hydrolytically stable analogues of sphingomyelin. These novel analogues replace the phosphodiester moiety of sphingomyelin with carbamate and urea moiety, resulting in inhibition of neutral sphingomyelinase. Compound 1 prevented ceramide generation and apoptotic neuronal cell death in a model of ischemia based on organotypic hippocampal slice cultures.

Sphingomyelin analogues as inhibitors of sphingomyelinase.

To search for neutral sphingomyelinase inhibitors we designed and synthesized hydrolytically stable analogues of sphingomyelin. The novel compounds 8 and 9 which were replaced the phosphodiester moiety of sphingomyelin with the carbamate moiety showed inhibitory activity with an IC(50) value of micro M on neutral sphingomyelinase in rat brain microsomes. Compound 8i showed a selective neutral sphingomyelinase inhibitory activity.