Mohammed Shahid

Asenapine: a novel psychopharmacologic agent with a unique human receptor signature:

Asenapine is a novel psychopharmacologic agent under development for the treatment of schizophrenia and bipolar disorder. We determined and compared the human receptor binding affinities and functional characteristics of asenapine and several antipsychotic drugs. Compounds were tested under comparable assay conditions using cloned human receptors. In comparison with the antipsychotics, asenapine showed high affinity and a different rank order of binding affinities (pK i) for serotonin receptors (5-HT1A [8.6], 5-HT1B [8.4], 5-HT2A [10.2], 5-HT2B [9.8], 5-HT2C [10.5], 5-HT 5 [8.8], 5-HT6 [9.6] and 5-HT7 [9.9]), adrenoceptors (α1 [8.9], α2A [8.9], α2B [9.5] and α2C [8.9]), dopamine receptors (D1 [8.9], D 2 [8.9], D3 [9.4] and D4 [9.0]) and histamine receptors (H1 [9.0] and H2 [8.2]). It had much lower affinity (pK i ≤ 5) for muscarinic receptors and was the only agent with affinity for H2 receptors. Relative to its D2 receptor affinity, asenapine had a higher affinity for 5-HT 2C, 5-HT2A, 5-HT2B, 5-HT7, 5-HT 6, α2B and D3 receptors, suggesting stronger engagement of these targets at therapeutic doses. Asenapine behaved as a potent antagonist (pK B) at 5-HT1A (7.4), 5-HT 1B (8.1), 5-HT2A (9.0), 5-HT2B (9.3), 5-HT 2C (9.0), 5-HT6 (8.0), 5-HT7 (8.5), D2 (9.1), D3 (9.1), α2A (7.3), α2B (8.3), α2C (6.8) and H1 (8.4) receptors. These functional effects differed from those of risperidone (pK B < 5 for 5-HT6) and olanzapine (pK B < 5 for 5-HT 1A and α2). Our results indicate that asenapine has a unique human receptor signature, with binding affinity and antagonistic properties that differ appreciably from those of antipsychotic drugs.

Human bronchial cyclic nucleotide phosphodiesterase isoenzymes: biochemical and pharmacological analysis using selective inhibitors.

1 The aims of the present study were to characterize the cyclic nucleotide phosphodiesterase (PDE) isoenzyme activities present in human bronchi and to examine the ability of selective isoenzyme inhibitors to relax histamine and methacholine precontracted preparations of human bronchi. 2 Three separations of pooled human bronchial tissue samples were performed. Ion‐exchange chromatography showed that the soluble fraction of human bronchial preparations contains PDE I, II, III, IV and V isoenzyme activities. Multiple forms of PDE I and PDE IV were observed and PDE IV was the main cyclic AMP hydrolytic activity. 3 3‐Isobutyl‐1‐methylxanthine (IBMX) non‐selectively inhibited all separated isoenzyme activities. Zaprinast selectively inhibited PDE V, but also effectively inhibited one of the two PDE I isoforms identified. The PDE IV selective inhibitors rolipram and RO‐201724, inhibited the PDE IV activities as did the dual PDE III/IV inhibitor, Org 30029. Org 9935, a PDE III selective inhibitor, potently attenuated part of the PDE IV activity peak in one of three separations performed, indicating that some PDE III activity may co‐elute with PDE IV under the experimental conditions employed. 4 PDE IV‐selective (rolipram), PDE III‐selective (Org 9935) and dual PDE III/IV (Org 30029) inhibitors were effective relaxants of human bronchial smooth muscle. The PDE V/PDE I inhibitor, zaprinast was relatively ineffective. 5 The present study demonstrates in human bronchi, as in animal airways smooth muscle, that inhibitors of PDE III, PDEIV and dual PDE III/IV have potentially useful bronchodilator activity and are worthy of further consideration as anti‐asthma drugs.

The presence of five cyclic nucleotide phosphodiesterase isoenzyme activities in bovine tracheal smooth muscle and the functional effects of selective inhibitors

1 The profile of cyclic nucleotide phosphodiesterase (PDE) isoenzymes and the relaxant effects of isoenzyme selective inhibitors were examined in bovine tracheal smooth muscle. The compounds examined were the non‐selective inhibitor 3‐isobutyl‐1‐methylxanthine (IBMX), zaprinast (PDE V selective), milrinone and Org 9935 (4,5‐dihydro‐6‐(5,6‐dimethoxy‐benzo[b]thien‐2‐yl)‐5‐methyl‐1(2H)‐pyridazinone; both PDE III selective), rolipram (PDE IV selective) and Org 30029 (N‐hydroxy‐5,6‐dimethoxy‐benzo[b]‐thiophene‐2‐carboximidamide HCl a dual PDE III/IV inhibitor). 2 Ion exchange chromatography showed three main peaks of PDE activity. The first peak was stimulated by Ca2+/calmodulin (PDE I), the adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) hydrolytic activity of the second peak was stimulated by guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) (PDE II) whilst that of the third peak was not significantly modified by any regulator (PDE IV). Calmodulin affinity chromatography revealed the additional presence of cyclic GMP‐specific PDE (PDE V) in the first peak. A clearly distinct peak of cyclic GMP‐inhibited PDE (PDE III) was not observed. However, Org 9935 inhibited the third activity peak more effectively in the presence, than in the absence, of rolipram (3 μmol l−1), indicating the presence of PDE III activity. 3 Rolipram was the most potent inhibitor of PDE IV. The mean −log50 IC50 values for rolipram, IBMX, milrinone, Org 30029, Org 9935 and zaprinast were 5.9 ± 0.1, 4.9 ± 0.1, 4.7 ± 0.1, 4.6 ± 0.1 and 4.6 ± 0.1, respectively. 4 Rolipram was a potent relaxant of both histamine (1 μmol1−1) and methacholine (0.03 μmol1−1) precontracted preparations; (pD2 values; histamine 7.1 ± 0.1, methacholine 6.8 ± 0.2 and 4.5 ± 0.1, biphasic relaxation). IBMX also relaxed all preparations (pD2 values; histamine 5.6 ± 0.1, methacholine 5.6 ± 0.1) whilst zaprinast (pD2 values; histamine 5.2 ± 0.1, methacholine 4.4 ± 0.3), milrinone (pD2 values; histamine 5.2 ± 0.1, methacholine 4.3 ± 0.3) and Org 9935 (pD2 values; histamine 4.1 ± 0.1, methacholine 4.1 ± 0.2) did not completely relax preparations at concentrations up to 100 μmol1−1. Org 30029 (pD2 values; histamine 6.2 ± 0.1, methacholine 5.4 ± 0.1) was a more effective relaxant than can be explained on the basis of PDE IV inhibition alone. 5 We conclude that bovine tracheal smooth muscle contains five distinct PDE isoenzymes. PDE IV appears to be more important in the modulation of tissue function than PDE III and PDE V.

Attenuation of Phencyclidine-Induced Object Recognition Deficits by the Combination of Atypical Antipsychotic Drugs and Pimavanserin (ACP 103), a 5-Hydroxytryptamine2A Receptor Inverse Agonist

Subchronic administration of the N-methyl-d-aspartate receptor antagonist, phencyclidine (PCP), in rodents has been shown to produce impairment in novel object recognition (NOR), a model of visual learning and memory. We tested the hypothesis that the selective 5-HT2A inverse agonists, pimavanserin and (R)-(+)-α-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl]-4-piperidinemethanol (M100907), would potentiate subeffective doses of atypical antipsychotic drugs (APDs) to reverse the NOR deficits. Female rats received vehicle or PCP (2 mg/kg b.i.d.) for 7 days, followed by a 7-day washout. Pimavanserin (3 mg/kg) or M100907 (1 mg/kg) alone, or four atypicial APDs, risperidone (0.05–0.1 mg/kg), melperone (1–3 mg/kg), olanzapine (1–2 mg/kg), or N-desmethylclozapine (1–2 mg/kg), and the typical APD, haloperidol (0.05–0.1 mg/kg), were administered alone, or in combination with pimavanserin or M100907, before NOR testing. The exploration times of objects during 3-min acquisition and retention trials, separated by a 1-min interval, were compared by analysis of variance. Vehicle-, but not PCP-treated, animals, explored the novel object significantly more than the familiar in the retention trial (p < 0.05–0.01). Pretreatment with the higher doses of the atypical APDs, but not pimavanserin, M100907, or haloperidol alone, reversed the effects of PCP. The effect of risperidone was blocked by haloperidol pretreatment. Coadministration of pimavanserin or M100907, with ineffective doses of the atypical APDs, but not haloperidol, also reversed the PCP-induced deficit in NOR. These results support the importance of 5-hydroxytryptamine2A receptor blockade relative to D2 receptor blockade in the ability of atypicals to ameliorate the effect of subchronic PCP, a putative measure of cognitive dysfunction in schizophrenia.

Testing the validity of c-fos expression profiling to aid the therapeutic classification of psychoactive drugs

RationaleDifferent stimuli, including pharmacological stimuli, induce different neuroanatomical profiles of c-fos expression. Can these profiles be used in classifying psychoactive drugs and predicting therapeutic utility?ObjectiveTo test the validity of c-fos expression profiling to aid therapeutic classification.MethodsAnxiolytics, antidepressants, antipsychotics and psychostimulants were compared. (i) A meta-analysis was performed and profiles compiled from literature reports of changes in c-fos expression in rat brain regions, measured by in situ hybridisation histochemistry or immunohistochemistry, after acute injection of psychoactive drugs. (ii) Male rat brains were profiled for changes in c-fos mRNA expression induced by acute injection of psychoactive drugs.Results(i) The meta-analysis showed that anxiolytics activate few (mostly stress-related) brain regions; antidepressants activate more regions, including the central amygdaloid nucleus; antipsychotics activate more regions still, including the nucleus accumbens and striatal areas; and psychostimulants activate the greatest number of all, including the most cortical regions (especially the piriform cortex). Profiles also varied within drug classes. (ii) Our experimental profiles confirmed and extended meta-analysis profiles, showing more downregulation. (iii) Sites activated by mirtazapine (an antidepressant not previously profiled) matched those of the antidepressant imipramine.Conclusions(i) Differences between drug classes support their classification by means of c-fos profiling. Differences within classes may reflect mechanistic variations. (ii) Greater downregulation in our experiments might be because of inclusion of low, clinically relevant, drug doses and fuller coverage of brain regions. (iii) The agreement between mirtazapine and imipramine increases our confidence in the validity of c-fos expression profiling to aid drug classification and predict therapeutic utility.

Mechanism and impact of allosteric AMPA receptor modulation by the AmpakineTM CX546

Glutamate release at central synapses is transduced into a characteristic fast postsynaptic response by AMPA receptor gating and agonist affinity. The effect of two classes of modulators of AMPA receptor desensitization, the benzothiadiazides (cyclothiazide and IDRA 21) and the benzoylpiperidines (CX516 and CX546), were studied on gating kinetics of recombinant, native AMPA receptors and on synaptic currents. CX546 reduced the degree of desensitization more potently than CX516 or IDRA 21, but not as efficiently as cyclothiazide. In presence of CX516/CX546, desensitization of GluR2(flip) receptors was inhibited more than of GluR1(flip), whereas they had no effect upon response shape or conductance. CX546 increased agonist affinity threefold on nondesensitizing AMPA receptors by slowing agonist unbinding. Analysis of modulatory action suggests that, in contrast to cyclothiazide or IDRA 21, the Ampakine CX546 binds specifically to the agonist bound nondesensitized receptor, most likely acting by destabilizing the desensitized receptor conformation. All modulators tested showed higher efficiency on native receptors as compared to homomeric receptors. At the glutamatergic synapse, evoked synaptic amplitudes were weakly potentiated, while EPSC decay was slowed by nearly a factor of three in the presence of CX546 or cyclothiazide. In the presence of CX546, the current induced by short pulses of glutamate from recombinant GluR2 receptors decayed with a time course that was approximately twentyfold faster than EPSCs. The unique properties of CX546 may be beneficial for therapeutical use.

Asenapine Increases Dopamine, Norepinephrine, and Acetylcholine Efflux in the Rat Medial Prefrontal Cortex and Hippocampus

Atypical antipsychotic drugs, which are more potent direct acting antagonists of brain serotonin (5-HT)2A than dopamine (DA) D2 receptors, preferentially enhance DA and acetylcholine (ACh) efflux in the rat medial prefrontal cortex (mPFC) and hippocampus (HIP), compared with the nucleus accumbens (NAc). These effects may contribute to their ability, albeit limited, to improve cognitive function and negative symptoms in patients with schizophrenia. Asenapine (ASE), a new multireceptor antagonist currently in development for the treatment of schizophrenia and bipolar disorder, has complex serotonergic properties based upon relatively high affinity for multiple serotonin (5-HT) receptors, particularly 5-HT2A and 5-HT2C receptors. In the current study, the effects of ASE on DA, norepinephrine (NE), 5-HT, ACh, glutamate, and γ-aminobutyric acid (GABA) efflux in rat mPFC, HIP, and NAc were investigated with microdialysis in awake, freely moving rats. ASE at 0.05, 0.1, and 0.5 mg/kg (s.c.), but not 0.01 mg/kg, significantly increased DA efflux in the mPFC and HIP. Only the 0.5 mg/kg dose enhanced DA efflux in the NAc. ASE, at 0.1 and 0.5 mg/kg, significantly increased ACh efflux in the mPFC, but only the 0.5 mg/kg dose of ASE increased HIP ACh efflux. ASE did not increase ACh efflux in the NAc at any of the doses tested. The effect of ASE (0.1 mg/kg) on DA and ACh efflux was blocked by pretreatment with WAY100635, a 5-HT1A antagonist/D4 agonist, suggesting involvement of indirect 5-HT1A agonism in both the actions. ASE, at 0.1 mg/kg, increased NE, but not 5-HT, efflux in the mPFC and HIP. ASE, at 0.1 mg/kg (s.c.), had no effect on glutamate and GABA efflux in either the mPFC or NAc. These findings indicate that ASE is similar to clozapine and other atypical antipsychotic drugs in preferentially increasing the efflux of DA, NE, and ACh in the mPFC and HIP compared with the NAC, and suggests that, like these agents, it may also improve cognitive function and negative symptoms in patients with schizophrenia.

Asenapine induces differential regional effects on serotonin receptor subtypes

Asenapine, a novel psychopharmacologic agent being developed for the treatment of schizophrenia and bipolar disorder, has high affinity for a wide range of receptors, including the serotonergic receptors 5-HT1A, 5-HT1B, 5-HT2A, 5-HT 2B, 5-HT2C, 5-HT5A, 5-HT6 and 5-HT 7. We examined the long-term effects in rat brain of multiple doses of asenapine on representative serotonin receptor subtypes: 5-HT1A, 5-HT2A and 5-HT2C. Rats were given asenapine (0.03, 0.1 or 0.3 mg/kg) subcutaneously twice daily or vehicle for 4 weeks. Brain sections were collected from the medial prefrontal cortex (mPFC), dorsolateral frontal cortex (DFC), caudate putamen, nucleus accumbens, hippocampal CA 1 and CA3 regions, and entorhinal cortex and processed for in-vitro receptor autoradiography. Asenapine 0.1 and 0.3 mg/kg significantly increased 5-HT1A binding in mPFC (by 24% and 33%, respectively), DFC (27%, 31%) and hippocampal CA1 region (23%, 25%) (all P < 0.05). All three asenapine doses (0.03, 0.1 and 0.3 mg/kg) significantly decreased 5-HT2A binding by a similar degree in mPFC (40%, 44%, 47%, respectively) and DFC (45%, 51%, 52%) (all P < 0.05), but did not alter 5-HT2A binding in the other brain regions studied. In contrast to the effects on 5-HT1A and 5-HT2A receptors, asenapine did not alter 5-HT2C binding in any brain region examined at the doses tested. Our results indicate that repeated administration of asenapine produces regional-specific effects on 5-HT1A and 5-HT2A receptors in rat forebrain regions, which may contribute to the distinctive psychopharmacologic profile of asenapine.

Electrophysiological characterization of the effects of asenapine at 5-HT1A, 5-HT2A, α2-adrenergic and D2 receptors in the rat brain

Asenapine is a psychopharmacologic agent being developed for schizophrenia and bipolar disorder. This study electrophysiologically characterized the in vivo effects of asenapine at dorsal raphe nucleus (DRN) and hippocampus serotonin-1A (5-HT(1A)), ventral tegmental area D(2), locus coeruleus 5-HT(2A,) and alpha(2)-adrenergic receptors in anesthetized rats. Asenapine displayed potent antagonistic activity at alpha(2)-adrenoceptors (ED(50), 85+/-2 microg/kg), 5-HT(2A) (ED(50), 75+/-2 microg/kg) and D(2) receptors (ED(50), 40+/-2 microg/kg) as evidenced by its reversal of clonidine-, DOI-, and apomorphine-induced inhibition of norepinephrine and dopamine neurons. In contrast, asenapine acted as a partial agonist at 5-HT(1A) receptors in DRN and hippocampus, as indicated by blockade of its inhibitory effect on neuronal firing by the 5-HT(1A) antagonist WAY 100635 and the partial inhibition of the suppressant action of 5-HT when co-applied by microiontophoresis. These results confirm that asenapine displays potent antagonistic activity at 5-HT(2A), D(2), alpha(2)-adrenergic receptors and provide evidence to support its 5-HT(1A) partial agonistic activity.

Effects of asenapine, olanzapine, and risperidone on psychotomimetic-induced reversal-learning deficits in the rat

BACKGROUND Asenapine is a new pharmacological agent for the acute treatment of schizophrenia and bipolar disorder. It has relatively higher affinity for serotonergic and alpha(2)-adrenergic than dopaminergic D(2) receptors. We evaluated the effects of asenapine, risperidone, and olanzapine on acute and subchronic psychotomimetic-induced disruption of cued reversal learning in rats. METHODS After operant training, rats were treated acutely with d-amphetamine (0.75 mg/kg intraperitoneally [i.p.]) or phencyclidine (PCP; 1.5mg/kg i.p.) or subchronically with PCP (2mg/kg i.p. for 7 days). We assessed the effects of acute coadministration of asenapine, risperidone, or olanzapine on acute d-amphetamine- and PCP-induced deficits and the effects of long-term coadministration of these agents (for 28 additional days) on the deficits induced by subchronic PCP. RESULTS Deficits in reversal learning induced by acute d-amphetamine were attenuated by risperidone (0.2mg/kg i.p.). Acute PCP-induced impairment of reversal learning was attenuated by acute asenapine (0.025 mg/kg subcutaneously [s.c.]), risperidone (0.2mg/kg i.p.), and olanzapine (1.0mg/kg i.p.). Subchronic PCP administration induced an enduring deficit that was attenuated by acute asenapine (0.075 mg/kg s.c.) and by olanzapine (1.5mg/kg i.p.). Asenapine (0.075 mg/kg s.c.), risperidone (0.2mg/kg i.p.), and olanzapine (1.0mg/kg i.p.) all showed sustained efficacy with chronic (29 days) treatment to improve subchronic PCP-induced impairments. CONCLUSION These data suggest that asenapine may have beneficial effects in the treatment of cognitive symptoms in schizophrenia. However, this remains to be validated by further clinical evaluation.