The 5-hydroxytryptamine 2C (5-HT2C) receptor subtype has received considerable attention as a target for drug discovery, having been implicated in a wide variety of disorders. Here, we describe the in vitro pharmacological profile of the novel 5-HT2C receptor-selective agonist vabicaserin [(−)-4,5,6,7,9,9a,10,11,12,12a-decahydrocyclopenta[c] [1,4]diazepino[6,7,1-ij]quinoline hydrochloride] (SCA-136), including a comprehensive strategy to assess 5-HT2B receptor selectivity using diverse preparations and assays of receptor activation. Vabicaserin displaced 125I-(2,5-dimethoxy)phenylisopropylamine binding from human 5-HT2C receptor sites in Chinese hamster ovary cell membranes with a Ki value of 3 nM and was >50-fold selective over a number of serotonergic, noradrenergic, and dopaminergic receptors. Binding affinity determined for the human 5-HT2B receptor subtype using [3H]5HT was 14 nM. Vabicaserin was a potent and full agonist (EC50, 8 nM; Emax, 100%) in stimulating 5-HT2C receptor-coupled calcium mobilization and exhibited 5-HT2A receptor antagonism and 5-HT2B antagonist or partial agonist activity in transfected cells, depending on the level of receptor expression. In rat stomach fundus and human colonic longitudinal muscle endogenously expressing 5-HT2B receptors, vabicaserin failed to induce a 5-HT2B receptor-dependent contraction and produced a rightward shift of the 5-HT and α-methyl-5-HT concentration-response curves in these preparations, respectively, consistent with 5-HT2B competitive antagonism. Likewise, vabicaserin failed to induce a 5-HT2B receptor-mediated contraction in arteries from deoxycorticosterone acetate-salt-treated rats, a model of hypersensitized 5-HT2B receptor function, and produced a rightward shift in the 5-HT-induced response that was consistent with 5-HT2B receptor antagonism. In summary, vabicaserin is a novel, potent, and selective 5-HT2C receptor agonist.

A new practical synthesis of a 5-HT2C receptor agonist has been developed and implemented on multikilogram scale. The key step, the selective epoxide opening in the glycidyl tosylate with the aryl Grignard reagent, allowed the incorporation of this commercially available chiral C-3 synthon into the molecule and elaboration of the resulting intermediate into the target aminomethyldihydrobenzofuran without loss of enantiomeric purity.

Dopamine replacement therapy in Parkinson's disease (PD) using L-dopa is invariably associated with a loss of drug efficacy ("wearing off") and the onset of dyskinesia. The use of dopamine receptor partial agonists might improve therapeutic benefit without increased dyskinesia expression but may antagonise the effects of L-dopa. We now examine the effects of the novel high affinity, dopamine D(2) receptor partial agonist, aplindore alone and in combination with L-dopa in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmoset. In non-dyskinetic MPTP treated animals, aplindore (0.05-1.0 mg/kg p.o.) produced a dose-dependent reversal of motor disability and an increase in locomotor activity that was maximal at doses of 0.2 mg/kg and above. In animals previously exposed to L: -dopa to induce dyskinesia, escalating and repeated dosing of aplindore (0.05-0.5 mg/kg p.o.) produced a sustained, dose-related improvement in motor disability and an increase in locomotor activity. The effects were maximal at a dose of 0.1 mg/kg and above and not different from those produced by L-dopa (12.5 mg/kg plus carbidopa 12.5 mg/kg p.o.). Aplindore administration also led to dose-dependent expression of dyskinesia but at 0.1 mg/kg, this was significantly less intense than that produced by L-dopa. Administration of aplindore (1.0 mg/kg p.o.) in combination with L-dopa (2.5 mg/kg plus carbidopa 12.5 mg/kg p.o.) did not inhibit the reversal of motor deficits but improved motor disability and increased both locomotor activity and dyskinesia expression equivalent to that produced by L-dopa (12.5 mg/kg plus carbidopa 12.5 mg/kg p.o.). These data suggest that dopamine receptor partial agonists would be effective in the treatment of Parkinson's disease and would not inhibit the beneficial actions of L-dopa.

Sexual dysfunction associated with antidepressant treatment continues to be a major compliance issue for antidepressant therapies. 5-HT(1A) antagonists have been suggested as beneficial adjunctive treatment in respect of antidepressant efficacy; however, the effects of 5-HT(1A) antagonism on antidepressant-induced side-effects has not been fully examined. The present study was conducted to evaluate the ability of acute or chronic treatment with 5-HT(1A) antagonists to alter chronic fluoxetine-induced impairments in sexual function. Chronic 14-d treatment with fluoxetine resulted in a marked reduction in the number of non-contact penile erections in sexually experienced male rats, relative to vehicle-treated controls. Acute administration of the 5-HT(1A) antagonist WAY-101405 resulted in a complete reversal of chronic fluoxetine-induced deficits on non-contact penile erections at doses that did not significantly alter baselines. Chronic co-administration of the 5-HT(1A) antagonists WAY-100635 or WAY-101405 with fluoxetine prevented fluoxetine-induced deficits in non-contact penile erections in sexually experienced male rats. Moreover, withdrawal of WAY-100635 from co-treatment with chonic fluoxetine, resulted in a time-dependent reinstatement of chronic fluoxetine-induced deficits in non-contact penile erections. Additionally, chronic administration of SSA-426, a molecule with dual activity as both a SSRI and 5-HT(1A) antagonist, did not produce deficits in non-contact penile erections at doses demonstrated to have antidepressant-like activity in the olfactory bulbectomy model. Taken together, these data suggest that 5-HT(1A) antagonist treatment may have utility for the management of SSRI-induced sexual dysfunction.

On the basis of the previously reported clinical candidate, SSA-426 (1), a series of related 2-piperazin-1-ylquinoline derivatives 3-16 were synthesized and evaluated as dual-acting serotonin (5-HT) reuptake inhibitors and 5-HT1A receptor antagonists. In particular, compound 7 exhibits potent functional activities at both the 5-HT transporter and 5-HT1A receptor, good selectivity over the alpha(1)-adrenergic and dopaminergic receptors, acceptable pharmacokinetic properties, and a favorable in vivo profile.

An alternative synthesis of WAY-253752, 1, a novel, dual-acting SSRI/5HT(1A) antagonist, was developed and used for the first scale-up. Initially, the target compound was synthesized as part of a diasteromeric mixture separated by chiral preparative HPLC. The new route was designed around intermediates suitable for chiral resolution, and its conditions were successfully determined.

INTRODUCTION:5-HT(2C) agonists, by decreasing mesolimbic dopamine without affecting nigrostriatal dopamine, are predicted to have antipsychotic efficacy with low extrapyramidal side effects (EPS). Combining 5-HT(2C) agonists with low doses of existing antipsychotics could increase treatment efficacy while reducing treatment liabilities such as EPS (typical antipsychotics), and the propensity for weight gain (atypical antipsychotics).OBJECTIVES:The objectives of these studies were to combine WAY-163909, a selective 5-HT(2C) agonist, with either the typical antipsychotic haloperidol, or the atypical antipsychotic clozapine, at doses that were ineffective on their own, with the expectation that a shift in potency in several rodent behavior models predictive of antipsychotic activity would occur.RESULTS AND DISCUSSION:In mice, co-administration of either haloperidol, or clozapine, produced a significant leftward shift in the ability of WAY-163909 to block apomorphine-induced climbing behavior, without any affect on apomorphine-induced stereotypy or an increased propensity for catalepsy. In the rat-conditioned avoidance model, WAY-163909 was combined with either haloperidol or clozapine at doses that individually produced reductions in avoidance response on the order of 10%, while the combination of WAY-163909 and either of the antipsychotics resulted in a greater than 70% reduction in avoidance, with no evidence of response failures, or pharmacokinetic interaction.CONCLUSION:Doses of either haloperidol or clozapine, that failed to antagonize an MK-801 induced deficit in prepulse inhibition, significantly attenuated the sensory gating deficit when combined with WAY-163909. Data support the notion that 5-HT(2C) receptor agonists, co-administered with other marketed antipsychotics, allow for dose sparing with a more favorable side-effect profile.

Further exploration of the cycloalkanol ethylamine scaffold, of which venlafaxine ( 1) is a member, was undertaken to develop novel and selective norepinephrine reuptake inhibitors (NRIs) for evaluation in a variety of predictive animal models. These efforts led to the discovery of a piperazine-containing analogue, 17g (WY-46824), that exhibited potent norepinephrine reuptake inhibition, excellent selectivity over the serotonin transporter, but no selectivity over the dopamine transporter. Synthesis and testing of a series of cyclohexanol ethylpiperazines identified ( S)-(-)- 17i (WAY-256805), a potent norepinephrine reuptake inhibitor (IC 50 = 82 nM, K i = 50 nM) that exhibited excellent selectivity over both the serotonin and dopamine transporters and was efficacious in animal models of depression, pain, and thermoregulatory dysfunction.

An alternative synthesis of WAY-262398, 1, a novel, dual-acting SSRI/5-HT1A antagonist, has been developed. The target compound was initially synthesized as a part of diastereomeric mixture which was separated by chiral preparative HPLC. The new route was designed around intermediates suitable for chiral resolution and/or chiral reduction of a suitable intermediate. Both processes had to be employed to achieve the target optical purity.

Departments of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 327232-8548 (J.N.M, R.L.R, R.D.B.) Department of Psychiatry, Vanderbilt University School of Medicine, Nashville, TN 327232-8548 (R.D.B.) Center for Molecular Neuroscience, Vanderbilt University School of Medicine, Nashville, TN 327232-8548 (R.D.B.) Women’s Health Research, Wyeth Pharmaceuticals, Collegeville, PA 19426 (D.C.D., R.C.W.) Chemical and Screening Sciences, Wyeth Pharmaceuticals, Collegeville, PA 19426 (G.S., P.E.M., E.T.) JPET Fast Forward. Published on August 6, 2007 as DOI:10.1124/jpet.107.125716