Neurokinin-3 receptor-specific antagonists talnetant and osanetant show distinct mode of action in cellular Ca2+ mobilization but display similar binding kinetics and identical mechanism of binding in ligand cross-competition

G-protein coupled receptor and kinase targets: advances in drug discovery from molecular to clinical

The conference was organized by Visiongain and focused on a number of industrially relevant advances in G-protein coupled receptor and kinase research. Commercial stands were provided by Genscript (Bioassays), Merck Millipore (profiling services), Schrödinger (modeling) and Corning (assay development). The overall attendance was approximately 40 delegates taking part in four sessions over the two days.

Pharmacological characterization of senktide-induced tail whips

The tachykinin NK(3) receptor shows promise as a novel target for antipsychotics, but knowledge of downstream activity following tachykinin NK(3) receptor activation is lacking. To determine the practical utility of senktide-induced tail whips in mice as a tool for determining and characterizing downstream activity following tachykinin NK(3) receptor activation, mice were injected with 0.05 nmol of senktide i.c.v. and the number of tail whip bouts was counted for 20 min. Strain differences were observed, with NMRI mice showing a stronger tail whip response than C57Bl/6J mice. Tachykinin NK(3) receptor specificity was confirmed by the absence of the senktide-induced tail whip response in tachykinin NK(3) receptor knockout mice. Effects of tachykinin receptor pharmacological agents were tested by pretreatment with tachykinin NK(3) receptor antagonists (SB222200, talnetant and osanetant), which attenuated senktide-induced tail whips, and the tachykinin NK(1) receptor antagonist MK869, which had no effect on senktide-induced tail whips. Pharmacological interactions with other neurotransmitter systems were determined by pretreatment with dopamine D(1), D(2), and D(3) receptor antagonists, atypical antipsychotics, serotonin 5HT(1a) receptor antagonists, serotonin 5HT(2a/c) receptor antagonists, benzodiazepine and putative anxiolytics, antidepressants, and an anticholinergic. Senktide-induced tail whips were attenuated by dopamine D(2) receptor antagonists, atypical antipsychotics, serotonin 5HT(2a/c) antagonists, and benzodiazepine anxiolytics, but unaffected by drugs from other classes. Thus, the senktide-induced tail whip response is easily quantifiable, specific to the tachykinin NK(3) receptor, and provides valuable information on the downstream pharmacology of tachykinin NK(3) receptor activation.

Multifaceted approach to determine the antagonist molecular mechanism and interaction of ibodutant ([1-(2-phenyl-1R-[[1-(tetrahydropyran-4-ylmethyl)-piperidin-4-ylmethyl]-carbamoyl]-ethylcarbamoyl)-cyclopentyl]-amide) at the human tachykinin NK2 receptor

Ibodutant (MEN15596, [1-(2-phenyl-1R-[[1-(tetrahydropyran-4-ylmethyl)-piperidin-4-ylmethyl]-carbamoyl]-ethylcarbamoyl)-cyclopentyl]-amide) is a tachykinin NK(2) receptor (NK(2)R) antagonist currently under phase II clinical trials for irritable bowel syndrome. This study focuses on the ibodutant pharmacodynamic profile at the human NK(2)R and compares it with two other antagonists, nepadutant (MEN11420, (cyclo-[[Asn(beta-D-GlcNAc)-Asp-Trp-Phe-Dpr-Leu]cyclo(2beta-5beta)]) and saredutant [SR48968, (S)-N-methyl-N[4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)butyl]benzamide]. In functional experiments (phosphatidylinositol accumulation) in Chinese hamster ovary cells expressing the human NK(2)R, ibodutant potency measured toward concentration-response curves to neurokinin A as pK(B) was 10.6, and its antagonism mechanism was surmountable and competitive. In the same assay, antagonism equilibration and reversibility experiments of receptor blockade indicated that ibodutant quickly attains equilibrium and that reverts from receptor compartment in a slower manner. Kinetic properties of ibodutant were assessed through competitive binding kinetics experiments performed at [(3)H]nepadutant and [(3)H]saredutant binding sites. Determined K(on) and K(off) values indicated a fast association and slow dissociation rate of ibodutant at the different antagonist binding sites. Last, by radioligand binding experiments at some mutated human tachykinin NK(2)Rs, the amino acidic determinants crucial for the high affinity of ibodutant were identified at the transmembrane (TM) level: Cys167 in TM4; Ile202 and Tyr206 in TM5; Phe270, Tyr266, and Trp263 in TM6; and Tyr289 in TM7. These results indicated an extended antagonist binding pocket in the TM portion of the receptor, which is conceived crucial for TM3 and 6 arrangement and leads to G protein-coupled receptor activation. By combining this information and molecular modeling, the docking mode of ibodutant-human NK(2)R complex is proposed.

The tachykinin NK3 receptor agonist senktide induces locomotor activity in male Mongolian gerbils

The tachykinin family of receptors has been of strong interest recently due to the potential of the tachykinin NK(3) receptor antagonism in treatment of schizophrenia. However, critical differences in the tachykinin NK(3) receptor between rats, mice and humans make rats and mice less acceptable species for testing tachykinin NK(3) receptor antagonism. This has led to testing of tachykinin NK(3) receptor activity in gerbils and guinea pigs. As these species are much less common laboratory animals than rats and mice, there is a relative paucity of in vivo testing models for tachykinin NK(3) receptor activation. In the present study, locomotor activity induced by the tachykinin NK(3) receptor agonist senktide was characterized. Injection of senktide i.c.v. was found to dose-dependently induce hyperlocomotion from a dose of 0.06 nmol to the maximal dose tested, 0.6 nmol. Locomotion induced by 0.1 nmol of senktide could be blocked by injection of the tachykinin NK(3) receptor antagonists SB222200 (10 and 30 mg/kg i.p.) and talnetant (SB223412; 10 and 30 mg/kg i.p.), as well as by osanetant (SR142801; 10 and 30 mg/kg i.p.) when administered in a vehicle containing vitamin E and glycofurol. Senktide-induced activity was also reversed by the antipsychotics haloperidol (0.3 and 1 mg/kg p.o.) and risperidone (1 mg/kg p.o.), but not by the serotonin 5HT(2a/c) receptor antagonist MDL100907 (tested at 0.1, 0.3 and 1 mg/kg p.o.). Hyperlocomotion induced by 0.03 nmol of senktide was potentiated by antagonism of the tachykinin NK(1) receptor with aprepitant (1, 3 and 10 mg/kg, p.o.). Thus, hyperlocomotion induced by senktide in gerbils is a tachykinin NK(3) receptor-mediated behavior that is appropriate for use in testing tachykinin NK(3) receptor activity of novel compounds.

Me-talnetant and osanetant interact within overlapping but not identical binding pockets in the human tachykinin neurokinin 3 receptor transmembrane domains

Recent clinical trials have indicated that neurokinin 3 receptor antagonists (S)-(+)-N-{{3-[1-benzoyl-3-(3,4-dichlorophenyl)-piperidin-3-yl]prop-1-yl}-4-phenylpiperidin-4-yl}-N-methylacetamine (SR142801; osanetant) and (S)-(-)-N-(alpha-ethylbenzyl)-3-hydroxy-2-phenylquinoline-4-carboxamide (SB223412; talnetant) may treat symptoms of schizophrenia. Using site-directed mutagenesis, rhodopsin-based modeling, [(3)H](S)-(-)-N-(alpha-ethylbenzyl)-3-methoxy-2-phenylquinoline-4-carboxamide (Me-talnetant) and [(3)H]osanetant binding, and functional Schild analyses, we have demonstrated the important molecular determinants of neurokinin B (NKB), Me-talnetant, and osanetant binding pockets. The residues Asn138(2.57), Asn142(2.61), Leu232(45.49), Tyr315(6.51), Phe342(7.39), and Met346(7.43) were found to be crucial for the NKB binding site. We observed that the M134(2.53)A, V169(3.36)M, F342(7.39)M, and S341(7.38)I/F342(7.39)M mutations resulted in the complete loss of [(3)H]Metalnetant and [(3)H]osanetant binding affinities and also abolished their functional potencies in an NKB-evoked accumulation of [(3)H]inositol phosphates assay, whereas the mutations V95(1.42)A, N142(2.61)A, Y315(6.51)F, and M346(7.43)A behaved differently between the interacting modes of two antagonists. V95(1.42)A and M346(7.43)A significantly decreased the affinity and potency of Me-talnetant. Y315(6.51)F, although not affecting Me-talnetant, led to a significant decrease in affinity and potency of osanetant. The mutation N142(2.61)A, which abolished the potency and affinity of osanetant, led to a significant increase in the affinity and potency of Me-talnetant. The proposed docking mode was further validated using (S)-2-(3,5-bis-trifluoromethyl-phenyl)-N-[4-(4-fluoro-2-methyl-phenyl)-6-((S)-4-methanesulfonyl-3-methyl-piperazin-1-yl)-pyridin-3-yl]-N-methyl-isobutyramide (RO49085940), from another chemical class. It is noteworthy that the mutation F342(7.39)A caused an 80-fold gain of RO4908594 binding affinity, but the same mutation resulted in the complete loss of the affinity of Me-talnetant and partial loss of the affinity of osanetant. These observations show that the binding pocket of Me-talnetant and osanetant are overlapping, but not identical. Taken together, our data are consistent with the proposed docking modes where Me-talnetant reaches deeply into the pocket formed by transmembrane (TM)1, -2, and -7, whereas osanetant fills the pocket TM3, -5, and -6 with its phenyl-piperidine moiety.