Potent NK2 Receptor Antagonist Research Articles

Antagonist profile of ibodutant at the tachykinin NK2 receptor in guinea pig isolated bronchi

In this study we have characterized the pharmacological profile of the non-peptide tachykinin NK2 receptor antagonist ibodutant (MEN15596) in guinea pig isolated main bronchi contractility. The antagonist potency of ibodutant was evaluated using the selective NK2 receptor agonist [βAla8]NKA(4-10)-mediated contractions of guinea pig isolated main bronchi. In this assay ibodutant (30, 100 and 300nM) induced a concentration-dependent rightward shift of the [βAla8]NKA(4-10) concentration-response curves without affecting the maximal contractile effect. The analysis of the results yielded a Schild-plot linear regression with a slope not different from unity (0.95, 95% c.l. 0.65–1.25), thus, indicating a surmountable behavior. The calculated apparent antagonist potency as pKB value was 8.31±0.05. Ibodutant (0.3–100nM) produced a concentration-dependent inhibition of the nonadrenergic–noncholinergic (NANC) contractile response induced by electrical field stimulation (EFS) of intrinsic airway nerves in guinea pig isolated main bronchi. At the highest concentration tested (100nM) ibodutant almost abolished the EFS-induced bronchoconstriction (95±4% inhibition), the calculated IC50 value was 2.98nM (95% c.l. 1.73–5.16nM). In bronchi from ovalbumin (OVA) sensitized guinea pigs ibodutant (100nM) did not affect the maximal contractile response to OVA, but completely prevented the slowing in the fading of the motor response induced by phosphoramidon pretreatment linked to the endogenous neurokinin A release. Altogether, the present study demonstrates that ibodutant is a potent NK2 receptor antagonist in guinea pig airways.

Spiro-substituted piperidines as neurokinin receptor antagonists. I. Design and synthesis of (+/-)-N-[2-(3,4-dichlorophenyl)-4-(spiro [isobenzofuran-1(3H),4'piperidin]-1'-yl)butyl]-N-methylbenzamide, YM-35375, as a new lead compound for novel neurokinin receptor antagonists.

Analysis of the structural requirements of compound 1 (SR48968), a potent NK2 receptor antagonist, revealed that the 4-phenyl group of the piperidine is essential for binding with the NK2 receptor and occupies an equatorial position. Energy calculation of a variety of substituted 4-phenyl piperidines revealed that spiro[isobenzofuran-1(3H),4'-piperidine] possesses a conformationally restricted equatorial phenyl group. Our compound 12 (YM-35375) possessing this spiro-substituted piperidine bound to the NK2 receptor with an IC50 value of 84 nM and to the NK1 receptor with an IC50 value of 710 nM. It showed more potent inhibitory activity (ID50 41 micrograms/kg (i.v.)) against [beta-Ala8]-NKA(4-10)-induced bronchoconstriction in guinea pigs than (+/-)-SR48968 (ID50 68 micrograms/kg (i.v.)). YM-35375 may be a new lead compound for novel NK2 receptor antagonists or NK1-NK2 dual antagonists.

Characterization of receptors mediating contraction induced by tachykinins in the guinea-pig isolated common bile duct.

1. We studied the effect of the natural tachykinins and of synthetic agonists selective for the tachykinin NK1, NK2 and NK3 receptors, on the motility of guinea-pig isolated common bile duct longitudinally-oriented smooth muscle. 2. All the tachykinins tested (both natural and synthetic) produced a concentration-dependent contractile response of the guinea-pig isolated common bile duct: these effects underwent a marked tachyphylaxis, especially the responses elicited by NK1 and NK3 receptor-selective agonists. 3. Among the natural tachykinins neurokinin B (EC50 = 3.2 nM; 95% c.l. = 2.0-5.1; n = 4) was the most potent, being about 40 and 25 fold more potent than substance P (EC50 = 121.6 nM; 95% c.l. = 94-157; P < 0.01; n = 4) and neurokinin A (EC50 = 83.4 nM; 95% c.l. = 62-112; P < 0.01; n = 4), respectively. Among the synthetic analogues the NK3 receptor-selective agonist senktide (EC50 = 1.1 nM; 95% c.l. = 0.7-1.8; n = 8) was the most potent, being about 120, 110 and 20 fold more potent than [Sar9]substance P sulfone (NK1 receptor-selective) (EC50 = 130.4 nM; 95% c.l. = 99-172; P < 0.01; n = 8), [beta Ala8]NKA (4-10) (NK2 receptor-selective) (EC50 = 120.1 nM; 95% c.l. = 95-151; P < 0.01; n = 8) and septide (NK1 receptor-selective) (EC50 = 22.6 nM; 95% c.l. = 18-28; P < 0.01; n = 8), respectively. All tachykinins (natural or synthetic receptor agonists) produced a similar Emax, averaging about 50% of that produced by KCl (80 mM). 4. Atropine (1 microM) did not affect the responses to either NK1 or NK2 receptor-selective agonists, whereas it reduced the Emax of senktide by about 50%, without affecting its potency (EC50). Tetrodotoxin (1 microM) totally blocked senktide-induced contractions, as did the combined pretreatment with atropine plus the tachykinin NK1 and NK2 receptor-selective antagonists GR 82334 and MEN 11420 (1 microM each), respectively. 5. GR 82334 (1 microM) blocked with apparent competitive kinetics septide- (apparent pKB = 7.46 +/- 0.10; n = 5) and [Sar9]substance P sulfone- (apparent pKB = 6.80 +/- 0.04; n = 4) induced contractions. MEN 11420 (30-300 nM), a novel potent NK2 receptor antagonist, potently antagonized [beta Ala8]NKA (4-10), with competitive kinetics (pKB = 8.25 +/- 0.08; n = 12: Schild plot slope = -0.90; 95% c.l. = -1.4; -0.35). The NK3 receptor-selective antagonist SR 142801 (30 nM) produced insurmountable antagonism of the senktide-induced contractions (Emax inhibited by 64%). None of the above antagonists, tested at the highest concentrations employed against tachykinins, affected the concentration-response curve to methacholine (0.1-300 microM). 6. We conclude that tachykinins produce contraction of the guinea-pig isolated common bile duct by stimulating NK1, NK2 and NK3 receptors. The responses obtained by activating NK1 and NK2 receptors are atropine-resistant. The contraction obtained by stimulating NK3 receptors is totally neurogenic, being mediated by the release of endogenous acetylcholine and tachykinins; the latter act, in turn, on postjunctional tachykinin NK1/NK2 receptors. The role of the NK3 receptor as prejunctional mediator of the excitatory transmission operated by tachykinins is discussed.

New spiropiperidines as potent and selective non-peptide tachykinin NK2 receptor antagonists.

The synthesis of a series of 2-(5-fluoro-1H-indol-3-yl)ethyl spiropiperidines is described together with their tachykinin NK2 receptor affinities measured in a rat colon binding assay. Equivalent NK2 receptor binding affinity was observed for the spirooxazolidinone 3-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-1-oxa-3,8-diazaspiro[4.5] decan-2-one (3a), the imidazolidinone 3-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-1,3,8-triazaspiro[4.5 ] decan-2-one (3s), and the pyrrolidinone 2-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-2,8-diazaspiro[4.5]decan -3 - one (3t). Substitution in the phenyl ring of compound 3a produced no significant enhancement in NK2 binding affinity. Replacement of the phenyl ring in 3a with other aromatic rings resulted in a significant loss in binding affinity. Compound 3a was shown to be a potent NK2 receptor antagonist in guinea pig trachea where it also demonstrated 1000-fold selectivity for NK2 receptors over NK1. In the anesthetized guinea pig, compound 3a administered by the intravenous or oral route displayed potent and long-lasting antagonist activity against NK2 receptor agonist induced bronchoconstriction.