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.