Characterization of ibodutant at NK2 receptor in human colon

Abstract We have characterized the pharmacological profile of the nonpeptide tachykinin NK 2 receptor antagonist ibodutant (MEN15596) through radioligand binding and contractility assays in the human colon smooth muscle. The antagonist affinity of ibodutant was evaluated through concentration-dependent inhibition curves at the [ 125 I]NKA specific binding by using membranes prepared from human colon smooth muscle. In this assay the affinity of ibodutant ( pK i 9.9) was compared to that of other two selective NK 2 receptor antagonists, nepadutant ( pK i 8.4) and saredutant ( pK i 9.2). The antagonist potency of ibodutant was evaluated towards the [βAla 8 ]NKA(4-10)-mediated contractions of human colon smooth muscle strips. In this assay ibodutant (3, 10, 30 and 100 nM) induced a concentration-dependent rightward shift of the [βAla 8 ]NKA(4-10) concentration-response curves without depressing the maximal contractile effect. The analysis of the curves yielded a Schild-plot linear regression with a slope not different from unity (1.02), thus indicating a surmountable antagonist behavior. The calculated apparent antagonist potency as pK B value was 9.1. No sex related differences were observed in NK 2 receptor pharmacology for [βAla 8 ]NKA(4-10) or ibodutant in colonic strips obtained from male or female patients. Reversibility experiments of tachykinin NK 2 receptor blockade indicated that the inhibition of the agonist-induced contractions in preparations pre-exposed to ibodutant, and afterwards subjected to repeated washing cycles remained almost constant showing no sign of recovery during the 3 h observation period. Overall, the present study indicates ibodutant as a potent tachykinin NK 2 receptor antagonist in the human colon tissue, also endowed with a persistent duration of action.