Vol. 289, Issue 3, 1250-1256, June 1999

MEN 11270, A Novel Selective Constrained Peptide Antagonist with High Affinity at the Human B₂ Kinin Receptor

Stefania Meini, Laura Quartara, Anna Rizzi, Riccardo Patacchini, Paola Cucchi, Alessandro Giolitti, Girolamo Calò, Domenico Regoli, Marco Criscuoli and Carlo A. Maggi

Department of Pharmacology, Menarini Ricerche S.p.A., Florence, Italy (S.M., R.P., P.C., M.C., C.A.M); Department of Chemistry, Menarini Ricerche S.p.A., Florence, Italy (L.Q., A.G.); Department of Experimental and Clinical Medicine, Section of Pharmacology, University of Ferrara, Italy (A.R., G.C., D.R.)

We investigated the pharmacological profile of MEN 11270, or H-D-Arg-Arg-Pro-Hyp-Gly-Thi-c(Dab-DTic-Oic-Arg)c(7-10 ), a conformationally constrained derivative of the B₂ kinin receptor antagonist Icatibant. MEN 11270 bound with high-affinity to the B₂ kinin receptor constitutively expressed by WI38 human fibroblasts, inhibiting ³H-bradykinin (BK) with a pK_i value of 10.3 ± 0.08 (n = 5). The rank order of affinity of several peptide and nonpeptide antagonists was also assessed: Icatibant (pK_i = 10.6)  MEN 11270 (pK_i = 10.3)  B9430 (pK_i = 10.0) > B9858 (pKi = 8.0) > FR173657 (pK_i = 7.6) > WIN64338 (pK_i = 7.2) > Lys-[des-Arg⁹,Leu⁸]-BK (pK_i < 6) > [des-Arg⁹,Leu⁸]-BK (pK_i < 5). MEN 11270 showed a low affinity in inhibiting ³H-Lys-[des-Arg⁹]-BK binding at the human B₁ kinin receptor constitutively expressed by the same cells (pK_i 6.0 ± 0.33; n = 3). MEN 11270 showed no binding affinity (pIC₅₀ < 5.5) at 29 different receptors and ion channels. In the human umbilical vein contraction assay, MEN 11270, shifted the concentration-response curve to BK to the right in a concentration-dependent manner (pA₂ 8.14 ± 0.22, n = 7). The Schild plot was linear (slope 0.95 ± 0.11), consistent with a competitive antagonism. In the same bioassay, MEN 11270 (10 µM) did not affect the concentration-response curve to the B₁ agonist Lys-[des-Arg⁹]-BK nor the contractile responses elicited by noradrenaline or serotonin. These findings indicate MEN 11270 as an antagonist at the human B₂ kinin receptor, with potency and selectivity comparable to those of the linear peptide antagonist, supporting the hypothesis that a constrained C-terminal -turn conformation preserves a high affinity for the interaction of Icatibant with the B₂ kinin receptor.