MEN 11270, a novel selective constrained peptide antagonist with high affinity at the human B-2 kinin receptor

We investigated the pharmacological profile of MEN 11270, or H-D-Arg-Arg-Pr o-Hyp-Gly-Thi-c(Dab-DTic-Oic-Arg)c(7 gamma-10 alpha), a conformationally co nstrained derivative of the B-2 kinin receptor antagonist Icatibant. MEN 11 270 bound with high-affinity to the B-2 kinin receptor constitutively expre ssed by WI38 human fibroblasts, inhibiting H-3-bradykinin (BK) with a pK(i) value of 10.3 +/- 0.08 (n = 5). The rank order of affinity of several pept ide and nonpeptide antagonists was also assessed: Icatibant (pKi = 10.6) ap proximate to MEN 11270 (pK(i) = 10.3) approximate to B9430 (pK(i) = 10.0) > B9858 (pKi = 8.0) > FR173657 (pK(i) = 7.6) > WIN64338 (pK(i) = 7.2)> Lys-[ des-Arg(9),Leu(8)]-BK (pK(i) < 6)> [des-Arg(9),Leu(8)]-BK (pK(i) < 5). MEN 11270 showed a low affinity in inhibiting H-3-Lys-[des-Arg(9)]-BK binding a t the human B-2 kinin receptor constitutively expressed by the same cells ( pK(i) 6.0 +/- 0.33; n = 3). MEN 11270 showed no binding affinity (pIC(50) < 5.5) at 29 different receptors and ion channels. In the human umbilical ve in contraction assay, MEN 11270, shifted the concentration-response curve t o BK to the right in a concentration-dependent manner (pA(2) 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 mu M) did not affect the concentration-response curve to the B-1 agonist Lys-[des-Arg(9) ]BK nor the contractile responses elicited by noradrenaline or serotonin. T hese findings indicate MEN 11270 as an antagonist at the human B-2 kinin re ceptor, with potency and selectivity comparable to those of the linear pept ide antagonist, supporting the hypothesis that a constrained C-terminal bet a-turn conformation preserves a high affinity for the interaction of Icatib ant with the B-2 kinin receptor.