LF-16.0335, A NOVEL POTENT AND SELECTIVE NONPEPTIDE ANTAGONIST OF THEHUMAN BRADYKININ B-2 RECEPTOR

1 In the present paper, we describe the in vitro pharmacological prope rties of LF 16.0335 [4-[4-(aminoiminomethyl)phenyl-carbonyl]piperazin- 1-yl]carbonyl]pyrrolidine), a novel and potent nonpeptide antagonist of the human bradykinin (BK) B-2 receptor. 2 LF 16.0335 displaced [H-3 ]-BK binding to membrane preparations from CHO cells expressing the cl oned human B2 receptor, INT 407 cells and human umbilical vein with K- i values of 0.84 +/- 0.39 nM, 1.26 +/- 0.68 nM and 2.34 +/- 0.36 nM, r espectively. 3 In saturation binding studies performed in INT 407 cell membranes in the presence or absence of LF 16.0335, B-max values of [ H-3]-BK were not significantly changed suggesting that LF 16.0335 beha ves as a competitive antagonist. 4 LF 16.0335 had no affinity for the cloned human kinin B-1 receptor stably expressed in 293 cells. In addi tion, this compound at 1 mu M did not significantly bind to a range of 40 different membrane receptors and eight ion channels except muscari nic M-2 and M-1 receptors for which an IC50 value of 0.9 and 1 mu M wa s obtained. 5 BK stimulates in a concentration-dependent manner phosph oinositosides (IPs) production in cultured INT 407 cells. Concentratio n-response-curves to BK were shifted to the right in the presence of L F 16.0335 (0.1 mu M) without reduction of the maximum. LF 16.0335 inhi bited the concentration-contraction curve to BK in the human umbilical vein giving a pA(2) value of 8.30 +/- 0.30 with a Schild plot slope t hat was not different from unity. 6 These results demonstrate that LF 16.0335 is a potent, selective and competitive antagonist of the human bradykinin B-2 receptor.