Pharmacology and structure--activity relationships of the nonpeptide bradykinin receptor antagonist WIN 64338.

A series of competitive, nonpeptide bradykinin receptor antagonists based on an alpha-amino acid scaffold have been developed and biologically characterized. The lead compound in the series, WIN 64338, demonstrates competitive inhibition of bradykinin-mediated functional responses through B2 receptors in a variety of tissues and species. WIN64338 is a specific for the bradykinin B2 receptor; it is inactive at both the B1 and B2 kinin receptors. In conscious guinea pigs, WIN 64338 inhibits kinin-mediated bronchoconstriction but does not attenuate a similar response to acetylcholine. A series of WIN 64338 analogues display a well-defined structure-activity relationship, strongly suggesting binding in a specific manner to the B2 receptor. Structure-activity data suggest that a hydrophobic binding pocket that prefers large aromatic groups in a specific conformational orientation exists in the receptor ligand binding domain. This class of nonpeptide bradykinin receptor antagonists may lead to the design of other compounds with enhanced receptor affinity and optimal in vivo biological activity.

Effects of peptide and nonpeptide antagonists of bradykinin B2 receptors on the venoconstrictor action of bradykinin.

The isolated rabbit jugular and human umbilical veins respond to bradykinin (BK) by contractions that are mediated by the BK B2 type receptors. In this report, the pharmacology of recently developed BK B2 receptor antagonists is assessed by using these preparations. The nonpeptide kinin antagonist WIN 64338 (phosphonium, [[4-[[2-[[bis(cyclohexylamino)methylene]amino]- 3-(2-naphthalenyl)-1-oxopropyl]amino]phenyl]methyl]tributyl chloride monohydrochloride) demonstrates competitive and surmountable antagonism of BK in both the jugular and the umbilical veins (pA2 values of 6.14 and 5.99, respectively). WIN 64338 shows selectivity in its antagonist action as it does not inhibit the effect of various other contractile agents in either of the preparations. HOE-140 (D-Arg[hydroxyproline3,beta-thienylalanine5, D-Tic7, octahydroindol-2-yl-carbonyl residue8]-BK), a "second generation" peptide antagonist of BK, behaves as an insurmountable and irreversible antagonist in the rabbit jugular vein, but appears to be competitive in the umbilical vein (pA2 = 8.2). In the jugular vein, [L-Tic7]HOE-140 is an insurmountable antagonist about 2000-fold less potent than HOE-140; the L-Tic7 isomer demonstrates no significant antagonist activity on the umbilical vein at 30 microM. This study confirms that WIN 64338 behaves as a competitive and selective kinin antagonist of the BK B2 type receptors. The pharmacological profile of the L-Tic7 analog of HOE-140 may provide useful information in discerning the molecular interaction of noncompetitive BK antagonists with their receptors.

Synthesis, characterization, and conformational analysis of the D/L-Tic7 stereoisomers of the bradykinin receptor antagonist D-Arg0[Hyp3,Thi5,D-Tic7,Oic8]bradykinin.

D-Arg0[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (HOE-140) is a potent (Ki = 0.11 nM) inhibitor of [3H]bradykinin binding to bradykinin B2 receptors found on human IMR-90 fetal lung fibroblasts. During the synthesis of this compound, we isolated and unambiguously identified the L-Tic7 stereoisomer (WIN 65365), which exhibits a 2000-fold lower binding affinity (Ki = 130 nM) than HOE-140 to the bradykinin receptor. A similar decrease in potency is observed for WIN 65365 inhibition of bradykinin-stimulated 45Ca2+ efflux from IMR-90 cells. Both HOE-140 and WIN 65365 appear to be competitive antagonists at the IMR-90 bradykinin receptor. This is the first documentation of bradykinin binding and functional antagonist activity by a bradykinin peptide analogue with an L amino acid replacing Pro7. In an attempt to rationalize the differences in binding affinities of HOE-140 and WIN 65365, a conformational analysis of the peptides was undertaken using annealed molecular dynamics (AMD). Conformational analysis of HOE-140 reveals a strong preference for the formation of a type II' beta-turn in the carboxy-terminal region. Analogous modeling of WIN 65365 reveals that its conformation is strikingly different from HOE-140 in that the four carboxy-terminal residues of WIN 65365 do not form a beta-turn. These differences in low-energy conformations between the two peptides may lead to a better understanding of the molecular interaction of antagonists with the bradykinin receptor.

Bradykinin receptor types and B2 subtypes.

Bradykinin, desArg9BK, some agonist analogues and several antagonists have been tested in isolated organs in order to identify bradykinin B2 receptor subtypes. The initial pharmacological characterization was made in the rabbit jugular vein and the guinea pig ileum, two widely used B2 preparations which have shown marked differences in their sensitivities to both agonists and antagonists. The study has then been extended to peripheral tissues (stomach, colon, urinary bladder) of four species (the rat, guinea pig, rabbit and man) and to isolated vessels (rabbit jugular vein, rabbit vena cava, guinea pig pulmonary artery, rat portal vein) in order to determine if pharmacologic receptor subtypes may be related to species. It has been shown that B2 receptors in rat and guinea pig tissues belong to a similar pharmacological entity, a receptor which is different from that mediating the responses of rabbit and human tissues. Agonists order of potency ([Hyp3]BK > BK > [Aib7]BK) obtained in the rabbit jugular vein is different from that found in the guinea pig ileum (BK < or = [Aib7]BK > [Hyp3]BK). Affinities of competitive antagonists (for instance DArg[Hyp3,DPhe7,Leu8]BK) in rabbit tissues are higher than in guinea pig and rat tissues by at least 2 log units, while the non peptidic compound WIN 64338 is more active (also by two log units) in guinea pig than in human and rabbit tissues. The non competitive long-acting antagonist HOE 140 is very potent and equally active in the four species. Some antagonists (peptides without unnatural residues, peptides with unnatural residues, non peptides) have been shown to be specific for kinin receptors and selective for the B2. Altogether, the present results a) confirm the existence of two B2 receptor subtypes, b) suggest that receptor subtypes may be species dependent and c) indicate that the B2 receptor subtype found in the rabbit is similar to that found in man.