Potent, long-acting bradykinin antagonists for a wide range of applications

Actions of bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg; BK) are mediated by constitutively expressed B2 receptors (which require the full BK peptide chain) and by B1 receptors (which require BK (1-8) as ligand) that are induced in inflammation. BK has many functions in normal and pathological physiology, including initiation of most, if not all, inflammation. BK also evidently functions as an autocrine stimulant for growth of small cell lung cancer (SCLC). A new group of BK antagonists containing the novel amino acid alpha-(2-indanyl)glycine (Igl) provides both broad-spectrum and selective antagonists for all these functions. As examples, D-Arg-Arg-Pro-Hyp-Gly-Igl-Ser-D-Igl-Oic-Arg (B9430) is an extremely potent and long-acting antagonist of both B1 and B2 receptors, is stable against endogeneous kininase enzymes, and is active in various in vivo models, including by intragastric administration. Acylation of B9430 with dehydroquinuclidine-2-carboxylic acid (Dhq) gives B9562, a highly selective B2 antagonist. In contrast, Lys-Lys-Arg-Pro-Hyp-Gly-Igl-Ser-D-Igl-Oic (B9858) is a highly potent and selective B1 antagonist. The dimer of B9430 linked at the amino terminus with suberimide is a potent selectively cytotoxic agent for SCLC cells. Results with these peptides suggest that a new generation of antiinflammatory and anticancer drugs may be at hand.