Development of an efficient and selective radioligand for bradykinin B1 receptor occupancy studies

Aryl sulfonamides containing tetralin allylic amines as potent and selective bradykinin B1 receptor antagonists

The bradykinin B1 receptor has been shown to mediate pain response and is rapidly induced upon injury. Blocking this receptor may provide a promising treatment for inflammation and pain. We previously reported tetralin benzyl amines as potent B1 antagonists. Here we describe the synthesis and SAR of B1 receptor antagonists with homobenzylic amines. The SAR of different linkers led to the discovery of tetralin allylic amines as potent and selective B1 receptor antagonists (hB1 IC(50)=1.3 nM for compound 16). Some of these compounds showed modest oral bioavailability in rats.

Potent bradykinin B1 receptor antagonists: 4-Substituted phenyl cyclohexanes

Selective bradykinin (BK) B(1) receptor antagonists have been shown to be antinociceptive in animal models and could be novel therapeutic agents for the treatment of pain and inflammation. Elucidation of the structure-activity relationships of the biphenyl moiety of the lead compound 1 provided a potent new structural class of BK B(1) receptor antagonists.

Dual antagonists of the bradykinin B1 and B2 receptors based on a postulated common pharmacophore from existing non-peptide antagonists

We have recently drawn attention to the fact that most non-peptide antagonists of the kinin B1 receptor reported so far are structurally related, possessing the core motif phenyl-SO2-NR-(spacer(2-4))-CO-NRR. This is found in compound A (N-[2-[4-(4,5-dihydro-1H-imidazol-2- yl)phenyl]ethyl] - 2- [(2R)-1-(2-napthylsulfonyl)-3-oxo-1,2,3,4-tetrahydroquinoxalin-2-yl]acetamide), a very potent and selective B1 receptor antagonist. A subset of specific bradykinin B2 receptor antagonists (LF16-0687, bradyzide and derivatives) possesses a similar 'scaffold' (phenyl-SO2-NR-CRR-CO-NRR). We investigated whether simple molecules mimicking the postulated pharmacophores could be identified in two public chemical databases. Receptor binding to B1 and B2 receptors expressed by rabbit cultured smooth-muscle cells was confirmed for some of these newly identified agents, with a loss of receptor subtype selectivity. For instance, compound 3[2-(3-oxo-1-(toluene-4-sulfonyl)-1,2,3,4-4H-quinoxalin-2-yl)-N-phenyl-acetamide] exhibits IC50 values of 2.13 and 126 microM in the radioligand competition assays for B1 and B2 receptors, respectively, and a pA2 of 6.27 at the rabbit B1 receptor in a functional test (Lys-des-Arg9-bradykinin-induced contractility of the isolated aorta). Compound 5 (a close analog of compound 3) is a more balanced dual antagonist of low potency (IC50 values of 30 and 117 microM, respectively). As predicted, compounds modeled on a postulated pharmacophore common to some non-peptide B1 or B2 receptor antagonists exhibit measurable binding with decreased receptor subtype selectivity. Dual B1/B(2) receptor antagonists are of possible therapeutic interest and should be developed.

Molecular identification and pharmacological profile of the bovine kinin B1 receptor

To support the study of kinin pharmacology in bovine models of cultured endothelial cells (ECs), the Bovine Genome Project was searched for a B1receptor (B1R) gene ortholog (BDKRB1). A contig complementary to an intronless coding nucleotide sequence was found. The sequence was amplified from bovine EC DNA, further cloned into pcDNA3 and expressed in COS-1 cells. The bovine B1R sequence was confirmed and extended. A putative Zn2+-binding motif HEXXH is not present (replaced by HDAWP). The receptor binds [3H]Lys-des-Arg9-bradykinin in a saturable manner (Kd0.36 nM) and exhibits a pharmacological profile similar to that of human B1R.

Generation and characterization of a humanized bradykinin B1 receptor mouse

Antagonists of the B1 bradykinin receptor (B1R), encoded by the BDKRB1 gene, offer the promise of novel therapeutic agents for inflammatory and neuropathic pain. However, the in vivo characterization of the pharmacodynamics of B1R antagonists is hindered by the low level of B1R expression in healthy tissue and the profound species selectivity exhibited by many compounds for the B1R. To circumvent these issues we generated two genetically engineered rodent models. The first is a transgenic rat over-expressing the human B1R under the control of the neuronal-specific enolase promoter; we previously reported the utility of this model in assessing human B1R receptor occupancy in the central nervous system of the rat. The second model, reported here, utilized gene-targeting by homologous recombination to replace the genomic coding sequence for the endogenous mouse B1R with that of the human B1R. The mRNA expression profile of the humanized Bdkrb1 (hBkdrb1) allele is similar to that of the mouse Bdkrb1 (mBkdrb1) in the wild-type animal. Furthermore, in vitro assays indicate that tissues isolated from the humanized mouse possess pharmacological properties characteristic of the human B1R. Therefore, we have generated a humanized B1R mouse model that is suitable for testing the efficacy of human B1R-selective compounds.