The in vitro pharmacological profile of KR31080, a nonpeptide AT1 receptor antagonist

KR31080 (2-butyl-5-methyl-6-(1-oxopyridin-2-yl)-3-[[2'-(1H-tetrazol- 5-yl) biphenyl-4-yl]methyl]-3H-imidazo[4,5-b] pyridine) is a potent inhibitor of angiotensin type 1 (AT1) receptors in rabbit aorta and human recombinant AT1 receptors. In the isolated rabbit thoracic aorta, KR31080 caused a nonparallel shift to the right of the concentration-response curves to angiotensin II (AII) with decreased maximal response (pD'2 = 10.1 +/- 0.1), but had no effect on the contractile response induced by norepinephrine. KR31080 inhibited specific [125I]AII binding to rabbit aortic membranes (AT1 receptors) and [125I][Sar1, Ile8]AII binding to human recombinant AT1 receptors in a concentration-dependent manner with IC50 values of 0.84 +/- 0.08 nM and 1.92 +/- 0.15 nM, respectively, but did not inhibit specific [125I]AII binding to bovine cerebellum membranes (AT2 receptors). In the Scatchard analysis, KR31080 interacted with rabbit aortic AT1 receptors in a competitive manner, similar to losartan. These results demonstrate that KR31080 is a potent and AT1 selective angiotensin receptor antagonist which exerts a competitive antagonism in the [125I]AII binding assay and insurmountable AT1 receptor antagonism in the functional study.