Inhibition of rabbit aortic angiotensin II (AII) receptor by CV-11974, a new nonpeptide AII antagonist.
The angiotensin II (AII) antagonistic action of CV-11974 (2-ethoxy-1-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl] benzimidazole-7-carboxylic acid) was investigated in an AII-receptor binding assay using rabbit aortic membranes and an AII-induced contraction assay using rabbit aortic strips. A single class of [125I]AII-(Sar1,Ile8) binding sites was found in the membranes with a dissociation constant (Kd) of 0.15 nM and a receptor concentration (Bmax) of 86.9 fmol/mg protein. CV-11974 markedly reduced Kd without affecting Bmax. The specific binding of [125I]AII-(Sar1,Ile8) in this preparation was inhibited completely by CV-11974 [the inhibition constant (Ki) = 0.64 nM], DuP 753 [an angiotensin II type I (AT1) receptor-selective antagonist] (Ki = 51 nM) and EXP3174 (an active metabolite of DuP 753) (Ki = 6.8 nM), but was not affected by PD123177 (an AT2 receptor-selective antagonist). These results suggest that the single binding site in rabbit aortic membranes is an AT1 receptor subtype. The affinity of CV-11974 to these AT1 receptors was approximately 80 and 10 times higher than that of DuP 753 and EXP3174, respectively. CV-11974 showed no appreciable affinity for the AT2 receptors found in bovine cerebellum. In the in vitro functional study, CV-11974 markedly reduced the AII-induced maximal contractile response of rabbit aortic strips (pD'2 = 9.97). In contrast, Compound 7-H, which lacks the carboxyl group at the benzimidazole ring of CV-11974, inhibited the contraction in a competitive manner. The inhibition by CV-11974 was long lasting. These results suggest that CV-11974 is a potent and long-acting AT1 receptor-selective, competitive antagonist. The carboxyl group at the benzimidazole ring plays an important role in the interaction between CV-11974 and the AT1 receptor.
Noda
M
M
Pharmaceutical Division, Takeda Chemical Industries, Ltd., Osaka, Japan.
Shibouta
Y
Y
Inada
Y
Y
Ojima
M
M
Wada
T
T
Sanada
T
T
Kubo
K
K
Kohara
Y
Y
Naka
T
T
Nishikawa
K
K
D000804:Angiotensin II / Q000037:antagonists & inhibitors / Q000378:metabolism; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism*; D001562:Benzimidazoles / Q000494:pharmacology*; D001665:Binding Sites; D001667:Binding, Competitive; D001713:Biphenyl Compounds; D007457:Iodine Radioisotopes; D007536:Isomerism; D008297:Male; D011817:Rabbits; D013777:Tetrazoles / Q000494:pharmacology*
D057911:Angiotensin Receptor Antagonists; D001562:Benzimidazoles; D001713:Biphenyl Compounds; D007457:Iodine Radioisotopes; D013777:Tetrazoles; D000804:Angiotensin II; C082544:2-ethoxy-1-((2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl)benzimidazole; C081643:candesartan