In vitro pharmacology of a novel non-peptide angiotensin II-receptor antagonist, E4177.

E4177, 3-[(2'-carboxybiphenyl-4-yl)methyl]-2-cyclopropyl-7-methyl-3H- imidazo[4,5-b]pyridine, was characterized by in vitro autoradiography and by examining functional antagonism upon angiotensin II (Ang II)-induced contraction of isolated vessels. In rat adrenal cortex and liver, E4177 competitively inhibited the specific binding of 125I-[Sar1,Ile8]Ang II, with IC50 being (5.2 +/- 1.0) x 10(-8) M for the adrenal cortex and (1.2 +/- 0.3) x 10(-7) M for the liver. These IC50 values were similar to those for losartan, which showed an IC50 of (6.0 +/- 0.9) x 10(-8) M for the adrenal cortex and (1.3 +/- 0.5) x 10(-7) M for the liver. In contrast, E4177 and losartan had little effect on the binding to rat adrenal medulla where AT2-receptors predominate. These results indicate that E4177 is AT1-specific as is losartan. E4177 and losartan competitively antagonized the Ang II-induced contraction of human and rabbit arterial strips without any agonistic action. The obtained IC50 values indicated that E4177 was twice as potent as losartan in human arteries and three times more so in rabbit aortic strips. Responses to norepinephrine, serotonin, histamine or KCl were not affected by E4177. In addition, E4177 (10(-5) M) had no effect on angiotensin-converting enzyme activity. These data indicate that E4177 is a potent AT1 Ang II-receptor antagonist that may be clinically useful for the treatment of cardiovascular diseases such as hypertension.