Pharmacological characterization of PD 156707, an orally active ETA receptor antagonist.

We describe the pharmacological characteristics of PD 156707 (sodium 2-benzo[1,3]dioxol-5-yl-4-(4-methoxy-phenyl)-4-oxo-3-(3,4,5- trimethoxy-benzyl)-but-2-enoate), a potent, orally active, nonpeptide antagonist of the endothelin A (ETA) receptor subtype. PD 156707 was designed on the basis of a compound identified by screening the Parke-Davis chemical library. PD 156707 is highly selective for the ETA receptor (ETAR) and inhibits the binding of [125I]-ET-1 to cloned human ETAR and ETBR with Ki values of 0.17 and 133.8 nM, respectively. PD 156707 antagonizes ET-1-stimulated phosphoinositide hydrolysis in Ltk- cells expressing cloned human ETAR with an IC50 value of 2.4 nM. PD 156707 inhibits vasoconstriction in isolated blood vessels mediated by ETAR (rabbit femoral artery) and ETBR (rabbit pulmonary artery) with pA2 values of 7.5 and 4.7, respectively. PD 156707 administered orally to rats blocked subsequent ETAR-mediated pressor responses in vivo but had no effect on ETBR-mediated dilator responses. As a potent and orally active ETA-selective antagonist, PD 156707 will be useful in defining the physiological and pathological roles of ETAR.