Pharmacological characterization of YM087, a potent, nonpeptide human vasopressin V(1A) and V₂ receptor antagonist

The effects of YM087 (4'-[(2-methyl-1,4,5,6-tetrahydroimidazo[4,5-d][1]benzazepin-6-yl)-carbonyl]-2 -phenylbenzanilide monohydrochloride), a novel nonpeptide vasopressin (AVP) receptor antagonist, on [³H]AVP binding to human AVP receptors (V(1A), V(1B) and V₂) cloned and transiently expressed in COS-1 cells generated from monkey renal tissue were studied. Scatchard analysis of saturation isotherms for the specific binding of [³H]AVP to membranes, prepared from COS-1 cells transfected with human V(1A), V(1B) and V₂ receptors, yielded an apparent equilibrium dissociation constant (K(d)) of 0.67 nM, 0.28 nM and 2.14 nM and a maximum receptor density (B(max)) of 2180 fmol/mg protein, 369 fmol/mg protein and 2660 fmol/mg protein, respectively. YM087 showed high affinity for AVP V(1A) and V₂ receptors with K(i) values of 6.3 and 1.1 nM, respectively, but had no effect on [³H]AVP binding to AVP V(1B) receptors. In COS-1 cells expressing either AVP V(1A) or V(1B) receptors, AVP caused a concentration-dependent increase in intracellular Ca²⁺ concentration ([Ca²⁺](i)). YM087 inhibited the AVP-induced increase in [Ca²⁺](i) in COS-1 cells expressing AVP V(1A) receptors in a concentration-dependent manner with an IC₅₀ value of 14.3 nM, but did not influence this increase in AVP V(1B)-receptor expressing cells. In contrast, stimulation of COS-1 cells expressing AVP V₂ receptors resulted in an accumulation of cAMP. YM087 inhibited AVP-induced cAMP production in COS-1 cells expressing AVP V₂ receptors in a concentration-dependent manner with an IC₅₀ value of 1.95 nM. In all assays used, YM087 was devoid of any agonistic activity. These results suggest that YM087 is a potent nonpeptide dual human AVP V(1A) and V₂ receptor antagonist, and that YM087 will be a powerful tool in investigation of the physiological and pathophysiological roles of AVP.