Mutational analysis of the histamine H1-receptor binding pocket of histaprodifens

Histaprodifens constitute a new class of histamine H-1-receptor agonists. These ligands can be regarded as hybrid molecules, consisting of a histamine moiety linked at the two-position of the imidazole ring by a propyl chain to two phenyl rings, one of the characteristic features of several H-1-receptor antagonists. To delineate the binding site of various histaprodifen-like ligands, we generated mutant histamine H-1 receptors, in which various amino acids, involved in the binding of either histamine or H-1-receptor antagonists, were replaced by alanine. Wild-type and mutant H-1 receptors were transiently expressed in African green monkey kidney cells (COS-7) and evaluated for their interaction with histamine and various histaprodifens by [H-3]mepyramine radioligand-binding studies and by nuclear factor kappaB (NF-kappaB) reporter-gene assays. Our data show that, within the histamine H-1-receptor binding pocket, histaprodifens interact with both agonist and antagonist binding sites, resulting in high affinity histamine H-1-receptor agonists. (C) 2004 Elsevier B.V. All rights reserved.