In vitro and in vivo characterization of A-940894: a potent histamine H4 receptor antagonist with anti-inflammatory properties

The histamine H-4 receptor is widely expressed in cells of immune origin and has been shown to play a role in a variety of inflammatory processes mediated by histamine. In this report, we describe the in vitro and in vivo anti-inflammatory properties of a potent histamine H-4 receptor antagonist, A-940894 (4-piperazin-1-yl-6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d]pyrimidin-2-ylamine). We have analysed the pharmacological profile of A-940894 at mouse native, rat recombinant and human recombinant and native, histamine H-4 receptors by radioligand binding, calcium mobilization, mast cell shape change, eosinophil chemotaxis assays and in the mouse model of zymosan-induced peritonitis. A-940894 potently binds to both human and rat histamine H-4 receptors and exhibits considerably lower affinity for the human histamine H-1, H-2 or H-3 receptors. It potently blocked histamine-evoked calcium mobilization in the fluorometric imaging plate reader assays and inhibited histamine-induced shape change of mouse bone marrow-derived mast cells and chemotaxis of human eosinophils in vitro. In a mouse mast cell-dependent model of zymosan-induced peritonitis, A-940894 significantly blocked neutrophil influx and reduced intraperitoneal prostaglandin D-2 levels. Finally, A-940894 has good pharmacokinetic properties, including half-life and oral bioavailability in rats and mice. These data suggest that A-940894 is a potent and selective histamine H-4 receptor antagonist with pharmacokinetic properties suitable for long-term in vivo testing and could serve as a useful tool for the further characterization of histamine H-4 receptor pharmacology.