RT Journal Article SR Electronic T1 Analysis of Multiple Histamine H4 Receptor Compound Classes Uncovers Gαi Protein- and β-Arrestin2-Biased Ligands JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 1174 OP 1182 DO 10.1124/mol.112.080911 VO 82 IS 6 A1 Nijmeijer, Saskia A1 Vischer, Henry F. A1 Rosethorne, Elizabeth M. A1 Charlton, Steven J. A1 Leurs, Rob YR 2012 UL http://molpharm.aspetjournals.org/content/82/6/1174.abstract AB After the recent description of β-arrestin2 recruitment to the human histamine H4 receptor (hH4R) in response to the well known H4R antagonist 1-[(5-chloro-1H-indol-2-yl)carbonyl]-4-methyl-piperazine (JNJ 7777120), we evaluated in this study the efficacy of 31 known hH4R ligands to induce Gαi protein signaling and β-arrestin2 recruitment by the hH4R. The selected hH4R ligands belong to nine different structural classes that partly cover (pre)clinical trial candidates. We have identified hH4R ligands with a significant bias for the Gαi protein or β-arrestin2 pathway on the basis of efficacy differences. In addition, hH4R antagonists that did not show positive efficacy in either functional readouts were found. A common trend in pathway preference for the nine different ligand classes could not be observed. In particular, the isothiourea class shows very diverse results, varying from Gαi protein-biased or β-arrestin2-biased to nonbiased antagonists upon minor structural changes. The identified biased hH4R ligands are important pharmacological tools to unravel the significance of biased hH4R signaling in H4R pharmacology.