posted on 2020-05-18, 13:42authored byEdith Bartole, Lukas Grätz, Timo Littmann, David Wifling, Ulla Seibel, Armin Buschauer, Günther Bernhardt
Comprehensively characterized
fluorescent probes for the histamine
H3 receptor (H3R) and especially for the H4R orthologs [e.g., human (h) and mouse (m)] are highly needed
as versatile complementary tools to radioligands. In view of fluorescent
probes for BRET-based binding studies and for localizing the H4R in live cells, we synthesized and biologically characterized
Py-5-labeled histamine derivatives. The most notable compound was
UR-DEBa242 (26, 1-[4-(1H-Imidazol-4-yl)butyl]-4-{(1E,3E)-4-[4-(dimethylamino)phenyl]buta-1,3-dienyl}-2,6-dimethylpyridinium
hydrotrifluoroacetate trifluoroacetate), acting as a partial agonist
at the hH3R [pEC50 (reporter gene) 8.77] and
as an inverse agonist/antagonist at the h/mH4Rs [pIC50 (reporter gene) 8.76/7.08; pIC50/pKb (β-arrestin2) 7.81/7.30]. In confocal microscopy, 26 proved suitable for hH4R localization and trafficking
studies in live cells. BRET-based binding at the NLuc-hH3,4Rs/mH4R [pKd 8.78/7.75/7.18,
comparable to binding constants from radioligand binding/flow cytometry;
fast association/dissociation (∼2 min)] revealed 26 as a useful molecular tool to determine hH3,4Rs/mH4R binding affinities of ligands binding to these receptors.