UR-DEBa242: A Py-5-Labeled Fluorescent Multipurpose Probe for Investigations on the Histamine H-3 and H-4 Receptors

• Published in: Journal of medicinal chemistry Vol. 63; no. 10; pp. 5297 - 5311
• Main Authors: Bartole, Edith, Graetz, Lukas, Littmann, Timo, Wifling, David, Seibel, Ulla, Buschauer, Armin, Bernhardt, Guenther
• Format: Journal Article
• Language: English
• Published: WASHINGTON Amer Chemical Soc 28.05.2020
• Subjects: Chemistry, Medicinal; Life Sciences & Biomedicine; Pharmacology & Pharmacy; Science & Technology; H-2-RECEPTOR; LIGAND-BINDING; CLONING; PHARMACOLOGICAL CHARACTERIZATION; 1ST POTENT; H-4-RECEPTOR; ANTAGONISTS
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/acs.jmedchem.0c00160

Comprehensively characterized fluorescent probes for the histamine H-3 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 hH(3)R [pEC(50) (reporter gene) 8.77] and as an inverse agonist/antagonist at the h/mH(4)Rs [pIC(50) (reporter gene) 8.76/7.08; pIC(50)/pK(b) (beta-arrestin2) 7.81/7.30]. In confocal microscopy, 26 proved suitable for hH(4)R localization and trafficking studies in live cells. BRET-based binding at the NLuc-hH(3,4)Rs/mH(4)R [pK(d) 8.78/7.75/7.18, comparable to binding constants from radioligand binding/flow cytometry; fast association/dissociation (similar to 2 min)] revealed 26 as a useful molecular tool to determine hH(3,4)Rs/mH(4)R binding affinities of ligands binding to these receptors.