Chromenopyrazole-based High Affinity, Selective Fluorescent Ligands for Cannabinoid Type 2 Receptor

Sameek Singh; Caitlin R M Oyagawa; Christa Macdonald; Natasha L Grimsey; Michelle Glass; Andrea J Vernall

doi:10.1021/acsmedchemlett.8b00597

Chromenopyrazole-based High Affinity, Selective Fluorescent Ligands for Cannabinoid Type 2 Receptor

ACS Med Chem Lett. 2019 Jan 30;10(2):209-214. doi: 10.1021/acsmedchemlett.8b00597. eCollection 2019 Feb 14.

Authors

Sameek Singh¹, Caitlin R M Oyagawa², Christa Macdonald², Natasha L Grimsey², Michelle Glass², Andrea J Vernall¹

Affiliations

¹ School of Pharmacy, University of Otago, Dunedin, New Zealand.
² Department of Pharmacology and Clinical Pharmacology, and Centre for Brain Research, School of Medical Sciences, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.

Abstract

Cannabinoid type 2 receptor (CB₂R) is an attractive target for the treatment of pain and inflammatory disorders. Availability of a selective CB₂R fluorescent ligand to study CB₂R expression and localization in healthy and disease conditions would greatly contribute to improving our understanding of this receptor. Herein, we report a series of chromenopyrazole-based CB₂R fluorescent ligands. The highest affinity fluorescent ligand was Cy5-containing 24 (hCB₂R pK _i = 7.38 ± 0.05), which had 131-fold selectivity over CB₁R. In a cAMP BRET assay, 24 behaved as a potent CB₂R inverse agonist. Widefield imaging experiments showed that 24 binds to CB₂R in live cells with good selectivity and low levels of nonspecific fluorescence. The high affinity, selectivity, and suitable imaging properties of fluorescent ligand 24 make it a valuable tool for studying CB₂R.