Title: Real-time characterisation of Cannabinoid Receptor 1 (CB1) allosteric modulators reveals novel mechanism of action. Authors: Erin E. Cawstona, William J. Redmondb, Courtney M. Breena, Natasha L. Grimseya, Mark Connorb, Michelle Glassa,* a Centre for Brain Research and Department of Pharmacology and Clinical Pharmacology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand. b Australian School of Advanced Medicine, 2 Technology Place, Macquarie University, NSW 2109 Australia. * Corresponding author: Michelle Glass,
[email protected], Phone: +649 9236247, Fax: +649 9231769, Department of Pharmacology and Clinical Pharmacology, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand. Short Running Title: Allosteric Modulators of CB1 1 Summary BACKGROUND AND PURPOSE The cannabinoid receptor type 1 (CB1) has an allosteric binding site. The drugs ORG27569 and PSNCBAM-1 have been extensively characterised with regard to their effects on signalling of the orthosteric ligand CP55,940 and studies have suggested that these allosteric modulators increase binding affinity but act as non-competitive antagonists in functional assays. To gain a deeper understanding of allosteric modulation of CB1, we examined real- time signalling and trafficking responses of the receptor in the presence of allosteric modulators. EXPERIMENTAL APPROACH Studies of CB1 signalling were carried out in HEK 293 and AtT20 cells expressing HA- tagged human and rat CB1. We measured real-time accumulation of cAMP, activation and desensitization of potassium channel-mediated cellular hyperpolarisation and CB1 internalisation. KEY RESULTS ORG27569 and PSNCBAM-1 produce a complex, concentration and time-dependent modulation of agonist-mediated regulation of cAMP levels, as well as an increased rate of desensitisation of CB1-mediated cellular hyperpolarisation and a decrease in agonist-induced receptor internalisation.