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Updated: Jan 19, 2026

Detection of Orexin and Cannabinoid Receptor Co-localization in Diet-Induced Obese Zebrafish
Probing the CB1 Cannabinoid Receptor Binding Pocket with AM6538, a High-Affinity Irreversible Antagonist
Robert B Laprairie1, Kiran Vemuri1, Edward L Stahl1
1Departments of Molecular Medicine and Neuroscience, The Scripps Research Institute, Jupiter, Florida (R.B.L., E.L.S., J.-H.H., T.W.G., L.M.B.); Center for Drug Discovery and Departments of Chemistry and Chemical Biology and Pharmaceutical Sciences, Northeastern University, Boston, Massachusetts (K.V., A.K., A.M.); iHuman Institute, ShanghaiTech University, Shanghai, China (T.H., Y.W., Z.-J.L.); and Departments of Biological Sciences and Chemistry, Bridge Institute, Michelson Center for Convergent Bioscience, University of Southern California, Los Angeles, California (R.C.S.).
Abstract:
Cannabinoid receptor 1 (CB1) is a potential therapeutic target for the treatment of pain, obesity and obesity-related metabolic disorders, and addiction. The crystal structure of human CB1 has been determined in complex with the stabilizing antagonist AM6538. In the present study, we characterize AM6538 as a tight-binding/irreversible antagonist of CB1, as well as two derivatives of AM6538 (AM4112 and AM6542) as slowly dissociating CB1 antagonists across binding simulations and cellular signaling assays. The long-lasting nature of AM6538 was explored in vivo wherein AM6538 continues to block CP55,940-mediated behaviors in mice up to 5 days after a single injection. In contrast, the effects of SR141716A abate in mice 2 days after injection. These studies demonstrate the functional outcome of CB1 antagonist modification and open the path for development of long-lasting CB1 antagonists.
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