Pharmacological modulation of cannabinoid type 2 receptor (CB2R) holds promise for the treatment of numerous conditions, including inflammatory diseases, autoimmune disorders, pain, and cancer. Despite the significance of this receptor, researchers lack reliable tools to address questions concerning the expression and complex mechanism of CB2R signaling, especially in cell-type and tissue-dependent context. Herein, we report for the first time a versatile ligand platform for the modular design of a collection of highly specific CB2R fluorescent probes, used successfully across applications, species and cell types. These include flow cytometry of endogenously expressing cells, real-time confocal microscopy of mouse splenocytes and human macrophages, as well as FRET-based kinetic and equilibrium binding assays. High CB2R specificity was demonstrated by competition experiments in living cells expressing CB2R at native levels. The probes were effectively applied to FACS analysis of microglial cells derived from a mouse model relevant to Alzheimer's disease and to the detection of CB2R in human breast cancer cells.

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The endocannabinoid (eCB) system is implied in various human diseases ranging from central nervous system to autoimmune disorders. Cannabinoid receptor 2 (CB2R) is an integral component of the eCB system. Yet, the downstream effects elicited by this G protein‐coupled receptor upon binding of endogenous or synthetic ligands are insufficiently understood—likely due to the limited arsenal of reliable biological and chemical tools. Herein, we report the design and synthesis of CB2R‐selective cannabinoids along with their in vitro pharmacological characterization (binding and functional studies). They combine structural features of HU‐308 and AM841 to give chimeric ligands that emerge as potent CB2R agonists with high selectivity over the closely related cannabinoid receptor 1 (CB1R). The synthesis work includes convenient preparation of substituted resorcinols often found in cannabinoids. The utility of the synthetic cannabinoids in this study is showcased by preparation of the most selective high‐affinity fluorescent probe for CB2R to date.

Despite its essential role in the (patho)physiology of several diseases, CB2R tissue expression profiles and signaling mechanisms are not yet fully understood. We report the development of a highly potent,...

Cannabinoid type 2 receptor (CB2R) is a fundamental part of the endocannabinoid signaling system (eCB system), and is known to play an important role in tissue injury, inflammation, cancer and pain. In stark contrast to its significance, the underlying signaling mechanisms and tissue expression profiles are poorly understood. Due to its low expression in healthy tissue and lack of reliable chemical tools, CB2R visualization in live cells remains uncharted. Here we report the development of a drug derived toolbox of highly potent, CB2Rselective fluorescent probes based on reverse design. Extensive validation in several applications such as CB2R detection in flow cytometry and time-resolved imaging, and the development of a novel fluorescent-based TR-FRET assay to generate kinetic and equilibrium binding data demonstrate the high versatility of our toolbox. These probes are the first to preserve affinity and efficacy in both human and mouse CB2R, a crucial aspect for preclinical translatability, and to enable imaging of CB2R internalization in living cells using confocal microscopy.