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

Area of Science:

• Medicinal Chemistry
• Neuroscience
• Pharmacology

Background:

• The cannabinoid type 2 receptor (CB2R) is a key target for managing pain and inflammatory conditions.
• Developing selective fluorescent ligands is crucial for understanding CB2R expression and localization in health and disease.

Purpose of the Study:

• To synthesize and characterize novel chromenopyrazole-based fluorescent ligands for CB2R.
• To evaluate the affinity, selectivity, and imaging capabilities of these ligands for CB2R research.

Main Methods:

• Synthesis of chromenopyrazole derivatives.
• Binding assays to determine affinity and selectivity (e.g., against CB1R).
• Cell-based assays (cAMP BRET) and widefield imaging to assess functional activity and cellular localization.

Main Results:

• Identified a high-affinity fluorescent ligand, Cy5-containing 24, with a pKi of 7.38 ± 0.05 for human CB2R.
• Ligand 24 demonstrated significant selectivity, showing 131-fold greater affinity for CB2R over CB1R.
• Compound 24 exhibited potent inverse agonism in a cAMP BRET assay and showed selective binding in live-cell imaging with minimal background fluorescence.

Conclusions:

• Fluorescent ligand 24 possesses high affinity, excellent selectivity, and suitable properties for imaging.
• This novel ligand represents a valuable tool for advancing the study of CB2R in biological systems and disease states.