Development of Radioligands for In Vivo Imaging of Type 1 Cannabinoid Receptors (CB1) in Human Brain

Cerebral cannabinoid receptor (CB1) and cannabinoid drugs constitute a vibrant field in modern medicine and pharmacology. However, the physiological and pharmacological roles played by the cannabinoid receptor in the central nervous system are still not fully understood. Positron-emission tomography (PET) is the most advanced technique for non-invasive research of cerebral receptors. Quantitative PET imaging of CB1 in animal and human brains has been limited by drawbacks of the available CB1 radioligands that manifested low specific binding, high non-specific binding and/or low brain uptake. The latest research revealed three CB1 PET radioligands ([(11)C]JHU75528, [(18)F]MK9470 and [(11)C]MePPEP) with improved imaging properties. These compounds are now being employed for the quantitative evaluation of CB1 in human subjects with PET. Molecular imaging of the CB1 receptor with these radioligands has now become possible and their application in healthy humans and in patients is underway. Despite the substantial progress in development of CB1 PET radioligands even the latest radioligands manifest certain disadvantages. Current research efforts on the development of CB1 radioligands with higher binding potential, greater brain uptake and more optimal brain kinetics.