Non-invasive imaging of the type 2 cannabinoid receptor, focus on positron emission tomography

The type 2 cannabinoid receptor (CB(2)R) is a relatively new target for drug development, as the receptor was only discovered in 1993. The CB(2)R is mainly expressed in tissues and organs related to the immune system. However, in pathological conditions, mostly inflammatory, a strong upregulation has been observed. Because of its expression in activated microglia, the type 2 cannabinoid receptor might play an important role in pathologies with a neuroinflammatory component. Positron emission tomography provides a sensitive non-invasive imaging technique to study and quantify receptor expression. In this review, the importance of CB(2)R imaging, the current status and the future possibilities for the development of CB(2)R PET radioligands are discussed.