Cannabinoids, the active ingredients in marijuana, have dramatic effects on various organ systems. They exert their effects through two receptor types: CB1, primarily located in the brain, and CB2, primarily located in the immune system.
Vertebrates also produce their own cannabinoid-like substances called endocannabinoids, including anandamide and 2-arachidonoylglyceral. Interestingly, some effects of endocannabinoids could not be explained by the signals through either CB1 or CB2.
Recently, the orphan G protein-coupled receptor 55 (GPR55) was proposed to be an atypical cannabinoid receptor.
Two groups demonstrated that GPR55 is expressed in various cancer types in an aggressiveness-related manner, suggesting a novel cancer biomarker and a potential therapeutic target.