Cannabinoid Receptor Antagonist - History

History

For centuries hashish and marijuana from the Indian hemp Cannabis sativa L. have been used for medicinal and recreational purposes. In 1840, Schlesinger S. was apparently the first investigator to obtain an active extract from the leaves and flowers of hemp. A few years later, in 1848, Decourtive E. described the preparation of an ethanol extract that on evaporation of the solvent gave a dark resin, which he named “cannabin”.. In 1964 the main active constituent of C. sativa L., Δ9-tetrahydrocannabinol (THC), was isolated and synthesized by Mechoulam's laboratory. Two types of cannabinoid receptors, CB₁ and CB₂, responsible for the effects of THC were discovered and cloned in the early 1990s. Once cannabinoid receptors had been discovered, it became important to establish whether their agonists occur naturally in the body. This search led to the discovery of the first endogenous cannabinoid (endocannabinoid), anandamide (arachidonoyl ethanolamide). Later on other endocannabinoids were found, for example 2-AG (2-arachidonoyl glycerol). These findings raised further questions about the pharmacological and physiological role of the cannabinoid system. This revived the research on cannabinoid receptor antagonists which were expected to help answer these questions. The use of the cannabinoid agonist, THC, in its many preparations to enhance appetite is a well known fact. This fact led to the logical extension that blocking of the cannabinoid receptors might be useful in decreasing appetite and food intake. It was then discovered that the blockage of the CB₁ receptor represented a new pharmacological target. The first specific CB₁ receptor antagonist / inverse agonist was rimonabant, discovered in 1994.