Cannabinoids are several structural classes of compounds found in the Cannabis plant primarily and most animal organisms or as synthetic compounds. The most notable cannabinoid is the phytocannabinoid tetrahydrocannabinol (THC) (delta-9-THC), the primary intoxicating compound in cannabis. Cannabidiol (CBD) is a major constituent of temperate Cannabis plants and a minor constituent in tropical varieties. At least 113 distinct phytocannabinoids have been isolated from cannabis, although only four have been demonstrated to have a biogenetic origin. It was reported in 2020 that phytocannabinoids can be found in other plants such as rhododendron, licorice and liverwort, and earlier in Echinacea.
Rimonabant (also known as SR141716; trade names Acomplia, Zimulti) is an anorectic antiobesity drug that was first approved in Europe in 2006 but was withdrawn worldwide in 2008 due to serious psychiatric side effects; it was never approved in the United States. Rimonabant is an inverse agonist for the cannabinoid receptor CB1 and was the first drug approved in that class.
Tetrahydrocannabivarin is a homologue of tetrahydrocannabinol (THC) having a propyl (3-carbon) side chain instead of a pentyl (5-carbon) group on the molecule, which makes it produce very different effects from THC.
Cannabinoid receptor type 1 (CB1), also known as cannabinoid receptor 1, is a G protein-coupled cannabinoid receptor that in humans is encoded by the CNR1 gene. The human CB1 receptor is expressed in the peripheral nervous system and central nervous system. It is activated by: endocannabinoids, a group of retrograde neurotransmitters that include anandamide and 2-arachidonoylglycerol (2-AG); plant phytocannabinoids, such as the compound THC which is an active ingredient of the psychoactive drug cannabis; and, synthetic analogs of THC. CB1 is antagonized by the phytocannabinoid tetrahydrocannabivarin (THCV).
The cannabinoid receptor type 2, abbreviated as CB2, is a G protein-coupled receptor from the cannabinoid receptor family that in humans is encoded by the CNR2 gene. It is closely related to the cannabinoid receptor type 1 (CB1), which is largely responsible for the efficacy of endocannabinoid-mediated presynaptic-inhibition, the psychoactive properties of tetrahydrocannabinol (THC), the active agent in cannabis, and other phytocannabinoids (plant cannabinoids). The principal endogenous ligand for the CB2 receptor is 2-Arachidonoylglycerol (2-AG).
Taranabant (codenamed MK-0364) is a cannabinoid receptor type 1 (CB1) inverse agonist that was investigated as a potential treatment for obesity due to its anorectic effects. It was discovered by Merck & Co.
VCHSR is a drug used in scientific research which acts as a selective antagonist of the cannabinoid receptor CB1. It is derived from the widely used CB1 antagonist rimonabant, and has similar potency and selectivity for the CB1 receptor, but has been modified to remove the hydrogen bonding capability in the C-3 substituent region, which removes the inverse agonist effect that rimonabant produces at high doses, so that VCHSR instead acts as a neutral antagonist, blocking the receptor but producing no physiological effect of its own.
A cannabinoid receptor antagonist, also known simply as a cannabinoid antagonist or as an anticannabinoid, is a type of cannabinoidergic drug that binds to cannabinoid receptors (CBR) and prevents their activation by endocannabinoids. They include antagonists, inverse agonists, and antibodies of CBRs. The discovery of the endocannabinoid system led to the development of CB1 receptor antagonists. The first CBR inverse agonist, rimonabant, was described in 1994. Rimonabant blocks the CB1 receptor selectively and has been shown to decrease food intake and regulate body-weight gain. The prevalence of obesity worldwide is increasing dramatically and has a great impact on public health. The lack of efficient and well-tolerated drugs to cure obesity has led to an increased interest in research and development of CBR antagonists. Cannabidiol (CBD), a naturally occurring cannabinoid, is a non-competitive CB1/CB2 receptor antagonist. And Δ9-tetrahydrocannabivarin (THCV), a naturally occurring cannabinoid, modulate the effects of THC via direct blockade of cannabinoid CB1 receptors, thus behaving like first-generation CB1 receptor inverse agonists, such as rimonabant. CBD is a very low-affinity CB1 ligand, that can nevertheless affect CB1 receptor activity in vivo in an indirect manner, while THCV is a high-affinity CB1 receptor ligand and potent antagonist in vitro and yet only occasionally produces effects in vivo resulting from CB1 receptor antagonism. THCV has also high affinity for CB2 receptors and signals as a partial agonist, differing from both CBD and rimonabant.
CB-13 (CRA13, SAB-378) is a cannabinoid drug, which acts as a potent agonist at both the CB1 and CB2 receptors, but has poor blood–brain barrier penetration, and so produces only peripheral effects at low doses, with symptoms of central effects such as catalepsy only appearing at much higher dose ranges. It has antihyperalgesic properties in animal studies, and has progressed to preliminary human trials.
AM-1241 (1-(methylpiperidin-2-ylmethyl)-3-(2-iodo-5-nitrobenzoyl)indole) is a chemical from the aminoalkylindole family that acts as a potent and selective agonist for the cannabinoid receptor CB2, with a Ki of 3.4 nM at CB2 and 80 times selectivity over the related CB1 receptor. It has analgesic effects in animal studies, particularly against "atypical" pain such as hyperalgesia and allodynia. This is thought to be mediated through CB2-mediated peripheral release of endogenous opioid peptides, as well as direct activation of the TRPA1 channel. It has also shown efficacy in the treatment of amyotrophic lateral sclerosis in animal models.
AM-630 (6-Iodopravadoline) is a drug that acts as a potent and selective inverse agonist for the cannabinoid receptor CB2, with a Ki of 32.1 nM at CB2 and 165x selectivity over CB1, at which it acted as a weak partial agonist. It is used in the study of CB2 mediated responses and has been used to investigate the possible role of CB2 receptors in the brain. AM-630 is significant as one of the first indole derived cannabinoid ligands substituted on the 6-position of the indole ring, a position that has subsequently been found to be important in determining affinity and efficacy at both the CB1 and CB2 receptors, and has led to the development of many related derivatives.
SR144528 is a drug that acts as a potent and highly selective CB2 receptor inverse agonist, with a Ki of 0.6 nM at CB2 and 400 nM at the related CB1 receptor. It is used in scientific research for investigating the function of the CB2 receptor, as well as for studying the effects of CB1 receptors in isolation, as few CB1 agonists that do not also show significant activity as CB2 agonists are available. It has also been found to be an inhibitor of sterol O-acyltransferase, an effect that appears to be independent from its action on CB2 receptors.
O-1269 is a drug that is a diarylpyrazole derivative, related to potent cannabinoid antagonist drugs such as rimonabant and surinabant. However O-1269 and several related drugs were unexpectedly found to act as full or partial agonists at the cannabinoid receptors rather than antagonists, and so produce the usual effects expected of cannabinoid agonists in animal tests, such as sedation and analgesic effects. The N-heptyl homolog O-1270 and the N-propyl homolog O-1399 also act as cannabinoid agonists with similar potency in vivo, despite weaker binding affinity at cannabinoid receptors compared to the pentyl homolog O-1269. Agonist-like and atypical cannabinoid activity has also been observed with a number of related compounds.
AM-6545 is a drug which acts as a peripherally selective silent antagonist for the CB1 receptor, and was developed for the treatment of obesity. Other cannabinoid antagonists such as rimonabant have been marketed for this application, but have subsequently been withdrawn from sale because of centrally mediated side effects such as depression and nausea. Because AM-6545 does not cross the blood–brain barrier to any significant extent, it does not produce these kinds of side effects, but has still been shown to effectively reduce appetite and food consumption in animal studies.
Rosonabant (INN; E-6776) is a drug acting as a CB1 receptor antagonist/inverse agonist that was under investigation by Esteve as an appetite suppressant for the treatment of obesity. Development of the drug for clinical use was apparently halted shortly after the related CB1 antagonist rimonabant was discontinued in November 2008, due to the reports of severe psychiatric adverse effects such as anxiety, depression, and suicidal ideation associated with it and with similarly acting agents.
Drinabant (INN; AVE-1625) is a drug that acts as a selective CB1 receptor antagonist, which was under investigation varyingly by Sanofi-Aventis as a treatment for obesity, schizophrenia, Alzheimer's disease, Parkinson's disease, and nicotine dependence. Though initially studied as a potential treatment for a variety of different medical conditions, Sanofi-Aventis eventually narrowed down the therapeutic indications of the compound to just appetite suppression. Drinabant reached phase IIb clinical trials for this purpose in the treatment of obesity but was shortly thereafter discontinued, likely due to the observation of severe psychiatric side effects including anxiety, depression, and thoughts of suicide in patients treated with the now-withdrawn rimonabant, another CB1 antagonist that was also under development by Sanofi-Aventis.
JD5037 is an antiobesity drug candidate which acts as a peripherally-restricted cannabinoid inverse agonist at CB1 receptors. It is very selective for the CB1 subtype, with a Ki of 0.35nM, >700-fold higher affinity than it has for CB2 receptors.
PipISB is a drug used in scientific research which acts as a potent and selective inverse agonist of the cannabinoid receptor CB1. It is highly selective for the CB1 receptor over CB2, with a Kd at CB1 of 1.5nM vs over 7000nM at CB2, has good blood-brain barrier penetration, and can be conveniently radiolabelled with either 11C or 18F, making it useful for mapping the distribution of CB1 receptors in the brain.
5F-AB-FUPPYCA (also known as AZ-037) is a pyrazole-based synthetic cannabinoid that is presumed to be an agonist of the CB1 receptor and has been sold online as a designer drug. It was first detected by the EMCDDA as part of a seizure of 540 g white powder in France in February 2015.
