The cannabinoid receptor 2(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 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. The principal endogenous ligand for the CB2 receptor is 2-Arachidonoylglycerol (2-AG).
JWH-015 is a chemical from the naphthoylindole family that acts as a subtype-selective cannabinoid agonist. Its affinity for CB2 receptors is 13.8 nM, while its affinity for CB1 is 383 nM, meaning that it binds almost 28 times more strongly to CB2 than to CB1. However, it still displays some CB1 activity, and in some model systems can be very potent and efficacious at activating CB1 receptors, and therefore it is not as selective as newer drugs such as JWH-133. It has been shown to possess immunomodulatory effects, and CB2 agonists may be useful in the treatment of pain and inflammation. It was discovered and named after John W. Huffman.
NESS-0327 is a drug used in scientific research which acts as an extremely potent and selective antagonist of the cannabinoid receptor CB1. It is much more potent an antagonist, and more selective for the CB1 receptor over CB2, than the more commonly used ligand rimonabant, with a Ki at CB1 of 350fM (i.e. 0.00035nM) and a selectivity of over 60,000x for CB1 over CB2. Independently, two other groups have described only modest nanomolar CB1 affinity for this compound (125nM and 18.4nM). Also unlike rimonabant, NESS-0327 does not appear to act as an inverse agonist at higher doses, instead being a purely neutral antagonist which blocks the CB1 receptor but does not produce any physiological effect of its own.
AM-4030 is an analgesic drug which is a cannabinoid receptor agonist. It is a derivative of HU-210 which has been substituted with a 6β-((E)-3-hydroxyprop-1-enyl) group. This adds a "southern" aliphatic hydroxyl group to the molecule as seen in the CP-series of nonclassical cannabinoid drugs, and so AM-4030 represents a hybrid structure between the classical and nonclassical cannabinoid families, with the 6-hydroxyalkyl chain rigidified with a double bond with defined stereochemistry. This gives AM-4030 a greater degree of selectivity, so while it is still a potent agonist at both CB1 and CB2, it is reasonably selective for CB1, with a Ki of 0.7nM at CB1 and 8.6nM at CB2, a selectivity of around 12x. Resolution of the enantiomers of AM-4030 yields an even more potent compound, although with less selectivity, with the (-) enantiomer AM-4030a having a Ki of 0.6nM at CB1 and 1.1nM at CB2.
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.
GW-405,833 (L-768,242) is a drug that acts as a potent and selective partial agonist for the cannabinoid receptor subtype CB2, with an EC50 of 0.65 nM and selectivity of around 1200x for CB2 over CB1 receptors. Animal studies have shown it to possess antiinflammatory and anti-hyperalgesic effects at low doses, followed by ataxia and analgesic effects when the dose is increased. Selective CB2 agonist drugs such as GW-405,833 are hoped to be particularly useful in the treatment of allodynia and neuropathic pain for which current treatment options are often inadequate.
A-836,339 is a drug developed by Abbott Laboratories that acts as a potent cannabinoid receptor full agonist. It is selective for CB2, with Ki values of 0.64 nM at CB2 vs 270 nM at the psychoactive CB1 receptor, but while it exhibits selective analgesic, anti-inflammatory and anti-hyperalgesic effects at low doses, its high efficacy at both targets results in typical cannabis-like effects appearing at higher doses, despite its low binding affinity for CB1. In 2012 A-836,339 was detected via X-ray crystallography in a "dubious product" sold in Japan, though the product was described as a white powder, not herbal incense, it was suggested to be for human consumption.
SER-601 (COR-167) is a drug which acts as a potent and selective cannabinoid CB2 receptor agonist, based on a quinolone-3-carboxylic acid core structure, with 190 times selectivity for CB2 over the related CB1 receptor. It has analgesic effects in animal studies, as well as neuroprotective effects, but without a "cannabis high" due to its low affinity for CB1. A number of related compounds are known, almost all of which have high selectivity for CB2.
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.
AZ-11713908 is a drug developed by AstraZeneca which is a peripherally selective cannabinoid agonist, acting as a potent agonist at the CB1 receptor and a partial agonist at CB2. It has poor blood–brain barrier penetration, and so while it is an effective analgesic in animal tests, it produces only peripheral effects at low doses, with much weaker symptoms of central effects compared to other cannabinoid drugs such as WIN 55,212-2. Many related benzimidazole-derived cannabinoid ligands are known.
MN-25 (UR-12) is a drug invented by Bristol-Myers Squibb, that acts as a reasonably selective agonist of peripheral cannabinoid receptors. It has moderate affinity for CB2 receptors with a Ki of 11 nM, but 22x lower affinity for the psychoactive CB1 receptors with a Ki of 245 nM. The indole 2-methyl derivative has the ratio of affinities reversed however, with a Ki of 8 nM at CB1 and 29 nM at CB2, which contrasts with the usual trend of 2-methyl derivatives having increased selectivity for CB2 (cf. JWH-018 vs JWH-007, JWH-081 vs JWH-098).
MDA-19 (also known as BZO-HEXOXIZID) is a drug that acts as a potent and selective agonist for the cannabinoid receptor CB2, with reasonable selectivity over the psychoactive CB1 receptor, though with some variation between species. In animal studies it was effective for the treatment of neuropathic pain, but did not effect rat locomotor activity in that specific study. The pharmacology of MDA-19 in rat cannabinoid receptors have been demonstrated to function differently than human cannabinoid receptors with MDA-19 binding to human CB1 receptors 6.9x higher than rat CB1 receptors.
LBP-1 is a drug originally developed by Organon for the treatment of neuropathic pain, It acts as a potent and selective cannabinoid receptor agonist, with high potency at both the CB1 and CB2 receptors, but low penetration of the blood–brain barrier. This makes LBP-1 peripherally selective, and while it was effective in animal models of neuropathic pain and allodynia, it did not produce cannabinoid-appropriate responding suggestive of central effects, at any dose tested.
NNE1 (also known as NNEI, MN-24 and AM-6527) is an indole-based synthetic cannabinoid, representing a molecular hybrid of APICA and JWH-018 that is an agonist for the cannabinoid receptors, with Ki values of 60.09 nM at CB1 and 45.298 nM at CB2 and EC50 values of 9.481 nM at CB1 and 1.008 nM at CB2. It was invented by Abbott and has a CB1 receptor pEC50 of 8.9 with around 80x selectivity over the related CB2 receptor. It is suspected that metabolic hydrolysis of the amide group of NNE1 may release 1-naphthylamine, a known carcinogen, given the known metabolic liberation (and presence as an impurity) of amantadine in the related compound APINACA, and NNE1 was banned in New Zealand in 2012 as a temporary class drug to stop it being used as an ingredient in then-legal synthetic cannabis products. NNE1 was subsequently found to be responsible for the death of a man in Japan in 2014.
BIM-018 is a synthetic cannabinoid that is the benzimidazole analog of JWH-018. It is presumed to be a potent agonist of the CB2 receptor and has been sold online as a designer drug.
QMPSB is an arylsulfonamide-based synthetic cannabinoid that has been sold as a designer drug.
AZD-1940 is a drug developed by AstraZeneca, that is a peripherally selective cannabinoid agonist which binds with high affinity to both the CB1 and CB2 receptors. It was developed for the treatment of neuropathic pain, but while it showed good peripheral selectivity in animal studies, in human clinical trials it failed to show sufficient analgesic efficacy and produced unexpectedly strong side effects associated with central cannabinoid activity, and so was discontinued from further development.
Cannabinor (PRS-211,375) is a drug which acts as a potent and selective cannabinoid CB2 receptor agonist. It is classed as a "nonclassical" cannabinoid with a chemical structure similar to that of cannabidiol. It has a CB2 affinity of 17.4nM vs 5585nM at CB1, giving it over 300x selectivity for CB2. It showed analgesic effects in animal studies especially in models of neuropathic pain, but failed in Phase IIb human clinical trials due to lack of efficacy.
