An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the agonist, while an inverse agonist causes an action opposite to that of the agonist.
5-HT receptors, 5-hydroxytryptamine receptors, or serotonin receptors, are a group of G protein-coupled receptor and ligand-gated ion channels found in the central and peripheral nervous systems. They mediate both excitatory and inhibitory neurotransmission. The serotonin receptors are activated by the neurotransmitter serotonin, which acts as their natural ligand.
Functional selectivity is the ligand-dependent selectivity for certain signal transduction pathways relative to a reference ligand at the same receptor. Functional selectivity can be present when a receptor has several possible signal transduction pathways. To which degree each pathway is activated thus depends on which ligand binds to the receptor. Functional selectivity, or biased signaling, is most extensively characterized at G protein coupled receptors (GPCRs). A number of biased agonists, such as those at muscarinic M2 receptors tested as analgesics or antiproliferative drugs, or those at opioid receptors that mediate pain, show potential at various receptor families to increase beneficial properties while reducing side effects. For example, pre-clinical studies with G protein biased agonists at the μ-opioid receptor show equivalent efficacy for treating pain with reduced risk for addictive potential and respiratory depression. Studies within the chemokine receptor system also suggest that GPCR biased agonism is physiologically relevant. For example, a beta-arrestin biased agonist of the chemokine receptor CXCR3 induced greater chemotaxis of T cells relative to a G protein biased agonist.
Trazodone, sold under many brand names, is an antidepressant medication, used to treat major depressive disorder, anxiety disorders, and insomnia. It is a phenylpiperazine compound of the serotonin antagonist and reuptake inhibitor (SARI) class. The medication is taken orally.
The 5-HT2A receptor is a subtype of the 5-HT2 receptor that belongs to the serotonin receptor family and is a G protein-coupled receptor (GPCR). The 5-HT2A receptor is a cell surface receptor, but has several intracellular locations.
A serotonin receptor agonist is an agonist of one or more serotonin receptors. They activate serotonin receptors in a manner similar to that of serotonin, a neurotransmitter and hormone and the endogenous ligand of the serotonin receptors.
The δ-opioid receptor, also known as delta opioid receptor or simply delta receptor, abbreviated DOR or DOP, is an inhibitory 7-transmembrane G-protein coupled receptor coupled to the G protein Gi/G0 and has enkephalins as its endogenous ligands. The regions of the brain where the δ-opioid receptor is largely expressed vary from species model to species model. In humans, the δ-opioid receptor is most heavily expressed in the basal ganglia and neocortical regions of the brain.
Ariadne, also known chemically as 4C-D or 4C-DOM, by its developmental code name BL-3912, and by its former tentative brand name Dimoxamine, is a little-known psychoactive drug of the phenethylamine, amphetamine, and phenylisobutylamine families. It is a homologue of the psychedelics 2C-D and DOM.
5-Hydroxytryptamine receptor 2B (5-HT2B) also known as serotonin receptor 2B is a protein that in humans is encoded by the HTR2B gene. 5-HT2B is a member of the 5-HT2 receptor family that binds the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). Like all 5-HT2 receptors, the 5-HT2B receptor is Gq/G11-protein coupled, leading to downstream activation of phospholipase C.
Vabicaserin was a novel antipsychotic and anorectic under development by Wyeth. As of 2010 it is no longer in clinical trials for the treatment of psychosis. It was also under investigation as an antidepressant but this indication appears to have been dropped as well.
Osemozotan (MKC-242) is a selective 5-HT1A receptor agonist with some functional selectivity, acting as a full agonist at presynaptic and a partial agonist at postsynaptic 5-HT1A receptors. 5-HT1A receptor stimulation influences the release of various neurotransmitters including serotonin, dopamine, norepinephrine, and acetylcholine. 5-HT1A receptors are inhibitory G protein-coupled receptor.
WAY-161503 is a full agonist of 5-HT2C receptors (Ki = 3.3 nM for displacement of DOI), ~6-fold less potent at 5-HT2A receptors (Ki = 18 nM) and 20-fold less potent at 5-HT2B receptors (Ki = 60 nM). In functional studies, it stimulates calcium mobilization coupled to 5-HT2C, 5-HT2B, and 5-HT2A receptors with EC50 values of 0.8, 1.8, and 7 nM, respectively. WAY-161503 has been reported to produce dose-dependent decreases in food intake in 24-hour fasted normal Sprague-Dawley rats, diet-induced obese mice, and obese Zucker rats with ED50 values of 1.9, 6.8, and 0.73 mg/kg, respectively.
5-HT2C receptor agonists are a class of drugs that activate 5-HT2C receptors. They have been investigated for the treatment of a number of conditions including obesity, psychiatric disorders, sexual dysfunction and urinary incontinence.
25CN-NBOH is a compound indirectly derived from the phenethylamine series of hallucinogens, which was discovered in 2014 at the University of Copenhagen. This compound is notable as one of the most selective agonist ligands for the 5-HT2A receptor yet discovered, with a pKi of 8.88 at the human 5-HT2A receptor and with 100x selectivity for 5-HT2A over 5-HT2C, and 46x selectivity for 5-HT2A over 5-HT2B. A tritiated version of 25CN-NBOH has also been accessed and used for more detailed investigations of the binding to 5-HT2 receptors and autoradiography.
25N-NBPh (NBPh-2C-N) is a phenethylamine derivative from the 25-NB class, which acts as a potent agonist at the 5-HT2A receptor with weaker activity at 5-HT2B and 5-HT2C. 25N-NBPh is a biased agonist, producing robust activation of 5-HT2A coupled signalling pathways mediated by beta arrestin 2, but with only slight activation of pathways mediated via Gq. In animal studies it produces a modest head-twitch response when administered by itself, but blocks the effects of the fully active psychedelic DOI.
25N-N1-Nap is a phenethylamine derivative from the 25-NB class, which acts as a potent agonist at the 5-HT2A receptor with weaker activity at 5-HT2B and 5-HT2C. 25N-N1-Nap is a biased agonist, producing robust activation of 5-HT2A coupled signalling pathways mediated by beta arrestin 2, but with little or no activation of pathways mediated via Gq. In animal studies it produces antipsychotic effects but without producing the head-twitch response associated with psychedelic activity.
RS134-49 is a tetrahydropyridine derivative related to psychedelic tryptamines which acts as a 5-HT2A receptor agonist, with a 5-HT2A Ki of 11.5nM and an EC50 of 22nM. It is a biased agonist selective for activation of the Gq coupled signalling pathway with weaker activation of the β-arrestin 2 coupled pathway, but shows a more balanced profile than related compounds such as (R)-69.
LPH-5 is a psychedelic discovered by Emil Marcher-Rørsted, Jesper L. Kristensen and Anders A. Jensen at Danish biopharmaceutical company Lophora. It is a conformationally-restricted derivative of the phenethylamine 2C-TFM, also a hallucinogen, and acts as a potent agonist of the 5-HT2A receptor (EC50 = 3.2 nM, Emax = 78%). It shows 10- to 100-fold selectivity for the 5-HT2A receptor over the 5-HT2B and 5-HT2C receptors and, along with related compounds like 25CN-NBOH, is said to be one of the few truly selective 5-HT2A receptor agonists. LPH-5 is expected to avoid the cardiac risks of 5-HT2B receptor activation.
Lysergine, also known as 9,10-didehydro-6,8β-dimethylergoline, is an ergot alkaloid and serotonin receptor agonist of the ergoline family. It is a minor constituent of ergot.
ITI-1549 is a putatively non-hallucinogenic serotonin 5-HT2A receptor agonist which is under development for the treatment of mood disorders and other psychiatric disorders. In addition to acting at the serotonin 5-HT2A receptor, it is also an antagonist of the serotonin 5-HT2B receptor and an agonist of the serotonin 5-HT2C receptor. The drug's route of administration has not been specified.
