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.
Azapirones are a class of drugs used as anxiolytics, antidepressants, and antipsychotics. They are commonly used as add-ons to other antidepressants, such as selective serotonin reuptake inhibitors (SSRIs).
Pindolol, sold under the brand name Visken among others, is a nonselective beta blocker which is used in the treatment of hypertension. It is also an antagonist of the serotonin 5-HT1A receptor, preferentially blocking inhibitory 5-HT1A autoreceptors, and has been researched as an add-on therapy to various antidepressants, such as clomipramine and the selective serotonin reuptake inhibitors (SSRIs), in the treatment of depression and obsessive-compulsive disorder.
The serotonin 1A receptor is a subtype of serotonin receptors, or 5-HT receptors, that binds serotonin, also known as 5-HT, a neurotransmitter. 5-HT1A is expressed in the brain, spleen, and neonatal kidney. It is a G protein-coupled receptor (GPCR), coupled to the Gi protein, and its activation in the brain mediates hyperpolarization and reduction of firing rate of the postsynaptic neuron. In humans, the serotonin 1A receptor is encoded by the HTR1A gene.
WAY-100635 is a piperazine drug and research chemical widely used in scientific studies. It was originally believed to act as a selective 5-HT1A receptor antagonist, but subsequent research showed that it also acts as potent full agonist at the D4 receptor. It is sometimes referred to as a silent antagonist at the former receptor. It is closely related to WAY-100135.
5-Carboxamidotryptamine (5-CT) is a tryptamine derivative closely related to the neurotransmitter serotonin.
Robalzotan is a selective antagonist at the 5-HT1A receptor. It was shown to completely reverse the autoreceptor-mediated inhibition of serotonin release induced by the administration of selective serotonin reuptake inhibitors like citalopram in rodent studies. It was subsequently investigated by AstraZeneca as a potential antidepressant but like many other 5-HT1A ligands was discontinued. Later on it was researched for other indications such as irritable bowel syndrome but was dropped once again.
WAY-100135 is a serotonergic drug of the phenylpiperazine family which is used in scientific research. It acts as potent 5-HT1A receptor antagonist, and was originally believed to be highly selective, but further studies have demonstrated that it also acts as a partial agonist of the 5-HT1D receptor (pKi = 7.58; virtually the same affinity for 5-HT1A), and to a much lesser extent, of the 5-HT1B receptor (pKi = 5.82). These findings may have prompted the development of the related compound WAY-100635, another purportedly selective and even more potent 5-HT1A antagonist, which was synthesized shortly thereafter. However, WAY-100635 turned out to be non-selective as well, having been shown to act additionally as a potent D4 receptor agonist later on.
(S)-UH-301 is a drug and research chemical widely used in scientific studies. It acts as a selective 5-HT1A receptor silent antagonist. It is structurally related to 8-OH-DPAT. UH-301 was found to produce a head-twitch response in mice which is usually typical of 5-HT2A agonist drugs, and has subsequently been used to investigate how 5-HT1A receptor activity modulates 5-HT2A receptors downstream.
Naluzotan is a serotonergic drug of the phenylpiperazine class that was under investigation by EPIX Pharmaceuticals Inc for the treatment of generalized anxiety disorder and major depressive disorder. It acts as a selective and potent 5-HT1A receptor partial agonist, readily stimulating prolactin responses, though it has also been found to bind to and activate the σ receptor. Naluzotan was well tolerated in clinical trials, with more patients in the control group dropping out due to adverse effects than in the active group in one study. The most frequently reported side effect was headache in 15% of patients. In addition, naluzotan demonstrated significant antidepressant and anxiolytic effects as per the HAM-D and MADRS and the HAM-A, respectively, in some trials, but in others it did not. In the end it was not found to be significantly superior enough to placebo and development was stopped.
S-15535 is a phenylpiperazine drug which is a potent and highly selective 5-HT1A receptor ligand that acts as an agonist and antagonist at the presynaptic and postsynaptic 5-HT1A receptors, respectively. It has anxiolytic properties.
Befiradol is an experimental drug being studied for the treatment of levodopa-induced dyskinesia. It is a potent and selective 5-HT1A receptor full agonist.
Eptapirone (F-11,440) is a very potent and highly selective 5-HT1A receptor full agonist of the azapirone family. Its affinity for the 5-HT1A receptor was reported to be 4.8 nM (Ki), and its intrinsic activity approximately equal to that of serotonin.
F-15,599, also known as NLX-101, is a potent and selective 5-HT1A receptor full agonist. It displays functional selectivity by strongly activating 5-HT1A receptors in the postsynaptic prefrontal cortex while having little effect on somatodendritic autoreceptors in the raphe nucleus. As a result, it has been touted as a preferential postsynaptic 5-HT1A receptor agonist and has been investigated as a novel potential antidepressant.
Repinotan (BAYx3702), an aminomethylchroman derivative, is a selective 5-HT1A receptor full agonist with high potency and efficacy. It has neuroprotective effects in animal studies, and was trialed in humans for reducing brain injury following head trauma. It was subsequently trialed up to phase II for treatment of stroke, but while side effects were mild and consisted mainly of nausea, repinotan failed to demonstrate sufficient efficacy to justify further clinical trials. However, repinotan continues to be investigated for other applications, and was found to be effective at counteracting the respiratory depression produced by morphine, though with slight reduction in analgesic effects.
Piclozotan (SUN-N4057) is a selective 5-HT1A receptor partial agonist, which has neuroprotective effects in animal studies. It has been through early clinical trials in humans for treatment of acute stroke, but results have not yet been announced.
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.
LY-293284 is a research chemical developed by the pharmaceutical company Eli Lilly and used for scientific studies. It acts as a potent and selective 5-HT1A receptor full agonist. It was derived through structural simplification of the ergoline based psychedelic LSD, but is far more selective for 5-HT1A with over 1000× selectivity over other serotonin receptor subtypes and other targets. It has anxiogenic effects in animal studies.
CSP-2503 is a potent and selective 5-HT1A receptor agonist, 5-HT2A receptor antagonist, and 5-HT3 receptor antagonist of the naphthylpiperazine class. First synthesized in 2003, it was designed based on computational models and QSAR studies. In rat studies, CSP-2503 has demonstrated anxiolytic effects, and thus has been suggested as a treatment for anxiety in humans with a multimodal mechanism of action.
Hypidone (developmental code name YL-0919) is an investigational serotonergic antidepressant which is under development for the treatment of major depressive disorder. It acts as a serotonin reuptake inhibitor, 5-HT1A receptor partial agonist, and 5-HT6 receptor full agonist. It is used as the hydrochloride salt. As of January 2021, hypidone is in phase 2 clinical trials for major depressive disorder.
