Nicotinic agonist

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A nicotinic agonist is a drug that mimics the action of acetylcholine (ACh) at nicotinic acetylcholine receptors (nAChRs). The nAChR is named for its affinity for nicotine.

Contents

Examples include nicotine (by definition), acetylcholine (the endogenous agonist of nAChRs), choline, epibatidine, lobeline, varenicline and cytisine. [1]

History

Chemical structure of ABT-418 ABT-418.svg
Chemical structure of ABT-418

Nicotine has been known for centuries for its intoxicating effect. It was first isolated in 1828 from the tobacco plant by German chemists Posselt and Reimann. [2]

The discovery of positive effects from nicotine on animal memory was discovered by in vivo researches in the mid 1980s. Those researches led to a new era in studies of nicotinic acetylcholine receptor (nAChR) and their stimulation but until then the focus had mainly been on nicotine addiction. [3] [4] The development of nAChR agonists began in the early 1990s after the discovery of nicotine's positive effects. Some research showed a possible therapy option in preclinical researches. ABT-418 was one of the first in a series of nAChR agonists and it was designed by Abbott Labs. [4] ABT-418 showed significant increase of delayed matching-to-sample (DMTS) performance in matured macaque apes of different species and sex. [5] ABT-418 has also been examined as a possible treatment to Alzheimer's disease, Parkinson's disease and attention-deficit hyperactivity disorder: those experiments showed positive outcomes. [4]

One of the first nAChR active compounds, besides nicotine, that was marketed as a drug was galantamine, a plant alkaloid that works as a weak cholinesterase inhibitor (IC50 = 5 μM) as well as an allosteric sensitizer for nAChRs (EC50=50 nM). [6]

Nicotinic acetylcholine receptors and their signaling system

Nicotinic acetylcholine receptor classification Nikotinvidtakaflaedirit.png
Nicotinic acetylcholine receptor classification

Signaling system

In the human nervous system nicotinic cholinergic signals are extended throughout the system, where the neurotransmitter acetylcholine (ACh) plays a key role in activating ligand-gated ion channels. [7] The cholinergic system is a vital nervous pathway, where cholinergic neurons synthesize, store and release the neurotransmitter ACh. The main receptors that convert the ACh messages are the cholinergic muscarinic acetylcholine receptors, neuronal and muscular nAChRs. When looking back at evolutionary history, ACh is considered to be the oldest transmitter molecule and became present before the nervous cell. In the nervous system cholinergic stimulation mediated through nAChRs controls pathways such as release of transmitters and cell sensitivity, which can influence physiological activity including sleep, anxiety, processing of pain and cognitive functions. [8]

Nicotinic acetylcholine receptors

nAChRs are cholinergic receptors found in the central nervous system (CNS), peripheral nervous systems (PNS) and skeletal muscles, these receptors are ligand-gated ion channels with binding sites for acetylcholine and other molecules. When ACh or other agonists bind to the receptors it stabilizes the open state of the ion channel allowing influx of cations such as potassium, calcium and sodium ions. The nAChRs are made up by different subunits which determine the quaternary structure of the receptor, those subunits are α subunits (α1−α10), β subunits (β1−β4), one δ subunits, one γ subunit and one ε subunit. nAChRs can be either heteromeric or homomeric. The heteromeric receptors found in the central nervous system are made up by two α subunits and three β subunits with the binding site at the interface of α and the adjacent subunit. These receptors contain two binding sites per receptor and have different affinity for chemicals based on the composition of subunits. Both binding sites work together and thus, both sites need to be occupied with a nAChR agonist so that channel activation can take place. [9] nAChRs containing α2−α6 and β2−β4 subunits have been shown to have higher affinity for ACh than other receptors. Homomeric receptors contain 5 identical subunits, they have 5 binding sites located at the interface between two adjacent subunits. In the year 2000 two homomeric receptors had been identified in humans, the α7 and α8 receptors. [8] [10] [11] [12]

Binding site

There are two binding sites on heteromeric nAChRs; to stabilize the open form of nAChRs, both binding sites must be occupied by agonist, such as nicotine or ACh. [11]
The ACh binding site of nAChR is made up by six loops, termed A–F. The A, B and C loops of the binding site are part of the α subunit and are the principal components of the binding site. The adjacent subunit to the α subunit (γ, δ, ε or β) contains the D, E and F loops. [11]

Mechanism of action

Two different subtypes of nicotinic acetylcholine receptors Nicotinic receptors.png
Two different subtypes of nicotinic acetylcholine receptors

α4β2 receptor agonists

α4β2 nAChRs contain two α4 subunits and three β2 subunits, therefore it has two binding sites for ACh and other agonists. α4β2 nAChRs account for approximately 90% of the nAChRs in the human brain and when chronically exposed to nicotine or other nicotine agonists leads to increase in density of α4β2 receptors which is the opposite of what usually happens when other receptors are chronically exposed to their agonists. The α4β2 receptor has been widely studied in regards to Alzheimer's disease as well as for nicotine dependence and in 2009 several drugs are on the market that target the α4β2 nAChR specifically. [13] [14]

α7 receptor agonists

α7 receptors are homomeric neuronal acetylcholine receptors consisting of five α7 subunits and has five ACh binding sites. Abnormality in the α7 receptors expression have been reported to influence progression of diseases such as Alzheimer's disease and schizophrenia. The α7 are not believed to have as much affinity for nicotine as the heteromeric receptor but instead they have shown more affinity for alpha bungarotoxin which is a nicotinic antagonist found in venom of some snakes. Targeting of α7 receptors is therefore thought to be useful in treatment of Alzheimer's disease and schizophrenia. [9] [15]

Muscle type receptor agonists

nAChR are found in the neuromuscular junction on skeletal muscles. Two different receptors have been found, one of which has primarily been found in adults contains two α1 subunits, one β1, one ε and one δ, the other one has been found in fetuses and contains γ subunit instead of the ε subunit. The nAChRs take part in the depolarization of the muscular endplate by increasing cation permeability leading to contraction of skeletal muscles. [16] The nAChRs found in the skeletal muscle system have two ACh binding sites, one of which is found at the interface between α1 and δ subunits while the other one is found at the interface between α1 and γ or ε subunits. Among nAChR antagonists designed specifically for the neuromuscular system are nerve gases and other poisons designed to quickly kill humans or other animals and insects. [12]

Binding

ACh binds to nAChR because of charge difference between the molecule and the surface of the receptor. When binding to nAChR ACh fits into a binding pocket shaped by loops A, B and C which belong to α subunit and the adjacent subunit. When ACh is fitted into the binding pocket the loops of the nAChR undergo movement that leads to a coordination of the ACh molecule in the pocket enhancing the chemical bonds between the molecule and the receptor. After movement of the loops that belong to α subunit it's sometimes possible for the ACh molecule to form a bond, e.g. salt bridge, to the adjacent subunit enhancing the bonds between the receptor and ACh even further. [17]

Drug design

Drugs that influence nAChRs can be agonists, partial agonists or antagonists. [1] Agonists, e.g. nicotine, can however act as depolarizing agents when encountered to nAChRs for some time (seconds or minutes, depending on concentration and nAChR subtype), chronic exposure to agonist can also lead to long lasting functional deactivation because of rapid and persistent desensitization. Partial nAChR agonists have been studied since they seem to be helpful in smoking cessation. The partial agonists are believed to bind to the nAChRs and stimulate the release of dopamine in smaller portions than the agonists and therefore compensate for the absence of nicotine. [18]
The lack of specificity among some of the nicotinic agonists is well known and is a potential problem when using them to treat illnesses that require targeting a specific subtype of nAChRs. Among these nonspecific agonists are for example ACh, nicotine and epibatidine that all target more than one subtype of nAChRs. [19] [20]

Pharmacophore

Chemical structure of nicotine Nicotine.svg
Chemical structure of nicotine

The development of nAChR agonist pharmacophore started in 1970 when it was proposed that the binding of the agonists to a receptor was dependent on a positively charged nitrogen atom and a hydrogen bond forming from carbonyl oxygen atom in acetylcholine or a nitrogen atom in (S)-nicotine. Since then it has been shown that a cationic center, atoms that are electronegative and able to form hydrogen bonds along with the center of the pyridine ring in (S)-nicotine are favorable. Stereochemistry is a part of the pharmacophore as is clearly seen with (S)- and (R)- nicotine where the (S)-enantiomer is 10-100 times more potent. The azabicyclic ring of epibatidine is another example of favorable steric interactions to the receptors. It has been suggested that a specific internitrogen distance, N+-N, is important for agonist affinity but debate has arisen over its influence. A newer theory is that a distance of 7-8 Å between points that complement the protonated nitrogen atom and hydrogen bond acceptor will enhance the potency. Low electronic density close to the protonated nitrogen and higher electron density close to the pyridine ring is favored in protonated nicotine ligands containing pyridine ring. In later years researchers have taken more interest in the α7 and α4β2 subtype receptors in drug development to treat nicotine dependence and cognitive impairment such as Alzheimer's. [21]

Structure-activity relationships

Structure-activity relationships: Muscle nAChR agonists

Various models have been run where the affinity of nAChR agonists to the receptor subtype are tested to help identify the molecules, groups and steric conformation that are vital to greater affinity. By using a nAChR muscle receptor subtype (α1)2β1δγ model the following results were obtained:

anatoxin > epibatidine > acetylcholine > DMPP >> cytisine > pyrantel > nicotine > coniine > tubocurare > lobeline,

where anatoxin had the highest activity efficacy and tubocurare the lowest. Acetylcholine on the other hand induced a much longer opening time of the receptor though anatoxin is more potent. The results suggest that anatoxin derivatives would be helpful in understanding structure-activity relationships (SAR) for muscle nAChRs. [22]

Succinylcholine chloride, which is a drug that's already on the market, is a bischoline ester and a short acting muscle relaxant. Bischoline esters are compounds that can act as a competitive agonist on muscle type nAChRs and have been used in SAR studies. In a Torpedo (α1)2β1δγ nAChR model it was demonstrated that the potency of bischoline ester agonists is dependent on the chain length as potency increases with longer chains. Efficacy seems to be independent of chain length since the highest efficacy is seen in bischoline esters with four to seven CH
2 units and is lower for both fewer CH
2 units and more. [23]

Structure-activity relationships: α4β2 nAChR agonists

Pyridin cyclopropan derivatives Linker2.png
Pyridin cyclopropan derivatives

Combination of structural elements of ACh and nicotine as well as reducing the conformational flexibility by using a cyclopropane ring has led to the discovery of potent and selective α4β2 nAChR ligands. The modulation of three structural elements, the linker, substitution on the amino group and the pyridine ring can be used to determine the influence on potency and selectivity of the ligands. Factors that decrease the binding are steric hindrance on the amino group and linkers that are saturated/unsaturated carbon chains. Short-chained ether linkers are preferred. Beneficial effects on the binding is seen with substitution on the pyridine ring both mono- and disubstitution with halogens among other groups. Substitution on the amino group with three different amides increased the binding affinity where methylamide had the highest binding. Lower binding in the other substituted amides was explained by steric hindrance or lack of a methyl group resulting in loss of hydrophobic interaction. Stereochemistry of pyridine nitrogen and/or the pyridine ring and its stereoelectronic effects has a subtle beneficial effect on the binding to the α4β2 nAChR. Thus it was shown that a pyridyl ether ligand with bromo substitution on the pyridine and metylatedamide on the amino group had the highest potency. [24]

Structure-activity relationships: α7 nAChR agonists

SEN12333/WAY-317538 SEN12333 structure.png
SEN12333/WAY-317538
Structure activity relationship model for a7 agonists SAR alfa72.png
Structure activity relationship model for α7 agonists

The search for selective and potent α7 nAChR agonists has produced a series of compounds that have good potential as drug candidates. One such search produced SEN12333/WAY-317538 among other compounds that have desirable pharmacokinetic profiles and are selective of α7 nAChRs over α1, α3 and α4β2 nAChRs. Structure activity relationships for these compounds have been proposed. [15] The optimal pharmacophore of α7 nAChR agonist is made of three parts. There is a basic moiety connected to a carbon chain linked to an aromatic moiety by an amide bridge. The amide bridge can be inverted without affecting the potency of the agonist. A biaryl group shows more potency than a monoaryl group as the aromatic moiety and substitution at position 2 on the later aryl group will further increase the potency. Potency is higher for agonists with H+ donor/acceptor on the later aryl group on the biaryl group. A high number of hydrogen bond acceptors could decrease permeability across the blood–brain barrier (BBB) due to the polar surface area and needs to be taken into account when designing agonists to target α7 nAChRs. [15]

Various cyclic amine groups can act as the basic moiety and potency stays relatively unchanged for example aryl piperazine, piperidine and morpholine. An acyclic tertiary amine is tolerated as the basic moiety but larger steric groups are less tolerated. [15]

Many derivatives of quinuclidine such as quinuclidine amide are known to be α7 nAChR agonists. SAR studies for quinuclidine amide have identified factors that are affecting the potency and affinity of these agonists. Para substitution on the quinuclidine ring and the 3-(R) configuration in the stereochemistry is favored. Enhanced activity is observed when a 5 membered ring is fused to aromatic moiety. Further enhancement is seen when the fused ring is able to supply electron resonance to the amide carbonyl whereas the activity will diminish when the fused ring contains a hydrogen bond donating atom. The rigidity of quinuclidine and the orthogonal orientation of the nitrogen bridge in relations to the amide carbonyl group is presumed important for the optimal binding. The stability of some of the more potent quinuclidine amide derivatives in rat in vitro models have been low however by adding a methyl group to position 2 on the quinuclidine ring the stability has increased greatly. [25]

Drug development

The development of nicotinic acetylcholine receptor agonists began in the early 1990s after the discovery of nicotine's positive effects on animal memory. [3] [4] The development of nicotinic acetylcholine receptor agonists has come a long way since then. Nicotinic acetylcholine receptor agonists are gaining increasing attention as drug candidates for multiple central nervous system disorders such as Alzheimer's disease, schizophrenia, attention-deficit hyperactivity disorder (ADHD) and nicotine addiction. [26] [27] Nicotinic acetylcholine receptors are receptors found in the central nervous system, the peripheral nervous systems and skeletal muscles. They are ligand-gated ion channels with binding sites for acetylcholine as well as other agonists. When agonists bind to a receptor it stabilizes the open state of the ion channel allowing influx of cations. [9]

In 2009 there were at least five drugs on the market that affect the nicotinic acetylcholine receptors.

Quinuclidine derivatives
Qhinoclidine carbamates.png Quinuclidine amides2.png Quinuclidine ethers2.png
Quinuclidine carbamatesQuinuclidine amidesQuinuclidine ethers

Products of nicotinic agonist

Active ingredientProduct nameChemical namePharmaceutical formPharmacodynamic propertiesTherapeutic useStructure
Varenicline tartrate Champix, Chantix7,8,9,10-tetrahydro-6,10-methano-6H-pyrazino[2,3-h][3]benzazepine [27] Film coated tabletPartial agonist of the nicotinic acetylcholine receptor, subtype α4β2 [28] Treatment of tobacco dependence [28] Varenicline struct.png
Galantamine hydrobromide Reminyl, Nivalin, Razadyne and Razadyn ER4a,5,9,10,11,12-hexahydro-3-methoxy-11-methyl-6H-benzofuro[3a,3,2-ef][2]-benzazepin-6-ol [29] Sustained release capsule, film coated tablet, oral solutionCholinesterase inhibitor and a noncompetitive agonist of the nicotinic acetylcholine receptor [4] Treatment of dementia caused by Alzheimer's disease [30] Galantamine Structural Formulae.png
Nicotine Nicorette, Nicotinell, Niquitin, Boots NicAssist, Commit, Habitrol, Nicoderm CQ, Nicotrol, Thrive3-[(2S)-1-methylpyrrolidine-2-yl]pyridineTransdermal patch, gum, inhaler, nasal spray, lozenge, microtab, and is naturally found in tobaccoAgonist of the nicotinic receptor, [31] both Ganglion type and α4β2 [32] Treatment of tobacco dependence [33] Nicotine skeletal.svg
Carbachol Miostat2-[(aminocarbonyl)oxy]-N,N,N-trimethylethanaminiumIntraocular solutionCholinergic agonist [34] Treatment of glaucoma Carbachol.svg
Suxamethonium chloride (Succinylcholine chloride)Anectine, Quelicin Suxamethonium Chloride2,2'-[(1,4-dioxobutane-1,4-diyl)bis(oxy)]bis(N,N,N-trimethylethanaminium)Intravenous or intramuscular injectionDepolarizing neuromuscular blocking agent [35] Short acting muscle relaxant [36] Suxamethonium.svg
Epibatidine Not listed2-(6-chloropyridin-3-yl)-7-azabicyclo[2.2.1]heptaneNot listedAgonist of the nicotinic acetylcholine receptor [37] Not used as a drug Epibatidine structure.svg

Other nicotinic agonists, albeit generally with limited clinical use, include:

Nicotinic versus muscarinic activity

Comparison of cholinergic agonists [38]
SubstanceReceptor specificityHydrolysis by
acetylcholinesterase 		Comments
MuscarinicNicotinic
Choline ++++++++Essential nutrient
Acetylcholine +++++++++Endogenous ligand
Carbachol +++++-Used in the treatment of glaucoma
Methacholine ++++++
Bethanechol +++--Used in bladder and
gastrointestinal hypotonia.
Muscarine +++--Natural alkaloid found in certain mushrooms. Cause of mushroom poisoning
Nicotine -+++-Natural alkaloid found in the tobacco plant.
Pilocarpine ++--Used in glaucoma
Oxotremorine ++--

Current status

Currently nicotine receptor agonist research and drug designing is aimed for treatment of multiple diseases and disorders of the CNS. [39]

Targacept has three drug candidates that are in clinical trials; AZD3480 (TC-1734) for ADHD which is currently in phase II clinical trials, AZD1446 (TC-6683) for Alzheimer's disease in collaboration with AstraZeneca and TC-5619 for cognitive dysfunctions in schizophrenia.

Memory pharmaceuticals with its partner Roche has one drug candidate, MEM 3454 (RG3487), a partial agonist of the nicotinic α7 receptor, for Alzheimer's disease. [40] [41]

Abbott Laboratories in partnership with NeuroSearch have two drug candidates in clinical trials, ABT-894, a selective α4β2 nicotine receptor agonist, for ADHD and ABT-560, a neuronal nicotinic receptor modulator, which was selected by Abbott in 2006 as a new development candidate for cognitive dysfunctions. [42]

EnVivo pharmaceuticals has one drug candidate in clinical trials, EVP-6124, a selective α7 nicotine receptor agonist for Alzheimer's disease and schizophrenia and one follow-up compound, EVP-4473, that has successfully completed pre-clinical development. [43]

See also

Related Research Articles

<span class="mw-page-title-main">Acetylcholine receptor</span> Integral membrane protein

An acetylcholine receptor or a cholinergic receptor is an integral membrane protein that responds to the binding of acetylcholine, a neurotransmitter.

<span class="mw-page-title-main">Nicotinic acetylcholine receptor</span> Acetylcholine receptors named for their selective binding of nicotine

Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral nervous system, muscle, and many other tissues of many organisms. At the neuromuscular junction they are the primary receptor in muscle for motor nerve-muscle communication that controls muscle contraction. In the peripheral nervous system: (1) they transmit outgoing signals from the presynaptic to the postsynaptic cells within the sympathetic and parasympathetic nervous system, and (2) they are the receptors found on skeletal muscle that receive acetylcholine released to signal for muscular contraction. In the immune system, nAChRs regulate inflammatory processes and signal through distinct intracellular pathways. In insects, the cholinergic system is limited to the central nervous system.

<span class="mw-page-title-main">Epibatidine</span> Toxic chemical from some poison dart frogs

Epibatidine is a chlorinated alkaloid that is secreted by the Ecuadoran frog Epipedobates anthonyi and poison dart frogs from the Ameerega genus. It was discovered by John W. Daly in 1974, but its structure was not fully elucidated until 1992. Whether epibatidine is the first observed example of a chlorinated alkaloid remains controversial, due to challenges in conclusively identifying the compound from the limited samples collected by Daly. By the time that high-resolution spectrometry was used in 1991, there remained less than one milligram of extract from Daly's samples, raising concerns about possible contamination. Samples from other batches of the same species of frog failed to yield epibatidine.

α-Bungarotoxin Chemical compound

α-Bungarotoxin is one of the bungarotoxins, components of the venom of the elapid Taiwanese banded krait snake. It is a type of α-neurotoxin, a neurotoxic protein that is known to bind competitively and in a relatively irreversible manner to the nicotinic acetylcholine receptor found at the neuromuscular junction, causing paralysis, respiratory failure, and death in the victim. It has also been shown to play an antagonistic role in the binding of the α7 nicotinic acetylcholine receptor in the brain, and as such has numerous applications in neuroscience research.

<span class="mw-page-title-main">Methyllycaconitine</span> Chemical compound

Methyllycaconitine (MLA) is a diterpenoid alkaloid found in many species of Delphinium (larkspurs). In common with many other diterpenoid alkaloids, it is toxic to animals, although the acute toxicity varies with species. Methyllycaconitine was identified one of the principal toxins in larkspurs responsible for livestock poisoning in the mountain rangelands of North America. Methyllycaconitine has been explored as a possible therapeutic agent for the treatment of spastic paralysis, and it has been shown to have insecticidal properties. It has become an important molecular probe for studying the pharmacology of the nicotinic acetylcholine receptor.

<span class="mw-page-title-main">Cobratoxin</span> Chemical compound

α-Cobratoxin is a substance of the venom of certain Naja cobras. It is a nicotinic acetylcholine receptor (nAChR) antagonist which causes paralysis by preventing the binding of acetylcholine to the nAChR.

The alpha-4 beta-2 nicotinic receptor, also known as the α4β2 receptor, is a type of nicotinic acetylcholine receptor implicated in learning, consisting of α4 and β2 subunits. It is located in the brain, where activation yields post- and presynaptic excitation, mainly by increased Na+ and K+ permeability.

<span class="mw-page-title-main">Alpha-7 nicotinic receptor</span> Type of cell receptor found in humans

The alpha-7 nicotinic receptor, also known as the α7 receptor, is a type of nicotinic acetylcholine receptor implicated in long-term memory, consisting entirely of α7 subunits. As with other nicotinic acetylcholine receptors, functional α7 receptors are pentameric [i.e., (α7)5 stoichiometry].

<span class="mw-page-title-main">Epiboxidine</span> Chemical compound

Epiboxidine is a chemical compound which acts as a partial agonist at neural nicotinic acetylcholine receptors, binding to both the α3β4 and the α4β2 subtypes. It was developed as a less toxic analogue of the potent frog-derived alkaloid epibatidine, which is around 200 times stronger than morphine as an analgesic but produces extremely dangerous toxic nicotinic side effects.

<span class="mw-page-title-main">Pozanicline</span> Synthetic nootropic drug

Pozanicline is a drug developed by Abbott, that has nootropic and neuroprotective effects. Animal studies suggested it useful for the treatment of ADHD and subsequent human trials have shown ABT-089 to be effective for this application. It binds with high affinity subtype-selective to the α4β2 nicotinic acetylcholine receptors and has partial agonism to the α6β2 subtype, but not the α7 and α3β4 subtypes familiar to nicotine. It has particularly low tendency to cause side effects compared to other drugs in the class.

<span class="mw-page-title-main">Intrinsic activity</span> Measure of relative response to a drug

Intrinsic activity (IA) and efficacy refer to the relative ability of a drug-receptor complex to produce a maximum functional response. This must be distinguished from the affinity, which is a measure of the ability of the drug to bind to its molecular target, and the EC50, which is a measure of the potency of the drug and which is proportional to both efficacy and affinity. This use of the word "efficacy" was introduced by Stephenson (1956) to describe the way in which agonists vary in the response they produce, even when they occupy the same number of receptors. High efficacy agonists can produce the maximal response of the receptor system while occupying a relatively low proportion of the receptors in that system. There is a distinction between efficacy and intrinsic activity.

<span class="mw-page-title-main">A-84,543</span> Chemical compound

A-84543 is a drug developed by Abbott, which acts as an agonist at neural nicotinic acetylcholine receptors with high selectivity for the α4β2 subtype. It is widely used in scientific research into the structure and function of this receptor subtype and has been the lead compound for the development of a large family of related derivatives.

The alpha-3 beta-4 nicotinic receptor, also known as the α3β4 receptor and the ganglion-type nicotinic receptor, is a type of nicotinic acetylcholine receptor, consisting of α3 and β4 subunits. It is located in the autonomic ganglia and adrenal medulla, where activation yields post- and/or presynaptic excitation, mainly by increased Na+ and K+ permeability.

<span class="mw-page-title-main">RJR-2429</span> Chemical compound

RJR-2429 is a drug that acts as an agonist at neural nicotinic acetylcholine receptors, binding to both the α3β4 and the α4β2 subtypes. RJR-2429 is stronger than nicotine but weaker than epibatidine in most assays, and with high affinity for both α3β4 and α4β2 subtypes, as well as the less studied α1βγδ subtype.

<span class="mw-page-title-main">3-Bromocytisine</span> Chemical compound

3-Bromocytisine is a derivative of the toxic alkaloid cytisine that acts as a highly potent agonist at neural nicotinic acetylcholine receptors, binding primarily to the α4β2 and α7 subtypes. 3-Bromocytisine is a full agonist at the α7 subtype while it is only a partial agonist at α4β2, but has an extremely strong binding affinity at α4β2 with 200-fold selectivity for α4β2 over α7. In animal studies 3-bromocytisine stimulates the release of dopamine and noradrenaline and increases locomotor activity.

The alpha-3 beta-2 nicotinic receptor, also known as the α3β2 receptor, is a type of nicotinic acetylcholine receptor, consisting of α3 and β2 subunits.

<span class="mw-page-title-main">Anabaseine</span> Chemical compound

Anabaseine (3,4,5,6-tetrahydro-2,3′-bipyridine) is an alkaloid toxin produced by Nemertines worms and Aphaenogaster ants. It is structurally similar to nicotine and anabasine. Similarly, it has been shown to act as an agonist on most nicotinic acetylcholine receptors in the central nervous system and peripheral nervous system.

<span class="mw-page-title-main">Pinnatoxin</span>

Pinnatoxins are paralytic chemical compounds that inhibit neuronal and muscle-type nicotinic acetylcholine receptors. Although first discovered in shellfish, they are produced by the peridinoid dinoflagellate Vulcanodinium rugosum. Eight subtypes, designated pinnatoxin A-H, have been described.

<span class="mw-page-title-main">JNJ-39393406</span> Chemical compound

JNJ-39393406 is an experimental medication which is under development by Janssen Pharmaceutica, a division of Johnson & Johnson, for the treatment of depressive disorders and smoking withdrawal. It acts as a selective positive allosteric modulator of the α7 nicotinic acetylcholine receptor (nAChR). It does not act on the α4β2 or α3β4 nAChRs or the serotonin 5-HT3 receptor, and does not interact with a panel of 62 other receptors and enzymes. The drug has been found to lower the agonist and nicotine threshold for activation of the α7 nAChR by 10- to 20-fold and to increase the maximum agonist response of the α7 nAChR by 17- to 20-fold.

<span class="mw-page-title-main">6-Chloronicotine</span> Chemical compound

6-Chloronicotine is a drug which acts as an agonist at neural nicotinic acetylcholine receptors. It substitutes for nicotine in animal studies with around twice the potency, and shows antinociceptive effects.

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