Acetylcholine (muscarinic)

Overview: Muscarinic acetylcholine receptors (nomenclature as agreed by NC-IUPHAR Subcommittee on Muscarinic Acetylcholine Receptors, Caulfield and Birdsall, 1998) are 7TM receptors of the rhodopsin-like family where the endogenous agonist is acetylcholine. In addition to the agents listed in the table, AC-42, its structural analogues AC-260584 and 77-LH-28-1, desmethylclozapine and TBPB have been described as selective agonists of the M₁ receptor subtype via binding in a mode distinct from that utilized by non-selective agonists (Spalding et al., 2002; 2006; Sur et al., 2003; Langmead et al., 2006; 2008; May et al., 2007; Jones et al., 2008). There are two allosteric sites on muscarinic receptors, one defined by it binding gallamine, strychnine and brucine, and the other binds KT5720, WIN62,577, WIN51,708 and staurosporine (Lazareno et al., 2000; 2002;). There are selective enhancers of acetylcholine binding and action: brucine, KT5720, VU0090157 and VU0029767 at M₁ receptors, PG135 at M₂ receptors, N-chloromethylbrucine and WIN62,577 at M₃ receptors, thiochrome, LY2033298, VU0152099 and VU0152100 at M₄ receptors and VU0238429 at M₅ receptors (Birdsall and Lazareno, 2005; Brady et al., 2008; Chan et al., 2008; Shirey et al., 2008; Bridges et al., 2009; Marlo et al., 2009). LY2033298 has also been suggested to activate the M₄ receptor directly via an allosteric site (Nawaratne et al., 2008). The allosteric site for gallamine and strychnine on M₂ receptors can be labelled by [³H]dimethyl-W84 (Tränkle et al., 2003). McN-A-343 is a functionally selective partial agonist that appears to interact in a bitopic mode with both the orthosteric and an allosteric site on the M₂ muscarinic receptor (Valant et al., 2008). THRX160209, hybrid 1 and hybrid 2, are multivalent ligands that also achieve selectivity for M₂ receptors by binding both to the orthosteric and a nearby allosteric site (Steinfeld et al., 2007; Antony et al., 2009). VU0255035 is a recently described competitive antagonist with selectivity for the M₁ receptor (Sheffler et al., 2009).

Nomenclature	M1	M2	M3
Ensembl ID	ENSG00000168539	ENSG00000181072	ENSG00000133019
Principal transduction	Gq/11	Gi/o	Gq/11
Antagonists (pKi)	MT7 (10.9–11.0), 4-DAMP (9.2), tripitramine (8.8), darifenacin (8.3), pirenzepine (6.3–8.3), VU0255035 (7.8), guanylpirenzepine (7.7), AFDX384 (7.3–7.5), MT3 (6.5–7.1), himbacine (6.7–7.1), AFDX116 (6.2)	tripitramine (9.6), AFDX384 (8.0–9.0), 4-DAMP (8.3), himbacine (7.9–8.4), darifenacin (7.3–7.6), AFDX116 (6.7–7.3), VU0255035 (6.2), pirenzepine (4.9–6.4), MT3 (<6), guanylpirenzepine (5.6), MT7 (<5)	4-DAMP (9.3), darifenacin (9.1), AFDX384 (7.2–7.8), tripitramine (7.1–7.4), himbacine (6.9–7.2), pirenzepine (5.6–6.7), guanylpirenzepine (6.5), VU0255035 (6.1), AFDX116 (6.1), MT3 (<6), MT7 (<5)
Probes (KD)	[3H]NMS (80–150 pM), [3H]QNB (15–60 pM), [3H]pirenzepine (3–15 nM), (R,R)-quinuclidinyl-4-[18F]-fluoromethyl-benzilate (PET ligand), [11C]xanomeline (PET ligand), [11C]butylthio-TZTP (PET ligand)	[3H]NMS (200–400 pM), [3H]QNB (20–50 pM), [18F]FP-TZTP (PET ligand)	[3H]NMS (150–250 pM), [3H]QNB (30–90 pM), [3H]darifenacin (300 pM)

Nomenclature	M4	M5
Ensembl ID	ENSG00000180720	ENSG00000184984
Principal transduction	Gi/o	Gq/11
Antagonists (pKi)	4-DAMP (8.9), MT3 (8.7), AFDX384 (8.0–8.7), AFDX116 (7–8.7), himbacine (7.9–8.2), tripitramine (7.8–8.2), darifenacin (8.1), pirenzepine (5.9–7.6), guanylpirenzepine (6.5), VU0255035 (5.9), MT7 (<5)	4-DAMP (9.0), darifenacin (8.6), tripitramine (7.3–7.5), guanylpirenzepine (6.8), pirenzepine (6.2–6.9), himbacine (5.4–6.5), AFDX384 (6.3), AFDX116 (5.3–5.6), VU0255035 (5.6), MT3 (<6), MT7 (<5)
Probes (KD)	[3H]NMS (50–100 pM), [3H]QNB (20–80 pM)	[3H]NMS (500–700 pM), [3H]QNB (20–60 pM)

Antagonist data tabulated are pK_i values determined for human recombinant receptors. MT3 (m4-toxin) and MT7 (m1-toxin1) are toxins contained with the venom of the Eastern green mamba (Dendroaspis augusticeps) (see Potter et al., 2004; Servent and Fruchart-Gaillard, 2009).

Glossary

Abbreviations:

77-LH-28-1

1-[3-(4-butyl-1-piperidinyl)propyl]-3,4-dihydro-2(1H)-quinolinone

4-DAMP

4-diphenylacetoxy-N-methylpiperidine methiodide

AC-42

4-n-butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine hydrogen chloride

AC-260584

4-[3-(4-butylpiperidin-1-yl)-propyl]-7-fluoro-4H-benzo[1,4]oxazin-3-one

AFDX116 (otenzepad)

1-[2-[2-(diethylaminomethyl)piperidin-1-yl]acetyl]-5H-pyrido[2,3-b][1,4]benozodiazepin-6-one

AFDX384

(±)-5,11-dihydro-11-([(2-[2-[dipropylamino)methyl]-1-piperidinyl)ethyl)amino)carbonyl)-6H-pyrido[2,3-b](1,4)benzodiazepine-6-one

Butylthio-TZTP

butylthio-thiadiazolyltetrahydro-1-methyl-pyridine

Dimethyl-W84

N,N′-bis[3-(1,3-dihydro-1,3-dioxo-4-methyl-2H-isoindol-2-yl)propyl]-N,N,N′,N′-tetramethyl-1,6-hexanediaminium diiodide

FP-TZTP

[3-(3-(3-Fluoropropyl)thio)-1,2,5-thiadiazol-4-yl]-1,2,5,6-tetrahydro-1-methylpyridine

Hybrid 1M

2-{3-[1-(6-{1,1-dimethyl-1-[4-(isoxazol-3-yloxy)but-2-ynyl]-ammonium}hexyl)-1,1 dimethylammonio]propyl}isoindoline-1,3-dione dibromide

Hybrid 2

2-{3-[1-(6-{1,1-dimethyl-1-[4-(isoxazol-3-yloxy)but-2-ynyl]-ammonium}hexyl)-1,1-dimethylammonio]-2,2-dimethylpropyl}-benzo[de]isoquinoline-1,3-dione dibromide

KT5720

(9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3′,2′,1′-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid hexyl ester

LY2033298

3-amino-5-chloro-6-methoxy-4-methyl-thieno(2,3-b)pyridine-2-carboxylic acid cyclopropylamide

McN-A-343

4-(3-chlorophenyl) carbamoyloxy)-2-butynyltrimethyl ammonium chloride

NMS

N-methylscopolamine

PG135

(3aS,12R,12aS,12bR)-2-amino-2,3,3a,4,11,12a,12b-octahydro-10-hydroxyisoquino[2,1,8-lma]carbazol-5(1H)-one hydrochloride

QNB

3-quinuclidinylbenzilate

TBPB

1-(1′-2-methylbenzyl)-1,4′-bipiperidin-4-yl)-1H-benzo[d]imidazol-2(3H)-one

THRX160209

4-{N-[7-(3-(S)-(1-carbamoyl-1,1-diphenylmethyl)pyrrolidin-1-yl)hept-1-yl]-N-(n-propyl)amino}-1-(2,6-dimethoxy-benzyl)piperidine

VU0029767

(E)-2-(4-ethoxyphenylamino)-N′-((2-hydroxynaphthalen-1-yl)methylene)acetohydrazide

VU0090157

cyclopentyl 1,6-dimethyl-4-(6-nitrobenzo[d][1,3]-dioxol-5-yl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate

VU0152099

3-amino-N-(benzo[d][1,3]dioxol-5-ylmethyl)-4,6-dimethylthieno[2,3-b]pyridine carboxamide

VU0152100

3-amino-N-(4-methoxybenzyl)-4,6-dimethylthieno[2,3-b]pyridine carboxamide

VU0238429

structure not available

VU0255035

N-(3-oxo-3-(4-(pyridine-4-yl)piperazin-1-yl)propyl)-benzo[c][1,2,5]thiadiazole-4 sulfonamide

WIN51,708

17-β-hydroxy-17-α-ethynyl-5-α-androstano[3,2-b]pyrimido[1,2-a]benzimidazole

WIN62,577

17-β-hydroxy-17-α-ethynyl-Δ⁴-androstano[3,2-b]pyrimido[1,2-a]benzimidazole

Further Reading

Abrams P, Andersson KE, Buccafusco JI, Chapple C, De Groat WC, Fryer AD et al. (2006). Muscarinic receptors: their distribution and function in body systems, and the implications for treating overactive bladder. Br J Pharmacol148: 565–578.

Birdsall NJM, Lazareno S. (2005). Allosterism at muscarinic receptors: ligands and mechanisms. Mini Rev Med Chem5: 523–543.

Caulfield MP, Birdsall NJM (1998). International Union of Pharmacology. XVII Classification of muscarinic acetylcholine receptors. Pharmacol. Rev50: 279–290.

Conn PJ, Christopoulos A, Lindsley CW (2009). Allosteric modulators of GPCRs: a novel approach for the treatment of CNS disorders. Nat Rev Drug Discov8: 41–54.

Conn PJ, Jones CK, Lindsley CW (2009). Subtype-selective allosteric modulators of muscarinic receptors for the treatment of CNS disorders. Trends Pharmacol Sci30: 148–155.

De Amici M, Dallanoce C, Holzgrabe U, Tränkle C, Mohr K (2009). Allosteric ligands for G protein-coupled receptors: A novel strategy with attractive therapeutic opportunities. Med Res Rev Jun 25. [Epub ahead of print].

Eckelman WC (2006). Imaging of muscarinic receptors in the central nervous system. Curr Pharm Des12: 3901–3913.

Eglen RM (2005). Muscarinic receptor subtype pharmacology and physiology. Prog Med Chem43: 105–136.

Eglen RM (2006). Muscarinic receptor subtypes in neuronal and non-neuronal cholinergic function. Auton Autacoid Pharmacol26: 219–233.

Gregory KJ, Sexton PM, Christopoulos A (2007). Allosteric modulation of muscarinic acetylcholine receptors. Curr Neuropharmacol5: 157–167.

Holzgrabe U, De Amici M, Mohr K (2006). Allosteric modulators and selective agonists of muscarinic receptors. J Mol Neurosci30: 165–168.

Ishii M, Kurachi Y (2006). Muscarinic acetylcholine receptors. Curr Pharm Des12: 3573–3581.

Langmead CJ, Watson J, Reavill C (2008). Muscarinic acetylcholine receptors as CNS drug targets. Pharmacol Ther117: 232–243.

Nathanson NM (2008). Synthesis, trafficking, and localization of muscarinic acetylcholine receptors. Pharmacol Ther119: 33–43.

Peretto I, Petrillo P, Imbimbo BP (2009). Medicinal chemistry and therapeutic potential of muscarinic M3 antagonists. Med Res Rev29: 867–902.

Potter LT, Flynn DD, Liang JS, McCollum MH (2004). Studies of muscarinic neurotransmission with antimuscarinic toxins. Prog Brain Res145: 121–128.

Servent D, Fruchart-Gaillard C (2009). Muscarinic toxins: tools for the study of the pharmacological and functional properties of muscarinic receptors. J Neurochem109: 1193–1202.

Tobin G, Giglio D, Lundgren O (2009) Muscarinic receptor subtypes in the alimentary tract. J Physiol Pharmacol60: 3–21.

Valant C, Sexton PM, Christopoulos A (2009) Orthosteric/allosteric bitopic ligands: Going hybrid at GPCRs. Mol Int9: 125–135.

Wess J, Eglen RM, Gautam D (2007). Muscarinic acetylcholine receptors: mutant mice provide new insights for drug development. Nat Rev Drug Discov6: 721–733.