case study/BPH

S.P.H. Alexander et al. The Concise Guide to PHARMACOLOGY 2015/16: G protein-coupled receptors. British Journal of Pharmacology (2015) 172, 5744–5869

THE CONCISE GUIDE TO PHARMACOLOGY 2015/16: G protein-coupled receptors

Stephen PH Alexander1, Anthony P Davenport2, Eamonn Kelly3, Neil Marrion3, John A Peters4, Helen E Benson5, Elena Faccenda5, Adam J Pawson5, Joanna L Sharman5, Christopher Southan5, Jamie A Davies5 and CGTP Collaborators

1School of Biomedical Sciences, University of Nottingham Medical School, Nottingham, NG7 2UH, UK, 2Clinical Pharmacology Unit, University of Cambridge, Cambridge, CB2 0QQ, UK, 3School of Physiology and Pharmacology, University of Bristol, Bristol, BS8 1TD, UK, 4Neuroscience Division, Medical Education Institute, Ninewells Hospital and Medical School, University of Dundee, Dundee, DD1 9SY, UK, 5Centre for Integrative Physiology, University of Edinburgh, Edinburgh, EH8 9XD, UK

Abstract

The Concise Guide to PHARMACOLOGY 2015/16 provides concise overviews of the key properties of over 1750 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/ 10.1111/bph.13348/full. G protein-coupled receptors are one of the eight major pharmacological targets into which the Guide is divided, with the others being: ligand-gated ion channels, voltage-gated ion channels, other ion channels, nuclear hormone receptors, catalytic receptors, enzymes and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The Concise Guide is published in landscape format in order to facilitate comparison of related targets. It is a condensed version of material contemporary to late 2015, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in the previous Guides to Receptors & Channels and the Concise Guide to PHARMACOLOGY 2013/14. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and GRAC and provides a permanent, citable, point-in-time record that will survive database updates.

Conflict of interest

The authors state that there are no conflicts of interest to declare.

c 2015 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of The British Pharmacological Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Overview: G protein-coupled receptors (GPCRs) are the largest class of membrane proteins in the human genome. The term "7TM receptor" is commonly used interchangeably with "GPCR", although there are some receptors with seven transmembrane domains that do not signal through G proteins. GPCRs share a common architecture, each consisting of a single polypeptide with an extracellular N-terminus, an intracellular C-terminus and seven hydrophobic transmembrane domains (TM1-TM7) linked by three extracellular loops (ECL1-ECL3) and three intracellular

loops (ICL1-ICL3). About 800 GPCRs have been identified in man, of which about half have sensory functions, mediating ol- faction ( 400), taste (33), light perception (10) and pheromone signalling (5) [1309]. The remaining 350 non-sensory GPCRs mediate intersignalling by ligands that range in size from small molecules to peptide to large proteins; they are the targets for the majority of drugs in clinical usage [1451, 1560], although only a minority of these receptors are exploited therapeutically. The first classification scheme to be proposed for GPCRs [984] di-

vided them, on the basic of sequence homology, into six classes. These classes and their prototype members were as follows: Class A (rhodopsin-like), Class B (secretin receptor family), Class C (metabotropic glutamate), Class D (fungal mating pheromone receptors), Class E (cyclic AMP receptors) and Class F (friz- zled/smoothened). Of these, classes D and E are not found in vertebrates. An alternative classification scheme "GRAFS" [1666] divides vertebrate GPCRs into five classes, overlapping with the A-F nomenclature, viz:

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S.P.H. Alexander et al. The Concise Guide to PHARMACOLOGY 2015/16: G protein-coupled receptors. British Journal of Pharmacology (2015) 172, 5744–5869

Glutamate family (class C), which includes metabotropic glutamate receptors, a calcium-sensing receptor and GABAB receptors, as well as three taste type 1 receptors [class C list] and a family of pheromone receptors (V2 receptors) that are abundant in rodents but absent in man [1309].

Rhodopsin family (class A), which includes receptors for a wide variety of small molecules, neurotransmitters, peptides and hormones, together with olfactory receptors, visual pigments, taste type 2 receptors and five pheromone receptors (V1 receptors). [Class A list]

Adhesion family GPCRs are phylogenetically related to class B receptors, from which they differ by possessing large extracellular N-termini that are autoproteolytically cleaved from their 7TM domains at a conserved "GPCR proteolysis site" (GPS) which lies within a much larger ( 320 residue) "GPCR autoproteolysis-inducing" (GAIN) domain, an evolutionary ancient mofif also found in polycystic kidney disease 1 (PKD1)-like proteins, which has been suggested to be both required and sufficient for autoproteolysis [1538]. [Adhesion family list].

Frizzled family (class F) consists of 10 Frizzled proteins (FZD(1-10)) and Smoothened (SMO). [Frizzled family list]. The FZDs are activated by secreted lipoglycoproteins of the WNT family, whereas SMO is indirectly activated by the Hedgehog (HH) family of proteins acting on the transmembrane protein Patched (PTCH).

Secretin family (class B), encoded by 15 genes in humans. The ligands for receptors in this family are polypeptide hormones of 27-141 amino-acid residues; nine of the mammalian receptors respond to ligands that are structurally related to one another (glucagon, glucagon-like peptides (GLP-1, GLP-2), glucose-dependent insulinotropic polypeptide (GIP), secretin, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP) and growth-hormone-releasing hormone (GHRH) [703].

GPCR families

Family Class A Class B (Secretin) Class C (Glutamate) Adhesion Frizzled

Receptors with known ligands 197a 15 12 0 11

Orphans 87 (54)a - 8 (1)a 26 (6)a 0

Sensory (olfaction) 390b,c - - - -

Sensory (vision) 10d opsins - - - -

Sensory (taste) 30c taste 2 - 3c taste 1 - -

Sensory (pheromone) 5c vomeronasal 1 - - - -

Total 719 15 22 33 11

aNumbers in brackets refer to orphan receptors for which an endogenous ligand has been proposed in at least one publication, see [396]; b[1443]; c[1309]; d[1866].

Much of our current understanding of the structure and function of GPCRs is the result of pioneering work on the visual pigment rhodopsin and on the β2 adrenoceptor, the latter culminating in the award of the 2012 Nobel Prize in chemistry to Robert Lefkowitz and Brian Kobilka [975, 1073].

Family structure

5746 Orphan and other 7TM receptors

5746 Class A Orphans

5756 Class C Orphans

5756 Taste 1 receptors

5757 Taste 2 receptors

5758 Other 7TM proteins

5759 5-Hydroxytryptamine receptors

5764 Acetylcholine receptors (muscarinic)

5766 Adenosine receptors

5768 Adhesion Class GPCRs 5770 Adrenoceptors

5774 Angiotensin receptors

5775 Apelin receptor

5777 Bile acid receptor

5778 Bombesin receptors

5780 Bradykinin receptors

5781 Calcitonin receptors

5783 Calcium-sensing receptors

5784 Cannabinoid receptors

5785 Chemerin receptor

5785 Chemokine receptors

5791 Cholecystokinin receptors

5792 Class Frizzled GPCRs 5793 Complement peptide receptors

5795 Corticotropin-releasing factor receptors

5796 Dopamine receptors

5798 Endothelin receptors

5799 G protein-coupled estrogen receptor

5800 Formylpeptide receptors

5801 Free fatty acid receptors

5803 GABAB receptors

5805 Galanin receptors

5806 Ghrelin receptor

5807 Glucagon receptor family

5809 Glycoprotein hormone receptors

5810 Gonadotrophin-releasing hormone receptors

5811 GPR18, GPR55 and GPR119

5812 Histamine receptors

5814 Hydroxycarboxylic acid receptors

5815 Kisspeptin receptor

5816 Leukotriene receptors

5818 Lysophospholipid (LPA) receptors

5819 Lysophospholipid (S1P) receptors

5820 Melanin-concentrating hormone receptors

5821 Melanocortin receptors

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5822 Melatonin receptors

5823 Metabotropic glutamate receptors

5826 Motilin receptor

5827 Neuromedin U receptors

5828 Neuropeptide FF/neuropeptide AF receptors

5829 Neuropeptide S receptor

5829 Neuropeptide W/neuropeptide B receptors

5830 Neuropeptide Y receptors

5832 Neurotensin receptors

5833 Opioid receptors

5835 Orexin receptors

5836 Oxoglutarate receptor

5836 P2Y receptors

5838 Parathyroid hormone receptors

5839 Platelet-activating factor receptor

5840 Prokineticin receptors

5841 Prolactin-releasing peptide receptor

5842 Prostanoid receptors

5844 Proteinase-activated receptors

5846 QRFP receptor

5846 Relaxin family peptide receptors

5848 Somatostatin receptors

5850 Succinate receptor

5850 Tachykinin receptors

5852 Thyrotropin-releasing hormone receptors

5852 Trace amine receptor

5854 Urotensin receptor

5854 Vasopressin and oxytocin receptors

5856 VIP and PACAP receptors

Orphan and other 7TM receptors G protein-coupled receptors ! Orphan and other 7TM receptors Class A Orphans G protein-coupled receptors ! Orphan and other 7TM receptors ! Class A Orphans Overview: Table 1 lists a number of putative GPCRs identified by NC-IUPHAR [530], for which preliminary evidence for an endogenous ligand has been published, or for which there exists a potential link to a disease, or disorder. These GPCRs have recently been reviewed in detail [396]. The GPCRs in Table 1 are all Class A, rhodopsin-like GPCRs. Class A orphan GPCRs not listed in Table 1 are putative GPCRs with as-yet unidentified endogenous ligands.

Table 1: Class A orphan GPCRs with putative endogenous ligands

GPR1 GPR3 GPR4 GPR6 GPR12 GPR15 GPR17 GPR20

GPR22 GPR26 GPR31 GPR34 GPR35 GPR37 GPR39 GPR50

GPR63 GRP65 GPR68 GPR75 GPR84 GPR87 GPR88 GPR132

GPR149 GPR161 GPR183 LGR4 LGR5 LGR6 MAS1 MRGPRD

MRGPRX1 MRGPRX2 P2RY10 TAAR2

In addition the orphan receptors GPR18, GPR55 and GPR119 which are reported to respond to endogenous agents analogous to the endogenous cannabinoid ligands have been grouped together (GPR18, GPR55 and GPR119).

Nomenclature GPR1 GPR3 GPR4 GPR6

HGNC, UniProt GPR1, P46091 GPR3, P46089 GPR4, P46093 GPR6, P46095

Endogenous ligand – – Protons –

Endogenous agonists chemerin (RARRES2, Q99969) (pKd 8.3) [95]

– – –

Agonists – diphenyleneiodonium chloride (pEC50 6) [2091]

– –

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(continued)

Nomenclature GPR1 GPR3 GPR4 GPR6

Comments Reported to act as a co-receptor for HIV [1724]. See review [396] for discussion of pairing with chemerin.

sphingosine 1-phosphate was reported to be an endogenous agonist [1921], but this finding was not replicated in subsequent studies [2093]. Reported to activate adenylyl cyclase constitutively through Gs [466]. Gene disruption results in premature ovarian ageing [1063], reduced β-amyloid deposition [1868] and hypersensitivity to thermal pain [1615] in mice. First small molecule inverse agonist [860] and agonists identified [2091].

An initial report suggesting activation by lysophosphatidylcholine and sphingosylphosphorylcholine [2131] has been retracted [2148]. GPR4, GPR65, GPR68 and GPR132 are now thought to function as proton-sensing receptors detecting acidic pH [396, 1704]. Gene disruption is associated with increased perinatal mortality and impaired vascular proliferation [2085]. Negative allosteric modulators of GPR4 have been reported [1889].

An initial report that sphingosine 1-phosphate (S1P) was a high-affinity ligand (EC50 value of 39nM) [815, 1921] was not repeated by arrestin PathHunter[TM] assays [1785, 2093]. Reported to activate adenylyl cyclase constitutively through Gs and to be located intracellularly [1453]. GPR6-deficient mice showed reduced striatal cyclic AMP production in vitro and selected alterations in instrumental conditioning in vivo. [1134].

Nomenclature GPR12 GPR15 GPR17 GPR19

HGNC, UniProt GPR12, P47775 GPR15, P49685 GPR17, Q13304 GPR19, Q15760

Endogenous agonists

– – UDP-glucose (pEC50 5.9–9.5) [130, 344], LTC4 (pEC50 7.8–9.5) [344], UDP-galactose (pEC50 6–8.9) [130, 344], uridine diphosphate (pEC50 6–8.8) [130, 344], LTD4 (pEC50 8.1–8.4) [344]

–

Comments Reports that sphingosine 1-phosphate is a ligand of GPR12 [814, 1921] have not been replicated in arrestin-based assays [1785, 2093]. Gene disruption results in dyslipidemia and obesity [154].

Reported to act as a co-receptor for HIV [462]. In an infection-induced colitis model, Gpr15 knockout mice were more prone to tissue damage and inflammatory cytokine expression [945].

Reported to be a dual leukotriene and uridine diphosphate receptor [344]. Another group instead proposed that GPR17 functions as a negative regulator of the CysLT1 receptor response to leukotriene D4 (LTD4). For further discussion, see [396]. Reported to antagonize CysLT1 receptor signalling in vivo and in vitro [1175]. See reviews [250] and [396].

–

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Nomenclature GPR20 GPR21 GPR22 GPR25 GPR26

HGNC, UniProt GPR20, Q99678 GPR21, Q99679 GPR22, Q99680 GPR25, O00155 GPR26, Q8NDV2

Comments Reported to inhibit adenylyl cyclase constitutively through Gi/o [708]. GPR20 deficient mice exhibit hyperactivity characterised by increased total distance travelled in an open field test [207].

Gpr21 knockout mice were resistant to diet-induced obesity, exhibiting an increase in glucose tolerance and insulin sensitivity, as well as a modest lean phenotype [1448].

Gene disruption results in increased severity of functional decompensation following aortic banding [10]. Identified as a susceptibility locus for osteoarthritis [494, 929, 1935].

– Has been reported to activate adenylyl cyclase constitutively through Gs [880]. Gpr26 knockout mice show increased levels of anxiety and depression-like behaviours [2117].

Nomenclature GPR27 GPR31 GPR32 GPR33 GPR34

HGNC, UniProt GPR27, Q9NS67 GPR31, O00270 GPR32, O75388 GPR33, Q49SQ1 GPR34, Q9UPC5

Rank order of potency

– – resolvin D1 > LXA4 – – Endogenous agonists

– 12S-HETE (Selective) (pEC50 9.6) [665] – Mouse

resolvin D1 (pEC50 11.1) [1006], LXA4 (pEC50 9.7) [1006]

– lysophosphatidylserine (Selective) (pEC50 6.6–6.9) [960, 1817]

Labelled ligands – – [3H]resolvin D1 (Agonist) (pKd 9.7) [1006]

– –

Comments Knockdown of Gpr27 reduces endogenous mouse insulin promotor activity and glucose-stimulated insulin secretion [1012].

See [396] for discussion of pairing.

resolvin D1 has been demonstrated to activate GPR32 in two publications [316, 1006]. The pairing was not replicated in a recent study based on arrestin recruitment [1785]. GPR32 is a pseudogene in mice and rats. See reviews [250] and [396].

GPR33 is a pseudogene in most individuals, containing a premature stop codon within the coding sequence of the second intracellular loop [1621].

Lysophosphatidylserine has been reported to be a ligand of GPR34 in several publications, but the pairing was not replicated in a recent study based on arrestin recruitment [1785]. Fails to respond to a variety of lipid-derived agents [2093]. Gene disruption results in an enhanced immune response [1102]. Characterization of agonists at this receptor is discussed in [819] and [396].

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Nomenclature GPR35 GPR37 GPR37L1 GPR39 GPR42

HGNC, UniProt GPR35, Q9HC97 GPR37, O15354 GPR37L1, O60883 GPR39, O43194 GPR42, O15529

Endogenous agonists 2-oleoyl-LPA (pEC50 7.3–7.5) [1436], kynurenic acid (pEC50 3.9–4.4) [1785, 1980]

– – Zn2+ [775] –

Agonists – neuropeptide head activator (pEC50 8–8.5) [1578]

– compound 1 [PMID: 24900608] (pEC50 4.9–7.2) [166]

–

Comments Several studies have shown that kynurenic acid is an agonist of GPR35 but it remains controversial whether the proposed endogenous ligand reaches sufficient tissue concentrations to activate the receptor [1015]. 2-oleoyl-LPA has also been proposed as an endogenous ligand [1436] but these results were not replicated in an arrestin assay [1785]. The phosphodiesterase inhibitor zaprinast [1863] has become widely used as a surrogate agonist to investigate GPR35 pharmacology and signalling [1863]. GPR35 is also activated by the pharmaceutical adjunct pamoic acid [2124]. See reviews [396] and [429].

Reported to associate and regulate the dopamine transporter [1207] and to be a substrate for parkin [1205]. Gene disruption results in altered striatal signalling [1206]. The peptides prosaptide and prosaposin are proposed as endogenous ligands for GPR37 and GPR37L1 [1264].

The peptides prosaptide and prosaposin are proposed as endogenous ligands for GPR37 and GPR37L1 [1264].

Zn2+ has been reported to be a potent and efficacious agonist of human, mouse and rat GPR39 [2089]. obestatin (GHRL, Q9UBU3), a fragment from the ghrelin precursor, was reported initially as an endogenous ligand, but subsequent studies failed to reproduce these findings. GPR39 has been reported to be down-regulated in adipose tissue in obesity-related diabetes [273]. Gene disruption results in obesity and altered adipocyte metabolism [1497]. Reviewed in [396].

–

Nomenclature GPR45 GPR50 GPR52 GPR61

HGNC, UniProt GPR45, Q9Y5Y3 GPR50, Q13585 GPR52, Q9Y2T5 GPR61, Q9BZJ8

Comments – GPR50 is structurally related to MT1 and MT2 melatonin receptors, with which it heterodimerises constitutively and specifically [1089]. Gpr50 knockout mice display abnormal thermoregulation and are much more likely than wild-type mice to enter fasting-induced torpor [111].

First small molecule agonist reported [1703].

GPR61 deficient mice exhibit obesity associated with hyperphagia [1363]. Although no endogenous ligands have been identified, 5-(nonyloxy)tryptamine has been reported to be a low affinity inverse agonist [1852].

Searchable database: http://www.guidetopharmacology.org/index.jsp Class A Orphans 5749

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Nomenclature GPR62 GPR63 GPR65 GPR68 GPR75

HGNC, UniProt GPR62, Q9BZJ7 GPR63, Q9BZJ6 GPR65, Q8IYL9 GPR68, Q15743 GPR75, O95800

Endogenous ligand

– – Protons Protons –

Comments – sphingosine 1-phosphate and dioleoylphosphatidic acid have been reported to be low affinity agonists for GPR63 [1394] but this finding was not replicated in an arrestin-based assay [2093].

GPR4, GPR65, GPR68 and GPR132 are now thought to function as proton-sensing receptors detecting acidic pH [396, 1704]. Reported to activate adenylyl cyclase; gene disruption leads to reduced eosinophilia in models of allergic airway disease [1000].

GPR68 was previously identified as a receptor for sphingosylphosphorylcholine (SPC) [2068], but the original publication has been retracted [2067]. GPR4, GPR65, GPR68 and GPR132 are now thought to function as proton-sensing receptors detecting acidic pH [396, 1704]. A family of 3,5-disubstituted isoxazoles were identified as agonists of GPR68 [1617].

CCL5 (CCL5, P13501) was reported to be an agonist of GPR75 [816], but the pairing could not be repeated in an arrestin assay [1785].

Nomenclature GPR78 GPR79 GPR82 GPR83 GPR84

HGNC, UniProt GPR78, Q96P69 GPR79, – GPR82, Q96P67 GPR83, Q9NYM4 GPR84, Q9NQS5

Agonists – – – Zn2+ (pEC50 5) [1351] – Mouse decanoic acid (pEC50 5–5.4) [1785, 1981], undecanoic acid (pEC50 5.1) [1981], lauric acid (pEC50 5) [1981]

Comments GPR78 has been reported to be constitutively active, coupled to elevated cAMP production [880].

– Mice with Gpr82 knockout have a lower body weight and body fat content associated with reduced food intake, decreased serum triglyceride levels, as well as higher insulin sensitivity and glucose tolerance [479].

One isoform has been implicated in the induction of CD4(+) CD25(+) regulatory T cells (Tregs) during inflammatory immune responses [696]. The extracellular N-terminal domain is reported as an intramolecular inverse agonist [1352].

Medium chain free fatty acids with carbon chain lengths of 9-14 activate GPR84 [1828, 1981]. A surrogate ligand for GPR84, 6-n-octylaminouracil has also been proposed [1828]. See review [396] for discussion of classification. Mutational analysis and molecular modelling of GPR84 has been reported [1397].

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Nomenclature GPR85 GPR87 GPR88 GPR101

HGNC, UniProt GPR85, P60893 GPR87, Q9BY21 GPR88, Q9GZN0 GPR101, Q96P66

Endogenous agonists

– LPA (pEC50 7.4) [1344, 1836]

– –

Agonists – – compound 2 [PMID: 24793972] (pEC50 6.2) [868]

–

Comments Proposed to regulate hippocampal neurogenesis in the adult, as well as neurogenesis-dependent learning and memory [303].

– Gene disruption results in altered striatal signalling [1137]. Small molecule agonists have been reported [147].

Mutations in GPR101 have been linked to gigantism and acromegaly [1906].

Nomenclature GPR132 GPR135 GPR139 GPR141 GPR142

HGNC, UniProt GPR132, Q9UNW8 GPR135, Q8IZ08 GPR139, Q6DWJ6 GPR141, Q7Z602 GPR142, Q7Z601

Endogenous ligand

Protons – – – –

Agonists – – compound 1a [PMID: 24900311] (pEC50 7.4) [1721]

– –

Comments GPR4, GPR65, GPR68 and GPR132 are now thought to function as proton-sensing receptors detecting acidic pH [396, 1704]. Reported to respond to lysophosphatidylcholine [891], but later retracted [2038].

– Peptide agonists have been reported [828].

– Small molecule agonists have been reported [1890, 2106].

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Nomenclature GPR146 GPR148 GPR149 GPR150 GPR151

HGNC, UniProt GPR146, Q96CH1 GPR148, Q8TDV2 GPR149, Q86SP6 GPR150, Q8NGU9 GPR151, Q8TDV0

Comments Yosten et al. demonstrated inhibition of proinsulin C-peptide (INS, P01308)-induced stimulation of cFos expression folllowing knockdown of GPR146 in KATO III cells, suggesting proinsulin C-peptide as an endogenous ligand of the receptor [2103].

– Gpr149 knockout mice displayed increased fertility and enhanced ovulation, with increased levels of FSH receptor and cyclin D2 mRNA levels [463].

– GPR151 responded to galanin with an EC50 value of 2 �M, suggesting that the endogenous ligand shares structural features with galanin (GAL, P22466) [813].

Nomenclature GPR152 GPR153 GPR160 GPR161 GPR162

HGNC, UniProt GPR152, Q8TDT2 GPR153, Q6NV75 GPR160, Q9UJ42 GPR161, Q8N6U8 GPR162, Q16538

Comments – – – A C-terminal truncation (deletion) mutation in Gpr161 causes congenital cataracts and neural tube defects in the vacuolated lens (vl) mouse mutant [1226]. The mutated receptor is associated with cataract, spina bifida and white belly spot phenotypes in mice [994]. Gene disruption is associated with a failure of asymmetric embryonic development in zebrafish [1085].

–

Nomenclature GPR171 GPR173 GPR174 GPR176 GPR182

HGNC, UniProt GPR171, O14626 GPR173, Q9NS66 GPR174, Q9BXC1 GPR176, Q14439 GPR182, O15218

Endogenous agonists

– – lysophosphatidylserine (pEC50 7.1) [825]

– –

Comments GPR171 has been shown to be activated by the endogenous peptide BigLEN {Mouse}. This receptor-peptide interaction is believed to be involved in regulating feeding and metabolism responses [621].

– See [819] which discusses characterization of agonists at this receptor.

– Rat GPR182 was first proposed as the adrenomedullin receptor [904]. However, it was later reported that rat and human GPR182 did not respond to adrenomedullin [927] and GPR182 is not currently considered to be a genuine adrenomedullin receptor [722].

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Nomenclature GPR183 LGR4 LGR5 LGR6 MAS1

HGNC, UniProt GPR183, P32249 LGR4, Q9BXB1 LGR5, O75473 LGR6, Q9HBX8 MAS1, P04201

Endogenous agonists

7α,25-dihydroxycholesterol (Selective) (pEC50 8.1–9.8) [694, 1125], 7α,27-dihydroxycholesterol (Selective) (pEC50 8.9) [1125], 7β, 25-dihydroxycholesterol (Selective) (pEC50 8.7) [1125], 7β, 27-dihydroxycholesterol (Selective) (pEC50 7.3) [1125]

R-spondin-2 (RSPO2, Q6UXX9) (pEC50 12.5) [266], R-spondin-1 (RSPO1, Q2MKA7) (pEC50 10.7) [266], R-spondin-3 (RSPO3, Q9BXY4) (pEC50 10.7) [266], R-spondin-4 (RSPO4, Q2I0M5) (pEC50 10.1) [266]

R-spondin-2 (RSPO2, Q6UXX9) (pEC50 12) [266], R-spondin-1 (RSPO1, Q2MKA7) (pEC50 11.1) [266], R-spondin-3 (RSPO3, Q9BXY4) (pEC50 11) [266], R-spondin-4 (RSPO4, Q2I0M5) (pEC50 9.4) [266]

R-spondin-1 (RSPO1, Q2MKA7) [266, 2140], R-spondin-2 (RSPO2, Q6UXX9) [266, 2140], R-spondin-3 (RSPO3, Q9BXY4) [266, 2140], R-spondin-4 (RSPO4, Q2I0M5) [266, 2140]

–

Agonists – – – – angiotensin-(1-7) (AGT, P01019) (pKi 7.3) [612] – Mouse

Comments Two independent publications have shown that 7α,25-dihydroxycholesterol is an agonist of GPR183 and have demonstrated by mass spectrometry that this oxysterol is present endogenously in tissues [694, 1125]. Gpr183-deficient mice show a reduction in the early antibody response to a T-dependent antigen. GPR183-deficient B cells fail to migrate to the outer follicle and instead stay in the follicle centre [923, 1488].

LGR4 does not couple to heterotrimeric G proteins or recruit arrestins when stimulated by the R-spondins, indicating a unique mechanism of action. R-spondins bind to LGR4, which specifically associates with Frizzled and LDL receptor-related proteins (LRPs) that are activated by the extracellular Wnt molecules and then trigger canonical Wnt signalling to increase gene expression [266, 1612, 2140]. Gene disruption leads to multiple developmental disorders [869, 1154, 1781, 2005].

The four R-spondins can bind to LGR4, LGR5, and LGR6, which specifically associate with Frizzled and LDL receptor-related proteins (LRPs), proteins that are activated by extracellular Wnt molecules and which then trigger canonical Wnt signalling to increase gene expression [266, 2140].

– –

Searchable database: http://www.guidetopharmacology.org/index.jsp Class A Orphans 5753

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Nomenclature MAS1L MRGPRD MRGPRE MRGPRF MRGPRG

HGNC, UniProt MAS1L, P35410 MRGPRD, Q8TDS7 MRGPRE, Q86SM8 MRGPRF, Q96AM1 MRGPRG, Q86SM5

Endogenous agonists

– β-alanine (pEC50 4.8) [1729, 1785] – – –

Comments – An endogenous peptide with a high degree of sequence similarity to angiotensin-(1-7) (AGT, P01019), alamandine (AGT), was shown to promote NO release in MRGPRD-transfected cells. The binding of alamandine to MRGPRD to was shown to be blocked by D-Pro7-angiotensin-(1-7), β-alanine and PD123319 [1045]. Genetic ablation of MRGPRD+ neurons of adult mice decreased behavioural sensitivity to mechanical stimuli but not to thermal stimuli [278]. See reviews [396] and [1779].

See reviews [396] and [1779].

MRGPRF has been reported to respond to stimulation by angiotensin metabolites [589]. See reviews [396] and [1779].

See reviews [396] and [1779].

Nomenclature MRGPRX1 MRGPRX2 MRGPRX3 MRGPRX4

HGNC, UniProt MRGPRX1, Q96LB2 MRGPRX2, Q96LB1 MRGPRX3, Q96LB0 MRGPRX4, Q96LA9

Endogenous agonists

bovine adrenal medulla peptide 8-22 (PENK, P01210) (Selective) (pEC50 5.3–7.8) [299, 1080, 1785]

PAMP-20 (ADM, P35318) (Selective) [899] – –

Agonists – cortistatin-14 {Mouse, Rat} (pEC50 6.9–7.6) [899, 1594, 1785]

– –

Selective agonists – PAMP-12 (human) (pEC50 7.2–7.7) [899] – –

Comments Reported to mediate the sensation of itch [1131, 1739]. Reports that bovine adrenal medulla peptide 8-22 (PENK, P01210) was the most potent of a series of proenkephalin A-derived peptides as an agonist of MRGPRX1 in assays of calcium mobilisation and radioligand binding [1080] were replicated in an independent study using an arrestin recruitment assay [1785]. See reviews [396] and [1779].

A diverse range of substances has been reported to be agonists of MRGPRX2, with cortistatin 14 the highest potency agonist in assays of calcium mobilisation [1594], also confirmed in an independent study using an arrestin recruitment assay [1785]. See reviews [396] and [1779].

– See reviews [396] and [1779].

Searchable database: http://www.guidetopharmacology.org/index.jsp Class A Orphans 5754

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Nomenclature OPN3 OPN4 OPN5 P2RY8

HGNC, UniProt OPN3, Q9H1Y3 OPN4, Q9UHM6 OPN5, Q6U736 P2RY8, Q86VZ1

Comments – – Evidence indicates OPN5 triggers a UV-sensitive Gi-mediated signalling pathway in mammalian tissues [982].

–

Nomenclature P2RY10 TAAR2 TAAR3 TAAR4P

HGNC, UniProt P2RY10, O00398 TAAR2, Q9P1P5 TAAR3, Q9P1P4 TAAR4P, –

Rank order of potency

– β-phenylethylamine > tryptamine [185]

– –

Endogenous agonists

sphingosine 1-phosphate (Selective) (pEC50 7.3) [1344], LPA (Selective) (pEC50 6.9) [1344]

– – –

Comments – Probable pseudogene in 10-15% of Asians due to a polymorphism (rs8192646) producing a premature stop codon at amino acid 168 [396].

TAAR3 is thought to be a pseudogene in man though functional in rodents [396].

Pseudogene in man but functional in rodents [396].

Nomenclature TAAR5 TAAR6 TAAR8 TAAR9

HGNC, UniProt TAAR5, O14804 TAAR6, Q96RI8 TAAR8, Q969N4 TAAR9, Q96RI9

Comments Trimethylamine is reported as an agonist [1974] and 3-iodothyronamine an inverse agonist [426].

– – TAAR9 appears to be functional in most individuals but has a polymorphic premature stop codon at amino acid 61 (rs2842899) with an allele frequency of 10-30% in different populations [1944].

Searchable database: http://www.guidetopharmacology.org/index.jsp Class A Orphans 5755

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Class C Orphans G protein-coupled receptors ! Orphan and other 7TM receptors ! Class C Orphans

Nomenclature GPR156 GPR158 GPR179 GPRC5A GPRC5B GPRC5C GPRC5D

HGNC, UniProt GPR156, Q8NFN8 GPR158, Q5T848 GPR179, Q6PRD1 GPRC5A, Q8NFJ5 GPRC5B, Q9NZH0 GPRC5C, Q9NQ84 GPRC5D, Q9NZD1

Taste 1 receptors G protein-coupled receptors ! Orphan and other 7TM receptors ! Taste 1 receptors Overview: Whilst the taste of acid and salty foods appear to be sensed by regulation of ion channel activity, bitter, sweet and umami tastes are sensed by specialised GPCR. Two classes of taste GPCR have been identified, T1R and T2R, which are similar in sequence and structure to Class C and Class A GPCR, respectively. Activation

of taste receptors appears to involve gustducin- (Gαt3) and Gα14- mediated signalling, although the precise mechanisms remain ob- scure. Gene disruption studies suggest the involvement of PLCβ2 [2122], TRPM5 [2122] and IP3 [764] receptors in post-receptor sig- nalling of taste receptors. Although predominantly associated with

the oral cavity, taste receptors are also located elsewhere, includ- ing further down the gastrointestinal system, in the lungs and in the brain.

Sweet/Umami

T1R3 acts as an obligate partner in T1R1/T1R3 and T1R2/T1R3 heterodimers, which sense umami or sweet, respectively. T1R1/T1R3 heterodimers respond to L-glutamic acid and may be positively allosterically modulated by 5’-nucleoside monophosphates, such as 5’-GMP [1096]. T1R2/T1R3 heterodimers respond to sugars, such as sucrose, and artificial sweeteners, such as saccharin [1376].

Nomenclature TAS1R1 TAS1R2 TAS1R3

HGNC, UniProt TAS1R1, Q7RTX1 TAS1R2, Q8TE23 TAS1R3, Q7RTX0

Searchable database: http://www.guidetopharmacology.org/index.jsp Taste 1 receptors 5756

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Taste 2 receptors G protein-coupled receptors ! Orphan and other 7TM receptors ! Taste 2 receptors Bitter

The composition and stoichiometry of bitter taste receptors is not yet established. Bitter receptors appear to separate into two groups, with very restricted ligand specificity or much broader responsiveness. For example, T2R5 responded to cycloheximide, but not 10 other bitter compounds [287], while T2R14 responded to at least eight different bitter tastants, including (-)-α-thujone and picrotoxinin [119].

Specialist database BitterDB contains additional information on bitter compounds and receptors [2023].

Nomenclature TAS2R1 TAS2R3 TAS2R4 TAS2R5 TAS2R7 TAS2R8

HGNC, UniProt TAS2R1, Q9NYW7 TAS2R3, Q9NYW6 TAS2R4, Q9NYW5 TAS2R5, Q9NYW4 TAS2R7, Q9NYW3 TAS2R8, Q9NYW2

Nomenclature TAS2R9 TAS2R10 TAS2R13 TAS2R14 TAS2R16 TAS2R19

HGNC, UniProt TAS2R9, Q9NYW1 TAS2R10, Q9NYW0 TAS2R13, Q9NYV9 TAS2R14, Q9NYV8 TAS2R16, Q9NYV7 TAS2R19, P59542

Nomenclature TAS2R20 TAS2R30 TAS2R31 TAS2R38 TAS2R39 TAS2R40

HGNC, UniProt TAS2R20, P59543 TAS2R30, P59541 TAS2R31, P59538 TAS2R38, P59533 TAS2R39, P59534 TAS2R40, P59535

Nomenclature TAS2R41 TAS2R42 TAS2R43 TAS2R45 TAS2R46 TAS2R50 TAS2R60

HGNC, UniProt TAS2R41, P59536 TAS2R42, Q7RTR8 TAS2R43, P59537 TAS2R45, P59539 TAS2R46, P59540 TAS2R50, P59544 TAS2R60, P59551

Searchable database: http://www.guidetopharmacology.org/index.jsp Taste 2 receptors 5757

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Other 7TM proteins G protein-coupled receptors ! Orphan and other 7TM receptors ! Other 7TM proteins Nomenclature GPR107 GPR137 OR51E1 TPRA1 GPR143 GPR157

HGNC, UniProt GPR107, Q5VW38 GPR137, Q96N19 OR51E1, Q8TCB6 TPRA1, Q86W33 GPR143, P51810 GPR157, Q5UAW9

Endogenous agonists

– – – – levodopa [1141] –

Comments GPR107 is a member of the LUSTR family of proteins found in both plants and animals, having similar topology to Gprotein-coupled receptors [461]

– OR51E1 is a putative olfactory receptor.

TPRA1 shows no homology to known G protein-coupled receptors.

Loss-of-function mutations underlie ocular albinism type 1 [103].

GPR157 has ambiguous sequence similarities to several different GPCR families (class A, class B and the slime mould cyclic AMP receptor). Because of its distant relationship to other GPCRs, it cannot be readily classified.

Searchable database: http://www.guidetopharmacology.org/index.jsp Other 7TM proteins 5758

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5-Hydroxytryptamine receptors G protein-coupled receptors ! 5-Hydroxytryptamine receptors Overview: 5-HT receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on 5-HT receptors [789] and subsequently revised [707]) are, with the exception of the ionotropic 5-HT3 class, GPCR receptors where the endogenous ag- onist is 5-hydroxytryptamine. The diversity of metabotropic 5-HT

receptors is increased by alternative splicing that produces isoforms of the 5-HT2A (non-functional), 5-HT2C (non-functional), 5-HT4, 5-HT6 (non-functional) and 5-HT7 receptors. Unique amongst the GPCRs, RNA editing produces 5-HT2C receptor isoforms that differ in function, such as efficiency and specificity of coupling to Gq/11

and also pharmacology [164, 2011]. Most 5-HT receptors (except 5-ht 1e and 5-ht 5a/5b) play specific roles mediating functional re- sponses in different tissues (reviewed by [1554, 1957].

Nomenclature 5-HT1A receptor 5-HT1B receptor 5-HT1D receptor 5-ht1e receptor 5-HT1F receptor

HGNC, UniProt HTR1A, P08908 HTR1B, P28222 HTR1D, P28221 HTR1E, P28566 HTR1F, P30939

Agonists U92016A (pKi 9.7) [1240], vilazodone (Partial agonist) (pKi 9.7) [402], vortioxetine (Partial agonist) (pKi 7.8) [90]

L-694,247 (pKi 9.2) [637], naratriptan (Partial agonist) (pKi 8.1) [1365], eletriptan (pKi 8) [1365], frovatriptan (pKi 8) [2069], zolmitriptan (Partial agonist) (pKi 7.7) [1365], vortioxetine (Partial agonist) (pKi 7.5) [90], rizatriptan (Partial agonist) (pKi 6.9) [1365]

dihydroergotamine (pKi 9.2–9.9) [684, 1084, 1091], ergotamine (pKi 9.1) [616], L-694,247 (pKi 9) [2052], naratriptan (pKi 8.4–9) [432, 1365, 1577], zolmitriptan (pKi 8.9) [1365], frovatriptan (pKi 8.4) [2069], rizatriptan (pKi 7.9) [1365]

BRL-54443 (pKi 8.7) [227] BRL-54443 (pKi 8.9) [227], eletriptan (pKi 8) [1365], sumatriptan (pKi 7.2–7.9) [11, 12, 1365, 1968]

Selective agonists

8-OH-DPAT (pKi 8.4–9.4) [406, 685, 896, 1079, 1280, 1386, 1388, 1389], NLX-101 (pKi 8.6) [1387]

CP94253 (pKi 8.7) [976] PNU109291 (pKi 9.1) [483] – Gorilla, eletriptan (pKi 8.9) [1365]

– lasmiditan (pKi 8.7) [1375], LY334370 (pKi 8.7) [1968], 5-BODMT (pKi 8.4) [966], LY344864 (pKi 8.2) [1502]

Antagonists (S)-UH 301 (pKi 7.9) [1386] – – – –

Selective antagonists

WAY-100635 (pKi 7.9–9.2) [1386, 1388], robalzotan (pKi 9.2) [872]

SB 224289 (Inverse agonist) (pKi 8.2–8.6) [583, 1384, 1696], SB236057 (Inverse agonist) (pKi 8.2) [1272], GR-55562 (pKB 7.4) [791]

SB 714786 (pKi 9.1) [1987] – –

Searchable database: http://www.guidetopharmacology.org/index.jsp 5-Hydroxytryptamine receptors 5759

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(continued)

Nomenclature 5-HT1A receptor 5-HT1B receptor 5-HT1D receptor 5-ht1e receptor 5-HT1F receptor

Labelled ligands [3H]robalzotan (Antagonist) (pKd 9.8) [861],

[3H]WAY100635 (Antagonist) (pKd 9.5) [933],

[3H]8-OH-DPAT (Agonist) (pKd 6–9.4) [156, 896, 1385, 1388], [3H]NLX-112 (Agonist) (pKd 8.9) [748], [11C]WAY100635 (Antagonist) [1915], p-[18F]MPPF (Antagonist) [368]

[3H]N-methyl-AZ10419369 (Agonist, Partial agonist) (pKd 9.4) [1182], [3H]GR 125,743 (Selective Antagonist) (pKd 8.6–9.2) [637, 2061], [3H]alniditan (Agonist) (pKd 8.6–9) [1084], [125I]GTI (Agonist) (pKd 8.9) [193, 232]

– Rat, [3H]eletriptan (Agonist, Partial agonist) (pKd 8.5)

[1365], [3H]sumatriptan (Agonist, Partial agonist) (pKd 8) [1365], [11C]AZ10419369 (Agonist, Partial agonist) [1950]

[3H]eletriptan (Agonist) (pKd 9.1) [1365], [3H]alniditan (Agonist) (pKd 8.8–8.9)

[1084], [125I]GTI (Selective Agonist) (pKd 8.9) [193, 232] –

Rat, [3H]GR 125,743 (Selective Antagonist) (pKd 8.6) [2061],

[3H]sumatriptan (Agonist) (pKd 8.2) [1365]

[3H]5-HT (Agonist) (pKd 8.1–8.2) [1237, 1463]

[3H]LY334370 (Agonist) (pKd 9.4) [1968], [125I]LSD (Agonist) (pKd 9) [44] – Mouse

Comments – Wang et al. (2013) report X-ray structures which reveal the binding modality of ergotamine and dihydroergotamine to the 5-HT1B receptor in comparison with the structure of the 5-HT2B receptor [1978].

– – –

Searchable database: http://www.guidetopharmacology.org/index.jsp 5-Hydroxytryptamine receptors 5760

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Nomenclature 5-HT2A receptor 5-HT2B receptor 5-HT2C receptor 5-HT4 receptor

HGNC, UniProt HTR2A, P28223 HTR2B, P41595 HTR2C, P28335 HTR4, Q13639

Agonists DOI (pKi 7.4–9.2) [204, 1374, 1755] methysergide (Partial agonist) (pKi 8–9.4) [970, 1605, 1969], DOI (pKi 7.6–7.7) [1025, 1374, 1659]

DOI (pKi 7.2–8.6) [465, 1374, 1659], Ro 60-0175 (pKi 7.7–8.2) [953, 970]

cisapride (Partial agonist) (pKi 6.4–7.4) [77, 128, 597, 1266, 1267, 1941]

Selective agonists – BW723C86 (pKi 7.3–8.6) [108, 970, 1659], Ro 60-0175 (pKi 8.3) [970]

WAY-163909 (pKi 6.7–8) [454], lorcaserin (pKi 7.8) [1878]

TD-8954 (pKi 9.4) [1250], ML 10302 (Partial agonist) (pKi 7.9–9) [136, 160, 1266, 1267, 1268], RS67506 (pEC50 8.8) [731] – Rat, relenopride (Partial agonist) (pKi 8.3) [607], velusetrag (pKi 7.7) [1139, 1763], BIMU 8 (pKi 7.3) [347]

Antagonists risperidone (Inverse agonist) (pKi 9.3–10) [986, 1008, 1675], mianserin (pKi 7.7–9.6) [970, 1001, 1280], ziprasidone (pKi 8.8–9.5) [986, 1008, 1675, 1711], volinanserin (pIC50 6.5–9.3) [970, 1142, 1568], blonanserin (pKi 9.1) [1421], clozapine (Inverse agonist) (pKi 7.6–9) [970, 1008, 1277, 1675, 1943], olanzapine (pKi 8.6–8.9) [986, 1008, 1675, 1711], nefazodone (pKi 8.2) [1698], chlorpromazine (Inverse agonist) (pKi 8.1) [1008], loxapine (Inverse agonist) (pKi 8.1) [1008], trifluoperazine (pKi 7.9) [1008], pimozide (pKi 7.1–7.7) [986, 1008], trazodone (pKi 7.4) [970], haloperidol (pKi 6.7–7.3) [1008, 1277, 1675, 1711, 1943], mesoridazine (pKi 7.3) [326], mirtazapine (pKi 7.2) [513], mirtazapine (pKi 7.2) [513], quetiapine (pKi 6.4–7) [986, 1008], molindone (pKi 6.5) [1008]

mianserin (pKi 7.9–8.8) [180, 970, 1969]

mianserin (Inverse agonist) (pKi 8.3–9.2) [524, 970, 1280], methysergide (pKi 8.6–9.1) [465, 970], ziprasidone (Inverse agonist) (pKi 7.9–9) [743, 1008, 1711], olanzapine (Inverse agonist) (pKi 8.1–8.4) [743, 1008, 1711], loxapine (Inverse agonist) (pKi 7.8–8) [743, 1008], mirtazapine (pKi 7.4) [513], mirtazapine (pKi 7.4) [513], trazodone (pKi 6.6) [970], trifluoperazine (pKi 6.4) [1008], agomelatine (pKi 6.2) [1276]

–

Searchable database: http://www.guidetopharmacology.org/index.jsp 5-Hydroxytryptamine receptors 5761

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(continued)

Nomenclature 5-HT2A receptor 5-HT2B receptor 5-HT2C receptor 5-HT4 receptor

Selective antagonists

ketanserin (pKi 8.1–9.7) [234, 970, 1559], pimavanserin (Inverse agonist) (pKi 9.3) [572, 1943]

BF-1 (pKi 10.1) [1671], RS-127445 (pKi 9–9.5) [180, 970], EGIS-7625 (pKi 9) [1001]

FR260010 (pKi 9) [700], SB 242084 (pKi 8.2–9) [928, 970], RS-102221 (pKi 8.3–8.4) [181, 970]

RS 100235 (pKi 8.7–12.2) [347, 1589], SB 204070 (pKi 9.8–10.4) [128, 1266, 1267, 1941], GR 113808 (pKi 9.3–10.3) [77, 128, 160, 347, 1267, 1589, 1941]

Labelled ligands [3H]fananserin (Antagonist) (pKd 9.9)

[1188] – Rat, [3H]ketanserin (Antagonist) (pKd 8.6–9.7) [970,

1559], [11C]volinanserin (Antagonist) [676], [18F]altanserin (Antagonist) [1601]

[3H]LSD (Agonist) (pKd 8.7) [1559],

[3H]5-HT (Agonist) (pKd 8.1) [1967]

– Rat, [3H]mesulergine (Antagonist, Inverse agonist) (pKd 7.9) [970],

[125I]DOI (Agonist) (pKd 7.7–7.6)

[125I]DOI (Agonist) (pKd 8.7–9)

[524], [3H]mesulergine (Antagonist, Inverse agonist) (pKd 9.3–8.7) [524,

1559], [3H]LSD (Agonist)

[123I]SB 207710 (Antagonist) (pKd 10.1) [228] – Pig, [3H]GR 113808 (Antagonist) (pKd 10.3–9.7) [77, 128,

1268, 1941], [3H]RS 57639 (Selective Antagonist) (pKd 9.7) [179] – Guinea

pig, [11C]SB207145 (Antagonist) (pKd 8.6) [1169]

Comments – LSD (lysergic acid) and ergotamine show a strong preference for arrestin recruitment over G protein coupling at the 5-HT2B receptor, with no such preference evident at 5-HT1B receptors, and they also antagonise 5-HT7A receptors [1963]. DHE (dihydroergocryptine), pergolide and cabergoline also show significant preference for arrestin recruitment over G protein coupling at 5-HT2B receptors [1963].

The serotonin antagonist mesulergine was key to the discovery of the 5-HT2C receptor [1479].

–

Nomenclature 5-ht5a receptor 5-ht5b receptor 5-HT6 receptor 5-HT7 receptor

HGNC, UniProt HTR5A, P47898 HTR5BP, – HTR6, P50406 HTR7, P34969

Selective agonists – – WAY-181187 (pKi 8.7) [1663], E6801 (Partial agonist) (pKi 8.7) [769], WAY-208466 (pKi 8.3) [135], EMD-386088 (pIC50 8.1) [1228]

LP-12 (pKi 9.9) [1082], LP-44 (pKi 9.7) [1082], LP-211 (pKi 9.2) [1083] – Rat, AS-19 (pKi 9.2) [947], E55888 (pKi 8.6) [206]

Searchable database: http://www.guidetopharmacology.org/index.jsp 5-Hydroxytryptamine receptors 5762

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(continued)

Nomenclature 5-ht5a receptor 5-ht5b receptor 5-HT6 receptor 5-HT7 receptor

Antagonists – – – lurasidone (pKi 9.3) [829], pimozide (pKi 9.3) [1604] – Rat, vortioxetine (pKi 6.3) [90]

Selective antagonists

SB 699551 (pKi 8.2) [366] – SB399885 (pKi 9) [763], SB 271046 (pKi 8.9) [224], cerlapirdine (pKi 8.9) [358], SB357134 (pKi 8.5) [225], Ro 63-0563 (pKi 7.9–8.4) [168, 1754]

SB269970 (pKi 8.6–8.9) [1874], SB656104 (pKi 8.7) [531], DR-4004 (pKi 8.7) [615, 938], JNJ-18038683 (pKi 8.2) [177], SB 258719 (Inverse agonist) (pKi 7.5) [1875]

Labelled ligands [125I]LSD (Agonist) (pKd 9.7) [636],

[3H]5-CT (Agonist) (pKd 8.6) [636]

[125I]LSD (Agonist) (pKd 9.3) [1227]

– Mouse, [3H]5-CT (Agonist) [1965] – Mouse

[11C]GSK215083 (Antagonist) (pKi 9.8)

[1462], [125I]SB258585 (Selective Antagonist) (pKd 9) [763], [

3H]LSD (Agonist) (pKd 8.7) [167],

[3H]Ro 63-0563 (Antagonist) (pKd 8.3)

[168], [3H]5-CT (Agonist)

[3H]5-CT (Agonist) (pKd 9.4) [1874],

[3H]5-HT (Agonist) (pKd 8.1–9) [93,

1793], [3H]SB269970 (Selective Antagonist) (pKd 8.9) [1874], [

3H]LSD (Agonist) (pKd 8.5–8.6) [1793]

Comments: Tabulated pKi and KD values refer to binding to hu- man 5-HT receptors unless indicated otherwise. The nomenclature of 5-HT1B/5-HT1D receptors has been revised [707]. Only the non- rodent form of the receptor was previously called 5-HT1D: the hu- man 5-HT1B receptor (tabulated) displays a different pharmacology to the rodent forms of the receptor due to Thr335 of the human

sequence being replaced by Asn in rodent receptors. NAS181 is a selective antagonist of the rodent 5-HT1B receptor. Fananserin and ketanserin bind with high affinity to dopamine D4 and histamine H1 receptors respectively, and ketanserin is a potent α1 adrenoceptor antagonist, in addition to blocking 5-HT2A receptors. The human 5- ht5A receptor has been claimed to couple to several signal transduc- tion pathways when stably expressed in C6 glioma cells [1404]. The

human orthologue of the mouse 5-ht5b receptor is non-functional due to interruption of the gene by stop codons. The 5-ht1e receptor appears not to have been cloned from mouse, or rat, impeding def- inition of its function. In addition to the receptors listed in the table, an ’orphan’ receptor, unofficially termed 5-HT1P, has been described [600].

Further Reading

Bockaert J et al. (2011) 5-HT(4) receptors, a place in the sun: act two. Curr Opin Pharmacol 11: 87-93 [PMID:21342787]

Codony X et al. (2011) 5-HT(6) receptor and cognition. Curr Opin Pharmacol 11: 94-100 [PMID:21330210]

Hartig PR et al. (1996) Alignment of receptor nomenclature with the human genome: classification of 5-HT1B and 5-HT1D receptor subtypes. Trends Pharmacol. Sci. 17: 103-5 [PMID:8936345]

Hayes DJ et al. (2011) 5-HT receptors and reward-related behaviour: a review. Neurosci Biobehav Rev 35: 1419-49 [PMID:21402098]

Hoyer D et al. (1994) International Union of Pharmacology classification of receptors for 5- hydroxytryptamine (Serotonin). Pharmacol. Rev. 46: 157-203 [PMID:7938165]

Leopoldo M et al. (2011) Serotonin 5-HT7 receptor agents: Structure-activity relationships and poten- tial therapeutic applications in central nervous system disorders. Pharmacol. Ther. 129: 120-48 [PMID:20923682]

Meltzer HY et al. (2011) The role of serotonin receptors in the action of atypical antipsychotic drugs. Curr Opin Pharmacol 11: 59-67 [PMID:21420906]

Roberts AJ et al. (2012) The 5-HT(7) receptor in learning and memory. Hippocampus 22: 762-71 [PMID:21484935]

Sargent BJ et al. (2011) Targeting 5-HT receptors for the treatment of obesity. Curr Opin Pharmacol 11: 52-8 [PMID:21330209]

Searchable database: http://www.guidetopharmacology.org/index.jsp 5-Hydroxytryptamine receptors 5763

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Acetylcholine receptors (muscarinic) G protein-coupled receptors ! Acetylcholine receptors (muscarinic) Overview: Muscarinic acetylcholine receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Mus- carinic Acetylcholine Receptors [275]) are GPCRs of the Class A, 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, N-desmethylclozapine, TBPB and LuAE51090 have been described as functionally selective agonists of the M1 receptor subtype via bind- ing in a mode distinct from that utilized by non-selective agonists [71, 878, 1040, 1041, 1232, 1635, 1786, 1787, 1825]. There are

two pharmacologically characterised allosteric sites on muscarinic re- ceptors, one defined by it binding gallamine, strychnine and brucine, and the other defined by the binding of KT 5720, WIN 62,577, WIN 51,708 and staurosporine [1052, 1053].

Nomenclature M1 receptor M2 receptor

HGNC, UniProt CHRM1, P11229 CHRM2, P08172

Agonists carbachol (pKi 3.2–5.3) [334, 846, 2040], pilocarpine (Partial agonist) (pKi 5.1) [846], bethanechol (pKi 4) [846]

bethanechol (pKi 4) [846]

Antagonists glycopyrrolate (pIC50 9.9) [1801], umeclidinium (pKi 9.8) [1035, 1632], AE9C90CB (pKi 9.7) [1749], propantheline (pKi 9.7) [797], atropine (pKi 8.5–9.6) [334, 552, 759, 797, 1486, 1762], tiotropium (pKi 9.6) [428], 4-DAMP (pKi 9.2) [458], dicyclomine (pKi 9.1) [68], scopolamine (pKi 9) [797], trihexyphenidyl (pKi 8.9) [68], tripitramine (pKi 8.8) [1176], UH-AH 37 (pKi 8.6–8.7) [609, 2012], tolterodine (pKi 8.5–8.7) [609, 1749], oxybutynin (pKi 8.6) [410, 818, 1749], darifenacin (pKi 7.5–8.3) [609, 730, 759, 818, 1749], pirenzepine (pKi 7.8–8.3) [238, 458, 730, 797, 875, 2012], solifenacin (pKi 7.6) [818, 1749], AFDX384 (pKi 7.5) [458], AQ-RA 741 (pKi 7.2–7.5) [458, 609], methoctramine (pKi 6.6–7.3) [458, 493, 730, 1762], himbacine (pKi 6.7–7.1) [458, 875, 1286], muscarinic toxin 3 (pKi 7.1) [875], otenzepad (pKd 6.2) [493]

tiotropium (pKi 9.9) [428], umeclidinium (pKi 9.8) [1035, 1632], propantheline (pKi 9.5) [797], glycopyrrolate (Full agonist) (pIC50 9.3) [1801], atropine (pKi 7.8–9.2) [238, 310, 759, 797, 1002, 1373, 1486], AE9C90CB (pKi 8.6) [1749], tolterodine (Inverse agonist) (pKi 8.4–8.6) [609, 1373, 1749], AQ-RA 741 (pKi 8.4) [458, 609], himbacine (pKi 7.9–8.4) [458, 875, 1002, 1286], methoctramine (pKi 7.3–8.4) [238, 458, 493, 730, 1002, 1373], 4-DAMP (pKi 8.3) [1002], AFDX384 (pKi 8.2) [458], biperiden (pKd 8.2) [173], oxybutynin (pKi 7.7–8.1) [818, 1749], darifenacin (Inverse agonist) (pKi 7–7.6) [609, 730, 759, 818, 1373, 1749], UH-AH 37 (pKi 7.3–7.4) [609, 2012], otenzepad (pKi 6.7–7.2) [238, 1002], solifenacin (pKi 6.9–7.1) [818, 1749], pirenzepine (pKi 6–6.7) [238, 458, 730, 797, 875, 1002, 1373, 2012], VU0255035 (pKi 6.2) [1717], muscarinic toxin 3 (pKi <6) [875], guanylpirenzepine (pKi 5.3) [1966] – Rat, muscarinic toxin 7 (pKi <5) [1414]

Selective antagonists

biperiden (pKd 9.3) [173], VU0255035 (pKi 7.8) [1717], guanylpirenzepine (pKi 7.3–7.6) [23, 1966] – Rat

tripitramine (pKi 9.6) [1176]

Allosteric modulators

muscarinic toxin 7 (Negative) (pKi 11–11.1) [1414], benzoquinazolinone 12 (Positive) (pKB 6.6) [4], KT 5720 (Positive) (pKd 6.4) [1052], brucine (Positive) (pKd 4.5–5.8) [846, 1051], BQCA (Positive) (pKB 4–4.8) [4, 5, 261, 1161], VU0029767 (Positive) [1208], VU0090157 (Positive) [1208]

W-84 (Negative) (pKd 6–7.5) [1299, 1908], C7/3-phth (Negative) (pKd 7.1) [335], alcuronium (Negative) (pKd 6.1–6.9) [846, 1908], gallamine (Negative) (pKd 5.9–6.3) [348, 1049], LY2119620 (Positive) (pKd 5.7) [383, 1010], LY2033298 (Positive) (pKd 4.4) [1933]

Labelled ligands [3H]QNB (Antagonist) (pKd 10.6–10.8) [336, 1486], Cy3B-telenzepine (Antagonist)

(pKd 10.5) [742], [ 3H]N-methyl scopolamine (Antagonist) (pKd 9.4–10.3) [280, 334,

336, 759, 846, 847, 875, 932, 1049], [3H](+)telenzepine (Antagonist) (pKi 9.4) [500] – Rat, Alexa-488-telenzepine (Antagonist) (pKd 9.3) [742], [

3H]pirenzepine (Antagonist)

(pKd 7.9) [1995], BODIPY-pirenzepine (Antagonist) (pKi 7) [820], [ 11C]butylthio-TZTP

(Agonist) [504], [11C]xanomeline (Agonist) [504], [18F](R,R)-quinuclidinyl-4-fluoromethyl-benzilate (Antagonist) [935] – Rat

[3H]QNB (Antagonist) (pKd 10.1–10.6) [1486], Cy3B-telenzepine (Antagonist) (pKi 10.4) [1380], [3H]tiotropium (Antagonist) (pKd 10.3) [1632],

[3H]N-methyl scopolamine (Antagonist) (pKd 9.3–9.9) [280, 310, 759, 846, 847, 875, 932, 1049, 1985], Alexa-488-telenzepine (Antagonist) (pKi 8.8) [1380],

[3H]acetylcholine (Agonist) (pKd 8.8) [1050], [ 3H]oxotremorine-M (Agonist) (pKd 8.7)

[137], [3H]dimethyl-W84 (Allosteric modulator, Positive) (pKd 8.5) [1908], [ 18F]FP-TZTP

(Agonist) [845] – Mouse

Searchable database: http://www.guidetopharmacology.org/index.jsp Acetylcholine receptors (muscarinic) 5764

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Nomenclature M3 receptor M4 receptor M5 receptor

HGNC, UniProt CHRM3, P20309 CHRM4, P08173 CHRM5, P08912

Agonists pilocarpine (Partial agonist) (pKi 5.1) [846], carbachol (pKi 4–4.4) [310, 846, 2040], bethanechol (pKi 4.2) [846]

pilocarpine (Partial agonist) (pKi 5.2) [846], carbachol (pKi 4.3–4.9) [846, 2040], bethanechol (pKi 4) [846]

pilocarpine (Partial agonist) (pKi 5) [639], carbachol (pKi 4.9) [2040]

Antagonists tiotropium (pKi 9.5–11.1) [428, 442], umeclidinium (pKi 10.2) [1035, 1632], propantheline (pKi 10) [797], AE9C90CB (pKi 9.9) [1749], atropine (pKi 8.9–9.8) [238, 442, 759, 797, 1486, 1762], ipratropium (pKi 9.3–9.8) [442, 759], aclidinium (pIC50 9.8) [1530], clidinium (pKi 9.6) [442], glycopyrrolate (pIC50 9.6) [1801], 4-DAMP (pKi 9.3) [458], darifenacin (pKi 8.6–9.1) [609, 730, 759, 818, 1749], dicyclomine (pKi 9) [68], oxybutynin (pKi 8.8–8.9) [410, 818, 1749], tolterodine (pKi 8.4–8.5) [609, 1749], biperiden (pKd 8.4) [173], UH-AH 37 (pKi 8.1–8.2) [609, 2012], solifenacin (pKi 7.7–8) [818, 1749], tropicamide (pKi 7.5) [68], AQ-RA 741 (pKi 7.2–7.3) [458, 609], AFDX384 (pKi 7.2) [458], himbacine (pKi 6.9–7.2) [458, 875, 1286], methoctramine (pKi 6.1–6.9) [238, 458, 493, 730, 1762], tripitramine (pKi 6.8) [1288], pirenzepine (pKi 6.5–6.8) [238, 458, 730, 797, 875, 2012], guanylpirenzepine (pKi 6.2) [1966] – Rat, VU0255035 (pKi 6.1) [1717], otenzepad (pKi 6.1) [238], muscarinic toxin 3 (pKi <6) [875], muscarinic toxin 7 (pKi <5) [1414]

umeclidinium (pKi 10.3) [1632], glycopyrrolate (pIC50 9.8) [1801], AE9C90CB (pKi 9.5) [1749], 4-DAMP (pKi 8.9) [458], oxybutynin (pKi 8.7) [1749], biperiden (pKd 8.6) [173], UH-AH 37 (pKi 8.3–8.4) [609, 2012], tolterodine (pKi 8.3–8.4) [609, 1749], AQ-RA 741 (pKi 7.8–8.2) [458, 609], himbacine (pKi 7.9–8.2) [458, 875, 1286], darifenacin (pKi 7.3–8.1) [609, 730, 759, 1749], AFDX384 (pKi 8) [458], tripitramine (pKi 7.9) [1288], pirenzepine (pKi 7–7.6) [458, 730, 797, 875, 2012], methoctramine (pKi 6.6–7.5) [238, 458, 493, 730], otenzepad (pKd 7) [493], solifenacin (pKi 6.8) [1749], guanylpirenzepine (pKi 6.2) [1966] – Rat, VU0255035 (pKi 5.9) [1717], muscarinic toxin 7 (pKi<5) [1414]

umeclidinium (pKi 9.9) [1632], glycopyrrolate (pIC50 9.7) [1801], AE9C90CB (pKi 9.5) [1749], 4-DAMP (pKi 9) [458], tolterodine (pKi 8.5–8.8) [609, 1749], darifenacin (pKi 7.9–8.6) [609, 730, 759, 1749], UH-AH 37 (pKi 8.3) [609, 2012], biperiden (pKd 8.2) [173], oxybutynin (pKi 7.9) [1749], AQ-RA 741 (pKi 6.1–7.8) [458, 609], tripitramine (pKi 7.5) [1176], methoctramine (pKi 6.3–7.2) [238, 458, 493, 730], solifenacin (pKi 7.2) [1749], pirenzepine (pKi 6.8–7.1) [730, 875, 2012], guanylpirenzepine (pKd 6.8) [514] – Unknown, himbacine (pKi 5.4–6.5) [458, 875, 1286], AFDX384 (pKi 6.3) [458], muscarinic toxin 3 (pKi <6) [875], otenzepad (pKi 5.6) [238], muscarinic toxin 7 (pKi <5) [1414]

Selective antagonists

– – ML381 (pKi 6.3) [593]

Allosteric modulators

WIN 62,577 (Positive) (pKd 5.1) [1053], N-chloromethyl-brucine (Positive) (pKd 3.3) [1051]

muscarinic toxin 3 (Negative) (pKi 8.7) [875, 1444], LY2119620 (Positive) (pKd 5.7) [383], thiochrome (Positive) (pKd 4) [1050], LY2033298 (Positive) [286], VU0152099 (Positive) [201], VU0152100 (Positive) [201]

ML380 (Positive) (pEC50 6.7) [595]

Selective allosteric modulators

– – ML375 (Negative) (pIC50 6.5) [594]

Labelled ligands [3H]tiotropium (Antagonist) (pKd 10.7) [1632],

[3H]QNB (Antagonist) (pKd 10.4) [1486],

[3H]N-methyl scopolamine (Antagonist) (pKd 9.7–10.2) [280, 310, 759, 797, 846, 875, 932, 1049], [3H]darifenacin (Antagonist) (pKd 9.5) [1762]

[3H]QNB (Antagonist) (pKd 9.7–10.5) [336, 1486],

[3H]N-methyl scopolamine (Antagonist) (pKd 9.9–10.2) [280, 310, 336, 759, 846, 875, 932, 1049, 1444, 1985], [3H]acetylcholine (Agonist) (pKd 8.2) [1050]

[3H]QNB (Antagonist) (pKd 10.2–10.7),

[3H]N-methyl scopolamine (Antagonist) (pKd 9.3–9.7) [280, 310, 759, 875, 932, 1985]

Searchable database: http://www.guidetopharmacology.org/index.jsp Acetylcholine receptors (muscarinic) 5765

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Comments: LY2033298 and BQCA have also been shown to di- rectly activate the M4 and M1 receptors, respectively, via an al- losteric site [1059, 1060, 1366, 1367]. The allosteric site for gallamine and strychnine on M2 receptors can be labelled by

[3H]dimethyl-W84 [1908]. 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 recep-

tor [1934]. THRX160209, hybrid 1 and hybrid 2, are multivalent (bitopic) ligands that also achieve selectivity for M2 receptors by binding both to the orthosteric and a nearby allosteric site [52, 1796].

Although numerous ligands for muscarinic acetylcholine receptors have been described, relatively few selective antagonists have been described, so it is common to assess the rank order of affinity

of a number of antagonists of limited selectivity (e.g. 4-DAMP, darifenacin, pirenzepine) in order to identify the involvement of par- ticular subtypes. It should be noted that the measured affinities of antagonists (and agonists) in radioligand binding studies are sensitive to ionic strength and can increase over 10-fold at low ionic strength compared to its value at physiological ionic strengths [151].

Further Reading

Caulfield MP et al. (1998) International Union of Pharmacology. XVII. Classification of muscarinic acetyl- choline receptors. Pharmacol. Rev. 50: 279-290 [PMID:9647869]

Eglen RM. (2012) Overview of muscarinic receptor subtypes. Handb Exp Pharmacol 3-28 [PMID:22222692]

Gregory KJ et al. (2007) Allosteric modulation of muscarinic acetylcholine receptors. Curr Neuropharmacol 5: 157-67 [PMID:19305798]

Kruse AC et al. (2014) Muscarinic acetylcholine receptors: novel opportunities for drug development. Nat Rev Drug Discov 13: 549-60 [PMID:24903776]

Leach K et al. (2012) Structure-function studies of muscarinic acetylcholine receptors. Handb Exp Phar- macol 29-48 [PMID:22222693]

Valant C et al. (2012) The best of both worlds? Bitopic orthosteric/allosteric ligands of g protein-coupled receptors. Annu. Rev. Pharmacol. Toxicol. 52: 153-78 [PMID:21910627]

Adenosine receptors G protein-coupled receptors ! Adenosine receptors Overview: Adenosine receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Adenosine Receptors [541]) are activated by the endogenous ligand adenosine (potentially inosine also at A3 receptors). Crystal structures for the antagonist-bound and agonist-bound A2A adenosine receptors have been described [835, 2065].

Searchable database: http://www.guidetopharmacology.org/index.jsp Adenosine receptors 5766

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Nomenclature A1 receptor A2A receptor A2B receptor A3 receptor

HGNC, UniProt ADORA1, P30542 ADORA2A, P29274 ADORA2B, P29275 ADORA3, P0DMS8

Agonists cyclopentyladenosine (pKi 6.5–9.4) [388, 570, 736, 839, 870, 1592, 2141]

– – –

(Sub)family- selective agonists

NECA (pKi 5.3–8.2) [570, 870, 1592, 1903, 2077]

NECA (pKi 6.9–8.7) [189, 427, 570, 943, 1021, 2077]

NECA (pKi 5.7–6.9) [146, 189, 862, 1113, 1798, 1945, 2077]

NECA (pKi 7.5–8.4) [189, 570, 840, 1634, 1946, 2077]

Selective agonists 5-Cl-5-deoxy-(�)-ENBA (pKi 9.3) [536], GR79236 (pKi 8.5) [839] – Rat, CCPA (pKi 7.7–8.1) [839, 1419]

apadenoson (pKi 9.3) [1481], UK-432,097 (pKi 8.3) [2065], CGS 21680 (pKi 6.7–8.1) [189, 427, 570, 839, 943, 968, 1021, 1419], regadenoson (pKi 6.5) [839]

BAY 60-6583 (pKi 8–8.5) [460] IB-MECA (pKi 8.7–9.2) [511, 561, 968, 1946], Cl-IB-MECA (pKi 8–8.9) [202, 840, 941], MRS5698 (pKi 8.5) [1898]

Antagonists caffeine (pKi 4.3–5) [6, 409, 838] SCH 58261 (pKi 8.3–9.2) [427, 1021, 1445], theophylline (pKi 5.2–5.8) [427, 838, 968, 1945], caffeine (pKi 4.6–5.6) [6, 838, 1021]

theophylline (pKi 4.1–5) [141, 511, 944, 1945], caffeine (pKi 4.5–5) [141, 188, 944]

caffeine (pKi 4.9) [838]

(Sub)family- selective antagonists

CGS 15943 (pKi 8.5) [1445], xanthine amine congener (pKd 7.5) [536]

CGS 15943 (pKi 7.7–9.4) [427, 943, 968, 1445], xanthine amine congener (pKi 8.4–9) [427, 968]

xanthine amine congener (pKi 6.9–8.8) [146, 862, 863, 968, 1113, 1798], CGS 15943 (pKi 6–8.1) [65, 862, 863, 968, 1445, 1798]

CGS 15943 (pKi 7–7.9) [949, 968, 1445, 1946], xanthine amine congener (pKi 7–7.4) [968, 1634, 1946]

Selective antagonists

PSB36 (pKi 9.9) [6] – Rat, DPCPX (pKi 7.4–9.2) [826, 1419, 1592, 2015, 2141], derenofylline (pKi 9) [897], WRC-0571 (pKi 8.8) [1210]

SCH442416 (pKi 8.4–10.3) [1728, 1891], ZM-241385 (pKi 8.8–9.1) [1445]

PSB-0788 (pKi 9.4) [188], PSB603 (pKi 9.3) [188], MRS1754 (pKi 8.8) [862, 948], PSB1115 (pKi 7.3) [723]

MRS1220 (pKi 8.2–9.2) [840, 949, 1818, 2090], VUF5574 (pKi 8.4) [2143], MRS1523 (pKi 7.7) [1092], MRS1191 (pKi 7.5) [840, 866, 1097]

Labelled ligands [3H]CCPA (Agonist) (pKd 9.2) [968,

1592], [3H]DPCPX (Antagonist) (pKd 8.4–9.2) [388, 511, 968, 1445, 1592, 1903]

[3H]ZM 241385 (Antagonist) (pKd 8.7–9.1) [36, 569], [3H]CGS 21680 (Agonist) (pKd 7.7–7.8) [852, 1976]

[3H]MRS1754 (Antagonist) (pKd 8.8) [862]

[125I]AB-MECA (Agonist) (pKd 9–9.1) [1445, 1946]

Comments: Adenosine inhibits many intracellular ATP-utilising en- zymes, including adenylyl cyclase (P-site). A pseudogene exists for the A2B adenosine receptor (ADORA2BP1) with 79% identity to the A2B adenosine receptor cDNA coding sequence, but which is unable to encode a functional receptor [841]. DPCPX also exhibits antago- nism at A2B receptors (pKi ca. 7,[34, 968]). Antagonists at A3 recep-

tors exhibit marked species differences, such that only MRS1523 and MRS1191 are selective at the rat A3 receptor. In the absence of other

adenosine receptors, [3H]DPCPX and [3H]ZM 241385 can also be used to label A2B receptors (KD ca. 30 and 60 nM respectively).

[125I]AB-MECA also binds to A1 receptors [968]. [ 3H]CGS 21680 is

relatively selective for A2A receptors, but may also bind to other sites

in cerebral cortex [384, 871]. [3H]NECA binds to other non-receptor elements, which also recognise adenosine [1143]. XAC-BY630 has been described as a fluorescent antagonist for labelling A1 adeno- sine receptors in living cells, although activity at other adenosine re- ceptors was not examined [212].

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Further Reading

Fredholm BB et al. (2011) International Union of Basic and Clinical Pharmacology. LXXXI. Nomenclature and classification of adenosine receptors–an update. Pharmacol. Rev. 63: 1-34 [PMID:21303899]

Göblyös A et al. (2011) Allosteric modulation of adenosine receptors. Biochim. Biophys. Acta 1808: 1309-18 [PMID:20599682]

Headrick JP et al. (2011) Adenosine and its receptors in the heart: regulation, retaliation and adaptation. Biochim. Biophys. Acta 1808: 1413-28 [PMID:21094127]

Lasley RD. (2011) Adenosine receptors and membrane microdomains. Biochim. Biophys. Acta 1808: 1284-9 [PMID:20888790]

Mundell S et al. (2011) Adenosine receptor desensitization and trafficking. Biochim. Biophys. Acta 1808: 1319-28 [PMID:20550943]

Ponnoth DS et al. (2011) Adenosine receptors and vascular inflammation. Biochim. Biophys. Acta 1808: 1429-34 [PMID:20832387]

Wei CJ et al. (2011) Normal and abnormal functions of adenosine receptors in the central nervous system revealed by genetic knockout studies. Biochim. Biophys. Acta 1808: 1358-79 [PMID:21185258]

Adhesion Class GPCRs G protein-coupled receptors ! Adhesion Class GPCRs Overview: Adhesion GPCRs are structurally identified on the basis of a large extracellular region, similar to the Class B GPCR, but which is linked to the 7TM region by a "stalk" motif containing a GPCR proteolytic site. The N-terminus often shares structural homology with proteins such as lectins and immunoglobulins, leading to the term adhesion GPCR [543, 2097]. The nomenclature of these receptors was revised in 2015 as recommended by NC-IUPHAR and the Adhesion GPCR Consortium [683].

Nomenclature ADGRA1 ADGRA2 ADGRA3 ADGRB1 ADGRB2

HGNC, UniProt ADGRA1, Q86SQ6 ADGRA2, Q96PE1 ADGRA3, Q8IWK6 ADGRB1, O14514 ADGRB2, O60241

Endogenous agonists – – – phosphatidylserine [1461] –

Comments – – – ADGRB1 is reported to respond to phosphatidylserine [1461].

–

Nomenclature ADGRB3 CELSR1 CELSR2 CELSR3 ADGRD1

HGNC, UniProt ADGRB3, O60242 CELSR1, Q9NYQ6 CELSR2, Q9HCU4 CELSR3, Q9NYQ7 ADGRD1, Q6QNK2

Nomenclature ADGRD2 ADGRE1 ADGRE2 ADGRE3 ADGRE4P

HGNC, UniProt ADGRD2, Q7Z7M1 ADGRE1, Q14246 ADGRE2, Q9UHX3 ADGRE3, Q9BY15 ADGRE4P, Q86SQ3

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Nomenclature ADGRE5 ADGRF1 ADGRF2 ADGRF3 ADGRF4

HGNC, UniProt ADGRE5, P48960 ADGRF1, Q5T601 ADGRF2, Q8IZF7 ADGRF3, Q8IZF5 ADGRF4, Q8IZF3

Nomenclature ADGRF5 ADGRG1 ADGRG2 ADGRG3 ADGRG4

HGNC, UniProt ADGRF5, Q8IZF2 ADGRG1, Q9Y653 ADGRG2, Q8IZP9 ADGRG3, Q86Y34 ADGRG4, Q8IZF6

Comments – Reported to bind tissue transglutaminase 2 [2066] and collagen, which activates the G12/13 pathway [1155].

– – –

Nomenclature ADGRG5 ADGRG6 ADGRG7 ADGRL1

HGNC, UniProt ADGRG5, Q8IZF4 ADGRG6, Q86SQ4 ADGRG7, Q96K78 ADGRL1, O94910

Nomenclature ADGRL2 ADGRL3 ADGRL4 ADGRV1

HGNC, UniProt ADGRL2, O95490 ADGRL3, Q9HAR2 ADGRL4, Q9HBW9 ADGRV1, Q8WXG9

Comments – – – Loss-of-function mutations are associated with Usher syndrome, a sensory deficit disorder [843].

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Adrenoceptors G protein-coupled receptors ! Adrenoceptors Overview:

Adrenoceptors, α1

α1-Adrenoceptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Adrenoceptors [248],

see also [752]) are activated by the endogenous ago- nists (-)-adrenaline and (-)-noradrenaline with equal potency. Phenylephrine, methoxamine and cirazoline are agonists selec- tive for α1-adrenoceptors relative to α2-adrenoceptors, while prazosin (8.5-10.5) and corynanthine (6.5-7.5) are antagonists con-

sidered selective for α1-adrenoceptors relative to α2-adrenoceptors.

[3H]prazosin (0.25 nM) and [125I]HEAT (0.1 nM; also known as BE2254) are relatively selective radioligands. The α1A-adrenoceptor

antagonist S(+)-niguldipine also has high affinity for L-type Ca2+

channels. The conotoxin rho-TIA acts as a negative allosteric mod- ulator at the α1B-adrenoceptor [1716], while the snake toxin�-Da1a acts as a selective non-competitive antagonist at the α1A- adrenoceptor [1236, 1548]. Fluorescent derivatives of prazosin (Bodipy PL-prazosin-QAPB) are increasingly used to examine cellu- lar localisation of α1-adrenoceptors. The vasoconstrictor effects of

selective α1-adrenoceptor agonists have led to their use as nasal de- congestants; antagonists are used to treat hypertension (doxazosin, prazosin) and benign prostatic hyperplasia (alfuzosin, tamsulosin). The combined α1- and β2-adrenoceptor antagonist carvedilol is widely used to treat congestive heart failure, although the contri- bution of α1-adrenoceptor blockade to the therapeutic effect is unclear. Several anti-depressants and anti-psychotic drugs possess α1-adrenoceptor blocking properties that are believed to contribute to side effects such as orthostatic hypotension and extrapyrami- dal effects.

Nomenclature α1A-adrenoceptor α1B-adrenoceptor α1D-adrenoceptor

HGNC, UniProt ADRA1A, P35348 ADRA1B, P35368 ADRA1D, P25100

Endogenous agonists – – (-)-adrenaline (pKi 7.2) [1722]

Agonists oxymetazoline (pKi 8–8.2) [780, 1420, 1722, 1862], phenylephrine (pKi 5.2–5.4) [1862], methoxamine (pKi 5–5.2) [1722, 1862]

phenylephrine (pIC50 6.3–7.5) [532, 1289] –

Selective agonists A61603 (pIC50 7.8–8.4) [532, 969], dabuzalgron (pKi 7.4) [162]

– –

Antagonists prazosin (Inverse agonist) (pKi 9–9.9) [289, 389, 532, 1722, 2029], doxazosin (pKi 9.3) [689], terazosin (pKi 8.7) [1263], phentolamine (pKi 8.6) [1722], alfuzosin (pKi 8.1) [750]

prazosin (Inverse agonist) (pKi 9.6–9.9) [532, 1722, 2029], tamsulosin (Inverse agonist) (pKi 9.5–9.7) [532, 1722, 2029], doxazosin (pKi 9.1) [689], alfuzosin (pKi 8.6) [751], terazosin (pKi 8.6) [1263], phentolamine (pKi 7.5) [1722]

prazosin (Inverse agonist) (pKi 9.5–10.2) [532, 1722, 2029], tamsulosin (pKi 9.8–10.2) [532, 1722, 2029], doxazosin (pKi 9.1) [689], terazosin (pKi 9.1) [1263], alfuzosin (pKi 8.4) [750], dapiprazole (pKi 8.4) [68], phentolamine (Inverse agonist) (pKi 8.2) [1722], RS-100329 (pKi 7.9) [2029], labetalol (pKi 6.6) [68]

Selective antagonists tamsulosin (pKi 10–10.7) [289, 389, 532, 1722, 2029], silodosin (pKi 10.4) [1722], S(+)-niguldipine (pKi 9.1–10) [532, 1722], RS-100329 (pKi 9.6) [2029], SNAP5089 (pKi 8.8–9.4) [750, 1081, 2014], �-Da1a (pKi 9.2–9.3) [1236, 1548], RS-17053 (pKi 9.2–9.3) [289, 389, 529, 532]

Rec 15/2615 (pKi 9.5) [1867], L-765314 (pKi 7.7) [1470], AH 11110 (pKi 7.5) [1652]

BMY-7378 (pKi 8.7–9.1) [268, 2102]

Adrenoceptors, α2

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α2-Adrenoceptors (nomenclature as agreed by NC-IUPHAR Subcommittee on Adrenoceptors; [248]) are activated by endogenous agonists with a relative potency of (-)-adrenaline > (-)-noradrenaline. Brimonidine and talipexole are agonists selective for α2-adrenoceptors relative to α1-adrenoceptors, rauwolscine and yohimbine are antagonists selective for α2-adrenoceptors relative

to α1-adrenoceptors. [ 3H]rauwolscine (1 nM), [3H]brimonidine (5

nM) and [3H]RX821002 (0.5 nM and 0.1 nM at α2C) are relatively selective radioligands. There is species variation in the pharmacol- ogy of the α2A-adrenoceptor; for example, yohimbine, rauwolscine and oxymetazoline have an 20-fold higher affinity for the human α2A-adrenoceptor compared to the rat, mouse and bovine recep-

tor. These α2A orthologues are sometimes referred to as α2D- adrenoceptors. Multiple mutations of α2-adrenoceptors have been described, some of which are associated with alterations in function. Presynaptic α2-adrenoceptors are widespread in the nervous system and regulate many functions, hence the multiplicity of actions. The effects of classical (not subtype selective) α2-adrenoceptor agonists such as clonidine, guanabenz and brimonidine on central barore- flex control (hypotension and bradycardia), as well as their ability to induce hypnotic effects and analgesia, and their ability to modu- late seizure activity and platelet aggregation are mediated by α2A- adrenoceptors. Clonidine has been used as an anti-hypertensive and also to counteract opioid withdrawal. Actions on imidazoline recog- nition sites may contribute to the pharmacological effects of cloni-

dine. α2-Adrenoceptor agonists such as dexmedetomidine have been widely used as sedatives and analgesics in veterinary medicine (also xylazine) and are now used frequently in humans. Dexmedeto- midine also has analgesic, sympatholytic and anxiolytic properties but is notable for the production of sedation without respiratory de- pression. α2-Adrenoceptor antagonists are relatively little used ther- apeutically although yohimbine has been used to treat erectile dys- function and several anti-depressants (e.g. Mirtazapine) that block α2-adrenoceptors may work through this mechanism. The roles of α2B and α2C-adrenoceptors are less clear but the α2B subtype ap- pears to be involved in neurotransmission in the spinal cord and α2C in regulating catecholamine release from adrenal chromaffin cells.

Nomenclature α2A-adrenoceptor α2B-adrenoceptor α2C-adrenoceptor

HGNC, UniProt ADRA2A, P08913 ADRA2B, P18089 ADRA2C, P18825

Endogenous agonists (-)-adrenaline (pKi 5.6–8.3) [854, 1503] (-)-noradrenaline (Partial agonist) (pKi 5.6–9.1) [854, 1484, 1503]

(-)-noradrenaline (pKi 5.9–8.7) [854, 1484, 1503]

Agonists dexmedetomidine (Partial agonist) (pKi 7.6–9.6) [854, 1163, 1484, 1503], clonidine (Partial agonist) (pKi 7.2–9.2) [854, 1484, 1503], brimonidine (pKi 6.7–8.7) [854, 1163, 1484, 1503], apraclonidine (pKi 8.5) [1343], guanabenz (pIC50 7.4) [68], guanfacine (Partial agonist) (pKi 7.1–7.3) [854, 1165]

dexmedetomidine (pKi 7.5–9.7) [854, 1163, 1484, 1503], clonidine (Partial agonist) (pKi 6.7–9.5) [854, 1484, 1503], brimonidine (Partial agonist) (pKi 6–8.3) [854, 1484, 1503], guanabenz (pIC50 6.8) [68], guanfacine (pKi 5.8–6.5) [854]

dexmedetomidine (pKi 7–9.3) [854, 1484, 1503], brimonidine (Partial agonist) (pKi 5.7–7.6) [854, 1163, 1484, 1503], apraclonidine (pKi 7.5) [1343], guanfacine (Partial agonist) (pKi 5.4–6.2) [854], guanabenz (pIC50 6) [68]

Selective agonists oxymetazoline (Partial agonist) (pKi 8–8.6) [854, 1163, 1922]

– –

Antagonists yohimbine (pKi 8.5–9.5) [247, 416, 1922], WB 4101 (pKi 8.4–9.4) [247, 416, 1922], spiroxatrine (pKi 9) [1922], mirtazapine (pKi 7.7) [513], tolazoline (pKi 5.4) [854]

yohimbine (pKi 8.4–9.2) [247, 416, 1922] yohimbine (pKi 7.9–8.9) [247, 416, 1922], phenoxybenzamine (pKi 8.5) [2002], tolazoline (pKi 5.5) [854]

Selective antagonists BRL 44408 (pKi 8.2–8.8) [1922, 2104] imiloxan (pKi 7.3) [1269] – Rat JP1302 (pKB 7.8) [1631]

Labelled ligands – – [3H]MK-912 (Antagonist) (pKd 10.1) [1922]

Adrenoceptors, β

β-Adrenoceptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Adrenoceptors, [248]) are activated by the endogenous agonists (-)-adrenaline and (-)-noradrenaline. Isoprenaline is a synthetic agonist selective for β-adrenoceptors relative to α1- and α2-adrenoceptors, while for β1 and β2 adrenoceptors, propranolol (pKi 8.2-9.2) and cyanopindolol (pKi 10.0-11.0) are relatively selective antagonists. (-)-noradrenaline, xamoterol and (-)-Ro 363 are agonists that show selectivity for β1-

relative to β2-adrenoceptors. Pharmacological differences exist between human and mouse β3-adrenoceptors, and the ’rodent selective’ agonists BRL 37344 and CL316243 have low efficacy at the human β3-adrenoceptor whereas CGP 12177 and L 755507 activate human β3-adrenoceptors [1649]. β3-Adrenoceptors are relatively resistant to blockade by propranolol (pKi 5.8-7.0), but can be blocked by high concentrations of bupranolol (pKi 8.65 [1650]). SR59230A has reasonably high affinity at β3-adrenoceptors [1197],

but does not discriminate well between the three β-adrenoceptor subtypes [262] and has been reported to have lower affinity for the β3-adrenoceptor in some circumstances [913]. L-748337 is the most

selective antagonist for β3 adrenoceptors. [ 125I]-cyanopindolol,

[125I]-hydroxybenzylpindolol and [3H]-alprenolol are high affinity radioligands widely used to label β1- and β2-adrenoceptors and β3-adrenoceptors can be labelled with higher concentrations (nM)

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of [125I]-cyanopindolol in the presence of appropriate concentra- tions of β1- and β2-adrenoceptor antagonists. [

3H]L-748337 is a β3-selective radioligand. Fluorescent ligands such as BODIPY-TMR- CGP12177 are also increasingly being used to track β-adrenoceptors at the cellular level [86]. Somewhat selective β1-adrenoceptor se- lective agonists (denopamine, dobutamine) are used short-term to

treat cardiogenic shock but, in the longer term, reduce survival. β1-Adrenoceptor-preferring antagonists are used to treat hyper- tension (atenolol, betaxolol, bisoprolol, metoprolol and nebivolol), cardiac arrhythmias (atenolol, bisoprolol, esmolol) and cardiac fail- ure (metoprolol, nebivolol). Cardiac failure is also succesfully treated with carvedilol which blocks both β1- and β2-adrenoceptors, as well as α1-adrenoceptors. β2-Adrenoceptor-selective agonists are

powerful bronchodilators widely used to treat respiratory disor- ders. There are both short (salbutamol, terbutaline) and long acting drugs (formoterol, salmeterol). Although many first generation β-adrenoceptor antagonists (propranolol) block both β1- and β2- adrenoceptors there are no β2-adrenoceptor-selective antagonists used therapeutically. The β3-adrenoceptor agonist mirabegron is used to control overactive bladder syndrome.

Nomenclature β1-adrenoceptor β2-adrenoceptor β3-adrenoceptor

HGNC, UniProt ADRB1, P08588 ADRB2, P07550 ADRB3, P13945

Rank order of potency (-)-noradrenaline > (-)-adrenaline (-)-adrenaline > (-)-noradrenaline (-)-noradrenaline = (-)-adrenaline Endogenous agonists noradrenaline (pKi 6) [549] – –

Agonists pindolol (Partial agonist) (pKi 9.3) [1011], isoprenaline (pKi 6.6–7) [549, 1651], dobutamine (Partial agonist) (pKi 5.5) [831]

pindolol (Partial agonist) (pKi 9.4) [1011], arformoterol (pKi 8.6) [37], isoprenaline (pKi 6.4) [1651], dobutamine (Partial agonist) (pKi 6.2) [1100], ephedrine (Partial agonist) (pKi 5.6) [851]

carazolol (pKi 8.7) [1256]

Selective agonists (-)-Ro 363 (pKi 8) [1301], xamoterol (Partial agonist) (pKi 7) [831], denopamine (Partial agonist) (pKi 5.8) [831, 1830]

formoterol (pEC50 10.1) [81], salmeterol (pEC50 9.9) [81], zinterol (pEC50 9.5) [81], vilanterol (pEC50 9.4) [1534], procaterol (pEC50 8.4) [81], indacaterol (pKi 7.8) [107], fenoterol (pKi 6.9) [55], salbutamol (Partial agonist) (pKi 5.8–6.1) [83, 831], terbutaline (Partial agonist) (pKi 5.6) [83], orciprenaline (pKd 5.3) [1784]

L 755507 (pEC50 10.1) [81], L742791 (pEC50 8.8) [2000], mirabegron (pEC50 7.7) [1849], CGP 12177 (Partial agonist) (pKi 6.1–7.3) [159, 1144, 1256, 1301], SB251023 (pEC50 7.1) [810] – Mouse, BRL 37344 (pKi 6.4–7) [159, 431, 768, 1256], CL316243 (pKi 5.2) [2080]

Antagonists carvedilol (pKi 9.5) [262], bupranolol (pKi 7.3–9) [262, 1144], levobunolol (pKi 8.4) [68], labetalol (pKi 8.2) [68], metoprolol (pKi 7–7.6) [83, 262, 768, 1144], esmolol (pKi 6.9) [68], nadolol (pKi 6.9) [262], practolol (pKi 6.1–6.8) [83, 1144], propafenone (pKi 6.7) [68], sotalol (pKi 6.1) [68]

carvedilol (pKi 9.4–9.9) [83, 262], timolol (pKi 9.7) [83], propranolol (pKi 9.1–9.5) [83, 86, 831, 1144], levobunolol (pKi 9.3) [68], bupranolol (pKi 8.3–9.1) [262, 1144], alprenolol (pKi 9) [83], nadolol (pKi 7–8.6) [83, 262], labetalol (pKi 8) [68], propafenone (pKi 7.4) [68], sotalol (pKi 6.5) [68]

carvedilol (pKi 9.4) [262], bupranolol (pKi 6.8–7.3) [159, 262, 1144, 1256], propranolol (pKi 6.3–7.2) [1144, 1517], levobunolol (pKi 6.8) [1517]

Selective antagonists CGP 20712A (pKi 8.5–9.2) [83, 262, 1144], levobetaxolol (pKi 9.1) [1715], betaxolol (pKi 8.8) [1144], nebivolol (pIC50 8.1–8.7) [1476] – Rabbit, atenolol (pKi 6.7–7.6) [83, 886, 1144], acebutolol (pKi 6.4) [68]

ICI 118551 (Inverse agonist) (pKi 9.2–9.5) [83, 86, 1144] L-748337 (pKi 8.4) [262], SR59230A (pKi 6.9–8.4) [262, 405, 768], L748328 (pKi 8.4) [262]

Labelled ligands [125I]ICYP (Selective Antagonist) (pKd 10.4–11.3) [831, 1144, 1651]

[125I]ICYP (Antagonist) (pKd 11.1) [1144, 1651] [ 125I]ICYP (Agonist, Partial agonist) (pKd 9.2–9.8) [1144, 1301, 1517, 1651, 1806]

Comments The agonists indicated have less than two orders of magnitude selectivity [81].

– Agonist SB251023 has a pEC50 of 6.9 for the splice variant of the mouse β3 receptor, β3b [810].

Comments:

Adrenoceptors, α1

The clone originally called the α1C-adrenoceptor corresponds to the pharmacologically defined α1A-adrenoceptor [752]. Some tis-

sues possess α1A-adrenoceptors (termed α1L-adrenoceptors [532, 1329]) that display relatively low affinity in functional and bind- ing assays for prazosin (pKi < 9) indicative of different receptor states or locations. α1A-adrenoceptor C-terminal splice variants form homo- and heterodimers, but fail to generate a functional α1L-

adrenoceptor [1557]. α1D-Adrenoceptors form heterodimers with α1B- or β2-adrenoceptors that show increased cell-surface expres- sion [1917]. Recombinant α1D-adrenoceptors have been shown in some heterologous systems to be mainly located intracellularly but cell-surface localization is attained by truncation of the N-terminus,

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or by co-expression of α1B- or β2-adrenoceptors to form het- erodimers [670, 1917]. In smooth muscle of native blood vessels all three α1-adrenoceptor subtypes are located on the surface and intracellularly [1260, 1261].

Signalling is predominantly via Gq/11 but α1-adrenoceptors also

couple to Gi/o, Gs and G12/13. Several ligands activating α1A- adrenoceptors display ligand directed signalling bias relative to nora- drenaline. For example, oxymetazoline is a full agonist for extracellu- lar acidification rate (ECAR) and a partial agonist for Ca2+ release but does not stimulate cAMP production. Phenylephrineis biased toward ECAR versus Ca2+ release or cAMP accumulation but not between Ca2+ release and cAMP accumulation [495]. There are also differ- ences between subtypes in coupling efficiency to different pathways- e.g. in some systems coupling efficiency to Ca2+ signalling is α1A > α1B > α1D, but for MAP kinase signalling is α1D > α1A > α1B. In vascular smooth muscle, the potency of agonists is related to the pre- dominant subtype, α1D- conveying greater agonist sensitivity than α1A-adrenoceptors [526].

Adrenoceptors, α2

ARC-239 (pKi 8.0) and prazosin (pKi 7.5) show selectivity for α2B- and α2C-adrenoceptors over α2A-adrenoceptors.Oxymetazoline is a reduced efficacy agonist and is one of many α2-adrenoceptor ag- onists that are imidazolines or closely related compounds. Other binding sites for imidazolines, distinct from α2-adrenoceptors, and structurally distinct from the 7TM adrenoceptors, have been identified and classified as I1, I2 and I3 sites [390]; cat- echolamines have a low affinity, while rilmenidine and mox- onidine are selective ligands for these sites, evoking hypoten- sive effects in vivo. I1-imidazoline receptors are involved in central inhibition of sympathetic tone, I2-imidazoline recep- tors are an allosteric binding site on monoamine oxidase B, and I3-imidazoline receptors regulate insulin secretion from pan- creatic β-cells. α2A-adrenoceptor stimulation reduces insulin

secretion from β-islets [2083], with a polymorphism in the 5’-UTR of the ADRA2A gene being associated with increased receptor ex- pression in β-islets and heightened susceptibility to diabetes [1599].

α2A- and α2C-adrenoceptors form homodimers [1758]. Het- erodimers between α2A- and either the α2c-adrenoceptor or � opi- oid peptide receptor exhibit altered signalling and trafficking prop- erties compared to the individual receptors [1758, 1858, 1956]. Sig- nalling by α2-adrenoceptors is primarily via Gi/o, however the α2A- adrenoceptor also couples to Gs [459]. Imidazoline compounds dis- play bias relative to each other at the α2A-adrenoceptor when as-

sayed by [35S] GTPγS binding compared to inhibition of cAMP accu- mulation [1477]. The noradrenaline reuptake inhibitor desipramine acts directly on the α2A-adrenoceptor, promoting internalisation via recruitment of arrestin without activating G proteins [371].

Adrenoceptors, β

Radioligand binding with [125I]ICYP can be used to define β1- or β2-adrenoceptors when conducted in the presence of a ’satu- rating’ concentration of either a β1- or β2-adrenoceptor-selective

antagonist. [3H]CGP12177 or [3H]dihydroalprenolol can be used in place of [125I]ICYP. Binding of a fluorescent analogue of CGP 12177 to β2-adrenoceptors in living cells has been described

[84]. [125I]ICYP at higher (nM) concentrations can be used to la- bel β3-adrenoceptors in systems where there are few if any other β- adrenoceptor subtypes. Pharmacological differences exist between human and mouse β3-adrenoceptors, and the ’rodent selective’ agonists BRL 37344 and CL316243 are partial agonists at the hu- man β3-adrenoceptor whereas CGP 12177 and L 755507 activate human β3-adrenoceptors with greater potency [1650]. The β3- adrenoceptor has an intron in the coding region, but splice vari- ants have only been described for the mouse [496], where the iso- forms display different signalling characteristics [810]. There are 3 β-adrenoceptors in turkey (termed the tβ, tβ3c and tβ4c) that have a pharmacology that differs from the human β-adrenoceptors

[82]. Numerous polymorphisms have been described for the three β-adrenoceptors; some are associated with alterations in agonist- evoked signalling and trafficking, altered susceptibility to disease and/or altered responses to pharmacotherapy [1103].

All β-adrenoceptors couple to Gs (activating adenylyl cyclase and elevating cAMP levels), but it is also clear that they activate other G proteins such as Gi and many other G protein-independent sig- nalling pathways, including arrestin-mediated signalling, which may in turn lead to activation of MAP kinases. Many antagonists at β1- and β2-adrenoceptors are agonists at β3-adrenoceptors (CL316243, CGP 12177 and carazolol). Many ‘antagonists’ that block agonist- stimulated cAMP accumulation, for example carvedilol and bucin- dolol, are able to activate MAP kinase pathways [85, 497, 559, 560, 1649, 1650] and thus display ’protean agonism’. Bupranolol appears to act as a neutral antagonist in most systems so far examined. Ago- nists also display biased signalling at the β2-adrenoceptor via Gs or arrestins [443].

The X-ray crystal structures have been described of the agonist bound [1988] and antagonist bound forms of the β1- [1989], agonist-bound [313] and antagonist-bound forms of the β2- adrenoceptor [1561, 1598], as well as a fully active agonist-bound, Gs protein-coupled β2-adrenoceptor [1562]. Carvedilol and bucin- dolol bind to an extended site of the β1-adrenoceptor involving con- tacts in TM2, 3, and 7 and extracellular loop 2 that may facilitate coupling to arrestins [1989]. Compounds displaying arrestin-biased signalling at the β2-adrenoceptor also have a greater effect on the conformation of TM7, whereas full agonists for Gs coupling promote movement of TM5 and TM6 [1127]. Recent studies using NMR spec- troscopy have demonstrated significant conformational flexibility in the β2-adrenoceptor which is stabilized by both agonist and G pro- teins highlighting the dynamic nature of interactions with both lig- and and downstream signalling partners [946, 1199, 1413]. Such flexibility will likely have consequences for our understanding of bi- ased agonism, and for the future therapeutic exploitation of this phenomenon.

Further Reading

Baker JG et al. (2011) Evolution of β-blockers: from anti-anginal drugs to ligand-directed signalling. Trends Pharmacol. Sci. 32: 227-34 [PMID:21429598]

Bylund DB et al. (1994) International Union of Pharmacology nomenclature of adrenoceptors. Pharmacol. Rev. 46: 121-136 [PMID:7938162]

Cazzola M et al. (2011) β(2) -adrenoceptor agonists: current and future direction. Br. J. Pharmacol. 163: 4-17 [PMID:21232045]

Daly CJ et al. (2011) Previously unsuspected widespread cellular and tissue distribution of β-adrenoceptors and its relevance to drug action. Trends Pharmacol. Sci. 32: 219-26 [PMID:21429599]

Evans BA et al. (2010) Ligand-directed signalling at beta-adrenoceptors. Br. J. Pharmacol. 159: 1022-38 [PMID:20132209]

Gilsbach R et al. (2012) Are the pharmacology and physiology of α_2 adrenoceptors determined by α_2- heteroreceptors and autoreceptors respectively? Br. J. Pharmacol. 165: 90-102 [PMID:21658028]

Jensen BC et al. (2011) Alpha-1-adrenergic receptors: targets for agonist drugs to treat heart failure. J. Mol. Cell. Cardiol. 51: 518-28 [PMID:21118696]

Kobilka BK. (2011) Structural insights into adrenergic receptor function and pharmacology. Trends Phar- macol. Sci. 32: 213-8 [PMID:21414670]

Searchable database: http://www.guidetopharmacology.org/index.jsp Adrenoceptors 5773

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S.P.H. Alexander et al. The Concise Guide to PHARMACOLOGY 2015/16: G protein-coupled receptors. British Journal of Pharmacology (2015) 172, 5744–5869

Langer SZ. (2015) α2-Adrenoceptors in the treatment of major neuropsychiatric disorders. Trends Phar- macol. Sci. 36: 196-202 [PMID:25771972]

McGrath JC. (2015) Localization of α-adrenoceptors: JR Vane Medal Lecture. Br. J. Pharmacol. 172: 1179-94 [PMID:25377869]

Michel MC et al. (2011) Are there functional β_3-adrenoceptors in the human heart? Br. J. Pharmacol. 162: 817-22 [PMID:20735409]

Michel MC et al. (2011) β-adrenoceptor agonist effects in experimental models of bladder dysfunction. Pharmacol. Ther. 131: 40-9 [PMID:21510978]

Michel MC et al. (2015) Selectivity of pharmacological tools: implications for use in cell physiology. A review in the theme: Cell signaling: proteins, pathways and mechanisms. Am. J. Physiol., Cell Physiol. 308: C505-20 [PMID:25631871]

Nishimune A et al. (2012) Phenotype pharmacology of lower urinary tract α(1)-adrenoceptors. Br. J. Pharmacol. 165: 1226-34 [PMID:21745191]

Vasudevan NT et al. (2011) Regulation of β-adrenergic receptor function: an emphasis on receptor re- sensitization. Cell Cycle 10: 3684-91 [PMID:22041711]

Walker JK et al. (2011) New perspectives regarding β(2) -adrenoceptor ligands in the treatment of asthma. Br. J. Pharmacol. 163: 18-28 [PMID:21175591]

Angiotensin receptors G protein-coupled receptors ! Angiotensin receptors Overview: The actions of angiotensin II (AGT, P01019) (Ang II) are mediated by AT1 and AT2 receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Angiotensin Receptors [2137]), which have around 30% sequence similarity. Endogenous ligands are angiotensin II (AGT, P01019) and angiotensin III (AGT, P01019) (Ang III), while angiotensin I (AGT, P01019) is weakly active in some systems.

Nomenclature AT1 receptor AT2 receptor

HGNC, UniProt AGTR1, P30556 AGTR2, P50052

Selective agonists L-162,313 (pIC50 7.8–7.9) [1490] CGP42112 (pIC50 9.6) [190], [p-aminoPhe6]ang II (pKd 9.1–9.4) [1789, 2139] – Rat

Antagonists telmisartan (pIC50 8.4) [1241], olmesartan (pIC50 8.1) [981] –

Selective antagonists candesartan (pIC50 9.5–9.7) [1942], EXP3174 (pIC50 7.4–9.5) [1887, 1942], eprosartan (pIC50 8.4–8.8) [464], irbesartan (pIC50 8.7–8.8) [1942], losartan (pIC50 7.4–8.7) [1887, 2139], valsartan (pIC50 8.6) [2138], azilsartan (pIC50 8.1–8.1) [1551, 1844]

PD123177 (pIC50 8.5–9.5) [291, 321, 450] – Rat, EMA401 (pIC50 8.5–9.3) [518, 1582, 1767], PD123319 (pKd 8.7–9.2) [449, 2025, 2139]

Labelled ligands [3H]A81988 (Antagonist) (pKd 9.2) [690] – Rat, [ 3H]L158809 (Antagonist)

(pKd 9.2) [305] – Rat, [ 3H]eprosartan (Antagonist) (pKd 9.1) [21] – Rat,

[3H]valsartan (Antagonist) (pIC50 8.8–9) [1954], [125I]EXP985 (Antagonist) (pKd 8.8) [322] – Rat, [

3H]losartan (Antagonist) (pKd 8.2) [294] – Rat

[125I]CGP42112 (Agonist) (pKd 10.6) [2017, 2018, 2139]

Searchable database: http://www.guidetopharmacology.org/index.jsp Angiotensin receptors 5774

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Comments: AT1 receptors are predominantly coupled to Gq/11, however they are also linked to arrestin recruitment and stimulate G protein-independent arrestin signalling [1156]. Most species express a single AGTR1 gene, but two related agtr1a and agtr1b receptor genes are expressed in rodents. The AT2 receptor counteracts sev- eral of the growth responses initiated by the AT1 receptors. The AT2 receptor is much less abundant than the AT1 receptor in adult tissues

and is upregulated in pathological conditions. AT1 receptor antago-

nists bearing substituted 4-phenylquinoline moieties have been syn-

thesized, which bind to AT1 receptors with nanomolar affinity and

are slightly more potent than losartan in functional studies [264].

The antagonist activity of CGP42112 at the AT2 receptor has also

been reported [2147].

The AT1 and bradykinin B2 receptors have been proposed to form a heterodimeric complex [3].

There is also evidence for an AT4 receptor that specifically binds angiotensin IV (AGT, P01019) and is located in the brain and kidney. An additional putative endogenous ligand for the AT4 receptor has been described (LVV-hemorphin (HBB, P68871), a globin decapep- tide) [1296].

Further Reading

Ellis B et al. (2012) Evidence for a functional intracellular angiotensin system in the proximal tubule of the kidney. Am. J. Physiol. Regul. Integr. Comp. Physiol. 302: R494-509 [PMID:22170616]

Karnik SS et al. (2015) International Union of Pharmacology. LXXXIX. Angiotensin Receptors: Interpreters of pathophysiological angiotensinergic stimuli. Pharmacological Reviews

MacKenzie A. (2011) Endothelium-derived vasoactive agents, AT1 receptors and inflammation. Pharma- col. Ther. 131: 187-203 [PMID:21115037]

Patel BM et al. (2012) Aldosterone and angiotensin: Role in diabetes and cardiovascular diseases. Eur. J. Pharmacol. 697: 1-12 [PMID:23041273]

Putnam K et al. (2012) The renin-angiotensin system: a target of and contributor to dyslipidemias, altered glucose homeostasis, and hypertension of the metabolic syndrome. Am. J. Physiol. Heart Circ. Physiol. 302: H1219-30 [PMID:22227126]

Sevá Pessôa B et al. (2013) Key developments in renin-angiotensin-aldosterone system inhibition. Nat Rev Nephrol 9: 26-36 [PMID:23165302]

Zhang H et al. (2015) Structure of the Angiotensin receptor revealed by serial femtosecond crystallogra- phy. Cell 161: 833-44 [PMID:25913193]

de Gasparo M et al. (2000) International Union of Pharmacology. XXIII. The angiotensin II receptors. Pharmacol. Rev. 52: 415-472 [PMID:10977869]

Apelin receptor G protein-coupled receptors ! Apelin receptor Overview: The apelin receptor (nomenclature as agreed by the NC-IUPHAR Subcommittee on the apelin receptor [1510]) responds to apelin, a 36 amino-acid peptide derived initially from bovine stomach. Apelin-36 (APLN, Q9ULZ1), apelin-13 (APLN, Q9ULZ1) and [Pyr1]apelin-13 (APLN, Q9ULZ1) are the predominant endogenous ligands which are cleaved from a 77 amino-acid precursor peptide (APLN, Q9ULZ1) by a so far unidentified enzymatic pathway [1864]. A second family of peptides discovered independently and named Elabela [323] or Toddler, that has little sequence similarity to apelin, has been proposed as a second endogenous apelin receptor ligand [1475].

Searchable database: http://www.guidetopharmacology.org/index.jsp Apelin receptor 5775

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Nomenclature apelin receptor

HGNC, UniProt APLNR, P35414

Rank order of potency

[Pyr1]apelin-13 (APLN, Q9ULZ1) � apelin-13 (APLN, Q9ULZ1) > apelin-36 (APLN, Q9ULZ1) [503, 1864] Endogenous agonists apelin-13 (APLN, Q9ULZ1) (Selective) (pIC50 8.8–9.5) [503, 785, 1254], apelin receptor early endogenous ligand (APELA, P0DMC3) (Selective) (pKd 9.3) [412], apelin-17

(APLN, Q9ULZ1) (Selective) (pIC50 7.9–9) [468, 1254], [Pyr 1]apelin-13 (APLN, Q9ULZ1) (Selective) (pIC50 7–8.8) [918, 1254], Elabela/Toddler-21 (APELA, P0DMC3) (pIC50

8.7) [2086], Elabela/Toddler-32 (APELA, P0DMC3) (pIC50 8.7) [2086], apelin-36 (APLN, Q9ULZ1) (Selective) (pIC50 8.2–8.6) [503, 785, 918, 1254], Elabela/Toddler-11 (APELA, P0DMC3) (pIC50 7.2) [2086]

Selective agonists MM07 (Biased agonist) (pEC50 9.5) [203]

Antagonists MM54 (pKi 8.2) [1166]

Labelled ligands [125I][Nle75,Tyr77]apelin-36 (human) (Agonist) (pKd 11.2) [918], [ 125I][Glp65Nle75,Tyr77]apelin-13 (Agonist) (pKd 10.7) [785], [

125I](Pyr1)apelin-13 (Agonist) (pKd 9.5)

[911], [125I]apelin-13 (Agonist) (pKd 9.2) [503], [ 3H](Pyr1)[Met(0)11]-apelin-13 (Agonist) (pKd 8.6) [1254]

Comments: Potency order determined for heterologously expressed human apelin receptor (pD2 values range from 9.5 to 8.6). The apelin receptor may also act as a co-receptor with CD4 for isolates of human immunodeficiency virus, with apelin blocking this function [279]. A modified apelin-13 peptide, apelin-13(F13A) was reported to block the hypotensive response to apelin in rat in vivo [1067], however, this peptide exhibits agonist activity in HEK293 cells stably expressing the recombinant apelin receptor [503].

Further Reading

Chandrasekaran B et al. (2008) The role of apelin in cardiovascular function and heart failure. Eur. J. Heart Fail. 10: 725-32 [PMID:18583184]

Cheng B et al. (2012) Neuroprotection of apelin and its signaling pathway. Peptides 37: 171-3 [PMID:22820556]

Davenport AP et al. (2007) Apelins. In Encyclopedic Reference of Molecular Pharmacology Edited by Offer- manns S, Rosenthal W: Springer: 201-206

Japp AG et al. (2008) The apelin-APJ system in heart failure: pathophysiologic relevance and therapeutic potential. Biochem. Pharmacol. 75: 1882-92 [PMID:18272138]

Langelaan DN et al. (2009) Structural insight into G-protein coupled receptor binding by apelin. Bio- chemistry 48: 537-48 [PMID:19123778]

O’Carroll AM et al. (2013) The apelin receptor APJ: journey from an orphan to a multifaceted regulator of homeostasis. J. Endocrinol. 219: R13-35 [PMID:23943882]

Pitkin SL et al. (2010) International Union of Basic and Clinical Pharmacology. LXXIV. Apelin re- ceptor nomenclature, distribution, pharmacology, and function. Pharmacol. Rev. 62: 331-42 [PMID:20605969]

Yang P et al. (2015) Apelin, Elabela/Toddler, and biased agonists as novel therapeutic agents in the cardiovascular system. Trends Pharmacol. Sci. [PMID:26143239]

Searchable database: http://www.guidetopharmacology.org/index.jsp Apelin receptor 5776

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Bile acid receptor G protein-coupled receptors ! Bile acid receptor Overview: The bile acid receptor (GPBA) responds to bile acids produced during the liver metabolism of cholesterol. Selective agonists are promising drugs for the treatment of metabolic disorders, such as type II diabetes, obesity and atherosclerosis.

Nomenclature GPBA receptor

HGNC, UniProt GPBAR1, Q8TDU6

Rank order of potency

lithocholic acid > deoxycholic acid > chenodeoxycholic acid, cholic acid (Unknown) [917, 1214] Selective agonists betulinic acid (pEC50 6) [590], oleanolic acid (pEC50 5.7) [1648]

Comments: The triterpenoid natural product betulinic acid has also been reported to inhibit inflammatory signalling through the NF�B pathway [1842]. Disruption of GPBA expression is reported to protect from cholesterol gallstone formation [1951]. A new series of 5-phenoxy-1,3-dimethyl-1H-pyrazole-4-carboxamides have been reported as highly potent agonists [1138].

Further Reading

Duboc H et al. (2014) The bile acid TGR5 membrane receptor: from basic research to clinical application. Dig Liver Dis 46: 302-12 [PMID:24411485]

Fiorucci S et al. (2010) Bile acid-activated receptors in the treatment of dyslipidemia and related disorders. Prog. Lipid Res. 49: 171-85 [PMID:19932133]

Fiorucci S et al. (2009) Bile-acid-activated receptors: targeting TGR5 and farnesoid-X-receptor in lipid and glucose disorders. Trends Pharmacol. Sci. 30: 570-80 [PMID:19758712]

Keitel V et al. (2012) Perspective: TGR5 (Gpbar-1) in liver physiology and disease. Clin Res Hepatol Gas- troenterol 36: 412-9 [PMID:22521118]

Lefebvre P et al. (2009) Role of bile acids and bile acid receptors in metabolic regulation. Physiol. Rev. 89: 147-91 [PMID:19126757]

Lieu T et al. (2014) GPBA: a GPCR for bile acids and an emerging therapeutic target for disorders of digestion and sensation. Br. J. Pharmacol. 171: 1156-66 [PMID:24111923]

Pols TW et al. (2011) The bile acid membrane receptor TGR5 as an emerging target in metabolism and inflammation. J. Hepatol. 54: 1263-72 [PMID:21145931]

Tiwari A et al. (2009) TGR5: an emerging bile acid G-protein-coupled receptor target for the potential treatment of metabolic disorders. Drug Discov. Today 14: 523-30 [PMID:19429513]

Searchable database: http://www.guidetopharmacology.org/index.jsp Bile acid receptor 5777

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Bombesin receptors G protein-coupled receptors ! Bombesin receptors Overview: Bombesin receptors (nomenclature recom- mended by the NC-IUPHAR Subcommittee on bombesin receptors, [857]) are activated by the endogenous ligands gastrin-releasing peptide (GRP, P07492) (GRP), neuromedin B (NMB, P08949) (NMB) and GRP-(18-27) (GRP, P07492) (previously named neuromedin C). Bombesin is a tetradecapeptide, originally derived from amphibians, and is an agonist at BB1 and BB2 receptors. These

receptors couple primarily to the Gq/11 family of G proteins (but

see also [857]). Each of these receptors is widely distributed in the CNS and peripheral tissues [625, 857, 1556, 1642]. Activation of BB1 and BB2 receptors causes a wide range of physiological actions, including the stimulation of normal and neoplastic tissue growth, smooth-muscle contraction, appetite and feeding behavior, secre- tion and many central nervous system effects [857, 858, 859, 1185,

1317, 1556]. A physiological role for the BB3 receptor has yet to be fully defined although recently studies using receptor knockout mice and newly described agonists/antagonists suggest an impor- tant role in glucose and insulin regulation, metabolic homeostasis, feeding and other CNS behaviors and growth of normal/neoplastic tissues [625, 1186, 1430].

Nomenclature BB1 receptor BB2 receptor BB3 receptor

HGNC, UniProt NMBR, P28336 GRPR, P30550 BRS3, P32247

Endogenous agonists neuromedin B (NMB, P08949) (Selective) (pKi 8.1–10.3) [857, 1556, 1919]

neuromedin C (pIC50 9.9) [1919], gastrin releasing peptide(14-27) (human) (Selective) (pIC50 9.7–9.8) [1919]

–

Selective agonists – – compound 8a [PMID: 24900283] (pIC50 8.9) [1129], compound 9g [PMID: 24412111] (pEC50 8.8) [1220], MK-7725 (pIC50 8.5) [324], MK-5046 (pKi 7.7–8.4) [1321, 1689], [D-Tyr6,Apa-4Cl11,Phe13,Nle14]bombesin-(6-14) (pKi 8.1) [1202], compound 17c [PMID: 25497965] (pEC50 7.9) [1219], compound 9f [PMID: 24412111] (pEC50 7.8) [1220], bag-1 (pIC50 7.7) [659], compound 22e [PMID: 20167483] (pIC50 7.6) [727], bag-2 (pIC50 7) [659]

Antagonists D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2 (pIC50 6.2–6.6) [624]

– –

Searchable database: http://www.guidetopharmacology.org/index.jsp Bombesin receptors 5778

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(continued)

Nomenclature BB1 receptor BB2 receptor BB3 receptor

Selective antagonists PD 176252 (pIC50 9.3–9.8) [624], PD 168368 (pIC50 9.3–9.6) [624], dNal-cyc(Cys-Tyr-dTrp-Orn-Val)-Nal-NH2

[D-Phe6, Leu13, Cpa14, 13-14]bombesin-(6-14) (pKi 9.8) [624], JMV641 (pIC50 9.3) [1892] – Mouse, [(3-Ph-Pr6), His7,D-Ala11,D-Pro13, 13-14),Phe14] bombesin-(6-14) (pIC50 9.2) [624, 1062], [D-Tpi6, Leu13 (CH2NH)-Leu14]bombesin-(6-14) (pIC50 8.9) [624], Ac-GRP-(20-26)-methylester (pIC50 8.7) [624], JMV594 (pIC50 8.7–8.7) [1133, 1892] – Mouse

bantag-1 (pIC50 8.6–8.7) [659, 1321], ML-18 (pIC50 5.3) [1316]

Labelled ligands [125I]BH-NMB (human, mouse, rat) (Agonist), [125I][Tyr4]bombesin (Agonist)

[125I][D-Tyr6]bombesin-(6-13)-methyl ester (Selective Antagonist) (pKd 9.3) [1201] – Mouse, [

125I][Tyr4]bombesin (Agonist) (pKd 8.2) [131], [125I]GRP (human) (Agonist)

[3H]bag-2 (Agonist) (pKd 8.6) [659] – Mouse,

[125I][D-Tyr6,β-Ala11,Phe13,Nle14]bombesin-(6-14) (Agonist) (pKd 8–8.4) [1203, 1321]

Comments: All three subtypes may be activated by [D-Phe6,β-Ala11,Phe13,Nle14]bombesin-(6-14) [1203]. [D-Tyr6,Apa-4Cl11,Phe13,Nle14]bombesin-(6-14) has more than 200-fold selectivity for BB3 receptors over BB1 and BB2 [1202].

Further Reading

Gonzalez N et al. (2008) Bombesin-related peptides and their receptors: recent advances in their role in physiology and disease states. Curr Opin Endocrinol Diabetes Obes 15: 58-64 [PMID:18185064]

González N et al. (2015) Bombesin receptor subtype 3 as a potential target for obesity and diabetes. Expert Opin. Ther. Targets 1-18 [PMID:26066663]

Jensen RT et al. (2008) International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states. Pharmacol. Rev. 60: 1-42 [PMID:18055507]

Jensen RT et al. (2013) Bombesin-Related Peptides. In Handbook of Biologically Active Peptides. 2nd Revised edition. Edited by Kastin AJ: Elsevier: 1188-1196 [ISBN: 9780123850959]

Jensen RT et al. (2013) Bombesin Peptides (Cancer). In Handbook of Biologically Active Peptides. 2nd Revised edition. Edited by Kastin AJ: Elsevier: 506-511 [ISBN: 9780123850959]

Ladenheim EE.. (2013) Bombesin. In Handbook of Biologically Active Peptides. 2nd Revised edition. Edited by Kastin AJ: Elsevier: 1064-1070 [ISBN: 9780123850959]

Majumdar ID et al. (2011) Biology of mammalian bombesin-like peptides and their receptors. Curr Opin Endocrinol Diabetes Obes 18: 68-74 [PMID:21042212]

Moody TW et al. (2015) Neuropeptides as lung cancer growth factors. Peptides [PMID:25836991]

Ramos-Álvarez I et al. (2015) Insights into bombesin receptors and ligands: Highlighting recent advances. Peptides [PMID:25976083]

Roesler R et al. (2012) Gastrin-releasing peptide receptors in the central nervous system: role in brain function and as a drug target. Front Endocrinol (Lausanne) 3: 159 [PMID:23251133]

Sun YG et al. (2009) Cellular basis of itch sensation. Science 325: 1531-4 [PMID:19661382]

Searchable database: http://www.guidetopharmacology.org/index.jsp Bombesin receptors 5779

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Bradykinin receptors G protein-coupled receptors ! Bradykinin receptors Overview: Bradykinin (or kinin) receptors (nomenclature as agreed by the NC-IUPHAR subcommittee on Bradykinin (kinin) Receptors [1072]) are activated by the endogenous peptides bradykinin (KNG1, P01042) (BK), [des-Arg9]bradykinin (KNG1, P01042), Lys-BK (kallidin (KNG1, P01042)), [des-Arg10]kallidin (KNG1, P01042), T-kinin (KNG1, P01042) (Ile-Ser-BK), [Hyp3]bradykinin (KNG1, P01042) and Lys-[Hyp3]-bradykinin (KNG1, P01042). The variation in affinity or inactivity of B2 receptor antagonists could reflect the existence of species homologues of B2 receptors.

Nomenclature B1 receptor B2 receptor

HGNC, UniProt BDKRB1, P46663 BDKRB2, P30411

Rank order of potency [des-Arg10]kallidin (KNG1, P01042) > [des-Arg9]bradykinin (KNG1, P01042) = kallidin (KNG1, P01042) > bradykinin (KNG1, P01042) kallidin (KNG1, P01042) > bradykinin (KNG1, P01042) � [des-Arg9]bradykinin(KNG1, P01042), [des-Arg10]kallidin (KNG1, P01042)

Endogenous agonists [des-Arg10]kallidin (KNG1, P01042) (Selective) (pKi 9.6–10) [69, 104, 876] –

Selective agonists [Sar,D-Phe8,des-Arg9]bradykinin (pKi 5.7) [876] [Hyp 3,Tyr(Me)8]BK, [Phe8, (CH2-NH)Arg9]BK

Antagonists [Leu9,des-Arg10]kallidin (pKi 9.1–9.3) [69, 104] –

Selective antagonists B-9958 (pKi 9.2–10.3) [596, 1570], R-914 (pA2 8.6) [617], R-715 (pA2 8.5) [618] icatibant (pKi 10.2) [39], FR173657 (pA2 8.2) [1593], anatibant (pKi 8.2) [1537]

Labelled ligands [125I]Hpp-desArg10HOE140 (pKd 10), [ 3H]Lys-[des-Arg9]BK (Agonist) (pKd 9.4),

[3H]Lys-[Leu8][des-Arg9]BK (Antagonist)

[3H]BK (human, mouse, rat) (Agonist) (pKd 9.4) [2034] – Mouse, [ 3H]NPC17731

(Antagonist) (pKd 9.1–9.4) [2119, 2120], [ 125I][Tyr8]bradykinin (Agonist)

Further Reading

Campos MM et al. (2006) Non-peptide antagonists for kinin B1 receptors: new insights into their thera- peutic potential for the management of inflammation and pain. Trends Pharmacol. Sci. 27: 646-51 [PMID:17056130]

Duchene J et al. (2009) The kinin B(1) receptor and inflammation: new therapeutic target for cardiovas- cular disease. Curr Opin Pharmacol 9: 125-31 [PMID:19124274]

Marceau F et al. (2004) Bradykinin receptor ligands: therapeutic perspectives. Nat Rev Drug Discov 3: 845-52 [PMID:15459675]

Paquet JL et al. (1999) Pharmacological characterization of the bradykinin B2 receptor: inter-species vari- ability and dissociation between binding and functional responses. Br. J. Pharmacol. 126: 1083-90 [PMID:10204994]

Thornton E et al. (2010) Kinin receptor antagonists as potential neuroprotective agents in central nervous system injury. Molecules 15: 6598-618 [PMID:20877247]

Searchable database: http://www.guidetopharmacology.org/index.jsp Bradykinin receptors 5780

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Calcitonin receptors G protein-coupled receptors ! Calcitonin receptors Overview: This receptor family comprises a group of receptors for the calcitonin/CGRP family of peptides. The calcitonin (CT), amylin (AMY), calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on CGRP, AM, AMY, and CT receptors

[721, 1528]) are generated by the genes CALCR (which codes for the CT receptor (CTR)) and CALCRL (which codes for the calcitonin receptor-like receptor, CLR, previously known as CRLR). Their func- tion and pharmacology are altered in the presence of RAMPs (recep- tor activity-modifying proteins), which are single TM domain pro-

teins of ca. 130 amino acids, identified as a family of three mem- bers; RAMP1, RAMP2 and RAMP3. There are splice variants of CTR; these in turn produce variants of the AMY receptor [1528], some of which can be potently activated by CGRP. The endogenous ago- nists are the peptides calcitonin (CALCA, P01258), α-CGRP (CALCA, P06881) (formerly known as CGRP-I), β-CGRP (CALCB, P10092) (formerly known as CGRP-II), amylin (IAPP, P10997) (occasionally called islet-amyloid polypeptide, diabetes-associated polypeptide), adrenomedullin (ADM, P35318) and adrenomedullin 2/intermedin (ADM2, Q7Z4H4). There are species differences in peptide se-

quences, particularly for the CTs. CTR-stimulating peptide {Pig} (CRSP) is another member of the family with selectivity for the CTR but it is not expressed in humans [907]. Olcegepant (also known as BIBN4096BS, pKi 10.5) and telcagepant (also known as MK0974, pKi 9) are the most selective antagonists available, having a high se- lectivity for CGRP receptors, with a particular preference for those of primate origin.

CLR by itself binds no known endogenous ligand, but in the pres- ence of RAMPs it gives receptors for CGRP, adrenomedullin and adrenomedullin 2/intermedin.

Nomenclature CT receptor AMY1 receptor AMY2 receptor AMY3 receptor

HGNC, UniProt CALCR, P30988 – – –

Subunits – RAMP1 (Accessory protein), CT receptor

CT receptor, RAMP2 (Accessory protein)

CT receptor, RAMP3 (Accessory protein)

Rank order of potency

calcitonin (salmon) � calcitonin (CALCA, P01258) � amylin (IAPP, P10997), α-CGRP (CALCA, P06881) > adrenomedullin (ADM, P35318), adrenomedullin 2/intermedin (ADM2, Q7Z4H4)

calcitonin (salmon) � amylin (IAPP, P10997) � α-CGRP (CALCA, P06881)> adrenomedullin 2/intermedin (ADM2, Q7Z4H4) � calcitonin (CALCA, P01258) > adrenomedullin (ADM, P35318)

Poorly defined calcitonin (salmon) � amylin (IAPP, P10997) > α-CGRP (CALCA, P06881)� adrenomedullin 2/intermedin (ADM2, Q7Z4H4) � calcitonin (CALCA, P01258) > adrenomedullin (ADM, P35318)

Endogenous agonists

calcitonin (CALCA, P01258) (Selective) (pEC50 9–11.2) [32, 58, 718, 1027, 1087, 1341]

amylin (IAPP, P10997) (pEC50 9–9.7) [610]

amylin (IAPP, P10997) (pEC50 8.3–9.1) [610]

amylin (IAPP, P10997) (pEC50 8.9–9.6) [610]

Labelled ligands [125I]CT (human) (Agonist) (pKd 9–10), [125I]CT (salmon) (Agonist) (pKd 10)

[125I]BH-AMY (rat, mouse) (Agonist) (pKd 9–10)

[125I]BH-AMY (rat, mouse) (Agonist) (pKd 9–10)

[125I]BH-AMY (rat, mouse) (Agonist) (pKd 9–10)

Searchable database: http://www.guidetopharmacology.org/index.jsp Calcitonin receptors 5781

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S.P.H. Alexander et al. The Concise Guide to PHARMACOLOGY 2015/16: G protein-coupled receptors. British Journal of Pharmacology (2015) 172, 5744–5869

Nomenclature calcitonin receptor- like receptor CGRP receptor AM1 receptor AM2 receptor

HGNC, UniProt CALCRL, Q16602 – – –

Subunits – calcitonin receptor-like receptor, RAMP1 (Accessory protein)

calcitonin receptor-like receptor, RAMP2 (Accessory protein)

calcitonin receptor-like receptor, RAMP3 (Accessory protein)

Rank order of potency

– α-CGRP (CALCA, P06881) > adrenomedullin (ADM, P35318) � adrenomedullin 2/intermedin (ADM2, Q7Z4H4) > amylin (IAPP, P10997) � calcitonin (salmon)

adrenomedullin (ADM, P35318) > adrenomedullin 2/intermedin (ADM2, Q7Z4H4) > α-CGRP (CALCA, P06881), amylin (IAPP, P10997) > calcitonin (salmon)

adrenomedullin (ADM, P35318) � adrenomedullin 2/intermedin (ADM2, Q7Z4H4) � α-CGRP (CALCA, P06881) > amylin (IAPP, P10997) > calcitonin (salmon)

Endogenous agonists

– β-CGRP (CALCB, P10092) (pKi 9.9–11) [20, 1251], α-CGRP (CALCA, P06881) (pKi 9.7–10) [20, 1251]

adrenomedullin (ADM, P35318) (pKi 8.3–9.2) [20, 1251]

adrenomedullin (ADM, P35318) (pKi 8.3–9) [20, 539]

Antagonists – olcegepant (pKi 10.2–10.7) [435, 719, 720, 1194], telcagepant (pKi 9.1) [1633]

– –

Selective antagonists

– – AM-(22-52) (human) (pKi 7–7.8) [20, 720, 1251]

–

Labelled ligands – [125I]αCGRP (human) (Agonist) (pKd 10),

[125I]αCGRP (mouse, rat) (Agonist)

[125I]AM (rat) (Agonist) (pKd 10–9) [ 125I]AM (rat) (Agonist) (pKd 9–10)

Comments: It is important to note that a complication with the in- terpretation of pharmacological studies with AMY receptors in trans- fected cells is that most of this work has likely used a mixed popula- tion of receptors, encompassing RAMP-coupled CTR as well as CTR alone. This means that although in binding assays human calcitonin (CALCA, P01258) has low affinity for 125I-AMY binding sites, cells transfected with CTR and RAMPs can display potent CT functional responses. Transfection of human CTR with any RAMP can gener- ate receptors with a high affinity for both salmon CT and AMY and varying affinity for different antagonists [337, 718, 719]. The ma- jor human CTR splice variant (hCT(a), which does not contain an insert) with RAMP1 (i.e. the AMY1(a) receptor) has a high affinity for CGRP, unlike hCT(a)-RAMP3 (i.e. AMY3(a) receptor) [337, 718]. However, the AMY receptor phenotype is RAMP-type, splice variant and cell-line-dependent [1886]. In particular, CGRP is a more po- tent agonist than amylin (IAPP, P10997) at increasing cAMP at the delta 47 hCT(a) receptor, when transfected with RAMP1 (to give the corresponding AMY1(a) receptor) in Cos 7 cells [1543].

The ligands described represent the best available but their selectivity is limited. For example, adrenomedullin has appreciable affinity for CGRP receptors. CGRP can show significant cross-reactivity at AMY receptors and AM2 receptors. Adrenomedullin 2/intermedin also has high affinity for the AM2 receptor [779]. CGRP-(8-37) acts as an an- tagonist of CGRP (pKi 8) and inhibits some AM and AMY responses (pKi 6-7). It is weak at CT receptors. Salmon CT-(8-32) is an antag- onist at both AMY and CT receptors. AC187, a salmon CT analogue, is also an antagonist at AMY and CT receptors. Human AM-(22-52) has some selectivity towards AM receptors, but with modest potency (pKi 7), limiting its use [720]. AM-(22-52) is slightly more effective at AM1 than AM2 receptors but this difference is not sufficient for this peptide to be a useful discriminator of the AM receptor subtypes. Olcegepant shows the greatest selectivity between receptors but still has significant affinity for AMY1 receptors [1973].

Ligand responsiveness at CT and AMY receptors can be affected by receptor splice variation and can depend on the pathway being mea- sured. Particularly for AMY receptors, relative potency can vary with

the type and level of RAMP present and can be influenced by other factors such as G proteins [1324, 1886].

Gs is a prominent route for effector coupling for CLR and CTR but other pathways (e.g. Ca2+, ERK, Akt), and G proteins can be acti- vated [1972]. There is evidence that CGRP-RCP (a 148 amino-acid hydrophilic protein, ASL (P04424) is important for the coupling of CLR to adenylyl cyclase [498].

[125I]-Salmon CT is the most common radioligand for CT receptors but it has high affinity for AMY receptors and is also poorly reversible. [125I]-Tyr0-CGRP is widely used as a radioligand for CGRP receptors.

Some early literature distinguished between CGRP1 and CGRP2 re- ceptors. It is now clear that the complex of CALCRL and RAMP1 rep- resents the CGRP1 subtype and is now known simply as the CGRP re- ceptor [721]. The CGRP2 receptor is now considered to have arisen from the actions of CGRP at AM2 and AMY receptors. This term should not be used [721].

Searchable database: http://www.guidetopharmacology.org/index.jsp Calcitonin receptors 5782

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