title: Characterization of [3H]LUF5834: A novel non-ribose high-affinity agonist radioligand for the adenosine A1 receptor.
abstract: The adenosine A(1) receptor is a promising therapeutic target for neurological disorders such as cognition deficits and is involved in cardiovascular preconditioning. Classically adenosine receptor agonists were all derivatives of adenosine, and thought to require a D-ribose moiety. More recently, however, the discovery of non-adenosine agonists for the human adenosine A(1) receptor (hA(1)R) has challenged this dogma (Beukers et al., 2004). In this study we characterize the tritiated form of one of these compounds, [(3)H]LUF5834, as the first non-ribose partial agonist radioligand with nanomolar affinity for the hA(1)R. Due to its partial agonist efficacy, [(3)H]LUF5834 labeled both G protein-coupled and uncoupled receptors with a similar high affinity. Using [(3)H]LUF5834 we performed competition binding experiments to characterize a range of A(1)R ligands varying in efficacy from the full agonist CPA to the inverse agonist DPCPX. Surprisingly, in the control condition both agonists and inverse agonists displayed biphasic isotherms. With the addition of 1mM GTP the high affinity isotherm of agonists or the low affinity isotherm of inverse agonists was lost revealing the mechanism of action of such inverse agonists at the A(1)R. Consequently, [(3)H]LUF5834 represents a novel high affinity radioligand for the A(1)R and may prove a useful tool to provide estimates of inverse agonist efficacy at this receptor.
authors.affiliation: Division of Medicinal Chemistry, Leiden/Amsterdam Centre for Drug Research, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands. jrlane@chem.leidenuniv.nl
authors.forename: J Robert
authors.initials: JR
authors.lastname: Lane
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Klaasse
authors.forename: Judy
authors.initials: J
authors.lastname: Lin
authors.forename: John
authors.initials: J
authors.lastname: van Bruchem
authors.forename: Margot W
authors.initials: MW
authors.lastname: Beukers
authors.forename: Adriaan P
authors.initials: AP
authors.lastname: Ijzerman
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives; D058907:Adenosine A1 Receptor Agonists; D058916:Adenosine A1 Receptor Antagonists; D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D000631:Aminopyridines / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane; D006224:Cricetinae; D005786:Gene Expression Regulation; D006801:Humans; D007093:Imidazoles / Q000737:chemistry / Q000494:pharmacology*; D011869:Radioligand Assay; D043682:Receptor, Adenosine A1 / Q000235:genetics / Q000378:metabolism; D043704:Receptor, Adenosine A2B / Q000235:genetics / Q000378:metabolism
chemical_list: C488438:2-amino-4-(4-hydroxyphenyl)-6-(1H-imidazol-2-ylmethylsulfanyl)pyridine-3,5-dicarbonitrile; D058907:Adenosine A1 Receptor Agonists; D058916:Adenosine A1 Receptor Antagonists; D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D000631:Aminopyridines; D007093:Imidazoles; D043682:Receptor, Adenosine A1; D043704:Receptor, Adenosine A2B; D000225:Adenine