title: Highly potent and selective fluorescent antagonists of the human adenosine A₃ receptor based on the 1,2,4-triazolo[4,3-a]quinoxalin-1-one scaffold.
abstract: The adenosine-A(3) receptor (A(3)AR) is a G protein-coupled receptor that shows promise as a therapeutic target for cancer, glaucoma, and various autoimmune inflammatory disorders, and as such, there is a need for molecular probes to study this receptor. Here, we report a series of fluorescent ligands containing different linkers and fluorophores based around a 1,2,4-triazolo[4,3-a]quinoxalin-1-one antagonist. One of these conjugates (19) displayed high affinity for the A(3)AR (pK(D) = 9.36 ± 0.12) and is >650-fold selective over other adenosine receptor subtypes. Confocal microscopy revealed clear, displaceable membrane labeling of CHO-A(3) cells with 19, with no detectable labeling of CHO-A(1) cells under identical conditions. This fluorescent ligand was also able to specifically label the A(3)AR in HEK293T cells containing a mixed adenosine receptor population. The subtype specificity, along with its excellent imaging properties, make 19 an ideal tool for studying A(3)AR distribution and organization, particularly in the presence of other adenosine receptor subtypes.
authors.affiliation: School of Pharmacy, Centre for Biomolecular Sciences, University of Nottingham, United Kingdom.
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Vernall
authors.forename: Leigh A
authors.initials: LA
authors.lastname: Stoddart
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Briddon
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Hill
authors.forename: Barrie
authors.initials: B
authors.lastname: Kellam
mesh_terms: D058918:Adenosine A3 Receptor Antagonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D001896:Boron Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D011810:Quinoxalines / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014230:Triazoles / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology
chemical_list: D058918:Adenosine A3 Receptor Antagonists; D001896:Boron Compounds; D005456:Fluorescent Dyes; D008024:Ligands; D011810:Quinoxalines; D014230:Triazoles