title: Novel Alexa Fluor-488 labeled antagonist of the A(2A) adenosine receptor: Application to a fluorescence polarization-based receptor binding assay.
abstract: Fluorescence polarization (FP) assay has many advantages over the traditional radioreceptor binding studies. We developed an A(2A) adenosine receptor (AR) FP assay using a newly synthesized fluorescent antagonist of the A(2A)AR (MRS5346), a pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine derivative conjugated to the fluorescent dye Alexa Fluor-488. MRS5346 displayed a K(i) value of 111+/-16nM in radioligand binding using [(3)H]CGS21680 and membranes prepared from HEK293 cells stably expressing the human A(2A)AR. In a cyclic AMP functional assay, MRS5346 was shown to be an A(2A)AR antagonist. MRS5346 did not show any effect on A(1) and A(3) ARs in binding or the A(2B)AR in a cyclic AMP assay at 10microM. Its suitability as a fluorescent tracer was indicated in an initial observation of an FP signal following A(2A)AR binding. The FP signal was optimal with 20nM MRS5346 and 150microg protein/mL HEK293 membranes. The association and dissociation kinetic parameters were readily determined using this FP assay. The K(d) value of MRS5346 calculated from kinetic parameters was 16.5+/-4.7nM. In FP competition binding experiments using MRS5346 as a tracer, K(i) values of known AR agonists and antagonists consistently agreed with K(i) values from radioligand binding. Thus, this FP assay, which eliminates using radioisotopes, appears to be appropriate for both routine receptor binding and high-throughput screening with respect to speed of analysis, displaceable signal and precision. The approach used in the present study could be generally applicable to other GPCRs.
authors.affiliation: Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0810, USA.
authors.forename: Miklós
authors.initials: M
authors.lastname: Kecskés
authors.forename: T Santhosh
authors.initials: TS
authors.lastname: Kumar
authors.forename: Lena
authors.initials: L
authors.lastname: Yoo
authors.forename: Zhan-Guo
authors.initials: ZG
authors.lastname: Gao
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Jacobson
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives*; D058917:Adenosine A2 Receptor Antagonists; D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D019411:Clinical Laboratory Techniques; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000737:chemistry; D006801:Humans; D058915:Purinergic P1 Receptor Antagonists; D043684:Receptor, Adenosine A3
chemical_list: D058917:Adenosine A2 Receptor Antagonists; D005456:Fluorescent Dyes; D058915:Purinergic P1 Receptor Antagonists; D043684:Receptor, Adenosine A3; D000241:Adenosine