| Assay Method Information | |
| | Adenosine Receptor Time-Resolved Fluorescence Resonance Energy Transfer (TRFRET) Binding Assay |
| Description: | All FRET binding experiments were conducted at room temperature in white 384-well plates, in assay binding buffer containing 1×LabMed (Cisbio, France), 100 μg/mL saponin, 1% DMSO and 0.02% pluronic acid. Binding of the fluorescently labelled Adenosine receptor antagonist XAC (CA200645, FRET acceptor) to terbium-labelled A1, A2a, A2b and A3 adenosine receptors (FRET donors) was detected by time-resolved FRET due to the close proximity of the donor and acceptor in a binding event. To investigate the ability of unlabelled test compounds to bind to Adenosine A1, A2a, A2b and A3 receptors, dose response curves were constructed that determined the ability of a range of concentrations to inhibit the binding of 30 nM CA200645 to the A2b receptor and 100 nM CA200645 to the A1, A2a, and A3 receptor. Serial dilution (1:3 dilutions) of test compounds in neat DMSO and transfer of a 400 nL sample of test compound into the assay plate was carried out using the Mosquito (TTP Labtech, UK). The compound samples were incubated for 2 hours at room temperature with a fixed concentration of CA200645 defined for each receptor (see above) and CHO cell membranes containing the human Adenosine A1 (0.5 μg/well), A2a (0.3 μg/well), A2b (1 μg/well) or A3 (1 μg/well) receptor in 40 μL of assay buffer. Total and non-specific binding of CA200645 was determined in the absence and presence of 10 μM XAC, respectively. Following 2 hours incubation, the level of CA200645 binding was detected on a Pherastar FSX (BMG Labtech, Germany) using standard TR-FRET settings. The terbium donor was excited with three laser flashes at a wavelength of 337 nm, and donor and acceptor emission was detected at 620 nm and 665 nm wavelengths, respectively. FRET ratios were obtained by multiplying the acceptor/donor ratio value by 10,000. Specific binding was determined by subtracting the non-specific binding FRET ratio from the total binding FRET ratio. Compound IC50 curves were analysed using GraphPad Prism 7.0 (GraphPad, USA) and Ki affinity values were determined from the obtained IC50 values using the method of Cheng and Prusoff |
| Affinity data for this assay | |
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