Assay Method Information

Assay Name:  ERalpha Binding Assay
Description:  The ability of compounds to bind to isolated Estrogen Receptor Alpha Ligand binding domain (ER alpha-LBD (GST)) was assessed in competition assays using a LanthaScreen Time-Resolved Fluorescence Resonance Energy Transfer (TR-FRET) detection end-point. For the LanthaScreen TR-FRET endpoint, a suitable fluorophore (Fluormone ES2, ThermoFisher, Product code P2645) and recombinant human Estrogen Receptor alpha ligand binding domain, residues 307-554 (expressed and purified in-house) were used to measure compound binding. The assay principle is that ER alpha-LBD (GST) is added to a fluorescent ligand to form a receptor/fluorophore complex. A terbium-labelled anti-GST antibody (Product code PV3551) is used to indirectly label the receptor by binding to its GST tag, and competitive binding is detected by a test compound's ability to displace the fluorescent ligand, resulting in a loss of TR-FRET signal between the Tb-anti-GST antibody and the tracer. The assay was performed as follows with all reagent additions carried out using the Beckman Coulter BioRAPTR FRD microfluidic workstation: 1. Acoustic dispense 120 nL of the test compound into a black low volume 384 well assay plates. 2. Prepare 1×ER alpha-LBD/Tb-antiGST Ab in ES2 screening buffer and incubate for 15 minutes. 3. Dispense 6 μL of the 1× AR-LBD/Tb-anti-GST Ab reagent into each well of the assay plate followed by 6 μL of Fluorophore reagent into each well of the assay plate 4. Cover the assay plate to protect the reagents from light and evaporation, and incubate at room temperature for 4 hours. 5. Excite at 337 nm and measure the fluorescent emission signal of each well at 490 nm and 520 nm using the BMG PheraSTAR.Compounds were dosed directly from a compound source microplate containing serially diluted compound (4 wells containing 10 mM, 0.1 mM, 1 μM and 10 nM final compound respectively) to an assay microplate using the Labcyte Echo 550. The Echo 550 is a liquid handler that uses acoustic technology to perform direct microplate-to-microplate transfers of DMSO compound solutions and the system can be programmed to transfer multiple small nL volumes of compound from the different source plate wells to give the desired serial dilution of compound in the assay which is then back-filled to normalise the DMSO concentration across the dilution range.In total 120 nL of compound plus DMSO were added to each well and compounds were tested in a 12-point concentration response format over a final compound concentration range of 10, 2.917, 1.042, 0.2083, 0.1, 0.0292, 0.0104, 0.002083, 0.001, 0.0002917, 0.0001042, and 0.00001 μM respectively. TR-FRET dose response data obtained with each compound was exported into a suitable software package (such as Origin or Genedata) to perform curve fitting analysis. Competitive ER alpha binding was expressed as an IC50 value. This was determined by calculation of the concentration of compound that was required to give a 50% reduction in tracer compound binding to ER alpha-LBD.
Affinity data for this assay

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