CHEMBL5735994

High Throughput Biochemical Assay: Syk activity was measured using KinEASE (Cisbio), a time-resolved fluorescence resonance energy transfer (TR-FRET) immunoassay. In this assay, Syk-catalyzes the phosporylation of a XL665-labeled peptide substrate. Europium conjugated phospho-tyrosine specific antibody binds the resulting phosphorylated peptide. Formation of phosphorylated peptide is quantified by TR-FRET with Europium as the donor and XL665 the acceptor in a 2-step endpoint assay. In brief, test compounds serially diluted in DMSO were delivered into Corning white, low volume, non-binding 384 well plates using the Echo 550 acoustic liquid dispenser (Labcyte®). Syk enzyme and substrates were dispensed into assay plates using a Multi-Flo (Bio-Tek Instruments). The standard 5 μL reaction mixture contained 20 μM ATP, 1 μM biotinylated peptide, 0.015 nM of Syk in reaction buffer (50 mM Hepes, pH 7.0, 0.02% NaN3, 0.1% BSA, 0.1 mM Orthovanadate, 5 mM MgCl2, 1 mM DTT, 0.025% NP-40). After 30 minutes of incubation at room temperature, 5 μL of Stop and Detect Solution (1:200 Europium Cryptate labeled anti-phosphorylated peptide antibody solution and 125 nM strepavidin-XL665 Tracer in a 50 mM Hepes pH 7.0 detection buffer containing sufficient EDTA) was added. The plate was then further incubated for 120 minutes at room temperature and read using an Envision 2103 Multilabeled reader (PerkinElmer) with excitation/emission/FRET emission at 340 nm/615 nm/665 nm, respectively. Fluorescence intensities at 615 nm and 665 nm emission wavelengths were expressed as a ratio (665 nm/615 nm). Percent inhibition was calculated as follows: % Inhibition=100×(RatioSample−Ratio0% Inhibition)/(Ratio100% Inhibition−Ratio0% Inhibition) where 0.1% DMSO (0% inhibition) was the negative control and 1 μM K252a (100% inhibition) was used as the positive control.