CHEMBL5737491

DNAPK Enzyme Potency Assay (DNA-PK Enz): The inhibitory activity of compounds against DNAPK was determined by TR-FRET measuring a fluorescent labelled peptide substrate converting to a phosphorylated product. fluorescently tagged peptide substrate were purchased from Thermo Fisher Scientific. 12 point half-log compound concentration-response curves, with a top concentration of 100 μM were generated from 10 mM stocks of compound solubilised in DMSO using an Echo 555 (Labcyte Inc., Sunnyvale, Calif.). All assays were preformed in white Greiner 1536 well low volume plates (Greiner Bio-One, UK), in a total reaction volume of 3 μL and 1% (v/v) final DMSO concentration. Enzymes and substrates were added separately to the compound plates and incubated at room temperature. The kinase reaction was then quenched by the addition of 3 μL of stop buffer. Stopped assay plates were read using a BMG Pherastar. IC50 values were calculated using a Genedata Screener® software (Genedata, Inc., Basel, Switzerland).Full length human DNAPK protein was purified from HeLa cell extract by ion exchange. Initially DNAPK protein was incubated with compound for 30 minutes at room temperature in reaction buffer (50 mM Hepes pH 7.5, 0.01% Brij-35, 10 mM MgCl2, 1 mM EGTA, 1 mM DTT, 2 μg/ml Calf Thymus DNA). The reaction was then initiated by the addition of ATP and fluorescently tagged peptide substrate (Fluorescein-EPPLSQEAFADLWKK, Thermo Fisher Scientific). The kinase reaction (18 μM ATP, 35 μM DNAPK, 1.6 μM peptide substrate) was quenched after 40 minutes by the addition of 3 μL of stop buffer (20 mM Tris pH7.5, 0.02% sodium azide, 0.01% Nonidet-P40, 20 m EDTA, 4 nM Tb anti-phospho-p53 [Ser15] Antibody. The reaction was incubated for a further hour and the plates were read on a BMG Pherastar.Data was analysed and IC50 values were calculated using Genedata Screener® software (Genedata, Inc., Basel, Switzerland). The pIC50 values were calculated as the negative logarithm of the molar concentration of compound required for 50% reduction in measured response.