CHEMBL5736737

Biological Assay: Kinase activities were assayed using the Transcreener-Fluorecescence polarization platform (BelBrook Labs, Madison, Wis., USA) that measures amounts of the reaction product, ADP. The IRAK4 reaction conditions were optimized using an IRAK1-derived peptide (sequence H-KKARFSRFAGSSPSQSSMVAR) to provide a linear reaction rate over the course of a 90 min incubation, which resulted in 10-12% conversion of the starting ATP to ADP. Final IRAK4 assay conditions were 1.25 nM IRAK4; 125 uM ATP; 10 uM MgCl2; 125 uM peptide in reaction buffer (25 mM HEPES (pH7.4); 2 mM Dithiothreitol; 0.015% Brij-35; and 0.5% dimethyl sulfoxide. The IRAK1 activity was optimized similarly, yielding final assay conditions of 3 mM IRAK1; 62.5 uM ATP; 5 uM MgCl2, and 62.5 uM IRAK1 peptide in reaction buffer for 60 min.Assays of compounds for kinase inhibition were performed using inhibitors serially-diluted in dimethyl sulfoxide, which was accomplished with a LabCyte Echo 555 liquid dispenser. 384 well assay plates spotted with compound received 4 ul of a 2× substrate (ATP+peptide) mix in reaction buffer, followed by 4 ul of 2× enzyme diluted in reaction buffer. Reactions were halted at 60 (IRAK1) or 90 (IRAK4) min by addition of 6 ul of detection buffer, containing EDTA (40 nM final concentration), 0.95 ug of the ADP-binding antibody ADP2, ADP tracer (3 nM final concentration), and 25 uM HEPES. Following a 1 hr incubation, fluorescence polarization of the ADP2-antibody TRACER complex was read on a Tecan M1000 plate reader using a 635/20 excitation filter in combination with a 670/20 emission filter.