CHEMBL5735534

Kinase Assay (ATP Concentration at Km): Activity of CDK9 was determined in-vitro using a mobility shift assay on a Caliper LC3000 reader (Caliper/PerkinElmer), which measures fluorescence of a phosphorylated and unphosphorylated fluorescent peptide substrate and calculates a ratiometric value to determine percent turnover. Phosphorylation of the peptide in the presence and absence of the compound of interest was determined. Enzyme/substrate/adenosine triphosphate (ATP) mix (3 nM CDK9/CycT1, 6 μM ATP, 1.5 μM CDK9 peptide substrate (FITC-X-GSRTPMY-NH2 (X: epsilon aminocaproic acid)), 50 mM HEPES (pH7.2), 1 mM dithiothreitol, 0.01% tween 20, 50 μg/mL bovine serum albumin, (final assay concentration)) (5 μl) was preincubated with 2 μl of compound for 15 minutes at 25° C. Reactions were initiated with 5 μl of 24 mM MgCl2 (10 mM final assay concentration) in buffer (50 mM HEPES (pH7.2), 1 mM dithiothreitol, 0.01% tween 20, 50 μg/mL bovine serum albumin, (final assay concentration) and incubated at 25° C. for 90 minutes and reactions were stopped by addition of 5 μl of Stop mix consisting of 65 mM HEPES (pH7.2), 35.5 mM EDTA, 0.227% Coatin Reagent 3 (Caliper/PerkinElmer), and 0.003% Tween. Phosphorylated and unphosphorylated substrate was detected by a Caliper LC3000 reader (Caliper/PerkinElmer) in the presence of separation buffer consisting of 100 mM HEPES (pH7.2), 15.8 mM EDTA, 0.1% Coatin Reagent 3 (Caliper/PerkinElmer), 0.015% Brij-35, 5% DMSO, and 5.6 mM MgCl2.