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| | Kinase Inhibition Assay |
| Description: | The in vitro kinase assays were performed at Nanosyn (Santa Clara, Calif.) utilizing microfluidic detection technology. The test compounds were serially pre-diluted in DMSO and added, by the acoustic dispensing (Labcyte 550), directly to 384 well assay plates into 10 uL of a buffer with enzyme (ITK, TXK, BTK or TEC) comprising: 100 mM HEPES, pH7.5, 5 mM MgCl2, 0.1% bovine serum albumin, 1 mM DTT, 0.01% Triton X-100 and the enzyme. Final DMSO concentration was maintained at 1% in all samples, including the controls. The reactions were initiated by addition of ATP (1 mM final concentration) and the fluorescently labeled peptide substrate to a final concentration of 1 uM, and incubated for 3 hours at 25° C. Following incubation, the reactions were quenched by addition of 40 μL of termination buffer (100 mM HEPES, pH7.5, 0.01% Triton X-100, 50 mM EDTA). Terminated plates were analyzed using Caliper LabChip 3000 microfluidic electrophoresis instrument (Caliper Life Sciences/Perkin Elmer). The enzymatic modification of the peptide substrate (phosphorylation) results in a change of net charge enabling electrophoretic separation of product from substrate. As substrate and product are separated by electrophoresis, two peaks of fluorescence are observed. Change in the relative fluorescence intensity of the substrate and product peaks was the parameter measured, reflecting enzyme activity. In the presence of inhibitor, the ratio between product and substrate is altered: signal of the product decreases, while the signal of the substrate increases. Activity in each test sample was determined as the product to sum ratio (PSR): P/(S+P), where P is the peak height of the product and S is the peak height of the FAM-cAMP substrate. For each compound, enzyme activity was measured at 12 concentrations spaced by 3× dilution intervals. Negative control samples (0%-inhibition in the absence of inhibitor, DMSO only) and positive control samples (100%-inhibition, in the absence of enzyme or in the presence of control inhibitor) were assembled in replicates of four and were used to calculate %-inhibition values in the presence of compounds. Percent inhibition (Pinh) was determined using the following equation: Pinh=(PSR0%−PSRinh)/(PSR0%−PSR100%)*100, where PSRinh is the product sum ratio in the presence of inhibitor, PSR0% is the product sum ratio in the absence of inhibitor and PSR100% is the product sum ratio in 100%-inhibition control samples. To determine IC50 values, the inhibition curves (Pinh versus inhibitor concentration) were fitted by 4 parameter sigmoid dose-response model using XLfit software (IDBS). |
| Affinity data for this assay | |
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