The potency of SP600125 towards kinases, including MPS1, JNK, and Aurora kinase A, is determined based on the specific measurement of radioactive phosphotransfer to the substrate. For each enzyme, the absolute Km values for ATP and the specific substrate are initially determined and each assay is then run at optimized [ATP] (2·αKm) and [substrate] (5·Km) concentrations. MPS1 activity is measured using 5 nM of MPS1 recombinant protein in 50 mM HEPES pH 7.5, 2.5 mM MgCl2, 1 mM MnCl2, 1 mM DTT, 3 μM NaVO3, 2 mM β-glycerophosphate, 0.2 mg/mL BSA, 200 μM P38-βtide substrate-peptide (KRQADEEMTGYVATRWYRAE), and 8 μM ATP with 1.5 nM 33P-γ-ATP. Ten serial 1:3 dilutions (from 30 μM to 1.5 nM) of SP600125 are tested and IC50 determined.
Method: Cells are seeded in 384 well-plates. One day after seeding, the cells are treated with SP600125 for 72 hours and the plates are then processed using a CellTiter-Glo assay. Inhibitory activity is evaluated comparing treated versus control data and IC50 value of proliferation is calculated.
Features:JNK-IN-8 and JNK-IN-7 are structurally very similar, but whereas the former is a specific covalent inhibitor of JNKs.