CHEMBL3705262

Fluorescence Polarization Competition Immunoassay: A fluorescence polarization competition immunoassay was used to measure compound inhibition of CSF-1R phosphorylation of tyrosine on a synthetic CSF-1R555-568 peptide (SYEGNSYTFIDPTQ). The assay was performed in black 96-well microplates (Cat #42-000-0117, Molecular Devices, Sunnyvale, Calif.). To each well, 5 μL of compound (in 4% DMSO) were mixed with 2 μL of 3.5 nM CSF-1R, 25 mM MgCl2 in assay buffer (100 mM HEPES, pH 7.5, 1 mM DTT, 0.01% Tween-20), and 2 μL of 1540 μM peptide in assay buffer. The kinase reaction was initiated by adding 1 μL of 10 mM ATP in assay buffer. The final concentrations in the 10 μL reaction mixture were 100 mM HEPES, pH 7.5, 1 mM DTT, 0.01% Tween-20, 2% DMSO, 308 μM SYEGNSYTFIDPTQ, 1 mM ATP, 5 mM MgCl2, and 0.7 nM CSF-1R. Positive and negative control wells were included on each plate, where 4% DMSO in assay buffer was substituted for the compound; in addition, positive control wells received 1.2 μL of 50 mM EDTA before the start of the reaction. The plates were covered and incubated at room temperature for 80 min. Reactions were stopped by addition of 1.2 μL of 50 mM EDTA. Each well then received 10 μL of a 1:1:3 mixture of 10× anti-phosphotyrosine antibody, 10× PTK green tracer, and FP dilution buffer, respectively (Cat. #P2837, Invitrogen, Carlsbad, Calif.). The plates were covered, incubated for 30 min at room temperature, and the fluorescence polarization was read on an Analyst plate reader (Molecular Devices). Instrument settings were: 485 nm excitation, 530 nm emission, with a 505 nm cut-off filter; Z height: middle of well; G factor: 0.93. Under these conditions, the fluorescence polarization values for positive and negative controls were approximately 290 and 160, respectively, and were used to define 100% and 0% inhibition of the CSF-1R reaction.