CHEMBL5735922

FPA Binding Assay: FPA Assay protocol adopted from Karatas et al. (J. Med. Chem. 2010, 5179.; J. Amer. Chem. Soc. 2013, 669.): WDR5 (Δ23, residues 24-334), is expressed and purified in sufficient quantities for screening. FITC-MLL peptide (FITC-GSARAEVHLRKS) and 10mer-Thr-FAM (ARTEVHLRKS-(Ahx-Ahx)(Lys-(5-FAM))) were purchased from GeneScript and used without additional purification. FITC-MLL peptide is used at 50 nM, while WDR5 is added at the Ki value of the protein:peptide interaction (WDR5-WIN Ki=2.5 μM). 10mer-Thr-FAM peptide is used at 4 nM, while WDR5 is added at the Ki value of the protein:peptide interaction (WDR5-10mer-Thr Ki=4 nM).Stock compounds are dispensed in barcoded 384-well plates as 30 mM solutions in DMSO. This plate is used as the source plate for the Echo Liquid Handler, which distributes the compounds to the assay plate (black, flat-bottom; Greiner) in a 10-point, 3-fold dilution scheme with a top concentration of 100 μM (5 nM low concentration) in a final volume of 50 μL. Both the top concentration and the dilution scheme can be adjusted to fit the anticipated potency of the compounds.For the FITC-MLL assay, 2.5 μM WDR5 and 50 nM FITC-MLL peptide in assay buffer (1× Phosphate Buffered Saline, pH 6.0, 300 mM NaCl, 0.5 mM TCEP, 0.1% CHAPS) is added to all compound-containing wells and to columns 2, 24 (negative control, 0% inhibition). 2 μL of 50 nM FITC-MLL peptide alone in assay buffer is added to columns 1, 23 (positive control, 100% inhibition). For the 10mer-Thr-FAM assay, a similar addition protocol is performed, using 4 nM WDR5 and 4 nM 10mer-Thr-FAM peptide in assay buffer (1× Phosphate Buffered Saline pH 6.0, 300 mM NaCl, 0.5 mM TCEP, 0.1% CHAPS).The plate is covered, shielded from light, and incubated for 60 min at room temperature, with rocking. Anisotropy is measured at excitation wavelength 480 nm and emission wavelength 535 nm using an EnVision Multi-label plate reader (PerkinElmer, Wellesley, Mass., USA) or a BioTek Cytation 3 (BioTek, Winooski, Vt., USA). Fluorescence anisotropy is plotted against compound concentration to generate an IC50 (inhibitor concentration at which 50% of bound peptide is displaced) by fitting the data to a 4-parameter logistic model using XLFit software (Guildford, Surrey, UK). IC50 is converted to a binding dissociation constant (Ki value) according to the formula of Wang Z. FEBS Lett (1996) 3, 245.K i=[I]50/([L]50 /K d+[P]0 /K d+1)where [I]50 is the concentration of the free inhibitor at 50% inhibition, [L]50 is the concentration of the free labeled ligand at 50% inhibition, [P]0 is the concentration of the free protein at 0% inhibition, Kd represents the dissociation constant of the FITC-MLL or 10mer-Thr-FAM probe for WDR5. Total fluorescence is also measured, to rule out compounds that are inherently fluorescent or able to act as quenchers in the assay.