Fluorescence Polarisation Assay: The fluorescence polarisation tests were carried out on microplates (384 wells). The Bcl-2 protein, at a final concentration of 2.50×10−8 M, is mixed with a fluorescent peptide (Fluorescein-REIGAQLRRMADDLNAQY), at a final concentration of 1.00×10−8 M in a buffer solution (Hepes 10 mM, NaCl 150 mM, Tween20 0.05%, pH 7.4), in the presence or in the absence of increasing concentrations of test compounds. After incubation for 2 hours, the fluorescence polarisation is measured.
Time Resolved-Fluorescence Resonance Energy Transfer (TR-FRET) Assay: The inhibition constant (Ki) is the dissociation constant of an enzyme-inhibitor complex or a protein/small molecule complex, wherein the small molecule is inhibiting binding of one protein to another protein or peptide. Where the Ki for a compound is represented as > (greater than) a certain numerical value, it is intended to mean that the binding affinity value (e.g., for Bcl-XL) is greater than the limits of detection of the assay used. Where the binding selectivity ratio for a compound is represented as > (greater than) a certain numerical value, it is intended to mean that the selectivity of a particular compound for Bcl-2 over Bcl-XL is at least as great as the number indicated. Where the Ki for a compound is represented as < (less than) a certain numerical value, it is intended to mean that the binding affinity value (e.g., for Bcl-2) is lower than the limit of detection of the assay used. Inhibition constants were determined using Wang's equation (Wang Z-X).
Fluorescence Polarization-Based Binding Assay: Sensitive and quantitative FP-based binding assays were developed and optimized to determine the binding affinities of small-molecule inhibitors to the recombinant Mcl-1, A1/Bfl-1, Bcl-w, Bcl-2, and Bcl-xL proteins. The concentrations of the proteins used in the competitive binding experiments were 10 nM for Mcl-1, 80 nM for Bcl-xL, and 60 nM for Bcl-2. The fluorescent probes, Flu-BID or FAM-BID were fixed at 2 nM for all assays, which binds with Kd values of 2.3 nM, 14.2 nM and 24.1 nM against Mcl-1, Bcl-2 and Bcl-xL respectively. 5 μL of the tested compound in DMSO and 120 μL of protein/probe complex in the assay buffer (20 mM phosphate pH 7.4, 50 mM NaCl, 1 mM EDTA. 0.05% Pluronic F68)s) were added to 96 well black assay plates, incubated at room temperature for 3 h and the polarization values (mP) were measured at an excitation wavelength at 485 nm and an emission wavelength at 530 nm using the plate reader Synergy H1 Hybrid, BioTek.