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| | Bcl-2 and Bcl-xL Inhibition |
| Description: | Fluorescein labeled BIM (81-106), BAK (72-87), and BID (79-99) peptides, named as Flu-BIM, Flu-BAK, and Flu-BID, respectively, were used as the fluorescent probes in FP assays for Bcl-2, Bcl-xL, and Mcl-1, respectively. By monitoring the total fluorescence polarization values of mixtures composed of fluorescent probes at fixed concentrations and proteins with increasing concentrations up to the full saturation, the Kd values of Flu-BIM to Bcl-2, Flu-BAK to Bcl-xL and Flu-BID to Mcl-1 were determined to be 0.55±0.15, 4.4±0.8 and 6.9±0.9 nM, respectively. Fluorescence polarization values were measured using the Infinite M-1000 plate reader (Tecan U.S., Research Triangle Park, N.C.) in Microfluor 1 96-well, black, round-bottom plates (Thermo Scientific). To each well, 1 nM of Flu-BIM, or 2 nM of Flu-BAK or 2 nM of Flu-BID and increasing concentrations of Bcl-2, or Bcl-xL, or Mcl-1 were added to a final volume of 125 μl in the assay buffer (100 mM potassium phosphate, pH 7.5, 100 μg/ml bovine γ-globulin, 0.02% sodium azide, Invitrogen, with 0.01% Triton X-100 and 4% DMSO). Plates were mixed and incubated at room temperature for 1 hour with gentle shaking to assure equilibrium. The polarization values in millipolarization units (mP) were measured at an excitation wavelength of 485 nm and an emission wavelength of 530 nm. Equilibrium dissociation constants (Kd) were then calculated by fitting the sigmoidal dose-dependent FP increases as a function of protein concentrations using Graphpad Prism 5.0 software (Graphpad Software, San Diego, Calif.). Ki values of representative Compounds of the Disclosure to Bcl-2, Bcl-xL, and Mcl-1 were determined from competitive binding experiments in which serial dilutions of inhibitors were added into 96-well plates containing fixed concentration of the fluorescent probes and proteins in each well. Mixtures of 5 μl of the tested inhibitors in DMSO and 120 μl of pre-incubated protein/probe complexes in the assay buffer were added into assay plates and incubated at room temperature for 2 hours with gentle shaking. Final concentrations of the protein and probe are 1.5 nM and 1 nM for the Bcl-2 assay, 10 nM and 2 nM for the Bcl-xL assay, and 20 nM and 2 nM for Mcl-1 assay, respectively. Negative controls containing protein/probe complex only (equivalent to 0% inhibition), and positive controls containing free probe only (equivalent to 100% inhibition), were included in each assay plate. FP values were measured as described above. IC50 values were determined by nonlinear regression fitting of the competition curves. The Ki values of competitive inhibitors were calculated using an equation described in Nikolovska-Coleska et al., Analytical Biochemistry 332: 261-73 (2004), based upon the measured IC50 values, the Kd values of the probes to the proteins, and the concentrations of the proteins and probes in the competitive assays. Ki values were also calculated using the equation of Huang, Journal of Biomolecular Screening 8:34-38 (2003). |
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