Example 28
SPR Assay to Determine Binding Affinity to FKBP12.
Biotinylated avi-FKBP12 was immobilized on a streptavidin chip (Cytiva Series S SA) using a Biacore 8K or 8 k+ (Cytiva). To achieve an immobilization level of 1000 RU, 2 μg/ml biotinylated avi-FKBP12 were injected for 100 sec at a flow rate of 10 μl/min. Rapalogs were diluted in DMSO to 100× working concentration. Each Rapalog was 100-fold diluted in 50 mM HEPES pH 7.5, 150 mM NaCl, 2 mM MgCl2, 1 mM DTT, 0.05% Tween-20 and a serial dilution prepared (9 concentrations, 3-fold dilutions, 0.08-500 nM). Rapamycin was used as reference sample (9 concentrations, 3-fold dilutions, 0.02-100 nM). The compound dilutions were then injected at 100 uL/min for 120 seconds contact time in sequence with increasing concentrations. Dissociation was monitored for 3600 seconds. 50 mM HEPES pH 7.5, 150 mM NaCl, 2 mM MgCl2, 1 mM DTT, 0.05% Tween-20, 1% DMSO was used as running buffer. The single-cycle kinetics data were fit to a 1:1 binding model to measure the association rate ka (1/Ms), the dissociation rate kd (1/s) and the affinity Kd (M). Table 8 includes FKBP12 direct binding Kd (nM) values of selected compounds; with compounds having a FKBP12 direct binding Kd of less than 0.3 nM as A, 0.3 nM to 1.0 nM as B, and greater than 1.0 nM as C.