The importance of measuring drug target residence times

Target-based approaches to drug discovery have traditionally sought compounds of high binding affinity to the drug target. Affinity of inhibitory compounds is classically assessed using a labeled ligand which is competed from binding to the drug target. The important attributes of the inhibitory compound are its IC50 evaluated from inhibitor dose-response curves and its dissociation constant of binding, Ki as calculated from this empirical data using the Cheng-Prusoff equation, knowing the concentration of labeled ligand used in the assay and its equilibrium dissociation constant, Kd.

However, in recent years drug target kinetics has become an alternate method of evaluating inhibitors rather than the thermodynamic approach as outlined above. In these assays, the reciprocal of the inhibitor off rate, 1/koff, or the inhibitor residence time on the drug target, computed with the Motulsky and Mahan equation, becomes the important attribute. Various studies have shown that drug residence times are a promising early stage indicator of in vivo drug activity.

Accurately measuring inhibitor residence times requires detection of readouts with adequate temporal resolution to determine the key variables of the Motulsky and Mahan equation. This is particularly important for ratiometric readouts where the readout consists of a ratio of two signals. The Synergy Neo2 Multi-Mode Reader is designed to provide high temporal resolution in drug target kinetics applications, even with ratiometric measurements like HTRF®, by the simultaneous detection of time-resolved fluorescence at 620 and 665nm which provides improved temporal resolution and more accurate data than fast sequential measurements. With a high power Xe flashlamp for excitation that limits the number of flashes/measurement required for good sensitivity, along with its simultaneous detection capabilities, the Synergy Neo2 can provide temporal resolution < 1sec with high sensitivity for drug target kinetic studies…