Cell-based assays are costly and complex to establish. They are not cost-effective especially for screening a large small molecule or PROTAC library. In vitro assays are the most efficient way to initiate a drug/PROTAC discovery program. First, in vitro assays are quicker to validate and optimize since it uses purified components. More importantly, they allow for the simultaneous screening for a large number of molecules. The effect of the selected molecules can then be confirmed through biophysical validation assays followed by cell-based assays.