InCELL Hunter™ assay detects degradation of a partner protein that is ordinarily stabilized by its natural interaction with the target protein. The cell lines are engineered to co-express an untagged target protein, and an Enzyme Donor (ED) tagged partner protein. Either protein may be full length or truncated. Addition of inhibitors disrupting the interaction of the two proteins results in degradation of the ED-tagged protein. Addition of exogenous Enzyme Acceptor (EA), and buffer, lyses the cell and forces complementation of the ED and EA enzyme fragments. This results in the formation of a functional enzyme that hydrolyzes substrate to generate a chemiluminescent signal.