SPRINTer Endogenous Protein Turnover Biosensor Cell Lines are stable clonal cell lines used for monitoring drug-induced protein turnover of a specific endogenous target. Genome engineering or editing techniques, such as CRISPR/Cas9, are used to introduce a small tag into the endogenous locus of interest. This allows for the quantitation of changes in target protein levels when cells are treated with therapeutic agents such as targeted protein degraders.