Substrate optimization for monitoring cathepsin C activity in live cells

A series of peptidic fluorogenic substrates were synthesized to develop a flow cytometry assay (FACS) to monitor the proteolytic activity of cathepsin C in live cells. Of the 16 substrates tested, (NH2-aminobutyric-homophenylalanine)2-rhodamine demonstrated the best reactivity and selectivity profile in the FACS assay using the B721 human B-lymphoblastoid cell line. The resulting FACS assay was validated through correlation of the IC50 values with a competitive radiolabeling assay against a series of small molecule inhibitors of cathepsin C.

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