Peptidyl arginine deiminase 4 (PAD4, Protein arginine deiminase 4) catalyzes the post-translational modification of arginine residues on histones to form citrulline, which plays a large role in regulating gene expression. Dysregulated PAD4 activity has been implicated in cancer and rheumatoid arthritis. F-amidine inhibits PAD4 activity with an IC50 value of 21.6 μM in an in vitro activity assay. It irreversibly inactivates (kinact/KI = 3,000 M-1min-1) PAD4 by covalently modifying an active site cysteine that is important for its catalytic activity. F-amidine also inhibits PAD1 and PAD3 with IC50 values of 29.5 and 350 μM, respectively. F-amidine is cytotoxic to HL-60, MCF-7, and HT-29 cancer cell lines (IC50s = 0.5, 0.5 and 1 μM, respectively).
