HDAC9 and cancer: Previous studies have shown that the inhibition of PADI enzymatic activity by Cl-amidine is effective in decreasing the growth of several cancer cell lines (i.e. HL-60, HT-29, U2OS, and MCF7 cells), and that administering the drug in combination with doxorubicin or the HDAC inhibitor SAHA can have synergistic cytotoxic effects on cells [8,9,11,45].