cis-4-Br-2,5-F2-PCPA (S1024) is a selective inhibitor of lysine-specific demethylase 1 ( LSD1 ), with a K i value of 94 nM instead of 8.4 μM for LSD2. There is aberrant expression of LSD1 in cancer stem cells , cis-4-Br-2,5-F2-PCPA inhibits LSD1 cell proliferation and by increasing the level of dimethylated histone H3 at K4 (H3K4) in CCRF-CEM cells.