S 2101 is a lysine-specific demethylase 1 (LSD1) inhibitor with an IC50 of 0.99 μM, Ki of 0.61 μM and Kinact/Ki of 4560 M/s. S 2101 is a lysine-specific demethylase 1 (LSD1) inhibitor with an IC50 of 0.99 μM, Ki of 0.61 μM and Kinact/Ki of 4560 M/s. S 2101 also displays much lower inhibition activity toward MAO-B (Ki=17 µM, Kinact/Ki=18 M/s) and MAO-A (Ki=110 µM, Kinact/Ki=60 M/s). The treatment of HEK293T cells with S 2101 results in a dose-dependent increase in the level of H3K4me2, which must have accumulated by the inactivation of LSD1. During the course of S 2101 treatment, the amounts of histone H3 and LSD1 in the nuclear extracts remain essentially unaffected. Because the treatment with 1 μM S 2101 generates a level of H3K4me2 similar to that elicited by 50 μM 2-PCPA, S 2101 is assumed to have approximately 50-fold stronger LSD1 inhibition activity than 2-PCPA in human cells.