lysine specific demethylase 1 (LSD1) has become an emerging and promising target for cancer immunotherapy. Herein, based on our previously reported LSD1inhibitor DXJ-1 (also called 6x), a series of novel acridine-based LSD1inhibitors were identified via structure optimizations. Among them, compound 5ac demonstrated significantly enhanced inhibitory activity against LSD1 with an IC50 value of 13 nM,