KDM5B-IN-4 (compound 11ad) is a lysine demethylase 5B ( KDM5B ) inhibitor with an IC 50 of 0.025 μM KDM5B-IN-4 increases substrate H3K4me1/2/3 level by inhibiting KDM5B in PC-3 cells. KDM5B-IN-4 downregulates PI3K/AKT. KDM5B-IN-4 reduces tumor volume in mice and shows less toxic to organs.