In Vitro: MM-401 maintains high binding affinity to WDR5 with a Ki value of < 1 nM and disrupts WDR5-MLL1 interaction with an IC50 value of 0.9 nM. MM-401 is able to specifically inhibit MLL1 activity (IC50 value of 0.32µM) by blocking MLL1-WDR5 interaction and thus the complex assembly. MM-401 (20 μM; 48 h) specifically inhibits MLL1-dependent H3K4 methylation in cells. MM-401 induces similar changes in MLL-AF9 transcriptome as the MLL1 deletion. MM-401 (10, 20, 40 μM; 48 h) specifically inhibits growth of MLL leukemia cells by inducing cell cycle arrest, apoptosis.