A WDR5/MLL interaction inhibitor (IC50 = 2.4 nM) that blocks MLL1 methyltransferase activity, reducing the expression of HoxA9 and Meis-1 genes, which are both critical MLL1 target genes in MLL1 fusion protein-mediated leukemogenesis; inhibits cell growth and induces apoptosis in leukemia cells harboring MLL1 fusion proteins.