An inhibitor of the Tcf4-β-catenin protein interaction; disrupts binding of β-catenin to a GST-Tcf4 fusion protein in HCT116 cell lysates (IC50 = 0.8 μM); blocks appearance of the Tcf4 and β-catenin complex bound to DNA in an EMSA assay; reduces levels of the β-catenin regulated proteins c-Myc and cyclin D1 in HCT116 cells; reduces growth of HCT116, HT-29, PC3, and DU145 cancer cells in vitro (IC50s = 170-300 nM); reduces tumor growth and expression of c-Myc, cyclin D1, and Survivin in a HepG2 mouse xenograft model (1 mg/kg twice per week)