A cell-permeable compound that targets β-catenin via direct affinity interaction within the C-terminal two thirds (a.a. 301-670) of the Armadillo repeat region (a.a. 136–686), inducing β-catenin ubiquitination and proteasomal degradation (Eff. conc. 1.25-5 µM in DLD-1, SW480 and LS174T cultures). MSAB selectively inhibits against Wnt sginaling-dependent proliferation of cancer cells (IC50 ﹤6 µM), while exhibiting little efficacy in Wnt-independent cultures (﹤10% inhibition at 10 µM). Likewise, daily intraperitoneal injection (10-20 mg/kg/day) is efficacious in suppressing the expansion of established tumors from HCT116, HT115, and H23 xenografts in mice, while exhibiting little efficacy against the Wnt-independent H460 tumor growth.