XAV939 is a potent, small molecule inhibitor of tankyrase 1 (TNKS) (IC₅₀ = 11 nM) and tankyrase 2 (IC₅₀ = 4 nM). By inhibiting TNKS activity, XAV939 increases the protein levels of the axin-GSK3β complex and promotes the degradation of β-catenin in SW480 cells. At concentrations as low as 0.3 μM, XAV939 inhibits colony formation of APC-deficient colorectal cancer cells.