XAV939 is a small molecule which selectively inhibits β-catenin-mediated transcription. It stimulates β-catenin degradation by stabilizing axin, the concentration-limiting component of the destruction complex. Using a quantitative chemical proteomic approach, XAV939 was found to stabilize axin by inhibiting the poly-ADP-ribosylating enzymes tankyrase 1 and tankyrase 2 with IC₅₀ of 11 nM and 4 nM.