Tankyrase1/2 Inhibitor, XAV939

A cell-permeable dihydrothiopyranopyrimidinol that binds TNKS1/PARP5a and TNKS2/PARP5b with high affinity (K_d = 99 and 93 nM, respectively) and potently inhibits their PARsylation (poly ADP-ribosylation) activity (IC₅₀ = 11 and 4 nM, respectively), while exhibiting much lower activity against PARP1 and PARP2 (IC₅₀ = 2.194 and 0.114 µM, respectively). TNKS, but not PARP1/2, function knockdown by siRNA or XAV939 treatment suppresses cellular axin1/2 PARsylation and ubiquitination/proteasomal degradation, resulting in axin build-up, β-catenin destruction, and blockage of Wnt signaling. XAV939 is shown to inhibit the growth of β-catenin-dependent DLD-1, but not that of β-catenin-independent RKO, cells (by >95% vs. no effect at 3.3 µM, respectively) in vitro and prevent the regeneration of zebrafish tail fin (by ~70% at 7 d post-amputation, 5 µM) after surgical removal in vivo.