In vitro activity: XAV-939 specifically inhibits tankyrase PARP activity. XAV-939 dramatically decreases DNA-PKcs protein levels, confirming the critical role of tankyrase poly-ADP-ribosylation activity in maintaining stability of the DNA-PKcs protein. The greatest reduction of DNA-PKcs protein levels (< 25% relative expression compared to DMSO treated controls) occurs at 12 hours with 1.0 μM XAV-939 exposure. Treatment of human lymphoblasts with 1.0 μM XAV-939 results in marked elevation of tankyrase 1 levels. XAV-939 is axin stabilizing agent. XAV-939 stimulates beta-catenin degradation by stabilizing axin, the concentration-limiting component of the destruction complex. XAV-939 stabilizes axin by blocking the poly-ADP-ribosylating enzymes tankyrase 1 and tankyrase 2. Both tankyrase isoforms interact with a highly conserved domain of axin and stimulate its degradation through the ubiquitin-proteasome pathway. XAV-939 deregulates the Wnt/b-catenin pathway which has been implicated in many cancers.

Kinase Assay: To assess the effect of compounds on auto-PARsylation of TNKS, 1 μM GST fusion protein containing the SAM domain and the PARP domain of TNKS2 (a.a. 872-1166) is mixed with 5 μM biotin-NAD+ and 2 μM XAV939 or LDW643 at 30°C for 2.5 hours. Samples are resolved by SDS-PAGE and probed with streptavidin AlexaFluor680. To assess PARsylation of axin, recombinant full-length TNKS2 (expressed/purified as a N-terminal His-tagged protein in bacteria) is incubated with GST-axin 1 (1-280) in the presence of biotin-NAD+ with or without XAV939. The products are resolved and probed with Streptavidin-HRP and imaged using a AlphaInnotech imager. To assess the effect of XAV939, IWR-1-enod, IWR-1-exo, and ABT-888 on auto-PARsylation of TNKS2, His-tagged full-length TNKS2 is incubated with 5 μM biotin-NAD+ and 3 mM of indicated compounds. The products are resolved and probed with Streptavidin-HRP. LC/MS-based high throughput auto-PARsylation assays for PARP1, PARP2, TNKS1, and TNKS2 are setup to monitor the formation of nicotinamide (a by-product of the PARsylation reaction) in the presence of small molecule inhibitors.

Cell Assay: XAV-939 is solubilized in DMSO at 55 °C to make a 10 mM stock solution which may be diluted later to a working concentration of 100 μM. WTK1 lymphoblasts treated with either DMSO or 1.0 μM XAV-939 for 8 hours are loaded into independent wells of a 4-20% gradient SDS-PAGE every 2 hours over the course of 6 hours. At each time point, DMSO and XAV-939 samples are loaded into wells immediately adjacent to the prior time point. The corresponding load times at 0, 2 and 4 hours results in total run times of 2, 4 and 6 hours respectively. The gel is analyzed via western blot for DNA-PKcs following completion of the final run time and is quantified after normalization to actin loading controls.

Nature. 2009 Oct 1;461(7264):614-20; Ann Rheum Dis. 2013 Sep 1;72(9):1575-80.