Inhibition of tankyrase by a novel small molecule significantly attenuates prostate cancer cell proliferation.

Tankyrase (TNKS) is a crucial mediator of Wnt signal transduction and has been recognized as a novel molecular target for Wnt-pathway dependent cancer. TNKS is stabilized by the ubiquitin-specific protease 25 (USP25). The effect of disruption of the interaction between TNKS and USP25 by small molecules on prostate cancer proliferation is unknown. In this study we conducted a hierarchical virtual screening with more than 200,000 compounds on the characterized structures of the USP25/TNKS-ARC5 protein complex. In silico analysis and in vitro validation revealed that a small molecule, called C44, binds to the protein-protein interaction (PPI) interface of TNKS and USP25. We show that C44 disrupts the interaction between TNKS and USP25 leading to a higher half-life of AXIN and the breakdown of -catenin protein. We also show that the selective inhibition of the TNKS-USP25 interaction by C44 significantly reduces proliferation of prostate cancer cells in vitro and in vivo. Our study reveals a new PPI inhibitor that lowers the stability of TNKS protein and inhibits Wnt pathway signaling. C44 is a promising new drug for the treatment of Wnt-pathway dependent prostate cancer.