Tankyrase inhibitors attenuate WNT/β-catenin signaling and inhibit growth of hepatocellular carcinoma cells

// Li Ma 1 , Xiaolin Wang 1, 3 , Tao Jia 2 , Wei Wei 1 , Mei-Sze Chua 1 , Samuel So 1 1 Asian Liver Center and Department of Surgery, Stanford University School of Medicine, Stanford University, Stanford, CA 94305, USA 2 School of Pharmaceutical Sciences, Wuhan University, Wuhan, Hubei, 430072, China 3 Guangdong Institute of Gastroenterology, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital, Sun Yat-Sen University, Guangzhou, Guangdong, 510655, China Correspondence to: Mei-Sze Chua, e-mail: mchua@stanford.edu Keywords: WNT/β-catenin signaling, hepatocellular carcinoma, tankyrase inhibitors, β-catenin/TCF complexes, targeted therapy Received: March 20, 2015 Accepted: June 15, 2015 Published: June 27, 2015 ABSTRACT Deregulated WNT/β-catenin signaling contributes to the development of a subgroup of hepatocellular carcinoma (HCC), the second leading cause of cancer deaths worldwide. Within this pathway, the tankyrase enzymes (TNKS1 and TNKS2) degrade AXIN and thereby enhance β-catenin activity. We evaluate TNKS enzymes as potential therapeutic targets in HCC, and the anti-tumor efficacy of tankyrase inhibitors (XAV939, and its novel nitro-substituted derivative WXL-8) in HCC cells. Using semi-quantitative RT-PCR, we found significantly elevated levels of TNKS1/2 mRNA in tumor liver tissues compared to adjacent non-tumor livers, at protein levels only TNKS1 is increased. In HepG2, Huh7cells, siRNA-mediated knockdown suppression of endogenous TNKS1 and TNKS2 reduced cell proliferation, together with decreased nuclear β-catenin levels. XAV939 and WXL-8 inhibited cell proliferation and colony formation in HepG2, Huh7, and Hep40 cells ( p < 0.05), with stabilization of AXIN1 and AXIN2, and decreased β-catenin protein levels. XAV939 and WXL-8 also attenuated rhWNT3A-induced TOPflash luciferase reporter activity in HCC cells, indicating reduced β-catenin transcriptional activity, consistent with decreased nuclear β-catenin levels. In vivo , intra-tumor injections of XAV939 or WXL-8 significantly inhibited the growth of subcutaneous HepG2 xenografts ( P < 0.05). We suggest that tankyrase inhibition is a potential therapeutic approach for treating a subgroup HCC with aberrant WNT/β-catenin signaling pathway.