CDDO-Me reveals USP7 as a novel target in ovarian cancer cells

// Dongjun Qin 1, * , Weiwei Wang 1, * , Hu Lei 1, * , Hao Luo 1, * , Haiyan Cai 1 , Caixia Tang 1 , Yunzhao Wu 1 , Yingying Wang 2 , Jin Jin 1 , Weilie Xiao 3 , Tongdan Wang 1 , Chunmin Ma 1 , Hanzhang Xu 1 , Jinfu Zhang 1 , Fenghou Gao 2 , Ying-Li Wu 1 1 Hongqiao International Institute of Medicine, Shanghai Tongren Hospital/Faculty of Basic Medicine, Chemical Biology Division of Shanghai Universities E-Institutes, Key Laboratory of Cell Differentiation and Apoptosis of the Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China 2 Institute of Oncology, Shanghai 9th People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China 3 State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Yunnan, China * These authors contributed equally to this work Correspondence to: Ying-Li Wu, email: wuyingli@shsmu.edu.cn Fenghou Gao, email: fenghougao@163.com Jinfu Zhang, email: zhangjinfu@tongji.edu.cn Keywords: CDDO-Me, ovarian cancer, USP7, CETSA, deubiquitinating enzymes Received: December 29, 2015      Accepted: October 14, 2016      Published: October 21, 2016 ABSTRACT Deubiquitinating enzyme USP7 has been involved in the pathogenesis and progression of several cancers. Targeting USP7 is becoming an attractive strategy for cancer therapy. In this study, we identified synthetic triterpenoid C-28 methyl ester of 2-cyano-3, 12-dioxoolen-1, 9-dien-28-oic acid (CDDO-Me) as a novel inhibitor of USP7 but not of other cysteine proteases such as cathepsin B and cathepsin D. CDDO-Me inhibits USP7 activity via a mechanism that is independent of the presence of α, β-unsaturated ketones. Molecular docking studies showed that CDDO-Me fits well in the ubiquitin carboxyl terminus-binding pocket on USP7. Given that CDDO-Me is known to be effective against ovarian cancer cells, we speculated that CDDO-Me may target USP7 in ovarian cancer cells. We demonstrated that ovarian cancer cells have higher USP7 expression than their normal counterparts. Knockdown of USP7 inhibits the proliferation of ovarian cancer cells both in vitro and in vivo . Using the cellular thermal shift assay and the drug affinity responsive target stability assay, we further demonstrated that CDDO-Me directly binds to USP7 in cells, which leads to the decrease of its substrates such as MDM2, MDMX and UHRF1. CDDO-Me suppresses ovarian cancer tumor growth in an xenograft model. In conclusion, we demonstrate that USP7 is a novel target of ovarian cancer cells; targeting USP7 may contribute to the anti-cancer effect of CDDO-Me. The development of novel USP7 selective compounds based on the CDDO-Me-scaffold warrants further investigation.