靶向肿瘤干细胞的治疗策略是改善传统肿瘤治疗效果的有效途径。Wnt信号通路是肿瘤干细胞自我更新和干性维持的关键通路，泛素蛋白酶体系统在Wnt信号通路调控中发挥重要作用。我们前期研究发现泛素特异性蛋白酶USP7通过稳定β-catenin正向调控Wnt信号通路，为靶向该信号通路的抗肿瘤药物提供了新的作用靶点。依托国家重点实验室的天然产物研究优势，我们对天然产物及衍生物库进行了USP7抑制剂筛选，发现β-咔啉化合物Z86具有明显活性。初步的研究表明Z86能促进β-catenin降解，抑制Wnt信号通路，显著抑制肿瘤干细胞自我更新，极具研究价值和开发潜力。本项目拟利用化学生物学和药理学手段，解析β-咔啉化合物作为新颖USP7抑制剂的分子机制和构效关系，阐明Z86调控Wnt信号通路的分子机制，系统评价Z86抑制肿瘤干细胞的药效和药理，为USP7抑制剂在靶向肿瘤干细胞药物中的可能应用提供理论依据。

The cancer-stem-cell (CSC) model indicates that anti-cancer therapies targeting the cancer stem cells would ultimately improve conventional cancer treatments like surgery, radiotherapy and chemotherapy. Accumulating evidences have revealed a critical role for Wnt signaling in maintaining stem-cell like properties of CSCs and its self-renewal, and thus suggesting that this signaling is a promising target for treating cancers through inhibiting CSCs. Given that Wnt signaling is stringently regulated by ubiquitin-proteasome system, our recent work revealed that USP7 played a positive role in Wnt pathway through deubiquitinating and stabilizing β-catenin and validated that USP7 could be a novel drug target for anti-cancer agents targeting Wnt signaling. Taking the advantage of the strong research capability on natural products of the state key laboratory of phytochemistry and the west plant resources, we screened the library of natural compounds and derivatives and discovered β-carboline molecule Z86 as a novel inhibitor of USP7 activity. Preliminary study suggested that Z86 antagonized Wnt signaling via destabilizing β-catenin and inhibited self-renewal of CSCs. In this project, with chemical biology and pharmacology techniques, the molecular mechanisms and the structure-activity relationship of the β-carbolines as USP7 inhibitors will be investigated. Further we will elucidate molecular mechanisms by which Z86 regulating Wnt signaling and perform comprehensive pharmacological investigation on the inhibitory effect of Z86 on cancer stem cells. Especially, we will explore the roles of USP7 in the maintenance of cancer stem cells, in order to provide theoretical basis for the application of USP7 inhibitors as valuable candidate antitumor agents targeting cancer stem cells.