Abstract 1835: Discovery of HSN003839, a highly potent inhibitor of ubiquitin-specific protease USP21 for cancer therapy

Abstract USP21 belongs to the ubiquitin-specific protease (USP) subfamily of deubiquitinating enzymes (DUBs), which catalyze the removal of ubiquitin chain from targeted proteins. Numerous efforts over the last decade have identified a wide range of USP21 substrates and revealed the momentous and multifaceted role of USP21 in physiological and pathological states, especially in tumorigenesis, indicating that USP21 is an appealing target for the therapy of many correlative diseases. Nevertheless, progress in the development of potent USP21 inhibitors remains limited. Herein, we present the discovery of HSN003839, a highly potent and selective USP21 inhibitor with excellent anticancer activity and drug-like properties. Following screening tool compounds to identify hits and subsequent optimization, we discovered a series of compounds with strong enzymatic inhibition for USP21 with IC50 < 100 nM. Among them, HSN003839 displayed low nanomolar cancer cells proliferation inhibitions and excellent ADMET properties. The mouse oral bioavailability (F) is 76.5% at 10 mg/kg. In a preliminary mouse CDX model, monotherapy of HSN003839 showed 105% tumor growth inhibition (TGI) at 30 mg/kg with no obvious body weight reduction. Further biological characterization, efficacy and toxicity studies are ongoing. The structure of HSN003839 was not presented and will not be disclosed at the time of presentation at AACR meeting. Citation Format: Xiaohui Liu, Ying Wang, Dongliang Xia, Wei Zhang, Yan He, Shijie Tian, Xuerong Feng, Xia Yang, Qi Zhang, Fei Liu, Shiyi Jiang, Ran Hu, Ming Tang, Xuelin Tang, Yuqing Liu, Weijiao Yuan, Xuedan You. Discovery of HSN003839, a highly potent inhibitor of ubiquitin-specific protease USP21 for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1835.