Abstract 519: A novel Skp1 inhibitor has potent preclinical efficacy against metastatic castration-resistant prostate cancer
Authors: Li Xin , Mamouni Kenza , Zhao Rui , Wu Yifei , Xie Zhong-Ru , Sautto Giuseppe , Liu Degang , Bowen Nathan , Danaher Alira , Gera Lajos , Wu Daqing 
Published: April 2023

Abstract
Purpose: Despite numerous therapeutic modalities, including chemotherapy and next-generation androgen deprivation therapy, metastatic castration-resistant prostate cancer (mCRPC) remains a dreadful evolution and still bears a poor prognosis for most patients who develop metastases to bones and other organs, which have no cure. It is urgent to identify new molecular targets and develop novel therapeutic agents against lethal mCRPC.
Methods: We developed a novel small-molecule anticancer compound named GH501 via a “molecular hybridization” approach. The in vitro cytotoxicity of GH501 was evaluated in the NCI-60 human cancer cell panel and human mCRPC cell lines. Molecular targets of GH501 were investigated using in silico docking, biolayer interferometry, cellular thermal shift assay, and other molecular and cellular approaches. The in vivo anticancer efficacy of GH501 against mCRPC was evaluated in clinically-relevant xenograft models.
Results: GH501 effectively inhibited the in vitro proliferation of NCI-60 human cancer cell lines and established mCRPC cell lines, including African American prostate cancer (PCa) cells, at nanomolar potency by inducing cell cycle arrest and apoptosis. Mechanistically, GH501 might bind S-phase kinase-associated protein 1 (Skp1) and disrupt the physical interaction between Skp1 and S-phase kinase-associated protein 2 (Skp2), thereby affecting multiple oncogenic signals implicated in mCRPC progression. RNA-Seq analyses indicated that GH501 treatment in C4-2 cells significantly inhibited E2F-, G2/M checkpoint, c-Myc- and β-catenin-regulated genes, androgen receptor (AR) transcription, androgen-responsive genes, and enhancer of zeste homolog 2 (EZH2)-activated genes. Proteomic studies identified 109 proteins upregulated and 154 proteins downregulated significantly by GH501 in CRW22Rv1 cells. The top physiological processes and signaling pathways affected by GH501 included cell cycle, autophagy, steroid biosynthesis, DNA replication, p53, AMP-activated protein kinase (AMPK), and mitogen-activated protein kinase (MAPK). As a lead compound, GH501 had excellent preclinical safety. In animal studies, GH501 monotherapy effectively inhibited the skeletal and subcutaneous growth of four mCRPC xenografts with heterogeneous genetic backgrounds.
Conclusion: These results support that pharmacological interruption of Skp1-Skp2 interaction is a promising therapeutic strategy for mCRPC. To our knowledge, GH501 is the first synthetic Skp1 inhibitor with a unique chemical structure that can serve as the basis for lead optimization and development.
Citation Format: Xin Li, Kenza Mamouni, Rui Zhao, Yifei Wu, Zhong-Ru Xie, Giuseppe Sautto, Degang Liu, Nathan Bowen, Alira Danaher, Lajos Gera, Daqing Wu. A novel Skp1 inhibitor has potent preclinical efficacy against metastatic castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 519.