Abstract B077: Pre-clinical evaluation of a potent and plasma-stable Pin1 degrader in a mouse model of pancreatic cancer

Abstract Background: The prolyl isomerase Pin1 regulates the function and stability of oncogenic and tumor suppressor proteins and is overexpressed in both tumor cells and cancer-associated fibroblasts (CAFs), contributing to tumor progression. While Pin1 has long been recognized as a potential therapeutic target, the development of clinically viable inhibitors has been limited. We previously reported a novel class of covalent Pin1 destabilizers that promote degradation of Pin1 in vitro. In this study, we optimized this class to improve pharmacokinetics and investigated the efficacy of a lead degrader, 164B8, in cellular and in vivo models of pancreatic cancer. Methods: DELFIA displacement assays and thermal shift analyses were used to assess compound binding and stability effects. Covalent binding was confirmed by mass spectrometry, and NMR spectroscopy was used to characterize ligand-induced conformational changes in Pin1. Stability was assessed in aqueous buffer and plasma from human and mouse donors. Western blotting quantified cellular Pin1 degradation in human (BxPC3, MIA PaCa-2) and mouse (KPC) pancreatic cancer cells, as well as in primary CAFs derived from peritoneal metastases of three gastrointestinal cancer patients. In vivo efficacy was tested in NSG mice injected intraperitoneally with KPC-GFP-Luc cells, treated daily with 164B8 (30 or 60 mg/kg, i.p.) for 14 days. Tumor burden was monitored by bioluminescence imaging, and compound accumulation and Pin1 levels in tumor tissues were quantified by LC-MS and immunoblotting, respectively. Results: 164B8 showed potent inhibition of Pin1 in vitro (IC50 = 4.65 ± 0.04 nM; ΔTm = –9.55 ± 0.19 °C) and improved plasma stability across human and mouse plasma samples (t1/2 > 4.5 h). It induced robust, dose-dependent degradation of Pin1 in all three pancreatic cancer cell lines and in CAFs derived from appendiceal, pancreaticobiliary, and colorectal peritoneal metastases. In vivo, both 30 and 60 mg/kg doses significantly reduced tumor burden compared to vehicle control (P = 0.0021 and P < 0.001, respectively). Drug accumulation was enriched in tumor tissues compared to adjacent normal tissues and liver (P = 0.035 and P = 0.0003, respectively). Western blotting confirmed Pin1 degradation in tumor samples. Treatment was generally well tolerated; mild anemia and moderate thrombocytopenia were observed only at the higher dose. Conclusions: These findings identify 164B8 as a potent, plasma-stable Pin1 degrader with robust anti-tumor activity in vitro and in vivo. Its dual activity in both cancer cells and CAFs, along with favorable tolerability and pharmacokinetics, highlights its potential as a therapeutic candidate for pancreatic and gastrointestinal cancers with peritoneal metastases. Citation Format: Tiane Li, Giulia Alboreggia, Mustafa Raoof, Maurizio Pellecchia. Pre-clinical evaluation of a potent and plasma-stable Pin1 degrader in a mouse model of pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_3):Abstract nr B077.