Abstract 2894: NTX-452: a non-covalent, potent, selective and highly efficacious WRN inhibitor with best-in-class potential for the treatment of MSI-H tumors

Abstract Microsatellite instability (MSI-H) is a phenotypic consequence of defective mismatch repair (dMMR) in cancer and is observed in over 20 solid tumor types, with the highest prevalence in colorectal, gastric and endometrial cancers. While the treatment landscape of MSI-H is improving with the use of immune checkpoint inhibitors, substantial unmet medical need remains for patients with MSI-H cancers that fail to respond or relapse on standard-of-care therapies. Werner Syndrome Helicase (WRN) has been validated as a promising synthetic lethal drug target for MSI-H tumors, thus inhibitors of WRN may offer a novel therapeutic option for patients with MSI-H tumors. Our efforts to develop inhibitors of WRN led to the generation of two series of novel small molecules that had either a covalent or non-covalent mechanism of action. Treatment of MSI-H cell lines with exemplars from each series led to dose-dependent and rapid degradation of WRN protein, followed by an accelerated WRN protein re-synthesis rate that was independent of inhibitor mechanism. Washout studies using covalent inhibitors revealed that substantial target engagement was lost in MSI-H cells within 24- hours, suggesting rapid WRN resynthesis may limit sustained target inhibition. Prioritization of our non-covalent inhibitor series led to the generation of NTX-452, our lead candidate with best-in-class potential for the treatment of MSI-H cancers. The preclinical profile of non-covalent NTX-452 was characterized and compared to clinical-stage WRN inhibitors, including those from Novartis (HRO761, non-covalent) and Roche/Vividion (RO7589831, covalent). NTX-452 displayed excellent metabolic stability- with low in vivo clearance, good oral bioavailability, and high oral exposures in rodents and non-rodents. In vivo, low dose NTX-452 treatment induced robust pharmacodynamic and tumor regression across multiple MSI-H Cell line Derived (CDX) and Patient Derived (PDX) xenograft models. Notably, NTX-452 outperformed existing clinical stage WRN inhibitors at lower doses across multiple MSI-H tumor models. NTX-452 has broad efficacy across MSI-H CDX and PDX models from colorectal, gastric and endometrial lineages and is highly efficacious in models with diverse genomic and clinical characteristics. Moreover, NTX-452 promoted durable tumor regression and complete responses in MSI-H PDX models that were refractory to immunotherapy (anti-PD1) or chemotherapy. Lastly, resistance to clinical stage WRN inhibitors was explored and the potential for NTX-452 efficacy in WRN inhibitor resistant cell lines and tumors was evaluated.Taken together, our results highlight the broad, best-in-class potential of NTX-452 in MSI-H tumors and support its advancement to clinical evaluation. Citation Format: Rob Svensson, Scott Boiko, Beth Browning, Sam Carreiro, Derun Li, Angela Toms, Justin Caravella, Silvana Leit, Suzanne Jacques-O'Hagan, Hyesun Oh, Emily Florine, Zhenhong Li, Avinash Phadke, Yuet Mei Khong, Anita Scheuber, Peter Tummino. NTX-452: a non-covalent, potent, selective and highly efficacious WRN inhibitor with best-in-class potential for the treatment of MSI-H tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2894.