Abstract 4431: ZW427, a Ly6E-targeting antibody drug conjugate bearing a novel pan-RAS inhibitor payload for the treatment of RAS mutated cancers

Abstract Aberrant RAS signaling is implicated as an oncogenic driver in up to 30% of cancers. Mutant selective RAS inhibitors (RASi) have been clinically approved in select indications, but their durable efficacy is hampered by acquired alterations that render tumors refractory to drug. Pan-RASi are showing broad clinical promise, but their full potential has been limited by toxicities likely arising from on-target inhibition of wild-type RAS in normal tissues, as well as by the emergence of resistance. These challenges may be improved upon by optimizing delivery of a RASi via an antibody drug conjugate mechanism. Lymphocyte antigen 6 family member E (Ly6E) is a GPI anchored cell surface protein with minimal presence in normal tissues that is prevalently overexpressed in many solid tumors including those which commonly feature oncogenic RAS mutations, such as NSCLC, PDAC, and CRC. We sought to leverage the ability of an ADC to increase the delivery of a novel pan-RASi payload to tumors for improved response, and to provide a differentiated safety profile that mitigates the toxicity limitations of current small molecule pan-RASi.ZW427 comprises a novel Ly6E-targeted humanized IgG1 antibody conjugated to a novel pan-RAS inhibitor via a cleavable linker. The anti-Ly6E antibody was discovered and optimized for ADC application, with a focus on binding, specificity, internalization and payload delivery to tumor cell lines. To study the therapeutic potential of ZW427, in vitro ADC cytotoxicity was assessed in spheroids derived from a panel of RAS mutated cancer cell lines. Internalization and spheroid penetration were evaluated, and tumor cell co-culture assays were performed to assess bystander-mediated cell killing potential. Anti-tumor activity of ZW427 was investigated in multiple RAS mutated mouse xenograft models with a range of Ly6E-expression. Pharmacodynamic aspects of RAS inhibition were also assessed.ZW427 exhibited target specific binding to cancer cells, highly effective internalization and bystander-mediated killing. Importantly, the ADC demonstrated potent and target-specific cytotoxicity in multiple Ly6E-expressing cancer cell spheroids. A single administration of ZW427 resulted in anti-tumor activity across a range of xenograft models. The pan-RASi ADC platform that has been developed shows encouraging tolerability in mice and an imminent toxicology study of ZW427 in non-human primates will further define its safety profile. Overall, the data supports the potential of ZW427 as a novel, highly differentiated therapeutic agent against Ly6E-expressing RAS mutant cancer indications. Citation Format: Dunja Urosev, Vidhi Khanna, Ambroise Wu, Jodi Wong, Saki Konomura, Elizabeth Porter, Matthew Bonderud, Victoria Harman-McKenna, Taixiang Wang, Linglan Fu, Diego Alonzo, Devika Sim, Adele Chan, Allysha Bissessur, Spencer Boisjoli, Michael Lee, Germanna Righetto, Jesse Leblanc, Raffaele Colombo, Graham Garnett, Jamie Rich, Stuart Barnscher. ZW427, a Ly6E-targeting antibody drug conjugate bearing a novel pan-RAS inhibitor payload for the treatment of RAS mutated cancers abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4431.