Abstract 2874: ZW327, a novel Ly6E-targeting antibody-drug conjugate bearing a topoisomerase 1 inhibitor payload

Abstract Ly6E (lymphocyte antigen 6 family member E) is a GPI anchored cell surface protein frequently expressed in a number of cancers such as TNBC, NSCLC, HNSCC, ESCC, OVCA, and PDAC, with minimal presence in normal tissues. ZW327 is an antibody-drug conjugate (ADC) targeting human Ly6E, composed of a humanized IgG1 antibody bearing Fc-silencing mutations, conjugated to a novel camptothecin-based topoisomerase 1 inhibitor, ZD06519, via a maleimide anchor and a glycyl glycyl phenylalanyl glycine (GGFG)-aminomethyl (AM) cleavable linker with DAR8. The antibody was discovered from animals immunized with Ly6E HEK293 transfected cells, utilizing proprietary B-cell culture-based technology followed by humanization. Antibody binding to human and cynomolgus monkey Ly6E was evaluated by KinExATM and flow cytometry. To understand therapeutic potential of ZW327, antibody internalization was assessed by flow cytometry in several Ly6E-expressing tumor cell lines and in vitro cytotoxicity of ADC was assessed in tumor spheroids using a panel of breast, lung and other tumor cell lines. Tumor spheroid penetration of ZW327 was also investigated, as well as tumor cell co-culture assays performed to assess bystander-mediated cell killing by ZW327. Developability was assessed utilizing methods such as, NS-ELISA, AC-SINS, cIEF, LC/MS and UPLC-SEC, under normal and stressed conditions. Anti-tumor activity of ZW327 and PK were investigated in a number of xenograft mouse models representing a range of Ly6E-expression. ZW327 antibody was successfully humanized and demonstrated low nanomolar binding affinity to both human and cynomolgus monkey Ly6E, as well as strong binding to target-expressing tumor cell lines. Robust internalization of ZW327 antibody was observed in Ly6E-expressing tumor cell lines, as well as spheroid penetration and ADC exhibited potent and target-specific cytotoxicity in a panel of breast, lung and other tumor cell spheroids. The antibody binding, internalization and spheroid penetration were all superior to the hu9B12.v12 clinical benchmark antibody and ZW327 exhibited pronounced cytotoxicity when compared to DLYE5953A clinical benchmark ADC. ZW327 showed good bystander-mediated killing of Ly6E-negative cells when co-cultured with target positive tumor cells. A single administration of ZW327 resulted in tumor regression across xenograft models and demonstrated a favorable PK profile. Overall, these results support the potential of ZW327 as a novel therapeutic agent against Ly6E-bearing cancers. Citation Format: Dunja Urosev, Saki Konomura, Michael Lee, Germanna Righetto, Elizabeth Porter, Katina Mak, Ambroise Wu, Amos Chua, Linglan Fu, Diego Alonzo, Spencer Boisjoli, Edward Lau, Janice Tsui, Vidhi Khanna, Alex Wu, Devika Sim, Mark E. Petersen, Jamie R. Rich, Stuart D. Barnscher. ZW327, a novel Ly6E-targeting antibody-drug conjugate bearing a topoisomerase 1 inhibitor payload [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 2874.