Abstract 332: Development of a novel therapeutic CLDN18.2 monoclonal antibody and antibody drug conjugate for the treatment of CLDN18.2 positive cancers

Abstract Background: Claudin 18 is a member of the claudin family of tight junction tetraspan cell surface proteins. The 18.2 isoform of claudin 18 (CLDN18.2) is expressed in healthy gastric mucosa cells and largely absent from other normal adult cell types. In contrast to the low expression in healthy tissues, CLDN18.2 is highly overexpressed in many cancer types including gastric and pancreatic malignancies at high frequencies (50-80%). The high tumor-normal expression differential of CLDN18.2 make it an attractive target for both therapeutic monoclonal antibodies (mAbs) and antibody drug conjugate (ADCs). Here, we describe the preclinical development of a novel therapeutic CLDN18.2 mAb and ADC. Materials and Methods: CLDN18.2 specific mAbs were generated through a multiplexed immunization strategy by which mice were immunized with either peptides spanning loop 2 of the CLDN18.2 extracellular domain or mouse NIH3T3 cells overexpressing the full length CLDN18.2 protein. Antibody clones were screened by flow cytometry for selective binding to cell surface CLDN18.2. A CLDN18.2-directed ADC was generated from the fully humanized clinical candidate CLDN18.2 mAb by MMAE conjugation with a cleavable linker. CLDN18.2 positivity in cell line (CDX) and patient derived xenograft (PDX) models was determined by IHC assay. Results: Selective binding of the CLDN18.2-mAb to CLDN18.2, without cross reactivity to the more widely expressed CLDN18.1 isoform, was confirmed in human cancer cell lines and cells engineered to overexpress each isoform. The CLDN18.2-mAb demonstrated strong induction of both antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cell-mediated phagocytosis (ADCP) in in vitro assays; suggesting that Fc effector function is a key component of the mechanism of action of the mAb. Treatment of CLDN18.2 positive gastric and pancreatic CDXs with CLDN18.2-mAb monotherapy induced significant inhibition of tumor growth in CD-1 nude mice. Binding of CLDN18.2-mAb or CLDN18.2-ADC to the cell surface CLDN18.2 induced internalization of the protein-antibody complex. Complete regression of CDX tumors was observed in response to treatment with the CLDN18.2-ADC in three separate CLDN18.2 positive models (two pancreas, one gastric). Moreover, complete loss of xenograft tumor burden was also observed in 4/5 CLDN18.2 positive pancreas PDX models. No impact on xenograft tumor growth as observed in response to treatment with either the CLDN18.2-mAb or CLDN18.2-ADC in CLDN18.2 negative CDX/PDX models. Discussion: These data support the clinical development of this CLDN18.2-mAb and CLDN18.2-ADC for the treatment of CLDN18.2 positive cancers. Each of these molecules will begin phase 1 clinical testing in early 2022. Citation Format: Neil A. O'brien, Martina S. McDermott, Jun Zhang, Ke Wei Gong, Ming Lu, Benjamin G. Hoffstrom, Dylan Conklin, Tong Luo, Kevin Chau, Min Liang, Timothy R. Donahue, John A. Glaspy, Leonard Presta, Dennis J. Slamon. Development of a novel therapeutic CLDN18.2 monoclonal antibody and antibody drug conjugate for the treatment of CLDN18.2 positive cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 332.