Abstract 7335: Comparison of ADCC-mediated efficacy of zolbetuximab in hCD16A-CB17SCID humanized mice and CB17SCID WT mice bearing the SNU-601 tumor model

Abstract Introduction: The mechanisms of action of cytotoxic monoclonal antibodies (mAbs) include FcγR-dependent mechanisms to induce antibody-dependent cell cytotoxicity (ADCC). In mice, ADCC relies on mFcγRIII expressed on NK cells, while human NK cells depend on hFcγRIIIA (hCD16A). However, human IgG1 display significant affinity differences between mouse and human FcγRs, which can impact their efficacy in preclinical models. Additionally, testing an affinity-enhanced Fc-engineered antibody in a mouse without the human FcγR counterparts provides limited predictive value. Therefore, preclinical mouse models expressing human FcγRs are essential to evaluate clinical Fc potent antibody. In this study, a hCD16A-CB17SCID humanized (HuGEMM) mouse model, featuring hCD16A knock-in on mouse NK cells, was used to evaluate the ADCC function of the CLDN18.2 mAb zolbetuximab. Using SNU-601 cell line, a high expression hCLDN18.2 model, the efficacy of zolbetuximab in hCD16A-CB17SCID mice was compared to CB17SCID WT mice in SNU-601 xenograft. Methods: Surface expression of human CD16 on NK cells from peripheral blood (PB) and spleen of hCD16A-CB17SCID HuGEMM mice was verified by flow cytometry. In vivo studies involved 1×107 SNU-601 cells subcutaneously inoculated into hCD16A-CB17SCID HuGEMM models or CB17SCID WT models. Tumor-bearing models were treated with zolbetuximab (10 mg/kg, i.p., BIW×13 doses) or hIgG1 (10 mg/kg, i.p., BIW×13 doses) as an isotype control. At the study endpoint, NK cell function related markers in PB, tumor tissues and hCLDN18.2+ tumor cell apoptosis from SNU-601 tumors were assessed by flow cytometry. Results: hCD16A expression was confirmed on NK cells from PB and spleen in hCD16A-CB17SCID HuGEMM mice. SNU-601 tumor showed similar growth profile as was observed in hCD16A-CB17SCID HuGEMM and WT models. Significant tumor growth inhibition (TGI) of SNU-601 tumor was observedwith zolbetuximab compared to the isotype control, with hCD16A-CB17SCID HuGEMM models showing 55% TGI, higher than the 33% TGI observed in CB17SCID WT models. At the study endpoint, similar percentages of mNKp46+ mCD49b+ NK cells, mCD107a+ mNKp46+ mCD49b+ NK cells, and mKi67+ mNKp46+ mCD49b+ NK cells were observed between hCD16A-CB17SCID HuGEMM and CB17SCID WT models. Apoptosis analysis indicated that zolbetuximab induced apoptosis in hCLDN18.2+ tumor cells compared to control groups in both hCD16A-CB17SCID HuGEMM and CB17SCID WT models. Conclusion: This study indicates that hCD16A-CB17SCID HuGEMM models exhibit enhanced tumor growth inhibition in response to zolbetuximab treatment compared to CB17SCID WT models, demonstrating the potential of this model as a more effective preclinical model for evaluating ADCC-mediated therapies. Citation Format: Rong Wang, Xiaoze Wang, Kaixia Lian, Rongfei Lu, Haijuan Yu, Jie Lin, Ludovic Bourre, Jingjing Wang. Comparison of ADCC-mediated efficacy of zolbetuximab in hCD16A-CB17SCID humanized mice and CB17SCID WT mice bearing the SNU-601 tumor model [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 7335.