Abstract 5654: Affinity tuned Xmab®2+1 anti-mesothelin x anti-CD3 bispecific antibody induces selective T cell-dependent cellular cytotoxicity of human ovarian cancer cells

Abstract

Abstract Mesothelin (MSLN) is a tumor-associated antigen highly expressed in ovarian tumors. Current treatment options for ovarian cancer have only modest efficacy and there remains a large unmet need for new targeted therapies. We generated targeted T cell engager bispecific antibodies that bind MSLN on tumor cells and CD3 on T cells. The humanized and affinity-optimized MSLN x CD3 bispecific antibodies are in an XmAb® 2+1 Fab2-scFv-Fc format that bind bivalently to MSLN and monovalently to CD3. The affinity of the MSLN-targeting arms was reduced to promote avid binding to MSLN expressing cancer cell lines and to minimize reactivity on normal surrogate cell lines. We correlated the expression of MSLN on cancer cell lines to 191 biopsy cores of serous and mucinous ovarian cancer tissues by IHC to identify surrogate cell lines to test for T cell-dependent cellular cytotoxicity (TDCC) activity. MSLN-transfected A549 cells were found to stain as intensely as ovarian cancer tumors expressing high amounts of MSLN. OVCAR-8 cancer cells were found to correlate with a medium MSLN level density on ovarian cancer tumors while ASPC-1 cells represented low MSLN-expressing tumors. Finally, we correlated expression of MSLN to non-cancer adjacent tissues and identified SKOV3, HT29, MCF7, and A549 (parental) cancer cells as appropriate surrogates of normal tissues. Reduction of MSLN affinity of MSLN x CD3 XmAb® 2+1 bispecific antibodies led to preferential killing of MSLN-high target cells, with up to 45-fold more potent TDCC activity on OVCAR8 and ASPC-1 cancer cells compared to the selected normal surrogate cell lines. Engineering of selective MSLN x CD3 bispecific antibodies allows for preferential killing of cancer cells, potentially minimizing on-target/off-tumor effects that may contribute to dose-limiting toxicities. Citation Format: Veronica G. Zeng, Matthew S. Faber, Matthew J. Bernett, Kendra N. Avery, John L. Zeytounian, Rumana Rashid, Umesh S. Muchhal, Gregory L. Moore, John R. Desjarlais, Michael Hedvat. Affinity tuned Xmab®2+1 anti-mesothelin x anti-CD3 bispecific antibody induces selective T cell-dependent cellular cytotoxicity of human ovarian cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5654.