Abstract 3176: Tumor-selective regression through MUC16-guided DR5 (TNFRSF10B) clustering by the bispecific anti-MUC16×anti-DR5 antibody IMV-M™

Abstract Background: IMV-M, a bispecific anti-MUC16×anti-DR5 antibody, previously showed potent MUC16-selective antitumor activity in vitro and in xenograft models without requiring secondary crosslinking. In a pilot non-human-primate study, repeated 10 and 20 mg/kg dosing produced no detectable toxicity. Here, we demonstrate that IMV-M induces clustering of death receptor 5 (DR5; TNFRSF10B) through a novel MUC16-dependent mechanism: assembly of multiple IMV-M molecules on a single MUC16 molecule. IMV-M also lacked cytotoxicity toward hepatic cell lines. Methods: Three bispecific antibodies sharing identical anti-DR5 arms were generated: Sofituzumab (h5A3)×Lexatumumab scFv, 11D10/DR5×Lexatumumab scFv, and (anti-fluorescein)×Lexatumumab scFv. Sofituzumab recognizes multiple tandem repeats within human MUC16, whereas 11D10 binds a single non-repetitive epitope. The anti-fluorescein construct, which does not bind human cells, served as a negative control. Binding to MUC16 was evaluated by (i) ELISA with shed MUC16 and (ii) flow cytometry using MUC16-positive cells. Cytotoxicity was assessed by CellTiter-Glo after 48h exposure. Results: IMV-M bound shed MUC16 ≈11-fold and cell-surface MUC16 ≈8-fold more strongly than 11D10/DR5 at saturation, while apparent affinities were similar. Only IMV-M induced cytotoxicity in MUC16-positive PK-59 cells, demonstrating that MUC16-mediated clustering of DR5 is required for apoptosis. In hepatocyte-derived HepG2 and Hep3B cells (MUC16-/DR5+), IMV-M showed no cytotoxicity, whereas MUC16+/DR5+ OVCAR-3 cells were highly sensitive across all concentrations. Secondary crosslinking did not elicit killing in MUC16-negative cells. These findings indicate a low risk of off-target hepatic toxicity, consistent with the benign safety profile of earlier anti-DR5 antibodies. Conclusions: Effective DR5 agonism by bispecific antibodies requires high-order receptor clustering. IMV-M achieves this through MUC16-mediated assembly of multiple antibody molecules on a single MUC16 molecule, enabling potent, tumor-selective apoptosis without hepatotoxicity. Citation Format: Iosif M. Gershteyn, Viktor Goldmakher. Tumor-selective regression through MUC16-guided DR5 (TNFRSF10B) clustering by the bispecific anti-MUC16×anti-DR5 antibody IMV-M™ [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 3176.