Cytotoxic activity and safety characterization of IMV-M™, a MUC16 × DR5 bispecific antibody

IMV-M is a MUC16 × DR5 bispecific antibody that has demonstrated MUC16-selective antitumor activity. However, it remained unclear whether multisite binding to MUC16 is required for cytotoxicity, and whether circulating CA125 (soluble MUC16) or antidrug antibodies could affect efficacy or cause toxicity.

A comparative analysis of three bispecific antibodies, IMV-M (sofituzumab × DR5), 11D10 × DR5, and fluor × DR5, sharing an identical IgG1-anti-DR5 scFv architecture, was performed. Sofituzumab binds to multiple epitopes on a single MUC16 molecule, whereas 11D10 binds a single MUC16 epitope, and fluor does not bind any human antigen. Antibody binding to shed and cell-surface MUC16 was evaluated by ELISA and flow cytometry. Cytotoxicity was assessed in a MUC16⁺/DR5⁺ tumor cell line and MUC16^-/DR5⁺ hepatic cell lines. Additional studies examined the effects of soluble CA125 and Fc-directed polyclonal antibodies on IMV-M activity.

IMV-M bound MUC16 to a markedly higher extent than the 11D10 × DR5 comparator, consistent with its multivalent engagement, while binding of fluor × DR5 to MUC16 was negligible. Only IMV-M induced potent cytotoxicity in MUC16⁺ tumor cells, whereas 11D10 × DR5 and fluor × DR5 control antibodies were inactive, even at concentrations where binding of 11D10 × DR5 exceeded that of cytotoxic concentrations of IMV-M. These findings support the notion that multivalent clustering on MUC16 is required for apoptosis. IMV-M showed no significant cytotoxicity toward hepatic cell lines, even in the presence of Fc-directed polyclonal antibodies or clinically relevant concentrations of soluble CA125.

These findings suggest that IMV-M cytotoxic activity requires clustering on MUC16, that CA125 at clinically relevant concentrations does not mediate IMV-M neutralization, and that aggregate formation with secondary antibodies or soluble MUC16 does not induce off-target toxicity.