Abstract
Objective
This study aimed to develop a high-affinity therapeutic antagonist to overcome tumor-produced MUC16/CA125 (herein CA125) mediated immunosuppression of anticancer therapeutic antibodies and antibody-drug conjugates (ADCs). The goal was to generate an antagonist that blocks CA125 binding to IgG1 antibodies, restores antibody interaction with CD16a Fc-γ-activating receptors (herein CD16a) and C1q protein, and re-enables maximal antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against cancer cells. Since CA125 binding to ADCs impairs its cytotoxicity by reducing ADC internalization, the antagonist was further designed to restore maximal ADC activity. Achieving these aims supports the clinical development of CA125 antagonists for treating cancers marked by humoral immunosuppression.Methods
Human IgG1 Fc fusion proteins with varying mesothelin binding domain (MBD) motifs were engineered and tested for high-affinity CA125 binding. Antagonist efficacy was assessed by measuring restoration of CD16a and C1q binding to IgG1 antibodies suppressed by CA125. ADC internalization assays evaluated the effect of CA125 and antagonists on ADC uptake. Cellular assays, including Jurkat-CD16a reporter and PBMC-based ADCC assays, measured restoration of antibody-CD16a mediated immune effector cell killing of target cells. Cytotoxicity assays assessed CDC and ADC mediated cell killing.Results
NAV-005 (MBD2-Fc), a lead antagonist, bound CA125 with high affinity and blocked its binding to IgG1-type antibodies. NAV-005 reversed CA125-induced antibody immunosuppression, thereby restoring IgG1 mediated ADCC and CDC by preventing CA125-IgG1 interaction. NAV-005 also prevented CA125-ADC cell surface interactions, thereby restoring maximal ADC internalization and target cell killing.Conclusion
Tumor-produced CA125 impairs therapeutic antibody and ADC efficacy via humoral immunosuppression. NAV-005 counteracts this effect, restoring antitumor activity of antibodies and ADCs in CA125-expressing cancers. These results support the continued development of CA125 antagonists as adjuncts to antibody-based cancer therapies.