Novel fully human IgG1 targeting folate receptor α demonstrates antitumor efficacy driven by avidity rather than monovalent binding affinity.

Folate receptor alpha (FRα), a membrane protein involved in folate transport, is a promising therapeutic target for ovarian cancer and other malignancies. The murine Monoclonal antibody (MAb) MOv19, developed in our lab, has pioneered the development of chimeric antibody-drug conjugates currently approved or in clinical trials for the treatment of FRα-positive cancers. To further reduce antibody’s immunogenicity, we engineered and characterized a new fully human IgG1 antibody (AFRA hIgG1) to FRα starting from MOv19. AFRA hIgG1 was constructed and characterized for binding affinity, specificity to purified FRα and various FRα-expressing tumor cells and ability to recruit effector cells in vitro in comparison to the chimeric version of MOv19 (ChiMOv19). AFRA hIgG1 and ChiMOv19 have comparable functional affinities being 10−9 M and 10−10 M, respectively although AFRA hIgG1 has an intrinsic constant affinity 103 lower than that of ChiMOv19, 2.6 × 10−7 M vs. 3.5 × 10−10 M, respectively. Furthermore, AFRA hIgG1 demonstrated a better binding kinetic with an overall efficacy comparable to ChiMOv19 in recruiting effector cell functions. These findings highlight that functional affinity, rather than intrinsic affinity, is a key determinant of biological response. AFRA hIgG1 shows promise as a biologic agent for the treatment of FRα-positive cancers.