The effect of Fc region affinity of protein-based antibody-recruiting molecules on antibody-dependent cellular cytotoxicity.

Previously, we reported anticancer molecules, Fc-binding antibody-recruiting molecules (Fc-ARMs), which crosslink proteins on cancer cells with endogenous immunoglobulin Gs (IgGs) via their Fc region. The mobilized IgGs on cancer cells can accommodate natural killer cells to induce antibody-dependent cellular cytotoxicity (ADCC). Because previous Fc-ARMs utilized Fc-binding peptides, their affinity to IgGs is weak, which resulted in the limited induction capability of ADCC. Previous Fc-ARMs also unitized small molecular ligands to cancer cells, which limited their universal applicability to any cancer cells. A recent study reported that protein-based Fc-ARMs might overcome the issues associated with non-proteinous Fc-ARMs. Here, we examined the universality of a protein-based Fc-ARM by replacing its tumor-binding domain with a human epidermal growth factor receptor 2 (HER2)-specific affibody (ZHER2:342). We also examined the requirement of its Fc-binding domain affinity. We found that the Fc-ARMs accepted an affibody as a tumor-binding domain to induce ADCC. Furthermore, the required residence time of the complex between Fc-ARM and IgG was ∼102 min, which was comparable to that when monoclonal antibodies bind to their specific antigens. However, we found that the extent of ADCC induced by Fc-ARM was lower than that of conventional IgG-mediated ADCC, indicating that further enhancement of the affinity of the antibody-binding terminus and tumor-binding terminus of Fc-ARM may be needed to achieve ADCC equivalent to that of conventional IgG-mediated ADCC.

Characterization of polypropyleneimine as an alternative transfection reagent.

Polypropyleneimine (PPI) was examined as a transfection reagent comparing with most widely used polymer, polyethyleneimine (PEI). PPI had better responsiveness to the endosomal pH and showed more condensation ability of plasmid DNA than PEI. Although the cytotoxicity of PPI was somewhat higher than PEI, the transfection efficacy of PPI was comparable with PEI or higher than PEI in some cell line. Thus, PPI would be an alternative transfection reagent.