Antibody Labeling With FITC Facilitates Controlled Release From Peptide Hydrogels Bearing Fc-Binding Motifs

Controlled release systems can enhance the efficacy of therapeutic antibodies, particularly for subcutaneous delivery where high or frequent doses are needed. Herein, we designed a peptide hydrogel that displays the binding motif HWRGWV, which targets the Fc-region of IgG. Release studies of FITC-labeled IgG from gel formulations demonstrated slow-release dependent on the Fc-binding motif's content as expected. However, the slow-release profile was diminished when using unlabeled IgG or the antibody Cetuximab, which lacks FITC. This observation and subsequent experiments show that the FITC label directly interacts with the Fc-binding motif displayed from the peptide nanofiber network to modulate release. Further, hydrogels bearing a scrambled version of the Fc-binding motif provide a similar slow-release profile for IgG-FITC but fast release for unlabeled antibodies, indicating that FITC binding of the Fc-binding motif is not specific in nature. Rather, nonspecific electrostatic and aromatic interactions most likely dictate binding and the observed slow-release kinetics of antibody from the gel. This work highlights the importance of considering fluorophore interactions when developing systems for the controlled release of antibodies and more importantly suggests that fluorophores can be used as affinity tags to control the release of protein from hydrogels with possible applications in theragnostic delivery.