Enzymatically cross-linked peptide hydrogels for enhanced self-assembling capability and controlled drug release

Self-assembled peptide hydrogels are a class of versatile materials with inherent biocompatibility and sound biological activities; however, they tend to exhibit weak mechanical properties and unsatisfactory release profiles of drugs. To address these problems, we propose an enzymatic approach to synthesize an enzymatically cross-linked peptide hydrogel (Fmoc-Gly-Phe-Tyr-Tyr, or Fmoc-GFYY) on the basis of inter-cross-linking of tyrosines (Tyr) under the action of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). Compared to Fmoc-GFYY without HRP or H2O2, the Fmoc-GFYY/enzymatically cross-linked hydrogels exhibited denser cross-linking networks, a more orderly secondary structure, and greater mechanical strength. Further characterizations using HPLC, UV, fluorescence, and LC-MS confirmed that the tyrosines of Fmoc-GFYY were inter-cross-linked to give dimeric tyrosines under the action of HRP and H2O2. By taking doxorubicin (DOX) and rhodamine B (RhB) as model drugs, the Fmoc-GFYY/enzymatically cross-linked hydrogel displayed slow release of DOX in vitro and a long retention time of RhB in vivo. Cell experiments revealed that the DOX-loaded enzymatically cross-linked hydrogel formulation exhibited higher anticancer efficacy compared to DOX solution alone. The utility of enzymatic cross-linking in this study represents a new approach for the structural optimization of peptide hydrogels, which could have broad prospects in the controlled release of various therapeutics.