Dual enzymes regulate the molecular self-assembly of tetra-peptide derivatives

Small molecular hydrogels that can respond to external stimuli have great potentials for controlled drug release. In this study, we report on a small molecular hydrogel of Ac-YYYY-OMe whose gel–sol phase transition could be triggered by an oxidase enzyme of tyrosinase. We also synthesized three compounds with similar chemical structures to Ac-YYYpY-OMe by replacing tyrosine (Y) with phenylalanine (F). Though they could also form hydrogels with phosphatase, the gels formed by the compounds with F couldn't change to clear solutions with tyrosinase. The hydrogels in this study were characterized by rheology, TEM, and MTT assay. To demonstrate the potential application of gels formed by Ac-YYYY-OMe in controlled drug release, we incorporated Congo red as a model drug in hydrogels and the releasing profiles were recorded by using different concentrations of tyrosinase. Since tyrosinase is over-expressed in malignant melanoma, hydrogels that could respond to tyrosinase have potentials for the controlled release of anti-cancer drugs for the treatment of malignant melanoma.