Dextrin-rhEGF conjugates as bioresponsive nanomedicines for wound repair

Abstract

Growth factors are known to act in concert to promote wound repair, but their topical application rarely leads to a significant clinical improvement of chronic wounds due to premature inactivation in wound environment. The aim of this study was to synthesise a polymer-growth factor conjugate and investigate whether the novel concept called Polymer-masking-UnMasking-Protein Therapy (PUMPT) might be used to generate bioresponsive polymer therapeutics as nanomedicines able to promote tissue repair. Succinoylated dextrin ( approximately 85,000 g/mol; approximately 19 mol% succinoylation), and rhEGF were chosen as a first model combination. The conjugate synthesised contained approximately 16%wt rhEGF and <1% free protein. It exhibited increased stability towards proteolytic degradation by trypsin and the clinically relevant enzyme neutrophil elastase. The dextrin component was degraded on addition of alpha-amylase leading to sustained release of free rhEGF over time (52.7% release after 168 h). When biological activity was assessed (+/-alpha-amylase) in proliferation assays using epidermoid carcinoma (HEp2) cells and HaCaT keratinocytes, as anticipated, polymer conjugation reduced rhEGF bioactivity (p=0.0035). However, exposure to physiological concentrations of alpha-amylase triggered dextrin degradation and this led to protein unmasking with restoration of bioactivity to the level seen for unmodified rhEGF. Indeed, prolongation of HEp2 proliferation was observed over 8 days. The inability of dextrin, succinoylated dextrin or alpha-amylase alone to induce proliferative effects, and the ability of alpha-amylase-exposed dextrin-rhEGF to induce phosphorylation of the epidermal growth factor receptor (EGFR) in HEp2 cells confirmed a mechanism of action by stimulation of classical signal transduction pathways. These observations suggest that this dextrin-rhEGF, and other dextrin-growth factor conjugates have potential for further development as bioresponsive nanomedicines for tissue repair.