Engineered toxins: New therapeutics

Abstract

Understanding the structure-function relationship of the botulinum neurotoxins (BoNTs) has enabled creation of novel recombinant proteins in which the binding domain of the neurotoxin is replaced by a ligand to a cell surface receptor. The resulting protein can deliver neurotoxin endopeptidase to a cell based upon its receptor specificity, inhibiting secretion from the selected cell. The approach is exemplified by a protein targeting airway epithelial cells responsible for mucin release. A synthetic gene encoding the endopeptidase and translocation domains of BoNT type C1 together with epidermal growth factor (EGF) was expressed in Escherichia coli . The encoded protein (EGF-C) included a protease cleavage site to allow activation to a di-chain protein. The recombinant protein was purified via an affinity tag. In vitro, EGF-C inhibited both stimulated mucin secretion and mucin gene expression in airway epithelial cell lines at sub-nanomolar concentrations. In vivo, EGF-C inhibited stimulated mucus hypersecretion in a rat model of COPD and this effect was maintained for several weeks following a single administration. These results show that novel proteins incorporating the endopeptidase activity of BoNTs can be produced to inhibit secretion from specified cell types with a prolonged duration of action. This opens up an opportunity to produce novel recombinant proteins for the treatment of chronic diseases not amenable to therapy with the native neurotoxins.