A multi-functional polyhydroxybutyrate nanoparticle for theranostic applications

Biopolymer-based multi-functional nanoparticles have been developed through a one-step enzymatic polymerization reaction using engineered polyhydroxyalkanoate (PHA) synthase fused with green fluorescent protein (GFP) and a single chain variable fragment antibody (A33scFv) specific to colon cancer. PHA synthase possesses unique catalytic characteristics, namely covalent catalysis, by which the synthesized polyhydroxybutyrate chain remains covalently attached to the enzyme. The amphiphilic nature of the resulting protein-polymer hybrid gives rise to spontaneous self-assembly into a micellar structure with GFP and A33scFv displayed on the surface (AGPHB nanoparticle). A model compound, Nile red, was loaded into the hydrophobic core of the AGPHB nanoparticle during the polymerization and self-assembly process. The specificity of the fluorescent multi-functional AGPHB nanoparticle towards the colon cancer cell lines SW1222 (A33+) and HT29 (A33-) was confirmed and analysed quantitatively in vitro. This new biological approach provides a simple means of producing nanocarriers with a range of surface functionality and the sizes desired for imaging and targeted drug delivery.