Polyhydroxyalkanoates (PHA) is a family of intracellular biopolyesters produced by many bacteria. PHA granule
binding protein PhaP is able to bind to hydrophobic
polymers via strong hydrophobic interaction. A receptor-mediated drug delivery system was developed in this study based on PhaP. The system consists of PHA nanoparticles, PhaP and
polypeptide or
protein ligands fused to PhaP. The PHA nanoparticles were used to package mostly hydrophobic drugs; PhaP fused with
ligands produced by over-expression of their corresponding genes in Pichia pastoris, or E. coli was able to attach to hydrophobic PHA nanoparticle. At the end, the
ligands were able to pull the PhaP-PHA nanoparticles to the targeted cells with receptors recognized by the
ligands. It was found in this study that the receptor-mediated
drug specific delivery system
ligand-PhaP-PHA nanoparticles were taken up by macrophages,
hepatocellular carcinoma cell BEL7402 in vitro and liver,
hepatocellular carcinoma cells in vivo, respectively, when the
ligands were mannosylated human alpha1-acid
glycoprotein (hAGP) and human
epidermal growth factor (hEGF), respectively, which were able to bind to receptors of macrophages or
hepatocellular carcinoma cells. The nanoparticle system was clearly visible in the targeted cells and organs (liver or
tumor) under fluorescence microscopy when
rhodamine B isothiocyanate (RBITC) was used as a delivery model
drug due to the specific targeting effect created by specific
ligand and receptor binding. The delivery system of hEGF-PhaP-nanoparticles carrying RBITC was found to be endocytosed by the
tumor cells in tumorous model mice. Thus, the
ligand-PhaP-PHA specific drug delivery system was proven effective both in vitro and in vivo.