A novel receptor-targeted gene delivery system for cancer gene therapy

Some growth factor receptors, such as insulin like growth factor I and II receptor (IGF I R, IGF II R) and epidermal growth factor receptor (EGF R), have been proved to be over-expressed in a variety of human cancers derived from different tissue origins. Based on this molecular alteration, a polypeptide conjugate gene delivery system was designed and synthesized. It contains three essential moieties: a ligand oligopeptide (LOP) for receptor recognition, a polycationic polypeptide (PCP) such as protamine (PA) or poly-L-lysine (PL) as a backbone for DNA binding and an endosome-releasing oligopeptide (EROP) such as influenza haemagglutinin oligopeptide (HA20) for endosomolysis. These components are covalently conjugated as LOP-PCP-HA20 or in the form of a mixture of LOP-PCP and HA20-PCP. A 14 amino acid E5 was designed and synthesized as LOP for IGF I R and IGF II R, and a 16 amino acid GE7 as LOP for EGF R. Both E5 and GE7 systems could form stable complex with the plasmid DNA as E5-PCP/ DNA/PCP-HA20 and GE7-PCP/DNA/PCP-HA20. Using bacterial beta-galactosidase gene (pSVbeta-gal) as a reporter, the present system is able to efficiently target exogenous gene to human cancer cells of different tissue types with high efficiency both in vitro and in implanted tumors in nude mice. It was also demonstrated that the transduced genes were highly expressed in cancer cells both in vitro and in vivo. The present system will provide a novel effective vehicle to target therapeutic genes into cancer cells in gene therapy.