3PO, a novel nonviral gene delivery system using engineered Ad5 penton proteins

This study describes the development of 3PO, a nonviral, protein-based gene delivery vector which utilizes the highly evolved cell-binding, cell-entry and intracellular transport functions of the adenovirus serotype 5 (Ad5) c apsid penton protein. A penton fusion protein containing a polylysine seque nce was produced by recombinant methods and tested for gene delivery capabi lity. As the protein itself is known to bind integrins through a conserved consensus motif, the penton inherently possesses the ability to bind and en ter cells through receptor-mediated internalization. The ability to lyse th e cellular endosome encapsulating internalized receptors is also attributed to the penton. The recombinant protein gains the additional function of DN A binding and transport with the appendage of a polylysine motif. This prot ein retains the ability to form pentamers and mediates delivery of a report er gene to cultured cells. Interference by oligopeptides bearing the integr in binding motif suggests that delivery is mediated specifically through in tegrin receptor binding and internalization. The addition of protamine to p enton-DNA complexes allows gene delivery in the presence of serum.