Short multi-armed polylysine-graft-polyamidoamine copolymer as efficient gene vectors

Polyamidoamine-polylysine graft copolymers (PAMAM-g-PLL) were prepared by ring-opening polymerization of benzyloxycarbonyl lysine N-carboxyanhydride (Lys(Z)-NCA) initiated with primary amine of generation 4 polyamidoamine (PAMAM G4) and subsequent deprotection of polyamidoamine-poly-(benzyloxycarbonyl lysine) copolymer (PAMAM-PLL(Z)). The chemical structure and composition of the PAMAM-g-PLL with varying length of PLL arms were characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy ((1)H NMR). Agarose gel electrophoresis test revealed that the PAMAM-g-PLL could completely combine DNA to form complexes. The scanning electronic microscopy (SEM) and atomic force microscopy (AFM) observation showed that the morphology of these complexes was spherical. Dynamic light scattering (DLS) measurement illustrated that the sizes of complexes were in range of 100-200 nm. The MTT assay demonstrated that cytotoxicity of PAMAM-g-PLL were lower than the either PAMAM G4 or the poly-L-lysine-15k (PLL-15k). The in vitro transfection test indicated that the PAMAM-g-PLL with 3.8 average polymerization degrees of PLL arms (PAMAM-PLL-3.8) displayed significantly higher transfection efficiency than that of PAMAM G4 and PLL-15k at the same N/P ratio, Furthermore, PAMAM-PLL-3.8 at the N/P of 40 or 80 displayed better serum-resistant capability than that of PEI-25k and Lipofectamine 2000. The DNA local delivery test in rabbit vessel exhibited that the restenosis was inhibited to a significant extent. The above facts revealed that PAMAM-PLL-3.8 is a promising gene vector with low cytotoxicity, high transfection efficiency and serum-resistant ability.