Development of polymeric gene delivery carriers: PEGylated copolymers of L-lysine and L-phenylalanine.

Department of Materials Science and Engineering, Hyperstructured Organic Materials Research Center (HOMRC), Seoul National University, Seoul, South Korea.
Journal of Drug Targeting (Impact Factor: 2.74). 08/2007; 15(6):391-8. DOI: 10.1080/10611860701401561
Source: PubMed


Block copolymers consisting of poly(ethylene glycol) (PEG) and poly(amino acid)-based random copolymers were successfully synthesized by the ring opening polymerization of the N-carboxy anhydrides (NCA) of L-lysine and L-phenylalanine. The synthesized copolymers had a molecular weight of around 30,000 and contained L-lysine and L-phenylalanine residues with molar ratios of 10/0, 9/1, 8/2, 7/3 and 6/4. The complex formation of the copolymer and pCMV-luc plasmid DNA was confirmed by the gel retardation assay and zeta potential measurement. Complete neutralization was achieved at an N/P ratio of more than 1.0 and the size of the complex was determined to be around 150 nm by dynamic light scattering. The cytotoxicity and transfection efficiency were tested on the HEK 293T cell line. The synthesized copolymers displayed negligible cytotoxicity, resulting in a cell viability of more than 95%, while those of the poly(L-lysine) (PLL) and poly(ethylenimine) (PEI) homopolymer were around 65 and 55%, respectively, under comparable conditions. The introduction of the hydrophilic PEG is believed to reduce the toxicity of the copolymer, due to its enhanced biocompatibility, and to impart improved stability to the complex under physiological conditions. The transfection efficiency at the optimized charge ratio of 7 was dramatically improved as the molar content of the L-phenylalanine residues in the copolymers increased and reached a maximum value at an L-phenylalanine content of 30 mol%. The transfection efficiency of the PEGK7/plasmid DNA complex was around 80 times higher than that of PLL, despite the presence of neutral PEG as a block segment.

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Article: Development of polymeric gene delivery carriers: PEGylated copolymers of L-lysine and L-phenylalanine.

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    • "plasmid DNA. A host of other copolymers, structurally and chemcially similar to PGC, were under consideration as potential non-viral gene delivery vehicles in the late 1990s 1-5. However, despite the efficient formation of homogenous populations of small (<100 nm) complexes with plasmid DNA, the in vitro and in vivo efficacy of intracellular delivery was insufficiently high to grant further development of protected graft polycations for gene delivery 4. "
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    ABSTRACT: Initially developed in 1992 as an MR imaging agent, the family of protected graft copolymers (PGC) is based on a conjugate of polylysine backbone to which methoxypoly(ethylene glycol) (MPEG) chains are covalently linked in a random fasion via N-ε-amino groups. While PGC is relatively simple in terms of its chemcial composition and structure, it has proved to be a versatile platform for in vivo drug delivery. The advantages of poly amino acid backbone grafting include multiple available linking sites for drug and adaptor molecules. The grafting of PEG chains to PGC does not compromise biodegradability and does not result in measurable toxicity or immunogenicity. In fact, the biocompatablility of PGC has resulted in its being one of the few 100% synthetic non-proteinaceous macromolecules that has suceeded in passing the initial safety phase of clinical trials. PGC is capable of long circulation times after injection into the blood stream and as such found use early on as a carrier system for delivery of paramagnetic imaging compounds for angiography. Other PGC types were later developed for use in nuclear medicine and optical imaging applications in vivo. Recent developments in PGC-based drug carrier formulations include the use of zinc as a bridge between the PGC carrier and zinc-binding proteins and re-engineering of the PGC carrier as a covalent amphiphile that is capabe of binding to hydrophobic residues of small proteins and peptides. At present, PGC-based formulations have been developed and tested in various disease models for: 1) MR imaging local blood circulation in stroke, cancer and diabetes; 2) MR and nuclear imaging of blood volume and vascular permeability in inflammation; 3) optical imaging of proteolytic activity in cancer and inflammation; 4) delivery of platinum(II) compounds for treating cancer; 5) delivery of small proteins and peptides for treating diabetes, obesity and myocardial infarction. This review summarizes the experience accumulated by various research groups that chose to use PGC as a drug delivery platform.
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    • "However, the transfection efficiency remained very low in comparison to conventional viral agents (Lonez et al., 2008; Morille et al., 2008). Non-viral vectors are mainly composed of cationic polymers and cationic lipids such as polyethyleneimine (PEI) (Breunig et al., 2005), poly (l-lysine) (PLL) (Choi et al., 2007), chitosan (Romoren et al., 2002), 3␤-[N-(N ,N -dimethylaminoethane)carbamoyl]cholesterol (DC-Chol) (Choi et al., 2008), 1,2-dioleyl-3- trimethylammonium-propane (DOTAP) (Vaysse et al., 2006) and so on. Some cationic lipid-based gene delivery systems are also explored later, including liposomes, emulsions and lipid nanoparticles . "
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