Characterization of Vectors for Gene Therapy Formed by Self-Assembly of DNA with Synthetic Block Co-Polymers

Abstract

Cationic polymers can self-assemble with DNA to form polyelectrolyte complexes capable of gene delivery, although biocompatibility of the complexes is generally limited. Here we have used A-B type cationic-hydrophilic block co-polymers to introduce a protective surface hydrophilic shielding following oriented self-assembly with DNA. Block co-polymers of poly(ethylene glycol)–poly-l-lysine (pEG-pLL) and poly-N-(2-hydroxypropyl)methacrylamide–poly(trimethylammonioethyl methacrylate chloride) (pHPMA–pTMAEM) both show spontaneous formation of complexes with DNA. Surface charge measured by zeta potential is decreased compared with equivalent polycation–DNA complexes in each case. Atomic force microscopy shows that pHPMA–pTMAEM/DNA complexes are discrete spheres similar to those formed between DNA and simple polycations, whereas pEG–pLL/DNA complexes adopt an extended structure. Biological properties depend on the charge ratio of formation. At optimal charge ratio, pEG–pLL/DNA complexes show efficient transfection of 293 cells in vitro, while pHPMA–pTMAEM/DNA complexes are more inert. Both block co-polymer-DNA complexes show only limited cytotoxicity. Careful selection of block co-polymer structure can influence the physicochemical and biological properties of the complexes and should permit design of materials for specific applications, including targeted delivery of genes in vivo. Cationic-hydrophilic linear block co-polymers are shown to self-assemble with DNA expression vectors, forming complexes with physicochemical and biological properties that depend on the block co-polymer used. Polymer choice influences overall configuration, ranging from discrete spheres to extended coated toroids, shielding of surface charge, and also governs the ability to mediate transfection in vitro. This approach permits design of DNA particles with specific properties, and could yield particles self-assembling with a surface shielding of hydrophilic polymer, suitable for targeted delivery of genes in vivo.