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Monolith columns from macroporous polyacrylamide gel were grafted with polycations, poly(N,N-dimethylaminoethyl methacrylate) (polyDMAEMA), (2-(methacryloyloxy)ethyl)-trimethyl ammonium chloride (polyMETA) and partially quaternized polyDMAEMA prepared via treating polyDMAEMA-grafted columns with propylbromide. The polymer grafting degrees varied between 34 and 110%. The polycation-grafted monolithic columns are able to capture plasmid DNA directly from alkaline lysate of Escherichia coli cells. Due to the large pore size in macroporous monoliths the particulate material present in non-clarified feeds did not block the columns. The captured plasmid DNA was eluted with 1M NaCl as particulate-free preparation with significantly reduced content of protein and RNA as compared to the applied lysate.

The demand for highly purified plasmids in gene therapy and plasmid-based vaccines requires large-scale production of pharmaceutical-grade plasmid. Plasmid DNA was selectively precipitated from a clarified alkaline lysate using the polycation poly(N,N'-dimethyldiallylammonium) chloride which formed insoluble polyelectrolyte complex (PEC) with the plasmid DNA. Soluble PECs of DNA with polycations have earlier been used for cell transformation, but now the focus has been on insoluble PECs. Both DNA and RNA form stable PECs with synthetic polycations. However, it was possible to find a range of salt concentration where plasmid DNA was quantitatively precipitated whereas RNA remained in solution. The precipitated plasmid DNA was resolubilised at high salt concentration and the polycation was removed by gel-filtration.

Complexation of plasmid DNA with polycations is a popular method by which to transfer therapeutic nucleic acid sequences to cells. One caveat of the approach is that the positive zeta potential of the complexes facilitates interaction with blood constituents, leading to serum protein adsorption and complement activation. As a countermeasure, investigators have developed polycations combined with polyethylene glycol (PEG) to create complexes with reduced protein adsorption potential. We have designed and synthesized PEG-polyhistidine conjugates to evaluate the material class as potential gene delivery vehicles. Two conjugate architectures (comb-shaped and linear A-B block copolymers) were synthesized and formulated with plasmid DNA. The complexes were characterized with respect to DNA complexation capacity, hydrodynamic diameter, zeta potential, in vitro cytotoxicity and transfection capacity in a model cell line. PEG content of the conjugate significantly influenced the hydrodynamic diameter of the DNA:conjugate composite in aqueous solution. For comb-shaped conjugates steric hindrance attributed to PEG led to a direct relationship between the PEG content and the complex size. Both architectures could condensed plasmid DNA into complexes with hydrodynamic diameters <150 nm. Complexation of DNA with the polyhistidine-PEG conjugates resulted in nanocomposites with negative zeta potentials that retarded DNase I-mediated hydrolysis, and all conjugates showed low cytotoxicity to macrophages cultured in vitro. The transfection efficiency was approximately equivalent to DNA:polylysine complexes. The formulation characteristics and low cytotoxicity suggest that polyhistidine-PEG conjugates may be useful for gene delivery.