The effect of poly(ethylene glycol) molecular architecture on cellular interaction and uptake of DNA complexes

The cellular uptake of plasmid DNA complexes with a series of tertiary amine methacrylate-ethylene glycol (DMAEMA-EG) copolymers with various architectures was studied using flow cytofluorometry and laser confocal microscopy. The complexes displayed different rates and extents of cellular interaction and internalisation, depending on the copolymer molecular architecture. In general, introduction of oligo(ethylene glycol) [OEG] or poly(ethylene glycol) [PEG] chains decreased both the interaction and cellular internalisation of the DNA complexes but subtle differences were observed. Two block copolymers, a ‘bottle-brush’ type DMAEMA-block-OEGMA and a linear DMAEMA-block-PEG copolymer (each containing a total of 45 EG units), displayed similar uptake profiles. In contrast, only relatively low uptake of complexes formed by a comb-type statistical copolymer, DMAEMA-stat-PEGMA, was observed, despite each PEG chain comprising 45 EG units. Similar trends were observed with three cell lines, A549, HepG2 and COS-7. However, the absolute values were cell-dependent, with COS-7 cells displaying both the highest rate and extent of uptake. Studies of the association and uptake of the complexes demonstrated that cell associations generally increased over time, with the uptake level and the time profile depending on the polymer architecture. Confocal microscopy studies confirmed that, with the exception of the poorly transfecting comb-type copolymer, the association of complexes with cells resulted in endocytosis.