PEGylation affects cytotoxicity and cell-compatibility of poly(ethylene imine) for lung application: structure-function relationships.

Poly(ethylene imine) (PEI) has widely been used as non-viral gene carrier due to its capability to form stable complexes by electrostatic interactions with nucleic acids. To reduce cytotoxicity of PEI, several studies have addressed modified PEIs such as block or graft copolymers containing cationic and hydrophilic non-ionic components. Copolymers of PEI and hydrophilic poly(ethylene glycol) (PEG) with various molecular weights and graft densities were shown to exhibit decreased cytotoxicity and potential for DNA and siRNA delivery. In this study, we evaluated the cytotoxicity and cell-compatibility of different PEGylated PEI polymers in two murine lung cell lines. We found that the degree of PEGylation correlated with both cytotoxicity and oxidative stress, but not with proinflammatory effects. AB type copolymers with long PEG blocks caused high membrane damage and significantly decreased the metabolic activity of lung cells. In addition, they significantly increased the release of two lipid mediators such as 8-isoprostanes (8-IP) and prostaglandin E(2) (PGE(2)) in a dose-dependent manner. In contrast, the cytokine profiles which indicated high levels of acute-phase cytokines such as TNF-alpha, IL-6, and G-CSF did not follow any clear structure-function relationship. In conclusion, we found that modification of PEI 25 kDa with high degree of PEGylation and low PEG chain length reduced cytotoxic and oxidative stress response in lung cells, while the proinflammatory potential remained unaffected. A degree of substitution in the range of 10 to 30 and PEG-chain lengths up to 2000 Da seem to be beneficial and merit further investigations.