Abstract
Branched disulfide-containing poly(amido ethyleneimines) (SS-PAEIs) are biodegradable polymeric gene carrier analogues of the well-studied, nondegradable, and often toxic branched polyethylenimines (bPEIs), but with distinct advantages for cellular transgene delivery. Clinical success of polycationic gene carriers is hampered by obscure design and formulation requirements. This present work reports synthetic and formulation properties for a graft copolymer of poly(ethylene glycol) (PEG) and a branched SS-PAEI, poly(triethylentetramine/cystaminebisacrylamide) (p(TETA/CBA)). Several laboratories have previously demonstrated the advantages of PEG conjugation to gene carriers, but have also shown that PEG conjugation may perturb plasmid DNA (pDNA) condensation, thereby interfering with nanoparticle formation. With this foundation, our studies sought to mix various amounts of p(TETA/CBA) and p(TETA/CBA)-g-PEG2k to alter the relative amount of PEG in each formulation used for polyplex formation. The influence of different PEG/polycation amounts in the formulations on polymer/nucleic acid nanoparticle (polyplex) size, surface charge, morphology, serum stability and transgene delivery was studied. Polyplex formulations were prepared using p(TETA/CBA)-g-PEG2k, p(TETA/CBA), and mixtures of the two species at 10/90 and 50/50 volumetric mixture ratios (wt/wt %), respectively. As expected, increasing the amount of PEG in the formulation adversely affects polyplex formation. However, optimal polymer mixtures could be identified using this facile approach to further clarify design and formulation requirements necessary to understand and optimize carrier stability and biological activity. This work demonstrates the feasibility to easily overcome typical problems observed when polycations are modified and thus avoids the need to synthesize multiple copolymers to identify optimal gene carrier candidates. This approach may be applied to other polycation-PEG preparations to alter polyplex characteristics for optimal stability and biological activity.