Understanding the mechanisms of cellular internalization is necessary for rational design of efficient polymers for DNA delivery. In this paper, we present evidence that poly(glycoamidoamine) (PGAA)-DNA complexes (polyplexes) interact with cell-surface glycosaminoglycans (GAGs) in a manner that is not solely dependent on charge. The presence of GAGs appears to be necessary for efficient cellular uptake, as polyplex internalization was decreased in GAG-deficient CHO (pgsA-745) cells. However, uptake was nearly unaffected in cells deficient only in heparan sulfate. Internalization of PGAA polyplexes appears to be dependent on GAG sulfation in mammalian cell lines, yet the PGAA polymers are decomplexed from pDNA by high concentrations of GAGs in a charge-independent manner. This finding suggests that interactions between the carbohydrates on the polymer and GAGs may contribute to polyplex binding. Quartz crystal microbalance studies support the findings that relative PGAA polyplex-GAG binding affinities are also not completely mediated by charge. As measured by dynamic light scattering and TEM, GAGs appear to accumulate on the surface of polyplexes without disrupting them at a lower concentration, which may stimulate cellular internalization due to close interactions between the polyplexes and the GAGs. Gel electrophoresis and fluorescence measurements of an intercalating dye suggest that polyplex interaction with GAGs can induce dissociation, which could represent a potential pDNA release mechanism. These results imply that similar interactions may occur on cell surfaces, and strongly supports the hypothesis that GAGs function as cell surface receptors for polyplexes formed with PGAA vehicles.
- cellular internalization