described to be mainly endocytosed by caveolae include polymeric micelles with a
crosslinked anionic core, DOXIL, polysiloxanes, coated quantum dots, and Abraxane
[8, 14–17].
Apart from clathrin- and caveolin-mediated endocytosis, there also exist multiple
other pathways independent of clatherin and caveoli-1 that also play an important
role in nanoparticle endocytosis. Exploring the clathrin- and caveolin-independent
uptake mechanisms has only recently gained attention in endocytosis research, and
these less-understood uptake mechanisms might have implications for drug delivery
research.
In this chapter, the design of structurally defined dendritic and protein-based
polyelectrolyte nanocarriers is presented and the impact of their macromolecular
architectures and the presence of multiple charges and charge densities on cellular
uptake, trafficking, and cell toxicity is discussed.
1.2 Polycationic and Polyanionic Core–Shell
Polyphenylene Dendrimers
Polycationic proteins such as nuclear histone proteins possess high densities of the
positively charged amino acids lysine and arginine located at their periphery, as well
as a lipophilic interior. These “natural” polycations are able to complex and to store
DNA in the cell nucleus. Based on these structural considerations, dendritic
core–shell macromolecules have been designed that possess a lipophilic and relatively stiff polyphenylene scaffold that determines the size and the shape of the
macromolecules, as well as a second polymer shell containing multiple positive or
negative charges (Fig. 1a) [18]. The position of these charged polymer chains at the
dendrimer surface is predetermined by molecular design. The approximate number of
charged groups (monomer units) within the polymer chains has been varied by atom
transfer radical polymerization (ATRP). In this way, structurally defined
macromolecules have been obtained that allow the qualitative correlation of the
impact of the architecture and the number and nature of charges of a globular
macromolecule on its ability to cross biological membranes [18]. As an additional
structural feature, the lipophilic inner part contains a fluorescent perylene3,4,9,10-tetracarboxdiimide (PDI) chromophore to allow cell uptake studies by
fluorescence microscopy (Fig. 1b, c). Polycationic and polyanionic shells have been
achieved after polymerization of 2-tert-butoxycarbonylaminoethyl methacrylate or
tert-butyl acrylate, respectively, from the inner polyphenylene core that serves as
macroinitiator carrying a defined number of 2-bromo-2-methylpropionic ester groups
[18]. After removal of the tert-butoxycarbonyl or tert-butyl protective groups, the
synthesized core–shell macromolecules possesses good water solubility, which is
essential for in vitro cell experiments.
The impact of the macromolecular architecture on cell uptake and toxicity
revealed that the presence of positively charged primary amino groups is essential
214
J. Hedrich et al.
crosslinked anionic core, DOXIL, polysiloxanes, coated quantum dots, and Abraxane
[8, 14–17].
Apart from clathrin- and caveolin-mediated endocytosis, there also exist multiple
other pathways independent of clatherin and caveoli-1 that also play an important
role in nanoparticle endocytosis. Exploring the clathrin- and caveolin-independent
uptake mechanisms has only recently gained attention in endocytosis research, and
these less-understood uptake mechanisms might have implications for drug delivery
research.
In this chapter, the design of structurally defined dendritic and protein-based
polyelectrolyte nanocarriers is presented and the impact of their macromolecular
architectures and the presence of multiple charges and charge densities on cellular
uptake, trafficking, and cell toxicity is discussed.
1.2 Polycationic and Polyanionic Core–Shell
Polyphenylene Dendrimers
Polycationic proteins such as nuclear histone proteins possess high densities of the
positively charged amino acids lysine and arginine located at their periphery, as well
as a lipophilic interior. These “natural” polycations are able to complex and to store
DNA in the cell nucleus. Based on these structural considerations, dendritic
core–shell macromolecules have been designed that possess a lipophilic and relatively stiff polyphenylene scaffold that determines the size and the shape of the
macromolecules, as well as a second polymer shell containing multiple positive or
negative charges (Fig. 1a) [18]. The position of these charged polymer chains at the
dendrimer surface is predetermined by molecular design. The approximate number of
charged groups (monomer units) within the polymer chains has been varied by atom
transfer radical polymerization (ATRP). In this way, structurally defined
macromolecules have been obtained that allow the qualitative correlation of the
impact of the architecture and the number and nature of charges of a globular
macromolecule on its ability to cross biological membranes [18]. As an additional
structural feature, the lipophilic inner part contains a fluorescent perylene3,4,9,10-tetracarboxdiimide (PDI) chromophore to allow cell uptake studies by
fluorescence microscopy (Fig. 1b, c). Polycationic and polyanionic shells have been
achieved after polymerization of 2-tert-butoxycarbonylaminoethyl methacrylate or
tert-butyl acrylate, respectively, from the inner polyphenylene core that serves as
macroinitiator carrying a defined number of 2-bromo-2-methylpropionic ester groups
[18]. After removal of the tert-butoxycarbonyl or tert-butyl protective groups, the
synthesized core–shell macromolecules possesses good water solubility, which is
essential for in vitro cell experiments.
The impact of the macromolecular architecture on cell uptake and toxicity
revealed that the presence of positively charged primary amino groups is essential
214
J. Hedrich et al.