complexes. This study clearly demonstrates that high numbers of amino groups on
cBSA are essential for DNA complex formation but that the number of cBSA
molecules in the complexes should be low to facilitate efficient DNA transfection
and release. Also, cBSA-147/DNA complexes at low P/N charge ratios reveal
considerably reduced cytotoxicity compared to the commercially available transfection reagent Lipofectamine.
In addition, more sophisticated albumin polycation architectures have been
designed. Serum albumins offer a single reactive thiol group that is accessible for
site-directed chemistry, e.g., Michael reactions with a maleimide functionality that can
react exclusively at this position. Two cBSA-147 molecules have been interconnected
by a poly(ethylene oxide) (PEO) polymer linker and the successful formation of the
cBSA dimers has been visualized by transmission electron microscopy (TEM). These
cBSA-dimers revealed efficient cellular uptake as well as transfection of pDNA-GFP.
Furthermore, polycationic albumins have been investigated for the immobilization of viable cells based on electrostatic interactions. cBSA-147, which is readily
available on a large scale, allows coating of the walls of a microchannel reactor so
that bacterial cells can attach with high cell densities. These whole-cell catalysts are
able to enantioselectively reduce ethyl acetoacetate to R-ethyl hydroxybutyrate for
several days with high productivity and revealed a better profile than the standard
polylysine coating [24]. In addition, giant liposomes have been immobilized on
cBSA-coated surfaces, which is attractive for in vitro protein synthesis [25]. Coating
of primary human cells proved to be less efficient. However, the attachment of
cyclic RGD groups to cHSA (cationized human serum albumin) interacting with
integrin receptors allowed the immobilization of NIH 3 T3 fibroblast cells, which
could have a great impact for, e.g., coating implants with a more biocompatible
human protein platform [26].
Biopolymers like cBSA offer many reactive groups suitable for multiple surface
modifications, making them useful not only for gene delivery but also for drug
delivery. Efficient drug delivery is still a high concern of health research because
many treatment strategies are still limited by low drug concentrations at the target
site or by significant side effects due to high drug doses. Drug delivery systems
based on macromolecules such as polymers, dendrimers, or proteins have thus been
developed for passive targeting of cancerous cells. These systems make use of the
characteristic features of tumor biology that allow the macromolecules to accumulate in the tumor through the enhanced retention and permeation (EPR) effect
[27]. The molecular size of the macromolecule plays an important role in tumor
cell uptake and the EPR effect is typically observed for macromolecules with
molecular weight greater than 20 kDa [28, 29]. Serum albumins are carriers of
fatty acids in the blood and, due to their ability to bind to various exogenous and
endogenous ligands, they are one of the most exploited proteins for use as a drug
delivery vehicle [30, 31] in therapeutics and clinical biochemistry [32], especially
for the delivery of lipophilic drug molecules and in particular lipophilic antitumor
drugs. HSA drug conjugates are commercially available, e.g., as HSA nanoparticle
formulations with the drug paclitacel (Abraxane) [33]. In addition, HSA–drug
conjugates have been achieved that combine the drug molecule and targeting
220
J. Hedrich et al.
cBSA are essential for DNA complex formation but that the number of cBSA
molecules in the complexes should be low to facilitate efficient DNA transfection
and release. Also, cBSA-147/DNA complexes at low P/N charge ratios reveal
considerably reduced cytotoxicity compared to the commercially available transfection reagent Lipofectamine.
In addition, more sophisticated albumin polycation architectures have been
designed. Serum albumins offer a single reactive thiol group that is accessible for
site-directed chemistry, e.g., Michael reactions with a maleimide functionality that can
react exclusively at this position. Two cBSA-147 molecules have been interconnected
by a poly(ethylene oxide) (PEO) polymer linker and the successful formation of the
cBSA dimers has been visualized by transmission electron microscopy (TEM). These
cBSA-dimers revealed efficient cellular uptake as well as transfection of pDNA-GFP.
Furthermore, polycationic albumins have been investigated for the immobilization of viable cells based on electrostatic interactions. cBSA-147, which is readily
available on a large scale, allows coating of the walls of a microchannel reactor so
that bacterial cells can attach with high cell densities. These whole-cell catalysts are
able to enantioselectively reduce ethyl acetoacetate to R-ethyl hydroxybutyrate for
several days with high productivity and revealed a better profile than the standard
polylysine coating [24]. In addition, giant liposomes have been immobilized on
cBSA-coated surfaces, which is attractive for in vitro protein synthesis [25]. Coating
of primary human cells proved to be less efficient. However, the attachment of
cyclic RGD groups to cHSA (cationized human serum albumin) interacting with
integrin receptors allowed the immobilization of NIH 3 T3 fibroblast cells, which
could have a great impact for, e.g., coating implants with a more biocompatible
human protein platform [26].
Biopolymers like cBSA offer many reactive groups suitable for multiple surface
modifications, making them useful not only for gene delivery but also for drug
delivery. Efficient drug delivery is still a high concern of health research because
many treatment strategies are still limited by low drug concentrations at the target
site or by significant side effects due to high drug doses. Drug delivery systems
based on macromolecules such as polymers, dendrimers, or proteins have thus been
developed for passive targeting of cancerous cells. These systems make use of the
characteristic features of tumor biology that allow the macromolecules to accumulate in the tumor through the enhanced retention and permeation (EPR) effect
[27]. The molecular size of the macromolecule plays an important role in tumor
cell uptake and the EPR effect is typically observed for macromolecules with
molecular weight greater than 20 kDa [28, 29]. Serum albumins are carriers of
fatty acids in the blood and, due to their ability to bind to various exogenous and
endogenous ligands, they are one of the most exploited proteins for use as a drug
delivery vehicle [30, 31] in therapeutics and clinical biochemistry [32], especially
for the delivery of lipophilic drug molecules and in particular lipophilic antitumor
drugs. HSA drug conjugates are commercially available, e.g., as HSA nanoparticle
formulations with the drug paclitacel (Abraxane) [33]. In addition, HSA–drug
conjugates have been achieved that combine the drug molecule and targeting
220
J. Hedrich et al.