ENGINEERING OF CELL-PENETRATING PEPTIDE-CONJUGATED INTRACELLULAR DELIVERY SYSTEMS - Biologically-Responsive Hybrid Biomaterials - page 210

efficiency [93]. The authors prepared the conjugates with 52, 104 and 210 CPP
moieties per particle, which were then evaluated for biocompatibility in vitro and
in vivo [94]. In vitro studies showed the inflammatory responses to the
conjugates, but in vivo evaluation of the conjugates in mouse did not result in
major incompatible responses. Thus, TAT peptide-SCK conjugate can be used
as scaffolds for preparing antigen for immunization.
TATp (48-57) was also conjugated to FITC-doped silica nanoparticles
(FSNPs) for bioimaging purposes. TATp- FSNPs were prepared by
microemulsion system and showed labeling of human lung adenocarcinoma cells
(A-549) in vitro unlike FSNPs that showed no effective labeling. TATp-modified
nanoparticles have also been investigated for their capability to deliver the
diagnostic and therapeutic agents across the blood brain barrier. For in vivo
bioimaging potential, TATp- FSNPs were administered intra-arterially to the
brain of rats. TATp-conjugated FSNPs labeled the brain blood vessels, showing
the potential for delivering agents to the brain without compromising the blood
brain barrier [95].
Gold particles are also intracellular delivery vectors of choice because of
some important properties. They can be synthesized in sizes varying from 0.8 to
200 nm and can be further modified with a variety of small molecules, peptides,
proteins, DNA, and polymers. Tkachenko et al. prepared peptide-gold particle
complexes by conjugating peptides to bovine serum albumin (BSA) and then
attaching BSA-peptide conjugates to gold nanoparticles. Initial studies found that
the conjugates were internalized by endocytosis and did not localize into the
nuclei of NIH3T3 or HepG2 cells [88]. Conversely, it was shown that smaller
(3nm) gold particles functionalized with TATp traversed through the cell
membrane of human fibroblast cells and accumulated within the nuclei [96]. The
reason for this success could depend on method of gold nanoparticles synthesis,
the difference in particle size or cell types used. Also here, the authors used
transmission electron microscopy (TEM) to avoid the fixation induced artifacts.
Recently Nativo et al., studied the uptake of ca. 16 nm surface-modified gold
nanoparticles by human fibroblast cells (HeLa cells) by TEM [97]. They found
that TATp- modified gold nanoparticles located in the endosomes, supporting
the assumption that the predominant uptake mechanism enabled by TAT
is endocytosis. Successful nuclear targeting was observed after surface
modification with a cocktail of CPPs and a peptide acting as a nuclear
localization signal (GGFSTSLRARKA).
To study the effect of nanoparticle shape/size on cellular uptake, Zhang et al.
constructed a spherical and two cylindrical nanoparticles, with different lengths.
It was found that when the nanoparticles were functionalized with the TAT PTD,