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86 Cell-Penetrating Peptides: Processes and Applications
pmol/mg protein
12
10
8
6
4
2
0
15-mer PTO PTO-I PTO-XV
FIGURE 4.12 Quantities of internalized oligonucleotide after exposure of CHO cells to
0.5 µM 15-mer PTO alone and conjugated to peptides I and XV for 30 min at 37°C determined
by gel-capillary electrophoresis with laser-induced fluorescence detection. Each bar represents
the mean from three cells ± SEM.
and oligonucleotide length, appeared to operate. 45 Aspects other than membrane
translocation ability — probably interactions with nucleic acid binding proteins —
might thus have more importance for the biological activity of oligonucleotides and
oligonucleotide–peptide conjugates.
In context, the outlined results obtained with peptides and oligonucleotides as
cargo molecules provide strong evidence for cell-penetrating ability of conjugates
between MAPs and hydrophilic bioactive compounds and for a shuttling activity of
MAPs comparable to that of natural protein-derived cell-penetrating peptides.
4.5 OTHER MODEL AMPHIPATHIC PEPTIDES APPLIED
IN UPTAKE STUDIES
Although this chapter summarizes mainly the uptake studies of our own group using
I-derived peptides, efforts of other groups in designing amphipathic peptides in order
to improve the cellular uptake of biomolecules will be briefly reviewed next.
A quite simple decapeptide, (KFF)3K was shown by Vaara and Porro 46 to act
synergistically with antibiotics against gram-negative bacteria, propably due to its
cell wall-permeating properties. This peptide, which possesses no significant intrinsic
antibacterial activity, was conjugated to 12- and 15-mer anti-lacZ PNAs via a flexible
ethylene glycol linker. The PNA–peptide conjugates were 15- to 20-fold more active
in inhibiting lacZ expression in E. coli than the corresponding PNAs without attached
peptides. 47 Obviously, proline-containing, nonhelical peptides such as ILPWKWP-
WWPWRRGC are also able to carry PNA oligomers into bacteria, and the corresponding
peptide–PNA conjugates evoke the inhibition of bacterial growth. (For
conjugates of other peptides with ODNs see the review of Tung and Stein. 48 )