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10 Cell-Penetrating Peptides: Processes and Applications
(a)
FIGURE 1.4 Internalization of a Rhodamine-labeled ODN-Tat CPP in HeLa cells. Tat-SS-
5′-ODN-3′-Rhodamine conjugate was incubated with HeLa cells for 30 min at 37°C. Cells
were fixed and the intracellular fluorescence distribution was observed by fluorescence microscopy.
(a) Hoescht staining showing the cell nuclei; (b) immunofluorescence detection of the
chimera, indicating nuclear accumulation.
R.L. Juliano. 28,29 We reasoned that this would be the ideal situation to allow intracellular
release of a minimally modified antisense ODN and thus avoid the risk of
changing hybridization properties.
An alternative strategy would consist in stable conjugation (through a thioether
or an amide bond, for example) of the antisense ODN to the carrier Tat peptide.
Cationic peptide conjugation should indeed accelerate hybridization by increasing
the effective ODN concentration at the target sequence. 31 Whether this will occur at
the expense of diminished sequence-specific recognition should be verified.
A second class of medium-size biomolecules of interest to us consisted of
nonpermeant peptides. Recall that biological processes (for instance, intracellular
signaling cascades) often involve complex networks of protein–protein interactions.
Rapid technological developments in functional genomics have allowed the identification
of peptide domains involved in protein–ligand recognition in increasing
number, thus paving the way for design of peptidic competitors. A severe limitation
to the use of peptides in intact cells and, as a consequence, to their development as
(b)