Background: Development of effective drug delivery systems (DDS) is a critical issue in
health care and medicine. Advances in molecular biology and nanotechnology have allowed the introduction
of nanomaterial-based drug delivery systems. Cell-penetrating peptides (CPPs) can form the
basis of drug delivery systems by virtue of their ability to support the transport of cargoes into the cell.
Potential cargoes include proteins, DNA, RNA, liposomes, and nanomaterials. These cargoes generally
retain their bioactivities upon entering cells.
Method: In the present study, the smallest, fully-active lactoferricin-derived CPP, L5a is used to demonstrate
the primary contributor of cellular internalization.
Results: The secondary helical structure of L5a encompasses symmetrical positive charges around the
periphery. The contributions of cell-specificity, peptide length, concentration, zeta potential, particle
size, and spatial structure of the peptides were examined, but only zeta potential and spatial structure
affected protein transduction efficiency. FITC-labeled L5a appeared to enter cells via direct membrane
translocation insofar as endocytic modulators did not block FITC-L5a entry. This is the same mechanism
of protein transduction active in Cy5 labeled DNA delivery mediated by FITC-L5a. A significant
reduction of transduction efficiency was observed with structurally incomplete FITC-L5a formed by
tryptic destruction, in which case the mechanism of internalization switched to a classical energydependent
Conclusion: These results support the continued development of the non-cytotoxic L5a as an efficient
tool for drug delivery.