• cell permeability;
  • cell-penetrating peptides;
  • circular dichroism;
  • globular nanoparticles;
  • photon correlation spectroscopy

Transdermal drug delivery of proteins is challenging because the skin acts as a natural and protective barrier. Several techniques including using the cell-penetrating peptides have been studied to increase the penetration of therapeutic proteins into and through the skin. Cell-penetrating peptides facilitate and improve the transduction of large and hydrophilic cargo molecules through plasma membrane. We have recently reported an efficient skin delivery of elastin protein in complex with a cell-penetrating peptide called Pep-1. As the biophysical characteristics of cell-penetrating peptide/protein complexes have been linked with their biological responses, in this study, we investigated biophysical properties of Pep-1/elastin complexes (ratio 10:1) stored in three temperatures (−20 °C, 4 °C and 25 °C) by photon correlation spectroscopy, circular dichroism and isothermal denaturation. We also evaluated the ability of transduction of this complex into cells and skin tissue using both fluorescence microscopy and Kodak In-Vivo FX Pro Imaging System.