Design and evaluation of drug delivery vehicles

A crucial aspect of drug delivery is efficient transport to the site of action. Thus, there is a need to design and evaluate new delivery vehicles. In this thesis two delivery vehicles, cell-penetrating peptides and bacterial ghosts, were evaluated. The understanding of the internalization and degradation kinetics of cell-penetrating peptides is important for the practical aspects of cargo delivery since peptides have a notorious reputation of being rapidly degraded. If the cell-penetrating peptide remains intact inside the cellular environment, there is a possibility that the peptide-cargo conjugate leaks back to the extracellular environment. However, if it is degraded outside the cell, the cargo will never be delivered. In order to improve uptake efficiency and to be able to foresee side effects, the translocation mechanism needs to be fully elucidated. Data gathered from the first two papers led to the proposal of a new mechanism involved in cell-penetrating peptide uptake: the membrane repair response, a resealing mechanism rapidly patching up broken membranes. This mechanism could explain the divergence in perception concerning the uptake pathways. Furthermore a new assay to produce the second delivery vehicle, bacterial ghosts, was developed based on data from the cellpenetrating peptide investigations. Bacterial ghosts are dead bacteria devoid of cytoplasmic contents but still retaining their structural and morphological characteristics, after protein E lysis of the bacterial cell membrane. By using a cell-penetrating peptide with antimicrobial effects, a new rapid peptidebased strategy to produce ghosts was developed and the capability to deliver plasmid DNA into the cell for expression was evaluated.