Peptide nanocarriers for intracellular delivery of photosensitizers

Previously we have shown that recombinantly produced amphiphilic oligopeptides with amino acid sequence Ac-Ala-Ala-Val-Val-Leu-Leu-Leu-Trp-Glu-Glu spontaneously assemble into nano-sized vesicles with an average diameter of 120 nm. Moreover, peptide vesicles could be stabilized by introducing multiple cysteine residues within the hydrophobic domain of these amphiphilic oligopeptides, allowing the formation of intermolecular disulfide bridges. In this study, the cellular association and internalization of peptide vesicles were assessed. Flow cytometry and confocal laser-scanning microscopy showed that peptide vesicles were internalized by cells predominantly via adsorptive macropinocytosis. Furthermore, the potential of these peptide vesicles as delivery system for photosensitizers was explored. Water-insoluble phthalocyanines could be quantitatively entrapped within the hydrophobic domains of these peptide vesicles. Confocal laser-scanning microscopy analysis showed that internalized peptides co-localized with the phthalocyanine, suggesting that peptide vesicles are internalized in their intact form. Upon illumination, the phthalocyanine-containing peptide vesicles showed an active photodynamic response towards the cells leading to effective cell killing. In contrast, the free phthalocyanine or empty peptide vesicles did not show any cytotoxicity. In conclusion, this is the first demonstration that peptide vesicles show promise as delivery systems for photosensitizers to be used in photodynamic therapy.