Professor, PhD Ülo Langel
Senior Research Fellow, PhD Kaido Kurrikoff
Professor, PhD Hanne Mørck Nielsen, University of Copenhagen, Denmark
The advancement of gene technology has made it possible to connect malfunctioning genes with certain illnesses. This has led to the realization, that if we could “fix” these genes, we could also cure the disease at its root. This treatment strategy is called gene therapy, and it uses nucleic acids like DNA and RNA, as therapeutic agents. Those nucleic acid molecules have to get inside cells to be effective, but can’t cross the cell membranes by themselves because of their large size and high negative charge. For this reason, gene delivery vectors are needed to transport nucleic acids into cells. One type of gene delivery vectors are called cell penetrating peptides (CPPs). These are short peptides that bind to nucleic acids and are capable of delivering them across the cell membrane. However, many cell penetrating peptides tend to be non-specific, and exhibit acute toxic effects. These problems are addressed in the work presented in this dissertation, where the focus was on exploring different strategies to improve the safety and tissue specificity of cell penetrating peptides. First, the CPPs were modified to increase tumor specificity and reduce accumulation in non-targeted tissues like the liver and lung. This was done by introducing the hydrophilic polymer polyethylene glycol (PEG) to the CPPs which decreases non-specific interactions of the particles with cells. The PEG chain was introduced to the CPP in a tumor sensitive manner, meaning that the PEG is removed specifically in the tumor tissue, leading to CPP activation and delivery of the nucleic acid cargo into surrounding tumor cells. This tumor specific CPP was also used to deliver therapeutic nucleic acids to tumor bearing mice to confirm they are capable of reducing tumor growth. Secondly, the strategies of forming CPP/nucleic acid particles, changing cationic charge density and hydrophilicity were investigated in the context of decreasing acute toxicity of the peptide. To conclude, we saw that specific modifications can be introduced to CPPs to increase their tumor specificity and reduce acute toxicity, and these principles can be applied for the design of new safer and more efficient CPPs.