Supervisor: prof. Ülo Langel (Tartu Ülikool)
Opponent: prof. Ines Neundorf. Institute of Biochemistry, Department of Chemistry, University of Cologne, Cologne Germany.
Nucleic acids and their analogues are highly potential candidates to be utilized for the treatment of various devastating diseases. The clinical potential of these biomolecules remains restricted so far because of their poor stability in the presence of serum and low uptake into the cells resulting from the high molecular weight, negative charge and hydrophilic nature of the nucleic acids. Therefore, the development of macromolecule-based drugs is dependent on the progress and improvement of carrier molecules that can facilitate their transfection and protect the cargo from degradation. CPPs are relatively short peptides, 5-30 amino acids in length, with the ability to gain access to the cell interior via energy-dependent and/or independent mechanisms, and facilitate intracellular delivery of associated cargo molecules to intracellular targets. This thesis focuses on the design and characterization of a new family of CPPs, named NickFect. The peptides are designed to deliver various types of bio-active cargos, including plasmid DNA, splice-correcting oligonucleotides and small interfering RNAs, using non-covalent nanoparticle formation approach. In order to enhance the nanoparticle formation activity, uptake efficacy and endosomolytic properties, we insert different modifications or make amino acid substitutions to the backbone of the parental peptide, stearyl-TP10. For instance, addition of phosphoryl-group yielded NF1 and NF2, highly efficient peptide-based transfection reagents for the intracellular delivery of splice-correcting oligonucleotides. Another radical modification, insertion of a kink, resulted in NF51 that proved to deliver nucleic acids to the targets both in the nucleus and cytoplasm. Additionally, we demonstrate the applicability of NF51 in protein production system. Furthermore, we unravel the uptake mechanism of two NickFect family members, NF1 and NF51, related to the biological activity of transfected plasmid DNA. Taken together, our results demonstrate that the performed chemical modifications in NickFects enhanced the activity of these peptides for delivering nucleic acids. Studies of the uptake mechanism gave us valuable information on how to enhance the bioavailability of different genetic materials non-covalently linked to NickFects for further in vivo applications and for designing more efficient carrier vectors and achieving bioavailability of the macromolecule-based drugs. Conclusively, NickFects have remarkable potential for the delivery of nucleic acids both in vitro and in vivo.