Cell-penetrating peptides and oligonucleotides: Design, uptake and therapeutic applications

Regulation of biological processes through the use of genetic elements is a central part of biological research and also holds great promise for future therapeutic applications. Oligonucleotides comprise a class of versatile biomolecules capable of modulating gene regulation. Gene therapy, the concept of introducing genetic elements in order to treat disease, presents a promising therapeutic strategy based on such macromolecular agents. Applications involving charged macromolecules such as nucleic acids require the development of the active pharmaceutical ingredient as well as efficient means of intracellular delivery. Cell-penetrating peptides are a promising class of drug delivery vehicles, capable of translocation across the cell membrane together with molecules otherwise unable to permeate cells, which has gained significant attention. In order to increase the effectiveness of cell-penetrating peptide-mediated delivery, further understanding of the mechanisms of uptake is needed in addition to improved design to make the cell-penetrating peptides more stable and, in some cases, targeted. This thesis encompasses four scientific studies aimed at investigating cell-penetrating peptide and oligonucleotide designs amenable to therapeutic applications as well as elucidating the mechanisms underlying uptake of cell-penetrating peptide:oligonucleotide nanoparticles. It also includes an example of a therapeutic application of cell-penetrating peptide-mediated delivery of oligonucleotides. Paper I presents a study evaluating a range of chemically modified anti-miRNAs for use in the design of therapeutic oligonucleotides. All varieties of oligonucleotides used in the study target miRNA-21 and are evaluated using a dual luciferase reporter system. Paper II introduces a novel cell-penetrating peptide, PepFect15, aiming at combining the desirable properties of improved peptide stability and efficient cellular uptake with a propensity for endosomal escape, to produce a delivery vector well suited for delivery of oligonucleotides. The performance of this new cell-penetrating peptide was evaluated based on its delivery capabilities pertaining to splice-correcting oligonucleotides and anti-miRNAs. Paper III investigates the involvement of scavenger receptor class A in the uptake of various cell-penetrating peptides together with their oligonucleotide cargo. Finally, paper IV aims at using cell-penetrating peptide-mediated delivery to improve the efficiency of telomerase inhibition by antisense oligonucleotides targeting the telomerase enzyme ribonucleotide component.