Therapeutic and diagnostic applications of antisense peptide nucleic acids

Abstract

Peptide nucleic acids (PNAs) are synthetic nucleic acid analogs with a neutral N-(2-aminoethyl) glycine backbone. PNAs possess unique physicochemical characteristics such as increased resistance to enzymatic degradation, ionic strength and stability over a wide range of temperatures and pH, and low intrinsic electrostatic repulsion against complementary target oligonucleotides. PNA has been widely used as an antisense oligonucleotide (ASO). Despite the favorable characteristics of PNA, in comparison with other ASO technologies, the use of antisense PNA for novel therapeutics has lagged. This review provides a brief overview of PNA, its antisense mechanisms of action, delivery strategies, and highlights successful applications of PNA, focusing on anti-pathogenic, anti-neurodegenerative disease, anti-cancer, and diagnostic agents. For each application, several studies are discussed focusing on the different target sites of the PNA, design of different PNAs and the therapeutic outcome in different cell lines and animal models. Thereafter, persisting limitations slowing the successful integration of antisense PNA therapeutics are discussed in order to highlight actionable next steps in the development and optimization of PNA as an ASO.

Keywords: ASO; MT: Oligonucleotides; Nucleic acid Therapies and Applications; PNA; antisense; miRNA; oligonucleotide; peptide nucleic acids.

Graphical abstract

Figure 1

Antigene vs antisense and structures of DNA and PNA (A–C) Antisense versus antigene mechanisms of PNA. (D) Structural comparison of DNA and PNA, with the backbones depicted in blue showing DNA’s negatively charged phosphate backbone versus PNA’s neutral N-(2-aminoethyl) glycine backbone.

Figure 2

Schematic showing mechanisms of action of PNA (A) PNA targeting pre-mRNA through splicing modulations and targeting mRNA through translational block and translational arrest. (B) PNA targeting various ncRNAs. PNA binds to ncRNA and prevents its interaction with rRNA and mRNA binding sites.

Figure 3

Methods of assisted PNA entry across cellular membranes Methods of assisted PNA entry across cellular membranes include conjugation to cell-penetrating peptides (CPPs) (both natural and synthetically derived), conjugation to small molecules and vitamin B, liposomal encapsulation, nanoparticle encapsulation, and association with tetrahedral DNA nanostructures (TDN).

Figure 4

Applications of PNA as diagnostic agents (A) Development of a pyrrolidinyl PNA polypyrrole/silver nanofoam electrode biosensor. (B) Detection of mRNA for T790M-mutated EGFR protein. (C) f-CNNS preparation, cellular endocytosis, and miRNA detection. (D) Hybridization and analysis of pure bacterial culture samples using acoustic flow cytometry.