Morpholinos and PNAs Compared

Targeted Gene Modification of Hematopoietic Progenitor Cells in Mice Following Systemic Administration of a PNA-peptide Conjugate

In recent years, there has been considerable interest in developing gene‐targeting drugs. Synthetic molecules that bind effectively with high sequence specificity to a desired target in a particular “destined” gene sequence are of major interest in medicine and molecular biotechnological research. They show hope for the development of gene therapeutic agents, high‐precision diagnostic devices for genetic analysis and convenient tools for nucleic acid manipulations. Peptide nucleic acid (PNA) is a nucleic acid analog in which the sugar–phosphate backbone of natural nucleic acid has been replaced by a synthetic peptide backbone usually formed from N‐(2‐aminoethyl)glycine units resulting in an achiral and uncharged mimic. It is chemically stable and, in contrast to nucleic acids and peptides, is naturally resistant to hydrolytic (enzymatic) cleavage and thereby not expected to be degraded by cell extracts or inside a living cell. It is capable of sequence‐specific recognition of DNA and RNA obeying a Watson–Crick hydrogen bonding scheme and the hybrid complexes exhibit extraordinary thermal stability and unique ionic strength effects. It also recognizes duplex homopurine sequences of DNA to which it binds by strand invasion, forming a stable PNA·DNA–PNA triplex with a looped‐out DNA strand. This potential synthetic mimic of DNA, since its discovery in 1991, has attracted great attention within medicinal chemistry and molecular biology and also various other fields such as organic and physical chemistry because of its interesting chemical and physical properties. It has been regarded to have great potential for both diagnostic and pharmaceutical applications. In vitro studies have shown successful attempts to use PNA as an inhibitor for both transcription and translation of specific genes. This holds promise for using PNA for antigene and antisense therapy. However, the most exciting use of PNA, as an antisense or antigene drug, requires an efficient and safe method to deliver PNA into living cells, a problem that still remains to be solved.

Peptide nucleic acids (PNAs) are analogs of nucleic acids in which the ribose-phosphate backbone is replaced by a backbone held together by amide bonds. PNAs are interesting as models of alternative genetic systems because they form potentially informational base paired helical structures. Oligocytidylates have been shown to act as templates for formation of longer oligomers of G from PNA G2 dimers. In this paper we show that information can be transferred from DNA to PNA. DNA C4T2C4 is an efficient template for synthesis of PNA G4A2G4 using G2 and A2 units as substrates. The corresponding synthesis of PNA G4C2G4 on DNA C4G2C4 is less efficient. Incorporation of PNA T2 into PNA products on DNA C4A2C4 is the least efficient of the three reactions. These results, obtained using PNA dimers as substrates, parallel those obtained using monomeric activated nucleotides.

Vitamin B12 also called cobalamin (Cbl) is an important enzymatic cofactor taken up by mammalian and also by many bacterial cells. Peptide nucleic acid (PNA) is a synthetic DNA analogue that has the ability to bind in a complementary manner to natural nucleic acids. Provided that PNA is efficiently delivered to cells, it could act as a steric blocker of functional DNA or RNA and regulate gene expression at the level of transcription or translation. Recently, Cbl has been examined as a transporter of various molecules to cells. Also, PNA, if covalently linked with Cbl, can be delivered to bacterial cells, but it is crucial to verify that Cbl does not change the desired PNA biological properties. We have analyzed the structure and conformational dynamics of conjugates of Cbl with a PNA monomer and oligomer. We synthesized a cyanocobalamin derivative with a PNA monomer C connected via the triazole linker and determined its NMR spectra. Using microsecond-long molecular dynamics simulations, we examined the internal dynamics of cyanocobalamin-C, its conjugate with a 14-mer PNA, and free PNA. The results suggest that all compounds acquire rather compact structures but the PNA oligomer conformations vary. For the Cbl-C conjugate the cross-peaks from the ROESY spectrum corroborated with the clusters from molecular dynamics trajectories. Within PNA the dominant interaction is stacking but the stacking bases are not necessarily neighboring in the PNA sequence. More bases stack in free PNA than in PNA of the conjugate, but stacking is less stable in free PNA. PNA in the conjugate is slightly more exposed to solvent. Overall, cyanocobalamin attached to a PNA oligomer increases the flexibility of PNA in a way that could be beneficial for its hybridization with natural nucleic acid oligomers.

Nucleic acid biosensors have a growing number of applications in genetics and biomedicine. This contribution is a critical review of the current state of the art concerning the use of nucleic acid analogues, in particular peptide nucleic acids (PNA) and locked nucleic acids (LNA), for the development of high-performance affinity biosensors. Both PNA and LNA have outstanding affinity for natural nucleic acids, and the destabilizing effect of base mismatches in PNA- or LNA-containing heterodimers is much higher than in double-stranded DNA or RNA. Therefore, PNA- and LNA-based biosensors have unprecedented sensitivity and specificity, with special applicability in DNA genotyping. Herein, the most relevant PNA- and LNA-based biosensors are presented, and their advantages and their current limitations are discussed. Some of the reviewed technology, while promising, still needs to bridge the gap between experimental status and the harder reality of biotechnological or biomedical applications.

Inhibition of the bovine papillomavirus E2 protein activity by peptide nucleic acid

Since Adleman's seminal paper, DNA computing is emerging as a very promising alternative to electronic computing. Its massive parallelism, its low energy needs, even its possible ability to break the NP barrier make its study irresistible. But for all its promise DNA computing has few results to show. This is because there are many biochemical problems in handling DNA that are still to be solved. Peptide Nucleic Acid (PNA) is a new class of informational biomolecule, a nucleic acid analogue with a backbone consisting of a peptide-like chain formed of glycine units to which the usual nucleobases are attached. PNA molecules have some properties, relevant to the area of computation with biomolecules, unique among nucleic acids: they hybridize to both complementary DNA and RNA with higher affinity that DNA itself, they can be used to enhance PCR amplification, and they can be used to restrict the action of restriction enzymes on DNA strands. The goal of this paper is to introduce PNA in the area of computation with biomolecules, and to discuss its possible role in overcoming some of the drawbacks that appear with DNA.

Aptamers, nucleic acid molecules that fold into specific three-dimensional structures, have been extensively used in the biosensing field to accomplish sensitive and specific monitoring of a wide range of biomarkers. Peptide nucleic acid (PNA), in this context, can be considered as a potential next-generation scaffold for aptamer synthesis and biomarker sensing, owing to its high stability in comparison to DNA counterparts. In this work, we investigated the performance of a series of PNA aptamers for monitoring of a prominent cardiac biomarker, cardiac troponin I (cTnI), using surface plasmon resonance (SPR) and showed that PNA sequences shorter than those previously reported for DNA can exhibit picomolar affinity, provided the essential structural features are preserved. Two different immobilization strategies (covalent and non-covalent) are validated in parallel for PNAs. The stability of sensor response in the presence of endonucleases such as DNase I was investigated further, as their occurrence in blood, plasma, and serum hydrolyses phosphodiester bonds and could be a limiting factor for point-of-care (PoC) application of DNA aptamers. Owing to their unnatural backbone, PNAs exhibited higher stability against DNase I in comparison to their DNA aptamer counterpart. Additionally, molecular dynamics (MD) simulations of DNA and PNA aptamers revealed similarities in their secondary structures, as well as distinctions in their propensity to adopt compact conformations. Overall, our findings not only provided a comprehensive framework for PNA design, surface functionalization, and cTnI biomarker detection using PNA-based bio-recognition scaffolds but also substantiated the biostability of PNAs, suggesting their high relevance for future PoC diagnostic applications. • Structural aspects of a series of PNA aptamers targeted towards cTnI were investigated. • Analysis of PNAs of varying lengths revealed that the nucleobase sequence within the 3′end part of the aptamer rather than the hairpin structure is the decisive factor governing the interaction with cTnI. • Pyrene-modified counterparts of some of the strongest PNA aptamers showed minimal variation to azide-terminated PNA aptamers. • Demonstration of higher stability of PNA bioreceptors against endonucleases in comparison to their DNA aptamer counterpart.

Single-stranded peptide nucleic acid (PNA) probes interact strongly with several nanomaterials, and the interaction was diminished in the presence of complementary nucleic acid targets which forms the basis of many nucleic acid sensing platforms. As opposed to the negatively charged DNA probes, the charges on the PNA probes may be fine-tuned by incorporating amino acids with charged side chains. The contribution of electrostatic effects to the interaction between PNA probes and nanomaterials has been largely overlooked. This work reveals that electrostatic effects substantially enhanced the quenching of dye-labeled conformationally constrained pyrrolidinyl PNA probes by several nanomaterials including graphene oxide (GO), reduced graphene oxide, gold nanoparticles (AuNPs), and silver nanoparticles. The fluorescence quenching and the color change from red to purple in the case of AuNPs because of aggregation were inhibited in the presence of complementary nucleic acid targets. Thus, fluorescence and colorimetric assays for DNA and RNA that can distinguish even single-base-mismatched nucleic acids with improved sensitivity over conventional DNA probes were established. Both the GO- and AuNP-based sensing platforms have been successfully applied for the detection of real DNA and RNA samples in vitro and in living cells. This study emphasizes the active roles of electrostatic effects in the PNA-nanomaterial interactions, which paves the way toward improving the performance of PNA-nanomaterial based assays of nucleic acids.

Nuclear localization and antisense effect of PNA internalized by ASGP-R-mediated endocytosis with protein/DNA conjugates

The importance of peptide nucleic acids (PNAs) for alteration of gene expression is nowadays firmly established. PNAs are characterized by a pseudo-peptide backbone composed of N-(2-aminoethyl)glycine units and have been found to be excellent candidates for antisense and antigene therapies. Recently, PNAs have been demonstrated to alter the action of microRNAs and thus can be considered very important tools for miRNA therapeutics. In fact, the pharmacological modulation of microRNA activity appears to be a very interesting approach in the development of new types of drugs. Among the limits of PNAs in applied molecular biology, the delivery to target cells and tissues is of key importance. The aim of this chapter is to describe methods for the efficient delivery of unmodified PNAs designed to target microRNAs involved in cancer, using as model system miR-221-3p and human glioma cells as in vitro experimental cellular system. The methods employed to deliver PNAs targeting miR-221-3p here presented are based on a macrocyclic multivalent tetraargininocalix[4]arene used as non-covalent vector for anti-miR-221-3p PNAs. High delivery efficiency, low cytotoxicity, maintenance of the PNA biological activity, and easy preparation makes this vector a candidate for a universal delivery system for this class of nucleic acid analogs.

Peptide nucleic acids (PNAs) are oligonucleotide mimics widely used as antisense, antigene molecules, and biotechnological tools. Recently, several microarrays and other biosensors based on PNAs have been developed. The construction of PNA molecular beacons or light-up probes for DNA detection requires the labelling of the PNA moiety. Labels are usually attached at the C or N terminal end by a flexible linker or in the middle of a PNA sequence, substituting one PNA base with an artificial base or by attaching fluorophores to a modified PNA backbone. The need to develop simple protocols to label PNAs encouraged us to design a new procedure for the synthesis of γ-mercaptomethyl-modified PNA. Here we propose a new strategy for the synthesis of modified PNAs, bearing amino acid side chains. The synthesis is straightforward and is an improvement to the procedures reported so far, as it uses stable intermediates and proceeds with better yields.

Peptide nucleic acids (PNAs) are polyamide analogues of nucleic acids, very effective in terms of affinity and selectivity in DNA/RNA recognition. As other supramolecular entities, the PNA structure has been an interesting scaffold for the development of new molecules, aimed to DNA and RNA recognition, with improved or completely new properties. This review describes recent work, with the aim of describing how the design of these molecules has evolved in recent years, using increasingly effective tools, from simple crystal structure analysis to molecular dynamics and metadynamics. Modified PNA with additional modules appended, either on the backbone or on the nucleobase, are described. Polyfunctional molecules with both backbone and nucleobase modification are then considered. Finally, recent examples of architectures obtained by conjugation of PNAs to inorganic nanostructures as cargo systems for diagnostics and nano-biotechnology are presented.

We have subjected several analogs of DNA that have been widely used as antisense oligonucleotide (ASO) inhibitors of gene expression to comparative molecular dynamics (MD) calculations of their ability to form duplexes with DNA and RNA. The analogs included in this study are the phosphorothioate (PS), peptide nucleic acid (PNA), locked nucleic acid (LNA), morpholino nucleic acid (PMO), the 2'-OMe, 2'-F, 2'-methoxyethyl (2'-MOE) and the constrained cET analogs, as well as the natural phosphodiester (PO) as control, for a total of nine structures, in both XNA-DNA and XNA-RNA duplexes. This is intended as an objective criterion for their relative ability to duplex with an RNA complement and their comparative potential for antisense applications. We have found that the constrained furanose ring analogs show increased stability when considering this study's structural and energetic parameters. The 2'-MOE modification, even though energetically stable, has an elevated dynamic range and breathing properties due to the bulkier moiety in the C2' position of the furanose. The smaller modifications in the C2' position, 2'-F, 2'-OMe and PS also form stable and energetically favored duplexes with both DNA and RNA. The morpholino moiety allows for increased tolerance in accommodating either DNA or RNA and the PNA, with the PNA being the most energetically stable, although with a preference for the B-form DNA. In summary, we can rank the overall preference of hybrid strand formations as PNA>cET/LNA>PS/2'-F/2'-OMe>morpholino>2'-MOE for the efficacy of duplex formation.

Orientation Preferences of Backbone Secondary Amide Functional Groups in Peptide Nucleic Acid Complexes: Quantum Chemical Calculations Reveal an Intrinsic Preference of Cationic D-Amino Acid-Based Chiral PNA Analogues for the P-form