Imaging mRNA Expression in Live Cells via PNA·DNA Strand Displacement-Activated Probes

Cationic Calix[4]arene Vectors to Efficiently Deliver AntimiRNA Peptide Nucleic Acids (PNAs) and miRNA Mimics

One of the most appealing approaches for regulating gene expression, named the "microRNA therapeutic" method, is based on the regulation of the activity of microRNAs (miRNAs), the intracellular levels of which are dysregulated in many diseases, including cancer. This can be achieved by miRNA inhibition with antimiRNA molecules in the case of overexpressed microRNAs, or by using miRNA-mimics to restore downregulated microRNAs that are associated with the target disease. The development of new efficient, low-toxic, and targeted vectors of such molecules represents a key topic in the field of the pharmacological modulation of microRNAs. We compared the delivery efficiency of a small library of cationic calix[4]arene vectors complexed with fluorescent antimiRNA molecules (Peptide Nucleic Acids, PNAs), pre-miRNA (microRNA precursors), and mature microRNAs, in glioma- and colon-cancer cellular models. The transfection was assayed by cytofluorimetry, cell imaging assays, and RT-qPCR. The calix[4]arene-based vectors were shown to be powerful tools to facilitate the uptake of both neutral (PNAs) and negatively charged (pre-miRNAs and mature microRNAs) molecules showing low toxicity in transfected cells and ability to compete with commercially available vectors in terms of delivery efficiency. These results could be of great interest to validate microRNA therapeutics approaches for future application in personalized treatment and precision medicine.

Integration of chemically modified nucleotides with DNA strand displacement reactions for applications in living systems

Watson-Crick base pairing rules provide a powerful approach for engineering DNA-based nanodevices with programmable and predictable behaviors. In particular, DNA strand displacement reactions have enabled the development of an impressive repertoire of molecular devices with complex functionalities. By relying on DNA to function, dynamic strand displacement devices represent powerful tools for the interrogation and manipulation of biological systems. Yet, implementation in living systems has been a slow process due to several persistent challenges, including nuclease degradation. To circumvent these issues, researchers are increasingly turning to chemically modified nucleotides as a means to increase device performance and reliability within harsh biological environments. In this review, we summarize recent progress toward the integration of chemically modified nucleotides with DNA strand displacement reactions, highlighting key successes in the development of robust systems and devices that operate in living cells and in vivo. We discuss the advantages and disadvantages of commonly employed modifications as they pertain to DNA strand displacement, as well as considerations that must be taken into account when applying modified oligonucleotide to living cells. Finally, we explore how chemically modified nucleotides fit into the broader goal of bringing dynamic DNA nanotechnology into the cell, and the challenges that remain. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Biosensing.

Multifunctional Delivery Systems for Peptide Nucleic Acids

The number of applications of peptide nucleic acids (PNAs)-oligonucleotide analogs with a polyamide backbone-is continuously increasing in both in vitro and cellular systems and, parallel to this, delivery systems able to bring PNAs to their targets have been developed. This review is intended to give to the readers an overview on the available carriers for these oligonucleotide mimics, with a particular emphasis on newly developed multi-component- and multifunctional vehicles which boosted PNA research in recent years. The following approaches will be discussed: (a) conjugation with carrier molecules and peptides; (b) liposome formulations; (c) polymer nanoparticles; (d) inorganic porous nanoparticles; (e) carbon based nanocarriers; and (f) self-assembled and supramolecular systems. New therapeutic strategies enabled by the combination of PNA and proper delivery systems are discussed.

Fluorogenic PNA probes

Fluorogenic oligonucleotide probes that can produce a change in fluorescence signal upon binding to specific biomolecular targets, including nucleic acids as well as non-nucleic acid targets, such as proteins and small molecules, have applications in various important areas. These include diagnostics, drug development and as tools for studying biomolecular interactions in situ and in real time. The probes usually consist of a labeled oligonucleotide strand as a recognition element together with a mechanism for signal transduction that can translate the binding event into a measurable signal. While a number of strategies have been developed for the signal transduction, relatively little attention has been paid to the recognition element. Peptide nucleic acids (PNA) are DNA mimics with several favorable properties making them a potential alternative to natural nucleic acids for the development of fluorogenic probes, including their very strong and specific recognition and excellent chemical and biological stabilities in addition to their ability to bind to structured nucleic acid targets. In addition, the uncharged backbone of PNA allows for other unique designs that cannot be performed with oligonucleotides or analogues with negatively-charged backbones. This review aims to introduce the principle, showcase state-of-the-art technologies and update recent developments in the areas of fluorogenic PNA probes during the past 20 years.

Split Spinach Aptamer for Highly Selective Recognition of DNA and RNA at Ambient Temperatures

Split spinach aptamer (SSA) probes for fluorescent analysis of nucleic acids were designed and tested. In SSA design, two RNA or RNA/DNA strands hybridized to a specific nucleic acid analyte and formed a binding site for low-fluorescent 3,5-difluoro-4-hydroxybenzylidene imidazolinone (DFHBI) dye, which resulted in up to a 270-fold increase in fluorescence. The major advantage of the SSA over state-of-the art fluorescent probes is high selectivity: it produces only background fluorescence in the presence of a single-base-mismatched analyte, even at room temperature. SSA is therefore a promising tool for label-free analysis of nucleic acids at ambient temperatures.

Nanotechnology for delivery of peptide nucleic acids (PNAs)

Over the past three decades, peptide nucleic acids have been employed in numerous chemical and biological applications. Peptide nucleic acids possess enormous potential because of their superior biophysical properties, compared to other oligonucleotide chemistries. However, for therapeutic applications, intracellular delivery of peptide nucleic acids remains a challenge. In this review, we summarize the progress that has been made in delivering peptide nucleic acids to intracellular targets. In addition, we emphasize recent nanoparticle-based strategies for efficient delivery of conventional and chemically-modified peptides nucleic acids.

Antisense peptide nucleic acid-functionalized cationic nanocomplex for in vivo mRNA detection

Acute lung injury (ALI) is a complex syndrome with many aetiologies, resulting in the upregulation of inflammatory mediators in the host, followed by dyspnoea, hypoxemia and pulmonary oedema. A central mediator is inducible nitric oxide synthase (iNOS) that drives the production of NO and continued inflammation. Thus, it is useful to have diagnostic and therapeutic agents for targeting iNOS expression. One general approach is to target the precursor iNOS mRNA with antisense nucleic acids. Peptide nucleic acids (PNAs) have many advantages that make them an ideal platform for development of antisense theranostic agents. Their membrane impermeability, however, limits biological applications. Here, we report the preparation of an iNOS imaging probe through electrostatic complexation between a radiolabelled antisense PNA-YR9 · oligodeoxynucleotide (ODN) hybrid and a cationic shell-cross-linked knedel-like nanoparticle (cSCK). The Y (tyrosine) residue was used for (123)I radiolabelling, whereas the R9 (arginine9) peptide was included to facilitate cell exit of untargeted PNA. Complete binding of the antisense PNA-YR9 · ODN hybrid to the cSCK was achieved at an 8 : 1 cSCK amine to ODN phosphate (N/P) ratio by a gel retardation assay. The antisense PNA-YR9 · ODN · cSCK nanocomplexes efficiently entered RAW264.7 cells, whereas the PNA-YR9 · ODN alone was not taken up. Low concentrations of (123)I-labelled antisense PNA-YR9 · ODN complexed with cSCK showed significantly higher retention of radioactivity when iNOS was induced in lipopolysaccharide+interferon-γ-activated RAW264.7 cells when compared with a mismatched PNA. Moreover, statistically, greater retention of radioactivity from the antisense complex was also observed in vivo in an iNOS-induced mouse lung after intratracheal administration of the nanocomplexes. This study demonstrates the specificity and sensitivity by which the radiolabelled nanocomplexes can detect iNOS mRNA in vitro and in vivo and their potential for early diagnosis of ALI.

Imaging mRNA expression levels in living cells with PNA·DNA binary FRET probes delivered by cationic shell-crosslinked nanoparticles

Optical imaging of gene expression through the use of fluorescent antisense probes targeted to the mRNA has been an area of great interest. The main obstacles to developing highly sensitive antisense fluorescent imaging agents have been the inefficient intracellular delivery of the probes and high background signal from unbound probes. Binary antisense probes have shown great promise as mRNA imaging agents because a signal can only occur if both probes are bound simultaneously to the mRNA target site. Selecting an accessible binding site is made difficult by RNA folding and protein binding in vivo and the need to bind two probes. Even more problematic, has been a lack of methods for efficient cytoplasmic delivery of the probes that would be suitable for eventual applications in vivo in animals. Herein we report the imaging of iNOS mRNA expression in live mouse macrophage cells with PNA·DNA binary FRET probes delivered by a cationic shell crosslinked knedel-like nanoparticle (cSCK). We first demonstrate that FRET can be observed on in vitro transcribed mRNA with both the PNA probes and the PNA·DNA hybrid probes. We then demonstrate that the FRET signal can be observed in live cells when the hybrid probes are transfected with the cSCK, and that the strength of the FRET signal is sequence specific and depends on the mRNA expression level.

Recent advances in chemical modification of Peptide nucleic acids

Peptide nucleic acid (PNA) has become an extremely powerful tool in chemistry and biology. Although PNA recognizes single-stranded nucleic acids with exceptionally high affinity and sequence selectivity, there is considerable ongoing effort to further improve properties of PNA for both fundamental science and practical applications. The present paper discusses selected recent studies that improve on cellular uptake and binding of PNA to double-stranded DNA and RNA. The focus is on chemical modifications of PNA's backbone and heterocyclic nucleobases. The paper selects representative recent studies and does not attempt to provide comprehensive coverage of the broad and vibrant field of PNA modification.