Sequence-unrestricted, Watson-Crick recognition of double helical B-DNA by (R)-miniPEG-γPNAs

Electrophoretically Snagging Viral Genomes in Wormlike Micelle Networks Using Peptide Nucleic Acid Amphiphiles and dsDNA Oligomers

We demonstrate that the attachment of 30-170 bp dsDNA oligomers to ssDNA viral genomes gives a significant additional mobility shift in micelle-tagging electrophoresis (MTE). In MTE, a modified peptide nucleic acid amphiphile is attached to the viral genome to bind drag-inducing micelles present in capillary electrophoresis running buffers. Further attachment of 30-170 bp dsDNA oligomers drastically shifts the mobility of the 5.1 kB ssDNA genome of mouse minute virus (MMV), providing a new mechanism to improve resolution in CE-based analysis of kilobase nucleic acids. A model based on biased-reptation electrophoresis, end-labeled free-solution electrophoresis, and Ferguson gel-filtration theory is presented to describe the observed mobility shifts.

Recent Advancements in Development and Therapeutic Applications of Genome-Targeting Triplex-Forming Oligonucleotides and Peptide Nucleic Acids

Recent developments in artificial nucleic acid and drug delivery systems present possibilities for the symbiotic engineering of therapeutic oligonucleotides, such as antisense oligonucleotides (ASOs) and small interfering ribonucleic acids (siRNAs). Employing these technologies, triplex-forming oligonucleotides (TFOs) or peptide nucleic acids (PNAs) can be applied to the development of symbiotic genome-targeting tools as well as a new class of oligonucleotide drugs, which offer conceptual advantages over antisense as the antigene target generally comprises two gene copies per cell rather than multiple copies of mRNA that are being continually transcribed. Further, genome editing by TFOs or PNAs induces permanent changes in the pathological genes, thus facilitating the complete cure of diseases. Nuclease-based gene-editing tools, such as zinc fingers, CRISPR-Cas9, and TALENs, are being explored for therapeutic applications, although their potential off-target, cytotoxic, and/or immunogenic effects may hinder their in vivo applications. Therefore, this review is aimed at describing the ongoing progress in TFO and PNA technologies, which can be symbiotic genome-targeting tools that will cause a near-future paradigm shift in drug development.

DNA recognition and induced genome modification by a hydroxymethyl-γ tail-clamp peptide nucleic acid

Peptide nucleic acids (PNAs) can target and stimulate recombination reactions in genomic DNA. We have reported that γPNA oligomers possessing the diethylene glycol γ-substituent show improved efficacy over unmodified PNAs in stimulating recombination-induced gene modification. However, this structural modification poses a challenge because of the inherent racemization risk in O-alkylation of the precursory serine side chain. To circumvent this risk and improve γPNA accessibility, we explore the utility of γPNA oligomers possessing the hydroxymethyl-γ moiety for gene-editing applications. We demonstrate that a γPNA oligomer possessing the hydroxymethyl modification, despite weaker preorganization, retains the ability to form a hybrid with the double-stranded DNA target of comparable stability and with higher affinity than that of the diethylene glycol-γPNA. When formulated into poly(lactic-co-glycolic acid) nanoparticles, the hydroxymethyl-γPNA stimulates higher frequencies (≥ 1.5-fold) of gene modification than the diethylene glycol γPNA in mouse bone marrow cells.

Parameterization of the miniPEG-Modified γPNA Backbone: Toward Induced γPNA Duplex Dissociation

γ-Modified peptide nucleic acids (γPNAs) serve as potential therapeutic agents against genetic diseases. Miniature poly(ethylene glycol) (miniPEG) has been reported to increase solubility and binding affinity toward genetic targets, yet details of γPNA structure and dynamics are not understood. Within our work, we parameterized missing torsional and electrostatic terms for the miniPEG substituent on the γ-carbon atom of the γPNA backbone in the CHARMM force field. Microsecond timescale molecular dynamics simulations were carried out on six miniPEG-modified γPNA duplexes from NMR structures (PDB ID: 2KVJ). Three NMR models for the γPNA duplex (PDB ID: 2KVJ) were simulated as a reference for structural and dynamic changes captured for the miniPEG-modified γPNA duplex. Principal component analysis performed on the γPNA backbone atoms identified a single isotropic conformational substate (CS) for the NMR simulations, whereas four anisotropic CSs were identified for the ensemble of miniPEG-modified γPNA simulations. The NMR structures were found to have a 23° helical bend toward the major groove, consistent with our simulated CS structure of 19.0°. However, a significant difference between simulated methyl- and miniPEG-modified γPNAs involved the opportunistic invasion of miniPEG through the minor and major groves. Specifically, hydrogen bond fractional analysis showed that the invasion was particularly prone to affect the second G-C base pair, reducing the Watson-Crick base pair hydrogen bond by 60% over the six simulations, whereas the A-T base pairs decreased by only 20%. Ultimately, the invasion led to base stack reshuffling, where the well-ordered base stacking was reduced to segmented nucleobase stacking interactions. Our 6 μs timescale simulations indicate that duplex dissociation suggests the onset toward γPNA single strands, consistent with the experimental observation of decreased aggregation. To complement the insight of miniPEG-modified γPNA structure and dynamics, the new miniPEG force field parameters allow for further exploration of such modified γPNA single strands as potential therapeutic agents against genetic diseases.

Ultrasound-assisted Peptide Nucleic Acids synthesis (US-PNAS)

Herein, we developed an innovative and easily accessible solid-phase synthetic protocol for Peptide Nucleic Acid (PNA) oligomers by systematically investigating the ultrasonication effects in all steps of the PNA synthesis (US-PNAS). When compared with standard protocols, the application of the so-obtained US-PNAS approach succeeded in improving the crude product purities and the isolated yields of different PNA, including small or medium-sized oligomers (5-mer and 9-mer), complex purine-rich sequences (like a 5-mer Guanine homoligomer and the telomeric sequence TEL-13) and longer oligomers (such as the 18-mer anti-IVS2-654 PNA and the 23-mer anti-mRNA 155 PNA). Noteworthy, our ultrasound-assisted strategy is compatible with the commercially available PNA monomers and well-established coupling reagents and only requires the use of an ultrasonic bath, which is a simple equipment generally available in most synthetic laboratories.

Nanoparticle-mediated genome editing in single-cell embryos via peptide nucleic acids

Through preimplantation genetic diagnosis, genetic diseases can be detected during the early stages of embryogenesis, but effective treatments for many of these disorders are lacking. Gene editing could allow for correction of the underlying mutation during embryogenesis to prevent disease pathogenesis or even provide a cure. Here, we demonstrate that administration of peptide nucleic acids and single-stranded donor DNA oligonucleotides encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles to single-cell embryos allows for editing of an eGFP-beta globin fusion transgene. Blastocysts from treated embryos exhibit high levels of editing (~94%), normal physiological development, normal morphology, and no detected off-target genomic effects. Treated embryos reimplanted to surrogate moms show normal growth without gross developmental abnormalities and with no identified off-target effects. Mice from reimplanted embryos consistently show editing, characterized by mosaicism across multiple organs with some organ biopsies showing up to 100% editing. This proof-of-concept work demonstrates for the first time the use of peptide nucleic acid (PNA)/DNA nanoparticles as a means to achieve embryonic gene editing.

Pseudo-Complementary G:C Base Pair for Mixed Sequence dsDNA Invasion and Its Applications in Diagnostics (SARS-CoV-2 Detection)

Pseudo-complementary oligonucleotides contain artificial nucleobases designed to reduce duplex formation in the pseudo-complementary pair without compromising duplex formation to targeted (complementary) oligomers. The development of a pseudo-complementary A:T base pair, U^s:D, was important in achieving dsDNA invasion. Herein, we report pseudo-complementary analogues of the G:C base pair leveraged on steric and electrostatic repulsion between the cationic phenoxazine analogue of cytosine (G-clamp, C⁺) and N-7 methyl guanine (G⁺), which is also cationic. We show that while complementary peptide nucleic acids (PNA) form a much more stable homoduplex than the PNA:DNA heteroduplex, oligomers based on pseudo-C:G complementary PNA favor PNA:DNA hybridization. We show that this enables dsDNA invasion at physiological salt concentration and that stable invasion complexes are obtained with low equivalents of PNAs (2-4 equiv). We harnessed the high yield of dsDNA invasion for the detection of RT-RPA amplicon using a lateral flow assay (LFA) and showed that two strains of SARS-CoV-2 can be discriminated owing to single nucleotide resolution.

Two-Helix Supramolecular Proteomimetic Binders Assembled via PNA-Assisted Disulfide Crosslinking

Peptidic motifs folded in a defined conformation are able to inhibit protein-protein interactions (PPIs) covering large interfaces and as such they are biomedical molecules of interest. Mimicry of such natural structures with synthetically tractable constructs often requires complex scaffolding and extensive optimization to preserve the fidelity of binding to the target. Here, we present a novel proteomimetic strategy based on a 2-helix binding motif that is brought together by hybridization of peptide nucleic acids (PNA) and stabilized by a rationally positioned intermolecular disulfide crosslink. Using a solid phase synthesis approach (SPPS), the building blocks are easily accessible and such supramolecular peptide-PNA helical hybrids could be further coiled using precise templated chemistry. The elaboration of the structural design afforded high affinity SARS CoV-2 RBD (receptor binding domain) binders without interference with the underlying peptide sequence, creating a basis for a new architecture of supramolecular proteomimetics.

Targeting a KRAS i-motif forming sequence by unmodified and gamma-modified peptide nucleic acid oligomers

Growing interest in i-motif DNA as a transcriptional regulatory element motivates development of synthetic molecules capable of targeting these structures. In this study, we designed unmodified peptide nucleic acid (PNA) and gamma-modified PNA (γPNA) oligomers complementary to an i-motif forming sequence derived from the promoter of the KRAS oncogene. Biophysical techniques such as circular dichroism (CD) spectroscopy, CD melting, and fluorescence spectroscopy demonstrated the successful invasion of the i-motif by PNA and γPNA. Both PNA and γPNA showed very strong binding to the target sequence with high thermal stability of the resulting heteroduplexes. Interestingly fluorescence and CD experiments indicated formation of an intermolecular i-motif structure via the overhangs of target-probe heteroduplexes formed by PNA/γPNA invasion of the intramolecular i-motif. Targeting promoter i-motif forming sequences with high-affinity oligonucleotide mimics like γPNAs may represent a new approach for inhibiting KRAS transcription, thereby representing a potentially useful anti-cancer strategy.

Factors Impacting Invader-Mediated Recognition of Double-Stranded DNA

The development of chemically modified oligonucleotides enabling robust, sequence-unrestricted recognition of complementary chromosomal DNA regions has been an aspirational goal for scientists for many decades. While several groove-binding or strand-invading probes have been developed towards this end, most enable recognition of DNA only under limited conditions (e.g., homopurine or short mixed-sequence targets, low ionic strength, fully modified probe strands). Invader probes, i.e., DNA duplexes modified with +1 interstrand zippers of intercalator-functionalized nucleotides, are predisposed to recognize DNA targets due to their labile nature and high affinity towards complementary DNA. Here, we set out to gain further insight into the design parameters that impact the thermal denaturation properties and binding affinities of Invader probes. Towards this end, ten Invader probes were designed, and their biophysical properties and binding to model DNA hairpins and chromosomal DNA targets were studied. A Spearman's rank-order correlation analysis of various parameters was then performed. Densely modified Invader probes were found to result in efficient recognition of chromosomal DNA targets with excellent binding specificity in the context of denaturing or non-denaturing fluorescence in situ hybridization (FISH) experiments. The insight gained from the initial phase of this study informed subsequent probe optimization, which yielded constructs displaying improved recognition of chromosomal DNA targets. The findings from this study will facilitate the design of efficient Invader probes for applications in the life sciences.

Serine-γPNA, Invader probes, and chimeras thereof: three probe chemistries that enable sequence-unrestricted recognition of double-stranded DNA

Three probe chemistries are evaluated with respect to thermal denaturation temperatures, UV-Vis and fluorescence characteristics, recognition of complementary and mismatched DNA hairpin targets, and recognition of chromosomal DNA targets in the context of non-denaturing fluorescence in situ hybridization (nd-FISH) experiments: (i) serine-γPNAs (SγPNAs), i.e., single-stranded peptide nucleic acid (PNA) probes that are modified at the γ-position with (R)-hydroxymethyl moieties, (ii) Invader probes, i.e., DNA duplexes modified with +1 interstrand zippers of 2'-O-(pyren-1-yl)methyl-RNA monomers, a molecular arrangement that results in a violation of the neighbor exclusion principle, and (iii) double-stranded chimeric SγPNAs:Invader probes, i.e., duplexes between complementary SγPNA and Invader strands, which are destabilized due to the poor compatibility between intercalators and PNA:DNA duplexes. Invader probes resulted in efficient, highly specific, albeit comparatively slow recognition of the model DNA hairpin targets. Recognition was equally efficient and faster with the single-stranded SγPNA probes but far less specific, whilst the double-stranded chimeric SγPNAs:Invader probes displayed recognition characteristics that were intermediate of the parent probes. All three probe chemistries demonstrated the capacity to target chromosomal DNA in nd-FISH experiments, with Invader probes resulting in the most favorable and consistent characteristics (signals in >90% of interphase nuclei against a low background and no signal in negative control experiments). These probe chemistries constitute valuable additions to the molecular toolbox needed for DNA-targeting applications.

In vivo correction of cystic fibrosis mediated by PNA nanoparticles

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. We sought to correct the multiple organ dysfunction of the F508del CF-causing mutation using systemic delivery of peptide nucleic acid gene editing technology mediated by biocompatible polymeric nanoparticles. We confirmed phenotypic and genotypic modification in vitro in primary nasal epithelial cells from F508del mice grown at air-liquid interface and in vivo in F508del mice following intravenous delivery. In vivo treatment resulted in a partial gain of CFTR function in epithelia as measured by in situ potential differences and Ussing chamber assays and correction of CFTR in both airway and GI tissues with no off-target effects above background. Our studies demonstrate that systemic gene editing is possible, and more specifically that intravenous delivery of PNA NPs designed to correct CF-causing mutations is a viable option to ameliorate CF in multiple affected organs.

Perspectives on conformationally constrained peptide nucleic acid (PNA): insights into the structural design, properties and applications

Peptide nucleic acid or PNA is a synthetic DNA mimic that contains a sequence of nucleobases attached to a peptide-like backbone derived from N-2-aminoethylglycine. The semi-rigid PNA backbone acts as a scaffold that arranges the nucleobases in a proper orientation and spacing so that they can pair with their complementary bases on another DNA, RNA, or even PNA strand perfectly well through the standard Watson-Crick base-pairing. The electrostatically neutral backbone of PNA contributes to its many unique properties that make PNA an outstanding member of the xeno-nucleic acid family. Not only PNA can recognize its complementary nucleic acid strand with high affinity, but it does so with excellent specificity that surpasses the specificity of natural nucleic acids and their analogs. Nevertheless, there is still room for further improvements of the original PNA in terms of stability and specificity of base-pairing, direction of binding, and selectivity for different types of nucleic acids, among others. This review focuses on attempts towards the rational design of new generation PNAs with superior performance by introducing conformational constraints such as a ring or a chiral substituent in the PNA backbone. A large collection of conformationally rigid PNAs developed during the past three decades are analyzed and compared in terms of molecular design and properties in relation to structural data if available. Applications of selected modified PNA in various areas such as targeting of structured nucleic acid targets, supramolecular scaffold, biosensing and bioimaging, and gene regulation will be highlighted to demonstrate how the conformation constraint can improve the performance of the PNA. Challenges and future of the research in the area of constrained PNA will also be discussed.

Impact of bPNA Backbone Structural Constraints and Composition on Triplex Hybridization with DNA

We report herein a study on the impact of bifacial peptide nucleic acid (bPNA) amino acid composition and backbone modification on DNA binding. A series of bPNA backbone variants with identical net charge were synthesized to display either 4 or 6 melamine (M) bases. These bases form thymine-melamine-thymine (TMT) base-triples, resulting in triplex hybrid stem structures with T-rich DNAs. Analyses of 6 M bPNA-DNA hybrids suggested that hybrid stability was linked to amino acid secondary structure propensities, prompting a more detailed study in shorter 4 M bPNAs. We synthesized 4 M bPNAs predisposed to adopt helical secondary structure via helix-turn nucleation in 7-residue bPNAs using double-click covalent stapling. Generally, hybrid stability improved upon stapling, but amino acid composition had a more significant effect. We also pursued an alternative strategy for bPNA structural preorganization by incorporation of residues with strong backbone amide conformational preferences such as 4R- and 4S-fluoroprolines. Notably, these derivatives exhibited an additional improvement in hybrid stability beyond both unsubstituted proline bPNA analogues and the helically patterned bPNAs. Overall, these findings demonstrate the tunability of bPNA-DNA hybrid stability through bPNA backbone structural propensities and amino acid composition.

Nicked Invader probes: multistranded and sequence-unrestricted recognition of double-stranded DNA

Major efforts have been devoted to the development of constructs that enable sequence-specific recognition of double-stranded (ds) DNA, fueled by the promise for enabling tools for applications in molecular biology, diagnostics, and medicine. Towards this end, we have previously introduced Invader probes, i.e., short DNA duplexes with +1 interstrand zipper arrangements of intercalator-functionalized nucleotides. The individual strands of these labile probes display high affinity towards complementary DNA (cDNA), which drives sequence-unrestricted dsDNA-recognition. However, recognition of long targets is challenging due to the high stability of the corresponding probes. To address this, we recently introduced toehold Invader probes, i.e., Invader probes with 5'-single-stranded overhangs. The toehold architecture allows for shorter double-stranded segments to be used, which facilitates probe dissociation and dsDNA-recognition. As an extension thereof, we here report the biophysical and dsDNA-targeting properties of nicked Invader probes. In this probe architecture, the single-stranded overhangs of toehold Invader probes are hybridized to short intercalator-modified auxiliary strands, leading to formation of additional labile segments. The extra binding potential from the auxiliary strands imparts nicked Invader probes with greater dsDNA-affinity than the corresponding toehold or blunt-ended probes. Recognition of chromosomal DNA targets, refractory to recognition by conventional Invader probes, is demonstrated for nicked Invader probes in the context of non-denaturing FISH experiments, which highlights their utility as dsDNA-targeting tools.

Recognition of double-stranded DNA using LNA-modified toehold Invader probes

Development of molecules capable of binding to specific sequences of double-stranded (ds) DNA continues to attract considerable interest, as this may yield useful tools for applications in life science, biotechnology, and medicine. We have previously demonstrated sequence-unrestricted of dsDNA using Invader probes, i.e., DNA duplexes that are energetically activated through incorporation of +1 interstrand zipper arrangements of O2'-intercalator-functionalized RNA monomers. Nonetheless, recognition of extended dsDNA target regions remains challenging due to the high stability of the corresponding probes. To address this, we introduce toehold Invader probes, i.e., Invader probes with 5'-single-stranded overhangs. This design provides access to probes with shortened double-stranded segments, which facilitates probe denaturation. The single-stranded overhangs can, furthermore, be modified with affinity-enhancing modifications like LNA (locked nucleic acid) monomers to additionally increase target affinity. Herein, we report the biophysical and dsDNA-targeting properties of different toehold Invader designs and compare them to conventional Invader probes. LNA-modified toehold Invader probes display promising recognition characteristics, including greatly improved affinity to dsDNA, excellent binding specificity, and fast recognition kinetics, which enabled recognition of chromosomal DNA targets that have proven refractory to recognition by conventional Invader probes. Thus, toehold Invader probes represent another step toward a robust, oligonucleotide-based approach for sequence-unrestricted dsDNA-recognition.

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

Peptide nucleic acid (PNA) is arguably one of the most successful DNA mimics, despite a most dramatic departure from the native structure of DNA. The present review summarizes 30 years of research on PNA's chemistry, optimization of structure and function, applications as probes and diagnostics, and attempts to develop new PNA therapeutics. The discussion starts with a brief review of PNA's binding modes and structural features, followed by the most impactful chemical modifications, PNA enabled assays and diagnostics, and discussion of the current state of development of PNA therapeutics. While many modifications have improved on PNA's binding affinity and specificity, solubility and other biophysical properties, the original PNA is still most frequently used in diagnostic and other in vitro applications. Development of therapeutics and other in vivo applications of PNA has notably lagged behind and is still limited by insufficient bioavailability and difficulties with tissue specific delivery. Relatively high doses are required to overcome poor cellular uptake and endosomal entrapment, which increases the risk of toxicity. These limitations remain unsolved problems waiting for innovative chemistry and biology to unlock the full potential of PNA in biomedical applications.

PNA-Assisted DNAzymes to Cleave Double-Stranded DNA for Genetic Engineering with High Sequence Fidelity

DNAzymes have been widely used in many sensing and imaging applications but have rarely been used for genetic engineering since their discovery in 1994, because their substrate scope is mostly limited to single-stranded DNA or RNA, whereas genetic information is stored mostly in double-stranded DNA (dsDNA). To overcome this major limitation, we herein report peptide nucleic acid (PNA)-assisted double-stranded DNA nicking by DNAzymes (PANDA) as the first example to expand DNAzyme activity toward dsDNA. We show that PANDA is programmable in efficiently nicking or causing double strand breaks on target dsDNA, which mimics protein nucleases and can act as restriction enzymes in molecular cloning. In addition to being much smaller than protein enzymes, PANDA has a higher sequence fidelity compared with CRISPR/Cas under the condition we tested, demonstrating its potential as a novel alternative tool for genetic engineering and other biochemical applications.

Recent Advances in Peptide Nucleic Acids as Antibacterial Agents

The emergence of antibiotic-resistant bacteria and the slow progress in searching for new antimicrobial agents makes it hard to treat bacterial infections and cause problems for the healthcare system worldwide, including high costs, prolonged hospitalizations, and increased mortality. Therefore, the discovery of effective antibacterial agents is of great importance. One attractive alternative is antisense peptide nucleic acid (PNA), which inhibits or eliminates gene expression by binding to the complementary messenger RNA (mRNA) sequence of essential genes or the accessible and functionally important regions of the ribosomal RNA (rRNA). Following 30 years of development, PNAs have played an extremely important role in the treatment of Gram-positive, Gram-negative, and acidfast bacteria due to their desirable stability of hybrid complex with target RNA, the strong affinity for target mRNA/rRNA, and the stability against nucleases. PNA-based antisense antibiotics can strongly inhibit the growth of pathogenic and antibiotic-resistant bacteria in a sequence-specific and dose-dependent manner at micromolar concentrations. However, several fundamental challenges, such as intracellular delivery, solubility, physiological stability, and clearance still need to be addressed before PNAs become broadly applicable in clinical settings. In this review, we summarize the recent advances in PNAs as antibacterial agents and the challenges that need to be overcome in the future.

Peptide nucleic acid Hoogsteen strand linker design for major groove recognition of DNA thymine bases

Sequence-specific targeting of double-stranded DNA and non-coding RNA via triple-helix-forming peptide nucleic acids (PNAs) has attracted considerable attention in therapeutic, diagnostic and nanotechnological fields. An E-base (3-oxo-2,3-dihydropyridazine), attached to the polyamide backbone of a PNA Hoogsteen strand by a side-chain linker molecule, is typically used in the hydrogen bond recognition of the 4-oxo group of thymine and uracil nucleic acid bases in the major groove. We report on the application of quantum chemical computational methods, in conjunction with spatial constraints derived from the experimental structure of a homopyrimidine PNA·DNA-PNA hetero-triplex, to investigate the influence of linker flexibility on binding interactions of the E-base with thymine and uracil bases in geometry-optimised model systems. Hydrogen bond formation between the N2 E-base atom and target pyrimidine base 4-oxo groups in model systems containing a β-alanine linker (J Am Chem Soc 119:11116, 1997) was found to incur significant internal strain energy and the potential disruption of intra-stand aromatic base stacking interactions in an oligomeric context. In geometry-optimised model systems containing a 3-trans olefin linker (Bioorg Med Chem Lett 14:1551, 2004) the E-base swung out away from the target pyrimidine bases into the solvent. These findings are in qualitative agreement with calorimetric measurements in hybridisation experiments at T-A and U-A inversion sites. In contrast, calculations on a novel 2-cis olefin linker design indicate that it could permit simultaneous E-base hydrogen bonding with the thymine 4-oxo group, circumvention and solvent screening of the thymine 5-methyl group, and maintenance of triplex intra-stand base stacking interactions.

A Robust Method for Preparing Optically Pure MiniPEG-Containing Gamma PNA Monomers

We report the syntheses of chemical building blocks of a particular class of chiral PNAs, called miniPEG-containing (R)-gamma PNAs (or (R)-MPγPNAs). The strategy involves the application of 9-(4-bromophenyl)-9-fluorenyl as a temporary, safety-catch protecting group for the suppression of racemization in the alkylation and reductive amination steps. The methodology is general and robust, ideally suited for large-scale monomer productions with most synthetic steps providing excellent chemical yields without the need for purification other than a simple workup and precipitation.

Synthesis and Characterisation of Photolabile SPhNPPOC-Protected (R)-MiniPEG Containing Chiral γ-Peptide Nucleic Acid Monomers

Peptide nucleic acid (PNA) microarrays are expected to be developed as a new generation of gene detection tools. However, poor water solubility and the limitation of the sequence design of achiral PNA probes mainly hinder their application. Accordingly, (R)-diethylene glycol containing a chiral PNA (miniPEG-γPNA) has been developed to solve these problems. Light-directed synthesis is an effective method to fabricate high-density microarrays. Thiophenyl-2-(2-nitrophenyl)propoxycarbonyl (SPhNPPOC) is a newly synthesised photolabile protective group with high photolytic efficiency. Protecting the PNA monomers with SPhNPPOC may improve the preparation process of PNA microarrays by light-directed synthesis in terms of shortening the deprotection time and restraining side reactions. In this article, SPhNPPOC/carbobenzoxy (Cbz)-protected chiral miniPEG-γPNA monomers are synthesised, and the photo-deprotection rate is approximately twice that of a 2-(2-nitrophenyl)propyloxycarbonyl (NPPOC)-protected monomer. The monomers are expected to be used for the efficient and rapid fabrication of chiral miniPEG-γPNA microarrays through a photolithographic strategy.

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.

Peptide Nucleic Acids: Applications in Biomedical Sciences

The DNA mimic, PNA (peptide nucleic acid), has been with us now for almost 3 decades [...].

Impact of non-nucleotidic bulges on recognition of mixed-sequence dsDNA by pyrene-functionalized Invader probes

Invader probes, i.e., DNA duplexes modified with +1 interstrand zippers of intercalator-functionalized nucleotides like 2'-O-(pyren-1-yl)methyl-RNA monomers, are energetically activated for sequence-unrestricted recognition of double-stranded DNA (dsDNA) as they are engineered to violate the neighbor exclusion principle, while displaying high affinity towards complementary DNA sequences. The impact on Invader-mediated dsDNA-recognition upon additional modification with different non-nucleotidic bulges is studied herein, based on the hypothesis that bulge-containing Invader probes will display additionally disrupted base-stacking, more extensive denaturation, and improved dsDNA-recognition efficiency. Indeed, Invader probes featuring a single central large bulge - e.g., a nonyl (C9) monomer - display improved recognition of model DNA hairpin targets vis-à-vis conventional Invader probes (C50 values ∼1.5 μM vs. ∼3.9 μM). In contrast, probes with two opposing central bulges display less favorable binding characteristics. Remarkably, C9-modified Invader probes display perfect discrimination between fully complementary dsDNA and dsDNA differing in only one of eighteen base-pairs, underscoring the high binding specificity of double-stranded probes. Cy3-labeled bulge-containing Invader probes are demonstrated to signal the presence of gender-specific DNA sequences in fluorescent in situ hybridization assays (FISH) performed under non-denaturing conditions, highlighting one potential application of dsDNA-targeting Invader probes.

Head-to-head comparison of LNA, MPγPNA, INA and Invader probes targeting mixed-sequence double-stranded DNA

Four probe chemistries are characterized and compared with respect to thermal denaturation temperatures (Tms), thermodynamic parameters associated with duplex formation, and recognition of mixed-sequence double-stranded (ds) DNA targets: (i) oligodeoxyribonucleotides (ONs) modified with Locked Nucleic Acid (LNA) monomers, (ii) MPγPNAs, i.e., single-stranded peptide nucleic acid (PNA) probes that are functionalized at the γ-position with (R)-diethylene glycol (mini-PEG, MP) moieties, (iii) Invader probes, i.e., DNA duplexes modified with +1 interstrand zipper arrangements of 2'-O-(pyren-1-yl)methyl-RNA monomers, and (iv) intercalating nucleic acids (INAs), i.e., DNA duplexes with opposing insertions of 1-O-(1-pyrenylmethyl)glycerol bulges. Invader and INA probes, which are designed to violate the nearest-neighbor exclusion principle, denature readily, whereas the individual probe strands display exceptionally high affinity towards complementary DNA (cDNA) as indicated by increases in Tms of up to 8 °C per modification. Optimized Invader and INA probes enable efficient and highly specific recognition of mixed-sequence dsDNA targets with self-complementary regions (C50 = 30-50 nM), whereas recognition is less efficient with LNA-modified ONs and fully modified MPγPNAs due to lower cDNA affinity (LNA) and a proclivity for dimerization (LNA and MPγPNA). A Cy3-labeled Invader probe is shown to stain telomeric DNA of individual chromosomes in metaphasic spreads under non-denaturing conditions with excellent specificity.

Bifunctional small molecule-oligonucleotide hybrid as microRNA inhibitor

miRNAs are key regulators of various biological processes. Dysregulation of miRNA is linked to many diseases. Development of miRNA inhibitor has implication in disease therapy and study of miRNA function. The biogenesis pathway of miRNA involves the processing of pre-miRNA into mature miRNA by Dicer enzyme. We previously reported a proximity enabled approach that employs bifunctional small molecules to regulate miRNA maturation through inhibiting the enzymatic activity of Dicer. By conjugating to an RNA targeting unit, an RNase inhibitor could be delivered to the cleavage site of specific pre-miRNA to deactivate the complexed Dicer enzyme. Herein, we expanded this bifunctional strategy by showing that antisense oligonucleotides (ASOs), including morpholinos and γPNAs, could be readily used as the RNA recognition unit to generate bifunctional small molecule-oligonucleotide hybrids as miRNA inhibitors. A systematic comparison revealed that the potency of these hybrids is mainly determined by the RNA binding of the targeting ASO molecules. Since the lengths of the ASO molecules used in this approach were much shorter than commonly used anti-miRNA ASOs, this may provide benefits to the specificity and cellular delivery of these hybrids. We expect that this approach could be complementary to traditional ASO and small molecule based miRNA inhibition and contribute to the study of miRNA.

Peptide Nucleic Acids and Gene Editing: Perspectives on Structure and Repair

Unusual nucleic acid structures are salient triggers of endogenous repair and can occur in sequence-specific contexts. Peptide nucleic acids (PNAs) rely on these principles to achieve non-enzymatic gene editing. By forming high-affinity heterotriplex structures within the genome, PNAs have been used to correct multiple human disease-relevant mutations with low off-target effects. Advances in molecular design, chemical modification, and delivery have enabled systemic in vivo application of PNAs resulting in detectable editing in preclinical mouse models. In a model of β-thalassemia, treated animals demonstrated clinically relevant protein restoration and disease phenotype amelioration, suggesting a potential for curative therapeutic application of PNAs to monogenic disorders. This review discusses the rationale and advances of PNA technologies and their application to gene editing with an emphasis on structural biochemistry and repair.

Peptide nucleic acids harness dual information codes in a single molecule

Nature encodes the information required for life in two fundamental biopolymers: nucleic acids and proteins. Peptide nucleic acid (PNA), a synthetic analog comprised of nucleobases arrayed along a pseudopeptide backbone, has the ability to combine the power of nucleic acids to encode information with the versatility of amino acids to encode structure and function. Historically, PNA has been perceived as a simple nucleic acid mimic having desirable properties such as high biostability and strong affinity for complementary nucleic acids. In this feature article, we aim to adjust this perception by highlighting the ability of PNA to act as a peptide mimic and showing the largely untapped potential to encode information in the amino acid sequence. First, we provide an introduction to PNA and discuss the use of conjugation to impart tunable properties to the biopolymer. Next, we describe the integration of functional groups directly into the PNA backbone to impart specific physical properties. Lastly, we highlight the use of these integrated amino acid side chains to encode peptide-like sequences in the PNA backbone, imparting novel activity and function and demonstrating the ability of PNA to simultaneously mimic both a peptide and a nucleic acid.

Chimeric γPNA-Invader probes: using intercalator-functionalized oligonucleotides to enhance the DNA-targeting properties of γPNA

Gamma peptide nucleic acids (γPNAs), i.e., single-stranded PNA strands that are modified at the γ-position with (R)-diethylene glycol, and Invader probes, i.e., DNA duplexes with +1 interstrand zipper arrangements of 2'-O-(pyren-1-yl)methyl-RNA monomers, are two types of nucleic acid mimics that are showing promise for sequence-unrestricted recognition of double-stranded (ds) DNA targets. We recently demonstrated that recognition of dsDNA targets with self-complementary regions is challenging for single-stranded high-affinity probes like γPNAs due to their proclivity for secondary structure formation, but not so for Invader probes, which are engineered to form readily denaturing duplexes irrespective of the target sequence context. In the present study, we describe an approach that mitigates these limitations and improves the dsDNA-recognition properties of γPNAs in partially self-complementary target contexts. Chimeric probes between γPNAs and individual Invader strands are shown to form metastable duplexes that (i) are energetically activated for recognition of complementary mixed-sequence dsDNA target regions, (ii) reduce γPNA dimerization, and (iii) substantially improve the fidelity of the dsDNA-recognition process. Chimeric γPNA-Invader probes are characterized with respect to thermal denaturation properties, thermodynamic parameters associated with duplex formation, UV-Vis and fluorescence trends to establish pyrene binding modes, and dsDNA-recognition properties using DNA hairpin model targets.

Recognition of mixed-sequence DNA targets using spermine-modified Invader probes

Double-stranded oligodeoxyribonucleotides with +1 interstrand zipper arrangements of 2'-O-(pyren-1-yl)methyl-RNA monomers are additionally activated for highly specific recognition of mixed-sequence DNA targets upon incorporation of non-nucleotidic spermine bulges.

Poly(Lactic-co-Glycolic Acid) Nanoparticle Delivery of Peptide Nucleic Acids In Vivo

Many important biological applications of peptide nucleic acids (PNAs) target nucleic acid binding in eukaryotic cells, which requires PNA translocation across at least one membrane barrier. The delivery challenge is further exacerbated for applications in whole organisms, where clearance mechanisms rapidly deplete and/or deactivate exogenous agents. We have demonstrated that nanoparticles (NPs) composed of biodegradable polymers can encapsulate and release PNAs (alone or with co-reagents) in amounts sufficient to mediate desired effects in vitro and in vivo without deleterious reactions in the recipient cell or organism. For example, poly(lactic-co-glycolic acid) (PLGA) NPs can encapsulate and deliver PNAs and accompanying reagents to mediate gene editing outcomes in cells and animals, or PNAs alone to target oncogenic drivers in cells and correct cancer phenotypes in animal models. In this chapter, we provide a primer on PNA-induced gene editing and microRNA targeting-the two PNA-based biotechnological applications where NPs have enhanced and/or enabled in vivo demonstrations-as well as an introduction to the PLGA material and detailed protocols for formulation and robust characterization of PNA/DNA-laden PLGA NPs.

Advances in Nanoparticle-based Delivery of Next Generation Peptide Nucleic Acids

BACKGROUND

Peptide nucleic acids (PNAs) belong to the next generation of synthetic nucleic acid analogues. Their high binding affinity and specificity towards the target DNA or RNA make them the reagent of choice for gene therapy-based applications.

OBJECTIVE

To review important gene therapy based applications of regular and chemically modified peptide nucleic acids in combination with nanotechnology.

METHOD

Selective research of the literature.

RESULTS

Poor intracellular delivery of PNAs has been a significant challenge. Among several delivery strategies explored till date, nanotechnology-based strategies hold immense potential. Recent studies have shown that advances in nanotechnology can be used to broaden the range of therapeutic applications of PNAs. In this review, we discussed significant advances made in nanoparticle-based on PLGA polymer, silicon, oxidized carbon and graphene oxide for the delivery of PNAs.

CONCLUSION

Nanoparticles delivered PNAs can be implied in diverse gene therapy based applications including gene editing as well as gene targeting (antisense) based strategies.

Peptide nucleic acid (PNA) and its applications in chemical biology, diagnostics, and therapeutics

Peptide nucleic acid (PNA) stands as one of the most successful artificial oligonucleotide mimetics. Salient features include the stability of hybridization complexes (either as duplexes or triplexes), metabolic stability, and ease of chemical modifications. These features have enabled important applications such as antisense agents, gene editing, nucleic acid sensing and as a platform to program the assembly of PNA-tagged molecules. Here, we review recent advances in these areas.

Applications of PNA-laden nanoparticles for hematological disorders

Safe and efficient genome editing has been an unmitigated goal for biomedical researchers since its inception. The most prevalent strategy for gene editing is the use of engineered nucleases that induce DNA damage and take advantage of cellular DNA repair machinery. This includes meganucleases, zinc-finger nucleases, transcription activator-like effector nucleases, and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR/Cas9) systems. However, the clinical viability of these nucleases is marred by their off-target cleavage activity (≥ 50% in RNA-guided endonucleases). In addition, in vivo applications of CRISPR require systemic administration of Cas9 protein, mRNA, or DNA, which presents a significant delivery challenge. The development of nucleic acid probes that can recognize specific double-stranded DNA (dsDNA) regions and activate endogenous DNA repair machinery holds great promise for gene editing applications. Triplex-forming oligonucleotides (TFOs), which were introduced more than 25 years ago, are among the most extensively studied oligomeric dsDNA-targeting agents. TFOs bind duplex DNA to create a distorted helical structure, which can stimulate DNA repair and the exchange of a nearby mutated region-otherwise leading to an undesired phenotype-for a short single-stranded donor DNA that contains the corrective nucleotide sequence. Recombination can be induced within several hundred base-pairs of the TFO binding site and has been shown to depend on triplex-induced initiation of the nucleotide excision repair pathway and engagement of the homology-dependent repair pathway. Since TFOs do not possess any direct nuclease activity, their off-target effects are minimal when compared to engineered nucleases. This review comprehensively covers the advances made in peptide nucleic acid-based TFOs for site-specific gene editing and their therapeutic applications.

Synthesis and biophysical characterization of oligonucleotides modified with O2'-alkylated RNA monomers featuring substituted pyrene moieties

Over the past three decades, a wide range of pyrene-functionalized oligonucleotides have been developed and explored for potential applications in material science and nucleic acid diagnostics. Our efforts have focused on their possible use as components of Invader probes, i.e., DNA duplexes with +1 interstrand zipper arrangements of intercalator-functionalized nucleotides. We have previously demonstrated that Invader probes based on 2'-O-(pyren-1-yl)methyl-RNA monomers are energetically activated for sequence-unrestricted recognition of chromosomal DNA targets under non-denaturing conditions. As part of ongoing efforts towards delineating structure-property relationships and optimizing Invader probes, we report the synthesis and biophysical characterization of oligodeoxyribonucleotides (ONs) modified with 2'-O-(7-neo-pentylpyren-1-yl)methyl-uridine monomer V and 2'-O-(7-tert-butyl-1-methoxypyren-5-yl)methyl-uridine monomer Y. ONs modified with monomer V display increased DNA affinity (ΔTm up to +10.5 °C), while Y-modified ONs display lower DNA affinity and up to 22-fold increases in fluorescence emission upon RNA binding. Although these monomers display limited potential as building blocks for Invader probes, their photophysical properties render them of interest for diagnostic RNA-targeting applications.

Synthesis of ( R)- and ( S)-Fmoc-Protected Diethylene Glycol Gamma PNA Monomers with High Optical Purity

A robust synthetic route has been developed for preparing optically pure, Fmoc-protected diethylene glycol-containing ( R)- and ( S)-γPNA monomers. The strategy involves the application of 9-(4-bromophenyl)-9-fluorenyl as a temporary, safety-catch protecting group for the suppression of epimerization in the O-alkylation and reductive amination steps. The optical purities of the final monomers were determined to be greater than 99.5% ee, as assessed by 19F-NMR and HPLC. The new synthetic methodology is well-suited for large-scale monomer production, with most synthetic steps providing excellent chemical yields without the need for chromatographic purification other than a simple workup and precipitation.

In utero nanoparticle delivery for site-specific genome editing

Genetic diseases can be diagnosed early during pregnancy, but many monogenic disorders continue to cause considerable neonatal and pediatric morbidity and mortality. Early intervention through intrauterine gene editing, however, could correct the genetic defect, potentially allowing for normal organ development, functional disease improvement, or cure. Here we demonstrate safe intravenous and intra-amniotic administration of polymeric nanoparticles to fetal mouse tissues at selected gestational ages with no effect on survival or postnatal growth. In utero introduction of nanoparticles containing peptide nucleic acids (PNAs) and donor DNAs corrects a disease-causing mutation in the β-globin gene in a mouse model of human β-thalassemia, yielding sustained postnatal elevation of blood hemoglobin levels into the normal range, reduced reticulocyte counts, reversal of splenomegaly, and improved survival, with no detected off-target mutations in partially homologous loci. This work may provide the basis for a safe and versatile method of fetal gene editing for human monogenic disorders.

Peptide Nucleic Acids as a Tool for Site-Specific Gene Editing

Peptide nucleic acids (PNAs) can bind duplex DNA in a sequence-targeted manner, forming a triplex structure capable of inducing DNA repair and producing specific genome modifications. Since the first description of PNA-mediated gene editing in cell free extracts, PNAs have been used to successfully correct human disease-causing mutations in cell culture and in vivo in preclinical mouse models. Gene correction via PNAs has resulted in clinically-relevant functional protein restoration and disease improvement, with low off-target genome effects, indicating a strong therapeutic potential for PNAs in the treatment or cure of genetic disorders. This review discusses the progress that has been made in developing PNAs as an effective, targeted agent for gene editing, with an emphasis on recent in vivo, nanoparticle-based strategies.

Shape selective bifacial recognition of double helical DNA

An impressive array of antigene approaches has been developed for recognition of double helical DNA over the past three decades; however, few have exploited the 'Watson-Crick' base-pairing rules for establishing sequence-specific recognition. One approach employs peptide nucleic acid as a molecular reagent and strand invasion as a binding mode. However, even with integration of the latest conformationally-preorganized backbone design, such an approach is generally confined to sub-physiological conditions due to the lack of binding energy. Here we report the use of a class of shape-selective, bifacial nucleic acid recognition elements, namely Janus bases, for targeting double helical DNA or RNA. Binding occurs in a highly sequence-specific manner under physiologically relevant conditions. The work may provide a foundation for the design of oligonucleotides for targeting the secondary and tertiary structures of nucleic acid biopolymers.

25 years and still going strong: 2'-O-(pyren-1-yl)methylribonucleotides - versatile building blocks for applications in molecular biology, diagnostics and materials science

Oligonucleotides (ONs) modified with 2'-O-(pyren-1-yl)methylribonucleotides have been explored for a range of applications in molecular biology, nucleic acid diagnostics, and materials science for more than 25 years. The first part of this review provides an overview of synthetic strategies toward 2'-O-(pyren-1-yl)methylribonucleotides and is followed by a summary of biophysical properties of nucleic acid duplexes modified with these building blocks. Insights from structural studies are then presented to rationalize the reported properties. In the second part, applications of ONs modified with 2'-O-(pyren-1-yl)methyl-RNA monomers are reviewed, which include detection of RNA targets, discrimination of single nucleotide polymorphisms, formation of self-assembled pyrene arrays on nucleic acid scaffolds, the study of charge transfer phenomena in nucleic acid duplexes, and sequence-unrestricted recognition of double-stranded DNA. The predictable binding mode of the pyrene moiety, coupled with the microenvironment-dependent properties and synthetic feasibility, render 2'-O-(pyren-1-yl)methyl-RNA monomers as a promising class of pyrene-functionalized nucleotide building blocks for new applications in molecular biology, nucleic acid diagnostics, and materials science.

Synthesis and Improved Cross-Linking Properties of C5-Modified Furan Bearing PNAs

Over the past decades, peptide nucleic acid/DNA (PNA:DNA) duplex stability has been improved via backbone modification, often achieved via introducing an amino acid side chain at the α- or γ-position in the PNA sequence. It was previously shown that interstrand cross-linking can further enhance the binding event. In this work, we combined both strategies to fine-tune PNA crosslinking towards single stranded DNA sequences using a furan oxidation-based crosslinking method; for this purpose, γ-l-lysine and γ-l-arginine furan-PNA monomers were synthesized and incorporated in PNA sequences via solid phase synthesis. It was shown that the l-lysine γ-modification had a beneficial effect on crosslink efficiency due to pre-organization of the PNA helix and a favorable electrostatic interaction between the positively-charged lysine and the negatively-charged DNA backbone. Moreover, the crosslink yield could be optimized by carefully choosing the type of furan PNA monomer. This work is the first to describe a selective and biocompatible furan crosslinking strategy for crosslinking of γ-modified PNA sequences towards single-stranded DNA.

Recognition of mixed-sequence DNA using double-stranded probes with interstrand zipper arrangements of O2'-triphenylene- and coronene-functionalized RNA monomers

Development of hybridization-based probes that enable recognition of specific mixed-sequence double-stranded DNA (dsDNA) regions is of considerable interest due to their potential applications in molecular biology, biotechnology, and medicine. We have recently demonstrated that nucleic acid duplexes with +1 interstrand zipper arrangements of intercalator-functionalized nucleotides such as 2'-O-(pyren-1-yl)methyl RNA monomers are inherently activated for recognition of mixed-sequence dsDNA targets, including chromosomal DNA. In the present work, we follow up on our previous structure-activity relationship studies and explore if the dsDNA-recognition efficiency of these so-called Invader probes can be improved by using larger intercalators than pyrene. Oligodeoxyribonucleotides modified with 2'-O-(triphenylen-2-yl)methyl-uridine monomer X and 2'-O-(coronen-1-yl)methyl-uridine monomer Z form extraordinarily stabilized duplexes with complementary DNA (ΔTm's per modification of up to 13 °C and 20 °C, respectively). Invader probes based on X- and Z-monomers are shown to recognize model dsDNA targets with exceptional binding specificity, but are less efficient than reference probes modified with 2'-O-(pyren-1-yl)methyl-uridine monomer Y. The insight from this study will inform further optimization of Invader probes.

Anti-tumor Activity of miniPEG-γ-Modified PNAs to Inhibit MicroRNA-210 for Cancer Therapy

MicroRNAs (miRs) are frequently overexpressed in human cancers. In particular, miR-210 is induced in hypoxic cells and acts to orchestrate the adaptation of tumor cells to hypoxia. Silencing oncogenic miRs such as miR-210 may therefore offer a promising approach to anticancer therapy. We have developed a miR-210 inhibition strategy based on a new class of conformationally preorganized antisense γ peptide nucleic acids (γPNAs) that possess vastly superior RNA-binding affinity, improved solubility, and favorable biocompatibility. For cellular delivery, we encapsulated the γPNAs in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs). Our results show that γPNAs targeting miR-210 cause significant delay in growth of a human tumor xenograft in mice compared to conventional PNAs. Further, histopathological analyses show considerable necrosis, fibrosis, and reduced cell proliferation in γPNA-treated tumors compared to controls. Overall, our work provides a chemical framework for a novel anti-miR therapeutic approach using γPNAs that should facilitate rational design of agents to potently inhibit oncogenic microRNAs.

In vivo correction of anaemia in β-thalassemic mice by γPNA-mediated gene editing with nanoparticle delivery

The blood disorder, β-thalassaemia, is considered an attractive target for gene correction. Site-specific triplex formation has been shown to induce DNA repair and thereby catalyse genome editing. Here we report that triplex-forming peptide nucleic acids (PNAs) substituted at the γ position plus stimulation of the stem cell factor (SCF)/c-Kit pathway yielded high levels of gene editing in haematopoietic stem cells (HSCs) in a mouse model of human β-thalassaemia. Injection of thalassemic mice with SCF plus nanoparticles containing γPNAs and donor DNAs ameliorated the disease phenotype, with sustained elevation of blood haemoglobin levels into the normal range, reduced reticulocytosis, reversal of splenomegaly and up to 7% β-globin gene correction in HSCs, with extremely low off-target effects. The combination of nanoparticle delivery, next generation γPNAs and SCF treatment may offer a minimally invasive treatment for genetic disorders of the blood that can be achieved safely and simply by intravenous administration.

Duplex DNA-Invading γ-Modified Peptide Nucleic Acids Enable Rapid Identification of Bloodstream Infections in Whole Blood

Bloodstream infections are a leading cause of morbidity and mortality. Early and targeted antimicrobial intervention is lifesaving, yet current diagnostic approaches fail to provide actionable information within a clinically viable time frame due to their reliance on blood culturing. Here, we present a novel pathogen identification (PID) platform that features the use of duplex DNA-invading γ-modified peptide nucleic acids (γPNAs) for the rapid identification of bacterial and fungal pathogens directly from blood, without culturing. The PID platform provides species-level information in under 2.5 hours while reaching single-CFU-per-milliliter sensitivity across the entire 21-pathogen panel. The clinical utility of the PID platform was demonstrated through assessment of 61 clinical specimens, which showed >95% sensitivity and >90% overall correlation to blood culture findings. This rapid γPNA-based platform promises to improve patient care by enabling the administration of a targeted first-line antimicrobial intervention.

Bloodstream infections continue to be a major cause of death for hospitalized patients, despite significant improvements in both the availability of treatment options as well their application. Since early and targeted antimicrobial intervention is one of the prime determinants of patient outcome, the rapid identification of the pathogen can be lifesaving. Unfortunately, current diagnostic approaches for identifying these infections all rely on time-consuming blood culture, which precludes immediate intervention with a targeted antimicrobial. To address this, we have developed and characterized a new and comprehensive methodology, from patient specimen to result, for the rapid identification of both bacterial and fungal pathogens without the need for culturing. We anticipate broad interest in our work, given the novelty of our technical approach combined with an immense unmet need.

Merging Two Strategies for Mixed-Sequence Recognition of Double-Stranded DNA: Pseudocomplementary Invader Probes

The development of molecular strategies that enable recognition of specific double-stranded DNA (dsDNA) regions has been a longstanding goal as evidenced by the emergence of triplex-forming oligonucleotides, peptide nucleic acids (PNAs), minor groove binding polyamides, and—more recently—engineered proteins such as CRISPR/Cas9. Despite this progress, an unmet need remains for simple hybridization-based probes that recognize specific mixed-sequence dsDNA regions under physiological conditions. Herein, we introduce pseudocomplementary Invader probes as a step in this direction. These double-stranded probes are chimeras between pseudocomplementary DNA (pcDNA) and Invader probes, which are activated for mixed-sequence dsDNA-recognition through the introduction of pseudocomplementary base pairs comprised of 2-thiothymine and 2,6-diaminopurine, and +1 interstrand zipper arrangements of intercalator-functionalized nucleotides, respectively. We demonstrate that certain pseudocomplementary Invader probe designs result in very efficient and specific recognition of model dsDNA targets in buffers of high ionic strength. These chimeric probes, therefore, present themselves as a promising strategy for mixed-sequence recognition of dsDNA targets for applications in molecular biology and nucleic acid diagnostics.