Therapeutic Oligonucleotides: State of the Art

Development of a bioanalytical method for an antisense therapeutic using high-resolution mass spectrometry

Background: Ion-pairing reverse-phase LC coupled with high-resolution mass spectrometry (IP-LC/HRMS) has gained attention in oligonucleotide therapeutic bioanalyses owing to its high sensitivity and selectivity. However, optimization and validation of IP-LC/HRMS-based methods are rare. The objective of this study is the development of a sensitive and reproducible IP-LC/HRMS-based bioanalytical method using clinically approved mipomersen as a model for antisense oligonucleotides. Materials & methods/results: Mipomersen was extracted from rat plasma using Clarity OTX SPE and quantified by IP-LC/HRMS. The calibration range was 0.5-250.0 ng/ml. The developed method met the general regulatory criteria for accuracy, precision, carry-over, selectivity, matrix effect and dilution integrity. Conclusion: A highly sensitive and reliable method for mipomersen measurement with potential antisense oligonucleotide bioanalysis applications has been developed.

L, D-Polydeoxyribonucleotides to provide an essential inhibitory effect on DNA polymerase β of human myeloid leukemia HL60 cells

The inhibitory effect of D and L-polynucleotides of a given length (40-50n) on the catalytic activity of DNA polymerase β isolated from chromatin cells of acute myeloid leukemia HL-60 was evaluated. The synthesized L enantiomer was found to have a higher inhibitory activity than the synthesized and isolated D enantiomers of polynucleotides. The work also proposes a biophysical model that describes this effect.

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The inhibitory activity of L, D-polydeoxyribonucleotides of various compositions was evaluated.

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Inhibition of DNA polymerase β is due to a nonspecific interaction between the enzyme and the substrate.

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L-polynucleotide exhibits the highest inhibiting activity, compared to the D-enantiomers.

Towards Zwitterionic Oligonucleotides with Improved Properties: the NAA/LNA-Gapmer Approach

Oligonucleotides (ON) are promising therapeutic candidates, for instance by blocking endogenous mRNA (antisense mechanism). However, ON usually require structural modifications of the native nucleic acid backbone to ensure satisfying pharmacokinetic properties. One such strategy to design novel antisense oligonucleotides is to replace native phosphate diester units by positively charged artificial linkages, thus leading to (partially) zwitterionic backbone structures. Herein, we report a "gapmer" architecture comprised of one zwitterionic central segment ("gap") containing nucleosyl amino acid (NAA) modifications and two outer segments of locked nucleic acid (LNA). This NAA/LNA-gapmer approach furnished a partially zwitterionic ON with optimised properties: i) the formation of stable ON-RNA duplexes with base-pairing fidelity and superior target selectivity at 37 °C; and ii) excellent stability in complex biological media. Overall, the NAA/LNA-gapmer approach is thus established as a strategy to design partially zwitterionic ON for the future development of novel antisense agents.

Biomolecular Densely Grafted Brush Polymers: Oligonucleotides, Oligosaccharides and Oligopeptides

In this Minireview, we describe synthetic polymers densely functionalized with sequence-defined biomolecular sidechains. We focus on synthetic brush polymers of oligonucleotides, oligosaccharides, and oligopeptides, prepared via graft-through polymerization from biomolecule functionalized monomers. The resulting structures are brush polymers wherein a biomolecular graft is positioned at each monomer backbone unit. We describe key synthetic milestones, identify synthetic opportunities, and highlight recent advances in the field, including biological applications.

Formation of an RNA Quadruplex-Duplex Hybrid in Living Cells between mRNA of the Epidermal Growth Factor Receptor (EGFR) and a G-Rich Antisense Oligoribonucleotide

Antisense DNA oligonucleotides, short interfering RNAs (siRNAs), and CRISPR/Cas9 genetic tools are the most useful therapeutic nucleic acids regulating gene expression based on the antisense specificity towards messenger RNA. Here, we present an effective novel strategy for inhibiting translation based on the antisense-controlled formation of an RNA quadruplex-duplex hybrid (QDH) between a G-rich RNA antisense oligoribonucleotide (Q-ASO) and specific mRNA, comprising two distant G-tracts. We selected epidermal growth factor receptor (EGFR) as a well-established target protein in anticancer therapy. The chemically modified, bi-functional anti-EGFR Q-ASO and a 56-nt long EGFR mRNA fragment, in the presence of potassium ions, were shown to form in vitro very stable parallel G-quadruplex containing a 28-nt long external loop folding to two duplex-stem structure. Besides, the Q-ASOs effectively reduced EGFR mRNA levels compared to the non-modified RNA and DNA antisense oligonucleotides (rASO, dASO). In addition, the hybridization specificity of Q-ASO comprising a covalently attached fluorescent tag was confirmed in living cells by visualization of the G4 green fluorescent species in the presence of other antisense inhibitors under competitive conditions. The results presented here offer novel insights into the potential application of Q-ASOs for the detection and/or alteration of (patho)biological processes through RNA:RNA quadruplex-duplex formation in cellular systems.

Cγ(S/R)-Bimodal Peptide Nucleic Acids (Cγ-bm-PNA) Form Coupled Double Duplexes by Synchronous Binding to Two Complementary DNA Strands

Peptide nucleic acids (PNAs) are linear equivalents of DNA with a neutral acyclic polyamide backbone that has nucleobases attached via tert-amide link on repeating units of aminoethylglycine. They bind complementary DNA or RNA with sequence specificity to form hybrids that are more stable than the corresponding DNA/RNA self-duplexes. A new type of PNA termed bimodal PNA [Cγ(S/R)-bm-PNA] is designed to have a second nucleobase attached via amide spacer to a side chain at Cγ on the repeating aeg units of PNA oligomer. Cγ-bimodal PNA oligomers that have two nucleobases per aeg unit are demonstrated to concurrently bind two different complementary DNAs, to form duplexes from both tert-amide side and Cγ side. In such PNA:DNA ternary complexes, the two duplexes share a common PNA backbone. The ternary DNA 1:Cγ(S/R)-bm-PNA:DNA 2 complexes exhibit better thermal stability than the isolated duplexes, and the Cγ(S)-bm-PNA duplexes are more stable than Cγ(R)-bm-PNA duplexes. Bimodal PNAs are first examples of PNA analogues that can form DNA2:PNA:DNA1 double duplexes via recognition through natural bases. The conjoined duplexes of Cγ-bimodal PNAs can be used to generate novel higher-level assemblies.

Polyglutamine spinocerebellar ataxias: emerging therapeutic targets

INTRODUCTION

Six of the most frequent dominantly inherited spinocerebellar ataxias (SCAs) worldwide - SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17 - are caused by an expansion of a polyglutamine (polyQ) tract in the corresponding proteins. While the identification of the causative mutation has advanced knowledge on the pathogenesis of polyQ SCAs, effective therapeutics able to mitigate the severe clinical manifestation of these highly incapacitating disorders are not yet available.

AREAS COVERED

This review provides a comprehensive and critical perspective on well-established and emerging therapeutic targets for polyQ SCAs; it aims to inspire prospective drug discovery efforts.

EXPERT OPINION

The landscape of polyQ SCAs therapeutic targets and strategies includes (1) the mutant genes and proteins themselves, (2) enhancement of endogenous protein quality control responses, (3) abnormal protein-protein interactions of the mutant proteins, (4) disturbed neuronal function, (5) mitochondrial function, energy availability and oxidative stress, and (6) glial dysfunction, growth factor or hormone imbalances. Challenges include gaining a clearer definition of therapeutic targets for the drugs in clinical development, the discovery of novel drug-like molecules for challenging key targets, and the attainment of a stronger translation of preclinical findings to the clinic.

MiR-29 coordinates age-dependent plasticity brakes in the adult visual cortex

Visual cortical circuits show profound plasticity during early life and are later stabilized by molecular "brakes" limiting excessive rewiring beyond a critical period. The mechanisms coordinating the expression of these factors during the transition from development to adulthood remain unknown. We found that miR-29a expression in the visual cortex dramatically increases with age, but it is not experience-dependent. Precocious high levels of miR-29a blocked ocular dominance plasticity and caused an early appearance of perineuronal nets. Conversely, inhibition of miR-29a in adult mice using LNA antagomirs activated ocular dominance plasticity, reduced perineuronal nets, and restored their juvenile chemical composition. Activated adult plasticity had the typical functional and proteomic signature of critical period plasticity. Transcriptomic and proteomic studies indicated that miR-29a manipulation regulates the expression of plasticity brakes in specific cortical circuits. These data indicate that miR-29a is a regulator of the plasticity brakes promoting age-dependent stabilization of visual cortical connections.

Antisense Oligonucleotides as Potential Therapeutics for Type 2 Diabetes

Type 2 diabetes (T2D) is a chronic metabolic disorder characterized by persistent hyperglycemia resulting from inefficient signaling and insufficient production of insulin. Conventional management of T2D has largely relied on small molecule-based oral hypoglycemic medicines, which do not halt the progression of the disease due to limited efficacy and induce adverse effects as well. To this end, antisense oligonucleotide has attracted immense attention in developing antidiabetic agents because of their ability to downregulate the expression of disease-causing genes at the RNA and protein level. To date, seven antisense agents have been approved by the United States Food and Drug Administration for therapies of a variety of human maladies, including genetic disorders. Herein, we provide a comprehensive review of antisense molecules developed for suppressing the causative genes believed to be responsible for insulin resistance and hyperglycemia toward preventing and treating T2D.

Addressing cancer signal transduction pathways with antisense and siRNA oligonucleotides

Signal transduction pathways play key roles in the initiation, progression and dissemination of cancer. Thus, signaling molecules are attractive targets for cancer therapeutics and enormous efforts have gone into the development of small molecule inhibitors of these pathways. However, regrettably, there has been only moderate progress to date, primarily in connection with the RAS signaling pathway. Oligonucleotide-based drugs potentially offer several advantages for addressing signaling pathways, including their exquisite selectivity and their ability to exploit both enzymatic and nonenzymatic targets. Nonetheless, there are problems inherent in the oligonucleotide approach, not the least being the challenge of effectively delivering these complex molecules to intracellular sites within tumors. This survey article will provide a selective review of recent studies where oligonucleotides were used to address cancer signaling and will discuss both positive aspects and limitations of those studies. This will be set in the context of an overview of various cancer signaling pathways and small molecule approaches to regulate those pathways. The survey will also evaluate the challenges and opportunities implicit in the oligonucleotide-based approach to cancer signaling and will point out several possibilities for future research.

Analytical characterization of liposomes and other lipid nanoparticles for drug delivery

Lipid nanoparticles, especially liposomes and lipid/nucleic acid complexed nanoparticles have shown great success in the pharmaceutical industry. Their success is attributed to stable drug loading, extended pharmacokinetics, reduced off-target side effects, and enhanced delivery efficiency to disease targets with formidable blood-brain or plasma membrane barriers. Therefore, they offer promising formulation options for drugs limited by low therapeutic indexes in traditional dosage forms and current "undruggable" targets. Recent development of siRNA, antisense oligonucleotide, or the CRISPR complex-loaded lipid nanoparticles and liposomal vaccines also shed light on their potential in enabling versatile formulation platforms for new pharmaceutical modalities. Analytical characterization of these nanoparticles is critical to drug design, formulation development, understanding in vivo performance, as well as quality control. The multi-lipid excipients, unique core-bilayer structure, and nanoscale size all underscore their complicated critical quality attributes, including lipid species, drug encapsulation efficiency, nanoparticle characteristics, product stability, and drug release. To address these challenges and facilitate future applications of lipid nanoparticles in drug development, we summarize available analytical approaches for physicochemical characterizations of lipid nanoparticle-based pharmaceutical modalities. Furthermore, we compare advantages and challenges of different techniques, and highlight the promise of new strategies for automated high-throughput screening and future development.

Synthesis and Characterization of Thiophosphoramidate Morpholino Oligonucleotides and Chimeras

This Article outlines the optimized chemical synthesis and preliminary biochemical characterization of a new oligonucleotide analogue called thiophosphoramidate morpholinos (TMOs). Their rational design hinges upon integrating two well-studied pharmacophores, namely, phosphorothioates (pS) and morpholinos, to create morpholino-pS hybrid oligonucleotides. Our simple synthesis strategy enables the easy incorporation of morpholino-pS moieties and therapeutically relevant sugar modifications in tandem to create novel oligonucleotide (ON) analogues that are hitherto unexplored in the oligotherapeutics arena. Exclusively TMO-modified ONs demonstrate high stability toward 3'-exonuclease. Hybridization studies show that TMO chimeras consisting of alternating TMO and DNA-pS subunits exhibit higher binding affinity toward complementary RNA relative to the canonical DNA/RNA duplex (∼10 °C). Oligonucleotides that consist entirely of TMO linkages also show higher RNA binding affinity but do not recruit ribonuclease H1 (RNase H1). Chimeric TMO analogues demonstrate high gene silencing efficacy, comparable to that of a chimeric 2'-OMe-pS/pO control, during in vitro bioassay screens designed to evaluate their potential as microRNA inhibitors of hsa-miR-15b-5p in HeLa cells.

AntagomiRs: A novel therapeutic strategy for challenging COVID-19 cytokine storm

Is it possible to develop a reliable, safe treatment for the widespread COVID-19 pandemic shortly? COVID-19 is characterized by a disruptive cytokine storm, quickly and often irreversibly damaging the patient’s lungs, as its main target organ, leading to lung failure and death. Actual experimental therapies are trying to reduce the activation of some specific cytokines, such as IL-6, somewhat reducing the burden for the patient. However, they are often unable to block the whole storm occurring at the cytokine level. In presence of the cytokine storm, especially in severe patients, antagomiRs, already demonstrated to be efficient and secure in cardiovascular disease, could represent a useful alternative to such treatment, customizable upon the disease specificities and applicable to other coronaviruses possibly associated with such clinical manifestations, while a reliable, efficient vaccine is being distributed.

Tracing Long-Term Outcomes of Basic Research Using Citation Networks

In recent years, the science of science policy has been facilitated by the greater availability of and access to digital data associated with the science, technology, and innovation enterprise. Historically, most of the studies from which such data are derived have been econometric or "scientometric" in nature, focusing on the development of quantitative data, models, and metrics of the scientific process as well as outputs and outcomes. Broader definitions of research impact, however, necessitate the use of qualitative case-study methods. For many years, U.S. federal science agencies such as the National Institutes of Health have demonstrated the impact of the research they support through tracing studies that document critical events in the development of successful technologies. A significant disadvantage and barrier of such studies is the labor-intensive nature of a case study approach. Currently, however, the same data infrastructures that have been developed to support scientometrics may also facilitate historical tracing studies. In this paper, we describe one approach we used to discover long-term, downstream outcomes of research supported in the late 1970's and early 1980's by the National Institute of General Medical Sciences, a component of the National Institutes of Health.

Modified nucleic acids: replication, evolution, and next-generation therapeutics

Modified nucleic acids, also called xeno nucleic acids (XNAs), offer a variety of advantages for biotechnological applications and address some of the limitations of first-generation nucleic acid therapeutics. Indeed, several therapeutics based on modified nucleic acids have recently been approved and many more are under clinical evaluation. XNAs can provide increased biostability and furthermore are now increasingly amenable to in vitro evolution, accelerating lead discovery. Here, we review the most recent discoveries in this dynamic field with a focus on progress in the enzymatic replication and functional exploration of XNAs.

Anti-α-synuclein ASO delivered to monoamine neurons prevents α-synuclein accumulation in a Parkinson's disease-like mouse model and in monkeys

BACKGROUND

Progressive neuronal death in monoaminergic nuclei and widespread accumulation of α-synuclein are neuropathological hallmarks of Parkinson's disease (PD). Given that α-synuclein may be an early mediator of the pathological cascade that ultimately leads to neurodegeneration, decreased α-synuclein synthesis will abate neurotoxicity if delivered to the key affected neurons.

METHODS

We used a non-viral gene therapy based on a new indatraline-conjugated antisense oligonucleotide (IND-ASO) to disrupt the α-synuclein mRNA transcription selectively in monoamine neurons of a PD-like mouse model and elderly nonhuman primates. Molecular, cell biology, histological, neurochemical and behavioral assays were performed.

FINDINGS

Intracerebroventricular and intranasal IND-ASO administration for four weeks in a mouse model with AAV-mediated wild-type human α-synuclein overexpression in dopamine neurons prevented the synthesis and accumulation of α-synuclein in the connected brain regions, improving dopamine neurotransmission. Likewise, the four-week IND-ASO treatment led to decreased levels of endogenous α-synuclein protein in the midbrain monoamine nuclei of nonhuman primates, which are affected early in PD.

CONCLUSIONS

The inhibition of α-synuclein production in dopamine neurons and its accumulation in cortical/striatal projection areas may alleviate the early deficits of dopamine function, showing the high translational value of antisense oligonucleotides as a disease modifying therapy for PD and related synucleinopathies.

FUNDING

Grants SAF2016-75797-R, RTC-2014-2812-1 and RTC-2015-3309-1, Ministry of Economy and Competitiveness (MINECO) and European Regional Development Fund (ERDF), UE; Grant ID 9238, Michael J. Fox Foundation; and Centres for Networked Biomedical Research on Mental Health (CIBERSAM), and on Neurodegenerative Diseases (CIBERNED).

Simultaneous Targeting of Two Master Regulators of Apoptosis with Dual-Action PNA- and DNA-Peptide Conjugates

Conjugation of peptides with oligonucleotides offers opportunities for combining the strengths of both biopolymer classes. Herein, we show that the combination of a peptide-based module with an antisense oligonucleotide module provides for enhancements of potency and a widened scope of cell delivery options. The peptide unit comprises a Smac mimetic compound (SMCs) which antagonizes the action of inhibitor of apoptosis proteins (IAPs) frequently overexpressed in cancer cells. To counteract SMC resistance, the antisense module downregulates the cellular FLICE-like protein (c-FLIP), a master regulator of the extrinsic apoptosis pathway. We compared c-FLIP antisense units based on oligophosphorothioate (PSO) and peptide nucleic acid (PNA) architectures. Owing to the ease of synthesis, PNA conjugates combined with a cell penetrating peptide (CPP) offer a seemingly ideal solution for cell delivery of dual activity agents. However, our investigations revealed that such congeners have to be handled with care to avoid off-target effects. By contrast, PSO conjugates provided a more robust and specific activity for inducing death of SMC-resistant A549 cells due to a simultaneous activation of caspases and c-FLIP knockdown. We show that lipofection is a convenient approach for delivery of peptide-PSO conjugates into cells. The results highlight that the combination of the peptide and the DNA world confers properties inaccessible by the unconjugated components.

Phosphorothioate Modification of mRNA Accelerates the Rate of Translation Initiation to Provide More Efficient Protein Synthesis

Messenger RNAs (mRNAs) with phosphorothioate modification (PS-mRNA) to the phosphate site of A, G, C, and U with all 16 possible combinations were prepared, and the translation reaction was evaluated using an E. coli cell-free translation system. Protein synthesis from PS-mRNA increased in 12 of 15 patterns when compared with that of unmodified mRNA. The protein yield increased 22-fold when the phosphorothioate modification at A/C sites was introduced into the region from the 5'-end to the initiation codon. Single-turnover analysis of PS-mRNA translation showed that phosphorothioate modification increases the number of translating ribosomes, thus suggesting that the rate of translation initiation (rate of ribosome complex formation) is positively affected by the modification. The method provides a new strategy for improving translation by using non-natural mRNA.

In Vitro and In Vivo Assessment of PEGylated PEI for Anti-IL-8/CxCL-1 siRNA Delivery to the Lungs

Inhalation offers a means of rapid, local delivery of siRNA to treat a range of autoimmune or inflammatory respiratory conditions. This work investigated the potential of a linear 10 kDa Poly(ethylene glycol) (PEG)-modified 25 kDa branched polyethyleneimine (PEI) (PEI-LPEG) to effectively deliver siRNA to airway epithelial cells. Following optimization with anti- glyceraldehyde 3-phosphate dehydrogenase (GAPDH) siRNA, PEI and PEI-LPEG anti-IL8 siRNA nanoparticles were assessed for efficacy using polarised Calu-3 human airway epithelial cells and a twin stage impinger (TSI) in vitro lung model. Studies were then advanced to an in vivo lipopolysaccharide (LPS)-stimulated rodent model of inflammation. In parallel, the suitability of the siRNA-loaded nanoparticles for nebulization using a vibrating mesh nebuliser was assessed. The siRNA nanoparticles were nebulised using an Aerogen^® Pro vibrating mesh nebuliser and characterised for aerosol output, droplet size and fine particle fraction. Only PEI anti-IL8 siRNA nanoparticles were capable of significant levels of IL-8 knockdown in vitro in non-nebulised samples. However, on nebulization through a TSI, only PEI-PEG siRNA nanoparticles demonstrated significant decreases in gene and protein expression in polarised Calu-3 cells. In vivo, both anti-CXCL-1 (rat IL-8 homologue) nanoparticles demonstrated a decreased CXCL-1 gene expression in lung tissue, but this was non-significant. However, PEI anti-CXCL-1 siRNA-treated rats were found to have significantly less infiltrating macrophages in their bronchoalveolar lavage (BAL) fluid. Overall, the in vivo gene and protein inhibition findings indicated a result more reminiscent of the in vitro bolus delivery rather than the in vitro nebulization data. This work demonstrates the potential of nebulised PEI-PEG siRNA nanoparticles in modulating pulmonary inflammation and highlights the need to move towards more relevant in vitro and in vivo models for respiratory drug development.

Pyrazolone ligation-mediated versatile sequential bioconjugations

Bioconjugation chemistries are critical tools in biotherapeutics discovery. The past efforts have been exclusively focused on two-segment conjugations. However, emerging research directions, such as polypharmacy biotherapeutics, desire multiple-component bioconjugations where more than two pharmacologically related biomolecules can be assembled into a single construct in high efficiency. We present here a set of sequential bioconjugation chemistries centered on a pyrazolone structural motif. It starts with a clickable “pyrazolone ligation” between a hydrazine group and a β-ketoester moiety followed by the conjugation between the newly formed pyrazolone core and an aldehyde-bearing biomolecule through a Knoevenagel reaction forming a Michael addition acceptor that can effectively capture a thiol-bearing biomolecule. When utilized intermolecularly, it quickly assembles four segments together forming a quadruple functional construct. When applied intramolecularly, it offers a set of highly diverse biomolecule scaffolds including stapled peptides and poly-macrocyclic peptides. We envision broad utilities of such sequential ligation chemistries.

A multiple component sequential bioconjugation chemistry establishes upon the joined force of hydrazine, β-keto ester, thiol and aldehyde.

Structural Design and Synthesis of Bimodal PNA That Simultaneously Binds Two Complementary DNAs To Form Fused Double Duplexes

Bimodal PNAs are new PNA constructs designed to bind two different cDNA sequences synchronously to form double duplexes. They are synthesized on solid phase using sequential coupling and click reaction to introduce a second base in each monomer at C_α via alkyltriazole linker. The ternary bimodal PNA:DNA complexes show stability higher than that of individual duplexes. Bimodal PNAs are appropriate to create higher-order fused nucleic acid assemblies.

Aptamers as Therapeutic Agents: Has the Initial Euphoria Subsided?

Aptamers are synthetic DNA or RNA oligonucleotide ligands with great potential for therapeutic applications. A vast number of disease-related targets have been used to identify agonistic, antagonistic, or inhibitory aptamers, or aptamer-based targeting ligands. However, only a few aptamers have reached late-stage clinical trials so far and the commercial infrastructure is still far behind that of other therapeutic agents such as monoclonal antibodies. The desirable properties of aptamers such as selectivity, chemical flexibility, or cost-efficiency are faced by challenges, including a short half-life in vivo, immunogenicity, and entrapment in cellular organelles. Aptamer research is still in an early stage, and a deeper understanding of their structure, target interactions, and pharmacokinetics is necessary to catch up to the clinical market. In this review, we will discuss the benefits and limitations in the development of therapeutic aptamers, as well as the advances and future directions of aptamer research. The progress towards effective therapies seems to be slow, but it has not stopped and the best is yet to come.

Attachment of hybridizable oligonucleotides to a silica support and its application for selective extraction of unmodified and antisense oligonucleotides from serum samples

The main aim of the present study was the synthesis of an oligonucleotide-based material with high chemical stability, repeatability and specificity to complementary oligonucleotides. The oligonucleotides were attached to a silica gel surface modified with amino acids during one-step synthesis. The amount of the oligonucleotides immobilized on the support surface had an impact on adsorption effectiveness, due to steric interference. The adsorption capacity corresponds to 4.7 μg of complementary oligonucleotide per 1 mg of material, which reflects 50% of immobilized oligonucleotides. The presented results contain comprehensive studies on hybridization and release of fully complementary, partially complementary, non-complementary and antisense oligonucleotides from the newly synthesized adsorbent. The salt concentration and time period were the most influential parameters in the case of adsorption, while high temperature and low salt content were indispensable for effective desorption. Selectivity studies revealed that the adsorption percentage increases with the decreasing number of base mismatches. Consequently, the desorption of low complementarity oligonucleotides was always greater in comparison with the fully complementary sequence. Furthermore, it was shown that oligonucleotide-based materials may be successfully used for the extraction of antisense oligonucleotides and their metabolites from serum samples with recoveries ranging between 65 and 73%.

Lipid-based nanoparticle formulations for small molecules and RNA drugs

Introduction: Liposomes and lipid-based nanoparticles (LNPs) effectively deliver cargo molecules to specific tissues, cells, and cellular compartments. Patients benefit from these nanoparticle formulations by altered pharmacokinetic properties, higher efficacy, or reduced side effects. While liposomes are an established delivery option for small molecules, Onpattro® (Sanofi Genzyme, Cambridge, MA) is the first commercially available LNP formulation of a small interfering ribonucleic acid (siRNA). Areas covered: This review article summarizes key features of liposomal formulations for small molecule drugs and LNP formulations for RNA therapeutics. We describe liposomal formulations that are commercially available or in late-stage clinical development and the most promising LNP formulations for ASOs, siRNAs, saRNA, and mRNA therapeutics. Expert opinion: Similar to liposomes, LNPs for RNA therapeutics have matured but still possess a niche application status. RNA therapeutics, however, bear an immense hope for difficult to treat diseases and fuel the imagination for further applications of RNA drugs. LNPs face similar challenges as liposomes including limitations in biodistribution, the risk to provoke immune responses, and other toxicities. However, since properties of RNA molecules within the same group are very similar, the entire class of therapeutic molecules would benefit from improvements in a few key parameters of the delivery technology.

Characterization of therapeutic oligonucleotides by liquid chromatography

Marketed therapies in the pharmaceutical landscape are rapidly evolving and getting more diverse. Small molecule medicines have dominated in the past while antibodies have grown dramatically in recent years. However, the failure of traditional small and large molecules in accessing certain targets has led to increased R&D efforts to develop alternative modalities. Therapeutic oligonucleotides (ONs) can accurately be directed against their ribonucleic acid (RNA) target and represent a promising approach in previously untreated diseases. Established automated synthesis of ONs coupled with chemical improvements and the advance of new drug delivery technologies has recently brought ONs to a heightened level of interest. The first part of the present review describes the different classes of oligonucleotides, namely antisense oligonucleotide (ASO), small interfering RNA (siRNA), microRNA (miRNA), aptamer and immunostimulatory ON, with a focus on their delivery systems relevant for future analytical characterization. The second part reviews the typical impurities in therapeutic ON products. The third part discusses the use of historical methods anion exchange chromatography (AEX), ion-pair reversed phase liquid chromatography (IP-RP), mixed-mode chromatography (MMC) and recent analytical methodologies of hydrophilic interaction liquid chromatography (HILIC), two-dimensional liquid chromatography (2D-LC) mass spectrometry for the characterization of ASO and siRNA modalities. The effects of physicochemical properties of RPLC columns and ion-pair agents on ON separation are specifically addressed with possible future directions for method development provided. Finally, some innovative analytical developments for the analysis of siRNAs and their delivery materials to pave the way toward the use of multi-attribute methods in the near future are discussed.

Assessing Oligonucleotide Binding to Double-Stranded DNA

Sequence-specific targeting of double-stranded DNA (dsDNA) using synthetic oligonucleotides (ONs) has been under investigation in different therapeutic approaches. Several methods can be used to evaluate ONs effect and binding capacity to their target sequence. Here we describe some of the methods, which have been frequently used for assessing ONs binding to dsDNA.

Chemical Development of Therapeutic Oligonucleotides

The development of several different chemical modifications of nucleic acids, with improved base-pairing affinity and specificity as well as increased resistance against nucleases, has been described. These new chemistries have allowed the synthesis of different types of therapeutic oligonucleotides. Here we discuss selected chemistries used in antisense oligonucleotide (ASO) applications (e.g., small interfering RNA (siRNA), RNase H activation, translational block, splice-switching, and also as aptamers). Recently approved oligonucleotide-based drugs are also presented briefly.

Delivery of Antisense Oligonucleotides Mediated by a Hydrogel System: In Vitro and In Vivo Application in the Context of Spinal Cord Injury

Biomaterials-based hydrogels are attractive drug-eluting vehicles in the context of RNA therapeutics, such as those utilizing antisense oligonucleotide or RNA interference based drugs, as they can potentially reduce systemic toxicity and enhance in vivo efficacy by increasing in situ concentrations. Here we describe the preparation of antisense oligonucleotide-loaded fibrin hydrogels exploring their applications in the context of the nervous system utilizing an organotypic dorsal root ganglion explant in vitro system and an in vivo model of spinal cord injury.

Antisense Oligonucleotide in LNA-Gapmer Design Targeting TGFBR2-A Key Single Gene Target for Safe and Effective Inhibition of TGFβ Signaling

Antisense Oligonucleotides (ASOs) are an emerging drug class in gene modification. In our study we developed a safe, stable, and effective ASO drug candidate in locked nucleic acid (LNA)-gapmer design, targeting TGFβ receptor II (TGFBR2) mRNA. Discovery was performed as a process using state-of-the-art library development and screening. We intended to identify a drug candidate optimized for clinical development, therefore human specificity and gymnotic delivery were favored by design. A staggered process was implemented spanning in-silico-design, in-vitro transfection, and in-vitro gymnotic delivery of small batch syntheses. Primary in-vitro and in-vivo toxicity studies and modification of pre-lead candidates were also part of this selection process. The resulting lead compound NVP-13 unites human specificity and highest efficacy with lowest toxicity. We particularly focused at attenuation of TGFβ signaling, addressing both safety and efficacy. Hence, developing a treatment to potentially recondition numerous pathological processes mediated by elevated TGFβ signaling, we have chosen to create our data in human lung cell lines and human neuronal stem cell lines, each representative for prospective drug developments in pulmonary fibrosis and neurodegeneration. We show that TGFBR2 mRNA as a single gene target for NVP-13 responds well, and that it bears great potential to be safe and efficient in TGFβ signaling related disorders.

Modulation of DNA and RNA by PNA

Peptide nucleic acid (PNA), a synthetic DNA mimic that is devoid of the (deoxy)ribose-phosphate backbone yet still perfectly retains the ability to recognize natural nucleic acids in a sequence-specific fashion, can be employed as a tool to modulate gene expressions via several different mechanisms. The unique strength of PNA compared to other oligonucleotide analogs is its ability to bind to nucleic acid targets with secondary structures such as double-stranded and quadruplex DNA as well as RNA. This digest aims to introduce general readers to the advancement in the area of modulation of DNA/RNA functions by PNA, its current status and future research opportunities, with emphasis on recent progress in new targeting modes of structured DNA/RNA by PNA and PNA-mediated gene editing.

Leading RNA Interference Therapeutics Part 1: Silencing Hereditary Transthyretin Amyloidosis, with a Focus on Patisiran

In 2018, patisiran was the first-ever RNA interference (RNAi)-based drug approved by the US Food and Drug Administration. Now pharmacology textbooks may include a new drug class that results in the effect first described by Fire and Mello 2 decades ago: post-transcriptional gene silencing by a small-interfering RNA (siRNA). Patients with hereditary transthyretin-mediated amyloidosis (hATTR amyloidosis) present with mutations in the transthyretin (TTR) gene that lead to the formation of amyloid deposits in peripheral nerves and heart. The disease may also affect the eye and central nervous system. The formulation of patisiran comprises the RNAi drug encapsulated into a nanoparticle especially developed to deliver the anti-TTR siRNA into the main TTR producer: the liver. Hepatic cells contain apolipoprotein E receptors that recognize ApoE proteins opsonized in the lipid carrier and internalize the drug by endocytosis. Lipid vesicles are disrupted in the cell cytoplasm, and siRNAs are free to trigger the RNAi-based TTR gene silencing. The silencing process involves the binding of siRNA guide strand to 3'-untranslated region sequence of both mutant and wild-type TTR messenger RNA, which culminates in the TTR mRNA cleavage by the RNA-induced silencing complex (RISC) as the first biochemical drug effect. Patisiran 0.3 mg/kg is administered intravenously every 3 weeks. Patients require premedication with anti-inflammatory drugs and antagonists of histamine H1 and H2 receptors to prevent infusion-related reactions and may require vitamin A supplementation. Following patisiran treatment, TTR knockdown remained stable for at least 2 years. Adverse effects were mild to moderate with unchanged hematological, renal, or hepatic parameters. No drug-related severe adverse effects occurred in a 24-month follow-up phase II open-label extension study. At the recommended dosage of patisiran, Cmax and AUC values (mean ± standard deviation) were 7.15 ± 2.14 μg/mL and 184 ± 159 μg·h/mL, respectively. The drug showed stability in circulation with > 95% encapsulated in lipid particles. Metabolization occurred by ribonuclease enzymes, with less than 1% excreted unchanged in the urine. Patisiran ameliorated neuropathy impairment according to the modified Neuropathy Impairment Score + 7 analysis of the phase III study. The Norfolk Quality of Life-Diabetic Neuropathy score and gait speed improved in 51% of the patisiran-treated group in 18 months. Additionally, the modified body mass index showed positive outcomes. Altogether, the data across phase I-III clinical trials points to patisiran as an effective and safe drug for the treatment of hATTR amyloidosis. It is hoped that real-world data from a larger number of patients treated with patisiran will confirm the effectiveness of this first-approved siRNA-based drug.

Antisense Oligonucleotide Reverses Leukodystrophy in Canavan Disease Mice

Marked elevation in the brain concentration of N-acetyl-L-aspartate (NAA) is a characteristic feature of Canavan disease, a vacuolar leukodystrophy resulting from deficiency of the oligodendroglial NAA-cleaving enzyme aspartoacylase. We now demonstrate that inhibiting NAA synthesis by intracisternal administration of a locked nucleic acid antisense oligonucleotide to young-adult aspartoacylase-deficient mice reverses their pre-existing ataxia and diminishes cerebellar and thalamic vacuolation and Purkinje cell dendritic atrophy. Ann Neurol 2020;87:480-485.

Synthesis and applications of theranostic oligonucleotides carrying multiple fluorine atoms

The use of various oligonucleotide (ON) syntheses and post-synthetic strategies for targeted chemical modification enables improving their efficacy as potent modulators of gene expression levels in eukaryotic cells. However, the search still continues for new approaches designed for increasing internalization, lysosomal escape, and tissue specific delivery of ON. In this review we emphasized all aspects related to the synthesis and properties of ON derivatives carrying multifluorinated (MF) groups. These MF groups have unique physico-chemical properties because of their simultaneous hydrophobicity and lipophobicity. Such unusual combination of properties results in the overall modification of ON mode of interaction with the cells and making multi-fluorination highly relevant to the goal of improving potency of ON as components of new therapies. The accumulated evidence so far is pointing to high potential of ON probes, RNAi components and ON imaging beacons carrying single or multiple MF groups for improving the stability, specificity of interaction with biological targets and delivery of ONs in vitro and potentially in vivo.

Ionizable lipid nanoparticles encapsulating barcoded mRNA for accelerated in vivo delivery screening

Messenger RNA (mRNA) has recently emerged as a promising class of nucleic acid therapy, with the potential to induce protein production to treat and prevent a range of diseases. However, the widespread use of mRNA as a therapeutic requires safe and effective in vivo delivery technologies. Libraries of ionizable lipid nanoparticles (LNPs) have been designed to encapsulate mRNA, prevent its degradation, and mediate intracellular delivery. However, these LNPs are typically characterized and screened in an in vitro setting, which may not fully replicate the biological barriers that they encounter in vivo. Here, we designed and evaluated a library of engineered LNPs containing barcoded mRNA (b-mRNA) to accelerate the screening of mRNA delivery platforms in vivo. These b-mRNA are similar in structure and function to regular mRNA, and contain barcodes that enable their delivery to be quantified via deep sequencing. Using a mini-library of b-mRNA LNPs formulated via microfluidic mixing, we show that these different formulations can be pooled together, administered intravenously into mice as a single pool, and their delivery to multiple organs (liver, spleen, brain, lung, heart, kidney, pancreas, and muscle) can be quantified simultaneously using deep sequencing. In the context of liver and spleen delivery, LNPs that exhibited high b-mRNA delivery also yielded high luciferase expression, indicating that this platform can identify lead LNP candidates as well as optimal formulation parameters for in vivo mRNA delivery. Interestingly, LNPs with identical formulation parameters that encapsulated different types of nucleic acid barcodes (b-mRNA versus a DNA barcode) altered in vivo delivery, suggesting that the structure of the barcoded nucleic acid affects LNP in vivo delivery. This platform, which enables direct barcoding and subsequent quantification of a functional mRNA, can accelerate the in vivo screening and design of LNPs for mRNA therapeutic applications such as CRISPR-Cas9 gene editing, mRNA vaccination, and other mRNA-based regenerative medicine and protein replacement therapies.

RNA Secondary Structure Motifs of the Influenza A Virus as Targets for siRNA-Mediated RNA Interference

The influenza A virus is a human pathogen that poses a serious public health threat due to rapid antigen changes and emergence of new, highly pathogenic strains with the potential to become easily transmitted in the human population. The viral genome is encoded by eight RNA segments, and all stages of the replication cycle are dependent on RNA. In this study, we designed small interfering RNA (siRNA) targeting influenza segment 5 nucleoprotein (NP) mRNA structural motifs that encode important functions. The new criterion for choosing the siRNA target was the prediction of accessible regions based on the secondary structure of segment 5 (+)RNA. This design led to siRNAs that significantly inhibit influenza virus type A replication in Madin-Darby canine kidney (MDCK) cells. Additionally, chemical modifications with the potential to improve siRNA properties were introduced and systematically validated in MDCK cells against the virus. A substantial and maximum inhibitory effect was achieved at concentrations as low as 8 nM. The inhibition of viral replication reached approximately 90% for the best siRNA variants. Additionally, selected siRNAs were compared with antisense oligonucleotides targeting the same regions; this revealed that effectiveness depends on both the target accessibility and oligonucleotide antiviral strategy. Our new approach of target-site preselection based on segment 5 (+)RNA secondary structure led to effective viral inhibition and a better understanding of the impact of RNA structural motifs on the influenza replication cycle.

Sugar and Polymer Excipients Enhance Uptake and Splice-Switching Activity of Peptide-Dendrimer/Lipid/Oligonucleotide Formulations

Non-viral transfection vectors are commonly used for oligonucleotide (ON) delivery but face many challenges before reaching the desired compartments inside cells. With the support of additional compounds, it might be more feasible for a vector to endure the barriers and achieve efficient delivery. In this report, we screened 18 different excipients and evaluated their effect on the performance of peptide dendrimer/lipid vector to deliver single-stranded, splice-switching ONs under serum conditions. Transfection efficiency was monitored in four different reporter cell lines by measuring splice-switching activity on RNA and protein levels. All reporter cell lines used had a mutated human β-globin intron 2 sequence interrupting the luciferase gene, which led to an aberrant splicing of luciferase pre-mRNA and subsidence of luciferase protein translation. In the HeLa Luc/705 reporter cell line (a cervical cancer cell line), the lead excipients (Polyvinyl derivatives) potentiated the splice-switching activity up to 95-fold, compared to untreated cells with no detected cytotoxicity. Physical characterization revealed that lead excipients decreased the particle size and the zeta potential of the formulations. In vivo biodistribution studies emphasized the influence of formulations as well as the type of excipients on biodistribution profiles of the ON. Subsequently, we suggest that the highlighted impact of tested excipients would potentially assist in formulation development to deliver ON therapeutics in pre-clinical and clinical settings.

Modulation of DNA structure formation using small molecules

Genome integrity is essential for proper cell function such that genetic instability can result in cellular dysfunction and disease. Mutations in the human genome are not random, and occur more frequently at "hotspot" regions that often co-localize with sequences that have the capacity to adopt alternative (i.e. non-B) DNA structures. Non-B DNA-forming sequences are mutagenic, can stimulate the formation of DNA double-strand breaks, and are highly enriched at mutation hotspots in human cancer genomes. Thus, small molecules that can modulate the conformations of these structure-forming sequences may prove beneficial in the prevention and/or treatment of genetic diseases. Further, the development of molecular probes to interrogate the roles of non-B DNA structures in modulating DNA function, such as genetic instability in cancer etiology are warranted. Here, we discuss reported non-B DNA stabilizers, destabilizers, and probes, recent assays to identify ligands, and the potential biological applications of these DNA structure-modulating molecules.

Evaluation of hydrophilic interaction liquid chromatography, capillary zone electrophoresis and drift tube ion-mobility quadrupole time of flight mass spectrometry for the characterization of phosphodiester and phosphorothioate oligonucleotides

Oligonucleotide-based medicines that can modulate gene expression have numerous potential applications in targeted therapies. Most of the commercialized therapeutic oligonucleotides are chemically modified to increase their in vivo lifetime. In this work, we studied poly-deoxy(thymidylic) acids (dT) and modified phosphorothioate oligonucleotides (PS). Several analytical techniques, including ion-pair reverse phase liquid chromatography, are described in the literature to assess their quality but most of them present significant drawbacks. In the present study, dT and PS mixtures were analyzed by hydrophilic interaction liquid chromatography (HILIC) and capillary zone electrophoresis (CZE) coupled to ultraviolet detection. In HILIC, the selectivities of three types of stationary phases (dihydroxypropane, phosphorylcholine and amide) were compared. Optimal conditions were determined and consisted of an amide stationary phase with a mobile phase made up of water, acetonitrile and 15 mM ammonium acetate (pH 5.5). In those conditions, high resolving power and good repeatability were achieved. In CZE, the effect of the background electrolyte (BGE), its pH and concentration were evaluated. A BGE made up of 300 mM ammonium acetate adjusted to pH 6.0 was selected. Finally, the two techniques were compared in terms of selectivity, repeatability and peak efficiency. In the second part of the study, HILIC and CZE were both coupled to a drift-tube ion-mobility quadrupole time-of-flight MS detector (DTIMS-QTOF) to assess the added value of this coupling for oligonucleotide characterization. Indeed, by using the measured collision cross section (CCS), the evaluation of the number of nucleotides was performed. Looking across the results, HILIC and CZE coupled to DTIMS-QTOF can be considered as promising tools for the quality control of oligonucleotides.

Molecular Dynamics Study of the Hybridization between RNA and Modified Oligonucleotides

MicroRNAs (miRNAs) are attractive drug candidates for many diseases as they can modulate the expression of gene networks. Recently, we discovered that DNAs targeting microRNA-22-3p (miR-22-3p) hold the potential for treating obesity and related metabolic disorders (type 2 diabetes mellitus, hyperlipidemia, and nonalcoholic fatty liver disease (NAFLD)) by turning fat-storing white adipocytes into fat-burning adipocytes. In this work, we explored the effects of chemical modifications, including phosphorothioate (PS), locked nucleic acid (LNA), and peptide nucleic acid (PNA), on the structure and energy of DNA analogs by using molecular dynamics (MD) simulations. To achieve a reliable prediction of the hybridization free energy, the AMOEBA polarizable force field and the free energy perturbation technique were employed. The calculated hybridization free energies are generally compatible with previous experiments. For LNA and PNA, the enhanced duplex stability can be explained by the preorganization mechanism, i.e., the single strands adopt stable helical structures similar to those in the duplex. For PS, the S and R isomers (Sp and Rp) have preferences for C2'-endo and C3'-endo sugar puckering conformations, respectively, and therefore Sp is less stable than Rp in DNA/RNA hybrids. In addition, the solvation penalty of Rp accounts for its destabilization effect. PS-LNA is similar to LNA as the sugar puckering is dominated by the locked sugar ring. This work demonstrated that MD simulations with polarizable force fields are useful for the understanding and design of modified nucleic acids.

Importance of probe design for bioanalysis of oligonucleotides using hybridization-based LC-fluorescence assays

Aim: The importance of the length and/or structure of fluorescently labeled PNA (peptide nucleic acid) probes for quantitative determination of oligodeoxynucleotides (ODNs) is demonstrated in human plasma using hybridization-based LC-fluorescence assays. The length of the PNA probes impacts the peak shape and chromatographic separation of the resulting PNA/ODN hybridization complexes and affects assay sensitivity, dynamic range and carryover. Methods: For quantitative determination of an 18-mer phosphodiester ODN (DNL1818) in human plasma, an assay utilizing an Atto dye-labeled 12-mer PNA probe provided a linear quantitation range of 0.1-50 ng/ml with excellent accuracy and precision (within -5.3-7.73%). Conclusion: This method provides a convenient method for sensitive and specific quantification of ODNs in biological matrix with limited sample volume and no special extraction.

Shifting Paradigms Revisited: Biotechnology and the Pharmaceutical Sciences

In 2003, Crommelin et al. published an article titled: "Shifting paradigms: biopharmaceuticals versus low molecular weight drugs" (https://doi.org/10.1016/S0378-5173(03)00376-4). In the present commentary, 16 years later, we discuss pharmaceutically relevant aspects of the evolution of biologics since then. First, we discuss the increasing repertoire of biologics, in particular, the rapidly growing monoclonal antibody family and the advent of advanced therapy medicinal products. Next, we discuss trends in formulation and characterization as well as summarize our current insights into immunogenicity of biologics. We spend a separate section on new product(ion) paradigms for biologics, such as cell-free production systems, production of advanced therapy medicinal products, and downscaled production approaches. Furthermore, we share our views on issues related to reaching the patient, including routes and techniques of administration, alternative development models for affordable biologics, biosimilars, and handling of biologics. In the concluding section, we outline outstanding issues and make some suggestions for resolving those.

A new dawn for managing dyslipidemias: The era of rna-based therapies

The high occurrence of atherosclerotic cardiovascular disease (ASCVD) events is still a major public health issue. Although a major determinant of ASCVD event reduction is the absolute change of low-density lipoprotein-cholesterol (LDL-C), considerable residual risk remains and new therapeutic options are required, in particular, to address triglyceride-rich lipoproteins and lipoprotein(a) [Lp(a)]. In the era of Genome Wide Association Studies and Mendelian Randomization analyses aimed at increasing the understanding of the pathophysiology of ASCVD, RNA-based therapies may offer more effective treatment options. The advantage of oligonucleotide-based treatments is that drug candidates are targeted at highly specific regions of RNA that code for proteins that in turn regulate lipid and lipoprotein metabolism. For LDL-C lowering, the use of inclisiran - a silencing RNA that inhibits proprotein convertase subtilisin/kexin type 9 (PCSK9) synthesis - has the advantage that a single s.c. injection lowers LDL-C for up to 6 months. In familial hypercholesterolemia, the use of the antisense oligonucleotide (ASO) mipomersen, targeting apolipoprotein (apoB) to reduce LDL-C, has been a valuable therapeutic approach, despite unquestionable safety concerns. The availability of specific ASOs lowering Lp(a) levels will allow rigorous testing of the Lp(a) hypothesis; by dramatically reducing plasma triglyceride levels, Volanesorsen (APOC3) and angiopoietin-like 3 (ANGPTL3)-LRx will further clarify the causality of triglyceride-rich lipoproteins in ASCVD. The rapid progress to date heralds a new dawn in therapeutic lipidology, but outcome, safety and cost-effectiveness studies are required to establish the role of these new agents in clinical practice.

Leveraging Signaling Pathways to Treat Heart Failure With Reduced Ejection Fraction

Advances in the treatment of heart failure with reduced ejection fraction due to systolic dysfunction are engaging an ever-expanding compendium of molecular signaling targets. Well established approaches modifying hemodynamics and cell biology by neurohumoral receptor blockade are evolving, exploring the role and impact of modulating intracellular signaling pathways with more direct myocardial effects. Even well-tread avenues are being reconsidered with new insights into the signaling engaged and thus opportunity to treat underlying myocardial disease. This review explores therapies that have proven successful, those that have not, those that are moving into the clinic but whose utility remains to be confirmed, and those that remain in the experimental realm. The emphasis is on signaling pathways that are tractable for therapeutic manipulation. Of the approaches yet to be tested in humans, we chose those with a well-established experimental history, where clinical translation may be around the corner. The breadth of opportunities bodes well for the next generation of heart failure therapeutics.

Efficient Conjugation to Phosphorothioate Oligonucleotides by Cu-Catalyzed Huisgen 1,3-Dipolar Cycloaddition

Improving oligonucleotide delivery is critical for the further development of oligonucleotide-based therapeutics. Covalent attachment of reporter molecules is one of the most promising approaches toward efficient oligonucleotide-based therapies. An efficient methods for the attachment of a variety of reporter groups is Cu(I)-catalyzed Huisgen azide-alkyne 1,3-dipolar cycloaddition. However, the majority of potential oligonucleotide (ON) therapeutics in clinical trials are carrying phosphorothioate (PS) linkages, and this robust conjugation method is not yet established for these ONs due to a general concern of Cu-S interaction. Here, we developed a method allowing for efficient conjugation of peptides to PS oligonucleotides. The method utilizes solid supported oligonucleotides that can be readily transformed into "clickable ONs" by simple linker conjugation and further reacted with an azido containing moiety (e.g., a peptide) using the CuBr × Me₂S complex as a superior catalyst in that reaction. This study opens the way for further development of PS oligonucleotide-conjugates by means of efficient Cu(I)-catalyzed Huisgen azide-alkyne 1,3-dipolar cycloaddition.