Biological activity and biotechnological aspects of locked nucleic acids

Improved In Vivo Metabolic Stability and Silencing Efficacy of siRNAs with Phosphorothioate Linkage-Free, GalNAc-Conjugated Sense Strands Containing Morpholino-LNA Modifications

To ensure specificity, loading of the sense strand of small interfering RNAs (siRNAs) into RISC must be inhibited. We show here that siRNAs with 5'- and 6'-morpholino LNA residues or 6'-OH-LNA at the 5' terminus of a fully phosphodiester sense strand resulted in metabolically stable siRNAs with a potency and a duration of action in mice that were greater than those of an siRNA in which the 5' terminus of the sense strand has two terminal phosphorothioate linkages and regular LNA.

The West Nile virus genome harbors essential riboregulatory elements with conserved and host-specific functional roles

West Nile virus (WNV) is an arthropod-borne, positive-sense RNA virus that poses an increasing global threat due to warming climates and lack of effective therapeutics. Like other enzootic viruses, little is known about how host context affects the structure of the full-length RNA genome. Here, we report a complete secondary structure of the entire WNV genome within infected mammalian and arthropod cell lines. Our analysis affords structural insights into multiple, conserved aspects of flaviviral biology. We show that the WNV genome folds with minimal host dependence, and we prioritize well-folded regions for functional validation using structural homology between hosts as a guide. Using structure-disrupting, antisense locked nucleic acids, we then demonstrate that the WNV genome contains riboregulatory structures with conserved and host-specific functional roles. These results reveal promising RNA drug targets within flaviviral genomes, and they highlight the therapeutic potential of ASO-LNAs as both WNV-specific and pan-flaviviral therapeutic agents.

LINC01432 binds to CELF2 in newly diagnosed multiple myeloma promoting short progression-free survival to standard therapy

Multiple Myeloma (MM) is a highly prevalent and incurable form of cancer that arises from malignant plasma cells, with over 35,000 new cases diagnosed annually in the United States. While there are a growing number of approved therapies, MM remains incurable and nearly all patients will relapse and exhaust all available treatment options. Mechanisms for disease progression are unclear and in particular, little is known regarding the role of long non-coding RNAs (lncRNA) in mediating disease progression and response to treatment. In this study, we used transcriptome sequencing to compare newly diagnosed MM patients who had short progression-free survival (PFS) to standard first-line treatment (PFS < 24 months) to patients who had prolonged PFS (PFS > 24 months). We identified 157 differentially upregulated lncRNAs with short PFS and focused our efforts on characterizing the most upregulated lncRNA, LINC01432. We investigated LINC01432 overexpression and CRISPR/Cas9 knockdown in MM cell lines to show that LINC01432 overexpression significantly increases cell viability and reduces apoptosis, while knockdown significantly reduces viability and increases apoptosis, supporting the clinical relevance of this lncRNA. Next, we used individual-nucleotide resolution cross-linking immunoprecipitation with RT-qPCR to show that LINC01432 directly interacts with the RNA binding protein, CELF2. Lastly, we showed that LINC01432-targeted locked nucleic acid antisense oligonucleotides reduce viability and increases apoptosis. In summary, this fundamental study identified lncRNAs associated with short PFS to standard NDMM treatment and further characterized LINC01432, which inhibits apoptosis.

Using QUASR-PCR as a field-based genotyping assay for a tick acaricide resistance marker

A novel, turnkey, field-based workflow was developed and validated using Rhipicephalus microplus DNA as a template to detect the presence of the voltage-gated sodium channel kdr mutation. The field-based compatible workflow comprises manual sample homogenization for DNA extraction, PCR amplification of the targets in a closed tube, and end-point detection of the PCR products. An R. microplus species-specific assay was also included to confirm species identity and ensure the validity of the kdr mutation assay. The assays were sensitive and specific to the targets, and the workflow resulted in a turnaround time of approximately 1 h at a low cost. The novel combination of PCR with closed-tube and end-point fluorescent detection allows for easy conversion of existing conventional lab-based PCR assays into field-based detection assays. The incorporation of custom-designed 3D-printed components in the workflow provides easy adaptability and modification of the components for diverse nucleic acid detection workflows.

Interferon-Regulated Expression of Cellular Splicing Factors Modulates Multiple Levels of HIV-1 Gene Expression and Replication

Type I interferons (IFN-Is) are pivotal in innate immunity against human immunodeficiency virus I (HIV-1) by eliciting the expression of IFN-stimulated genes (ISGs), which encompass potent host restriction factors. While ISGs restrict the viral replication within the host cell by targeting various stages of the viral life cycle, the lesser-known IFN-repressed genes (IRepGs), including RNA-binding proteins (RBPs), affect the viral replication by altering the expression of the host dependency factors that are essential for efficient HIV-1 gene expression. Both the host restriction and dependency factors determine the viral replication efficiency; however, the understanding of the IRepGs implicated in HIV-1 infection remains greatly limited at present. This review provides a comprehensive overview of the current understanding regarding the impact of the RNA-binding protein families, specifically the two families of splicing-associated proteins SRSF and hnRNP, on HIV-1 gene expression and viral replication. Since the recent findings show specifically that SRSF1 and hnRNP A0 are regulated by IFN-I in various cell lines and primary cells, including intestinal lamina propria mononuclear cells (LPMCs) and peripheral blood mononuclear cells (PBMCs), we particularly discuss their role in the context of the innate immunity affecting HIV-1 replication.

Unlocking the therapeutic potential of locked nucleic acids through lipid nanoparticle delivery

Locked nucleic acids (LNAs) are a subtype of antisense oligonucleotides (ASOs) that are characterized by a bridge within the sugar moiety. LNAs owe their robustness to this chemical modification, which as the name suggests, locks it in one conformation. This perspective includes two components: a general overview on ASOs from one side and on delivery issues focusing on lipid nanoparticles (LNPs) on the other side. Throughout, a screening of the ongoing clinical trials involving ASOs is given, as well as a take on the versatility and challenges of using LNAs. Finally, we highlight the potential of LNPs as carriers for the successful delivery of LNAs.

Synthesis and Properties of Oligonucleotides Containing LNA-Sulfamate and Sulfamide Backbone Linkages

Oligonucleotides hold great promise as therapeutic agents but poor bioavailability limits their utility. Hence, new analogues with improved cell uptake are urgently needed. Here, we report the synthesis and physical study of reduced-charge oligonucleotides containing artificial LNA-sulfamate and sulfamide linkages combined with 2'-O-methyl sugars and phosphorothioate backbones. These oligonucleotides have high affinity for RNA and excellent nuclease resistance.

Anisamide-conjugated hairpin antisense oligonucleotides prodrug co-delivering doxorubicin exhibited enhanced anticancer efficacy

Antisense oligonucleotides (ASONs)-based therapeutics offers tremendous promise for the treatment of diverse diseases. However, there is still a need to develop ASONs with enhanced stability against enzymes, improved drug delivery, and enhanced biological potency. In this study, we propose a novel anisamide (AA)-conjugated hairpin oligonucleotide prodrug loading with chemotherapeutic agent (doxorubicin, DOX) (AA-loop-ASON/DOX) for oncotherapy. Results indicated that the introduction of a hairpin conformation and AA ligand in prodrug significantly improved the stability against enzymatic hydrolysis, as well as the cellar uptake of ASONs and DOX. The incorporation of disulfide bonds could trigger mechanical opening, resulting in the release of ASON and DOX in response to the intracellular glutathione (GSH) in tumors. Moreover, the composite of DOX-loading ASONs prodrug exhibited a robust and selective inhibition of tumor cell proliferation. This paper introduces a novel design concept for nucleic acid-based therapeutics, aiming to enhance the delivery of drug and improve biological effectiveness.

Triazole-linked Nucleic Acids: Synthesis, Therapeutics and Synthetic Biology Applications

This article covers the triazole-linked nucleic acids where the triazole linkage (TL) replaces the natural phosphate backbone. The replacement is done at either a few selected linkages or all the phosphate linkages. Two triazole linkages, the four-atom TL1 and the six-atom TL2, have been discussed in detail. These triazole-modified oligonucleotides have found a wide range of applications, from therapeutics to synthetic biology. For example, the triazole-linked oligonucleotides have been used in the antisense oligonucleotide (ASO), small interfering RNA (siRNA) and clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 technology as therapeutic agents. Due to the ease of the synthesis and a wide range of biocompatibility, the triazole linkage TL2 has been used to assemble a functional 300-mer DNA from alkyne- and azide-functionalized 100-mer oligonucleotides as well as an epigenetically modified variant of a 335 base-pair gene from ten short oligonucleotides. These outcomes highlight the potential of triazole-linked nucleic acids and open the doors for other TL designs and artificial backbones to fully exploit the vast potential of artificial nucleic acids in therapeutics, synthetic biology and biotechnology.

Chemical Modifications and Design Influence the Potency of Huntingtin Anti-Gene Oligonucleotides

Huntington's disease is a neurodegenerative, trinucleotide repeat (TNR) disorder affecting both males and females. It is caused by an abnormal increase in the length of CAG•CTG TNR in exon 1 of the Huntingtin gene (HTT). The resultant, mutant HTT mRNA and protein cause neuronal toxicity, suggesting that reduction of their levels would constitute a promising therapeutic approach. We previously reported a novel strategy in which chemically modified oligonucleotides (ONs) directly target chromosomal DNA. These anti-gene ONs were able to downregulate both HTT mRNA and protein. In this study, various locked nucleic acid (LNA)/DNA mixmer anti-gene ONs were tested to investigate the effects of varying ON length, LNA content, and fatty acid modification on HTT expression. Altering the length did not significantly influence the ON potency, while LNA content was critical for activity. Utilization of palmitoyl-modified LNA monomers enhanced the ON activity relatively to the corresponding nonmodified LNA under serum starvation conditions. Furthermore, the number of palmitoylated LNA monomers and their positioning greatly affected ON potency. In addition, we performed RNA sequencing analysis, which showed that the anti-gene ONs affect the "immune system process, mRNA processing, and neurogenesis." Furthermore, we observed that for repeat containing genes, there is a higher tendency for antisense off-targeting. Taken together, our findings provide an optimized design of anti-gene ONs that could potentially be developed as DNA-targeting therapeutics for this class of TNR-related diseases.

Aptamer Technology and Its Applications in Bone Diseases

Aptamers are single-stranded nucleic acids (DNA, short RNA, or other artificial molecules) produced by the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) technology, which can be tightly and specifically combined with desired targets. As a comparable alternative to antibodies, aptamers have many advantages over traditional antibodies such as a strong chemical stability and rapid bulk production. In addition, aptamers can bind targets in various ways, and are not limited like the antigen-antibody combination. Studies have shown that aptamers have tremendous potential to diagnose and treat clinical diseases. However, only a few aptamer-based drugs have been used because of limitations of the aptamers and SELEX technology. To promote the development and applications of aptamers, we present a review of the methods optimizing the SELEX technology and modifying aptamers to boost the selection success rate and improve aptamer characteristics. In addition, we review the application of aptamers to treat bone diseases.

Critical points for the design and application of RNA silencing constructs for plant virus resistance

Control of plant virus diseases is a big challenge in agriculture as is resistance in plant lines to infection by viruses. Recent progress using advanced technologies has provided fast and durable alternatives. One of the most promising techniques against plant viruses that is cost-effective and environmentally safe is RNA silencing or RNA interference (RNAi), a technology that could be used alone or along with other control methods. To achieve the goals of fast and durable resistance, the expressed and target RNAs have been examined in many studies, with regard to the variability in silencing efficiency, which is regulated by various factors such as target sequences, target accessibility, RNA secondary structures, sequence variation in matching positions, and other intrinsic characteristics of various small RNAs. Developing a comprehensive and applicable toolbox for the prediction and construction of RNAi helps researchers to achieve the acceptable performance level of silencing elements. Although the attainment of complete prediction of RNAi robustness is not possible, as it also depends on the cellular genetic background and the nature of the target sequences, some important critical points have been discerned. Thus, the efficiency and robustness of RNA silencing against viruses can be improved by considering the various parameters of the target sequence and the construct design. In this review, we provide a comprehensive treatise regarding past, present and future prospective developments toward designing and applying RNAi constructs for resistance to plant viruses.

2'-O-(N-(Aminoethyl)carbamoyl)methyl Modification Allows for Lower Phosphorothioate Content in Splice-Switching Oligonucleotides with Retained Activity

2′-O-(N-(Aminoethyl)carbamoyl)methyl (2′-O-AECM)-modified oligonucleotides (ONs) and their mixmers with 2′-O-methyl oligonucleotides (2′-OMe ONs) with phosphodiester linkers as well as with partial and full phosphorothioate (PS) inclusion were synthesized and functionally evaluated as splice-switching oligonucleotides in several different reporter cell lines originating from different tissues. This was enabled by first preparing the AECM-modified A, C, G and U, which required a different strategy for each building block. The AECM modification has previously been shown to provide high resistance to enzymatic degradation, even without PS linkages. It is therefore particularly interesting and unprecedented that the 2′-O-AECM ONs are shown to have efficient splice-switching activity even without inclusion of PS linkages and found to be as effective as 2′-OMe PS ONs. Importantly, the PS linkages can be partially included, without any significant reduction in splice-switching efficacy. This suggests that AECM modification has the potential to be used in balancing the PS content of ONs. Furthermore, conjugation of 2′-O-AECM ONs to an endosomal escape peptide significantly increased splice-switching suggesting that this effect could possibly be due to an increase in uptake of ON to the site of action.

Safety Testing of an Antisense Oligonucleotide Intended for Pediatric Indications in the Juvenile Göttingen Minipig, including an Evaluation of the Ontogeny of Key Nucleases

The adult Göttingen Minipig is an acknowledged model for safety assessment of antisense oligonucleotide (ASO) drugs developed for adult indications. To assess whether the juvenile Göttingen Minipig is also a suitable nonclinical model for pediatric safety assessment of ASOs, we performed an 8-week repeat-dose toxicity study in different age groups of minipigs ranging from 1 to 50 days of age. The animals received a weekly dose of a phosphorothioated locked-nucleic-acid-based ASO that was assessed previously for toxicity in adult minipigs. The endpoints included toxicokinetic parameters, in-life monitoring, clinical pathology, and histopathology. Additionally, the ontogeny of key nucleases involved in ASO metabolism and pharmacologic activity was investigated using quantitative polymerase chain reaction and nuclease activity assays. Similar clinical chemistry and toxicity findings were observed; however, differences in plasma and tissue exposures as well as pharmacologic activity were seen in the juvenile minipigs when compared with the adult data. The ontogeny study revealed a differential nuclease expression and activity, which could affect the metabolic pathway and pharmacologic effect of ASOs in different tissues and age groups. These data indicate that the juvenile Göttingen Minipig is a promising nonclinical model for safety assessment of ASOs intended to treat disease in the human pediatric population.

The Clinical Assessment of MicroRNA Diagnostic, Prognostic, and Theranostic Value in Colorectal Cancer

Simple Summary

MiRNAs are of great interest within colorectal cancers in diagnosis, prognosis, and within the field of personalized treatments; they are present within different biological fluids such as blood and can lead to specific information for daily clinical use. Herein, we review the current literature focusing on miRNAs as potential diagnostic and prognostic biomarkers in patients treated for colorectal cancers. Detection and analysis of miRNA expression are cost-effective and lead to high sensitivity and specificity rates. However, it is now necessary to highlight the most sensitive and specific miRNAs for each goal, either diagnostic, prognostic, or theranostic, thanks to multicentric prospective studies.

Abstract

MiRNAs have recently become a subject of great interest within cancers and especially colorectal cancers in diagnosis, prognosis, and therapy decisions; herein we review the current literature focusing on miRNAs in colorectal cancers, and we discuss future challenges to use this tool on a daily clinical basis. In liquid biopsies, miRNAs seem easily accessible and can give important information toward each step of the management of colorectal cancers. However, it is now necessary to highlight the most sensitive and specific miRNAs for each goal thanks to multicentric prospective studies. Conclusions: by their diversity and the feasibility of their use, miRNAs are getting part of the armamentarium of healthcare management of colorectal cancers.

Non-coding RNAs in Cardiac Regeneration

The adult heart has a limited capacity to replace or regenerate damaged cardiac tissue following severe myocardial injury. Thus, therapies facilitating the induction of cardiac regeneration holds great promise for the treatment of end-stage heart failure, and for pathologies invoking severe cardiac dysfunction as a result of cardiomyocyte death. Recently, a number of studies have demonstrated that cardiac regeneration can be achieved through modulation and/or reprogramming of cardiomyocyte proliferation, differentiation, and survival signaling. Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), are reported to play critical roles in regulating key aspects of cardiomyocyte physiologic and pathologic signaling, including the regulation of cardiac regeneration both in vitro and in vivo. In this review, we will explore and detail the current understanding of ncRNA function in cardiac regeneration, and highlight established and novel strategies for the treatment of heart failure through modulation of ncRNAs-driven cardiac regeneration.

Design and Application of a Short (16-mer) Locked Nucleic Acid Splice-Switching Oligonucleotide for Dystrophin Production in Duchenne Muscular Dystrophy Myotubes

Splice-switching oligonucleotides (SSOs) have been used to modulate gene expression by interfering with pre-mRNA splicing with the intent to treat disease. For Duchenne muscular dystrophy, splicing modulation has been used to induce the skipping of exon 51 of the dystrophin transcript, allowing the production of a truncated but functional protein. Although oligonucleotide-based therapies are promising, the rapid degradation of oligonucleotides (ONs) by intracellular nucleases has been a major obstacle. Locked nucleic acid (LNA) substitution in SSOs protects oligonucleotides from nuclease degradation and enhances the hybridization properties of the oligo. However, the best optimum size of the oligo depends on the LNA substitution rate. Here we show that 16-mer DNA SSOs with 60% LNA substitution and full phosphorothioate (PS) linkage backbone efficiently induce exon 51 skipping in myogenic cells derived from a DMD patient, allowing expression of the dystrophin protein.

Comprehensive in vivo secondary structure of the SARS-CoV-2 genome reveals novel regulatory motifs and mechanisms

Severe-acute-respiratory-syndrome-related coronavirus 2 (SARS-CoV-2) is the positive-sense RNA virus that causes coronavirus disease 2019 (COVID-19). The genome of SARS-CoV-2 is unique among viral RNAs in its vast potential to form RNA structures, yet as much as 97% of its 30 kilobases have not been structurally explored. Here, we apply a novel long amplicon strategy to determine the secondary structure of the SARS-CoV-2 RNA genome at single-nucleotide resolution in infected cells. Our in-depth structural analysis reveals networks of well-folded RNA structures throughout Orf1ab and reveals aspects of SARS-CoV-2 genome architecture that distinguish it from other RNA viruses. Evolutionary analysis shows that several features of the SARS-CoV-2 genomic structure are conserved across β-coronaviruses, and we pinpoint regions of well-folded RNA structure that merit downstream functional analysis. The native, secondary structure of SARS-CoV-2 presented here is a roadmap that will facilitate focused studies on the viral life cycle, facilitate primer design, and guide the identification of RNA drug targets against COVID-19.

RNA therapeutics in ophthalmology - translation to clinical trials

The use of RNA interference technology has proven to inhibit the expression of many target genes involved in the underlying pathogenesis of several diseases affecting various systems. First established in in vitro and later in animal studies, small interfering RNA (siRNA) and antisense oligonucleotide (ASO) therapeutics are now entering clinical trials with the potential of clinical translation to patients. Gene-silencing therapies have demonstrated promising responses in ocular disorders, predominantly due to the structure of the eye being a closed and compartmentalised organ. However, although the efficacy of such treatments has been observed in both preclinical studies and clinical trials, there are issues pertaining to the use of these drugs which require more extensive research with regards to the delivery and stability of siRNAs and ASOs. This would improve their use for long-term treatment regimens and alleviate the difficulties experienced by patients with ocular diseases. This review provides a detailed insight into the recent developments and clinical trials that have been conducted for several gene-silencing therapies, including ISTH0036, SYL040012, SYL1001, PF-04523655, Sirna-027, QR-110, QR-1123, QR-421a and IONIS-FB-L_RX in glaucoma, dry eye disease, age-related macular degeneration, diabetic macular oedema and various inherited retinal diseases. Our aim is to explore the potential of these drugs whilst evaluating their associated advantages and disadvantages, and to discuss the future translation of RNA therapeutics in ophthalmology.

In Vitro Silencing of lncRNAs Using LNA GapmeRs

Despite substantial advancements have been achieved in the identification of long noncoding RNA (lncRNA) molecules, many challenges still remain into their functional characterization. Loss-of-function approaches are needed to study oncogenic lncRNAs, which appear more difficult to knock down by RNA interference as compared to mRNAs. In this chapter, we present a protocol based on the use of a novel class of antisense oligonucleotides, named locked nucleic acid (LNA) GapmeRs, to inhibit the oncogenic lncRNA NEAT1 in multiple myeloma cells. Overall, this approach holds many advantages, including its possible independence from delivery reagents as well as the capability to knock down lncRNAs even in hard-to-transfect suspension cells, like hematopoietic cells.

Nanoparticle-complexed antimiRs for inhibiting tumor growth and metastasis in prostate carcinoma and melanoma

Background

MiRNAs act as negative regulators of gene expression through target mRNA degradation or inhibition of its translation. In cancer, several miRNAs are upregulated and play crucial roles in tumorigenesis, making the inhibition of these oncomiRs an interesting therapeutic approach. This can be achieved by directly complementary single-stranded anti-miRNA oligonucleotides (antimiRs). A major bottleneck in antimiR therapy, however, is their efficient delivery. The nanoparticle formation with polyethylenimine (PEI) may be particularly promising, based on the PEI’s ability to electrostatically interact with oligonucleotides. This leads to their protection and supports delivery. In the present study, we explore for the first time PEI for antimiR formulation and delivery. We use the branched low molecular weight PEI F25-LMW for the complexation of different antimiRs, and analyse tumor- and metastasis-inhibitory effects of PEI/antimiR complexes in different tumor models.

Results

In prostate carcinoma, transfection of antimiRs against miR-375 and miR-141 leads to tumor cell inhibition in 2D- and 3D-models. More importantly, an in vivo tumor therapy study in prostate carcinoma xenografts reveals anti-tumor effects of the PEI/antimiR complexes. In advanced melanoma and metastasis, we identify by a microRNA screen miR-150 as a particularly relevant oncomiR candidate, and validate this result in vitro and in vivo. Again, the systemic application of PEI/antimiR complexes inhibiting this miRNA, or the previously described antimiR-638, leads to profound tumor growth inhibition. These effects are associated with the upregulation of direct miRNA target genes. In a melanoma metastasis mouse model, anti-metastatic effects of PEI/antimiR treatment are observed as well.

Conclusions

We thus describe PEI-based complexes as efficient platform for antimiR therapy, as determined in two different tumor entities using in vivo models of tumor growth or metastasis. Our study also highlights the therapeutic relevance of miR-375, miR-141, miR-150 and miR-638 as target miRNAs for antimiR-mediated inhibition.

Carbazole modified oligonucleotides: synthesis, hybridization studies and fluorescence properties

Synthesis of the novel thiophenyl carbazole phosphoramidite DNA building block 5 was accomplished in four steps using a Suzuki-Miyaura cross-coupling reaction from the core carbazole and it was seamlessly accommodated into a 9-mer DNA-based oligonucleotide by incorporation at the flanking 5'-end in combination with a central insertion of an LNA-T nucleotide. The carbazole-containing oligonucleotide was combined in different duplex hybrids, which were characterized by thermal denaturation, circular dichroism and fluorescence studies. The carbazole monomer modulates the duplex stability in various ways. Thus, monomer Z increased the thermal stability of the 9-mer towards the complementary 9-mer/15-mer DNA duplex by 4.2 °C. Furthermore, indications of its intercalation into the duplex were obtained by modeling studies and robust decreases in fluorescence emission intensities upon duplex formation. In contrast, no clear intercalating tendency was corroborated for monomer Z within the DNA/RNA hybrid duplex as indicated by moderate quenching of the fluorescence and similar duplex thermal stabilities relative to the corresponding control duplex. The recognition efficiencies of the carbazole modified oligonucleotide toward single nucleotide mismatches were studied with two 15-mer model targets (DNA and RNA). For both systems, mismatches positioned at the juxtaposition of the carbazole monomer showed pronounced deceases in thermal denaturation temperature. Steady-state fluorescence emission studies of all mismatched duplexes with incorporation of Z monomer typically displayed efficient fluorescence quenching.

An artificial cationic oligosaccharide combined with phosphorothioate linkages strongly improves siRNA stability

Small interfering RNAs (siRNAs) are potential tools for gene-silencing therapy, but their instability is one of the obstacles in the development of siRNA-based drugs. To improve siRNA stability, we synthesised a double-stranded RNA-binding cationic oligodiaminogalactose 4mer (ODAGal4) and investigated here its characteristics for siRNA stabilisation in vitro. ODAGal4 improved the resistance of various siRNAs against serum degradation. The effect of ODAGal4 on siRNA stabilisation was further amplified by introduction of modified nucleotides into the siRNA. In particular, a combination of ODAGal4 and incorporation of phosphorothioate linkages into the siRNA prominently prevented degradation by serum. The half-lives of fully phosphorothioate-modified RNA duplexes with ODAGal4 were more than 15 times longer than those of unmodified siRNAs without ODAGal4; this improvement in serum stability was superior to that observed for other chemical modifications. Serum degradation assays of RNAs with multiple chemical modifications showed that ODAGal4 preferentially improves the stability of RNAs with phosphorothioate modification among chemical modifications. Furthermore, melting temperature analysis showed that ODAGal4 greatly increases the thermal stability of phosphorothioate RNAs. Importantly, ODAGal4 did not interrupt gene-silencing activity of all the RNAs tested. Collectively, these findings demonstrate that ODAGal4 is a potent stabiliser of siRNAs, particularly nucleotides with phosphorothioate linkages, representing a promising tool in the development of gene-silencing therapies.

Detection of Spinal Muscular Atrophy Using a Duplexed Real-Time PCR Approach With Locked Nucleic Acid-Modified Primers

BACKGROUND

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder mainly caused by homozygous deletions that include exon 7 of the survival motor neuron 1 (SMN1) gene. A nearby paralog gene, SMN2, obstructs the specific detection of SMN1. We optimized a duplexed real-time PCR approach using locked nucleic acid (LNA)-modified primers to specifically detect SMN1.

METHODS

An LNA-modified primer pair with 3' ends targeting SMN1 specific sites c.835-44g and c.840C was designed, and its specificity was examined by real-time PCR and Sanger Sequencing. A duplexed real-time PCR approach for amplifying SMN1 and control gene albumin (ALB) was developed. A randomized double-blind trial with 97 fresh peripheral blood samples and 25 dried blood spots (DBS) was conducted to evaluate the clinical efficacy of the duplexed approach. This new approach was then used to screen 753 newborn DBS.

RESULTS

The LNA-modified primers exhibited enhanced specificity and 6.8% increased efficiency for SMN1 amplification, compared with conventional primers. After stabilizing the SMN1 test by optimizing the duplexed real-time PCR approach, a clinical trial validated that the sensitivity and specificity of our new approach for detecting SMA patients and carriers was 100%. Using this new approach, 15 of the screened 753 newborns were identified as carriers via DBS, while the rest were identified as normal individuals. These data reveal a carrier rate of 1.99% in Hunan province, South Central China.

CONCLUSIONS

We have developed a novel, specific SMN1 detection approach utilizing real-time PCR with LNA-modified primers, which could be applied to both prenatal carrier and newborn screening.

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.

Novel approaches for efficient in vivo fermentation production of noncoding RNAs

Genome-derived noncoding RNAs (ncRNAs), including microRNAs (miRNAs), small interfering RNAs (siRNAs), and long noncoding RNAs (lncRNAs), play an essential role in the control of target gene expression underlying various cellular processes, and dysregulation of ncRNAs is involved in the pathogenesis and progression of various diseases in virtually all species including humans. Understanding ncRNA biology has opened new avenues to develop novel RNA-based therapeutics. Presently, ncRNA research and drug development is dominated by the use of ncRNA mimics that are synthesized chemically in vitro and supplemented with extensive and various types of artificial modifications and thus may not necessarily recapitulate the properties of natural RNAs generated and folded in living cells in vivo. Therefore, there are growing interests in developing novel technologies for in vivo production of RNA molecules. The two most recent major breakthroughs in achieving an efficient, large-scale, and cost-effective fermentation production of recombinant or bioengineered RNAs (e.g., tens of milligrams from 1 L of bacterial culture) are (1) using stable RNA carriers and (2) direct overexpression in RNase III-deficient bacteria, while other approaches offer a low yield (e.g., nano- to microgram scales per liter). In this article, we highlight these novel microbial fermentation-based technologies that have shifted the paradigm to the production of true biological ncRNA molecules for research and development.

Dose-Finding Study and Pharmacokinetics Profile of the Novel 13-Mer Antisense miR-221 Inhibitor in Sprague-Dawley Rats

miR-221 is overexpressed in several malignancies where it promotes tumor growth and survival by interfering with gene transcripts, including p27Kip1, PUMA, PTEN, and p57Kip2. We previously demonstrated that a novel 13-mer miR-221 inhibitor (locked nucleic acid [LNA]-i-miR-221) exerts antitumor activity against human cancer with a pilot-favorable pharmacokinetics and safety profile in mice and non-naive monkeys. In this study, we report a non-good laboratory practice (GLP)/GLP dose-finding investigation of LNA-i-miR-221 in Sprague-Dawley rats. The safety of the intravenous dose (125 mg/kg/day) for 4 consecutive days, two treatment cycles, was investigated by a first non-GLP study. The toxicokinetics profile of LNA-i-miR-221 was next explored in a GLP study at three different doses (5, 12.5, and 125 mg/kg/day). Slight changes in blood parameters and histological findings in kidney were observed at the highest dose. These effects were reversible and consistent with an in vivo antisense oligonucleotide (ASO) class effect. The no-observed-adverse-effect level (NOAEL) was established at 5 mg/kg/day. The plasma exposure of LNA-i-miR-221, based on C₀ (estimated concentration at time 0 after bolus intravenous administration) and area under the curve (AUC), suggested no differential sex effect. Slight accumulation occurred between cycles 1 and 2 but was not observed after four consecutive administrations. Taken together, our findings demonstrate a safety profile of LNA-i-miR-221 in Sprague-Dawley rats and provide a reference translational framework and path for the development of other LNA miR inhibitors in phase I clinical study.

TCR validation toward gene therapy for cancer

The speed of T cell receptor (TCR) discovery has been revolutionized by barcode-based TCR sequencing approaches that allow the reconstitution of a T cell's paired alpha and beta TCR chain, and the process of TCR discovery promises to become ever faster and cheaper with the continuing development single cell analysis techniques. This technological progress has generated an urgent need to develop efficient TCR validation platforms for the rapid and safe clinical translation of TCRs into therapeutic agents. Whereas much attention has in the past focused on CD8-positive cytotoxic T cells recognizing MHC class I presented epitopes, the increasing demand to validate TCRs expressed on neoepitope-reactive CD4 T cells requires the implementation of large-scale T cell activation-based readout assays to complement existing multimer and cytotoxicity-based assays. Here, we present commonly used TCR validation assays, and include detailed guidance on TCR synthesis, delivery, and appropriate experimental control TCRs. We also comment on upcoming methods that hold promise for further speeding the process of TCR validation, hastening the translation of TCRs from the laboratory into the clinic.

Therapy with 2'-O-Me Phosphorothioate Antisense Oligonucleotides Causes Reversible Proteinuria by Inhibiting Renal Protein Reabsorption

Antisense oligonucleotide therapy has been reported to be associated with renal injury. Here, the mechanism of reversible proteinuria was investigated by combining clinical, pre-clinical, and in vitro data. Urine samples were obtained from Duchenne muscular dystrophy (DMD) patients treated with drisapersen, a modified 2′O-methyl phosphorothioate antisense oligonucleotide (6 mg/kg). Urine and kidney tissue samples were collected from cynomolgus monkeys (Macaca fascicularis) dosed with drisapersen (39 weeks). Cell viability and protein uptake were evaluated in vitro using human conditionally immortalized proximal tubule epithelial cells (ciPTECs). Oligonucleotide treatment in DMD patients was associated with an increase in urinary alpha-1-microglobulin (A1M), which returned to baseline following treatment interruptions. In monkeys, increased urinary A1M correlated with dose-dependent accumulation of oligonucleotide in kidney tissue without evidence of tubular damage. Furthermore, oligonucleotides accumulated in the lysosomes of ciPTECs and reduced the absorption of A1M, albumin, and receptor-associated protein, but did not affect cell viability when incubated for up to 7 days. In conclusion, phosphorothioate oligonucleotides appear to directly compete for receptor-mediated endocytosis in proximal tubules. We postulate that oligonucleotide-induced low molecular weight proteinuria in patients is therefore a transient functional change and not indicative of tubular damage.

Significant epitranscriptomes in heterogeneous cancer

Precision medicine places significant emphasis on techniques for the identification of DNA mutations and gene expression by deep sequencing of gene panels to obtain medical data. However, other diverse information that is not easily readable using bioinformatics, including RNA modifications, has emerged as a novel diagnostic and innovative therapy owing to its multifunctional aspects. It is suggested that this breakthrough innovation might open new avenues for the elucidation of uncharacterized cancer cellular functions to develop more precise medical applications. The functional characteristics and regulatory mechanisms of RNA modifications, ie, the epitranscriptome (ETR), which reflects RNA metabolism, remains unclear, mainly due to detection methods being limited. Recent studies have revealed that N6‐methyl adenosine, the most common modification in mRNA in eukaryotes, is affected in various types of cancer and, in some cases, cancer stem cells, but also affects cellular responses to viral infections. The ETR can control cancer cell fate through mRNA splicing, stability, nuclear export, and translation. Here we report on the recent progress of ETR detection methods, and biological findings regarding the significance of ETR in cancer precision medicine.

Screening substrate-binding positions by rolling circle amplification suggesting a binding model of Nt.BstNBI

Nicking endonucleases (NEs) become increasingly attractive for their promising applications in isothermal amplification. Unfortunately, in comparison with their applications, their catalytic mechanism studies have relatively lagged behind due to a paucity of crystal structure information. Nt.BstNBI is one of those widely used NEs. However, many aspects of its catalytic mechanism still remained to be explored. Herein, we employed only rolling circle amplification (RCA) assay as a major analytic tool and succeeded in identifying the potential binding positions and regions of the DNA substrate based on locked nucleic acid modification, DNA duplex length of substrate, and substrate mismatch designs. Based on these data, we, for the first time, revealed that Nt.BstNBI was likely to recognize six adjacent positions of the recognition sequence (G1rt, A2rt, G3rt, A2rb, C3rb, and T4rb) in the major groove and hold three positions of the cleavage sequence (N3ct, N4ct, and N7cb) in the minor groove of DNA duplex for nicking. Moreover, this work also demonstrated the unexpected efficiency of RCA to study the macromolecular interaction for certain kind of nucleases in an easy and high-throughput way.

RNA therapy: Are we using the right molecules?

Small-molecule and protein/antibody drugs mainly act on genome-derived proteins to exert pharmacological effects. RNA based therapies hold the promise to expand the range of druggable targets from proteins to RNAs and the genome, as evidenced by several RNA drugs approved for clinical practice and many others under active trials. While chemo-engineered RNA mimics have found their success in marketed drugs and continue dominating basic research and drug development, these molecules are usually conjugated with extensive and various modifications. This makes them completely different from cellular RNAs transcribed from the genome that usually consist of unmodified ribonucleotides or just contain a few posttranscriptional modifications. The use of synthetic RNA mimics for RNA research and drug development is also in contrast with the ultimate success of protein research and therapy utilizing biologic or recombinant proteins produced and folded in living cells instead of polypeptides or proteins synthesized in vitro. Indeed, efforts have been made recently to develop RNA bioengineering technologies for cost-effective and large-scale production of biologic RNA molecules that may better capture the structures, functions, and safety profiles of natural RNAs. In this article, we provide an overview on RNA therapeutics for the treatment of human diseases via RNA interference mechanisms. By illustrating the structural differences between natural RNAs and chemo-engineered RNA mimics, we focus on discussion of a novel class of bioengineered/biologic RNA agents produced through fermentation and their potential applications to RNA research and drug development.

Gymnotic Delivery of LNA Mixmers Targeting Viral SREs Induces HIV-1 mRNA Degradation

Transcription of the HIV-1 provirus generates a viral pre-mRNA, which is alternatively spliced into more than 50 HIV-1 mRNAs encoding all viral proteins. Regulation of viral alternative splice site usage includes the presence of splicing regulatory elements (SREs) which can dramatically impact RNA expression and HIV-1 replication when mutated. Recently, we were able to show that two viral SREs, G_I3-2 and ESE_tat, are important players in the generation of viral vif, vpr and tat mRNAs. Furthermore, we demonstrated that masking these SREs by transfected locked nucleic acid (LNA) mixmers affect the viral splicing pattern and viral particle production. With regard to the development of future therapeutic LNA mixmer-based antiretroviral approaches, we delivered the G_I3-2 and the ESE_tat LNA mixmers “nakedly”, without the use of transfection reagents (gymnosis) into HIV-1 infected cells. Surprisingly, we observed that gymnotically-delivered LNA mixmers accumulated in the cytoplasm, and seemed to co-localize with GW bodies and induced degradation of mRNAs containing their LNA target sequence. The G_I3-2 and the ESE_tat LNA-mediated RNA degradation resulted in abrogation of viral replication in HIV-1 infected Jurkat and PM1 cells as well as in PBMCs.

Effective syntheses of 2',4'-BNANC monomers bearing adenine, guanine, thymine, and 5-methylcytosine, and the properties of oligonucleotides fully modified with 2',4'-BNANC

We efficiently synthesized 2'-O,4'-C-aminomethylene-bridged nucleic acid (2',4'-BNA^NC) monomers bearing the four nucleobases, guanine, adenine, thymine, and 5-methylcytosine and incorporated these monomers into oligonucleotides. Initially, we carried out the transglycosylation reaction on several 2'-O-substituted 5-methyluridines to evaluate the effects of 2'-substitutions on this reaction. Under the optimized conditions, purine nucleobases were successfully introduced, and 2',4'-BNA^NC monomers bearing adenine or guanine were obtained over several steps. In addition, the improved synthesis of the 2',4'-BNA^NC monomers bearing thymine or 5-methylcytosine was also achieved. The obtained 2',4'-BNA^NC monomers were subsequently incorporated into oligonucleotides and the duplex-forming abilities of the modified oligonucleotides were investigated. Duplexes containing 2',4'-BNA^NC monomers in both or either strands were found to possess excellent thermal stabilities.

Synthesis of ENA Nucleotides and ENA Oligonucleotides

2'-O,4'-C-Ethylene-bridged nucleic acid (ENA) is a sugar-modified oligonucleotide with an ethylene bridge between the 2'-oxygen and 4'-carbon of ribose. ENA not only has as high binding affinity to complementary RNA as conventional bridged/locked nucleic acid, but also has much higher nuclease resistance in plasma, which makes it a promising candidate for antisense therapeutics. This unit presents detailed protocols for the synthesis and characterization of ENA nucleosides and oligonucleotides. © 2018 by John Wiley & Sons, Inc.

The ability of locked nucleic acid oligonucleotides to pre-structure the double helix: A molecular simulation and binding study

Locked nucleic acid (LNA) oligonucleotides bind DNA target sequences forming Watson-Crick and Hoogsteen base pairs, and are therefore of interest for medical applications. To be biologically active, such an oligonucleotide has to efficiently bind the target sequence. Here we used molecular dynamics simulations and electrophoresis mobility shift assays to elucidate the relation between helical structure and affinity for LNA-containing oligonucleotides. In particular, we have studied how LNA substitutions in the polypyrimidine strand of a duplex (thus forming a hetero duplex, i.e. a duplex with a DNA polypurine strand and an LNA/DNA polypyrimidine strand) enhance triplex formation. Based on seven polypyrimidine single strand oligonucleotides, having LNAs in different positions and quantities, we show that alternating LNA with one or more non-modified DNA nucleotides pre-organizes the hetero duplex toward a triple-helical-like conformation. This in turn promotes triplex formation, while consecutive LNAs distort the duplex structure disfavoring triplex formation. The results support the hypothesis that a pre-organization in the hetero duplex structure enhances the binding of triplex forming oligonucleotides. Our findings may serve as a criterion in the design of new tools for efficient oligonucleotide hybridization.

Nanomaterials and molecular transporters to overcome the bacterial envelope barrier: Towards advanced delivery of antibiotics

With the dramatic consequences of bacterial resistance to antibiotics, nanomaterials and molecular transporters have started to be investigated as alternative antibacterials or anti-infective carrier systems to improve the internalization of bactericidal drugs. However, the capability of nanomaterials/molecular transporters to overcome the bacterial cell envelope is poorly understood. It is critical to consider the sophisticated architecture of bacterial envelopes and reflect how nanomaterials/molecular transporters can interact with these envelopes, being the major aim of this review. The first part of this manuscript overviews the permeability of bacterial envelopes and how it limits the internalization of common antibiotic and novel oligonucleotide drugs. Subsequently we critically discuss the mechanisms that allow nanomaterials/molecular transporters to overcome the bacterial envelopes, focusing on the most promising ones to this end - siderophores, cyclodextrins, metal nanoparticles, antimicrobial/cell-penetrating peptides and fusogenic liposomes. This review may stimulate drug delivery and microbiology scientists in designing effective nanomaterials/molecular transporters against bacterial infections.

Direct Quantification of Trace Amounts of a Chronic Myeloid Leukemia Biomarker Using Locked Nucleic Acid Capture Probes

Molecular monitoring is indispensable for the clinical management of chronic myeloid leukemia (CML) patients. Real-time quantitative polymerase chain reaction (RT-qPCR) is the gold standard for the quantitative assessment of BCR-ABL transcript levels, which are critical in clinical decision-making. However, the frequent recurrence of the disease after drug discontinuation for 60% of patients has necessitated more sensitive and specific techniques to detect residual BCR-ABL transcripts. Here, we describe a quantification method for the detection of BCR-ABL targets at very low concentrations (<10 copies/sample) in the presence of a million copies of normal BCR and ABL genes. In this method, a fully modified locked nucleic acid (LNA) and a LNA/DNA chimera were used as capture probes, and the quantitative imaging mode of atomic force microscopy (AFM) was employed. Targets with one of the major breakpoints (found in more than 95% of CML patients), b3a2 and b2a2, were quantified. The BCR-ABL target captured on a miniaturized LNA-probe spot was scanned at nanometric resolution, and the samples containing one to ten copies of the BCR-ABL genes were examined. It was observed that the highest sensitivity, i.e., the detection of a single copy of the target gene, could be achieved through multiple runs, and the observed cluster number was well correlative (adjusted R² = 0.999) to the target copy number in the sample solution. This observation clearly demonstrates that the LNA-based platform is effective in quantifying BCR-ABL targets with extremely low copy numbers, highlighting the potential applicability of AFM for use in the direct quantification of such targets without amplification or labeling.

Development of Locked Nucleic Acid Antisense Oligonucleotides Targeting Ebola Viral Proteins and Host Factor Niemann-Pick C1

The Ebola virus is a zoonotic pathogen that can cause severe hemorrhagic fever in humans, with up to 90% lethality. The deadly 2014 Ebola outbreak quickly made an unprecedented impact on human lives. While several vaccines and therapeutics are under development, current approaches contain several limitations, such as virus mutational escape, need for formulation or refrigeration, poor scalability, long lead-time, and high cost. To address these challenges, we developed locked nucleic acid (LNA)-modified antisense oligonucleotides (ASOs) to target critical Ebola viral proteins and the human intracellular host protein Niemann-Pick C1 (NPC1), required for viral entry into infected cells. We generated noninfectious viral luciferase reporter assays to identify LNA ASOs that inhibit translation of Ebola viral proteins in vitro and in human cells. We demonstrated specific inhibition of key Ebola genes VP24 and nucleoprotein, which inhibit a proper immune response and promote Ebola virus replication, respectively. We also identified LNA ASOs targeting human host factor NPC1 and demonstrated reduced infection by chimeric vesicular stomatitis virus harboring the Ebola glycoprotein, which directly binds to NPC1 for viral infection. These results support further in vivo testing of LNA ASOs in infectious Ebola virus disease animal models as potential therapeutic modalities for treatment of Ebola.

Behind the scenes of HIV-1 replication: Alternative splicing as the dependency factor on the quiet

Alternative splicing plays a key role in the HIV-1 life cycle and is essential to maintain an equilibrium of mRNAs that encode viral proteins and polyprotein-isoforms. In particular, since all early HIV-1 proteins are expressed from spliced intronless and late enzymatic and structural proteins from intron containing, i.e. splicing repressed viral mRNAs, cellular splicing factors and splicing regulatory proteins are crucial for the replication capacity. In this review, we will describe the complex network of cis-acting splicing regulatory elements (SREs), which are mainly localized in the neighbourhoods of all HIV-1 splice sites and warrant the proper ratio of individual transcript isoforms. Since SREs represent binding sites for trans-acting cellular splicing factors interacting with the cellular spliceosomal apparatus we will review the current knowledge of interactions between viral RNA and cellular proteins as well as their impact on viral replication. Finally, we will discuss potential therapeutic approaches targeting HIV-1 alternative splicing.

MALAT1: a druggable long non-coding RNA for targeted anti-cancer approaches

The deeper understanding of non-coding RNAs has recently changed the dogma of molecular biology assuming protein-coding genes as unique functional biological effectors, while non-coding genes as junk material of doubtful significance. In the last decade, an exciting boom of experimental research has brought to light the pivotal biological functions of long non-coding RNAs (lncRNAs), representing more than the half of the whole non-coding transcriptome, along with their dysregulation in many diseases, including cancer.In this review, we summarize the emerging insights on lncRNA expression and functional role in cancer, focusing on the evolutionary conserved and abundantly expressed metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) that currently represents the best characterized lncRNA. Altogether, literature data indicate aberrant expression and dysregulated activity of MALAT1 in human malignancies and envision MALAT1 targeting as a novel treatment strategy against cancer.

Hydrogel-Assisted Antisense LNA Gapmer Delivery for In Situ Gene Silencing in Spinal Cord Injury

After spinal cord injury (SCI), nerve regeneration is severely hampered due to the establishment of a highly inhibitory microenvironment at the injury site, through the contribution of multiple factors. The potential of antisense oligonucleotides (AONs) to modify gene expression at different levels, allowing the regulation of cell survival and cell function, together with the availability of chemically modified nucleic acids with favorable biopharmaceutical properties, make AONs an attractive tool for novel SCI therapy developments. In this work, we explored the potential of locked nucleic acid (LNA)-modified AON gapmers in combination with a fibrin hydrogel bridging material to induce gene silencing in situ at a SCI lesion site. LNA gapmers were effectively developed against two promising gene targets aiming at enhancing axonal regeneration-RhoA and GSK3β. The fibrin-matrix-assisted AON delivery system mediated potent RNA knockdown in vitro in a dorsal root ganglion explant culture system and in vivo at a SCI lesion site, achieving around 75% downregulation 5 days after hydrogel injection. Our results show that local implantation of a AON-gapmer-loaded hydrogel matrix mediated efficient gene silencing in the lesioned spinal cord and is an innovative platform that can potentially combine gene regulation with regenerative permissive substrates aiming at SCI therapeutics and nerve regeneration.

Development of Novel Therapeutic Agents by Inhibition of Oncogenic MicroRNAs

MicroRNAs (miRs, miRNAs) are regulatory small noncoding RNAs, with their roles already confirmed to be important for post-transcriptional regulation of gene expression affecting cell physiology and disease development. Upregulation of a cancer-causing miRNA, known as oncogenic miRNA, has been found in many types of cancers and, therefore, represents a potential new class of targets for therapeutic inhibition. Several strategies have been developed in recent years to inhibit oncogenic miRNAs. Among them is a direct approach that targets mature oncogenic miRNA with an antisense sequence known as antimiR, which could be an oligonucleotide or miRNA sponge. In contrast, an indirect approach is to block the biogenesis of miRNA by genome editing using the CRISPR/Cas9 system or a small molecule inhibitor. The development of these inhibitors is straightforward but involves significant scientific and therapeutic challenges that need to be resolved. In this review, we summarize recent relevant studies on the development of miRNA inhibitors against cancer.

CTG repeat-targeting oligonucleotides for down-regulating Huntingtin expression

Huntington's disease (HD) is a fatal, neurodegenerative disorder in which patients suffer from mobility, psychological and cognitive impairments. Existing therapeutics are only symptomatic and do not significantly alter the disease progression or increase life expectancy. HD is caused by expansion of the CAG trinucleotide repeat region in exon 1 of the Huntingtin gene (HTT), leading to the formation of mutant HTT transcripts (muHTT). The toxic gain-of-function of muHTT protein is a major cause of the disease. In addition, it has been suggested that the muHTT transcript contributes to the toxicity. Thus, reduction of both muHTT mRNA and protein levels would ideally be the most useful therapeutic option. We herein present a novel strategy for HD treatment using oligonucleotides (ONs) directly targeting the HTT trinucleotide repeat DNA. A partial, but significant and potentially long-term, HTT knock-down of both mRNA and protein was successfully achieved. Diminished phosphorylation of HTT gene-associated RNA-polymerase II is demonstrated, suggestive of reduced transcription downstream the ON-targeted repeat. Different backbone chemistries were found to have a strong impact on the ON efficiency. We also successfully use different delivery vehicles as well as naked uptake of the ONs, demonstrating versatility and possibly providing insights for in vivo applications.

LNA effects on DNA binding and conformation: from single strand to duplex and triplex structures

The anti-gene strategy is based on sequence-specific recognition of double-strand DNA by triplex forming (TFOs) or DNA strand invading oligonucleotides to modulate gene expression. To be efficient, the oligonucleotides (ONs) should target DNA selectively, with high affinity. Here we combined hybridization analysis and electrophoretic mobility shift assay with molecular dynamics (MD) simulations to better understand the underlying structural features of modified ONs in stabilizing duplex- and triplex structures. Particularly, we investigated the role played by the position and number of locked nucleic acid (LNA) substitutions in the ON when targeting a c-MYC or FXN (Frataxin) sequence. We found that LNA-containing single strand TFOs are conformationally pre-organized for major groove binding. Reduced content of LNA at consecutive positions at the 3'-end of a TFO destabilizes the triplex structure, whereas the presence of Twisted Intercalating Nucleic Acid (TINA) at the 3'-end of the TFO increases the rate and extent of triplex formation. A triplex-specific intercalating benzoquinoquinoxaline (BQQ) compound highly stabilizes LNA-containing triplex structures. Moreover, LNA-substitution in the duplex pyrimidine strand alters the double helix structure, affecting x-displacement, slide and twist favoring triplex formation through enhanced TFO major groove accommodation. Collectively, these findings should facilitate the design of potent anti-gene ONs.

Short (16-mer) locked nucleic acid splice-switching oligonucleotides restore dystrophin production in Duchenne Muscular Dystrophy myotubes

Splice-switching antisense oligonucleotides (SSOs) offer great potential for RNA-targeting therapies, and two SSO drugs have been recently approved for treating Duchenne Muscular Dystrophy (DMD) and Spinal Muscular Atrophy (SMA). Despite promising results, new developments are still needed for more efficient chemistries and delivery systems. Locked nucleic acid (LNA) is a chemically modified nucleic acid that presents several attractive properties, such as high melting temperature when bound to RNA, potent biological activity, high stability and low toxicity in vivo. Here, we designed a series of LNA-based SSOs complementary to two sequences of the human dystrophin exon 51 that are most evolutionary conserved and evaluated their ability to induce exon skipping upon transfection into myoblasts derived from a DMD patient. We show that 16-mers with 60% of LNA modification efficiently induce exon skipping and restore synthesis of a truncated dystrophin isoform that localizes to the plasma membrane of patient-derived myotubes differentiated in culture. In sum, this study underscores the value of short LNA-modified SSOs for therapeutic applications.

Construction of DNAzyme-Encapsulated Fibermats Using the Precursor Network Polymer of Poly(γ-glutamate) and 4-Glycidyloxypropyltrimethoxysilane

Here, we developed functional nucleic acid (FNA)-encapsulated electrospun fibermats. To facilitate stable FNA encapsulation in the γ-PGA/GPTMS fibermats, we used the FNA as an FNA/streptavidin complex, and as a representative FNA, we selected a DNAzyme, the DNA/hemin complex, which is composed of G-quadraplex-forming single-stranded DNA and hemin and exhibits oxidation activity with the aid of a cocatalyst, H₂O₂. Scanning electron microscopy and Fourier-transform infrared spectroscopy measurements revealed that encapsulation of the DNA/hemin complex (∼1 wt % against the γ-PGA/GPTMS hybrid) in the nanofibers of the γ-PGA/GPTMS fibermats did not affect the structure of the original nanofibers. However, because a unique MW-dependent molecular permeability originated from the 3D network structure of the γ-PGA/GPTMS hybrid, low-MW substrates such as 4-aminoantipyrine, N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3-methylaniline, and luminol were able to reach the encapsulated DNA/hemin complex by permeating to the inside of the nanofibers from an immersion buffer and then underwent catalytic oxidation. Conversely, nucleases, which are proteins featuring high MWs (>5 kDa), could not penetrate the γ-PGA/GPTMS nanofibers, and the encapsulated DNA/hemin complex was therefore effectively protected against nuclease digestion. Thus, encapsulating FNAs on the inside of the nanofibers of fibermats offers clear advantages for the practical application of FNAs in sensors and drugs, particularly for use in the in vivo circumstances.

Analysis of in Situ LNA and DNA Hybridization Events on Microspheres

The hybridization activity of single-stranded DNA and locked nucleic acid (LNA) sequences on microspheres is quantified in situ using flow cytometry. In contrast to conventional sample preparation for flow cytometry that involves several wash steps for posthybridization analysis, the current work entails directly monitoring hybridization events as they occur between oligonucleotide-functionalized microspheres and fluorescently tagged 9 or 15 base-long targets. We find that the extent of hybridization between single-stranded, immobilized probes and soluble targets generally increases with target sequence length or with the incorporation of LNA nucleotides in one or both oligonucleotide strands involved in duplex formation. The rate constants for duplex formation, on the other hand, remain nearly identical for all but one probe-target sequence combination. The exception to this trend involves the LNA probe and shortest perfectly matched DNA target, which exhibit a rate constant that is an order of magnitude lower than any other probe-target pair, including a mismatched duplex case. Separate studies entailing brief heat treatments to suspensions generally do not consistently yield appreciable differences in associated target densities to probe-functionalized microspheres.

Double duplex invasion of DNA induced by ultrafast photo-cross-linking using 3-cyanovinylcarbazole for antigene methods

New photoresponsive antigene probes containing^CNVK and^CNU have a high double-duplex invasion capability upon photoirradiation because of the inhibition of photo-cross-linking between the probes.