Synthesis and biophysical evaluation of 2',4'-constrained 2'O-methoxyethyl and 2',4'-constrained 2'O-ethyl nucleic acid analogues

Oligonucleotide therapies for nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) represents a severe disease subtype of nonalcoholic fatty liver disease (NAFLD) that is thought to be highly associated with systemic metabolic abnormalities. It is characterized by a series of substantial liver damage, including hepatocellular steatosis, inflammation, and fibrosis. The end stage of NASH, in some cases, may result in cirrhosis and hepatocellular carcinoma (HCC). Nowadays a large number of investigations are actively under way to test various therapeutic strategies, including emerging oligonucleotide drugs (e.g., antisense oligonucleotide, small interfering RNA, microRNA, mimic/inhibitor RNA, and small activating RNA) that have shown high potential in treating this fatal liver disease. This article systematically reviews the pathogenesis of NASH/NAFLD, the promising druggable targets proven by current studies in chemical compounds or biological drug development, and the feasibility and limitations of oligonucleotide-based therapeutic approaches under clinical or pre-clinical studies.

RNA-encapsulating lipid nanoparticles in cancer immunotherapy: From pre-clinical studies to clinical trials

Nanoparticle-based delivery systems such as RNA-encapsulating lipid nanoparticles (RNA LNPs) have dramatically advanced in function and capacity over the last few decades. RNA LNPs boast of a diverse array of external and core configurations that enhance targeted delivery and prolong circulatory retention, advancing therapeutic outcomes. Particularly within the realm of cancer immunotherapies, RNA LNPs are increasingly gaining prominence. Pre-clinical in vitro and in vivo studies have laid a robust foundation for new and ongoing clinical trials that are actively enrolling patients for RNA LNP cancer immunotherapy. This review explores RNA LNPs, starting from their core composition to their external membrane formulation, set against a backdrop of recent clinical breakthroughs. We further elucidate the LNP delivery avenues, broach the prevailing challenges, and contemplate the future perspectives of RNA LNP-mediated immunotherapy.

DELE1 promotes translation-associated homeostasis, growth, and survival in mitochondrial myopathy

Mitochondrial dysfunction causes devastating disorders, including mitochondrial myopathy. Here, we identified that diverse mitochondrial myopathy models elicit a protective mitochondrial integrated stress response (mt-ISR), mediated by OMA1-DELE1 signaling. The response was similar following disruptions in mtDNA maintenance, from knockout of Tfam, and mitochondrial protein unfolding, from disease-causing mutations in CHCHD10 (G58R and S59L). The preponderance of the response was directed at upregulating pathways for aminoacyl-tRNA biosynthesis, the intermediates for protein synthesis, and was similar in heart and skeletal muscle but more limited in brown adipose challenged with cold stress. Strikingly, models with early DELE1 mt-ISR activation failed to grow and survive to adulthood in the absence of Dele1, accounting for some but not all of OMA1's protection. Notably, the DELE1 mt-ISR did not slow net protein synthesis in stressed striated muscle, but instead prevented loss of translation-associated proteostasis in muscle fibers. Together our findings identify that the DELE1 mt-ISR mediates a stereotyped response to diverse forms of mitochondrial stress and is particularly critical for maintaining growth and survival in early-onset mitochondrial myopathy.

A High-Throughput Workflow for Mass Spectrometry Analysis of Nucleic Acids by Nanoflow Desalting

Broad interest in nucleic acids, both their therapeutic capabilities and understanding the nuances of their structure and resulting function, has increased in recent years. Post-transcriptional modifications, in particular, have become an important analysis target, as these covalent modifications to the sugars, nitrogenous bases, and phosphate backbone impart differential functionality to synthetic and biological nucleic acids. Characterizing these post-transcriptional modifications can be difficult with traditional sequencing workflows; however, advancements in top-down mass spectrometry address these challenges. Online desalting platforms have enabled facile sample cleanup and reliable ionization of increasingly large (100 nt) oligonucleotides, and application of existing tandem mass spectrometry techniques has yielded information-rich spectra which can be used to interrogate primary sequences. To extend the capabilities of top-down MS and its analysis of nucleic acids, we have developed a nanoflow desalting platform for high-throughput and low sample-use desalting coupled with collision-induced dissociation (CID), 213 nm ultraviolet photodissociation (UVPD), and activated-ion electron photodetachment dissociation (a-EPD) to yield high-quality MS/MS spectra. Fragments identified using an m/z-domain isotope matching strategy yielded high sequence coverage (>70%) of a yeast phenylalanine tRNA.

Targeting RNA with synthetic oligonucleotides: Clinical success invites new challenges

Synthetic antisense oligonucleotides (ASOs) and duplex RNAs (dsRNAs) are an increasingly successful strategy for drug development. After a slow start, the pace of success has accelerated since the approval of Spinraza (nusinersen) in 2016 with several drug approvals. These accomplishments have been achieved even though oligonucleotides are large, negatively charged, and have little resemblance to traditional small-molecule drugs-a remarkable achievement of basic and applied science. The goal of this review is to summarize the foundation underlying recent progress and describe ongoing research programs that may increase the scope and impact of oligonucleotide therapeutics.

Recent insights into the functions and mechanisms of antisense RNA: emerging applications in cancer therapy and precision medicine

The antisense RNA molecule is a unique DNA transcript consisting of 19-23 nucleotides, characterized by its complementary nature to mRNA. These antisense RNAs play a crucial role in regulating gene expression at various stages, including replication, transcription, and translation. Additionally, artificial antisense RNAs have demonstrated their ability to effectively modulate gene expression in host cells. Consequently, there has been a substantial increase in research dedicated to investigating the roles of antisense RNAs. These molecules have been found to be influential in various cellular processes, such as X-chromosome inactivation and imprinted silencing in healthy cells. However, it is important to recognize that in cancer cells; aberrantly expressed antisense RNAs can trigger the epigenetic silencing of tumor suppressor genes. Moreover, the presence of deletion-induced aberrant antisense RNAs can lead to the development of diseases through epigenetic silencing. One area of drug development worth mentioning is antisense oligonucleotides (ASOs), and a prime example of an oncogenic trans-acting long noncoding RNA (lncRNA) is HOTAIR (HOX transcript antisense RNA). NATs (noncoding antisense transcripts) are dysregulated in many cancers, and researchers are just beginning to unravel their roles as crucial regulators of cancer's hallmarks, as well as their potential for cancer therapy. In this review, we summarize the emerging roles and mechanisms of antisense RNA and explore their application in cancer therapy.

Synthesis and properties of RNA constrained by a 2'-O-disulfide bridge

We recently reported the properties of RNA hairpins constrained by a dimethylene (DME) disulfide (S-S) linker incorporated between two adjacent nucleosides in the loop and showed that this linker locked the hairpin conformation thus disturbing the duplex/hairpin equilibrium. We have now investigated the influence of the length of the linker and synthesized oligoribonucleotides containing diethylene (DEE) and dipropylene (DPE) S-S bridges. This was achieved via the preparation of building blocks, namely 2'-O-acetylthioethyl (2'-O-AcSE) and 2'-O-acetylthiopropyl (2'-O-AcSP) uridine phosphoramidites, which were successfully incorporated into RNA sequences. Thermal denaturation analysis revealed that the DEE and DPE disulfide bridges destabilize RNA duplexes but do not disrupt the hairpin conformation. Furthermore, our investigation of the duplex/hairpin equilibrium indicated that sequences modified with DME and DEE S-S linkers predominantly lock the hairpin form, whereas the DPE S-S linker provides flexibility. These findings highlight the potential of S-S linkers to study RNA interactions.

A single-cell map of antisense oligonucleotide activity in the brain

Antisense oligonucleotides (ASOs) dosed into cerebrospinal fluid (CSF) distribute broadly throughout the central nervous system (CNS). By modulating RNA, they hold the promise of targeting root molecular causes of disease and hold potential to treat myriad CNS disorders. Realization of this potential requires that ASOs must be active in the disease-relevant cells, and ideally, that monitorable biomarkers also reflect ASO activity in these cells. The biodistribution and activity of such centrally delivered ASOs have been deeply characterized in rodent and non-human primate (NHP) models, but usually only in bulk tissue, limiting our understanding of the distribution of ASO activity across individual cells and across diverse CNS cell types. Moreover, in human clinical trials, target engagement is usually monitorable only in a single compartment, CSF. We sought a deeper understanding of how individual cells and cell types contribute to bulk tissue signal in the CNS, and how these are linked to CSF biomarker outcomes. We employed single nucleus transcriptomics on tissue from mice treated with RNase H1 ASOs against Prnp and Malat1 and NHPs treated with an ASO against PRNP. Pharmacologic activity was observed in every cell type, though sometimes with substantial differences in magnitude. Single cell RNA count distributions implied target RNA suppression in every single sequenced cell, rather than intense knockdown in only some cells. Duration of action up to 12 weeks post-dose differed across cell types, being shorter in microglia than in neurons. Suppression in neurons was generally similar to, or more robust than, the bulk tissue. In macaques, PrP in CSF was lowered 40% in conjunction with PRNP knockdown across all cell types including neurons, arguing that a CSF biomarker readout is likely to reflect ASO pharmacodynamic effect in disease-relevant cells in a neuronal disorder. Our results provide a reference dataset for ASO activity distribution in the CNS and establish single nucleus sequencing as a method for evaluating cell type specificity of oligonucleotide therapeutics and other modalities.

Development of nucleic acid medicines based on chemical technology

Oligonucleotide-based therapeutics have attracted attention as an emerging modality that includes the modulation of genes and their binding proteins related to diseases, allowing us to take action on previously undruggable targets. Since the late 2010s, the number of oligonucleotide medicines approved for clinical uses has dramatically increased. Various chemistry-based technologies have been developed to improve the therapeutic properties of oligonucleotides, such as chemical modification, conjugation, and nanoparticle formation, which can increase nuclease resistance, enhance affinity and selectivity to target sites, suppress off-target effects, and improve pharmacokinetic properties. Similar strategies employing modified nucleobases and lipid nanoparticles have been used for developing coronavirus disease 2019 mRNA vaccines. In this review, we provide an overview of the development of chemistry-based technologies aimed at using nucleic acids for developing therapeutics over the past several decades, with a specific emphasis on the structural design and functionality of chemical modification strategies.

N. Uppuladinne M, Sarma PJ, Biswakarma N, Sonavane UB, Joshi RR, Ray SK, Namsa ND, Deka RC. Design of LNA Analogues Using a Combined Density Functional Theory and Molecular Dynamics Approach for RNA Therapeutics

Antisense therapeutics treat a wide spectrum of diseases, many of which cannot be addressed with the current drug technologies. In the quest to design better antisense oligonucleotide drugs, we propose five novel LNA analogues (A1-A5) for modifying antisense oligonucleotides and establishing each with the five standard nucleic acids: adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). Monomer nucleotides of these modifications were considered for a detailed Density Functional Theory (DFT)-based quantum chemical analysis to determine their molecular-level structural and electronic properties. A detailed MD simulation study was done on a 14-mer ASO (5'-CTTAGCACTGGCCT-3') containing these modifications targeting PTEN mRNA. Results from both molecular- and oligomer-level analysis clearly depicted LNA-level stability of the modifications, the ASO/RNA duplexes maintaining stable Watson-Crick base pairing preferring RNA-mimicking A-form duplexes. Notably, monomer MO isosurfaces for both purines and pyrimidines were majorly distributed on the nucleobase region in modifications A1 and A2 and in the bridging unit in modifications A3, A4, and A5, suggesting that A3/RNA, A4/RNA, and A5/RNA duplexes interact more with the RNase H and solvent environment. Accordingly, solvation of A3/RNA, A4/RNA, and A5/RNA duplexes was higher compared to that of LNA/RNA, A1/RNA, and A2/RNA duplexes. This study has resulted in a successful archetype for creating advantageous nucleic acid modifications tailored for particular needs, fulfilling a useful purpose of designing novel antisense modifications, which may overcome the drawbacks and improve the pharmacokinetics of existing LNA antisense modifications.

Nanotechnology-enabled gene delivery for cancer and other genetic diseases

INTRODUCTION

Despite gene therapy is ideal for genetic abnormality-related diseases, the easy degradation, poor targeting, and inefficiency in entering targeted cells are plaguing the effective delivery of gene therapy. Viral and non-viral vectors have been used for delivering gene therapeutics in vivo by safeguarding nucleic acid agents to target cells and to reach the specific intracellular location. A variety of nanotechnology-enabled safe and efficient systems have been successfully developed to improve the targeting ability for effective therapeutic delivery of genetic drugs.

AREAS COVERED

In this review, we outline the multiple biological barriers associated with gene delivery process, and highlight recent advances to gene therapy strategy in vivo, including gene correction, gene silencing, gene activation and genome editing. We point out current developments and challenges exist of non-viral and viral vector systems in association with chemical and physical gene delivery technologies and their potential for the future.

EXPERT OPINION

This review focuses on the opportunities and challenges to various gene therapy strategy, with specific emphasis on overcoming the challenges through the development of biocompatibility and smart gene vectors for potential clinical application.

A single-cell map of antisense oligonucleotide activity in the brain

Antisense oligonucleotides (ASOs) dosed into cerebrospinal fluid (CSF) distribute broadly throughout the brain and hold the promise of treating myriad brain diseases by modulating RNA. CNS tissue is not routinely biopsied in living individuals, leading to reliance on CSF biomarkers to inform on drug target engagement. Animal models can link CSF biomarkers to brain parenchyma, but our understanding of how individual cells contribute to bulk tissue signal is limited. Here we employed single nucleus transcriptomics on tissue from mice treated with RNase H1 ASOs against Prnp and Malat1 and macaques treated with an ASO against PRNP . Activity was observed in every cell type, though sometimes with substantial differences in magnitude. Single cell RNA count distributions implied target suppression in every single sequenced cell, rather than intense knockdown in only some cells. Duration of action up to 12 weeks post-dose differed across cell types, being shorter in microglia than in neurons. Suppression in neurons was generally similar to, or more robust than, the bulk tissue. In macaques, PrP in CSF was lowered 40% in conjunction with PRNP knockdown across all cell types including neurons, arguing that a CSF biomarker readout is likely to reflect disease-relevant cells in a neuronal disorder.

Modified Nucleotides for Chemical and Enzymatic Synthesis of Therapeutic RNA

In recent years, RNA has emerged as a medium with a broad spectrum of therapeutic potential, however, for years, a group of short RNA fragments was studied and considered therapeutic molecules. In nature, RNA plays both functions, with coding and non-coding potential. For RNA, like any other therapeutic, to be used clinically, certain barriers must be crossed. Among them, there are biocompatibility, relatively low toxicity, bioavailability, increased stability, target efficiency and low off-target effects. In the case of RNA, most of these obstacles can be overcome by incorporating modified nucleotides into its structure. This may be achieved by both, in vitro and in vivo biosynthetic methods, as well as chemical synthesis. Some advantages and disadvantages of each approach are summarized here. The wide range of nucleotide analogues has been tested for their utility as monomers for RNA synthesis. Many of them have been successfully implemented, and a lot of pre-clinical and clinical studies involving modified RNA have been carried out. Some of these medications have already been introduced into clinics. After the huge success of RNA-based vaccines that were introduced into widespread use in 2020, and the introduction to the market of some RNA-based drugs, RNA therapeutics containing modified nucleotides appear to be the future of medicine.

Parallel synthesis of oligonucleotides containing N-acyl amino-LNA and their therapeutic effects as anti-microRNAs

2'-Amino-locked nucleic acid (ALNA), maintains excellent duplex stability, and the nitrogen at the 2'-position is an attractive scaffold for functionalization. Herein, a facile and efficient method for the synthesis of various 2'-N-acyl amino-LNA derivatives by direct acylation of the 2'-amino moiety contained in the synthesized oligonucleotides and its fundamental properties are described. The introduction of the acylated amino-LNA enhances the potency of the molecules as therapeutic anti-microRNA oligonucleotides.

Influence of Sugar Modifications on the Nucleoside Conformation and Oligonucleotide Stability: A Critical Review

Ribofuranose sugar conformation plays an important role in the structure and dynamics of functional nucleic acids such as siRNAs, AONs, aptamers, miRNAs, etc. To improve their therapeutic potential, several chemical modifications have been introduced into the sugar moiety over the years. The stability of the oligonucleotide duplexes as well as the formation of stable and functional protein-oligonucleotide complexes are dictated by the conformation and dynamics of the sugar moiety. In this review, we systematically categorise various ribofuranose sugar modifications employed in DNAs and RNAs so far. We discuss different stereoelectronic effects imparted by different substituents on the sugar ring and how these effects control sugar puckering. Using this data, it would be possible to predict the precise use of chemical modifications and design novel sugar-modified nucleosides for therapeutic oligonucleotides that can improve their physicochemical properties.

Safety, tolerability, pharmacokinetics and preliminary antitumour activity of an antisense oligonucleotide targeting STAT3 (danvatirsen) as monotherapy and in combination with durvalumab in Japanese patients with advanced solid malignancies: a phase 1 study

OBJECTIVES

We assessed the safety, tolerability, pharmacokinetics, preliminary antitumour activity and pharmacodynamics of danvatirsen, an antisense oligonucleotide targeting signal transducer and activator of transcription 3 (STAT3), monotherapy and danvatirsen plus durvalumab, an antiprogrammed cell death ligand 1 monoclonal antibody, in patients with advanced solid malignancies.

DESIGN

Phase 1, open-label study with two cohorts.

SETTING

Two centres in Japan.

PARTICIPANTS

Japanese individuals aged ≥20 years, with histologically confirmed solid malignancies, except for hepatocellular carcinoma, refractory to standard therapy.

INTERVENTIONS

In cohort 1, patients received danvatirsen monotherapy; in cohort 2, patients received danvatirsen plus durvalumab combination therapy.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary endpoint was safety and tolerability based on adverse events (AEs). Secondary endpoints were pharmacokinetics, immunogenicity, antitumour activity and pharmacodynamics.

RESULTS

Eleven patients were assigned to treatment and included in the analysis. Danvatirsen dose reductions were only required in cohort 2 for hepatic function abnormal (alanine aminotransferase (ALT)/ aspartate aminotransferase (AST)/gamma-glutamyl transferase (γGT) increased), neutrophil count decreased and platelet count decreased. One patient experienced grade 3 ALT/AST increased and new appearance of eosinophilia as a dose-limiting toxicity. AEs were reported in 90.9% (10/11) patients. Commonly reported AEs causally related to the danvatirsen were platelet count decreased (60% (3/5)) and ALT/AST/γGT increased (50% (3/6)) in cohorts 1 and 2, respectively; none was causally related to durvalumab. One serious AE occurred in cohort 1 (pancreatitis; unrelated to study treatment). One case of ALT/AST/γGT increased occurred in cohort 2, leading to discontinuation. No AEs led to death. Danvatirsen did not accumulate in plasma after multiple dosing. In cohort 2, three patients had disease control at 12 weeks and one had unconfirmed partial response. STAT3 expression tended to decrease regardless of monotherapy or combination therapy.

CONCLUSIONS

Danvatirsen was well tolerated by Japanese patients with advanced solid tumours as monotherapy and combined with durvalumab. No new safety signals arose.

TRIAL REGISTRATION NUMBER

NCT03394144; ClinicalTrials.gov.

Generation of 4'-Carbon Radicals via 1,5-Hydrogen Atom Transfer for the Synthesis of Bridged Nucleosides

The rapid and facile generation of 4'-carbon radicals from oxime imidates of nucleosides via 1,5-hydrogen atom transfer induced by iminyl radicals was developed. The cyclization of 4'-carbon radicals with olefins, followed by the hydrolysis of imidate residues, provided various 2'-O,4'-C- and 3'-O,4'-C-bridged nucleosides. This operationally simple approach can be applied to the few-step syntheses of 6'S-methyl-2'-O,4'-C-ethylene-bridged 5-methyluridine (6'S-Me-ENA-T) and S-constrained ethyl-bridged 5-methyluridine (S-cEt-T).

Towards Personalized Allele-Specific Antisense Oligonucleotide Therapies for Toxic Gain-of-Function Neurodegenerative Diseases

Antisense oligonucleotides (ASOs) are single-stranded nucleic acid strings that can be used to selectively modify protein synthesis by binding complementary (pre-)mRNA sequences. By specific arrangements of DNA and RNA into a chain of nucleic acids and additional modifications of the backbone, sugar, and base, the specificity and functionality of the designed ASOs can be adjusted. Thereby cellular uptake, toxicity, and nuclease resistance, as well as binding affinity and specificity to its target (pre-)mRNA, can be modified. Several neurodegenerative diseases are caused by autosomal dominant toxic gain-of-function mutations, which lead to toxic protein products driving disease progression. ASOs targeting such mutations—or even more comprehensively, associated variants, such as single nucleotide polymorphisms (SNPs)—promise a selective degradation of the mutant (pre-)mRNA while sparing the wild type allele. By this approach, protein expression from the wild type strand is preserved, and side effects from an unselective knockdown of both alleles can be prevented. This makes allele-specific targeting strategies a focus for future personalized therapies. Here, we provide an overview of current strategies to develop personalized, allele-specific ASO therapies for the treatment of neurodegenerative diseases, such Huntington’s disease (HD) and spinocerebellar ataxia type 3 (SCA3/MJD).

OMA1 mediates local and global stress responses against protein misfolding in CHCHD10 mitochondrial myopathy

Mitochondrial stress triggers a response in the cell’s mitochondria and nucleus, but how these stress responses are coordinated in vivo is poorly understood. Here, we characterize a family with myopathy caused by a dominant p.G58R mutation in the mitochondrial protein CHCHD10. To understand the disease etiology, we developed a knockin (KI) mouse model and found that mutant CHCHD10 aggregated in affected tissues, applying a toxic protein stress to the inner mitochondrial membrane. Unexpectedly, the survival of CHCHD10-KI mice depended on a protective stress response mediated by the mitochondrial metalloendopeptidase OMA1. The OMA1 stress response acted both locally within mitochondria, causing mitochondrial fragmentation, and signaled outside the mitochondria, activating the integrated stress response through cleavage of DAP3-binding cell death enhancer 1 (DELE1). We additionally identified an isoform switch in the terminal complex of the electron transport chain as a component of this response. Our results demonstrate that OMA1 was critical for neonatal survival conditionally in the setting of inner mitochondrial membrane stress, coordinating local and global stress responses to reshape the mitochondrial network and proteome.

Prevention and regression of megamitochondria and steatosis by blocking mitochondrial fusion in the liver

Non-alcoholic steatohepatitis (NASH) is a most common chronic liver disease that is manifested by steatosis, inflammation, fibrosis, and tissue damage. Hepatocytes produce giant mitochondria termed megamitochondria in patients with NASH. It has been shown that gene knockout of OPA1, a mitochondrial dynamin-related GTPase that mediates mitochondrial fusion, prevents megamitochondria formation and liver damage in a NASH mouse model induced by a methionine-choline-deficient (MCD) diet. However, it is unknown whether blocking mitochondrial fusion mitigates NASH pathologies. Here, we acutely depleted OPA1 using antisense oligonucleotides in the NASH mouse model before or after megamitochondria formation. When OPA1 ASOs were applied at the disease onset, they effectively prevented megamitochondria formation and liver pathologies in the MCD model. Notably, even when applied after mice robustly developed NASH pathologies, OPA1 targeting effectively regressed megamitochondria and the disease phenotypes. Thus, our data show the efficacy of mitochondrial dynamics as a unique therapy for megamitochondria-associated liver disease.

Advances in siRNA therapeutics and synergistic effect on siRNA activity using emerging dual ribose modifications

Nucleic acid-based therapeutics that control gene expression have been steadily progressing towards achieving their full clinical potential throughout the last few decades. Rapid progress has been achieved in RNAi-based therapy by optimizing high specificity and gene silencing efficiency using chemically modified siRNAs. Since 2018, four siRNA drugs – patisiran, givosiran, lumasiran, and inclisiran, were approved by the US FDA, providing a testament to the promise of RNAi therapeutics. Despite these promising results, safe and efficient siRNA delivery at the target site remains a major obstacle for efficient siRNA-based therapeutics. In this review, we have outlined the synergistic effects of emerging dual ribose modifications, including 2’,4’- and 2’,5’-modifications, 5’-E/Z-vinylphosphonate, and northern methanocarbacyclic (NMC) modifications that have contributed to drug-like effects in siRNA. These modifications enhance nuclease stability, prolong gene silencing efficiency, improve thermal stability, and exhibit high tissue accumulation. We also highlight the current progress in siRNA clinical trials. This review will help to understand the potential effects of dual ribose modifications and provides alternative ways to use extensive 2’-modifications in siRNA drugs. Moreover, the minimal number of these dual ribose modifications could be sufficient to achieve the desired therapeutic effect. In future, detailed in vivo studies using these dual ribose modifications could help to improve the therapeutic effects of siRNA. Rational design could further open doors for the rapid progress in siRNA therapeutics.

Antisense Oligonucleotide Technologies to Combat Obesity and Fatty Liver Disease

Synthetic oligonucleotide technologies are DNA or RNA based molecular compounds that are utilized to disrupt gene transcription or translation in target tissues or cells. Optimally, oligonucleotides are 10–30 base pairs in length, and mediate target gene suppression through directed sequence homology with messenger RNA (mRNA), leading to mRNA degradation. Examples of specific oligonucleotide technologies include antisense oligonucleotides (ASO), short hairpin RNAs (shRNA), and small interfering RNAs (siRNA). In vitro and in vivo studies that model obesity related disorders have demonstrated that oligonucleotide technologies can be implemented to improve the metabolism of cells and tissues, exemplified by improvements in fat utilization and hepatic insulin signaling, respectively. Oligonucleotide therapy has also been associated with reductions in lipid accumulation in both the liver and adipose tissue in models of diet-induced obesity. Recent advances in oligonucleotide technologies include the addition of chemical modifications such as N-acetylgalactosamine (GalNAc) conjugates that have been successful at achieving affinity for the liver, in turn improving specificity, and thus reducing off target effects. However, some challenges are still yet to be overcome relating to hepatic injury and off-target effects that have been reported with some compounds, including ASOs. In summary, oligonucleotide-based therapies are an effective tool to elucidate mechanistic insights into metabolic pathways and provide an attractive avenue for translational research into the clinic.

Long Noncoding RNAs as Therapeutic Targets

Long noncoding RNAs (lncRNAs) have emerged as critical regulators of cellular functions including maintenance of cellular homeostasis as well as the onset and progression of disease. LncRNAs often exhibit cell-, tissue-, and disease-specific expression patterns, making them desirable therapeutic targets. LncRNAs are commonly targeted using oligonucleotide therapeutics, and advances in oligonucleotide chemistry including C2 ribose sugar modifications such as 2'-fluoro, 2'-O-methyl, and 2-O-methoxyethyl modifications; 2'4'-constrained nucleotides such as locked nucleic acids and constrained 2'-O-ethyl (cEt) nucleotides; and phosphorothioate bonds have dramatically improved efficacy of oligonucleotide therapies. Novel delivery platforms such as viral vectors and nanoparticles have also improved pharmacokinetic properties of oligonucleotides targeting lncRNAs. Accumulating pre-clinical studies have utilized these strategies to therapeutically target lncRNAs and alter progression of many different disease states including Snhg12 and Chast in cardiovascular disease, Mirt2 and HOTTIP in sepsis and autoimmune disease, and Malat1 and HOXB-AS3 in cancer. Emerging oligonucleotide conjugation methods including the use of peptide nucleic acids hold promise to facilitate targeting to specific tissue types. Here, we review recent advances in lncRNA therapeutics and provide examples of how lncRNAs have been successfully targeted in pre-clinical models of disease. Finally, we detail remaining challenges facing the lncRNA field and how advances in delivery platforms and oligonucleotide chemistry might help overcome these barriers to catalyze the translation of pre-clinical studies to successful pharmaceutical development.

Antisense Oligonucleotide-Mediated Silencing of Mitochondrial Fusion and Fission Factors Modulates Mitochondrial Dynamics and Rescues Mitochondrial Dysfunction

Mitochondria are highly dynamic organelles that produce ATP and maintain metabolic, catabolic, and redox homeostasis. Mitochondria owe this dynamic nature to their constant fission and fusion—processes that are regulated, in part, by fusion factors (MFN1 and MFN2) and fission factors (DRP1, FIS1, MFF, MIEF1, MIEF2) located on the outer mitochondrial membrane. While mitochondrial fusion and fission are known to influence mitochondrial morphology and function, a key question is whether rebalancing mitochondrial morphology can ameliorate mitochondrial dysfunction in the context of mitochondrial pathology. In this study, we used antisense oligonucleotides (ASOs) to systematically evaluate the effects of fusion and fission factors in vitro. Free uptake by cells of fusion or fission factor ASOs caused robust decreases in target gene expression and altered a variety of mitochondrial parameters, including mitochondrial size and respiration, which were dose dependent. In Mfn1 knockout mouse embryonic fibroblasts (MEFs) and MFN2-R94Q (Charcot-Marie-Tooth Type 2 Disease-associated mutation) MEFs, two cellular models of mitochondrial dysfunction, we found that ASO-mediated silencing of only Drp1 restored mitochondrial morphology and enhanced mitochondrial respiration. Together, these data demonstrate in vitro proof-of-concept for rebalancing mitochondrial morphology to rescue function using ASOs and suggest that ASO-mediated modulation of mitochondrial dynamics may be a viable therapeutic approach to restore mitochondrial homeostasis in diseases driven by mitochondrial dysfunction.

Evaluation of Phosphorus and Non-Phosphorus Neutral Oligonucleotide Backbones for Enhancing Therapeutic Index of Gapmer Antisense Oligonucleotides

The phosphorothioate (PS) linkage in an essential component of therapeutic oligonucleotides. PS in the DNA region of gapmer antisense oligonucleotides (ASOs) supports RNaseH1 activity and enhances nuclease stability. PS also promotes binding to plasma, cell surface, and intracellular proteins, which facilitates tissue distribution, cellular uptake, and endosomal escape of PS ASOs. We recently showed that site-specific replacement of PS in the DNA gap with methoxylpropyl phosphonate (MOP) linkages can enhance the therapeutic index of gapmer ASOs. In this article, we explored 18 phosphorus- and non-phosphorus-based neutral backbone modifications to determine the structure-activity relationship of neutral linkages for enhancing therapeutic index. Replacing MOP with other alkyl phosphonate and phosphotriester linkages enhanced therapeutic index, but these linkages were susceptible to chemical degradation during oligonucleotide deprotection from solid supports following synthesis. Replacing MOP with non-phosphorus linkages resulted in improved chemical stability, but these linkages were introduced into ASOs as nucleotide dimers, which limits their versatility. Overall, linkages such as isopropyl and isobutyl phosphonates and O-isopropyl and O-tetrahydrofuranosyl phosphotriesters, formacetal, and C3-amide showed improved activity in mice relative to MOP. Our data suggest that site-specific incorporation of any neutral backbone linkage can improve therapeutic index, but the size, hydrophobicity, and RNA-binding affinity of the linkage influence ASO activity.

Nucleic Acid Drugs-Current Status, Issues, and Expectations for Exosomes

Simple Summary

Nucleic acid drugs provide novel therapeutic modalities with characteristics that differ from those of small molecules and antibodies. In this review, I focus on the various mechanisms through which nucleic acid drugs act on, the status of their clinical development, and discuss several hurdles that need to be surmounted. In addition, by listing examples of how the progress in exosome biology can lead to the solution of problems in nucleic acid drug therapy, I hope that many more nucleic acid drugs including anticancer drugs will be developed in the future.

Abstract

Nucleic acid drugs are being developed as novel therapeutic modalities. They have great potential to treat human diseases such as cancers, viral infections, and genetic disorders due to unique characteristics that make it possible to approach undruggable targets using classical small molecule or protein/antibody-based biologics. In this review, I describe the advantages, classification, and clinical status of nucleic acid therapeutics. To date, more than 10 products have been launched, and many products have been tested in clinics. To promote the use of nucleic acid therapeutics such as antibodies, several hurdles need to be surmounted. The most important issue is the delivery of nucleic acids and several other challenges have been reported. Recent advanced delivery platforms are lipid nanoparticles and ligand conjugation approaches. With the progress of exosome biology, exosomes are expected to contribute to the solution of various problems associated with nucleic acid drugs.

Towards next generation antisense oligonucleotides: mesylphosphoramidate modification improves therapeutic index and duration of effect of gapmer antisense oligonucleotides

The PS modification enhances the nuclease stability and protein binding properties of gapmer antisense oligonucleotides (ASOs) and is one of very few modifications that support RNaseH1 activity. We evaluated the effect of introducing stereorandom and chiral mesyl-phosphoramidate (MsPA) linkages in the DNA gap and flanks of gapmer PS ASOs and characterized the effect of these linkages on RNA-binding, nuclease stability, protein binding, pro-inflammatory profile, antisense activity and toxicity in cells and in mice. We show that all PS linkages in a gapmer ASO can be replaced with MsPA without compromising chemical stability and RNA binding affinity but these designs reduced activity. However, replacing up to 5 PS in the gap with MsPA was well tolerated and replacing specific PS linkages at appropriate locations was able to greatly reduce both immune stimulation and cytotoxicity. The improved nuclease stability of MsPA over PS translated to significant improvement in the duration of ASO action in mice which was comparable to that of enhanced stabilized siRNA designs. Our work highlights the combination of PS and MsPA linkages as a next generation chemical platform for identifying ASO drugs with improved potency and therapeutic index, reduced pro-inflammatory effects and extended duration of effect.

A critical role of hepatic GABA in the metabolic dysfunction and hyperphagia of obesity

Hepatic lipid accumulation is a hallmark of type II diabetes (T2D) associated with hyperinsulinemia, insulin resistance, and hyperphagia. Hepatic synthesis of GABA, catalyzed by GABA-transaminase (GABA-T), is upregulated in obese mice. To assess the role of hepatic GABA production in obesity-induced metabolic and energy dysregulation, we treated mice with two pharmacologic GABA-T inhibitors and knocked down hepatic GABA-T expression using an antisense oligonucleotide. Hepatic GABA-T inhibition and knockdown decreased basal hyperinsulinemia and hyperglycemia and improved glucose intolerance. GABA-T knockdown improved insulin sensitivity assessed by hyperinsulinemic-euglycemic clamps in obese mice. Hepatic GABA-T knockdown also decreased food intake and induced weight loss without altering energy expenditure in obese mice. Data from people with obesity support the notion that hepatic GABA production and transport are associated with serum insulin, homeostatic model assessment for insulin resistance (HOMA-IR), T2D, and BMI. These results support a key role for hepatocyte GABA production in the dysfunctional glucoregulation and feeding behavior associated with obesity.

Vascular Endothelial Senescence: Pathobiological Insights, Emerging Long Noncoding RNA Targets, Challenges and Therapeutic Opportunities

Cellular senescence is a stable form of cell cycle arrest in response to various stressors. While it serves as an endogenous pro-resolving mechanism, detrimental effects ensue when it is dysregulated. In this review, we introduce recent advances for cellular senescence and inflammaging, the underlying mechanisms for the reduction of nicotinamide adenine dinucleotide in tissues during aging, new knowledge learned from p16 reporter mice, and the development of machine learning algorithms in cellular senescence. We focus on pathobiological insights underlying cellular senescence of the vascular endothelium, a critical interface between blood and all tissues. Common causes and hallmarks of endothelial senescence are highlighted as well as recent advances in endothelial senescence. The regulation of cellular senescence involves multiple mechanistic layers involving chromatin, DNA, RNA, and protein levels. New targets are discussed including the roles of long noncoding RNAs in regulating endothelial cellular senescence. Emerging small molecules are highlighted that have anti-aging or anti-senescence effects in age-related diseases and impact homeostatic control of the vascular endothelium. Lastly, challenges and future directions are discussed including heterogeneity of endothelial cells and endothelial senescence, senescent markers and detection of senescent endothelial cells, evolutionary differences for immune surveillance in mice and humans, and long noncoding RNAs as therapeutic targets in attenuating cellular senescence. Accumulating studies indicate that cellular senescence is reversible. A better understanding of endothelial cellular senescence through lifestyle and pharmacological interventions holds promise to foster a new frontier in the management of cardiovascular disease risk.

Diffuse Large B-Cell Lymphoma: Recognition of Markers for Targeted Therapy

Diffuse large B-cell lymphomas (DLBCL)s, the most common type of Non-Hodgkin’s Lymphoma, constitute a heterogeneous group of disorders including different disease sites, strikingly diverse molecular features and a profound variability in the clinical behavior. Molecular studies and clinical trials have partially revealed the underlying causes for this variability and have made possible the recognition of some molecular variants susceptible of specific therapeutic approaches. The main histogenetic groups include the germinal center, activated B cells, thymic B cells and terminally differentiated B cells, a basic scheme where the large majority of DLBCL cases can be ascribed. The nodal/extranodal origin, specific mutational changes and microenvironment peculiarities provide additional layers of complexity. Here, we summarize the status of the knowledge and make some specific proposals for addressing the future development of targeted therapy for DLBC cases.

Beyond ribose and phosphate: Selected nucleic acid modifications for structure-function investigations and therapeutic applications

Over the past 25 years, the acceleration of achievements in the development of oligonucleotide-based therapeutics has resulted in numerous new drugs making it to the market for the treatment of various diseases. Oligonucleotides with alterations to their scaffold, prepared with modified nucleosides and solid-phase synthesis, have yielded molecules with interesting biophysical properties that bind to their targets and are tolerated by the cellular machinery to elicit a therapeutic outcome. Structural techniques, such as crystallography, have provided insights to rationalize numerous properties including binding affinity, nuclease stability, and trends observed in the gene silencing. In this review, we discuss the chemistry, biophysical, and structural properties of a number of chemically modified oligonucleotides that have been explored for gene silencing.

Synthesis and properties of oligonucleotides modified with an N-methylguanidine-bridged nucleic acid (GuNA[Me]) bearing adenine, guanine, or 5-methylcytosine nucleobases

Chemical modifications have been extensively used for therapeutic oligonucleotides because they strongly enhance the stability against nucleases, binding affinity to the targets, and efficacy. We previously reported that oligonucleotides modified with an N-methylguanidine-bridged nucleic acid (GuNA[Me]) bearing the thymine (T) nucleobase show excellent biophysical properties for applications in antisense technology. In this paper, we describe the synthesis of GuNA[Me] phosphoramidites bearing other typical nucleobases including adenine (A), guanine (G), and 5-methylcytosine (^mC). The phosphoramidites were successfully incorporated into oligonucleotides following the method previously developed for the GuNA[Me]-T-modified oligonucleotides. The binding affinity of the oligonucleotides modified with GuNA[Me]-A, -G, or -^mC toward the complementary single-stranded DNAs or RNAs was systematically evaluated. All of the GuNA[Me]-modified oligonucleotides were found to have a strong affinity for RNAs. These data indicate that GuNA[Me] could be a useful modification for therapeutic antisense oligonucleotides.

siRNAs containing 2'-fluorinated Northern-methanocarbacyclic (2'-F-NMC) nucleotides: in vitro and in vivo RNAi activity and inability of mitochondrial polymerases to incorporate 2'-F-NMC NTPs

We recently reported the synthesis of 2'-fluorinated Northern-methanocarbacyclic (2'-F-NMC) nucleotides, which are based on a bicyclo[3.1.0]hexane scaffold. Here, we analyzed RNAi-mediated gene silencing activity in cell culture and demonstrated that a single incorporation of 2'-F-NMC within the guide or passenger strand of the tri-N-acetylgalactosamine-conjugated siRNA targeting mouse Ttr was generally well tolerated. Exceptions were incorporation of 2'-F-NMC into the guide strand at positions 1 and 2, which resulted in a loss of the in vitro activity. Activity at position 1 was recovered when the guide strand was modified with a 5' phosphate, suggesting that the 2'-F-NMC is a poor substrate for 5' kinases. In mice, the 2'-F-NMC-modified siRNAs had comparable RNAi potencies to the parent siRNA. 2'-F-NMC residues in the guide seed region position 7 and at positions 10, 11 and 12 were well tolerated. Surprisingly, when the 5'-phosphate mimic 5'-(E)-vinylphosphonate was attached to the 2'-F-NMC at the position 1 of the guide strand, activity was considerably reduced. The steric constraints of the bicyclic 2'-F-NMC may impair formation of hydrogen-bonding interactions between the vinylphosphonate and the MID domain of Ago2. Molecular modeling studies explain the position- and conformation-dependent RNAi-mediated gene silencing activity of 2'-F-NMC. Finally, the 5'-triphosphate of 2'-F-NMC is not a substrate for mitochondrial RNA and DNA polymerases, indicating that metabolites should not be toxic.

Glucagon Like Peptide 1 Receptor Agonists for Targeted Delivery of Antisense Oligonucleotides to Pancreatic Beta Cell

The extra hepatic delivery of antisense oligonucleotides (ASOs) remains a challenge and hampers the widespread application of this powerful class of therapeutic agents. In that regard, pancreatic beta cells are a particularly attractive but challenging cell type because of their pivotal role in diabetes and the fact that they are refractory to uptake of unconjugated ASOs. To circumvent this, we have expanded our understanding of the structure activity relationship of ASOs conjugated to Glucagon Like Peptide 1 Receptor (GLP1R) agonist peptide ligands. We demonstrate the key role of the linker chemistry and its optimization to design maleimide based conjugates with improved in vivo efficacy. In addition, truncation studies and scoping of a diverse set of GLP1R agonists proved fruitful to identify additional targeting ligands efficacious in vivo including native hGLP1(7-36)NH2. Variation of the carrier peptide also shed some light on the dramatic impact of subtle sequence differences on the corresponding ASO conjugate performance in vivo, an area which clearly warrant further investigations. We have confirmed the remarkable potential of GLP1R agonist conjugation for the delivery of ASOs to pancreatic beta cell by effectively knocking down islet amyloid polypeptide (IAPP) mRNA, a potential proapoptotic target, in mice.

α-Synuclein antisense oligonucleotides as a disease-modifying therapy for Parkinson's disease

Parkinson's disease (PD) is a prevalent neurodegenerative disease with no approved disease-modifying therapies. Multiplications, mutations, and single nucleotide polymorphisms in the SNCA gene, encoding α-synuclein (aSyn) protein, either cause or increase risk for PD. Intracellular accumulations of aSyn are pathological hallmarks of PD. Taken together, reduction of aSyn production may provide a disease-modifying therapy for PD. We show that antisense oligonucleotides (ASOs) reduce production of aSyn in rodent preformed fibril (PFF) models of PD. Reduced aSyn production leads to prevention and removal of established aSyn pathology and prevents dopaminergic cell dysfunction. In addition, we address the translational potential of the approach through characterization of human SNCA-targeting ASOs that efficiently suppress the human SNCA transcript in vivo. We demonstrate broad activity and distribution of the human SNCA ASOs throughout the nonhuman primate brain and a corresponding decrease in aSyn cerebral spinal fluid (CSF) levels. Taken together, these data suggest that, by inhibiting production of aSyn, it may be possible to reverse established pathology; thus, these data support the development of SNCA ASOs as a potential disease-modifying therapy for PD and related synucleinopathies.

Perspectives on the Designation of Oligonucleotide Starting Materials

The designation of starting materials (SMs) for pharmaceuticals has been a topic of great interest and debate since the first ICH quality guidance was published. The increase in the number and variety of commercialized oligonucleotides (antisense oligonucleotides—ASOs, small interfering RNAs—siRNAs, etc.) in recent years has reignited dialogue on this topic because of the unique complexity of the monomeric nucleotides and other contributory materials used to manufacture oligonucleotides. The SM working group in the European Pharma Oligonucleotide Consortium (EPOC) was formed to help establish simple, risk-based criteria to guide the justification of oligonucleotide SMs. This article provides a description of the common types of SMs, classes of SM impurities, and control strategies that will be helpful to maintain manufacturing consistency.

Solid-Phase Separation of Toxic Phosphorothioate Antisense Oligonucleotide-Protein Nucleolar Aggregates Is Cytoprotective

Phosphorothioate antisense oligonucleotides (PS-ASOs) interact with proteins and can localize to or induce the formation of a variety of subcellular PS-ASO-protein or PS-ASO-ribonucleoprotein aggregates. In this study, we show that these different aggregates that form with varying compositions at various concentrations in the cytosol, nucleus, and nucleolus may undergo phase separations in cells. Some aggregates can form with both nontoxic and toxic PS-ASOs, such as PS bodies, paraspeckles, and nuclear filaments. However, toxic PS-ASOs have been shown to form unique nucleolar aggregates that result in nucleolar dysfunction and apoptosis. These include liquid-like aggregates that we labeled "cloudy nucleoli" and solid-like perinucleolar filaments. Toxic nucleolar aggregates may undergo solid-phase separation and in the solid phase, protein mobility in and out of the aggregates is limited. Other aggregates appear to undergo liquid-phase separation, including paraspeckles and perinucleolar caps, in which protein mobility is negatively correlated with the binding affinity of the proteins to PS-ASOs. However, PS bodies and nuclear filaments are solid-like aggregates. Importantly, in cells that survived treatment with toxic PS-ASOs, solid-like PS-ASO aggregates accumulated, especially Hsc70-containing nucleolus-like structures, in which modest pre-rRNA transcriptional activity was retained and appeared to mitigate the nucleolar toxicity. This is the first demonstration that exogenous drugs, PS-ASOs, can form aggregates that undergo phase separations and that solid-phase separation of toxic PS-ASO-induced nucleolar aggregates is cytoprotective.

High-resolution visualization and quantification of nucleic acid-based therapeutics in cells and tissues using Nanoscale secondary ion mass spectrometry (NanoSIMS)

Nucleic acid therapeutics (NATs) have proven useful in promoting the degradation of specific transcripts, modifying gene expression, and regulating mRNA splicing. In each situation, efficient delivery of nucleic acids to cells, tissues and intracellular compartments is crucial—both for optimizing efficacy and reducing side effects. Despite successes in NATs, our understanding of their cellular uptake and distribution in tissues is limited. Current methods have yielded insights into distribution of NATs within cells and tissues, but the sensitivity and resolution of these approaches are limited. Here, we show that nanoscale secondary ion mass spectrometry (NanoSIMS) imaging can be used to define the distribution of 5-bromo-2′-deoxythymidine (5-BrdT) modified antisense oligonucleotides (ASO) in cells and tissues with high sensitivity and spatial resolution. This approach makes it possible to define ASO uptake and distribution in different subcellular compartments and to quantify the impact of targeting ligands designed to promote ASO uptake by cells. Our studies showed that phosphorothioate ASOs are associated with filopodia and the inner nuclear membrane in cultured cells, and also revealed substantial cellular and subcellular heterogeneity of ASO uptake in mouse tissues. NanoSIMS imaging represents a significant advance in visualizing uptake and distribution of NATs; this approach will be useful in optimizing efficacy and delivery of NATs for treating human disease.

Antisense Drugs Make Sense for Neurological Diseases

The genetic basis for most inherited neurodegenerative diseases has been identified, yet there are limited disease-modifying therapies for these patients. A new class of drugs-antisense oligonucleotides (ASOs)-show promise as a therapeutic platform for treating neurological diseases. ASOs are designed to bind to the RNAs either by promoting degradation of the targeted RNA or by elevating expression by RNA splicing. Intrathecal injection into the cerebral spinal fluid results in broad distribution of antisense drugs and long-term effects. Approval of nusinersen in 2016 demonstrated that effective treatments for neurodegenerative diseases can be identified and that treatments not only slow disease progression but also improve some symptoms. Antisense drugs are currently in development for amyotrophic lateral sclerosis, Huntington's disease, Alzheimer's disease, Parkinson's disease, and Angelman syndrome, and several drugs are in late-stage research for additional neurological diseases. This review highlights the advances in antisense technology as potential treatments for neurological diseases.

Recent progress in non-native nucleic acid modifications

While Nature harnesses RNA and DNA to store, read and write genetic information, the inherent programmability, synthetic accessibility and wide functionality of these nucleic acids make them attractive tools for use in a vast array of 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.

LRRK2 and Rab10 coordinate macropinocytosis to mediate immunological responses in phagocytes

Genetic variation in LRRK2 associates with the susceptibility to Parkinson's disease, Crohn's disease, and mycobacteria infection. High expression of LRRK2 and its substrate Rab10 occurs in phagocytic cells in the immune system. In mouse and human primary macrophages, dendritic cells, and microglia-like cells, we find that Rab10 specifically regulates a specialized form of endocytosis known as macropinocytosis, without affecting phagocytosis or clathrin-mediated endocytosis. LRRK2 phosphorylates cytoplasmic PI(3,4,5)P3-positive GTP-Rab10, before EEA1 and Rab5 recruitment to early macropinosomes occurs. Macropinosome cargo in macrophages includes CCR5, CD11b, and MHCII, and LRRK2-phosphorylation of Rab10 potently blocks EHBP1L1-mediated recycling tubules and cargo turnover. EHBP1L1 overexpression competitively inhibits LRRK2-phosphorylation of Rab10, mimicking the effects of LRRK2 kinase inhibition in promoting cargo recycling. Both Rab10 knockdown and LRRK2 kinase inhibition potently suppress the maturation of macropinosome-derived CCR5-loaded signaling endosomes that are critical for CCL5-induced immunological responses that include Akt activation and chemotaxis. These data support a novel signaling axis in the endolysosomal system whereby LRRK2-mediated Rab10 phosphorylation stalls vesicle fast recycling to promote PI3K-Akt immunological responses.

The Interaction of Phosphorothioate-Containing RNA Targeted Drugs with Proteins Is a Critical Determinant of the Therapeutic Effects of These Agents

Recent progress in understanding phosphorothioate antisense oligonucleotide (PS-ASO) interactions with proteins has revealed that proteins play deterministic roles in the absorption, distribution, cellular uptake, subcellular distribution, molecular mechanisms of action, and toxicity of PS-ASOs. Similarly, such interactions can alter the fates of many intracellular proteins. These and other advances have opened new avenues for the medicinal chemistry of PS-ASOs and research on all elements of the molecular pharmacology of these molecules. These advances have recently been reviewed. In this Perspective article, we summarize some of those learnings, the general principles that have emerged, and a few of the exciting new questions that can now be addressed.

Therapeutic siRNA: state of the art

RNA interference (RNAi) is an ancient biological mechanism used to defend against external invasion. It theoretically can silence any disease-related genes in a sequence-specific manner, making small interfering RNA (siRNA) a promising therapeutic modality. After a two-decade journey from its discovery, two approvals of siRNA therapeutics, ONPATTRO® (patisiran) and GIVLAARI™ (givosiran), have been achieved by Alnylam Pharmaceuticals. Reviewing the long-term pharmaceutical history of human beings, siRNA therapy currently has set up an extraordinary milestone, as it has already changed and will continue to change the treatment and management of human diseases. It can be administered quarterly, even twice-yearly, to achieve therapeutic effects, which is not the case for small molecules and antibodies. The drug development process was extremely hard, aiming to surmount complex obstacles, such as how to efficiently and safely deliver siRNAs to desired tissues and cells and how to enhance the performance of siRNAs with respect to their activity, stability, specificity and potential off-target effects. In this review, the evolution of siRNA chemical modifications and their biomedical performance are comprehensively reviewed. All clinically explored and commercialized siRNA delivery platforms, including the GalNAc (N-acetylgalactosamine)-siRNA conjugate, and their fundamental design principles are thoroughly discussed. The latest progress in siRNA therapeutic development is also summarized. This review provides a comprehensive view and roadmap for general readers working in the field.

A novel and translational role for autophagy in antisense oligonucleotide trafficking and activity

Endocytosis is a mechanism by which cells sense their environment and internalize various nutrients, growth factors and signaling molecules. This process initiates at the plasma membrane, converges with autophagy, and terminates at the lysosome. It is well-established that cellular uptake of antisense oligonucleotides (ASOs) proceeds through the endocytic pathway; however, only a small fraction escapes endosomal trafficking while the majority are rendered inactive in the lysosome. Since these pathways converge and share common molecular machinery, it is unclear if autophagy-related trafficking participates in ASO uptake or whether modulation of autophagy affects ASO activity and localization. To address these questions, we investigated the effects of autophagy modulation on ASO activity in cells and mice. We found that enhancing autophagy through small-molecule mTOR inhibition, serum-starvation/fasting, and ketogenic diet, increased ASO-mediated target reduction in vitro and in vivo. Additionally, autophagy activation enhanced the localization of ASOs into autophagosomes without altering intracellular concentrations or trafficking to other compartments. These results support a novel role for autophagy and the autophagosome as a previously unidentified compartment that participates in and contributes to enhanced ASO activity. Further, we demonstrate non-chemical methods to enhance autophagy and subsequent ASO activity using translatable approaches such as fasting or ketogenic diet.

Chemical Synthesis and Biological Application of Modified Oligonucleotides

RNA plays a myriad of roles in the body including the coding, decoding, regulation, and expression of genes. RNA oligonucleotides have garnered significant interest as therapeutics via antisense oligonucleotides or small interfering RNA strategies for the treatment of diseases ranging from hyperlipidemia, HCV, and others. Additionally, the recently developed CRISPR-Cas9 mediated gene editing strategy also relies on Cas9-associated RNA strands. However, RNA presents numerous challenges as both a synthetic target and a potential therapeutic. RNA is inherently unstable, difficult to deliver into cells, and potentially immunogenic by itself or upon modification. Despite these challenges, with the help of chemically modified oligonucleotides, multiple RNA-based drugs have been approved by the FDA. The progress is made possible due to the nature of chemically modified oligonucleotides bearing advantages of nuclease stability, stronger binding affinity, and some other unique properties. This review will focus on the chemical synthesis of RNA and its modified versions. How chemical modifications of the ribose units and of the phosphatediester backbone address the inherent issues with using native RNA for biological applications will be discussed along the way.