Disposition and Pharmacology of a GalNAc3-conjugated ASO Targeting Human Lipoprotein (a) in Mice

New insights into the therapeutic options to lower lipoprotein(a)

BACKGROUND

Elevated levels of lipoprotein(a) [Lp(a)] represent a risk factor for cardiovascular disease including aortic valve stenosis, myocardial infarction and stroke. While the patho-physiological mechanisms linking Lp(a) with atherosclerosis are not fully understood, from genetic studies that lower Lp(a) levels protect from CVD independently of other risk factors including lipids and lipoproteins. Hereby, Lp(a) has been considered an appealing pharmacological target.

RESULTS

However, approved lipid lowering therapies such as statins, ezetimibe or PCSK9 inhibitors have a neutral to modest effect on Lp(a) levels, thus prompting the development of new strategies selectively targeting Lp(a). These include antisense oligonucleotides and small interfering RNAs (siRNAs) directed towards apolipoprotein(a) [Apo(a)], which are in advanced phase of clinical development. More recently, additional approaches including inhibitors of Apo(a) and gene editing approaches via CRISPR-Cas9 technology entered early clinical development.

CONCLUSION

If the results from the cardiovascular outcome trials, designed to demonstrate whether the reduction of Lp(a) of more than 80% as observed with pelacarsen, olpasiran or lepodisiran translates into the decrease of cardiovascular mortality and major adverse cardiovascular events, will be positive, lowering Lp(a) will become a new additional target in the management of patients with elevated cardiovascular risk.

New approaches to triglyceride reduction: Is there any hope left?

Triglycerides play a crucial role in the efficient storage of energy in the body. Mild and moderate hypertriglyceridemia (HTG) is a heterogeneous disorder with significant association with atherosclerotic cardiovascular disease (ASCVD), including myocardial infarction, ischemic stroke, and peripheral artery disease and represents an important component of the residual ASCVD risk in statin treated patients despite optimal low-density lipoprotein cholesterol reduction. Individuals with severe HTG (>1,000 mg/dL) rarely develop atherosclerosis but have an incremental incidence of acute pancreatitis with significant morbidity and mortality. HTG can occur from a combination of genetic (both mono and polygenic) and environmental factors including poor diet, low physical activity, obesity, medications, and diseases like insulin resistance and other endocrine pathologies. HTG represents a potential target for ASCVD risk and pancreatitis risk reduction, however data on ASCVD reduction by treating HTG is still lacking and HTG-associated acute pancreatitis occurs too rarely to effectively demonstrate treatment benefit. In this review, we address the key aspects of HTG pathophysiology and examine the mechanisms and background of current and emerging therapies in the management of HTG.

siRNA as potential therapeutic strategy for hypertension

Hypertension, a well-known cardiovascular disorder noticed by rise in blood pressure, poses a significant global health challenge. The development RNA interfering (RNAi)-based therapies offers a ground-breaking molecular tool, holds promise for addressing hypertension's intricate molecular mechanisms. Harnessing the power of small interfering RNA (siRNA), researchers aim to selectively target and modulate genes associated with hypertension. Furthermore, they aim to downregulate the levels of mRNA by activating cellular nucleases in response to sequence homology between the siRNA and the corresponding mRNA molecule. As a result, genes involved in the cause of disorders linked to a known genetic background can be silenced using siRNA strategy. In the realm of hypertension, siRNA therapy emerges as a potential therapy for prognostics, diagnostics and treatments. It plays an important role in execution of targeting suppression of genes involved in vascular tone regulation, sodium handling, and pathways contributing to high blood pressure. A clinical trial involving intervention like angiotensinogen siRNA (AGT siRNA) is currently being carried out to treat hypertension. Genetic correlations between uromodulin (UMOD) and hypertension are investigated as emerging Non AGT siRNA target. Furthermore, expression of UMOD is responsible for regulation of sodium by modulating the tumor necrosis factor-α and regulating the Na + -K + -2Cl-cotransporter (NKCC2) in the thick ascending limb, which makes it an important target for blood pressure regulation.

A splice-switching oligonucleotide treatment ameliorates glycogen storage disease type 1a in mice with G6PC c.648G>T

Glycogen storage disease type 1a (GSD1a) is caused by a congenital deficiency of glucose-6-phosphatase-α (G6Pase-α, encoded by G6PC), which is primarily associated with life-threatening hypoglycemia. Although strict dietary management substantially improves life expectancy, patients still experience intermittent hypoglycemia and develop hepatic complications. Emerging therapies utilizing new modalities such as adeno-associated virus and mRNA with lipid nanoparticles are under development for GSD1a but potentially require complicated glycemic management throughout life. Here, we present an oligonucleotide-based therapy to produce intact G6Pase-α from a pathogenic human variant, G6PC c.648G>T, the most prevalent variant in East Asia causing aberrant splicing of G6PC. DS-4108b, a splice-switching oligonucleotide, was designed to correct this aberrant splicing, especially in liver. We generated a mouse strain with homozygous knockin of this variant that well reflected the pathophysiology of patients with GSD1a. DS-4108b recovered hepatic G6Pase activity through splicing correction and prevented hypoglycemia and various hepatic abnormalities in the mice. Moreover, DS-4108b had long-lasting efficacy of more than 12 weeks in mice that received a single dose and had favorable pharmacokinetics and tolerability in mice and monkeys. These findings together indicate that this oligonucleotide-based therapy could provide a sustainable and curative therapeutic option under easy disease management for GSD1a patients with G6PC c.648G>T.

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.

Enhancing the Effectiveness of Oligonucleotide Therapeutics Using Cell-Penetrating Peptide Conjugation, Chemical Modification, and Carrier-Based Delivery Strategies

Oligonucleotide-based therapies are a promising approach for treating a wide range of hard-to-treat diseases, particularly genetic and rare diseases. These therapies involve the use of short synthetic sequences of DNA or RNA that can modulate gene expression or inhibit proteins through various mechanisms. Despite the potential of these therapies, a significant barrier to their widespread use is the difficulty in ensuring their uptake by target cells/tissues. Strategies to overcome this challenge include cell-penetrating peptide conjugation, chemical modification, nanoparticle formulation, and the use of endogenous vesicles, spherical nucleic acids, and smart material-based delivery vehicles. This article provides an overview of these strategies and their potential for the efficient delivery of oligonucleotide drugs, as well as the safety and toxicity considerations, regulatory requirements, and challenges in translating these therapies from the laboratory to the clinic.

Assessment of the Effect of Organ Impairment on the Pharmacokinetics of 2'-MOE and Phosphorothioate Modified Antisense Oligonucleotides

The pharmacokinetics (PK) of 2'-O-methoxyethyl and phosphorothioate antisense oligonucleotides (ASOs), with or without N-acetyl galactosamine conjugation, have been well characterized following subcutaneous or intravenous drug administration. However, the effect of organ impairment on ASO PK, primarily hepatic or renal impairment, has not yet been reported. ASOs distribute extensively to the liver and kidneys, where they are metabolized slowly by endo- and exonucleases, with minimal renal excretion as parent drug (<1%-3%). This short review evaluated the effect of organ impairment on ASO PK using 3 case studies: (1) a phase 1 renal impairment study evaluating a N-acetyl galactosamine-conjugated ASO in healthy study participants and study participants with moderate renal impairment, (2) a phase 2 study evaluating an unconjugated ASO in patients with end-stage renal disease; and (3) a phase 3 study evaluating an unconjugated ASO, which included patients with mild hepatic or renal impairment. Results showed that patients with end-stage renal disease had a mild increase (≈34%) in total plasma exposure, whereas mild or moderate renal impairment showed no effect on plasma PK. The effect of hepatic impairment on ASO PK could not be fully evaluated due to lack of data in moderate and severe hepatic impairment study participants. Nonetheless, available data suggest that mild hepatic impairment had no effect on ASO exposure.

Clinical Pharmacokinetics of Approved RNA Therapeutics

RNA-mediated drugs are a rapidly growing class of therapeutics. Over the last five years, the list of FDA-approved RNA therapeutics has expanded owing to their unique targets and prolonged pharmacological effects. Their absorption, distribution, metabolism, and excretion (ADME) have important clinical im-plications, but their pharmacokinetic properties have not been fully understood. Most RNA therapeutics have structural modifications to prevent rapid elimination from the plasma and are administered intravenously or subcutaneously, with some exceptions, for effective distribution to target organs. Distribution of drugs into tissues depends on the addition of a moiety that can be transported to the target and RNA therapeutics show a low volume of distribution because of their molecular size and negatively-charged backbone. Nucleases metabolize RNA therapeutics to a shortened chain, but their metabolic ratio is relatively low. Therefore, most RNA therapeutics are excreted in their intact form. This review covers not only ADME features but also clinical pharmacology data of the RNA therapeutics such as drug-drug interaction or population pharmacokinetic analyses. As the market of RNA therapeutics is expected to rapidly expand, comprehensive knowledge will contribute to interpreting and evaluating the pharmacological properties.

Integrated Assessment of Phase 2 Data on GalNAc3-Conjugated 2'-O-Methoxyethyl-Modified Antisense Oligonucleotides

Receptor-mediated delivery of an antisense oligonucleotide (ASO) using the ligand-conjugated antisense technology is establishing a new benchmark for antisense therapeutics. The triantennary N-acetylgalactosamine (GalNAc3) cluster is the first conjugated ligand to yield a marked increase in ASO potency for RNA targets expressed by hepatocytes, compared to the unconjugated form. In this study, we present an integrated safety assessment of data available from randomized, placebo-controlled, phase 2 studies for six GalNAc3-conjugated 2'-O-methoxyethyl (2'MOE)-modified ASOs. The total study population included 642 participants (130 placebo; 512 ASO) with up to 1 year of exposure. The primary measures were the incidence of signals from standardized laboratory tests and the mean test results over time. The GalNAc3-conjugated ASOs were well tolerated with no class effect identified across all doses tested compared to placebo. These results extend prior observations from phase 1 studies, now with treatment up to 1 year.

Recent Progress and Challenges in the Development of Antisense Therapies for Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is a dominant genetic disease in which the expansion of long CTG trinucleotides in the 3' UTR of the myotonic dystrophy protein kinase (DMPK) gene results in toxic RNA gain-of-function and gene mis-splicing affecting mainly the muscles, the heart, and the brain. The CUG-expanded transcripts are a suitable target for the development of antisense oligonucleotide (ASO) therapies. Various chemical modifications of the sugar-phosphate backbone have been reported to significantly enhance the affinity of ASOs for RNA and their resistance to nucleases, making it possible to reverse DM1-like symptoms following systemic administration in different transgenic mouse models. However, specific tissue delivery remains to be improved to achieve significant clinical outcomes in humans. Several strategies, including ASO conjugation to cell-penetrating peptides, fatty acids, or monoclonal antibodies, have recently been shown to improve potency in muscle and cardiac tissues in mice. Moreover, intrathecal administration of ASOs may be an advantageous complementary administration route to bypass the blood-brain barrier and correct defects of the central nervous system in DM1. This review describes the evolution of the chemical design of antisense oligonucleotides targeting CUG-expanded mRNAs and how recent advances in the field may be game-changing by forwarding laboratory findings into clinical research and treatments for DM1 and other microsatellite diseases.

Elevated Lipoprotein(a) Linked to Recurrent Cardiovascular Events – A Case Report

The role of lipoprotein(a) [Lp(a)] in the development of atherosclerosis has been recently recognized, and the current recommendation is to measure Lp(a) once in a lifetime in all individuals, in order to identify those at risk for developing an acute coronary syndrome or recurrent events, even in the absence of other cardiovascular risk factors. We present the case of a middle-aged patient with recurrent cardiovascular events, in whom we identified high levels of Lp(a) as a possible explanation of the recurrent events.

Beyond GalNAc! Drug delivery systems comprising complex oligosaccharides for targeted use of nucleic acid therapeutics

Nucleic Acid Therapeutics (NATs) are establishing a leading role for the management and treatment of genetic diseases following FDA approval of nusinersen, patisiran, and givosiran in the last 5 years, the breakthrough of milasen, with more approvals undoubtedly on the way. Givosiran takes advantage of the known interaction between the hepatocyte specific asialoglycoprotein receptor (ASGPR) and N-acetyl galactosamine (GalNAc) ligands to deliver a therapeutic effect, underscoring the value of targeting moieties. In this review, we explore the history of GalNAc as a ligand, and the paradigm it has set for the delivery of NATs through precise targeting to the liver, overcoming common hindrances faced with this type of therapy. We describe various complex oligosaccharides (OSs) and ask what others could be used to target receptors for NAT delivery and the opportunities awaiting exploration of this chemical space.

The development and improvement of ribonucleic acid therapy strategies

The biological understanding of RNA has evolved since the discovery of catalytic RNAs in the early 1980s and the establishment of RNA interference (RNAi) in the 1990s. RNA is no longer seen as the simple mid-product between transcription and translation but as potential molecules to be developed as RNA therapeutic drugs. RNA-based therapeutic drugs have gained recognition because of their ability to regulate gene expression and perform cellular functions. Various nucleobase, backbone, and sugar-modified oligonucleotides have been synthesized, as natural oligonucleotides have some limitations such as poor low nuclease resistance, binding affinity, poor cellular uptake, and toxicity, which affect their use as RNA therapeutic drugs. In this review, we briefly discuss different RNA therapeutic drugs and their internal connections, including antisense oligonucleotides, small interfering RNAs (siRNAs) and microRNAs (miRNAs), aptamers, small activating RNAs (saRNAs), and RNA vaccines. We also discuss the important roles of RNA vaccines and their use in the fight against COVID-19. In addition, various chemical modifications and delivery systems used to improve the performance of RNA therapeutic drugs and overcome their limitations are discussed.

Programmed Instability of Ligand Conjugation Manifold for Efficient Hepatocyte Delivery of Therapeutic Oligonucleotides

Ligand-targeted drug delivery (LTDD) has gained more attention in the field of nucleic acid therapeutics. To further elicit the potential of therapeutic oligonucleotides by means of LTDD, we newly developed (R)- and (S)-3-amino-1,2-propanediol (APD) manifold for ligand conjugation. N-acetylgalactosamine (GalNAc)/asialoglycoprotein receptor (ASGPr) system has been shown to be a powerful and robust paradigm of LTDD. Our novel APD-based GalNAc (GalNAc_APD) was shown to have intrinsic chemical instability that could play a role in better manipulation of active drug release. The APD manifold also enables facile production of conjugates through an on-support ligand cluster synthesis. We showed in a series of in vivo studies that while the knockdown activity of antisense oligonucleotides (ASOs) bearing 5'-GalNAc_APD was comparable to the conventional hydroxy-L-prolinol-linked GalNAc (GalNAc_HP), 3'-GalNAc_APD elicited ASO activity by more than twice as much as the conventional 3'-GalNAc_HP. This was ascribed partly to the GalNAc_APD's ideal susceptibility to nucleolytic digestion, which is expected to facilitate cytosolic internalization of ASO drugs. Moreover, an in vivo/ex vivo imaging study visualized the enhancement effect of monoantennary GalNAc_APD on liver localization of ASOs. This versatile manifold with chemical and biological instability would benefit therapeutic oligonucleotides that target both the liver and extrahepatic tissues.

Silencing of ceramide synthase 2 in hepatocytes modulates plasma ceramide biomarkers predictive of cardiovascular death

Emerging clinical data show that three ceramide molecules, Cer d18:1/16:0, Cer d18:1/24:1, and Cer d18:1/24:0, are biomarkers of a fatal outcome in patients with cardiovascular disease. This finding raises basic questions about their metabolic origin, their contribution to disease pathogenesis, and the utility of targeting the underlying enzymatic machinery for treatment of cardiometabolic disorders. Here, we outline the development of a potent N-acetylgalactosamine-conjugated antisense oligonucleotide engineered to silence ceramide synthase 2 specifically in hepatocytes in vivo. We demonstrate that this compound reduces the ceramide synthase 2 mRNA level and that this translates into efficient lowering of protein expression and activity as well as Cer d18:1/24:1 and Cer d18:1/24:0 levels in liver. Intriguingly, we discover that the hepatocyte-specific antisense oligonucleotide also triggers a parallel modulation of blood plasma ceramides, revealing that the biomarkers predictive of cardiovascular death are governed by ceramide biosynthesis in hepatocytes. Our work showcases a generic therapeutic framework for targeting components of the ceramide enzymatic machinery to disentangle their roles in disease causality and to explore their utility for treatment of cardiometabolic disorders.

Lipids and Lipoproteins in Health and Disease: Focus on Targeting Atherosclerosis

Despite advances in pharmacotherapy, intervention devices and techniques, residual cardiovascular risks still cause a large burden on public health. Whilst most guidelines encourage achieving target levels of specific lipids and lipoproteins to reduce these risks, increasing evidence has shown that molecular modification of these lipoproteins also has a critical impact on their atherogenicity. Modification of low-density lipoprotein (LDL) by oxidation, glycation, peroxidation, apolipoprotein C-III adhesion, and the small dense subtype largely augment its atherogenicity. Post-translational modification by oxidation, carbamylation, glycation, and imbalance of molecular components can reduce the capacity of high-density lipoprotein (HDL) for reverse cholesterol transport. Elevated levels of triglycerides (TGs), apolipoprotein C-III and lipoprotein(a), and a decreased level of apolipoprotein A-I are closely associated with atherosclerotic cardiovascular disease. Pharmacotherapies aimed at reducing TGs, lipoprotein(a), and apolipoprotein C-III, and enhancing apolipoprotein A-1 are undergoing trials, and promising preliminary results have been reported. In this review, we aim to update the evidence on modifications of major lipid and lipoprotein components, including LDL, HDL, TG, apolipoprotein, and lipoprotein(a). We also discuss examples of translating findings from basic research to potential therapeutic targets for drug development.

Lipoprotein(a) Where Do We Stand? From the Physiopathology to Innovative Terapy

A number of epidemiologic studies have demonstrated a strong association between increasing lipoprotein a [Lp(a)] and cardiovascular disease. This correlation was demonstrated independent of other known cardiovascular (CV) risk factors. Screening for Lp(a) in the general population is not recommended, although Lp(a) levels are predominantly genetically determined so a single assessment is needed to identify patients at risk. In 2019 ESC/EAS guidelines recommend Lp(a) measurement at least once a lifetime, fo subjects at very high and high CV risk and those with a family history of premature cardiovascular disease, to reclassify patients with borderline risk. As concerning medications, statins play a key role in lipid lowering therapy, but present poor efficacy on Lp(a) levels. Actually, treatment options for elevated serum levels of Lp(a) are very limited. Apheresis is the most effective and well tolerated treatment in patients with high levels of Lp(a). However, promising new therapies, in particular antisense oligonucleotides have showed to be able to significantly reduce Lp(a) in phase II RCT. This review provides an overview of the biology and epidemiology of Lp(a), with a view to future therapies.

Liver-Targeted Delivery of Oligonucleotides with N-Acetylgalactosamine Conjugation

The potential therapeutic application of oligonucleotides (ONs) that selectively suppress target genes through antisense and RNA interference mechanisms has attracted great attention. The clinical applications of ONs have overcome multiple obstacles and become one of the most active areas for the development of novel therapeutics. To achieve efficient and specific cellular internalization, conjugation of a variety of functional groups to ONs has been the subject of intensive investigations over the past decade. Among them, a promising liver-targeted N-acetylgalactosamine (GalNAc) ligand has been evaluated in multiple preclinical and clinical trials for improving the cellular uptake and tissue specific delivery of ONs. GalNAc-based delivery relies on the fact that liver hepatocytes abundantly and specifically express the asialoglycoprotein receptor that binds and uptakes circulating glycoproteins via receptor-mediated endocytosis. In recent years, encouraging progress has been made in the field of GalNAc conjugates. This review aims to provide an overview of GalNAc-mediated liver-targeted delivery of small interfering RNA and antisense oligonucleotides, and the immense effort as well as recent advances in the development of GalNAc-conjugated agents are described.

iRGD-liposomes enhance tumor delivery and therapeutic efficacy of antisense oligonucleotide drugs against primary prostate cancer and bone metastasis

Nucleotide-based drugs, such as antisense oligonucleotides (ASOs), have unique advantages in treating human diseases as they provide virtually unlimited ability to target any gene. However, their clinical translation faces many challenges, one of which is poor delivery to the target tissue in vivo. This problem is particularly evident in solid tumors. Here, we functionalized liposomes with a tumor-homing and -penetrating peptide, iRGD, as a carrier of an ASO against androgen receptor (AR) for prostate cancer treatment. The iRGD-liposomes exhibited a high loading efficiency of AR-ASO, and an efficient knockdown of AR gene products was achieved in vitro, including AR splice variants. In vivo, iRGD-liposomes significantly increased AR-ASO accumulation in the tumor tissue and decreased AR expression relative to free ASOs in prostate tumors established as subcutaneous xenografts. Similar results were obtained with intra-tibial xenografts modeling metastasis to bones, the predominant site of metastasis for prostate cancer. In treatment studies, iRGD-liposomes markedly improved the AR-ASO efficacy in suppressing the growth of both subcutaneous xenografts and intra-tibial xenografts. The inhibitory effect on tumor growth was also significantly prolonged by the delivery of the AR-ASO in the iRGD-liposomes. Meanwhile, iRGD-liposomes did not increase ASO accumulation or toxicity in healthy organs. Overall, we provide here a delivery system that can significantly increase ASO accumulation and efficacy in solid tumors. These benefits are achieved without significant side effects, providing a way to increase the antitumor efficacy of ASOs.

An Overview of RNA-Based Scaffolds for Osteogenesis

Tissue engineering provides new hope for the combination of cells, scaffolds, and bifactors for bone osteogenesis. This is achieved by mimicking the bone's natural behavior in recruiting the cell's molecular machinery for our use. Many researchers have focused on developing an ideal scaffold with specific features, such as good cellular adhesion, cell proliferation, differentiation, host integration, and load bearing. Various types of coating materials (organic and non-organic) have been used to enhance bone osteogenesis. In the last few years, RNA-mediated gene therapy has captured attention as a new tool for bone regeneration. In this review, we discuss the use of RNA molecules in coating and delivery, including messenger RNA (mRNA), RNA interference (RNAi), and long non-coding RNA (lncRNA) on different types of scaffolds (such as polymers, ceramics, and metals) in osteogenesis research. In addition, the effect of using gene-editing tools-particularly CRISPR systems-to guide RNA scaffolds in bone regeneration is also discussed. Given existing knowledge about various RNAs coating/expression may help to understand the process of bone formation on the scaffolds during osseointegration.

Ligand conjugate SAR and enhanced delivery in NHP

N-Acetylgalactosamine (GalNAc) conjugated short interfering RNAs (siRNAs) are a leading RNA interference (RNAi) platform allowing targeted inhibition of disease-causing genes in hepatocytes. More than a decade of development has recently resulted in the first approvals for this class of drugs. While substantial effort has been made to improve nucleic acid modification patterns for better payload stability and efficacy, relatively little attention has been given to the GalNAc targeting ligand. In addition, the lack of an intrinsic endosomal release mechanism has limited potency. Here, we report a stepwise analysis of the structure activity relationships (SAR) of the components comprising these targeting ligands. We show that there is relatively little difference in biological performance between bi-, tri-, and tetravalent ligand structures while identifying other features that affect their biological activity more significantly. Further, we demonstrate that subcutaneous co-administration of a GalNAc-functionalized, pH responsive endosomal release agent markedly improved the activity and duration of effect for siRNA conjugates, without compromising tolerability, in non-human primates. These findings could address a significant bottleneck for future siRNA ligand conjugate development.

Syntheses of Morpholine-Based Nucleotide Analogs for Hepatic siRNA Targeting and Stabilization

A morpholine-based nucleotide analog was developed as a building block for hepatic siRNA targeting and stabilization. Attachment of an asialoglycoprotein-binding GalNAc ligand at the morpholine nitrogen was realized with different linkers. The obtained morpholino GalNAc scaffolds were coupled to the sense strand of a transthyretin-targeting siRNA and tested for their knockdown potency in vitro and in vivo. A clear structure-activity relationship was developed with regard to the linker type and length as well as the attachment site of the morpholino GalNAc moieties at the siRNA sense strand. Further, simple alkylation of the morpholine nitrogen led to a nucleotide analog, which increased siRNA stability, when used as a double 3'-overhang at the sense strand sequence. Combination of the best morpholino GalNAc building blocks as targeting nucleotides with an optimized stabilizing alkyl-substituted morpholine as 3'-overhangs resulted in siRNAs without any phosphorothioate stabilization in the sense strand and clearly improved the duration of action in vivo.

Distribution and biotransformation of therapeutic antisense oligonucleotides and conjugates

Drug properties of antisense oligonucleotides (ASOs) differ significantly from those of traditional small-molecule therapeutics. In this review, we focus on ASO disposition, mainly as characterized by distribution and biotransformation, of nonconjugated and conjugated ASOs. We introduce ASO chemistry to allow the following in-depth discussion on bioanalytical methods and determination of distribution and elimination kinetics at low concentrations over extended periods of time. The resulting quantitative data on the parent oligonucleotide, and the identification and quantification of formed metabolites define the disposition. Proper quantitative understanding of disposition is pivotal for nonclinical to clinical predictions, supports communication with health agencies, and increases the probability of delivering optimal ASO therapy to patients.

DNA-RNA Heteroduplex Oligonucleotide for Highly Efficient Gene Silencing

Heteroduplex oligonucleotides (HDOs) were a novel type of nucleic acid drugs based on an antisense oligonucleotide (ASO) strand and its complementary RNA (cRNA ) strand. HDOs were originally designed to improve the properties of RNase H-dependent ASOs and we reported in our first paper that HDOs conjugated with an α-tocopherol ligand (Toc-HDO ) based on a gapmer ASO showed 20 times higher silencing effect to liver apolipoprotein B (apoB) mRNA in vivo than the parent ASO. Thereafter the HDO strategy was found to be also effective for improving the properties of ASOs modulating blood-brain barrier function and ASO antimiRs which are RNase H-independent ASOs. Therefore, the HDO strategy has been shown to be versatile technology platform to develop effective nucleic acid drugs.

Recent Progress in Aptamer Discoveries and Modifications for Therapeutic Applications

Aptamers are oligonucleotide sequences with a length of about 25-80 bases which have abilities to bind to specific target molecules that rival those of monoclonal antibodies. They are attracting great attention in diverse clinical translations on account of their various advantages, including prolonged storage life, little batch-to-batch differences, very low immunogenicity, and feasibility of chemical modifications for enhancing stability, prolonging the half-life in serum, and targeted delivery. In this Review, we demonstrate the emerging aptamer discovery technologies in developing advanced techniques for producing aptamers with high performance consistently and efficiently as well as requiring less cost and resources but offering a great chance of success. Further, the diverse modifications of aptamers for therapeutic applications including therapeutic agents, aptamer-drug conjugates, and targeted delivery materials are comprehensively summarized.

Emerging RNA Therapeutics to Lower Blood Levels of Lp(a): JACC Focus Seminar 2/4

Lipoprotein(a) [Lp(a)] has risen to the level of an accepted cardiovascular disease risk factor, but final proof of causality awaits a randomized trial of Lp(a) lowering. Inhibiting apolipoprotein(a) production in the hepatocyte with ribonucleic acid therapeutics has emerged as an elegant and effective solution to reduce plasma Lp(a) levels. Phase 2 clinical trials have shown that the antisense oligonucleotide pelacarsen reduced mean Lp(a) levels by 80%, allowing 98% of subjects to reach on-treatment levels of <125 nmol/l (∼50 mg/dl). The phase 3 Lp(a)HORIZON (Assessing the Impact of Lipoprotein(a) Lowering With TQJ230 on Major Cardiovascular Events in Patients With CVD) outcomes trial is currently enrolling approximately 7,680 patients with history of myocardial infarction, ischemic stroke, and symptomatic peripheral arterial disease and controlled low-density lipoprotein cholesterol to pelacarsen versus placebo. The co-primary endpoints are major adverse cardiovascular events in subjects with Lp(a) >70 mg/dl and >90 mg/dl, in which either of the two being positive will lead to a successful trial. Additional ribonucleic acid-targeted therapies to lower Lp(a) are in preclinical and clinical development. The testing of the Lp(a) hypothesis will provide proof whether Lp(a)-mediated risk can be abolished by potent Lp(a) lowering.

Advances in biological therapies for dyslipidemias and atherosclerosis

Atherosclerosis is a multifactorial disease influenced by genetics, lifestyle and environmental factors. Despite therapeutic advances that reduce the risk of cardiovascular events, atherosclerosis-related diseases remain the leading cause of mortality worldwide. Precise targeting of genes involved in lipoprotein metabolism is an emerging approach for atherosclerosis prevention and treatment. This article focuses on the latest developments, clinical potential and current challenges of monoclonal antibodies, vaccines and genome/transcriptome modification strategies, including antisense oligonucleotides, genome/base editing and gene therapy. Multiple lipid lowering biological therapies have already been approved by the FDA with impressive results to date, while many more promising targets are being pursued in clinical trials or pre-clinical animal models.

Therapeutic Advances in Oncology

Around 77 new oncology drugs were approved by the FDA in the past five years; however, most cancers remain untreated. Small molecules and antibodies are dominant therapeutic modalities in oncology. Antibody-drug conjugates, bispecific antibodies, peptides, cell, and gene-therapies are emerging to address the unmet patient need. Advancement in the discovery and development platforms, identification of novel targets, and emergence of new technologies have greatly expanded the treatment options for patients. Here, we provide an overview of various therapeutic modalities and the current treatment options in oncology, and an in-depth discussion of the therapeutics in the preclinical stage for the treatment of breast cancer, lung cancer, and multiple myeloma.

Ligand conjugated antisense oligonucleotide for the treatment of transthyretin amyloidosis: preclinical and phase 1 data

AIMS

Amyloidogenic transthyretin (ATTR) amyloidosis is a fatal disease characterized by progressive cardiomyopathy and/or polyneuropathy. AKCEA-TTR-LRx (ION-682884) is a ligand-conjugated antisense drug designed for receptor-mediated uptake by hepatocytes, the primary source of circulating transthyretin (TTR). Enhanced delivery of the antisense pharmacophore is expected to increase drug potency and support lower, less frequent dosing in treatment.

METHODS AND RESULTS

AKCEA-TTR-LRx demonstrated an approximate 50-fold and 30-fold increase in potency compared with the unconjugated antisense drug, inotersen, in human hepatocyte cell culture and mice expressing a mutated human genomic TTR sequence, respectively. This increase in potency was supported by a preferential distribution of AKCEA-TTR-LRx to liver hepatocytes in the transgenic hTTR mouse model. A randomized, placebo-controlled, phase 1 study was conducted to evaluate AKCEA-TTR-LRx in healthy volunteers (ClinicalTrials.gov: NCT03728634). Eligible participants were assigned to one of three multiple-dose cohorts (45, 60, and 90 mg) or a single-dose cohort (120 mg), and then randomized 10:2 (active : placebo) to receive a total of 4 SC doses (Day 1, 29, 57, and 85) in the multiple-dose cohorts or 1 SC dose in the single-dose cohort. The primary endpoint was safety and tolerability; pharmacokinetics and pharmacodynamics were secondary endpoints. All randomized participants completed treatment. No serious adverse events were reported. In the multiple-dose cohorts, AKCEA-TTR-LRx reduced TTR levels from baseline to 2 weeks after the last dose of 45, 60, or 90 mg by a mean (SD) of -85.7% (8.0), -90.5% (7.4), and -93.8% (3.4), compared with -5.9% (14.0) for pooled placebo (P < 0.001). A maximum mean (SD) reduction in TTR levels of -86.3% (6.5) from baseline was achieved after a single dose of 120 mg AKCEA-TTR-LRx .

CONCLUSIONS

These findings suggest an improved safety and tolerability profile with the increase in potency achieved by productive receptor-mediated uptake of AKCEA-TTR-LRx by hepatocytes and supports further development of AKCEA-TTR-LRx for the treatment of ATTR polyneuropathy and cardiomyopathy.

Cellular Targeting of Oligonucleotides by Conjugation with Small Molecules

Drug candidates derived from oligonucleotides (ON) are receiving increased attention that is supported by the clinical approval of several ON drugs. Such therapeutic ON are designed to alter the expression levels of specific disease-related proteins, e.g., by displaying antigene, antisense, and RNA interference mechanisms. However, the high polarity of the polyanionic ON and their relatively rapid nuclease-mediated cleavage represent two major pharmacokinetic hurdles for their application in vivo. This has led to a range of non-natural modifications of ON structures that are routinely applied in the design of therapeutic ON. The polyanionic architecture of ON often hampers their penetration of target cells or tissues, and ON usually show no inherent specificity for certain cell types. These limitations can be overcome by conjugation of ON with molecular entities mediating cellular 'targeting', i.e., enhanced accumulation at and/or penetration of a specific cell type. In this context, the use of small molecules as targeting units appears particularly attractive and promising. This review provides an overview of advances in the emerging field of cellular targeting of ON via their conjugation with small-molecule targeting structures.

Mesyl phosphoramidate backbone modified antisense oligonucleotides targeting miR-21 with enhanced in vivo therapeutic potency

The design of modified oligonucleotides that combine in one molecule several therapeutically beneficial properties still poses a major challenge. Recently a new type of modified mesyl phosphoramidate (or µ-) oligonucleotide was described that demonstrates high affinity to RNA, exceptional nuclease resistance, efficient recruitment of RNase H, and potent inhibition of key carcinogenesis processes in vitro. Herein, using a xenograft mouse tumor model, it was demonstrated that microRNA miR-21-targeted µ-oligonucleotides administered in complex with folate-containing liposomes dramatically inhibit primary tumor growth via long-term down-regulation of miR-21 in tumors and increase in biosynthesis of miR-21-regulated tumor suppressor proteins. This antitumoral effect is superior to the effect of the corresponding phosphorothioate. Peritumoral administration of µ-oligonucleotide results in its rapid distribution and efficient accumulation in the tumor. Blood biochemistry and morphometric studies of internal organs revealed no pronounced toxicity of µ-oligonucleotides. This new oligonucleotide class provides a powerful tool for antisense technology.

N-acetyl galactosamine-conjugated antisense drug to APOC3 mRNA, triglycerides and atherogenic lipoprotein levels

Aims

Elevated apolipoprotein C-III (apoC-III) levels are associated with hypertriglyceridaemia and coronary heart disease. AKCEA-APOCIII-L_Rx is an N-acetyl galactosamine-conjugated antisense oligonucleotide targeted to the liver that selectively inhibits apoC-III protein synthesis.

Methods and results

The safety, tolerability, and efficacy of AKCEA-APOCIII-L_Rx was assessed in a double-blind, placebo-controlled, dose-escalation Phase 1/2a study in healthy volunteers (ages 18–65) with triglyceride levels ≥90 or ≥200 mg/dL. Single-dose cohorts were treated with 10, 30, 60, 90, and 120 mg subcutaneously (sc) and multiple-dose cohorts were treated with 15 and 30 mg weekly sc for 6 weeks or 60 mg every 4 weeks sc for 3 months. In the single-dose cohorts treated with 10, 30, 60, 90, or 120 mg of AKCEA-APOCIII-L_Rx, median reductions of 0, −42%, −73%, −81%, and −92% in apoC-III, and −12%, −7%, −42%, −73%, and −77% in triglycerides were observed 14 days after dosing. In multiple-dose cohorts of 15 and 30 mg weekly and 60 mg every 4 weeks, median reductions of −66%, −84%, and −89% in apoC-III, and −59%, −73%, and −66% in triglycerides were observed 1 week after the last dose. Significant reductions in total cholesterol, apolipoprotein B, non-high-density lipoprotein cholesterol (HDL-C), very low-density lipoprotein cholesterol, and increases in HDL-C were also observed. AKCEA-APOCIII-L_Rx was well tolerated with one injection site reaction of mild erythema, and no flu-like reactions, platelet count reductions, liver, or renal safety signals.

Conclusion

Treatment of hypertriglyceridaemic subjects with AKCEA-APOCIII-L_Rx results in a broad improvement in the atherogenic lipid profile with a favourable safety and tolerability profile. ClinicalTrials.gov Identifier: NCT02900027.

Transport Oligonucleotides-A Novel System for Intracellular Delivery of Antisense Therapeutics

Biological activity of antisense oligonucleotides (asON), especially those with a neutral backbone, is often attenuated by poor cellular accumulation. In the present proof-of-concept study, we propose a novel delivery system for asONs which implies the delivery of modified antisense oligonucleotides by so-called transport oligonucleotides (tON), which are oligodeoxyribonucleotides complementary to asON conjugated with hydrophobic dodecyl moieties. Two types of tONs, bearing at the 5′-end up to three dodecyl residues attached through non-nucleotide inserts (TD series) or anchored directly to internucleotidic phosphate (TP series), were synthesized. tONs with three dodecyl residues efficiently delivered asON to cells without any signs of cytotoxicity and provided a transfection efficacy comparable to that achieved using Lipofectamine 2000. We found that, in the case of tON with three dodecyl residues, some tON/asON duplexes were excreted from the cells within extracellular vesicles at late stages of transfection. We confirmed the high efficacy of the novel and demonstrated that MDR1 mRNA targeted asON delivered by tON with three dodecyl residues significantly reduced the level of P-glycoprotein and increased the sensitivity of KB-8-5 human carcinoma cells to vinblastine. The obtained results demonstrate the efficacy of lipophilic oligonucleotide carriers and shows they are potentially capable of intracellular delivery of any kind of antisense oligonucleotides.

Delivery of Oligonucleotides to the Liver with GalNAc: From Research to Registered Therapeutic Drug

Targeted delivery of oligonucleotides to liver hepatocytes using N-acetylgalactosamine (GalNAc) conjugates that bind to the asialoglycoprotein receptor has become a breakthrough approach in the therapeutic oligonucleotide field. This technology has led to the approval of givosiran for the treatment of acute hepatic porphyria, and there are another seven conjugates in registrational review or phase 3 trials and at least another 21 conjugates at earlier stages of clinical development. This review highlights some of the recent chemical and preclinical advances in this space, leading to a large number of clinical candidates against a diverse range of targets in liver hepatocytes. The review focuses on the use of this delivery system for small interfering RNAs (siRNAs) and antisense molecules that cause downregulation of target mRNA and protein. A number of other approaches such as anti-microRNAs and small activating RNAs are starting to exploit the technology, broadening the potential of this approach for therapeutic oligonucleotide intervention.

Novel emerging therapies in atherosclerosis targeting lipid metabolism

INTRODUCTION

Recent years have brought significant developments in lipid and atherosclerosis research. Although statins are a cornerstone in hyperlipidemia management, new non-statin therapies have had an impact. The reduction of low-density lipoprotein cholesterol (LDL-C) further translates into the lowering of cardiovascular mortality. Additionally, lipid research has progressed beyond LDL-C reduction and this has brought triglyceride (TG) and other apoprotein-B containing lipids into focus.

AREAS COVERED

Inclisiran and pemafibrate, with expected approval soon, come under the spotlight. We discuss other therapeutics such as lomitapide, mipomersen, volanesorsen, and evinacumab and newly approved non-statin-based therapies such as ezetimibe, icosapent ethyl (IPE), and bempedoic acid.

EXPERT OPINION

New options now exist for the prevention of atherosclerosis in patients that are not optimized on statin therapy. Multiple guidelines endorse ezetimibe, PCSK9 inhibitors, bempedoic, and IPE as add-on therapy. Recently approved bempedoic acid/ezetimibe combination might gain popularity among clinicians. Inclisiran and pemafibrate show promise in the reduction of LDL-C and TG, respectively, and results are pending in cardiovascular outcome trials. Combination strategies could improve outcomes, but the challenge will be balancing cost and selecting the correct patient population for each treatment modality to maximize benefit with the fewest medications.

ADME: Assessing Pharmacokinetic-Pharmacodynamic Parameters of Oligonucleotides

We describe tactics to assess pharmacokinetic (PK) and pharmacodynamic (PD) parameters of oligonucleotides. The chapter includes recommendations on the design of single-dose preclinical PK studies, preclinical PKPD studies, and toxicological studies, and on best practice for scaling PK and PD parameters from animal to human. We focus on single-stranded oligonucleotides, but relevant differences to double-stranded RNAs are also addressed.

Potential Causality and Emerging Medical Therapies for Lipoprotein(a) and Its Associated Oxidized Phospholipids in Calcific Aortic Valve Stenosis

The prevalence of calcific aortic valve disease is increasing with aging of the population. Current treatment options for advanced or symptomatic aortic stenosis are limited to traditional surgical or percutaneous aortic valve replacement. Medical therapies that impact the progression of calcific aortic valve disease do not currently exist. New pathophysiological insights suggest that the processes leading to calcific aortic valve disease are metabolically active for many years before and during the clinical expression of disease. The identification of genetic and potentially causal mediators of calcific aortic valve disease allows opportunities for therapies that may slow progression to the point where aortic valve replacement can be avoided. Recent studies suggest that approximately one-third of aortic stenosis cases are associated with highly elevated lipoprotein(a) [Lp(a)] and pathways related to the metabolism of procalcifying oxidized phospholipids. Oxidized phospholipids can be carried by Lp(a) into valve leaflets but can also be formed in situ from cell membranes, lipoproteins, and apoptotic cells. This review will summarize the clinical data implicating the potential causality of Lp(a)/oxidized phospholipids, describe emerging therapeutic agents, and propose clinical trial designs to test the hypothesis that lowering Lp(a) will reduce progression aortic stenosis and the need for aortic valve replacement.

Impurity Qualification Toxicology Study for a 2'-O-Methoxyethyl-Modified Antisense Inhibitor in Mice

Safety assessment of drug impurities is a routine part of the drug development process. For oligonucleotide-based drugs, impurities can arise from impurities in starting materials, as by-products of the manufacturing process or from degradation, and are generally structurally similar to the parent oligonucleotide. To study the potential impact of impurities, a representative batch of a 2'-O-methoxyethyl (MOE) antisense oligonucleotide (ASO) was compared to batches of drug that were enriched with nine of the common impurities encountered with the chemical class. Mice were treated for 3 months with weekly subcutaneous injection of 10 or 30 mg/kg. The impurity content of the parent batch was 0.25%-2.5% of total drug substance. The enriched impurity mixtures contained from 3% to 10% of the various impurities. The expected common class effects were observed at the 30 mg/kg/week dose level in hematology, serum chemistry, and histopathology. However, there were no differences between the representative batch of material and those enriched with impurities. Based on these data, common oligonucleotide impurity studies do not appear to contribute to the overall toxicology profile.

Nonviral Nanoparticles for CRISPR-Based Genome Editing: Is It Just a Simple Adaption of What Have Been Developed for Nucleic Acid Delivery?

Genome-editing technologies hold tremendous potential for treating genetic diseases. However, the efficient and safe delivery of genome-editing elements to the location of interest, and the achievement of specific targeted gene correction without off-target side effect remains a big challenge. In this Perspective, we highlight recent developments and discuss the challenges of nonviral nanoparticles for the delivery of genome-editing tools. Finally, we will propose promising strategies to improve the delivery efficacy and advance the clinical translation of gene-editing technology.

Metabolism and Disposition of Volanesorsen, a 2'-O-(2 methoxyethyl) Antisense Oligonucleotide, Across Species

Volanesorsen (previously known as ISIS 304801) is a 20-nucleotide partially 2'-O-(2-methoxyethyl) (2'-MOE)-modified antisense oligonucleotide (ASO) gapmer, which was recently approved in the European Union as a novel, first-in-class treatment in the reduction of triglyceride levels in patients with familial chylomicronemia syndrome. We characterized the absorption, distribution, metabolism, and excretion characteristics of volanesorsen in mice, rats, monkeys, and humans, in either radiolabeled or nonradiolabeled studies. This also included the characterization of all of the observed ASO metabolite species excreted in urine. Volanesorsen is highly bound to plasma proteins that are similar in mice, monkeys, and humans. In all species, plasma concentrations declined in a multiphasic fashion, characterized by a relatively fast initial distribution phase and then a much slower terminal elimination phase following subcutaneous bolus administration. The plasma metabolite profiles of volanesorsen are similar across species, with volanesorsen as the major component. Various shortened oligonucleotide metabolites (5-19 nucleotides long) were identified in tissues in the multiple-dose mouse and monkey studies, but fewer in the [³H]-volanesorsen rat study, likely due to a lower accumulation of metabolites following a single dose in rats. In urine, all metabolites identified in tissues were observed, consistent with both endo- and exonuclease-mediated metabolism and urinary excretion being the major elimination pathway for volanesorsen and its metabolites. SIGNIFICANCE STATEMENT: We characterized the absorption, distribution, metabolism, and excretion (ADME) of volanesorsen, a partially 2'-MOE-modified antisense oligonucleotide, from mouse to man utilizing novel extraction and quantitation techniques in samples collected from preclinical toxicology studies, a ³H rat ADME study, and a phase 1 clinical trial.

Pharmacokinetics and Clinical Pharmacology Considerations of GalNAc3-Conjugated Antisense Oligonucleotides

Introduction: Triantennary N-acetyl galactosamine (GalNAc₃) - conjugated antisense oligonucleotides (ASOs) have demonstrated improved hepatocyte uptake and pharmacologic activity over their parent unconjugated ASOs in animals and humans. Areas covered: In this review, the ADME (absorption, distribution, metabolism, and excretion) characteristics of GalNAc₃-conjugated ASOs in animals and in humans are summarized, and their clinical relevance is evaluated from the clinical pharmacology perspectives. Expert opinion: ASOs distribute to tissues via receptor-mediated processes, and conjugation to a ligand specific to certain cell types can improve target tissue delivery. GalNAc₃-conjugation represents a good example on this regard and has demonstrated ideal characteristics of a prodrug to target delivery of ASOs to hepatocytes via the asialoglycoprotein receptor (ASGPR). The improved potency and safety margin permit more flexible dosing (e.g. monthly or less frequently if needed) taking full advantage of the long half-life of the parent ASO in humans. However, while still speculative, it should be noted that ASGPR-mediated uptake could become nonlinear with dose and factors that impact ASGPR expression or compete with ASGPR-mediated uptake could potentially affect the uptake of GalNAc₃-conjugated ASOs, further studies are warranted.

Harnessing nucleic acid-based therapeutics for atherosclerotic cardiovascular disease: state of the art

Dyslipidemia is one of the major but modifiable risk factors for atherosclerotic cardiovascular disease (ACVD). Despite the accessibility of statins and other lipid-lowering drugs, the burden of ACVD is still high globally, highlighting the need for new therapeutic approaches. Nucleic acid-based technologies, including antisense oligonucleotides (ASOs), small interfering (si)RNAs, miRNAs, and decoys, are emerging therapeutic modalities for the treatment of ACVD. These technologies aim to degrade gene mRNA transcripts to decrease the levels of atherogenic lipoproteins. Using gene-silencing approaches, the levels of atherogenic lipoproteins can be decreased by targeting proteins that have key roles in lipoprotein metabolism. Here, we highlight preclinical and clinical findings using these approaches for the development of novel therapies against ACVD.

Bioconjugated Oligonucleotides: Recent Developments and Therapeutic Applications

Oligonucleotide-based agents have the potential to treat or cure almost any disease, and are one of the key therapeutic drug classes of the future. Bioconjugated oligonucleotides, a subset of this class, are emerging from basic research and being successfully translated to the clinic. In this Review, we first briefly describe two approaches for inhibiting specific genes using oligonucleotides-antisense DNA (ASO) and RNA interference (RNAi)-followed by a discussion on delivery to cells. We then summarize and analyze recent developments in bioconjugated oligonucleotides including those possessing GalNAc, cell penetrating peptides, α-tocopherol, aptamers, antibodies, cholesterol, squalene, fatty acids, or nucleolipids. These novel conjugates provide a means to enhance tissue targeting, cell internalization, endosomal escape, target binding specificity, resistance to nucleases, and more. We next describe those bioconjugated oligonucleotides approved for patient use or in clinical trials. Finally, we summarize the state of the field, describe current limitations, and discuss future prospects. Bioconjugation chemistry is at the centerpiece of this therapeutic oligonucleotide revolution, and significant opportunities exist for development of new modification chemistries, for mechanistic studies at the chemical-biology interface, and for translating such agents to the clinic.

Comparison of the Class Effects of Antisense Oligonucleotides in CByB6F1-Tg(HRAS)2Jic and CD-1 Mice

The 6-month Tg.rasH2 mouse carcinogenicity model provides an acceptable alternative to the 2-year carcinogenicity study in CD-1 mice. However, key questions related to the use of this model for testing antisense oligonucleotides (ASOs) include the similarity in the biologic response between mouse strains and the feasibility of using data from the CD-1 mouse to set doses and dose schedules for a Tg.rasH2 carcinogenicity study. To evaluate the potential strain differences, four distinct 2'- O-(2-methoxyethyl) ASOs were administered to CByB6F1 (wild type), Tg.rasH2 (hemizygous), and CD-1 mice. There were no meaningful differences in clinical signs, body weight, food consumption, or serum chemistry and hematology parameters. Histopathology evaluation indicated little to no difference in the spectrum or magnitude of changes present. The cytokine/chemokine response was also not appreciably different between the strains. This was consistent with the similarity in ASO concentration in the liver between the mouse strains tested. As the class effects of the ASOs were not meaningfully different between CD-1, CByB6F1, or Tg.rasH2 mice, data from nonclinical studies in CD-1 mice can be used for dose selection and expectation of effect in the Tg.rasH2 mouse.