Investigation into the Mechanism(s) That Leads to Platelet Decreases in Cynomolgus Monkeys During Administration of ISIS 104838, a 2'-MOE-Modified Antisense Oligonucleotide

Post-transcriptional control of haemostatic genes: mechanisms and emerging therapeutic concepts in thrombo-inflammatory disorders

The haemostatic system is pivotal to maintaining vascular integrity. Multiple components involved in blood coagulation have central functions in inflammation and immunity. A derailed haemostasis is common in prevalent pathologies such as sepsis, cardiovascular disorders, and lately, COVID-19. Physiological mechanisms limit the deleterious consequences of a hyperactivated haemostatic system through adaptive changes in gene expression. While this is mainly regulated at the level of transcription, co- and posttranscriptional mechanisms are increasingly perceived as central hubs governing multiple facets of the haemostatic system. This layer of regulation modulates the biogenesis of haemostatic components, for example in situations of increased turnover and demand. However, they can also be 'hijacked' in disease processes, thereby perpetuating and even causally entertaining associated pathologies. This review summarizes examples and emerging concepts that illustrate the importance of posttranscriptional mechanisms in haemostatic control and crosstalk with the immune system. It also discusses how such regulatory principles can be used to usher in new therapeutic concepts to combat global medical threats such as sepsis or cardiovascular disorders.

Complement C3d/C4d Deposition on Platelets Correlates with 2'-O-Methoxyethyl Antisense Oligonucleotide-Induced Thrombocytopenia in Monkeys

2'-O-Methoxyethyl antisense oligonucleotide (2'-MOE ASO)-induced severe thrombocytopenia (TCP) [platelet (PLT) count <50 K/μL] was observed in the Asian-sourced cynomolgus monkeys with low incidence (2%-4% at doses >5 mg/kg/week). The potential mechanisms for TCP were studied using the Mauritian-sourced cynomolgus monkeys, which were shown to be more susceptible to ASO-induced TCP, along with the Asian-sourced animals. ISIS 405879, a 2'-MOE ASO, induced severe TCP (PLT <50 K/μL) in seven of nine Mauritian-sourced monkeys but not in the Asian-sourced monkeys after 16 weeks of treatment at 40 mg/kg/week. Marked increases in PLT-bound C3d/C4d were detected in all thrombocytopenic Mauritian-sourced monkeys but not in the unaffected Mauritian- or Asian-sourced monkeys, suggesting increased PLT clearance due to complement deposition on the PLTs. However, this effect was independent of the ASO-mediated fluid-phase alternative complement activation. A correlation was also observed between serum antiglycoprotein (GP) IIb/IIIa immunoglobulin G (IgG) and PLT reduction. In addition, increases in total serum IgM, anti-PLT IgM, and anti-PLT factor 4 IgM levels were observed in monkeys from both sources but were more evident in the Mauritian-sourced monkeys. These data suggest an enhanced innate immune cell activation to ISIS 405879, leading to increased PLT destruction through complement fixation on the PLTs or PLT crossreacting polyclonal antibody production.

Platelet Activation by Antisense Oligonucleotides (ASOs) in the Göttingen Minipig, including an Evaluation of Glycoprotein VI (GPVI) and Platelet Factor 4 (PF4) Ontogeny

Antisense oligonucleotide (ASO) is a therapeutic modality that enables selective modulation of undruggable protein targets. However, dose- and sequence-dependent platelet count reductions have been reported in nonclinical studies and clinical trials. The adult Göttingen minipig is an acknowledged nonclinical model for ASO safety testing, and the juvenile Göttingen minipig has been recently proposed for the safety testing of pediatric medicines. This study assessed the effects of various ASO sequences and modifications on Göttingen minipig platelets using in vitro platelet activation and aggregometry assays. The underlying mechanism was investigated further to characterize this animal model for ASO safety testing. In addition, the protein abundance of glycoprotein VI (GPVI) and platelet factor 4 (PF4) was investigated in the adult and juvenile minipigs. Our data on direct platelet activation and aggregation by ASOs in adult minipigs are remarkably comparable to human data. Additionally, PS ASOs bind to platelet collagen receptor GPVI and directly activate minipig platelets in vitro, mirroring the findings in human blood samples. This further corroborates the use of the Göttingen minipig for ASO safety testing. Moreover, the differential abundance of GPVI and PF4 in minipigs provides insight into the influence of ontogeny in potential ASO-induced thrombocytopenia in pediatric patients.

The mechanism of thrombocytopenia caused by cholesterol-conjugated antisense oligonucleotides

In this study, we investigated thrombocytopenia caused by cholesterol-conjugated antisense oligonucleotides (Chol-ASO). First, we evaluated platelet activation induced by Chol-ASO in mice by flow cytometry after administration of platelet-rich plasma (PRP). An increase in the number of large particle-size events with platelet activation was detected in the Chol-ASO-treated group. In a smear study, numerous platelets were observed to attach to nucleic acid-containing aggregates. A competition binding assay showed that the conjugation of cholesterol to ASOs increased their affinity for glycoprotein VI. Platelet-free plasma was then mixed with Chol-ASO to form aggregates. The assembly of Chol-ASO was confirmed by dynamic light scattering measurements in the concentration range in which the formation of aggregates with plasma components was observed. In conclusion, the mechanism by which Chol-ASOs causes thrombocytopenia is proposed to be as follows: (1) Chol-ASOs form polymers, (2) the nucleic acid portion of the polymers interacts with plasma proteins and platelets, which cross-links them to form aggregates, and (3) platelets bound to aggregates become activated, resulting in platelet aggregation, leading to a decrease in platelet count in vivo. The details of the mechanism revealed in this study could contribute to creating safer oligonucleotide therapies without the risk of thrombocytopenia.

Advances in the mechanisms and applications of inhibitory oligodeoxynucleotides against immune-mediated inflammatory diseases

Inhibitory oligodeoxynucleotides (ODNs) are short single-stranded DNA, which capable of folding into complex structures, enabling them to bind to a large variety of targets. With appropriate modifications, the inhibitory oligodeoxynucleotides exhibited many features of long half-life time, simple production, low toxicity and immunogenicity. In recent years, inhibitory oligodeoxynucleotides have received considerable attention for their potential therapeutic applications in immune-mediated inflammatory diseases (IMIDs). Inhibitory oligodeoxynucleotides could be divided into three categories according to its mechanisms and targets, including antisense ODNs (AS-ODNs), DNA aptamers and immunosuppressive ODNs (iSup ODNs). As a synthetic tool with immunomodulatory activity, it can target RNAs or proteins in a specific way, resulting in the reduction, increase or recovery of protein expression, and then regulate the state of immune activation. More importantly, inhibitory oligodeoxynucleotides have been used to treat immune-mediated inflammatory diseases, including inflammatory disorders and autoimmune diseases. Several inhibitory oligodeoxynucleotide drugs have been developed and approved on the market already. These drugs vary in their chemical structures, action mechanisms and cellular targets, but all of them could be capable of inhibiting excessive inflammatory responses. This review summarized their chemical modifications, action mechanisms and applications of the three kinds of inhibitory oligodeoxynucleotidesin the precise treatment of immune-mediated inflammatory diseases.

Considerations in the Preclinical Assessment of the Safety of Antisense Oligonucleotides

The nucleic acid therapeutics field has made tremendous progress in the past decades. Continuous advances in chemistry and design have led to many successful clinical applications, eliciting even more interest from researchers including both academic groups and drug development companies. Many preclinical studies in the field focus on improving the delivery of antisense oligonucleotide drugs (ONDs) and/or assessing their efficacy in target tissues, often neglecting the evaluation of toxicity, at least in early phases of development. A series of consensus recommendations regarding regulatory considerations and expectations have been generated by the Oligonucleotide Safety Working Group and the Japanese Research Working Group for the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use S6 and Related Issues (WGS6) in several white papers. However, safety aspects should also be kept in sight in earlier phases while screening and designing OND to avoid subsequent failure in the development phase. Experts and members of the network "DARTER," a COST Action funded by the Cooperation in Science and Technology of the EU, have utilized their collective experience working with OND, as well as their insights into OND-mediated toxicities, to generate a series of consensus recommendations to assess OND toxicity in early stages of preclinical research. In the past few years, several publications have described predictive assays, which can be used to assess OND-mediated toxicity in vitro or ex vivo to filter out potential toxic candidates before moving to in vivo phases of preclinical development, that is, animal toxicity studies. These assays also have the potential to provide translational insight since they allow a safety evaluation in human in vitro systems. Yet, small preliminary in vivo studies should also be considered to complement this early assessment. In this study, we summarize the state of the art and provide guidelines and recommendations on the different tests available for these early stage preclinical assessments.

Assessment of the Immunogenicity Potential for Oligonucleotide-Based Drugs

Therapeutic oligonucleotides (ONs) have characteristics of both small molecules and biologics. Although safety assessment of ONs largely follows guidelines established for small molecules, the unique characteristics of ONs often require incorporation of concepts from the safety assessment of biologics. The assessment of immunogenicity for ON therapeutics is one area where the approach is distinct from either established small molecule or biologic platforms. Information regarding immunogenicity of ONs is limited, but indicates that administration of ONs can result in antidrug antibody formation. In this study, we summarize the collective experience of the Oligonucleotide Safety Working Group in designing the immunogenicity assessment appropriate for this class of therapeutic, including advice on assay development, clinical monitoring, and evaluation of the impact of immunogenicity on exposure, efficacy, and safety of therapeutic ONs.

Nanodiamond-Induced Thrombocytopenia in Mice Involve P-Selectin-Dependent Nlrp3 Inflammasome-Mediated Platelet Aggregation, Pyroptosis and Apoptosis

Nanodiamond (ND) has been developed as a carrier to conduct various in vivo diagnostic and therapeutic uses. Safety is one of the major considerations, while the hemocompatibility of ND is not clearly addressed. Here we found that, compared to the other sizes of ND with relatively inert properties, treatments of 50 nm ND induced stronger platelet aggregation, platelet pyroptosis, apoptosis and thrombocytopenia in mice. Blockage treatments of soluble P-selectin, reactive oxygen species (ROS), and Nlrp3 inflammasome inhibitors markedly suppressed such adverse effects, suggesting ND-induced platelet activation and pyroptosis involves surface P-selectin-mediated enhancement of mitochondrial superoxide levels and Nlrp3 inflammasome activation. In addition, challenges of NDs induced less platelet pyroptosis and displayed less thrombocytopenia in P-selectin (Selp^-/-), Nlrp3 (Nlrp3^-/-) and caspase-1 (Casp1^-/-) mutants, as compared to the wild type mice. Blockers of P-selectin, ROS, and Nlrp3 inflammasome pathways could be considered as antidotes for ND induced platelet activation and thrombocytopenia.

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

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

Delivery of oligonucleotide-based therapeutics: challenges and opportunities

Nucleic acid-based therapeutics that regulate gene expression have been developed towards clinical use at a steady pace for several decades, but in recent years the field has been accelerating. To date, there are 11 marketed products based on antisense oligonucleotides, aptamers and small interfering RNAs, and many others are in the pipeline for both academia and industry. A major technology trigger for this development has been progress in oligonucleotide chemistry to improve the drug properties and reduce cost of goods, but the main hurdle for the application to a wider range of disorders is delivery to target tissues. The adoption of delivery technologies, such as conjugates or nanoparticles, has been a game changer for many therapeutic indications, but many others are still awaiting their eureka moment. Here, we cover the variety of methods developed to deliver nucleic acid-based therapeutics across biological barriers and the model systems used to test them. We discuss important safety considerations and regulatory requirements for synthetic oligonucleotide chemistries and the hurdles for translating laboratory breakthroughs to the clinic. Recent advances in the delivery of nucleic acid-based therapeutics and in the development of model systems, as well as safety considerations and regulatory requirements for synthetic oligonucleotide chemistries are discussed in this review on oligonucleotide-based therapeutics.

ANGPTL3 and Apolipoprotein C-III as Novel Lipid-Lowering Targets

PURPOSE OF REVIEW

Despite significant progress in plasma lipid lowering strategies, recent clinical trials highlight the existence of residual cardiovascular risk. Angiopoietin-like protein 3 (ANGPTL3) and apolipoprotein C-III (Apo C-III) have been identified as novel lipid-lowering targets.

RECENT FINDINGS

Apo C-III and ANGPTL3 have emerged as novel regulators of triglyceride (TG) and low-density lipoprotein-cholesterol (LDL-C) levels. ANGPTL3 is an inhibitor of lipoprotein lipase (LPL), reducing lipolysis of Apo B-containing lipoproteins. Loss-of-function ANGPLT3 mutations are associated with reduced plasma cholesterol and TG, while novel ANGPLT3 inhibition strategies, including monoclonal antibodies (evinacumab), ANGPLT3 antisense oligonucleotides (IONIS-ANGPTL3-L_Rx), and small interfering RNA (siRNA) silencing techniques (ARO-ANG3), result in increased lipolysis and significant reductions of LDL-C and TG levels in phase I and II clinical trials. Similarly, Apo C-III inhibits LPL while promoting the hepatic secretion of TG-rich lipoproteins and preventing their clearance. Loss-of-function APOC3 mutations have been associated with reduced TG levels. Targeting of Apo C-III with volanesorsen, an APOC3 siRNA, results in significant reduction in plasma TG levels but possibly also increased risk for thrombocytopenia, as recently demonstrated in phase I, II, and III clinical trials. ARO-APOC3 is a novel siRNA-based agent targeting Apo C-III which is currently under investigation with regard to its lipid-lowering efficiency. ANGPTL3 and Apo C-III targeting agents have demonstrated striking lipid-lowering effects in recent clinical trials; however, more thorough safety and efficacy data are required. Here, we evaluate the role of ANGPLT3 and Apo C-III in lipid metabolism, present the latest clinical advances targeting those molecules, and outline the remaining scientific challenges on residual lipid-associated cardiovascular risk.

Pooled Patient-Level Analysis of Inclisiran Trials in Patients With Familial Hypercholesterolemia or Atherosclerosis

BACKGROUND

Inclisiran is a double-stranded small interfering RNA that suppresses proprotein convertase subtilisin-kexin type 9 (PCSK9) translation in the liver, leading to sustained reductions in low-density lipoprotein cholesterol (LDL-C) and other atherogenic lipoproteins with twice-yearly dosing.

OBJECTIVES

The purpose of this study was to conduct a patient-level pooled analysis from 3 phase 3 studies of inclisiran.

METHODS

Participants with heterozygous familial hypercholesterolemia (ORION-9 [Trial to Evaluate the Effect of Inclisiran Treatment on Low Density Lipoprotein Cholesterol (LDL-C) in Subjects With Heterozygous Familial Hypercholesterolemia (HeFH)]), atherosclerotic cardiovascular disease (ASCVD) (ORION-10 [Inclisiran for Participants With Atherosclerotic Cardiovascular Disease and Elevated Low-density Lipoprotein Cholesterol]), or ASCVD and ASCVD risk equivalents (ORION-11 [Inclisiran for Subjects With ASCVD or ASCVD-Risk Equivalents and Elevated Low-density Lipoprotein Cholesterol]) taking maximally tolerated statin therapy, with or without other LDL-C-lowering agents, were randomly assigned in a 1:1 ratio to receive either inclisiran or placebo, administered by subcutaneous injection on day 1, day 90, and every 6 months thereafter for 540 days. The coprimary endpoints were the placebo-corrected percentage change in LDL-C level from baseline to day 510 and the time-adjusted percentage change in LDL-C level from baseline after day 90 to day 540. Levels of other atherogenic lipoproteins and treatment-emergent adverse events were also assessed.

RESULTS

A total of 3,660 participants (n = 482, n = 1,561, and n = 1,617 from ORION-9, -10, and -11, respectively) underwent randomization. The placebo-corrected change in LDL-C with inclisiran at day 510 was -50.7% (95% confidence interval: -52.9% to -48.4%; p < 0.0001). The corresponding time-adjusted change in LDL-C was -50.5% (95% confidence interval: -52.1% to -48.9%; p < 0.0001). Safety was similar in both groups. Treatment-emergent adverse events at the injection site were more frequent with inclisiran than placebo (5.0% vs. 0.7%), but were predominantly mild, and none were severe or persistent. Liver and kidney function tests, creatine kinase values, and platelet counts did not differ between groups.

CONCLUSIONS

These pooled safety and efficacy data show that inclisiran, given twice yearly in addition to maximally tolerated statin therapy with or without other LDL-C lowering agents, is an effective, safe, and well-tolerated treatment to lower LDL-C in adults with heterozygous familial hypercholesterolemia, ASCVD, or ASCVD risk equivalents.

Sequence-specific 2'-O-methoxyethyl antisense oligonucleotides activate human platelets through glycoprotein VI, triggering formation of platelet-leukocyte aggregates

Antisense oligonucleotides (ASO) are DNA-based, disease-modifying drugs. Clinical trials with 2'-O-methoxyethyl (2’MOE) ASO have shown dose- and sequence-specific lowering of platelet counts according to two phenotypes. Phenotype 1 is a moderate (but not clinically severe) drop in platelet count. Phenotype 2 is rare, severe thrombocytopenia. This article focuses on the underlying cause of the more common phenotype 1, investigating the effects of ASO on platelet production and platelet function. Five phosphorothioate ASO were studied: three 2’MOE sequences; 487660 (no effects on platelet count), 104838 (associated with phenotype 1), and 501861 (effects unknown) and two CpG sequences; 120704 and ODN 2395 (known to activate platelets). Human cord bloodderived megakaryocytes were treated with these ASO to study their effects on proplatelet production. Platelet activation (determined by surface P-selectin) and platelet-leukocyte aggregates were analyzed in ASO-treated blood from healthy human volunteers. None of the ASO inhibited proplatelet production by human megakaryocytes. All the ASO were shown to bind to the platelet receptor glycoprotein VI (KD ~0.2-1.5 μM). CpG ASO had the highest affinity to glycoprotein VI, the most potent platelet-activating effects and led to the greatest formation of platelet-leukocyte aggregates. 2’MOE ASO 487660 had no detectable platelet effects, while 2’MOE ASOs 104838 and 501861 triggered moderate platelet activation and SYKdependent formation of platelet-leukocyte aggregates. Donors with higher platelet glycoprotein VI levels had greater ASO-induced platelet activation. Sequence-dependent ASO-induced platelet activation and platelet-leukocyte aggregates may explain phenotype 1 (moderate drops in platelet count). Platelet glycoprotein VI levels could be useful as a screening tool to identify patients at higher risk of ASO-induced platelet side effects.

Antisense oligonucleotides and nucleic acids generate hypersensitive platelets

INTRODUCTION

Despite the great promise for therapies using antisense oligonucleotides (ASOs), their adverse effects, which include pro-inflammatory effects and thrombocytopenia, have limited their use. Previously, these effects have been linked to the phosphorothioate (PS) backbone necessary to prevent rapid ASO degradation in plasma. The main aim of this study was to assess the impact of the nucleic acid portion of an ASO-type drug on platelets and determine if it may contribute to thrombosis or thrombocytopenia.

METHODS

Platelets were isolated from healthy donors and men with advanced prostate cancer. Effects of antisense oligonucleotides (ASO), oligonucleotides, gDNA, and microRNA on platelet activation and aggregation were evaluated. A mouse model of lung thrombosis was used to confirm the effects of PS-modified oligonucleotides in vivo.

RESULTS

Platelet exposure to gDNA, miRNA, and oligonucleotides longer than 16-mer at a concentration above 8 mM resulted in the formation of hypersensitive platelets, characterized by an increased sensitivity to low-dose thrombin (0.1 nM) and increase in p-Selectin expression (6-8 fold greater than control; p < 0.001). The observed nucleic acid (NA) effects on platelets were toll-like receptor (TLR) -7 subfamily dependent. Injection of a p-Selectin inhibitor significantly (p = 0.02) reduced the formation of oligonucleotide-associated pulmonary microthrombosis in vivo.

CONCLUSION

Our results suggest that platelet exposure to nucleic acids independent of the presence of a PS modification leads to a generation of hypersensitive platelets and requires TLR-7 subfamily receptors. ASO studies conducted in cancer patients may benefit from testing the ASO effects on platelets ex vivo before initiation of patient treatment.

Safety, Pharmacokinetic, and Pharmacodynamic Evaluation of a 2'-(2-Methoxyethyl)-D-ribose Antisense Oligonucleotide-Triantenarry N-Acetyl-galactosamine Conjugate that Targets the Human Transmembrane Protease Serine 6

Cellular uptake of antisense oligonucleotides (ASOs) is one of the main determinants of in vivo activity and potency. A significant advancement in improving uptake into cells has come through the conjugation of ASOs to triantenarry N-acetyl-galactosamine (GalNAc₃), a ligand for the asialoglycoprotein receptor on hepatocytes. The impact for antisense oligonucleotides, which are already taken up into hepatocytes, is a 10-fold improvement in potency in mice and up to a 30-fold potency improvement in humans, resulting in overall lower effective dose and exposure levels. 2'-Methoxyethyl-modified antisense oligonucleotide conjugated to GalNAc₃ (ISIS 702843) is specific for human transmembrane protease serine 6 and is currently in clinical trials for the treatment of β-thalassemia. This report summarizes a chronic toxicity study of ISIS 702843 in nonhuman primates (NHPs), including pharmacokinetic and pharmacology assessments. Suprapharmacologic doses of ISIS 702843 were well tolerated in NHPs after chronic dosing, and the data indicate that the overall safety profile is very similar to that of the unconjugated 2'-(2-methoxyethyl)-D-ribose (2'-MOE) ASOs. Notably, the GalNAc₃ moiety did not cause any new toxicities nor exacerbate the known nonspecific class effects of the 2'-MOE ASOs. This observation was confirmed with multiple GalNAc₃-MOE conjugates by querying a data base of monkey studies containing both GalNAc₃-conjugated and unconjugated 2'-MOE ASOs. SIGNIFICANCE STATEMENT: This report documents the potency, pharmacology, and overall tolerability profile of a triantenarry N-acetyl-galactosamine (GalNAc₃)-conjugated 2'-(2-methoxyethyl)-D-ribose (2'-MOE) antisense oligonucleotide (ASO) specific to transmembrane protease serine 6 after chronic treatment in the cynomolgus monkey. Collective analysis of 15 independent GalNAc₃-conjugated and unconjugated 2'-MOE ASOs shows the consistency in the dose response and character of hepatic and platelet tolerability across sequences that will result in much larger safety margins for the GalNAc₃-conjugated 2'-MOE ASOs when compared with the unconjugated 2'-MOE ASOs given the increased potency.

Chemical Development of Therapeutic Oligonucleotides

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

Underlying Immune Disorder May Predispose Some Transthyretin Amyloidosis Subjects to Inotersen-Mediated Thrombocytopenia

Inotersen, a 2'-O-methoxyethyl (2'-MOE) phosphorothioate antisense oligonucleotide, reduced disease progression and improved quality of life in patients with hereditary transthyretin amyloidosis with polyneuropathy (hATTR-PN) in the NEURO-TTR and NEURO-TTR open-label extension (OLE) trials. However, 300 mg/week inotersen treatment was associated with platelet count reductions in several patients. Mean platelet counts in patients in the NEURO-TTR-inotersen group remained ≥140 × 10⁹/L in 50% and ≥100 × 10⁹/L in 80% of the subjects. However, grade 4 thrombocytopenia (<25 × 10⁹/L) occurred in three subjects in NEURO-TTR trial, and one of these suffered a fatal intracranial hemorrhage. The two others were treated successfully with corticosteroids and discontinuation of inotersen. Investigations in a subset of subjects in NEURO-TTR (n = 17 placebo; n = 31 inotersen) and OLE (n = 33) trials ruled out direct myelotoxicity, consumptive coagulopathy, and heparin-induced thrombocytopenia. Antiplatelet immunoglobulin G (IgG) antibodies were detected at baseline in 5 of 31 (16%) inotersen-treated subjects in NEURO-TTR, 4 of whom eventually developed grade 1 or 2 thrombocytopenia while on the drug. In addition, 24 subjects in the same group developed treatment-emergent antiplatelet IgG antibodies, of which 2 developed grade 2, and 3 developed grade 4 thrombocytopenia. Antiplatelet IgG antibodies in two of the three grade 4 thrombocytopenia subjects targeted GPIIb/IIIa. Plasma cytokines previously implicated in immune dysregulation, such as interleukin (IL)-23 and a proliferation-inducing ligand (APRIL) were often above the normal range at baseline. Collectively, these findings suggest an underlying immunologic dysregulation predisposing some individuals to immune-mediated thrombocytopenia during inotersen treatment.

Oligonucleotides to the (Gene) Rescue: FDA Approvals 2017-2019

Four decades have passed since oligonucleotides were first used to manipulate gene expression. There were few FDA approvals prior to 2016, mostly of drugs that eventually exhibited poor performance in the market. The aura of their younger siRNA relatives had also faded during the past 15 years. However, several FDA approvals have occurred in the past 4 years, restoring hope that a new era has dawned in oligonucleotide/siRNA clinical therapeutics. Here, we review the field of oligonucleotide therapeutics and provide an update on FDA approvals of oligonucleotides from 2017 until the second quarter of 2019. We take into consideration the ethical issues looming over the still somewhat limited efficacy of these molecules, the toxicity of treatment, and the exorbitant cost of these therapeutic agents, which limits accessibility for many.

Emerging Evidence that ApoC-III Inhibitors Provide Novel Options to Reduce the Residual CVD

Purpose of Review

Apolipoprotein C-III (apoC-III) is known to inhibit lipoprotein lipase (LPL) and function as an important regulator of triglyceride metabolism. In addition, apoC-III has also more recently been identified as an important risk factor for cardiovascular disease. This review summarizes the mechanisms by which apoC-III induces hypertriglyceridemia and promotes atherogenesis, as well as the findings from recent clinical trials using novel strategies for lowering apoC-III.

Recent Findings

Genetic studies have identified subjects with heterozygote loss-of-function (LOF) mutations in APOC3, the gene coding for apoC-III. Clinical characterization of these individuals shows that the LOF variants associate with a low-risk lipoprotein profile, in particular reduced plasma triglycerides. Recent results also show that complete deficiency of apoC-III is not a lethal mutation and is associated with very rapid lipolysis of plasma triglyceride-rich lipoproteins (TRL). Ongoing trials based on emerging gene-silencing technologies show that intervention markedly lowers apoC-III levels and, consequently, plasma triglyceride. Unexpectedly, the evidence points to apoC-III not only inhibiting LPL activity but also suppressing removal of TRLs by LPL-independent pathways.

Summary

Available data clearly show that apoC-III is an important cardiovascular risk factor and that lifelong deficiency of apoC-III is cardioprotective. Novel therapies have been developed, and results from recent clinical trials indicate that effective reduction of plasma triglycerides by inhibition of apoC-III might be a promising strategy in management of severe hypertriglyceridemia and, more generally, a novel approach to CHD prevention in those with elevated plasma triglyceride.

Targeted Oligonucleotides for Treating Neurodegenerative Tandem Repeat Diseases

Nucleotide repeat disorders encompass more than 30 diseases, most of which show dominant inheritance, such as Huntington's disease, spinocerebellar ataxias, and myotonic dystrophies. Yet others, including Friedreich's ataxia, are recessively inherited. A common feature is the presence of a DNA tandem repeat in the disease-associated gene and the propensity of the repeats to expand in germ and in somatic cells, with ensuing neurological and frequently also neuromuscular defects. Repeat expansion is the most frequent event in these diseases; however, sequence contractions, deletions, and mutations have also been reported. Nucleotide repeat sequences are predisposed to adopt non-B-DNA conformations, such as hairpins, cruciform, and intramolecular triple-helix structures (triplexes), also known as H-DNA. For gain-of-function disorders, oligonucleotides can be used to target either transcripts or duplex DNA and in diseases with recessive inheritance oligonucleotides may be used to alter repressive DNA or RNA conformations. Most current treatment strategies are aimed at altering transcript levels, but therapies directed against DNA are also emerging, and novel strategies targeting DNA, instead of RNA, are described. Different mechanisms using modified oligonucleotides are discussed along with the structural aspects of repeat sequences, which can influence binding modes and efficiencies.

An Integrated Safety Analysis of Infants and Children with Symptomatic Spinal Muscular Atrophy (SMA) Treated with Nusinersen in Seven Clinical Trials

BACKGROUND

Treatment with nusinersen has demonstrated significant and clinically meaningful benefits in clinical trials in infants and children with spinal muscular atrophy (SMA).

OBJECTIVE

The objective of this analysis was to characterize the safety of nusinersen across the clinical trial program in infants and children with symptomatic SMA.

METHODS

An integrated safety analysis evaluated end of study data from seven completed clinical trials that enrolled infants and children with symptomatic SMA who were treated with intrathecal nusinersen or underwent sham procedures. Two of the studies were conducted in symptomatic infants with infantile-onset SMA (most likely to develop SMA type I or II) and the remaining five in symptomatic children and adolescents with later-onset SMA (have or are most likely to develop SMA type II or III). Safety assessments included incidence of adverse events (AEs), physical and neurological examinations, vital signs, clinical laboratory tests (serum chemistry, hematology, and urinalysis), and electrocardiograms.

RESULTS

Data were analyzed from 323 infants and children, including 240 treated with nusinersen (100 with infantile-onset SMA and 140 with later-onset SMA) and 83 who underwent sham procedures (41 infantile-onset, 42 later-onset). Median (range) exposure to nusinersen was 449.0 (6-1538) days (375.9 participant-years). The most common AEs with nusinersen were pyrexia, upper respiratory tract infection, nasopharyngitis, vomiting, headache, and constipation. The incidence of serious AEs was lower with nusinersen than with the sham procedure (41% vs. 61%). The overall incidence of respiratory, thoracic, and mediastinal AEs was higher in participants with symptomatic infantile-onset SMA than those with symptomatic later-onset SMA and similar in nusinersen- versus sham procedure-treated participants. Rates of post-lumbar puncture syndrome and related events were higher with nusinersen versus sham procedure in later-onset SMA participants. No abnormal patterns or trends in laboratory test results were observed.

CONCLUSIONS

Nusinersen demonstrated a favorable safety profile in children with symptomatic infantile- and later-onset SMA. Most reported AEs and serious AEs were consistent with the nature and frequency of events typically seen with SMA or in the context of lumbar puncture procedures.

REGISTRATION

NCT01494701, NCT01703988, NCT01839656, NCT02193074, NCT02292537, NCT01780246, NCT02052791.

Therapeutic Oligonucleotides: State of the Art

Oligonucleotides (ONs) can interfere with biomolecules representing the entire extended central dogma. Antisense gapmer, steric block, splice-switching ONs, and short interfering RNA drugs have been successfully developed. Moreover, antagomirs (antimicroRNAs), microRNA mimics, aptamers, DNA decoys, DNAzymes, synthetic guide strands for CRISPR/Cas, and innate immunity-stimulating ONs are all in clinical trials. DNA-targeting, triplex-forming ONs and strand-invading ONs have made their mark on drug development research, but not yet as medicines. Both design and synthetic nucleic acid chemistry are crucial for achieving biologically active ONs. The dominating modifications are phosphorothioate linkages, base methylation, and numerous 2'-substitutions in the furanose ring, such as 2'-fluoro, O-methyl, or methoxyethyl. Locked nucleic acid and constrained ethyl, a related variant, are bridged forms where the 2'-oxygen connects to the 4'-carbon in the sugar. Phosphorodiamidate morpholino oligomers, carrying a modified heterocyclic backbone ring, have also been commercialized. Delivery remains a major obstacle, but systemic administration and intrathecal infusion are used for treatment of the liver and brain, respectively.