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Nucleic acid-based phosphorothioate containing antisense oligonucleotides (PS-ASOs) have the potential to activate cellular innate immune responses, and the level of activation can vary quite dramatically with sequence. Minimizing the degree of proinflammatory effect is one of the main selection criteria for compounds intended to move into clinical trials. While a recently developed human peripheral blood mononuclear cell (hPBMC)-based assay showed excellent ability to detect innate immune active PS-ASOs, which can then be discarded from the developmental process, this assay is highly resource intensive and easily affected by subject variability. This compelled us to develop a more convenient high-throughput assay. In this study, we describe a new

A human peripheral blood mononuclear cell (PBMC)-based assay was developed to identify antisense oligonucleotide (ASO) with the potential to activate a cellular innate immune response outside of an acceptable level. The development of this assay was initiated when ISIS 353512 targeting the messenger ribonucleic acid for human C-reactive protein (CRP) was tested in a phase I clinical trial, in which healthy human volunteers unexpectedly experienced increases in interleukin-6 (IL-6) and CRP. This level of immune stimulation was not anticipated following rodent and nonhuman primate safety studies in which no evidence of exaggerated proinflammatory effects were observed. The IL-6 increase induced by ISIS 353512 was caused by activation of B cells. The IL-6 induction was inhibited by chloroquine pretreatment of PBMCs and the nature of ASOs suggested that the response is mediated by a Toll-like receptor (TLR), in all likelihood TLR9. While assessing the inter PBMC donor variability, two classes of human PBMC responders to ISIS 353512 were identified (discriminator and nondiscriminators). The discriminator donor PBMCs were shown to produce low level of IL-6 after 24 h in culture, in the absence of ASO treatment. The PBMC assay using discriminator donors was shown to be reproducible, allowing to assess reliably the immune potential of ASOs by comparison to known benchmark ASO controls that were previously shown to be either safe or inflammatory in clinical trials. Clinical Trial registration numbers: NCT00048321 NCT00330330 NCT00519727.

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.

Inotersen (TEGSEDI™) is a 2'-O-(2-methoxyethyl)-modified antisense oligonucleotide, intended for treating hereditary transthyretin (TTR) amyloidosis with polyneuropathy. The potential immunogenicity (IM) response to inotersen was evaluated in chronic nonclinical safety studies and the pivotal phase 2/3 clinical study. The evaluation was designed to assess the characteristics of antidrug antibodies (ADAs) and their effects on the pharmacokinetics, pharmacodynamics, clinical efficacy, and safety in animals and humans. No immunogenic response was observed after long-term treatment with inotersen in mice. In monkeys, the incidence rate of IM to inotersen appeared to be dose dependent, with 28.6%-50.0% of animals developing ADAs after 36 weeks of treatment. This was characterized as late onset (median onset of 185 days) with low titers (median titer of 8, or 400 if minimum required dilution of 50 is included). The overall incidence rate of patients who developed ADAs was 30% after 65 weeks of treatment with median onset of 203 days and median peak titer of 300. IM had minimal effect on plasma peak (Cmax) and total exposure (i.e. area under curve, AUC) of inotersen, but showed elevated plasma trough levels in both IM-positive animals and humans. However, ADAs had no effect on tissue exposure, TTR messenger RNA, or plasma TTR levels in the long-term monkey study. Similarly, IM showed no effect on plasma TTR levels in clinical studies. Thus, ADAs antibodies were binding antibodies, but not neutralizing antibodies. Finally, no association was observed between IM and toxicity findings (eg, platelet, complement activation, and histopathology findings) in the inotersen 9-month monkey study. In humans, no difference was observed in hematology, including platelets, kidney function tests, or incidence of adverse events between IM-positive and -negative patients. Overall, IM showed no effect on toxicity or safety of inotersen evaluated in both monkeys and humans. ClinicalTrials.gov Identifier: NCT01737398.

A population pharmacokinetic (PK) and pharmacodynamic (PD) model was developed for inotersen to evaluate exposure–response relationships and to optimize therapeutic dosing regimen in patients with hereditary transthyretin (TTR) amyloidosis polyneuropathy (hATTR-PN). Inotersen PK and TTR level (PD) data were composed of one Phase 1 study in healthy subjects, one Phase 2/3 study in hATTR patients, and its one open-label extension study. Effects of intrinsic and extrinsic factors (covariates) on PK and PK/PD of inotersen were evaluated using a full model approach. Inotersen PK was characterized by a two-compartment model with elimination from the central compartment. The population PK analysis identified disease status and lean body mass (LBM) as significant covariates for inotersen PK. Nonetheless, the contribution of disease status and LBM on PK was small, as the difference in clearance (CL/F) was 11.1% between healthy subjects and patients with hATTR-PN and 38% between the lowest and highest LBM quartiles of the patient population. Age, race, sex, baseline renal function estimated glomerular filtration rate, and hepatic function markers (baseline albumin, bilirubin, and alanine aminotransferase values) were not statistically significant covariates affecting inotersen PK. An inhibitory effect indirect-response model (inhibition of TTR production) was used to describe the drug effect on TTR-time profiles, with baseline TTR included as a covariate. The overall population Imax and IC50, together with 95% confidence interval, was estimated to be 0.913 (0.899–0.925) and 9.07 (8.08–10.1) ng/mL, respectively. V30M mutation showed no effect on the estimated IC50 value for hATTR patients. The final population PK and PK/PD model was used to simulate four different treatment regimens. The population PK/PD model developed well described the PK and PD of inotersen in patients with hATTR-PN and has been used for label recommendation and trial simulations.

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 × 10

Nucleic acid-based PS-ASOs have the potential to activate cellular innate immune responses, and the level of activation can vary quite dramatically with sequence. Minimizing degree of proinflammatory effect is one of the main selection criteria for compounds intended to move into clinical trials. While a recently developed hPBMC-based assay showed excellent ability to detect innate immune active PS-ASOs, which can then be discarded from the developmental process, this assay is highly resource-intensive and easily affected by subject variability. This compelled us to develop of a more convenient high-throughput assay. Here, we describe a new in vitro assay, utilizing a cultured human Bjab cell line, which was developed and validated to identify PS-ASOs that may cause innate immune activation. The assay was calibrated to replicate results from the hPMBC assay. The Bjab assay was designed to be high throughput and more convenient by using RT-qPCR readout of mRNA of the chemokine Ccl22. The Bjab assay was also shown to be highly reproducible and to provide a large dynamic range in determining the immune potential of PS-ASOs via comparison to known benchmark PS-ASO controls that were previously shown to be either safe or inflammatory in clinical trials. In addition, we demonstrate that Bjab cells can be used to provide mechanistic information on PS-ASO-TLR9 dependent innate immune activation.

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.

Thrombocytopenia is one of the most commonly observed drug-induced adverse hematologic toxicities in the clinic. Therefore, in vitro and in vivo evaluations of effect of drugs on platelets are an important component in preclinical safety assessment in drug development. To date, a number of mechanisms have been identified to be associated with drug-mediated thrombocytopenia. Amongst these, some are conserved across species whereas others are not. Therefore, a case-by-case approach is needed to assess drug-induced thrombocytopenia at preclinical stages to understand translatability to humans. The present chapter reviews mechanisms in drug-mediated thrombocytopenia with a focus on nonimmune (direct myelotoxicity) as well as immune-mediated thrombocytopenia by both small and large molecule therapeutics. Several in vitro and in vivo models as well as challenges in assessing drug-mediated thrombocytopenia in preclinical stages will also be discussed.

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.

It is well documented and generally accepted that human clearance (CL) of unconjugated single-strand antisense oligonucleotides (ASOs) can be directly predicted from monkeys by body weight (BW) on a mg/kg dose basis. However, the scaling for triantennary N-acetyl galactosamine (GalNAc3)-conjugated ASOs has not been fully established. In this study, we retrospectively analyzed pharmacokinetic data from 9 GalNAc3-conjugated and 12 unconjugated single-stranded ASOs (ten 2'-methoxyethyl and two 2', 4'-constrained ethyl ASOs) to identify an appropriate allometric scaling factor between the two species. In addition, we compared the trough plasma concentrations (Ctrough, a surrogate for tissue exposure) between monkeys and humans at comparable dose levels, aiming at predicting tissue distribution in humans from monkeys. Overall, the median plasma CL ratios (monkey CL/human CL) were 1.05 and 0.94 when CL was normalized by BW, as compared with 0.33 and 0.29 when CL was normalized by body surface area (BSA) for the 12 unconjugated and 9 GalNAc3-conjugated ASOs, respectively. Similarly, the median Ctrough ratios (Ctrough in monkeys/Ctrough in humans) were 0.96 and 1.71, respectively, when Ctrough was normalized by mg/kg dose as compared with 3.10 and 5.50 when Ctrough was normalized by mg/m2 dose for the same unconjugated and conjugated ASOs, respectively. Equivalent CL and dose-normalized plasma Ctrough between monkeys and humans suggest similar pharmacokinetic profiles and tissue distribution between the two species on a per kilogram BW basis. In conclusion, human CL and plasma Ctrough (a surrogate of tissue distribution) can be directly predicted (1:1 or within twofold) from monkeys by BW on a mg/kg dose basis but these parameters can be under- or over-predicted by BSA on a mg/m2 dose basis. These results provide evidence for single species scaling from monkeys to humans directly and, thus, they can facilitate early human dose prediction in ASO drug development.

Background: AZD8233 is a chemically modified 16-mer antisense oligonucleotide linked to N-acetyl galactosamine (GalNAc) for efficient targeting of PCSK9 mRNA in hepatocytes to prevent the synthesis of PCSK9. We are reporting preliminary data from the first in human study. The aim with the study was to evaluate the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of single doses of AZD8233 in subjects with LDL-C ≥100 mg/dL. Methods: This was a randomized, single-blind, placebo-controlled; single ascending dose study (NCT03593785) of AZD8233 administered subcutaneously (SC) to 56 subjects enrolled in 7 cohorts (6 on active and 2 on placebo in each cohort). Doses studied ranged from 4 to 120 mg. Serial blood samples were collected to assess PK, PCSK9 and LDL-C profiles after administration of AZD8233. PK parameters were calculated using non-compartmental methods. Results: After SC administration, AZD8233 was generally well tolerated, no clinically relevant safety and tolerability findings were observed and no serious adverse events were reported. Peak plasma concentrations were achieved within 1 to 3 hours after dosing. After peaking, plasma concentrations declined biphasically with a terminal half-life of 2 to 3 weeks. A dose dependent decrease in plasma levels of PCSK9 and LDL-C was observed. The largest mean percent reductions from baseline were >90 % for PCSK9 and 70% for LDL-C. PCSK9 and LDL-C levels slowly returned to baseline or close to baseline levels over the 16 weeks post dose follow up period. Conclusions: The safety, PK and PD support further evaluation of AZD8233 in multiple ascending dose studies. The PD data indicate that a high level of PCSK9 and LDL-C reduction can be maintained over a dose interval of once monthly or less frequent at a dose below 100mg.

Inotersen (TEGSEDI™) is a 2'

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

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 Pselectin) 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 mM). 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.

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.

Advances in antisense oligonucleotide (ASO) chemistry and screening have enabled the design and selection of molecules that are optimized for a particular therapeutic application in terms of both potency and tolerability. The most-well studied of the chemically modified ASOs are single-stranded antisense inhibitors with phosphorothioate backbones and 2'-O-methoxyethyl modifications (2'-MOE ASO). The 2'-MOE chemical modification in the design of the ASO has conferred increased hybridization affinity, increased stability, and/or enhanced tissue residence time, resulting in better potency and pharmacokinetics. Compound screening and selection are also important in optimizing the tolerability of intended therapeutic antisense inhibitors. In this study, we report the chronic toxicity of multiple 2'-MOE ASOs in mice for several representative compounds that have progressed to later phases of clinical development. The results show that these 2'-MOE ASOs selected for development have consistent behavior between sequences, have tolerability profiles suitable for chronic administration, and exhibit a relative lack of progression of findings observed in subchronic studies in mice.

ISIS 104838, a 2'-O-methoxyethyl (2'-MOE)-modified antisense oligonucleotide (ASO), causes a moderate, reproducible, dose-dependent, but selflimiting decrease in platelet (PLT) counts in monkeys and humans. To determine the etiology of PLT decrease in cynomolgus monkeys, a 12-week repeat dose toxicology study in 5 cynomolgus monkeys given subcutaneous injections of ISIS 104838 (30-60 mg/kg/week). Monkeys were also injected intravenously with 111Indium(In)-oxine-labeled PLTs to investigate PLT sequestration. In response to continued dosing, PLT counts were decreased by 50%-90% by day 30 in all monkeys. PLT decreases were accompanied by 2- to 4.5-fold increases in immunoglobulin M(IgM), which were typified by a 2- to 5-fold increase in antiplatelet factor 4 (antiPF4) IgM and antiPLT IgM, respectively. Monocyte chemotactic protein 1 increased upon dosing of ISIS 104838, concomitant with a 2- to 6-fold increase in monocyte-derived extracellular vesicles (EVs), indicating monocyte activation but not PLT activation. Despite a 2- to 3-fold increase in von Willebrand factor antigen in all monkeys following ASO administration, only 2 monkeys showed a 2- to 4-fold increase in endothelial EVs. Additionally, a ∼60 - 80%% increase in PLT sequestration in liver and spleen was also observed. Collectively, these results suggest the overall increase in total IgM, antiPLT IgM and/or antiPF4 IgM, in concert with monocyte activation contributed to increased PLT sequestration in spleen and liver, leading to decreased PLTs in peripheral blood.

Antisense oligonucleotides are metabolized by nucleases and drug interactions with small drug molecules at either the cytochrome P450 (CYP) enzyme or transporter levels have not been observed to date. Herein, a comprehensive in vitro assessment of the drug-drug interaction (DDI) potential was carried out with four 2′-O-(2-methoxyethyl)-modified antisense oligonucleotides (2′-MOE-ASOs), including a single triantennary N-acetyl galactosamine (GalNAc3)-conjugated ASO. Several investigations to describe the DDI potential of a 2′-MOE-ASO conjugated to a high-affinity ligand for hepatocyte-specific asialoglycoprotein receptors are explored. The inhibition on CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 and induction on CYP1A2, CYP2B6, and CYP3A4 were investigated in cryopreserved hepatocytes using up to 100 μM of each ASO. No significant inhibition (half maximal inhibitory concentration [IC50] > 100 μM) or induction was observed based on either enzymatic phenotype or mRNA levels. In addition, transporter interaction studies were conducted with nine major transporters per recommendations from regulatory guidances and included three hepatic uptake transporters, organic cation transporter 1 (OCT1), organic anion transporting polypeptide 1B1 (OATP1B1), and OATP1B3; three renal uptake transporters, organic anion transporter 1 (OAT1), OAT3, and OCT2; and three efflux transporters, P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and bile salt export pump (BSEP). None of the four ASOs (10 μM) were substrates of any of the nine transporters, with uptake

This white paper, which is the 10th in a series intended to address issues associated with the development of therapeutic oligonucleotides, examines the subject of product-related impurities. The authors consider chemistry and safety aspects and advance arguments in favor of platform approaches to impurity identification and qualification. Reporting, identification, and qualification thresholds suitable for product-related impurities of therapeutic oligonucleotides are proposed.

Decreases in platelet (PLT) counts observed in nonhuman primates (NHPs) given 2'-O-methoxyethyl modified antisense inhibitors (2'-MOE ASOs) have been reported, but the incidence and severity of the change vary considerably between sequences, studies, and animals. This article will broadly illustrate the spectrum of effects on PLT count in NHPs. From queries of an NHP safety database representing over 102 independent 2'-MOE ASOs, from 61 studies and2200 NHPs, two patterns of PLT changes emerged. The first is a consistent and reproducible decrease in group mean values, observed with about 30% of the compounds, in which PLT count typically remains ≥150K cells/μL. The second is a sporadic decrease in PLTs to50K cells/μL (2%-4% incidence at doses5 mg/kg) that is often not reproducible. In both cases, the reduction in PLT count is dose dependent and reversible. The human relevance of PLT change observed in NHPs was investigated using ISIS 404173. In a chronic NHP study (20 mg/kg/wk for 26 weeks), a gradual decrease in group mean PLT count was observed at ≥10 mg/kg/wk, which plateaued by 13 weeks generally within the normal range and was maintained through 26 weeks of treatment. However, PLT counts50K cells/μL occurred in 1 of 16 NHP at 10 mg/kg/wk and 3 of 16 NHP at 20 mg/kg/wk. In a 26-week double-blind, placebo-controlled Phase 2 trial, 62 patients were treated with 200 mg/wk ISIS 404173 (∼3.3 mg/kg/wk) there was an increased incidence of PLT count30% decreased compared to baseline but no incidence of PLT75K cells/μL. Based on these data, the consistent, self-limiting PLT reduction seen in NHP may translate to humans, but these changes appear to be of limited clinical significance. However, NHPs appear to overpredict the incidence of sporadic PLT50K cells/μL compared to humans.

Nusinersen is an antisense oligonucleotide intended for the treatment of spinal muscular atrophy. The pharmacokinetics of nusinersen, following intrathecal administrations, in the cerebrospinal fluid (CSF) and plasma of 72 pediatric patients (3 months to 17 years) with spinal muscular atrophy across 5 clinical trials was analyzed via population-based modeling. With sparse data in the CSF and profile data in the plasma, a linear 4-compartment model simultaneously described the time-concentration profiles in both matrices. The typical population parameters were: Qp = 0.572 L/h, QCSF = 0.069 L/h, CLp = 2.50 L/h, CLCSF = 0.133 L/hr, VCSF = 0.441 L, Vp = 32.0 L, Vsystemic_tissue = 429 L, and VCNS_tissue = 258 L. A full covariate modeling approach identified baseline body weight to be a statistically and clinically relevant covariate on VCSF , Vp , and CLp . The model predicted that the CSF volume of distribution increased steadily with age from 0 to 2 years but became relatively steady for children >2 years. Simulations from the final model showed that age-based dosing in children under 2 years ensured a more comparable exposure (peak concentration and area under the concentration-time curve) across subjects in the population relative to a fixed dosing scheme. However, because no dose-limiting toxicity has been reported in any of the trials, a fixed-dose scheme (12 mg across all age groups) was recommended. The median terminal half-life of nusinersen in the CSF was determined from the model to be 163 days, which supported infrequent dosing, once every 4 to 6 months in pediatric patients with spinal muscular atrophy.

IONIS-GCGRRx (ISIS 449884) is an antisense oligonucleotide inhibitor of the glucagon receptor (GCGR). The objective of this study was to evaluate the pharmacokinetics (PK) and pharmacodynamics (PD) of IONIS-GCGRRx via population-based modeling. The observed data were obtained from a Phase 1 (50, 100, 200, 300 and 400 mg) single- and multiple-dose study in healthy volunteers and a Phase 2 (100 and 200 mg) multiple-dose study in T2DM patients. The PK of IONIS GCGRRx was characterized by two primary systemic compartments and three absorption transit compartments with elimination out of the peripheral compartment. The fasting plasma glucose (FPG) PD was an indirect-response model (inhibition of FPG production) linked to the HbA1c PD model which was a semi-mechanistic model capturing RBC maturation dynamics. Stepwise covariate modeling was performed to identify relevant covariates. In the PK model, bodyweight (BW) was the only significant covariate influencing tissue clearance, tissue volume and plasma volume. Plots of parameter–covariate relations indicate the influence of BW is clinically relevant. In the PD models, baseline HbA1c had a positive correlation with I max and baseline FPG had a negative correlation with the glycosylation rate (k gl ). Simulations from the final model showed that the doses tested in the Phase 2 were at or close to the maximum of the dose–response curve and that dose reduction down to 50 mg resulted in minimal effect to efficacy. The model was useful in supporting the decision for dose reduction in a subsequent trial.

The common chemical and biological properties of antisense oligonucleotides provide the opportunity to identify and characterize chemical class effects across species. The chemical class that has proven to be the most versatile and best characterized is the 2'-O-methoxyethyl chimeric antisense oligonucleotides. In this report we present an integrated safety assessment of data obtained from controlled dose-ranging studies in nonhuman primates (macaques) and healthy human volunteers for 12 unique 2'-O-methoxyethyl chimeric antisense oligonucleotides. Safety was assessed by the incidence of safety signals in standardized laboratory tests for kidney and liver function, hematology, and complement activation; as well as by the mean test results as a function of dose level over time. At high doses a number of toxicities were observed in nonhuman primates. However, no class safety effects were identified in healthy human volunteers from this integrated data analysis. Effects on complement in nonhuman primates were not observed in humans. Nonhuman primates predicted safe doses in humans, but over predicted risk of complement activation and effects on platelets. Although limited to a single chemical class, comparisons from this analysis are considered valid and accurate based on the carefully controlled setting for the specified study populations and within the total exposures studied.

The effects of repeated complement activation in cynomolgus monkeys after chronic antisense oligonucleotide (ASO) treatment were evaluated by using ISIS 104838, a representative 2'-O-methoxyethyl (2'-MOE) modified ASO. The treatment was up to 9 months with a total weekly dose of 30 mg/kg, given either as daily [4.3 mg/kg/day, subcutaneous (s.c.) injection] or once weekly [30 mg/kg, either as s.c. injection or 30-min intravenous (i.v.) infusion]. Acute elevations of complement split products (Bb and C3a) and a transient decrease in C3 occurred after the first dose and were drug plasma concentration dependent. However, with repeated complement activation after chronic ASO treatment, there were progressive increases in basal (predose) levels of Bb and C3a, and a sustained C3 reduction in all treated groups. There was also a progressive increase in C3d-bound circulating immune complex (CIC) that was considered secondary to the C3 depletion. Evidence of vascular inflammation was observed, mostly in the liver, kidney, and heart, and correlated with severe C3 depletion and increases in plasma IgG and IgM. Vascular inflammation was accompanied by increased C3 and IgM immunereactivity in the affected vasculatures and endothelial activation markers in serum. In summary, repeated complement activations in monkeys lead to a sustained decrease in circulating C3 over time. The concomitantly increased inflammatory signals and decreased CIC clearance due to impairment of complement function may lead to vascular inflammation after chronic ASO treatment in monkeys. However, based on the known sensitivity of monkeys to ASO-induced complement activation, these findings have limited relevance to humans.

Systemic lupus erythematosus is an autoimmune disease that manifests in widespread complement activation and deposition of complement fragments in the kidney. The complement pathway is believed to play a significant role in the pathogenesis and in the development of lupus nephritis. Complement factor B is an important activator of the alternative complement pathway and increasing evidence supports reducing factor B as a potential novel therapy to lupus nephritis. Here we investigated whether pharmacological reduction of factor B expression using antisense oligonucleotides could be an effective approach for the treatment of lupus nephritis. We identified potent and well tolerated factor B antisense oligonucleotides that resulted in significant reductions in hepatic and plasma factor B levels when administered to normal mice. To test the effects of factor B antisense oligonucleotides on lupus nephritis, we used two different mouse models, NZB/W F1 and MRL/lpr mice, that exhibit lupus nephritis like renal pathology. Antisense oligonucleotides mediated reductions in circulating factor B levels were associated with significant improvements in renal pathology, reduced glomerular C3 deposition and proteinuria, and improved survival. These data support the strategy of using factor B antisense oligonucleotides for treatment of lupus nephritis in humans.

Nucleoside analogs with 2'-modified sugar moieties are often used to improve the RNA target affinity and nuclease resistance of therapeutic oligonucleotides in preclinical and clinical development. Despite their enhanced nuclease resistance, oligonucleotides could slowly degrade releasing nucleoside analogs that have the potential to become phosphorylated and incorporated into cellular DNA and RNA. For the first time, the phosphorylation and DNA/RNA incorporation of 2'-O-(2-methoxyethyl) (2'-O-MOE) nucleoside analogs have been investigated. Using liquid chromatography/tandem mass spectrometry, we showed that enzymes in the nucleotide salvage pathway including deoxycytidine kinase (dCK) and thymidine kinase (TK1) displayed poor reactivity toward 2'-O-MOE nucleoside analogs. On the other hand, 2'-fluoro (F) nucleosides, regardless of the nucleobase, were efficiently phosphorylated to their monophosphate forms by dCK and TK1. Consistent with their efficient phosphorylation by dCK and TK1, 2'-F nucleoside analogs were incorporated into cellular DNA and RNA while no incorporation was detected with 2'-O-MOE nucleoside analogs. In conclusion, these data suggest that the inability of dCK and TK1 to create the monophosphates of 2'-O-MOE nucleoside analogs reduces the risk of their incorporation into cellular DNA and RNA.

The potential of QT prolongation of ten 2′-O-methoxyethyl-modified (2′-MOE) antisense oligonucleotides (ASOs) was evaluated retrospectively via exposure/response (ER) analysis using data from Phase 1 clinical studies in healthy subjects. All Phase 1 studies were double-blind, placebo-controlled, single and multiple ascending dose studies designed to assess the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics of the ASOs in healthy subjects. The active doses in these studies ranged from 50 to 450 mg administered by subcutaneous (SC) injection in single and multiple ascending dose cohorts. Two of the ten studies also included 2-h intravenous (IV) infusions up to 600 mg. Electrocardiogram (ECG) measurements were performed at baseline and selected time points (including Tmax). The correlation between QTcF intervals corrected for baseline (ΔQTcF) and the mean time-matched placebo (ΔΔQTcF) with PK plasma exposure when available was evaluated using a linear mixed-effects approach. There was no evidence for QTc prolongation associated with increasing plasma concentrations in healthy subjects, including exposures with treatment up to 450 mg administered SC or 600 mg by IV infusions, and concentrations that are 4–20 times the Cmax of the therapeutic dose, as assessed by both ΔQTcF and ΔΔQTcF. The ER analysis of the relationship between drug plasma concentration and ΔΔQTcF showed that the slope of the regression line was close to zero, and the upper bound of the 90% confidence interval at twice the mean observed (or predicted) Cmax (2 × Cmax) of the clinical therapeutic dose (ie, the highest clinically relevant plasma concentration) was well below 10 ms for all 10 compounds evaluated. Therefore, no concentration-dependent effect on QT prolongation was observed for any one of the ten 2′-MOE ASOs evaluated in Phase 1 studies. These results confirmed that 2′-MOE ASOs, as a chemical class, do not cause QT prolongation at clinically relevant dose levels.

Differences in sensitivity of monkeys and humans to antisense oligonucleotide (ASO)-induced complement alternative pathway (AP) activation were evaluated in monkeys, humans, and in serum using biochemical assays. Transient AP activation was evident in monkeys at higher doses of two 2'-O-methoxyethyl (2'-MOE) ASOs (ISIS 426115 and ISIS 183750). No evidence of AP activation was observed in humans for either ASO, even with plasma ASO concentrations that reached the threshold for activation in monkeys. The absence of complement activation in humans is consistent with a query of the Isis Clinical Safety Database containing 767 subjects. The in vivo difference in sensitivity was confirmed in vitro, as monkey and human serum exposed to increasing concentrations of ASO indicated that monkeys were more sensitive to AP activation with this class of compounds. The mechanistic basis for the greater sensitivity of monkeys to AP activation by 2'-MOE ASO was evaluated using purified human or monkey factor H protein. The binding affinities between a representative 2'-MOE ASO and either purified protein are similar. However, the IC50 of fluid-phase complement inhibition for monkey factor H is about 3-fold greater than that for human protein using either monkey serum or factor H-depleted human serum. Interestingly, there is a sequence variant in the monkey complement factor H gene similar to a single nucleotide polymorphism in humans that is correlated with decreased factor H protein function. These findings show that monkeys are more sensitive to 2'-MOE ASO-mediated complement activation than humans likely because of differences in factor H inhibitory capacity.

This white paper summarizes the current consensus of the Reproductive Subcommittee of the Oligonucleotide Safety Working Group on strategies to assess potential reproductive and/or developmental toxicities of therapeutic oligonucleotides (ONs). The unique product characteristics of ONs require considerations when planning developmental and reproductive toxicology studies, including (a) chemical characteristics, (b) assessment of intended and unintended mechanism of action, and (c) the optimal exposure, including dosing regimen. Because experience across the various classes of ONs as defined by their chemical backbone is relatively limited, best practices cannot be defined. Rather, points to consider are provided to help in the design of science-based reproductive safety evaluation programs based upon product attributes.

Spinal muscular atrophy (SMA) is a debilitating neuromuscular disease caused by the loss of survival of motor neuron (SMN) protein. Previously, we demonstrated that ISIS 396443, an antisense oligonucleotide (ASO) targeted to the SMN2 pre-mRNA, is a potent inducer of SMN2 exon 7 inclusion and SMN protein expression, and improves function and survival of mild and severe SMA mouse models. Here, we demonstrate that ISIS 396443 is the most potent ASO in central nervous system (CNS) tissues of adult mice, compared with several other chemically modified ASOs. We evaluated methods of ISIS 396443 delivery to the CNS and characterized its pharmacokinetics and pharmacodynamics in rodents and nonhuman primates (NHPs). Intracerebroventricular bolus injection is a more efficient method of delivering ISIS 396443 to the CNS of rodents, compared with i.c.v. infusion. For both methods of delivery, the duration of ISIS 396443-mediated SMN2 splicing correction is long lasting, with maximal effects still observed 6 months after treatment discontinuation. Administration of ISIS 396443 to the CNS of NHPs by a single intrathecal bolus injection results in widespread distribution throughout the spinal cord. Based upon these preclinical studies, we have advanced ISIS 396443 into clinical development.

Triantennary N-acetyl galactosamine (GalNAc3)-conjugated antisense oligonucleotides (ASOs) have greatly improved potency due to receptor-mediated uptake into hepatocyte. The disposition and pharmacokinetics of ISIS 681257, a GalNAc3-conjugated ASO, were studied in monkeys. Following subcutaneous (SC) injection, ISIS 681257 was rapidly absorbed into the systemic circulation, with peak plasma levels observed within hours after dosing. After reaching Cmax, plasma concentrations rapidly declined in a multiexponential manner and were characterized by a dominant initial rapid distribution phase in which drug transferred to tissues from circulation, followed by a much slower terminal elimination phase (half-life of 4 weeks). Intact ISIS 681257 is the major full-length oligonucleotide species in plasma (≥70%). In tissues, the conjugated-GalNAc sugar moiety was rapidly metabolized, leaving the fully unconjugated form as the only full-length oligonucleotide detected at 48 h after dosing. Unconjugated ISIS 681257 cl...

To investigate the pharmacokinetics (PKs) and pharmacodynamics (PDs) for ION-353382, an antisense oligonucleotide (ASO) targeting scavenger receptor class B type I (SRB1) mRNA, using alpha-2-macroglobulin (A2M), murinoglobulin double-knockout (DKO), and wild-type mice. Wild-type and DKO homozygous mice were administered a single subcutaneous injection of ION-353382 at 0, 5, 15, 30, and 60 mg/kg. Mice were sacrificed at 72 h with plasma and organs harvested. Both liquid chromatography-mass spectrometry (LC-MS) and enzyme-linked immunosorbent assay (ELISA) were used to determine ASO exposure with real-time PCR for SRB1 expression. Immunohistochemistry was evaluated to explore hepatic uptake of ASOs. The total plasma protein binding and profiling was assessed. Finally, two-dimensional gel electrophoresis identified protein expression differences. PK exposures were comparable between wild-type and DKO mice in plasma, liver, and kidney, yet a near twofold reduction in EC50 was revealed for DKO mice based on an inhibitory effect liver exposure response model. Total plasma protein binding and profiling revealed no major dissimilarities between both groups. Plasma proteome fingerprinting confirmed protein expression variations related to A2M. Histological examination revealed enhanced ASO distribution into hepatocytes and less nonparenchymal uptake for DKO mice compared to wild-type mice. Knocking out A2M showed improved PD activities without an effect on total plasma and tissue exposure kinetics. Binding to A2M could mediate ASOs to nonproductive compartments, and thus, decreased binding of ASOs to A2M could potentially improve ASO pharmacology.

This article provides an overview of the discussions held by the Immunomodulatory Subcommittee of the Oligonucleotide Safety Working Group on complement activation induced by oligonucleotides, most notably the phosphorothioate-containing oligonucleotides. Alternative complement pathway activation in monkeys is a common effect of single-stranded phosphorothioate backbone oligonucleotides in toxicology studies. This article discusses the mechanism for activation, general investigational strategy, and the impact of various chemical modifications. The goal is to provide the best practice approach to characterizing this effect, understanding the implication of the species specificity, and the interpretation of clinical relevance.

The primary target organ for uptake of systemically administered phosphorothioate oligonucleotides is the kidney cortex and the proximal tubular epithelium in particular. To determine the effect of oligonucleotide uptake on renal function, a detailed renal physiology study was performed in cynomolgus monkeys treated with 10–40 mg/kg/week ISIS 113715 for 4 weeks. The concentrations of oligonucleotide in the kidney cortex ranged from 1400 to 2600 μg/g. These concentrations were associated with histologic changes in proximal tubular epithelial cells that ranged from the appearance of cytoplasmic basophilic granules to atrophic and degenerative changes at higher concentrations. However, there were no renal functional abnormalities as determined by the typical measurements of blood urea nitrogen, serum creatinine, creatinine clearance, or urine specific gravity. Nor were there changes in glomerular filtration rate, or renal blood flow. Specific urinary markers of tubular epithelial cell damage, such as N-acetyl-glucosaminidase, and α-glutathione-s-transferase were not affected. Tubular function was further evaluated by monitoring the urinary excretion of amino acids, β 2 -microglobulin, or glucose. Renal function was challenged by administering a glucose load and by examining concentrating ability after a 4-h water deprivation. Neither challenge produced any evidence of change in renal function. The only change observed was a low incidence of increased urine protein/creatinine ratio in monkeys treated with ≥40 mg/kg/week which was rapidly reversible. Collectively, these data indicate that ISIS 113715-uptake by the proximal tubular epithelium has little or no effect on renal function at concentrations of 2600 μg/g.

ISIS 388626, a 2'-methoxyethyl (MOE)-modified antisense oligonucleotide (ASO) that targets human sodium glucose cotransporter 2 (SGLT2) mRNA, is in clinical trials for the management of diabetes. SGLT2 plays a pivotal role in renal glucose reabsorption, and inhibition of SGLT2 is anticipated to reduce hyperglycemia in diabetic subjects by increasing urinary glucose elimination. To selectively inhibit SGLT2 in the kidney, ISIS 388626 was designed as a "shortmer" ASO, consisting of only 12 nucleotides with two 2'-MOE-modified nucleotides at the termini. Mice and monkeys received up to 30 mg/kg/week ISIS 388626 via subcutaneous injection for 6 or 13 weeks. Dose-dependent decreases in renal SGLT2 mRNA expression were observed, which correlated with dose-related increases in glucosuria without concomitant hypoglycemia. There were no histologic changes in the kidney attributed to SGLT2 inhibition after 6 or 13 weeks of treatment. The remaining changes observed in these studies were typical of those produced in these species by the administration of oligonucleotides, correlated with high doses of ISIS 388626, and were unrelated to the inhibition of SGLT2 expression. The kidney contained the highest concentration of ISIS 388626, and dose-dependent basophilic granule accumulation in tubular epithelial cells of the kidney, which is evidence of oligonucleotide accumulation in these cells, was the only histologic change identified. No changes in kidney function were observed. These results revealed only readily reversible changes after the administration of ISIS 388626 and support the continued investigation of the safety and efficacy of ISIS 388626 in human trials.

Introduction Antisense oligonucleotides (ASOs) are a new class of single-stranded DNA based drugs that hold great therapeutic promise for their disease modifying potential in a wide range of genetic diseases. Preclinical toxicology studies in monkeys, as well as late stage clinical trials in humans, have upon repeated dosing, reported events of ASO sequence-specific lowering of platelet counts (mild to severe thrombocytopenia) (Henry et al. Nucleic acid therapeutics 2017). The underlying cause of this platelet decrease is still unclear in humans. We have investigated if the thrombocytopenia associated with ASOs is due to either impaired platelet production and/or destruction of platelets (clearance) due to increased platelet reactivity (activation/aggregation status). Preliminary data from mouse derived fetal liver megakaryocytes suggest that pro-platelet production does not seem to be reduced by ASOs and hence in the current study we hypothesized that the ASO-induced thrombocytopenia is due to increased clearance of platelets from the circulation. Methods In the current study we explored how ASOs affect platelet aggregation in platelet rich plasma (PRP) and platelet-leukocyte aggregates in whole blood (WB) obtained from healthy volunteers after informed consent. PRP or WB was treated with a clinically relevant concentration of ASO (5µM) corresponding to expected maximum plasma concentration levels, or a 20x-supra-therapeutic concentration (100µM). Four ASOs were tested: two CpG-rich phosphorothioate deoxyoligonucleotide (PS ODN) sequences: 818290 and 120704, and two non-CpG 2'-MOE containing sequences: 104838 and 501861. 818290 was included as a positive control since it has been shown to cause direct platelet activation (Flierl et al. JEM 2015). 104838 have been reported to cause moderate, dose dependent drops in platelet counts in monkeys and humans, with platelet sequestration in the liver and spleen (Narayanan PK, et al. Toxicol Sci. 2018). 501861 has triggered sporadic severe thrombocytopenia in select monkeys. ASO treated PRP was analyzed for platelet aggregation using 96-well optimul aggregometry (Lordkipanidzé et al. Blood 2014) in the presence of vehicle (PBS) or 6 concentrations of thrombin receptor activating peptide-6 (0.08-80µM,TRAP6). In a separate experiment, PRP was incubated with ASOs plus the spleen tyrosine kinase (Syk) inhibitor PRT-060318 (10µM). ASO treated WB was incubated with fluorescently labelled CD41/61 antibody to label platelets and a leukocyte-specific antibody CD14, and platelet-leukocyte aggregates were analyzed by FACS according to (Gerrits et al. Curr. Protoc. 2016). Results The two non-CpG rich 2'-MOE ASO sequences 104838 and 501861 did not affect platelet aggregation at either concentration (5µM + 100µM) (Figure 1 A+B). Whilst the two CpG-rich PS ODN ASOs (818290 and 120704) triggered spontaneous platelet aggregation in PRP at 100µM (Figure 1 C+D), that was normalized by co-incubating these ASOs with a Syk inhibitor (Figure 2). 5µM of ASO treatment triggered a significant increase in platelet-leukocyte aggregates in WB for all the ASOs tested (Figure 3). Conclusion We have shown that the two CpG-rich PS ODN ASOs (818290 and 120704) triggered spontaneous platelet aggregation in PRP at 100µM. This effect was inhibited by a Syk inhibitor. 818290 has previously been identified to activate platelets through a Syk-dependent, GPVI receptor mediated mechanism (Flierl et al. JEM 2015). Here, we report for the first time that the aggregatory effects of 120704 have been identified to be Syk dependent as well, possibly through a similar interaction with platelet GPVI receptors. We have also presented novel data that therapeutically relevant concentrations of all the ASOs tested cause an increase in platelet-leukocyte aggregates in WB. Based on these data we highlight the importance of screening ASOs in multi-cellular assays, not just PRP, since there was no effect of the ASOs 104838 or 501861 on platelet aggregation. Enhanced formation of platelet-leukocyte aggregates could be one contributing factor for increased platelet clearance, explaining ASO-induced thrombocytopenia. Further investigation into the ASO-induced interactions between platelets and immune cells are warranted. Defining the mechanisms by which ASO-based drugs cause low platelet count may yield strategies to manage this drug-induced thrombocytopenia in patients. Disclosures Thon: Platelet Biogenesis: Employment, Equity Ownership, Other: Co-founder, Patents & Royalties. Henry:Ionis Pharmaceuticals: Employment. Narayanan:Ionis Pharmaceuticals: Employment. Italiano:Platelet Biogenesis: Equity Ownership, Other: Co-founder, Patents & Royalties.

Diabetic retinopathy is one of the leading causes of blindness in the United States and other parts of the world. Historically, laser photocoagulation and vitrectomy surgery have been used for the treatment of diabetic retinopathy, including diabetic macular edema. Both procedures have proven to be useful under certain conditions but have their limitations. New pathways and processes that promote diabetic retinopathy have been identified, and several new therapeutic approaches are under investigation. These new therapies may be beneficial in the treatment of diabetic retinopathy and include antivascular endothelial growth factor agents, corticosteroids, and therapies that may potentially target a number of additional diabetic retinopathy-related factors and processes, including antisense oligonucleotides. Second-generation antisense oligonucleotides, such as iCo-007, may offer a significant advantage in the treatment of diabetic retinopathy by downregulating the signal pathways of multiple growth factors that seem to play a critical role in the process of ocular angiogenesis and vascular leakage. Benefits of such molecules are expected to include the specificity of the kinase target and an extended half-life, resulting in less frequent intravitreal drug administration, resistance to molecule degradation, and a good safety profile.

High affinity antisense oligonucleotides (ASOs) containing bicylic modifications (BNA) such as locked nucleic acid (LNA) designed to induce target RNA cleavage have been shown to have enhanced potency along with a higher propensity to cause hepatotoxicity. In order to understand the mechanism of this hepatotoxicity, transcriptional profiles were collected from the livers of mice treated with a panel of highly efficacious hepatotoxic or non-hepatotoxic LNA ASOs. We observed highly selective transcript knockdown in mice treated with non-hepatotoxic LNA ASOs, while the levels of many unintended transcripts were reduced in mice treated with hepatotoxic LNA ASOs. This transcriptional signature was concurrent with on-target RNA reduction and preceded transaminitis. Remarkably, the mRNA transcripts commonly reduced by toxic LNA ASOs were generally not strongly associated with any particular biological process, cellular component or functional group. However, they tended to have much longer pre-mRNA transcripts. We also demonstrate that the off-target RNA knockdown and hepatotoxicity is attenuated by RNase H1 knockdown, and that this effect can be generalized to high affinity modifications beyond LNA. This suggests that for a certain set of ASOs containing high affinity modifications such as LNA, hepatotoxicity can occur as a result of unintended off-target RNase H1 dependent RNA degradation.