Less Is More: Novel Hepatocyte-Targeted siRNA Conjugates for Treatment of Liver-Related Disorders

GalNac-siRNA conjugate delivery technology promotes the treatment of typical chronic liver diseases

INTRODUCTION

Nucleic acid-based therapeutics have become a key pillar of the 'third wave' of modern medicine, following the eras of small molecule inhibitors and antibody drugs. Their rapid progress is heavily dependent on delivery technologies, with the development of N-acetylgalactosamine (GalNAc) conjugates marking a breakthrough in targeting liver diseases. This technology has gained significant attention for its role in addressing chronic conditions like chronic hepatitis B (CHB) and nonalcoholic steatohepatitis (NASH), which are challenging to treat with conventional methods.

AREAS COVERED

This review explores the origins, mechanisms, and advantages of GalNAc-siRNA delivery systems, highlighting their ability to target hepatocytes via the asialoglycoprotein receptor (ASGPR). The literature reviewed covers preclinical and clinical advancements, particularly in CHB and NASH. Key developments in stabilization chemistry and conjugation technologies are examined, emphasizing their impact on enhancing therapeutic efficacy and patient compliance.

EXPERT OPINION

GalNAc-siRNA technology represents a transformative advancement in RNA interference (RNAi) therapies, addressing unmet needs in liver-targeted diseases. While significant progress has been made, challenges remain, including restricted targeting scope and scalability concerns. Continued innovation is expected to expand applications, improve delivery efficiency, and overcome limitations, establishing GalNAc-siRNA as a cornerstone for future nucleic acid-based treatments.

Trivalent siRNA-Conjugates with Guanosine as ASGPR-Binder Show Potent Knock-Down In Vivo

To increase the chemical space around the well-known GalNAc-ligand as ASGPR-binder, a high-throughput screening campaign was performed, testing approximately 550,000 compounds. After evaluation of the potential screening hits, only one compound, which showed high similarity with guanosine nucleosides, was chosen for further profiling. Crystal structure analysis revealed the coordination of the Ca2+-ion within the ASGPR-binding site by the cis-diol motif of the ribose unit as well as an additional π-π-interaction of the purine heterocycle to tryptophan-243. Based on these findings, guanosine was attached via the 5'-OH group to a recently described morpholino-based nucleotide using two different linker units. The resulting morpholino-guanosine building blocks were conjugated to the 5'-end of a literature-known transthyretin targeting small interfering RNA (siRNA), leading to trivalent siRNA-guanosine conjugates, which were tested for their TTR knockdown and exhibited similar potencies as the analogous GalNAc-conjugates in vitro and in vivo.

Expanding Conjugate Space of RNAi Therapeutics: Ligand at the 3' End of the Antisense Strand Achieves Uncompromised In Vivo Potency and Efficacy and Reveals Interactions with the Argonaute-2 PAZ Domain

The conjugation of the sense strands of small interfering RNA (siRNA) to tri-N-acetylgalactosamine (GalNAc), the ligand for a hepatocyte-specific receptor, enables the delivery of multiple clinically approved therapeutic agents that act through the RNA interference pathway. Here, we report the systematic evaluation of siRNAs with the 3' termini of antisense strands conjugated to GalNAc for the first time. These designs retained the same receptor affinity, in vitro and in vivo activities, as well as the same level of loading into the RNA-induced silencing complex as siRNAs with a GalNAc-conjugated sense strand. A siRNA with a GalNAc-conjugated antisense strand of 22 nucleotides had better activity than a siRNA with a 23-nucleotide antisense strand. Computational modeling of a complex of a GalNAc-conjugated antisense strand with the PAZ domain of Ago2 rationalizes the importance of the interaction of phosphate at the 3' terminus with the PAZ domain to explain the observed activity of these siRNAs.

Hepatocyte targeting via the asialoglycoprotein receptor

This review highlights the potential of asialoglycoprotein receptor (ASGPR)-mediated targeting in advancing liver-specific treatments and underscores the ongoing progress in the field. First, we provide a comprehensive examination of the nature of ASGPR ligands, both natural and synthetic. Next, we explore various drug delivery strategies leveraging ASGPR, with a particular emphasis on the delivery of therapeutic nucleic acids such as small interfering RNAs (siRNAs) and antisense oligonucleotides (ASOs). An in-depth analysis of the current status of RNA interference (RNAi) and ASO-based therapeutics is included, detailing approved therapies and those in various stages of clinical development (phases 1 to 3). Afterwards, we give an overview of other ASGPR-targeted conjugates, such as those with peptide nucleic acids or aptamers. Finally, targeted protein degradation of extracellular proteins through ASGPR is briefly discussed.

Development of bioconjugate-based delivery systems for nucleic acids

Nucleic acids are a class of drugs that can modulate gene and protein expression by various mechanisms, namely, RNAi, mRNA degradation by RNase H cleavage, splice modulation, and steric blocking of protein binding or mRNA translation, thus exhibiting immense potential to treat various genetic and rare diseases. Unlike protein-targeted therapeutics, the clinical use of nucleic acids relies on Watson-Crick sequence recognition to regulate aberrant gene expression and impede protein translation. Though promising, targeted delivery remains a bottleneck for the clinical adoption of nucleic acid-based therapeutics. To overcome the delivery challenges associated with nucleic acids, various chemical modifications and bioconjugation-based delivery strategies have been explored. Currently, liver targeting by N-acetyl galactosamine (GalNAc) conjugation has been at the forefront for the treatment of rare and various metabolic diseases, which has led to FDA approval of four nucleic acid drugs. In addition, various other bioconjugation strategies have been explored to facilitate active organ and cell-enriched targeting. This review briefly covers the different classes of nucleic acids, their mechanisms of action, and their challenges. We also elaborate on recent advances in bioconjugation strategies in developing a diverse set of ligands for targeted delivery of nucleic acid drugs.

The beauty of symmetry: siRNA phosphorodithioate modifications reduce stereocomplexity, ease analysis, and can improve in vivo potency

Phosphorothioates (PSs) can be essential in stabilizing therapeutic oligonucleotides against enzymatic degradation. However, unless synthesis is performed with stereodefined amidites, each PS introduces a chemically undefined stereocenter, resulting in 2 n unique molecules in the final product and affecting downstream analytics and purification. Replacing the second non-bridging oxygen with sulfur results in phosphorodithioate (PS2) linkages, thereby removing the stereocenter. We describe synthesis and analytical data for N-acetylgalactosamine (GalNAc)-conjugated small interfering RNAs (siRNAs) with PS2 in the GalNAc cluster and at the siRNA termini. All siRNA conjugates with PS2 internucleotide linkages were produced with good yield and showed improved analytical properties. PS2 in the GalNAc cluster had no, or only minor, effect on in vitro and in vivo activity. Except for the 5'-antisense position, PS2 modifications were well tolerated at the siRNA termini, and a single PS2 internucleotide linkage gave similar or improved stabilization and in vitro activity as the two PSs typically used for end stabilization. Surprisingly, several of the PS2-containing siRNA conjugates resulted in increased in vivo activity and duration of action compared to the same siRNA sequence stabilized with PS linkages, suggesting PS2 linkages as interesting options for siRNA strand design with a reduced number of undefined stereocenters.

Engineering an Ultrasound-Responsive Glycopolymersome for Hepatocyte-Specific Gene Delivery

The ability to design liver-targeted gene delivery vectors is plagued with difficulties ranging from carrier-mediated cellular toxicity to challenges in encapsulating sensitive nucleic acids. Herein, we present an ultrasound-responsive glycopolymersome strategy for in situ loading of nucleic acids and achieving hepatocyte-specific gene delivery. This glycopolymersome is self-assembled from a block copolymer, N-acetylgalactosamine-grafted poly(glutamic acid)-block-poly(ε-caprolactone) (PGAGalNAc-b-PCL). GalNAc is introduced to afford liver targeting through the selective binding to the asialoglycoprotein receptor overexpressed on hepatocytes. External ultrasound is utilized to assist in encapsulating nucleic acids within the hydrophilic lumen of glycopolymersomes by exploiting their ultrasound responsiveness nature. Biological studies confirmed the successful encapsulation of plasmid DNA (pDNA) and small interfering RNA (siRNA), rapid nuclear internalization, and efficient gene transfection. These findings collectively demonstrated that this ultrasound-responsive glycopolymersome could be exploited as a novel safe and efficient gene vector targeting hepatocytes.

Efficacy of GalNAc C3 siRNAs in factor H-deficient mice with C3 glomerulopathy

Complement alternative pathway (AP) dysregulation drives C3 glomerulopathy (C3G), a rare renal disorder characterized by glomerular C3 deposition and glomerular damage, for which no effective treatments are available. Blockade of complement C3 is emerging as a viable therapeutic option. In an earlier study we showed that SLN500, a small interfering RNA targeting liver C3 synthesis, was able to limit AP dysregulation and glomerular C3d deposits in mice with partial factor H (FH) deficiency (Cfh+/- mice). Here, we assessed the pharmacological effects of SLN501 - an optimized SLN500 version - in mice with complete FH deficiency (Cfh-/- mice) that exhibit a more severe C3G phenotype. SLN501 effectively prevented liver C3 synthesis, thus limiting AP dysregulation, glomerular C3d deposits and the development of ultrastructural alterations. These data provide firm evidence of the use of siRNA-mediated liver C3 gene silencing as a potential therapy for treating C3G patients with either partial or complete FH loss of function.

Application of improved GalNAc conjugation in development of cost-effective siRNA therapies targeting cardiovascular diseases

N-Acetylgalactosamine (GalNAc)-conjugated small interfering RNA (siRNA) therapies have received approval for treating both orphan and prevalent diseases. To improve in vivo efficacy and streamline the chemical synthesis process for efficient and cost-effective manufacturing, we conducted this study to identify better designs of GalNAc-siRNA conjugates for therapeutic development. Here, we present data on redesigned GalNAc-based ligands conjugated with siRNAs against angiopoietin-like 3 (ANGPTL3) and lipoprotein (a) (Lp(a)), two target molecules with the potential to address large unmet medical needs in atherosclerotic cardiovascular diseases. By attaching a novel pyran-derived scaffold to serial monovalent GalNAc units before solid-phase oligonucleotide synthesis, we achieved increased GalNAc-siRNA production efficiency with fewer synthesis steps compared to the standard triantennary GalNAc construct L96. The improved GalNAc-siRNA conjugates demonstrated equivalent or superior in vivo efficacy compared to triantennary GalNAc-conjugated siRNAs.

Glycomimetics for the inhibition and modulation of lectins

Carbohydrates are essential mediators of many processes in health and disease. They regulate self-/non-self- discrimination, are key elements of cellular communication, cancer, infection and inflammation, and determine protein folding, function and life-times. Moreover, they are integral to the cellular envelope for microorganisms and participate in biofilm formation. These diverse functions of carbohydrates are mediated by carbohydrate-binding proteins, lectins, and the more the knowledge about the biology of these proteins is advancing, the more interfering with carbohydrate recognition becomes a viable option for the development of novel therapeutics. In this respect, small molecules mimicking this recognition process become more and more available either as tools for fostering our basic understanding of glycobiology or as therapeutics. In this review, we outline the general design principles of glycomimetic inhibitors (Section 2). This section is then followed by highlighting three approaches to interfere with lectin function, i.e. with carbohydrate-derived glycomimetics (Section 3.1), novel glycomimetic scaffolds (Section 3.2) and allosteric modulators (Section 3.3). We summarize recent advances in design and application of glycomimetics for various classes of lectins of mammalian, viral and bacterial origin. Besides highlighting design principles in general, we showcase defined cases in which glycomimetics have been advanced to clinical trials or marketed. Additionally, emerging applications of glycomimetics for targeted protein degradation and targeted delivery purposes are reviewed in Section 4.

Metabolically Stable Anomeric Linkages Containing GalNAc-siRNA Conjugates: An Interplay among ASGPR, Glycosidase, and RISC Pathways

Conjugation of synthetic triantennary N-acetyl-d-galactosamine (GalNAc) to small interfering RNA (siRNA) mediates binding to the asialoglycoprotein receptor (ASGPR) on the surface of hepatocytes, facilitating liver-specific uptake and siRNA-mediated gene silencing. The natural β-glycosidic bond of the GalNAc ligand is rapidly cleaved by glycosidases in vivo. Novel GalNAc ligands with S-, and C-glycosides with both α- and β-anomeric linkages, N-glycosides with β-anomeric linkage, and the O-glycoside with α-anomeric linkage were synthesized and conjugated to siRNA either on-column during siRNA synthesis or through a high-throughput, post-synthetic method. Unlike natural GalNAc, modified ligands were resistant to glycosidase activity. The siRNAs conjugated to newly designed ligands had similar affinities for ASGPR and similar silencing activity in mice as the parent GalNAc-siRNA conjugate. These data suggest that other factors, such as protein-nucleic acid interactions and loading of the antisense strand into the RNA-induced silencing complex (RISC), are more critical to the duration of action than the stereochemistry and stability of the anomeric linkage between the GalNAc moiety of the ligand conjugated to the sense strand of the siRNA.

Targeted delivery of oligonucleotides using multivalent protein-carbohydrate interactions

Cell surface protein-carbohydrate interactions are essential for tissue-specific recognition and endocytosis of viruses, some bacteria and their toxins, and many glycoproteins. Often protein-carbohydrate interactions are multivalent - multiple copies of glycans bind simultaneously to multimeric receptors. Multivalency enhances both affinity and binding specificity, and is of interest for targeted delivery of drugs to specific cell types. The first such example of carbohydrate-mediated drug delivery to reach the clinic is Givosiran, a small interfering ribonucleic acid (siRNA) that is conjugated to a trivalent N-acetylgalactosamine (GalNAc) ligand. This ligand enables efficient uptake of the nucleic acid by the asialoglycoprotein receptor (ASGP-R) on hepatocytes. Synthetic multivalent ligands for ASGP-R were among the first 'cluster glycosides' developed at the birth of multivalent glycoscience around 40 years ago. In this review we trace the history of 'GalNAc targeting' from early academic studies to current pharmaceuticals and consider what other opportunities could follow the success of this delivery technology.

Engineering a Novel Self-Assembled Multi-siRNA Nanocaged Architecture with Controlled Enzyme-Mediated siRNA Release

The RNA interference (RNAi) chemical and structural design space has evolved since its original definitions. Although this has led to the development of RNAi molecules that are starting to address the issues of silencing efficiency and delivery to target organs and cells, there is an on-going interest to improve upon their properties to attain wider therapeutic applicability. Taking advantage of the flexibility given by DNA and RNA structural and chemical properties, we here investigated unconventional RNAi encoding structures, designated by caged-siRNA structures (CsiRNAs), to explore novel features that could translate into advantageous properties for cellular delivery and intracellular activity. Using the principles of controlled nucleic acid self-assembly, branched DNA-RNA hybrid intermediates were formed, ultimately leading to the assembly of a "closed" structure encompassing multiple RNAi units. The RNAi active regions are further triggered by an encoded RNAse H-mediated release mechanism, while the overall structure possesses easily addressable anchors for hybridization-based functionalization with active biological moieties. We confirmed the production of correct structures and demonstrated that the encoded RNAi sequences maintain gene silencing activity even within this novel unconventional nanoarchitecture, aided by the intracellularly triggered RNAse H release mechanism. With this design, functionalization is easily achieved with no negative effects on the silencing activity, warranting further development of these novel molecular structures as a multi-RNAi platform for therapeutic delivery.

Restoring cellular magnesium balance through Cyclin M4 protects against acetaminophen-induced liver damage

Acetaminophen overdose is one of the leading causes of acute liver failure and liver transplantation in the Western world. Magnesium is essential in several cellular processess. The Cyclin M family is involved in magnesium transport across cell membranes. Herein, we identify that among all magnesium transporters, only Cyclin M4 expression is upregulated in the liver of patients with acetaminophen overdose, with disturbances in magnesium serum levels. In the liver, acetaminophen interferes with the mitochondrial magnesium reservoir via Cyclin M4, affecting ATP production and reactive oxygen species generation, further boosting endoplasmic reticulum stress. Importantly, Cyclin M4 mutant T495I, which impairs magnesium flux, shows no effect. Finally, an accumulation of Cyclin M4 in endoplasmic reticulum is shown under hepatoxicity. Based on our studies in mice, silencing hepatic Cyclin M4 within the window of 6 to 24 h following acetaminophen overdose ingestion may represent a therapeutic target for acetaminophen overdose induced liver injury.

Therapeutic Small Interfering RNA Targeting Complement C3 in a Mouse Model of C3 Glomerulopathy

Alternative pathway complement dysregulation with abnormal glomerular C3 deposits and glomerular damage is a key mechanism of pathology in C3 glomerulopathy (C3G). No disease-specific treatments are currently available for C3G. Therapeutics inhibiting complement are emerging as a potential strategy for the treatment of C3G. In this study, we investigated the effects of N-acetylgalactosamine (GalNAc)-conjugated small interfering RNA (siRNA) targeting the C3 component of complement that inhibits liver C3 expression in the C3G model of mice with heterozygous deficiency of factor H (Cfh ^+/- mice). We showed a duration of action for GalNAc-conjugated C3 siRNA in reducing the liver C3 gene expression in Cfh ^+/- mice that were dosed s.c. once a month for up to 7 mo. C3 siRNA limited fluid-phase alternative pathway activation, reducing circulating C3 fragmentation and activation of factor B. Treatment with GalNAc-conjugated C3 siRNA reduced glomerular C3d deposits in Cfh ^+/- mice to levels similar to those of wild-type mice. Ultrastructural analysis further revealed the efficacy of the C3 siRNA in slowing the formation of mesangial and subendothelial electron-dense deposits. The present data indicate that RNA interference-mediated C3 silencing in the liver may be a relevant therapeutic strategy for treating patients with C3G associated with the haploinsufficiency of complement factor H.

Engineering miRNA features into siRNAs: Guide-strand bulges are compatible with gene repression

Synthetic siRNA guide strands are typically designed with perfect complementarity to the passenger strand and the target mRNA. We examined whether siRNAs with intentional guide-strand bulges are functional in vitro and in vivo. Importantly, this was done by systematic shortening of the passenger strand, evaluating identical 19-mer guide-strand sequences but forcing them into conformations with 1- to 4-nt bulges after annealing. We demonstrate that guide-strand bulges can be well tolerated at several positions of unmodified and modified siRNAs. Beyond that, we show that GalNAc-conjugated siRNAs with bulges at certain positions of the guide strand repress transthyretin in murine primary hepatocytes and in vivo in mice. In vivo, a GalNAc-conjugated siRNA with a 1-nt bulge at position 14 of the guide strand was as active as the perfectly complementary siRNA. Finally, in a luciferase reporter system, mRNA target sequences were systematically shortened so that RNA-induced silencing complex activity could only occur with a guide-strand bulge. Here, luciferase reporters were repressed when 1- and 2-nt deletions of the reporter were applied to the edges of the sequence. We conclude that some guide-strand bulges versus target transcript can result in target repression and therefore should be evaluated as off-target risks.

Nanotechnology-Assisted RNA Delivery: From Nucleic Acid Therapeutics to COVID-19 Vaccines

In recent years, the main quest of science has been the pioneering of the groundbreaking biomedical strategies needed for achieving a personalized medicine. Ribonucleic acids (RNAs) are outstanding bioactive macromolecules identified as pivotal actors in regulating a wide range of biochemical pathways. The ability to intimately control the cell fate and tissue activities makes RNA-based drugs the most fascinating family of bioactive agents. However, achieving a widespread application of RNA therapeutics in humans is still a challenging feat, due to both the instability of naked RNA and the presence of biological barriers aimed at hindering the entrance of RNA into cells. Recently, material scientists' enormous efforts have led to the development of various classes of nanostructured carriers customized to overcome these limitations. This work systematically reviews the current advances in developing the next generation of drugs based on nanotechnology-assisted RNA delivery. The features of the most used RNA molecules are presented, together with the development strategies and properties of nanostructured vehicles. Also provided is an in-depth overview of various therapeutic applications of the presented systems, including coronavirus disease vaccines and the newest trends in the field. Lastly, emerging challenges and future perspectives for nanotechnology-mediated RNA therapies are discussed.

Feasibility of cRGD conjugation at 5'-antisense strand of siRNA by phosphodiester linkage extension

Small interfering RNAs (siRNAs) are widely studied for their highly specific gene silencing activity. However, obstacles remain to the clinical application of siRNAs. Attaching conjugates to siRNAs can improve their stability and broaden their application, and most functional conjugates of siRNAs locate at the 3'-terminus of the sense or antisense strand. In this work, we found that conjugating a group at the 5'-terminus of the antisense strand via phosphodiester was practicable, especially when the group was a flexible moiety such as an alkyl linker. When conjugating a bulky ligand, such as cRGD, the length of the 5'-phosphodiester linker between the ligand and the 5'-terminus of the antisense strand was the key in terms of RNA interference (RNAi). With a relative longer linker, the conjugates showed potency similar to siRNA. A highly efficient transfection system composed of a neutral cytidinyl lipid (DNCA) and a gemini-like cationic lipid (CLD) was employed to deliver siRNAs or their conjugates. The cRGD conjugates showed superior targeting delivery and antitumor efficacy in vivo and also selective cellular uptake in vitro. This unity of encapsulation and conjugation strategy may provide potential strategies for siRNA-based gene therapy.

Rare Treatments for Rare Dyslipidemias: New Perspectives in the Treatment of Homozygous Familial Hypercholesterolemia (HoFH) and Familial Chylomicronemia Syndrome (FCS)

Purpose of Review

This review aims to summarize the most recent published literature concerning lomitapide and volanesorsen that are approved for the use in HoFH and FCS patients, respectively. Moreover, it will briefly revise the published evidence on novel, non-approved treatments that are under evaluation for the management of these rare forms of dyslipidemias

Recent Findings

The definition of rare dyslipidemias identifies a large number of severe disorders of lipid metabolism of genetic origin. Among them were homozygous familial hypercholesterolemia (HoFH) (OMIM #143890) and familial chylomicronemia syndrome (FCS) (OMIM #238600), which are characterized by a markedly impaired cholesterol- and triglyceride-containing lipoproteins metabolism. They are being particularly associated with poor health outcomes and quality of life. Considering the severity of these diseases, common lipid-lowering drugs are often ineffective or do not allow to achieve the recommended lipid targets to prevent the development of complications. Nowadays, several new drugs have been found to effectively treat HoFH and FCS with an acceptable safety profile.

Summary

Treating patients with HoFH and FCS remains very challenging. However, novel treatment options are emerging and might be considered in addition to conventional therapy for managing these diseases. These novel drugs will possibly change the natural history of these two rare and life-threatening diseases.

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

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

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

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

SLN124, a GalNac-siRNA targeting transmembrane serine protease 6, in combination with deferiprone therapy reduces ineffective erythropoiesis and hepatic iron-overload in a mouse model of β-thalassaemia

Beta‐thalassaemia is an inherited blood disorder characterised by ineffective erythropoiesis and anaemia. Consequently, hepcidin expression is reduced resulting in increased iron absorption and primary iron overload. Hepcidin is under the negative control of transmembrane serine protease 6 (TMPRSS6) via cleavage of haemojuvelin (HJV), a co‐receptor for the bone morphogenetic protein (BMP)‐mothers against decapentaplegic homologue (SMAD) signalling pathway. Considering the central role of the TMPRSS6/HJV/hepcidin axis in iron homeostasis, the inhibition of TMPRSS6 expression represents a promising therapeutic strategy to increase hepcidin production and ameliorate anaemia and iron overload in β‐thalassaemia. In the present study, we investigated a small interfering RNA (siRNA) conjugate optimised for hepatic targeting of Tmprss6 (SLN124) in β‐thalassaemia mice (Hbb^th3/+). Two subcutaneous injections of SLN124 (3 mg/kg) were sufficient to normalise hepcidin expression and reduce anaemia. We also observed a significant improvement in erythroid maturation, which was associated with a significant reduction in splenomegaly. Treatment with the iron chelator, deferiprone (DFP), did not impact any of the erythroid parameters. However, the combination of SLN124 with DFP was more effective in reducing hepatic iron overload than either treatment alone. Collectively, we show that the combination therapy can ameliorate several disease symptoms associated with chronic anaemia and iron overload, and therefore represents a promising pharmacological modality for the treatment of β‐thalassaemia and related disorders.

Treatment and prevention of lipoprotein(a)-mediated cardiovascular disease: the emerging potential of RNA interference therapeutics

Lipid- and lipoprotein-modifying therapies have expanded substantially in the last 25 years, resulting in reduction in the incidence of major adverse cardiovascular events. However, no specific lipoprotein(a) [Lp(a)]-targeting therapy has yet been shown to reduce cardiovascular disease risk. Many epidemiological and genetic studies have demonstrated that Lp(a) is an important genetically determined causal risk factor for coronary heart disease, aortic valve disease, stroke, heart failure, and peripheral vascular disease. Accordingly, the need for specific Lp(a)-lowering therapy has become a major public health priority. Approximately 20% of the global population (1.4 billion people) have elevated levels of Lp(a) associated with higher cardiovascular risk, though the threshold for determining ‘high risk’ is debated. Traditional lifestyle approaches to cardiovascular risk reduction are ineffective at lowering Lp(a). To address a lifelong risk factor unmodifiable by non-pharmacological means, Lp(a)-lowering therapy needs to be safe, highly effective, and tolerable for a patient population who will likely require several decades of treatment. N-acetylgalactosamine-conjugated gene silencing therapeutics, such as small interfering RNA (siRNA) and antisense oligonucleotide targeting LPA, are ideally suited for this application, offering a highly tissue- and target transcript-specific approach with the potential for safe and durable Lp(a) lowering with as few as three or four doses per year. In this review, we evaluate the causal role of Lp(a) across the cardiovascular disease spectrum, examine the role of established lipid-modifying therapies in lowering Lp(a), and focus on the anticipated role for siRNA therapeutics in treating and preventing Lp(a)-related disease.

Physiologically based pharmacokinetic (PBPK) modeling of RNAi therapeutics: Opportunities and challenges

Physiologically based pharmacokinetic (PBPK) modeling is a powerful tool with many demonstrated applications in various phases of drug development and regulatory review. RNA interference (RNAi)-based therapeutics are a class of drugs that have unique pharmacokinetic properties and mechanisms of action. With an increasing number of RNAi therapeutics in the pipeline and reaching the market, there is a considerable amount of active research in this area requiring a multidisciplinary approach. The application of PBPK models for RNAi therapeutics is in its infancy and its utility to facilitate the development of this new class of drugs is yet to be fully evaluated. From this perspective, we briefly discuss some of the current computational modeling approaches used in support of efficient development and approval of RNAi therapeutics. Considerations for PBPK model development are highlighted both in a relative context between small molecules and large molecules such as monoclonal antibodies and as it applies to RNAi therapeutics. In addition, the prospects for drawing upon other recognized avenues of PBPK modeling and some of the foreseeable challenges in PBPK model development for these chemical modalities are briefly discussed. Finally, an exploration of the potential application of PBPK model development for RNAi therapeutics is provided. We hope these preliminary thoughts will help initiate a dialogue between scientists in the relevant sectors to examine the value of PBPK modeling for RNAi therapeutics. Such evaluations could help standardize the practice in the future and support appropriate guidance development for strengthening the RNAi therapeutics development program.

Epigenetic mechanisms in hepatitis B virus-associated hepatocellular carcinoma

Chronic infection of the liver by the hepatitis B virus (HBV) is associated with increased risk for developing hepatocellular carcinoma (HCC). A multitude of studies have investigated the mechanism of liver cancer pathogenesis due to chronic HBV infection. Chronic inflammation, expression of specific viral proteins such as HBx, the integration site of the viral genome into the host genome, and the viral genotype, are key players contributing to HCC pathogenesis. In addition, the genetic background of the host and exposure to environmental carcinogens are also predisposing parameters in hepatocarcinogenesis. Despite the plethora of studies, the molecular mechanism of HCC pathogenesis remains incompletely understood. In this review, the focus is on epigenetic mechanisms involved in the pathogenesis of HBV-associated HCC. Epigenetic mechanisms are dynamic molecular processes that regulate gene expression without altering the host DNA, acting by modifying the host chromatin structure via covalent post-translational histone modifications, changing the DNA methylation status, expression of non-coding RNAs such as microRNAs and long noncoding RNAs, and altering the spatial, 3-D organization of the chromatin of the virus-infected cell. Herein, studies are described that provide evidence in support of deregulation of epigenetic mechanisms in the HBV-infected/-replicating hepatocyte and their contribution to hepatocyte transformation. In contrast to genetic mutations which are permanent, epigenetic alterations are dynamic and reversible. Accordingly, the identification of essential molecular epigenetic targets involved in HBV-mediated HCC pathogenesis offers the opportunity for the design and development of novel epigenetic therapeutic approaches.

Understanding In Vivo Fate of Nucleic Acid and Gene Medicines for the Rational Design of Drugs

Nucleic acid and genetic medicines are increasingly being developed, owing to their potential to treat a variety of intractable diseases. A comprehensive understanding of the in vivo fate of these agents is vital for the rational design, discovery, and fast and straightforward development of the drugs. In case of intravascular administration of nucleic acids and genetic medicines, interaction with blood components, especially plasma proteins, is unavoidable. However, on the flip side, such interaction can be utilized wisely to manipulate the pharmacokinetics of the agents. In other words, plasma protein binding can help in suppressing the elimination of nucleic acids from the blood stream and deliver naked oligonucleotides and gene carriers into target cells. To control the distribution of these agents in the body, the ligand conjugation method is widely applied. It is also important to understand intracellular localization. In this context, endocytosis pathway, endosomal escape, and nuclear transport should be considered and discussed. Encapsulated nucleic acids and genes must be dissociated from the carriers to exert their activity. In this review, we summarize the in vivo fate of nucleic acid and gene medicines and provide guidelines for the rational design of drugs.

Restoration of RNA helicase DDX5 suppresses hepatitis B virus (HBV) biosynthesis and Wnt signaling in HBV-related hepatocellular carcinoma

Rationale: RNA helicase DDX5 is downregulated during hepatitis B virus (HBV) replication, and poor prognosis HBV-related hepatocellular carcinoma (HCC). The aim of this study is to determine the mechanism and significance of DDX5 downregulation for HBV-driven HCC, and identify biologics to prevent DDX5 downregulation. Methods: Molecular approaches including immunoblotting, qRT-PCR, luciferase transfections, hepatosphere assays, Assay for Transposase-Accessible Chromatin sequencing (ATAC-seq), and RNA-seq were used with cellular models of HBV replication, HBV infection, and HBV-related liver tumors, as well as bioinformatic analyses of liver cancer cells from two independent cohorts. Results: We demonstrate that HBV infection induces expression of the proto-oncogenic miR17~92 and miR106b~25 clusters which target the downregulation of DDX5. Increased expression of these miRNAs is also detected in HBV-driven HCCs exhibiting reduced DDX5 mRNA. Stable DDX5 knockdown (DDX5^KD) in HBV replicating hepatocytes increased viral replication, and resulted in hepatosphere formation, drug resistance, Wnt activation, and pluripotency gene expression. ATAC-seq of DDX5^KD compared to DDX5 wild-type (WT) cells identified accessible chromatin regions enriched in regulation of Wnt signaling genes. RNA-seq analysis comparing WT versus DDX5^KD cells identified enhanced expression of multiple genes involved in Wnt pathway. Additionally, expression of Disheveled, DVL1, a key regulator of Wnt pathway activation, was significantly higher in liver cancer cells with low DDX5 expression, from two independent cohorts. Importantly, inhibitors (antagomirs) to miR17~92 and miR106b~25 restored DDX5 levels, reduced DVL1 expression, and suppressed both Wnt activation and viral replication. Conclusion : DDX5 is a negative regulator of Wnt signaling and hepatocyte reprogramming in HCCs. Restoration of DDX5 levels by miR17~92 / miR106b~25 antagomirs in HBV-infected patients can be explored as both antitumor and antiviral strategy.