Expanding RNAi therapeutics to extrahepatic tissues with lipophilic conjugates

Advances in locally administered nucleic acid therapeutics

Nucleic acid drugs represent the latest generation of precision therapeutics, holding significant promise for the treatment of a wide range of intractable diseases. Delivery technology is crucial for the clinical application of nucleic acid drugs. However, extrahepatic delivery of nucleic acid drugs remains a significant challenge. Systemic administration often fails to achieve sufficient drug enrichment in target tissues. Localized administration has emerged as the predominant approach to facilitate extrahepatic delivery. While localized administration can significantly enhance drug accumulation at the injection sites, nucleic acid drugs still face biological barriers in reaching the target lesions. This review focuses on non-viral nucleic acid drug delivery techniques utilized in local administration for the treatment of extrahepatic diseases. First, the classification of nucleic acid drugs is described. Second, the current major non-viral delivery technologies for nucleic acid drugs are discussed. Third, the bio-barriers, administration approaches, and recent research advances in the local delivery of nucleic acid drugs for treating lung, brain, eye, skin, joint, and heart-related diseases are highlighted. Finally, the challenges associated with the localized therapeutic application of nucleic acid drugs are addressed.

Pathogenesis, manifestations, diagnosis, and management of CNS complications in hereditary ATTR amyloidosis

The clinical efficacy of transthyretin (TTR) tetramer stabilisers and TTR gene silencers in addition to liver transplantation has been established for hereditary ATTR (ATTRv) amyloidosis. Accordingly, non-central nervous system (CNS) systemic amyloidosis manifestations, such as peripheral neuropathy and cardiomyopathy, are now being overcome. However, emerging disease-modifying therapeutics have limited effects on CNS amyloidosis since they target the blood-circulating TTR produced in the liver, and not the cerebral spinal fluid (CSF) TTR synthesised in the choroid plexus. CNS involvement is therefore becoming the most common and severe complication in patients with ATTRv amyloidosis, including transient focal neurologic episodes, haemorrhagic and ischaemic stroke, cognitive decline, and cranial nerve dysfunction. Pathologically, extensive amyloid depositions are observable in the leptomeninges and leptomeningeal vessels, which are in direct contact with the CSF. Amyloid positron emission tomography is a useful biomarker for the early detection and treatment evaluation of early-onset ATTRv amyloidosis with the V30M (p.V50M) variant. Treatment-wise, blood-brain barrier-permeable stabilisers, intrathecal injection of silencers, and monoclonal antibodies against misfolded TTR and/or ATTR amyloid may potentially ameliorate CNS ATTR amyloidosis. The development of novel imaging/CSF biomarkers and disease-modifying therapies are the greatest unmet medical need in ATTRv amyloidosis and require further clinical trials.

Advances in gene and cellular therapeutic approaches for Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by the abnormal expansion of CAG trinucleotide repeats in the Huntingtin gene (HTT) located on chromosome 4. It is transmitted in an autosomal dominant manner and is characterized by motor dysfunction, cognitive decline, and emotional disturbances. To date, there are no curative treatments for HD have been developed; current therapeutic approaches focus on symptom relief and comprehensive care through coordinated pharmacological and nonpharmacological methods to manage the diverse phenotypes of the disease. International clinical guidelines for the treatment of HD are continually being revised in an effort to enhance care within a multidisciplinary framework. Additionally, innovative gene and cell therapy strategies are being actively researched and developed to address the complexities of the disorder and improve treatment outcomes. This review endeavours to elucidate the current and emerging gene and cell therapy strategies for HD, offering a detailed insight into the complexities of the disorder and looking forward to future treatment paradigms. Considering the complexity of the underlying mechanisms driving HD, a synergistic treatment strategy that integrates various factors-such as distinct cell types, epigenetic patterns, genetic components, and methods to improve the cerebral microenvironment-may significantly enhance therapeutic outcomes. In the future, we eagerly anticipate ongoing innovations in interdisciplinary research that will bring profound advancements and refinements in the treatment of HD.

Chemical Insights into Oligonucleotide-Protein Binding for Therapeutic Applications

Plasma protein binding is an important determinant in the clinical success of oligonucleotide-based drugs. Optimal protein binding of the oligonucleotide is critical to its tissue distribution and retention by preventing renal excretion. This property can be modulated through suitable chemical modifications depending on the oligonucleotide backbone to achieve a balanced pharmacokinetic profile and minimize off-target effects. The macromolecular structure of the oligonucleotide leads to dynamic protein binding characteristics as compared to small-molecule-based drugs, which are not associated with additional barriers such as intracellular delivery. This perspective provides insight into the diverse plasma protein interactions of various classes of oligonucleotides and explores chemical strategies for modulating these interactions. Furthermore, we have discussed different methods for the quantification of plasma protein binding along with the correlation of chemistry and therapeutic outcomes of FDA-approved oligonucleotides.

siRNA conjugate with high albumin affinity and degradation resistance for delivery and treatment of arthritis in mice and guinea pigs

Osteoarthritis and rheumatoid arthritis are debilitating joint diseases marked by pain, inflammation and cartilage destruction. Current osteoarthritis treatments only relieve symptoms, while rheumatoid arthritis therapies can cause immune suppression and provide variable efficacy. Here we developed an optimized small interfering RNA targeting matrix metalloproteinase 13 for preferential delivery to arthritic joints. Chemical modifications in a stabilizing 'zipper' pattern improved RNA resistance to degradation, and two independent linkers with 18 ethylene glycol repeats connecting to tandem C18 lipids enhanced albumin binding and targeted delivery to inflamed joints following intravenous administration. In preclinical models of post-traumatic osteoarthritis and rheumatoid arthritis, a single intravenous injection of the albumin-binding small interfering RNA achieved long-term joint retention, sustained gene silencing and reduced matrix metalloproteinase 13 activity over 30 days, resulting in decreased cartilage erosion and improved clinical outcomes, including reduced joint swelling and pressure sensitivity. This approach demonstrated superior efficacy over corticosteroids and small-molecule MMP inhibitors, highlighting the therapeutic promise of albumin 'hitchhiking' for targeted, systemic delivery of gene-silencing therapeutics to treat osteoarthritis and rheumatoid arthritis.

Furan-Derived Lipid Nanoparticles for Transporting mRNA to the Central Nervous System

Delivery of mRNA (mRNA) to the central nervous system (CNS) remains a significant challenge. Herein, we design a library of furan-derived lipids and, to our knowledge, for the first time, leverage the meningeal lymphatic vessels (MLVs) route to achieve efficient delivery of mRNA to the brain. These furan-derived lipids were engineered with different furan cores, functional groups, and tails. We found that tetrahydrofuran (THF)-derived lipid nanoparticles (LNPs) generally displayed exceptional mRNA delivery compared to their furan-based counterparts. Specifically, LNPs formulated with four-acetal-tail mono-THF-derived lipid F10T5 and four-acetal-tail di-THF-derived lipid F11T6 demonstrated significantly higher mRNA delivery efficiency to the brain compared with FDA-approved SM102 LNPs. The data revealed that these LNPs bypassed the blood-brain barrier (BBB) via the lymphatic pathway, traveling from deep cervical lymph nodes (dCLNs) to the meninges and subsequently entering brain cells. Collectively, this work provides valuable insights into engineering LNPs and exploring alternative approaches for the delivery of mRNA to the brain.

Modulation of TTR gene expression in the eye using modified siRNAs

Small interfering RNAs (siRNAs) are a proven therapeutic approach for controlling gene expression in the liver. Expanding the clinical potential of RNA interference requires developing strategies to enhance delivery to extra-hepatic tissues. In this study, we examine inhibiting transthyretin (TTR) gene expression by siRNAs in the eye. Anti-TTR siRNAs have been developed as successful drugs to treat TTR amyloidosis. When administered systemically, anti-TTR siRNAs alleviate symptoms by blocking TTR expression in the liver. However, TTR amyloidosis also affects the eye, suggesting a need for reducing ocular TTR gene expression. Here, we demonstrate that pyrimidine C5- and 2'-O-linked lipid-modified siRNAs formulated in saline can inhibit TTR expression in the eye when administered locally by intravitreal injection. Modeling suggests that length and accessibility of the lipid chains contribute to in vivo silencing. GalNAc-modified siRNAs also inhibit TTR expression, albeit less potently. These data support lipid-modified siRNAs as an approach to treating the ocular consequences of TTR amyloidosis. Inhibition of TTR expression throughout the eye demonstrates that lipid-siRNA conjugates have the potential to be a versatile platform for ocular drug discovery.

RNAi-mediated silencing of SOD1 profoundly extends survival and functional outcomes in ALS mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition, with 20% of familial and 2%-3% of sporadic cases linked to mutations in the cytosolic superoxide dismutase (SOD1) gene. Mutant SOD1 protein is toxic to motor neurons, making SOD1 gene suppression a promising approach, supported by preclinical data and the 2023 Federal Drug Administration (FDA) approval of the GapmeR ASO targeting SOD1, tofersen. Despite the approval of an ASO and the optimism it brings to the field, the pharmacodynamics and pharmacokinetics of therapeutic SOD1 modulation can be improved. Here, we developed a chemically stabilized divalent siRNA scaffold (di-siRNA) that effectively suppresses SOD1 expression in vitro and in vivo. With optimized chemical modification, it achieves remarkable CNS tissue permeation and SOD1 silencing in vivo. Administered intraventricularly, di-siRNASOD1 extended survival in SOD1-G93A ALS mice, increasing survival beyond that previously seen in these mice by ASO modalities, slowed disease progression according to the standard ALS preclinical endpoints, and attenuated ALS neuropathology. These properties offer an improved therapeutic strategy for SOD1-mediated ALS and may extend to other dominantly inherited neurological disorders.

Durable suppression of seizures in a preclinical model of KCNT1 genetic epilepsy with divalent small interfering RNA

OBJECTIVE

Gain-of-function variants in the KCNT1 gene, which encodes a sodium-activated potassium ion channel, drive severe early onset developmental epileptic encephalopathies including epilepsy of infancy with migrating focal seizures and sleep-related hypermotor epilepsy. No therapy provides more than sporadic or incremental improvement. Here, we report suppression of seizures in a genetic mouse model of KCNT1 epilepsy by reducing Kcnt1 transcript with divalent small interfering RNA (siRNA), an emerging variant of oligonucleotide technology developed for the central nervous system.

METHODS

The ATL-201 molecule is two identical synthetic double-stranded siRNAs, covalently linked, with 100% nucleotide base pair match to sequence present in both human KCNT1 and mouse Kcnt1 that does not contain any known pathogenic variant. ATL-201 activity was tested in cortical neurons cultured from wild-type mice and in mice homozygous for Kcnt1-Y777H, the mouse ortholog to the human pathogenic KCNT1-Y796H missense variant. Seizures and nest-building behavior were measured in freely behaving Kcnt1-Y777H mice. The number and duration of seizures were measured by electrocorticography in mice dosed with ATL-201 or phosphate-buffered saline in a 6-month durability study and in a 2-month dose-efficacy study.

RESULTS

In vitro, ATL-201 reduced KCNT1 transcript from whole-cell lysate and eliminated potassium currents from KCNT1 channels in heterologous expression. ATL-201 also eliminated sodium-activated potassium currents recorded from individual cortical neurons. In vivo, ATL-201 suppressed seizures in Kcnt1-Y777H homozygous mice in a dose-dependent manner with near-complete suppression from 2 weeks to at least 4 months. Kcnt1-Y777H mice had defects in nest building, whereas in ATL-201-treated mice nest building was equivalent to wild-type mice.

SIGNIFICANCE

Patients with KCNT1-driven epilepsy experience up to hundreds of seizures per day and have severe impairment in cognitive, motor, and language development and high mortality. The dose-dependent efficacy and long durability of ATL-201 in mice show promise for ATL-201 as a disease-modifying treatment of KCNT1 epilepsy.

Unlocking the future: Precision oligonucleotide therapy for targeted treatment of neurodegenerative disorders

Neurodegenerative disorders are complex and devastating conditions of the central nervous system that profoundly impact quality of life. Given the limited treatment options available, there is a pressing need to develop novel therapeutic strategies. Oligonucleotides have emerged as key players in precision medicine for these disorders, but their potential is hindered by poor translocation across the blood-brain barrier. This review focuses on neurodegenerative disorders other than Alzheimer's and Parkinson's, which are widely reported in the literature, and aims to address the significant hurdles in oligonucleotide delivery for neurodegenerative diseases. It highlights recent advancements in CNS-targeting approaches, such as chemical conjugation, antibody-oligonucleotide conjugates, focused ultrasound, and viral and nanocarrier-based delivery systems. Each strategy's strengths and limitations are discussed, with potential solutions proposed for more effective treatments. Additionally, the review offers valuable insights into regulatory requirements and prospects for clinical translation, which are crucial for shaping the future of neurodegenerative therapies. By exploring these innovative approaches, the goal is to surmount challenges posed by the blood-brain barrier and develop more effective treatments, thereby enhancing the quality of life of the patients suffering from these debilitating conditions.

The Fomivirsen, Patisiran, and Givosiran Odyssey: How the Success Stories May Pave the Way for Future Clinical Translation of Nucleic Acid Drugs

Over the past 25 years, the approval of several nucleic acid-based drugs by the US Food and Drug Administration (FDA) has marked a significant milestone, establishing nucleic acid drugs as a viable therapeutic modality. These groundbreaking discoveries are the result of some crucial points in the timeline of nucleic acid drug development. The inventions used in fomivirsen (Vitravene; Isis Pharmaceuticals) development paved the road for structural backbone modifications as well as nucleobase and sugar modifications. The approval of patisiran (Onpattro; Alnylam) demonstrated an effective and safe delivery system for small interfering RNA (siRNA), extending potential applications to other nucleic acids such as messenger RNA (mRNA). Givosiran (Givlaari; Alnylam) further revolutionized the field with a carrier-free, targeted platform, utilizing N-Acetylgalactosamine (GalNAc)-siRNA conjugates to enable efficient delivery, expanding therapeutic applications beyond rare genetic disorders to more common conditions such as hyperlipidemia and hypertension. In this review paper, we highlight the evolution of nucleic acid-based drug development, focusing on the pioneering agents fomivirsen, patisiran, and givosiran, and discuss the ongoing challenges in advancing these therapeutics and vaccines.

Expanding the binding space of argonaute-2: incorporation of either E or Z isomers of 6'-vinylphosphonate at the 5' end of the antisense strand improves RNAi activity

A phosphate or a phosphate mimic at the 5' terminus of the antisense strand of a small interfering RNA (siRNA) is required for efficient loading into the RISC complex through the MID domain binding pocket of Ago2. Introduction of 5'-E-vinylphosphonate improves this binding and siRNA potency, but the Z isomer does not. Here, we demonstrate that both the E and Z isomers of 6'-vinylphosphonate at the 5' ends of antisense strands of siRNAs have equivalent potencies.

TAMing Gliomas: Unraveling the Roles of Iba1 and CD163 in Glioblastoma

Gliomas, the most common type of primary brain tumor, are a significant cause of morbidity and mortality worldwide. Glioblastoma, a highly malignant subtype, is particularly common, aggressive, and resistant to treatment. The tumor microenvironment (TME) of gliomas, especially glioblastomas, is characterized by a distinct presence of tumor-associated macrophages (TAMs), which densely infiltrate glioblastomas, a hallmark of these tumors. This macrophage population comprises both tissue-resident microglia as well as macrophages derived from the walls of blood vessels and the blood stream. Ionized calcium-binding adapter molecule 1 (Iba1) and CD163 are established cellular markers that enable the identification and functional characterization of these cells within the TME. This review provides an in-depth examination of the roles of Iba1 and CD163 in malignant gliomas, with a focus on TAM activation, migration, and immunomodulatory functions. Additionally, we will discuss how recent advances in AI-enhanced cell identification and visualization techniques have begun to transform the analysis of TAMs, promising unprecedented precision in their characterization and providing new insights into their roles within the TME. Iba1 and CD163 appear to have both unique and shared roles in glioma pathobiology, and both have the potential to be targeted through different molecular and cellular mechanisms. We discuss the therapeutic potential of Iba1 and CD163 based on available preclinical (experimental) and clinical (human tissue-based) evidence.

Metabolic Stability and Targeted Delivery of Oligonucleotides: Advancing RNA Therapeutics Beyond The Liver

Oligonucleotides have emerged as a formidable new class of nucleic acid therapeutics. Fully modified oligonucleotides exhibit enhanced metabolic stability and display successful clinical applicability for targets formerly considered "undruggable". Accumulating studies show that conjugation to targeting modalities of stabilized oligonucleotides, especially small interfering RNAs (siRNAs), has enabled robust delivery to intended cells/tissues. However, the major challenge in the field has been the stability and targeted delivery of oligonucleotides (siRNAs and antisense oligonucleotides (ASOs)) to extrahepatic tissues. In this Perspective, we review chemistry innovations and emerging delivery approaches that have revolutionized oligonucleotide drug discovery and development. We explore findings from both academia and industry that highlight the potential of oligonucleotides for indications involving different extrahepatic organs─including skeletal muscles, brain, lungs, skin, heart, adipose tissue, and eyes. In all, continued advances in chemistry coupled with conjugation-based approaches or novel administration routes will further advance the delivery of oligonucleotides to extrahepatic tissues.

Polymersome-mediated Cbl-b silencing activates T cells against solid tumors

Unleashing T cell function is critical for efficacious cancer immunotherapy. Here, we present an in vivo T cell activation strategy by silencing Casitas B-lineage lymphoma proto-oncogene b (Cbl-b), an intracellular checkpoint, to effectively combat solid tumors. The polymersomes are able to efficiently load and deliver siRNA against cblb to T cells both in vitro and in vivo, successfully silencing the cblb gene expression in primary T cells and enhancing the IL-2 receptor CD25 expression, which in turn enhances T cell function and prevents T cell exhaustion. In vitro and in vivo studies showed that siRNA against cblb caused an effective inhibition of tumor progression in subcutaneous B16-F10 and LLC models, in which a significant increase of effector T cells in peripheral blood mononuclear cells and an increase of effector T cells and a significant decrease of Treg cells in the tumor were clearly observed. This polymersome-mediated down-regulation of the cblb gene in T cells provides a promising approach for activating T cells and enhancing their anti-tumor capacity.

Oxytocin lipidation expanding therapeutics for long-term reversal of autistic behaviors in rats

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social interaction and repetitive, stereotyped behaviors. There is no universally effective pharmacological treatment targeting its core symptoms.Oxytocin, an endogenous polypeptide known as the "social hormone", has shown potential in improving emotional recognition and social interactions in individuals with ASD. However, its clinical application has been limited due to its short half-life and poor blood-brain barrier penetration. To address these challenges, we utilized peptide lipidation technology to enhance the pharmacokinetic properties and brain bioavailability of oxytocin. A series of lipidated oxytocin analogs was designed and synthesized, exhibiting superior brain distribution and pharmacokinetic profiles in valproic acid-induced autistic rat models compared to unmodified oxytocin. Among theseanalogs, C16-modified oxytocin (C16-OT), administered intrathecally, achieved the most extensive brain distribution with limited presence in the blood, resulting in long-lasting improvements in autistic behaviors. These improvements, including enhanced social behaviors and reduced stereotypical actions, were sustained for up to 42 days, contrasting with the brief effects typically reported in previous studies. Furthermore, a comparison of administration routes revealed that intrathecal injection achieved higher brain concentrations and more prolonged social behavioral improvements than intranasal delivery. These findings provide robust preclinical evidence that C16-OT, through optimized lipidation and intrathecal delivery, offers sustained central nervous system activity and significant, long-term reversal of social behavioral deficits in rats with autism.

Modulation of TTR Gene Expression in the Eye using Modified Duplex RNAs

Small interfering RNAs (siRNAs) are a proven therapeutic approach for controlling gene expression in the liver. Expanding the clinical potential of RNA interference (RNAi) requires developing strategies to enhance delivery to extra-hepatic tissues. In this study we examine inhibiting transthyretin (TRR) gene expression by short interfering RNAs (siRNAs) in the eye. Anti-TTR siRNAs have been developed as successful drugs to treat TTR amyloidosis. When administered systemically, anti-TTR siRNAs alleviate symptoms by blocking TTR expression in the liver. However, TTR amyloidosis also affects the eye, suggesting a need for reducing ocular TTR gene expression. Here, we demonstrate that C5 and 2'-O-linked lipid-modified siRNAs formulated in saline can inhibit TTR expression in the eye when administered locally by intravitreal (IVT) injection. Modeling suggests that length and accessibility of the lipid chains contributes to in vivo silencing. GalNAc modified anti-dsRNAs also inhibit TTR expression, albeit less potently. These data support lipid modified siRNAs as an approach to treating the ocular consequences of TTR amyloidosis. Inhibition of TTR expression throughout the eye demonstrates that lipid-siRNA conjugates have the potential to be a versatile platform for ocular drug discovery.

RNA Therapies in Cardio-Kidney-Metabolic Syndrome: Advancing Disease Management

Cardio-Kidney-Metabolic (CKM) Syndrome involves metabolic, kidney, and cardiovascular dysfunction, disproportionately affecting disadvantaged groups. Its staging (0-4) highlights the importance of early intervention. While current management targets hypertension, heart failure, dyslipidemia, and diabetes, RNA-based therapies offer innovative solutions by addressing molecular mechanisms of CKM Syndrome. Emerging RNA treatments, including antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs), show promise in slowing disease progression across CKM stages. For example, ASOs and siRNAs targeting ApoC-III and ANGPTL3 reduce triglycerides and LDL cholesterol, while siRNAs improve blood pressure control by targeting the renin-angiotensin-aldosterone system. Obesity treatments leveraging miRNAs and circRNAs tackle a key CKM risk factor. In heart failure and diabetes, RNA-based therapies improve cardiac function and glucose control, while early kidney disease trials show potential for RNAi in acute injury. Further research is essential to refine these therapies and ensure equitable access.

Clinical applications of oligonucleotides for cancer therapy

Oligonucleotide therapeutics (ONTs) represent a rapidly evolving modality for cancer treatment, capitalizing on their ability to modulate gene expression with high specificity. With more than 20 nucleic acid-based therapies that gained regulatory approval, advances in chemical modifications, sequence optimization, and novel delivery systems have propelled ONTs from research tools to clinical realities. ONTs, including siRNAs, antisense oligonucleotides, saRNA, miRNA, aptamers, and decoys, offer promising solutions for targeting previously "undruggable" molecules, such as transcription factors, and enhancing cancer immunotherapy by overcoming tumor immune evasion. The promise of ONT application in cancer treatment is exemplified by the recent FDA approval of the first oligonucleotide-based treatment to myeloproliferative disease. At the same time, there are challenges in delivering ONTs to specific tissues, mitigating off-target effects, and improving cellular uptake and endosomal release. This review provides a comprehensive overview of ONTs in clinical trials, emerging delivery strategies, and innovative therapeutic approaches, emphasizing the role of ONTs in immunotherapy and addressing hurdles that hinder their clinical translation. By examining advances and remaining challenges, we highlight opportunities for ONTs to revolutionize oncology and enhance patient outcomes.

Cerebral Amyloid Angiopathy: Clinical Presentation, Sequelae and Neuroimaging Features-An Update

The prevalence of cerebral amyloid angiopathy (CAA) has been shown to increase with age, with rates reported to be around 50-60% in individuals over 80 years old who have cognitive impairment. The disease often presents as spontaneous lobar intracerebral hemorrhage (ICH), which carries a high risk of recurrence, along with transient focal neurologic episodes (TFNE) and progressive cognitive decline, potentially leading to Alzheimer's disease (AD). In addition to ICH, neuroradiologic findings of CAA include cortical and subcortical microbleeds (MB), cortical subarachnoid hemorrhage (cSAH) and cortical superficial siderosis (cSS). Non-hemorrhagic pathologies include dilated perivascular spaces in the centrum semiovale and multiple hyperintense lesions on T2-weighted magnetic resonance imaging (MRI). A definitive diagnosis of CAA still requires histological confirmation. The Boston criteria allow for the diagnosis of a probable or possible CAA by considering specific neurological and MRI findings. The recent version, 2.0, which includes additional non-hemorrhagic MRI findings, increases sensitivity while maintaining the same specificity. The characteristic MRI findings of autoantibody-related CAA-related inflammation (CAA-ri) are similar to the so-called "amyloid related imaging abnormalities" (ARIA) observed with amyloid antibody therapies, presenting in two variants: (a) vasogenic edema and leptomeningeal effusions (ARIA-E) and (b) hemorrhagic lesions (ARIA-H). Clinical and MRI findings enable the diagnosis of a probable or possible CAA-ri, with biopsy remaining the gold standard for confirmation. In contrast to spontaneous CAA-ri, only about 20% of patients treated with monoclonal antibodies who show proven ARIA on MRI also experience clinical symptoms, including headache, confusion, other psychopathological abnormalities, visual disturbances, nausea and vomiting. Recent findings indicate that treatment should be continued in cases of mild ARIA, with ongoing MRI and clinical monitoring. This review offers a concise update on CAA and its associated consequences.

Oligonucleotide therapeutics for neurodegenerative diseases

Recently there has been a surge in interest involving the application of oligonucleotides, including small interfering RNA (siRNA) and antisense oligonucleotides (ASOs), for the treatment of chronic diseases that have few available therapeutic options. This emerging class of drugs primarily operates by selectively suppressing target genes through antisense and/or RNA interference mechanisms. While various commercial medications exist for delivering oligonucleotides to the hepatic tissue, achieving effective delivery to extra hepatic tissues remains a formidable challenge. Here, we review recent advances in oligonucleotide technologies, including nanoparticle delivery, local administration, and 2'-O-hexadecyl (C16)-conjugation that work to extend the applicability of siRNAs and ASOs to nerve tissues. We discuss critical factors pivotal for the successful clinical translations of these modified or engineered oligonucleotides in the context of treating neurodegenerative diseases such as Alzheimer's disease and amyotrophic lateral sclerosis.

Application of small interfering RNA technology in cytochrome P450 gene modulation

Cytochrome P450 plays key roles in the biotransformation of endogenous and exogenous chemicals including drugs and environmental pollutants. The inhibition and downregulation of P450s can have therapeutic effects, and/or modulate drug metabolism. P450s are largely inhibited by small molecules; however, this strategy is often hampered by intrinsic toxicity and drug-drug interactions. Furthermore, it is challenging for small molecules to exhibit high selectivity and inhibitory efficiencies. Recently, small interfering RNA (siRNA) technology has demonstrated the potential for P450 modulation. Examples of recent applications of siRNAs in P450 gene modulation, in vitro and in vivo, are highlighted in this review. The necessity of siRNA techniques and their advantages as P450 modulators are discussed, along with a review of current obstacles and a perspective on future advancements. SIGNIFICANCE STATEMENT: This article reviews studies on the application of small interfering RNA technology to cytochrome P450 gene modulation. The necessity of siRNA methods and the benefits of their use as P450 modulators have been suggested by comparison with small-molecule drugs. Additionally, the challenges that presently limit the broader implementation of this topic are examined, and a perspective for future developments is proposed.

Nucleic Acid Conjugates: Unlocking Therapeutic Potential

Nucleic acids have emerged as a powerful class of therapeutics. Through simple base pair complementarity, nucleic acids allow the targeting of a variety of pathologically relevant proteins and RNA molecules. However, despite the preliminary successes of nucleic acids as drugs in the clinic, limited biodistribution, inadequate delivery mechanisms, and target engagement remain key challenges in the field. A key area of research has been the chemical optimization of nucleic acid backbones to significantly enhance their "drug-like" properties. Alternatively, this review focuses on the next generation of nucleic acid chemical modifications: covalent biochemical conjugates. These conjugates are being applied to improve the delivery, functionality, and targeting. Exploiting research on heterobifunctionals, such as PROTACs, RIBOTACs, molecular glues, etc., has the potential to dramatically expand nucleic acid drug functionality and target engagement capabilities. Such next-generation chemistry-based enhancements have the potential to unlock nucleic acids as effective and versatile therapeutic agents.

Blood-brain-barrier-crossing lipid nanoparticles for mRNA delivery to the central nervous system

The systemic delivery of mRNA molecules to the central nervous system is challenging as they need to cross the blood-brain barrier (BBB) to reach into the brain. Here we design and synthesize 72 BBB-crossing lipids fabricated by conjugating BBB-crossing modules and amino lipids, and use them to assemble BBB-crossing lipid nanoparticles for mRNA delivery. Screening and structure optimization studies resulted in a lead formulation that has substantially higher mRNA delivery efficiency into the brain than those exhibited by FDA-approved lipid nanoparticles. Studies in distinct mouse models show that these BBB-crossing lipid nanoparticles can transfect neurons and astrocytes of the whole brain after intravenous injections, being well tolerated across several dosage regimens. Moreover, these nanoparticles can deliver mRNA to human brain ex vivo samples. Overall, these BBB-crossing lipid nanoparticles deliver mRNA to neurons and astrocytes in broad brain regions, thereby being a promising platform to treat a range of central nervous system diseases.

Assessing Hybridization-Dependent Off-Target Risk for Therapeutic Oligonucleotides: Updated Industry Recommendations

Hybridization-dependent off-target (OffT) effects, occurring when oligonucleotides bind via Watson-Crick-Franklin hybridization to unintended RNA transcripts, remain a critical safety concern for oligonucleotide therapeutics (ONTs). Despite the importance of OffT assessment of clinical trial ONT candidates, formal guidelines are lacking, with only brief mentions in Japanese regulatory documents (2020) and US Food and Drug Administration (FDA) recommendations for hepatitis B virus treatments (2022). This article presents updated industry recommendations for assessing OffTs of ONTs, building upon the 2012 Oligonucleotide Safety Working Group (OSWG) recommendations and accounting for recent technological advancements. A new OSWG subcommittee, comprising industry experts in RNase H-dependent and steric blocking antisense oligonucleotides and small interfering RNAs, has developed a comprehensive framework for OffT assessment. The proposed workflow encompasses five key steps: (1) OffT identification through in silico complementarity prediction and transcriptomics analysis, (2) focus on cell types with relevant ONT activity, (3) in vitro verification and margin assessment, (4) risk assessment based on the OffT biological role, and (5) management of unavoidable OffTs. The authors provide detailed considerations for various ONT classes, emphasizing the importance of ONT-specific factors such as chemistry, delivery systems, and tissue distribution in OffT evaluation. The article also explores the potential of machine learning models to enhance OffT prediction and discusses strategies for experimental verification and risk assessment. These updated recommendations aim to improve the safety profile of ONTs entering clinical trials and to manage unavoidable OffTs. The authors hope that these recommendations will serve as a valuable resource for ONT development and for the forthcoming finalization of the FDA draft guidance and the International Council for Harmonization S13 guidance on Nonclinical Safety Assessment of Oligonucleotide-Based Therapeutics.

"Current and emerging drug therapies in Alzheimer's disease: A pathophysiological Perspective"

The analytical and experimental investigation of several targets and biomarkers that help in explaining significant cognitive deficits, covering drug development and precision medicine aimed at different chronic neurodegenerative conditions such as Alzheimer's disease (AD), Parkinson's disease, synaptic dysfunction, brain damage from neuronal apoptosis, and other disease pathologies; this served as the foundation for all phase studies. The focus of current therapeutic approaches is on developing humanized antibodies, agonist and antagonist drugs, receptors, signaling molecules, major targeted drug-metabolizing enzymes, and other metabolites to treat neurodegeneration in the AD brain brought on by tau hyperphosphorylation, amyloid plagues, or other cholinergic effects. The five A's-amnesia, agnosia, aphasia, apraxia, and anomia-are the typical symptoms associated with AD. While the main goal of drug therapeutics studies is modified amino acids acting as pro-drugs, pharmacokinetics studies and trends in evaluating drug-drug interactions focus on interactions between drugs and antibodies, drugs and therapeutic biologics like metabolites, herbs, interleukin-based, and gene silencing mechanism-based. Studies on the biotransformation of xenobiotic compounds and the metabolism of exogenous and endogenous substances are conducted under Phase I, Phase II, and Phase III trials because the pivotal pharmacokinetic properties of drugs, such as absorption, distribution, metabolism, and excretion (ADME), aid in understanding variations in the crucial improvement of various target drugs. This review also highlights the developments in soon-to-be genetically created targeted medications that may serve as ground-breaking treatments for cholinergic illnesses in the brains of AD patients and other neurodegenerative conditions.

Harnessing antiviral RNAi therapeutics for pandemic viruses: SARS-CoV-2 and HIV

Using the knowledge from decades of research into RNA-based therapies, the COVID-19 pandemic response saw the rapid design, testing and production of the first ever mRNA vaccines approved for human use in the clinic. This breakthrough has been a significant milestone for RNA therapeutics and vaccines, driving an exponential growth of research into the field. The development of novel RNA therapeutics targeting high-threat pathogens, that pose a substantial risk to global health, could transform the future of health delivery. In this review, we provide a detailed overview of the two RNA interference (RNAi) pathways and how antiviral RNAi therapies can be used to treat acute or chronic diseases caused by the pandemic viruses SARS-CoV-2 and HIV, respectively. We also provide insights into short-interfering RNA (siRNA) delivery systems, with a focus on how lipid nanoparticles can be functionalized to achieve targeted delivery to specific sites of disease. This review will provide the current developments of SARS-CoV-2 and HIV targeted siRNAs, highlighting strategies to advance the progression of antiviral siRNA along the clinical development pathway.

High resistance barrier and prophylactic protection in preclinical models of SARS-CoV-2 with two siRNA combination

RNA interference is a natural antiviral mechanism that could be harnessed to combat SARS-CoV-2 infection by targeting and destroying the viral RNA. We identified potent lipophilic small interfering RNA (siRNA) conjugates targeting highly conserved regions of SARS-CoV-2 outside of the spike-encoding region capable of achieving ≥3-log viral reduction. Serial passaging studies demonstrated that a two-siRNA combination prevented development of resistance compared to a single siRNA approach. Viral resistance to single siRNA treatment occurred due to emergence of point mutations at critical positions required for siRNA-mediated target binding and cleavage, which led to a loss of siRNA efficacy. With a two-siRNA combination, emergence of mutations within the siRNA binding site was abolished. When delivered intranasally, two-siRNA combination protected Syrian hamsters from weight loss and lung pathology by viral infection upon prophylactic administration but not following onset of infection. Together, the data support potential utility of RNAi as a prophylactic approach with high resistance barrier to counteract SARS-CoV-2 emergent variants and complement vaccination. Most importantly, given that the siRNAs can be rapidly developed from a new pathogen sequence, this strategy has implications as a new type of preventive medicine that may protect against future coronavirus pandemics.

A dual-locked cyclopeptide-siRNA conjugate for tumor-specific gene silencing

Strategies allowing tumor-selective siRNA delivery while minimizing off-tumor gene silencing effects are highly demanded to advance cancer gene therapy, which however still remain challenging. We herein report a dual-locking bioconjugation approach to address this challenge. A dual-locked cyclopeptide-siRNA conjugate (DPRC) was designed to simultaneously endow siRNA with tumor-targeting properties and tumor-biomarker/visible-light dually controllable action. The DPRC consisted of a programmed death-ligand 1 (PD-L1)-targeting cyclopeptide as a tumor-homing ligand and B-cell lymphoma-2 (Bcl-2)-targeting siRNA as a payload. They were conjugated via a tandem-responsive cleavable linker containing a photocleavable coumarin moiety quenched by naphthylamide through a disulfide linkage. Owing to the interaction between cell-membrane PD-L1 and the cyclopeptide, the DPRC was efficiently taken up by PD-L1-positive cancer cells. Notably, the internalized DPRC could only release and restore the gene silencing activity of siBcl-2 upon GSH-mediated disulfide bond breakage followed by visible light irradiation on the coumarin moiety to induce photo-cleavage. The released siBcl-2 further silenced the expression of anti-apoptotic Bcl-2 to suppress cancer cell growth. We demonstrated the tumor-targeting and dual-locked action of siRNA by the DPRC in both two-dimensional and three-dimensional cancer cell cultures. This study thus presents a novel strategy for precise tumor-specific gene silencing by siRNA.

Molecular Therapeutics in Development to Treat Alzheimer's Disease

Until recently, only symptomatic therapies, in the form of acetylcholine esterase inhibitors and NMDA-receptor antagonists, have been available for the treatment of Alzheimer's disease. However, advancements in our understanding of the amyloid cascade hypothesis have led to a development of disease-modifying therapeutic strategies. These include immunotherapies based on an infusion of monoclonal antibodies against amyloid-β, three of which have been approved for the treatment of Alzheimer's disease in the USA (one of them, lecanemab, has also been approved in several other countries). They all lead to a dramatic reduction of amyloid plaques in the brain, whereas their clinical effects have been more limited. Moreover, they can all lead to side effects in the form of amyloid-related imaging abnormalities. Ongoing developments aim at facilitating their administration, further improving their effects and reducing the risk for amyloid-related imaging abnormalities. Moreover, a number of anti-tau immunotherapies are in clinical trials, but none has so far shown any robust effects on symptoms or pathology. Another line of development is represented by gene therapy. To date, only antisense oligonucleotides against amyloid precursor protein/amyloid-β and tau have reached the clinical trial stage but a variety of gene editing strategies, such as clustered regularly interspaced short palindromic repeats/Cas9-mediated non-homologous end joining, base editing, and prime editing, have all shown promise on preclinical disease models. In addition, a number of other pharmacological compounds targeting a multitude of biochemical processes, believed to be centrally involved in Alzheimer's disease, are currently being evaluated in clinical trials. This article delves into current and future perspectives on the treatment of Alzheimer's disease, with an emphasis on immunotherapeutic and gene therapeutic strategies.

Preventing acute neurotoxicity of CNS therapeutic oligonucleotides with the addition of Ca2+ and Mg2+ in the formulation

Oligonucleotide therapeutics (ASOs and siRNAs) have been explored for modulation of gene expression in the central nervous system (CNS), with several drugs approved and many in clinical evaluation. Administration of highly concentrated oligonucleotides to the CNS can induce acute neurotoxicity. We demonstrate that delivery of concentrated oligonucleotides to the CSF in awake mice induces acute toxicity, observable within seconds of injection. Electroencephalography and electromyography in awake mice demonstrated seizures. Using ion chromatography, we show that siRNAs can tightly bind Ca2+ and Mg2+ up to molar equivalents of the phosphodiester/phosphorothioate bonds independently of the structure or phosphorothioate content. Optimization of the formulation by adding high concentrations (above biological levels) of divalent cations (Ca2+ alone, Mg2+ alone, or Ca2+ and Mg2+) prevents seizures with no impact on the distribution or efficacy of the oligonucleotide. The data here establish the importance of adding Ca2+ and Mg2+ to the formulation for the safety of CNS administration of therapeutic oligonucleotides.

Nanotechnology used for siRNA delivery for the treatment of neurodegenerative diseases: Focusing on Alzheimer's disease and Parkinson's disease

Neurodegenerative diseases (ND) are often accompanied by dementia, motor dysfunction, or disability. Caring for these patients imposes a significant psychological and financial burden on families. Until now, there are no effective methods for the treatment of NDs. Among them, Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common. Recently, studies have revealed that the overexpression of certain genes may be linked to the occurrence of AD and PD. Small interfering RNAs (siRNAs) are a powerful tool for gene silencing because they can specifically bind to and cleave target mRNA. However, the intrinsic properties of naked siRNA and various physiological barriers limit the application of siRNA in the brain. Nanotechnology is a promising option for addressing these issues. Nanoparticles are not only able to protect siRNA from degradation but also have the advantage of crossing various physiological barriers to reach the brain target of siRNA. In this review, we aim to introduce diverse nanotechnology used for delivering siRNA to treat AD and PD. Finally, we will briefly discuss our perspectives on this promising field.

Efficient and selective kidney targeting by chemically modified carbohydrate conjugates

We investigated a renal tubule-targeting carbohydrate (RENTAC) that can selectively deliver small-molecule and nucleic acid analogs to the proximal convoluted tubules of the kidney following systemic delivery in mice. We comprehensively evaluated anti-miR-21-peptide nucleic acid-RENTAC, and fluorophore-RENTAC conjugates in cell culture and in vivo. We established that RENTAC conjugates showed megalin- and cubilin-dependent endocytic uptake in the immortalized kidney cell line. In vivo biodistribution studies confirmed the retention of RENTAC conjugates in the kidneys for several days compared with other organs. Immunofluorescence staining confirmed the selective distribution of the RENTAC conjugates in proximal convoluted tubules. We further demonstrated proximal convoluted tubule targeting features of RENTAC conjugates in a folic acid-induced kidney fibrosis mouse model. As a biological readout, we targeted miR-33 using antisense peptide nucleic acid (PNA) 33-RENTAC conjugates in the fibrotic kidney disease model. The targeted delivery of PNA 33-RENTAC resulted in slower fibrosis progression and decreased collagen deposition. We also confirmed that the RENTAC ligand did not exert any adverse reactions. Thus, we established that the RENTAC ligand can be used for broad clinical applications targeting the kidneys selectively.

Controversies and insights into PTBP1-related astrocyte-neuron transdifferentiation: neuronal regeneration strategies for Parkinson's and Alzheimer's disease

Promising therapeutic strategies are being explored to replace or regenerate the neuronal populations that are lost in patients with neurodegenerative disorders. Several research groups have attempted direct reprogramming of astrocytes into neurons by manipulating the expression of polypyrimidine tract-binding protein 1 (PTBP1) and claimed putative converted neurons to be functional, which led to improved disease outcomes in animal models of several neurodegenerative disorders. However, a few other studies reported data that contradict these claims, raising doubt about whether PTBP1 suppression truly reprograms astrocytes into neurons and the therapeutic potential of this approach. This review discusses recent advances in regenerative therapeutics including stem cell transplantations for central nervous system disorders, with a particular focus on Parkinson's and Alzheimer's diseases. We also provide a perspective on this controversy by considering that astrocyte heterogeneity may be the key to understanding the discrepancy in published studies, and that certain subpopulations of these glial cells may be more readily converted into neurons.

Sele-targeted siRNA liposome nanoparticles inhibit pathological scars formation via blocking the cross-talk between monocyte and endothelial cells: a preclinical study based on a novel mice scar model

BACKGROUND

Pathological scars (PS) are one of the most common complications in patients with trauma and burns, leading to functional impairments and aesthetic concerns. Mechanical tension at injury sites is a crucial factor in PS formation. However, the precise mechanisms remain unclear due to the lack of reliable animal models.

RESULTS

We developed a novel mouse model, the Retroflex Scar Model (RSM), which induces PS by applying controlled tension to wounds in vivo. RNA sequencing identified significant transcriptome changes in RSM-induced scars. Elevated expression of E-Selectin (Sele) was observed in endothelial cells from both the RSM model and human PS (Keloid) samples. In vitro studies demonstrated that cyclic mechanical stretching (CMS) increased Sele expression, promoting monocyte adhesion and the release of pro-inflammatory factors. Single-cell sequencing analysis from the GEO database, complemented by Western blotting, immunofluorescence, and co-immunoprecipitation, confirmed the role of Sele-mediated monocyte adhesion in PS formation. Additionally, we developed Sele-targeted siRNA liposome nanoparticles (LNPs) to inhibit monocyte adhesion. Intradermal administration of these LNPs effectively reduced PS formation in both in vivo and in vitro studies.

CONCLUSIONS

This study successfully established a reliable mouse model for PS, highlighting the significant roles of mechanical tension and chronic inflammation in PS formation. We identified Sele as a key therapeutic target and developed Sele-targeted siRNA LNPs, which demonstrated potential as a preventive strategy for PS. These findings provide valuable insights into PS pathogenesis and open new avenues for developing effective treatments for pathological scars.

Intravenous administration of blood-brain barrier-crossing conjugates facilitate biomacromolecule transport into central nervous system

Delivery of biomacromolecules to the central nervous system (CNS) remains challenging because of the restrictive nature of the blood-brain barrier (BBB). We developed a BBB-crossing conjugate (BCC) system that facilitates delivery into the CNS through γ-secretase-mediated transcytosis. Intravenous administration of a BCC10-oligonucleotide conjugate demonstrated effective transportation of the oligonucleotide across the BBB and gene silencing in wild-type mice, human brain tissues and an amyotrophic lateral sclerosis mouse model.

Amphiphilic Oligonucleotide Derivatives-Promising Tools for Therapeutics

Recent advances in genetics and nucleic acid chemistry have created fundamentally new tools, both for practical applications in therapy and diagnostics and for fundamental genome editing tasks. Nucleic acid-based therapeutic agents offer a distinct advantage of selectively targeting the underlying cause of the disease. Nevertheless, despite the success achieved thus far, there remain unresolved issues regarding the improvement of the pharmacokinetic properties of therapeutic nucleic acids while preserving their biological activity. In order to address these challenges, there is a growing focus on the study of safe and effective delivery methods utilising modified nucleic acid analogues and their lipid bioconjugates. The present review article provides an overview of the current state of the art in the use of chemically modified nucleic acid derivatives for therapeutic applications, with a particular focus on oligonucleotides conjugated to lipid moieties. A systematic analysis has been conducted to investigate the ability of amphiphilic oligonucleotides to self-assemble into micelle-like structures, as well as the influence of non-covalent interactions of such derivatives with serum albumin on their biodistribution and therapeutic effects.

Antitumor Effect of Oleoyl-siRNA against Pancreatic Cancer Using a Portal Vein Infusion Liver-Metastatic Mouse Model

In this study, we developed an oleoyl-siRNA conjugate in which oleic acid was conjugated at the 5'-end of the sense strand of the siRNA. Furthermore, we examined the effects of RNAi in a mouse model of pancreatic cancer with liver metastasis. The mouse model of pancreatic cancer with liver metastasis was developed by implanting Sui67Luc human pancreatic cancer cells into the portal veins of mice. Sui67Luc cells have high expression of tumor-related genes such as β-catenin, vascular endothelial growth factor, and programmed cell death ligand-1. All genes were knocked down using siRNA, among which siRNA targeting β-catenin exhibited the most suitable RNAi effect. Therefore, we investigated the in vitro RNAi effect of oleoyl-siRNA (Ole-siRNA) targeting the β-catenin gene in Sui67Luc cells and found that it was stronger than that of unmodified siRNA. For in vivo experiments, we investigated the biodistribution, antitumor effect, and change in life expectancy of mice upon systemic administration of Ole-siRNA complexed with Invivofectamine 3.0 (IVF). In terms of biodistribution, the Ole-siRNA/IVF complex likely accumulates in the liver of mice. The antitumor effect of Ole-siRNA in a portal vein infusion liver-metastatic Sui67Luc tumor mouse model was evaluated using an in vivo imaging system. Ole-siRNA had a significant antitumor effect compared with nonmodified siRNA. In addition, mice with metastatic liver Sui67Luc tumors treated with Ole-siRNA showed increased survival. These results suggest that Ole-siRNAs are useful novel RNAi molecules for treating pancreatic cancer and liver metastasis.

Single-Stranded Hairpin Loop RNAs (loopmeRNAs) Potently Induce Gene Silencing through the RNA Interference Pathway

Synthetic small interfering RNAs conjugated to trivalent N-acetylgalactosamine (GalNAc) are clinically validated drugs for treatment of liver diseases. Incorporation of phosphorothioate linkages and ribose modifications are necessary for stability, potency, and duration of pharmacology. Although multiple alternative siRNA designs such as Dicer-substrate RNA, shRNA, and circular RNA have been evaluated in vitro and in preclinical studies with some success, clinical applications of these designs are limited as it is difficult to incorporate chemical modifications in these designs. An alternative siRNA design that can incorporate chemical modifications through straightforward synthesis without compromising potency will significantly advance the field. Here, we report a facile synthesis of GalNAc ligand-containing single-stranded loop hairpin RNAs (loopmeRNAs) with clinically relevant chemical modifications. We evaluated the efficiency of novel loopmeRNA designs in vivo and correlated their structure-activity relationship with the support of in vitro metabolism data. Sequences and chemical modifications in the loop region of the loopmeRNA design were optimized for maximal potency. Our studies demonstrate that loopmeRNAs can efficiently silence expression of target genes with comparable efficacy to conventional double-stranded siRNAs but reduced environmental and regulatory burdens.

Combinatorial Synthesis of Alkyl Chain-Capped Poly(β-Amino Ester)s for Effective siRNA Delivery

Poly (β-amino ester) (PBAE) is a class of biodegradable polymers containing ester bonds in their main chain, extensively investigated as cationic polymer carriers for siRNA. Most current PBAE carriers rely on termination with hydrophilic or charged amines. In this study, a polymer platform consisting of 168 PBAE polymers with hydrophobic alkyl chain terminals is constructed through sequential aza-Michael addition. A large number of effective carriers are identified through in vitro screening of the PBAE platform for siLuc delivery to HeLa-Luc cells. Specifically, PA8-C6 and PA8-C8 achieve remarkable gene knockdown efficacies of up to 80% with low cytotoxicity. Certain materials from the PA2 and PA5 series demonstrate potent siRNA delivery capabilities associated with elevated cytotoxicity. The pKa value of PBAE is predominantly determined by the hydrophilic amine side chains rather than the end-capping groups. A pKa range of ≈6.2-6.5 may contribute to the excellent delivery capability for PA8 series carriers. The co-formulation of PBAE carriers with helper lipids leads to the reduced size and surface charges of the polyplex NPs with siRNA, consequently decreasing the cytotoxicity and enhancing siRNA delivery efficacy. These findings hold significant implications for the development of novel degradable polymer carriers for siRNA delivery.

Non-Viral RNA Delivery During Pregnancy: Opportunities and Challenges

During pregnancy, the risk of maternal and fetal adversities increases due to physiological changes, genetic predispositions, environmental factors, and infections. Unfortunately, treatment options are severely limited because many essential interventions are unsafe, inaccessible, or lacking in sufficient scientific data to support their use. One potential solution to this challenge may lie in emerging RNA therapeutics for gene therapy, protein replacement, maternal vaccination, fetal gene editing, and other prenatal treatment applications. In this review, the current landscape of RNA platforms and non-viral RNA delivery technologies that are under active development for administration during pregnancy is explored. Advancements of pregnancy-specific RNA drugs against SARS-CoV-2, Zika, influenza, preeclampsia, and for in-utero gene editing are discussed. Finally, this study highlights bottlenecks that are impeding translation efforts of RNA therapies, including the lack of accurate cell-based and animal models of human pregnancy and concerns related to toxicity and immunogenicity during pregnancy. Overcoming these challenges will facilitate the rapid development of this new class of pregnancy-safe drugs.

Near Sequence Homology Does Not Guarantee siRNA Cross-Species Efficacy

Small interfering RNAs (siRNAs) represent a novel class of drugs capable of potent and sustained modulation of genes across various tissues. Preclinical development of siRNAs necessitates assessing efficacy and toxicity in animal models. While identifying therapeutic leads with cross-species activity can expedite development, it may compromise efficacy and be infeasible for certain gene targets. Here, we investigate whether deriving species-active siRNAs from potent human-targeting leads-an approach termed mismatch conversion-can yield potent compounds. We systematically altered potent siRNAs targeting human genes associated with diseases-SOD1 (ALS), JAK1 (inflammation), and HTT (HD)-to generate species-matching variants with full complementarity to their target in NHPs, mice, rats, sheep, and dogs. Variants potency and efficacy were measured in corresponding cell lines. We demonstrate that sequence, position, and number of mismatches significantly influence the ability to generate potent species-active compounds via mismatch conversion. Across tested sequences, mismatch conversion strategy ability to identify a species-active lead varied from 0% to 70%. For SOD1, lead compounds identified from species-focus screening in mouse and dog cells were more potent than leads obtained from mismatch conversion. Thus, a focused screening of therapeutic lead and model compounds may represent a more reliable strategy for the clinical advancement of siRNAs.

Targeting DNA damage repair mechanism by using RAD50-silencing siRNA nanoparticles to enhance radiotherapy in triple negative breast cancer

Radiotherapy (RT) is one of major therapeutic modalities in combating breast cancer. In RT, ionizing radiation is employed to induce DNA double-strand breaks (DSBs) as a primary mechanism that causes cancer cell death. However, the induced DNA damage can also trigger the activation of DNA repair mechanisms, reducing the efficacy of RT treatment. Given the pivotal role of RAD50 protein in the radiation-responsive DNA repair pathways involving DSBs, we developed a novel polymer-lipid based nanoparticle formulation containing RAD50-silencing RNA (RAD50-siRNA-NPs) and evaluated its effect on the RAD50 downregulation as well as cellular and tumoral responses to ionizing radiation using human triple-negative breast cancer as a model. The RAD50-siRNA-NPs successfully preserved the activity of the siRNA, facilitated its internalization by cancer cells via endocytosis, and enabled its lysosomal escape. The nanoparticles significantly reduced RAD50 expression, whereas RT alone strongly increased RAD50 levels at 24 h. Pretreatment with RAD50-siRNA-NPs sensitized the cancer cells to RT with ∼2-fold higher level of initial DNA DSBs as determined by a γH2AX biomarker and a 2.5-fold lower radiation dose to achieve 50 % colony reduction. Intratumoral administration of RAD50-siRNA-NPs led to a remarkable 53 % knockdown in RAD50. The pretreatment with RAD50-siRNA-NPs followed by RT resulted in approximately a 2-fold increase in DNA DSBs, a 4.5-fold increase in cancer cell apoptosis, and 2.5-fold increase in tumor growth inhibition compared to RT alone. The results of this work demonstrate that RAD50 silencing by RAD50-siRNA-NPs can disrupt RT-induced DNA damage repair mechanisms, thereby significantly enhancing the radiation sensitivity of TNBC MDA-MB-231 cells in vitro and in orthotopic tumors as measured by colony forming and tumor regrowth assays, respectively.

Structure-Activity Relationship of Antibody-Oligonucleotide Conjugates: Evaluating Bioconjugation Strategies for Antibody-siRNA Conjugates for Drug Development

Antibody-oligonucleotide conjugates are a promising class of therapeutics for extrahepatic delivery of small interfering ribonucleic acids (siRNAs). These conjugates can be optimized for improved delivery and mRNA knockdown (KD) through understanding of structure-activity relationships. In this study, we systematically examined factors including antibody isotype, siRNA chemistry, linkers, conjugation chemistry, PEGylation, and drug-to-antibody ratios (DARs) for their impact on bioconjugation, pharmacokinetics (PK), siRNA delivery, and bioactivity. Conjugation site (cysteine, lysine, and Asn297 glycan) and DAR proved critical for optimal conjugate PK and siRNA delivery. SiRNA chemistry including 2' sugar modifications and positioning of phosphorothioates were found to be critical for delivery and duration of action. By utilizing cleavable and noncleavable linkers, we demonstrated the impact of linkers on PK and mRNA KD. To achieve optimal properties of antibody-siRNA conjugates, a careful selection of siRNA chemistry, DAR, conjugation sites, linkers, and antibody isotype is necessary.

Preclinical evaluation of stereopure antisense oligonucleotides for allele-selective lowering of mutant HTT

Huntington's disease (HD) is an autosomal dominant disease caused by the expansion of cytosine-adenine-guanine (CAG) repeats in one copy of the HTT gene (mutant HTT, mHTT). The unaffected HTT gene encodes wild-type HTT (wtHTT) protein, which supports processes important for the health and function of the central nervous system. Selective lowering of mHTT for the treatment of HD may provide a benefit over nonselective HTT-lowering approaches, as it aims to preserve the beneficial activities of wtHTT. Targeting a heterozygous single-nucleotide polymorphism (SNP) where the targeted variant is on the mHTT gene is one strategy for achieving allele-selective activity. Herein, we investigated whether stereopure phosphorothioate (PS)- and phosphoryl guanidine (PN)-containing oligonucleotides can direct allele-selective mHTT lowering by targeting rs362273 (SNP3). We demonstrate that our SNP3-targeting molecules are potent, durable, and selective for mHTT in vitro and in vivo in mouse models. Through comparisons with a surrogate for the nonselective investigational compound tominersen, we also demonstrate that allele-selective molecules display equivalent potency toward mHTT with improved durability while sparing wtHTT. Our preclinical findings support the advancement of WVE-003, an investigational allele-selective compound currently in clinical testing (NCT05032196) for the treatment of patients with HD.

Identification of selective and non-selective C9ORF72 targeting in vivo active siRNAs

A hexanucleotide (G4C2) repeat expansion (HRE) within intron one of C9ORF72 is the leading genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). C9ORF72 haploinsufficiency, formation of RNA foci, and production of dipeptide repeat (DPR) proteins have been proposed as mechanisms of disease. Here, we report the first example of disease-modifying siRNAs for C9ORF72 driven ALS/FTD. Using a combination of reporter assay and primary cortical neurons derived from a C9-ALS/FTD mouse model, we screened a panel of more than 150 fully chemically stabilized siRNAs targeting different C9ORF72 transcriptional variants. We demonstrate the lack of correlation between siRNA efficacy in reporter assay versus native environment; repeat-containing C9ORF72 mRNA variants are found to preferentially localize to the nucleus, and thus C9ORF72 mRNA accessibility and intracellular localization have a dominant impact on functional RNAi. Using a C9-ALS/FTD mouse model, we demonstrate that divalent siRNAs targeting C9ORF72 mRNA variants specifically or non-selectively reduce the expression of C9ORF72 mRNA and significantly reduce DPR proteins. Interestingly, siRNA silencing all C9ORF72 mRNA transcripts was more effective in removing intranuclear mRNA aggregates than targeting only HRE-containing C9ORF72 mRNA transcripts. Combined, these data support RNAi-based degradation of C9ORF72 as a potential therapeutic paradigm.

Targeting the transferrin receptor to transport antisense oligonucleotides across the mammalian blood-brain barrier

Antisense oligonucleotides (ASOs) are promising therapeutics for treating various neurological disorders. However, ASOs are unable to readily cross the mammalian blood-brain barrier (BBB) and therefore need to be delivered intrathecally to the central nervous system (CNS). Here, we engineered a human transferrin receptor 1 (TfR1) binding molecule, the oligonucleotide transport vehicle (OTV), to transport a tool ASO across the BBB in human TfR knockin (TfRmu/hu KI) mice and nonhuman primates. Intravenous injection and systemic delivery of OTV to TfRmu/hu KI mice resulted in sustained knockdown of the ASO target RNA, Malat1, across multiple mouse CNS regions and cell types, including endothelial cells, neurons, astrocytes, microglia, and oligodendrocytes. In addition, systemic delivery of OTV enabled Malat1 RNA knockdown in mouse quadriceps and cardiac muscles, which are difficult to target with oligonucleotides alone. Systemically delivered OTV enabled a more uniform ASO biodistribution profile in the CNS of TfRmu/hu KI mice and greater knockdown of Malat1 RNA compared with a bivalent, high-affinity TfR antibody. In cynomolgus macaques, an OTV directed against MALAT1 displayed robust ASO delivery to the primate CNS and enabled more uniform biodistribution and RNA target knockdown compared with intrathecal dosing of the same unconjugated ASO. Our data support systemically delivered OTV as a potential platform for delivering therapeutic ASOs across the BBB.

Advances in structural-guided modifications of siRNA

To date, the US Food and Drug Administration (FDA) has approved six small interfering RNA (siRNA) drugs: patisiran, givosiran, lumasiran, inclisiran, vutrisiran, and nedosiran, serving as compelling evidence of the promising potential of RNA interference (RNAi) therapeutics. The successful implementation of siRNA therapeutics is improved through a combination of various chemical modifications and diverse delivery approaches. The utilization of chemically modified siRNA at specific sites on either the sense strand (SS) or antisense strand (AS) has the potential to enhance resistance to ribozyme degradation, improve stability and specificity, and prolong the efficacy of drugs. Herein, we provide comprehensive analyses concerning the correlation between chemical modifications and structure-guided siRNA design. Various modifications, such as 2'-modifications, 2',4'-dual modifications, non-canonical sugar modifications, and phosphonate mimics, are crucial for the activity of siRNA. We also emphasize the essential strategies for enhancing overhang stability, improving RISC loading efficacy and strand selection, reducing off-target effects, and discussing the future of targeted delivery.