Small interfering RNA-induced TLR3 activation inhibits blood and lymphatic vessel growth. Proc Natl Acad Sci U S A. 2009;106:7137-7142. [PMID: 19359485 DOI: 10.1073/pnas.0812317106]

Gemogenovatucel-T (Vigil): bi-shRNA plasmid-based targeted immunotherapy

We describe in this review the historical evidence leading up to the concept and design of Vigil and subsequent clinical applications including safety and efficacy in a randomized, controlled Phase IIB trial. Vigil (gemogenovatucel-T) is a unique triple function targeted immunotherapy that demonstrates preclinical and clinical systemic anticancer activity. Construction of Vigil involves harvest of autologous malignant tissue for neoantigen targeting (ideally containing clonal neoantigens) followed by a two-day process involving transfection with a plasmid to provide a permissive 'training environment' for the patient's immune system. Transfected plasmid components contain an expressive human GMCSF DNA segment to enhance anticancer immune functional response and a second component expressing bi-shRNAfurin which reduces TGFβ isomers (TGFβ1 and TGFβ2) thereby reducing cancer inhibition of the targeted immune response. Results generated to date justify advancement to confirmatory clinical trials supporting product regulatory approval.

Multifunctional nanocomposites modulating the tumor microenvironment for enhanced cancer immunotherapy

Cancer immunotherapy has gained momentum for treating malignant tumors over the past decade. Checkpoint blockade and chimeric antigen receptor cell therapy (CAR-T) have shown considerable potency against liquid and solid cancers. However, the tumor microenvironment (TME) is highly immunosuppressive and hampers the effect of currently available cancer immunotherapies on overall treatment outcomes. Advancements in the design and engineering of nanomaterials have opened new avenues to modulate the TME. Progress in the current nanocomposite technology can overcome immunosuppression and trigger robust immunotherapeutic responses by integrating synergistic functions of different molecules. We will review recent advancements in nanomedical applications and discuss specifically designed nanocomposites modulating the TME for cancer immunotherapy. In addition, we provide information on the current landscape of clinical-stage nanocomposites for cancer immunotherapy.

Pharmacokinetics and Pharmacodynamics of GalNAc-Conjugated siRNAs

Small interfering RNAs (siRNAs) represent a new class of drugs with tremendous potential for battling previously "undruggable" diseases. After nearly 2 decades of efforts in addressing the problems of the poor drug profile of naked unmodified siRNAs, this new modality has finally come to fruition, with 5 agents (patisiran, givosiran, lumasiran, inclisiran, and vutrisiran) being approved since 2018, and with many others in the different phases of clinical development. Unlike small-molecule drugs and protein therapeutics, siRNAs have different sizes, distinct mechanisms of action, differing physicochemical and pharmacological properties, and, accordingly, a unique pharmacokinetic/pharmacodynamic (PK/PD) relationship. To support the continuous development of siRNAs, it is important to have a thorough and deep understanding of the PK/PD and clinical pharmacology related features of siRNAs. As most of the current siRNA products are conjugated by N-acetylgalactosamine (GalNAc), this review focuses on the PK/PD relationships and clinical pharmacology of GalNAc-conjugated siRNAs, including their absorption, distribution, metabolism, excretion (ADME) properties, PK/PD models, drug-drug interactions, clinical pharmacology in special populations, and safety evaluation. In addition, necessary background information related to the development of siRNAs as a therapeutic modality, including the mechanisms of action, the advantages of siRNAs, the problems of naked siRNAs, as well as the strategies used to enhance the clinical utility of siRNAs, have also been covered. The goal of this review is to serve as a "primer" on siRNA PK/PD, and I hope the readers, especially those who have a limited background on siRNA therapeutics, will have a fundamental understanding of siRNA PK/PD and clinical pharmacology after reading this review.

Molecular Therapies in Cardiovascular Diseases: Small Interfering RNA in Atherosclerosis, Heart Failure, and Hypertension

Small interfering RNA (siRNA) represents a novel, fascinating therapeutic strategy that allows for selective reduction in the production of a specific protein through RNA interference. In the cardiovascular (CV) field, several siRNAs have been developed in the last decade. Inclisiran has been shown to significantly reduce low-density lipoprotein cholesterol (LDL-C) circulating levels with a reassuring safety profile, also in older patients, by hampering proprotein convertase subtilisin/kexin type 9 (PCSK9) production. Olpasiran, directed against apolipoprotein(a) mRNA, prevents the assembly of lipoprotein(a) [Lp(a)] particles, a lipoprotein linked to an increased risk of ischemic CV disease and heart valve damage. Patisiran, binding transthyretin (TTR) mRNA, has demonstrated an ability to improve heart failure and polyneuropathy in patients with TTR amyloidosis, even in older patients with wild-type form. Zilebesiran, designed to reduce angiotensinogen secretion, significantly decreases systolic and diastolic blood pressure (BP). Thanks to their effectiveness, safety, and tolerability profile, and with a very low number of administrations in a year, thus overcoming adherence issues, these novel drugs are the leaders of a new era in molecular therapies for CV diseases.

A Comprehensive Review of Small Interfering RNAs (siRNAs): Mechanism, Therapeutic Targets, and Delivery Strategies for Cancer Therapy

Small interfering RNA (siRNA) delivery by nanocarriers has been identified as a promising strategy in the study and treatment of cancer. Short nucleotide sequences are synthesized exogenously to create siRNA, which triggers RNA interference (RNAi) in cells and silences target gene expression in a sequence-specific way. As a nucleic acid-based medicine that has gained popularity recently, siRNA exhibits novel potential for the treatment of cancer. However, there are still many obstacles to overcome before clinical siRNA delivery devices can be developed. In this review, we discuss prospective targets for siRNA drug design, explain siRNA drug properties and benefits, and give an overview of the current clinical siRNA therapeutics for the treatment of cancer. Additionally, we introduce the siRNA chemical modifications and delivery systems that are clinically sophisticated and classify bioresponsive materials for siRNA release in a methodical manner. This review will serve as a reference for researchers in developing more precise and efficient targeted delivery systems, promoting ongoing advances in clinical applications.

Innate immune regulations and various siRNA modalities

RNAi therapeutics are designed to produce the precise silencing effects against the gene-linked diseases which were known to be untreatable in the past. The highly immunostimulatory nature of siRNA enhances the off-target effects and easily get attacked by nucleases; hence, their modulation is essentially required for accurate alterations to be made in the structures to intensify the pharmacological attributes. The phosphonate modifications act as shield against undue phosphorylation effects, and the molecular changes in ribose sugar lowers the level of immunogenicity and increases the binding efficacy. When bases are substituted with virtual/or pseudo bases, they eventually reduce the off-target effects. These changes modulate the nucleic acid sensors and control the hyper-activation of innate immune response. Various modification designs based on STC (universal pattern), ESC, ESC + (advanced patterns) and disubstrate have been explored to silence the gene expression of various diseases e.g., hepatitis, HIV, influenza, RSV, CNV and acute kidney injury. This review describes the various innovative siRNA therapeutics and their implications on the developed immune regulations to silence the disease effects. siRNA causes the silencing effects through RISC processing. The innate immune signalling is induced by both TLR-dependent and TLR-independent pathways. Modification chemistries are utilized to modulate the immune response.

Toll-like Receptors as Pro-Thrombotic Drivers in Viral Infections: A Narrative Review

Toll-like receptors (TLRs) have a critical role in the pathogenesis and disease course of viral infections. The induced pro-inflammatory responses result in the disturbance of the endovascular surface layer and impair vascular homeostasis. The injury of the vessel wall further promotes pro-thrombotic and pro-coagulatory processes, eventually leading to micro-vessel plugging and tissue necrosis. Moreover, TLRs have a direct role in the sensing of viruses and platelet activation. TLR-mediated upregulation of von Willebrand factor release and neutrophil, as well as macrophage extra-cellular trap formation, further contribute to (micro-) thrombotic processes during inflammation. The following review focuses on TLR signaling pathways of TLRs expressed in humans provoking pro-thrombotic responses, which determine patient outcome during viral infections, especially in those with cardiovascular diseases.

Toll-like receptor-3 contributes to the development of aortic valve stenosis

Aortic valve stenosis (AS) development is driven by distinct molecular and cellular mechanisms which include inflammatory pathways. Toll-like-receptor-3 (TLR3) is a lysosomal pattern-recognition receptor that binds double-stranded RNA and promotes pro-inflammatory cellular responses. In recent years, TLR3 has emerged as a major regulator of vascular inflammation. The exact role of TLR3 in the development of AS has not been investigated. Isolated human valvular interstitial cells (VICs) were stimulated with the TLR3-agonist polyIC and the resulting pro-inflammatory and pro-osteogenic response measured. Severe AS was induced in wildtype- and TLR3^-/- mice via mechanical injury of the aortic valve with a coronary springwire. TLR3 activation was achieved by polyIC injection every 24 h after wire injury, while TLR3 inhibition was realized using Compound 4a (C4a) every 48 h after surgery. Endothelial mesenchymal transition (EndoMT) of human valvular endothelial cells (VECs) was assessed after polyIC stimulation. Stimulation of human VICs with polyIC promoted a strong inflammatory and pro-osteogenic reaction. Similarly, injection of polyIC marginally increased AS development in mice after wire injury. AS induction was significantly decreased in TLR3^-/- mice, confirming the role of endogenous TLR3 ligands in AS pathology. Pharmacological inhibition of TLR3 with C4a not only prevented the upregulation of inflammatory cytokines and osteogenic markers in VICs, and EndoMT in VECs, but also significantly abolished the development of AS in vivo. Endogenous TLR3 activation significantly contributes to AS development in mice. Pharmacological inhibition of TLR3 with C4a prevented AS formation. Therefore, targeting TLR3 may be a viable treatment option.

Surface Design Options in Polymer- and Lipid-Based siRNA Nanoparticles Using Antibodies

The mechanism of RNA interference (RNAi) could represent a breakthrough in the therapy of all diseases that arise from a gene defect or require the inhibition of a specific gene expression. In particular, small interfering RNA (siRNA) offers an attractive opportunity to achieve a new milestone in the therapy of human diseases. The limitations of siRNA, such as poor stability, inefficient cell uptake, and undesired immune activation, as well as the inability to specifically reach the target tissue in the body, can be overcome by further developments in the field of nanoparticulate drug delivery. Therefore, types of surface modified siRNA nanoparticles are presented and illustrate how a more efficient and safer distribution of siRNA at the target site is possible by modifying the surface properties of nanoparticles with antibodies. However, the development of such efficient and safe delivery strategies is currently still a major challenge. In consideration of that, this review article aims to demonstrate the function and targeted delivery of siRNA nanoparticles, focusing on the surface modification via antibodies, various lipid- and polymer-components, and the therapeutic effects of these delivery systems.

Therapeutic siRNA: State-of-the-Art and Future Perspectives

The highly specific induction of RNA interference-mediated gene knockdown, based on the direct application of small interfering RNAs (siRNAs), opens novel avenues towards innovative therapies. Two decades after the discovery of the RNA interference mechanism, the first siRNA drugs received approval for clinical use by the US Food and Drug Administration and the European Medicines Agency between 2018 and 2022. These are mainly based on an siRNA conjugation with a targeting moiety for liver hepatocytes, N-acetylgalactosamine, and cover the treatment of acute hepatic porphyria, transthyretin-mediated amyloidosis, hypercholesterolemia, and primary hyperoxaluria type 1. Still, the development of siRNA therapeutics faces several challenges and issues, including the definition of optimal siRNAs in terms of target, sequence, and chemical modifications, siRNA delivery to its intended site of action, and the absence of unspecific off-target effects. Further siRNA drugs are in clinical studies, based on different delivery systems and covering a wide range of different pathologies including metabolic diseases, hematology, infectious diseases, oncology, ocular diseases, and others. This article reviews the knowledge on siRNA design and chemical modification, as well as issues related to siRNA delivery that may be addressed using different delivery systems. Details on the mode of action and clinical status of the various siRNA therapeutics are provided, before giving an outlook on issues regarding the future of siRNA drugs and on their potential as one emerging standard modality in pharmacotherapy. Notably, this may also cover otherwise un-druggable diseases, the definition of non-coding RNAs as targets, and novel concepts of personalized and combination treatment regimens.

Microneedle systems for delivering nucleic acid drugs

Background

Nucleic acid-based gene therapy is a promising technology that has been used in various applications such as novel vaccination platforms for infectious/cancer diseases and cellular reprogramming because of its fast, specific, and effective properties. Despite its potential, the parenteral nucleic acid drug formulation exhibits instability and low efficacy due to various barriers, such as stability concerns related to its liquid state formulation, skin barriers, and endogenous nuclease degradation. As promising alternatives, many attempts have been made to perform nucleic acid delivery using a microneedle system. With its minimal invasiveness, microneedle can deliver nucleic acid drugs with enhanced efficacy and improved stability.

Area covered

This review describes nucleic acid medicines' current state and features and their delivery systems utilizing non-viral vectors and physical delivery systems. In addition, different types of microneedle delivery systems and their properties are briefly reviewed. Furthermore, recent advances of microneedle-based nucleic acid drugs, including featured vaccination applications, are described.

Expert opinion

Nucleic acid drugs have shown significant potential beyond the limitation of conventional small molecules, and the current COVID-19 pandemic highlights the importance of nucleic acid therapies as a novel vaccination platform. Microneedle-mediated nucleic acid drug delivery is a potential platform for less invasive nucleic acid drug delivery. Microneedle system can show enhanced efficacy, stability, and improved patient convenience through self-administration with less pain.

Therapeutic siRNA targeting the cancer cell stemness regulator PRDI-BF1 and RIZ domain zinc finger protein 14

PRDI-BF1 and RIZ (PR) domain zinc finger protein 14 (PRDM14), first reported in 2007 to be overexpressed in breast cancer, plays an important role in breast cancer proliferation. Subsequent studies reported that PRDM14 is expressed in embryonic stem cells, primordial germ cells, and various cancers. PRDM14 was reported to confer stemness properties to cancer cells. These properties induce cancer initiation, cancer progression, therapeutic resistance, distant metastasis, and recurrence in refractory tumors. Therefore, PRDM14 may be an ideal therapeutic target for various types of tumors. Silencing PRDM14 expression using PRDM14-specific siRNA delivered through an innovative intravenous drug delivery system reduced the size of inoculated tumors, incidence of distant metastases, and increased overall survival in nude mice without causing adverse effects. Therapeutic siRNA targeting PRDM14 is now being evaluated in a human phase I clinical trial for patients with refractory breast cancer, including triple-negative breast cancer.

Introduction and History of the Chemistry of Nucleic Acids Therapeutics

This introduction charts the history of the development of the major chemical modifications that have influenced the development of nucleic acids therapeutics focusing in particular on antisense oligonucleotide analogues carrying modifications in the backbone and sugar. Brief mention is made of siRNA development and other applications that have by and large utilized the same modifications. We also point out the pitfalls of the use of nucleic acids as drugs, such as their unwanted interactions with pattern recognition receptors, which can be mitigated by chemical modification or used as immunotherapeutic agents.

MicroRNA mimics can distort physiological microRNA effects on immune checkpoints by triggering an antiviral interferon response

The microRNA-200 family has wide-ranging regulatory functions in cancer development and progression. Above all, it is strongly associated with the epithelial-to-mesenchymal transition (EMT), a process during which cells change their epithelial to a mesenchymal phenotype and acquire invasive characteristics. More recently, miR-200 family members have also been reported to impact the immune evasion of cancer cells by regulating the expression of immunoinhibitory immune checkpoints (ICs) like PD-L1. Therefore, we aimed to comprehensively characterize this miR-200 family as a regulatory interface between EMT and immune evasion mechanisms in biliary tract cancer. Initial correlation analyses and transient overexpression experiments using miRNA mimics suggested miR-200c-3p as a putative regulator of ICs including PD-L1, LGALS9, and IDO1. However, these effects could not be confirmed in stable miR-200c-3p overexpression cell lines, nor in cells transiently transfected with miR-200c-3p mimic from an independent manufacturer. By shifting our efforts towards dissecting the mechanisms leading to these disparate effects, we observed that the initially used miR-200c-3p mimic triggered a double-stranded (ds)RNA-dependent antiviral response. Besides upregulating the ICs, this had substantial cellular consequences including an induction of interferon type I and type III expression, increased levels of intracellular dsRNA sensors, and a significantly altered cellular growth and apoptotic activity.Our study highlights the capability of miRNA mimics to non-specifically induce a dsRNA-mediated antiviral interferon response. Consequently, phenotypic alterations crucially distort physiological miRNA functions and might result in a major misinterpretation of previous and future miRNA studies, especially in the context of IC regulation.

Lipid nanoparticle formulations for targeting leukocytes with therapeutic RNA in liver fibrosis

Obesity and low-grade inflammation are promoters of a multitude of diseases including liver fibrosis. Activation of the mobile leukocytes has a major impact on the outcome of inflammatory disease and can hence foster or mitigate liver fibrosis. This renders immunological targets valuable for directed interventions using nanomedicines. Particularly, RNA-based drugs formulated as lipid nanoparticles (LNP) can open new avenues for the personalized treatment of liver fibrosis both through specific interference and via the induction of the expression of functional and therapeutic proteins. Using microfluidics technology, all components, including lipid-anchored targeting ligands, are assembled in a single-step mixing process. A highlight is set to immunologically relevant liver cell types that are most vulnerable for being reached by LNP. A selection of LNP from other therapeutic fields applicable for reaching these cells in liver fbrosis is summarized. Furthermore, recent proceedings and major obstacles in the field of these targeted LNP are presented.

Canine Parvovirus and Its Non-Structural Gene 1 as Oncolytic Agents: Mechanism of Action and Induction of Anti-Tumor Immune Response

The exploration into the strategies for the prevention and treatment of cancer is far from complete. Apart from humans, cancer has gained considerable importance in animals because of increased awareness towards animal health and welfare. Current cancer treatment regimens are less specific towards tumor cells and end up harming normal healthy cells. Thus, a highly specific therapeutic strategy with minimal side effects is the need of the hour. Oncolytic viral gene therapy is one such specific approach to target cancer cells without affecting the normal cells of the body. Canine parvovirus (CPV) is an oncolytic virus that specifically targets and kills cancer cells by causing DNA damage, caspase activation, and mitochondrial damage. Non-structural gene 1 (NS1) of CPV, involved in viral DNA replication is a key mediator of cytotoxicity of CPV and can selectively cause tumor cell lysis. In this review, we discuss the oncolytic properties of Canine Parvovirus (CPV or CPV2), the structure of the NS1 protein, the mechanism of oncolytic action as well as role in inducing an antitumor immune response in different tumor models.

RNA therapeutics in ophthalmology - translation to clinical trials

The use of RNA interference technology has proven to inhibit the expression of many target genes involved in the underlying pathogenesis of several diseases affecting various systems. First established in in vitro and later in animal studies, small interfering RNA (siRNA) and antisense oligonucleotide (ASO) therapeutics are now entering clinical trials with the potential of clinical translation to patients. Gene-silencing therapies have demonstrated promising responses in ocular disorders, predominantly due to the structure of the eye being a closed and compartmentalised organ. However, although the efficacy of such treatments has been observed in both preclinical studies and clinical trials, there are issues pertaining to the use of these drugs which require more extensive research with regards to the delivery and stability of siRNAs and ASOs. This would improve their use for long-term treatment regimens and alleviate the difficulties experienced by patients with ocular diseases. This review provides a detailed insight into the recent developments and clinical trials that have been conducted for several gene-silencing therapies, including ISTH0036, SYL040012, SYL1001, PF-04523655, Sirna-027, QR-110, QR-1123, QR-421a and IONIS-FB-L_RX in glaucoma, dry eye disease, age-related macular degeneration, diabetic macular oedema and various inherited retinal diseases. Our aim is to explore the potential of these drugs whilst evaluating their associated advantages and disadvantages, and to discuss the future translation of RNA therapeutics in ophthalmology.

Modulating the Crosstalk between the Tumor and the Microenvironment Using SiRNA: A Flexible Strategy for Breast Cancer Treatment

Simple Summary

With this review we aimed to collect the most relevant scientific findings regarding siRNA therapeutic tools against breast cancer microenvironment. Remarkably, breast cancer treatments have been redirected towards the tumor microenvironment components, mainly involved in patients’ relapse and pharmacological resistance. Therefore, siRNAs represent a promising strategy to jeopardize the tumor microenvironment interplay thanks to their non-toxic and specific effects.

Abstract

Tumorigenesis is a complex and multistep process in which sequential mutations in oncogenes and tumor-suppressor genes result in enhanced proliferation and apoptosis escape. Over the past decades, several studies have provided evidence that tumors are more than merely a mass of malignant cancer cells, with the tumor microenvironment (TME) also contributing to cancer progression. For this reason, the focus of cancer research in recent years has shifted from the malignant cancer cell itself to the TME and its interactions. Since the TME actively participates in tumor progression, therapeutic strategies targeting it have created great interest. In this context, much attention has been paid to the potential application of small interfering RNA (siRNA), a class of non-coding RNA that has the ability to downregulate the expression of target genes in a sequence-specific way. This is paving the way for a novel therapeutic approach for the treatment of several diseases, including cancer. In this review, we describe recent efforts in developing siRNA therapeutics for the treatment of breast cancer, with particular emphasis on TME regulation. We focus on studies that adapt siRNA design to reprogram/re-educate the TME and eradicate the interplay between cancer cells and TME.

Gene Therapy Intervention in Neovascular Eye Disease: A Recent Update

Aberrant growth of blood vessels (neovascularization) is a key feature of severe eye diseases that can cause legal blindness, including neovascular age-related macular degeneration (nAMD) and diabetic retinopathy (DR). The development of anti-vascular endothelial growth factor (VEGF) agents has revolutionized the treatment of ocular neovascularization. Novel proangiogenic targets, such as angiopoietin and platelet-derived growth factor (PDGF), are under development for patients who respond poorly to anti-VEGF therapy and to reduce adverse effects from long-term VEGF inhibition. A rapidly advancing area is gene therapy, which may provide significant therapeutic benefits. Viral vector-mediated transgene delivery provides the potential for continuous production of antiangiogenic proteins, which would avoid the need for repeated anti-VEGF injections. Gene silencing with RNA interference to target ocular angiogenesis has been investigated in clinical trials. Proof-of-concept gene therapy studies using gene-editing tools such as CRISPR-Cas have already been shown to be effective in suppressing neovascularization in animal models, highlighting the therapeutic potential of the system for treatment of aberrant ocular angiogenesis. This review provides updates on the development of anti-VEGF agents and novel antiangiogenic targets. We also summarize current gene therapy strategies already in clinical trials and those with the latest approaches utilizing CRISPR-Cas gene editing against aberrant ocular neovascularization.

Prospects for the potential of RNA interference in the treatment of autoimmune diseases: Small interfering RNAs in the spotlight

The identification of RNA interference (RNAi) has caused a growing interest in harnessing its potential in the treatment of different diseases. Modulation of dysregulated genes through targeting by RNAi represents a potential approach with which to alter the biological pathways at a post-transcriptional level, especially as it pertains to autoimmunity and malignancy. Short hairpin RNAs (shRNA), short interfering RNAs (siRNA), and microRNAs (miRNA) are mainly involved as effector mechanisms in the targeting of RNAi biological pathways. The manipulation and delivery of these molecules in an efficient way promotes the specificity and stability of RNAi-based systems, while minimizing the unwanted adverse reactions by the immune system and reducing cytotoxicity and off-target effects. Advances made to date in identifying the etiopathogenesis of autoimmune diseases has prompted the utilization of RNAi-based systems in vitro and in vivo. Future investigations aimed at deciphering the molecular basis of RNAi and optimizing the delivery of RNAi-based targeting systems will hopefully promote the applicability of such regulatory mechanisms and, ultimately, transfer the acquired knowledge from bench-to-bedside to ameliorate human diseases. In this review, we seek to clarify the potential of RNAi, with a focus on siRNAs, in designing therapeutics for potential treatment of human autoimmune disorders.

Therapeutic siRNA: state of the art

RNA interference (RNAi) is an ancient biological mechanism used to defend against external invasion. It theoretically can silence any disease-related genes in a sequence-specific manner, making small interfering RNA (siRNA) a promising therapeutic modality. After a two-decade journey from its discovery, two approvals of siRNA therapeutics, ONPATTRO® (patisiran) and GIVLAARI™ (givosiran), have been achieved by Alnylam Pharmaceuticals. Reviewing the long-term pharmaceutical history of human beings, siRNA therapy currently has set up an extraordinary milestone, as it has already changed and will continue to change the treatment and management of human diseases. It can be administered quarterly, even twice-yearly, to achieve therapeutic effects, which is not the case for small molecules and antibodies. The drug development process was extremely hard, aiming to surmount complex obstacles, such as how to efficiently and safely deliver siRNAs to desired tissues and cells and how to enhance the performance of siRNAs with respect to their activity, stability, specificity and potential off-target effects. In this review, the evolution of siRNA chemical modifications and their biomedical performance are comprehensively reviewed. All clinically explored and commercialized siRNA delivery platforms, including the GalNAc (N-acetylgalactosamine)-siRNA conjugate, and their fundamental design principles are thoroughly discussed. The latest progress in siRNA therapeutic development is also summarized. This review provides a comprehensive view and roadmap for general readers working in the field.

RNA Signaling in Pulmonary Arterial Hypertension-A Double-Stranded Sword

Recognition of and response to pathogens and tissue injury is driven by the innate immune system via activation of pattern recognition receptors. One of the many patterns recognized is RNA and, while several receptors bind RNA, Toll-like receptor 3 (TLR3) is well placed for initial recognition of RNA molecules due to its localization within the endosome. There is a growing body of work describing a role for TLR3 in maintenance of vascular homeostasis. For example, TLR3 deficiency has been shown to play repair and remodeling roles in the systemic vasculature and in lung parenchyma. A hallmark of pulmonary arterial hypertension (PAH) is pulmonary vascular remodeling, yet drivers and triggers of this remodeling remain incompletely understood. Based on its role in the systemic vasculature, our group discovered reduced endothelial TLR3 expression in PAH and revealed a protective role for a TLR3 agonist in rodent models of pulmonary hypertension. This review will provide an overview of RNA signaling in the vasculature and how it relates to PAH pathobiology, including whether targeting double-stranded RNA signaling is a potential treatment option for PAH.

Toll-like receptors: exploring their potential connection with post-operative infectious complications and cancer recurrence

Cancer is the leading cause of death in North America. Despite modern advances in cancer therapy, many patients will ultimately develop cancer metastasis resulting in mortality. Surgery to resect early stage solid malignancies remains the cornerstone of cancer treatment. However, surgery places patients at risk of developing post-operative infectious complications that are linked to earlier cancer metastatic recurrence and cancer mortality. Toll-like receptors (TLRs) are evolutionarily-conserved sentinel receptors of the innate immune system that are activated by microbial products present during infection, leading to activation of innate immunity. Numerous types of solid cancer cells also express TLRs, with their activation augmenting their ability to metastasize. Similarly, healthy host-tissue TLRs activated during infection induce a prometastatic environment in the host. Cancer cells additionally secrete TLR activating ligands that activate both cancer TLRs and host TLRs to promote metastasis. Consequently, TLRs are an attractive therapeutic candidate to target infection-induced cancer metastasis and progression.

Nucleic Acid Sensors and Programmed Cell Death

Nucleic acids derived from microorganisms are powerful triggers for innate immune responses. Proteins called RNA and DNA sensors detect foreign nucleic acids and, in mammalian cells, include RIG-I, cGAS, and AIM2. On binding to nucleic acids, these proteins initiate signaling cascades that activate host defense responses. An important aspect of this defense program is the production of cytokines such as type I interferons and IL-1β. Studies conducted over recent years have revealed that nucleic acid sensors also activate programmed cell death pathways as an innate immune response to infection. Indeed, RNA and DNA sensors induce apoptosis, pyroptosis, and necroptosis. Cell death via these pathways prevents replication of pathogens by eliminating the infected cell and additionally contributes to the release of cytokines and inflammatory mediators. Interestingly, recent evidence suggests that programmed cell death triggered by nucleic acid sensors plays an important role in a number of noninfectious pathologies. In addition to nonself DNA and RNA from microorganisms, nucleic acid sensors also recognize endogenous nucleic acids, for example when cells are damaged by genotoxic agents and in certain autoinflammatory diseases. This review article summarizes current knowledge on the links between nucleic acid sensing and cell death and explores important open questions for future studies in this area.

IRF3 and IRF7 mediate neovascularization via inflammatory cytokines

OBJECTIVE

To elucidate the role of interferon regulatory factor (IRF)3 and IRF7 in neovascularization.

METHODS

Unilateral hind limb ischaemia was induced in Irf3-/- , Irf7-/- and C57BL/6 mice by ligation of the left common femoral artery. Post-ischaemic blood flow recovery in the paw was measured with laser Doppler perfusion imaging. Soleus, adductor and gastrocnemius muscles were harvested to investigate angiogenesis and arteriogenesis and inflammation.

RESULTS

Post-ischaemic blood flow recovery was decreased in Irf3-/- and Irf7-/- mice compared to C57BL/6 mice at all time points up to and including sacrifice, 28 days after surgery (t28). This was supported by a decrease in angiogenesis and arteriogenesis in soleus and adductor muscles of Irf3-/- and Irf7-/- mice at t28. Furthermore, the number of macrophages around arterioles in adductor muscles was decreased in Irf3-/- and Irf7-/- mice at t28. In addition, mRNA expression levels of pro-inflammatory cytokines (tnfα, il6, ccl2) and growth factor receptor (vegfr2), were decreased in gastrocnemius muscles of Irf3-/- and Irf7-/- mice compared to C57BL/6 mice.

CONCLUSION

Deficiency of IRF3 and IRF7 results in impaired post-ischaemic blood flow recovery caused by attenuated angiogenesis and arteriogenesis linked to a lack of inflammatory components in ischaemic tissue. Therefore, IRF3 and IRF7 are essential regulators of neovascularization.

siRNA therapeutics: a clinical reality

Since the revolutionary discovery of RNA interference (RNAi), a remarkable progress has been achieved in understanding and harnessing gene silencing mechanism; especially in small interfering RNA (siRNA) therapeutics. Despite its tremendous potential benefits, major challenges in most siRNA therapeutics remains unchanged-safe, efficient and target oriented delivery of siRNA. Twenty years after the discovery of RNAi, siRNA therapeutics finally charts its way into clinics. As we journey through the decades, we reminisce the history of siRNA discovery and its application in a myriad of disease treatments. Herein, we highlight the breakthroughs in siRNA therapeutics, with special feature on the first FDA approved RNAi therapeutics Onpattro (Patisiran) and the consideration of effective siRNA delivery system focusing on current siRNA nanocarrier in clinical trials. Lastly, we present some challenges and multiple barriers that are yet to be fully overcome in siRNA therapeutics.

Toll-like receptor 3 acts as a suppressor gene in breast cancer initiation and progression: a two-stage association study and functional investigation

Toll-like receptor 3 (TLR3) is a receptor recognizing double-stranded RNA (dsRNA) from viruses as well as from lytic mammalian cells. In the present study, we performed a two-stage association study (n = 3,551) and found that the minor alleles of two SNPs (the T-allele of rs5743312 and the T-allele of rs3775296) conferred increased risks of breast cancer incidence. The adjusted odds ratios (ORs) were 2.281 (P = 7.01 × 10-5) and 2.086 (P = 8.69 × 10-5), respectively. Specifically, the susceptibility variants within TLR3 were significantly associated with larger tumor size (adjusted P-values: 0.004 for rs5743312 and 0.004 for rs3775296). Furthermore, we investigated the biological function of the TLR3 protein in breast cancer cell lines. Notably, the stable expression of TLR3 directly inhibited cell proliferation both in vitro and in vivo. We also verified that TLR3 conferred less invasive phenotypes on breast cancer cells by regulating the mRNA expression of a panel of genes. TLR3-mediated inhibition of proliferation was caused by downregulation of the EGFR/PI3K/AKT pathway. In summary, our findings strongly suggest that common genetic changes in the TLR3 gene may influence breast cancer susceptibility and development, and TLR3 plays a negative regulatory role in the initiation and progression of human breast cancer cells, at least in part by downregulating the EGFR/PI3K/AKT pathway.

Stimulation of TLR3 triggers release of lysosomal ATP in astrocytes and epithelial cells that requires TRPML1 channels

Cross-reactions between innate immunity, lysosomal function, and purinergic pathways may link signaling systems in cellular pathologies. We found activation of toll-like receptor 3 (TLR3) triggers lysosomal ATP release from both astrocytes and retinal pigmented epithelial (RPE) cells. ATP efflux was accompanied by lysosomal acid phosphatase and beta hexosaminidase release. Poly(I:C) alkalinized lysosomes, and lysosomal alkalization with bafilomycin or chloroquine triggered ATP release. Lysosomal rupture with glycyl-L-phenylalanine-2-naphthylamide (GPN) eliminated both ATP and acid phosphatase release. Secretory lysosome marker LAMP3 colocalized with VNUT, while MANT-ATP colocalized with LysoTracker. Unmodified membrane-impermeant 21-nt and "non-targeting" scrambled 21-nt siRNA triggered ATP and acid phosphatase release, while smaller 16-nt RNA was ineffective. Poly(I:C)-dependent ATP release was reduced by TBK-1 block and in TRPML1-/- cells, while TRPML activation with ML-SA1 was sufficient to release both ATP and acid phosphatase. The ability of poly(I:C) to raise cytoplasmic Ca2+ was abolished by removing extracellular ATP with apyrase, suggesting ATP release by poly(I:C) increased cellular signaling. Starvation but not rapamycin prevented lysosomal ATP release. In summary, stimulation of TLR3 triggers lysosomal alkalization and release of lysosomal ATP through activation of TRPML1; this links innate immunity to purinergic signaling via lysosomal physiology, and suggests even scrambled siRNA can influence these pathways.

Periostin in vitreoretinal diseases

Proliferative vitreoretinal diseases such as diabetic retinopathy, proliferative vitreoretinopathy (PVR), and age-related macular degeneration are a leading cause of decreased vision and blindness in developed countries. In these diseases, retinal fibro(vascular) membrane (FVM) formation above and beneath the retina plays an important role. Gene expression profiling of human FVMs revealed significant upregulation of periostin. Subsequent analyses demonstrated increased periostin expression in the vitreous of patients with both proliferative diabetic retinopathy and PVR. Immunohistochemical analysis showed co-localization of periostin with α-SMA and M2 macrophage markers in FVMs. In vitro, periostin blockade inhibited migration and adhesion induced by PVR vitreous and transforming growth factor-β2 (TGF-β2). In vivo, a novel single-stranded RNAi agent targeting periostin showed the inhibitory effect on experimental retinal and choroidal FVM formation without affecting the viability of retinal cells. These results indicated that periostin is a pivotal molecule for FVM formation and a promising therapeutic target for these proliferative vitreoretinal diseases.

DAMP-TLR-cytokine axis dictates the fate of tumor

Random mutations leading to loss of cell cycle control is not a rare occurrence in an organism but the mutated cells are recognized and eliminated preventing the development of a tumor. These potentially tumorigenic cells release damage-associated molecular patterns (DAMPs), which are recognized by toll-like receptors (TLRs) on macrophages and dendritic cells. The initial TLR-DAMP interactions lead to different responses such as altered antigen presentation and cytokine release that directly affect T cell activation and removal of the tumorigenic cells. The indirect effects of TLR-DAMP interaction include chemokine-directed altered T cell trafficking, angiogenesis for both T cell infiltration and tumor cell metastasis, and alteration of intra-tumoral milieu contributing to the development of tumor cells heterogeneity. Thus, the initial TLR-DAMP interaction has a set of local effects that modulate tumor cell growth and heterogeneity and a disseminating set of central effects that dynamically affect T cell trafficking and functions. Herein, we argue that the DAMP-TLR-cytokine axis in the tumor microenvironment serves as the mainstay that orchestrates and regulates the pro- and anti-tumor elements which dynamically interact between themselves eventuating in tumor regression or growth. The knowledge of this TLR-based immuno-surveillance framework is a key to developing a novel immunotherapy against cancer.

Activation of cell membrane-localized Toll-like receptor 3 by siRNA

Small interfering RNA molecules (siRNA) are short dsRNAs that are used for different therapeutic applications. On the other hand, dsRNAs can bind to and activate cell RNA sensors and consequently trigger inflammatory response. Here we show that siRNA activates primary human endothelial cells and human lymphatic endothelial cells and that this response is inhibited by antibodies against TLR3. In contrast, the activation of human lymphatic endothelial cells by poly(I:C) was inhibited by bafilomycin but not by anti-TLR3 antibodies. Bafilomycin also inhibited poly(I:C) but not siRNA cell stimulation in TLR3-transfected HEK293. The response to siRNA required the expression of UNC93B1, which directs TLR3 to the surface of HEK293 cells. We propose that the engaged signaling pathway of TLR3 depends on the receptor localization and on the length of the dsRNA, where the activation of cell membrane TLR3 by short dsRNA leads to a predominantly proinflammatory response, whereas TLR3 activation in endosomal compartments by long dsRNA is characterized by the production of type I IFN. A molecular model suggests that the siRNA can bind to the binding sites of the TLR3 ectodomain and trigger receptor dimerization. These results contribute to understanding of the mechanism of side effects seen in the therapeutic application of naked, unmodified siRNA as a result of the activation of TLR3 localized at the plasma membrane.

Therapeutic Effect of Novel Single-Stranded RNAi Agent Targeting Periostin in Eyes with Retinal Neovascularization

Retinal neovascularization (NV) due to retinal ischemia remains one of the principal causes of vision impairment in patients with ischemic retinal diseases. We recently reported that periostin (POSTN) may play a role in the development of preretinal fibrovascular membranes, but its role in retinal NV has not been determined. The purpose of this study was to examine the expression of POSTN in the ischemic retinas of a mouse model of oxygen-induced retinal NV. We also studied the function of POSTN on retinal NV using Postn KO mice and human retinal endothelial cells (HRECs) in culture. In addition, we used a novel RNAi agent, NK0144, which targets POSTN to determine its effect on the development of retinal NV. Our results showed that the expression of POSTN was increased in the vascular endothelial cells, pericytes, and M2 macrophages in ischemic retinas. POSTN promoted the ischemia-induced retinal NV by Akt phosphorylation through integrin αvβ3. NK0144 had a greater inhibitory effect than canonical double-stranded siRNA on preretinal pathological NV in vivo and in vitro. These findings suggest a causal relationship between POSTN and retinal NV, and indicate a potential therapeutic role of intravitreal injection of NK0144 for retinal neovascular diseases.

Clinical potential of oligonucleotide-based therapeutics in the respiratory system

The discovery of an ever-expanding plethora of coding and non-coding RNAs with nodal and causal roles in the regulation of lung physiology and disease is reinvigorating interest in the clinical utility of the oligonucleotide therapeutic class. This is strongly supported through recent advances in nucleic acids chemistry, synthetic oligonucleotide delivery and viral gene therapy that have succeeded in bringing to market at least three nucleic acid-based drugs. As a consequence, multiple new candidates such as RNA interference modulators, antisense, and splice switching compounds are now progressing through clinical evaluation. Here, manipulation of RNA for the treatment of lung disease is explored, with emphasis on robust pharmacological evidence aligned to the five pillars of drug development: exposure to the appropriate tissue, binding to the desired molecular target, evidence of the expected mode of action, activity in the relevant patient population and commercially viable value proposition.

Poly (I:C) enhances the anti-tumor activity of canine parvovirus NS1 protein by inducing a potent anti-tumor immune response

The canine parvovirus NS1 (CPV2.NS1) protein selectively induces apoptosis in the malignant cells. However, for an effective in vivo tumor treatment strategy, an oncolytic agent also needs to induce a potent anti-tumor immune response. In the present study, we used poly (I:C), a TLR3 ligand, as an adjuvant along with CPV2.NS1 to find out if the combination can enhance the oncolytic activity by inducing a potent anti-tumor immune response. The 4T1 mammary carcinoma cells were used to induce mammary tumor in Balb/c mice. The results suggested that poly (I:C), when given along with CPV2.NS1, not only significantly reduced the tumor growth but also augmented the immune response against tumor antigen(s) as indicated by the increase in blood CD4+ and CD8+ counts and infiltration of immune cells in the tumor tissue. Further, blood serum analysis of the cytokines revealed that Th1 cytokines (IFN-γ and IL-2) were significantly upregulated in the treatment group indicating activation of cell-mediated immune response. The present study reports the efficacy of CPV2.NS1 along with poly (I:C) not only in inhibiting the mammary tumor growth but also in generating an active anti-tumor immune response without any visible toxicity. The results of our study may help in developing CPV2.NS1 and poly (I: C) combination as a cancer therapeutic regime to treat various malignancies.

From selection hits to clinical leads: progress in aptamer discovery

Aptamers were discovered more than 25 years ago, yet only one has been approved by the US Food and Drug Administration to date. With some noteworthy advances in their chemical design and the enzymes we use to make them, aptamers and aptamer-based therapeutics have seen a resurgence in interest. New aptamer drugs are being approved for clinical evaluation, and it is certain that we will see increasingly more aptamers and aptamer-like drugs in the future. In this review, we will discuss the production of aptamers with an emphasis on the advances and modifications that enabled early aptamers to succeed in clinical trials as well as those that are likely to be important for future generations of these drugs.

Human IgG1 antibodies suppress angiogenesis in a target-independent manner

Aberrant angiogenesis is implicated in diseases affecting nearly 10% of the world’s population. The most widely used anti-angiogenic drug is bevacizumab, a humanized IgG1 monoclonal antibody that targets human VEGFA. Although bevacizumab does not recognize mouse Vegfa, it inhibits angiogenesis in mice. Here we show bevacizumab suppressed angiogenesis in three mouse models not via Vegfa blockade but rather Fc-mediated signaling through FcγRI (CD64) and c-Cbl, impairing macrophage migration. Other approved humanized or human IgG1 antibodies without mouse targets (adalimumab, alemtuzumab, ofatumumab, omalizumab, palivizumab and tocilizumab), mouse IgG2a, and overexpression of human IgG1-Fc or mouse IgG2a-Fc, also inhibited angiogenesis in wild-type and FcγR humanized mice. This anti-angiogenic effect was abolished by Fcgr1 ablation or knockdown, Fc cleavage, IgG-Fc inhibition, disruption of Fc-FcγR interaction, or elimination of FcRγ-initated signaling. Furthermore, bevacizumab’s Fc region potentiated its anti-angiogenic activity in humanized VEGFA mice. Finally, mice deficient in FcγRI exhibited increased developmental and pathological angiogenesis. These findings reveal an unexpected anti-angiogenic function for FcγRI and a potentially concerning off-target effect of hIgG1 therapies.

Intravenous immune globulin suppresses angiogenesis in mice and humans

Human intravenous immune globulin (IVIg), a purified IgG fraction composed of ~60% IgG1 and obtained from the pooled plasma of thousands of donors, is clinically used for a wide range of diseases. The biological actions of IVIg are incompletely understood and have been attributed both to the polyclonal antibodies therein and also to their IgG (IgG) Fc regions. Recently, we demonstrated that multiple therapeutic human IgG1 antibodies suppress angiogenesis in a target-independent manner via FcγRI, a high-affinity receptor for IgG1. Here we show that IVIg possesses similar anti-angiogenic activity and inhibited blood vessel growth in five different mouse models of prevalent human diseases, namely, neovascular age-related macular degeneration, corneal neovascularization, colorectal cancer, fibrosarcoma and peripheral arterial ischemic disease. Angioinhibition was mediated by the Fc region of IVIg, required FcγRI and had similar potency in transgenic mice expressing human FcγRs. Finally, IVIg therapy administered to humans for the treatment of inflammatory or autoimmune diseases reduced kidney and muscle blood vessel densities. These data place IVIg, an agent approved by the US Food and Drug Administration, as a novel angioinhibitory drug in doses that are currently administered in the clinical setting. In addition, they raise the possibility of an unintended effect of IVIg on blood vessels.

Toll-like receptor 3 signalling mediates angiogenic response upon shock wave treatment of ischaemic muscle

AIMS

Shock wave therapy (SWT) represents a clinically widely used angiogenic and thus regenerative approach for the treatment of ischaemic heart or limb disease. Despite promising results in preclinical and clinical trials, the exact mechanism of action remains unknown. Toll-like receptor 3, which is part of the innate immunity, is activated by binding double-stranded (ds) RNA. It plays a key role in inflammation, a process that is needed also for angiogenesis. We hypothesize that SWT causes cellular cavitation without damaging the target cells, thus liberating cytoplasmic RNA that in turn activates TLR3.

METHODS AND RESULTS

SWT induces TLR3 and IFN-β1 gene expression as well as RNA liberation from endothelial cells in a time-dependant manner. Conditioned medium from SWT-treated HUVECs induced TLR3 signalling in reporter cells. The response was lost when the medium was treated with RNase III to abolish dsRNAs or when TLR3 was silenced using siRNAs. In a mouse hind limb ischaemia model using wt and TLR3(-/-) mice (n = 6), SWT induced angiogenesis and arteriogenesis only in wt animals. These effects were accompanied by improved blood perfusion of treated limbs. Analysis of main molecules of the TLR3 pathways confirmed TLR3 signalling in vivo following SWT.

CONCLUSION

Our data reveal a central role of the innate immune system, namely Toll-like receptor 3, to mediate angiogenesis upon release of cytoplasmic RNAs by mechanotransduction of SWT.

Advances, nuances, and potential pitfalls when exploiting the therapeutic potential of RNA interference

The discovery of RNA interference (RNAi) holds the potential to alter the paradigm of medical therapeutics. With the ability to selectively silence the function of a gene, RNAi not only provides an indispensable research tool for determining the function of a gene, but also offers potential for the development of novel therapeutics that will inhibit specific genes involved in disease. New concepts in therapeutics have been uncovered through the study of RNAi. Nuances have emerged. For instance, global RNAi pathways can be affected by somatic mutations in cancer and cellular stress, such as hypoxia. Also, viral gene therapy can have unexpected effects on endogenous short noncoding RNA pathways. Therefore, it is important to understand where RNAi therapeutics enter the processing pathways. We highlight the evolving use of RNAi as a new class of therapeutics, such as for amyloidosis, and address some of the anticipated challenges associated with its clinical application.

Clinical translation of RNAi-based treatments for respiratory diseases

The ability to harness the RNA interference (RNAi) mechanism as a potential potent therapeutic has attracted great interest from academia and industry. Numerous preclinical and recent clinical trials have demonstrated the effectiveness of RNAi triggers such as synthetic small interfering RNA (siRNA). Chemical modification and delivery technologies can be utilized to avoid immune stimulation and improve the bioactivity and pharmacokinetics. Local application to the respiratory epithelia allows direct access to the site of respiratory pathogens that include influenza and respiratory syncytial virus (RSV). This review outlines the essential steps required for the clinical translation of RNAi-based respiratory therapies including disease and RNA target selection, siRNA design, respiratory barriers, and delivery solutions. Attention is given to antiviral therapies and preclinical evaluation with focus on the current status of anti-RSV clinical trials.

A comprehensive review and update on the biologic treatment of adult noninfectious uveitis: part II

INTRODUCTION

Treatment of adult, noninfectious uveitis remains a major challenge for ophthalmologists around the world, especially in regard to recalcitrant cases. It is reported to comprise approximately 10% of preventable blindness in the USA. The cause of uveitis can be idiopathic or associated with infectious and systemic disorders. The era of biologic medical therapies provides new options for patients with otherwise treatment-resistant inflammatory eye disease.

AREAS COVERED

This two-part review gives a comprehensive overview of the existing medical treatment options for patients with adult, noninfectious uveitis, as well as important advances for the treatment ocular inflammation. Part I covers classic immunomodulation and latest information on corticosteroid therapy. In part II, emerging therapies are discussed, including biologic response modifiers, experimental treatments and ongoing clinical studies for uveitis.

EXPERT OPINION

The hazard of chronic corticosteroid use in the treatment of adult, noninfectious uveitis is well documented. Corticosteroid-sparing therapies, which offer a very favorable risk-benefit profile when administered properly, should be substituted. Although nothing is currently approved for on-label use in this indication, many therapies, through either translation or novel basic science research, have the potential to fill the currently exposed gaps.

Small-interfering RNAs (siRNAs) as a promising tool for ocular therapy

RNA interference (RNAi) can be used to inhibit the expression of specific genes in vitro and in vivo, thereby providing an extremely useful tool for investigating gene function. Progress in the understanding of RNAi-based mechanisms has opened up new perspectives in therapeutics for the treatment of several diseases including ocular disorders. The eye is currently considered a good target for RNAi therapy mainly because it is a confined compartment and, therefore, enables local delivery of small-interfering RNAs (siRNAs) by topical instillation or direct injection. However, delivery strategies that protect the siRNAs from degradation and are suitable for long-term treatment would be help to improve the efficacy of RNAi-based therapies for ocular pathologies. siRNAs targeting critical molecules involved in the pathogenesis of glaucoma, retinitis pigmentosa and neovascular eye diseases (age-related macular degeneration, diabetic retinopathy and corneal neovascularization) have been tested in experimental animal models, and clinical trials have been conducted with some of them. This review provides an update on the progress of RNAi in ocular therapeutics, discussing the advantages and drawbacks of RNAi-based therapeutics compared to previous treatments.

Challenging the future of siRNA therapeutics against cancer: the crucial role of nanotechnology

The identification of numerous deregulated signaling pathways on cancer cells and supportive stromal cells has revealed several molecular targets whose downregulation can elicit significant benefits for cancer treatment. In this respect, gene downregulation can be efficiently achieved by exploiting the RNA interference mechanism, particularly by the delivery of chemical synthesized small-interfering RNAs (siRNAs), which have the ability to mediate, in a specific manner, the degradation of any mRNA with complementary nucleotide sequence. However, several concerns regarding off-target effects and immune stimulation have been raised. Depending on their sequence, siRNAs can trigger an innate immune response, which might mediate undesirable side effects that ultimately compromise their clinical utility. This is a very relevant effect that will be discussed in the present manuscript. Moreover, the major drawback in the translation of siRNAs into the clinical practice is undoubtedly their inability to accumulate in tumor sites, particularly in organs other than the liver. In fact, upon systemic administration, owing to siRNAs physico-chemical features, they are rapidly cleared from the blood stream. Therefore, the development of a proper drug delivery system is of utmost importance. In this review, some of the latest advances on different nanotechnological platforms for siRNA delivery under clinical evaluation will be discussed. Along with this, targeting approaches towards cancer and/or endothelial cells will also be addressed, as these are some of the most promising strategies to enhance specific tumor accumulation while avoiding healthy tissues. Finally, clinical information on ongoing studies in patients with advanced solid tumors will be also provided.

Generation of stable 3'-mRNA cleavage fragments induced by siRNA in cells with high-levels of duck hepatitis B virus replication

Therapeutic small interfering RNAs (siRNAs) have attracted a lot of interest both in basic biomedical sciences as well as in translational medicine. Apart from their therapeutic efficacy adverse effects of siRNAs must be addressed. The generation of stable mRNA cleavage fragments and the translation of N-truncated proteins induced by antisense oligodeoxynucleotides (ASOs) have been reported. Similar to ASOs, siRNAs are considered to function via an antisense mechanism that promotes the cleavage of the target mRNA. To further investigate whether the stable mRNA cleavage fragments also occur in siRNA we constructed a short hairpin RNA (shRNA) expression plasmid, pshRNA794, containing the same sequence reported in experiments using ASOs which directly targeted the overlapping region of the pre-genomic mRNA (pgmRNA) and sub-genomic mRNA (sgmRNA) of duck hepatitis B virus (DHBV). The shRNA resulted in a 70.9% and 69.9% reduction of the DHBV mRNAs in LMH and HuH-7 cells, respectively. In addition a 70% inhibition of the DHBV DNA level was observed. Interestingly, 3'-mRNA cleavage fragments were detected in LMH but not in HuH-7 cells. Taken together, our findings demonstrate that the ASO sequence was also effective in siRNA. Importantly, our results provide direct evidence that stable 3'-mRNA fragments were generated by siRNA in cells with high levels of DHBV replication. Whether these can cause adverse RNAi effects needs to be explored further.