Cellular uptake and intracellular trafficking of antisense and siRNA oligonucleotides

Model-based meta-analysis to quantify the effects of short interfering RNA therapeutics on hepatitis B surface antigen turnover in hepatitis B-infected mice

The objective of this study was to compare the efficacy of short interfering RNA therapeutics (siRNAs) in reducing hepatitis B surface antigen (HBsAg) levels in hepatitis B-infected (HBV) mice across multiple siRNA therapeutic classes using model-based meta-analysis (MBMA) techniques. Literature data from 10 studies in HBV-infected mice were pooled, including 13 siRNAs, formulated as liposomal nanoparticles (LNPs) or conjugated to either cholesterol (chol) or N-acetylgalactosamine (GalNAc). Time course of the baseline- and placebo-corrected mean HBsAg profiles were modeled using kinetics of drug effect (KPD) model coupled to an indirect response model (IRM) within a longitudinal non-linear mixed-effects MBMA framework. Single and multiple dose simulations were performed exploring the role of dosing regimens across evaluated siRNA classes. The HBsAg degradation rate (0.72 day-1) was consistent across siRNAs but exhibited a large between-study variability of 31.4% (CV%). The siRNA biophase half-life was dependent on the siRNA class and was highest for GalNAc-siRNAs (21.06 days) and lowest for chol-siRNAs (2.89 days). ID50 estimates were compound-specific and were lowest for chol-siRNAs and highest for GalNAc-siRNAs. Multiple dose simulations suggest GalNAc-siRNAs may require between 4 and 7 times less frequent dosing at higher absolute dose levels compared to LNP-siRNAs and chol-siRNAs, respectively, to reach equipotent HBsAg-lowering effects in HBV mice. In conclusion, non-clinical HBsAg concentration-time data after siRNA administration can be described using the presented KPD-IRM MBMA framework. This framework allows to quantitatively compare the effects of siRNAs on the HBsAg time course and inform dose and regimen selection across siRNA classes. These results may support siRNA development, optimize preclinical study designs, and inform data analysis methodology of future anti-HBV siRNAs; and ultimately, support siRNA model-informed drug development (MIDD) strategies.

Intrinsically Disordered Ku Protein-Derived Cell-Penetrating Peptides

Efficient delivery of bioactive ingredients into cells is a major challenge. Cell-penetrating peptides (CPPs) have emerged as promising vehicles for this purpose. We have developed novel CPPs derived from the flexible and disordered tail extensions of DNA-binding Ku proteins. Ku-P4, the lead CPP identified in this study, is biocompatible and displays high internalization efficacy. Biophysical studies show that the proline residue is crucial for preserving the intrinsically disordered state and biocompatibility. DNA binding studies showed effective DNA condensation to form a positively charged polyplex. The polyplex exhibited effective penetration through the cell membrane and delivered the plasmid DNA inside the cell. These novel CPPs have the potential to enhance the cellular uptake and therapeutic efficacy of peptide-drug or gene conjugates.

Enhancing Antisense Oligonucleotide-Based Therapeutic Delivery with DG9, a Versatile Cell-Penetrating Peptide

Antisense oligonucleotide-based (ASO) therapeutics have emerged as a promising strategy for the treatment of human disorders. Charge-neutral PMOs have promising biological and pharmacological properties for antisense applications. Despite their great potential, the efficient delivery of these therapeutic agents to target cells remains a major obstacle to their widespread use. Cellular uptake of naked PMO is poor. Cell-penetrating peptides (CPPs) appear as a possibility to increase the cellular uptake and intracellular delivery of oligonucleotide-based drugs. Among these, the DG9 peptide has been identified as a versatile CPP with remarkable potential for enhancing the delivery of ASO-based therapeutics due to its unique structural features. Notably, in the context of phosphorodiamidate morpholino oligomers (PMOs), DG9 has shown promise in enhancing delivery while maintaining a favorable toxicity profile. A few studies have highlighted the potential of DG9-conjugated PMOs in DMD (Duchenne Muscular Dystrophy) and SMA (Spinal Muscular Atrophy), displaying significant exon skipping/inclusion and functional improvements in animal models. The article provides an overview of a detailed understanding of the challenges that ASOs face prior to reaching their targets and continued advances in methods to improve their delivery to target sites and cellular uptake, focusing on DG9, which aims to harness ASOs' full potential in precision medicine.

Localization of unlabeled bepirovirsen antisense oligonucleotide in murine tissues using in situ hybridization and CARS imaging

Current methods for detecting unlabeled antisense oligonucleotide (ASO) drugs rely on immunohistochemistry (IHC) and/or conjugated molecules, which lack sufficient sensitivity, specificity, and resolution to fully investigate their biodistribution. Our aim was to demonstrate the qualitative and quantitative distribution of unlabeled bepirovirsen, a clinical stage ASO, in livers and kidneys of dosed mice using novel staining and imaging technologies at subcellular resolution. ASOs were detected in formalin-fixed paraffin-embedded (FFPE) and frozen tissues using an automated chromogenic in situ hybridization (ISH) assay: miRNAscope. This was then combined with immunohistochemical detection of cell lineage markers. ASO distribution in hepatocytes versus nonparenchymal cell lineages was quantified using HALO AI image analysis. To complement this, hyperspectral coherent anti-Stokes Raman scattering (HS-CARS) imaging microscopy was used to specifically detect the unique cellular Raman spectral signatures following ASO treatment. Bepirovirsen was localized primarily in nonparenchymal liver cells and proximal renal tubules. Codetection of ASO with distinct cell lineage markers of liver and kidney populations aided target cell identity facilitating quantification. Positive liver signal was quantified using HALO AI, with 12.9% of the ASO localized to the hepatocytes and 87.1% in nonparenchymal cells. HS-CARS imaging specifically detected ASO fingerprints based on the unique vibrational signatures following unlabeled ASO treatment in a totally nonperturbative manner at subcellular resolution. Together, these novel detection and imaging modalities represent a significant increase in our ability to detect unlabeled ASOs in tissues, demonstrating improved levels of specificity and resolution. These methods help us understand their underlying mechanisms of action and ultimately improve the therapeutic potential of these important drugs for treating globally significant human diseases.

Chloroquine and cytosolic galectins affect endosomal escape of antisense oligonucleotides after Stabilin-mediated endocytosis

Non-DNA-binding Stabilin-2/HARE receptors expressed on liver sinusoidal endothelial cells specifically bind to and internalize several classes of phosphorothioate antisense oligonucleotides (PS-ASOs). After Stabilin-mediated uptake, PS-ASOs are trafficked within endosomes (>97%-99%), ultimately resulting in destruction in the lysosome. The ASO entrapment in endosomes lowers therapeutic efficacy, thereby increasing the overall dose for patients. Here, we use confocal microscopy to characterize the intracellular route transverse by PS-ASOs after Stabilin receptor-mediated uptake in stable recombinant Stabilin-1 and -2 cell lines. We found that PS-ASOs as well as the Stabilin-2 receptor transverse the classic path: clathrin-coated vesicle-early endosome-late endosome-lysosome. Chloroquine exposure facilitated endosomal escape of PS-ASOs leading to target knockdown by more than 50% as compared to untreated cells, resulting in increased PS-ASO efficacy. We also characterize cytosolic galectins as novel contributor for PS-ASO escape. Galectins knockdown enhances ASO efficacy by more than 60% by modulating EEA1, Rab5C, and Rab7A mRNA expression, leading to a delay in the endosomal vesicle maturation process. Collectively, our results provide additional insight for increasing PS-ASO efficacy by enhancing endosomal escape, which can further be utilized for other nucleic acid-based modalities.

Gymnotic uptake of AntimiRs alter microRNA-34a levels in 2D and 3D epithelial cell culture

MicroRNAs are attractive therapeutic targets in many diseases, including chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. Among microRNA inhibitors antimiRs have been proven successful in lowering aberrant microRNA levels in the clinic. We present a set of antimiRs targeting miR-34a, which has been shown to be dysregulated in chronic lung diseases. The tool compounds were taken up by a bronchial epithelial cell line and primary human bronchial epithelial cells, followed by efficient knockdown of miR-34a. Similar results were observed in 3D differentiated primary human bronchial epithelial cells cultured at the air-liquid interface. Varying chemical properties of antimiRs had significant impact on cellular uptake and potency, resulting in effective tool compounds for use in lung-relevant cellular systems. This report demonstrates gymnotic antimiR uptake and activity in 3D epithelial cell culture after apical administration, mimicking inhalation conditions.

Nucleic acid-based therapeutics for the treatment of central nervous system disorders

Nucleic acid-based therapeutics (NBTs) are an emerging class of drugs with potential for the treatment of a wide range of central nervous system conditions. To date, pertaining to CNS indications, there are two commercially available NBTs and a large number of ongoing clinical trials. However, these NBTs are applied directly to the brain due to very low blood brain barrier permeability. In this review, we outline recent advances in chemical modifications of NBTs and NBT delivery techniques intended to promote brain exposure, efficacy, and possible future systemic application.

Enhancing the Effectiveness of Oligonucleotide Therapeutics Using Cell-Penetrating Peptide Conjugation, Chemical Modification, and Carrier-Based Delivery Strategies

Oligonucleotide-based therapies are a promising approach for treating a wide range of hard-to-treat diseases, particularly genetic and rare diseases. These therapies involve the use of short synthetic sequences of DNA or RNA that can modulate gene expression or inhibit proteins through various mechanisms. Despite the potential of these therapies, a significant barrier to their widespread use is the difficulty in ensuring their uptake by target cells/tissues. Strategies to overcome this challenge include cell-penetrating peptide conjugation, chemical modification, nanoparticle formulation, and the use of endogenous vesicles, spherical nucleic acids, and smart material-based delivery vehicles. This article provides an overview of these strategies and their potential for the efficient delivery of oligonucleotide drugs, as well as the safety and toxicity considerations, regulatory requirements, and challenges in translating these therapies from the laboratory to the clinic.

Serum albumin and nucleic acids biodistribution: from molecular aspects to biotechnological applications

Serum albumin (SA) is the most abundant protein in plasma and represents the main carrier of endogenous and exogenous compounds. Several evidence supports the notion that SA binds single and double stranded deoxy- and ribonucleotides at two sites, with values of the dissociation equilibrium constant (i.e., K_d ) ranging from micromolar to nanomolar values. This can be relevant from a physiological and pathological point of view as in human plasma circulate cell-free nucleic acids (cfNAs), which are single and double stranded NAs released by different tissues via apoptosis, necrosis, and secretions. Albeit SA shows low hydrolytic reactivity toward DNA and RNA, the high plasma concentration of this protein and the occurrence of several SA receptors may be pivotal for sequestering and hydrolyzing cfNAs. Therefore, pathological conditions like cancer, characterized by altered levels of human SA or by altered SA post-translational modifications, may influence cfNAs distribution and metabolism. Besides, the stability, solubility, biocompatibility, and low immunogenicity make SA a golden share for biotechnological applications related to the delivery of therapeutic NAs (TNAs). Indeed, pre-clinical studies report the therapeutic potential of SA:TNAs complexes in precision cancer therapy. Here, the molecular and biotechnological implications of SA:NAs interaction are discussed, highlighting new perspectives into SA plasmatic functions. This article is protected by copyright. All rights reserved.

Biotechnological Evolution of siRNA Molecules: From Bench Tool to the Refined Drug

The depth and versatility of siRNA technologies enable their use in disease targets that are undruggable by small molecules or that seek to achieve a refined turn-off of the genes for any therapeutic area. Major extracellular barriers are enzymatic degradation of siRNAs by serum endonucleases and RNAases, renal clearance of the siRNA delivery system, the impermeability of biological membranes for siRNA, activation of the immune system, plasma protein sequestration, and capillary endothelium crossing. To overcome the intrinsic difficulties of the use of siRNA molecules, therapeutic applications require nanometric delivery carriers aiming to protect double-strands and deliver molecules to target cells. This review discusses the history of siRNAs, siRNA design, and delivery strategies, with a focus on progress made regarding siRNA molecules in clinical trials and how siRNA has become a valuable asset for biopharmaceutical companies.

Quantitative Measurement of Cytosolic and Nuclear Penetration of Oligonucleotide Therapeutics

A major obstacle in the development of effective oligonucleotide therapeutics is a lack of understanding about their cytosolic and nuclear penetration. To address this problem, we have applied the chloroalkane penetration assay (CAPA) to oligonucleotide therapeutics. CAPA was used to quantitate cytosolic delivery of antisense oligonucleotides (ASOs) and siRNAs and to explore the effects of a wide variety of commonly used chemical modifications and their patterning. We evaluated potential artifacts by exploring the effects of serum, comparing activity data and CAPA data, and assessing the impact of the chloroalkane tag and its linker chemistry. We also used viral transduction to expand CAPA to the nuclear compartment in epithelial and neuronal cell lines. Using this enhanced method, we measured a 48-h time course of nuclear penetration for a panel of chemically diverse modified RNAs. Moving forward, CAPA will be a useful tool for deconvoluting the complex processes of endosomal uptake, escape into the cytosol, and subcellular trafficking of oligonucleotide therapeutics in therapeutically relevant cell types.

Assessing the Cellular Uptake, Endosomal Escape, and Cytosolic Entry Efficiencies of Cyclic Peptides

Intracellular biologics such as cyclic peptides are an emerging class of macromolecular drugs that are either intrinsically cell permeable or can be effectively delivered into the cell interior to modulate the activity of previously intractable drug targets. They generally enter the mammalian cell by endocytosis mechanisms and are initially localized inside the endosomes. They subsequently escape from the endosomes (and/or lysosomes) into the cytosol with varying efficiencies. In this chapter, we provide the detailed protocol for a flow cytometry-based assay method to quantitate the overall cellular uptake, endosomal escape, and cytosolic entry efficiencies of biomolecules (e.g., linear and cyclic peptides, proteins, and nucleic acids), by using cell-penetrating peptides as an example. The scope of applicability, strengths, and weaknesses of this assay are also discussed.

Chemistry of Peptide-Oligonucleotide Conjugates: A Review

Peptide-oligonucleotide conjugates (POCs) represent one of the increasingly successful albeit costly approaches to increasing the cellular uptake, tissue delivery, bioavailability, and, thus, overall efficiency of therapeutic nucleic acids, such as, antisense oligonucleotides and small interfering RNAs. This review puts the subject of chemical synthesis of POCs into the wider context of therapeutic oligonucleotides and the problem of nucleic acid drug delivery, cell-penetrating peptide structural types, the mechanisms of their intracellular transport, and the ways of application, which include the formation of non-covalent complexes with oligonucleotides (peptide additives) or covalent conjugation. The main strategies for the synthesis of POCs are viewed in detail, which are conceptually divided into (a) the stepwise solid-phase synthesis approach and (b) post-synthetic conjugation either in solution or on the solid phase, especially by means of various click chemistries. The relative advantages and disadvantages of both strategies are discussed and compared.

MicroRNAs Involved in Small-cell Lung Cancer as Possible Agents for Treatment and Identification of New Targets

Small-cell lung cancer, a neuro-endocrine type of lung cancers, responds very well to chemotherapy-based agents. However, a high frequency of relapse due to adaptive resistance is observed. Immunotherapy-based treatments with checkpoint inhibitors has resulted in improvement of treatment but the responses are not as impressive as in other types of tumor. Therefore, identification of new targets and treatment modalities is an important issue. After searching the literature, we identified eight down-regulated microRNAs involved in radiation- and chemotherapy-induced resistance, as well as three up-regulated and four down-regulated miRNAs with impacts on proliferation, invasion and apoptosis of small-cell lung cancer cells in vitro. Furthermore, one up-regulated and four down-regulated microRNAs with in vivo activity in SCLC cell xenografts were identified. The identified microRNAs are candidates for inhibition or reconstitution therapy. The corresponding targets are candidates for inhibition or functional reconstitution with antibody-based moieties or small molecules.

Recent Advances in the Delivery Carriers and Chemical Conjugation Strategies for Nucleic Acid Drugs

With the development of new anticancer medicines, novel modalities are being explored for cancer treatment. For many years, conventional modalities, such as small chemical drugs and antibody drugs, have worked by "inhibiting the function" of target proteins. In recent years, however, nucleic acid drugs, such as ASOs and siRNAs, have attracted attention as a new modality for cancer treatment because nucleic acid drugs can directly promote the "loss of function" of target genes. Recently, nucleic acid drugs for use in cancer therapy have been extensively developed and some of them have currently been under investigation in clinical trials. To develop novel nucleic acid drugs for cancer treatment, it is imperative that cancer researchers, including ourselves, cover and understand those latest findings. In this review, we introduce and provide an overview of various DDSs and ligand modification technologies that are being employed to improve the success and development of nucleic acid drugs, then we also discuss the future of nucleic acid drug developments for cancer therapy. It is our belief this review will increase the awareness of nucleic acid drugs worldwide and build momentum for the future development of new cancer-targeted versions of these drugs.

Fluorescent base analogues in gapmers enable stealth labeling of antisense oligonucleotide therapeutics

To expand the antisense oligonucleotide (ASO) fluorescence labeling toolbox beyond covalent conjugation of external dyes (e.g. ATTO-, Alexa Fluor-, or cyanine dyes), we herein explore fluorescent base analogues (FBAs) as a novel approach to endow fluorescent properties to ASOs. Both cytosine and adenine analogues (tC, tC^O, 2CNqA, and pA) were incorporated into a 16mer ASO sequence with a 3-10-3 cEt-DNA-cEt (cEt = constrained ethyl) gapmer design. In addition to a comprehensive photophysical characterization, we assess the label-induced effects on the gapmers' RNA affinities, RNA-hybridized secondary structures, and knockdown efficiencies. Importantly, we find practically no perturbing effects for gapmers with single FBA incorporations in the biologically critical gap region and, except for pA, the FBAs do not affect the knockdown efficiencies. Incorporating two cytosine FBAs in the gap is equally well tolerated, while two adenine analogues give rise to slightly reduced knockdown efficiencies and what could be perturbed secondary structures. We furthermore show that the FBAs can be used to visualize gapmers inside live cells using fluorescence microscopy and flow cytometry, enabling comparative assessment of their uptake. This altogether shows that FBAs are functional ASO probes that provide a minimally perturbing in-sequence labeling option for this highly relevant drug modality.

Zwitterionic Nanogels and Microgels: An Overview on Their Synthesis and Applications

Zwitterionic polymers by virtue of their unique chemical and physical attributes have attracted researchers in recent years. The simultaneous presence of positive and negative charges in the same repeat unit renders them of various interesting properties such as superhydrophilicity, which has significantly broadened their scope for being used in different applications. Among polyzwitterions of different architectures, micro- and/or nano-gels have started receiving attention only until recently. These 3D cross-linked colloidal structures show peculiar characteristics in context to their solution properties, which are attributable either to the comonomers present or the presence of different electrolytes and biological specimens. In this review, a concise yet detailed account is provided of the different synthetic techniques and application domains of zwitterion-based micro- and/or nanogels that have been explored in recent years. Here, the focus is kept solely on the "polybetaines," which have garnered maximum research interest and remain the extensively studied polyzwitterions in literature. While their vast application potential in the biomedical sector is being detailed here, some other areas of scope such as using them as microreactors for the synthesis of metal nanoparticles or making smart membranes for water-treatment are discussed in this minireview as well.

Synthesis and Application of Peptide-siRNA Nanoparticles from Disulfide-Constrained Cyclic Amphipathic Peptides for the Functional Delivery of Therapeutic Oligonucleotides to the Lung

The potential of RNAi therapies has been largely impeded by the inherent challenges in the functional delivery of siRNA to cells. Herein, we describe protocols for the synthesis and characterization of novel peptide-siRNA nanoparticles prepared from disulfide-constrained amphipathic peptides complexed with siRNA as promising siRNA delivery vectors. We also describe protocols for the application of these nanoparticles to the in vitro and in vivo delivery of siRNA to lung cells for the functional knockdown of lung proteins.

RNA-based therapies: A cog in the wheel of lung cancer defense

Lung cancer (LC) is a heterogeneous disease consisting mainly of two subtypes, non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), and remains the leading cause of death worldwide. Despite recent advances in therapies, the overall 5-year survival rate of LC remains less than 20%. The efficacy of current therapeutic approaches is compromised by inherent or acquired drug-resistance and severe off-target effects. Therefore, the identification and development of innovative and effective therapeutic approaches are critically desired for LC. The development of RNA-mediated gene inhibition technologies was a turning point in the field of RNA biology. The critical regulatory role of different RNAs in multiple cancer pathways makes them a rich source of targets and innovative tools for developing anticancer therapies. The identification of antisense sequences, short interfering RNAs (siRNAs), microRNAs (miRNAs or miRs), anti-miRs, and mRNA-based platforms holds great promise in preclinical and early clinical evaluation against LC. In the last decade, RNA-based therapies have substantially expanded and tested in clinical trials for multiple malignancies, including LC. This article describes the current understanding of various aspects of RNA-based therapeutics, including modern platforms, modifications, and combinations with chemo-/immunotherapies that have translational potential for LC therapies.

Expanding the Scope of the Cleavable N-(methoxy)oxazolidine Linker for the Synthesis of Oligonucleotide Conjugates

Oligonucleotides modified by a 2′-deoxy-2′-(N-methoxyamino) ribonucleotide react readily with aldehydes in slightly acidic conditions to yield the corresponding N-(methoxy)oxazolidine-linked oligonucleotide-conjugates. The reaction is reversible and dynamic in slightly acidic conditions, while the products are virtually stable above pH 7, where the reaction is in a ‘‘switched off-state’’. Small molecular examinations have demonstrated that aldehyde constituents affect the cleavage rate of the N-(methoxy)oxazolidine-linkage. This can be utilized to adjust the stability of this pH-responsive cleavable linker for drug delivery applications. In the present study, Fmoc-β-Ala-H was immobilized to a serine-modified ChemMatrix resin and used for the automated assembly of two peptidealdehydes and one aldehyde-modified peptide nucleic acid (PNA). In addition, a triantennary N-acetyl-d-galactosamine-cluster with a β-Ala-H unit has been synthesized. These aldehydes were conjugated via N-(methoxy)oxazolidine-linkage to therapeutically relevant oligonucleotide phosphorothioates and one DNA-aptamer in 19–47% isolated yields. The cleavage rates of the conjugates were studied in slightly acidic conditions. In addition to the diverse set of conjugates synthesized, these experiments and a comparison to published data demonstrate that the simple conversion of Gly-H to β-Ala-H residue resulted in a faster cleavage of the N-(methoxy)oxazolidine-linker at pH 5, being comparable (T_0.5 ca 7 h) to hydrazone-based structures.

Cellular Targeting of Oligonucleotides by Conjugation with Small Molecules

Drug candidates derived from oligonucleotides (ON) are receiving increased attention that is supported by the clinical approval of several ON drugs. Such therapeutic ON are designed to alter the expression levels of specific disease-related proteins, e.g., by displaying antigene, antisense, and RNA interference mechanisms. However, the high polarity of the polyanionic ON and their relatively rapid nuclease-mediated cleavage represent two major pharmacokinetic hurdles for their application in vivo. This has led to a range of non-natural modifications of ON structures that are routinely applied in the design of therapeutic ON. The polyanionic architecture of ON often hampers their penetration of target cells or tissues, and ON usually show no inherent specificity for certain cell types. These limitations can be overcome by conjugation of ON with molecular entities mediating cellular 'targeting', i.e., enhanced accumulation at and/or penetration of a specific cell type. In this context, the use of small molecules as targeting units appears particularly attractive and promising. This review provides an overview of advances in the emerging field of cellular targeting of ON via their conjugation with small-molecule targeting structures.

An ATP synthase beta subunit is required for internalization of dsRNA into shrimp cells

Extracellular double-stranded RNA (dsRNA) is an important modulator in innate immunity in both vertebrates and invertebrates. In shrimp, extracellular dsRNA can trigger RNAi pathway and serves as antiviral defense mechanism. However, the mechanism of dsRNA internalization into the cells has not yet known in shrimp cells. This study identified candidate cell surface proteins from shrimp hepatopancreatic cells that could interact with dsRNA by a ligand blot assay. Among the candidate proteins, a cell-surface beta subunit of ATP synthase was shown to be capable of internalizing dsRNA into shrimp hepatopancreatic cells that could rapidly occur in just 1 min upon dsRNA challenge. Colocalization between dsRNA and ATP synthase beta subunit implied correlation between dsRNA and ATP synthase beta subunit during dsRNA internalization. Furthermore, dsRNA showed colocalization with Ras-related endocytic proteins, Rab5 and Rab7 indicating that dsRNA was internalized via the receptor-mediated endocytosis. For the above evidences as well as the reduction of dsRNA internalization by angiostatin and antibodies against ATP synthase beta subunit, we propose that dsRNA interacts with ATP synthase via a nucleotide binding site in the beta subunit prior to internalize dsRNA into cells.

Antisense oligonucleotide-based therapies for the treatment of osteoarthritis: Opportunities and roadblocks

Osteoarthritis (OA) is a debilitating disease with no approved disease-modifying therapies. Among the challenges for developing treatment is achieving targeted drug delivery to affected joints. This has contributed to the failure of several drug candidates for the treatment of OA. Over the past 20 years, significant advances have been made in antisense oligonucleotide (ASO) technology for achieving targeted delivery to tissues and cells both in vitro and in vivo. Since ASOs are able to bind specific gene regions and regulate protein translation, they are useful for correcting aberrant endogenous mechanisms associated with certain diseases. ASOs can be delivered locally through intra-articular injection, and can enter cells through natural cellular uptake mechanisms. Despite this, ASOs have yet to be successfully tested in clinical trials for the treatment of OA. Recent chemical modification to ASOs have further improved cellular uptake and reduced toxicity. Among these are locked nucleic acid (LNA)-based ASOs, which have shown promising results in clinical trials for diseases such as hepatitis and dyslipidemia. Recently, LNA-based ASOs have been tested both in vitro and in vivo for their therapeutic potential in OA, and some have shown promising joint-protective effects in preclinical OA animal models. In order to accelerate the testing of ASO therapies in a clinical trial setting for OA, further investigation into delivery mechanisms is required. In this review article, we discuss opportunities for viral-, particle-, biomaterial-, and chemical modification-based therapies, which are currently in preclinical testing. We also address potential roadblocks in the clinical translation of ASO-based therapies for the treatment of OA, such as the limitations associated with OA animal models and the challenges with drug toxicity. Taken together, we review what is known and what would be useful to accelerate translation of ASO-based therapies for the treatment of OA.

Combined Chemisorption and Complexation Generate siRNA Nanocarriers with Biophysics Optimized for Efficient Gene Knockdown and Air-Blood Barrier Crossing

Current nucleic acid (NA) nanotherapeutic approaches face challenges because of shortcomings such as limited control on loading efficiency, complex formulation procedure involving purification steps, low load of NA cargo per nanoparticle, endosomal trapping, and hampered release inside the cell. When combined, these factors significantly limit the amount of biologically active NA delivered per cell in vitro, delivered dosages in vivo for a prolonged biological effect, and the upscalability potential, thereby warranting early consideration in the design and developmental phase. Here, we report a versatile nanotherapeutic platform, termed auropolyplexes, for improved and efficient delivery of small interfering RNA (siRNA). Semitelechelic, thiolated linear polyethylenimine (PEI) was chemisorbed onto gold nanoparticles to endow them with positive charge. A simple two-step complexation method offers tunable loading of siRNA at concentrations relevant for in vivo studies and the flexibility for inclusion of multiple functionalities without any purification steps. SiRNA was electrostatically complexed with these cationic gold nanoparticles and further condensed with polycation or polyethyleneglycol-polycation conjugates. The resulting auropolyplexes ensured complete complexation of siRNA into nanoparticles with a high load of ∼15,500 siRNA molecules/nanoparticle. After efficient internalization into the tumor cell, an 80% knockdown of the luciferase reporter gene was achieved. Auropolyplexes were applied intratracheally in Balb/c mice for pulmonary delivery, and their biodistribution were studied spatio-temporally and quantitatively by optical tomography. Auropolyplexes were well tolerated with ∼25% of the siRNA dose remaining in the lungs after 24 h. Importantly, siRNA was released from auropolyplexes in vivo and a fraction also crossed the air-blood barrier, which was then excreted via kidneys, whereas >97% of gold nanoparticles were retained in the lung. Linear PEI-based auropolyplexes offer a combination of successful endosomal escape and better biocompatibility profile in vivo. Taken together, combined chemisorption and complexation endow auropolyplexes with crucial biophysical attributes, enabling a versatile and upscalable nanogold-based platform for siRNA delivery in vitro and in vivo.

Tumor microenvironment-induced structure changing drug/gene delivery system for overcoming delivery-associated challenges

Nano-drug/gene delivery systems (DDS) are powerful weapons for the targeted delivery of various therapeutic molecules in treatment of tumors. Nano systems are being extensively investigated for drug and gene delivery applications because of their exceptional ability to protect the payload from degradation in vivo, prolong circulation of the nanoparticles (NPs), realize controlled release of the contents, reduce side effects, and enhance targeted delivery among others. However, the specific properties required for a DDS vary at different phase of the complex delivery process, and these requirements are often conflicting, including the surface charge, particle size, and stability of DDS, which severely reduces the efficiency of the drug/gene delivery. Therefore, researchers have attempted to fabricate structure, size, or charge changeable DDS by introducing various tumor microenvironment (TME) stimuli-responsive elements into the DDS to meet the varying requirements at different phases of the delivery process, thus improving drug/gene delivery efficiency. This paper summarizes the most recent developments in TME stimuli-responsive DDS and addresses the aforementioned challenges.

Nusinersen as a Therapeutic Agent for Spinal Muscular Atrophy

The reduction of survival motor neuron (SMN) protein causes spinal muscular atrophy (SMA), an autosomal recessive neuromuscular disease. Nusinersen is an antisense oligonucleotide, approved by the FDA, which specifically binds to the repressor within SMN2 exon 7 to enhance exon 7 inclusion and augment production of functional SMN protein. Nusinersen is the first new oligonucleotide-based drug targeting the central nervous system for the treatment of SMA. This review of nusinersen will discuss its action mechanism, cellular uptake, trafficking mechanisms, and administration approaches to cross the blood-brain barrier. Furthermore, nusinersen clinical trials will be assessed in terms of pharmacokinetics, tolerability and safety, the clinical outcomes of multiple intrathecal doses, and a discussion on the primary and secondary endpoints.

Polyarginine-Mediated siRNA Delivery: A Mechanistic Study of Intracellular Trafficking of PCL-R15/siRNA Nanoplexes

As a cell-penetrating peptide, polyarginine is widely used in drug delivery systems based on its membrane permeation ability. Previously, we developed the mPEG-PLA-b-polyarginine(R15) triblock copolymer, which exhibited a high siRNA delivery efficiency both in vitro and in vivo. As a continued effort, here the amphiphilic diblock polymer PCL-R15 was synthesized as a simplified model to further elucidate the structure-activity relationship of arginine-based amphiphilic polymers as siRNA delivery systems, and the cellular trafficking mechanisms of the PCL-R15/siRNA nanoplexes were investigated to understand the interaction patterns between the nanoplexes and cells. Compared to the R15/siRNA complexes, the introduction of PCL moiety was found to result in the stronger interactions with cells and the enhanced transfection efficiency after the formation of condensed nanoplexes. Caveolae-mediated endocytosis and clathrin-mediated endocytosis were major routes for the internalization of PCL-R15/siRNA nanoplexes. The intracellular release of siRNA from nanoplexes was confirmed by fluorescence resonance energy transfer assay. It was also noticed that the internalized PCL-R15/siRNA nanoplexes were transported through digestive routes and trapped in lysosomes, which may be the bottleneck for efficient siRNA delivery of PCL-R15/siRNA nanoplexes. This study investigated the relationship between the polymer structure of PCL-R15 and the cellular interaction patterns, which may render implications on the rational design of polyarginine-based siRNA delivery systems.

Triazine-cored polymeric vectors for antisense oligonucleotide delivery in vitro and in vivo

BACKGROUND

The polymer-based drug/gene delivery is promising for the treatment of inherent or acquire disease, because of the polymer's structural flexibility, larger capacity for therapeutic agent, low host immunogenicity and less cost. Antisense therapy is an approach to fighting genetic disorders or infections using antisense oligonucleotides (AOs). Unfortunately, the naked AOs showed low therapeutic efficacy in vivo and in clinical trial due to their poor cellular uptake and fast clearance in bloodstream. In this study, a series of triazine-cored amphiphilic polymers (TAPs) were investigated for their potential to enhance delivery of AOs, 2'-O-methyl phosphorothioate RNA (2'-OMePS) and phosphorodiamidate morpholino oligomer (PMO) both in vitro and in vivo.

RESULTS

TAPs significantly enhanced AO-induced exon-skipping in a GFP reporter-based myoblast and myotube culture system, and observed cytotoxicity of the TAPs were lower than Endoporter, Lipofectamine-2000 or PEI 25K. Application of optimized formulations of TAPs with AO targeted to dystrophin exon 23 demonstrated a significant increase in exon-skipping efficiency in dystrophic mdx mice. The best ones for PMO and 2'-OMePS delivery have reached to 11-, 15-fold compared with the AO only in mdx mice, respectively.

CONCLUSION

The study of triazine-cored amphiphilic polymers for AO delivery in vitro and in mdx mice indicated that the carrier's performances are related to the molecular size, compositions and hydrophilic-lipophilic balance (HLB) of the polymers, as well as the AO's structure. Improved exon-skipping efficiency of AOs observed in vitro and in mdx mice accompanied with low cytotoxicity demonstrated TAP polymers are potentials as safe and effective delivery carrier for gene/drug delivery.

Therapeutic Targeting of TGFβ Ligands in Glioblastoma Using Novel Antisense Oligonucleotides Reduces the Growth of Experimental Gliomas

PURPOSE

Transforming growth factor (TGF)-β is expressed at high levels by glioma cells and contributes to the malignant phenotype of glioblastoma. However, its therapeutic targeting remains challenging. Here, we examined an alternative therapeutic approach of TGFβ inhibition using two novel phosphorothioate-locked nucleic acid (LNA)-modified antisense oligonucleotide gapmers, ISTH1047 and ISTH0047, which specifically target TGFβ₁ and TGFβ₂.

EXPERIMENTAL DESIGN

We characterized the effects of ISTH1047 and ISTH0047 on TGFβ_1/2 expression, downstream signaling and growth of human LN-308, LN-229, and ZH-161 cells as well as murine SMA-560 glioma cells in vitro. Furthermore, we assessed their target inhibition and effects on survival in orthotopic xenogeneic and syngeneic rodent glioma models in vivo.

RESULTS

Both antisense oligonucleotides specifically silenced their corresponding target and abrogated SMAD2 phosphorylation in several glioma cell lines. Moreover, inhibition of TGFβ₁ or TGFβ₂ expression by ISTH1047 or ISTH0047 reduced the migration and invasiveness of LN-308 and SMA-560 glioma cells. Systemic antisense oligonucleotide administration to glioma-bearing mice suppressed TGFβ₁ or TGFβ₂ mRNA expression as well as the expression of the downstream target PAI-1 in orthotopic gliomas. Glioma-bearing mice had significantly prolonged survival upon systemic treatment with ISTH1047 or ISTH0047, which was associated with a reduction of intratumoral SMAD2 phosphorylation and, in a fully immunocompetent model, with increased immune cell infiltration.

CONCLUSIONS

Targeting TGFβ expression with the novel LNA antisense oligonucleotides ISTH1047 or ISTH0047 results in strong antiglioma activity in vitro and in vivo, which may represent a promising approach to be examined in human patients with glioma.

Piperine Modulates Protein Mediated Toxicity in Fragile X-Associated Tremor/Ataxia Syndrome through Interacting Expanded CGG Repeat (r(CGG)exp) RNA

An expansion of CGG tandem repeats in the 5' untranslated region (5'-UTR) of fragile X mental retardation 1 (FMR1) gene causes fragile X-associated tremor/ataxia syndrome (FXTAS). The transcripts of these expanded repeats r(CGG)^exp either form RNA foci or undergo the repeat-associated non-ATG (RAN) translation that produces toxic homopolymeric proteins in neuronal cells. The discovery of small molecule modulators that possess a strong binding affinity and high selectivity to these toxic expanded repeats RNA could be a promising therapeutic approach to cure the expanded repeat-associated neurological diseases. Therefore, here we sought to test the therapeutic potential of a natural alkaloid, piperine, by assessing its ability to bind and neutralize the toxicity of r(CGG)^exp RNA motif. To accomplish this first, we have determined the affinity of piperine to r(CGG)^exp RNA using fluorescence-based binding assay and isothermal titration calorimetry assay. These assays showed that piperine forms a thermodynamically favorable interaction with r(CGG)^exp RNA with high selectivity to the G-rich RNA motif. Interaction of piperine with r(CGG)^exp motif was further validated using several biophysical techniques such as CD, CD melting, NMR spectroscopy, and gel retardation assay. Moreover, piperine was also found to be effective for improving the r(CGG)^exp associated splicing defects and RAN translation in a FXTAS cell model system. Our results effectively provided the evidence that piperine strongly interacts with r(CGG)^exp RNA and could be used as a suitable candidate for therapeutic development against FXTAS.

Codelivery of Genistein and miRNA-29b to A549 Cells Using Aptamer-Hybrid Nanoparticle Bioconjugates

This study aimed to evaluate the anti-cancer effect of a combination therapy of miRNA-29b and genistein loaded in mucin-1 (MUC 1)-aptamer functionalized hybrid nanoparticles in non-small cell lung cancer (NSCLC) A549 cell line. Genistein-miRNA-29b-loaded hybrid nanoparticles (GMLHN) was prepared and characterized. Particle size and zeta potential were measured using photon correlation spectroscopy (PCS). Encapsulation efficiency and loading efficiency were determined using HPLC. Preferential internalization of MUC 1-aptamer functionalized GMLHN by A549 cells was evaluated and compared to normal MRC-5 cells. The ability of GMLHN to downregulate targeted oncoproteins Phosphorylated protein kinase, strain AK, Thymoma (Phosphorylated protein kinase B) (pAKT), Phosphorylated phosphoinositide 3-kinase (p-PI3K), DNA (cytosine-5-)-methyltransferase 3 beta (DNMT3B) and Myeloid Cell Leukemia Sequence 1 (MCL 1) was evaluated using western blot, while antiproliferative effect and ability to initiate apoptosis was also assessed in A549 cells. MUC 1-aptamer functionalized GMLHN nanoparticles were prepared. These nanoparticles were preferentially internalized by A549 cells but less so, in MRC-5 cells. pAKT, p-PI3K, DNMT3B and MCL 1 were efficiently downregulated by these nanoparticles without affecting the levels of AKT and PI3K in A549 cells. GMLHN demonstrated a superior antiproliferative effect compared to individual genistein and miRNA-29b-loaded nanoparticles. Results generated were able to demonstrate that genistein-miRNA-29b-loaded hybrid nanoparticles (GMLHN) could be a potential treatment modality for NSCLC because of the ability of the payloads to attack multiple targets.

Structure-activity relationships and cellular mechanism of action of small molecules that enhance the delivery of oligonucleotides

The pharmacological effects of antisense and siRNA oligonucleotides are hindered by the tendency of these molecules to become entrapped in endomembrane compartments thus failing to reach their targets in the cytosol or nucleus. We have previously used high throughput screening to identify small molecules that enhance the escape of oligonucleotides from intracellular membrane compartments and have termed such molecules OECs (oligonucleotide enhancing compounds). Here, we report on the structure-activity relationships of a family of OECs that are analogs of a hit that emerged from our original screen. These studies demonstrate key roles for the lipophilic aromatic groups, the tertiary nitrogen, and the carbamate moiety of the parent compound. We have also investigated the intracellular site of action of the OECs and have shown that activity is due to the release of oligonucleotides from intermediate endosomal compartments rather than from early endosomes or from highly acidic downstream compartments. At high concentrations of OECs toxicity occurs in a manner that is independent of caspases or of lysosomal cathepsins but instead involves increased plasma membrane permeability. Thus, in addition to describing specific characteristics of this family of OECs, the current study provides insights into basic mechanisms of oligonucleotide trafficking and their implications for oligonucleotide delivery.

Lipid Conjugates Enhance Endosomal Release of Antisense Oligonucleotides Into Cells

Antisense oligonucleotides modified with phosphorothioate linkages (PS-ASOs) can enter cells via endocytic pathways and must escape from membraned organelles to reach target RNAs. We recently found that membrane destabilization induced by different lipid species contributes to PS-ASO release from late endosomes (LEs). In this study, we characterized intracellular uptake, trafficking, and activities of PS-ASOs conjugated with different lipid species. We found that palmitic acid-, tocopherol-, and cholesterol-conjugated PS-ASOs have increased protein binding and enhanced intracellular uptake compared to unconjugated PS-ASOs. Similar to the parental PS-ASO, the lipid-conjugated PS-ASOs traffic from early to LEs without incorporation into lipid droplets. Unlike parental PS-ASOs, the lipid-conjugated PS-ASOs tend to remain associated with plasma or endosomal membranes, and this appears to influence their release from endosomes. The lipid-conjugated PS-ASOs were released more rapidly than parental PS-ASO. These results suggest that lipid conjugation enhances the interactions of PS-ASOs with proteins or membranes, in turn facilitating intracellular trafficking and endosomal release.

Differential uptake, kinetics and mechanisms of intracellular trafficking of next-generation antisense oligonucleotides across human cancer cell lines

Antisense oligonucleotides (ASOs) modulate cellular target gene expression through direct binding to complementary RNA. Advances in ASO chemistry have led to the development of phosphorothioate (PS) ASOs with constrained-ethyl modifications (cEt). These next-generation cEt-ASOs can enter cells without transfection reagents. Factors involved in intracellular uptake and trafficking of cEt-ASOs leading to successful target knockdown are highly complex and not yet fully understood. AZD4785 is a potent and selective therapeutic KRAS cEt-ASO currently under clinical development for the treatment of cancer. Therefore, we used this to investigate mechanisms of cEt-ASO trafficking across a panel of cancer cells. We found that the extent of ASO-mediated KRAS mRNA knockdown varied significantly between cells and that this did not correlate with bulk levels of intracellular accumulation. We showed that in cells with good productive uptake, distribution of ASO was perinuclear and in those with poor productive uptake distribution was peripheral. Furthermore, ASO rapidly trafficked to the late endosome/lysosome in poor productive uptake cells compared to those with more robust knockdown. An siRNA screen identified several factors mechanistically involved in productive ASO uptake, including the endosomal GTPase Rab5C. This work provides novel insights into the trafficking of cEt-ASOs and mechanisms that may determine their cellular fate.

Tissue engineering strategies for the induction of angiogenesis using biomaterials

Angiogenesis is touted as a fundamental procedure in the regeneration and restoration of different tissues. The induction of de novo blood vessels seems to be vital to yield a successful cell transplantation rate loaded on various scaffolds. Scaffolds are natural or artificial substances that are considered as one of the means for delivering, aligning, maintaining cell connection in a favor of angiogenesis. In addition to the potential role of distinct scaffold type on vascularization, the application of some strategies such as genetic manipulation, and conjugation of pro-angiogenic factors could intensify angiogenesis potential. In the current review, we focused on the status of numerous scaffolds applicable in the field of vascular biology. Also, different strategies and priming approaches useful for the induction of pro-angiogenic signaling pathways were highlighted.

A NanoFlare-Based Strategy for In Situ Tumor Margin Demarcation and Neoadjuvant Gene/Photothermal Therapy

Accurate tumor margin demarcation in situ remains a paramount challenge. Herein, a NanoFlare (also known as spherical-nucleic-acid technology) based strategy is reported for in situ tumor margin delineation by transforming and amplifying the pathophysiological redox signals of tumor microenvironment. The NanoFlare designed (named AuNS-ASON) is based on gold nanostar (AuNS) coated with a dense shell of disulfide bridge-inserted and cyanine dyes-labeled antisense oligonucleotides (ASON) targeting survivin mRNA. The unique anisotropic ASON-spike nanostructure endows the AuNS-ASON with universal cellular internalization of tumor cells, while the disulfide bridge inserted confers response specificity toward redox activation. In vitro experiments demonstrate that the AuNS-ASON can discriminate tumor cells rapidly with activated fluorescence signals (>100-fold) in 2 h, and further achieve synergistic gene/photothermal tumor cells ablation upon near-infrared laser irradiation. Remarkably, in situ tumor margin delineation with high accuracy and outstanding spatial resolution (<100 µm) in mice bearing different tumors is obtained based on the AuNS-ASON, providing intraoperative guidance for tumor resection. Moreover, the AuNS-ASON can enable efficient neoadjuvant gene/photothermal therapy before surgery to reduce tumor extent and increase resectability. The concept of NanoFlare-based microenvironment signal transformation and amplification could be used as a general strategy to guide the design of activatable nanoprobes for cancer theranostics.

COPII vesicles can affect the activity of antisense oligonucleotides by facilitating the release of oligonucleotides from endocytic pathways

RNase H1-dependent, phosphorothioate-modified antisense oligonucleotides (PS-ASOs) can enter cells through endocytic pathways and need to be released from the membrane-enclosed organelles, a limiting step for antisense activity. Accumulating evidence has suggested that productive PS-ASO release mainly occurs from late endosomes (LEs). However, how PS-ASOs escape from LEs is not well understood. Here, we report that upon PS-ASO incubation, COPII vesicles, normally involved in ER-Golgi transport, can re-locate to PS-ASO-containing LEs. Reduction of COPII coat proteins significantly decreased PS-ASO activity, without affecting the levels of PS-ASO uptake and early-to-late endosome transport, but caused slower PS-ASO release from LEs. COPII co-localization with PS-ASOs at LEs does not require de novo assembly of COPII at ER. Interestingly, reduction of STX5 and P115, proteins involved in tethering and fusion of COPII vesicles with Golgi membranes, impaired COPII re-localization to LEs and decreased PS-ASO activity. STX5 can re-locate to LEs upon PS-ASO incubation, can bind PS-ASOs, and the binding appears to be required for this pathway. Our study reveals a novel release pathway in which PS-ASO incubation causes LE re-localization of STX5, which mediates the recruitment of COPII vesicles to LEs to facilitate endosomal PS-ASO release, and identifies another key PS-ASO binding protein.

Membrane Destabilization Induced by Lipid Species Increases Activity of Phosphorothioate-Antisense Oligonucleotides

Chemically modified antisense oligonucleotides with phosphorothioate linkages (PS-ASOs) mediate site-specific cleavage of RNA by RNase H1 and are broadly used as research and therapeutic tools. PS-ASOs can enter cells via endocytic pathways and escape from membrane-enclosed endocytic organelles to reach target RNAs. We recently found that lysobisphosphatidic acid is required for release of PS-ASOs from late endosomes. Here, we evaluated the effects of other lipids on PS-ASO intracellular trafficking and activities. We show that free fatty acids, ceramide, and cholesterol increase PS-ASO activities. Free fatty acids induced formation of lipid droplets without changing the intracellular localization of PS-ASOs in early or late endosomes. Ceramide and cholesterol did not obviously induce the formation of lipid droplets, but cholesterol caused enlargement of endosome size and volume. Although none of those lipids appeared to influence PS-ASO internalization or intracellular trafficking processes, all led to an increase in leakiness of late endosomes. Thus, the membrane destabilization induced by these lipids likely contributes to PS-ASO release from late endosomes, which, in turn, increases PS-ASO activity.

Methods of the Synthesis of Silicon-Containing Nanoparticles Intended for Nucleic Acid Delivery

A promising new approach to the treatment of viral infections and genetic diseases associated with damaged or foreign nucleic acids in the body is gene therapy, i.e., the use of antisense oligonucleotides, ribozymes, deoxyribozymes, siRNA, plasmid DNA, etc. (therapeutic nucleic acids). Selective recognition of target nucleic acids by these compounds based on highly specific complementary interaction can minimize negative side effects, which occur with currently used low molecular weight drugs. To apply a new generation of therapeutic agents in medical practice, it is necessary to solve the problem of their delivery into cells. Silicon-containing nanoparticles are considered as promising carriers for this purpose due to their biocompatibility, low toxicity, ability to biodegradation and excretion from the body, as well as the simplicity of the synthesis and modification. Silicon-containing nanoparticles are divided into two broad categories: solid (nonporous) and mesoporous silicon nanoparticles (MSN). This review gives a brief overview of the creation of mesoporous, multilayer, and other silicon-based nanoparticles. The publications concerning solid silicon-organic nanoparticles capable of binding and delivering nucleic acids into cells are discussed in more detail with emphasis on methods for their synthesis. The review covers publications over the past 15 years, which describe the classical Stöber method, the microemulsion method, modification of commercial silica nanoparticles, and other strategies.

Functional Microgels: Recent Advances in Their Biomedical Applications

Here, a spotlight is shown on aqueous microgel particles which exhibit a great potential for various biomedical applications such as drug delivery, cell imaging, and tissue engineering. Herein, different synthetic methods to develop microgels with desirable functionality and properties along with degradable strategies to ensure their renal clearance are briefly presented. A special focus is given on the ability of microgels to respond to various stimuli such as temperature, pH, redox potential, magnetic field, light, etc., which helps not only to adjust their physical and chemical properties, and degradability on demand, but also the release of encapsulated bioactive molecules and thus making them suitable for drug delivery. Furthermore, recent developments in using the functional microgels for cell imaging and tissue regeneration are reviewed. The results reviewed here encourage the development of a new class of microgels which are able to intelligently perform in a complex biological environment. Finally, various challenges and possibilities are discussed in order to achieve their successful clinical use in future.

Current Challenges in Delivery and Cytosolic Translocation of Therapeutic RNAs

RNA interference (RNAi) is a fundamental cellular process for the posttranscriptional regulation of gene expression. RNAi can exogenously be modulated by small RNA oligonucleotides, such as microRNAs (miRNAs) and small interfering RNAs (siRNAs), or by antisense oligonucleotides. These small oligonucleotides provided the scientific community with powerful and versatile tools to turn off the expression of genes of interest, and hold out the promise of new therapeutic solutions against a wide range of gene-associated pathologies. However, unmodified nucleic acids are highly instable in biological systems, and their weak interaction with plasma proteins confers an unfavorable pharmacokinetics. In this review, we first provide an overview of the most efficient chemical strategies that, over the past 30 years, have been used to significantly improve the therapeutic potential of oligonucleotides. Oligonucleotides targeting and delivery technologies are then presented, including covalent conjugates between oligonucleotides and targeting ligand, and noncovalent association with lipid or polymer nanoparticles. Finally, we specifically focus on the endosomal escape step, which represents a major stumbling block for the effective use of oligonucleotides as therapeutic agents. The need for approaches to quantitatively measure endosomal escape and cytosolic arrival of biomolecules is discussed in the context of the development of efficient oligonucleotide targeting and delivery vectors.

Intracellular Trafficking and Endosomal Release of Oligonucleotides: What We Know and What We Don't

Understanding the cellular uptake and intracellular trafficking of oligonucleotides provides an important basic underpinning for the developing field of oligonucleotide-based therapeutics. Whether delivered as "free" oligonucleotides, as ligand-oligonucleotide conjugates, or in association with various nanocarriers, all forms of oligonucleotide enter cells by endocytosis and are initially ensconced within membrane-limited vesicles. Accordingly, the locus and extent of release to the cytosol and nucleus are key determinants of the pharmacological actions of oligonucleotides. A number of recent studies have explored the intracellular trafficking of various forms of oligonucleotides and their release from endomembrane compartments. These studies reveal a surprising convergence on an early-intermediate compartment in the trafficking pathway as the key locus of release for oligonucleotides administered in "free" form as well as those delivered with lipid complexes. Thus, oligonucleotide release from multivesicular bodies or from late endosomes seems to be the crucial endogenous process for attaining pharmacological effects. This intrinsic process of oligonucleotide release may be amplified by delivery agents such as lipid complexes or small molecule enhancers.

Fluorination Enhances Serum Stability of Bioreducible Poly(amido amine) Polyplexes and Enables Efficient Intravenous siRNA Delivery

The use of small interfering RNA (siRNA) in cancer treatment has been limited by the lack of effective systemic delivery methods. Although synthetic polycations have been widely explored in siRNA delivery, polycation/siRNA polyplexes often suffer from insufficient stability in vivo. Here, rationally designed siRNA delivery systems that meet the requirements for systemic siRNA delivery to distant tumors are reported. The hypothesis that modular design of delivery systems based on poly(amido amine)s that combine fluorination for systemic stability with bioreducibility for easy intracellular siRNA release, and PEGylation for improved safety and colloidal stability will overcome problems with contradicting siRNA delivery demands is tested. PEGylated, fluorinated, and bioreducible copolymers (PEG-PCD-F) with different degree of fluorination are thus synthesized. The fluorinated copolymers readily formed polyplexes with siRNA and achieved greatly improved gene silencing efficacy in multiple cell lines in vitro when compared with nonfluorinated controls. The results show fluorination-induced enhancement of stability, cellular uptake, and endosomal escape of the polyplexes, while exhibiting efficient siRNA release in reducing intracellular environment. PEG-PCD-F polyplexes with siRNA against Bcl2 inhibit breast tumor growth following systemic intravenous administration. The results provide strong evidence of successful combination of bioreducibility with fluorination and PEGylation to achieve systemic siRNA polyplex delivery.

Dual-responsive polyplexes with enhanced disassembly and endosomal escape for efficient delivery of siRNA

Despite the extracellular barriers for siRNA delivery have been overcome by utilizing advanced nanoparticle delivery systems, the key intracellular barriers after internalization including efficient disassembly of siRNA and endosomal escape still remains challenging. To address the issues, we developed a unique pH- and redox potential-responsive polyplex delivery system based on the copolymer of mPEG-b-PLA-PHis-ssPEI1.8 k, which is composed of a pH-responsive copolymer of PEG-b-PLA-PHis (Mw 5 k) and a branched PEI (Mw1.8 k) linked with redox cleavable disulfide bond. The copolymer showed excellent siRNA complexation and protection abilities against endogenous substances at the relatively low N/P ratio of 6. The siRNA release from the polyplexes (N/P 6) was markedly increased from 13.62% to 58.67% under conditions simulating the endosomal microenvironment. Fluorescence resonance energy transfer (FRET) test also indicated a higher disassembly extent of siRNA from the copolymer. The accelerated siRNA release from the polyplexes was markedly restrained when the N/P ratio was raised above 10 due to the increasing of electrostatic interactions. The efficient endosomal escape of siRNA after internalization was confirmed by confocal microscopy, which was attributed to the cleavaged PEI chains inducing membrane destabilization, the "proton sponge effect" of PHis and PEI as well as the relative small size of after disassembly. The enhanced disassembly and endosomal escape were elucidated as the leading cause for polyplexes (N/P 6) showed more efficient Bcl-2 silencing (85.45%) than those polyplexes with higher N/P ratios (N/P 10 and 15). In vivo results further demonstrated that polyplexes (N/P 6) delivery of siBcl-2 significantly inhibited the MCF-7 breast tumor growth as compared to its counterparts. The incorporation of convertible non-electrical interactions at a balance with electrostatic interactions in complexation siRNA has been demonstrated as an effective strategy to achieve efficient disassembly from stable polyplexes. Moreover, polyplexes equipped with the enhanced disassembly and endosomal escape provides a new potential way to tackle the intracellular delivery bottleneck for siRNA delivery.

The Role of micro RNAs in Breast Cancer Metastasis: Preclinical Validation and Potential Therapeutic Targets

Despite the approval of several molecular therapies in the last years, breast cancer-associated death ranks as the second highest in women. This is due to metastatic disease, which represents a challenge for treatment. A better understanding of the molecular mechanisms of metastasis is, therefore, of paramount importance. In this review we summarize the role of micro RNAs (miRs) involved in metastasis of breast cancer. We present an overview on metastasis-promoting, -suppressing and context-dependent miRs with both activities. We have categorized the corresponding miRs according to their target classes, interaction with stromal cells or exosomes. The pathways affected by individual miRs are outlined in regard to in vitro properties, activity in metastasis-related in vivo models and clinical significance. Current approaches that may be suitable for therapeutic inhibition or restauration of miR activity are outlined. Finally, we discuss the delivery bottlenecks which present as a major challenge in nucleic acid (miR)-based therapies.