Tf-lipoplexes for neuronal siRNA delivery: A promising system to mediate gene silencing in the CNS

Rational design and structure-activity relationship of random copolymers for enhanced siRNA delivery

HYPOTHESIS

Cationic polymers and their derivatives have garnered significant interest as advanced vectors for siRNA delivery. Recently, we developed a robust diblock copolymer featuring an innovative binding block and a stealth block that work synergistically to facilitate efficient delivery of biotherapeutics. However, the fundamental mechanisms underlying its superior delivery capacity remain to be fully elucidated.

EXPERIMENTS

Since the binding block dominantly regulate the delivery performance, we synthesized a series of adapted copolymers, P(AAPBAm-co-DMAPMAn), by solely incorporating the key involved units, namely 3-acrylamidophenylboronic acid (AAPBA) and N-(3-dimethylaminopropyl)methacrylamide (DMAPMA). We thoroughly varied the block combinations, sequences and lengths, and investigated their effects on siRNA delivery.

FINDINGS

AAPBA and DMAPMA can bound to siRNA through reversible ester bonds and electrostatic interactions, respectively. The former enhanced siRNA release due to its responsive properties, while the cationic DMAPMA promoted endosomal escape of the complexes through its inherent interaction with membrane. Notably, only the rational combination of 20 units of each monomer, defined as copolymer P(AAPBA20-co-DMAPMA20), integrated the multiple yet balanced functions that sequentially promoted siRNA loading, endocytosis, endosome escape, and cytoplasmic release, ultimately leading to superior gene silencing. The clarified structure-activity relationships and revealed principles are valuable for the rational design of novel polymeric vectors to improve siRNA delivery and therapeutic applications.

The role of ladderlectin in spermatogenesis and ovarian sperm storage in the black rockfish (Sebastes schlegelii)

Ladderlectin, a teleost-specific C-type lectin, has been primarily associated with innate immune defense. However, this study unveils an important role of ladderlectin in the reproductive processes of Sebastes schlegelii. Seven ladderlectin genes (SscLLs) are identified, with SscLL3604 and SscLL3605 exhibiting high testis-specificity expression. Both genes contain a C-type lectin domain (CTLD) and two carbohydrate-binding motifs (QPD and WSD), with SscLL3605 also containing a signal peptide. Notably, SscLL3604 is predominantly cytoplasmic, while SscLL3605 is found both in the cytoplasm and cell membrane. Additionally, SscLLs are primarily localized in Sertoli cells at the mRNA level but also exist in spermatids and spermatozoa at the protein level. Further analysis reveals that SscLLs are present in sperm heads and can bind to ovarian cells, hinting at a pivotal role in long-term sperm storage in ovaries. Knockdown of SscLLs in vitro demonstrates their critical role in maintaining Sertoli cells and Leydig cells within the testis. Finally, inhibition of glycosylation or treatment with antibody of SscLLs leads to an increased incidence of embryonic malformation in S. schlegelii. These findings suggest that ladderlectin may also play an important role in the regulation of reproductive processes, thereby providing an additional adaptive mechanism for the reproduction of viviparous fish.

Exploring the promise of lipoplexes: From concept to clinical applications

Lipoplexes are non-viral lipid vectors that effectively form complexes with genetic material, positioning them as promising alternatives to viral vectors in gene therapy. Their advantages include lower toxicity, reduced immunogenicity, improved targetability, and ease of large-scale production. A typical lipoplex is composed of cationic lipids, neutral lipids, and anionic nucleic acids (e.g., DNA, mRNA, miRNA, siRNA, shRNA). Neutral lipids play an auxiliary role and are often used as transfection enhancers. Enhancing lipoplex efficiency often involves modifying the cationic lipid structure through functional groups like PEG polymers and targeting ligands. The assembly of lipoplexes occurs spontaneously. This process involves the binding of the positively charged polar head group of the cationic lipid to the negatively charged DNA spontaneously as a result of electrostatic interaction, then irreversible rearrangement and condensation of the lipoplex occurs to form either lamellar or hexagonal structures. The transfection process encompasses several steps: cellular entry, endosomal escape and cargo release, cytoplasmic trafficking, and nuclear entry. The physicochemical and biological properties of lipoplexes are influenced by factors such as lipid structure, charge ratio, and environmental conditions. Despite certain limitations like low gene transfer efficiency and rapid clearance by serum proteins, lipoplexes show promise for clinical applications. They can be administered through various routes, offering potential treatments for diseases such as cancer, bone damage, infection, and cystic fibrosis. The study aims to examine the potential of lipoplexes as a promising vehicle for delivering therapeutic agents and their progression from theoretical concepts to practical clinical applications.

Stem cell therapeutics and gene therapy for neurologic disorders

Rapid advances in biological knowledge and technological innovation have greatly advanced the fields of stem cell and gene therapies to combat a broad spectrum of neurologic disorders. Researchers are currently exploring a variety of stem cell types (e.g., embryonic, progenitor, induced pluripotent) and various transplantation strategies, each with its own advantages and drawbacks. Similarly, various gene modification techniques (zinc finger, TALENs, CRISPR-Cas9) are employed with various delivery vectors to modify underlying genetic contributors to neurologic disorders. While these two individual fields continue to blaze new trails, it is the combination of these technologies which enables genetically engineered stem cells and vastly increases investigational and therapeutic opportunities. The capability to culture and expand stem cells outside the body, along with their potential to correct genetic abnormalities in patient-derived cells or enhance cells with extra gene products, unleashes the full biological potential for innovative, multifaceted approaches to treat complex neurological disorders. In this review, we provide an overview of stem cell and gene therapies in the context of neurologic disorders, highlighting recent advances and current shortcomings, and discuss prospects for future therapies in clinical settings.

RNA therapies for CNS diseases

Neurological disorders are a diverse group of conditions that pose an increasing health burden worldwide. There is a general lack of effective therapies due to multiple reasons, of which a key obstacle is the presence of the blood-brain barrier, which limits drug delivery to the central nervous system, and generally restricts the pool of candidate drugs to small, lipophilic molecules. However, in many cases, these are unable to target key pathways in the pathogenesis of neurological disorders. As a group, RNA therapies have shown tremendous promise in treating various conditions because they offer unique opportunities for specific targeting by leveraging Watson-Crick base pairing systems, opening up possibilities to modulate pathological mechanisms that previously could not be addressed by small molecules or antibody-protein interactions. This potential paradigm shift in disease management has been enabled by recent advances in synthesizing, purifying, and delivering RNA. This review explores the use of RNA-based therapies specifically for central nervous system disorders, where we highlight the inherent limitations of RNA therapy and present strategies to augment the effectiveness of RNA therapeutics, including physical, chemical, and biological methods. We then describe translational challenges to the widespread use of RNA therapies and close with a consideration of future prospects in this field.

Physiological Barriers and Strategies of Lipid-Based Nanoparticles for Nucleic Acid Drug Delivery

Lipid-based nanoparticles (LBNPs) are currently the most promising vehicles for nucleic acid drug (NAD) delivery. Although their clinical applications have achieved success, the NAD delivery efficiency and safety are still unsatisfactory, which are, to a large extent, due to the existence of multi-level physiological barriers in vivo. It is important to elucidate the interactions between these barriers and LBNPs, which will guide more rational design of efficient NAD vehicles with low adverse effects and facilitate broader applications of nucleic acid therapeutics. This review describes the obstacles and challenges of biological barriers to NAD delivery at systemic, organ, sub-organ, cellular, and subcellular levels. The strategies to overcome these barriers are comprehensively reviewed, mainly including physically/chemically engineering LBNPs and directly modifying physiological barriers by auxiliary treatments. Then the potentials and challenges for successful translation of these preclinical studies into the clinic are discussed. In the end, a forward look at the strategies on manipulating protein corona (PC) is addressed, which may pull off the trick of overcoming those physiological barriers and significantly improve the efficacy and safety of LBNP-based NADs delivery.

Directing the Way-Receptor and Chemical Targeting Strategies for Nucleic Acid Delivery

Nucleic acid therapeutics have shown great potential for the treatment of numerous diseases, such as genetic disorders, cancer and infections. Moreover, they have been successfully used as vaccines during the COVID-19 pandemic. In order to unfold full therapeutical potential, these nano agents have to overcome several barriers. Therefore, directed transport to specific tissues and cell types remains a central challenge to receive carrier systems with enhanced efficiency and desired biodistribution profiles. Active targeting strategies include receptor-targeting, mediating cellular uptake based on ligand-receptor interactions, and chemical targeting, enabling cell-specific delivery as a consequence of chemically and structurally modified carriers. With a focus on synthetic delivery systems including polyplexes, lipid-based systems such as lipoplexes and lipid nanoparticles, and direct conjugates optimized for various types of nucleic acids (DNA, mRNA, siRNA, miRNA, oligonucleotides), we highlight recent achievements, exemplified by several nucleic acid drugs on the market, and discuss challenges for targeted delivery to different organs such as brain, eye, liver, lung, spleen and muscle in vivo.

Lipid-based nanoparticles and RNA as innovative neuro-therapeutics

RNA-delivery is a promising tool to develop therapies for difficult to treat diseases such as neurological disorders, by silencing pathological genes or expressing therapeutic proteins. However, in many cases RNA delivery requires a vesicle that could effectively protect the molecule from bio-degradation, bypass barriers i.e., the blood brain barrier, transfer it to a targeted tissue and efficiently release the RNA inside the cells. Many vesicles such as viral vectors, and polymeric nanoparticles have been mentioned in literature. In this review, we focus in the discussion of lipid-based advanced RNA-delivery platforms. Liposomes and lipoplexes, solid lipid nanoparticles and lipid nanoparticles are the main categories of lipidic platforms for RNA-delivery to the central nervous systems (CNS). A variety of surface particles' modifications and routes of administration have been studied to target CNS providing encouraging results in vivo. It is concluded that lipid-based nanoplatforms will play a key role in the development of RNA neuro-therapies.

Non-viral vectors for RNA delivery

RNA-based therapy is a promising and potential strategy for disease treatment by introducing exogenous nucleic acids such as messenger RNA (mRNA), small interfering RNA (siRNA), microRNA (miRNA) or antisense oligonucleotides (ASO) to modulate gene expression in specific cells. It is exciting that mRNA encoding the spike protein of COVID-19 (coronavirus disease 2019) delivered by lipid nanoparticles (LNPs) exhibits the efficient protection of lungs infection against the virus. In this review, we introduce the biological barriers to RNA delivery in vivo and discuss recent advances in non-viral delivery systems, such as lipid-based nanoparticles, polymeric nanoparticles, N-acetylgalactosamine (GalNAc)-siRNA conjugate, and biomimetic nanovectors, which can protect RNAs against degradation by ribonucleases, accumulate in specific tissue, facilitate cell internalization, and allow for the controlled release of the encapsulated therapeutics.

Mendonça L, Matos L, Prata MJ, S. Jurado A, Pedroso de Lima MC, Alves S. Lysosomal Storage Disease-Associated Neuropathy: Targeting Stable Nucleic Acid Lipid Particle (SNALP)-Formulated siRNAs to the Brain as a Therapeutic Approach

More than two thirds of Lysosomal Storage Diseases (LSDs) present central nervous system involvement. Nevertheless, only one of the currently approved therapies has an impact on neuropathology. Therefore, alternative approaches are under development, either addressing the underlying enzymatic defect or its downstream consequences. Also under study is the possibility to block substrate accumulation upstream, by promoting a decrease of its synthesis. This concept is known as substrate reduction therapy and may be triggered by several molecules, such as small interfering RNAs (siRNAs). siRNAs promote RNA interference, a naturally occurring sequence-specific post-transcriptional gene-silencing mechanism, and may target virtually any gene of interest, inhibiting its expression. Still, naked siRNAs have limited cellular uptake, low biological stability, and unfavorable pharmacokinetics. Thus, their translation into clinics requires proper delivery methods. One promising platform is a special class of liposomes called stable nucleic acid lipid particles (SNALPs), which are characterized by high cargo encapsulation efficiency and may be engineered to promote targeted delivery to specific receptors. Here, we review the concept of SNALPs, presenting a series of examples on their efficacy as siRNA nanodelivery systems. By doing so, we hope to unveil the therapeutic potential of these nanosystems for targeted brain delivery of siRNAs in LSDs.

The Complex Network between MYC Oncogene and microRNAs in Gastric Cancer: An Overview

Despite the advancements in cancer treatments, gastric cancer is still one of the leading causes of death worldwide. In this context, it is of great interest to discover new and more effective ways of treating this disease. Accumulated evidences have demonstrated the amplification of 8q24.21 region in gastric tumors. Furthermore, this is the region where the widely known MYC oncogene and different microRNAs are located. MYC deregulation is key in tumorigenesis in various types of tissues, once it is associated with cell proliferation, survival, and drug resistance. microRNAs are a class of noncoding RNAs that negatively regulate the protein translation, and which deregulation is related with gastric cancer development. However, little is understood about the interactions between microRNAs and MYC. Here, we overview the MYC role and its relationship with the microRNAs network in gastric cancer aiming to identify potential targets useful to be used in clinic, not only as biomarkers, but also as molecules for development of promising therapies.

A window into the brain: Tools to assess pre-clinical efficacy of biomaterials-based therapies on central nervous system disorders

Therapeutic conveyance into the brain is a cardinal requirement for treatment of diverse central nervous system (CNS) disorders and associated pathophysiology. Effectual shielding of the brain by the blood-brain barrier (BBB) sieves out major proportion of therapeutics with the exception of small lipophilic molecules. Various nano-delivery systems (NDS) provide an effective solution around this obstacle owing to their small size and targeting properties. To date, these systems have been used for several pre-clinical disease models including glioma, neurodegenerative diseases and psychotic disorders. An efficacy screen for these systems involves a test battery designed to probe into the multiple facets of therapeutic delivery. Despite their wide application in redressing various disease targets, the efficacy evaluation strategies for all can be broadly grouped into four modalities, namely: histological, bio-imaging, molecular and behavioural. This review presents a comprehensive insight into all of these modalities along with their strengths and weaknesses as well as perspectives on an ideal design for a panel of tests to screen brain nano-delivery systems.

Extrahepatic Targeting of Oligonucleotides with Receptor-Binding Non-Immunoglobulin Scaffold Proteins

Although recent clinical successes of antisense, splice-switching, and siRNA oligonucleotides have established the therapeutic utility of this novel class of medicines, the efficient systemic application for non-liver targets remains elusive. Exploitation of active receptor-mediated targeting followed by efficient and productive cellular uptake is required for enabling the therapy of extrahepatic diseases on the expressional level. Evasion of liver accumulation and organ-specific targeting and also efficient cytosolic delivery after endosomal internalization are currently insufficiently solved issues. Lipid and polymer-based nanoparticles can be engineered for efficient cellular uptake and enhancement of endosomal escape, but are characterized by preferential liver accumulation based on biodistribution largely determined by particle size and biophysical properties. Oligonucleotide bioconjugates with receptor-binding ligands have been evolved for highly efficient targeting, but frequently result in a large extent of endosomal entrapment and consequently a lack of sufficient cytosolic concentrations. Non-immunoglobulin protein-based receptor recognition affords high cell-type selectivity and is promising for achieving nonhepatic oligonucleotide targeting. The use of such novel protein scaffolds, including designed ankyrin repeat proteins (DARPins), for oligonucleotide delivery is attractive for achieving effective tissue targeting. Issues for further development and optimization to advance approaches for extrahepatic oligonucleotide delivery by nanoparticles or bioconjugates are discussed.

Therapeutic targeting of non-coding RNAs in cancer

The majority of the human genome encodes RNAs that do not code for proteins. These non-coding RNAs (ncRNAs) affect normal expression of the genes, including oncogenes and tumour suppressive genes, which make them a new class of targets for drug development in cancer. Although microRNAs (miRNAs) are the most studied regulatory ncRNAs to date, and miRNA-targeted therapeutics have already reached clinical development, including the mimics of the tumour suppressive miRNAs miR-34 and miR-16, which reached phase I clinical trials for the treatment of liver cancer and mesothelioma, the importance of long non-coding RNAs (lncRNAs) is increasingly being recognised. Here, we describe obstacles and advances in the development of ncRNA therapeutics and provide the comprehensive overview of the ncRNA chemistry and delivery technologies. Furthermore, we summarise recent knowledge on the biological functions of miRNAs and their involvement in carcinogenesis, and discuss the strategies of their therapeutic manipulation in cancer. We review also the emerging insights into the role of lncRNAs and their potential as targets for novel treatment paradigms. Finally, we provide the up-to-date summary of clinical trials involving miRNAs and future directions in the development of ncRNA therapeutics.

Therapeutic effects of protein kinase N3 small interfering RNA and doxorubicin combination therapy on liver and lung metastases

It has been reported that suppression of protein kinase N3 (PKN3) expression in vascular and lymphatic endothelial cells results in the inhibition of tumor progression and lymph node metastasis formation. The present study investigated whether combination therapy of small interfering RNA (siRNA) against PKN3 and doxorubicin (DXR) could increase therapeutic efficacy against liver and lung metastases. In vitro transfection of PKN3 siRNA into PKN3-positive MDA-MB-231, LLC, and Colon 26 cells and PKN3-negative MCF-7 cells did not inhibit cell growth and did not increase sensitivity to DXR. However, following in vivo treatment, PKN3 siRNA suppressed the growth of liver MDA-MB-231 and lung LLC and MCF-7 metastases, although combination therapy with DXR did not increase the therapeutic efficacy. By contrast, in liver MCF-7 metastases, PKN3 siRNA or DXR alone did not exhibit significant inhibition of tumor growth, but their combination significantly improved therapeutic efficacy. Treatment of liver MDA-MB-231 metastases with PKN3 siRNA induced a change in vasculature structure via suppression of PKN3 mRNA expression. PKN3 siRNA may induce antitumor effects in lung and liver metastases by suppression of PKN3 expression in stroma cells, such as endothelial cells. From these findings, PKN3 siRNA alone or in combination with DXR may reduce the tumor growth of liver and lung metastases regardless of PKN3 expression in tumor cells.

Protein-lipid nanohybrids as emerging platforms for drug and gene delivery: Challenges and outcomes

Nanoparticulate drug delivery systems have been long used to deliver a vast range of drugs and bioactives owing to their ability to demonstrate novel physical, chemical, and/or biological properties. An exponential growth has spurred in research and development of these nanocarriers which led to the evolution of a great number of diverse nanosystems including liposomes, nanoemulsions, solid lipid nanoparticles (SLNs), micelles, dendrimers, polymeric nanoparticles (NPs), metallic NPs, and carbon nanotubes. Among them, lipid-based nanocarriers have made the largest progress whether commercially or under development. Despite this progress, these lipid-based nanocarriers suffer from several limitations that led to the development of many protein-coated lipid nanocarriers. To less extent, protein-based nanocarriers suffer from limitations that led to the fabrication of some lipid bilayer enveloping protein nanocarriers. This review discusses in-depth some limitations associated with the lipid-based or protein-based nanocarriers and the fruitful outcomes brought by protein-lipid hybridization. Also discussed are the various hybridization techniques utilized to formulate these protein-lipid nanohybrids and the mechanisms involved in the drug loading process.

Non-Viral Nucleic Acid Delivery Strategies to the Central Nervous System

With an increased prevalence and understanding of central nervous system (CNS) injuries and neurological disorders, nucleic acid therapies are gaining promise as a way to regenerate lost neurons or halt disease progression. While more viral vectors have been used clinically as tools for gene delivery, non-viral vectors are gaining interest due to lower safety concerns and the ability to deliver all types of nucleic acids. Nevertheless, there are still a number of barriers to nucleic acid delivery. In this focused review, we explore the in vivo challenges hindering non-viral nucleic acid delivery to the CNS and the strategies and vehicles used to overcome them. Advantages and disadvantages of different routes of administration including: systemic injection, cerebrospinal fluid injection, intraparenchymal injection and peripheral administration are discussed. Non-viral vehicles and treatment strategies that have overcome delivery barriers and demonstrated in vivo gene transfer to the CNS are presented. These approaches can be used as guidelines in developing synthetic gene delivery vectors for CNS applications and will ultimately bring non-viral vectors closer to clinical application.

Transferrin functionalized chitosan-PEG nanoparticles for targeted delivery of paclitaxel to cancer cells

The present investigation was aimed to utilize the stealth property of polyethylene glycol (PEG) modified chitosan nanoparticles (NPs) and active targeting function of transferrin (Tf) by transferrin receptor-mediated endocytosis to promote drug delivery to cancer cells. Paclitaxel (PTX) loaded nanoparticles (PTX-NP) were prepared by solvent evaporation method; PEGylation was carried out by coupling amine group present on the surface of NPs with hydroxyl group present on the PEG (NP-PEG). Tf conjugation was carried out by coupling carboxylic group present on the surface of ligand and hydroxyl group present on the PEG (NP-PEG-Tf). The uptake of NP-PEG-Tf into cancer cells was found to be higher as compared to non-targeted NPs. Compared with free PTX, PTX-NPs and PTX-NPs-PEG, the PTX-NPs-PEG-Tf demonstrated higher cytotoxicity to human Non-Small Cell Lung cancer cell lines (HOP-62), higher intracellular uptake especially in nuclei and lower hemolytic toxicity. Tf conjugated NPs showed increased retention time in the lungs as well as in blood. These findings indicate that Tf conjugated PEGylated nanoparticles are promising nanoconstructs for the delivery of anti-cancer drugs to cancer cells.

Inorganic nanovectors for nucleic acid delivery

Nucleic acids show immense potential to treat cancer, acquired immune deficiency syndrome, neurological diseases and other incurable human diseases. Upon systemic administration, they encounter a series of barriers and hence barely reach the site of action, the cell. Intracellular delivery of nucleic acids is facilitated by nanovectors, both viral and non-viral. A major advantage of non-viral vectors over viral vectors is safety. Nanovectors evaluated specifically for nucleic acid delivery include polyplexes, lipoplexes and other cationic carrier-based vectors. However, more recently there is an increased interest in inorganic nanovectors for nucleic acid delivery. Nevertheless, there is no comprehensive review on the subject. The present review would cover in detail specific properties and types of inorganic nanovectors, their preparation techniques and various biomedical applications as therapeutics, diagnostics and theranostics. Future prospects are also suggested.

PEGylated cyclodextrins as novel siRNA nanosystems: correlations between polyethylene glycol length and nanoparticle stability

Silencing disease-related genes in the central nervous system (CNS) using short interfering RNA (siRNA) holds great promise for treating neurological disorders. Yet, delivery of RNAi therapeutics to the brain poses major challenges to non-viral systems, especially when considering systemic administration. Cationic nanoparticles have been widely investigated for siRNA delivery, but the tendency of these to aggregate in physiological environments limits their intravenous application. Thus, strategies to increase the stability of nanoparticles have been developed. Here, we investigated the ability of modified cationic amphiphilic or PEGylated amphiphilic cyclodextrins (CD) to formulate stable CD.siRNA nanoparticles. To this end, we describe a simple method for post-modification of pre-formed cationic CD.siRNA nanoparticles at their surface using PEGylated CDs of different PEG lengths. PEGylated CD.siRNA nanoparticles presented reduced surface charges and increased stability in physiological salt conditions. Stability of PEGylated CD.siRNA nanoparticles in vitro increased with both PEG length and PEG density at the surface. Furthermore, in a comparative pharmacokinetic study, increased systemic exposure and reduced clearance were achieved with CD-formulations when compared to naked siRNAs. However, no significant differences were observed among non-PEGylated and PEGylated CD.siRNAs suggesting that longer PEG lengths might be required for improving stability in vivo.

Delivery of RNAi therapeutics: work in progress

RNA interference (RNAi) therapeutics appear to offer substantial opportunities for future therapy. However, post-administration RNAi effectors are typically unable to reach disease target cells in vivo without the assistance of a delivery system or vector. The main focus of this review is on lipid-based nanoparticle (LNP) delivery systems in current research and development that have at least been shown to act as effective delivery systems for functional delivery of RNAi effectors to disease target cells in vivo. The potential utility of these LNP delivery systems is growing rapidly, and LNPs are emerging as the preferred synthetic delivery systems in preclinical studies and current nonviral RNAi effector clinical trials. Moreover, studies on LNP-mediated delivery in vivo are leading to the emergence of useful biophysical parameters and physical organic chemistry rules that provide a framework for understanding in vivo delivery behaviors and outcomes. These same parameters and rules should also suggest ways and means to develop next generations of LNPs with genuine utility and long-term clinical viability.

Delivering the promise of small ncRNA therapeutics

Small non-coding RNA (ncRNA) therapeutics make use of small ncRNA effectors for desired therapeutic purposes that are essentially short (10–20 kD) RNA segments. These small ncRNA effectors are potentially tremendously powerful therapeutic agents, but are typically unable to reach disease target cells in vivo without the assistance of a delivery system or vector. The main focus of this review is the use of lipid-based nanoparticles (LNPs) for the functional delivery of small ncRNA effectors in vivo. LNPs appear to be amongst the most effective delivery systems currently available for this purpose. Moreover, studies on LNP-mediated delivery in vivo are leading to the emergence of useful biophysical parameters and physical organic chemistry rules that provide a framework for understanding LNP-mediated in vivo delivery behaviors and outcomes. These same parameters and rules should also suggest ways and means to develop next generations of LNPs with genuine utility and long-term clinical viability.

Oligonucleotide-based therapy for neurodegenerative diseases

Molecular genetics insight into the pathogenesis of several neurodegenerative diseases, such as Alzheimer׳s disease, Parkinson׳s disease, Huntington׳s disease and amyotrophic lateral sclerosis, encourages direct interference with the activity of neurotoxic genes or the molecular activation of neuroprotective pathways. Oligonucleotide-based therapies are recently emerging as an efficient strategy for drug development and these can be employed as new treatments of neurodegenerative states. Here we review advances in this field in recent years which suggest an encouraging assessment that oligonucleotide technologies for targeting of RNAs will enable the development of new therapies and will contribute to preservation of brain integrity.

Dendrimer advances for the central nervous system delivery of therapeutics

The effectiveness of noninvasive treatment for central nervous system (CNS) diseases is generally limited by the poor access of therapeutic agents into the CNS. Most CNS drugs cannot permeate into the brain parenchyma because of the blood-brain barrier (BBB), and overcoming this has become one of the most significant challenges in the development of CNS therapeutics. Rapid advances in nanotechnology have provided promising solutions to this challenge. This review discusses the latest applications of dendrimers in the treatment of CNS diseases with an emphasis on brain tumors. Dendrimer-mediated drug delivery, imaging, and diagnosis are also reviewed. The toxicity, biodistribution, and transport mechanisms in dendrimer-mediated delivery of CNS therapeutic agents bypassing or crossing the BBB are also discussed. Future directions and major challenges of dendrimer-mediated delivery of CNS therapeutic agents are included.

Delivery of therapeutic nucleic acids via transferrin and transferrin receptors: lipoplexes and other carriers

INTRODUCTION

The overexpression of transferrin (Tf) receptors on cancer cells renders them a useful target for the delivery of small-molecule drugs and nucleic acid therapeutics to these cells. This approach could alleviate the non-target effects of the drugs.

AREAS COVERED

The function of the Tf receptor, the development of Tf-lipid-DNA complexes (Tf lipoplexes), therapeutic use of lipoplexes and polymer-DNA complexes (poylplexes), and the therapeutic use of Tf-lipoplexes and anti-Tf-receptor antibody-lipoplexes are outlined. The literature search for this review was based primarily on the terms 'lipoplexes,' 'lipopolyplexes' 'transferrin,' 'transferrin receptor,' and 'gene therapy.' However, the review was not intended to be comprehensive.

EXPERT OPINION

Complexes of Tf with cationic liposomes and nucleic acids, or liposomes with covalently attached Tf or anti-transferrin receptor antibodies have been used for the delivery of therapeutic genes, antisense oligodeoxynucleotides, and short interfering RNA. Although such targeted nonviral delivery vehicles may benefit from further enhancement of their efficacy, current achievements at the cell culture and animal model level should be translated into clinical applications, restricted initially to localized delivery into accessible tissues to avoid potential systemic side-effects and non-target delivery.

Current trends in the use of liposomes for tumor targeting

The use of liposomes for drug delivery began early in the history of pharmaceutical nanocarriers. These nanosized, lipid bilayered vesicles have become popular as drug delivery systems owing to their efficiency, biocompatibility, nonimmunogenicity, enhanced solubility of chemotherapeutic agents and their ability to encapsulate a wide array of drugs. Passive and ligand-mediated active targeting promote tumor specificity with diminished adverse off-target effects. The current field of liposomes focuses on both clinical and diagnostic applications. Recent efforts have concentrated on the development of multifunctional liposomes that target cells and cellular organelles with a single delivery system. This review discusses the recent advances in liposome research in tumor targeting.

Non-viral nanosystems for gene and small interfering RNA delivery to the central nervous system: formulating the solution

The application of gene and RNAi-based therapies to the central nervous system (CNS), for neurological and neurodegenerative disease, offers immense potential. The issue of delivery to the target site remains the single greatest barrier to achieving this. There are challenges to gene and siRNA (small interfering RNA) delivery which are specific to the CNS, including the post-mitotic nature of neurons, their resistance to transfection and the blood-brain barrier. Viral vectors are highly efficient and have been used extensively in pre-clinical studies for CNS diseases. However, non-viral delivery offers an exciting alternative. In this review, we will discuss the extracellular and intracellular barriers to gene and siRNA delivery in the CNS. Our focus will be directed towards various non-viral strategies used to overcome these barriers. In this regard, we describe selected non-viral vectors and categorise them according to the barriers that they overcome by their formulation and targeting strategies. Some of the difficulties associated with non-viral vectors such as toxicity, large-scale manufacture and route of administration are discussed. We provide examples of optimised formulation approaches and discuss regulatory hurdles to clinical validation. Finally, we outline the components of an "ideal" formulation, based on a critical analysis of the approaches highlighted throughout the review.

Tumor-targeted Chlorotoxin-coupled Nanoparticles for Nucleic Acid Delivery to Glioblastoma Cells: A Promising System for Glioblastoma Treatment

The present work aimed at the development and application of a lipid-based nanocarrier for targeted delivery of nucleic acids to glioblastoma (GBM). For this purpose, chlorotoxin (CTX), a peptide reported to bind selectively to glioma cells while showing no affinity for non-neoplastic cells, was covalently coupled to liposomes encapsulating antisense oligonucleotides (asOs) or small interfering RNAs (siRNAs). The resulting targeted nanoparticles, designated CTX-coupled stable nucleic acid lipid particles (SNALPs), exhibited excellent features for in vivo application, namely small size (<180 nm) and neutral surface charge. Cellular association and internalization studies revealed that attachment of CTX onto the liposomal surface enhanced particle internalization into glioma cells, whereas no significant internalization was observed in noncancer cells. Moreover, nanoparticle-mediated miR-21 silencing in U87 human GBM and GL261 mouse glioma cells resulted in increased levels of the tumor suppressors PTEN and PDCD4, caspase 3/7 activation and decreased tumor cell proliferation. Preliminary in vivo studies revealed that CTX enhances particle internalization into established intracranial tumors. Overall, our results indicate that the developed targeted nanoparticles represent a valuable tool for targeted nucleic acid delivery to cancer cells. Combined with a drug-based therapy, nanoparticle-mediated miR-21 silencing constitutes a promising multimodal therapeutic approach towards GBM.

Click-modified cyclodextrins as nonviral vectors for neuronal siRNA delivery

RNA interference (RNAi) holds great promise as a strategy to further our understanding of gene function in the central nervous system (CNS) and as a therapeutic approach for neurological and neurodegenerative diseases. However, the potential for its use is hampered by the lack of siRNA delivery vectors which are both safe and highly efficient. Cyclodextrins have been shown to be efficient and low toxicity gene delivery vectors in various cell types in vitro. However, to date, they have not been exploited for delivery of oligonucleotides to neurons. To this end, a modified β-cyclodextrin (CD) vector was synthesized, which complexed siRNA to form cationic nanoparticles of less than 200 nm in size. Furthermore, it conferred stability in serum to the siRNA cargo. The in vitro performance of the CD in both immortalized hypothalamic neurons and primary hippocampal neurons was evaluated. The CD facilitated high levels of intracellular delivery of labeled siRNA, while maintaining at least 80% cell viability. Significant gene knockdown was achieved, with a reduction in luciferase expression of up to 68% and a reduction in endogenous glyceraldehyde phosphate dehydrogenase (GAPDH) expression of up to 40%. To our knowledge, this is the first time that a modified CD has been used as a safe and efficacious vector for siRNA delivery into neuronal cells.

Medicinal chemistry based approaches and nanotechnology-based systems to improve CNS drug targeting and delivery

The central nervous system (CNS) is protected by various barriers, which regulate nervous tissue homeostasis and control the selective and specific uptake, efflux, and metabolism of endogenous and exogenous molecules. Among these barriers is the blood-brain barrier (BBB), a physical and physiological barrier that filters very efficiently and selectively the entry of compounds from the blood to the brain and protects nervous tissue from harmful substances and infectious agents present in the bloodstream. The BBB also prevents the entry of potential drugs. As a result, various drug targeting and delivery strategies are currently being developed to enhance the transport of drugs from the blood to the brain. Following a general introduction, we briefly overview in this review article the fundamental physiological properties of the BBB. Then, we describe current strategies to bypass the BBB (i.e., invasive methods, alternative approaches, and temporary opening) and to cross it (i.e., noninvasive approaches). This section is followed by a chapter addressing the chemical and technological solutions developed to cross the BBB. A special emphasis is given to prodrug-targeting approaches and targeted nanotechnology-based systems, two promising strategies for BBB targeting and delivery of drugs to the brain.

Intranasal delivery of HMGB1 siRNA confers target gene knockdown and robust neuroprotection in the postischemic brain

Noninvasive intranasal drug administration has been noted to allow direct delivery of drugs to the brain. In the present study, the therapeutic efficacy of intranasal small interfering RNA (siRNA) delivery was investigated in the postischemic rat brain. Fluorescein isothiocyanate (FITC)-labeled control siRNA was delivered intranasally in normal adult rats using e-PAM-R, a biodegradable PAMAM dendrimer, as gene carrier. Florescence-tagged siRNA was found in the cytoplasm and processes of neurons and of glial cells in many brain regions, including the hypothalamus, amygdala, cerebral cortex, and striatum, in 1 hour after infusion, and the FITC-fluorescence was continuously detected for at least 12 hours. When siRNA for high mobility group box 1 (HMGB1), which functions as an endogenous danger molecule and aggravates inflammation, was delivered intranasally, the target gene was significantly depleted in many brain regions, including the prefrontal cortex and striatum. More importantly, intranasal delivery of HMGB1 siRNA markedly suppressed infarct volume in the postischemic rat brain (maximal reduction to 42.8 ± 5.6% at 48 hours after 60 minutes middle cerebral artery occlusion (MCAO)) and this protective effect was manifested by recoveries from neurological and behavioral deficits. These results indicate that the intranasal delivery of HMGB1 siRNA offers an efficient means of gene knockdown-mediated therapy in the ischemic brain.

Local siRNA delivery by non-viral vectors

Since the discovery of the RNA interference (RNAi) phenomenon, RNAi-based therapies now present a huge potential for the treatment of many diseases, including inflammatory and infectious diseases and cancers. While numerous reports have described the development of small interfering RNA (siRNA) delivery systems for in-vivo applications, only a small number of siRNA-based therapies are currently under clinical development. This is essentially due to the lack of efficient and safe siRNA delivery systems for intravenous administration. However, the delivery of siRNA after local injection could represent an attractive route of administration to limit the issues of toxicity associated with systemic injection. We will describe here the different synthetic vectors which have been developed for the local delivery of siRNA in various organs.

Progress toward in vivo use of siRNAs-II

RNA interference (RNAi) has been extensively employed for in vivo research since its use was first demonstrated in mammalian cells 10 years ago. Design rules have improved, and it is now routinely possible to obtain reagents that suppress expression of any gene desired. At the same time, increased understanding of the molecular basis of unwanted side effects has led to the development of chemical modification strategies that mitigate these concerns. Delivery remains the single greatest hurdle to widespread adoption of in vivo RNAi methods. However, exciting advances have been made and new delivery systems under development may help to overcome these barriers. This review discusses advances in RNAi biochemistry and biology that impact in vivo use and provides an overview of select publications that demonstrate interesting applications of these principles. Emphasis is placed on work with synthetic, small interfering RNAs (siRNAs) published since the first installment of this review which appeared in 2006.

RNAi medicine for the brain: progresses and challenges

RNAi interference (RNAi) is a powerful gene silencing technology that has immense potential for treating a vast array of human ailments, for which suppressing disease-associated genes may provide clinical benefit. Here, we review the development of RNAi as a therapeutic modality for neurodegenerative diseases affecting the central nervous system (CNS). We overview promising preclinical data for the application of RNAi in the CNS and discuss key challenges (e.g. delivery and specificity) that remain as these approaches transition to the clinic.