Efficient encapsulation of antisense oligonucleotides in lipid vesicles using ionizable aminolipids: formation of novel small multilamellar vesicle structures

Biomaterials in siRNA Delivery: A Comprehensive Review

With the dearth of effective treatment options for prominent diseases including Ebola and cancer, RNA interference (RNAi), a sequence-specific mechanism for genetic regulation that can silence nearly any gene, holds the promise of unlimited potential in treating illness ever since its discovery in 1999. Given the large size, unstable tertiary structure in physiological conditions and negative charge of small interfering RNAs (siRNAs), the development of safe and effective delivery vehicles is of critical importance in order to drive the widespread use of RNAi therapeutics into clinical settings. Immense amounts of time and billions of dollars have been devoted into the design of novel and diverse delivery strategies, and there are a handful of delivery systems that have been successfully translated into clinic. This review provides an introduction to the in vivo barriers that need to be addressed by siRNA delivery systems. We also discuss the progress up to the most effective and clinically advanced siRNA delivery systems including liposomal, polymeric and siRNA conjugate delivery systems, as well as their design to overcome the challenges.

Lipid Nanovectors to Deliver RNA Oligonucleotides in Cancer

The growing knowledge on the mechanisms of gene silencing and gene regulation by non-coding RNAs (ncRNA), mainly small interfering RNA (siRNA) and microRNA (miRNA), is providing a significant boost to the development of new therapeutic strategies for the treatment of cancer. However, the design of RNA-based therapeutics is hampered by biopharmaceutical issues, thus requiring the use of suitable delivery strategies. In this regards, lipid nanovectors have been successfully investigated to deliver RNA in different forms of cancer. Compared to other biomaterials, lipids offer advantages such as biocompatibility, biodegradability, easy production, low cost, limited toxicity and immunogenicity. The possibility to formulate these materials in the form of nanovectors allows overcoming biopharmaceutical issues associated to the therapeutic use of RNA, with the possibility to target tumors. This review takes stock of the main lipid nanovectors proposed to deliver ncRNA. For each considered delivery strategy, the rational design and the most meaningful in vitro and in vivo results are reported and discussed.

A Single Methylene Group in Oligoalkylamine-Based Cationic Polymers and Lipids Promotes Enhanced mRNA Delivery

The development of chemically modified mRNA holds great promise as a new class of biologic therapeutics. However, the intracellular delivery and endosomal escape of mRNA encapsulated in nanoparticles has not been systematically investigated. Here, we synthesized a diverse set of cationic polymers and lipids from a series of oligoalkylamines and subsequently characterized their mRNA delivery capability. Notably, a structure with an alternating alkyl chain length between amines showed the highest transfection efficiency, which was linked to a high buffering capacity in a narrow range of pH 6.2 to 6.5. Variation in only one methylene group resulted in enhanced mRNA delivery to both the murine liver as well as porcine lungs after systemic or aerosol administration, respectively. These findings reveal a novel fundamental structure-activity relationship for the delivery of mRNA that is independent of the class of mRNA carrier and define a promising new path of exploration in the field of mRNA therapeutics.

Targeting Liposomal Nanomedicine to Cancer Therapy

Drug delivery systems (DDS) are designed to improve the pharmacological and therapeutic effect. In the past few decades, there are some problems that impeded applications of particulate DDS have been resolved, with several DDS formulations of anticancer now approved for clinical use. Liposomal nanoparticles (LNs) encapsulating therapeutic agents have been recognized as one of the most advanced classes of DDS. Liposomal nanoparticles (LNs) could encapsulate both conventional anticancer drugs and the new genetic drugs with several properties such as high drug-to-lipid ratio, excellent retention of drug and a long circulation lifetime. These excellent properties of LNs have the potentials to offer new treatments in area of cancer therapy. Here, we will discuss recent advances in this field involving conventional anticancer drugs as well as the new genetic drugs.

Delivery of siRNA Complexed with Palmitoylated α-Peptide/β-Peptoid Cell-Penetrating Peptidomimetics: Membrane Interaction and Structural Characterization of a Lipid-Based Nanocarrier System

Proteolytically stable α-peptide/β-peptoid peptidomimetics constitute promising cell-penetrating carrier candidates exhibiting superior cellular uptake as compared to commonly used cell-penetrating peptides (CPPs). The aim of the present study was to explore the potential of these peptidomimetics for delivery of small interfering RNA (siRNA) to the cytosol by incorporation of a palmitoylated peptidomimetic construct into a cationic lipid-based nanocarrier system. The optimal construct was selected on the basis of the effect of palmitoylation and the influence of the length of the peptidomimetic on the interaction with model membranes and the cellular uptake. Palmitoylation enhanced the peptidomimetic adsorption to supported lipid bilayers as studied by ellipsometry. However, both palmitoylation and increased peptidomimetic chain length were found to be beneficial in the cellular uptake studies using fluorophore-labeled analogues. Thus, the longer palmitoylated peptidomimetic was chosen for further formulation of siRNA in a dioleoylphosphatidylethanolamine/cholesteryl hemisuccinate (DOPE/CHEMS) nanocarrier system, and the resulting nanoparticles were found to mediate efficient gene silencing in vitro. Cryo-transmission electron microscopy (cryo-TEM) revealed multilamellar, onion-like spherical vesicles, and small-angle X-ray scattering (SAXS) analysis confirmed that the majority of the lipids in the nanocarriers were organized in lamellar structures, yet coexisted with a hexagonal phase, which is important for efficient nanocarrier-mediated endosomal escape of siRNA ensuring cytosolic delivery. The present work is a proof-of-concept for the use of α-peptides/β-peptoid peptidomimetics in an efficient delivery system that may be more generally exploited for the intracellular delivery of biomacromolecular drugs.

Aerosol Delivery of siRNA to the Lungs. Part 2: Nanocarrier-based Delivery Systems

In this article, applications of engineered nanoparticles containing siRNA for inhalation delivery are reviewed and discussed. Diseases with identified protein malfunctions may be mitigated through the use of well-designed siRNA therapeutics. The inhalation route of administration provides local delivery of siRNA therapeutics to the lungs for various pulmonary diseases. A siRNA delivery system can be used to overcome the barriers of pulmonary delivery, such as anatomical barriers, mucociliary clearance, cough clearance, and alveolar macrophage clearance. Apart from naked siRNA aerosol delivery, previously studied siRNA carrier systems include those of lipidic, polymeric, peptide, or inorganic origin. These delivery systems can achieve pulmonary delivery through the generation of an aerosol via an inhaler or nebulizer. The preparation methodologies for these siRNA nanocarrier systems will be discussed herein. The use of inhalable nanocarrier siRNA delivery systems have barriers to their effective delivery, but overcoming these constraints while formulating a safe and effective delivery system will offer unique advances to the field of inhaled medicine.

Pieter Cullis: an outstanding lipid biophysicist, drug delivery scientist, educator, and entrepreneur

There are much said about Pieter Cullis in this special volume honoring him. He was the pioneer to study the role of hexagonal HII phase in membrane fusion and the one who applied this concept for the design of lipid nanoparticles. He was also the first to utilize remote loading techniques for the delivery of amphipathic bases. At the same time, he is a tremendous entrepreneur and an excellent mentor. He is, without doubt, an exceptional scientist and set us an excellent model to follow.

Nanoparticle delivery systems for siRNA-based therapeutics

RNA interference (RNAi) is a naturally occurring endogenous regulatory process in which the short double-stranded RNA causes sequence-specific post-transcriptional gene silencing.

Enhancing the pharmacokinetic/pharmacodynamic properties of therapeutic nucleotides using lipid nanoparticle systems

Although activity has been reported in vivo, free nucleic acid-based drugs are rapidly degraded and cleared following systemic administration. To address these challenges and improve the potency and bioavailability of genetic drugs, significant efforts have been made to develop effective delivery systems of which lipid nanoparticles (LNP) represent the most advanced technology currently available. In this review, we will describe and discuss the improvements to the pharmacokinetic and pharmacodynamic properties of nucleic acid-based drugs mediated by LNP delivery. It is envisioned that the significant improvements in potency and safety, largely driven by the development of LNP encapsulated siRNA drugs, will be translatable to other types of genetic drugs and enable the rapid development of potent molecular tools and drugs.

Gene interference strategies as a new tool for the treatment of prostate cancer

Prostate cancer (PCa) is one of the most common cancer in men. It affects older men and the incidence increases with age; the median age at diagnosis is 67 years. The diagnosis of PCa is essentially based on three tools: digital rectal exam, serum concentration of prostate specific antigen, and transrectal ultrasound-guided biopsy. Currently, the therapeutic treatments of this cancer are different and range from the prostatectomy to hormonal therapy, to radiation therapy, to immunotherapy, and to chemotherapy. However, additional efforts are required in order to find new weapons for the treatment of metastatic setting of disease. The purpose of this review is to highlight new therapeutic strategies based on gene interference; in fact, numerous siRNA and miRNA in the therapeutic treatment of PCa are reported below.

Lipid nanoparticles for short interfering RNA delivery

The discovery of RNA interference (RNAi) in mammalian cells has created a new class of therapeutics based on the reversible silencing of specific disease-causing genes. This therapeutic potential depends on the ability to deliver inducers of RNAi, such as short-interfering RNA (siRNA) and micro-RNA (miRNA), to cells of target tissues. This chapter reviews various challenges and delivery strategies for siRNA, with a particular focus on the development of lipid nanoparticle (LNP) delivery technologies. Currently, LNP delivery systems are the most advanced technology for systemic delivery of siRNA, with numerous formulations under various stages of clinical trials. We also discuss methods to improve gene silencing potency of LNP-siRNA, as well as application of LNP technologies beyond siRNA to the encapsulation of other nucleic acids such as mRNA and clustered regularly interspaced short palindromic repeats (CRISPR).

Delivery of oligonucleotides with lipid nanoparticles

Since their inception in the 1980s, oligonucleotide-based (ON-based) therapeutics have been recognized as powerful tools that can treat a broad spectrum of diseases. The discoveries of novel regulatory methods of gene expression with diverse mechanisms of action are still driving the development of novel ON-based therapeutics. Difficulties in the delivery of this class of therapeutics hinder their in vivo applications, which forces drug delivery systems to be a prerequisite for clinical translation. This review discusses the strategy of using lipid nanoparticles as carriers to deliver therapeutic ONs to target cells in vitro and in vivo. A discourse on how chemical and physical properties of the lipid materials could be utilized during formulation and the resulting effects on delivery efficiency constitutes the major part of this review.

Lipid nanoparticle delivery systems for siRNA-based therapeutics

Therapeutics based on small interfering RNA (siRNA) have a huge potential for the treatment of disease but requires sophisticated delivery systems for in vivo applications. Lipid nanoparticles (LNP) are proven delivery systems for conventional small molecule drugs with over eight approved LNP drugs. Experience gained in the clinical development of LNP for the delivery of small molecules, combined with an understanding of the physical properties of lipids, can be applied to design LNP systems for in vivo delivery of siRNA. In particular, cationic lipids are required to achieve efficient encapsulation of oligonucleotides; however, the presence of a charge on LNP systems can result in toxic side effects and rapid clearance from the circulation. To address these problems, we have developed ionizable cationic lipids with pKa values below 7 that allow oligonucleotide encapsulation at low pH (e.g., pH 4) and a relatively neutral surface at physiological pH. Further optimization of cationic lipids to achieve maximized endosomal destabilization following uptake has resulted in LNP siRNA systems that can silence genes in hepatocytes at doses as low as 0.005 mg siRNA/kg body weight in mouse models. These systems have been shown to be highly effective clinically, with promising results for the treatment of hypercholesterolemia and transthyretin-induced amyloidosis among others. More LNP siRNA therapeutics, targeting different tissues and diseases, are expected to become available in the near future.

Systemic delivery of stable siRNA-encapsulating lipid vesicles: optimization, biodistribution, and tumor suppression

Lipid-based nanoparticles are considered as promising candidates for delivering siRNA into the cytoplasm of targeted cells. However, in vivo efficiency of these nanoparticles is critically dependent on formulation strategies of lipid-siRNA complexes. Adsorption of serum proteins to lipid-siRNA complexes and its charge determine siRNA degradation and serum half-life, thus significantly altering the bioavailability of siRNA. To address these challenges, we developed a formulation comprising dihydroxy cationic lipid, N,N-di-n-hexadecyl-N,N-dihydroxyethylammonium chloride (DHDEAC), cholesterol, and varying concentrations of 1,2-distearoryl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol-2000)] (DSPE-PEG 2000). Using an ethanol dilution method, addition of these lipids to siRNA solution leads to formation of stable and homogeneous population of siRNA-encapsulated vesicles (SEVs). Biodistribution of these SEVs, containing 5 mol % of DSPE-PEG 2000 in xenograft mice, as monitored by live animal imaging and fluorescence microscopy, revealed selective accumulation in the tumor. Remarkably, four intravenous injections of the modified vesicles with equimolar amounts of siRNA targeting ErbB2 and AURKB genes led to significant gene silencing and concomitant tumor suppression in the SK-OV-3 xenograft mouse model. Safety parameters as evaluated by various markers of hepatocellular injury indicated the nontoxic nature of this formulation. These results highlight improved pharmacokinetics and effective in vivo delivery of siRNA by DHDEAC-based vesicles.

Biophysical, biopharmaceutical and toxicological significance of biomedical nanoparticles

Understanding of interplay between nanoparticles physicochemical and biophysical properties, and their impact on pharmacokinetic biodistribution and toxicological properties help designing of appropriate nanoparticle products for biomedical applications.

Shielding of Lipid Nanoparticles for siRNA Delivery: Impact on Physicochemical Properties, Cytokine Induction, and Efficacy

Formulation of short interfering RNA (siRNA) into multicomponent lipid nanoparticles (LNP) is an effective strategy for hepatic delivery and therapeutic gene silencing. This study systematically evaluated the effect of polyethylene glycol (PEG) density on LNP physicochemical properties, innate immune response stimulation, and in vivo efficacy. Increased PEG density not only shielded LNP surface charge but also reduced hemolytic activity, suggesting the formation of a steric barrier. In addition, increasing the PEG density reduced LNP immunostimulatory potential as reflected in cytokine induction both in vivo and in vitro. Higher PEG density also hindered in vivo efficacy, presumably due to reduced association with apolipoprotein E (ApoE), a protein which serves as an endogenous targeting ligand to hepatocytes. This effect could be overcome by incorporating an exogenous targeting ligand into the highly shielded LNPs, thereby circumventing the requirement for ApoE association. Therefore, these studies provide useful information for the rational design of LNP-based siRNA delivery systems with an optimal safety and efficacy profile.

Instructive nanofibrous scaffold comprising runt-related transcription factor 2 gene delivery for bone tissue engineering

Inducer molecules capable of regulating mesenchymal stem cell differentiation into specific lineages have proven effective in basic science and in preclinical studies. Runt-related transcription factor 2 (RUNX2) is considered to be the central gene involved in the osteoblast phenotype induction, which may be advantageous for inducing bone tissue regeneration. This work envisions the development of a platform for gene delivery, combining liposomes as gene delivery devices, with electrospun nanofiber mesh (NFM) as a tissue engineering scaffold. pDNA-loaded liposomes were immobilized at the surface of functionalized polycaprolactone (PCL) NFM. Human bone-marrow-derived mesenchymal stem cells (hBMSCs) cultured on RUNX2-loaded liposomes immobilized at the surface of electrospun PCL NFM showed enhanced levels of metabolic activity and total protein synthesis. RUNX2-loaded liposomes immobilized at the surface of electrospun PCL NFMs induce a long-term gene expression of eGFP and RUNX2 by cultured hBMSCs. Furthermore, osteogenic differentiation of hBMSCs was also achieved by the overexpression of other osteogenic markers in medium free of osteogenic supplementation. These findings demonstrate that surface immobilization of RUNX2 plasmid onto elestrospun PCL NFM can produce long-term gene expression in vitro, which may be employed to enhance the osteoinductive properties of scaffolds used for bone tissue engineering strategies.

Extracellular vesicles as drug delivery systems: lessons from the liposome field

Extracellular vesicles (EVs) are membrane-derived particles surrounded by a (phospho)lipid bilayer that are released by cells in the human body. In addition to direct cell-to-cell contact and the secretion of soluble factors, EVs function as another mechanism of intercellular communication. These vesicles are able to efficiently deliver their parental cell-derived molecular cargo to recipient cells, which can result in structural changes at an RNA, protein, or even phenotypic level. For this reason, EVs have recently gained much interest for drug delivery purposes. In contrast to these 'natural delivery systems', synthetic (phospho)lipid vesicles, or liposomes, have been employed as drug carriers for decades, resulting in several approved liposomal nanomedicines used in the clinic. This review discusses the similarities and differences between EVs and liposomes with the focus on features that are relevant for drug delivery purposes such as circulation time, biodistribution, cellular interactions and cargo loading. By applying beneficial features of EVs to liposomes and vice versa, improved drug carriers can be developed which will advance the field of nanomedicines and ultimately improve patient outcomes. While the application of EVs for therapeutic drug delivery is still in its infancy, issues regarding the understanding of EV biogenesis, large-scale production and in vivo interactions need to be addressed in order to develop successful and cost-effective EV-based drug delivery systems.

Next generation delivery system for proteins and genes of therapeutic purpose: why and how?

Proteins and genes of therapeutic interests in conjunction with different delivery systems are growing towards new heights. "Next generation delivery systems" may provide more efficient platform for delivery of proteins and genes. In the present review, snapshots about the benefits of proteins or gene therapy, general procedures for therapeutic protein or gene delivery system, and different next generation delivery system such as liposome, PEGylation, HESylation, and nanoparticle based delivery have been depicted with their detailed explanation.

Effective nanoparticle-based gene delivery by a protease triggered charge switch

Gene carriers made from synthetic materials are of interest in relation to gene therapy but suffer from lack of transfection efficiency upon systemic delivery. To address this problem, a novel lipo-peptide-PEG conjugate constituted by a lipid-anchor, a peptide sensitive to proteases and a poly (ethylene glycol) (PEG) chain is investigated. Utilizing ethanol-mediated nucleic acid encapsulation to prepare lipo-nanoparticles (LNPs), LNPs that are stable in serum are obtained. The LNPs constitute a highly effective gene delivery systems in vitro and possess the right features for further investigation in vivo including a PEG layer and a net negative charge that should ensure long-circulating properties before being activated by proteases in diseased tissue. Protease activation leads to detachment of PEG and a charge switching where the LNPs become positive due to the presence of glutamates in the cleaved peptide moiety. The cationic lipid DOTAP is used mainly to complex DNA and proton titratable DODAP is used to increase endosomal escape and enhance transfection efficiency. The idea of using a mixture of permanently charged and titratable cationic lipids shielded by a protease sensitive negatively charged lipo-peptide-PEG coat appears to be a highly efficient solution for achieving effective non-viral gene delivery and the results warrant further investigations.

A novel nonviral gene delivery system: multifunctional envelope-type nano device

In this review we introduce a new concept for developing a nonviral gene delivery system which we call "Programmed Packaging." Based on this concept, we succeeded in developing a multifunctional envelope-type nano device (MEND), which exerts high transfection activities equivalent to those of an adenovirus in a dividing cell. The use of MEND has been extended to in vivo applications. PEG/peptide/DOPE ternary conjugate (PPD)-MEND, a new in vivo gene delivery system for the targeting of tumor cells that dissociates surface-modified PEG in tumor tissue by matrix metalloproteinase (MMP) and exerts significant transfection activities, was developed. In parallel with the development of MEND, a quantitative gene delivery system, Confocal Image-assisted 3-dimensionally integrated quantification (CIDIQ), also was developed. This method identified the rate-limiting step of the nonviral gene delivery system by comparing it with adenoviral-mediated gene delivery. The results of this analysis provide a new direction for the development of rational nonviral gene delivery systems.

Enhancing siRNA delivery by employing lipid nanoparticles

For several decades extensive research has been conducted into the development of fusogenic lipid nanoparticles (LNPs) capable of introducing large, charged molecules into the cytoplasm of target cells. The majority of this work has focused on cationic LNPs encapsulating nucleic acids ranging from small oligonucleotides to large plasmid constructs thousands of bases long. However, since the introduction of siRNA payloads this quest for a non-viral, intracellular delivery systems has advanced significantly. Of particular importance was the demonstration that LNPs containing ionizable, dialkylamino lipids, enable potent hepatic gene silencing across species including humans. This review focuses on the evolution of this delivery system, summarizes the promising data now emerging from clinical trials and considers future directions for the platform.

Cationic vesicles based on non-ionic surfactant and synthetic aminolipids mediate delivery of antisense oligonucleotides into mammalian cells

A formulation based on a synthetic aminolipid containing a double-tailed with two saturated alkyl chains along with a non-ionic surfactant polysorbate-80 has been used to form lipoplexes with an antisense oligonucleotide capable of inhibiting the expression of Renilla luciferase mRNA. The resultant lipoplexes were characterized in terms of morphology, Zeta potential, average size, stability and electrophoretic shift assay. The lipoplexes did not show any cytotoxicity in cell culture up to 150 mM concentration. The gene inhibition studies demonstrated that synthetic cationic vesicles based on non-ionic surfactant and the appropriate aminolipid play an important role in enhancing cellular uptake of antisense oligonucleotides obtaining promising results and efficiencies comparable to commercially available cationic lipids in cultured mammalian cells. Based on these results, this amino lipid moiety could be considered as starting point for the synthesis of novel cationic lipids to obtain potential non-viral carriers for antisense and RNA interference therapies.

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

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

In vivo activity of miR-34a mimics delivered by stable nucleic acid lipid particles (SNALPs) against multiple myeloma

Multiple myeloma (MM) is a disease with an adverse outcome and new therapeutic strategies are urgently awaited. A rising body of evidence supports the notion that microRNAs (miRNAs), master regulators of eukaryotic gene expression, may exert anti-MM activity. Here, we evaluated the activity of synthetic miR-34a in MM cells. We found that transfection of miR-34a mimics in MM cells induces a significant change of gene expression with relevant effects on multiple signal transduction pathways. We detected early inactivation of pro-survival and proliferative kinases Erk-2 and Akt followed at later time points by caspase-6 and -3 activation and apoptosis induction. To improve the in vivo delivery, we encapsulated miR-34a mimics in stable nucleic acid lipid particles (SNALPs). We found that SNALPs miR-34a were highly efficient in vitro in inhibiting growth of MM cells. Then, we investigated the activity of the SNALPs miR-34a against MM xenografts in SCID mice. We observed significant tumor growth inhibition (p<0.05) which translated in mice survival benefits (p = 0.0047). Analysis of miR-34a and NOTCH1 expression in tumor retrieved from animal demonstrated efficient delivery and gene modulation induced by SNALPs miR-34a in the absence of systemic toxicity. We here therefore provide evidence that SNALPs miR-34a may represent a promising tool for miRNA-therapeutics in MM.

Transferrin-conjugated SNALPs encapsulating 2'-O-methylated miR-34a for the treatment of multiple myeloma

Stable nucleic acid lipid vesicles (SNALPs) encapsulating miR-34a to treat multiple myeloma (MM) were developed. Wild type or completely 2'-O-methylated (OMet) MiR-34a was used in this study. Moreover, SNALPs were conjugated with transferrin (Tf) in order to target MM cells overexpressing transferrin receptors (TfRs). The type of miR-34a chemical backbone did not significantly affect the characteristics of SNALPs in terms of mean size, polydispersity index, and zeta potential, while the encapsulation of an OMet miR-34a resulted in a significant increase of miRNA encapsulation into the SNALPs. On the other hand, the chemical conjugation of SNALPs with Tf resulted in a significant decrease of the zeta potential, while size characteristics and miR-34a encapsulation into SNALPs were not significantly affected. In an experimental model of MM, all the animals treated with SNALPs encapsulating miR-34a showed a significant inhibition of the tumor growth. However, the use of SNALPs conjugated with Tf and encapsulating OMet miR-34a resulted in the highest increase of mice survival. These results may represent the proof of concept for the use of SNALPs encapsulating miR-34a for the treatment of MM.

Inhibiting metastatic breast cancer cell migration via the synergy of targeted, pH-triggered siRNA delivery and chemokine axis blockade

Because breast cancer patient survival inversely correlates with metastasis, we engineered vehicles to inhibit both the C-X-C chemokine receptor type 4 (CXCR4) and lipocalin-2 (Lcn2) mediated migratory pathways. pH-responsive liposomes were designed to protect and trigger the release of Lcn2 siRNA. Liposomes were modified with anti-CXCR4 antibodies to target metastatic breast cancer (MBC) cells and block migration along the CXCR4-CXCL12 axis. This synergistic approach--coupling the CXCR4 axis blockade with Lcn2 silencing--significantly reduced migration in triple-negative human breast cancer cells (88% for MDA-MB-436 and 92% for MDA-MB-231). The results suggested that drug delivery vehicles engineered to attack multiple migratory pathways may effectively slow progression of MBC.

Microfluidic-based manufacture of siRNA-lipid nanoparticles for therapeutic applications

A simple, efficient, and scalable manufacturing technique is required for developing siRNA-lipid nanoparticles (siRNA-LNP) for therapeutic applications. In this chapter we describe a novel microfluidic-based manufacturing process for the rapid manufacture of siRNA-LNP, together with protocols for characterizing the size, polydispersity, RNA encapsulation efficiency, RNA concentration, and total lipid concentration of the resultant nanoparticles.

Influence of Polyethylene Glycol Lipid Desorption Rates on Pharmacokinetics and Pharmacodynamics of siRNA Lipid Nanoparticles

Lipid nanoparticles (LNPs) encapsulating short interfering RNAs that target hepatic genes are advancing through clinical trials, and early results indicate the excellent gene silencing observed in rodents and nonhuman primates also translates to humans. This success has motivated research to identify ways to further advance this delivery platform. Here, we characterize the polyethylene glycol lipid (PEG-lipid) components, which are required to control the self-assembly process during formation of lipid particles, but can negatively affect delivery to hepatocytes and hepatic gene silencing in vivo. The rate of transfer from LNPs to plasma lipoproteins in vivo is measured for three PEG-lipids with dialkyl chains 14, 16, and 18 carbons long. We show that 1.5 mol % PEG-lipid represents a threshold concentration at which the chain length exerts a minimal effect on hepatic gene silencing but can still modify LNPs pharmacokinetics and biodistribution. Increasing the concentration to 2.5 and 3.5 mol % substantially compromises hepatocyte gene knockdown for PEG-lipids with distearyl (C18) chains but has little impact for shorter dimyristyl (C14) chains. These data are discussed with respect to RNA delivery and the different rates at which the steric barrier disassociates from LNPs in vivo.Molecular Therapy-Nucleic Acids (2013) 2, e139; doi:10.1038/mtna.2013.66; published online 17 December 2013.

Preclinical development of siRNA therapeutics: towards the match between fundamental science and engineered systems

The evolution of synthetic RNAi faces the paradox of interfering with the human biological environment. Due to the fact that all cell physiological processes can be target candidates, silencing a precise biological pathway could be challenging if target selectivity is not properly addressed. Molecular biology has provided scientific tools to suppress some of the most critical issues in gene therapy, while setting the standards for siRNA clinical application. However, the protein down-regulation through the mRNA silencing is intimately related to the sequence-specific siRNA ability to interact accurately with the potential target. Moreover, its in vivo biological fate is highly dependent on the successful design of a vehicle able to overcome both extracellular and intracellular barriers. Anticipating a great deal of innovation, crucial to meet the challenges involved in the RNAi therapeutics, the present review intends to build up a synopsis on the delivery strategies currently developed.

FROM THE CLINICAL EDITOR

This review discusses recent progress and pertinent limiting factors related to the use of siRNA-s as efficient protein-specific "silencing" agents, focusing on targeted delivery not only to cells of interest, but to the proper intracellular destination.

Advances in Lipid Nanoparticles for siRNA Delivery

Technological advances in both siRNA (small interfering RNA) and whole genome sequencing have demonstrated great potential in translating genetic information into siRNA-based drugs to halt the synthesis of most disease-causing proteins. Despite its powerful promises as a drug, siRNA requires a sophisticated delivery vehicle because of its rapid degradation in the circulation, inefficient accumulation in target tissues and inability to cross cell membranes to access the cytoplasm where it functions. Lipid nanoparticle (LNP) containing ionizable amino lipids is the leading delivery technology for siRNA, with five products in clinical trials and more in the pipeline. Here, we focus on the technological advances behind these potent systems for siRNA-mediated gene silencing.

TRAIL and microRNAs in the treatment of prostate cancer: therapeutic potential and role of nanotechnology

Disruption of spatiotemporal behavior of intracellular signaling cascades including tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL)-mediated signaling in prostate cancer has gained tremendous attention in the past few years. There is an increasing effort in translating the emerging information about TRAIL-mediated signaling obtained through experimental and preclinical data to clinic. Fascinatingly, novel targeting approaches are being developed to enhance the tissue- or subcellular-specific delivery of drugs with considerable focus on prostate cancer. These applications have the potential to revolutionize prostate cancer therapeutic strategies and include the accumulation of drugs in target tissue as well as the selection of internalizing ligands for enhanced receptor-mediated uptake of drugs. In this mini-review, we outline outstanding developments in therapeutic strategies based on the regulation and/or targeting of TRAIL pathway for the treatment of prostate cancer. Moreover, microRNAs (miRNAs), with potential transcriptional and posttranscriptional regulation of gene expression, will be presented for their potential in prostate cancer treatment. Emphasis has been given to the use of delivery approaches, especially based on nanotechnology. Considerably, enhanced information regarding miRNA regulation of TRAIL-mediated signaling in prostate cancer cells may provide potential biomarkers for the characterization of patients as responders and nonresponders of TRAIL-based therapy and could provide rationalized basis for combination therapies with TRAIL death receptor-targeting drugs.

A neutral envelope-type nanoparticle containing pH-responsive and SS-cleavable lipid-like material as a carrier for plasmid DNA

SS-cleavable proton-activated lipid-like material (ssPalm) functions as a key element in a lipid nanoparticle in which pDNA is encapsulated. The ssPalm contains dual sensing motifs that can respond to the intracellular environment; a proton-sponge unit (tertiary amines) that functions in response to an acidic environment (endosome/lysosome), and disulfide bonding that can be cleaved in a reducing environment (cytosol).

Improving cellular uptake and in vivo tumor suppression efficacy of liposomal oligonucleotides by urea as a chemical penetration enhancer

BACKGROUND

Liposomes are among the most widely used carriers for the delivery of antisense oligonucleotides (AsODNs) to intracellular targets. Although different strategies have been employed, the question of how to improve liposomal uptake and enhance the release of AsODN into cytoplasm still remains to be answered with respect to the use of a safe, easy and economic method. In the present study, the possibility of enhancing such processes at cellular and animal levels using urea as a penetration enhancer was investigated.

METHODS

To perform this investigation, a cationic liposome containing an AsODN against protein kinase (PKC)-α was prepared, and the effect of urea on its cellular internalization and the related sequence-specific inhibition of gene expression in human lung adenocarcinoma A549 cells were investigated by flow cytometry and the reverse transcriptase-polymerase chain reaction, respectively. In in vivo studies, a xenograft lung tumor was established in nude mice by A549 cells and the enhancement effect of urea toward the effects of liposomal AsODN on tumor growth was investigated.

RESULTS

Cellular studies revealed that urea treatment increases liposomal uptake and the release of AsODN into the cytoplasm by approximately 40%. Sequence-specific inhibition of target gene PKC-α expression was also increased by approximately two-fold by urea at 200-300 nM AsODN. In animal studies, urea significantly decreased the tumor volume (approximately 40%) and increased its doubling time from approximately 13 days to 17 days.

CONCLUSIONS

Urea, and possibly other membrane fluidizers, could be regarded as penetration enhancers for liposomal AsODN delivery and may improve the therapeutic effect of these gene-therapy vectors at both cellular and animal levels.

Preparation and characterization of liposome-encapsulated plasmid DNA for gene delivery

The success of common nonviral gene delivery vehicles, lipoplexes and polyplexes, is limited by the toxicity and instability of these charged molecules. Stealth liposomes could provide a stable, safe alternative to cationic DNA complexes for effective gene delivery. DNA encapsulations in three stealth liposomal formulations prepared by thin film, reverse phase evaporation, and asymmetric liposome formation were compared, and the thin film method was found to produce the highest yields of encapsulated DNA. A DNA quantification method appropriate for DNA encapsulated within liposomes was also developed and verified for accuracy. The effect of initial lipid and DNA concentrations on the encapsulation yield and fraction of DNA-filled liposomes was evaluated. Higher encapsulation yields were achieved by higher lipid contents, while a higher fraction of DNA-filled liposomes was produced by either lower lipid content or higher DNA concentration. Control of these parameters allows for the design of gene delivery nanoparticles with high DNA encapsulation yields or higher fraction of DNA-filled liposomes.

Asymmetric liposome particles with highly efficient encapsulation of siRNA and without nonspecific cell penetration suitable for target-specific delivery

The discovery of siRNA has been an important step in gene therapy, but the problem of delivering siRNA to a target organ limits its use as a therapeutic drug. Liposomes can be used as a nonviral vector to deliver siRNA to target cells. In this study we developed a novel method of producing asymmetric liposome particles (ALPs) with highly efficient siRNA encapsulation. Two kinds of lipid inverted micelles were prepared for the purpose of obtaining ALPs. The inner one is composed of ionizable cationic 1,2-dioleoyl-3-dimethylammonium-propane (DODAP) and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), which entrap siRNA, and the outer one is composed of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), DOPE, polyethylene glycol-1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine (PEG-PE), and cholesterol. After mixing the inverted micelles, ALPs encapsulating siRNA were obtained by solvent evaporation and dialysis. This process allowed more than 90% siRNA encapsulation as well as the negatively charged surface. The ALPs protected siRNA from ribonuclease A degradation. ALPs without any surface modification elicited almost no uptake into cells, while the surface-modified ALPs with a polyarginine peptide (R12) induced nonspecific cell penetration. The conjugation of the anti-human epidermal growth factor receptor antibody (anti-EGFR) to ALPs induces an EGFR-mediated uptake into the non-small cell lung cancer cell lines but not into NIH-3T3 cells without the receptor. The siRNA encapsulated in ALPs showed the R12- or anti-EGFR-dependent target gene silencing in NCI-H322 cells. These properties of ALPs are useful for target-specific delivery of siRNA after modification of ALPs with a target-specific ligand.

Surface-mediated nucleic acid delivery by lipoplexes prepared in microwell arrays

Many delivery methods have been developed to improve the therapeutic efficacy and facilitate the clinical translation of nucleic acid-based therapeutics. A facile surface-mediated nucleic acid delivery by lipoplexes is prepared in a microwell array, which combines the advantages of lipoplexes as an efficient carrier system, surface-mediated delivery, and the control of surface topography. Uniform disc-like lipoplexes containing nucleic acids are formed in the microwell array with a diameter of ∼818 nm and thickness of ∼195 nm. The microwell array-mediated delivery of lipoplexes containing FAM-oligodeoxynucleotides is ∼18.6 and ∼10.6 times more efficient than the conventional transfection method in an adherent cell line (A549 non-small cell lung cancer cells) and a suspension cell line (KG-1a acute myelogenous leukemia cells), respectively. MicroRNA-29b is then used as a model nucleic acid to investigate the therapeutic efficacy of lipoplexes delivered by the microwell array. Compared to conventional transfection methods, the effective therapeutic dosage of microRNA-29b is reduced from the microgram level to the nanogram level by lipoplexes prepared in the microwell array. The microwell array is also a very flexible platform. Both nucleic acid therapeutics and imaging reagents are incorporated in lipoplexes and successfully delivered to A549 cells, demonstrating its potential applications in theranostic medicine.

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.