Development of lipid nanoparticle formulations of siRNA for hepatocyte gene silencing following subcutaneous administration

Development of Lipid Nanoparticles for the Delivery of Macromolecules Based on the Molecular Design of pH-Sensitive Cationic Lipids

Considerable efforts have been made on the development of lipid nanoparticles (LNPs) for delivering of nucleic acids in LNP-based medicines, including a first-ever short interfering RNA (siRNA) medicine, Onpattro, and the mRNA vaccines against the coronavirus disease 2019 (COVID-19), which have been approved and are currently in use worldwide. The successful rational design of ionizable cationic lipids was a major breakthrough that dramatically increased delivery efficiency in this field. The LNPs would be expected to be useful as a platform technology for the delivery of various therapeutic modalities for genome editing and even for undiscovered therapeutic mechanisms. In this review, the current progress of my research, including the molecular design of pH-sensitive cationic lipids, their applications for various tissues and cell types, and for delivering various macromolecules, including siRNA, antisense oligonucleotide, mRNA, and the clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) system will be described. Mechanistic studies regarding relationships between the physicochemical properties of LNPs, drug delivery, and biosafety are also summarized. Furthermore, current issues that need to be addressed for next generation drug delivery systems are discussed.

Spontaneous, solvent-free entrapment of siRNA within lipid nanoparticles

Lipid nanoparticle (LNP) formulations of nucleic acid are leading vaccine candidates for COVID-19, and enabled the first approved RNAi therapeutic, Onpattro. LNPs are composed of ionizable cationic lipids, phosphatidylcholine, cholesterol, and polyethylene glycol (PEG)-lipids, and are produced using rapid-mixing techniques. These procedures involve dissolution of the lipid components in an organic phase and the nucleic acid in an acidic aqueous buffer (pH 4). These solutions are then combined using a continuous mixing device such as a T-mixer or microfluidic device. In this mixing step, particle formation and nucleic acid entrapment occur. Previous work from our group has shown that, in the absence of nucleic acid, the particles formed at pH 4 are vesicular in structure, a portion of these particles are converted to electron-dense structures in the presence of nucleic acid, and the proportion of electron-dense structures increases with nucleic acid content. What remained unclear from previous work was the mechanism by which vesicles form electron-dense structures. In this study, we use cryogenic transmission electron microscopy and dynamic light scattering to show that efficient siRNA entrapment occurs in the absence of ethanol (contrary to the established paradigm), and suggest that nucleic acid entrapment occurs through inversion of preformed vesicles. We also leverage this phenomenon to show that specialized mixers are not required for siRNA entrapment, and that preformed particles at pH 4 can be used for in vitro transfection.

Dawn of lipid nanoparticles in lymph node targeting: Potential in cancer immunotherapy

It is generally known that the lymph nodes (LNs) are important tissues in cancer immunotherapy. Therefore, delivering immune functional compounds to LNs is a useful strategy for enhancing cancer immunotherapy. Lipid-based nanocarriers have been widely used as delivery systems that target LNs, but lipid nanoparticle (LNP) technology has recently attracted increased interest. High levels of nucleic acids can be efficiently loaded in LNPs, they can be used to actively deliver nucleic acids into the cytoplasm, and they can be produced on an industrial scale. The use of microfluidic devices has been particularly valuable for producing small-sized LNPs, thus paving the way for successful LN targeting. In the review, we focus on the potential of LNP technology for targeting LNs.

Base-modified aptamers obtained by cell-internalization SELEX facilitate cellular uptake of an antisense oligonucleotide

Intracellular delivery of oligonucleotides is important for their use as therapeutic drugs. The conjugation of molecules interacting with cell membrane proteins to enhance their internalization into cells is an effective strategy for delivering oligonucleotides. In the present study, we focused on creating aptamers, which are single-stranded oligonucleotides that bind target molecules with high affinity and specificity, as membrane protein-binding molecules. With an evolutionary selection approach using a random DNA library containing a uracil derivative with a hydrophobic functional group at the 5 position, we successfully obtained aptamers that are efficiently internalized into A549 cells. The efficacies of the aptamers were tested by further conjugation with MALAT1-targeting antisense oligonucleotides (ASOs), and the expression levels of MALAT1 RNA were examined. The aptamer-ASO conjugates were taken up by A549 cells, although there was no observable reduction in MALAT1 RNA levels. In contrast, the activity of the aptamer-ASO conjugate was potentiated when endosomal/lysosomal escape was enhanced by the addition of chloroquine. Thus, we showed that the hydrophobic modification of the nucleobase moiety is useful for developing highly internalizing aptamers and that endosomal/lysosomal escape is important for the intracellular delivery of ASOs by aptamers.

The Importance of Poly(ethylene glycol) and Lipid Structure in Targeted Gene Delivery to Lymph Nodes by Lipid Nanoparticles

Targeted delivery of nucleic acids to lymph nodes is critical for the development of effective vaccines and immunotherapies. However, it remains challenging to achieve selective lymph node delivery. Current gene delivery systems target mainly to the liver and typically exhibit off-target transfection at various tissues. Here we report novel lipid nanoparticles (LNPs) that can deliver plasmid DNA (pDNA) to a draining lymph node, thereby significantly enhancing transfection at this target organ, and substantially reducing gene expression at the intramuscular injection site (muscle). In particular, we discovered that LNPs stabilized by 3% Tween 20, a surfactant with a branched poly(ethylene glycol) (PEG) chain linking to a short lipid tail, achieved highly specific transfection at the lymph node. This was in contrast to conventional LNPs stabilized with a linear PEG chain and two saturated lipid tails (PEG-DSPE) that predominately transfected at the injection site (muscle). Interestingly, replacing Tween 20 with Tween 80, which has a longer unsaturated lipid tail, led to a much lower transfection efficiency. Our work demonstrates the importance of PEGylation in selective organ targeting of nanoparticles, provides new insights into the structure-property relationship of LNPs, and offers a novel, simple, and practical PEGylation technology to prepare the next generation of safe and effective vaccines against viruses or tumours.

Effects of PEG anchors in PEGylated siRNA lipoplexes on in vitro gene‑silencing effects and siRNA biodistribution in mice

Polyethylene glycol (PEG)‑modifications (PEGylations) of cationic liposome/small interfering RNA complexes (siRNA lipoplexes) can enhance their systemic stability. The present study determined the effects of PEG anchors in PEGylated siRNA lipoplexes on in vitro gene‑silencing effects and siRNA biodistribution after intravenous injection. Three types of dialkyl or trialkyl cationic lipids were used in the current study for the preparation of cationic liposomes. Additionally, various PEGylated siRNA lipoplexes that contained PEG‑1,2‑distearoyl‑sn‑-glycero‑-3‑phosphoethanolamine (DSPE), PEG‑1,2‑distearoyl‑rac‑glycero‑3‑-methylpolyoxyethylene (DSG), PEG‑cholesterol (PEG‑Chol) and PEG‑chondroitin sulfate conjugate (PEG‑CS) were prepared. The results revealed that PEGylation of siRNA lipoplexes with PEG‑DSPE strongly decreased gene‑silencing effects in cells. In contrast, those with PEG‑DSG, PEG‑Chol and PEG‑CS did not largely decrease gene-silencing effects. However, regardless of the PEG‑derivative type, PEGylation of siRNA lipoplexes decreased their agglutination with erythrocytes. Furthermore, intravenous injection of PEGylated siRNA lipoplexes markedly decreased the accumulation of siRNA in the lungs, regardless of the type of PEG‑derivative. However, non‑PEGylated siRNA lipoplexes accumulated mainly in the lungs regardless of the siRNA lipoplex cationic lipid type. The results indicated that PEGylation of siRNA lipoplexes with PEG‑DSG, PEG‑Chol and PEG‑CS may improve systemic stability without losing transfection activity by PEGylation.

Deep Phenotyping by Mass Cytometry and Single-Cell RNA-Sequencing Reveals LYN-Regulated Signaling Profiles Underlying Monocyte Subset Heterogeneity and Lifespan

RATIONALE

Monocytes are key effectors of the mononuclear phagocyte system, playing critical roles in regulating tissue homeostasis and coordinating inflammatory reactions, including those involved in chronic inflammatory diseases such as atherosclerosis. Monocytes have traditionally been divided into 2 major subsets termed conventional monocytes and patrolling monocytes (pMo) but recent systems immunology approaches have identified marked heterogeneity within these cells, and much of what regulates monocyte population homeostasis remains unknown. We and others have previously identified LYN tyrosine kinase as a key negative regulator of myeloid cell biology; however, LYN's role in regulating specific monocyte subset homeostasis has not been investigated.

OBJECTIVE

We sought to comprehensively profile monocytes to elucidate the underlying heterogeneity within monocytes and dissect how Lyn deficiency affects monocyte subset composition, signaling, and gene expression. We further tested the biological significance of these findings in a model of atherosclerosis.

METHODS AND RESULTS

Mass cytometric analysis of monocyte subsets and signaling pathway activation patterns in conventional monocytes and pMos revealed distinct baseline signaling profiles and far greater heterogeneity than previously described. Lyn deficiency led to a selective expansion of pMos and alterations in specific signaling pathways within these cells, revealing a critical role for LYN in pMo physiology. LYN's role in regulating pMos was cell-intrinsic and correlated with an increased circulating half-life of Lyn-deficient pMos. Furthermore, single-cell RNA sequencing revealed marked perturbations in the gene expression profiles of Lyn^-/- monocytes with upregulation of genes involved in pMo development, survival, and function. Lyn deficiency also led to a significant increase in aorta-associated pMos and protected Ldlr^-/- mice from high-fat diet-induced atherosclerosis.

CONCLUSIONS

Together our data identify LYN as a key regulator of pMo development and a potential therapeutic target in inflammatory diseases regulated by pMos.

Hydrophobic scaffolds of pH-sensitive cationic lipids contribute to miscibility with phospholipids and improve the efficiency of delivering short interfering RNA by small-sized lipid nanoparticles

Despite the fact that small-sized lipid nanoparticles (LNPs) are important for improved tissue penetration and efficient drug delivery, their poor stability and intracellular trafficking significantly hinders their use as potent small-sized LNPs. It has been reported that both the diffusion of lipid components from LNPs and the adsorption of proteins on the surface of LNPs are responsible for their decreased potency. To overcome this issue, we focused on the chemical structure of hydrophobic scaffolds of pH-sensitive cationic lipids with various lengths and shapes. LNPs composed of a pH-sensitive cationic lipid with long, linear scaffolds induced gene silencing in a dose-dependent manner, while LNPs with a classical scaffold length (C18) failed. Replacing the helper lipid from cholesterol to egg sphingomyelin (ESM) resulted in the formation of smaller LNPs with a diameter of ~22 nm and enhanced gene silencing activity. Most of the ESMs were located in the outer layer and functioned to stabilize the LNPs. Long, linear scaffolds contributed to immiscibility with phosphocholine-containing lipids including ESM. This contribution was dependent on the scaffold length of pH-sensitive cationic lipids. Although phosphocholine-containing lipids usually inhibit membrane fusion-mediated endosomal escape, long, linear scaffolds contributed to avoiding the inhibitory effect and to enhance the potency of the LNPs. These findings provide useful information needed for the rational design of pH-sensitive cationic lipid structures and the selection of appropriate helper lipids and will facilitate the development of highly potent small-sized LNPs. STATEMENT OF SIGNIFICANCE: Despite the fact that small-sized lipid nanoparticles (LNPs) are important for improved tissue penetration and efficient drug delivery, the size reduction-associated decrease in the stability and intracellular trafficking significantly hinders the development of potent small-sized LNPs. Our limited understanding of the mechanism underlying the reduced potency has also hindered the development of more potent small-sized LNPs. The findings of the present study indicate that long and linear hydrophobic scaffolds of pH-sensitive cationic lipids could overcome the loss of efficiency for nucleic acid delivery. In addition, the long hydrophobic scaffolds led to immiscibility with neutral phospholipids, resulting in efficient endosomal escape. These findings provide useful information needed for the rational design of pH-sensitive cationic lipid structures and will facilitate the development of highly potent small-sized LNPs.

Lipid Nanoparticles Potentiate CpG-Oligodeoxynucleotide-Based Vaccine for Influenza Virus

Current influenza vaccines are generally effective against highly similar (homologous) strains, but their effectiveness decreases markedly against antigenically mismatched (heterologous) strains. One way of developing a universal influenza vaccine with a broader spectrum of protection is to use appropriate vaccine adjuvants to improve a vaccine's effectiveness and change its immune properties. Oligodeoxynucleotides (ODNs) with unmethylated cytosine-phosphate-guanine (CpG) motifs (CpG ODNs), which are Toll-like-receptor 9 (TLR9) agonists, are among the most promising adjuvants and are already being used in humans. However, the development of novel delivery vehicles to improve adjuvant effects in vivo is highly desirable. Here, we assessed the potential of lipid nanoparticles (LNPs) as CpG ODN delivery vehicles in mice to augment the vaccine adjuvant effects of CpG ODN and enhance the protective spectrum of conventional influenza split vaccine (SV). In vitro, compared with CpG ODN, LNPs containing CpG ODNs (LNP-CpGs) induced significantly greater production of cytokines such as IL-12 p40 and IFN-α by mouse dendritic cells (DCs) and significantly greater expression of the co-stimulatory molecules CD80 and CD86 on DCs. In addition, after subcutaneous administration in mice, compared with CpG ODN, LNP-CpGs enhanced the expression of CD80 and CD86 on plasmacytoid DCs in draining lymph nodes. LNP-CpGs given with SV from H1N1 influenza A virus improved T-cell responses and gave a stronger not only SV-specific but also heterologous-virus-strain-specific IgG2c response than CpG ODN. Furthermore, immunization with SV plus LNP-CpGs protected against not only homologous strain challenge but also heterologous and heterosubtypic strain challenge, whereas immunization with SV plus CpG ODNs protected against homologous strain challenge only. We therefore demonstrated that LNP-CpGs improved the adjuvant effects of CpG ODN and broadened the protective spectrum of SV against influenza virus. We expect that this strategy will be useful in developing adjuvant delivery vehicles and universal influenza vaccines.

Lipid-based nanoparticle technologies for liver targeting

Liver diseases such as hepatitis, cirrhosis, and hepatocellular carcinoma are global health problems accounting for approximately 800 million cases and over 2 million deaths per year worldwide. Major drawbacks of standard pharmacological therapies are the inability to deliver a sufficient concentration of a therapeutic agent to the diseased liver, and nonspecific drug delivery leading to undesirable systemic side effects. Additionally, depending on the specific liver disease, drug delivery to a subset of liver cells is required. In recent years, lipid nanoparticles have been developed to passively and actively target drugs to the liver. The success of this approach has been highlighted by the FDA-approval of the first liver-targeting lipid nanoparticle, ONPATTRO, in 2018 and many other promising candidate technologies are expected to follow. This review summarizes recent developments of various lipid-based liver-targeting technologies, namely solid-lipid nanoparticles, liposomes, niosomes and micelles, and discusses the challenges and future perspectives in this field.

Lipid nanoparticle technology for therapeutic gene regulation in the liver

Hereditary genetic disorders, cancer, and infectious diseases of the liver affect millions of people around the globe and are a major public health burden. Most contemporary treatments offer limited relief as they generally aim to alleviate disease symptoms. Targeting the root cause of diseases originating in the liver by regulating malfunctioning genes with nucleic acid-based drugs holds great promise as a therapeutic approach. However, employing nucleic acid therapeutics in vivo is challenging due to their unfavorable characteristics. Lipid nanoparticle (LNP) delivery technology is a revolutionary development that has enabled clinical translation of gene therapies. LNPs can deliver siRNA, mRNA, DNA, or gene-editing complexes, providing opportunities to treat hepatic diseases by silencing pathogenic genes, expressing therapeutic proteins, or correcting genetic defects. Here we discuss the state-of-the-art LNP technology for hepatic gene therapy including formulation design parameters, production methods, preclinical development and clinical translation.

On the role of helper lipids in lipid nanoparticle formulations of siRNA

Onpattro, the first RNAi-based therapeutic to receive FDA approval, is enabled by a lipid nanoparticle (LNP) system that facilitates siRNA delivery into the cytoplasm of target cells (hepatocytes) following intravenous (i.v.) administration. These LNP-siRNA systems consist of four lipid components (ionizable cationic lipid, distearolyphosphatidycholine or DSPC, cholesterol, and PEG-lipid) and siRNA. The ionizable cationic lipid has been optimised for RNA encapsulation and intracellular delivery, and the PEG-lipids have been engineered to regulate LNP size and transfection potency. The roles of the other "helper" lipids, DSPC and cholesterol, remain less clear. Here we show that in empty LNP systems that do not contain siRNA, DSPC-cholesterol resides in outer layers, whereas in loaded systems a portion of the DSPC-cholesterol is internalised together with siRNA. It is concluded that the presence of internalised helper lipid is vital to the stable encapsulation of siRNA in the LNP and thus to LNP-siRNA function.

Quantification of Surface GalNAc Ligands Decorating Nanostructured Lipid Carriers by UPLC-ELSD

Nanoparticles have been extensively studied for drug delivery and targeting to specific organs. The functionalization of the nanoparticle surface by site-specific ligands (antibodies, peptides, saccharides) can ensure efficient recognition and binding with relevant biological targets. One of the main challenges in the development of these decorated nanocarriers is the accurate quantification of the amount of ligands on the nanoparticle surface. In this study, nanostructured lipid carriers (NLC) were functionalized with N-acetyl-D-galactosamine (GalNAc) units, known to target the asialoglycoprotein receptor (ASGPR). Different molar percentages of GalNAc-functionalized surfactant (0%, 2%, 5%, and 14%) were used in the formulation. Based on ultra-high-performance liquid chromatography separation and evaporative light-scattering detection (UPLC-ELSD), an analytical method was developed to specifically quantify the amount of GalNAc units present at the NLC surface. This method allowed the accurate quantification of GalNAc surfactant and therefore gave some insights into the structural parameters of these multivalent ligand systems. Our data show that the GalNAc decorated NLC possess large numbers of ligands at their surface and suitable distances between them for efficient multivalent interaction with the ASGPR, and therefore promising liver-targeting efficiency.

The current state and future directions of RNAi-based therapeutics

The RNA interference (RNAi) pathway regulates mRNA stability and translation in nearly all human cells. Small double-stranded RNA molecules can efficiently trigger RNAi silencing of specific genes, but their therapeutic use has faced numerous challenges involving safety and potency. However, August 2018 marked a new era for the field, with the US Food and Drug Administration approving patisiran, the first RNAi-based drug. In this Review, we discuss key advances in the design and development of RNAi drugs leading up to this landmark achievement, the state of the current clinical pipeline and prospects for future advances, including novel RNAi pathway agents utilizing mechanisms beyond post-translational RNAi silencing.

Endocytic Profiling of Cancer Cell Models Reveals Critical Factors Influencing LNP-Mediated mRNA Delivery and Protein Expression

Lipid nanoparticles have great potential for delivering nucleic-acid-based therapeutics, but low efficiency limits their broad clinical translation. Differences in transfection capacity between in vitro models used for nanoparticle pre-clinical testing are poorly understood. To address this, using a clinically relevant lipid nanoparticle (LNP) delivering mRNA, we highlight specific endosomal characteristics in in vitro tumor models that impact protein expression. A 30-cell line LNP-mRNA transfection screen identified three cell lines having low, medium, and high transfection that correlated with protein expression when they were analyzed in tumor models. Endocytic profiling of these cell lines identified major differences in endolysosomal morphology, localization, endocytic uptake, trafficking, recycling, and endolysosomal pH, identified using a novel pH probe. High-transfecting cells showed rapid LNP uptake and trafficking through an organized endocytic pathway to lysosomes or rapid exocytosis. Low-transfecting cells demonstrated slower endosomal LNP trafficking to lysosomes and defective endocytic organization and acidification. Our data establish that efficient LNP-mRNA transfection relies on an early and narrow endosomal escape window prior to lysosomal sequestration and/or exocytosis. Endocytic profiling should form an important pre-clinical evaluation step for nucleic acid delivery systems to inform model selection and guide delivery-system design for improved clinical translation.

Translational challenges in advancing regenerative therapy for treating neurological disorders using nanotechnology

The focus of regenerative therapies is to replace or enrich diseased or injured cells and tissue in an attempt to replenish the local environment and function, while slowing or halting further degeneration. Targeting neurological diseases specifically is difficult, due to the complex nature of the central nervous system, including the difficulty of bypassing the brain's natural defense systems. While cell-based regenerative therapies show promise in select tissues, preclinical and clinical studies have been largely unable to transfer these successes to the brain. Advancements in nanotechnologies have provided new methods of central nervous system access, drug and cell delivery, as well as new systems of cell maintenance and support that may bridge the gap between regenerative therapies and the brain. In this review, we discuss current regenerative therapies for neurological diseases, nanotechnology as nanocarriers, and the technical, manufacturing, and regulatory challenges that arise from inception to formulation of nanoparticle-regenerative therapies.

Sterically stabilized liposomes production using staggered herringbone micromixer: Effect of lipid composition and PEG-lipid content

Preparation of lipid-based drug delivery systems by microfluidics has been increasingly popular, due to the reproducible, continuous and scalable nature of the microfluidic process. Despite exciting development in the field, versatility and superiority of microfluidics over conventional methods still need further evidence, since preparing clinically-relevant sterically stabilised liposomes has been lacking. The present study describes the optimisation of PEGylated liposomal formulations of various rigidity using staggered herringbone micromixer (SHM). The effect of both processing parameters (total flow rate (TFR) and aqueous-to-ethanol flow rate ratio (FRR)) and formulation parameters (lipid components and composition, initial lipid concentration and aqueous media) was investigated and discussed. Liposomal formulations consist of 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) or 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC), with cholesterol and PEGylated lipid (DSPE-PEG₂₀₀₀) were successfully prepared with the desired size (∼100 nm) and dispersity (<0.2). Doxorubicin was successfully encapsulated in these liposomes at high (>80%) encapsulation efficiency using the pH-gradient remote loading method, illustrating their bilayer integrity and capability as drug delivery systems. We demonstrated that clinically-relevant PEGylated liposomal formulations could be prepared with properties comparable to conventional techniques. Limitations and recommendations on the microfluidic production of PEGylated liposomes were also discussed.

Targeted delivery of atorvastatin via asialoglycoprotein receptor (ASGPR)

Targeted drug delivery platforms can increase the concentration of drugs in specific cell populations, reduce adverse effects, and hence improve the therapeutic effect of drugs. Herein, we designed two conjugates by installing the targeting ligand GalNAc (N-acetylgalactosamine) onto atorvastatin (AT). Compared to the parent drug, these two conjugates, termed G2-AT and G2-K-AT, showed increased hepatic cellular uptake. Moreover, both conjugates were able to release atorvastatin, and consequently showed dramatic inhibition of β-hydroxy-β-methylglutaryl-CoA (HMG-CoA) reductase and increased LDL receptors on cell surface.

Fusion-dependent formation of lipid nanoparticles containing macromolecular payloads

The success of Onpattro™ (patisiran) clearly demonstrates the utility of lipid nanoparticle (LNP) systems for enabling gene therapies. These systems are composed of ionizable cationic lipids, phospholipid, cholesterol, and polyethylene glycol (PEG)-lipids, and are produced through rapid-mixing of an ethanolic-lipid solution with an acidic aqueous solution followed by dialysis into neutralizing buffer. A detailed understanding of the mechanism of LNP formation is crucial to improving LNP design. Here we use cryogenic transmission electron microscopy and fluorescence techniques to further demonstrate that LNP are formed through the fusion of precursor, pH-sensitive liposomes into large electron-dense core structures as the pH is neutralized. Next, we show that the fusion process is limited by the accumulation of PEG-lipid on the emerging particle. Finally, we show that the fusion-dependent mechanism of formation also applies to LNP containing macromolecular payloads including mRNA, DNA vectors, and gold nanoparticles.

Increasing lean muscle mass in mice via nanoparticle-mediated hepatic delivery of follistatin mRNA

Muscle atrophy occurs during chronic diseases, resulting in diminished quality of life and compromised treatment outcomes. There is a high demand for therapeutics that increase muscle mass while abrogating the need for special dietary and exercise requirements. Therefore, we developed an efficient nanomedicine approach capable of increasing muscle mass.

Methods: The therapy is based on nanoparticle-mediated delivery of follistatin messenger RNA (mRNA) to the liver after subcutaneous administration. The delivered mRNA directs hepatic cellular machinery to produce follistatin, a glycoprotein that increases lean mass through inhibition of negative regulators of muscle mass (myostatin and activin A). These factors are elevated in numerous disease states, thereby providing a target for therapeutic intervention.

Results: Animal studies validated that mRNA-loaded nanoparticles enter systemic circulation following subcutaneous injection, accumulate and internalize in the liver, where the mRNA is translated into follistatin. Follistatin serum levels were elevated for 72 h post injection and efficiently reduced activin A and myostatin serum concentrations. After eight weeks of repeated injections, the lean mass of mice in the treatment group was ~10% higher when compared to that of the controls.

Conclusion: Based on the obtained results demonstrating an increased muscle mass as well as restricted fat accumulation, this nanoplatform might be a milestone in the development of mRNA technologies and the treatment of muscle wasting disorders.

Dexamethasone prodrugs as potent suppressors of the immunostimulatory effects of lipid nanoparticle formulations of nucleic acids

Lipid nanoparticles (LNPs) are playing a leading role in enabling clinical applications of gene therapies based on DNA or RNA polymers. One factor impeding clinical acceptance of LNP therapeutics is that LNP formulations of nucleic acid polymers can be immunostimulatory, necessitating co-administration of potent corticosteroid immunosuppressive agents. Here, we describe the development of hydrophobic prodrugs of a potent corticosteroid, dexamethasone, that can be readily incorporated into LNP systems. We show that the presence of the dexamethasone prodrug LD003 effectively suppresses production of cytokines such as KC-GRO, TNFα, IL-1β and IL-6 following intravenous administration of LNP loaded with immune stimulatory oligodeoxynucleotides containing cytosine-guanine dinucleotide motifs. Remarkably, LD003 dose levels corresponding to 0.5 mg/kg dexamethasone achieve a greater immunosuppressive effect than doses of 20 mg/kg of free dexamethasone. Similar immunosuppressive effects are observed for subcutaneously administered LNP-siRNA. Further, the incorporation of low levels of LD003 in LNP containing unmodified mRNA or plasmid DNA significantly reduced pro-inflammatory cytokine levels following intravenous administration. Our results suggest that incorporation of hydrophobic prodrugs such as LD003 into LNP systems could provide a convenient method for avoiding the immunostimulatory consequences of systemic administration of genetic drug formulations.

Lipid Nanoparticle Formulations for Enhanced Co-delivery of siRNA and mRNA

Although mRNA and siRNA have significant therapeutic potential, their simultaneous delivery has not been previously explored. To facilitate the treatment of diseases associated with aberrant gene upregulation and downregulation, we sought to co-formulate siRNA and mRNA in a single lipidoid nanoparticle (LNP) formulation. We accommodated the distinct molecular characteristics of mRNA and siRNA in a formulation consisting of an ionizable and biodegradable amine-containing lipidoid, cholesterol, DSPC, DOPE, and PEG-lipid. Surprisingly, the co-formulation of siRNA and mRNA in the same LNP enhanced the efficacy of both drugs in vitro and in vivo. Compared to LNPs encapsulating siRNA only, co-formulated LNPs improved Factor VII gene silencing in mice from 44 to 87% at an siRNA dose of 0.03 mg/kg. Co-formulation also improved mRNA delivery, as a 0.5 mg/kg dose of mRNA co-formulated with siRNA induced three times the luciferase protein expression compared to when siRNA was not included. As not all gene therapy applications require both RNA drugs, we sought to extend the benefit of co-formulated LNPs to formulations encapsulating only a single type of RNA. We accomplished this by substituting the "helper" RNA with a negatively charged polymer, polystyrenesulfonate (PSS). LNPs containing PSS mediated the same level of protein silencing or expression as standard LNPs using 2-3-fold less RNA. For example, LNPs formulated with and without PSS induced 50% Factor VII silencing at siRNA doses of 0.01 and 0.03 mg/kg, respectively. Together, these studies demonstrate potent co-delivery of siRNA and mRNA and show that inclusion of a negatively charged "helper polymer" enhances the efficacy of LNP delivery systems.

Development of the iLiNP Device: Fine Tuning the Lipid Nanoparticle Size within 10 nm for Drug Delivery

The precise size control of the lipid nanoparticle (LNP)-based nanodrug delivery system (DDS) carriers, such as 10 nm size tuning of LNPs, is one major challenge for the development of next-generation nanomedicines. Size-controlled LNPs would realize size-selective tumor targeting and deliver DNA and RNA to target tumor tissues effectively by passing through the stromal cells. Herein, we developed a baffle mixer device named the invasive lipid nanoparticle production device, or iLiNP device for short, which has a simple two-dimensional microchannel and mixer structure, and we achieved the first reported LNP size tuning at 10 nm intervals in the size range from 20 to 100 nm. In comparison with the conventional LNP preparation methods and reported micromixer devices, our iLiNP device showed better LNP size controllability, robustness of device design, and LNP productivity. Furthermore, we prepared 80 nm sized LNPs with encapsulated small interfering RNA (siRNA) using the iLiNP device; these LNPs effectively performed as nano-DDS carriers in an in vivo experiment. We expect iLiNP devices will become novel apparatuses for LNP production in nano-DDS applications.

On the Formation and Morphology of Lipid Nanoparticles Containing Ionizable Cationic Lipids and siRNA

Lipid nanoparticles (LNPs) containing short interfering RNA (LNP-siRNA) and optimized ionizable cationic lipids are now clinically validated systems for silencing disease-causing genes in hepatocytes following intravenous administration. However, the mechanism of formation and certain structural features of LNP-siRNA remain obscure. These systems are formed from lipid mixtures (cationic lipid, distearoylphosphatidylcholine, cholesterol, and PEG-lipid) dissolved in ethanol that is rapidly mixed with siRNA in aqueous buffer at a pH (pH 4) where the ionizable lipid is positively charged. The resulting dispersion is then dialyzed against a normal saline buffer to remove residual ethanol and raise the pH to 7.4 (above the p K_a of the cationic lipid) to produce the finished LNP-siRNA systems. Here we provide cryogenic transmission electron microscopy (cryo-TEM) and X-ray evidence that the complexes formed between siRNA and ionizable lipid at pH 4 correspond to tightly packed bilayer structures with siRNA sandwiched between closely apposed monolayers. Further, it is shown that ionizable lipid not complexed to siRNA promotes formation of very small vesicular structures at pH 4 that coalesce to form larger LNP structures with amorphous electron dense cores at pH 7.4. A mechanism of formation of LNP-siRNA systems is proposed whereby siRNA is first sandwiched between closely apposed lipid monolayers at pH 4 and subsequently trapped in these structures as the pH is raised to 7.4, whereas ionizable lipid not interacting with siRNA moves from bilayer structure to adopt an amorphous oil phase located in the center of the LNP as the pH is raised. This model is discussed in terms of previous hypotheses and potential relevance to the design of LNP-siRNA systems.

Successful reprogramming of cellular protein production through mRNA delivered by functionalized lipid nanoparticles

mRNA treatments represent an exciting approach to cure diseases that cannot be tackled with current therapeutics. However, the delivery of mRNA to target cells remains a challenge, but among the existing alternatives, lipid nanoparticles (LNPs) offer a promising answer to this. Here we determine the structure of LNPs encapsulating mRNA, consisting of a lipid mixture already evaluated in clinical trials. We show that the lipids are not homogeneously distributed across the LNP, and one of the lipids is localized mainly at its surface. The structural information enabled us to design LNPs that successfully modify intracellular protein production in two clinically relevant cell types. Our findings and approach provide a framework for understanding and optimizing vehicles for mRNA delivery.

The development of safe and efficacious gene vectors has limited greatly the potential for therapeutic treatments based on messenger RNA (mRNA). Lipid nanoparticles (LNPs) formed by an ionizable cationic lipid (here DLin-MC3-DMA), helper lipids (distearoylphosphatidylcholine, DSPC, and cholesterol), and a poly(ethylene glycol) (PEG) lipid have been identified as very promising delivery vectors of short interfering RNA (siRNA) in different clinical phases; however, delivery of high-molecular weight RNA has been proven much more demanding. Herein we elucidate the structure of hEPO modified mRNA-containing LNPs of different sizes and show how structural differences affect transfection of human adipocytes and hepatocytes, two clinically relevant cell types. Employing small-angle scattering, we demonstrate that LNPs have a disordered inverse hexagonal internal structure with a characteristic distance around 6 nm in presence of mRNA, whereas LNPs containing no mRNA do not display this structure. Furthermore, using contrast variation small-angle neutron scattering, we show that one of the lipid components, DSPC, is localized mainly at the surface of mRNA-containing LNPs. By varying LNP size and surface composition we demonstrate that both size and structure have significant influence on intracellular protein production. As an example, in both human adipocytes and hepatocytes, protein expression levels for 130 nm LNPs can differ as much as 50-fold depending on their surface characteristics, likely due to a difference in the ability of LNP fusion with the early endosome membrane. We consider these discoveries to be fundamental and opening up new possibilities for rational design of synthetic nanoscopic vehicles for mRNA delivery.

Advances in microfluidics for lipid nanoparticles and extracellular vesicles and applications in drug delivery systems

Lipid-based nanobiomaterials as liposomes and lipid nanoparticles (LNPs) are the most widely used nanocarriers for drug delivery systems (DDSs). Extracellular vesicles (EVs) and exosomes are also expected to be applied as DDS nanocarriers. The performance of nanomedicines relies on their components such as lipids, targeting ligands, encapsulated DNA, encapsulated RNA, and drugs. Recently, the importance of the nanocarrier sizes smaller than 100nm is attracting attention as a means to improve nanomedicine performance. Microfluidics and lab-on-a chip technologies make it possible to produce size-controlled LNPs by a simple continuous flow process and to separate EVs from blood samples by using a surface marker, ligand, or electric charge or by making a mass or particle size discrimination. Here, we overview recent advances in microfluidic devices and techniques for liposomes, LNPs, and EVs and their applications for DDSs.

Pharmacokinetic Profiling of Conjugated Therapeutic Oligonucleotides: A High-Throughput Method Based Upon Serial Blood Microsampling Coupled to Peptide Nucleic Acid Hybridization Assay

Therapeutic oligonucleotides, such as small interfering RNAs (siRNAs), hold great promise for the treatment of incurable genetically defined disorders by targeting cognate toxic gene products for degradation. To achieve meaningful tissue distribution and efficacy in vivo, siRNAs must be conjugated or formulated. Clear understanding of the pharmacokinetic (PK)/pharmacodynamic behavior of these compounds is necessary to optimize and characterize the performance of therapeutic oligonucleotides in vivo. In this study, we describe a simple and reproducible methodology for the evaluation of in vivo blood/plasma PK profiles and tissue distribution of oligonucleotides. The method is based on serial blood microsampling from the saphenous vein, coupled to peptide nucleic acid hybridization assay for quantification of guide strands. Performed with minimal number of animals, this method allowed unequivocal detection and sensitive quantification without the need for amplification, or further modification of the oligonucleotides. Using this methodology, we compared plasma clearances and tissue distribution profiles of two different hydrophobically modified siRNAs (hsiRNAs). Notably, cholesterol-hsiRNA presented slow plasma clearances and mainly accumulated in the liver, whereas, phosphocholine-docosahexaenoic acid-hsiRNA was rapidly cleared from the plasma and preferably accumulated in the kidney. These data suggest that the PK/biodistribution profiles of modified hsiRNAs are determined by the chemical nature of the conjugate. Importantly, the method described in this study constitutes a simple platform to conduct pilot assessments of the basic clearance and tissue distribution profiles, which can be broadly applied for evaluation of new chemical variants of siRNAs and micro-RNAs.

Design of nanocarriers for nanoscale drug delivery to enhance cancer treatment using hybrid polymer and lipid building blocks

Polymer-lipid hybrid nanoparticles (PLN) are an emerging nanocarrier platform made from building blocks of polymers and lipids. PLN integrate the advantages of biomimetic lipid-based nanoparticles (i.e. solid lipid nanoparticles and liposomes) and biocompatible polymeric nanoparticles. PLN are constructed from diverse polymers and lipids and their numerous combinations, which imparts PLN with great versatility for delivering drugs of various properties to their nanoscale targets. PLN can be classified into two types based on their hybrid nanoscopic structure and assembly methods: Type-I monolithic matrix and Type-II core-shell systems. This article reviews the history of PLN development, types of PLN, lipid and polymer candidates, fabrication methods, and unique properties of PLN. The applications of PLN in delivery of therapeutic or imaging agents alone or in combination for cancer treatment are summarized and illustrated with examples. Important considerations for the rational design of PLN for advanced nanoscale drug delivery are discussed, including selection of excipients, synthesis processes governing formulation parameters, optimization of nanoparticle properties, improvement of particle surface functionality to overcome macroscopic, microscopic and cellular biological barriers. Future directions and potential clinical translation of PLN are also suggested.

The Niemann-Pick C1 Inhibitor NP3.47 Enhances Gene Silencing Potency of Lipid Nanoparticles Containing siRNA

The therapeutic applications of lipid nanoparticle (LNP) formulations of small interfering RNA (siRNA), are hampered by inefficient delivery of encapsulated siRNA to the cytoplasm following endocytosis. Recent work has shown that up to 70% of endocytosed LNP-siRNA particles are recycled to the extracellular medium and thus cannot contribute to gene silencing. Niemann-Pick type C1 (NPC1) is a late endosomal/lysosomal membrane protein required for efficient extracellular recycling of endosomal contents. Here we assess the influence of NP3.47, a putative small molecule inhibitor of NPC1, on the gene silencing potency of LNP-siRNA systems in vitro. Intracellular uptake and colocalization studies revealed that the presence of NP3.47 caused threefold or higher increases in accumulation of LNP-siRNA in late endosomes/lysosomes as compared with controls in a variety of cell lines. The gene silencing potency of LNP siRNA was enhanced up to fourfold in the presence of NP3.47. Mechanisms of action studies are consistent with the proposal that NP3.47 acts to inhibit NPC1. Our findings suggest that the pharmacological inhibition of NPC1 is an attractive strategy to enhance the therapeutic efficacy of LNP-siRNA by trapping LNP-siRNA in late endosomes, thereby increasing opportunities for endosomal escape.

ε-Caprolactone-Modified Polyethylenimine as Efficient Nanocarriers for siRNA Delivery in Vivo

RNA interference (RNAi) therapy is a promising treatment for various diseases. However, its application is still restricted by the lack of efficient and safe delivery systems. A novel siRNA delivery vehicle based on ε-caprolactone-modified polyethylenimine (PEI-CL) is presented here. The PEI-CL macromolecules with different grafting degrees were synthesized via a simple ring-opening reaction. This macromolecule strongly protects the siRNA from degradation in serum and promotes the cellular uptake and endosomal escape detected via chemical exchange saturation transfer magnetic resonance analysis and fluorescence imaging. The in vivo measurement was performed with HCT-116 colon tumor xenograft that stably expressed luciferase. The data showed that the PEI-CL/siRNA nanocomplexes elicited strong RNAi response. More interestingly, enhanced gene transfection efficiency was achieved by simultaneous cotransfection with siRNA and DNA plasmid via this novel nanosystem. Overall, our study suggests the PEI-CL macromolecule with great promise for siRNA delivery.

Lipid Nanoparticle Delivery of siRNA to Osteocytes Leads to Effective Silencing of SOST and Inhibition of Sclerostin In Vivo

Sclerostin is a protein secreted by osteocytes that is encoded by the SOST gene; it decreases bone formation by reducing osteoblast differentiation through inhibition of the Wnt signaling pathway. Silencing the SOST gene using RNA interference (RNAi) could therefore be an effective way to treat osteoporosis. Here, we investigate the utility of lipid nanoparticle (LNP) formulations of siRNA to silence the SOST gene in vitro and in vivo. It is shown that primary mouse embryonic fibroblasts (MEF) provide a useful model system in which the SOST gene can be induced by incubation in osteogenic media, allowing development of optimized SOST siRNA for silencing the SOST gene. Incubation of MEF cells with LNP containing optimized SOST siRNA produced significant, prolonged knockdown of the induced SOST gene in vitro, which was associated with an increase in osteogenic markers. Intravenous (i.v.) administration of LNP containing SOST siRNA to mice showed significant accumulation of LNP in osteocytes in compact bone, depletion of SOST mRNA and subsequent reduction of circulating sclerostin protein, establishing the potential utility for LNP siRNA systems to promote bone formation.

Lipid nanoparticles for targeted siRNA delivery - going from bench to bedside

This review covers the basic aspects of small interfering RNA delivery by lipid nano-particles (LNPs) and elaborates on the current status of clinical trials for these systems. We briefly describe the roles of all LNP components and possible strategies for their improvement. We also focus on the current clinical trials using LNP-formulated RNA and the possible outcomes for therapy in the near future. Also, we present a critical analysis of selected clinical trials that reveals the common logic behind target selection. We address this review to a wide audience, especially to medical doctors who are interested in the application of RNA interference-based treatment platforms. We anticipate that this review may spark interest in this particular audience and generate new ideas in target selection for the disorders they are dealing with.

Influence of particle size on the in vivo potency of lipid nanoparticle formulations of siRNA

Lipid nanoparticles (LNP) can provide a clinically effective method for delivering small interfering RNA (siRNA) to silence pathological genes in hepatocytes. The gene silencing potency of these LNP-siRNA systems has been shown to depend on a variety of factors including association with serum factors such as ApoE and the pKa of component ionizable lipids. Here we investigate the influence of LNP size, an important parameter affecting tissue penetration of LNP systems, on the pharmacokinetics, biodistribution, and hepatic gene silencing potency of LNP-siRNA systems following intravenous administration. For LNP systems stabilized by a polyethylene glycol (PEG)-lipid that can dissociate from the LNP following injection, it is shown that small (diameter≤30nm) systems are considerably less potent than their larger counterparts. This is attributed in part to the ability of other lipid components, particularly the ionizable amino-lipid, to dissociate from the LNP following dissociation of the PEG-lipid. Small LNP stabilized by PEG-lipids with slow dissociation rates exhibited much reduced amino-lipid dissociation rates, however such systems are relatively impotent due to the continued presence of the PEG coating. These results demonstrate the delicate balance between the in vivo potency of LNP-siRNA systems and the residence times of component lipids in the LNP particle itself and suggest new directions to optimize the in vivo gene silencing potency of small LNP-siRNA systems.

Treatment of a multiple sclerosis animal model by a novel nanodrop formulation of a natural antioxidant

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system and is associated with demyelination, neurodegeneration, and sensitivity to oxidative stress. In this work, we administered a nanodroplet formulation of pomegranate seed oil (PSO), denominated Nano-PSO, to mice induced for experimental autoimmune encephalomyelitis (EAE), an established model of MS. PSO comprises high levels of punicic acid, a unique polyunsaturated fatty acid considered as one of the strongest natural antioxidants. We show here that while EAE-induced mice treated with natural PSO presented some reduction in disease burden, this beneficial effect increased significantly when EAE mice were treated with Nano-PSO of specific size nanodroplets at much lower concentrations of the oil. Pathological examinations revealed that Nano-PSO administration dramatically reduced demyelination and oxidation of lipids in the brains of the affected animals, which are hallmarks of this severe neurological disease. We propose that novel formulations of natural antioxidants such as Nano-PSO may be considered for the treatment of patients suffering from demyelinating diseases. On the mechanistic side, our results demonstrate that lipid oxidation may be a seminal feature in both demyelination and neurodegeneration.

Therapeutic Oligonucleotides Targeting Liver Disease: TTR Amyloidosis

The liver has become an increasingly interesting target for oligonucleotide therapy. Mutations of the gene encoding transthyretin (TTR), expressed in vast amounts by the liver, result in a complex degenerative disease, termed familial amyloid polyneuropathy (FAP). Misfolded variants of TTR are linked to the establishment of extracellular protein deposition in various tissues, including the heart and the peripheral nervous system. Recent progress in the chemistry and formulation of antisense (ASO) and small interfering RNA (siRNA) designed for a knockdown of TTR mRNA in the liver has allowed to address the issue of gene-specific molecular therapy in a clinical setting of FAP. The two therapeutic oligonucleotides bind to RNA in a sequence specific manner but exploit different mechanisms. Here we describe major developments that have led to the advent of therapeutic oligonucleotides for treatment of TTR-related disease.

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.

Therapeutic potential of small interfering RNAs/micro interfering RNA in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the predominant form of primary liver cancer and represents the third leading cause of cancer-related death worldwide. Current available therapeutic approaches are poorly effective, especially for the advanced forms of the disease. In the last year, short double stranded RNA molecules termed small interfering RNAs (siRNAs) and micro interfering RNAs (miRNA), emerged as interesting molecules with potential therapeutic value for HCC. The practical use of these molecules is however limited by the identification of optimal molecular targets and especially by the lack of effective and targeted HCC delivery systems. Here we focus our discussion on the most recent advances in the identification of siRNAs/miRNAs molecular targets and on the development of suitable siRNA/miRNAs delivery systems.

Systemic Gene Silencing in Primary T Lymphocytes Using Targeted Lipid Nanoparticles

Modulating T cell function by down-regulating specific genes using RNA interference (RNAi) holds tremendous potential in advancing targeted therapies in many immune-related disorders including cancer, inflammation, autoimmunity, and viral infections. Hematopoietic cells, in general, and primary T lymphocytes, in particular, are notoriously hard to transfect with small interfering RNAs (siRNAs). Herein, we describe a novel strategy to specifically deliver siRNAs to murine CD4(+) T cells using targeted lipid nanoparticles (tLNPs). To increase the efficacy of siRNA delivery, these tLNPs have been formulated with several lipids designed to improve the stability and efficacy of siRNA delivery. The tLNPs were surface-functionalized with anti-CD4 monoclonal antibody to permit delivery of the siRNAs specifically to CD4(+) T lymphocytes. Ex vivo, tLNPs demonstrated specificity by targeting only primary CD4(+) T lymphocytes and no other cell types. Systemic intravenous administration of these particles led to efficient binding and uptake into CD4(+) T lymphocytes in several anatomical sites including the spleen, inguinal lymph nodes, blood, and the bone marrow. Silencing by tLNPs occurs in a subset of circulating and resting CD4(+) T lymphocytes. Interestingly, we show that tLNP internalization and not endosome escape is a fundamental event that takes place as early as 1 h after systemic administration and determines tLNPs' efficacy. Taken together, these results suggest that tLNPs may open new avenues for the manipulation of T cell functionality and may help to establish RNAi as a therapeutic modality in leukocyte-associated diseases.

Production of limit size nanoliposomal systems with potential utility as ultra-small drug delivery agents

Previous studies from this group have shown that limit size lipid-based systems--defined as the smallest achievable aggregates compatible with the packing properties of their molecular constituents--can be efficiently produced using rapid microfluidic mixing technique. In this work, it is shown that similar procedures can be employed for the production of homogeneously sized unilamellar vesicular systems of 30-40 nm size range. These vesicles can be remotely loaded with the protonable drug doxorubicin and exhibit adequate drug retention properties in vitro and in vivo. In particular, it is demonstrated that whereas sub-40 nm lipid nanoparticle (LNP) systems consisting entirely of long-chain saturated phosphatidylcholines cannot be produced, the presence of such lipids may have a beneficial effect on the retention properties of limit size systems consisting of mixed lipid components. Specifically, a 33-nm diameter doxorubicin-loaded LNP system composed of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC), 1,2-dipalmitoyl phosphatidylcholine (DPPC), cholesterol, and PEGylated lipid (DSPE-PEG2000) demonstrated adequate, stable drug retention in the circulation, with a half-life for drug release of ∼ 12 h. These results indicate that microfluidic mixing is the technique of choice for the production of bilayer LNP systems with sizes less than 50 nm that could lead to development of a novel class of ultra-small drug delivery vehicles.