Nucleic acid transfer with hemifluorinated polycationic lipids

Fluorinated vectors for gene delivery

INTRODUCTION

Gene delivery vectors are a crucial determinant for gene therapeutic efficacy. Usually, it is necessary to use an excess of cationic vectors to achieve better transfection efficiency. However, it will cause severe cytotoxicity. In addition, cationic vectors are not resistant to serum, suffering from reduced transfection efficiency by forming large aggregates. Therefore, there is an urgent need to develop optimized gene delivery vectors. Recently, fluorination of vectors has been extensively applied to increase the gene delivery performance because of the unique properties of both hydrophobicity and lipophobicity, and chemical and biological inertness.

AREAS COVERED

This review will discuss the fluorophilic effects that impact gene delivery efficiency, and chemical modification approaches for fluorination. Next, recent advances and applications of fluorinated polymeric and lipidic vectors in gene therapy and gene editing are summarized.

EXPERT OPINION

Fluorinated vectors are a promising candidate for gene delivery. However, it still needs further studies to obtain pure and well-defined fluorinated polymers, guarantee the biosafety, and clarify the detailed mechanism. Apart from the improvements in gene delivery, exploiting other versatility of fluorinated vectors, such as oxygen-carrying ability, high affinity with fluorine-containing drugs, and imaging property upon introducing 19^F, will further facilitate their applications in gene therapy.

Fluorination Promotes the Cytosolic Delivery of Genes, Proteins, and Peptides

The cytosolic delivery of biomolecules such as genes, proteins, and peptides is of great importance for biotherapy but usually limited by multiple barriers during the process. Cell membrane with high hydrophobic character is one of the representative biological barriers for cytosolic delivery. The introduction of hydrophobic ligands such as aliphatic lipids onto materials or biomolecules could improve their membrane permeability. However, these ligands are lipophilic and tend to interact with the phospholipids in the membrane as well as serum proteins, which may hinder efficient intracellular delivery. To solve this issue, our research group proposed the use of fluorous ligands with both hydrophobicity and lipophobicity as ideal alternatives to aliphatic lipids to promote cytosolic delivery.In our first attempt, fluorous ligands were conjugated onto cationic polymers to increase their gene delivery efficacy. The fluorination dramatically increased the gene delivery performance at low polymer doses. In addition, the strategy greatly improved the serum tolerance of cationic polymers, which is critical for efficient gene delivery in vivo. Besides serum tolerance, mechanism studies revealed that fluorination increases multiple steps such as cellular uptake and endosomal escape. Fluorination also allowed the assembly of low-molecular-weight polymers and achieved highly efficient gene delivery with minimal material toxicity. The method showed robust efficiency for polymers, including linear polymers, branched polymers, dendrimers, bola amphiphilies, and dendronized polymers.Besides gene delivery, fluorinated polymers were also used for intracellular protein delivery via a coassembly strategy. For this purpose, two lead fluoropolymers were screened from a library of amphiphilic materials. The fluoropolymers are greatly superior to their nonfluorinated analogues conjugated with aliphatic lipids. The fluorous lipids are beneficial for polymer assembly and protein encapsulation, reduced protein denaturation, facilitated endocytosis, and decreased polymer toxicity compared to nonfluorinated lipids. The materials exhibited potent efficacy in therapeutic protein and peptide delivery to achieve cancer therapy and were able to fabricate a personalized nanovaccine for cancer immunotherapy. Finally, the fluorous lipids were directly conjugated to peptides via a disulfide bond for cytosolic peptide delivery. Fluorous lipids drive the assembly of cargo peptides into uniform nanoparticles with much improved proteolytic stability and promote their delivery into various types of cells. The delivery efficacy of this strategy is greatly superior to traditional techniques such as cell-penetrating peptides both in vitro and in vivo. Overall, the fluorination techniques provide efficient and promising strategies for the cytosolic delivery of biomolecules.

Dendritic peptide bolaamphiphiles for siRNA delivery to primary adipocytes

Obesity is a major risk factor for diabetes, heart disease and other health problems. Adipose tissue plays a central role in the development of obesity and obesity-associated diseases. Gene therapy targeting adipose tissue may provide a promising strategy for obesity treatment. However, nucleic acid delivery to adipose tissue or even cultured adipocytes is challenging due to low delivery efficacy and high toxicity of the current cationic lipid based delivery systems, or monoamphiphiles. Herein, we report using dendritic peptide bolaamphiphiles (bolas) to deliver siRNA to primary adipocytes and hepatocytes. The bola consists of two l-Lysine dendrons connected to a fluorocarbon core through disulfide linkages. The Lysine dendrons are functionalized with l-histidine and l-tryptophan to promote endosomal escape and cellular uptake. The bola exhibited over 70% knockdown of GAPDH gene in both primary adipocytes and hepatocytes. Importantly, different from Lipofectamine that significantly reduced genes involved in lipolysis, lipogenesis, fatty acid oxidation and ketogenesis, the bolas had little to no effect on these genes. These results demonstrate the bola as a promising new vector for clinical and experimental applications for delivery of siRNA to metabolic organs.

Fluorocarbon Modified Low-Molecular-Weight Polyethylenimine for siRNA Delivery

We report the synthesis and study of fluorocarbon (FC) modified polyethylenimine (PEI) for the purpose of siRNA delivery. Low-molecular-weight PEI (Mn = 600) was functionalized with fluorocarbon epoxides of varying length. All FC-modified samples with greater than 2.0 equiv of FC epoxide per PEI induced potent gene silencing in vitro. Compared to hydrocarbon (HC) analogues, the FC vectors showed greater general silencing efficacy, higher cell uptake, and reduced association with serum components. Collectively, the data suggest that modification of polyamines with FCs is a promising approach for the discovery of novel vectors for siRNA delivery.

Structure-Based Design of Dendritic Peptide Bolaamphiphiles for siRNA Delivery

Development of safe and effective delivery vectors is a critical challenge for the application of RNA interference (RNAi)-based biotechnologies. In this study we show the rational design of a series of novel dendritic peptide bolaamphiphile vectors that demonstrate high efficiency for the delivery of small interfering RNA (siRNA) while exhibiting low cytotoxicity and hemolytic activity. Systematic investigation into structure-property relationships revealed an important correlation between molecular design, self-assembled nanostructure, and biological activity. The unique bolaamphiphile architecture proved a key factor for improved complex stability and transfection efficiency. The optimal vector contains a fluorocarbon core and exhibited enhanced delivery efficiency to a variety of cell lines and improved serum resistance when compared to hydrocarbon analogues and lipofectamine RNAiMAX. In addition to introducing a promising new vector system for siRNA delivery, the structure-property relationships and "fluorocarbon effect" revealed herein offer critical insight for further development of novel materials for nucleic acid delivery and other biomaterial applications.

Fluorination on polyethylenimine allows efficient 2D and 3D cell culture gene delivery

Polyethylenimine (PEI) is one of the most promising polymeric gene vectors, however its applications are limited by serious cytotoxicity and moderate transfection efficacy. Fluorination is an efficient strategy to improve the transfection efficacy of cationic polymers while reducing their cytotoxicity. Here we grafted different fluoroalkyl chains to PEI via oxirane and anhydride reactions. The fluorinated PEIs show superior transfection efficacy on both 2D and 3D cell cultures to unmodified PEI. These fluorinated polymers allow efficient gene transfection at relatively low nitrogen to phosphorus ratios and thereby ensure low cytotoxicity on the transfected cells. Fluorinated PEIs prepared via the oxirane reaction are much more stable in aqueous solutions than the ones prepared by the anhydride reaction and show reproducible gene transfection during a period of 6 months. This study extends the applicable scope of fluorination on improving the transfection efficacy of polymers and generates a list of gene vectors for efficient 2D and 3D cell culture gene transfection.

Cationic liposome-nucleic acid complexes for gene delivery and gene silencing

Cationic liposomes (CLs) are studied worldwide as carriers of DNA and short interfering RNA (siRNA) for gene delivery and gene silencing, and related clinical trials are ongoing. Optimization of transfection efficiency and silencing efficiency by cationic liposome carriers requires a comprehensive understanding of the structures of CL-nucleic acid complexes and the nature of their interactions with cell membranes as well as events leading to release of active nucleic acids within the cytoplasm. Synchrotron x-ray scattering has revealed that CL-nucleic acid complexes spontaneously assemble into distinct liquid crystalline phases including the lamellar, inverse hexagonal, hexagonal, and gyroid cubic phases, and fluorescence microscopy has revealed CL-DNA pathways and interactions with cells. The combining of custom synthesis with characterization techniques and gene expression and silencing assays has begun to unveil structure-function relations in vitro. As a recent example, this review will briefly describe experiments with surface-functionalized PEGylated CL-DNA nanoparticles. The functionalization, which is achieved through custom synthesis, is intended to address and overcome cell targeting and endosomal escape barriers to nucleic acid delivery faced by PEGylated nanoparticles designed for in vivo applications.

Nonviral gene delivery with dendritic self-assembling architectures

In this review, we outline the concept and applicability of self-assembling dendrimers for gene-delivery applications. Low-molecular-weight, well-defined cationic dendritic arrays which have been modified with hydrophobic domains can form self-organized multivalent systems that have significant advantages over nonassembling, high-molecular-weight/polymeric gene vectors. Particular structural variations have been highlighted with respect to the individual components of the displayed dendritic amphiphiles, namely, the employed amine termini, the hydrophobic segment, the size of the dendritic array, and the integration of special features such as targeting ability and cleavability/degradability, which can all have a crucial effect on gene-transfection efficiencies. Accordingly, the scientific efforts to create new synthetic gene-delivery vectors to act as promising in vivo transfection agents in the future will be presented and discussed here.

siRNA delivery: from lipids to cell-penetrating peptides and their mimics

To deliver siRNA for therapeutic use, several hurdles must be addressed. Metabolic degradation must be blocked, and the RNAi cellular machinery is located in the cytoplasm, while double-stranded siRNA is large, highly charged and impermeable to cell membranes. To date, the solutions to the delivery issues have mostly involved different forms of lipid particle encapsulation. Cell-penetrating peptides and their mimics or analogues offer a different approach and this is an emerging field with the first in vivo examples now reported. Recent reports point to lipid receptors being involved in the cellular uptake of both types of transporter. This review examines the delivery of siRNA with a focus on cell-penetrating peptides and their small molecule and oligomeric mimics. The current status of siRNA delivery methods in clinical trials is examined. It now seems that the goal of delivering siRNA therapeutically is achievable but will they form part of a sustainable healthcare portfolio for the future.

Heterogeneous cationic liposomes modified with 3β-{N-[(N',N'-dimethylamino)ethyl]carbamoyl}cholesterol can induce partial conformational changes in messenger RNA and regulate translation in an Escherichia coli cell-free translation system

The effect of cationic liposomes (CLs) on messenger RNA(mRNA) conformation and translation was studied, focusing on membrane heterogeneity. CLs, composed of 1,2-dioleoyl-sn-glycerol-3-phosphocholine/1,2-dioleoyl-3-timethylammonium propane (DOPC/DOTAP) and DOPC/3β-{N-[(N',N'-dimethylamino)ethyl]carbamoyl}cholesterol (DOPC/DC-Ch), inhibited mRNA translation in an Escherichia coli cell-free translation system. Analysis of the membrane fluidity and polarity indicated a heterogeneous DOPC/DC-Ch (70/30) membrane, while other CLs exhibited homogeneous disordered membranes. mRNA adsorbed onto DOPC/DC-Ch liposomes showed translational activity, while DOPC/DOTAP liposomes inhibited mRNA translation in proportion to its adsorption onto membranes. Dehydration of DOPC/DOTAP (70/30) and DOPC/DC-Ch (70/30) was observed in the presence of mRNA but not in the case of zwitterionic DOPC liposomes, indicating that mRNA binds in regions between the phosphate [-PO(2)(-)-] and carbonyl [-C=O-] moieties of lipids. UV resonance Raman spectroscopy suggests that adenine, cytosine, and guanine interact with DOPC/DOTAP (70/30) and DOPC/DC-Ch (70/30) but not with DOPC. Circular dichroism indicates that DOPC/DOTAP (70/30) extensively denatured the mRNA. In contrast, heterogeneous DOPC/DC-Ch (70/30) induced partial conformational changes but maintained the translational activity of mRNA.

Efficient silencing of EGFP reporter gene with siRNA delivered by asymmetrical N4,N9-diacyl spermines

It is important to obtain structure-activity relationship (SAR) data across cationic lipids for the self-assembly and nonviral intracellular delivery of siRNA. The aims of this work are to carry out a SAR study on the efficiency of asymmetrical N(4),N(9)-diacyl spermines in siRNA delivery and EGFP reporter gene silencing, with comparisons to selected mixtures composed of symmetrical N(4),N(9)-diacyl spermines. Another important aim of these studies is to quantify the changes in cell viability, assayed with alamarBlue, as a function of lipid structure. Therefore, we have designed, synthesized, purified, and assayed novel cationic lipids that are asymmetrical lipopolyamines based on spermine. Flow cytometry and fluorescence microscopy in an EGFP stably transfected HeLa cell line, measuring both delivery of fluorescently tagged siRNAs and silencing the EGFP signal, allowed quantitation of the differences between asymmetrical cationic lipids, mixtures of their symmetrical counterparts, and comparison with commercial nonviral delivery agents. Intracellular delivery of siRNA and gene silencing by siRNA differ with different hydrophobic domains. In these asymmetrical N(4),N(9)-diacyl spermines, lipids that enhance siRNA uptake do not necessarily enhance siRNA-induced inhibition of gene expression: C18 and longer saturated chains promote uptake, while more unsaturated C18 chains promote gene silencing. These properties are efficiently demonstrated in a new nontoxic cationic lipid siRNA vector, N(4)-linoleoyl-N(9)-oleoyl-1,12-diamino-4,9-diazadodecane (LinOS), which is also shown to be comparable with or superior to TransIT-TKO and Lipofectamine 2000.

C/EBP-α and C/EBP-β-mediated adipogenesis of human mesenchymal stem cells (hMSCs) using PLGA nanoparticles complexed with poly(ethyleneimmine)

In this study, to drive efficient adipogenic differentiation, the adipogenic transcription factors C/EBP-α and C/EBP-β fused to green fluorescent protein (GFP) or red fluorescent protein (RFP) were complexed with poly-ethyleneimine (PEI) coupled with biodegradable PLGA nanospheres and delivered to human mesenchymal stem cell (hMSC). FACS analysis revealed that the transfection efficiency of C/EBP-α, C/EBP-β, or both genes complexed with PEI-coated PLGA nanospheres was 12.59%, 21.74%, and 28.96% of hMSCs. Expression and localization of C/EBP-α and C/EBP-β were confirmed by Western blotting and confocal laser microscopy. Overexpression of exogenous C/EBP-α and C/EBP-β significantly elevated adipogenic differentiation processes as indicated by RT-PCR, real-time PCR, Western blotting, histology, and immunofluorescence microscopy. During adipogenesis, PEI-coupled PLGA nanospheres complexed with C/EBP-α and C/EBP-β greatly increased the adipogenic capability of in vitro cultured cells, as well of in vivo transplanted cells. The expression of genes and proteins specific to adipogenic differentiation in hMSCs was significantly elevated compared to the controls.

Efficient Gene Silencing by Self-Assembled Complexes of siRNA and Symmetrical Fatty Acid Amides of Spermine

Gene silencing by siRNA (synthetic dsRNA of 21-25 nucleotides) is a well established biological tool in gene expression studies and has a promising therapeutic potential for difficult-to-treat diseases. Five fatty acids of various chain length and oxidation state (C12:0, C18:0, C18:1, C18:2, C22:1) were conjugated to the naturally occurring polyamine, spermine, and evaluated for siRNA delivery and gene knock-down. siRNA delivery could not be related directly to gene silencing efficiency as N⁴,N⁹-dierucoyl spermine resulted in higher siRNA delivery compared to N⁴,N⁹-dioleoyl spermine. GFP silencing in HeLa cells showed that the unsaturated fatty acid amides are more efficient than saturated fatty acid amides, with N⁴,N⁹-dioleoyl spermine resulting in the most efficient gene silencing in the presence of serum. The alamarBlue cell viability assay showed that fatty acid amides of spermine have good viability (75%–85% compared to control) except N⁴,N⁹-dilauroyl spermine which resulted in low cell viability. These results prove that unsaturated fatty acid amides of spermine are efficient, non-toxic, non-viral vectors for siRNA mediated gene silencing.

Recent advances of siRNA delivery by nanoparticles

INTRODUCTION

The field of RNA interference technology has been researched extensively in recent years. However, the development of clinically suitable, safe and effective drug delivery vehicles is still required.

AREAS COVERED

This paper reviews the recent advances of non-viral delivery of small interfering RNA (siRNA) by nanoparticles, including biodegradable nanoparticles, liposomes, polyplex, lipoplex and dendrimers. The characteristics, composition, preparation, applications and advantages of different nanoparticle delivery strategies are also discussed in detail, along with the recent progress of non-viral nanoparticle carrier systems for siRNA delivery in preclinical and clinical studies.

EXPERT OPINION

Non-viral carrier systems, especially nanoparticles, have been investigated extensively for siRNA delivery, and may be utilized in clinical applications in the future. So far, a few preliminary clinical trials of nanoparticles have produced promising results. However, further research is still required to pave the way to successful clinical applications. The most important issues that need to be focused on include encapsulation efficiency, formulation stability of siRNA, degradation in circulation, endosomal escape and delivery efficiency, targeting, toxicity and off-target effects. Pharmacology and pharmacokinetic studies also present another great challenge for nanoparticle delivery systems, owing to the unique nature of siRNA oligonucleotides compared with small molecules.