Distinct effects of endosomal escape and inhibition of endosomal trafficking on gene delivery via electrotransfection

Endolysosomal trapping of therapeutics and endosomal escape strategies

Internalizing therapeutic molecules or genes into cells and safely delivering them to the target tissue where they can perform the intended tasks is one of the key characteristics of the smart gene/drug delivery vector. Despite much research in this field, endosomal escape continues to be a significant obstacle to the development of effective gene/drug delivery systems. In this review, we discuss in depth the several types of endocytic pathways involved in the endolysosomal trapping of therapeutic agents. In addition, we describe numerous mechanisms involved in nanoparticle endosomal escape. Furthermore, many other techniques are employed to increase endosomal escape to minimize entrapment of therapeutic compounds within endolysosomes, which have been reviewed at length in this study.

Bifunctional Molecules That Induce Both Targeted Degradation and Transcytosis of Extracellular Proteins in Brain Cells

Targeted protein degradation (TPD) has emerged as an effective therapeutic strategy for a wide range of diseases; however, the blood-brain barrier (BBB) limits access of degraders into the central nervous system (CNS). Here, we present a new class of bifunctional small molecules, called TransMoDEs (Transcytosis-inducing molecular degraders of extracellular proteins), capable of both (1) removal of target protein via lysosomal proteolysis and (2) transcytosis of protein targets across brain endothelial cells. TransMoDEs are derived from Angiopep-2, a peptide motif previously employed as a covalent tag to facilitate receptor-mediated transcytosis across the BBB. We demonstrate that TransMoDEs containing either a biotin or chloroalkane ligand can trigger endocytosis of streptavidin or HaloTag protein, respectively. Interestingly, although low-density lipoprotein receptor-related protein 1 (LRP1) has been reported as the primary receptor for Angiopep-2, TransMoDE-mediated target uptake does not rely exclusively on this pathway. Furthermore, TransMoDE-mediated endocytosis of streptavidin in a bEnd.3 BBB model occurs in a clathrin-mediated mechanism and results in both lysosomal localization and transcytosis of the target protein. This study demonstrates that TransMoDEs can recruit, transcytose, and degrade proteins of interest in cells relevant to the CNS, supporting their further development for the removal of pathogenic neuroproteins.

Sucrose Treatment Enhances the Electrotransfer of DNA by Activating Phospholipase A2

Our previous study discovered that sucrose and other non-reducing sugars (e.g., trehalose and raffinose) could be used to improve the electrotransfer (ET) of molecular cargo, including DNA, mRNA, and ribonucleoprotein in various cell lines and primary human cells in vitro and in vivo. To understand the molecular mechanisms of this improvement, we used RNA sequencing technology to analyze changes in the cell transcriptome after sucrose treatment. The results from our analysis demonstrated that the sucrose treatment upregulated phospholipase A2 and V-ATPase gene families, which could potentially influence the acidity of intracellular vesicles through augmenting vesicle fusion and the influx of proton, respectively. To determine how this upregulation affects ET efficiency, we treated cells with pharmaceutical inhibitors of phospholipase A2 and V-ATPase. The data demonstrated that the treatment with the phospholipase A2 inhibitor could reverse the ET improvement elicited by the sucrose treatment. The V-ATPase inhibitor treatment either had little influence or further enhanced the effect of the sucrose treatment on the ET efficiency. These observations provide a molecular explanation for our previous findings, demonstrating that the sucrose treatment primarily enhanced the ET efficiency by promoting vesicle trafficking and fusion through the activation of phospholipase A2.

Expression of GFP and DsRed fluorescent proteins after gene electrotransfer of tumour cells in vitro

Fluorescent reporter genes are widely used to study the transfection of various types of primary cells and cell lines. The aim of our research was to investigate the expression dynamics of GFP and DsRed reporter genes individually and combined after gene electrotransfer of plasmids with two different electroporation protocols in B16F10 and CT26 cells in vitro. The cytotoxicity after gene electrotransfer of both plasmids was first determined. Second, the intensity of fluorescence and the percentage of cells transfected with both plasmids individually and in combination were monitored in real time. The results show that the percentage of viability after gene electrotransfer of plasmids using the EP2 pulses was significantly higher compared to the EP1 pulses. In contrast, the percentage of transfected cells and fluorescence intensity were higher after gene electrotransfer with the EP1 pulse protocol. Moreover, the percentage of transfected cells was higher and started earlier in the B16F10 cell line than in the CT26 cell line. However, fluorescence intensity was higher in CT26 cells. Co-expression of fluorescent proteins was achieved only in a small number of cells. In conclusion, this study elucidated some of the dynamics of reporter gene expression in cancer cell lines after gene electrotransfer.

Copy number of naked DNA delivered into nucleus of mammalian cells by electrotransfection

Electrotransfection is a non-viral method for delivery of nucleic acids into cells. In our previous study, we have determined the minimal copy number of plasmid DNA (pDNA) per cell required for transgene expression post electrotransfection, and developed a statistical framework to predict the pDNA copy number in the nucleus. To experimentally verify the prediction, the current study was designed to quantify the average copy number of pDNA per nucleus post electrotransfection. To achieve it, we developed a novel approach to effectively obtain isolated nuclei with minimal contamination by extranuclear pDNA. This sample preparation method enabled us to accurately measure intranuclear pDNA using quantitative real-time PCR. The data showed that the copy number of pDNA per nucleus was dependent on the period of cell culture post pulsing and the pDNA dose for electrotransfection. Additionally, the data were used to improve the statistical framework for understanding kinetics of pDNA transport in cells, and predicting how the kinetics depended on different factors. It is expected that the framework and the methodology developed in the current study will be useful for evaluating factors that may affect kinetics and mechanisms of pDNA transport in cells.

Cellular uptake of modified mRNA occurs via caveolae-mediated endocytosis, yielding high protein expression in slow-dividing cells

Nucleic acids have clear clinical potential for gene therapy. Plasmid DNA (pDNA) was the first nucleic acid to be pursued as a therapeutic molecule. Recently, mRNA came into play as it offers improved safety and affordability. In this study, we investigated the uptake mechanisms and efficiencies of genetic material by cells. We focused on three main variables (1) the nucleic acid (pDNA, or chemically modified mRNA), (2) the delivery vector (Lipofectamine 3000 or 3DFect), and (3) human primary cells (mesenchymal stem cells, dermal fibroblasts, and osteoblasts). In addition, transfections were studied in a 3D environment using electrospun scaffolds. Cellular internalization and intracellular trafficking were assessed by using enhancers or inhibitors of endocytosis and endosomal escape. The polymeric vector TransIT-X2 was included for comparison purposes. While lipoplexes utilized several entry routes, uptake via caveolae served as the main route for gene delivery. pDNA yielded higher expression levels in fast-dividing fibroblasts, whereas, in slow-dividing osteoblasts, cmRNA was responsible for high protein production. In the case of mesenchymal stem cells, which presented an intermediate doubling time, the combination vector/nucleic acid seemed more relevant than the nucleic acid per se. In all cases, protein expression was higher when the cells were seeded on 3D scaffolds.

Nanoenhancer for improving naked DNA electrotransfection In vivo

Introduction: Electrotransfection (ET) is a non-viral approach widely used for delivery of naked nucleic acids. Its efficiency can be increased in vitro by treatment of cells with various small molecule enhancers. However, these enhancers often fail to improve ET in vivo, presumably due to rapid clearance in tissues after local injection, reducing their cellular uptake. To this end, we propose to develop a new type of ET enhancers, which we term nanoenhancer, that diffuse slowly in tissues and are poorly absorbed by blood and lymph microvessels. Methods: Two nanoenhancers were synthesized with alginate (Alg) and chitosan (Chi) with or without poly (ethylene imine) (PEI). They were used to treat cells in vitro or mouse muscle in the hind leg in vivo prior to ET of plasmid DNA coding reporter genes. At 24 hours post ET, the efficiency of ET was quantified, and compared with that in the untreated controls. Changes in lysosomal size and acidity post nanoenhancer treatment were measured with fluorescence microscopy techniques. Results and discussion: We observed that the pretreatment of cells with the nanoenhancers could enhance the ET efficiency and cell viability in both C2C12 and HCT116 cells in vitro, and the nanoenhancer pretreatment had similar effects on the ET efficiency in vivo. Mechanisms of the enhancement were related to transient inactivation of lysosomal functions triggered by the nanoenhancer treatment. The concept of nanoenhancer will lead to development of new enhancers that can be used to improve ET efficiency in vivo, highlighting its potential in clinical applications.

Potential therapeutic strategies for photoreceptor degeneration: the path to restore vision

Photoreceptors (PRs), as the most abundant and light-sensing cells of the neuroretina, are responsible for converting light into electrical signals that can be interpreted by the brain. PR degeneration, including morphological and functional impairment of these cells, causes significant diminution of the retina's ability to detect light, with consequent loss of vision. Recent findings in ocular regenerative medicine have opened promising avenues to apply neuroprotective therapy, gene therapy, cell replacement therapy, and visual prostheses to the challenge of restoring vision. However, successful visual restoration in the clinical setting requires application of these therapeutic approaches at the appropriate stage of the retinal degeneration. In this review, firstly, we discuss the mechanisms of PR degeneration by focusing on the molecular mechanisms underlying cell death. Subsequently, innovations, recent developments, and promising treatments based on the stage of disorder progression are further explored. Then, the challenges to be addressed before implementation of these therapies in clinical practice are considered. Finally, potential solutions to overcome the current limitations of this growing research area are suggested. Overall, the majority of current treatment modalities are still at an early stage of development and require extensive additional studies, both pre-clinical and clinical, before full restoration of visual function in PR degeneration diseases can be realized.

Effect of Experimental Electrical and Biological Parameters on Gene Transfer by Electroporation: A Systematic Review and Meta-Analysis

The exact mechanisms of nucleic acid (NA) delivery with gene electrotransfer (GET) are still unknown, which represents a limitation for its broader use. Further, not knowing the effects that different experimental electrical and biological parameters have on GET additionally hinders GET optimization, resulting in the majority of research being performed using a trial-and-error approach. To explore the current state of knowledge, we conducted a systematic literature review of GET papers in in vitro conditions and performed meta-analyses of the reported GET efficiency. For now, there is no universal GET strategy that would be appropriate for all experimental aims. Apart from the availability of the required electroporation device and electrodes, the choice of an optimal GET approach depends on parameters such as the electroporation medium; type and origin of cells; and the size, concentration, promoter, and type of the NA to be transfected. Equally important are appropriate controls and the measurement or evaluation of the output pulses to allow a fair and unbiased evaluation of the experimental results. Since many experimental electrical and biological parameters can affect GET, it is important that all used parameters are adequately reported to enable the comparison of results, as well as potentially faster and more efficient experiment planning and optimization.

The replacement of helper lipids with charged alternatives in lipid nanoparticles facilities targeted mRNA delivery to the spleen and lungs

The broad clinical application of mRNA therapeutics has been hampered by a lack of delivery vehicles that induce protein expression in extrahepatic organs and tissues. Recently, it was shown that mRNA delivery to the spleen or lungs is possible upon the addition of a charged lipid to a standard four-component lipid nanoparticle formulation. This approach, while effective, further complicates an already complex drug formulation and has the potential to slow regulatory approval and adversely impact manufacturing processes. We were thus motivated to maintain a four-component nanoparticle system while achieving shifts in tropism. To that end, we replaced the standard helper lipid in lipidoid nanoparticles, DOPE, with one of eight alternatives. These lipids included the neutral lipids, DOPC, sphingomyelin, and ceramide; the anionic lipids, phosphatidylserine (PS), phosphatidylglycerol, and phosphatidic acid; and the cationic lipids, DOTAP and ethyl phosphatidylcholine. While neutral helper lipids maintained protein expression in the liver, anionic and cationic lipids shifted protein expression to the spleen and lungs, respectively. For example, replacing DOPE with DOTAP increased positive LNP surface charge at pH 7 by 5-fold and altered the ratio of liver to lung protein expression from 36:1 to 1:56. Similarly, replacing DOPE with PS reduced positive charge by half and altered the ratio of liver to spleen protein expression from 8:1 to 1:3. Effects were consistent across ionizable lipidoid chemistries. Regarding mechanism, nanoparticles formulated with neutral and anionic helper lipids best transfected epithelial and immune cells, respectively. Further, the lung-tropic effect of DOTAP was linked to reduced immune cell infiltration of the lungs compared to neutral or anionic lipids. Together, these data show that intravenous non-hepatocellular mRNA delivery is readily achievable while maintaining a four-component formulation with modified helper lipid chemistry.

Incorporation of Endosomolytic Peptides with Varying Disruption Mechanisms into EGFR-Targeted Protein Conjugates: The Effect on Intracellular Protein Delivery and EGFR Specificity in Breast Cancer Cells

Intracellular delivery of protein therapeutics remains a significant challenge limiting the majority of clinically available protein drugs to extracellular targets. Strategies to deliver proteins to subcellular compartments have traditionally relied on cell-penetrating peptides, which can drive enhanced internalization but exhibit unreliable activity and are rarely able to target specific cells, leading to off-target effects. Moreover, few design rules exist regarding the relative efficacy of various endosomal escape strategies in proteins. Accordingly, we developed a simple fusion modification approach to incorporate endosomolytic peptides onto epidermal growth factor receptor (EGFR)-targeted protein conjugates and performed a systematic comparison of the endosomal escape efficacy, mechanism of action, and capacity to maintain EGFR-targeting specificity of conjugates modified with four different endosomolytic sequences of varying modes of action (Aurein 1.2, GALA, HA2, and L17E). Use of the recently developed Gal8-YFP assay indicated that the fusion of each endosomolytic peptide led to enhanced endosomal disruption. Additionally, the incorporation of each endosomolytic peptide increased the half-life of the internalized protein and lowered lysosomal colocalization, further supporting the membrane-disruptive capacity. Despite this, only EGFR-targeted conjugates modified with Aurein 1.2 or GALA maintained EGFR specificity. These results thus demonstrated that the choice of endosomal escape moiety can substantially affect targeting capability, cytotoxicity, and bioactivity and provided important new insights into endosomolytic peptide selection for the design of targeted protein delivery systems.

Dual-Modality Poly-l-histidine Nanoparticles to Deliver Peptide Nucleic Acids and Paclitaxel for In Vivo Cancer Therapy

Cationic polymeric nanoformulations have been explored to increase the transfection efficiency of small molecules and nucleic acid-based drugs. However, an excessive positive charge density often leads to severe cell and tissue-based toxicity that restricts the clinical translation of cationic polymeric nanoformulations. Herein, we investigate a series of cationic poly(lactic-co-glycolic acid) (PLGA)-histidine-based nanoformulations for enhanced cytoplasmic delivery with minimal toxicity. PLGA/poly-l-histidine nanoparticles show promising physico-biochemical features and transfection efficiency in a series of in vitro and cell culture-based studies. Further, the use of acetone/dichloromethane as a solvent mixture during the formulation process significantly improves the morphology and size distribution of PLGA/poly-l-histidine nanoparticles. PLGA/poly-l-histidine nanoformulations undergo clathrin-mediated endocytosis. A contrast-matched small-angle neutron scattering experiment confirmed poly-l-histidine's distribution on the PLGA nanoformulations. PLGA/poly-l-histidine formulations containing paclitaxel as a small molecule-based drug and peptide nucleic acids targeting microRNA-155 as nucleic acid analog are efficacious in in vitro and in vivo studies. PLGA/poly-l-histidine NPs significantly decrease tumor growth in PNA-155 (∼6 fold) and paclitaxel (∼6.5 fold) treatment groups in a lymphoma cell line derived xenograft mice model without inducing any toxicity. Hence, PLGA/poly-l-histidine nanoformulations exhibit substantial transfection efficiency and are safe to deliver reagents ranging from small molecules to synthetic nucleic acid analogs and can serve as a novel platform for drug delivery.

Aluminum particles generated during millisecond electric pulse application enhance adenovirus-mediated gene transfer in L929 cells

Gene electrotransfer is an attractive method of non-viral gene delivery. However, the mechanism of DNA penetration across the plasma membrane is widely discussed. To explore this process for even larger structures, like viruses, we applied various combinations of short/long and high/low-amplitude electric pulses to L929 cells, mixed with a human adenovirus vector expressing GFP. We observed a transgene expression increase, both in the number of GFP-converted cells and GFP levels, when we added a low-voltage/millisecond-pulse treatment to the adenovirus/cell mixture. This increase, reflecting enhanced virus penetration, was proportional to the applied electric field amplitude and pulse number, but was not associated with membrane permeabilization, nor to direct cell modifications. We demonstrated that this effect is mainly due to adenovirus particle interactions with aggregated aluminum particles released from energized electrodes. Indeed, after centrifugation of the pulsed viral suspension and later on addition to cells, the activity was found mainly associated with the aluminum aggregates concentrated in the lower fraction and was proportional to generated quantities. Overall, this work focused on the use of electrotransfer to facilitate the adenovirus entry into cell, demonstrating that modifications of the penetrating agent can be more important than modifications of the target cell for transfer efficacy.

Bifunctional small molecules that mediate the degradation of extracellular proteins

Targeted protein degradation (TPD) has emerged as a promising therapeutic strategy. Most TPD technologies use the ubiquitin-proteasome system, and are therefore limited to targeting intracellular proteins. To address this limitation, we developed a class of modular, bifunctional synthetic molecules called MoDE-As (molecular degraders of extracellular proteins through the asialoglycoprotein receptor (ASGPR)), which mediate the degradation of extracellular proteins. MoDE-A molecules mediate the formation of a ternary complex between a target protein and ASGPR on hepatocytes. The target protein is then endocytosed and degraded by lysosomal proteases. We demonstrated the modularity of the MoDE-A technology by synthesizing molecules that induce depletion of both antibody and proinflammatory cytokine proteins. These data show experimental evidence that nonproteinogenic, synthetic molecules can enable TPD of extracellular proteins in vitro and in vivo. We believe that TPD mediated by the MoDE-A technology will have widespread applications for disease treatment.

Escaping the endosome: assessing cellular trafficking mechanisms of non-viral vehicles

Non-viral vehicles hold therapeutic promise in advancing the delivery of a variety of cargos in vitro and in vivo, including small molecule drugs, biologics, and especially nucleic acids. However, their efficacy at the cellular level is limited by several delivery barriers, with endolysosomal degradation being most significant. The entrapment of vehicles and their cargo in the acidified endosome prevents access to the cytosol, nucleus, and other subcellular compartments. Understanding the factors that contribute to uptake and intracellular trafficking, especially endosomal entrapment and release, is key to overcoming delivery obstacles within cells. In this review, we summarize and compare experimental techniques for assessing the extent of endosomal escape of a variety of non-viral vehicles and describe proposed escape mechanisms for different classes of lipid-, polymer-, and peptide-based delivery agents. Based on this evaluation, we present forward-looking strategies utilizing information gained from mechanistic studies to inform the rational design of efficient delivery vehicles.

Evaluating Endosomal Escape of Caspase-3-Containing Nanomaterials Using Split GFP

The ability for biologics to access intracellular targets hinges on the translocation of active, unmodified proteins. This is often achieved using nanoscale formulations, which enter cells through endocytosis. This uptake mechanism often limits the therapeutic potential of the biologics, as the propensity of the nanocarrier to escape the endosome becomes the key determinant. To appropriately evaluate and compare competing delivery systems of disparate compositions, it is therefore critical to assess endosomal escape efficiencies. Unfortunately, quantitative tools to assess endosomal escape are lacking, and standard approaches often lead to an erroneous interpretation of cytosolic localization. In this study we use a split-complementation endosomal escape (SEE) assay to evaluate levels of cytosolic caspase-3 following delivery by polymer nanogels and mesoporous silica nanoparticles. In particular, we use SEE as a means to enable the systematic investigation of the effect of polymer composition, polymer architecture (random vs block), hydrophobicity, and surface functionality. Although polymer structure had little influence on endosomal escape, nanogel functionalization with cationic and pH-sensitive peptides significantly enhanced endosomal escape levels and, further, significantly increased the amount of nanogel per endosome. This work serves as a guide for developing an optimal caspase-3 delivery system, as this caspase-3 variant can be easily substituted for a therapeutic caspase-3 cargo in any system that results in cytosolic accumulation and cargo release. In addition, these data provide a framework that can be readily applied to a wide variety of protein cargos to assess the independent contributions of both uptake and endosomal escape of a wide range of protein delivery vehicles.

Application of chloroquine as an endosomal escape enhancing agent: new frontiers for an old drug

INTRODUCTION

Adequate transfection efficiency is indispensable to safe and effective delivery of therapeutically active agents, particularly in cancer. Endosomal escape is regarded as a critical and determining step devoted a significant number of studies of the drug/gene delivery field.

AREAS COVERED

This paper critically reviews the fundamental properties of chloroquine (CQ), its pharmacokinetics, pharmacodynamics, and clinical applications and the present knowledge of CQ application as an endosomal escape enhancing agent. Different approaches to enhance the endosomal escape process of nanoparticles have been introduced including use of endosomal escape enhancing agents. Application of CQ as either a pre-treatment modality in which cells or animals are exposed to CQ prior to the main treatment or a component of co-delivery systems where CQ and other anti-cancer agents are simultaneously entered the cancer cells, is discussed with recent studies.

EXPERT OPINION

CQ is founded to intervene with the natural process of endosomal maturation. Moreover, CQ seems to increase the effectiveness of gene delivery by its electrostatic interaction with negatively charged components of the transferred genetic molecules. Endosomal escape might be regarded as the bottleneck of efficient gene delivery and CQ as an effective and available endosomal escape enhancing agent deserves more sophisticated studies.

A statistical framework for determination of minimal plasmid copy number required for transgene expression in mammalian cells

Plasmid DNA (pDNA) has been widely used for non-viral gene delivery. After pDNA molecules enter a mammalian cell, they may be trapped in subcellular structures or degraded by nucleases. Only a fraction of them can function as templates for transcription in the nucleus. Thus, an important question is, what is the minimal amount of pDNA molecules that need to be delivered into a cell for transgene expression? At present, it is technically a challenge to experimentally answer the question. To this end, we developed a statistical framework to establish the relationship between two experimentally quantifiable factors - average copy number of pDNA per cell among a group of cells after transfection and percent of the cells with transgene expression. The framework was applied to the analysis of electrotransfection under different experimental conditions in vitro. We experimentally varied the average copy number per cell and the electrotransfection efficiency through changes in extracellular pDNA dose, electric field strength, and pulse number. The experimental data could be explained or predicted quantitatively by the statistical framework. Based on the data and the framework, we could predict that the minimal number of pDNA molecules in the nucleus for transgene expression was on the order of 10. Although the prediction was dependent on the cell and experimental conditions used in the study, the framework may be generally applied to analysis of non-viral gene delivery.

High-throughput continuous-flow microfluidic electroporation of mRNA into primary human T cells for applications in cellular therapy manufacturing

Implementation of gene editing technologies such as CRISPR/Cas9 in the manufacture of novel cell-based therapeutics has the potential to enable highly-targeted, stable, and persistent genome modifications without the use of viral vectors. Electroporation has emerged as a preferred method for delivering gene-editing machinery to target cells, but a major challenge remaining is that most commercial electroporation machines are built for research and process development rather than for large-scale, automated cellular therapy manufacturing. Here we present a microfluidic continuous-flow electrotransfection device designed for precise, consistent, and high-throughput genetic modification of target cells in cellular therapy manufacturing applications. We optimized our device for delivery of mRNA into primary human T cells and demonstrated up to 95% transfection efficiency with minimum impact on cell viability and expansion potential. We additionally demonstrated processing of samples comprising up to 500 million T cells at a rate of 20 million cells/min. We anticipate that our device will help to streamline the production of autologous therapies requiring on the order of 10[Formula: see text]-10[Formula: see text] cells, and that it is well-suited to scale for production of trillions of cells to support emerging allogeneic therapies.

The challenging nature of primary T lymphocytes for transfection: Effect of protamine sulfate on the transfection efficiency of chemical transfection reagents

Background and purpose:

The optimization of an effective non-viral gene delivery method for genetic manipulation of primary human T cells has been a major challenge in immunotherapy researches. Due to the poor transfection efficiency of conventional methods in T cells, there has been an effort to increase the transfection rate in these cells. Protamine is an FDA-approved compound with a documented safety profile that enhances DNA condensation for gene delivery.

Experimental approach:

In this study, the effect of protamine sulfate on the transfection efficiency of standard transfection reagents, was evaluated to transfect primary human T cells. In this regard, pre-condensation of DNA was applied using protamine, and the value of the zeta potential of DNA/protamine/cargo complexes was determined. T cells were transfected with DNA/protamine/cargo complexes. The transfection efficiency rate was evaluated by flow cytometry. Also, the green fluorescent protein expression level and cytotoxicity of each complex were identified using real-time polymerase chain reaction and MTT assay, respectively.

Findings/Results:

Our results demonstrated that protamine efficiently increases the positive charge of DNA/cargo complex without any cytotoxic effect on the primary human T cells. We observed that the transfection efficiency in DNA/protamine/ Lipofectamine^® 2000 and DNA/protamine/TurboFect™ was 87.2% and 78.9%, respectively, while transfection of T cells by Lipofectamine^® 2000 and TurboFect™ would not result in sufficient transfection.

Conclusion and implications:

Protamine sulfate enhanced the transfection rate of T cells; and could be a promising non-viral gene delivery method to achieve a safe, rapid, cost-effective, and efficient system which will be further applied in gene therapy and T cells manipulation methods.

Gene Editing by Extracellular Vesicles

CRISPR/Cas technologies have advanced dramatically in recent years. Many different systems with new properties have been characterized and a plethora of hybrid CRISPR/Cas systems able to modify the epigenome, regulate transcription, and correct mutations in DNA and RNA have been devised. However, practical application of CRISPR/Cas systems is severely limited by the lack of effective delivery tools. In this review, recent advances in developing vehicles for the delivery of CRISPR/Cas in the form of ribonucleoprotein complexes are outlined. Most importantly, we emphasize the use of extracellular vesicles (EVs) for CRISPR/Cas delivery and describe their unique properties: biocompatibility, safety, capacity for rational design, and ability to cross biological barriers. Available molecular tools that enable loading of desired protein and/or RNA cargo into the vesicles in a controllable manner and shape the surface of EVs for targeted delivery into specific tissues (e.g., using targeting ligands, peptides, or nanobodies) are discussed. Opportunities for both endogenous (intracellular production of CRISPR/Cas) and exogenous (post-production) loading of EVs are presented.

Redirecting Vesicular Transport to Improve Nonviral Delivery of Molecular Cargo

Cell engineering relies heavily on viral vectors for the delivery of molecular cargo into cells due to their superior efficiency compared to nonviral ones. However, viruses are immunogenic and expensive to manufacture, and have limited delivery capacity. Nonviral delivery approaches avoid these limitations but are currently inefficient for clinical applications. This work demonstrates that the efficiency of nonviral delivery of plasmid DNA, mRNA, Sleeping Beauty transposon, and ribonucleoprotein can be significantly enhanced through pretreatment of cells with the nondegradable sugars (NDS), such as sucrose, trehalose, and raffinose. The enhancement is mediated by the incorporation of the NDS into cell membranes, causing enlargement of lysosomes and formation of large (>500 nm) amphisome-like bodies (ALBs). The changes in subcellular structures redirect transport of cargo to ALBs rather than to lysosomes, reducing cargo degradation in cells. The data indicate that pretreatment of cells with NDS is a promising approach to improve nonviral cargo delivery in biomedical applications.

Enhancing Cell Viability and Efficiency of Plasmid DNA Electrotransfer Through Reducing Plasma Membrane Permeabilization

Background

Pulsed electric field has been widely used to facilitate molecular cargo transfer into cells. However, the cell viability is often decreased when trying to increase the electrotransfer efficiency. We hypothesize that the decrease is due to electropermeabilization of cell membrane that disrupts homeostasis of intracellular microenvironment. Thus, a reduction in the membrane permeabilization may increase the cell viability.

Materials and Methods

Different compounds were supplemented into the pulsing buffer prior to electrotransfer for reduction of cell membrane damage. Extent of the damage was quantified by leakiness of the membrane to a fluorescent dye, calcein, preloaded into cells. At 24 hours post electrotransfer, cell viability and electrotransfer efficiency were quantified with flow cytometry.

Results

The cell viability could be substantially increased by supplementation of either type B gelatin or bovine serum albumin (BSA), without compromising the electrotransfer efficiency. The supplementation also decreased the amount of calcein leaking out of the cells, suggesting that the improvement in cell viability was due to the reduction in electrotransfer-induced membrane damage.

Conclusion

Data from the study demonstrate that type B gelatin and BSA can be used as inexpensive supplements for improving cell viability in electrotransfer.

Effect of small molecule signaling in PepFect14 transfection

Cell-penetrating peptides can be used to deliver oligonucleotide-based cargoes into cells. Previous studies have shown that the use of small molecule drugs could be an efficient method to increase the efficacy of delivery of oligonucleotides by cell-penetrating peptides either as targeting agents that can be used in formulation with the cell-penetrating peptide and its cargo or as cell signaling modulators that facilitates the cellular uptake of the treatment. This study presents two aims. The first aim is the identification of small molecule drugs that would induce a synergic effect on the transfection of splice correcting oligonucleotides assisted by PepFect14. The second aim is to identify the mechanisms behind the effect of small molecule drugs modulation of cell-penetrating peptide assisted transfection of oligonucleotides. Through an optimized, high-throughput luciferase assay for short oligonucleotide delivery using cell-penetrating peptides, and the simultaneous addition of a small molecule drug library, we show that three small molecule drugs (MPEP, VU0357121 and Ciproxifan) induced an increase in the transfection efficacy of PepFect14 in complex with a short single-stranded oligonucleotide in HeLa pLuc705 cells. These three drugs are described in the literature to be highly specific for their respective target receptors. However, none of those receptors are expressed in our cell line, indicating a yet non-described pathway of action for these small molecules. We show that the indicated small molecules, without interfering with the particles formed by PepFect14 and the oligonucleotide, interfere via still unidentified interactions in cell signaling, leading to an up-regulation of endocytosis and a higher efficacy in the delivery of short splice correcting oligonucleotides in complex with PepFect14.

Multiple cytosolic DNA sensors bind plasmid DNA after transfection

Mammalian cells express a variety of nucleic acid sensors as one of the first lines of defense against infection. Despite extensive progress in the study of sensor signaling pathways during the last decade, the detailed mechanisms remain unclear. In our previous studies, we reported increased type I interferon expression and the upregulation of several proposed cytosolic DNA sensors after transfection of several tumor cell types with plasmid DNA (pDNA). In the present study, we sought to reveal the early events in the cytosolic sensing of this nucleic acid in a myoblast cell line. We demonstrated that DNA-dependent activator of interferon regulatory factors/Z-DNA binding protein 1 (DAI/ZBP1) bound plasmid DNA in the cytosol within 15 minutes of transfection and at consistent levels for 4 h. Interferon activated gene 204 protein (p204) and DEAH box helicase 9 (DHX9) also bound pDNA, peaking 15 and 30 min respectively. Plasmid DNA was not detectably bound by DEAD box helicase 60 (DDX60) protein, despite a similar level of mRNA upregulation to DAI/ZBP1, or by cyclic GMP-AMP synthase (cGAS), despite its presence in the cell cytosol. Taken together, these results indicate several DNA sensors may participate and cooperate in the complex process of cytosolic DNA sensing.

Ocular gene therapies in clinical practice: viral vectors and nonviral alternatives

Ocular gene therapy has entered into clinical practice. Although viral vectors are currently the best option to replace and/or correct genes, the optimal method to deliver these treatments to the retinal pigment epithelial (RPE) cells and/or photoreceptor cells remains to be improved to increase transduction efficacy and reduce iatrogenic risks. Beyond viral-mediated gene replacement therapies, nonviral gene delivery approaches offer the promise of sustained fine-tuned expression of secreted therapeutic proteins that can be adapted to the evolving stage of the disease course and can address more common nongenetic retinal diseases, such as age-related macular degeneration (AMD). Here, we review current gene therapy strategies for ocular diseases, with a focus on clinical stage products.

Antibody-targeted chromatin enables effective intracellular delivery and functionality of CRISPR/Cas9 expression plasmids

We report a novel system for efficient and specific targeted delivery of large nucleic acids to and into cells. Plasmid DNA and core histones were assembled to chromatin by salt gradient dialysis and subsequently connected to bispecific antibody derivatives (bsAbs) via a nucleic acid binding peptide bridge. The resulting reconstituted vehicles termed 'plasmid-chromatin' deliver packaged nucleic acids to and into cells expressing antigens that are recognized by the bsAb, enabling intracellular functionality without detectable cytotoxicity. High efficiency of intracellular nucleic acid delivery is revealed by intracellular expression of plasmid encoded genes in most (∼90%) target cells to which the vehicles were applied under normal growth/medium conditions in nanomolar concentrations. Specific targeting, uptake and transgene expression depends on antibody-mediated cell surface binding: plasmid chromatin of identical composition but with non-targeting bsAbs or without bsAbs is ineffective. Examples that demonstrate applicability, specificity and efficacy of antibody-targeted plasmid chromatin include reporter gene constructs as well as plasmids that enable CRISPR/Cas9 mediated genome editing of target cells.

Gene delivery to the rat retina by non-viral vectors based on chloroquine-containing cationic niosomes

The incorporation of chloroquine within nano formulations, rather than as a co-treatment of the cells, could open a new avenue for in vivo retinal gene delivery. In this manuscript, we evaluated the incorporation of chloroquine diphosphate into the cationic niosome formulation composed of poloxamer 188, polysorbate 80 non-ionic surfactants, and 2,3-di (tetradecyloxy) propan-1-amine (hydrochloride salt) cationic lipid, to transfect rat retina. Niosome formulations without and with chloroquine diphosphate (DPP80, and DPP80-CQ, respectively) were prepared by the reverse phase evaporation technique and characterized in terms of size, PDI, zeta potential, and morphology. After the incorporation of the pCMS-EGFP plasmid, the resultant nioplexes -at different cationic lipid/DNA mass ratios- were further evaluated to compact, liberate, and secure the DNA against enzymatic digestion. In vitro procedures were achieved in ARPE-19 cells to assess transfection efficacy and intracellular transportation. Both nioplexes formulations transfected efficiently ARPE-19 cells, although the cell viability was clearly better in the case of DPP80-CQ nioplexes. After subretinal and intravitreal injections, DPP80 nioplexes were not able to transfect the rat retina. However, chloroquine containing vector showed protein expression in many retinal cells, depending on the administration route. These data provide new insights for retinal gene delivery based on chloroquine-containing niosome non-viral vectors.

Upregulation of DNA Sensors in B16.F10 Melanoma Spheroid Cells After Electrotransfer of pDNA

Increased expression of cytosolic DNA sensors, a category of pattern recognition receptor, after control plasmid DNA electrotransfer was observed in our previous studies on B16.F10 murine melanoma cells. This expression was correlated with the upregulation of proinflammatory cytokines and chemokines and was associated with cell death. Here, we expanded our research to include the influence of features of cells in a 3-dimensional environment, which better represents the tumors' organization in vivo. Our results show that lower number of cells were transfected in spheroids compared to 2-dimensional cultures, that growth was delayed after electroporation alone or after electrotransfer of plasmid DNA, and that DNA sensors DDX60, DAI/ZBP1, and p204 were upregulated 4 hours and 24 hours after electrotransfer of plasmid DNA. Moreover, the cytokines interferon β and tumor necrosis factor α were also upregulated but only 4 hours after electrotransfer of plasmid DNA. Thus, our results confirm the results obtained in 2-dimensional cell cultures demonstrating that electrotransfer of plasmid DNA to tumor cells in spheroids also upregulated cytosolic DNA sensors and cytokines.

Ultrastructural Analysis of Vesicular Transport in Electrotransfection

Emerging evidence from various studies indicates that plasmid DNA (pDNA) is internalized by cells through an endocytosis-like process when it is used for electrotransfection. To provide morphological evidence of the process, we investigated ultrastructures in cells that were associated with the electrotransfected pDNA, using immunoelectron microscopy. The results demonstrate that four endocytic pathways are involved in the uptake of the pDNA, including caveolae- and clathrin-mediated endocytosis, macropinocytosis, and the clathrin-independent carrier/glycosylphosphatidylinositol-anchored protein-enriched early endosomal compartment (CLIC/GEEC) pathway. Among them, macropinocytosis is the most common pathway utilized by cells having various pDNA uptake capacities, and the CLIC/GEEC pathway is observed primarily in human umbilical vein endothelial cells. Quantitatively, the endocytic pathways are more active in easy-to-transfect cells than in hard-to-transfect ones. Taken together, our data provide ultrastructural evidence showing that endocytosis plays an important role in cellular uptake and intracellular transport of electrotransfected pDNA.

Current Progress in Electrotransfection as a Nonviral Method for Gene Delivery

Electrotransfection (ET) is a nonviral method for delivery of various types of molecules into cells both in vitro and in vivo. Close to 90 clinical trials that involve the use of ET have been performed, and approximately half of them are related to cancer treatment. Particularly, ET is an attractive technique for cancer immunogene therapy because treatment of cells with electric pulses alone can induce immune responses to solid tumors, and the responses can be further enhanced by ET of plasmid DNA (pDNA) encoding therapeutic genes. Compared to other gene delivery methods, ET has several unique advantages. It is relatively inexpensive, flexible, and safe in clinical applications, and introduces only naked pDNA into cells without the use of additional chemicals or viruses. However, the efficiency of ET is still low, partly because biological mechanisms of ET in cells remain elusive. In previous studies, it was believed that pDNA entered the cells through transient pores created by electric pulses. As a result, the technique is commonly referred to as electroporation. However, recent discoveries have suggested that endocytosis plays an important role in cellular uptake and intracellular transport of electrotransfected pDNA. This review will discuss current progresses in the study of biological mechanisms underlying ET and future directions of research in this area. Understanding the mechanisms of pDNA transport in cells is critical for the development of new strategies for improving the efficiency of gene delivery in tumors.

Enhancing Electrotransfection Efficiency through Improvement in Nuclear Entry of Plasmid DNA

The nuclear envelope is a physiological barrier to electrogene transfer. To understand different mechanisms of the nuclear entry for electrotransfected plasmid DNA (pDNA), the current study investigated how manipulation of the mechanisms could affect electrotransfection efficiency (eTE), transgene expression level (EL), and cell viability. In the investigation, cells were first synchronized at G2-M phase prior to electrotransfection so that the nuclear envelope breakdown (NEBD) occurred before pDNA entered the cells. The NEBD significantly increased the eTE and the EL while the cell viability was not compromised. In the second experiment, the cells were treated with a nuclear pore dilating agent (i.e., trans-1,2-cyclohexanediol). The treatment could increase the EL, but had only minor effects on eTE. Furthermore, the treatment was more cytotoxic, compared with the cell synchronization. In the third experiment, a nuclear targeting sequence (i.e., SV40) was incorporated into the pDNA prior to electrotransfection. The incorporation was more effective than the cell synchronization for enhancing the EL, but not the eTE, and the effectiveness was cell type dependent. Taken together, the data described above suggested that synchronization of the NEBD could be a practical approach to improving electrogene transfer in all dividing cells.

Synergism between a cell penetrating peptide and a pH-sensitive cationic lipid in efficient gene delivery based on double-coated nanoparticles

We report on the development of a highly efficient gene delivery system based on synergism between octaarginine (R8), a representative cell penetrating peptide, and YSK05, a recently developed pH-sensitive cationic lipid. Attaching a high density of R8 on the surface of YSK05 nanoparticles (NPs) that contained encapsulated plasmid DNA resulted in the formation of positively charged NPs with improved transfection efficiency. To avoid the development of a net positive charge, we controlled the density and topology of the R8 peptide through the use of a two-step coating methodology, in which the inner lipid coat was modified with a low density of R8 which was then covered with an outer neutral YSK05 lipid layer. Although used in low amounts, the R8 peptide improved cellular uptake and endosomal escape of the DNA encapsulated in YSK05 NPs, which resulted in a high transfection efficiency. The two-step coating design was essential for achieving a high degree of transfection, as evidenced by the low activity of NPs modified with the same amount of R8 in a regular single-coated design. In addition, a high transfection efficiency was not observed when R8 or YSK05 were used alone, which confirms the existence of a synergistic effect between both components. The results of this study indicate that cationic cell penetrating peptides have the ability to improve transfection activities without imparting a net positive charge when used in the proper amount and in conjunction with the appropriate design. This is expected to significantly increase the potential applications of these peptides as tools for augmenting the activity of lipid nanoparticles used in gene delivery.

An efficient PEGylated gene delivery system with improved targeting: Synergism between octaarginine and a fusogenic peptide

Because of their ability to translocate different cargos into cells, arginine-rich cell penetrating peptides (CPPs) are promising vehicles for drug and gene delivery. The use of CPP-based carriers, however, is hampered by the lack of specificity and by interactions with negative serum components. Polyethylene glycol (PEG) is used to decrease such non-specific interactions, albeit its use is associated with reduced transfection efficiency. In this study, we describe the development of PEGylated CPP-based gene carrier with an improved targeting and a high transfection activity. The system was prepared by condensing DNA with a polycation followed by coating with a lipid envelope containing the octaarginine (R8) peptide as a model CPP. R8-modified nanoparticles produced high transfection activities, but the efficiency was reduced by PEG shielding. The reduced activity could be fully restored by the addition of a targeting ligand and a pH-sensitive fusogenic peptide. The efficiency of the proposed system is quite high, even in the presence of serum, and shows improved targeting and selectivity. Surprisingly, the effect of the fusogenic peptide was dramatically reduced in the absence of R8. Although shielded, R8 augmented the activity of the fusogenic peptide, suggesting a synergistic effect between the two peptides at the intracellular level.