Visualization of intracellular trafficking of exogenous DNA delivered by cationic liposomes

The intracellular visualization of exogenous DNA in fluorescence microscopy

In the development of non-viral gene delivery vectors, it is essential to reliably localize and quantify transfected DNA inside the cell. To track DNA, fluorescence microscopy methods are commonly applied. These mostly rely on fluorescently labeled DNA, DNA binding proteins fused to a fluorescent protein, or fluorescence in situ hybridization (FISH). In addition, co-stainings are often used to determine the colocalization of the DNA in specific cellular compartments, such as the endolysosomes or the nucleus. We provide an overview of these DNA tracking methods, advice on how they should be combined, and indicate which co-stainings or additional methods are required to draw precise conclusions from a DNA tracking experiment. Some emphasis is given to the localization of exogenous DNA inside the nucleus, which is the last step of DNA delivery. We argue that suitable tools which allow for the nuclear detection of faint signals are still missing, hampering the rational development of more efficient non-viral transfection systems.

Engineered smart materials for RNA based molecular therapy to treat Glioblastoma

Glioblastoma (GBM) is an aggressive malignancy of the central nervous system (CNS) that remains incurable despite the multitude of improvements in cancer therapeutics. The conventional chemo and radiotherapy post-surgery have only been able to improve the prognosis slightly; however, the development of resistance and/or tumor recurrence is almost inevitable. There is a pressing need for adjuvant molecular therapies that can successfully and efficiently block tumor progression. During the last few decades, non-coding RNAs (ncRNAs) have emerged as key players in regulating various hallmarks of cancer including that of GBM. The levels of many ncRNAs are dysregulated in cancer, and ectopic modulation of their levels by delivering antagonists or overexpression constructs could serve as an attractive option for cancer therapy. The therapeutic potential of several types of ncRNAs, including miRNAs, lncRNAs, and circRNAs, has been validated in both in vitro and in vivo models of GBM. However, the delivery of these RNA-based therapeutics is highly challenging, especially to the tumors of the brain as the blood-brain barrier (BBB) poses as a major obstacle, among others. Also, since RNA is extremely fragile in nature, careful considerations must be met while designing a delivery agent. In this review we have shed light on how ncRNA therapy can overcome the limitations of its predecessor conventional therapy with an emphasis on smart nanomaterials that can aide in the safe and targeted delivery of nucleic acids to treat GBM. Additionally, critical gaps that currently exist for successful transition from viral to non-viral vector delivery systems have been identified. Finally, we have provided a perspective on the future directions, potential pathways, and target areas for achieving rapid clinical translation of, RNA-based macromolecular therapy to advance the effective treatment of GBM and other related diseases.

Cloning and expressing of interleukine 2 in amniotic membrane-derived mesenchymal stem cells, as a potent feeder layer

The application of mesenchymal stem cells (MSCs) is rapidly expanding due to their unique properties in cell therapy, especially as the feeder layer in the ex-vivo expansion of immune cells. Also, Interleukin 2 (IL-2) is an essential human cytokine in the expansion of hematopoietic precursors and progenitors, i.e., NK cells and T cells, while there is no endogenous expression of IL-2 in MSCs. This study aimed to examine the potency of amniotic membrane (AM)-MSCs as the IL-2 secretory cells. IL-2-containing pCMV3-C-GFPspark shuttle vector was transformed in E.coli DH5-alpha. After cloning, the plasmid DNA was extracted and transfected in isolated AM-MSCs, by lipofectamine-2000. Then, the RNA and protein expression levels of exogenous IL-2 were evaluated 3 to 15 days after transfection, using ELISA and qRT-PCR. Fluorescent microscopy and flowcytometry assays were used for evaluating the GFP-positivity of transfected AM-MSCs, as IL-2 expression control. There was a significant increase in RNA expression of exogenous IL-2 in transfected AM-MSCs in 3 to 15 days after transfection. (p<0.001) Also, IL-2 concentration released in the medium was increased in 3rd day after transfection (611 pg/ml). However, the RNA and protein expression of IL-2 was reduced through passing the time. The results show AM-MSC is a suitable host for the expression and secretion of IL-2 as a critical cytokine in the ex-vivo expansion of hematopoietic precursors and progenitors, i.e., NK cells and T cells. Also, the survival time of IL-2 expression in AM-MSCs was long enough for use as a feeder layer.

Cellular Uptake and Distribution of Gemini Surfactant Nanoparticles Used as Gene Delivery Agents

Gemini surfactants are promising molecules utilized as non-viral gene delivery vectors. However, little is known about their cellular uptake and distribution after they release their therapeutic cargo. Therefore, we quantitatively evaluated the cellular uptake and distribution of three gemini surfactants: unsubstituted (16-3-16), with pyridinium head groups (16(Py)-S-2-S-16(Py)) and substituted with a glycyl-lysine di-peptide (16-7N(GK)-16). We also assessed the relationship between cellular uptake and distribution of each gemini surfactant and its overall efficiency and toxicity. Epidermal keratinocytes PAM 212 were treated with gemini surfactant nanoparticles formulated with plasmid DNA and harvested at various time points to collect the enriched nuclear, mitochondrial, plasma membrane, and cytosolic fractions. Gemini surfactants were then extracted from each subcellular fraction and quantified using a validated flow injection analysis-tandem mass spectrometry (FIA-MS/MS) method. Mass spectrometry is superior to the use of fluorescent tags that alter the physicochemical properties and pharmacokinetics of the nanoparticles and can be cleaved from the gemini surfactant molecules within biological systems. Overall, a significantly higher cellular uptake was observed for 16-7N(GK)-16 (17.0%) compared with 16-3-6 (3.6%) and 16(Py)-S-2-S-16(Py) (1.4%), which explained the relatively higher transfection efficiency of 16-7N(GK)-16. Gemini surfactants 16-3-16 and 16(Py)-S-2-S-16(Py) displayed similar subcellular distribution patterns, with major accumulation in the nucleus, followed by the mitochondrion, cytosol, and plasma membrane. In contrast, 16-7N(GK)-16 was relatively evenly distributed across all four subcellular fractions. However, accumulation within the nucleus after 5 h of treatment was the highest for 16(Py)-S-2-S-16(Py) (50.3%), followed by 16-3-16 (41.8%) and then 16-7N(GK)-16 (33.4%), possibly leading to its relatively higher toxicity. Graphical Abstract.

Synthetic Approaches for Nucleic Acid Delivery: Choosing the Right Carriers

The discovery of the genetic roots of various human diseases has motivated the exploration of different exogenous nucleic acids as therapeutic agents to treat these genetic disorders (inherited or acquired). However, the physicochemical properties of nucleic acids render them liable to degradation and also restrict their cellular entrance and gene translation/inhibition at the correct cellular location. Therefore, gene condensation/protection and guided intracellular trafficking are necessary for exogenous nucleic acids to function inside cells. Diversified cationic formulation materials, including natural and synthetic lipids, polymers, and proteins/peptides, have been developed to facilitate the intracellular transportation of exogenous nucleic acids. The chemical properties of different formulation materials determine their special features for nucleic acid delivery, so understanding the property-function correlation of the formulation materials will inspire the development of next-generation gene delivery carriers. Therefore, in this review, we focus on the chemical properties of different types of formulation materials and discuss how these formulation materials function as protectors and cellular pathfinders for nucleic acids, bringing them to their destination by overcoming different cellular barriers.

Ultrasound and microbubble mediated plasmid DNA uptake: A fast, global and multi-mechanisms involved process

Ultrasound application combined with microbubbles has shown great potential for intracellular gene delivery. However, the fundamental mechanistic question of how plasmid DNA enters the intracellular space mediated by ultrasound and microbubble has not been fully explored and understood. The goal of this study is to unveil the detailed intracellular uptake process of plasmid DNA stimulated by ultrasound and microbubbles, uniquely highlighting the role of microbubbles play in this process. The usage of targeted microbubbles pinpointed the subcellular membrane site, where ultrasound exerted acoustic force onto the cell membrane. With the combination of high-speed video microscopy and 3D confocal fluorescence microscopy, we show the spatiotemporal correlation between the microbubble dynamics and intracellular plasmid DNA distribution. Two ultrasound modes (high pressure short pulse and low pressure long pulse) were chosen to trigger different plasmid DNA uptake routes. We found that reversible cell membrane disruption, induced by high pressure short pulse ultrasound, permitted plasmid DNA passage across cell membrane, but not in an exclusive way. Under both ultrasound modes, with or without cell membrane disruption, global plasmid DNA internalization, even nuclear-localization, was observed immediately post ultrasound application. Our results show that plasmid DNA uptake evoked by localized acoustically excited microbubbles is a fast (<2min), global (not limited to the site where microbubbles were attached), and multi-mechanisms involved process.

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

A recent theory suggests that endocytosis is involved in uptake and intracellular transport of electrotransfected plasmid DNA (pDNA). The goal of the current study was to understand if approaches used previously to improve endocytosis of gene delivery vectors could be applied to enhancing electrotransfection efficiency (eTE). Results from the study showed that photochemically induced endosomal escape, which could increase poly-L-lysine (PLL)-mediated gene delivery, decreased eTE. The decrease could not be blocked by treatment of cells with endonuclease inhibitors (aurintricarboxylic acid and zinc ion) or antioxidants (L-glutamine and ascorbic acid). Chemical treatment of cells with an endosomal trafficking inhibitor that blocks endosome progression, bafilomycin A1, resulted in a significant decrease in eTE. However, treatment of cells with lysosomotropic agents (chloroquine and ammonium chloride) had little effects on eTE. These data suggested that endosomes played important roles in protecting and intracellular trafficking of electrotransfected pDNA.

Properties of internalization factors contributing to the uptake of extracellular DNA into tumor-initiating stem cells of mouse Krebs-2 cell line

Background

Previously, we demonstrated that poorly differentiated cells of various origins, including tumor-initiating stem cells present in the ascites form of mouse cancer cell line Krebs-2, are capable of naturally internalizing both linear double-stranded DNA and circular plasmid DNA.

Methods

The method of co-incubating Krebs-2 cells with extracellular plasmid DNA (pUC19) or TAMRA-5’-dUTP-labeled polymerase chain reaction (PCR) product was used. It was found that internalized plasmid DNA isolated from Krebs-2 can be transformed into competent Escherichia coli cells. Thus, the internalization processes taking place in the Krebs-2 cell subpopulation have been analyzed and compared, as assayed by E. coli colony formation assay (plasmid DNA) and cytofluorescence (TAMRA-DNA).

Results

We showed that extracellular DNA both in the form of plasmid DNA and a PCR product is internalized by the same subpopulation of Krebs-2 cells. We found that the saturation threshold for Krebs-2 ascites cells is 0.5 μg DNA/10⁶ cells. Supercoiled plasmid DNA, human high-molecular weight DNA, and 500 bp PCR fragments are internalized into the Krebs-2 tumor-initiating stem cells via distinct, non-competing internalization pathways. Under our experimental conditions, each cell may harbor 340–2600 copies of intact plasmid material, or up to 3.097 ± 0.044×10⁶ plasmid copies (intact or not), as detected by quantitative PCR.

Conclusion

The internalization dynamics of extracellular DNA, copy number of the plasmids taken up by the cells, and competition between different types of double-stranded DNA upon internalization into tumor-initiating stem cells of mouse ascites Krebs-2 have been comprehensively analyzed. Investigation of the extracellular DNA internalization into tumor-initiating stem cells is an important part of understanding their properties and possible destruction mechanisms. For example, a TAMRA-labeled DNA probe may serve as an instrument to develop a target for the therapy of cancer, aiming at elimination of tumor stem cells, as well as developing a straightforward test system for the quantification of poorly differentiated cells, including tumor-initiating stem cells, in the bulk tumor sample (biopsy or surgery specimen).

Synthesis of silica nanoparticles with controllable surface roughness for therapeutic protein delivery

Silica nanoparticles with controllable surface roughness have been successfully prepared for therapeutic anti-pAkt antibody delivery.

Novel serum-tolerant lipoplexes target the folate receptor efficiently

Gene transfer using non-viral vectors is a promising approach for the safe delivery of nucleic acid therapeutics. In this study, we investigate a lipid-based system for targeted gene delivery to malignant cells overexpressing the folate receptor (FR). Cationic liposomes were formulated with and without the targeting ligand folate conjugated to distearoylphosphatidyl ethanolamine polyethylene glycol 2000 (DSPE-PEG2000), the novel cytofectin 3β[N(N(1),N(1)-dimethlaminopropylsuccinamidoethane)-carbamoyl]cholesterol (SGO4), which contains a 13atom, 15Å spacer element, and the helper lipid, dioleoylphosphatidylethanolamine (DOPE). Physicochemical parameters of the liposomes and lipoplexes were obtained by zeta sizing, zeta potential measurement and cryo-TEM. DNA-binding and protection capabilities of liposomes were confirmed by gel retardation assays, EtBr intercalation and nuclease protection assays. The complexes were assessed in an in vitro system for their effect on cell viability using the MTT assay, and gene transfection activity using the luciferase assay in three cell lines; HEK293 (FR-negative), HeLa (FR(+)-positive), KB (FR(++)-positive). Low cytotoxicities were observed in all cell lines, while transgene activity promoted by folate-tagged lipoplexes in FR-positive lines was tenfold greater than that by untargeted constructs and cell entry by folate complexes was demonstrably by FR mediation. These liposome formulations have the design capacity for in vivo application and may therefore be promising candidates for further development.

Development of a non-viral gene delivery vector based on the dynein light chain Rp3 and the TAT peptide

Gene therapy and DNA vaccination trials are limited by the lack of gene delivery vectors that combine efficiency and safety. Hence, the development of modular recombinant proteins able to mimic mechanisms used by viruses for intracellular trafficking and nuclear delivery is an important strategy. We designed a modular protein (named T-Rp3) composed of the recombinant human dynein light chain Rp3 fused to an N-terminal DNA-binding domain and a C-terminal membrane active peptide, TAT. The T-Rp3 protein was successfully expressed in Escherichia coli and interacted with the dynein intermediate chain in vitro. It was also proven to efficiently interact and condense plasmid DNA, forming a stable, small (∼100nm) and positively charged (+28.6mV) complex. Transfection of HeLa cells using T-Rp3 revealed that the vector is highly dependent on microtubule polarization, being 400 times more efficient than protamine, and only 13 times less efficient than Lipofectamine 2000™, but with a lower cytotoxicity. Confocal laser scanning microcopy studies revealed perinuclear accumulation of the vector, most likely as a result of transport via microtubules. This study contributes to the development of more efficient and less cytotoxic proteins for non-viral gene delivery.

Breaking limitations of complex culture media: functional non-viral miRNA delivery into pharmaceutical production cell lines

MicroRNAs (miRNAs) are promising targets for cell engineering through modulation of crucial cellular pathways. An effective introduction of miRNAs into the cell is a prerequisite to reliably study microRNA function. Previously, non-viral delivery of nucleic acids has been demonstrated to be cell type as well as culture medium dependent. Due to their importance for biopharmaceutical research and manufacturing, Chinese hamster ovary (CHO) and Cevec's Amniocyte Production (CAP) cells were used as host cell lines to investigate transfection reagents with respect to successful delivery of small non-coding RNAs (ncRNAs) and their ability to allow for biological activity of miRNAs and small interfering RNAs (siRNAs) within the cell. In the present study, we screened numerous transfection reagents for their suitability to successfully deliver miRNA mimics into CHO DG44 and CAP cells. Our investigation revealed that the determination of transfection efficiency for a given transfection reagent alone is not sufficient to draw conclusions about its ability to maintain the functionality of the miRNA. We could show that independent from high transfection rates observed for several reagents only one was suitable for efficient introduction of functional miRNA mimics into cells cultured in complex protein production media. We provide evidence for the functionality of transferred ncRNAs by demonstrating siRNA-mediated changes in protein levels and cellular phenotype as well as decreased twinfilin-1 (twf-1) transcript levels by its upstream miR-1 regulator. Furthermore, the process could be shown to be scalable which has important implications for biotechnological applications.

Improving ultrasound gene transfection efficiency by controlling ultrasound excitation of microbubbles

Ultrasound application in the presence of microbubbles has shown great potential for non-viral gene transfection via transient disruption of cell membrane (sonoporation). However, improvement of its efficiency has largely relied on empirical approaches without consistent and translatable results. The goal of this study is to develop a rational strategy based on new results obtained using novel experimental techniques and analysis to improve sonoporation gene transfection. In this study, we conducted experiments using targeted microbubbles that were attached to cell membrane to facilitate sonoporation. We quantified the dynamic activities of microbubbles exposed to pulsed ultrasound and the resulting sonoporation outcome, and identified distinct regimes of characteristic microbubble behaviors: stable cavitation, coalescence and translation, and inertial cavitation. We found that inertial cavitation generated the highest rate of membrane poration. By establishing direct correlation of ultrasound-induced bubble activities with intracellular uptake and pore size, we designed a ramped pulse exposure scheme for optimizing microbubble excitation to improve sonoporation gene transfection. We implemented a novel sonoporation gene transfection system using an aqueous two phase system (ATPS) for efficient use of reagents and high throughput operation. Using plasmids coding for the green fluorescence protein (GFP), we achieved a sonoporation transfection efficiency in rate aortic smooth muscle cells (RASMCs) of 6.9%±2.2% (n=9), comparable with lipofection (7.5%±0.8%, n=9). Our results reveal characteristic microbubble behaviors responsible for sonoporation and demonstrated a rational strategy to improve sonoporation gene transfection.

Comparative anti-inflammatory activity of poly(amidoamine) (PAMAM) dendrimer-dexamethasone conjugates with dexamethasone-liposomes

Lipophilicity vs hydrophicility physicochemical traits are extremely important variables that are active considerations for optimizing drug delivery systems. The comparative anti-inflammatory delivery potential of dexamethasone (dex) in an encapsulation-based (liposome-lipophilic) and poly (amidoamine) (PAMAM) dendrimer prodrug conjugation-based delivery systems (hydrophilic) was performed in this work. Dendrimer prodrug conjugates were characterized by (1)H NMR. The drug encapsulation efficiency for drug in liposomes was observed to be 14.02% and this was correlated with a dose-dependent tumor necrosis factor (TNF)-α inhibition (39-57% inhibition). The biological evaluation of nanocarriers for drug was demonstrated in a standard, conventionally used in vitro cell-based system for TNF-α inhibition. This served as a comparative tool to demonstrate a quantitatively higher TNF-α inhibition (67-71.48%) produced by the dendrimer-dex drug conjugate. The structure activity relationship (dose-for-dose) was inferred by relatively lesser inhibition of TNF-α by variants of PAMAM G4 (NH2) dendrimer-dex conjugates and was compared with liposomes carrying dex. In vitro results suggest that the prodrug conjugates of PAMAM dendrimer deliver dex to be more efficient in comparison with liposome-based dex in terms of higher TNF-α inhibition. This study has implications in designing efficient prodrug nanocarrier systems for delivering dex.

Recent advances in the rational design of silica-based nanoparticles for gene therapy

Gene therapy has attracted much attention in modern society and provides a promising approach for treating genetic disorders, diseases and cancers. Safe and effective vectors are vital tools to deliver genetic molecules to cells. This review summarizes recent advances in the rational design of silica-based nanoparticles and their applications in gene therapy. An overview of different types of genetic agents available for gene therapy is provided. The engineering of various silica nanoparticles is described, which can be used as versatile complexation tools for genetic agents and advanced gene therapy. Several challenges are raised and future research directions in the area of gene therapy using silica-based nanoparticles are proposed.

The statistics of protein expression ratios for cellular fluorescence studies

Fluorescence studies of cellular protein-protein interactions commonly employ transient cotransfection to express two proteins carrying distinct fluorescent labels. Because transiently transfected cells differ significantly in their expression level, the concentration ratio of the two expressed proteins varies, which in turn influences the measured fluorescence signal. Knowledge of the statistics of protein expression ratios is of considerable interest both from a fundamental point of view and for cellular fluorescence studies. Despite the perceived randomness of transient transfection, we were able to develop a quantitative model that describes the average and distribution of the protein expression ratio from a cell population. We show that the expression ratio is proportional to the molar plasmid ratio and relate the distribution to the finite number of active plasmids in the cell. The process of cationic lipid-mediated transfection is explored in more detail. Specifically, the influence of lipoplexes on the statistics of the expression ratio is examined. We further demonstrate that the transfection model provides a quantitative description of fluorescence fluctuation experiments, where only a fraction of the proteins are labeled.

[Regulation and analysis of intracellular trafficking of nucleic acids based on quantitative and dynamic imaging]

In the 21st century the category of biomedicine is now expanding from low-molecular drugs to recombinant proteins, antibodies, and nucleic acids (e.q., siRNA and plasmid DNA). In this era also, development of a novel nanotechnology to control intracellular trafficking is highly desired. For a promising gene therapy, an efficient nuclear delivery vector is a minimum requirement. Quantitative and mechanism-based information on differences in transfection efficiency between viral and non-viral vectors would be highly useful to improve the effectiveness of non-viral vectors. In this review, we will summarize our recent progress in quantitative comparison and underlying mechanisms of the intracellular trafficking between adenovirus vectors and plasmid DNA (pDNA) transfected by non-viral vectors. Our analysis has revealed that poor post-nuclear delivery events, as well as the nuclear delivery process itself are key processes to focus on. Especially, less effective transcription and translation are most likely due to poor nuclear decondensation and excess electrostatic interaction between mRNA and the gene carrier, respectively. Meanwhile, we have developed a multi-functional envelope-type nano device (MEND), in which the pDNA/polycation core is encapsulated in the lipid bilayers. Based on feedback information concerning the rate-limiting processes of gene carriers, we controlled the number of lipid envelopes to enhance the decoating of encapsulated pDNA from the envelope structure. As an expanded application of this concept, we have developed a tetra-lamellar MEND (T-MEND), which is designed to overcome the endosome and nuclear membranes by step-wise membrane fusion.

Barriers to non-viral vector-mediated gene delivery in the nervous system

Efficient methods for cell line transfection are well described, but, for primary neurons, a high-yield method different from those relying on viral vectors is lacking. Viral transfection has several drawbacks, such as the complexity of vector preparation, safety concerns, and the generation of immune and inflammatory responses when used in vivo. However, one of the main problems for the use of non-viral gene vectors for neuronal transfection is their low efficiency when compared with viral vectors. Transgene expression, or siRNA delivery mediated by non-viral vectors, is the result of multiple processes related to cellular membrane crossing, intracellular traffic, and/or nuclear delivery of the genetic material cargo. This review will deal with the barriers that different nanoparticles (cationic lipids, polyethyleneimine, dendrimers and carbon nanotubes) must overcome to efficiently deliver their cargo to central nervous system cells, including internalization into the neurons, interaction with intracellular organelles such as lysosomes, and transport across the nuclear membrane of the neuron in the case of DNA transfection. Furthermore, when used in vivo, the nanoparticles should efficiently cross the blood-brain barrier to reach the target cells in the brain.

Improved transfection efficiency of an aliphatic lipid substituted 2 kDa polyethylenimine is attributed to enhanced nuclear association and uptake in rat bone marrow stromal cell

BACKGROUND

Lipid substitutions of cationic polymers are actively explored to enhance the efficiency of nonviral gene carriers. We recently took this approach to develop a novel gene carrier by grafting linoleic acid (LA) to relatively biocompatible 2 kDa polyethylenimine (PEI2). The resulting polymer (PEI2LA) displayed improved transfection efficiency over the unmodified PEI2. The intracellular kinetics and distribution of the respective polyplexes were investigated in the present study to gain a better understanding of the role of lipid modification in intracellular trafficking of gene carriers.

METHODS

A Cy5-labeled plasmid DNA (pDNA) expressing the green fluorescent protein (GFP) was complexed with PEI2, PEI2LA, and 25 kDa polyethylenimine (PEI25) to transfect rat bone marrow stromal cells (BMSC). Subcellular fractionation was performed to measure the amount of nuclear associated pDNA. pDNA uptake, GFP-expression and nuclear-associated pDNA were measured by both flow cytometry and confocal laser scanning microscopy.

RESULTS

PEI2LA mediated higher transgene expression and percentages of transfected cells than PEI25 and PEI2, respectively. There was a strong correlation between nuclear associated pDNA and transgene expression. PEI2LA polyplexes were significantly larger in size than PEI25. The amounts of pDNA associated with the nuclei were greater in PEI2LA than PEI25 polyplexes. The perinuclear pDNA distribution between GFP-expressing and nonGFP-expressing indicated that GFP-positive cells had a higher amount of pDNA associated with their nuclei.

CONCLUSIONS

Improved transfection efficiency of PEI2LA was attributed to enhanced association with the nucleus, which may be a result of hydrophobic interaction between the lipid moieties on the modified lipopolymer and the nuclear membrane.

Non-covalent association of folate to lipoplexes: a promising strategy to improve gene delivery in the presence of serum

The success of gene therapy depends on the efficient delivery of therapeutic genes into target cells in vitro and in vivo. Non-viral vectors, such as cationic liposome-DNA complexes (lipoplexes), have been used for numerous gene delivery applications, although their efficacy is still limited, particularly when compared to that of viral vectors. In this work, we assessed the efficacy of a new gene delivery system generated by non-covalent association of folate to lipoplexes (FA-associated lipoplexes) in two different cancer cell lines (SCC-VII and TSA cells). Association of FA with liposomes composed of DOTAP and cholesterol, and subsequent complexation with DNA greatly increased transfection efficiency above that obtained with plain lipoplexes in both cell lines. The addition of 40μg of FA to lipoplexes was optimal for transfection and allowed to overcome the inhibitory effect induced by the presence of serum. Notably, the biological activity of the FA-associated complexes was even significantly improved under these conditions. Transfection activity mediated by FA-associated lipoplexes was compared with that by FA-conjugated lipoplexes, and the results showed that electrostatic association of FA to the lipoplexes led to considerably higher levels of biological activity than that involving covalent coupling of FA. Moreover, FA-associated lipoplexes confer greater DNA protection than FA-conjugated lipoplexes. To our knowledge, this is the first study reporting the characterization and application of FA-associated lipoplexes in gene delivery and showing their greater efficacy than that of FA-conjugated lipoplexes. Overall, the results obtained in the present work constitute a strong indication that the developed FA-associated lipoplexes are promising candidates for in vivo gene delivery.

Nonviral gene delivery to mesenchymal stem cells using cationic liposomes for gene and cell therapy

Mesenchymal stem cells (MSCs) hold a great promise for application in several therapies due to their unique biological characteristics. In order to harness their full potential in cell-or gene-based therapies it might be advantageous to enhance some of their features through gene delivery strategies. Accordingly, we are interested in developing an efficient and safe methodology to genetically engineer human bone marrow MSC (BM MSC), enhancing their therapeutic efficacy in Regenerative Medicine. The plasmid DNA delivery was optimized using a cationic liposome-based reagent. Transfection efficiencies ranged from ~2% to ~35%, resulting from using a Lipid/DNA ratio of 1.25 with a transgene expression of 7 days. Importantly, the number of plasmid copies in different cell passages was quantified for the first time and ~20,000 plasmid copies/cell were obtained independently of cell passage. As transfected MSC have shown high viabilities (>90%) and recoveries (>52%) while maintaining their multipotency, this might be an advantageous transfection strategy when the goal is to express a therapeutic gene in a safe and transient way.

Predictive modeling of non-viral gene transfer

In non-viral gene delivery, the variance of transgenic expression stems from the low number of plasmids successfully transferred. Here, we experimentally determine Lipofectamine- and PEI-mediated exogenous gene expression distributions from single cell time-lapse analysis. Broad Poisson-like distributions of steady state expression are observed for both transfection agents, when used with synchronized cell lines. At the same time, co-transfection analysis with YFP- and CFP-coding plasmids shows that multiple plasmids are simultaneously expressed, suggesting that plasmids are delivered in correlated units (complexes). We present a mathematical model of transfection, where a stochastic, two-step process is assumed, with the first being the low-probability entry step of complexes into the nucleus, followed by the subsequent release and activation of a small number of plasmids from a delivered complex. This conceptually simple model consistently predicts the observed fraction of transfected cells, the cotransfection ratio and the expression level distribution. It yields the number of efficient plasmids per complex and elucidates the origin of the associated noise, consequently providing a platform for evaluating and improving non-viral vectors.

The biological routes of gene delivery mediated by lipid-based non-viral vectors

Cationic lipid/DNA complexes (lipoplexes) represent an attractive alternative to viral vectors for cell transfection in vitro and in vivo but still suffer from relatively low efficiency. Comprehension of the interactions between vectors and DNA as well as cellular pathways and mechanisms in DNA entry into cells and ultimately nuclei will lead to the design of better adapted non-viral vectors for gene therapy applications. Here, some recent developments in the field on the pathways and mechanisms involved in lipoplex-mediated transfection are discussed. The techniques that are widely used to study the mechanism of gene delivery are also discussed.

Quantification of plasmid DNA copies in the nucleus after lipoplex and polyplex transfection

Nuclear uptake of plasmid DNA is one of the many cellular barriers that limit the efficiency of non-viral gene delivery systems. We have determined the number of plasmids that reach the nucleus of a transfected cell using an internally standardized quantitative PCR (qPCR) assay. We isolated nuclei using two different protocols: a density gradient technique and a detergent-based method. The density gradient procedure yielded nuclei with substantially less adhering plasmids on the outside of the nuclei. Using the density gradient protocol we determined that cells transfected with Lipofectamine lipoplexes or polyethylenimine polyplexes contained between 75 and 50,000 plasmids/nucleus, depending on the applied plasmid dose. Any increase above 3000 plasmids/nucleus resulted in only marginal increases in transgene expression. Furthermore, lipoplex-delivered plasmids were more efficiently expressed, on the basis of protein expression per plasmid number in the nucleus, than polyplex-delivered plasmids. This indicates that polymer may remain bound to some plasmids in the nucleus. Lastly, by sorting transfected cells into high- and low-expressing sub-populations, we observe that a sub-population of cells contain 3x greater plasmids/nucleus but express nearly 100x more transgene than other cells within a single transfection reaction. Taken together these results suggest the importance of considering the processes downstream from nuclear entry for strategies to improve the efficiency of gene transfer reagents.

An artificial virus-like nano carrier system: enhanced endosomal escape of nanoparticles via synergistic action of pH-sensitive fusogenic peptide derivatives

We previously reported that transferrin (Tf)-modified liposomes (Tf-L) additionally modified with a cholesterylated pH-sensitive fusogenic peptide (Chol-GALA) can release an encapsulated aqueous phase marker to cytosol via endosomal membrane fusion. However, further obstacles need to be overcome to bring the Tf-L to the level of a viral-like gene delivery system. In this study, we developed a novel packaging method to encapsulate condensed plasmid DNA into PEgylated Tf-L (Tf-PEG-L) to form a core-shell-type nanoparticle. The most difficult challenge was to provide a mechanism of escape for the condensed core from endosome to cytosol in the presence of polyethylene glycol (PEG). We hypothesized that a membrane-introduced Chol-GALA and a PEgylated GALA would interact synergistically to induce membrane fusion between liposome and endosome. By simultaneously incorporating Chol-GALA into the membrane of Tf-PEG-L and GALA at tips of PEG chains, a condensed core was released into cytosol, and transfection activity increased 100-fold. We concluded that topological control was responsible for the synergistic effect of GALA derivatives introduced on Tf-PEG-L.

Cell cycle dependent transcription, a determinant factor of heterogeneity in cationic lipid-mediated transgene expression

BACKGROUND

Heterogeneity of transgene expression, the presence or absence (below the limit of detection) of transgene expression on a cell-by-cell basis, is a severe disadvantage in the use of cationic lipid-mediated gene vectors for gene therapy and experiments in molecular biology. Understandings of intracellular trafficking and the function (transgene expression) of vectors related to cellular physiology are essential in terms of clarifying the mechanism underlying the heterogeneity.

METHODS

To distinguish the contribution of nuclear transfer efficiency and subsequent intranuclear transcription efficiency to the overall heterogeneity in transgene expression, a novel imaging system was established for the dual visualization of the nuclear transfer of pDNA and marker gene expression (lacZ) in single cells.

RESULTS

The expression of LacZ occurred in only approximately 30% of HeLa cells of the nuclear pDNA-positive cells, indicating that intranuclear transcription efficiency contributed to the heterogeneity. Dual imaging against synchronized cells further revealed that the efficiency of nuclear delivery was comparable irrespective of cell cycle status, which is contrary to the generally accepted hypothesis that nuclear import of pDNA is enhanced during cell division when the nuclear membrane structure is perturbed. The most significant finding in the present study is that nuclear transcription efficiency in terms of the ratio of LacZ-positive cells to nuclear pDNA-positive cells drastically increased in the late S and G2/M phase.

CONCLUSIONS

This is the first demonstration to show that cell cycle dependent intranuclear transcription appears to be responsible for the overall heterogeneity of transgene expression.

Quantitative and mechanism-based investigation of post-nuclear delivery events between adenovirus and lipoplex

Quantitative and mechanism-based information on differences in transfection efficiency between viral and non-viral vectors would be highly useful for improving the effectiveness of non-viral vectors. A previous quantitative comparison of intracellular trafficking between adenovirus and LipofectAMINE PLUS (LFN) revealed that the three orders of magnitude lower transfection efficiency of LFN was dominantly rate limited by the post-nuclear delivery process. In the present study, the contribution of transcription and translation processes to the overall differences in the transgene expression efficiency of nucleus-delivered DNA was independently evaluated by quantifying mRNA. As a result, transcription efficiency (E_transcript) of LFN, denoted as transgene expression divided by the amount of nuclear pDNA was about 16 times less than that for adenovirus. Furthermore, translation efficiency (E_translate), denoted as transfection activity divided by mRNA expression was approximately 460 times less in LFN. Imaging of the decondensed form of DNA by in situ hybridization revealed that poor decondensation efficiency of LFN is involved in the inferior E_transcript. Moreover, the inferior translation efficiency (E_translate) of LFN was mainly due to electrostatic interactions between LFN and mRNA. Collectively, an improvement in nuclear decondensation and the diminution of the interaction between vector and mRNA is essential for the development of new generations of non-viral vectors.

Transferrin-mediated PEGylated nanoparticles for delivery of DNA/PLL

The purpose of this work was to determine the stability of pDNA/poly(L-lysine) complex (DNA/PLL) during microencapsulation, prepare transferrin (TF) conjugated PEGylated nanoparticles (TF-PEG-NP) loading DNA/PLL, and assess its physicochemical characteristics and in vitro transfection efficiency. The DNA/PLL was prepared by mixing plasmid DNA (pDNA) in deionized water with various amounts of PLL. PEGylated nanoparticles (PEG-NP) loading DNA/PLL were prepared by a water-oil-water double emulsion solvent evaporation technique. TF-PEG-NP was prepared by coupling TF with PEG-NP. The physicochemical characteristics of TF-PEG-NP and in vitro transfection efficiency on K562 cells were measured. The results showed that free pDNA reserved its double supercoiled form (dsDNA) for only on average 25.7% after sonification, but over 70% of dsDNA was reserved after pDNA was contracted with PLL. The particle size range of TF-PEG-NP loading DNA/PLL was 150-450 nm with entrapment efficiency over 70%. TF-PEG-NP exhibited the low burst effect (<10%) within 1 day. After the first phase, DNA/PLL displayed a sustained release. The amount of cumulated DNA/PLL release from TF-PEG-NP with 2% polymer over 7 days was 85.4% for DNA/PLL (1:0.3 mass ratio), 59.8% and 43.1% for DNA/PLL (1:0.6) and DNA/PLL (1:1.0), respectively. To TF-PEG-NP loading DNA/PLL without chloroquine, the percentage of EGFP expressing cells was 28.9% for complexes consisting of DNA/PLL (1:0.3), 38.5% and 39.7% for DNA/PLL (1:0.6) and DNA/PLL (1:1.0), respectively. In TF-PEG-NP loading DNA/PLL with chloroquine, more cells were transfected, the percentage of positive cells was 37.6% (DNA/PLL, 1:0.3), 47.1% (DNA/PLL, 1:0.6) and 45.8% (DNA/PLL, 1:1.0), which meant that the transfection efficiency of pDNA was increased by over 50 times when PLL and TF-PEG-NP were jointly used as a plasmid DNA carrier, in particular, the maximal percentage of positive cells (47.1%) from TF-PEG-NP loading DNA/PLL (1:0.6) was about 70 times the transfection efficiency of free plasmid DNA. The average cell viability of TF-PEG-NP loading DNA/PLL was about 90%, which meant that TF-PEG-NP appeared to be safer than PLL alone. As a result, TF-PEG-NP loading DNA/PLL could be a more effective non-viral vector for the delivery of pDNA.

Uptake pathways and subsequent intracellular trafficking in nonviral gene delivery

The successful delivery of therapeutic genes to the designated target cells and their availability at the intracellular site of action are crucial requirements for successful gene therapy. Nonviral gene delivery is currently a subject of increasing attention because of its relative safety and simplicity of use; however, its use is still far from being ideal because of its comparatively low efficiency. Most of the currently available nonviral gene vectors rely on two main components, cationic lipids and cationic polymers, and a variety of functional devices can be added to further optimize the systems. The design of these functional devices depends mainly on our understanding of the mechanisms involved in the cellular uptake and intracellular disposition of the therapeutic genes as well as their carriers. Macromolecules are internalized into cells by a variety of mechanisms, and their intracellular fate is usually linked to the entry mechanism. Therefore, the successful design of a nonviral gene delivery system requires a deep understanding of gene/carrier interactions as well as the mechanisms involved in the interaction of the systems with the target cells. In this article, we review the different uptake pathways that are involved in nonviral gene delivery from a gene delivery point of view. In addition, available knowledge concerning cellular entry and the intracellular trafficking of cationic lipid-DNA complexes (lipoplexes) and cationic polymer-DNA complexes (polyplexes) is summarized.

Formation and intracellular trafficking of lipoplexes and polyplexes

Cationic lipid/DNA lipoplexes and cationic polymer/DNA polyplexes represent an attractive alternative to viral vectors for cell transfection in vitro and in vivo but still suffer from a relatively low efficiency. Optimization of their transfection efficiency may be attempted by using a trial and error approach consisting of synthesizing and testing a large number of derivatives. On the other hand, rational design of highly efficient cationic lipids and polymers requires a deeper understanding of the interactions between the vector and the DNA as well as the cellular pathways and mechanisms involved in DNA entry into the cell and ultimately the nucleus. In the present review, the pathways and mechanisms involved in lipoplex- and polyplex-mediated transfection are comparatively addressed and unresolved questions are highlighted.

Construction of a multifunctional envelope-type nano device by a SUV*-fusion method

A novel assembly method "SUV*-fusion method" was developed for the construction of a small and homogenous multifunctional envelope-type nano device (MEND) by utilizing a detergent-rich small unilamellar vesicle (SUV*). The method consists of three steps: (1) DNA condensation with a polycation, (2) electrostatic interaction of the SUV* with the DNA/polycation complex (DPC) and (3) lipid coating of DPC by SUV* fusion via removal of the detergent. We confirmed the construction of the MEND by sucrose density gradient centrifugation, and isolated the MEND only from the boundary between 25% and 40% sucrose. The isolated MEND had a small diameter (155 nm), was negatively charged (-24 mV), and encapsulated 30% of the total DNA. The MEND was formed by only SUV*, not by a lipid/detergent micelle. This confirms that a small and homogenous MEND can be constructed by the SUV*-fusion method. Furthermore, we confirmed that a transferrin-modified MEND could deliver a gene into a cell through receptor-mediated endocytosis. Consequently, we report on the successful construction of a small and homogenous MEND by a novel SUV*-fusion method.

Quantitative Three-Dimensional Analysis of the Intracellular Trafficking of Plasmid DNA Transfected by a Nonviral Gene Delivery System Using Confocal Laser Scanning Microscopy

Since endosomal escape and the nuclear delivery of plasmid DNA (pDNA) constitute major barriers for transgene expression, a quantitative evaluation of intracellular trafficking of pDNA would be highly desirable in terms of optimizing a nonviral gene delivery system. In the present study, a novel strategy is proposed for the quantification of rhodamine-labeled pDNA in endosomes/lysosomes, cytosol, and nucleus. Endosomes/lysosomes and nucleus were stained with LysoSensor DND-189 and Hoechst 33258, respectively, to distinguish them from the cytosol. The pixel areas of the clusters derived from the rhodamine were used as an index for the amount of pDNA. This approach was applied to the analysis of the intracellular trafficking of pDNA transfected by LipofectAMINE PLUS, stearylated octaarginine (STR-R8), and octaarginine (R8). In the case of R8, most of the pDNA was trapped by endosomes/lysosomes. STR-R8 exhibited endosomal escape followed by nuclear translocation in a time-dependent manner. LipofectAMINE PLUS was the most effective in rapidly delivering pDNA to the nucleus as well as the cytosol. These differences in the intracellular trafficking of pDNA correlated well with the transgene expression. Therefore, this method enables the quantitative analysis of the intracellular pharmacokinetics of pDNA and promises to provide useful information for optimizing nonviral gene delivery systems.

Pharmacokinetic and pharmacodynamic considerations in gene therapy

During gene therapy the concentration of plasmid DNA or oligonucleotides in the plasma can be quite different from their concentrations in the nucleus or cytosol where they exert their actions. For a better understanding of the apparent discrepancies between pharmacokinetics (PK) and pharmacodynamics (PD), a new concept for intracellular PK with an emphasis on the final efficacy of gene transcription is needed. Here, the conventional PK and intracellular PK and PD of non-viral gene delivery systems are discussed, together with a new concept, referred to as controlled intracellular disposition, which integrates these factors to gain a better understanding of gene expression in the nucleus. The importance of optimizing the system from a transcriptional point of view in the nucleus is also discussed. These new concepts must be integrated to develop an optimized non-viral gene delivery system.