The mechanism of polyplex internalization into cells: testing the GM1/caveolin-1 lipid raft mediated endocytosis pathway

Direct Cell Reprogramming and Phenotypic Conversion: An Analysis of Experimental Attempts to Transform Astrocytes into Neurons in Adult Animals

Central nervous system (CNS) repair after injury or disease remains an unresolved problem in neurobiology research and an unmet medical need. Directly reprogramming or converting astrocytes to neurons (AtN) in adult animals has been investigated as a potential strategy to facilitate brain and spinal cord recovery and advance fundamental biology. Conceptually, AtN strategies rely on forced expression or repression of lineage-specific transcription factors to make endogenous astrocytes become "induced neurons" (iNs), presumably without re-entering any pluripotent or multipotent states. The AtN-derived cells have been reported to manifest certain neuronal functions in vivo. However, this approach has raised many new questions and alternative explanations regarding the biological features of the end products (e.g., iNs versus neuron-like cells, neural functional changes, etc.), developmental biology underpinnings, and neurobiological essentials. For this paper per se, we proposed to draw an unconventional distinction between direct cell conversion and direct cell reprogramming, relative to somatic nuclear transfer, based on the experimental methods utilized to initiate the transformation process, aiming to promote a more in-depth mechanistic exploration. Moreover, we have summarized the current tactics employed for AtN induction, comparisons between the bench endeavors concerning outcome tangibility, and discussion of the issues of published AtN protocols. Lastly, the urgency to clearly define/devise the theoretical frameworks, cell biological bases, and bench specifics to experimentally validate primary data of AtN studies was highlighted.

Preparation and characterization of polyamidoamine dendrimers conjugated with cholesteryl-dipeptide as gene carriers in HeLa cells

Improving the transfection efficiency of non-viral carriers by using cationic polymers is a useful approach to addressing several challenges in gene therapy, such as cellular uptake, endosomal escape, and toxicity. Among the various cationic polymers, polyamidoamine (PAMAM) dendrimers have been widely utilized because of the abundance of terminal functional groups, thereby enabling further functionalization and enhancing DNA condensation and internalization into cells. The combination of various functional groups is required for these PAMAM dendrimer derivatives to function appropriately for gene delivery. Herein, we synthesized PAMAM G2-HRChol by conjugating dipeptide (histidine-arginine) and cholesterol at different ratios (6% or 23%) on the surface of PAMAM dendrimer generation 2 (PAMAM G2). Both PAMAM G2-HRChol 6% and PAMAM G2-HRChol 23% have buffering capacity, leading to improved endosomal escape after entering the cells. PAMAM G2-HRChol 6% and PAMAM G2-HRChol 23% dendrimers were condensed with pDNA to form nano-polyplexes at a weight ratio of 4 (polymer/pDNA). Polyplexes are positively charged, which facilitates cellular uptake. The transfection efficiency of PAMAM G2-HRChol 6% and PAMAM G2-HRChol 23% dendrimers was similar to that of PEI 25 kDa under optimum conditions, and the cytotoxicity was much lower than that of PEI 25 kDa in HeLa cells. In addition, after apoptin gene transfection was performed, cell death ratios of 34.47% and 22.47% were observed for PAMAM G2-HRChol 6% and PAMAM G2-HRChol 23%, respectively. The results show that a suitable amount of cholesterol can improve gene transfection efficiency, and the PAMAM G2-HRChol 6% dendrimer could be a potential gene carrier in HeLa cells.

Highly Efficient Method for Intracellular Delivery of Proteins Mediated by Cholera Toxin-Induced Protein Internalization

Delivery of functional proteins into cells may help us understand how specific protein influences cell behavior as well as treat diseases caused by protein deficiency or loss-of-function mutations. However, protein cannot enter cells by diffusion. In this work, a novel cell biology tool for delivering recombinant proteins into mammalian cells was developed. We hijacked the intracellular transport routes used by the cholera toxin and took advantage of recent development on split intein that is compatible with denatured conditions and shows an exceptional splicing activity to deliver a protein of interest into mammalian cells. Here, we used green fluorescent protein and apoptin as proofs-of-concept. The results demonstrate that the cholera toxin B subunit alone could deliver other recombinant proteins into cells through either covalent conjugation or noncovalent interaction. Our method offers more than 10-fold better delivery efficiency than the tat cell-penetrating peptide and is selective for ganglioside-rich cells. This study adds a useful tool to the receptor-mediated intracellular targeting toolkit and opens possibility for the selective delivery of therapeutic proteins into ganglioside-rich cells.

Polycation-Mediated Transfection: Mechanisms of Internalization and Intracellular Trafficking

Polyplex-mediated gene transfection is now in its' fourth decade of serious research, but the promise of polyplex-mediated gene therapy has yet to fully materialize. Only approximately one in a million applied plasmids actually expresses. A large part of this is due to an incomplete understanding of the mechanism of polyplex transfection. There is an assumption that internalization must follow a canonical mechanism of receptor mediated endocytosis. Herein, we present arguments that untargeted (and most targeted) polyplexes do not utilize these routes. By incorporating knowledge of syndecan-polyplex interactions, we can show that syndecans are the "target" for polyplexes. Further, it is known that free polycations (which disrupt cell-membranes by acid-catalyzed hydrolysis of phospholipid esters) are necessary for (untargeted) endocytosis. This can be incorporated into the model to produce a novel mechanism of endocytosis, which fits the observed phenomenology. After membrane translocation, polyplex containing vesicles reach the endosome after diffusing through the actin mesh below the cell membrane. From there, they are acidified and trafficked toward the lysosome. Some polyplexes are capable of escaping the endosome and unpacking, while others are not. Herein, it is argued that for some polycations, as acidification proceeds the polyplexes excluding free polycations, which disrupt the endosomal membrane by acid-catalyzed hydrolysis, allowing the polyplex to escape. The polyplex's internal charge ratio is now insufficient for stability and it releases plasmids which diffuse to the nucleus. A small proportion of these plasmids diffuse through the nuclear pore complex (NPC), with aggregation being the major cause of loss. Those plasmids that have diffused through the NPC will also aggregate, and this appears to be the reason such a small proportion of nuclear plasmids express mRNA. Thus, the structural features which promote unpacking in the endosome and allow for endosomal escape can be determined, and better polycations can be designed.

GM1-Binding Conjugates To Improve Intestinal Permeability

Drugs and proteins with poor intestinal permeability have a limited oral bioavailability. To remediate this problem, a receptor-mediated endocytosis and transcytosis approach was explored. Indeed, the nontoxic β subunit of cholera toxin (CTB) can cross the intestinal barrier by binding to receptor GM1. In this study, we explored the use of GM1-binding peptides and CTB as potential covalent carriers of poorly permeable molecules. GM1-binding peptides (G23, P3) and CTB were conjugated to poorly permeable fluorescent probes such as fluorescein isothiocyanate (FITC) and albumin-FITC using triethylene glycol spacers and click chemistry. The affinity of the peptide conjugates with receptor GM1 was confirmed by isothermal titration calorimetry or microscale thermophoresis, and the results suggested the involvement of nonspecific interactions. Conjugating the model drugs to G23 and P3 improved the internalization into Caco-2 and T84 cells, although the process was not dependent on the amount of GM1 receptor. However, conjugation of bovine serum albumin FITC to CTB increased the internalization in the same cells in a GM1-dependent pathway. Peptide conjugates demonstrated a limited permeability through a Caco-2 monolayer, whereas G23 and CTB conjugates slightly enhanced permeability through a T84 cell monolayer compared to model drugs alone. Since CTB can improve the permeability of large macromolecules such as albumin, it is an interesting carrier for the improvement of oral bioavailability of various other macromolecules such as heparins, proteins, and siRNAs.

Alpha-Tocopheryl Succinate-Conjugated G5 PAMAM Dendrimer Enables Effective Inhibition of Ulcerative Colitis

Ulcerative colitis (UC) is a severe inflammatory disease in colon, however, the therapeutic efficacy of the standard-of-care in clinic for UC patients is unsatisfactory. To explore new drugs for effective and safe treatment of UC, alpha-tocopheryl succinate (α-TOS) is conjugated to generation 5 (G5) poly(amidoamine) (PAMAM) dendrimer to construct a nanodevice of G5-NH-acetamide (Ac)-TOS. The inhibitory effects of the G5-NH-Ac-TOS on UC are evaluated in vivo in a dextran sulfate sodium induced UC mouse model, and its mechanisms are explored in vitro in lipopolysaccharide stimulated mouse peritoneal macrophages. The results indicate that the G5-NH-Ac-TOS exhibits greater inhibitive effects on UC than free α-TOS, through significant attenuation of the disease activity index and reduction of macrophage infiltration in the colon tissues. The protective mechanisms of the G5-NH-Ac-TOS are revealed to be related to inhibition of expression of nuclear translocation of NF-κB, phosphorylation of Akt, and reduction of reactive oxygen species production in the macrophages.

siRNA delivery using polyelectrolyte-gold nanoassemblies in neuronal cells for BACE1 gene silencing

Small interfering RNA (siRNA) mediated RNA interference is a versatile therapeutic tool for many intractable genetic disorders. Various nanoassemblies specifically designed to deliver the siRNAs could be utilized for efficient siRNA delivery which is one of the major concern for the success of this therapeutic. Thus, in the present study, polyelectrolyte-gold nanoassemblies (PE-Gold NAs) were selected for siRNA delivery of an in vitro verified siRNA. Three different polyelectrolytes (polyethyleneimine, citraconic anhydride modified poly (allylamine) hydrochloride and poly l-arginine) were used to formulate the PE-Gold NAs using the layer-by-layer technique. Successful physico-chemical characterizations of these PE-Gold NAs were performed using UV-Visible, FTIR, ¹H-NMR spectroscopies, XRD, TEM, DLS and Zeta potential measurements. In vitro studies for the cytotoxicity, the uptake of these nanoassemblies and the gene silencing were carried out using these PE-Gold NAs in N2a and NB4 1A3 (murine neuronal) cell lines. The three selected PE-Gold NAs showed significant BACE1 (β-site APP cleaving enzyme 1) gene silencing (50-60%). This work demonstrates the potential of PE-Gold NAs to deliver siRNA targeting BACE1 in neuronal cells. Finally, it was concluded that different polyelectrolytes used in the PE-Gold NAs achieve different gene silencing due to the variation in their delivery efficiencies.

Role of Cell Membrane-Vector Interactions in Successful Gene Delivery

Cationic polymers have been investigated as nonviral vectors for gene delivery due to their favorable safety profile when compared to viral vectors. However, nonviral vectors are limited by poor efficacy in inducing gene expression. The physicochemical properties of cationic polymers enabling successful gene expression have been investigated in order to improve expression efficiency and safety. Studies over the past several years have focused on five possible rate-limiting processes to explain the differences in gene expression: (1) endosomal release, (2) transport within specific intracellular pathways, (3) protection of DNA from nucleases, (4) transport into the nucleus, and (5) DNA release from vectors. However, determining the relative importance of these processes and the vector properties necessary for optimization remain a challenge to the field. In this Account, we describe over a decade of studies focused on understanding the interaction of cationic polymer and cationic polymer/oligonucleotide (polyplex) interactions with model lipid membranes, cell membranes, and cells in culture. In particular, we have been interested in how the interaction between cationic polymers and the membrane influences the intracellular transport of intact DNA to the nucleus. Recent advances in microfluidic patch clamp techniques enabled us to quantify polyplex cell membrane interactions at the cellular level with precise control over material concentrations and exposure times. In attempting to relate these findings to subsequent intracellular transport of DNA and expression of protein, we needed to develop an approach that could distinguish DNA that was intact and potentially functional for gene expression from the much larger pool of degraded, nonfunctional DNA within the cell. We addressed this need by developing a FRET oligonucleotide molecular beacon (OMB) to monitor intact DNA transport. The research highlighted in this Account builds to the conclusion that polyplex transported DNA is released from endosomes by free cationic polymer intercalated into the endosomal membrane. This cationic polymer initially interacts with the cell plasma membrane and appears to reach the endosome by lipid cycling mechanisms. The fraction of cells displaying release of intact DNA from endosomes quantitatively predicts the fraction of cells displaying gene expression for both linear poly(ethylenimine) (L-PEI; an effective vector) and generation five poly(amidoamine) dendrimer (G5 PAMAM; an ineffective vector). Moreover, intact OMB delivered with G5 PAMAM, which normally is confined to endosomes, was released by the subsequent addition of L-PEI with a corresponding 10-fold increase in transgene expression. These observations are consistent with experiments demonstrating that cationic polymer/membrane partition coefficients, not polyplex/membrane partition coefficients, predict successful gene expression. Interestingly, a similar partitioning of cationic polymers into the mitochondrial membranes has been proposed to explain the cytotoxicity of these materials. Thus, the proposed model indicates the same physicochemical property (partitioning into lipid bilayers) is linked to release from endosomes, giving protein expression, and to cytotoxicity.

Quantitative study of effects of free cationic chains on gene transfection in different intracellular stages

Previously, we revealed that in the application of using cationic polymer chains, polyethylenimine (PEI), to condense anionic plasmid DNA chains (pDNA) to form the DNA/polymer polyplexes, after all the pDNAs are complexed with PEI, further added PEIs exist individual chains and free in the solution mixture. It is those uncomplexed polycation chains that dramatically promote the gene transfection. In the current study, we studied how those free cationic chains with different lengths and topologies affect the intracellular trafficking of the polyplexes, the translocation of pDNA through the nuclear membrane, the transcription of pDNA to mRNA and the translocation of mRNA from nucleus to cytosol in HepG2 cells by using a combination of the three-dimensional confocal microscope and TaqMan real-time PCR. We found that free branched PEI chains with a molar mass of 25,000g/mol and a total concentration of 1.8×10(-6)g/mL promote the overall gene transfection efficiency by a factor of ~500 times. Our results quantitatively reveal that free chains help little in the cellular uptake, but clearly reduce the lysosomal entrapment of those internalized polyplexes (2-3 folds); assist the translocation of pDNA through nuclear membrane after it is released from the polyplexes in the cytosol (~5 folds); enhance the pDNA-to-mRNA transcription efficiency (~4 folds); and facilitate the nucleus-to-cytosol translocation of mRNA (7-8 folds). The total enhancement of those steps agrees well with the overall efficiency, demonstrating, for the first time, how free cationic polymer chains quantitatively promote the gene transfection in each step in the intracellular space.

Express in Vitro Plasmid Transfection Achieved with 16+ Asymmetric Peptide Dendrimers

Asymmetric cationic amino acid-based dendrimers are highly branched chemically derived gene vectors developed to transport cargo such as plasmid DNA across the plasma membrane. We have previously demonstrated their propensity to enter cells that form caveolae, driven by positive charge density and promoted by arginine head groups. Caveolae are plasma membrane subdomains serving a number of cellular functions including endocytosis. Their formation requires membrane proteins (caveolins) and cytoplasmic proteins (cavins), so that gene disruption of either caveolin-1 or cavin-1 (also known as PTRF, i.e., polymerase I and transcript release factor) results in caveola deficiency. Here we evaluated the ability of a 16⁺ charged asymmetric arginine dendrimer to transfect plasmid DNA into cultured cells. We unveiled efficient transfection efficiencies (≥30%) 24-48 h after exposing the cells to dendrimer/pDNA complexes for only 5 min. Using wild type (WT) and caveolin-1 or PTRF gene-disrupted, i.e., caveola-deficient mouse embryo fibroblasts, we further show that caveolae promote pDNA transfection by 16⁺ charged asymmetric arginine dendrimers.

Are caveolae a cellular entry route for non-viral therapeutic delivery systems?

The development of novel therapies increasingly relies on sophisticated delivery systems that allow the drug or gene expression-modifying agent of interest entry into cells. These systems can promote cellular targeting and/or entry, and they vary in size, charge, and functional group chemistry. Their optimization requires an in depth knowledge of the cellular routes of entry in normal and pathological states. Caveolae are plasma membrane invaginations that have the potential to undergo endocytosis. We critically review the literature exploring whether drug or nucleic acid delivery systems exploit and/or promote cellular entry via caveolae. A vast majority of studies employ pharmacological tools, co-localization experiments and very few make use of molecular tools. We provide clarification on how results of such studies should be interpreted and make suggestions for future studies.

G5 PAMAM dendrimer versus liposome: a comparison study on the in vitro transepithelial transport and in vivo oral absorption of simvastatin

This study compared formulation effects of a dendrimer and a liposome preparation on the water solubility, transepithelial transport, and oral bioavailability of simvastatin (SMV). Amine-terminated G5 PAMAM dendrimer (G5-NH2) was chosen to form SMV/G5-NH2 molecular complexes, and SMV-liposomes were prepared by using a thin film dispersion method. The effects of these preparations on the transepithelial transport were investigated in vitro using Caco-2 cell monolayers. Results indicated that the solubility and transepithelial transport of SMV were significantly improved by both formulations. Pharmacokinetic studies in rats also revealed that both the SMV/G5-NH2 molecular complexes and the SMV-liposomes significantly improved the oral bioavailability of SMV with the liposomes being more effective than the G5-NH2. The overall better oral absorption of SMV-liposomes as compared to SMV/G5-NH2 molecular complexes appeared to arise from better liposomal solubilization and encapsulation of SMV and more efficient intracellular SMV delivery.

FROM THE CLINICAL EDITOR

Various carrier systems have been designed to enhance drug delivery via the oral route. In this study, the authors compared G5 PAMAM dendrimers to liposome preparations in terms of solubility, transepithelial transport, and oral bioavailability of this poorly water-soluble drug. This understanding has improved our knowledge in the further development of drug carrier systems.

Quantification of cytosolic plasmid DNA degradation using high-throughput sequencing: implications for gene delivery

BACKGROUND

Although cytosolic DNA degradation plays an important role in decreasing transgene expression, the plasmid degradation pattern remains largely unexplored.

METHODS

Illumina dye sequencing was employed to provide degradation site information for S1 and cytosolic nucleases. S1 nuclease provided a positive control for a comparison between the agarose gel method and sequencing approaches.

RESULTS

The poly(A) region between the β-lactamase gene and the cytomegalovirus (CMV) promoter was identified as the most likely cut site for polyplex-treated cytosol. The second most likely site, at the 5' end of the β-lactamase gene, was identified by gel electrophoresis and sequencing. Additional sites were detected in the OriC region, the SV40/poly(A) region, the luciferase gene and the CMV promoter. Sequence analysis of plasmid treated with cytosol from control cells showed the greatest cut activity in the OriC region, the β-lactamase gene and the poly(A) region following the luciferase gene. Additional regions of cut activity include the SV40 promoter and the β-lactamase poly(A) termination sequence. Both cytosolic nucleases and the S1 nuclease showed substantial activity at the bacterial origin of replication (OriC).

CONCLUSIONS

High-throughput plasmid sequencing revealed regions of the luciferase plasmid DNA sequence that are sensitive to cytosolic nuclease degradation. This provides new targets for improving plasmid and/or polymer design to optimize the likelihood of protein expression.

Dependence of PEI and PAMAM Gene Delivery on Clathrin- and Caveolin-Dependent Trafficking Pathways

PURPOSE

Non-viral gene delivery vehicles such as polyethylenimine and polyamidoamine dendrimer effectively condense plasmid DNA, facilitate endocytosis, and deliver nucleic acid cargo to the nucleus in vitro. Better understanding of intracellular trafficking mechanisms involved in polymeric gene delivery is a prerequisite to clinical application. This study investigates the role of clathrin and caveolin endocytic pathways in cellular uptake and subsequent vector processing.

METHODS

We formed 25-kD polyethylenimine (PEI) and generation 4 (G4) polyamidoamine (PAMAM) polyplexes at N/P 10 and evaluated internalization pathways and gene delivery in HeLa cells. Clathrin- and caveolin-dependent endocytosis inhibitors were used at varying concentrations to elucidate the roles of these important pathways.

RESULTS

PEI and PAMAM polyplexes were internalized by both pathways. However, the amount of polyplex internalized poorly correlated with transgene expression. While the caveolin-dependent pathway generally led to effective gene delivery with both polymers, complete inhibition of the clathrin-dependent pathway was also deleterious to transfection with PEI polyplexes. Inhibition of one endocytic pathway may lead to an overall increase in uptake via unaffected pathways, suggesting the existence of compensatory endocytic mechanisms.

CONCLUSIONS

The well-studied clathrin- and caveolin-dependent endocytosis pathways are not necessarily independent, and perturbing one mechanism of trafficking influences the larger trafficking network.

Protective effects and mechanisms of G5 PAMAM dendrimers against acute pancreatitis induced by caerulein in mice

In this study, generation 5 (G5) polyamidoamine (PAMAM) dendrimers with two different surface groups, G4.5-COOH and G5-OH, were investigated for their protective effects on pancreas injury in a caerulein-induced acute pancreatitis (AP) mouse model. Both dendrimers significantly decreased pathological changes in the pancreas and reduced the inflammatory infiltration of macrophages in pancreatic tissues. In addition, the expression of pro-inflammatory cytokines was significantly inhibited by the two dendrimers, not only in pancreatic tissues from AP mice but also in vitro in mouse peritoneal macrophages with LPS-induced inflammation. G4.5-COOH, which had better in vivo protective effects for AP than G5-OH, led to a significant reduction in the total number of plasma white blood cells (WBCs) and monocytes in AP mice, and its anti-inflammatory mechanism was related to inhibition of the nuclear translocation of NF-κB in macrophages.

The role of caveolin-1 and syndecan-4 in the internalization of PEGylated PAMAM dendrimer polyplexes into myoblast and hepatic cells

To improve gene delivery efficiency of PEGylated poly(amidoamine) dendrimers in livers and muscles, the roles of syndecan-4 receptor and caveolin-1 protein in the endocytosis of PEGylated generation 5 (G5-PEG) or 7 (G7-PEG) dendrimers and plasmid DNA polyplexes were explored in C2C12 and HepG2 cells. Expression levels of syndecan-4 for both cell lines were downregulated by transfection of the cells with syndecan-4 specific siRNA. Caveolin-1 was upregulated by infecting the cells with adenovirus vector expressed caveolin-1 (Ad-CAV-1). The impact of syndecan-4 and caveolin-1 on endocytosis of G5-PEG/DNA or G7-PEG/DNA polyplexes was then measured by flow cytometry. Our results demonstrate that downregulation of syndecan-4 and upregulation of caveolin-1 significantly improved internalization of PEG-PAMAM dendrimer polyplexes in HepG2 cells; however, in C2C12 cells, downregulation of syndecan-4 decreased the internalization of the polyplexes while upregulation of caveolin-1 had no effect on internalization. Gene expression results for G5-PEG/pGFP on the two cell lines exhibited the same trends for syndecan-4 and caveolin-1 as was observed for endocytosis of the polyplexes. This study gives a clue how to take strategies by up- or down-regulation of the expressions of syndecan-4 and caveolin-1 to improve in vivo gene delivery efficiency of the PEG-PAMAM dendrimers in clinical transgenic therapy.

Intracellular trafficking and cellular uptake mechanism of mPEG-PLGA-PLL and mPEG-PLGA-PLL-Gal nanoparticles for targeted delivery to hepatomas

The lysosomal escape of nanoparticles is crucial to enhancing their delivery and therapeutic efficiency. Here, we report the cellular uptake mechanism, lysosomal escape, and organelle morphology effect of monomethoxy (polyethylene glycol)-poly (D,L-lactide-co-glycolide)-poly (L-lysine) (mPEG-PLGA-PLL, PEAL) and 4-O-beta-D-Galactopyranosyl-D-gluconic acid (Gal)-modified PEAL (PEAL-Gal) for intracellular delivery to HepG2, Huh7, and PLC hepatoma cells. These results indicate that PEAL is taken up by clathrin-mediated endocytosis of HepG2, Huh7 and PLC cells. For PEAL-Gal, sialic acid receptor-mediated endocytosis and clathrin-mediated endocytosis are the primary uptake pathways in HepG2 cells, respectively, whereas PEAL-Gal is internalized by sag vesicle- and clathrin-mediated endocytosis in Huh7 cells. In the case of PLC cells, clathrin-mediated endocytosis and sialic acid receptor play a primary role in the uptake of PEAL-Gal. TEM results verify that PEAL and PEAL-Gal lead to a different influence on organelle morphology of HepG2, Huh7 and PLC cells. In addition, the results of intracellular distribution reveal that PEAL and PEAL-Gal are less entrapped in the lysosomes of HepG2 and Huh7 cells, demonstrating that they effectively escape from lysosomes and contribute to enhance the efficiency of intracellular delivery and tumor therapy. In vivo tumor targeting image results demonstrate that PEAL-Gal specifically delivers Rhodamine B (Rb) to the tumor tissue of mice with HepG2, Huh7, and PLC hepatomas and remains at a high concentration in tumor tissue until 48 h, properties that will greatly contribute to enhanced antitumor efficiency.

Polyplex-induced cytosolic nuclease activation leads to differential transgene expression

Cytosolic nucleases have been proposed to play an important role in limiting the effectiveness of polyplex-based gene delivery agents. In order to explore the effect of cell membrane disruption on nuclease activation, nuclease activity upon polyplex uptake and localization, and nuclease activity upon gene expression, we employed an oligonucleotide molecular beacon (MB). The MB was incorporated as an integral part of the polymer/DNA polyplex, and two-color flow cytometry experiments were performed to explore the relationship of MB cleavage with propidium iodide (PI) uptake, protein expression, and polyplex uptake. In addition, confocal fluorescence microcopy was performed to examine both polyplex and cleaved MB localization. The impact of cell membrane disruption was also probed using whole-cell patch clamp measurement of the plasma membrane's electrical conductance. Differential activation of cytosolic nuclease was observed with substantial activity for B-PEI and G5 PAMAM dendrimer (G5), less cleavage for jetPEI, and little activity for L-PEI. jetPEI and L-PEI exhibited substantially greater transgene expression, consistent with the lower amounts of MB oligonucleotide cleavage observed. Cytosolic nuclease activity, although dependent on the choice of polymer employed, was not related to the degree of cell plasma membrane disruption that occurred as measured by PI uptake or whole-cell patch clamp.

Polymeric nucleic acid vehicles exploit active interorganelle trafficking mechanisms

Materials that self-assemble with nucleic acids into nanocomplexes (e.g. polyplexes) are widely used in many fundamental biological and biomedical experiments. However, understanding the intracellular transport mechanisms of these vehicles remains a major hurdle in their effective usage. Here, we investigate two polycation models, Glycofect (which slowly degrades via hydrolysis) and linear polyethyleneimine (PEI) (which does not rapidly hydrolyze), to determine the impact of polymeric structure on intracellular trafficking. Cells transfected using Glycofect underwent increasing transgene expression over the course of 40 h and remained benign over the course of 7 days. Transgene expression in cells transfected with PEI peaked at 16 h post-transfection and resulted in less than 10% survival after 7 days. While saccharide-containing Glycofect has a higher buffering capacity than PEI, polyplexes created with Glycofect demonstrate more sustained endosomal release, possibly suggesting an additional or alternative delivery mechanism to the classical "proton sponge mechanism". PEI appeared to promote release of DNA from acidic organelles more than Glycofect. Immunofluorescence images indicate that both Glycofect and linear PEI traffic oligodeoxynucleotides to the Golgi and endoplasmic reticulum, which may be a route towards nuclear delivery. However, Glycofect polyplexes demonstrated higher co-localization with the ER than PEI polyplexes, and co-localization experiments indicate the retrograde transport of polyplexes via COP I vesicles from the Golgi to the ER. We conclude that slow release and unique trafficking behaviors of Glycofect polyplexes may be due to the presence of saccharide units and the degradable nature of the polymer, allowing more efficacious and benign delivery.

Best practices for purification and characterization of PAMAM dendrimer

Poly(amidoamine) (PAMAM) dendrimer are branched polymers with low degrees of heterogeneity. Current synthesis methods, however, result in substantial batch variability. We present our optimized procedure for post-synthesis (and post-market) purification of a generation 5 PAMAM dendrimer by membrane dialysis and demonstrate its effectiveness and limitations using a representative lot of biomedical grade dendrimer. This method successfully removes trailing generation defect structures, thereby reducing the heterogeneity of the material (PDI reduced from 1.04 to 1.02). Optimized analytical techniques to characterize the unpurified and purified dendrimer are also detailed. The efficiency of the purification method is successfully monitored by these analytics and dendrimer parameters that are critical for subsequent modification reactions and biological evaluation (M(n), M(w), PDI, average number of end groups) obtained. To provide better definition of the variability that should be expected between lots of synthesized material, HPLC traces for three additional commercial lots of dendrimer are also presented.

Efficient in vitro siRNA delivery and intramuscular gene silencing using PEG-modified PAMAM dendrimers

Although siRNA techniques have been broadly applied as a tool for gene knockdown, substantial challenges remain in achieving efficient delivery and in vivo efficacy. In particular, the low efficiency of target gene silencing in vivo is a critical limiting step to the clinical application of siRNA therapies. Poly(amidoamine) (PAMAM) dendrimers are widely used as carriers for drug and gene delivery; however, in vivo siRNA delivery by PAMAM dendrimers remains to be carefully investigated. In this study, the effectiveness of G5 and G6 PAMAM dendrimers with 8% of their surface amines conjugated to MPEG-5000 was studied for siRNA delivery in vitro and for intramuscular in vivo delivery in mice. The results from the PEG-modified dendrimers were compared to the results from the parent dendrimers as well as Lipofectamine 2000 and INTERFERin. Both PEG-modifed dendrimers protect the siRNA from being digested by RNase and gave high transfection efficiency for FITC-labeled siRNA in the primary vascular smooth muscle cells (VSMC) and mouse peritoneal macrophages. The PEG-modified dendrimers achieved knockdown of both plasmid (293A cells) and adenovirus-mediated green fluorescence protein (GFP) expression (Cos7 cells) in vitro with efficiency similar to that shown for Lipofectamine 2000. We further demonstrated in vivo that intramuscular delivery of GFP-siRNA using PEG-modified dendrimer significantly suppressed GFP expression in both transiently adenovirus infected C57BL/6 mice and GFP transgenic mice.

Uptake and intracellular traffic of siRNA dendriplexes in glioblastoma cells and macrophages

BACKGROUND

Gene silencing using small interfering RNA (siRNA) is a promising new therapeutic approach for glioblastoma. The endocytic uptake and delivery of siRNA to intracellular compartments could be enhanced by complexation with polyamidoamine dendrimers. In the present work, the uptake mechanisms and intracellular traffic of siRNA/generation 7 dendrimer complexes (siRNA dendriplexes) were screened in T98G glioblastoma and J774 macrophages.

METHODS

The effect of a set of chemical inhibitors of endocytosis on the uptake and silencing capacity of dendriplexes was determined by flow cytometry. Colocalization of fluorescent dendriplexes with endocytic markers and occurrence of intracellular dissociation were assessed by confocal laser scanning microscopy.

RESULTS

Uptake of siRNA dendriplexes by T98G cells was reduced by methyl-β-cyclodextrin, and genistein, and cytochalasine D, silencing activity was reduced by genistein; dendriplexes colocalized with cholera toxin subunit B. Therefore, caveolin-dependent endocytosis was involved both in the uptake and silencing activity of siRNA dendriplexes. On the other hand, uptake of siRNA dendriplexes by J774 cells was reduced by methyl-β-cyclodextrin, genistein, chlorpromazine, chloroquine, cytochalasine D, and nocodazole, the silencing activity was not affected by chlorpromazine, genistein or chloroquine, and dendriplexes colocalized with transferrin and cholera toxin subunit B. Thus, both clathrin-dependent and caveolin-dependent endocytosis mediated the uptake and silencing activity of the siRNA dendriplexes. SiRNA dendriplexes were internalized at higher rates by T98G but induced lower silencing than in J774 cells. SiRNA dendriplexes showed relatively slow dissociation kinetics, and their escape towards the cytosol was not mediated by acidification independently of the uptake pathway.

CONCLUSION

The extent of cellular uptake of siRNA dendriplexes was inversely related to their silencing activity. The higher silencing activity of siRNA dendriplexes in J774 cells could be ascribed to the contribution of clathrin-dependent and caveolin-dependent endocytosis vs only caveolin-dependent endocytosis in T98G cells.