Role of polyplex intermediate species on gene transfer efficiency: polyethylenimine-DNA complexes and time-resolved fluorescence spectroscopy

Tuning plasmid DNA amounts for cost-effective transfections of mammalian cells: when less is more

Transient gene expression (TGE) in mammalian cells is a well-known approach to the fast expression of recombinant proteins. The human cell line HEK (human embryonic kidney) 293F is widely used in this field, due to its adaptability to grow in suspension to high cell densities in serum-free media, amenability to transfection, and production of recombinant proteins in satisfactory quantities for functional and structural analysis. Amounts of plasmid DNA (pDNA) required in transfections for TGE remain high (usually 1 µg pDNA/mL, or even higher), representing a noticeable proportion of the overall cost. Thus, there is an economic need to reduce amounts of coding pDNA in TGE processes. In this work, amounts of both pDNA and transfecting agent used for TGE in HEK 293F cells have been explored in order to reduce them without compromising (or even improving) the productivity of the process in terms of protein yield. In our hands, minimal polyethyleneimine (PEI) cytotoxicity and optimum protein yields were obtained when transfecting at 0.5 µg pDNA/mL (equal to 0.5 µg pDNA/million cells) and a DNA-to-PEI ratio of 1:3, a trend confirmed for several unrelated recombinant proteins. Thus, carefully tuning pDNA and transfecting agent amounts not only reduces the economic costs but also results in higher recombinant protein yields. These results surely have a direct application and interest for the biopharmaceutical industry, always concerned in increasing productivity while decreasing economic costs. KEY POINTS: • Mammalian cells are widely used to produce recombinant proteins in short times. • Tuning DNA and transfecting agent are of great interest to optimize economic costs. • Reducing DNA and transfecting agent amounts result in higher protein yields.

The Progress of Non-Viral Materials and Methods for Gene Delivery to Skeletal Muscle

Since Jon A. Wolff found skeletal muscle cells being able to express foreign genes and Russell J. Mumper increased the gene transfection efficiency into the myocytes by adding polymers, skeletal muscles have become a potential gene delivery and expression target. Different methods have been developing to deliver transgene into skeletal muscles. Among them, viral vectors may achieve potent gene delivery efficiency. However, the potential for triggering biosafety risks limited their clinical applications. Therefore, non-viral biomaterial-mediated methods with reliable biocompatibility are promising tools for intramuscular gene delivery in situ. In recent years, a series of advanced non-viral gene delivery materials and related methods have been reported, such as polymers, liposomes, cell penetrating peptides, as well as physical delivery methods. In this review, we summarized the research progresses and challenges in non-viral intramuscular gene delivery materials and related methods, focusing on the achievements and future directions of polymers.

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.

Histidine-Based Reduction-Sensitive Star-Polymer Inclusion Complex as a Potential DNA Carrier: Biophysical Studies Using Time-Resolved Fluorescence as an Important Tool

An ideal DNA carrier is one that is capable of effectively condensing DNA into complexes of optimum size and shape, preventing premature decomplexation in the bloodstream and efficiently releasing the DNA into affected cells. In this context, we have developed a novel β-cyclodextrin (β-CD)-based four-arm star-shaped polymer inclusion complex (IC) with arms made of a poly(l-histidine)-based cationic polymer. The polymer was well characterized by gel permeation chromatography, NMR, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. We have also investigated its DNA complexation and release properties. Bisadamantane containing a disulfide bond was synthesized that linked two such poly(l-histidine)-containing β-CD units via guest-host interactions to prepare the presented IC. Besides using the conventional steady-state fluorescence spectroscopy, the ability of this IC to condense DNA to form polyplexes and their release behavior have been established by using the time-resolved fluorescence spectroscopy technique. Thiazole orange (TO) was used for the first time as a DNA-intercalating dye in the time-resolved fluorescence spectroscopic study. The superior DNA-condensing ability of the IC as compared to that of the precursor two-arm β-CD and linear poly(l-histidine) of a comparable molecular weight, as confirmed by dynamic light scattering, zeta potential, atomic force microscopy, and gel electrophoresis studies, could be attributed to a higher charge density. The IC-DNA polyplexes were found to be stable in a medium similar to an extracellular fluid but could efficiently release DNA in the presence of 10 mM glutathione, a concentration prevalent in the intracellular fluid of cancer cells. Hence, here, we have successfully demonstrated the synthesis of a novel biocompatible star-shaped IC with the potential to carry and release DNA in cancer cells and also established the feasibility of using the time-resolved fluorescence spectroscopic technique to study the complexation behavior of the polycation and DNA using TO as a DNA-intercalating dye.

Smart Supra- and Macro-Molecular Tools for Biomedical Applications

Stimuli-responsive, “smart” polymeric materials used in the biomedical field function in a bio-mimicking manner by providing a non-linear response to triggers coming from a physiological microenvironment or other external source. They are built based on various chemical, physical, and biological tools that enable pH and/or temperature-stimulated changes in structural or physicochemical attributes, like shape, volume, solubility, supramolecular arrangement, and others. This review touches on some particular developments on the topic of stimuli-sensitive molecular tools for biomedical applications. Design and mechanistic details are provided concerning the smart synthetic instruments that are employed to prepare supra- and macro-molecular architectures with specific responses to external stimuli. Five major themes are approached: (i) temperature- and pH-responsive systems for controlled drug delivery; (ii) glycodynameric hydrogels for drug delivery; (iii) polymeric non-viral vectors for gene delivery; (iv) metallic nanoconjugates for biomedical applications; and, (v) smart organic tools for biomedical imaging.

Engineering DNA vaccines against infectious diseases

Engineering vaccine-based therapeutics for infectious diseases is highly challenging, as trial formulations are often found to be nonspecific, ineffective, thermally or hydrolytically unstable, and/or toxic. Vaccines have greatly improved the therapeutic landscape for treating infectious diseases and have significantly reduced the threat by therapeutic and preventative approaches. Furthermore, the advent of recombinant technologies has greatly facilitated growth within the vaccine realm by mitigating risks such as virulence reversion despite making the production processes more cumbersome. In addition, seroconversion can also be enhanced by recombinant technology through kinetic and nonkinetic approaches, which are discussed herein. Recombinant technologies have greatly improved both amino acid-based vaccines and DNA-based vaccines. A plateau of interest has been reached between 2001 and 2010 for the scientific community with regard to DNA vaccine endeavors. The decrease in interest may likely be attributed to difficulties in improving immunogenic properties associated with DNA vaccines, although there has been research demonstrating improvement and optimization to this end. Despite improvement, to the extent of our knowledge, there are currently no regulatory body-approved DNA vaccines for human use (four vaccines approved for animal use). This article discusses engineering DNA vaccines against infectious diseases while discussing advantages and disadvantages of each, with an emphasis on applications of these DNA vaccines.

Statement of Significance

This review paper summarizes the state of the engineered/recombinant DNA vaccine field, with a scope entailing “Engineering DNA vaccines against infectious diseases”. We endeavor to emphasize recent advances, recapitulating the current state of the field. In addition to discussing DNA therapeutics that have already been clinically translated, this review also examines current research developments, and the challenges thwarting further progression. Our review covers: recombinant DNA-based subunit vaccines; internalization and processing; enhancing immune protection via adjuvants; manufacturing and engineering DNA; the safety, stability and delivery of DNA vaccines or plasmids; controlling gene expression using plasmid engineering and gene circuits; overcoming immunogenic issues; and commercial successes. We hope that this review will inspire further research in DNA vaccine development.

Detailed investigation on how the protein corona modulates the physicochemical properties and gene delivery of polyethylenimine (PEI) polyplexes

Given the various cationic polymers developed as non-viral gene delivery vectors, polyethylenimine (PEI) has been/is frequently used in in vitro transfection.

Diacetylenic lipids in the design of stable lipopolymers able to complex and protect plasmid DNA

Different viral and non-viral vectors have been designed to allow the delivery of nucleic acids in gene therapy. In general, non-viral vectors have been associated with increased safety for in vivo use; however, issues regarding their efficacy, toxicity and stability continue to drive further research. Thus, the aim of this study was to evaluate the potential use of the polymerizable diacetylenic lipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) as a strategy to formulate stable cationic lipopolymers in the delivery and protection of plasmid DNA. Cationic lipopolymers were prepared following two different methodologies by using DC8,9PC, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and the cationic lipids (CL) 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), stearylamine (SA), and myristoylcholine chloride (MCL), in a molar ratio of 1:1:0.2 (DMPC:DC8,9PC:CL). The copolymerization methodology allowed obtaining cationic lipopolymers which were smaller in size than those obtained by the cationic addition methodology although both techniques presented high size stability over a 166-day incubation period at 4°C. Cationic lipopolymers containing DOTAP or MCL were more efficient in complexing DNA than those containing SA. Moreover, lipopolymers containing DOTAP were found to form highly stable complexes with DNA, able to resist serum DNAses degradation. Furthermore, neither of the cationic lipopolymers (with or without DNA) induced red blood cell hemolysis, although metabolic activity determined on the L-929 and Vero cell lines was found to be dependent on the cell line, the formulation and the presence of DNA. The high stability and DNA protection capacity as well as the reduced toxicity determined for the cationic lipopolymer containing DOTAP highlight the potential advantage of using lipopolymers when designing novel non-viral carrier systems for use in in vivo gene therapy. Thus, this work represents the first steps toward developing a cationic lipopolymer-based gene delivery system using polymerizable and cationic lipids.

Repulsion between oppositely charged rod-shaped macromolecules: Role of overcharging and ionic confinement

The interaction between two oppositely charged rod-shaped macro-ions in a micro-ion solution is investigated via Monte Carlo simulations of the primitive model. The focus is on the asymmetry in rod and/or ion charge, i.e., conditions where oppositely charged objects can repel one another. For equally and oppositely charged rods with asymmetric z:1 micro-ions, repulsion may be induced by overcharging one of the rods with the z valent ions. For asymmetrically charged rods in a symmetric z:z micro-ion solution, a repulsive interaction-at separation of the order of one ion diameter-can arise via an unbalanced osmotic pressure contribution from the ionic atmosphere in the inter-rod space, and an attractive interaction-at a smaller separation-may occur due to a "squeezing out" of the micro-ions from the space between the rods (with a consequent gain in entropy). The thermodynamics of each mechanism is investigated in terms of rod charge and size and micro-ion valence, size, and concentration. Our findings contribute to the understanding of the complex role of charge asymmetry on the interaction of, for example, oppositely charged polyelectrolytes, functionalized nanotubes, and rod-like biomolecules, e.g., viruses.

Exploring the role of peptides in polymer-based gene delivery

Polymers are widely studied as non-viral gene vectors because of their strong DNA binding ability, capacity to carry large payload, flexibility of chemical modifications, low immunogenicity, and facile processes for manufacturing. However, high cytotoxicity and low transfection efficiency substantially restrict their application in clinical trials. Incorporating functional peptides is a promising approach to address these issues. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we systematically summarize the role of peptides in polymer-based gene delivery, and elaborate how to rationally design polymer-peptide based gene delivery vectors.

STATEMENT OF SIGNIFICANCE

Polymers are widely studied as non-viral gene vectors, but suffer from high cytotoxicity and low transfection efficiency. Incorporating short, bioactive peptides into polymer-based gene delivery systems can address this issue. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we highlight the peptides' roles in polymer-based gene delivery, and elaborate how to utilize various functional peptides to enhance the transfection efficiency of polymers. The optimized peptide-polymer vectors should be able to alter their structures and functions according to biological microenvironments and utilize inherent intracellular pathways of cells, and consequently overcome the barriers during gene delivery to enhance transfection efficiency.

Optimization of Polyplex Formation between DNA Oligonucleotide and Poly(ʟ-Lysine): Experimental Study and Modeling Approach

The polyplexes formed by nucleic acids and polycations have received a great attention owing to their potential application in gene therapy. In our study, we report experimental results and modeling outcomes regarding the optimization of polyplex formation between the double-stranded DNA (dsDNA) and poly(l-Lysine) (PLL). The quantification of the binding efficiency during polyplex formation was performed by processing of the images captured from the gel electrophoresis assays. The design of experiments (DoE) and response surface methodology (RSM) were employed to investigate the coupling effect of key factors (pH and N/P ratio) affecting the binding efficiency. According to the experimental observations and response surface analysis, the N/P ratio showed a major influence on binding efficiency compared to pH. Model-based optimization calculations along with the experimental confirmation runs unveiled the maximal binding efficiency (99.4%) achieved at pH 5.4 and N/P ratio 125. To support the experimental data and reveal insights of molecular mechanism responsible for the polyplex formation between dsDNA and PLL, molecular dynamics simulations were performed at pH 5.4 and 7.4.

pH-Mediated Fluorescent Polymer Particles and Gel from Hyperbranched Polyethylenimine and the Mechanism of Intrinsic Fluorescence

We report that fluorescence properties and morphology of hyperbranched polyethylenimine (hPEI) cross-linked with formaldehyde are highly dependent on the pH values of the cross-linking reaction. Under acidic and neutral conditions, water-soluble fluorescent copolymer particles (CPs) were produced. However, under basic conditions, white gels with weak fluorescence emission would be obtained. The water-soluble hPEI-formaldehyde (hPEI-F) CPs show strong intrinsic fluorescence without the conjugation to any classical fluorescent agents. By the combination of spectroscopy and microscopy techniques, the mechanism of fluorescence emission was discussed. We propose that the intrinsic fluorescence originates from the formation of a Schiff base in the cross-linking process between hPEI and formaldehyde. Schiff base bonds are the fluorescence-emitting moieties, and the compact structure of hPEI-F CPs plays an important role in their strong fluorescence emission. The exploration on fluorescence mechanism may provide a new strategy to prepare fluorescent polymer particles. In addition, the investigation shows that the hPEI-F CPs hold potential as a fluorescent probe for the detection of copper ions in aqueous media.

Interaction modes between asymmetrically and oppositely charged rods

The interaction of oppositely and asymmetrically charged rods in salt-a simple model of (bio)macromolecular assembly-is observed via simulation to exhibit two free energy minima, separated by a repulsive barrier. In contrast to similar minima in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the governing mechanism includes electrostatic attraction at large separation, osmotic repulsion at close range, and depletion attraction near contact. A model accounting for ion condensation and excluded volume is shown to be superior to a mean-field treatment in predicting the effect of charge asymmetry on the free-energy profile.

Exploring the role of polymer structure on intracellular nucleic acid delivery via polymeric nanoparticles

Intracellular nucleic acid delivery has the potential to treat many genetically-based diseases, however, gene delivery safety and efficacy remains a challenging obstacle. One promising approach is the use of polymers to form polymeric nanoparticles with nucleic acids that have led to exciting advances in non-viral gene delivery. Understanding the successes and failures of gene delivery polymers and structures is the key to engineering optimal polymers for gene delivery in the future. This article discusses the polymer structural features that enable effective intracellular delivery of DNA and RNA, including protection of nucleic acid cargo, cellular uptake, endosomal escape, vector unpacking, and delivery to the intracellular site of activity. The chemical properties that aid in each step of intracellular nucleic acid delivery are described and specific structures of note are highlighted. Understanding the chemical design parameters of polymeric nucleic acid delivery nanoparticles is important to achieving the goal of safe and effective non-viral genetic nanomedicine.

Fluorophore:dendrimer ratio impacts cellular uptake and intracellular fluorescence lifetime

G5-NH2-TAMRAn (n = 1-4, 5+, and 1.5(avg)) were prepared with n = 1-4 as a precise dye:dendrimer ratio, 5+ as a mixture of dendrimers with 5 or more dye per dendrimer, and 1.5(avg) as a Poisson distribution of dye:dendrimer ratios with a mean of 1.5 dye per dendrimer. The absorption intensity increased sublinearly with n whereas the fluorescence emission and lifetime decreased with an increasing number of dyes per dendrimer. Flow cytometry was employed to quantify uptake into HEK293A cells. Dendrimers with 2-4 dyes were found to have greater uptake than dendrimer with a single dye. Fluorescence lifetime imaging microscopy (FLIM) showed that the different dye:dendrimer ratio alone was sufficient to change the fluorescence lifetime of the material observed inside cells. We also observed that the lifetime of G5-NH2-TAMRA5+ increased when present in the cell as compared to solution. However, cells treated with G5-NH2-TAMRA1.5(avg) did not exhibit the high lifetime components present in G5-NH2-TAMRA1 and G5-NH2-TAMRA5+. In general, the effects of the dye:dendrimer ratio on fluorescence lifetime were of similar magnitude to environmentally induced lifetime shifts.

The study of polyplex formation and stability by time-resolved fluorescence spectroscopy of SYBR Green I-stained DNA

Polyplexes are nanoparticles formed by the self-assembly of DNA/RNA and cationic polymers specifically designed to deliver exogenous genetic material to cells by a process called transfection. There is a general consensus that a subtle balance between sufficient extracellular protection and intracellular release of nucleic acids is a key factor for successful gene delivery. Therefore, there is a strong need to develop suitable tools and techniques for enabling the monitoring of the stability of polyplexes in the biological environment they face during transfection. In this work we propose time-resolved fluorescence spectroscopy in combination with SYBR Green I-DNA dye as a reliable tool for the in-depth characterization of the DNA/vector complexation state. As a proof of concept, we provide essential information on the assembly and disassembly of complexes formed between DNA and each of three cationic polymers, namely a novel promising chitosan-graft-branched polyethylenimine copolymer (Chi-g-bPEI), one of its building block 2 kDa bPEI and the gold standard transfectant 25 kDa bPEI. Our results highlight the higher information content provided by the time-resolved studies of SYBR Green I/DNA, as compared to conventional steady state measurements of ethidium bromide/DNA that enabled us to draw relationships among fluorescence lifetime, polyplex structural changes and transfection efficiency.

Quantitation of Complexed versus Free Polymers in Interpolyelectrolyte Polyplex Formulations

The quantity of free polymer in a polymer/DNA complex (polyplex) formulation critically impacts its gene transfection efficiency, cellular uptake, and toxicity. In this study, the compositions of three interpolyelectrolyte polyplex formulations were quantified by a facile NMR method. Using careful integration of a 1D ¹H NMR spectrum with a broad spectral width, the quantities of unbound polymer and polyplexes in solution were determined. Linear polyethyleneimine (PEI) mixed with DNA at polymer amine to DNA phosphate molar ratio (N/P ratio) of 5 revealed an effective binding N/P ratio of 3.5 without excess free polymer. This result is in strong agreement with the stoichiometric number of PEI/DNA binding obtained by isothermal titration calorimetry. The noninvasive nature of this method allows broad application to a range of polyelectrolyte coacervates, opening new opportunities for understanding and optimizing polyelectrolyte complex formation and providing quantitation of complex formation in a single measurement.

Independent versus cooperative binding in polyethylenimine-DNA and Poly(L-lysine)-DNA polyplexes

The mechanism of polyethylenimine-DNA and poly(L-lysine)-DNA complex formation at pH 5.2 and 7.4 was studied by a time-resolved spectroscopic method. The formation of a polyplex core was observed to be complete at approximately N/P = 2, at which point nearly all DNA phosphate groups were bound by polymer amine groups. The data were analyzed further both by an independent binding model and by a cooperative model for multivalent ligand binding to multisubunit substrate. At pH 5.2, the polyplex formation was cooperative at all N/P ratios, whereas for pH 7.4 at N/P < 0.6 the polyplex formation followed independent binding changing to cooperative binding at higher N/Ps.

The effect and role of carbon atoms in poly(β-amino ester)s for DNA binding and gene delivery

Polymeric vectors for gene delivery are a promising alternative for clinical applications, as they are generally safer than viral counterparts. Our objective was to further our mechanistic understanding of polymer structure-function relationships to allow the rational design of new biomaterials. Utilizing poly(β-amino ester)s (PBAEs), we investigated polymer-DNA binding by systematically varying the polymer molecular weight, adding single carbons to the backbone and side chain of the monomers that constitute the polymers, and varying the type of polymer end group. We then sought to correlate how PBAE binding affects the polyplex diameter and ζ potential, the transfection efficacy, and its associated cytotoxicity in human breast and brain cancer cells in vitro. Among other trends, we observed in both cell lines that the PBAE-DNA binding constant is biphasic with the transfection efficacy and that the optimal values of the binding constant with respect to the transfection efficacy are in the range (1-6) × 10(4) M(-1). A binding constant in this range is necessary but not sufficient for effective transfection.

Electrostatic assembly of a DNA superparamagnetic nano-tool for simultaneous intracellular delivery and in situ monitoring

A superparamagnetic γFe(2)O(3) nanocarrier was developed, characterized by spectroscopic methods and evaluated for the delivery of a decoy oligonucleotide (dODN) in human colon carcinoma SW 480 cells. This nanoparticle-dODN bioconjugate (γFe(2)O(3)@dODN) was designed to target the signal transducer and activator of transcription 3, STAT3, a key regulator of cell survival and proliferation. We exploited a simple precipitation-redispersion mechanism for the direct and one-step complexation of a labeled decoy oligonucleotide with iron oxide nanoparticles (NPs). The cell internalization of the decoy γFe(2)O(3)@dODN nanoparticles is demonstrated and suggests the potential for DNA delivery in biological applications. Despite the increasing use of NPs in biology and medicine, convenient methods to quantify them within cells are still lacking. In this work, taking advantage of the nonlinear magnetic behavior of our superparamagnetic NPs, we have developed a new method to quantify in situ their internalization by cells.

FROM THE CLINICAL EDITOR

In this study, the authors demonstrate methods to quantify superparamagnetic nanocarriers within cells, taking advantage of the nonlinear magnetic behavior of the studied NPs.

Mechanisms of polyethylenimine-mediated DNA delivery: free carrier helps to overcome the barrier of cell-surface glycosaminoglycans

BACKGROUND

Polyethylenimine (PEI) polyplexes mediate efficient gene transfer only at high +/- charge ratios at which free noncomplexed PEI is present. The excess of PEI gives polyplexes a positive surface charge that plays a role in polyplex binding on the cell membrane. Although positively charged PEI polyplexes are known to interact with anionic cell-surface glycosaminoglycans (GAGs), the exact role of free PEI in such interactions is unclear.

METHODS

Chinese hamster ovary wild-type cells and mutants lacking cell-surface GAGs were transfected with marker genes using PEI polyplexes with and without free PEI. The total amount of cell-associated plasmid DNA (pDNA) delivered by polyplexes was determined by quantitative real-time PCR and transgene expression was determined using β-galactosidase and luciferase assays.

RESULTS

Transfection activity of polyplexes without free PEI in cells expressing cell-surface GAGs was low even though pDNA was delivered to cells. In the absence of cell-surface GAGs, polyplexes without free PEI had high transfection efficacy. This indicates that the cell-surface GAGs inhibit transfection by purified polyplexes. PEI polyplexes with free carrier mediated transfection in both normal and GAG-deficient cells because free PEI overcomes the inhibitory effect of cell-surface GAGs on transfection. The intracellular elimination of pDNA was faster in the presence of GAGs and, despite improved transfection, free PEI reduced pDNA association with the cells.

CONCLUSIONS

Free PEI is essential for minimizing the undesirable binding of polyplexes to cell-surface GAGs that have a negative impact on transfection. The same mechanism may be important in transfections with other polyplexes that require high charge ratios for transfection.

Poly(β-amino ester)-DNA complexes: time-resolved fluorescence and cellular transfection studies

A large number of different polymers have been developed and studied for application as DNA carriers for non-viral gene delivery, but the DNA binding properties are not understood. This study describes the efficiency of nanoparticle formation by time-resolved fluorescence measurements for poly(β-amino esters), cationic biodegradable polymers with DNA complexation and transfection capability. From the large library of poly(β-amino esters) ten polymers with different transfection efficacies were chosen for this study. The binding constants for nanoparticle formation were determined and compared to with the same method. Although the DNA binding efficiency of the amine groups are similar for both types of polymers, the overall binding constants are an order of magnitude smaller for poly(β-amino esters) than for 25 kDa polyethylenimines, yet poly(β-amino esters) show comparable DNA transfection efficacy with polyethylenimines. Within this series of polymers the transfection efficacy showed increasing trend in association with relative efficiency of nanoparticle formation.