Interaction of poly(glycoamidoamine) DNA delivery vehicles with cell-surface glycosaminoglycans leads to polyplex internalization in a manner not solely dependent on charge

Internalization of PEI-based complexes in transient transfection of HEK293 cells is triggered by coalescence of membrane heparan sulfate proteoglycans like Glypican-4

Polymer-cationic mediated gene delivery is a well-stablished strategy of transient gene expression (TGE) in mammalian cell cultures. Nonetheless, its industrial implementation is hindered by the phenomenon known as cell density effect (CDE) that limits the cell density at which cultures can be efficiently transfected. The rise in personalized medicine and multiple cell and gene therapy approaches based on TGE, make more relevant to understand how to circumvent the CDE. A rational study upon DNA/PEI complex formation, stability and delivery during transfection of HEK293 cell cultures has been conducted, providing insights on the mechanisms for polyplexes uptake at low cell density and disruption at high cell density. DNA/PEI polyplexes were physiochemically characterized by coupling X-ray spectroscopy, confocal microscopy, cryo-transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). Our results showed that the ionic strength of polyplexes significantly increased upon their addition to exhausted media. This was reverted by depleting extracellular vesicles (EVs) from the media. The increase in ionic strength led to polyplex aggregation and prevented efficient cell transfection which could be counterbalanced by implementing a simple media replacement (MR) step before transfection. Inhibiting and labeling specific cell-surface proteoglycans (PGs) species revealed different roles of PGs in polyplexes uptake. Importantly, the polyplexes uptake process seemed to be triggered by a coalescence phenomenon of HSPG like glypican-4 around polyplex entry points. Ultimately, this study provides new insights into PEI-based cell transfection methodologies, enabling to enhance transient transfection and mitigate the cell density effect (CDE).

Dynamic Covalent Boronate Chemistry Accelerates the Screening of Polymeric Gene Delivery Vectors via In Situ Complexation of Nucleic Acids

Gene therapy provides exciting new therapeutic opportunities beyond the reach of traditional treatments. Despite the tremendous progress of viral vectors, their high cost, complex manufacturing, and side effects have encouraged the development of nonviral alternatives, including cationic polymers. However, these are less efficient in overcoming cellular barriers, resulting in lower transfection efficiencies. Although the exquisite structural tunability of polymers might be envisaged as a versatile tool for improving transfection, the need to fine-tune several structural parameters represents a bottleneck in current screening technologies. By taking advantage of the fast-forming and strong boronate ester bond, an archetypal example of dynamic covalent chemistry, a highly adaptable gene delivery platform is presented, in which the polycation synthesis and pDNA complexation occur in situ. The robustness of the strategy entitles the simultaneous evaluation of several structural parameters at will, enabling the accelerated screening and adaptive optimization of lead polymeric vectors using dynamic covalent libraries.

Lipofection with Lipofectamine™ 2000 in a heparin-free growth medium results in high transfection efficiency in chicken primordial germ cells

Primordial germ cells (PGCs) that can differentiate into gametes are used to produce genome-edited chickens. However, the transfection efficiency into PGCs is low in chickens; therefore, the yield efficiency of PGCs modified via genome editing is problematic. In this study, we improved transfection efficiency and achieved highly efficient genome editing in chicken PGCs. For transfection, we used lipofection, which is convenient for gene transfer. Chicken PGC cultures require adding heparin to support growth; however, heparin significantly reduces lipofection efficiency (p < 0.01). Heparin-induced lipofection efficiency was restored by adding protamine. Based on these results, we optimized gene transfer into chicken PGCs. Lipofectamine 2000 and our PGC medium were the most efficient transfection reagent and medium, respectively. Finally, based on established conditions, we compared the gene knock-out efficiencies of ovomucoid, a major egg allergen, and gene knock-in efficiencies at the ACTB locus. These results indicate that optimized lipofection is useful for CRISPR/Cas9-mediated knock-out and knock-in. Our findings may contribute to the generation of genome-edited chickens and stimulate research in various applications involving them.

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.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Polyplexes Are Endocytosed by and Trafficked within Filopodia

The improvement of nonviral gene therapies relies to a large extent on understanding many fundamental physical and biological properties of these systems. This includes interactions of synthetic delivery systems with the cell and mechanisms of trafficking delivery vehicles, which remain poorly understood on both the extra- and intracellular levels. In this study, the mechanisms of cellular internalization and trafficking of polymer-based nanoparticle complexes consisting of polycations and nucleic acids, termed polyplexes, have been observed in detail at the cellular level. For the first time evidence has been obtained that filopodia, actin projections that radiate out from the surface of cells, serve as a route for the direct endocytosis of polyplexes. Confocal microscopy images demonstrated that filopodia on HeLa cells detect external polyplexes and extend into the extracellular milieu to internalize these particles. Polyplexes are observed to be internalized into membrane-bound vesicles (i.e., clathrin-coated pits and caveolae) directly within filopodial projections and are subsequently transported along actin to the main cell body for potential delivery of the nucleic acids to the nucleus. The kinetics and speed of polyplex trafficking have also been measured. The polyplex-loaded vesicles were also discovered to traffic between two cells within filopodial bridges. These findings provide novel insight into the early events of cellular contact with polyplexes through filopodial-based interactions in addition to endocytic vesicle trafficking-an important fundamental discovery to enable advancement of nonviral gene editing, nucleic acid therapies, and biomedical materials.

Nonviral Gene Delivery with Cationic Glycopolymers

The field of gene therapy, which aims to treat patients by modulating gene expression, has come to fruition and has landed several landmark FDA approvals. Most gene therapies currently rely on viral vectors to deliver nucleic acid cargo into cells, but there is significant interest in moving toward chemical-based methods, such as polymer-based vectors, due to their low cost, immunocompatibility, and tunability. The full potential of polymer-based delivery systems has yet to be realized, however, because most polymeric transfection reagents are either too inefficient or too toxic for use in the clinic. In this Account, we describe developments in carbohydrate-based cationic polymers, termed glycopolymers, for enhanced nonviral gene delivery. As ubiquitous components of biological systems, carbohydrates are a rich class of compounds that can be harnessed to improve the biocompatibility of non-native polymers, such as linear polyamines used for promoting transfection. Reineke et al. developed a new class of carbohydrate-based polymers called poly(glycoamidoamine)s (PGAAs) by step-growth polymerization of linear monosaccharides with linear ethyleneamines. These glycopolymers were shown to be both efficient and biocompatible transfection reagents. Systematic modifications of the structural components of the PGAA system revealed structure-activity relationships important to its function, including its ability to degrade in situ. Expanding upon the development of step-growth glycopolymers, monosaccharides, such as glucose, were functionalized as vinyl-based monomers for the formation of diblock copolymers via radical addition-fragmentation chain-transfer (RAFT) polymerization. Upon complexation with plasmid DNA, the glucose-containing block creates a hydrophilic shell that promotes colloidal stability as effectively as PEG functionalization. An N-acetyl-d-galactosamine variant of this diblock polymer yields colloidally stable particles that show increased receptor-mediated uptake by liver hepatocytes in vitro and promotes liver targeting in mice. Finally, the disaccharide trehalose was incorporated into polycationic structures using both step-growth and RAFT techniques. It was shown that these trehalose-based copolymers imparted increased colloidal stability and yielded plasmid and siRNA polyplexes that resist aggregation upon lyophilization and reconstitution in water. The aforementioned series of glycopolymers use carbohydrates to promote effective and safe delivery of nucleic acid cargo into a variety of human cells types by promoting vehicle degradation, tissue-targeting, colloidal stabilization, and stability toward lyophilization to extend shelf life. Work is currently underway to translate the use of glycopolymers for safe and efficient delivery of nucleic acid cargo for gene therapy and gene editing applications.

Molecular Weight-Dependent Activity of Aminated Poly(α)glutamates as siRNA Nanocarriers

RNA interference (RNAi) can contribute immensely to the area of personalized medicine by its ability to target any gene of interest. Nevertheless, its clinical use is limited by lack of efficient delivery systems. Polymer therapeutics can address many of the challenges encountered by the systemic delivery of RNAi, but suffer from inherent drawbacks such as polydispersity and batch to batch heterogeneity. These characteristics may have far-reaching consequences when dealing with therapeutic applications, as both the activity and the toxicity may be dependent on the length of the polymer chain. To investigate the consequences of polymers' heterogeneity, we have synthesized two batches of aminated poly(α)glutamate polymers (PGAamine), differing in their degree of polymerization, but not in the monomer units or their conjugation. Isothermal titration calorimetry study was conducted to define the binding affinity of these polymers with siRNA. Molecular dynamics simulation revealed that Short PGAamine:siRNA polyplexes exposed a higher amount of amine moieties to the surroundings compared to Long PGAamine. This resulted in a higher zeta potential, leading to faster degradation and diminished gene silencing. Altogether, our study highlights the importance of an adequate physico-chemical characterization to elucidate the structure⁻function-activity relationship, for further development of tailor-designed RNAi delivery vehicles.

Excipients for the lyoprotection of MAPKAP kinase 2 inhibitory peptide nano-polyplexes

Herein, excipients are investigated to ameliorate the deleterious effects of lyophilization on peptide-polymer nano-polyplex (NP) morphology, cellular uptake, and bioactivity. The NPs are a previously-described platform technology for intracellular peptide delivery and are formulated from a cationic therapeutic peptide and the anionic, pH-responsive, endosomolytic polymer poly(propylacrylic acid) (PPAA). These NPs are effective when formulated and immediately used for delivery into cells and tissue, but they are not amenable to reconstitution following storage as a lyophilized powder due to aggregation. To develop a lyophilized NP format that facilitates longer-term storage and ease of use, MAPKAP kinase 2 inhibitory peptide-based NPs (MK2i-NPs) were prepared in the presence of a range of concentrations of the excipients sucrose, trehalose, and lactosucrose prior to lyophilization and storage. All excipients improved particle morphology post-lyophilization and significantly improved MK2i-NP uptake in human coronary artery smooth muscle cells relative to lyophilized NPs without excipient. In particular, MK2i-NPs lyophilized with 300 mM lactosucrose as an excipient demonstrated a 5.23 fold increase in cellular uptake (p < 0.001), a 2.52 fold increase in endosomal disruption (p < 0.05), and a 2.39 fold increase in ex vivo bioactivity (p < 0.01) compared to MK2i-NPs lyophilized without excipients. In sum, these data suggest that addition of excipients, particularly lactosucrose, maintains and even improves the uptake and therapeutic efficacy of peptide-polymer NPs post-lyophilization relative to freshly-made formulations. Thus, the use of excipients as lyoprotectants is a promising approach for the long-term storage of biotherapeutic NPs and poises this NP platform for clinical translation.

Spatiotemporal cellular imaging of polymer-pDNA nanocomplexes affords in situ morphology and trafficking trends

Synthetic polymers are ubiquitous in the development of drug and polynucleotide delivery vehicles, offering promise for personalized medicine. However, the polymer structure plays a central yet elusive role in dictating the efficacy, safety, mechanisms, and kinetics of therapeutic transport in a spatial and temporal manner. Here, we decipher the intracellular pathways pertaining to shape, size, location, and mechanism of four structurally divergent polymer vehicles (Tr455, Tr477, jetPEI, and Glycofect) that create colloidal nanoparticles (polyplexes) when complexed with fluorescently labeled plasmid DNA (pDNA). Multiple high resolution tomographic images of whole HeLa (human cervical adenocarcinoma) cells were captured via confocal microscopy at 4, 8, 12, and 24 h. The images were reconstructed to visualize and quantify trends in situ in a four-dimensional spatiotemporal manner. The data revealed heretofore-unseen images of polyplexes in situ and structure-function relationships, i.e., Glycofect polyplexes are trafficked as the smallest polyplex complexes and Tr455 polyplexes have expedited translocation to the perinuclear region. Also, all of the polyplex types appeared to be preferentially internalized and trafficked via early endosomes affiliated with caveolae, a Rab-5-dependent pathway, actin, and microtubules.

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.

Exploring the mechanism of plasmid DNA nuclear internalization with polymer-based vehicles

Cationic polymers are commonly used to transfect mammalian cells, but their mechanisms of DNA delivery are unknown. This study seeks to decipher the mechanism by which plasmid DNA delivered by a class of cationic polymers traffics to and enters the nucleus. While studies have been performed to elucidate the mechanism of naked plasmid DNA (pDNA) import into the nuclei of mammalian cells, our objectives were to determine the effects of polymer complexation on pDNA nuclear import and the impact of polymer structure on that import. We have performed studies in whole cells and in isolated nuclei using flow cytometry and confocal microscopy to characterize how polymer-DNA complexes (polyplexes) are able to deliver their pDNA cargo to the nuclei of their target cells. The polymers tested herein include (i) linear poly(ethylenimine) (JetPEI), a polyamine, and (ii) two poly(glycoamidoamine)s (PGAAs), polyamines that contain carbohydrate moieties (meso-galactarate, Glycofect (G4), and L-tartarate, T4) within their repeat units. Our results indicate that, when complexed with the PGAAs, pDNA association with the nuclei was severely hampered in isolated nuclei compared to whole cells. When the pDNA was complexed with JetPEI, there was slight inhibition of pDNA-nuclear interaction in isolated nuclei compared to whole cells. However, even in the case of PEI, the amount of pDNA imported into the nucleus increases in the presence of cytosolic extract, thus indicating that intracellular components also play a role in pDNA nuclear import for all polymers tested. Interestingly, PEI and G4 exhibit the highest reporter gene expression as well as inducing higher envelope permeability compared to T4, suggesting that the ability to directly permeabilize the nuclear envelope may play a role in increasing expression efficiency. In addition, both free T4 and G4 polymers are able to cross the nuclear membrane without their pDNA cargo in isolated nuclei, indicating the possibility of different modes of nuclear association for free polymers vs polyplexes. These results yield insight to how the incorporation of carbohydrate moieties influences intracellular mechanisms and will prove useful in the rational design of safe and effective polymer-based gene delivery vehicles for clinical use.

Effects of trehalose polycation end-group functionalization on plasmid DNA uptake and transfection

In this study, we have synthesized six analogs of a trehalose-pentaethylenehexamine glycopolymer (Tr4) that contain (1A) adamantane, (1B) carboxy, (1C) alkynyl-oligoethyleneamine, (1D) azido trehalose, (1E) octyl, or (1F) oligoethyleneamine end groups and evaluated the effects of polymer end group chemistry on the ability of these systems to bind, compact, and deliver pDNA to cultured HeLa cells. The polymers were synthesized in one-pot azide-alkyne cycloaddition reactions with an adaptation of the Carothers equation for step-growth polymerization to produce a series of polymers with similar degrees of polymerization. An excess of end-capping monomer was added at the end of the polymerizations to maximize functionalization efficiency, which was evaluated with GPC, NMR, and MALDI-TOF. The polymers were all found to bind and compact pDNA at similarly low N/P ratios and form polyplexes with plasmid DNA. The effects of the different end group structures were most evident in the polyplex internalization and transfection assays in the presence of serum as determined by flow cytometry and luciferase gene expression, respectively. The Tr4 polymers end-capped with carboxyl groups (1B) (N/P = 7), octyne (1E) (N/P = 7), and oligoethyleneamine (1F) (N/P = 7), were taken into cells as polyplex and exhibited the highest levels of fluorescence, resulting from labeled plasmid. Similarly, the polymers end-functionalized with carboxyl groups (1E at N/P = 7), octyl groups (1E at N/P = 15), and in particular oligoethyleneamine groups (1F at N/P = 15) yielded dramatically higher reporter gene expression in the presence of serum. This study yields insight into how very subtle structural changes in polymer chemistry, such as end groups can yield very significant differences in the biological delivery efficiency and transgene expression of polymers used for pDNA delivery.

Membrane and nuclear permeabilization by polymeric pDNA vehicles: efficient method for gene delivery or mechanism of cytotoxicity?

The aim of this study is to compare the cytotoxicity mechanisms of linear PEI to two analogous polymers synthesized by our group: a hydroxyl-containing poly(l-tartaramidoamine) (T4) and a version containing an alkyl chain spacer poly(adipamidopentaethylenetetramine) (A4) by studying the cellular responses to polymer transfection. We have also synthesized analogues of T4 with different molecular weights (degrees of polymerization of 6, 12, and 43) to examine the role of molecular weight on the cytotoxicity mechanisms. Several mechanisms of polymer-induced cytotoxicity are investigated, including plasma membrane permeabilization, the formation of potentially harmful polymer degradation products during transfection including reactive oxygen species, and nuclear membrane permeabilization. We hypothesized that since cationic polymers are capable of disrupting the plasma membrane, they may also be capable of disrupting the nuclear envelope, which could be a potential mechanism of how the pDNA is delivered into the nucleus (other than nuclear envelope breakdown during mitosis). Using flow cytometry and confocal microscopy, we show that the polycations with the highest amount of protein expression and toxicity, PEI and T4(43), are capable of inducing nuclear membrane permeability. This finding is important for the field of nucleic acid delivery in that direct nucleus permeabilization could be not only a mechanism for pDNA nuclear import but also a potential mechanism of cytotoxicity and cell death. We also show that the production of reactive oxygen species is not a main mechanism of cytotoxicity, and that the presence or absence of hydroxyl groups and polymer length play a role in polyplex size and charge in addition to protein expression efficiency and toxicity.

Poly(galactaramidoamine) is an efficient cationic polymeric non-viral vector with low cytotoxicity for transfecting human embryonic kidney (HEK293) and murine macrophage (RAW264.7) cells

Poly(galactaramidoamine) (PGAA) is a cationic co-polymer of dimethyl-meso-galactarate and pentaethylenehexamine. PGAA electrostatically complexes with plasmid DNA (pDNA) to form nano-sized particles. In this study, we show that PGAA-pDNA polyplexes generate high transfection efficiencies in human embryonic kidney (HEK293) and murine macrophage-like (RAW264.7) cell lines. PGAA-pDNA mediated transfection is a function of the amine:phosphate (N/P) ratio at which the polyplexes are prepared. The maximum expression of luciferase was obtained using polyplexes prepared at an N/P ratio of 40. Polyplexes prepared at increasing N/P ratios did not significantly increase in size but did result in decreasing luciferase expression. Cellular toxicity increased as the N/P ratios at which the polyplexes were prepared increased.

In vivo delivery of nucleic acids via glycopolymer vehicles affords therapeutic infarct size reduction in vivo

Using a new class of nontoxic and degradable glycopolymer-based vehicles termed poly(glycoamidoamine)s, we demonstrate virus-like delivery efficacy of oligodeoxynucleotide (ODN) decoys to cardiomyoblasts (H9c2), primary cardiomyocytes, and the mouse heart. These glycopolymers bind and compact ODN decoys into nanoparticle complexes that are internalized by the cell membrane and mediate nuclear uptake of DNA in 90+% of cultured primary cardiomyocytes and 87% of the mouse myocardium. Experimental results reveal that decoys delivered via these glycopolymers block the activation of the transcription factor NF-κB, a major contributor to ischemia/reperfusion injury. Decoy complexes formed with glycopolymer T4 significantly blocked downstream gene expression of Cox-2 and limited myocardial infarction in vivo, phenocopying a transgenic mouse model. These promising delivery vehicles may facilitate high-throughput genetic approaches in animal models. Additionally, the low toxicity, biodegradation, and outstanding delivery efficacy suggest that these nanomedicines may be clinically applicable for gene regulatory therapy.

Structure-activity examination of poly(glycoamidoguanidine)s: glycopolycations containing guanidine units for nucleic acid delivery

In this study we synthesized a new series of polymers known as poly(glycoamidoguanidine)s (PGAGs). These new polymer structures were synthesized by copolymerizing a carbohydrate monomer (diester; galatarate or tartarate) with a diamine incorporating guanidine or methylguanidine as a charge center to create a polyamide backbone. These materials were strategically designed and compared to our previously studied DNA delivery vehicles, poly(glycoamidoamine)s (PGAAs), which contain secondary amines as the charge groups along the polymer backbone to examine the effect of charge center type on the cellular delivery efficiency of plasmid DNA (pDNA). The guanidine moieties within the PGAGs facilitate electrostatic binding with the negatively charged phosphate backbone of plasmid DNA (pDNA). Stable polymer-pDNA complexes (polyplexes) with sizes in the range of 60-200 nm are formed at polymer/pDNA charge ratios (N/P) of 5 and above. When the PGAGs are complexed with Cy5-labeled pDNA (Cy5-pDNA) at N/P ratios of 10 and 25, between 80 and 95% of HeLa cells were positive for Cy5 fluorescence, indicating effective cellular internalization of the polyplexes. The toxicity of both PGAA and PGAG polyplexes was studied via MTT assays, and over 95% cell survival was observed at N/P ratios of 5, 10, 15, 20, 25, and 30 in HeLa cells. Transgene expression was examined via luciferase assays at various N/P ratios in the absence and presence of serum. In the absence of serum, the PGAG polyplexes revealed similar transgene expression when compared to polyplexes formed with their analogous PGAA structures. In the presence of serum, one analog (Gg) consisting of galactarate copolymerized with the guanidine monomer yielded gene expression similar to the positive control, Glycofect Transfection Reagent. This new series of guanidine-containing oligomers are promising as a new design strategy to incorporate an alternative charge center type within the backbone of glycopolymer-based nucleic acid delivery vehicles.

Cellular binding of nanoparticles in the presence of serum proteins

Cellular binding of cationic nanoparticles in the presence of serum proteins was probed with two-colour fluorescence microscopy. Cationic nanoparticles associate with serum proteins in solution and bind to the cell surface as a single anionic complex. Displacement of serum proteins from the nanoparticles was found to be protein dependent.