Differential uptake of DNA-poly(ethylenimine) polyplexes in cells cultured on collagen and fibronectin surfaces

Gene Delivery From Granular Scaffolds for Tunable Biologics Manufacturing

The understanding of the molecular basis for disease has generated a myriad of therapeutic biologics, including therapeutic proteins, antibodies, and viruses. However, the promise that biologics can resolve currently incurable diseases hinges in their manufacturability. These therapeutics require that their genetic material be introduced to mammalian cells such that the cell machinery can manufacture the biological components. These are then purified, validated, and packaged. Most manufacturing uses batch processes that collect the biologic a few days following genetic modification, due to toxicity or difficulty in separating product from cells in a continuous operation, limiting the amount of biologic that can be produced and resulting in yearlong backlogs. Here, a scaffold-based approach for continuous biologic manufacturing is presented, with sustained production of active antibodies and viruses for 30 days. The use of scaffold-based biologic production enabled perfusion-based bioreactors to be used, which can be incorporated into a fully continuous process.

In situ transient transfection of 3D cell cultures and tissues, a promising tool for tissue engineering and gene therapy

Various research fields use the transfection of mammalian cells with genetic material to induce the expression of a target transgene or gene silencing. It is a tool widely used in biological research, bioproduction, and therapy. Current transfection protocols are usually performed on 2D adherent cells or suspension cultures. The important rise of new gene therapies and regenerative medicine in the last decade raises the need for new tools to empower the in situ transfection of tissues and 3D cell cultures. This review will present novel in situ transfection methods based on a chemical or physical non-viral transfection of cells in tissues and 3D cultures, discuss the advantages and remaining gaps, and propose future developments and applications.

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.

Harnessing the perinuclear actin cap (pnAC) to influence nanocarrier trafficking and gene transfection efficiency in skeletal myoblasts using nanopillars

Gene transfection is important in biotechnology and is used to modify cells intrinsically. It can be conducted in cell suspension or after cell adhesion, where the efficiency is dependent on many factors such as the type of nanocarrier used and cell division processes. Anchor-dependent cells are sensitive to the substrate they are attached to and adapt their behavior accordingly, including plasmid trafficking during gene transfection. Previously, it was shown in our group that the cytoskeleton is an essential factor in influencing gene transfection in skeletal myoblasts using nanogrooves as a substrate. In this study, the effect of the cytoskeleton on gene transfection efficiency of skeletal myoblasts was studied using various nanopillars and nanocarriers. Nanopillars with different diameters (200-1000 nm) and depths (200 or 400 nm) were fabricated using colloidal self-assembly and reactive ion etching. All surfaces were treated with oxygen plasma or polydopamine (PD) to further control cell morphology. Plasmid DNA was delivered into cells using jetPRIME or Lipofectamine 3000 nanocarriers. After screening hundreds of images, two distinguishable F-actin distributions were found, i.e., cells with or without a perinuclear actin cap (pnAC). Cells attached to nanopillars, especially the deep pillars, had a smaller spreading area, shorter F-actin, more 3D-like cell nuclei, and a lower percentage of pnAC, which lead to a higher gene transfection efficiency using jetPRIME. On the other hand, cells attached to the shallow nanopillars or flat surfaces had a larger spreading area, longer F-actin, more 2D-like cell nuclei, and a higher percentage of pnAC that facilitates gene transfection using Lipofectamine. The effects of cell density, cytoskeleton (cytoD), and focal adhesions (RGD) on gene transfection were also studied, and the results were consistent with our hypothesis that F-actin distribution is one of the critical factors in gene transfection. In conclusion, pnAC plays a vital role in the intracellular trafficking of nanocarrier/plasmid complexes and this study provides new insights into gene transfection in anchor-dependent cells. STATEMENT OF SIGNIFICANCE: This study provides a new perspective in gene transfection using attached cells where perinuclear actin cap (pnAC) is an essential factor involved in transfection efficiency. A series of nanopillars were used to harness cell and cytoskeleton morphology. Two distinguishable cytoskeletal structures were found including cells with or without pnAC. 2D-like cells with pnAC facilitate gene delivery using liposome-based nanocarriers, while 3D-like cells without pnAC benefit gene delivery using cationic polymer-based nanocarriers. This study reveals the importance of the cytoskeleton during gene transfection that is beneficial in tissue transfection.

Extracellular matrix mechanics regulate transfection and SOX9-directed differentiation of mesenchymal stem cells

Gene delivery within hydrogel matrices can potentially direct mesenchymal stem cells (MSCs) towards a chondrogenic fate to promote regeneration of cartilage. Here, we investigated whether the mechanical properties of the hydrogel containing the gene delivery systems could enhance transfection and chondrogenic programming of primary human bone marrow-derived MSCs. We developed collagen-I-alginate interpenetrating polymer network hydrogels with tunable stiffness and adhesion properties. The hydrogels were activated with nanocomplexed SOX9 polynucleotides to direct chondrogenic differentiation of MSCs. MSCs transfected within the hydrogels showed higher expression of chondrogenic markers compared to MSCs transfected in 2D prior to encapsulation. The nanocomplex uptake and resulting expression of transfected SOX9 were jointly enhanced by increased stiffness and cell-adhesion ligand density in the hydrogels. Further, transfection of SOX9 effectively induced MSCs chondrogenesis and reduced markers of hypertrophy compared to control matrices. These findings highlight the importance of matrix stiffness and adhesion as design parameters in gene-activated matrices for regenerative medicine. STATEMENT OF SIGNIFICANCE: Gene-activated matrices (GAMs) are biodegradable polymer networks integrating gene therapies, and they are promising technologies for supporting tissue regeneration. Despite this interest, there is still limited information on how to rationally design these systems. Here, we provide a systematic study of the effect of matrix stiffness and cell adhesion ligands on gene transfer efficiency. We show that high stiffness and the presence of cell-binding sites promote transfection efficiency and that this result is related to more efficient internalization and trafficking of the gene therapies. GAMs with optimized mechanical properties can induce cartilage formation and result in tissues with better characteristics for articular cartilage tissue engineering as compared to previously described standard methods.

Novel Platform for Surface-Mediated Gene Delivery Assisted with Visible-Light Illumination

Surface-mediated gene delivery has attracted more and more attentions in biomedical research and applications because of its characteristics of low toxicity and localized delivery. Herein, a novel visible-light-regulated, surface-mediated gene-delivery platform is exhibited, arising from the photoinduced surface-charge accumulation on silicon. Silicon with a pn junction is used and tested subsequently for the behavior of surface-mediated gene delivery under visible-light illumination. It is found that positive-charge accumulation under light illumination changes the surface potential and then facilitates the delivery of gene-loaded carriers. As a result, the gene-expression efficiency shows a significant improvement from 6% to 28% under a 10 min visible-light illumination. Such improvement is ascribed to the increase in surface potential caused by light illumination, which promotes both the release of gene-loaded carriers and the cellular uptake. This work suggests that silicon with photovoltaic effect could offer a new strategy for surface-mediated, gene-delivery-related biomedical research and applications.

Screening a chemically defined extracellular matrix mimetic substrate library to identify substrates that enhance substrate-mediated transfection

Nonviral gene delivery, though limited by inefficiency, has extensive utility in cell therapy, tissue engineering, and diagnostics. Substrate-mediated gene delivery (SMD) increases efficiency and allows transfection at a cell-biomaterial interface, by immobilizing and concentrating nucleic acid complexes on a surface. Efficient SMD generally requires substrates to be coated with serum or other protein coatings to mediate nucleic acid complex immobilization, as well as cell adhesion and growth; however, this strategy limits reproducibility and may be difficult to translate for clinical applications. As an alternative, we screened a chemically defined combinatorial library of 20 different extracellular matrix mimetic substrates containing combinations of (1) different sulfated polysaccharides that are essential extracellular matrix glycosaminoglycans (GAGs), with (2) mimetic peptides derived from adhesion proteins, growth factors, and cell-penetrating domains, for use as SMD coatings. We identified optimal substrates for DNA lipoplex and polyplex SMD transfection of fibroblasts and human mesenchymal stem cells. Optimal extracellular matrix mimetic substrates varied between cell type, donor source, and transfection reagent, but typically contained Heparin GAG and an adhesion peptide. Multiple substrates significantly increased transgene expression (i.e. 2- to 20-fold) over standard protein coatings. Considering previous research of similar ligands, we hypothesize extracellular matrix mimetic substrates modulate cell adhesion, proliferation, and survival, as well as plasmid internalization and trafficking. Our results demonstrate the utility of screening combinatorial extracellular matrix mimetic substrates for optimal SMD transfection towards application- and patient-specific technologies.

Impact statement

Substrate-mediated gene delivery (SMD) approaches have potential for modification of cells in applications where a cell-material interface exists. Conventional SMD uses ill-defined serum or protein coatings to facilitate immobilization of nucleic acid complexes, cell attachment, and subsequent transfection, which limits reproducibility and clinical utility. As an alternative, we screened a defined library of extracellular matrix mimetic substrates containing combinations of different glycosaminoglycans and bioactive peptides to identify optimal substrates for SMD transfection of fibroblasts and human mesenchymal stem cells. This strategy could be utilized to develop substrates for specific SMD applications in which variability exists between different cell types and patient samples.

Microporous annealed particle hydrogel stiffness, void space size, and adhesion properties impact cell proliferation, cell spreading, and gene transfer

Designing scaffolds for polyplex-mediated therapeutic gene delivery has a number of applications in regenerative medicine, such as for tissue repair after wounding or disease. Microporous annealed particle (MAP) hydrogels are an emerging class of porous biomaterials, formed by annealing microgel particles to one another in situ to form a porous bulk scaffold. MAP gels have previously been shown to support and enhance proliferative and regenerative behaviors both in vitro and in vivo. Therefore, coupling gene delivery with MAP hydrogels presents a promising approach for therapy development. To optimize MAP hydrogels for gene delivery, we studied the effects of particle size and stiffness as well as adhesion potential on cell surface area and proliferation and then correlated this information with the ability of cells to become transfected while seeded in these scaffolds. We find that the void space size as well as the presentation of integrin ligands influence transfection efficiency. This work demonstrates the importance of considering MAP material properties for guiding cell spreading, proliferation, and gene transfer. STATEMENT OF SIGNIFICANCE: Microporous annealed particle (MAP) hydrogels are an emerging class of porous biomaterials, formed by annealing spherical microgels together in situ, creating a porous scaffold from voids between the packed beads. Here we investigated the effects of MAP physical and adhesion properties on cell spreading, proliferation, and gene transfer in fibroblasts. Particle size and void space influenced spreading and proliferation, with larger particles improving transfection. MAP stiffness was also important, with stiffer scaffolds increasing proliferation, spreading, and transfection, contrasting studies in nonporous hydrogels that showed an inverse response. Last, RGD ligand concentration and presentation modulated spreading similar to non-MAP hydrogels. These findings reveal relationships between MAP properties and cell processes, suggesting how MAP can be tuned to improve future design approaches.

Pathways Governing Polyethylenimine Polyplex Transfection in Microporous Annealed Particle Scaffolds

Gene delivery using injectable hydrogels can serve as a potential method for regulated tissue regeneration in wound healing. Our microporous annealed particle (MAP) hydrogel has been shown to promote cellular infiltration in both skin and brain wounds, while reducing inflammation. Although the scaffold itself can promote healing, it is likely that other signals will be required to promote healing of hard-to-treat wounds. Gene delivery is one approach to introduce desired bioactive signals. In this study, we investigated how the properties of MAP hydrogels influence non-viral gene delivery of polyethylenimine-condensed plasmid to cells seeded within the MAP gel. From past studies, we found that gene transfer to cells seeded in tissue culture plastic differed from gene transfer to cells seeded inside hydrogel scaffolds. Since MAP scaffolds are generated from hydrogel microparticles that are approximately 100 μm in diameter, they display local characteristics that can be viewed as two-dimensional or three-dimensional to cells. Thus, we sought to study if gene transfer inside MAP scaffolds differed from gene transfer to cells seeded in tissue culture plastic. We sought to understand the roles of the endocytosis pathway, actin and microtubule dynamics, RhoGTPases, and YAP/TAZ on transfection of human fibroblasts.

Free Polyethylenimine Enhances Substrate-Mediated Gene Delivery on Titanium Substrates Modified With RGD-Functionalized Poly(acrylic acid) Brushes

Substrate mediated gene delivery (SMD) is a method of immobilizing DNA complexes to a substrate via covalent attachment or nonspecific adsorption, which allows for increased transgene expression with less DNA compared to traditional bolus delivery. It may also increase cells receptivity to transfection via cell-material interactions. Substrate modifications with poly(acrylic) acid (PAA) brushes may improve SMD by enhancing substrate interactions with DNA complexes via tailored surface chemistry and increasing cellular adhesion via moieties covalently bound to the brushes. Previously, we described a simple method to graft PAA brushes to Ti and further demonstrated conjugation of cell adhesion peptides (i.e., RGD) to the PAA brushes to improve biocompatibility. The objective of this work was to investigate the ability of Ti substrates modified with PAA-RGD brushes (PAA-RGD) to immobilize complexes composed of branched polyethyleneimine and DNA plasmids (bPEI-DNA) and support SMD in NIH/3T3 fibroblasts. Transfection in NIH/3T3 cells cultured on bPEI-DNA complexes immobilized onto PAA-RGD substrates was measured and compared to transfection in cells cultured on control surfaces with immobilized complexes including Flat Ti, PAA brushes modified with a control peptide (RGE), and unmodified PAA. Transfection was two-fold higher in cells cultured on PAA-RGD compared to those cultured on all control substrates. While DNA immobilization measured with radiolabeled DNA indicated that all substrates (PAA-RGD, unmodified PAA, Flat Ti) contained nearly equivalent amounts of loaded DNA, ellipsometric measurements showed that more total mass (i.e., DNA and bPEI, both complexed and free) was immobilized to PAA and PAA-RGD compared to Flat Ti. The increase in adsorbed mass may be attributed to free bPEI, which has been shown to improve transfection. Further transfection investigations showed that removing free bPEI from the immobilized complexes decreased SMD transfection and negated any differences in transfection success between cells cultured on PAA-RGD and on control substrates, suggesting that free bPEI may be beneficial for SMD in cells cultured on bPEI-DNA complexes immobilized on PAA-RGD grafted to Ti. This work demonstrates that substrate modification with PAA-RGD is a feasible method to enhance SMD outcomes on Ti and may be used for future applications such as tissue engineering, gene therapy, and diagnostics.

Biomaterial substrate modifications that influence cell-material interactions to prime cellular responses to nonviral gene delivery

IMPACT STATEMENT

This review summarizes how biomaterial substrate modifications (e.g. chemical modifications like natural coatings, ligands, or functional side groups, and/or physical modifications such as topography or stiffness) can prime the cellular response to nonviral gene delivery (e.g. affecting integrin binding and focal adhesion formation, cytoskeletal remodeling, endocytic mechanisms, and intracellular trafficking), to aid in improving gene delivery for applications where a cell-material interface might exist (e.g. tissue engineering scaffolds, medical implants and devices, sensors and diagnostics, wound dressings).

It's All in the Delivery: Designing Hydrogels for Cell and Non-viral Gene Therapies

Hydrogels provide a regenerative medicine platform with their ability to create an environment that supports transplanted or endogenous infiltrating cells and enables these cells to restore or replace the function of tissues lost to disease or trauma. Furthermore, these systems have been employed as delivery vehicles for therapeutic genes, which can direct and/or enhance the function of the transplanted or endogenous cells. Herein, we review recent advances in the development of hydrogels for cell and non-viral gene delivery through understanding the design parameters, including both physical and biological components, on promoting transgene expression, cell engraftment, and ultimately cell function. Furthermore, this review identifies emerging opportunities for combining cell and gene delivery approaches to overcome challenges to the field.

Unifying in vitro and in vivo IVT mRNA expression discrepancies in skeletal muscle via mechanotransduction

The translational efficiency of an in vitro transcribed (IVT) mRNA was measured upon delivery to primary skeletal muscle cells and to a mouse model system, towards the development of a predictive in vitro assay for the screening and validation of intramuscular mRNA-based vaccines. When IVT mRNA was delivered either naked or complexed with novel aminoglycoside-based delivery vehicles, significant differences in protein expression in vitro and in vivo were observed. We hypothesized that this previously anticipated discrepancy was due to differences in the mechanism of IVT mRNA endosomal entry and release following delivery. To address this, IVT mRNA was fluorescently labeled prior to delivery, to visualize its distribution. Colocalization with endosomal markers indicated that different entry pathways were utilized in vivo and in vitro, depending on the delivery vehicle, resulting in variations in protein expression levels. Since extracellular matrix stiffness (ECM) influences mRNA entry, trafficking and release, the effect of mechanotransduction on mRNA expression was investigated in vitro upon delivery of IVT mRNA alone, and complexed with delivery vehicles to skeletal muscle cells grown on ∼10 kPa hydrogels. This in vitro hydrogel model more accurately recapitulated the results obtained in vivo upon IM injection, indicating that this approach may assist in the characterization of mRNA based vaccines.

Synergistic effects of hyperosmotic polymannitol based non-viral vectors and nanotopographical cues for enhanced gene delivery

Here, we report the synergistic effects of hyperosmotic and nanotopographical cues designed using non-viral vectors and nanopatterned matrices for gene delivery.

Encapsulation of PEGylated low-molecular-weight PEI polyplexes in hyaluronic acid hydrogels reduces aggregation

The effective delivery of DNA locally could increase the applicability of gene therapy in tissue regeneration and therapeutic angiogenesis. One promising approach is through use of porous hydrogel scaffolds that incorporate and deliver DNA in the form of nanoparticles to the affected sites. While we have previously reported on caged nanoparticle encapsulation (CnE) to load DNA polyplexes within hydrogels at high concentrations without aggregation, frequent issues with limited polyplex release following CnE have been encountered. In this study, we report two alternative approaches to polyplex presentation for decreasing aggregation in porous hydrogels. The first approach reduces polyplex aggregation by utilizing polyethylene glycol modification of the gene carrier polymer polyethyleneimine (sPEG-PEI) to mitigate charge-charge interactions between polyplexes and the scaffold during gelation. The second approach electrostatically presents polyplexes on the surfaces of scaffold pores as opposed to an encapsulated presentation. The sPEG-PEI polymer formed a smaller, less toxic, and more stable polyplex that exhibited less aggregation within HA gels when compared to the traditionally used linear PEI (LPEI) polymer. Surface-coated polyplexes also resulted in a more homogenous distribution of polyplexes in hydrogels. Furthermore, sPEG-PEI polyplexes retained transfection abilities comparable to LPEI in 3D surface-coated transfections. These results demonstrate a significant improvement in scaffold-mediated gene delivery and show promise in applications to multi-gene delivery systems.

STATEMENT OF SIGNIFICANCE

A promising gene delivery approach for regenerative medicine is implanting porous hydrogel scaffolds loaded with DNA nanoparticles for delivery to affected sites. However, loading DNA polyplexes at high concentrations within hydrogels results in significant aggregation. Here, we describe two methods for decreasing aggregation of DNA polyplexes in porous gels. First, the gene carrier polymer polyethyleneimine (PEI) was modified with polyethylene glycol (sPEG-PEI) to mitigate the electrostatic interactions between polyplexes and scaffold polymer to in turn decrease aggregation. Second, polyplexes were presented along the surfaces of the pores of the hydrogel instead of being encapsulated within the gel. These methods allow for highly tunable and sustained transgene expression from scaffold-mediated gene delivery while avoiding polyplex aggregation.

Enhancement of nucleic acid delivery to hard-to-transfect human colorectal cancer cells by magnetofection at laminin coated substrates and promotion of the endosomal/lysosomal escape

Optimization of nucleic acid delivery in hard-to-transfect colorectal cancer cells by magnetofection at coated laminin substrates and by the endosomal escape enhancement of magnetic complexes using INF-7 peptide.

The effect of substrate elasticity and actomyosin contractility on different forms of endocytosis

Substrate mechanical properties have emerged as potent determinants of cell functions and fate. We here tested the hypothesis that different forms of endocytosis are regulated by the elasticity of the synthetic hydrogels cells are cultured on. Towards this objective, we quantified cell-associated fluorescence of the established endocytosis markers transferrin (Tf) and cholera toxin subunit B (CTb) using a flow-cytometry based protocol, and imaged marker internalization using microscopy techniques. Our results demonstrated that clathrin-mediated endocytosis of Tf following a 10-minute incubation with a fibroblast cell line was lower on the softer substrates studied (5 kPa) compared to those with elasticities of 40 and 85 kPa. This effect was cancelled after 1-hour incubation revealing that intracellular accumulation of Tf at this time point did not depend on substrate elasticity. Lipid-raft mediated endocytosis of CTb, on the other hand, was not affected by substrate elasticity in the studied range of time and substrate elasticity. The use of pharmacologic contractility inhibitors revealed inhibition of endocytosis for both Tf and CTb after a 10-minute incubation and a dissimilar effect after 1 hour depending on the inhibitor type. Further, the internalization of fluorescent NPs, used as model drug delivery systems, showed a dependence on substrate elasticity, while transfection efficiency was unaffected by it. Finally, an independence on substrate elasticity of Tf and CTb association with HeLa cells indicated that there are cell-type differences in this respect. Overall, our results suggest that clathrin-mediated but not lipid-raft mediated endocytosis is potentially influenced by substrate mechanics at the cellular level, while intracellular trafficking and accumulation show a more complex dependence. Our findings are discussed in the context of previous work on how substrate mechanics affect the fundamental process of endocytosis and highlight important considerations for future studies.

Transfection in the third dimension

An understanding of parameters that modulate gene transfer in 3-D will assist in the formation of gene delivery systems and scaffolds, which can mediate efficient non-viral delivery for guiding in vivo tissue regeneration and therapy. We have previously demonstrated the cell area and length, integrin expression, and RhoGTPase mediated signalling to be pivotal parameters that guide gene transfer to mouse mesenchymal stem cells (mMSCs) cultured in 2-D and are modulated by ECM proteins. In this study, we were interested in determining if cationic polymer mediated gene transfer to cells seeded in 3-D would occur through different mechanisms as compared to those seeded in 2-D. In particular, we examined the endocytosis pathways used to internalize polyplexes, and the role of cytoskeletal dynamics and RhoGTPases in non-viral gene transfer for cells seeded in 2-D and 3-D. Inhibition of clathrin- and caveolae-mediated endocytosis resulted in a more drastic decrease in overall transgene expression for cells seeded in 3-D than for those in 2-D. In addition, polyplex internalization was only significantly decreased in 3-D when clathrin-mediated endocytosis was inhibited, while caveolae-mediated endocytosis inhibition for cells seeded in 2-D resulted in the strongest polyplex internalization inhibition. Actin and microtubule polymerization affected 2-D and 3-D transfection differently. Microtubule depolymerization enhanced transgene expression in 2-D, but inhibited transgene expression in 3-D. Lastly, inhibition of RhoGTPases also affected 2-D and 3-D transfection differently. The inhibition of ROCK effectors resulted in a decrease of transgene expression and internalization for cells seeded in 3-D, but not in 2-D, and the inhibition of the effector PAK1 resulted in an increase of transgene expression for both 2-D and 3-D. Overall, our study suggests that the process of gene transfer occurs through different mechanisms for cells seeded in 2-D compared to those seeded in 3-D.

Matrix stiffness affects endocytic uptake of MK2-inhibitor peptides

In this study, the role of substrate stiffness on the endocytic uptake of a cell-penetrating peptide was investigated. The cell-penetrating peptide, an inhibitor of mitogen-activated protein kinase activated protein kinase II (MK2), enters a primary mesothelial cell line predominantly through caveolae. Using tissue culture polystyrene and polyacrylamide gels of varying stiffness for cell culture, and flow cytometry quantification and enzyme-linked immunoassays (ELISA) for uptake assays, we showed that the amount of uptake of the peptide is increased on soft substrates. Further, peptide uptake per cell increased at lower cell density. The improved uptake seen on soft substrates in vitro better correlates with in vivo functional studies where 10–100 µM concentrations of the MK2 inhibitor cell penetrating peptide demonstrated functional activity in several disease models. Additional characterization showed actin polymerization did not affect uptake, while microtubule polymerization had a profound effect on uptake. This work demonstrates that cell culture substrate stiffness can play a role in endocytic uptake, and may be an important consideration to improve correlations between in vitro and in vivo drug efficacy.

Matrix-based gene delivery for tissue repair

Scaffolds for tissue repair must provide structural and biochemical cues to initiate the complex cascade of events that lead to proper tissue formation. Incorporating genes into these scaffolds is an attractive alternative to protein delivery since gene delivery can be tunable to any DNA sequence and genes utilize the cells' machinery to continuously produce therapeutic proteins, leading to longer lasting transgene expression and activation of autocrine and paracrine signaling that are not activated with bulk protein delivery. In this review, we discuss the importance of scaffold design and the impact of its design parameters (e.g. material, architecture, vector incorporation, biochemical cue presentation) on transgene expression and tissue repair.

Cyclic-RGD peptides increase the adenoviral transduction of human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) have been extensively explored for drug delivery applications due to their safety, immunomodulatory properties, and ability to differentiate into new tissues. The experiments presented in this study were designed to determine peptide-based mechanisms to increase the adenoviral transduction of hMSCs for the purpose of improving their capacity as drug delivery vehicles. Specifically, we demonstrated that cyclic- RGD peptides increased the internalization of adenoviruses into MSCs. MSCs treated with cyclic-RGD peptides had a transduction efficiency of 76.6%±4%, which was significantly greater than the 23.5%±12.2% transduction efficiency of untreated stem cells (P<0.05). Blocking endocytosis with inhibitors of dynamin or actin polymerization decreased the cyclic-RGD-mediated increase in transduction efficiency. MSCs treated with cyclic-RGD and adenoviruses carrying the gene for bone morphogenetic protein-2 produced significantly greater concentrations of this growth factor compared to stem cells treated with only adenoviruses or adenoviruses cocultured with cyclic-RAD peptides. Furthermore, this stem cell-produced bone morphogenetic protein induced alkaline phosphatase expression in C2C12 cells indicating growth factor bioactivity. Taken together, these studies suggest that cyclic-RGD peptides could be used to increase the adenoviral transduction of hMSCs and increase their therapeutic potential.

The role of surface chemistry-induced cell characteristics on nonviral gene delivery to mouse fibroblasts

Background

Gene delivery approaches serve as a platform to modify gene expression of a cell population with applications including functional genomics, tissue engineering, and gene therapy. The delivery of exogenous genetic material via nonviral vectors has proven to be less toxic and to cause less of an immune response in comparison to viral vectors, but with decreased efficiency of gene transfer. Attempts have been made to improve nonviral gene transfer efficiency by modifying physicochemical properties of gene delivery vectors as well as developing new delivery techniques. In order to further improve and understand nonviral gene delivery, our approach focuses on the cell-material interface, since materials are known to modulate cell behavior, potentially rendering cells more responsive to nonviral gene transfer. In this study, self-assembled monolayers of alkanethiols on gold were employed as model biomaterial interfaces with varying surface chemistries. NIH/3T3 mouse fibroblasts were seeded on the modified surfaces and transfected using either lipid- or polymer- based complexing agents.

Results

Transfection was increased in cells on charged hydrophilic surfaces presenting carboxylic acid terminal functional groups, while cells on uncharged hydrophobic surfaces presenting methyl terminations demonstrated reduced transfection for both complexing agents. Surface–induced cellular characteristics that were hypothesized to affect nonviral gene transfer were subsequently investigated. Cells on charged hydrophilic surfaces presented higher cell densities, more cell spreading, more cells with ellipsoid morphologies, and increased quantities of focal adhesions and cytoskeleton features within cells, in contrast to cell on uncharged hydrophobic surfaces, and these cell behaviors were subsequently correlated to transfection characteristics.

Conclusions

Extracellular influences on nonviral gene delivery were investigated by evaluating the upregulation and downregulation of transgene expression as a function of the cell behaviors induced by changes in the cells’ microenvronments. This study demonstrates that simple surface modifications can lead to changes in the efficiency of nonviral gene delivery. In addition, statistically significant differences in various surface-induced cell characteristics were statistically correlated to transfection trends in fibroblasts using both lipid and polymer mediated DNA delivery approaches. The correlations between the evaluated complexing agents and cell behaviors (cell density, spreading, shape, cytoskeleton, focal adhesions, and viability) suggest that polymer-mediated transfection is correlated to cell morphological traits while lipid-mediated transfection correlates to proliferative characteristics.

Subcellular trafficking and transfection efficacy of polyethylenimine-polyethylene glycol polyplex nanoparticles with a ligand to melanocortin receptor-1

We have synthesized and investigated properties of new PEI-PEG-based polyplexes containing MC1SP-peptide, a ligand specific for melanocortin receptor-1 (targeted polyplexes), and control polyplexes without this ligand peptide (non-targeted polyplexes). The targeted polyplexes demonstrated receptor-mediated transfection of Cloudman S91 (clone M-3) murine melanoma cells that was more efficient than with the non-targeted ones. Transfection with the targeted polyplexes was inhibited by chlorpromazine, an inhibitor of the clathrin-mediated endocytosis pathway, and, to a lesser extent, by filipin III or nystatin, inhibitors of the lipid-raft endocytosis pathway, whereas transfection with the non-targeted polyplexes was inhibited mainly by nystatin or filipin III. The targeted polyplexes caused significantly higher in vivo transfection of melanoma tumor cells after intratumoral administration compared to the non-targeted control. The targeted polyplexes carrying the HSVtk gene, after ganciclovir administration, more efficiently inhibited melanoma tumor growth and prolonged the lifespan of DBA/2 tumor-bearing mice compared to the non-targeted ones. Packed targeted polyplexes appeared and accumulated in the melanoma cells 6h earlier than the non-targeted ones. The targeted polyplexes enter into the nuclei of the melanoma cells more rapidly than the non-targeted control, and this difference may also be attributed to processes of receptor-mediated endocytosis. We believe that these data may be useful for the optimization of polyplex systems.

Gene-activated and cell-migration guiding PEG matrices based on three dimensional patterning of RGD peptides and DNA complexes

Essential to the design of genetic bioreactors used in the human body is a consideration of how the properties of biomaterials can combine to envelope, spatially guide, reprogramme by gene transfer, and then release cells. In order to approach this goal, poly(ethylene glycol) (PEG) matrices with modulated structural features and defined spatial patterns of bioactive signals have been designed and produced. In particular, within such PEG matrices, both an adhesive RGD peptide gradient, to directionally attract NIH3T3 cells, and a designed spatial distribution of immobilized poly(ethylenimine) (PEI)/DNA complexes, to obtain a localized transfection, have been realized. These bioactive biomaterials have been designed bearing in mind that cells following an RGD gradient migrate through the matrix, in which they find the bound DNA and become transfected. Both cell migration and transfection have been monitored by fluorescence microscopy. Results show that this system is able to envelope cells, spatially guide them towards the immobilized gene complexes and locally transfect them. Therefore, the system, acting as a genetic bioreactor potentially useful for the regulation of biology at a distance, could be used to directly control cell trafficking and activation in the human body, and has many potential biomedical applications.

Cellular cytoskeleton dynamics modulates non-viral gene delivery through RhoGTPases

Although it is well accepted that the constituents of the cellular microenvironment modulate a myriad of cellular processes, including cell morphology, cytoskeletal dynamics and uptake pathways, the underlying mechanism of how these pathways influence non-viral gene transfer have not been studied. Transgene expression is increased on fibronectin (Fn) coated surfaces as a consequence of increased proliferation, cell spreading and active engagement of clathrin endocytosis pathway. RhoGTPases mediate the crosstalk between the cell and Fn, and regulate cellular processes involving filamentous actin, in-response to cellular interaction with Fn. Here the role of RhoGTPases specifically Rho, Rac and Cdc42 in modulation of non-viral gene transfer in mouse mesenchymal stem (mMSCs) plated in a fibronectin microenvironment was studied. More than 90% decrease in transgene expression was observed after inactivation of RhoGTPases using difficile toxin B (TcdB) and C3 transferase. Expression of dominant negative RhoA (RhoAT19N), Rac1(Rac1T17N) and Cdc42 (Cdc42T17N) also significantly reduced polyplex uptake and transgene expression. Interactions of cells with Fn lead to activation of RhoGTPases. However, further activation of RhoA, Rac1 and Cdc42 by expression of constitutively active genes (RhoAQ63L, Rac1Q61L and Cdc42Q61L) did not further enhance transgene expression in mMSCs, when plated on Fn. In contrast, activation of RhoA, Rac1 and Cdc42 by expression of constitutively active genes for cells plated on collagen I, which by itself did not increase RhoGTPase activation, resulted in enhanced transgene expression. Our study shows that RhoGTPases regulate internalization and effective intracellular processing of polyplexes that results in efficient gene transfer.

Utilizing cell-matrix interactions to modulate gene transfer to stem cells inside hyaluronic acid hydrogels

The effective delivery of DNA locally would increase the applicability of gene therapy in tissue regeneration, where diseased tissue is to be repaired in situ. One promising approach is to use hydrogel scaffolds to encapsulate and deliver plasmid DNA in the form of nanoparticles to the diseased tissue, so that cells infiltrating the scaffold are transfected to induce regeneration. This study focuses on the design of a DNA nanoparticle-loaded hydrogel scaffold. In particular, this study focuses on understanding how cell-matrix interactions affect gene transfer to adult stem cells cultured inside matrix metalloproteinase (MMP) degradable hyaluronic acid (HA) hydrogel scaffolds. HA was cross-linked to form a hydrogel material using a MMP degradable peptide and Michael addition chemistry. Gene transfer inside these hydrogel materials was assessed as a function of polyplex nitrogen to phosphate ratio (N/P = 5 to 12), matrix stiffness (100-1700 Pa), RGD (Arg-Gly-Asp) concentration (10-400 μM), and RGD presentation (0.2-4.7 RGDs per HA molecule). All variables were found to affect gene transfer to mouse mensenchymal stem cells culture inside the DNA loaded hydrogels. As expected, higher N/P ratios lead to higher gene transfer efficiency but also higher toxicity; softer hydrogels resulted in higher transgene expression than stiffer hydrogels, and an intermediate RGD concentration and RGD clustering resulted in higher transgene expression. We believe that the knowledge gained through this in vitro model can be utilized to design better scaffold-mediated gene delivery for local gene therapy.

High-throughput screening of microscale pitted substrate topographies for enhanced nonviral transfection efficiency in primary human fibroblasts

Optimization of nonviral gene delivery typically focuses on the design of particulate carriers that are endowed with desirable membrane targeting, internalization, and endosomal escape properties. Topographical control of cell transfectability, however, remains a largely unexplored parameter. Emerging literature has highlighted the influence of cell-topography interactions on modulation of many cell phenotypes, including protein expression and cytoskeletal behaviors implicated in endocytosis. Using high-throughput screening of primary human dermal fibroblasts cultured on a combinatorial library of microscale topographies, we have demonstrated an improvement in nonviral transfection efficiency for cells cultured on dense micropit patterns compared to smooth substrates, as verified with flow cytometry. A 25% increase in GFP(+) cells was observed independent of proliferation rate, accompanied by SEM and confocal microscopy characterization to help explain the phenomenon qualitatively. This finding encourages researchers to investigate substrate topography as a new design consideration for the optimization of nonviral transfection systems.