Gene expression and internalization following vector adsorption to immobilized proteins: dependence on protein identity and density

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.

Further Enhancement in Intestinal Absorption of Paclitaxel by Using Transferrin-Modified Paclitaxel Nanocrystals

The intestinal epithelium is considered to be a major obstacle to the gastrointestinal administration for water-insoluble drugs. To enhance the intestinal absorption of paclitaxel by improving its solubility and overcoming the intestinal epithelium barrier, transferrin-modified paclitaxel nanocrystals were prepared based on the specific transferrin receptor expressed on the apical membrane of the intestinal epithelium and examined to exhibit a mean size of around 178 nm, a rod-like morphology, a sustained release property, and an enhanced in vitro antitumor effect. The in situ intestinal perfusion study proved that the intestinal absorption of transferrin-modified paclitaxel nanocrystals was remarkably enhanced compared with that of Taxol and unmodified paclitaxel nanocrystals, which was further evidenced by the result of pharmacokinetic study. Their transcytosis pathway and intracellular trafficking track were disclosed using Caco-2 cell monolayers. The transcytosis of transferrin-modified paclitaxel nanocrystals and unmodified paclitaxel nanocrystals was principally mediated by clathrin and lipid rafts. The colocalization of both paclitaxel nanocrystals with the organelles observed under confocal microscopy suggested that the late endosomes, lysosomes, ER, and Golgi apparatus played a part in the transcellular transport of both paclitaxel nanocrystals during their transcytosis. Therefore, the designed transferrin-modified drug nanocrystals might have a great potential in the enhancement of intestinal absorption of water-insoluble drugs.

Delivery of hepatocyte growth factor mRNA from nanofibrillar scaffolds in a pig model of peripheral arterial disease

Background: Chemical modification of mRNA (mmRNA) substantially improves their stability and translational efficiency within cells. Nanofibrillar collagen scaffolds were previously shown to enable the spatially localized delivery and temporally controlled release of mmRNA encoding HGF both in vitro and in vivo. Materials & methods: Herein we developed an improved slow-releasing HGF mmRNA scaffold and tested its therapeutic efficacy in a porcine model of peripheral arterial disease. Results & conclusion: The HGF mmRNA was released from scaffolds in a temporally controlled fashion in vitro with preserved transfection activity. The mmRNA scaffolds improved vascular regeneration when sutured to the ligated porcine femoral artery. These studies validate the therapeutic potential of HGF mmRNA delivery from nanofibrillar scaffolds for treatment of peripheral arterial disease.

Endocytosis: The Nanoparticle and Submicron Nanocompounds Gateway into the Cell

Nanoparticles (NPs) and submicron particles are increasingly used as carriers for delivering therapeutic compounds to cells. Their entry into the cell represents the initial step in this delivery process, being most of the nanoparticles taken up by endocytosis, although other mechanisms can contribute to the uptake. To increase the delivery efficiency of therapeutic compounds by NPs and submicron particles is very relevant to understand the mechanisms involved in the uptake process. This review covers the proposed pathways involved in the cellular uptake of different NPs and submicron particles types as well as the role that some of the physicochemical nanoparticle characteristics play in the uptake pathway preferentially used by the nanoparticles to gain access and deliver their cargo inside the cell.

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.

Enhance transgene responses through improving cellular uptake and intracellular trafficking by bio-inspired non-viral vectors

Background

Gene therapy remains a significant challenge due to lots of barriers limiting the genetic manipulation technologies. As for non-viral delivery vectors, they often suffer insufficient performance due to inadequate cellular uptake and gene degradation in endosome or lysosome. The importance of overcoming these conserved intracellular barriers is increasing as the delivery of genetic cargo.

Results

A surface-functionalized non-viral vector involving the biomimetic mannitol moiety is initiated, which can control the cellular uptake and promote the caveolae-mediated pathway and intracellular trafficking, thus avoiding acidic and enzymatic lysosomal degradation of loaded gene internalized by clathrin-mediated pathway. Different degrees of mannitol moiety are anchored onto the surface of the nanoparticles to form bio-inspired non-viral vectors and CaP-MA-40 exhibits remarkably high stability, negligible toxicity, and significantly enhanced transgene expression both in vitro and in vivo.

Conclusions

This strategy highlights a paradigmatic approach to construct vectors that need precise intracellular delivery for innovative applications.

Bioactive nanocomposite coatings under visible light illumination promoted surface-mediated gene delivery

Bioactive coatings with photothermal conversion ability were used to spatially and temporally control surface-mediated gene delivery under visible light illumination.

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.

Effect of lipopolysaccharide addition on the gene transfection of spermine-introduced pullulan-plasmid DNA complexes for human mesenchymal stem cells

The objective of this study is to investigate the effect of lipopolysaccharide (LPS) addition on the gene transfection of human mesenchymal stem cells (hMSC). hMSC were treated with the LPS at different concentrations and the complex of spermine-introduced pullulan and luciferase plasmid DNA for 3 h. The maximum level of gene expression was observed for hMSC treated with a certain concentration range of LPS. In addition, the cytotoxicity, cellular internalization of complexes, and cell cycle after LPS treatment were investigated. The cytotoxicity increased with an increase in the LPS concentration treated. On the other hand, the cellular internalization of complexes increased with the increased LPS concentration, although the internalization was sharply reduced at the high concentration. The LPS treatment increased the actin polymerization of cells to allow to spread more. The enhanced cells spreading would enhance the cellular internalization of complexes. In addition, the LPS treatment increased the rate of cell cycle. It is possible that the balance of cytotoxicity, cellular internalization, and cell cycle caused by the LPS addition results in the enhanced gene transfection at a certain LPS concentration. It is concluded that LPS treatment positively modified the cellular internalization and the cell cycle, resulting in the enhanced gene transfection.

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).

Surface- and Hydrogel-Mediated Delivery of Nucleic Acid Nanoparticles

Gene expression within a cell population can be directly altered through gene delivery approaches. Traditionally for nonviral delivery, plasmids or siRNA molecules, encoding or targeting the gene of interest, are packaged within nanoparticles. These nanoparticles are then delivered to the media surrounding cells seeded onto tissue culture plastic; this technique is termed bolus delivery. Although bolus delivery is widely utilized to screen for efficient delivery vehicles and to study gene function in vitro, this delivery strategy may not result in efficient gene transfer for all cell types or may not identify those delivery vehicles that will be efficient in vivo. Furthermore, bolus delivery cannot be used in applications where patterning of gene expression is needed. In this chapter, we describe methods that incorporate material surfaces (i.e., surface-mediated delivery) or hydrogel scaffolds (i.e., hydrogel-mediated delivery) to efficiently deliver genes. This chapter includes protocols for surface-mediated DNA delivery focusing on the simplest and most effective methods, which include nonspecific immobilization of DNA complexes (both polymer and lipid vectors) onto serum-coated cell culture polystyrene and self-assembled monolayers (SAMs) of alkanethiols on gold. Also, protocols for the encapsulation of DNA/cationic polymer nanoparticles into hydrogel scaffolds are described, including methods for the encapsulation of low amounts of DNA (<0.2 μg/μl) and high amounts of DNA (>0.2 μg/μl) since incorporation of high amounts of DNA pose significant challenges due to aggregation.

Aligned Nanofibrillar Scaffolds for Controlled Delivery of Modified mRNA

RNA-based vector delivery is a promising gene therapy approach. Recent advances in chemical modification of mRNA structure to form modified mRNA (mmRNA or cmRNA or modRNA) have substantially improved their stability and translational efficiency within cells. However, mmRNA conventionally delivered in solution can be taken up nonspecifically or become cleared away prematurely, which markedly limits the potential benefit of mmRNA therapy. To address this limitation, we developed mmRNA-incorporated nanofibrillar scaffolds that could target spatially localized delivery and temporally controlled release of the mmRNA both in vitro and in vivo. To establish the efficacy of mmRNA therapy, mmRNA encoding reporter proteins such as green fluorescence protein or firefly luciferase (Fluc) was loaded into aligned nanofibrillar collagen scaffolds. The mmRNA was released from mmRNA-loaded scaffolds in a transient and temporally controlled manner and induced transfection of human fibroblasts in a dose-dependent manner. In vitro transfection was further verified using mmRNA encoding the angiogenic growth factor, hepatocyte growth factor (HGF). Finally, scaffold-based delivery of HGF mmRNA to the site of surgically induced muscle injury in mice resulted in significantly higher vascular regeneration after 14 days, compared to implantation of Fluc mmRNA-releasing scaffolds. After transfection with Fluc mmRNA-releasing scaffold in vivo, Fluc activity was detectable and localized to the muscle region, based on noninvasive bioluminescence imaging. Scaffold-based local mmRNA delivery as an off-the-shelf form of gene therapy has broad translatability for treating a wide range of diseases or injuries.

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.

Molecular Recognition and In-Vitro-Targeted Inhibition of Renal Cell Carcinoma Using a DNA Aptamer

Renal cell carcinoma (RCC) is the most common malignant tumor of the urinary system, and it has a high frequency of local invasion and distant metastasis. Although multiple advances have been made in the diagnosis and therapy of RCC, the vast majority of patients with metastatic RCC remain incurable. In this study, an aptamer named SW-4 against RCC 786-O cells was identified from a known sequence pool. The identified aptamer exhibited high binding affinity for target cells with dissociation constants in the nanomolar range. Binding analysis revealed that SW-4 only bound to RCC 786-O cells, but not HEK293T cells or human proximal tubular HK-2 cells, indicating that SW-4 has excellent binding selectivity. By sequence optimization, the 26-nt truncated SW-4b demonstrated improved binding affinity, and it was internalized into target cells via caveolae-mediated endocytosis in a temperature-dependent manner. Furthermore, fluorescence imaging confirmed that SW-4b accumulated at tumor sites in 786-O xenograft nude mice models and specifically recognized clinical RCC tissues. Meanwhile, SW-4b inhibited proliferation of 786-O cells by arresting cell cycle progression at the S phase. Taken together, these results indicate that SW-4b is a potential candidate for development into a novel tool for diagnosis and targeted therapy of RCC.

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.

Design and application of cationic amphiphilic β-cyclodextrin derivatives as gene delivery vectors

The nano self-assembly profiles of amphiphilic gene delivery vectors could improve the density of local cationic head groups to promote their DNA condensation capability and enhance the interaction between cell membrane and hydrophobic tails, thus increasing cellular uptake and gene transfection. In this paper, two series of cationic amphiphilic β-cyclodextrin (β-CD) derivatives were designed and synthesized by using 6-mono-OTs-β-CD (1) as the precursor to construct amphiphilic gene vectors with different building blocks in a selective and controlled manner. The effect of different type and degree of cationic head groups on transfection and the endocytic mechanism of β-CD derivatives/DNA nanocomplexes were also investigated. The results demonstrated that the designed β-cyclodextrin derivatives were able to compact DNA to form stable nanocomplexes and exhibited low cytotoxicity. Among them, PEI-1 with PEI head group showed enhanced transfection activity, significantly higher than commercially available agent PEI25000 especially in the presence of serum, showing potential application prospects in clinical trials. Moreover, the endocytic uptake mechanism involved in the gene transfection of PEI-1 was mainly through caveolae-mediated endocytosis, which could avoid the lysosomal degradation of loaded gene, and had great importance for improving gene transfection activity.

Mechanisms of pH-Sensitivity and Cellular Internalization of PEOz-b-PLA Micelles with Varied Hydrophilic/Hydrophobic Ratios and Intracellular Trafficking Routes and Fate of the Copolymer

pH-responsive polymeric micelles have shown promise for the targeted and intracellular delivery of antitumor agents. The present study aimed to elucidate the possible mechanisms of pH-sensitivity and cellular internalization of PEOz-b-PLA micelles in detail, further unravel the effect of hydrophilic/hydrophobic ratio of the micelles on their cellular internalization, and examine the intracellular trafficking routes and fate of PEOz-b-PLA after internalization of the micelles. The results of variations in the size and Zeta potential of PEOz-b-PLA micelles and cross-sectional area of PEOz-b-PLA molecules with pH values suggested that electrostatic repulsion between PEOz chains resulting from ionization of the tertiary amide groups along PEOz chain at pH lower than its pK_a was responsible for pH-sensitivity of PEOz-b-PLA micelles. Furthermore, the studies on internalization of PEOz-b-PLA micelles by MCF-7 cells revealed that the uptake of PEOz-b-PLA micelles was strongly influenced by their structural features, and showed that PEOz-b-PLA micelles with hydrophilic/hydrophobic ratio of 1.7-2.0 exhibited optimal cellular uptake. No evident alteration in cellular uptake of PEOz-b-PLA micelles was detected by flow cytometry upon the existence of EIPA and chlorpromazine. However, the intracellular uptake of the micelles in the presence of MβCD and genistein was effectively inhibited. Hence, the internalization of such micelles by MCF-7 cells appeared to proceed mainly through caveolae/lipid raft-mediated endocytosis without being influenced by their hydrophilic/hydrophobic ratio. Confocal micrographs revealed that late endosomes, mitochondria and endoplasmic reticulum were all involved in the intracellular trafficking of PEOz-b-PLA copolymers following their internalization via endocytosis, and then part of them was excreted from tumor cells to extracellular medium. These findings provided valuable information for developing desired PEOz-b-PLA micelles to improve their therapeutic efficacy and reducing the potential safety risks associated with their intracellular accumulation.

MicroRNA delivery for regenerative medicine

MicroRNA (miRNA) directs post-transcriptional regulation of a network of genes by targeting mRNA. Although relatively recent in development, many miRNAs direct differentiation of various stem cells including induced pluripotent stem cells (iPSCs), a major player in regenerative medicine. An effective and safe delivery of miRNA holds the key to translating miRNA technologies. Both viral and nonviral delivery systems have seen success in miRNA delivery, and each approach possesses advantages and disadvantages. A number of studies have demonstrated success in augmenting osteogenesis, improving cardiogenesis, and reducing fibrosis among many other tissue engineering applications. A scaffold-based approach with the possibility of local and sustained delivery of miRNA is particularly attractive since the physical cues provided by the scaffold may synergize with the biochemical cues induced by miRNA therapy. Herein, we first briefly cover the application of miRNA to direct stem cell fate via replacement and inhibition therapies, followed by the discussion of the promising viral and nonviral delivery systems. Next we present the unique advantages of a scaffold-based delivery in achieving lineage-specific differentiation and tissue development.

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.

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.

Nanoparticle drug- and gene-eluting stents for the prevention and treatment of coronary restenosis

Percutaneous coronary intervention (PCI) has become the most common revascularization procedure for coronary artery disease. The use of stents has reduced the rate of restenosis by preventing elastic recoil and negative remodeling. However, in-stent restenosis remains one of the major drawbacks of this procedure. Drug-eluting stents (DESs) have proven to be effective in reducing the risk of late restenosis, but the use of currently marketed DESs presents safety concerns, including the non-specificity of therapeutics, incomplete endothelialization leading to late thrombosis, the need for long-term anti-platelet agents, and local hypersensitivity to polymer delivery matrices. In addition, the current DESs lack the capacity for adjustment of the drug dose and release kinetics appropriate to the disease status of the treated vessel. The development of efficacious therapeutic strategies to prevent and inhibit restenosis after PCI is critical for the treatment of coronary artery disease. The administration of drugs using biodegradable polymer nanoparticles as carriers has generated immense interest due to their excellent biocompatibility and ability to facilitate prolonged drug release. Despite the potential benefits of nanoparticles as smart drug delivery and diagnostic systems, much research is still required to evaluate potential toxicity issues related to the chemical properties of nanoparticle materials, as well as to their size and shape. This review describes the molecular mechanism of coronary restenosis, the use of DESs, and progress in nanoparticle drug- or gene-eluting stents for the prevention and treatment of coronary restenosis.

Femtosecond laser-patterned nanopore arrays for surface-mediated peptide treatment

The major goal of this study was to create easy-to-use, reusable substrates capable of storing any peptides or bioactive molecules for a desired period of time until cells uptake them without the need for bioactive molecule or peptide-specific techniques. Nanopore arrays of uniform size and distribution were machined into fused silica substrates using femtosecond laser ablation and loaded with peptides by simple adsorption. The nanopore substrates were validated by examining the effect of N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) loaded nanopores on macrophage phagocytosis and intracellular production of reactive oxygen species (ROS) with and without the pro-inflammatory lipopolysaccharide (LPS). Our results demonstrated that nanopores were generated in a uniform array fashion. Ac-SDKP peptides were stably stored in nanopores and internalized by macrophages. Significant reductions in ROS production and phagocytosis in macrophages were observed over control substrates, even in combination with LPS stimulation, indicating that loading Ac-SDKP peptides in pores significantly improved the anti-inflammatory effects.

FROM THE CLINICAL EDITOR

This team of scientists intended to create easy-to-use, reusable substrates for storing peptides or bioactive molecules for a desired period of time before cellular uptake occurs, and without the need for bioactive molecule or peptide-specific techniques. They demonstrate the successful generation of nanopores in a uniform array that stably stores Ac-SDKP peptides in the nanopores. When peptides were internalized by macrophages, significant reductions in ROS production and phagocytosis were observed, indicating improved anti-inflammatory effects.

Nanotopography-mediated reverse uptake for siRNA delivery into neural stem cells to enhance neuronal differentiation

RNA interference (RNAi) for controlling gene expression levels using siRNA or miRNA is emerging as an important tool in stem cell biology. However, the conventional methods used to deliver siRNA into stem cells result in significant cytotoxicity and undesirable side-effects. To this end, we have developed a nanotopography-mediated reverse uptake (NanoRU) delivery platform to demonstrate a simple and efficient technique for delivering siRNA into neural stem cells (NSCs). NanoRU consists of a self-assembled silica nanoparticle monolayer coated with extracellular matrix proteins and the desired siRNA. We use this technique to efficiently deliver siRNA against the transcription factor SOX9, which acts as a switch between neuronal and glial fate of NSCs. The knockdown of SOX9 enhanced the neuronal differentiation and decreased the glial differentiation of the NSCs. Our NanoRU platform demonstrates a novel application and the importance of nanotopography-mediated siRNA delivery into stem cells as an effective method for genetic manipulation.

Engineered nanomaterial uptake and tissue distribution: from cell to organism

Improved understanding of interactions between nanoparticles and biological systems is needed to develop safety standards and to design new generations of nanomaterials. This article reviews the molecular mechanisms of cellular uptake of engineered nanoparticles, their intracellular fate, and their distribution within an organism. We have reviewed the available literature on the uptake and disposition of engineered nanoparticles. Special emphasis was placed on the analysis of experimental systems and their limitations with respect to their usefulness to predict the in vivo situation. The available literature confirms the need to study particle characteristics in an environment that simulates the situation encountered in biological systems. Phenomena such as protein binding and opsonization are of prime importance since they may have a strong impact on cellular internalization, biodistribution, and immunogenicity of nanoparticles in vitro and in vivo. Extrapolation from in vitro results to the in vivo situation in the whole organism remains a challenge. However, improved understanding of physicochemical properties of engineered nanoparticles and their influence on biological systems facilitates the design of nanomaterials that are safe, well tolerated, and suitable for diagnostic or therapeutic use in humans.

Surface-mediated nucleic acid delivery by lipoplexes prepared in microwell arrays

Many delivery methods have been developed to improve the therapeutic efficacy and facilitate the clinical translation of nucleic acid-based therapeutics. A facile surface-mediated nucleic acid delivery by lipoplexes is prepared in a microwell array, which combines the advantages of lipoplexes as an efficient carrier system, surface-mediated delivery, and the control of surface topography. Uniform disc-like lipoplexes containing nucleic acids are formed in the microwell array with a diameter of ∼818 nm and thickness of ∼195 nm. The microwell array-mediated delivery of lipoplexes containing FAM-oligodeoxynucleotides is ∼18.6 and ∼10.6 times more efficient than the conventional transfection method in an adherent cell line (A549 non-small cell lung cancer cells) and a suspension cell line (KG-1a acute myelogenous leukemia cells), respectively. MicroRNA-29b is then used as a model nucleic acid to investigate the therapeutic efficacy of lipoplexes delivered by the microwell array. Compared to conventional transfection methods, the effective therapeutic dosage of microRNA-29b is reduced from the microgram level to the nanogram level by lipoplexes prepared in the microwell array. The microwell array is also a very flexible platform. Both nucleic acid therapeutics and imaging reagents are incorporated in lipoplexes and successfully delivered to A549 cells, demonstrating its potential applications in theranostic medicine.

Surface- and hydrogel-mediated delivery of nucleic acid nanoparticles

Gene expression within a cell population can be directly altered through gene delivery approaches. Traditionally for nonviral delivery, plasmids or siRNA molecules, encoding or targeting the gene of interest, are packaged within nanoparticles. These nanoparticles are then delivered to the media surrounding cells seeded onto tissue culture plastic; this technique is termed bolus delivery. Although bolus delivery is widely utilized to screen for efficient delivery vehicles and to study gene function in vitro, this delivery strategy may not result in efficient gene transfer for all cell types or may not identify those delivery vehicles that will be efficient in vivo. Furthermore, bolus delivery cannot be used in applications where patterning of gene expression is needed. In this chapter, we describe methods that incorporate material surfaces (i.e., surface-mediated delivery) or hydrogel scaffolds (i.e., hydrogel-mediated delivery) to efficiently deliver genes. This chapter includes protocols for surface-mediated DNA delivery focusing on the simplest and most effective methods, which include nonspecific immobilization of DNA complexes (both polymer and lipid vectors) onto serum-coated cell culture polystyrene and self-assembled monolayers of alkanethiols on gold. Also, protocols for the encapsulation of DNA/cationic polymer nanoparticles into hydrogel scaffolds are described, including methods for the encapsulation of low amounts of DNA (<0.2 μg/μL) and high amounts of DNA (>0.2 μg/μL) since incorporation of high amounts of DNA poses significant challenges due to aggregation.

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.

Microarray analysis of gene expression profiles in cells transfected with nonviral vectors

Inefficient gene delivery is a critical factor limiting the use of nonviral methods in therapeutic applications including gene therapy and tissue engineering. There have been few efforts to understand or engineer the molecular signaling pathways that dictate the efficacy of gene transfer. Microarray analysis was used to determine endogenous gene expression profiles modulated during nonviral gene transfer. Nonviral DNA lipoplexes were delivered to HEK 293T cells. Flow cytometry was used to isolate a population of transfected cells. Expression patterns were compared between transfected and nontransfected samples, which revealed three genes that were significantly upregulated in transfected cells, including RAP1A, a GTPase implicated in integrin-mediated cell adhesion, and HSP70B', a stress-inducible gene that may be important for maintaining cell viability. Furthermore, RAP1A was also significantly upregulated in untransfected cells that were exposed to lipoplexes but that had not expressed the transgene as compared to control, untreated cells. Transfection in the presence of activators of upregulated genes was enhanced, demonstrating the principle of altering endogenous gene expression profiles to enhance transfection. With a greater understanding of signaling pathways involved in gene delivery, more efficient nonviral delivery schemes capitalizing on endogenous factors can be developed to advance therapeutic applications.

Gene therapy vectors with enhanced transfection based on hydrogels modified with affinity peptides

Regenerative strategies for damaged tissue aim to present biochemical cues that recruit and direct progenitor cell migration and differentiation. Hydrogels capable of localized gene delivery are being developed to provide a support for tissue growth, and as a versatile method to induce the expression of inductive proteins; however, the duration, level, and localization of expression is often insufficient for regeneration. We thus investigated the modification of hydrogels with affinity peptides to enhance vector retention and increase transfection within the matrix. PEG hydrogels were modified with lysine-based repeats (K4, K8), which retained approximately 25% more vector than control peptides. Transfection increased 5- to 15-fold with K8 and K4 respectively, over the RDG control peptide. K8- and K4-modified hydrogels bound similar quantities of vector, yet the vector dissociation rate was reduced for K8, suggesting excessive binding that limited transfection. These hydrogels were subsequently applied to an in vitro co-culture model to induce NGF expression and promote neurite outgrowth. K4-modified hydrogels promoted maximal neurite outgrowth, likely due to retention of both the vector and the NGF. Thus, hydrogels modified with affinity peptides enhanced vector retention and increased gene delivery, and these hydrogels may provide a versatile scaffold for numerous regenerative medicine applications.

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.

Lentivirus delivery by adsorption to tissue engineering scaffolds

Biomaterial scaffolds capable of localized gene delivery are being investigated for numerous regenerative medicine applications and as model systems for fundamental studies of tissue formation. In this manuscript, we investigate the delivery of lentivirus from a tissue engineering scaffold using a surface immobilization strategy. Poly(lactide-co-glycolide) (PLG) was employed as the biomaterial for delivery, which has been widely used for a number of tissue engineering applications. The virus was immobilized by freezing and subsequent lyophilization of the virus with the scaffold. The presence of sucrose during freezing and lyophilization maintained the activity of the lentivirus, and was similar to an adenovirus control. Collagen and fibronectin were investigated for their ability to enhance surface immobilization. Fibronectin modestly increased binding and transduction of the adenovirus, yet did not significantly impact the lentivirus delivery. Most of the immobilized lentivirus was released from the scaffold within 24 h. In vivo implantation of the scaffolds yielded transgene expression that persisted for at least 4 weeks. These findings indicate the potential for delivering lentivirus from tissue engineering scaffolds using a surface immobilization strategy. To our knowledge, this report is the first to investigate lentivirus delivery from porous tissue engineering scaffolds. Delivery of lentiviral vectors from PLG scaffolds could provide an efficient and versatile gene delivery system for use with in vitro and in vivo models of tissue formation, and ultimately for therapeutic applications.

Emerging links between surface nanotechnology and endocytosis: impact on nonviral gene delivery

Significant effort continues to be exerted toward the improvement of transfection mediated by nonviral vectors. These endeavors are often focused on the design of particulate carriers with properties that encourage efficient accumulation at the membrane surface, particle uptake, and endosomal escape. Despite its demonstrated importance in successful nonviral transfection, relatively little investigation has been done to understand the pressures driving internalized vectors into favorable nondegradative endocytic pathways. Improvements in transfection efficiency have been noted for complexes delivered with a substrate-mediated approach, but the reasons behind such enhancements remain unclear. The phenotypic changes exhibited by cells interacting with nano- and micro-featured substrates offer hints that may explain these effects. This review describes nanoscale particulate and substrate parameters that influence both the uptake of nonviral gene carriers and the endocytic phenotype of interacting cells, and explores the molecular links that may mediate these interactions. Substrate-mediated control of endocytosis represents an exciting new design parameter that will guide the creation of efficient transgene carriers.

Biomineralized composite substrates increase gene expression with nonviral delivery

Current strategies to enhance gene transfer have focused on the development of vectors to increase the efficiency of DNA delivery. However, the extracellular matrix and microenvironment have a profound impact on numerous cellular activities including spreading and proliferation; two processes that have been associated with gene transfer efficiency. This study was designed to test the hypothesis that the presence of a biomineralized coating on biodegradable substrates would affect transgene expression following nonviral gene delivery. Thin films were prepared from polymeric microspheres, while biomineralized films were fabricated from microspheres previously soaked in modified simulated body fluid. Mineralized films were significantly more rigid and had widespread mineral coverage compared with nonmineralized substrates. Human mesenchymal stem cells (MSCs) were cultured on biomineralized or nonmineralized films and transfected with plasmid DNA condensed with linear polyethyleneimine (PEI). Compared with cells transfected on nonmineralized films, increases in gene expression were detected in the presence of biomineral at all charge ratios examined. We observed increased uptake of both PEI and DNA by cells on mineralized films. The results of these studies offer an approach to modulate gene delivery and improve the potential benefit of nonviral gene delivery approaches.

Localized cell uptake of His-tagged polyplexes immobilized on NTA self-assembled monolayers

A new method to study substrate-mediated gene delivery was developed using a hexahistidine-tagged polymeric gene delivery vehicle (His-tagged polyplex) and nickel nitrilotriacetic acid (Ni-NTA) self-assembled monolayers (SAMs) on gold surfaces. The His-tagged polyplexes showed specific interaction with Ni-NTA surfaces compared to control surfaces, with increasing NTA content in SAM formulations corresponding to increasing amounts of immobilized His-tagged polypexes on the surface. Cells seeded on NTA SAMs demonstrated uptake of His-tagged polyplexes in the presence of imidazole and EDTA with low cytotoxicity. Cells seeded on NTA SAMs without imidazole and EDTA showed minimal a amount of His-tagged polyplex uptake. This showed that the release of polyplexes from the surface by imidazole and EDTA was necessary for cell uptake. Thus, this system provides potential spatial specificity for polyplex delivery controlled by location of NTA surfaces and temporal specificity for polyplex delivery controlled by the addition of imidazole and EDTA.

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

Genetically modified bone marrow-derived mesenchymal stem cells (MSCs) have proven to be efficient cell carriers for local or systemic delivery of therapeutics as well as growth factors to augment tissue formation. However, efficient non-viral gene transfer to these cells is limiting their applicability. Although most studies have focused on designing more efficient condensation agents for DNA, our focus in this manuscript is to study the role of two extracellular matrix (ECM) proteins, collagen I (Col I) and fibronectin (Fn), on the ability of MSCs to become transfected. Here we report that plating MSCs on Col I-coated surfaces inhibits transfection, while plating MSCs on Fn-coated surfaces enhances transfection. The mechanism by which these ECM proteins affect non-viral gene transfer involves the endocytosis pathway used for polyplex uptake and intracellular tension. We found that Fn promoted internalization through clathrin-mediated endocytosis and that this pathway resulted in more efficient transfection than caveolae-mediated endocytosis and macropinocytosis. Further, the disruption of actin-myosin interactions resulted in an enhancement of gene transfer for cells plated on Fn-coated surfaces, but not for cells plated on Col I. We believe that the cellular microenvironment can be engineered to enhance the ability of cells to become transfected and that through understanding the mechanisms by which the ECM affects non-viral gene transfer better materials and transfection protocols can be realized.

Patterned transgene expression in multiple-channel bridges after spinal cord injury

Patterning of gene delivery on sub-millimeter length scales within tissue engineering scaffolds is fundamental to recreating the complex architectures of tissues. Surface-mediated delivery of lipoplexes mixed with fibronectin was investigated to pattern vectors within 250 microm channels in poly(lactide-co-glycolide) (PLG) bridges. Initial studies performed in vitro on PLG surfaces indicated that a DNA density of 0.07 microg mm(-2) inside each channel with a weight ratio of DNA to fibronectin of 1:20 maximized the number of transfected cells and the levels of transgene expression. Patterned vectors encoding for nerve growth factor (NGF) resulted in localized neurite extension within the channel. Translation to three-dimensional multiple-channel bridges enabled patterned transfection of different vectors throughout the channels for DNA:fibronectin ratios of 1:4 and multiple DNA depositions, with a large increase of neural cell bodies and neurite extension for delivery of DNA encoding for NGF. In vivo, the immobilization of non-viral vectors within the channels resulted in localized transfection within the pore structure of the bridge immediately around the channels of the bridge containing DNA. This surface immobilization strategy enables patterned gene delivery in vitro and in vivo on length scales of hundreds of microns and may find utility in strategies aimed at regenerating tissues with complex architectures.

Highly efficient gene transfer system using a laminin-DNA-apatite composite layer

BACKGROUND

We have recently developed a safe and efficient gene transfer system using a laminin-DNA-apatite composite layer. The objectives of the present study were to fully characterize and optimize the laminin-DNA-apatite composite layer in relation to the efficiency of gene transfer and to demonstrate the feasibility of the composite layer in the induction of cell differentiation.

METHODS

The laminin-DNA-apatite composite layer was prepared under various conditions. The efficiency of gene transfer on the resulting composite layer was evaluated using luciferase and ss-galactosidase gene expression assay systems. A laminin-DNA-apatite composite layer, prepared under the optimized condition using a plasmid including cDNA of nerve growth factor (NGF), was then applied to the neuron-like differentiation of PC12 cells.

RESULTS

The laminin content of the laminin-DNA-apatite composite layer was found to be a dominant factor improving the efficiency of gene transfer rather than the DNA content. The cell adhesion property of laminin in the composite layer should be responsible for the improvement in efficiency of gene transfer because the immobilization of albumin without the cell adhesion property in a DNA-apatite composite layer had no effect on the efficiency of gene transfer. A laminin-DNA-apatite composite layer, prepared under the optimized condition using a plasmid including cDNA of NGF, successfully induced the neuron-like differentiation of PC12 cells.

CONCLUSIONS

The present gene transfer system, with the potential to control cell differentiation and having features of safety and relatively high and controllable efficiency, would be a useful tool for tissue engineering applications and the production of transfection microarrays.

Fibrin-mediated lentivirus gene transfer: implications for lentivirus microarrays

We employed fibrin hydrogel as a bioactive matrix for lentivirus mediated gene transfer. Fibrin-mediated gene transfer was highly efficient and exhibited strong dependence on fibrinogen concentration. Efficient gene transfer was achieved with fibrinogen concentration between 3.75 and 7.5mg/ml. Lower fibrinogen concentrations resulted in diffusion of virus out of the gel while higher concentrations led to ineffective fibrin degradation by target cells. Addition of fibrinolytic inhibitors decreased gene transfer in a dose-dependent manner suggesting that fibrin degradation by target cells may be necessary for successful gene delivery. Under these conditions transduction may be limited only to cells interacting with the matrix thereby providing a method for spatially-localized gene delivery. Indeed, when lentivirus-containing fibrin microgels were spotted in an array format gene transfer was confined to virus-containing fibrin spots with minimal cross-contamination between neighboring sites. Collectively, our data suggest that fibrin may provide an effective matrix for spatially-localized gene delivery with potential applications in high-throughput lentiviral microarrays and in regenerative medicine.

Engineering surfaces for substrate-mediated gene delivery using recombinant proteins

Immobilized fibronectin and other natural proteins have been utilized to enhance substrate-mediated gene delivery, with apparent contributions from the intrinsic bioactivity and also physical properties of the immobilized proteins. In this report, we investigated the use of recombinant proteins, compared to the full-length fibronectin protein, as surface coatings for gene delivery to investigate the mechanisms by which fibronectin enhances gene transfer. The recombinant fibronectin fragment FNIII(7-10) (FNIII) contains the alpha(5)beta(1) binding domain of fibronectin and supports cell adhesion, whereas the recombinant protein polymer PP-12 is also negatively charged and has a molecular weight similar to FNIII, but lacks cell binding domains. Transfection was compared on surfaces modified with FNIII, full-length fibronectin, or PP-12. The full-length fibronectin provided the greatest extent of transgene expression relative to FNIII or PP-12, which was consistent with the amount of DNA that associated with cells. FNIII had 4.2-fold or 4.7-fold lower expression levels relative to fibronectin for polyplexes and lipoplexes, respectively. PP-12 produced expression levels that were 317-fold and 12.0-fold less than fibronectin for polyplexes and lipoplexes, respectively. Although expression was greater on FNIII relative to PP-12, the levels of DNA associated per cell with FNIII were similar to or less than those with PP-12, suggesting that the bioactive sequences may contribute to an enhanced intracellular trafficking. For lipoplexes delivered on FNIII, the efficiency of intracellular trafficking and levels of caveolar DNA were greater than that observed with either the full-length fibronectin or PP-12. For polyplexes, fibronectin fragment resulted in greater intracellular trafficking efficiency compared to PP-12 protein polymer. Recombinant proteins can be employed in place of full-length extracellular matrix proteins for substrate-mediated gene delivery, and bioactive sequences can influence one or more steps in the gene delivery process to maximize transfection.

Transfection of myeloid leukaemia cell lines is distinctively regulated by fibronectin substratum

Gene transfer into haematopoietic cells is a challenging approach. The extracellular matrix component fibronectin has been known to modulate the cell cycle dynamics, viability and differentiation of leukaemia cells. Thus, our aim was to investigate the influence of fibronectin substratum on the liposomal transfection of myeloid leukaemia cell lines. Liposomal transfection was performed with K562 and HL-60 as representative lines of transfection-competent and -incompetent myeloid leukaemia cells, respectively. Flow cytometry analyses were performed to determine transfection efficiency monitored by green fluorescent protein (GFP) expression and to assess cell viability and cell cycle status. Quantitation of GFP gene expression and DNA uptake was assayed by real time PCR. The current data showed that the adhesion to fibronectin deteriorated the transfection of K562 cells. In contrary, it enhanced the delivery of plasmid DNA into HL-60 cells. Correspondingly, the adhesion to fibronectin influenced the transfection efficiency mainly by modulating the intracellular presence of plasmid DNA. The cell cycle and viability which is regulated by fibronectin had a minor impact on the success of gene delivery. This phenomenon may be considered as an important factor which may modulate the potential gene transfer approaches for myeloid leukaemia.

Efficacy of immobilized polyplexes and lipoplexes for substrate-mediated gene delivery

Non-viral gene delivery by immobilization of complexes to cell-adhesive biomaterials, a process termed substrate-mediated delivery, has many in vitro research applications such as transfected cell arrays or models of tissue growth. In this report, we quantitatively investigate the efficiency of gene delivery by surface immobilization, and compare this efficiency to the more typical bolus delivery. The ability to immobilize vectors while allowing cellular internalization is impacted by the biomaterial and vector properties. Thus, to compare this efficiency between vector types and delivery methods, transfection conditions were initially identified that maximized transgene expression. For surface delivery from tissue culture polystyrene, DNA complexes were immobilized to pre-adsorbed serum proteins prior to cell seeding, while for bolus delivery, complexes were added to the media above adherent cells. Mathematical modeling of vector binding, release, and cell association using a two-site model indicated that the kinetics of polyplex binding to cells was faster than for lipoplexes, yet both vectors have a half-life on the surface of approximately 17 min. For bolus and surface delivery, the majority of the DNA in the system remained in solution or on the surface, respectively. For polyplexes, the efficiency of trafficking of cell-associated polyplexes to the nucleus for surface delivery is similar or less than bolus delivery, suggesting that surface immobilization may decrease the activity of the complex. The efficiency of nuclear association for cell-associated lipoplexes is similar or greater for surface delivery relative to bolus. These studies suggest that strategies to enhance surface delivery for polyplexes should target the vector design to enhance its potency, whereas enhancing lipoplex delivery should target the material design to increase internalization.

The use of reactive polymer coatings to facilitate gene delivery from poly (epsilon-caprolactone) scaffolds

To functionalize biomaterials for bioconjugation, a chemical vapor deposition (CVD) polymerization technique was utilized to modify material surfaces. Poly [(4-amino-p-xylylene)-co-(p-xylylene)] (PPX-NH(2)) was deposited on inert polycaprolactone (PCL) surfaces to provide a reactive amine layer on the substrate surfaces. The biocompatibility of PPX-NH(2) was evaluated by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) and lactate dehydrogenase (LDH) assays. The results demonstrated that cells continuously proliferated on CVD treated PCL surfaces with high survival rates. Biotin was conjugated on modified PCL surfaces to immobilize avidin for binding of biotinylated adenovirus. Scanning electron microscopy (SEM) examination illustrated that adenoviruses were evenly bound on both 2-D films and 3-D scaffolds, suggesting CVD was capable of modifying various substrates with different geometries. Using a wax masking technique, the biotin conjugation was controlled to immobilize avidin on specific sites. Due to the virus binding specificity on CVD-modified surfaces, cell transduction was restricted to the pattern of immobilized virus on biomaterials, by which transduced and non-transduced cells were controlled in different regions with a distinct interface. Because CVD was functional in different hierarchies, this surface modification should be able to custom-tailor bioconjugation for different applications.

Tissue-specific extracellular matrix coatings for the promotion of cell proliferation and maintenance of cell phenotype

Recent studies have shown that extracellular matrix (ECM) substitutes can have a dramatic impact on cell growth, differentiation and function. However, these ECMs are often applied generically and have yet to be developed for specific cell types. In this study, we developed tissue-specific ECM-based coating substrates for skin, skeletal muscle and liver cell cultures. Cellular components were removed from adult skin, skeletal muscle, and liver tissues, and the resulting acellular matrices were homogenized and dissolved. The ECM solutions were used to coat culture dishes. Tissue matched and non-tissue matched cell types were grown on these coatings to assess adhesion, proliferation, maintenance of phenotype and cell function at several time points. Each cell type showed better proliferation and differentiation in cultures containing ECM from their tissue of origin. Although subtle compositional differences in the three ECM types were not investigated in this study, these results suggest that tissue-specific ECMs provide a culture microenvironment that is similar to the in vivo environment when used as coating substrates, and this new culture technique has the potential for use in drug development and the development of cell-based therapies.

Cell-controlled and spatially arrayed gene delivery from fibrin hydrogels

We investigated fibrin-mediated gene transfer by embedding pDNA within the hydrogel during polymerization and using two modes of gene transfection with cells placed either on the surface (2D transfection) or within the hydrogel (3D transfection). Using this model, we found that cell transfection depended strongly on the local cell-pDNA microenvironment as defined by the 2D vs. 3D context, target cell type and density, as well as fibrinogen and pDNA concentrations. When cells were embedded within the fibrin matrix lipofectamine-induced cell death decreased significantly, especially at low target cell density. Addition of fibrinolytic inhibitors decreased gene transfer in a dose-dependent manner, suggesting that fibrin degradation may be necessary for efficient gene transfer. We also provided proof-of-concept that fibrin-mediated gene transfer can be used for spatially localized gene delivery, which is required in cell-transfection microarrays. When lipoplex-containing hydrogels were spotted in an array format gene transfer was strictly confined to pDNA-containing fibrin spots with no cross-contamination between neighboring sites. Collectively, our data suggest that fibrin may be used as a biomaterial to deliver genes in an efficient, cell-controlled and spatially localized manner for potential applications in vitro or in vivo.