Nonviral gene transfer into fetal mouse livers (a comparison between the cationic polymer PEI and naked DNA)

Polyethylenimine (PEI) in gene therapy: Current status and clinical applications

Polyethlyenimine (PEI) was introduced 1995 as a cationic polymer for nucleic acid delivery. PEI and its derivatives are extensively used in basic research and as reference formulations in the field of polymer-based gene delivery. Despite its widespread use, the number of clinical applications to date is limited. Thus, this review aims to consolidate the past applications of PEI in DNA delivery, elucidate the obstacles that hinder its transition to clinical use, and highlight potential prospects for novel iterations of PEI derivatives. The present review article is divided into three sections. The first section examines the mechanism of action employed by PEI, examining fundamental aspects of cellular delivery including uptake mechanisms, release from endosomes, and transport into the cell nucleus, along with potential strategies for enhancing these delivery phases. Moreover, an in-depth analysis is conducted concerning the mechanism underlying cellular toxicity, accompanied with approaches to overcome this major challenge. The second part is devoted to the in vivo performance of PEI and its application in various therapeutic indications. While systemic administration has proven to be challenging, alternative localized delivery routes hold promise, such as treatment of solid tumors, application as a vaccine, or serving as a therapeutic agent for pulmonary delivery. In the last section, the outcome of completed and ongoing clinical trials is summarized. Finally, an expert opinion is provided on the potential of PEI and its future applications. PEI-based formulations for nucleic acid delivery have a promising potential, it will be an important task for the years to come to introduce innovations that address PEI-associated shortcomings by introducing well-designed PEI formulations in combination with an appropriate route of administration.

Lyophilization enabled disentanglement of polyethylenimine on rambutan-like silica nanoparticles for enhanced plasmid DNA delivery

Polyethylenimine (PEI) functionalization onto nanoparticles is a widely used strategy for constructing particulate vectors for gene delivery. However, how to control the conformation of PEI chains and the resultant impact on gene transfection efficiency remains largely unexplored. Herein, we report that drying methods dramatically affect the conformation of PEI chains modified on the surface of silica nanoparticles and consequently the plasmid DNA transfection performance. Specifically, lyophilization renders less entangled PEI compared to commonly used vacuum drying as evidenced by an elevated glass transition temperature. The lyophilization induced disentangled conformation is likely associated with the solid-to-gas phase transition drying mechanism, which removes the bound crystal water content and thus reduces hydrogen bonding between amines. Moreover, we find that the stretched PEI chains on the surface of rambutan-like silica nanoparticles promote their binding capacity towards plasmid DNA molecules and thereby enhanced gene delivery and transfection efficiency. Our findings have provided new understanding about amine based polymers modified on nanoparticles, and have significant implications on the design of efficient particulate vectors for gene delivery.

Polyethylenimine-based micro/nanoparticles as vaccine adjuvants

Vaccines have shown great success in treating and preventing tumors and infections, while adjuvants are always demanded to ensure potent immune responses. Polyethylenimine (PEI), as one of the well-studied cationic polymers, has been used as a transfection reagent for decades. However, increasing evidence has shown that PEI-based particles are also capable of acting as adjuvants. In this paper, we briefly review the physicochemical properties and the broad applications of PEI in different fields, and elaborate on the intracellular processes of PEI-based vaccines. In addition, we sum up the proof of their in vivo and clinical applications. We also highlight some mechanisms proposed for the intrinsic immunoactivation function of PEI, followed by the challenges and future perspectives of the applications of PEI in the vaccines, as well as some strategies to elicit the desirable immune responses.

Antisense precision polymer micelles require less poly(ethylenimine) for efficient gene knockdown

Therapeutic nucleic acids are powerful molecules for shutting down protein expression. However, their cellular uptake is poor and requires transport vectors, such as cationic polymers. Of these, poly(ethylenimine) (PEI) has been shown to be an efficient vehicle for nucleic acid transport into cells. However, cytotoxicity has been a major hurdle in the development of PEI-DNA complexes as clinically viable therapeutics. We have synthesized antisense-polymer conjugates, where the polymeric block is completely monodisperse and sequence-controlled. Depending on the polymer sequence, these can self-assemble to produce micelles of very low polydispersity. The introduction of linear poly(ethylenimine) to these micelles leads to aggregation into size-defined PEI-mediated superstructures. Subsequently, both cellular uptake and gene silencing are greatly enhanced over extended periods compared to antisense alone, while at the same time cellular cytotoxicity remains very low. In contrast, gene silencing is not enhanced with antisense polymer conjugates that are not able to self-assemble into micelles. Thus, using antisense precision micelles, we are able to achieve significant transfection and knockdown with minimal cytotoxicity at much lower concentrations of linear PEI then previously reported. Consequently, a conceptual solution to the problem of antisense or siRNA delivery is to self-assemble these molecules into 'gene-like' micelles with high local charge and increased stability, thus reducing the amount of transfection agent needed for effective gene silencing.

Citrate-Based Biomaterials and Their Applications in Regenerative Engineering

Advances in biomaterials science and engineering are crucial to translating regenerative engineering, an emerging field that aims to recreate complex tissues, into clinical practice. In this regard, citrate-based biomaterials have become an important tool owing to their versatile material and biological characteristics including unique antioxidant, antimicrobial, adhesive, and fluorescent properties. This review discusses fundamental design considerations, strategies to incorporate unique functionality, and examples of how citrate-based biomaterials can be an enabling technology for regenerative engineering.

Stimulation of gene transfection by silicon nanowire arrays modified with polyethylenimine

In this work, a novel gene delivery strategy was proposed based on silicon nanowire arrays modified with high-molecular-weight 25 kDa branched polyethylenimine (SN-PEI). Both the plasmid DNA (pDNA) binding capacity and the in vitro gene transfection efficiency of silicon nanowire arrays (SiNWAs) were significantly enhanced after modification with high-molecular-weight bPEI. Moreover, the transfection efficiency was substantially further increased by the introduction of free pDNA/PEI complexes formed by low-molecular-weight branched PEI (bPEI, 2 kDa). Additionally, factors affecting the in vitro transfection efficiency of the novel gene delivery system were investigated in detail, and the transfection efficiency was optimized on SN-PEI with a bPEI grafting time of 3 h, an incubation time of 10 min for tethered pDNA/PEI complexes consisting of high-molecular-weight bPEI grafted onto SiNWAs, and with an N/P ratio of 80 for free pDNA/PEI complexes made of low-molecular-weight bPEI. Together, our results indicate that high-molecular-weight bPEI modified SiNWAs can serve as an efficient platform for gene delivery.

A polyethylenimine-linoleic acid conjugate for antisense oligonucleotide delivery

A novel antisense oligonucleotide (ASO) carrier, polyethylenimine conjugated to linoleic acid (PEI-LA), was synthesized and evaluated for delivery of LOR-2501 to tumor cells. LOR-2501 is an ASO targeting ribonucleotide reductase R1 subunit (RRM1). In this study, PEI-LA was synthesized by reacting PEI (Mw ~ 800) with linoleoyl chloride. Gel retardation assay showed complete complexation between PEI-LA and LOR-2501 at N/P ratio above 8. No significant cytotoxicity was observed with these complexes at the tested dosage levels. Interestingly, at N/P ratio of >6, levels of cellular uptake of PEI-LA/LOR-2501 were double that of PEI/LOR-2501 complexes of the same N/P ratio. PEI-LA/LOR-2501 induced downregulation of 64% and 70% of RRM1 at mRNA and protein levels, respectively. The highest transfection activity was shown by PEI-LA/LOR-2501 complexes at N/P ratio of 10. Finally, using pathway specific inhibitors, clathrin-mediated endocytosis was shown to be the principle mechanism of cellular internalization of these complexes. In conclusion, PEI-LA is a promising agent for the delivery of ASOs and warrants further investigation.

Transgene therapy for rat anti-Thy1.1 glomerulonephritis via mesangial cell vector with a polyethylenimine/decorin nanocomplex

Polyethylenimine (PEI), a cationic polymer, is one of the most efficient non-viral vectors for transgene therapy. Decorin (DCN), a leucine-rich proteoglycan secreted by glomerular mesangial cells (MC), is a promising anti-fibrotic agent for the treatment of glomerulonephritis. In this study, we used PEI-DCN nanocomplexes with different N/P ratios to transfect MC in vitro and deliver the MC vector with PEI-DCN expressing into rat anti-Thy1.1 nephritis kidney tissue via injection into the left renal artery in vivo. The PEI-plasmid DNA complex at N/P 20 had the highest level of transfection efficiency and the lowest level of cytotoxicity in cultured MC. Following injection, the ex vivo gene was transferred successfully into the glomeruli of the rat anti-Thy1.1 nephritis model by the MC vector with the PEI-DCN complex. The exogenous MC with DCN expression was located mainly in the mesangium and the glomerular capillary. Over-expression of DCN in diseased glomeruli could result in the inhibition of collagen IV deposition and MC proliferation. The pathological changes of rat nephritis were alleviated following injection of the vector. These findings demonstrate that the DCN gene delivered by the PEI-DNA nanocomplex with the MC vector is a promising therapeutic method for the treatment of glomerulonephritis.

Vector systems for prenatal gene therapy: principles of non-viral vector design and production

Gene therapy vectors based on viruses are the most effective gene delivery systems in use today and although efficient at gene transfer their potential toxicity (Hacein-Bey-Abina et al., Science 302:415-419, 2003) provides impetus for the development of safer non-viral alternatives. An ideal vector for human gene therapy should deliver sustainable therapeutic levels of gene expression without affecting the viability of the host at either the cellular or somatic level. Vectors, which comprise entirely human elements, may provide the most suitable method of achieving this. Non-viral vectors are attractive alternatives to viral gene delivery systems because of their low toxicity, relatively easy production, and great versatility. The development of more efficient, economically prepared, and safer gene delivery vectors is a crucial prerequisite for their successful clinical application and remains a primary strategic task of gene therapy research.

Hepatocyte-targeted psiRNA delivery mediated by galactosylated poly(ethylene glycol)-graft-polyethylenimine in vitro

Gene silencing in liver disease could be achieved by delivering siRNA with nonviral vectors. However, the transfection efficiency of plasmid siRNA (psiRNA) applied through this approach in hepatocytes is generally low. Based on the fact that the asialoglycoprotein receptors present on hepatocytes can recognize galactose, we synthesized galactosylated poly(ethylene glycol)-graft-polyethylenimine (Gal-PEG-PEI) as a nonviral psiRNA carrier for hepatocyte targeting. Our results indicate that 0.2% (molar percentage) of amine groups of PEI was conjugated with PEG having galactose on its distal end. Increasing the molar ratios of Gal-PEG-PEI to psiRNA in complexation led to a decrease in particle size but an increase in zeta potential of complexes. The transfection efficiency of nanocomplexes, that is, Gal-PEG-PEI/psiRNA, in HepG2 cell line depends on the N/P value, which reflects the molar ratio of Gal-PEG-PEI to psiRNA in the complex. The highest transfection efficiency was 37.34%, which was obtained at N/P 8. At the same N/P value, the transfection efficiency with the nontargeting PEG-PEI/psiRNA or Lipofectamine 2000/psiRNA was much lower. The transfection efficiency of Gal-PEG-PEI/psiRNA dropped to 3.60% from 37.34% after an excessive amount of free galactose was added into the medium for HepG2 cell incubation. By contrast, the similar phenomenon was observed neither when using PEG-PEI or Lipofectamine 2000 as a delivery vector nor in human embryonic kidney 293 cell line lacking ASGR. Real-time PCR analysis and western blot assay demonstrate that the knockdown of HLA-E gene expression by psiRNA/Gal-PEG-PEI (N/P 8) can reach about 60% in HepG2 cells after a 48-h transfection.

Systemic gene transfer of polyethylenimine (PEI)-plasmid DNA complexes to neonatal mice

Non-viral vectors have not been extensively investigated in neonatal mice due to the poor efficiency of the delivery methods available. Understanding the effects of non-viral vectors during early development is vital to develop safe gene therapy treatments where irreversible pathological processes may be avoided by early gene reconstitution. Here we describe a simple and effective method for the systemic administration of non-viral vectors via the superior temporal vein of mouse pups at 1.5 days of age. We show that injection of polyethylenimine (PEI)-complexed plasmid DNA (pDNA) intravenously results in effective transfection in the liver, lung, heart, spleen, brain and kidney. We also investigate the specific targeting of transgene expression to the proliferating neonate liver using a liver-specific plasmid containing a Scaffold Matrix Attachment Region (S/MAR) element, which has previously been shown to confer long-term expression in adult mouse liver. Using bioluminescent imaging, a gradual increase in transgene expression was observed which peaked at days 11-12, before the reduction of expression to background levels by day 25, suggestive of vector copy number loss. We conclude that non-viral vectors can successfully be used for systemic delivery to neonatal mice and that this technique is likely to open a host of early therapeutic possibilities for gene transfer by a range of non-viral vector formulations.

Chemically modified cell-penetrating peptides for the delivery of nucleic acids

Short nucleic acids targeting biologically important RNAs and plasmids have been shown to be promising future therapeutics; however, their hydrophilic nature greatly limits their utility in clinics and therefore efficient delivery vectors are greatly needed. Cell-penetrating peptides (CPPs) are relatively short amphipathic and/or cationic peptides that are able to transport various biologically active molecules inside mammalian cells, both in vitro and in vivo, in a seemingly non-toxic fashion. Although CPPs have proved to be appealing drug delivery vehicles, their major limitation in nucleic acid delivery is that most of the internalized peptide-cargo is entrapped in endosomal compartments following endocytosis and the bioavailability is therefore severely reduced. Several groups are working towards overcoming this obstacle and this review highlights the evidence that by introducing chemical modification in CPPs, the bioavailability of delivered nucleic acids increases significantly.

Vault nanoparticles containing an adenovirus-derived membrane lytic protein facilitate toxin and gene transfer

Nonviral methods of gene delivery possess several advantages over that of viral-based vectors, including having increased safety. However, the ability to achieve effective transport of therapeutic molecules across host cell membranes via nonviral methods remains a significant goal. Cell-derived nanoparticles known as vaults have been proposed as novel candidate transfer vehicles for various foreign molecules. Recombinant vault particles enter cells via macropinocytosis or phagocytosis but lack demonstrable membrane penetrating activity. To explore the feasibility of improving vault penetration into target cells, we incorporated the membrane lytic domain of adenovirus protein VI (pVI) into the interior of recombinant vault particles via fusion to the vault poly(ADP-ribose) polymerase (VPARP) interaction domain. The membrane lytic activity of the pVI domain was retained upon incorporation into vault particles. Moreover, internalization of vault-pVI complexes into murine macrophages promoted co-delivery of a soluble ribotoxin or a cDNA plasmid encoding GFP. These findings indicate that vault particles can be modified to enhance cell transfer of selected biomolecules.

Polymeric Materials for Gene Delivery and DNA Vaccination

Gene delivery holds great potential for the treatment of many different diseases. Vaccination with DNA holds particular promise, and may provide a solution to many technical challenges that hinder traditional vaccine systems including rapid development and production and induction of robust cell-mediated immune responses. However, few candidate DNA vaccines have progressed past preclinical development and none have been approved for human use. This Review focuses on the recent progress and challenges facing materials design for nonviral DNA vaccine drug delivery systems. In particular, we highlight work on new polymeric materials and their effects on protective immune activation, gene delivery, and current efforts to optimize polymeric delivery systems for DNA vaccination.

Influence of murine hepatitis induced by D-(+)-galactosamine hydrochloride and lipopolysaccharide on gene expression of polyethylenimine/plasmid DNA polyplex

We investigated the influence of murine hepatitis induced by D-(+)-galactosamine and lipopolysaccharide (D-GalN/LPS) on polyethylenimine (PEI)-mediated plasmid DNA (pDNA) delivery. pDNA encoding firefly luciferase was used as the model reporter gene. PEI was used as the non-viral vector because of its high gene expression and low toxicity. The activities of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in mice indicated the highest peaks at 12 h after D-GalN/LPS injection, then the activities of serum ALT and AST rapidly decreased. We determined luciferase activity in various organs of D-GalN/LPS-treated mice and control mice after an intravenous administration of PEI/pDNA complexes. High transgene expression was observed in the liver, spleen, and lung of both mice. Compared to the control mice, a significant increase of transgene expression was observed in the liver of D-GalN/LPS-treated mice after D-GalN/LPS injection. The transgene expression in the spleen and lung decreased at 6 and 12 h after D-GalN/LPS injection. In conclusion, we found that murine hepatitis induced by D-GalN/LPS injection can influence PEI-mediated pDNA delivery and its influence was different from that induced by CCl(4) injection which was reported previously. These results demonstrated the necessity of considering the timing and dose of gene therapy according to the disease and its stage.

Characterization of the transgene expression generated by branched and linear polyethylenimine-plasmid DNA nanoparticles in vitro and after intraperitoneal injection in vivo

Polyethylenimine (PEI) is a cationic polymer that has shown significant potential for delivering genes in vitro and in vivo. Mixing cationic PEI with negatively charged plasmid DNA (pDNA) results in the spontaneous electrostatic formation of stable nanoparticle complexes. The structure of PEI can be branched or linear. In this study, we show that branched PEI has a stronger electrostatic interaction with pDNA than linear PEI, which accounts for greater compaction, higher zeta potentials and smaller nanoparticle sizes at equivalent pDNA concentrations. For both linear and branched PEI, increasing the concentration of pDNA mixed in the same volume and at the same nitrogen to phosphate (N:P) ratio results in larger average particle sizes. Increasing the N:P ratio increases luciferase activity generated by branched PEI-pDNA nanoparticles and linear PEI-pDNA nanoparticles in HEK293, COS7 and HeLa cell lines. Increasing the N:P ratio at which branched PEI-pDNA nanoparticles are prepared also increases luciferase expression in HepG2 cells but does not increase luciferase expression generated by linear PEI-pDNA nanoparticles. In all of the cell lines, branched PEI-pDNA nanoparticles prepared at N:P ratios of 10 and above generated significantly higher luciferase activity than linear PEI-pDNA nanoparticles. Luciferase activity was highest in the HEK293 cells and luciferase expression in each of the cell lines followed the order of HEK293>COS7>HepG2>HeLa. Intraperitoneal (IP) injection of PEI-pDNA nanoparticles is attractive because it is simple, reproducible and often leads to a depot effect of nanoparticle complexes residing in the peritoneum. The IP route of administration avoids PEI-pDNA nanoparticle accumulation in the lung and the nanoparticles do not pass through the blood-brain barrier. In this study, using bioluminescent imaging (BLI), we show that changing the PEI structure and dose of the PEI-pDNA nanoparticles has a significant impact on the strength and duration of transgene expression after IP injection in vivo but increasing the N:P ratio does not. Increasing the dose and N:P ratio for all the PEI-pDNA nanoparticle formulations injected IP did not reduce mice survival and all mice remained in good health as determined by the Body Condition Scoring (BCS) technique.

Extracellular barriers to in Vivo PEI and PEGylated PEI polyplex-mediated gene delivery to the liver

Polyplex-mediated gene therapy is a promising alternative to viral gene therapy. One challenge to these synthetic carriers is reduced transfection efficiencies in vivo compared to those achieved in vitro. Many of the intracellular barriers to gene delivery have been elucidated, but similar quantification of extracellular barriers to gene delivery remains a need. In this study, the unpackaging of polyplexes by serum proteins, soluble glycosaminoglycans, and an extracellular matrix extract was demonstrated by a YOYO-1 fluorescence quenching assay. Additionally, exposing polyplexes to serum or proteoglycans before in vitro transfection caused decreased cellular uptake of DNA. Lastly, PEI polyplexes and PEGylated PEI polyplexes were injected into the portal vein of mice, and the intrahepatic distributions of labeled DNA and polymer were assessed by confocal microscopy. PEI polyplexes delivered DNA to the liver, but extensive vector unpackaging was observed, with PEI primarily colocalized with the extracellular matrix. PEGylated polyplexes mediated less DNA delivery to the liver, possibly due to premature vector unpackaging in the blood. Through this work, both the blood and the extracellular matrix have been determined to be significant extracellular barriers to polyplex-mediated in vivo gene delivery to the liver.

Polyethylenimine-DNA solid particles for gene delivery

Polyethylenimine (PEI), a cationic polymer, was used to develop a non-viral vector for gene delivery. A simple, reproducible process is described with which to condense plasmid DNA with PEI. When prepared at the optimum charge ratio of 6.3 ( +/- ; PEI:DNA, 5:1 w/w), PEI-DNA complexes were 30-60 nm in diameter and excluded intercalating dyes from the plasmid DNA. The particles were stable for more than one month at 4 degrees C with respect to size and transfection activity. PEI-condensed DNA transfected a broad range of murine and human tumor cell lines (B16, Lewis Lung, SK-OV-3 and LS180) in vitro in the presence of fetal calf serum. Intraperitoneal administration of PEI-condensed DNA resulted in significant gene expression in a human ovarian cancer peritoneal xenograft model.

Gene therapy for the fetus: is there a future?

Gene therapy uses the intracellular delivery of genetic material for the treatment of disease. A wide range of diseases - including cancer, vascular and neurodegenerative disorders and inherited genetic diseases - are being considered as targets for this therapy in adults. There are particular reasons why fetal application might prove better than application in the adult for treatment, or even prevention of early-onset genetic disorders such as cystic fibrosis and Duchenne muscular dystrophy. Research shows that gene transfer to the developing fetus targets rapidly expanding populations of stem cells, which are inaccessible after birth, and indicates that the use of integrating vector systems results in permanent gene transfer. In animal models of congenital disease such as haemophilia, studies show that the functionally immature fetal immune system does not respond to the product of the introduced gene, and therefore immune tolerance can be induced. This means that treatment could be repeated after birth, if that was necessary to continue to correct the disease. For clinicians and parents, fetal gene therapy would give a third choice following prenatal diagnosis of inherited disease, where termination of pregnancy or acceptance of an affected child are currently the only options. Application of this therapy in the fetus must be safe, reliable and cost-effective. Recent developments in the understanding of genetic disease, vector design, and minimally invasive delivery techniques have brought fetal gene therapy closer to clinical practice. However more research needs to be done in before it can be introduced as a therapy.

Gene delivery to differentiated neurotypic cells with RGD and HIV Tat peptide functionalized polymeric nanoparticles

A number of neurodegenerative disorders may potentially be treated by the delivery of therapeutic genes to neurons. Nonviral gene delivery systems, however, typically provide low transfection efficiency in post-mitotic differentiated neurons. To uncover mechanistic reasons for this observation, we compared gene transfer to undifferentiated and differentiated SH-SY5Y cells using polyethylenimine (PEI)/DNA nanocomplexes. Differentiated cells exhibited substantially lower uptake of gene vectors. To overcome this bottleneck, RGD or HIV-1 Tat peptides were attached to PEI/DNA nanocomplexes via poly(ethylene glycol) (PEG) spacer molecules. Both RGD and Tat improved the cellular uptake of gene vectors and enhanced gene transfection efficiency of primary neurons up to 14-fold. RGD functionalization resulted in a statistically significant increase in vector escape from endosomes, suggesting it may improve gene delivery by more than one mechanism.

Influence of disease stage on polyethylenimine-mediated plasmid DNA delivery in murine hepatitis

In order to determine the influence of hepatic disease-stage on polyethylenimine-mediated gene delivery, we investigated branched and linear polyethylenimine (B-PEI, L-PEI)-mediated plasmid DNA delivery with time in murine hepatitis induced by a subcutaneous injection of tetrachloro carbon (CCl(4)). Plasmid DNA (pDNA) encoding firefly luciferase was used as the model reporter gene. We determined luciferase activity in various organs of CCl(4)-treated mice and control mice after an intravenous administration of B-PEI and L-PEI/pDNA complexes. Both B-PEI and L-PEI/pDNA complexes showed significantly lower gene expression in the liver, spleen, and lung at the stage of severe hepatitis (18 h after CCl(4) injection), whereas the complexes induced gene expression in the liver at the liver regeneration stage (48 h after CCl(4) injection). Significant differences in gene expressions between CCl(4)-treated mice and control mice vanished in most organs at the hepatitis subsidence stage (168 h after CCl(4) injection), indicating that the influence of hepatitis induced by CCl(4) was reversible with PEI-mediated gene delivery. Our findings demonstrated that murine hepatitis induced by CCl(4) could influence polyethylenimine-mediated plasmid DNA delivery according to the disease stage. These results indicate the necessity of considering the timing and dose of gene therapy according to the disease stage.

Regional gene therapy for full-thickness articular cartilage lesions using naked DNA with a collagen matrix

A novel gene therapy approach for treating damaged cartilage is proposed that involves placing endotoxin-free cDNA containing the gene for bone morphogenetic protein-2 (BMP-2) in type I collagen sponges and then transferring the naked plasmid DNA construct to the injury site. A full-thickness cartilaginous defect in rabbits implanted with plasmid containing a marker gene (beta-galactosidase) showed expressed protein as detected by immunostaining. At 1 week postimplantation, mesenchymal cells subjacent to the defect had incorporated the implanted naked plasmid DNA and, once transfected, served as local bioreactors, transiently producing the gene product. Plasmids containing the gene for BMP-2 implanted in collagen sponges in cartilage lesions stimulated hyalinelike articular cartilage repair at 12 weeks postimplantation, nearly equivalent in quality to that induced by collagen sponges with recombinant BMP-2 protein. Our approach circumvents the risks of inflammation and immunogenic response associated with the use of viral vectors. Naked plasmid DNA as a vehicle for transferring therapeutic genes has been shown to be effective in a therapeutic model within rabbit articular cartilage and appears to be safe and cost effective.

Polyethylenimine-based non-viral gene delivery systems

Gene therapy has become a promising strategy for the treatment of many inheritable or acquired diseases that are currently considered incurable. Non-viral vectors have attracted great interest, as they are simple to prepare, rather stable, easy to modify and relatively safe, compared to viral vectors. Unfortunately, they also suffer from a lower transfection efficiency, requiring additional effort for their optimization. The cationic polymer polyethylenimine (PEI) has been widely used for non-viral transfection in vitro and in vivo and has an advantage over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. Here, we give some insight into strategies developed for PEI-based non-viral vectors to overcome intracellular obstacles, including the improvement of methods for polyplex preparation and the incorporation of endosomolytic agents or nuclear localization signals. In recent years, PEI-based non-viral vectors have been locally or systemically delivered, mostly to target gene delivery to tumor tissue, the lung or liver. This requires strategies to efficiently shield transfection polyplexes against non-specific interaction with blood components, extracellular matrix and untargeted cells and the attachment of targeting moieties, which allow for the directed gene delivery to the desired cell or tissue. In this context, materials, facilitating the design of novel PEI-based non-viral vectors are described.

In utero gene therapy: current challenges and perspectives

Over the past few years, considerable progress in prenatal diagnosis and surgery combined with improvements in vector design vindicate a reappraisal of the feasibility of in utero gene therapy for serious monogenetic diseases. As adult gene therapy gathers pace, several apparent obstacles to its application as a treatment may be overcome by pre- or early postnatal treatment. This review will examine the concepts and practice of prenatal vector administration. We aim to highlight the advantages of early therapeutic intervention focusing on diseases that could benefit greatly from a prenatal gene therapy approach. We will pay special attention to the strategies and vectors that are most likely to be used for this application and will speculate on their expected developments for the near future.

Efficacy and cytotoxicity of cationic-agent-mediated nonviral gene transfer into osteoblasts

Ex vivo gene transfer into osteoblastic cells is an advantageous strategy for bone tissue engineering. This study investigated the efficacy and cytotoxicity of in vitro cationic-agent-mediated nonviral gene transfer into osteoblasts. Various cationic agents, lipid, gelatin, and polyethylenimine (PEI) were tested. Each was formulated in various concentrations to form a complex with plasmid DNA encoding red fluorescent protein. The cationic agent/DNA complexes were transfected into human fetal osteoblastic cell line and rat bone-marrow-derived primary osteoblasts, as well as NIH 3T3 fibroblast controls. Rat primary osteoblasts were transfected more with cationic lipid and PEI agents than with gelatin carrier, yielding transfection efficacy up to 18.1% and 12.7 %, respectively. In contrast, human fetal osteoblastic cell line was transfected more with cationic lipid and gelatin than with PEI. There was a positive correlation between the lipid and PEI doses and cytotoxicity. When the lipid and PEI were used to transfect the rat primary osteoblasts in a dose that yielded the highest transfection efficacy, cell survival rates decreased as low as 40%. When their transfection efficacies into primary osteoblasts were compromised at two thirds of the highest value, that is, 12.6% and 8.3% for the lipid and PEI, respectively, the cell survival rate was nearly 80%. Cationic gelatin was associated with cell survival rates over 60 % in any cell type, regardless of the doses tested. These results suggest that different types of osteoblastic cells may possess different ability to the uptake and expression of cationic-agent-bound DNA. There seemed to be agent-specific threshold doses that dropped the cell survival rate. Cationic-agent-mediated nonviral gene transfer into osteoblastic cells may be successful when the agent- and dose-dependent transfection efficacy and cytotoxicity are optimized.