Nuclear localization signal peptides enhance transfection efficiency of chitosan/DNA complexes

Effect of Different Karyophilic Peptides on Physical Characteristics and In Vitro Transfection Efficiency of Chitosan-Plasmid Nanoparticles as Nonviral Gene Delivery Systems

A strategy to increase the transfection efficiency of chitosan-based nanoparticles for gene therapy is by adding nuclear localization signals through karyophilic peptides. Here, the effect of the length and sequence of these peptides and their interaction with different plasmids on the physical characteristics and biological functionality of nanoparticles is reported. The karyophilic peptides (P1 or P2) were used to assemble nanoparticles by complex coacervation with pEGFP-N1, pQBI25 or pSelect-Zeo-HSV1-tk plasmids, and chitosan. Size, polydispersity index, zeta potential, and morphology, as well as in vitro nucleus internalization and transfection capability of nanoparticles were determined. The P2 nanoparticles resulted smaller compared to the ones without peptides or P1 for the three plasmids. In general, the addition of either P1 or P2 did not have a significant impact on the polydispersity index and the zeta potential. P1 and P2 nanoparticles were localized in the nucleus after 30 min of exposure to HeLa cells. Nevertheless, the presence of P2 in pEGFP-N1 and pQBI25 nanoparticles raised their capability to transfect and express the green fluorescent protein. Thus, karyophilic peptides are an efficient tool for the optimization of nonviral vectors for gene delivery; however, the sequence and length of peptides have an impact on characteristics and functionality of nanoparticles.

Mediation of synergistic chemotherapy and gene therapy via nanoparticles based on chitosan and ionic polysaccharides

Nanoparticles (NPs)-based on various ionic polysaccharides, including chitosan, hyaluronic acid, and alginate have been frequently summarized for controlled release applications, however, most of the published reviews, to our knowledge, focused on the delivery of a single therapeutic agent. A comprehensive summarization of the co-delivery of multiple therapeutic agents by the ionic polysaccharides-based NPs, especially on the optimization of the polysaccharide structure for overcoming various extracellular and intracellular barriers toward maximized synergistic effects, to our knowledge, has been rarely explored so far. For this purpose, the strategies used for overcoming various extracellular and intracellular barriers in vivo were introduced first to provide guidance for the rational design of ionic polysaccharides-based NPs with desired features, including long-term circulation, enhanced cellular internalization, controllable drug/gene release, endosomal escape and improved nucleus localization. Next, four preparation strategies were summarized including three physical methods of polyelectrolyte complexation, ionic crosslinking, and self-assembly and a chemical conjugation approach. The challenges and future trends of this rapidly developing field were finally discussed in the concluding remarks. The important guidelines on the rational design of ionic polysaccharides-based NPs for maximized synergistic efficiency drawn in this review will promote the future generation and clinical translation of polysaccharides-based NPs for cancer therapy.

Nuclear-targeted carbon quantum dot mediated CRISPR/Cas9 delivery for fluorescence visualization and efficient editing

Nuclear targeted delivery has great potential in improving the efficiency of non-viral carrier mediated genome editing. However, direct and efficient delivery of CRISPR/Cas9 plasmid into the nucleus remains a challenge. In this study, a nuclear targeted gene delivery platform based on fluorescent carbon quantum dots (CQDs) was developed. Polyethylenimine (PEI) and polyethylene glycol (PEG) synergistically passivated the surface of CQDs, providing an excitation-independent green-emitting fluorescent CQDs-PEI-PEG conjugate (CQDs-PP) with an ultra-small size and positive surface charge. Here we show that CQDs-PP could bind CRISPR/Cas9 plasmid to form a nano-complex by electrostatic attraction, which can bypass lysosomes and enter the nucleus by passive diffusion, and thereby improve the transfection efficiency. Also, CQDs-PP could deliver CRISPR/Cas9 plasmid into HeLa cells, resulting in the insertion/deletion mutation of the target EFHD1 gene. More importantly, CQDs-PP exhibited a considerably higher gene editing efficiency as well as comparable or lower cytotoxicity relative to Lipo2000 and PEI-passivated CQDs-PEI (CQDs-P). Thus, the nuclear-targeted CQDs-PP is expected to constitute an efficient CRISPR/Cas9 delivery carrier in vitro with imaging-trackable ability.

A brief review on DNA vaccines in the era of COVID-19

This article provides a brief overview of DNA vaccines. First, the basic DNA vaccine design strategies are described, then specific issues related to the industrial production of DNA vaccines are discussed, including the production and purification of DNA products such as plasmid DNA, minicircle DNA, minimalistic, immunologically defined gene expression (MIDGE) and Doggybone™. The use of adjuvants to enhance the immunogenicity of DNA vaccines is then discussed. In addition, different delivery routes and several physical and chemical methods to increase the efficacy of DNA delivery into cells are explained. Recent preclinical and clinical trials of DNA vaccines for COVID-19 are then summarized. Lastly, the advantages and obstacles of DNA vaccines are discussed.

Chitosan Nanoparticles at the Biological Interface: Implications for Drug Delivery

The unique properties of chitosan make it a useful choice for various nanoparticulate drug delivery applications. Although chitosan is biocompatible and enables cellular uptake, its interactions at cellular and systemic levels need to be studied in more depth. This review focuses on the various physical and chemical properties of chitosan that affect its performance in biological systems. We aim to analyze recent research studying interactions of chitosan nanoparticles (NPs) upon their cellular uptake and their journey through the various compartments of the cell. The positive charge of chitosan enables it to efficiently attach to cells, increasing the probability of cellular uptake. Chitosan NPs are taken up by cells via different pathways and escape endosomal degradation due to the proton sponge effect. Furthermore, we have reviewed the interaction of chitosan NPs upon in vivo administration. Chitosan NPs are immediately surrounded by a serum protein corona in systemic circulation upon intravenous administration, and their biodistribution is mainly to the liver and spleen indicating RES uptake. However, the evasion of RES system as well as the targeting ability and bioavailability of chitosan NPs can be improved by utilizing specific routes of administration and covalent modifications of surface properties. Ongoing clinical trials of chitosan formulations for therapeutic applications are paving the way for the introduction of chitosan into the pharmaceutical market and for their toxicological evaluation. Chitosan provides specific biophysical properties for effective and tunable cellular uptake and systemic delivery for a wide range of applications.

Biologics and their delivery systems: Trends in myocardial infarction

Cardiovascular disease is the leading cause of death around the world, in which myocardial infarction (MI) is a precipitating event. However, current therapies do not adequately address the multiple dysregulated systems following MI. Consequently, recent studies have developed novel biologic delivery systems to more effectively address these maladies. This review utilizes a scientometric summary of the recent literature to identify trends among biologic delivery systems designed to treat MI. Emphasis is placed on sustained or targeted release of biologics (e.g. growth factors, nucleic acids, stem cells, chemokines) from common delivery systems (e.g. microparticles, nanocarriers, injectable hydrogels, implantable patches). We also evaluate biologic delivery system trends in the entire regenerative medicine field to identify emerging approaches that may translate to the treatment of MI. Future developments include immune system targeting through soluble factor or chemokine delivery, and the development of advanced delivery systems that facilitate the synergistic delivery of biologics.

Human-derived NLS enhance the gene transfer efficiency of chitosan

Nuclear import is considered as one of the major limitations for non-viral gene delivery systems and the incorporation of nuclear localization signals (NLS) that mediate nuclear intake can be used as a strategy to enhance internalization of exogenous DNA.

In this work, human-derived endogenous NLS peptides based on insulin growth factor binding proteins (IGFBP), namely IGFBP-3 and IGFBP-5, were tested for their ability to improve nuclear translocation of genetic material by non-viral vectors. Several strategies were tested to determine their effect on chitosan mediated transfection efficiency: co-administration with polyplexes, co-complexation at the time of polyplex formation, and covalent ligation to chitosan. Our results show that co-complexation and covalent ligation of the NLS peptide derived from IGFBP-3 to chitosan polyplexes yields a 2-fold increase in transfection efficiency, which was not observed for NLS peptide derived from IGFBP-5.

These results indicate that the integration of IGFBP-NLS-3 peptides into polyplexes has potential as a strategy to enhance the efficiency of non-viral vectors.

Duplex of Polyamidoamine Dendrimer/Custom-Designed Nuclear-Localization Sequence Peptide for Enhanced Gene Delivery

Background: Dendrimers are an attractive alternative to viral vectors due to the low cost of production, larger genetic insert-carrying capacity, and added control over immune- and genotoxic complications through versatile functionalization. However, their transfection rates pale in comparison to their viral counterparts, resulting in widespread research efforts in the attempt to improve transfection efficiency. Materials and Methods: In this work, we designed a synthetic diblock nuclear-localization sequence peptide (NLS) (DDDDDDVKRKKKP) and complexed it with polyamidoamine (PAMAM) dendrimer G4 to form a duplex for gene delivery. We conducted transmission electron microscopy, gel mobility shift assay, and intracellular trafficking studies. We also assessed its transfection efficiency for the delivery of a green fluorescent protein-encoding plasmid (pGFP) to NIH3T3 cells. Results: PAMAM dendrimer G4, NLS, and plasmid DNA can form a stable three-part polyplex and gain enhanced entry into the nucleus. We found transfection efficiency, in large part, depends on the ratio of G4:NLS:plasmid. The triplex prepared at the ratio of 1:60:1 for G4:NLS:pGFP has been shown to be more significantly efficient in transfecting cells than the control group (G4/pGFP, 0.5:1). Conclusions: This new diblock NLS peptide can facilely complex with dendrimers to improve dendrimer-based gene transfection. It can also complex with other polycationic polymers to produce more potent nonviral duplex gene delivery vehicles.

Nuclear localization signal peptide enhances transfection efficiency and decreases cytotoxicity of poly(agmatine/N,N'-cystamine-bis-acrylamide)/pDNA complexes

At present, nonviral gene vectors develop rapidly, especially cationic polymers. A series of bioreducible poly(amide amine) (PAA) polymers containing guanidino groups have been synthesized by our research team. These novel polymer vectors demonstrated significantly higher transfection efficiency and lower cytotoxicity than polyethylenimine (PEI)-25kDa. However, compared with viral gene vectors, relatively low transfection efficiency, and high cytotoxicity are still critical problems confronting these polymers. In this study, poly(agmatine/N,N'-cystamine-bis-acrylamide) p(AGM-CBA) was selected as a model polymer, nuclear localization signal (NLS) peptide PV7 (PKKKRKV) with good biocompatibility and nuclear localization effect was introduced to investigate its impact on transfection efficiency and cytotoxicity. NLS peptide-mediated in vitro transfection was performed in NIH 3T3 cells by directly incorporating NLS peptide with the complexes of p(AGM-CBA)/pDNA. Meanwhile, the transfection efficiency and cytotoxicity of these complexes were evaluated. The results showed that the transfection efficiency could be increased by 5.7 times under the appropriate proportion, and the cytotoxicity brought by the polymer vector could be significantly reduced.

Enhancement of Angiogenesis by Ultrasound-Targeted Microbubble Destruction Combined with Nuclear Localization Signaling Peptides in Canine Myocardial Infarction

Objective

This study aimed to develop a gene delivery system using ultrasound-targeted microbubbles destruction (UTMD) combined with nuclear localization signal (NLS) and investigate its efficacy and safety for therapeutic angiogenesis in canine myocardial infarction (MI) model.

Methods

Fifty MI dogs were randomly divided into 5 groups and transfected with Ang-1 gene plasmid: (i) group A: only injection of microbubbles and Ang-1 plasmid; (ii) group B: only UTMD mediated gene transfection; (iii) group C: UTMD combined with classical NLS mediated gene transfection; (iv) group D: UTMD combined with mutational NLS mediated transfection; and (v) group E: UTMD combined with classical NLS in the presence of a nucleus transport blocker. The mRNA and protein expression of Ang-1 gene, microvessel density (MVD) cardiac troponin I (cTnI), and cardiac function were determined after transfection.

Results

The expression of mRNA and protein of Ang-1 gene in group C was significantly higher than that of the other groups (all P < 0.01). The MVD of group C was 10.2-fold of group A and 8.1-fold of group E (P < 0.01). The cardiac function in group C was significant improvement without cTnI rising.

Conclusions

The gene delivery system composed of UTMD and NLS is efficient and safe.

Efficient gene therapy with a combination of ultrasound‑targeted microbubble destruction and PEI/DNA/NLS complexes

Current strategies of gene transfection are not efficient at achieving a notable therapeutic effect. The aim of the present study was to combine ultrasound‑targeted microbubble destruction (UTMD) with a polyethylenimine/pEGFP‑N3 plasmid/nuclear localization sequence (PEI/DNA/NLS) complex gene delivery system, and evaluate the transfection efficiency of enhanced green fluorescent protein (EGFP) gene delivery to 293T cells using this system. The formation of PEI/DNA/NLS complexes and the protective effects of PEI/NLS were verified by gel electrophoresis. Solutions consisting of the plasmid alone, PEI/DNA complexes, PEI/DNA/NLS complexes, UTMD+DNA, UTMD+PEI/DNA complexes, and UTMD+PEI/DNA/NLS complexes were transduced into 293T cells via ultrasound irradiation. The expression of GFP was observed using an inverted microscope and transfection efficiency was detected by flow cytometry following 24 h incubation in vitro. Cell activity was detected using a Cell Counting kit (CCK)‑8 assay. Gel electrophoresis confirmed the formation of PEI/DNA/NLS complexes and demonstrated that PEI/NLS exhibited protective effects on plasmid integrity for a limited time. Inverted microscope observations revealed that a greater GFP signal was observed with the combined action of PEI/DNA/NLS complexes with UTMD, and flow cytometry analysis demonstrated the highest level of transfection efficiency in this group. In addition, the viability of the cells detected by CCK‑8 and treated with PEI/DNA/NLS complexes with UTMD was >80%. In conclusion, the combination of UTMD and PEI/DNA/NLS complexes was highly effective for the efficient transfection of 293T cells without causing excessive cell damage. This method may provide a novel and effective gene transduction system to be applied in clinical treatments.

Exploring the role of peptides in polymer-based gene delivery

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

STATEMENT OF SIGNIFICANCE

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

Enhanced effect of nuclear localization signal peptide during ultrasound‑targeted microbubble destruction‑mediated gene transfection

Ultrasound‑targeted microbubble destruction (UTMD) can promote the entry of plasmid DNA (pDNA) into the cell cytoplasm, by increasing the permeability of the cell membrane. But the transfection efficiency remains low due to inability of the pDNA to enter the nucleus. Various methods have been explored to improve the UTMD transfection efficiency, but with little success. In cells, the classic nuclear localization signal (cNLS) peptide is an amino acid sequence that signals proteins that are due for nuclear transport. The present study aimed to investigate whether binding of a cNLS peptide to the pDNA may improve the transfection efficiency of UTMD. Four experimental groups were analyzed: Control group (UTMD + pDNA), group with cNLS (UTMD + pDNA + cNLS), group with mutated NLS (mNLS; UTMD + pDNA + mNLS), and group with cNLS and the nuclear import blocker, wheat germ agglutinin (WGA; UTMD + pDNA + cNLS + WGA). The NLS was labeled by fluorescein isothiocyanate, whereas pDNA was labeled with Cy3. Different molar ratios were tested for the NLS and pDNA combination in order to achieve optimal binding of the two molecules. Human umbilical vein endothelial cells were then transfected using the optimum ultrasonic irradiation parameters and NLS/pDNA molar ratio. At 6 h post‑transfection, the rates of Cy3‑labeled pDNA inside the cells and their nuclei were detected by flow cytometry and laser confocal microscopy, and the cellular vs. nuclear uptake of pDNA was calculated. In order to further evaluate the effect of NLS on UTMD‑mediated gene transfection, the transfection efficiency and relative expression levels of mRNA and protein were detected at 48 h post‑transfection. The results demonstrated that the optimal molar ratio of NLS with pDNA was 104:1. The rates of pDNA successful entry into the cell and nucleus were significantly higher in the cNLS group compared with the control group. The transfection efficiency, and relative expression levels of mRNA and protein from the plasmid were significantly increased in the cNLS group compared with the control group. The mNLS group displayed no significant difference compared with the control group, while the WGA group exhibited significant inhibition in most indicators of transfection efficiency compared to the cNLS group. These results suggest that combining a cNLS peptide with pDNA during UTMD‑mediated transfection significantly improved transfection efficiency. Thus, a cNLS peptide may be an important mediator and a new strategy in enhancing the efficiency of UTMD‑mediated gene transfection.

How successful is nuclear targeting by nanocarriers?

The nucleus is ultimately the final target for many therapeutics treating various disorders including cancers, heart dysfunction and brain disorders. Owing to their specialized cell uptake and trafficking mechanisms, nanoparticles (NPs) allow drug targeting where degradation sensitive therapeutics could be delivered to their target tissues and cell in active form and sufficient concentration. However, it has recently become increasingly obvious that cytosolic internalization of a drug molecule does not entail its interaction with its subcellular target and hence careful nanoparticle design and optimization is required to enable nuclear targeting. This review, discusses the barriers to NP nuclear delivery; crossing the cell membrane, endo/lysosomal escape, cytoplasmic trafficking and finally nuclear entry focusing on how NP synthesis and modification could allow for bypassing each of the aforementioned barriers and successfully reaching the nucleus. Examples of nuclear targeted NPs are also discussed, stressing on the critical aspects of nuclear targeting and pointing out how the disease state might change the normal NP path and how such change could be exploited to increase efficiency of nuclear targeting. Finally, the criteria set for the evaluation of nanocarriers for nuclear delivery are discussed highlighting that quantitative rather than qualitative evaluation is required to evaluate how successful nanocarriers for nuclear delivery are, particularly with regards to the amount of drug delivered and released in the nucleus.

Bio-reducible polycations from ring-opening polymerization as potential gene delivery vehicles

Bio-reducible polycations were prepared via ring-opening polymerization. These materials have relatively low molecular weights and cytotoxicity but have good DNA condensation ability, transfection efficiency and excellent serum tolerance.

Chitosan Nanoparticles for Nuclear Targeting: The Effect of Nanoparticle Size and Nuclear Localization Sequence Density

Many recently discovered therapeutic proteins exert their main function in the nucleus, thus requiring both efficient uptake and correct intracellular targeting. Chitosan nanoparticles (NPs) have attracted interest as protein delivery vehicles due to their biocompatibility and ability to escape the endosomes offering high potential for nuclear delivery. Molecular entry into the nucleus occurs through the nuclear pore complexes, the efficiency of which is dependent on NP size and the presence of nuclear localization sequence (NLS). Chitosan nanoparticles of different sizes (S-NPs ≈ 25 nm; L-NP ≈ 150 nm) were formulated, and they were modified with different densities of the octapeptide NLS CPKKKRKV (S-NPs, 0.25, 0.5, 2.0 NLS/nm(2); L-NPs, 0.6, 0.9, 2 NLS/nm(2)). Unmodified and NLS-tagged NPs were evaluated for their protein loading capacity, extent of cell association, cell uptake, cell surface binding, and finally nuclear delivery efficiency in L929 fibroblasts. To avoid errors generated with cell fractionation and nuclear isolation protocols, nuclear delivery was assessed in intact cells utilizing Förster resonance energy transfer (FRET) fluorometry and microscopy. Although L-NPs showed ≈10-fold increase in protein loading per NP when compared to S-NPs, due to higher cell association and uptake S-NPs showed superior protein delivery. NLS exerts a size and density dependent effect on nanoparticle uptake and surface binding, with a general reduction in NP cell surface binding and an increase in cell uptake with the increase in NLS density (up to 8.4-fold increase in uptake of High-NLS-L-NPs (2 NLS/nm(2)) compared to unmodified L-NPs). However, for nuclear delivery, unmodified S-NPs show higher nuclear localization rates when compared to NLS modified NPs (up to 5-fold by FRET microscopy). For L-NPs an intermediate NLS density (0.9 NLS/nm(2)) seems to provide highest nuclear localization (3.7-fold increase in nuclear delivery compared to High-NLS-L-NPs). Results indicate that a higher NLS density does not result in maximum protein nuclear localization and that a universal optimal density for NPs of different sizes does not exist.

Nanomedicine for gene therapy

Viruses are promising vehicles that result in high gene expression level, but issues of safety and virulent nature prevented its extensive use. Therefore, nonviral approach was investigated with the intervention of nanomedicine. The science of nanomedicine offered an excellent platform for therapeutic delivery as they provide options to include functionalities and engineer the system. As the term 'nano' refers to the generation of a very small dimension structure, their unique physicochemical characteristics with increased surface area/volume ratio made them potential vectors to perform gene therapy. Various forms of nanoparticles are continued to be synthesised, and this review discusses the immediate barriers that nanoparticles have to encounter both during systemic movement in the body and intracellular trafficking to deliver the genes at the site of action.

Ring-opening polymerization for hyperbranched polycationic gene delivery vectors with excellent serum tolerance

In order to improve the transfection efficiency (TE) and biocompatibility, we synthesized a series of hyperbranched cationic polymers by ring-opening polymerization between diepoxide and several polyamines. These materials can condense plasmid DNA efficiently into nanoparticles that have much lower cytotoxicity than those derived from bPEI. In vitro transfection experiments showed that polymers prepared from branched or cyclic polyamine (P1 and P5) exhibited TE several times higher than 25KDa bPEI. More significantly, serum seemed to have no negative effect on P1-P5 mediated transfection. On the contrary, the TE of P1 improved, even when the serum concentration reached 70%. Several assays demonstrated the excellent serum tolerance of such polycationic vectors: bovine serum albumin (BSA) adsorption assay revealed considerably lower protein adsorption of P1-P5 than PEI; P1 showed better DNA protection ability from degradation by DNase I than PEI; flow cytometry results suggested that any concentration of serum may not decrease the cellular uptake of P1/DNA polyplex; and confocal laser scanning microscopy also found that serum has little effect on the transfection. By using specific cellular uptake inhibitors, we found that the polyplexes enter the cells mainly via caveolae and microtubule-mediated pathways. We believe that this ring-opening polymerization may be an effective synthetic approach toward gene delivery materials with high biological activity.

Polymer-peptide delivery platforms: effect of oligopeptide orientation on polymer-based DNA delivery

The success of nonviral transfection using polymers hinges on efficient nuclear uptake of nucleic acid cargo and overcoming intra- and extracellular barriers. By incorporating PKKKRKV heptapeptide pendent groups as nuclear localization signals (NLS) on a polymer backbone, we demonstrate protein expression levels higher than those obtained from JetPEI and Lipofectamine 2000, the latter being notorious for coupling high transfection efficiency with cytotoxicity. The orientation of the NLS peptide grafts markedly affected transfection performance. Polymers with the sequence attached to the backbone from the valine residue achieved a level of nuclear translocation higher than the levels of those having the NLS groups attached in the opposite orientation. The differences in nuclear localization and DNA complexation strength between the two orientations correlated with a striking difference in protein expression, both in cell culture and in vivo. Polyplexes formed from these comb polymer structures exhibited transfection efficiencies superior to those of Lipofectamine 2000 but with greatly reduced toxicity. Moreover, these novel polymers, when administered by intramuscular ultrasound-mediated delivery, allowed a high level of reporter gene expression in mice, demonstrating their therapeutic promise in vivo.

Chemical modification of chitosan for efficient gene therapy

Gene therapy involves the introduction of foreign genetic material into cells in order to exert a therapeutic effect. Successful gene therapy relies on effective vector system. Viral vectors are highly efficient in transfecting cells, but the undesirable complications limit their therapeutic applications. As a natural biopolymer, chitosan has been considered to be a good gene carrier candidate due to its ideal character which combines biocompatibility, low toxicity with high cationic density together. However, the low cell specificity and low transfection efficiency of chitosan as a gene carrier need to be overcome before undertaking clinical trials. This chapter is principally on those endeavors such as chemical modifications using cell-specific ligands and stimuli-response groups as well as penetrating modifications that have been done to increase the performances of chitosan in gene therapy.

Nuclear location signal peptide–modified poly (ethyleneimine)/DNA complexes: An efficient gene delivery vector in vitro and in vivo

The low transfection efficiency of nonviral gene delivery systems limits their applications. In this study, we demonstrated a simple method to modify poly(ethyleneimine)/DNA complexes with a nuclear location signal peptide via bis(succinimidyl) penta(ethylene glycol) coupling. The amount of grafted nuclear location signal peptide was controlled within a range of 0–9 µg for poly(ethyleneimine)/DNA complexes containing 10 µg DNA and 100 µg poly(ethyleneimine) by adjusting the grafting agent and peptide feeds. The particle size and surface zeta-potential of the complexes were largely retained after nuclear location signal immobilization. Based on the results of the flow cytometry measurements, the nuclear location signal–modified poly(ethyleneimine)/DNA complexes were internalized into at bone marrow stem cells at a significantly faster rate and a higher amount than the unmodified complexes. In vitro transfection experiments, using plasmid DNA encoding bone morphogenetic protein 2, indicated that the nuclear location signal peptide–modified poly(ethyleneimine)/DNA complexes have significantly higher gene transfection ability toward bone marrow stem cells than unmodified complexes. The porous collagen scaffolds loaded with nuclear location signal–modified poly(ethyleneimine)/plasmid DNA encoding bone morphogenetic protein 2 complexes successfully transfected tissue cells and induced the human bone morphogenetic protein 2 expression in a rat. The modification of the poly(ethyleneimine)/DNA complexes with nuclear location signal peptide was effective in enhancing gene transfection of complexes in vitro and in vivo, thus indicating potential applications for bioactive scaffolds with enhanced tissue regeneration performance.

Inspired by nature: fundamentals in nanotechnology design to overcome biological barriers

Synergy between nanotechnology and drug delivery has created a multitude of novel drug-delivery systems with great therapeutic potential. However, directing these systems across the biological barriers to the target site has proven difficult. Nanotechnology is looking for inspiration in natural systems that have evolved to overcome such barriers. Here, we review nature-inspired strategies and fundamental features common to successful drug-delivery systems across biological barriers.

Use of biotinylated chitosan for substrate-mediated gene delivery

To improve transfection efficiency of nonviral vectors, biotinylated chitosan was applied to complex with DNA in different N/P ratios. The morphologies and the sizes of formed nanoparticles were suitable for cell uptake. The biotinylation decreased the surface charges of nanoparticles and hence reduced the cytotoxicity. The loading capacities of chitosan were slightly decreased with the increase of biotinylation, but most of the DNA molecules were still complexed. Using different avidin-coated surfaces, the interaction between biotinylated nanoparticles to the substrate may be manipulated. The in vitro transfection results demonstrated that biotinylated nanoparticles may be bound to avidin coated surfaces, and the transfection efficiencies were thus increased. Through regulating the N/P ratio, biotinylation levels, and surface avidin, the gene delivery can be optimized. Compared to the nonmodified chitosan, biotinylated nanoparticles on biomaterial surfaces can increase their chances to contact adhered cells. This spatially controlled gene delivery improved the gene transfer efficiency of nonviral vectors and could be broadly applied to different biomaterial scaffolds for tissue engineering applications.

Intravenous renal cell transplantation for rats with acute and chronic renal failure

Acute kidney injury (AKI) and chronic renal failure (CKD) are the most challenging problems in nephrology. Multiple therapies have been attempted but these interventions have minimal effects on the eventual outcomes, and all too often the result is end-stage renal disease (ESRD). The only effective therapy for ESRD is renal transplantation but only a small fraction of patients receive transplants. In this work we introduce a novel approach to transplantation designed to regenerate kidneys afflicted by severe AKI or CKD: intravenous renal cell transplantation (IRCT) with adult rat primary renal cells reprogrammed to express the SAA gene localized and engrafted in kidneys of rat recipients that had severe AKI or CKD. IRCT significantly resolved renal dysfunction and limited kidney damage, inflammation, and fibrosis. Severe CKD was successfully improved by IRCT using kidney cells from donor rats or by renal cell self-donation in a form of autotransplantation. We propose that IRCT with adult primary renal cells reprogrammed to express the SAA gene can be used to effectively treat AKI and CKD.

Intracellular organelle-targeted non-viral gene delivery systems

Gene therapy is a rapidly growing approach for the treatment of various diseases. To achieve successful gene therapy, a gene delivery system is necessary to overcome several barriers in the extracellular and intracellular spaces. Polymers, peptides, liposomes and nanoparticles developed as gene carriers have achieved efficient cellular uptake of genes. Among these carriers, cationic polymers and peptides have been further developed as intracellular organelle-targeted delivery systems. The cytoplasm, nucleus and mitochondria have been considered primary targets for gene delivery using targeting moieties or environment-responsive materials. In this review, we explore recently developed non-viral gene carriers based on reducible systems specialized to target the cytoplasm, nucleus and mitochondria.

Improved transfection efficiency of an aliphatic lipid substituted 2 kDa polyethylenimine is attributed to enhanced nuclear association and uptake in rat bone marrow stromal cell

BACKGROUND

Lipid substitutions of cationic polymers are actively explored to enhance the efficiency of nonviral gene carriers. We recently took this approach to develop a novel gene carrier by grafting linoleic acid (LA) to relatively biocompatible 2 kDa polyethylenimine (PEI2). The resulting polymer (PEI2LA) displayed improved transfection efficiency over the unmodified PEI2. The intracellular kinetics and distribution of the respective polyplexes were investigated in the present study to gain a better understanding of the role of lipid modification in intracellular trafficking of gene carriers.

METHODS

A Cy5-labeled plasmid DNA (pDNA) expressing the green fluorescent protein (GFP) was complexed with PEI2, PEI2LA, and 25 kDa polyethylenimine (PEI25) to transfect rat bone marrow stromal cells (BMSC). Subcellular fractionation was performed to measure the amount of nuclear associated pDNA. pDNA uptake, GFP-expression and nuclear-associated pDNA were measured by both flow cytometry and confocal laser scanning microscopy.

RESULTS

PEI2LA mediated higher transgene expression and percentages of transfected cells than PEI25 and PEI2, respectively. There was a strong correlation between nuclear associated pDNA and transgene expression. PEI2LA polyplexes were significantly larger in size than PEI25. The amounts of pDNA associated with the nuclei were greater in PEI2LA than PEI25 polyplexes. The perinuclear pDNA distribution between GFP-expressing and nonGFP-expressing indicated that GFP-positive cells had a higher amount of pDNA associated with their nuclei.

CONCLUSIONS

Improved transfection efficiency of PEI2LA was attributed to enhanced association with the nucleus, which may be a result of hydrophobic interaction between the lipid moieties on the modified lipopolymer and the nuclear membrane.

Advancing nonviral gene delivery: lipid- and surfactant-based nanoparticle design strategies

Gene therapy is a technique utilized to treat diseases caused by missing, defective or overexpressing genes. Although viral vectors transfect cells efficiently, risks associated with their use limit their clinical applications. Nonviral delivery systems are safer, easier to manufacture, more versatile and cost effective. However, their transfection efficiency lags behind that of viral vectors. Many groups have dedicated considerable effort to improve the efficiency of nonviral gene delivery systems and are investigating complexes composed of DNA and soft materials such as lipids, polymers, peptides, dendrimers and gemini surfactants. The bottom-up approach in the design of these nanoparticles combines components essential for high levels of transfection, biocompatibility and tissue-targeting ability. This article provides an overview of the strategies employed to improve in vitro and in vivo transfection, focusing on the use of cationic lipids and surfactants as building blocks for nonviral gene delivery systems.