Peptide-mediated Gene Transfer of Cationic Lipid/Plasmid DNA Complexes to Endothelial Cells

Challenges and strategies for in situ endothelialization and long-term lumen patency of vascular grafts

Vascular diseases are the most prevalent cause of ischemic necrosis of tissue and organ, which even result in dysfunction and death. Vascular regeneration or artificial vascular graft, as the conventional treatment modality, has received keen attentions. However, small-diameter (diameter < 4 mm) vascular grafts have a high risk of thrombosis and intimal hyperplasia (IH), which makes long-term lumen patency challengeable. Endothelial cells (ECs) form the inner endothelium layer, and are crucial for anti-coagulation and thrombogenesis. Thus, promoting in situ endothelialization in vascular graft remodeling takes top priority, which requires recruitment of endothelia progenitor cells (EPCs), migration, adhesion, proliferation and activation of EPCs and ECs. Chemotaxis aimed at ligands on EPC surface can be utilized for EPC homing, while nanofibrous structure, biocompatible surface and cell-capturing molecules on graft surface can be applied for cell adhesion. Moreover, cell orientation can be regulated by topography of scaffold, and cell bioactivity can be modulated by growth factors and therapeutic genes. Additionally, surface modification can also reduce thrombogenesis, and some drug release can inhibit IH. Considering the influence of macrophages on ECs and smooth muscle cells (SMCs), scaffolds loaded with drugs that can promote M2 polarization are alternative strategies. In conclusion, the advanced strategies for enhanced long-term lumen patency of vascular grafts are summarized in this review. Strategies for recruitment of EPCs, adhesion, proliferation and activation of EPCs and ECs, anti-thrombogenesis, anti-IH, and immunomodulation are discussed. Ideal vascular grafts with appropriate surface modification, loading and fabrication strategies are required in further studies.

Liposomal delivery of CRISPR/Cas9

Liposomes are one of the most widely investigated carriers for CRISPR/Cas9 delivery. The surface properties of liposomal carriers, including the surface charge, PEGylation, and ligand modification can significantly affect the gene silencing efficiency. Three barriers of systemic CRISPR/Cas9 delivery (long blood circulation, efficient tumor penetration, and efficient cellular uptake/endosomal escape) are analyzed on liposomal carriers with different surface charges, PEGylations, and ligand modifications. Cationic formulations dominate CRISPR/Cas9 delivery and neutral formulations also have good performance while anionic formulations are generally not proper for CRISPR/Cas9 delivery. The PEG dilemma (prolonged blood circulation vs. reduced cellular uptake/endosomal escape) and the side effect of repeated PEGylated formulation (accelerated blood clearance) were discussed. Effects of ligand modification on cationic and neutral formulations were analyzed. Finally, we summarized the achievements in liposomal CRISPR/Cas9 delivery, outlined existing problems, and provided some future perspectives. Liposomes are one of the most widely investigated carriers for CRISPR/Cas9 delivery. The surface properties of liposomal carriers, including the surface charge, PEGylation, and ligand modification can significantly affect the gene silencing efficiency. Three barriers of systemic siRNA delivery (long blood circulation, efficient tumor penetration, and efficient cellular uptake/endosomal escape) are analyzed on liposomal carriers with different surface charges, PEGylations, and ligand modifications. Cationic formulations dominate CRISPR/Cas9 delivery and neutral formulations also have good performance while anionic formulations are generally not proper for CRISPR/Cas9 delivery. The PEG dilemma (prolonged blood circulation vs. reduced cellular uptake/endosomal escape) and the side effect of repeated PEGylated formulation (accelerated blood clearance) were discussed. Effects of ligand modification on cationic and neutral formulations were analyzed. Finally, we summarized the achievements in liposomal CRISPR/Cas9 delivery, outlined existing problems, and provided some future perspectives.

RGD peptide-based non-viral gene delivery vectors targeting integrin αvβ3 for cancer therapy

Integrin α_vβ₃ is restrictedly expressed on angiogenic blood vessels and tumour cells. It plays a key role in angiogenesis for tumour growth and metastasis. RGD peptide can specifically recognise the integrin α_vβ₃, which serves as targeted molecular for anti-angiogenesis strategies. Therefore, the targeted delivery of therapeutics by RGD peptide-based non-viral vectors to tumour vasculature and tumour cells is recognised as a promising approach for treating cancer. In this review, we illustrate the interaction between RGD peptide and integrin α_vβ₃ from different perspectives. Meanwhile, four types of RGD peptide-based non-viral gene delivery vectors for cancer therapy, including RGD-based cationic polymers, lipids, peptides and hybrid systems, are summarised. The aim is to particularly highlight the enhanced therapeutic effects and specific targeting ability exhibited by these vectors for cancer gene therapy both in vitro and in vivo.

Surface modification and endothelialization of biomaterials as potential scaffolds for vascular tissue engineering applications

This review highlights the recent developments of surface modification and endothelialization of biomaterials in vascular tissue engineering applications.

A review of RGD-functionalized nonviral gene delivery vectors for cancer therapy

The development of effective treatments that enable many patients suffering from cancer to be successfully cured is highly demanded. Angiogenesis, which is a process for the formation of new capillary blood vessels, has a crucial role in solid tumor progression and the development of metastasis. Antiangiogenic therapy designed to prevent tumor angiogenesis, thereby arresting the growth or spread of tumors, has emerged as a non-invasive and safe option for cancer treatment. Due to the fact that integrin receptors are overexpressed on the surface of angiogenic endothelial cells, various strategies have been made to develop targeted delivery systems for cancer gene therapy utilizing integrin-targeting peptides with an exposed arginine-glycine-aspartate (RGD) sequence. The aim of this review is to summarize the progress and prospect of RGD-functionalized nonviral vectors toward targeted delivery of genetic materials in order to achieve an efficient therapeutic outcome for cancer gene therapy, including antiangiogenic therapy.

mRNA delivery through fibronectin associated liposome-apatite particles: a new approach for enhanced mRNA transfection to mammalian cell

It was believed for a long time that mRNA is very unstable, and can not be used for therapeutic purposes. In the last decade, however, many research groups proved its transfection feasibility along with advantages and applications. Our investigation is aimed at establishing a potent and efficient mRNA delivery system. We previously reported that an inorganic-organic hybrid carrier by exploiting the advantages of inorganic nano apatite particles onto organic carrier DOTAP {N-[1-(2,3-dioleoloxy)propyl]-N,N,N-trimethyl ammonium chloride} and showed potential effect of carbonate apatite particles on each of the mRNA delivery steps in dividing and non-dividing cell. Here, we report on the development of a more efficient mRNA carrier by complexing ECM protein, fibronectin with the DOTAP-apatite carrier. The carrier showed enhanced uptake of luciferase mRNA both qualitatively and quantitatively. Accelerated cellular endocytosis rate was evaluated using labeled endosome. Finally expression of lucifearse mRNA was higher for fibronectin complexed carrier in compared to the uncoated one.

Nonviral delivery of genetic medicine for therapeutic angiogenesis

Genetic medicines that induce angiogenesis represent a promising strategy for the treatment of ischemic diseases. Many types of nonviral delivery systems have been tested as therapeutic angiogenesis agents. However, their delivery efficiency, and consequently therapeutic efficacy, remains to be further improved, as few of these technologies are being used in clinical applications. This article reviews the diverse nonviral gene delivery approaches that have been applied to the field of therapeutic angiogenesis, including plasmids, cationic polymers/lipids, scaffolds, and stem cells. This article also reviews clinical trials employing nonviral gene therapy and discusses the limitations of current technologies. Finally, this article proposes a future strategy to efficiently develop delivery vehicles that might be feasible for clinically relevant nonviral gene therapy, such as high-throughput screening of combinatorial libraries of biomaterials.

Integrin targeted delivery of gene therapeutics

Integrins have become key targets for molecular imaging and for selective delivery of anti-cancer agents. Here we review recent work concerning the targeted delivery of antisense and siRNA oligonucleotides via integrins. A variety of approaches have been used to link oligonucleotides to ligands capable of binding integrins with high specificity and affinity. This includes direct chemical conjugation, incorporating oligonucleotides into lipoplexes, and use of various polymeric nanocarriers including dendrimers. The ligand-oligonucleotide conjugate or complex associates selectively with the integrin, followed by internalization into endosomes and trafficking through subcellular compartments. Escape of antisense or siRNA from the endosome to the cytosol and nucleus may come about through endogenous trafficking mechanisms, or because of membrane disrupting capabilities built into the conjugate or complex. Thus a variety of useful strategies are available for using integrins to enhance the pharmacological efficacy of therapeutic oligonucleotides.

Efficient gene delivery by EGF-lipoplexes in vitro and in vivo

Aims: In this work, we have evaluated the ability of targeted lipoplexes to enhance transgene expression in EGF receptor (EGFR) overexpressing tumor cells by using lipoplexes. Materials & methods: We prepared DOTAP/cholesterol liposomes modified with EGF at 0.5/1, 1/1, 2/1 and 5/1 lipid/DNA (+/-) charge ratio by sequentially mixing the liposomes with the ligand and adding the reporter or the therapeutic plasmid gene, pCMVLuc (pVR1216) or pCMVIL12, respectively. HepG2, DHDK12proB and SW620 cells were used for in vitro experiments, which were performed in the presence of 60% serum. Results: The characterization of EGF-lipoplexes indicated a size close to 300 nm and a variable net surface charge as a function of the amount of EGF associated to the cationic liposomes. EGF-lipoplexes, which showed an increased transfection activity, were positively charged, noncytotoxic and highly effective in protecting DNA from DNase I attack. Transfection activity in vitro resulted in an enhancement in the luciferase and IL-12 expression by EGF-lipoplexes compared with those without ligand (plain-lipoplexes) and to naked DNA. The results observed in SW620 cells, which are deficient in EGFR, confirmed that DNA uptake was predominantly via EGFR-mediated endocytosis. In vivo transfection activity was confirmed by luciferase imaging in living mice. Bioluminiscence could be detected mainly in the lung with a maximum signal 24 h after application. The resulting EGF-lipoplexes significantly increased the level of gene expression in mice compared with control or naked DNA. Conclusion: These findings indicate that these nanovectors may be an adequate alternative to viral vectors for gene therapy.

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.

Role of linker groups between hydrophilic and hydrophobic moieties of cationic surfactants on oligonucleotide-surfactant interactions

The interaction between DNA and amino-acid-based surfactants with different linker groups was investigated by gel electrophoresis, ethidium bromide exclusion assays, circular dichroism, and melting temperature determinations. The studies showed that the strength of the interaction between the oligonucleotides and the surfactants is highly dependent on the linker of the surfactant. For ester surfactants, no significant interaction was observed for surfactant-to-DNA charge ratios up to 12. On the other hand, amide surfactants were shown to interact strongly with the oligonucleotides; these surfactants could displace up to 75% of the ethidium bromide molecules bound to the DNA and induced significant changes in the circular dichroism spectra. When comparing the headgroups of the surfactants, it was observed that surfactants with more hydrophobic headgroups (proline vs alanine) interacted more strongly with the DNA, in good agreement with previous studies.

Ligand-directed cancer gene therapy to angiogenic vasculature

Gene therapy strategies in cancer have remained an active area of preclinical and clinical research. One of the current limitations to successful trials is the relative transduction efficiency to produce a therapeutic effect. While intratumoral injections are the mainstay of many treatment regimens to date, this approach is hindered by hydrostatic pressures within the tumor and is not always applicable to all tumor subtypes. Vascular-targeting strategies introduce an alternative method to deliver vectors with higher local concentrations and minimization of systemic toxicity. Moreover, therapeutic targeting of angiogenic vasculature often leads to enhanced bystander effects, improving efficacy. While identification of functional and systemically accessible molecular targets is challenging, approaches, such as in vivo phage display and phage-based viral delivery vectors, provide a platform upon which vascular targeting of vectors may become a viable and translational approach.

A flexible method for the conjugation of aminooxy ligands to preformed complexes of nucleic acids and lipids

Attachment of targeted ligands to nonviral DNA or RNA delivery systems is a promising strategy that seeks to overcome the poor target selectivity generally observed in systemic delivery applications. Several methods have been developed for the conjugation of ligands to lipids or polymers, however, direct conjugation of ligands onto lipid- or polymer-nucleic acid complexes is not as straightforward. Here, we examine an oximation approach to directly label a lipoplex formulation. Specifically, we report the synthesis of a cationic diketo lipid DMDK, and its use as a convenient ligation tool for attachment of aminooxy-functionalized reagents after its complexation with DNA. We demonstrate the feasibility of direct lipoplex labeling by attaching an aminooxy-functionalized fluorescent probe onto pre-formed plasmid DNA-DMDK lipoplexes (luciferase, GFP). The results reveal that DMDK protects DNA from degradation on exposure to either DNase or human cerebral spinal fluid, and that simple mixing of DMDK lipoplexes with the aminooxy probe labels the complexes without sacrificing transfection efficiency. The biocompatibility and selectivity of this method, as well as the ease of bioconjugation, make this labeling approach ideal for biological applications.

Development of peptide-targeted lipoplexes to CXCR4-expressing rat glioma cells and rat proliferating endothelial cells

A peptide analog, 4-fluorobenzoyl-RR-(L-3-(2-naphthyl)alanine)-CYEK-(L-citrulline)-PYR-(L-citrulline)-CR, covalently linked to a phospholipid, was used for targeting a lipid-based gene delivery vehicle to CXCR4(+)-cells. Characterization of transfection activity was done in vitro using a transformed rat glioma cell line (RG2) that expresses CXCR4. The substitution of the targeting lipid at increasing mole percentages in the place of helper lipids yielded a progressive increase in reporter gene expression, reaching a maximum of 2.5 times the control value at 20 mol% of ligand. The substitution of helper lipids with cysteine-derivatized phospholipid analog or phosphatidylethanolamine resulted in a progressive decrease in transfection activity, with complete inactivation of the complex occurring at 20 mol%. A DNA dose-response with 10 mol% of lipopeptide reduced the effective DNA dose at least fivefold with regard to the number of transfected cells and >20-fold with regard to the amount of gene expression. Gene transfer to rat endothelial cells was studied in the context of an arterial organ culture. Mesenteric arteries were cannulated and maintained in culture for up to 4 days. CXCR4 cell-surface expression on endothelial cells was induced after overnight incubation with vascular endothelial growth factor (VEGF). Gene transfer studies showed that only the peptide-targeted lipoplexes transfected the endothelium, and only after CXCR4 had been induced with VEGF. These results demonstrate that non-viral transfection complexes can be targeted to cells expressing CXCR4, and that gene transfer is dependent upon cell surface receptor expression levels.

DNA/Lipid complex incorporated with fibronectin to cell adhesion enhances transfection efficiency in prostate cancer cells and xenografts

Previously we have described the development and applications of lipid-based nanoparticles for gene delivery vector. In an attempt to improve transfection efficiency using the cell adhesion of extracellular matrix (ECM) to DNA/lipid complex (nanoplex), the mRNA expression of integrin alpha2beta1 and CD44 in prostate cancer cells was detected as adhesion molecules for fibronectin (Fn), collagen I (Col) and laminin (Lam) using a commercially available cDNA array (GEArray) system. These ECM proteins could enhance DNA transfection activity in cells when coated on the nanoplex. Among the ECM proteins, Fn-coating nanoplexes significantly increased transfection activity 2-fold in prostate cancer PC-3 cells, and exhibited higher DNA transfection activities to PC-3 xenografts, compared with commercially available cationic polymer in vivo jetPEI. These results indicated that Fn-coating nanoplexes could facilitate efficient transfection of prostate tumor cells.

RGD-based strategies for selective delivery of therapeutics and imaging agents to the tumour vasculature

During the past decade, RGD-peptides have become a popular tool for the targeting of drugs and imaging agents to alphavbeta3-integrin expressing tumour vasculature. RGD-peptides have been introduced by recombinant means into therapeutic proteins and viruses. Chemical means have been applied to couple RGD-peptides and RGD-mimetics to liposomes, polymers, peptides, small molecule drugs and radiotracers. Some of these products show impressive results in preclinical animal models and a RGD targeted radiotracer has already successfully been tested in humans for the visualization of alphavbeta3-integrin, which demonstrates the feasibility of this approach. This review will summarize the structural requirements for RGD-peptides and RGD-mimetics as ligands for alphavbeta3. We will show how they have been introduced in the various types of constructs by chemical and recombinant techniques. The importance of multivalent RGD-constructs for high affinity binding and internalization will be highlighted. Furthermore the in vitro and in vivo efficacy of RGD-targeted therapeutics and diagnostics reported in recent years will be reviewed.

Synthesis and application of a non-viral gene delivery system for immunogene therapy of cancer

The synthesis and gene delivery application of a novel lipopolymer, PEG-PEI-CHOL (PPC), is described. PPC is composed of a low molecular weight branched polyethylenimine (PEI) covalently linked with functional groups methoxypolyethyleneglycol (PEG) and cholesterol (CHOL). The potential utility of PPC as a gene delivery polymer was evaluated by showing its ability to form stable nanocomplexes with DNA, protect DNA from degradation by DNase and mediate gene transfer in vitro and in vivo in solid tumors. The ratio of PEG/PEI/CHOL and nitrogen to phosphate (Polymer/DNA) was optimized for physico-chemical properties and gene delivery efficiency of PPC/DNA complexes. The gene therapy application of the polymer was shown following administration of a murine IL-12 plasmid (pmIL-12) formulated with PPC into tumors in mice which resulted in significant inhibition of tumor growth. The inhibitory effects of pmIL-12/PPC were enhanced when combined with specific chemotherapeutic agents, demonstrating the potential usefulness of pIL-12/PPC as an adjuvant therapy for cancer treatment.