Polyplex-mediated gene transfer into human retinal pigment epithelial cells in vitro

A combinatorial library of biodegradable polyesters enables non-viral gene delivery to post-mitotic human stem cell-derived polarized RPE monolayers

Safe and effective delivery of DNA to post-mitotic cells, especially highly differentiated cells, remains a challenge despite significant progress in the development of gene delivery tools. Biodegradable polymeric nanoparticles (NPs) offer an array of advantages for gene delivery over viral vectors due to improved safety, carrying capacity, ease of manufacture, and cell-type specificity. Here we demonstrate the use of a high-throughput screening (HTS) platform to synthesize and screen a library of 148 biodegradable polymeric nanoparticles, successfully identifying structures that enable efficient transfection of human pluripotent stem cell differentiated human retinal pigment epithelial (RPE) cells with minimal toxicity. These NPs can deliver plasmid DNA (pDNA) to RPE monolayers more efficiently than leading commercially available transfection reagents. Novel synthetic polymers are described that enable high efficacy non-viral gene delivery to hard-to-transfect polarized human RPE monolayers, enabling gene loss- and gain-of-function studies of cell signaling, developmental, and disease-related pathways. One new synthetic polymer in particular, 3,3'-iminobis(N,N-dimethylpropylamine)-end terminated poly(1,5-pentanediol diacrylate-co-3 amino-1-propanol) (5-3-J12), was found to form self-assembled nanoparticles when mixed with plasmid DNA that transfect a majority of these human post-mitotic cells with minimal cytotoxicity. The platform described here can be utilized as an enabling technology for gene transfer to human primary and stem cell-derived cells, which are often fragile and resistant to conventional gene transfer approaches.

Dendrimer-Enabled Therapeutic Antisense Delivery Systems as Innovation in Medicine

Antisense oligonucleotide (AON)-based therapies concern the treatment for genetic disorders or infections such as a range of neurodegenerative and neuromuscular diseases and have shown benefits in animal models and patients. Nevertheless, successes in the clinic are still strongly limited by unfavorable biodistribution and poor cellular uptake of AONs. Dendrimer macromolecules are synthetically accessible and consist of a core with repeated iterations (named branches) surrounding this core, and on the periphery functional groups which can be modified for ligand attachment. The generations of these branched nanoparticles are based on the number of branches emanating from the core with layered architectures. Dendrimers show promise in several biomedical applications based on their tunable surface modifications allowing the adjustment of their in vivo behavior related to biocompatibility and pharmacokinetic parameters. Dendrimers can be used as nanocarriers of various types of drugs including AONs or nanodrugs. As nanocarriers, polycationic dendrimers can complex multiple negatively charged DNA oligonucleotides on their surface and form stable complexes to promote internalization into the cells based on a good cell membrane affinity. These nanocarriers complexing antisense oligonucleotides must be stable enough to reach the cellular target, but with adequate in vivo global clearance, and have good pharmacokinetic (PK) and pharmacodynamic (PD) profiles. This Review was designed to analyze the development of AONs carried by polycationic and polyanionic (few example) dendrimers. This Review strongly supports the idea that dendrimers, with adequate modulation of their terminal groups, could be used to carry AONs in cells.

Synthetic nanocarriers for the delivery of polynucleotides to the eye

This review is a comprehensive analysis of the progress made so far on the delivery of polynucleotide-based therapeutics to the eye, using synthetic nanocarriers. Attention has been addressed to the capacity of different nanocarriers for the specific delivery of polynucleotides to both, the anterior and posterior segments of the eye, with emphasis on their ability to (i) improve the transport of polynucleotides across the different eye barriers; (ii) promote their intracellular penetration into the target cells; (iii) protect them against degradation and, (iv) deliver them in a long-term fashion way. Overall, the conclusion is that despite the advantages that nanotechnology may offer to the area of ocular polynucleotide-based therapies (especially AS-ODN and siRNA delivery), the knowledge disclosed so far is still limited. This fact underlines the necessity of more fundamental and product-oriented research for making the way of the said nanotherapies towards clinical translation.

Efficient gene delivery to primary human retinal pigment epithelial cells: The innate and acquired properties of vectors

The purpose of this study is designing non-viral gene delivery vectors for transfection of the primary human retinal pigment epithelial cells (RPE). In the design process of gene delivery vectors, considering physicochemical properties of vectors alone does not seem to be enough since they interact with constituents of the surrounding environment and hence gain new characteristics. Moreover, due to these interactions, their cargo can be released untimely or undergo degradation before reaching to the target cells. Further, the characteristics of cells itself can also influence the transfection efficacy. For example, the non-dividing property of RPE cells can impede the transfection efficiency which in most studies was ignored by using immortal cell lines. In this study, vectors with different characteristics differing in mixing orders of pDNA, PEI polymer, and PLGA/PEI or PLGA nanoparticles were prepared and characterized. Then, their characteristics and efficacy in gene delivery to RPE cells in the presence of vitreous or fetal bovine serum (FBS) were evaluated. All formulations showed no cytotoxicity and were able to protect pDNA from premature release and degradation in extracellular media. Also, the adsorption of vitreous or serum proteins onto the surface of vectors changed their properties and hence cellular uptake and transfection efficacy.

Dendrimers for gene delivery – a potential approach for ocular therapy?

Objectives

A vast number of blinding diseases have genetic aetiologies and may be treated by molecular based therapies such as antisense oligonucleotides or short interfering RNA. However, treatment success of ocular gene therapy is highly dependent on efficient delivery of such molecules.

Key findings

The majority of clinical studies for ocular gene therapy utilize viral vectors. While these have proven highly efficient, they show limited loading capacity and pose significant safety risks owing to their oncogenic and immunogenic effects. Non-viral gene carriers have emerged as a promising alternative with dendrimers providing great potential for gene therapy because of their size, shape and high density of modifiable surface groups. However, while dendrimers have been used extensively for drug and gene delivery to other organs, only a few studies have been reported on the eye.

Summary

This review focuses on the development of dendrimers for gene delivery with special emphasis on ocular gene therapy. Different synthesis approaches and types of dendrimers are discussed. Ocular gene therapy targets are highlighted with an overview of current clinical studies. The use of dendrimers in ocular gene delivery in comparison to liposomes and nanoparticles is also discussed. Finally, future prospects of tailored multifunctional dendrimers for ocular gene therapy are highlighted.

Nano-vectors for the Ocular Delivery of Nucleic Acid-based Therapeutics

Nucleic acid-based therapeutics have gained a lot of interest for the treatment of diverse ophthalmic pathologies. The first to enter in clinic has been an oligonucleotide, Vitravene^® for the treatment of cytomegalovirus infection. More recently, research on aptamers for the treatment of age related macular degeneration has led to the development of Macugen^®. Despite intense potential, effective ocular delivery of nucleic acids is a major challenge since therapeutic targets for nucleic acid-based drugs are mainly located in the posterior eye segment, requiring repeated invasive administration. Of late, nanotechnology-based nano-vectors have been developed in order to overcome the drawbacks of viral and other non-viral vectors. The diversity of nano-vectors allows for ease of use, flexibility in application, low-cost of production, higher transfection efficiency and enhanced genomic safety. Using nano-vector strategies, nucleic acids can be delivered either encapsulated or complexed with cationic lipids, polymers or peptides forming sustained release systems, which can be tailored according to the ocular tissue being targeted. The present review focuses on developments and advances in various nano-vectors for the ocular delivery of nucleic acid-based therapeutics, the barriers that such delivery systems face and methods to overcome them.

Enhanced delivery of monomethoxypoly(ethylene glycol)-poly(lactic-co-glycolic acid)-poly l-lysine nanoparticles loading platelet-derived growth factor BB small interfering RNA by ultrasound and/or microbubbles to rat retinal pigment epithelium cells

BACKGROUND

A novel small interfering RNA (siRNA) delivery method based on the combined use of nanoparticles (NPs) with ultrasound (US) and/or microbubbles (MBs) was introduced in the present study. We investigated the efficacy and safety of US and/or MBs-enhanced delivery of monomethoxypoly(ethylene glycol)-poly(lactic-co-glycolic acid)-poly l-lysine (mPEG-PLGA-PLL) NPs loading platelet-derived growth factor BB (PDGF-BB) siRNA to rat retinal pigment epithelium (RPE)-J cells.

METHODS

The effect of US and/or MBs on the delivery of NPs containing Cy3-labeled siRNA was evaluated by fluorescence microscopy and flow cytometry. Potential toxicity of NPs and cell viability under different conditions of US and/or MBs were assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method.

RESULTS

The results obtained showed that low intensity US or 15-20% MBs could increase the delivery efficiency of a lower concentration of mPEG-PLGA-PLL NPs loading siRNA to RPE-J cells, whereas the combination of US with MBs under the optimal conditions for the enhancement of NPs delivery did not further increase the cellular uptake of NPs compared to either US or MBs alone (p = 0.072 and p = 0.488, respectively). Under the optimal condition for US-enhanced NPs delivery, the enhanced PDGF-BB gene silencing with a combination of US and NPs encapsulating siRNA resulted in a significant decrease of mRNA and protein expression levels compared to NPs alone.

CONCLUSIONS

US and/or MBs could be used safely to enhance the delivery of NPs loading siRNA to rat RPE-J cells. A combination of the chemical (mPEG-PLGA-PLL NPs loading siRNA) and physical (US) approaches could more effectively downregulate the mRNA and protein expression of PDGF-BB.

Long-Lasting Secretion of Transgene Product from Differentiated and Filter-Grown Retinal Pigment Epithelial Cells After Nonviral Gene Transfer

PURPOSE

The purpose of this study was to investigate the extent, duration, and direction of transgene expression after nonviral gene transfer to differentiated retinal pigment epithelial (RPE) cells.

METHODS

Polarized human RPE cells (ARPE-19) were transfected with nonviral vectors [DOTAP/DOPE with and without protamine sulfate (PS), DOTAP, PEI (polyethyleneimine), DHP-12] using secreted alkaline phosphatase (SEAP) as a reporter gene. Cellular uptake was studied by flow cytometry.

RESULTS

Up to 80-fold differences were observed in the peak reporter gene expression. The highest peak levels and the longest lifetime of SEAP expression (> 69 days) were obtained with DOTAP/DOPE/PS/pDNA complexes. With PEI, higher expression was seen to the apical side than to the basolateral side.

CONCLUSIONS

In contrast to most differentiated epithelial cells, the differentiated RPE cells can be transfected at high and prolonged levels with selected lipoplexes.

A proline-rich peptide improves cell transfection of solid lipid nanoparticle-based non-viral vectors

The aim of this work was to improve the transfection efficacy of solid lipid nanoparticle (SLN)-based non-viral vectors into ARPE-19 cells through the addition of Sweet Arrow Peptide (SAP). First, we prepared SAP-DNA complexes at ratios of at least 50:1, and then incorporated them into the SLNs. All formulations were able to protect DNA, and the peptide favoured the most bioactive form (supercoiled) of open circular DNA turns. In vitro transfection studies of the vectors containing the pCMS-EGFP plasmid in HEK293 and ARPE-19 cell lines revealed that incorporation of SAP led to greater transfection in both cell lines, although via different mechanisms. The presence of SAP in the formulations did not affect the viability of HEK293 or ARPE-19 cells. In HEK293 cells, SAP enabled greater uptake of the vectors, and an SAP to DNA ratio of 50:1 was sufficient for enhancing transfection. In contrast, in ARPE-19 cells, SAP induced a change in the dominant entrance mechanism, from clathrin endocytosis to caveolae/raft-dependent endocytosis, thereby decreasing use of the lysosomal pathway and consequently, reducing vector degradation. The extent to which SAP uses one mechanism or the other largely depends on its concentration in the formulation.

Solid lipid nanoparticles for retinal gene therapy: transfection and intracellular trafficking in RPE cells

Retinal pigment epithelial (RPE) cells are usually employed to study DNA systems for diseases related to problems in the retina. Solid lipid nanoparticles (SLNs) have been shown to be useful non-viral vectors for gene therapy. The objective of this work was to evaluate the transfection capacity of SLNs in the human retinal pigment epithelial established cell line (ARPE-19) in order to elucidate the potential application of this vector in the treatment of retinal diseases. Results showed a lower transfection level of SLNs in ARPE-19 cells than in HEK293 (2.5% vs. 14.9% EGFP positive cells at 72h post-transfection). Trafficking studies revealed a delay in cell uptake of the vectors in ARPE-19 cells. Differences in internalization process into the two cell lines studied explain, in part, the difference in the gene expression. The clathrin-mediated endocytosis in ARPE-19 cells directs the solid lipid nanoparticles to lysosomes; moreover, the low division rate of this cell line hampers the entrance of DNA into the nucleus. The knowledge of intracellular trafficking is very useful in order to design more efficient vectors taking into account the characteristics of the specific cell line to be transfected.

Post-pegylated lipoplexes are promising vehicles for gene delivery in RPE cells

The retinal pigment epithelium (RPE) is a potential tissue for gene therapy. We recently demonstrated that pegylation of lipoplexes prevents their aggregation in the vitreous of the eye. However, pegylation of lipoplexes may affect their gene transfer capacity. Therefore we studied the effect of pegylation of lipoplexes on the transfection of RPE cells. "Pre-pegylated" lipoplexes were prepared by mixing pDNA with pegylated liposomes, while "post-pegylated" lipoplexes were obtained by pegylation of (non-pegylated) cationic liposome/DNA complexes with PEG-ceramides. Pre-pegylation of lipoplexes severely inhibited their transfection efficacy. The poor transfection was attributed to an inefficient and slower internalization of pre-pegylated lipoplexes by RPE cells, compared to non-pegylated lipoplexes. In addition, pre-pegylated lipoplexes also remained entrapped in the endosomes of the RPE cells. In contrast, post-pegylation of the lipoplexes with PEG-ceramides strongly improved their transfection efficiency. As PEG-ceramides are believed to leave the lipoplexes upon contact with the cell membranes, this "de-pegylation" results in non-pegylated lipoplexes which successfully escape from the endosomes. In conclusion, post-pegylation of lipoplexes with PEG-ceramides appears to be an attractive strategy to deliver therapeutic DNA to RPE cells as (a) it prevents the lipoplexes from aggregation in vitreous and (b) de-pegylation upon contact with RPE membranes results in successful DNA delivery.

In vivo gene transfection via intravitreal injection of cationic liposome/plasmid DNA complexes in rabbits

To optimize the in vivo ocular transfection efficiency of plasmid DNA (pDNA)/cationic liposome complexes, N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA)/dioleoylphosphatidylethanolamine (DOPE) (1:1 molar ratio) liposomes and DOTMA/cholesterol (Chol) (1:1 molar ratio) liposomes were prepared with varying amounts of pDNA. pDNA/cationic liposome complexes were intravitreally injected (100 microL) in rabbits, and luciferase activity in the cornea, aqueous humor, iris-ciliary body, lens, vitreous body, and retina was measured. Transfection efficiency of pDNA alone did not change with pDNA ranging from 40 to 85 mg. In contrast, transfection efficiency of pDNA complexed with DOTMA/Chol liposomes significantly increased with the amount of pDNA ranging from 40 to 85 microg (P < 0.05). pDNA complexed with DOTMA/DOPE liposomes could not be prepared with pDNA greater than 60 microg. Among these experiments, pDNA (85 microg) complexed with DOTMA/Chol liposomes (pDNA:cationic liposome charge ratio (- : +) = 1.0:2.0) showed the highest transfection efficiency in the ocular tissue and its transfection-mediated luciferase activity peaked at 3 days. Among the ocular tissues, the highest gene expression was observed in the aqueous humor.

Gene therapy for genetic and acquired retinal diseases

We present an overview of the current status of basic science and translational research being applied to gene therapy for eye disease, focusing on diseases of the retina. We discuss the viral and nonviral methods being used to transfer genes to the retina and retinal pigment epithelium, and the advantages and disadvantages of each approach. We review the various genetic and somatic treatment strategies that are being used for genetically determined and acquired diseases of the retina, including gene replacement, gene silencing by ribozymes and antisense oligonucleotides, suicide gene therapy, antiapoptosis, and growth factor therapies. The rationales for the specific therapeutic approaches to each disease are discussed. Schematics of gene transfer methods and therapeutic approaches are presented together with a glossary of gene transfer terminology.

Comparative analysis of the uptake and expression of plasmid vectors in human ciliary and retinal pigment epithelial cells in vitro

The retinal pigment epithelium is uniquely suited to gene therapy that uses lipid-mediated DNA transfer due to its high phagocytic activity in situ. We compared the relative efficacy of phagocytosis on the uptake of labeled plasmid vectors by retinal pigment epithelial and ciliary epithelial cells in vitro. Relative levels of endocytosis were then compared with the efficiency of marker transgene expression in these cells. Human retinal pigment epithelial and ciliary epithelial cells from a single donor were isolated and expanded in vitro. Polyplex-mediated transfections were performed using a rhodamine-labeled expression vector for green fluorescent protein. Rhodamine-labeled endosomes were examined by fluorescence microscopy at different time points. Rhodamine labeling and green fluorescent protein expression were analyzed by flow cytometry 48 h after transfection. These gene transfer studies showed that expression of transgenes does occur in both human retinal pigment epithelial and ciliary epithelial cells in vitro. Endocytosis of labeled plasmid vectors occurs at a significantly higher number and density in retinal pigment epithelial cells than in ciliary epithelial cells (P < 0.04). However, the efficiency of marker transgene expression is similar in the two cell types. These studies demonstrate that the higher intrinsic phagocytic activity does not enhance the efficacy of transgene expression in retinal pigment epithelial cells in vitro. Both human retinal pigment epithelial and ciliary epithelial cells are competent recipients for lipid-mediated gene transfer, and transgene expression occurs at similar levels in both cell types.