Synergism in gene delivery by small PEIs and three different nonviral vectors

Polyethyleneimine-Based Lipopolyplexes as Carriers in Anticancer Gene Therapies

Recent years have witnessed rapidly growing interest in application of gene therapies for cancer treatment. However, this strategy requires nucleic acid carriers that are both effective and safe. In this context, non-viral vectors have advantages over their viral counterparts. In particular, lipopolyplexes—nanocomplexes consisting of nucleic acids condensed with polyvalent molecules and enclosed in lipid vesicles—currently offer great promise. In this article, we briefly review the major aspects of developing such non-viral vectors based on polyethyleneimine and outline their properties in light of anticancer therapeutic strategies. Finally, examples of current in vivo studies involving such lipopolyplexes and possibilities for their future development are presented.

Lipophilic Peptide Dendrimers for Delivery of Splice-Switching Oligonucleotides

Non-viral transfection reagents are continuously being developed in attempt to replace viral vectors. Among those non-viral vectors, dendrimers have gained increasing interest due to their unique molecular structure and multivalency. However, more improvements are still needed to achieve higher efficacy and lower toxicity. In this study, we have examined 18 peptide dendrimers conjugated to lipophilic moieties, such as fatty acids or hydrophobic amino acids, that were previously explored for siRNA. Reporter cells were employed to investigate the transfection of single strand splice-switching oligonucleotides (ONs) using these peptide dendrimers. Luciferase level changes reflecting efficiency varied with amino acid composition, stereochemistry, and complexation media used. 3rd generation peptide dendrimers with D-amino acid configuration were superior to L-form. Lead formulations with 3rd generation, D-amino acid peptide dendrimers increased the correction level of the delivered ON up to 93-fold over untreated HeLa Luc/705 cells with minimal toxicity. To stabilize the formed complexes, Polyvinyl alcohol 18 (PVA18) polymer was added. Although PVA18 addition increased activity, toxicity when using our best candidates G 2,3KL-(Leu)₄ (D) and G 2,3KL-diPalmitamide (D) was observed. Our findings demonstrate the potential of lipid-conjugated, D-amino acid-containing peptide dendrimers to be utilized as an effective and safe delivery vector for splice-switching ONs.

Sugar and Polymer Excipients Enhance Uptake and Splice-Switching Activity of Peptide-Dendrimer/Lipid/Oligonucleotide Formulations

Non-viral transfection vectors are commonly used for oligonucleotide (ON) delivery but face many challenges before reaching the desired compartments inside cells. With the support of additional compounds, it might be more feasible for a vector to endure the barriers and achieve efficient delivery. In this report, we screened 18 different excipients and evaluated their effect on the performance of peptide dendrimer/lipid vector to deliver single-stranded, splice-switching ONs under serum conditions. Transfection efficiency was monitored in four different reporter cell lines by measuring splice-switching activity on RNA and protein levels. All reporter cell lines used had a mutated human β-globin intron 2 sequence interrupting the luciferase gene, which led to an aberrant splicing of luciferase pre-mRNA and subsidence of luciferase protein translation. In the HeLa Luc/705 reporter cell line (a cervical cancer cell line), the lead excipients (Polyvinyl derivatives) potentiated the splice-switching activity up to 95-fold, compared to untreated cells with no detected cytotoxicity. Physical characterization revealed that lead excipients decreased the particle size and the zeta potential of the formulations. In vivo biodistribution studies emphasized the influence of formulations as well as the type of excipients on biodistribution profiles of the ON. Subsequently, we suggest that the highlighted impact of tested excipients would potentially assist in formulation development to deliver ON therapeutics in pre-clinical and clinical settings.

Novel peptide-dendrimer/lipid/oligonucleotide ternary complexes for efficient cellular uptake and improved splice-switching activity

Despite the advances in gene therapy and in oligonucleotide (ON) chemistry, efficient cellular delivery remains an obstacle. Most current transfection reagents suffer from low efficacy or high cytotoxicity. In this report, we describe the synergism between lipid and dendrimer delivery vectors to enhance the transfection efficiency, while avoiding high toxicity. We screened a library of 20 peptide dendrimers representing three different generations and evaluated their capability to deliver a single-stranded splice-switching ON after formulating with lipids (DOTMA/DOPE). The transfection efficiency was analyzed in 5 reporter cell lines, in serum-free and serum conditions, and with 5 different formulation protocols. All formulations displayed low cytotoxicity to the majority of the tested cell lines. The complex sizes were < 200 nm; particle size distributions of effective mixtures were < 80 nm; and, the zeta potential was dependent on the formulation buffer used. The best dendrimer enhanced transfection in a HeLa reporter cell line by 30-fold compared to untreated cells under serum-free conditions. Interestingly, addition of sucrose to the formulation enabled - for the first time - peptide dendrimers/lipid complexes to efficiently deliver splice-switching ON in the presence of serum, reaching 40-fold increase in splice switching. Finally, in vivo studies highlighted the potential of these formulae to change the biodistribution pattern to be more towards the liver (90% of injected dose) compared to the kidneys (5% of injected dose) or to unformulated ON. This success encourages further development of peptide dendrimer complexes active in serum and future investigation of mechanisms behind the influence of additives on transfection efficacy.

Collapse of DNA in packaging and cellular transport

The dawn of molecular biology and recombinant DNA technology arose from our ability to manipulate DNA, including the process of collapse of long extended DNA molecules into nanoparticles of approximately 100 nm diameter. This condensation process is important for the packaging of DNA in the cell and for transporting DNA through the cell membrane for gene therapy. Multivalent cations, such as natural polyamines (spermidine and spermine), were initially recognized for their ability to provoke DNA condensation. Current research is targeted on molecules such as linear and branched polymers, oligopeptides, polypeptides and dendrimers that promote collapse of DNA to nanometric particles for gene therapy and on the energetics of DNA packaging.

Optimized polyethylenimine (PEI)-based nanoparticles for siRNA delivery, analyzed in vitro and in an ex vivo tumor tissue slice culture model

The non-viral delivery of small RNA molecules like siRNAs still poses a major bottleneck for their successful application in vivo. This is particularly true with regard to crossing physiological barriers upon systemic administration. We have previously established polyethylenimine (PEI)-based complexes for therapeutic RNA formulation. These nanoplexes mediate full RNA protection against nucleolytic degradation, delivery to target tissues as well as cellular uptake, intracellular release and therapeutic efficacy in preclinical in vivo models. We herein present data on different polyplex modifications for the defined improvement of physicochemical and biological nanoparticle properties and for targeted delivery. (i) By non-covalent modifications of PEI polyplexes with phospholipid liposomes, ternary complexes ("lipopolyplexes") are obtained that combine the favorable features of PEI and lipid systems. Decreased cytotoxicity and highly efficient delivery of siRNA is achieved. Some lipopolyplexes also allow prolonged storage, thus providing formulations with higher stability. (ii) Novel tyrosine modifications of low molecular weight PEI offer further improvement of stability, biocompatibility, and knockdown efficacy of resulting nanoparticles. (iii) For ligand-mediated uptake, the shielding of surface charges is a critical requirement. This is achieved by PEI grafting with polyethylene glycol (PEG), prior to covalent coupling of anti-HER1 antibodies (Erbitux®) as ligand for targeted delivery and uptake. Beyond tumor cell culture, analyses are extended towards tumor slice cultures from tumor xenograft tissues which reflect more realistically the in vivo situation. The determination of siRNA-mediated knockdown of endogenous target genes, i.e., the oncogenic survival factor survivin and the oncogenic receptor tyrosine kinase HER2, reveals nanoparticle penetration and biological efficacy also under intact tissue and stroma conditions.

Comparative evaluation and optimization of off-the-shelf cationic polymers for gene delivery purposes

Commercially sourced cationic polymers for gene delivery are thoroughly characterized, compared and optimized.

Efficient down-regulation of PKC-α gene expression in A549 lung cancer cells mediated by antisense oligodeoxynucleotides in dendrosomes

The completion of human genome project has increased our knowledge of the molecular mechanisms of many diseases, including cancer, thus providing new opportunities for gene therapy. Antisense oligodeoxynucleotides (AsODN) possess great potential as sequence-specific therapeutic agents, which in contrast to classic treatments provide more efficient and target-specific approach to modulate disease-related genes. To be therapeutically effective, sufficient concentrations of intact AsODN must bypass membrane barriers and access the site of action. In this study, a dendrosome delivery strategy was designed to improve the encapsulation of AsODN in non-cationic liposomes to target PKC-α in lung cancer cells in vitro. Subcellular trafficking of fluorescently labeled AsODN was visualized using confocal microscopy. Uptake and expression of mRNA and target protein after AsODN delivery was measured by flow cytometry, qRT-PCR and Western blot analysis, respectively. Dendrosomes showed favorable physicochemical parameters: high encapsulation efficiency and uptake in serum-containing medium with no apparent cytotoxicity. AsODN encapsulated in dendrosome efficiently and specifically suppress the target gene at both mRNA and protein levels. Additional in vivo studies on the application of dendrosome as a delivery system for nucleic acid molecules may lead to improvement of this technology and facilitate the development of therapeutic antisense techniques.

Type and composition of surfactants mediating gene transfection of polyethylenimine-coated liposomes

Background:

The objective of this study was to compare the transfection efficiency of anionic liposomes coated with polyethylenimine (PEI) with that of PEI and Lipofectamine 2000^™ using the plasmid DNA encoding green fluorescent protein in a human hepatoma (Huh7) cell line.

Methods:

Factors affecting transfection efficiency, including type of surfactant, ratio of phosphatidylcholine (PC)/surfactant, carrier/DNA weight ratio, and the presence of serum have been investigated. Anionic liposomes, composed of PC and anionic surfactants, ie, sodium oleate (NaO), sodium taurocholate (NaT), or zwitterionic surfactant (3-[{3-cholamidopropyl}-dimethylammonio]-1-propanesulfonate, CHAPS) at molar ratios of 10:1, 10:1.5, and 10:2 were prepared by the sonication method. Subsequently, they were coated with PEI to produce polycationic liposomes (PCL).

Results:

PCL was able to condense with pDNA depending on the PCL/DNA weight ratio. PCL composed of PC:NaO (10:2) showed higher transfection efficiency than NaT and CHAPS at all weight ratios tested. Higher transfection efficiency and gene expression were observed when the carrier/DNA weight ratio increased. The highest transfection efficiency was found at a weight ratio of 0.5.

Conclusion:

This PCL showed remarkably high transfection efficiency with low cytotoxicity to Huh7 cells in vitro, in comparison with PEI and Lipofectamine 2000.

Hydrophobically modified dendrons: developing structure-activity relationships for DNA binding and gene transfection

This paper develops a structure-activity relationship understanding of the way in which surfactant-like dendrons with hydrophilic spermine surface groups and a variety of lipophilic units at their focal points can self-assemble and subsequently bind to DNA with high affinity. The choice of functional group at the focal point of the dendron and the high tunability of the molecular structure have a very significant impact on DNA binding. Mesoscale modeling of the mode of dendron self-assembly provides a direct insight into how the mode of self-assembly exerts its effect on the DNA binding process. In particular, the hydrophobic unit controls the number of dendrons in the self-assembled micellar structures, and hence their diameters and surface charge density. The DNA binding affinity correlates with the surface charge density of the dendron aggregates. Furthermore, these structure-activity effects can also be extended to cellular gene delivery, as surface charge density plays a role in controlling the extent of endosomal escape. It is reported that higher generation dendrons, although binding DNA less strongly than the self-assembling lower generation dendrons, are more effective for transfection. The impact of the lipophilic group at the focal point is less significant for the DNA binding ability of these larger dendrons, which is predominantly controlled by the spermine surface groups, but it does modify the levels of gene transfection. Significant synergistic effects on gene delivery were observed when employing combinations of the dendrons and polyethyleneimine (PEI, 25 kDa), with transfection becoming possible at low loading levels where the two components would not transfect individually, giving practically useful levels of gene delivery.

Role of polyplex intermediate species on gene transfer efficiency: polyethylenimine-DNA complexes and time-resolved fluorescence spectroscopy

Polyethylenimine (PEI) is a cationic DNA condensing polymer that facilitates gene transfer into the mammalian cells. The highest gene transfer with branched PEI is obtained at high nitrogen/phosphate (N/P) ratios with free PEI present. The small molecular weight PEI alone is not able to mediate DNA transfection. Here, we used recently developed time-resolved fluorescence spectroscopic method to study the mechanism of PEI-DNA complex formation and to investigate how free PEI, mean molecular weight, and branching of PEI affect the complexes. Analysis of fluorescence lifetimes and time-resolved spectra revealed that for both linear and branched high-molecular-weight PEI the complexation takes place in two steps, but the small-molecular-weight branched PEI complexed DNA at a single step. According to the binding constants obtained from time-resolved spectroscopic measurements, the affinity of N/P complexation per nitrogen atom is highest for LPEI and weakest for BPEI, whereas SPEI-DNA complexation showed intermediate values. Thus, the binding constant alone does not give adequate measure for transfection efficiency. On the other hand, the presence of intermediate states during the polyplex formation seems to be favorable for the gene transfection. Free PEI had no impact on the physical state of PEI-DNA complexes, even though it was essential for gene transfection in the cell culture. In conclusion, the molecular size and topology of PEI have direct influence on the DNA complexation but the free PEI does not. Free PEI must facilitate transfection at the cellular level and not via indirect effects on the PEI-DNA complexes.

Carbosilane dendrimers to transfect human astrocytes with small interfering RNA targeting human immunodeficiency virus

BACKGROUND

HIV infection of the CNS is the principle cause of HIV-associated dementia in adults and encephalopathy in children. Gene therapy techniques such as small interfering RNA (siRNA) possess great potential in drug development, but first they must overcome the key obstacle of reaching the interior of the affected cells. A successful delivery vector for anti-HIV drugs that is capable of crossing the blood-brain barrier (BBB) could provide a way of addressing this issue. Non-viral vectors such as dendrimers offer a means for effectively delivering and transfecting siRNA to the target cells.

OBJECTIVE

To evaluate the application of gene therapy for reducing HIV replication in human astrocytes.

METHODS

We used the 2G-NN16 amino-terminated carbosilane dendrimer as a method for delivering siRNA to HIV-infected human astrocytes. We tested the cytotoxicity in human astrocytoma cells caused by 2G-NN16 and dendriplexes formed with siRNA (siRNA/2G-NN16) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium-bromide (MTT) and lactate dehydrogenase assays. The ability to transfect human astrocytes with siRNA/2G-NN16 dendriplexes was tested by flow cytometry and immunofluorescence microscopy. To assess the potential capability of siRNA/2G-NN16 dendriplexes for crossing the BBB, we used an in vitro transcytosis assay with bovine brain microvascular endothelial cells. HIV-1 inhibition assays using 2G-NN16 and siRNA/2G-NN16 dendriplexes were determined by quantification of the viral load from culture supernatants of the astrocytes.

RESULTS

A gradual time-controlled degradation of the 2G-NN16 dendrimer and liberation of its siRNA cargo between 12 and 24 hours was observed via gel electrophoresis. There was no cytotoxicity in HIV-infected or non-infected human astrocytoma cells when treated with up to 24 microg/mL of 2G-NN16 dendrimer or siRNA/2G-NN16 dendriplexes, and siRNA/2G-NN16 dendriplexes were seen to successfully transfect human astrocytes even after crossing an in vitro BBB model. More interestingly, transfected siRNA was observed to exert a biologic effect, as dendriplexes were shown to down-regulate the housekeeping gene GAPDH and to reduce replication of HIV-1 strains X4-HIV NL4-3 and R5-HIV BaL in human astrocytes.

CONCLUSIONS

The 2G-NN16 dendrimer successfully delivers and transfects siRNA to HIV-infected human astrocytes and achieves gene silencing without causing cytotoxicity.

A reliable method for detecting complexed DNA in vitro

Quantification of eluted nucleic acids is a critical parameter in characterizing biomaterial based gene-delivery systems. The most commonly used method is to assay samples with an intercalating fluorescent dye such as PicoGreen®. However, this technique was developed for unbound DNA and the current trend in gene delivery is to condense DNA with transfection reagents, which interfere with intercalation. Here, for the first time, the DNA was permanently labeled with the fluorescent dye Cy5 prior to complexation, an alternative technique hypothesized to allow quantification of both bound and unbound DNA. A comparison of the two methods was performed by quantifying the elution of six different varieties of DNA complexes from a model biomaterial (collagen) scaffold. After seven days of elution, the PicoGreen® assay only allowed detection of three types of complexes (those formed using Lipofectin™ and two synthesised copolymers). However, the Cy5 fluorescent labeling technique enabled detection of all six varieties including those formed via common transfection agents poly(ethylene imine), poly-L-lysine and SuperFect™. This allowed reliable quantification of the elution of all these complexes from the collagen scaffold. Thus, while intercalating dyes may be effective and reliable for detecting double-stranded, unbound DNA, the technique described in this work allowed reliable quantification of DNA independent of complexation state.

Non-viral gene therapy for myocardial engineering

Despite significant advances in surgical and pharmacological techniques, myocardial infarction (MI) remains the main cause of morbidity in the developed world because no remedy has been found for the regeneration of infarcted myocardium. Once the blood supply to the area in question is interrupted, the inflammatory cascade, among other mechanisms, results in the damaged tissue becoming a scar. The goals of cardiac gene therapy are essentially to minimize damage, to promote regeneration, or some combination thereof. While the vector is, in theory, less important than the gene being delivered, the choice of vector can have a significant impact. Viral therapies can have very high transfection efficiencies, but disadvantages include immunogenicity, retroviral-mediated insertional mutagenesis, and the expense and difficulty of manufacture. For these reasons, researchers have focused on non-viral gene therapy as an alternative. In this review, naked plasmid delivery, or the delivery of complexed plasmids, and cell-mediated gene delivery to the myocardium will be reviewed. Pre-clinical and clinical trials in the cardiac tissue will form the core of the discussion. While unmodified stem cells are sometimes considered therapeutic vectors on the basis of paracrine mechanisms of action basic understanding is limited. Thus, only genetically modified cells will be discussed as cell-mediated gene therapy.

Synthesis and transfection properties of a series of lipidic neamine derivatives

With the view to develop novel bioinspired nonviral vectors for gene delivery, we synthesized a series of cationic lipids with a neamine headgroup, which incorporates rings I and II of the natural antibiotic aminoglycoside neomycin B. Indeed, we reasoned that neamine might constitute a straightforward and versatile building block for synthesizing a variety of lipophilic aminoglycosides and modulating their characteristics such as size, topology, lipophilicity, number of charges, and charge density. Neamine derivatives bearing long dialkyl chains, one or two neamine headgroups, and four to ten protonatable amine functions were prepared through the selective alkylation of the 4'- or 5-hydroxyl function in ring I and ring II of neamine, respectively. The transfection activity of the twelve derivatives synthesized was investigated in vitro in gene transfection experiments using several mammalian cell lines. The results allowed us to unveil interesting structure-activity relationships and to identify a formulation incorporating a small neamine derivative as a highly efficient gene delivery system.

How to study dendriplexes II: Transfection and cytotoxicity

This paper reviews different techniques for analyzing the transfection efficiencies and cytotoxicities of dendriplexes-complexes of nucleic acids with dendrimers. Analysis shows that three plasmids are mainly used in transfection experiments: plasmid DNA encoding luciferase from the firefly Photinus pyralis, beta-galactosidase, or green fluorescent protein. The effective charge ratio of transfection does not directly correlate with the charge ratio obtained from gel electrophoresis, zeta-potential or ethidium bromide intercalation data. The most popular cells for transfection studies are human embryonic kidney cells (HEK293), mouse embryonic cells (NIH/3T3), SV40 transformed monkey kidney fibroblasts (COS-7) and human epithelioid cervical carcinoma cells (HeLa). Cellular uptake is estimated using fluorescently-labeled dendrimers or nucleic acids. Transfection efficiency is measured by the luciferase reporter assay for luciferase, X-Gal staining or beta-galactosidase assay for beta-galactosidase, and confocal microscopy for green fluorescent protein. Cytotoxicity is determined by the MTT test and lactate dehydrogenase assays. On the basis of the papers reviewed, a standard essential set of techniques for characterizing dendriplexes was constructed: (1) analysis of size and shape of dendriplexes in dried/frozen state by electron or atomic force microscopy; (2) analysis of charge/molar ratio of complexes by gel electrophoresis or ethidium bromide intercalation assay or zeta-potential measurement; (3) analysis of hydrodynamic diameter of dendriplexes in solution by dynamic light scattering. For the evaluation of transfection efficiency the essential techniques are (4) luciferase reporter assay, beta-galactosidase assay or green fluorescent protein microscopy, and (5) cytotoxicity by the MTT test. All these tests allow the transfection efficiencies and cytotoxicities of different kinds of dendrimers to be compared.

Efficient siRNA delivery by the cationic liposome DOTAP in human hematopoietic stem cells differentiating into dendritic cells

RNA interference technology is an ideal strategy to elucidate the mechanisms associated with human CD34(+) hematopoietic stem cell differentiation into dendritic cells. Simple manipulations in vitro can unequivocally yield alloreactive or tolerogenic populations, suggesting key implications of biochemical players that might emerge as therapeutic targets for cancer or graft-versus-host disease. To knockdown proteins typically involved in the biology of dendritic cells, we employed an siRNA delivery system based on the cationic liposome DOTAP as the carrier. Freshly-isolated CD34(+) cells were transfected with siRNA for cathepsin S with negligible cytotoxicity and transfection rates (>60%) comparable to the efficiency shown by lentiviral vectors. Further, cathepsin S knockdown was performed during both cell commitment and through the entire 14-day differentiation process with repeated transfection rounds that had no effect per se on cell development. Tested in parallel, other commercially-available chemical reagents failed to meet acceptable standards. In addition to safe and practical handling, a direct advantage of DOTAP over viral-mediated techniques is that transient silencing effects can be dynamically appraised through the recovery of targeted proteins. Thus, our findings identify DOTAP as an excellent reagent for gene silencing in resting and differentiating CD34(+) cells, suggesting a potential for applications in related preclinical models.

A matrix reservoir for improved control of non-viral gene delivery

Non-viral gene delivery suffers from a number of limitations including short transgene expression times and low transfection efficiency. Collagen scaffolds have previously been investigated as in vitro DNA reservoirs, which allow sustained release of genetic information. Efficient viral gene-transfer from these scaffolds has previously been demonstrated. However, due to concerns about the safety of viral gene therapy, the use of non-viral vectors may be preferable. In this study a DNA-dendrimer complex embedded in a cross-linked collagen scaffold was investigated as a reservoir for non-viral delivery. Elution from the scaffolds and transfection of seeded rat mesenchymal stem cells were used to evaluate the scaffold's ability to act as a reservoir for the complexes. Elution from the scaffolds was minimal after 2 days with a total of 25% of the complexes released after 7 days. Extended transgene expression after DNA-dendrimer complex delivery from the scaffolds in comparison to direct delivery to cells was observed. The elongated transfection period and relatively high levels of reporter gene expression are significant advantages over other non-viral gene therapy techniques. This platform has the potential to be an effective method of scaffold-mediated gene delivery suitable for in vitro and in vivo applications.

Activated and non-activated PAMAM dendrimers for gene delivery in vitro and in vivo

Nanotechnology, though not a new concept, has gained importance in medical breakthroughs. The preparation of nanosystems like polymeric nanoparticles can be used for drug and gene delivery. In this study dendrimeric nanoparticles prepared with generations 4 and 5 (G4, G5) polyamidoamine (PAMAM) dendrimers and plasmid DNA were characterized and their ability to transfect cells in vitro and in vivo evaluated. Additionally, the efficacy of these dendrimers on activation after heat treatment has been tested to attempt an enhancement in transfection activity over that of intact dendrimers. Measurements of the particle size and zeta potential as a function of the charge ratio and the generation of the polymer reveal that no significant differences were obtained in size by using G4 or G5 polymers in nonactivated dendriplexes prepared at different charge ratios. The zeta potentials of the dendriplexes are strongly positive and differ only slightly. Atomic force microscopy images of complexes showed that they are spherical, individualized, and homogeneously distributed. These vectors were also highly effective in protecting DNA from attack by DNase I and increased the efficiency of plasmid-mediated gene transfer in vitro to liver (HepG2) and colon (CT26) cancer cells as compared with naked DNA, even in the presence of 60% fetal bovine serum. Expression is enhanced at higher charge ratios with maximal values obtained at a charge ratio of 10:1 (+/-) and by increasing the dendrimer generation. Finally, the transfection activity of G4 and G5 dendriplexes was significantly enhanced in HepG2 and CT26 cells by activation of the dendrimers. In this respect we have optimized the time of activation to obtain the optimal levels of gene expression. Also, intravenously administered activated G4 and G5 dendrimer-DNA complexes are superior to the nonactivated ones in terms of gene transfer efficiency in vivo. In conclusion, our results showed that G4 and G5 PAMAM dendrimers are an effective nanosystem for gene delivery to colon and liver cancer cells in vitro, as well as for in vivo therapeutic applications.

FROM THE CLINICAL EDITOR

This paper describes the synthesis and potential applications of mixed nanoparticles prepared with generations 4 and 5 (G4, G5) poly(amidoamine) (PAMAM) dendrimers and plasmid DNA. These mixed nanoparticles proved to be effective for gene delivery to colon and liver cancer cells in vitro, as well as in vivo.

Different viabilities and toxicity types after 6-OHDA and Ara-C exposure evaluated by four assays in five cell lines

Cell viability studies are useful when screening novel drugs for the diseases that are related to either increased cell death or enhanced cell survival. There are numerous assays but the results that they produce are rarely unanimous. Here we compared the performance of (1) morphological microscopic assay with double DNA staining, (2) propidium iodide-digitonin assay, (3) MTT-assay, and (4) ATP-assay in human neuroblastoma (SH-SY5Y), rat glioma (C6), rabbit smooth muscle (SMC), Chinese hamster ovary (CHO) and monkey fibroblast cells (CV1-P) exposed to cytosine arabinoside (Ara-C) and 6-hydroxydopamine (6-OHDA). We found that neuronal SH-SY5Y cells were most sensitive to both toxins and the results in all viability tests correlated well. All the other cell lines were much more resistant, particularly to Ara-C but also to 6-OHDA. Toxicity of the compounds was best revealed by MTT and ATP assays, measuring the metabolic activity of the cells, and only occasionally by morphological observations or with the propidium iodide-digitonin assay which is based on the cell membrane integrity. In this research, Ara-C induced pure apoptosis whereas the toxicity type of 6-OHDA was dose-dependent. The use of several viability tests and cell lines is recommended when studying cell death, particularly apoptosis, and performance of antiapoptotic compounds.

Low-Molecular-Weight Polyethylenimine Enhanced Gene Transfer by Cationic Cholesterol-Based Nanoparticle Vector

Both polyethylenimine (PEI) polymers and cationic nanoparticles have been widely used for non-viral DNA transfection. Previously, we reported that cationic nanoparticles composed of cholesteryl-3beta-carboxyamidoethylene-N-hydroxyethylamine and Tween 80 (NP-OH) could deliver plasmid DNA (pDNA) with high transfection efficiency. To increase the transfection activity of NP-OH, we investigated the potential synergism of PEI and NP-OH for the transfection of DNA into human prostate tumor PC-3, human cervices tumor Hela, and human lung adenocarcinoma A549 cells. The transfection efficiency with low-molecular PEI (MW 600) was low, but that with a combination of NP-OH and PEI was higher than with NP-OH alone, being comparable to commercially available lipofectamine 2,000 and lipofectamine LTX, with very low cytotoxicity. Low-molecular weight PEI could not compact pDNA in size, but rather might help to dissociate pDNA from the complex and release pDNA from the endosome to cytoplasm by the proton sponge effect. Therefore, the combination of cationic cholesterol-based nanoparticles and a low-molecular PEI has potential as a non-viral DNA vector for gene delivery.

Transcriptionally Targeted Nonviral Gene Transfer Using a β-Catenin/TCF-Dependent Promoter in a Series of Different Human Low Passage Colon Cancer Cells

Nonviral transfections of six low passage human colon cancer cell lines using the artificial beta-catenin/TCF-dependent promoter CTP4 demonstrated a high promoter activity which was 1000- to 70000-fold higher than in HeLa control cells. Luciferase gene expression levels obtained with CTP4 in epithelial-like tumor cell cultures were only slightly lower than with the strong viral CMV promoter/enhancer, whereas in less differentiated tumor cultures CTP4 expression levels exceeded the CMV expression levels up to 28-fold. Three cell lines representing different morphology typical of the original tumors, more differentiated epithelial-like (COGA-5), piled-up (COGA-12), and poorly differentiated rounded-up (COGA-3), were selected for further investigation. Gene transfer was optimized using lipopolyplex formulation of cationic lipid DOSPER and polycation PEI25br. Lipopolyplexes enabled up to 1300-fold or 400-fold higher luciferase expression compared to the corresponding lipoplexes or polyplexes, respectively. Lipopolyfection of an interleukin-2 (IL-2) gene expression construct driven by the CTP4 promoter resulted in very high levels of up to 95 ng of secreted IL-2 per 105 cells and 24 h. The lipopolyplexes were also able to transfect multicellular spheroids that mimic the three-dimensional structure of real tumors.

Optimized lipopolyplex formulations for gene transfer to human colon carcinoma cells underin vitro conditions

BACKGROUND

Polycation (PC, polyplex), cationic lipid (CL, lipoplex), and a combination of PC/CL (lipopolyplex) formulations were investigated for gene transfer to slow-proliferating human colon carcinoma cell lines (COGA).

METHODS

The luciferase reporter gene was complexed with either PC, CL, or PC/CL. PCs included linear (PEI22lin, 22 kDa) and branched polyethylenimine (PEI2k, 2 kDa; PEI25br, 25 kDa) and poly-L-lysine (PLL18 with 18 lysine monomers). CLs included DOCSPER, DOSPER and DOTAP. Lipopolyplexes were formed by either sequentially first mixing DNA with PC or CL, followed by addition of CL or PC, respectively, or simultaneously with both PC and CL. Particle size and zeta-potential were determined and gene transfer and cytotoxicity were quantified on COGA-3, -5, -12, HeLa and Sw480 cells.

RESULTS

The highest gene transfer was achieved when DNA was first complexed with PC followed by CL. At low ionic strength, particles were small (50-130 nm) with a zeta-potential of +20-40 mV. At physiological ionic strength, only lipoplexes of DOCSPER or DOSPER and their respective lipopolyplexes with PEI25br were stable to aggregation (140-220 nm). Lipopolyplexes of PEI25br were between 5- to 400-fold more efficient compared to the corresponding lipoplexes or polyplexes in all cases. Chloroquine did not significantly affect lipopolyplex-mediated gene transfer.

CONCLUSIONS

Lipopolyplex formulations of PEI25br in combination with multivalent CLs (DOCSPER, DOSPER) are promising tools for in vitro and potentially also in vivo gene transfer to colorectal cancer cells.

Polycationic Block Copolymers of Poly(ethylene oxide) and Poly(propylene oxide) for Cell Transfection

A facile, one-step synthesis of cationic block copolymers of poly(2-N-(dimethylaminoethyl) methacrylate) (pDMAEMA) and copolymers of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) has been developed. The PEO-PPO-PEO-pDMAEMA (L92-pDMAEMA) and PEO-pDMAEMA copolymers were obtained via free radical polymerization of DMAEMA initiated by polyether radicals generated by cerium(IV). Over 95% of the copolymer fraction was of molecular mass ranging from 6.9 to 7.1 kDa in size, indicating the prevalence of the polyether-monoradical initiation mechanism. The L92-pDMAEMA copolymers possess parent surfactant-like surface activity. In contrast, the PEO-pDMAEMA copolymers lack significant surface activity. Both copolymers can complex with DNA. Hydrodynamic radii of the complexes of the L92-pDMAEMA and PEO-pDMAEMA with plasmid DNA ranged in size from 60 to 400 nm, depending on the copolymer/DNA ratio. Addition of Pluronic P123 to the L92-pDMAEMA complexes with DNA masked charges and decreased the tendency of the complex to aggregate, even at stoichiometric polycation/DNA ratios. The transfection efficiency of the L92-pDMAEMA copolymer was by far greater than that of the PEO-pDMAEMA copolymer. An extra added Pluronic P123 further increased the transfecton efficacy of L92-pDMAEMA, but did not affect that of PEO-pDMAEMA.

Design of Polyphosphoester‐DNA Nanoparticles for Non‐Viral Gene Delivery

Development of safe and effective non-viral gene carriers is still critical to the ultimate success of gene therapy. This review highlights our attempt to design the gene carriers in a systematic manner. We have synthesized a series of polymers with a phosphoester backbone containing different charge groups in the sidechain connected to the backbone through a phosphate (PO) or a phosphoramide (PN) bond. These gene carriers have different charge groups, sidechain lengths, and branching structures, but they are structurally related to allow a systematic investigation of the structure-property relationship, including DNA binding capacity, cytotoxicity, DNA protection, biodegradability, DNA release kinetics, and transfection efficiency.