Promoter- and strain-selective enhancement of gene expression in a mouse skeletal muscle by a polymer excipient Pluronic P85

Strong immunogenicity & protection in mice with PlaCCine: A COVID-19 DNA vaccine formulated with a functional polymer

DNA- based vaccines have demonstrated the potential as a safe and effective modality. PlaCCine, a DNA-based vaccine approach described subsequently relies on a synthetic DNA delivery system and is independent of virus or device. The synthetic functionalized polymer combined with DNA demonstrated stability over 12 months at 4C and for one month at 25C. Transfection efficiency compared to naked DNA increased by 5-15-fold in murine skeletal muscle. Studies of DNA vaccines expressing spike proteins from variants D614G (pVAC15), Delta (pVAC16), or a D614G + Delta combination (pVAC17) were conducted. Mice immunized intramuscular injection (IM) with pVAC15, pVAC16 or pVAC17 formulated with functionalized polymer and adjuvant resulted in induction of spike-specific humoral and cellular responses. Antibody responses were observed after one immunization. And endpoint IgG titers increased to greater than 1x 105 two weeks after the second injection. Neutralizing antibodies as determined by a pseudovirus competition assay were observed following vaccination with pVAC15, pVAC16 or pVAC17. Spike specific T cell immune responses were also observed following vaccination and flow cytometry analysis demonstrated the cellular immune responses included both CD4 and CD8 spike specific T cells. The immune responses in vaccinated mice were maintained for up to 14 months after vaccination. In an immunization and challenge study of K18 hACE2 transgenic mice pVAC15, pVAC16 and pVAC17 induced immune responses lead to decreased lung viral loads by greater than 90 % along with improved clinical score. These findings suggest that PlaCCine DNA vaccines are effective and stable and further development against emerging SARS-CoV-2 variants is warranted.

The Interaction Mechanism of Intramuscular Gene Delivery Materials with Cell Membranes

It has been confirmed that skeletal muscle cells have the capability to receive foreign plasmid DNA (pDNA) and express functional proteins. This provides a promisingly applicable strategy for safe, convenient, and economical gene therapy. However, intramuscular pDNA delivery efficiency was not high enough for most therapeutic purposes. Some non-viral biomaterials, especially several amphiphilic triblock copolymers, have been shown to significantly improve intramuscular gene delivery efficiency, but the detailed process and mechanism are still not well understood. In this study, the molecular dynamics simulation method was applied to investigate the structure and energy changes of the material molecules, the cell membrane, and the DNA molecules at the atomic and molecular levels. From the results, the interaction process and mechanism of the material molecules with the cell membrane were revealed, and more importantly, the simulation results almost completely matched the previous experimental results. This study may help us design and optimize better intramuscular gene delivery materials for clinical applications.

The Progress of Non-Viral Materials and Methods for Gene Delivery to Skeletal Muscle

Since Jon A. Wolff found skeletal muscle cells being able to express foreign genes and Russell J. Mumper increased the gene transfection efficiency into the myocytes by adding polymers, skeletal muscles have become a potential gene delivery and expression target. Different methods have been developing to deliver transgene into skeletal muscles. Among them, viral vectors may achieve potent gene delivery efficiency. However, the potential for triggering biosafety risks limited their clinical applications. Therefore, non-viral biomaterial-mediated methods with reliable biocompatibility are promising tools for intramuscular gene delivery in situ. In recent years, a series of advanced non-viral gene delivery materials and related methods have been reported, such as polymers, liposomes, cell penetrating peptides, as well as physical delivery methods. In this review, we summarized the research progresses and challenges in non-viral intramuscular gene delivery materials and related methods, focusing on the achievements and future directions of polymers.

Self-Crosslinking Lipopeptide/DNA/PEGylated Particles: A New Platform for DNA Vaccination Designed for Assembly in Aqueous Solution

Delivery of plasmids for gene expression in vivo is an inefficient process that requires improvement and optimization to unlock the clinical potential of DNA vaccines. With ease of manufacture and biocompatibility in mind, we explored condensation of DNA in aqueous solution with a self-crosslinking, endosome-escaping lipopeptide (LP), stearoyl-Cys-His-His-Lys-Lys-Lys-amide (stearoyl-CH₂K₃), to produce cationic LP/DNA complexes. To test whether poly(ethylene glycol) (PEG)-ylation of these cationic complexes to neutralize the surface charge would improve the distribution, gene expression, and immune responses poly(ethylene glycol), these LP/DNA complexes were combined with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG₂₀₀₀). Fluorescence imaging illustrated that the cationic complexes exhibited the highest degree of localization and lowest degree of dispersion throughout the injected muscle, suggesting impaired mobility of cationic particles upon administration. Nanoluciferase reporter assays over a 90-day period demonstrated that gene expression levels in muscle were highest for PEGylated particles, with over a 200-fold higher level of expression than the cationic particles observed at 30 days. Humoral and cell-mediated immune responses were evaluated in vivo after injection of an ovalbumin expression plasmid. PEGylation improved both immune responses to the DNA complexes in mice. Overall, this suggests that PEGylation of cationic lipopeptide complexes can significantly improve both the transgene expression and immunogenicity of intramuscular DNA vaccines.

Characterization of the complexation phenomenon and biological activity in vitro of polyplexes based on Tetronic T901 and DNA

The complexation process and underlying mechanisms that rule the interaction of DNA with the cationic block copolymer Tetronic T901 to form polyplexes and their potential transfection efficiency have been studied under different solution conditions. We noted that T901 favors the formation of self-assembled structures with partially condensed DNA at smaller polymer concentrations than other Pluronic™/Tetronic™-type copolymers previously analysed. The observed polyplexes display sizes from the nano- to the micro- range as derived from DLS, electronic and optical microscopies. Also, copolymer micelles are observed at concentrations below the copolymer critical micellar concentration (cmc) induced by the presence of DNA. The complexation process is dependent on solution conditions, with electrostatic and ionic interactions being more important at acidic pH thanks to the predominant diprotonated form of the block copolymer which is less aggregation-prone, whilst dispersive forces are increasingly enhanced under basic conditions or when rising the solution temperature. Whatever the case, the complexation is mainly governed by entropic contributions, as denoted from ITC data. In vitro transfection experiments after complexing T901 with a pDNA encoding the expression of green fluorescein protein, GFP, show a relative successful fluorescence of transfected HeLa cells, which confirms the uptake, internalization and release of the genetic material within the cells at suitable [N]/[P] ratios with relatively low cytotoxicity. Despite the observed successful outcomes, the obtained transfection efficacies are slightly lower than those obtained with Lipofectamine2000, so further optimization of the polyplex formation conditions is envisaged in future studies.

Intracellular redox-responsive nanocarrier for plasmid delivery: in vitro characterization and in vivo studies in mice

Although some modifications of polyethyleneimine (PEI) properties have been explored to balance the transfection efficiency and cytotoxicity, its successful plasmid delivery in vitro and in vivo to realize its true therapeutic potentials remains a major challenge, mainly due to intracellular trafficking barriers. Herein, we present a delivery nanocarrier Pluronic-PEI-SS by conjugating reducible disulfide-linked PEI (PEI-SS) to biocompatible Pluronic for enhanced DNA delivery and transfection efficiency in vitro and in vivo. Pluronic-PEI-SS strongly condensed plasmid DNA to low positively charged nanocomplexes, exhibited good stability against deoxyribonuclease I digestion, and tended to be easily degraded in the presence of reducing agent 1,4-dithiothreitol. The in vitro transfection of the complex Pluronic-PEI-SS/DNA into HeLa and 293T cells resulted in lower cytotoxicity as well as significantly higher cellular uptake, nucleus transfection, and gene expression than Pluronic-PEI (25 kDa), PEI-SS, and PEI 25 kDa given alone. Furthermore, the in vivo transfection study demonstrated that Pluronic-PEI-SS/DNA complexes induced a higher enrichment than the commercial PEI/DNA complex in the tumor, indicating their potential application as biocompatible vector in gene delivery.

Synthesis of Electroneutralized Amphiphilic Copolymers with Peptide Dendrons for Intramuscular Gene Delivery

Intramuscular gene delivery materials are of great importance in plasmid-based gene therapy system, but there is limited information so far on how to design and synthesize them. A previous study showed that the peptide dendron-based triblock copolymer with its components arranged in a reversed biomembrane architecture could significantly increase intramuscular gene delivery and expression. Herein, we wonder whether copolymers with biomembrane-mimicking arrangement may have similar function on intramuscular gene delivery. Meanwhile, it is of great significance to uncover the influence of electric charge and molecular structure on the function of the copolymers. To address the issues, amphiphilic triblock copolymers arranged in hydrophilic-hydrophobic-hydrophilic structure were constructed despite the paradoxical characteristics and difficulties in synthesizing such hydrophilic but electroneutral molecules. The as-prepared two copolymers, dendronG2(l-lysine-OH)-poly propylene glycol2k(PPG2k)-dendronG2(l-lysine-OH) (rL2PL2) and dendronG3(l-lysine-OH)-PPG2k-dendronG3(l-lysine-OH) (rL3PL3), were in similar structure but had different hydrophilic components and surface charges, thus leading to different capabilities in gene delivery and expression in skeletal muscle. rL2PL2 was more efficient than Pluronic L64 and rL3PL3 when mediating luciferase, β-galactosidase, and fluorescent protein expressions. Furthermore, rL2PL2-mediated growth-hormone-releasing hormone expression could significantly induce mouse body weight increase in the first 21 days after injection. In addition, both rL2PL2 and rL3PL3 showed good in vivo biosafety in local and systemic administration. Altogether, rL2PL2-mediated gene expression in skeletal muscle exhibited applicable potential for gene therapy. The study revealed that the molecular structure and electric charge were critical factors governing the function of the copolymers for intramuscular gene delivery. It can be concluded that, combined with the previous study, both structural arrangements either reverse or similar to the biomembrane are effective in designing such copolymers. It also provides an innovative way in designing and synthesizing new electroneutralized triblock copolymers, which could be used safely and efficiently for intramuscular gene delivery.

Poly(ester amine) constructed from polyethylenimine and pluronic for gene delivery in vitro and in vivo

A series of poly (ester amines) (PEAs) constructed from low molecular weight polyethyleneimine (LPEI, Mw: 0.8k, 1.2k Da) and Pluronic (different molecular weight (Mw) and hydrophilic-lipophilic-balance (HLB)) components were synthesized, and evaluated in vitro and in vivo as gene delivery carriers. Most PEA polymers were able to bind and condense plasmid DNA effectively into particles of approximately 150 nm in solution at the polymer/DNA ratio of 5 and above. Transfection efficiency of the PEA polymers depends on particle size of the polymer/DNA complex, molecular weight and HLB of the Pluronics and the size of PEI within PEA composition, as well as the cell type. Significant improvement in gene delivery efficacy was achieved with PEA01/04/05 composed of Pluronic size (Mw: 3000-5000 Da), and HLB (12-18) in CHO, C2C12 and HSkM cell lines; and the effective transfection was reflected with PEA 01/04/07 composed of Pluronics with size (2000-5000 Da) and HLB (12-23) in mdx mice. The best formulation for pDNA delivery was obtained with PEA 01 producing transgene expression efficiency 5, 19-folds of that of PEI 25k in vitro and in vivo, respectively. These results potent some of these PEA polymers as attractive vehicles for gene or oligonucleotide delivery.

Horizontal gene transfer from macrophages to ischemic muscles upon delivery of naked DNA with Pluronic block copolymers

Intramuscular administration of plasmid DNA (pDNA) with non-ionic Pluronic block copolymers increases gene expression in injected muscles and lymphoid organs. We studied the role of immune cells in muscle transfection upon inflammation. Local inflammation in murine hind limb ischemia model (MHLIM) drastically increased DNA, RNA and expressed protein levels in ischemic muscles injected with pDNA/Pluronic. The systemic inflammation (MHLIM or peritonitis) also increased expression of pDNA/Pluronic in the muscles. When pDNA/Pluronic was injected in ischemic muscles the reporter gene, Green Fluorescent Protein (GFP) co-localized with desmin(+) muscle fibers and CD11b(+) macrophages (MØs), suggesting transfection of MØs along with the muscle cells. P85 enhanced (∼ 4 orders) transfection of MØs with pDNA in vitro. Moreover, adoptively transferred MØs were shown to pass the transgene to inflamed muscle cells in MHLIM. Using a co-culture of myotubes (MTs) and transfected MØs expressing a reporter gene under constitutive (cmv-luciferase) or muscle specific (desmin-luciferase) promoter we demonstrated that P85 enhances horizontal gene transfer from MØ to MTs. Therefore, MØs can play an important role in muscle transfection with pDNA/Pluronic during inflammation, with both inflammation and Pluronic contributing to the increased gene expression. pDNA/Pluronic has potential for therapeutic gene delivery in muscle pathologies that involve inflammation.

A Low Protein Binding Cationic Poly(2-oxazoline) as Non-Viral Vector

Developing safe and efficient non-viral gene delivery systems remains a major challenge. We present a new cationic poly(2-oxazoline) (CPOx) block copolymer for gene therapy that was synthesized by sequential polymerization of non-ionic 2-methyl-2-oxazoline and a new 2-oxazoline monomer, 2-(N-methyl, N-Boc-amino)-methyl-2-oxazoline, followed by deprotection of the pendant secondary amine groups. Upon mixing with plasmid DNA (pDNA), CPOx forms small (diameter ≈80 nm) and narrowly dispersed polyplexes (PDI <0.2), which are stable upon dilution in saline and against thermal challenge. These polyplexes exhibited low plasma protein binding and very low cytotoxicity in vitro compared to the polyplexes of pDNA and poly(ethylene glycol)-b-poly(L-lysine) (PEG-b-PLL). CPOx/pDNA polyplexes at N/P = 5 bound considerably less plasma protein compared to polyplexes of PEG-b-PLL at the same N/P ratio. This is a unique aspect of the developed polyplexes emphasizing their potential for systemic delivery in vivo. The transfection efficiency of the polyplexes in B16 murine melanoma cells was low after 4 h, but increased significantly for 10 h exposure time, indicative of slow internalization of polyplexes. Addition of Pluronic P85 boosted the transfection using CPOx/pDNA polyplexes considerably. The low protein binding of CPOx/pDNA polyplexes is particularly interesting for the future development of targeted gene delivery.

Increase in transgene expression by pluronic L64-mediated endosomal/lysosomal escape through its membrane-disturbing action

For efficient transgene delivery and expression, internalized nucleic acids should quickly escape from cellular endosomes and lysosomes to avoid enzymatic destruction and degradation. Here, we report a novel strategy for safe and efficient endosomal/lysosomal escape of transgenes mediated by Pluronic L64, a neutral amphiphilic triblock copolymer. L64 enhanced the permeability of biomembranes by structural disturbance and pore formation in a concentration- and time-dependent manner. When applied at optimal concentration, it rapidly reached the endosome/lysosome compartments, where it facilitated escape of the transfection complex from the compartments and dissociation of the complex. Therefore, when applied properly, L64 not only significantly increased polyethylenimine- and liposome-mediated transgene expression, but also decreased the cytotoxicity occasioned by transfection process. Our studies revealed the function and mechanism of neutral amphiphilic triblock copolymer as potent mediator for safe and efficient gene delivery.

Electroneutralized amphiphilic triblock copolymer with a peptide dendron for efficient muscular gene delivery

Hydrophilic-hydrophobic-hydrophilic triblock copolymers, such as Pluronic L64, P85, and P105, have attracted more attention due to their enhancement in muscular gene delivery. In the present study, a new kind of electroneutralized triblock copolymer, LPL, dendron G2(L-lysine-Boc)-PEG2k-dendron G2(L-lysine-Boc), was designed and investigated. This hydrophobic-hydrophilic-hydrophobic copolymer is composed of a structure reverse to that of L64, one of the most effective materials for intramuscular gene delivery so far. Our results showed that LPL exhibited good in vivo biocompatibility after intramuscular and intravenous administration. LPL mediated higher reporter gene expression than L64 in assays of β-galactosidase (LacZ), luciferase, and fluorescent protein E2-Crimson. Furthermore, LPL-mediated mouse growth hormone expression significantly accelerated mouse growth within the first 10 days. Altogether, LPL-mediated gene expression in skeletal muscle exhibits the potential of successful gene therapy. The current study also presented an innovative way to design and construct new electroneutralized triblock copolymers for safe and effective intramuscular gene delivery.

Pluronic L64-mediated stable HIF-1α expression in muscle for therapeutic angiogenesis in mouse hindlimb ischemia

Intramuscular injection of plasmid DNA (pDNA) to express a therapeutic protein is a promising method for the treatment of many diseases. However, the therapeutic applications are usually hindered by gene delivery efficiency and expression level. In this study, critical factors in a pDNA-based gene therapy system, such as gene delivery materials, a therapeutic gene, and its regulatory elements, were optimized to establish an integrated system for the treatment of mouse hindlimb ischemia. The results showed that Pluronic^® L64 (L64) was an efficient and safe material for gene delivery into mouse skeletal muscle. It also showed intrinsic ability to promote in vivo angiogenesis in a concentration-dependent manner, which might be through the activation of nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB)-regulated angiogenic factors. The combination of 0.1% L64 with a hybrid gene promoter (pSC) increased the gene expression level, elongated the gene expression duration, and enhanced the number of transfected muscle fibers. In mice ischemic limbs, a gene medicine (pSC-HIF1α^tri/L64) composed of L64 and pSC-based expression plasmid encoding hypoxia-inducible factor 1-alpha triple mutant (HIF-1α^tri), improved the expression of stable HIF-1α, and in turn, the expression of multiple angiogenic factors. As a result, the ischemic limbs showed accelerated function recovery, reduced foot necrosis, faster blood reperfusion, and higher capillary density. These results indicated that the pSC-HIF1α^tri/L64 combination presented a potential and convenient venue for the treatment of peripheral vascular diseases, especially critical limb ischemia.

NF-kB related transgene expression in mouse tibial cranial muscle after pDNA injection followed or not by electrotransfer

BACKGROUND

When activated, NF-κB can promote the nuclear import and transcription of DNA possessing NF-κB consensus sequences. Here, we investigated whether NF-κB is involved in the plasmid electrotransfer process.

METHODS

Mouse tibial cranial muscles were transfected with plasmids encoding luciferase bearing or not NF-κB consensus sequences. Luciferase transgene expression was evaluated noninvasively by luminescence imaging and the number of pDNA copies in the same muscles by qPCR. RT-PCR of heat shock protein HsP70 mRNA evidenced cell stress. Western blots of phosphorylated IkBα were studied as a marker of NF-κB activation.

RESULTS

Intra-muscular injection of a plasmid bearing a weak TATA-like promoter results in a very low muscle transfection level. Electrotransfer significantly increased both the number of pDNA copy and the transgene expression of this plasmid per DNA copy. Insertion of NF-κB consensus sequences into pDNA significantly increased the level of gene expression both with and without electrotransfer. Electrotransfer-induced cellular stress was evidenced by increased HsP70 mRNA. Phosphorylated IκBα was slightly increased by simple pDNA injection and a little more by electrotransfer. We also observed a basal level of phosphorylated IκBα and thus of free NF-κB in the absence of any stimulation.

GENERAL SIGNIFICANCE

pDNA electrotransfer can increase transgene expression independently of NF-κB. The insertion of NF-κB consensus sequences into pDNA bearing a weak TATA-like promoter leads to enhanced transgene expression in muscle with or without gene electrotransfer. Finally, our results suggest that the basal amount of free NF-κB in muscle might be sufficient to enhance the activity of pDNA bearing NF-κB consensus sequences.

Efficacy and mechanism of poloxamine-assisted polyplex transfection

BACKGROUND

Amphiphilic block copolymers acting as biological response modifiers provide an attractive approach for improving the transfection efficiency of polycationic polymer/DNA complexes (polyplexes) by altering cellular processes crucial for efficient transgene expression.

METHODS

The present study aimed to investigate the effect of the poloxamine Tetronic T904, a four-arm polyethylene oxide/polypropylene oxide block copolymer, on polyplex transfection and to determine its mechanism of action by analyzing the cellular uptake of polyplex, the nuclear localization of plasmid and RNA transcript production.

RESULTS

T904 significantly increased the transfection efficiency of polyplexes based on 25-kDa branched polyethylenimine in a dose-dependent manner in the presence of serum in C6 glioma cells, as well as human fibroblasts and mesenchymal stem cells. The activity of T904 was not promoter-dependent, increasing the expression of reporter genes under both cytomegalovirus and SV40 promoters. Although T904 did not affect the internalization or nuclear uptake of plasmid, mRNA expression levels from both promoters showed dose-dependent increases that closely paralleled increases in gene expression.

CONCLUSIONS

The present study demonstrates that T904 significantly increases polyplex transfection efficiency and suggests a mechanism of increased transcriptional activity. As a four-arm, hydroxyl-terminated polymer, T904 is amenable to a variety of end group functionalization and covalent cross-linking strategies that have been developed for preparing hydrogels from multi-arm polyethylene glycol, making it particularly attractive for scaffold-mediated gene delivery.

Polyethylenimine-modified pluronics (PCMs) improve morpholino oligomer delivery in cell culture and dystrophic mdx mice

We investigated a series of small-sized polyethylenimine (PEI, 0.8/1.2 k)-conjugated pluronic copolymers (PCMs) for their potential to enhance delivery of an antisense phosphorodiamidate morpholino oligomer (PMO) in vitro and in dystrophic mdx mice. PCM polymers containing pluronics of molecular weight (Mw) ranging 2-6 k, with hydrophilic-lipophilic balance (HLB) 7-23, significantly enhanced PMO-induced exon-skipping in a green fluorescent protein (GFP) reporter-based myoblast culture system. Application of optimized formulations of PCMs with PMO targeted to dystrophin exon 23 demonstrated a significant increase in exon-skipping efficiency in dystrophic mdx mice. Consistent with our observations in vitro, optimization of molecular size and the HLB of pluronics are important factors for PCMs to achieve enhanced PMO delivery in vivo. Observed cytotoxicity of the PCMs was lower than Endo-porter and PEI 25 k. Tissue toxicity of PCMs in muscle was not clearly detected with the concentrations used, indicating the potential of the PCMs as effective and safe PMO carriers for treating diseases such as muscular dystrophy.

Poly(alkylene oxide) copolymers for nucleic acid delivery

The advancement of gene-based therapeutics to the clinic is limited by the ability to deliver physiologically relevant doses of nucleic acids to target tissues safely and effectively. Over the last couple of decades, researchers have successfully employed polymer and lipid based nanoassemblies to deliver nucleic acids for the treatment of a variety of diseases. Results of phase I/II clinical studies to evaluate the efficacy and biosafety of these gene delivery vehicles have been encouraging, which has promoted the design of more efficient and biocompatible systems. Research has focused on designing carriers to achieve biocompatibility, stability in the circulatory system, biodistribution to target the disease site, and intracellular delivery, all of which enhance the resulting therapeutic effect. The family of poly(alkylene oxide) (PAO) polymers includes random, block, and branched structures, among which the ABA type triblocks copolymers of ethylene oxide (EO) and propylene oxide (PO) (commercially known as Pluronic) have received the greatest consideration. In this Account, we highlight examples of polycation-PAO conjugates, liposome-PAO formulations, and PAO micelles for nucleic acid delivery. Among the various polymer design considerations, which include molecular weight of polymer, molecular weight of blocks, and length of blocks, the overall hydrophobic-lipophilic balance (HLB) is a critical parameter in defining the behavior of the polymer conjugates for gene delivery. We discuss the effects of varying this parameter in the context of improving gene delivery processes, such as serum stability and association with cell membranes. Other innovative macromolecular modifications discussed in this category include our work to enhance the serum stability and efficiency of lipoplexes using PAO graft copolymers, the development of a PAO gel-based carrier for sustained and stimuli responsive delivery, and the development of biodegradable PAO-based amphiphilic block copolymers.

Phenylboronic-acid-modified amphiphilic polyether as a neutral gene vector

A phenylboronic-acid-modified amphiphilic block polyether is prepared via reaction of polyglycidol-block-poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)-block-polyglycidol (Pluronic-PG) with 2-(N,N-dimethylaminomethyl)-5-aminomethyl phenylboronic acid using phosgene as a coupling reagent. The boronic-acid-modified non-cationic polymer binds plasmid pGL3 effectively, forms sub-µm polymer/DNA complex particles, and greatly facilitates the cell uptake of the plasmid. The efficiency of the polymer as a gene vector is evaluated in vitro by transfection of pGL3 to HeLa, COS-7 and HepG2 cells. Pluronic-PG-BA enhances the transfection efficiency by 100 to 1000 times compared with Pluronic-PG. The presence of serum does not significantly affect the transfection efficiency.

Combined pluronic P85- and ultrasound contrast agents-mediated gene transfection to HepG2 cells

This study examined the effect of P85 (a pluronic block copolymer) and microbubble (MB) ultrasound contrast agents under ultrasound irradiation on gene transfection and expression. The pEGFP plasmids that can encode enhanced green fluorescent protein (pEGFP) served as a report gene and were mixed with different concentrations of MB/0.05% (w/v) P85. Then the plasmids were transfected into human hepatoma G2 (HepG2) cells. The HepG2 cells treated with MB/P85 or without treatment were exposed to ultrasound (US parameters: 1 MHz, 1.0 W/cm(2), 20 s, 20% duty cycle). Twenty-four hours later, the transfection efficiency was assessed by fluorescence microscopy and fluorescence activated cell sorting (FACS) analysis. The cell viability was evaluated by Trypan blue exclusion test. The results showed that the gene transfection efficiency in HepG2 cells under ultrasound irradiation was significantly higher than that without ultrasound irradiation. HepG2 cells in the MB or P85 group in the absence of ultrasound expressed less amount of green fluorescent protein. The expression efficiency reached (22.14 ± 3.06)% and the survival rate was as high as (55.73 ± 3.32)% in the 30% MB plus P85 group. It was concluded that MB and P85 in the presence of ultrasound can enhance gene transfection and expression.

P85, Optison microbubbles and ultrasound cooperate in mediating plasmid DNA transfection in mouse skeletal muscles in vivo

Pluronic block copolymers, a kind of non-ionic surfactant, also known as poloxamers, and ultrasound-targeted microbubble destruction have been respectively investigated as vectors for gene delivery in vitro and in vivo. However, they are limited for clinical application due to the relatively low transfer efficiency of each individual vector. In the present study, we explored if the combination of P85, a pluronic block copolymer, Optison, a microbubble contrast agent and ultrasound enhances the transfection of plasmid DNA in vivo using mouse skeletal muscle models. Plasmid encoding green fluorescent protein (GFP) was respectively conjugated with 0.05%P85, 10%Optison, or 0.05%P85 plus 10%Optison, and injected into mouse tibialis anterior (TA) muscles with or without ultrasound irradiation (1 MHz, 1 W/cm(2), 2 min and 20% duty cycle). Mice were sacrificed 1 week after injection. The TA muscles were collected and cryo-sectioned into a series of 7 μm slices. To assess the efficiency of plasmid DNA transfection, tissue sections were counterstained with DAPI and scored by counting the number of GFP-positive fibers. Meanwhile the area of damaged muscles was measured based on the tissues stained with hematoxylin and eosin. Both P85 and Optison significantly enhanced the delivery of plasmid DNA in mouse TA skeletal muscles (P<0.01 and P<0.05 respectively, compared to saline control). In combination with Ultrasound irradiation, P85 (P<0.01, compared to P85 alone) but not Optison (P>0.05, compared to Optison alone) exerted a more pronounced effect on the transfection efficiency. Furthermore P85-induced gene delivery was higher than that by Optison regardless of the presence of ultrasound (P<0.01). The highest transfection efficiency was observed when P85, Optison and ultrasound irradiation were administrated together (P<0.01, compared to any other treatment in this study). The area of damaged muscles was enlarged by ultrasound irradiation in the presence of Optison microbubbles (P<0.01, compared to those groups without ultrasound irradiation). These results suggest that P85, microbubbles and ultrasound irradiation synergistically enhance plasmid DNA delivery in mouse skeletal muscles in vivo.

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.

Polymer-related off-target effects in non-viral siRNA delivery

Since off-target effects in non-viral siRNA delivery are quite common but not well understood, in this study various polymer-related effects observed in transfection studies were described and their mechanisms of toxicity were investigated. A variety of stably luciferase-expressing cell lines was compared concerning polymer-mediated effects after transfection with polyplexes of siRNA and poly(ethylene imine) (PEI) or poly(ethylene glycol)-grafted PEI (PEG-PEI). Cell viability, LDH release, gene expression profiles of apoptosis-related genes and promoter activation were investigated. Interestingly, PEG-PEI, which is generally better tolerated than PEI, was found to activate apoptosis in a cell line- and concentration-dependent manner. While both polymers showed sigmoidal dose-response of cell viability in L929 cells (IC(50)(PEI) = 6 μg/ml, IC(50)(PEG-PEI) = 11 μg/ml), H1299/Luc cells exhibited biphasic dose-response for PEG-PEI and stronger apoptosis at 2 μg/ml than at 20 μg/ml PEG-PEI, as shown in TUNEL assays. Gene expression profiling confirmed that H1299/Luc cells underwent apoptosis via thousand-fold activation of TNF receptor-associated factors. Additionally, it was demonstrated that NFkB-mediated CMV promoter activation in stably transfected cells can lead to increased target gene levels after transfection instead of siRNA-mediated knockdown. With these results, polymeric vectors were shown not to be inert substances. Therefore, alterations in gene expression caused by the delivery agent must be known to correctly interpret gene-silencing experiments, to understand the mechanisms of off-target effects, and most of all to further develop vectors with reduced side effects. Taking these observations into account, one established cell line was eventually identified to be suitable for RNAi experiments. As shown by these experiments, materials that have been used for many years can elicit unexpected off-target effects. Therefore, non-viral vectors must be screened for several levels of toxicity to make them promising candidates.

Probing the in vitro mechanism of action of cationic lipid/DNA lipoplexes at a nanometric scale

Cationic lipids are used for delivering nucleic acids (lipoplexes) into cells for both therapeutic and biological applications. A better understanding of the identified key-steps, including endocytosis, endosomal escape and nuclear delivery is required for further developments to improve their efficacy. Here, we developed a labelling protocol using aminated nanoparticles as markers for plasmid DNA to examine the intracellular route of lipoplexes in cell lines using transmission electron microscopy. Morphological changes of lipoplexes, membrane reorganizations and endosomal membrane ruptures were observed allowing the understanding of the lipoplex mechanism until the endosomal escape mediated by cationic lipids. The study carried out on two cationic lipids, bis(guanidinium)-tris(2-aminoethyl)amine-cholesterol (BGTC) and dioleyl succinyl paramomycin (DOSP), showed two pathways of endosomal escape that could explain their different transfection efficiencies. For BGTC, a partial or complete dissociation of DNA from cationic lipids occurred before endosomal escape while for DOSP, lipoplexes remained visible within ruptured vesicles suggesting a more direct pathway for DNA release and endosome escape. In addition, the formation of new multilamellar lipid assemblies was noted, which could result from the interaction between cationic lipids and cellular compounds. These results provide new insights into DNA transfer pathways and possible implications of cationic lipids in lipid metabolism.

Amphiphilic block copolymers enhance the cellular uptake of DNA molecules through a facilitated plasma membrane transport

Amphiphilic block copolymers have been developed recently for their efficient, in vivo transfection activities in various tissues. Surprisingly, we observed that amphiphilic block copolymers such as Lutrol® do not allow the transfection of cultured cells in vitro, suggesting that the cell environment is strongly involved in their mechanism of action. In an in vitro model mimicking the in vivo situation we showed that pre-treatment of cells with Lutrol®, prior to their incubation with DNA molecules in the presence of cationic lipid, resulted in higher levels of reporter gene expression. We also showed that this improvement in transfection efficiency associated with the presence of Lutrol® was observed irrespective of the plasmid promoter. Considering the various steps that could be improved by Lutrol®, we concluded that the nucleic acids molecule internalization step is the most important barrier affected by Lutrol®. Microscopic examination of transfected cells pre-treated with Lutrol® confirmed that more plasmid DNA copies were internalized. Absence of cationic lipid did not impair Lutrol®-mediated DNA internalization, but critically impaired endosomal escape. Our results strongly suggest that in vivo, Lutrol® improves transfection by a physicochemical mechanism, leading to cellular uptake enhancement through a direct delivery into the cytoplasm, and not via endosomal pathways.

Pre-treatment of cells with pluronic L64 increases DNA transfection mediated by electrotransfer

Gene transfer into muscle cells is a key issue in biomedical research. Indeed, it is important for the development of new therapy for many genetic disorders affecting this tissue and for the use of muscle tissue as a secretion platform of therapeutic proteins. Electrotransfer is a promising method to achieve gene expression in muscles. However, this method can lead to some tissue damage especially on pathologic muscles. Therefore there is a need for the development of new and less deleterious methods. Triblock copolymers as pluronic L64 are starting to be used to improve gene transfer mediated by several agents into muscle tissue. Their mechanism of action is still under investigation. The combination of electrotransfer and triblock copolymers, in allowing softening electric field conditions leading to efficient DNA transfection, could potentially represent a milder and more secure transfection method. In the present study, we addressed the possible synergy that could be obtained by combining the copolymer triblock L64 and electroporation. We have found that a pre-treatment of cells with L64 could improve the transfection efficiency. This pre-treatment was shown to increase cell viability and this is partly responsible for the improvement of transfection efficiency. We have then labelled the plasmid DNA and the pluronic L64 in order to gain some insights into the mechanism of transfection of the combined physical and chemical methods. These experiences allowed us to exclude an action of L64 either on membrane permeabilization or on DNA/membrane interaction. Using plasmids containing or not binding sequences for NF-κB and an inhibitor of NF-κB pathway activation we have shown that this beneficial effect was rather related to the NF-κB signalling pathway, as it is described for other pluronics. Finally we address here some mechanistic issues on electrically mediated transfection, L64 mediated membrane permeabilization and the combination of both for gene transfer.

Evaluation of the muscle gene transfer activity of a series of amphiphilic triblock copolymers

BACKGROUND

Amphiphilic triblock copolymers such as the polyethylene oxide-polypropylene oxide-polyethylene oxide L64 (PEO(13)-PPO(30)-PEO(13)) significantly increase transgene expression after injection of DNA/polymer mixtures into skeletal muscles. To better understand the way such copolymers act, we studied the behaviour of different poloxamers, including L64, both in vitro and in vivo.

METHODS

The in vitro and in vivo transfection activity of five copolymers that differ either by their molecular weight or by their hydrophilic/hydrophobic balance was evaluated. Furthermore, we also studied the membrane permeabilizing properties of the poloxamers.

RESULTS

The results obtained indicate that, after intramuscular administration of DNA/poloxamer formulations, all five compounds were able to significantly increase the expression levels of luciferase compared to an injection of naked DNA. Using a LacZ expression cassette, up to 30% of the muscle fibers expressed the reporter gene. Furthermore, we show that the effect can be obtained using different promoters. Finally, we document that, to some extent, all five poloxamers possess membrane permeabilizing properties.

CONCLUSIONS

Taken together, the results obtained in the present study show that there is a large flexibility in terms of molecular weight and EO/PO ratio for obtaining increased levels of transgene expression in vivo.

Interactions of pluronic block copolymers on P-gp efflux activity: experience with HIV-1 protease inhibitors

The objective was to examine the influence of Pluronic block-copolymers on the interaction between the drug efflux transporter, P-glycoprotein and HIV-1 protease inhibitors (PIs). The ATPase assay determined the effect of various Pluronics on PI-stimulated P-gp ATPase activity. Cellular accumulation studies were conducted using MDCKII and LLC-PK1 cells transfected with human MDR1 to assess Pluronic modulation of PI efflux. Pluronic P85 inhibited both basal and nelfinavir-stimulated P-gp ATPase activity, while Pluronic F127 had no effect. In cell accumulation studies, Pluronic P85 restored the accumulation of nelfinavir in MDCKII-MDR1 cells while Pluronic F127 and F88 had no effect. Pluronic P85 increased saquinavir accumulation in wild-type and MDR1-transfected cells in both the MDCKII and LLC-PK1 cell models, suggesting inhibition of multiple transporters, including MRPs. In conclusion, this study provides evidence that a block-copolymer, Pluronic P85, effectively inhibits the interaction of P-gp with nelfinavir and saquinavir. These data indicate that effective inhibition of HIV-1 PI efflux by Pluronic P85 may influence the distribution of antiretroviral agents to sites protected by efflux mechanisms, such as the blood-brain barrier, and possibly increase the brain exposure of these drugs resulting in suppression of viral replication and reduction in the incidence of drug resistant mutants.

The effect of the nonionic block copolymer pluronic P85 on gene expression in mouse muscle and antigen-presenting cells

DNA vaccines can be greatly improved by polymer agents that simultaneously increase transgene expression and activate immunity. We describe here Pluronic P85 (P85), a triblock copolymer of ethylene oxide (EO) and propylene oxide (PO) EO(26)-PO(40)-EO(26). Using a mouse model we demonstrate that co-administration of a bacterial plasmid DNA with P85 in a skeletal muscle greatly increases gene expression in the injection site and distant organs, especially the draining lymph nodes and spleen. The reporter expression colocalizes with the specific markers of myocytes and keratinocytes in the muscle, as well as dendritic cells (DCs) and macrophages in the muscle, lymph nodes and spleen. Furthermore, DNA/P85 and P85 alone increase the systemic expansion of CD11c+ (DC), and local expansion of CD11c+, CD14+ (macrophages) and CD49b+ (natural killer) cell populations. DNA/P85 (but not P85) also increases maturation of local DC (CD11c+ CD86+, CD11c+ CD80 +, and CD11c+ CD40+. We suggest that DNA/P85 promotes the activation and recruitment of the antigen-presenting cells, which further incorporate, express and carry the transgene to the immune system organs.

Different internalization pathways of polymeric micelles and unimers and their effects on vesicular transport

Efficient entry of synthetic polymers inside cells is a central issue in polymeric drug delivery. Though polymers are widely believed to interact nonspecifically with plasma membrane, we present unexpected evidence that amphiphilic block copolymers, depending on their aggregation state, can distinguish between caveolae- and clathrin-mediated endocytosis. A block copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), Pluronic P85 (P85), below critical micelle concentration (CMC) exists as single molecule coils (unimers) and above CMC forms 14.6 nm aggregated micelles with a hydrophobic PPO core and hydrophilic PEO shell. The internalization pathways of P85 in mammalian cells were elucidated using endocytosis inhibitors and colocalization with endocytosis markers (clathrin-specific antibodies and transferrin for clathrin and caveolin-1-specific antibodies and cholera toxin B for caveolae). Altogether, our results indicate that P85 unimers internalize through caveolae-mediated endocytosis, while P85 micelles internalize through clathrin-mediated endocytosis. Furthermore, at concentrations above 0.01% P85 inhibits caveolae-mediated endocytosis (cholera toxin B), while having little or no effect on the clathrin-mediated endocytosis (transferrin). Selective interaction of Pluronic with caveolae may explain its striking pharmacological activities including inhibition of drug efflux transport, activation of gene expression, and dose-dependent hyperlipidemia.

Amphiphilic block copolymers enhance cellular uptake and nuclear entry of polyplex-delivered DNA

This work for the first time demonstrates that synthetic polymers enhance uptake and nuclear import of plasmid DNA (pDNA) through the activation of cellular trafficking machinery. Nonionic block copolymers of poly(ethylene oxide) and poly(propylene oxide), Pluronics, are widely used as excipients in pharmaceutics. We previously demonstrated that Pluronics increase the phosphorylation of IkappaB and subsequent NFkappaB nuclear localization as well as upregulate numerous NFkappaB-related genes. In this study, we show that Pluronics enhance gene transfer by pDNA/polycation complexes ("polyplexes") in a promoter-dependent fashion. Addition of Pluronic P123 or P85 to polyethyleneimine-based polyplexes had little effect on polyplex particle size but significantly enhanced pDNA cellular uptake, nuclear translocation, and gene expression in several cell lines. When added to polyplex-transfected cells after transfection, Pluronics enhanced nuclear import of pDNA containing NFkappaB binding sites, but have no effect on import of pDNA without these sites. Altogether, our studies suggest that Pluronics rapidly activate NFkappaB, which binds cytosolic pDNA that possesses promoters containing NFkappaB binding sites and consequently increase nuclear import of pDNA through NFkappaB nuclear translocation.

Pluronic block copolymers: evolution of drug delivery concept from inert nanocarriers to biological response modifiers

Polymer nanomaterials have sparked a considerable interest as vehicles used for diagnostic and therapeutic agents; research in nanomedicine has not only become a frontier movement but is also a revolutionizing drug delivery field. A common approach for building a drug delivery system is to incorporate the drug within the nanocarrier that results in increased solubility, metabolic stability, and improved circulation time. With this foundation, nanoparticles with stealth properties that can circumvent RES and other clearance and defense mechanisms are the most promising. However, recent developments indicate that select polymer nanomaterials can implement more than only inert carrier functions by being biological response modifiers. One representative of such materials is Pluronic block copolymers that cause various functional alterations in cells. The key attribute for the biological activity of Pluronics is their ability to incorporate into membranes followed by subsequent translocation into the cells and affecting various cellular functions, such as mitochondrial respiration, ATP synthesis, activity of drug efflux transporters, apoptotic signal transduction, and gene expression. As a result, Pluronics cause drastic sensitization of MDR tumors to various anticancer agents, enhance drug transport across the blood brain and intestinal barriers, and causes transcriptional activation of gene expression both in vitro and in vivo. Collectively, these studies suggest that Pluronics have a broad spectrum of biological response modifying activities which make it one of the most potent drug targeting systems available, resulting in a remarkable impact on the emergent field of nanomedicine.

Eye drop delivery of nano-polymeric micelle formulated genes with cornea-specific promoters

BACKGROUND

This study evaluates the eye drop delivery of genes with cornea-specific promoters, i.e., keratin 12 (K12) and keratocan (Kera3.2) promoters, by non-ionic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) polymeric micelles (PM) to mouse and rabbit eyes, and investigates the underlying mechanisms.

METHODS

Three PM-formulated plasmids (pCMV-Lac Z, pK12-Lac Z and pKera3.2-Lac Z) containing the Lac Z gene for beta-galactosidase (beta-Gal) whose expression was driven by the promoter of either the cytomegalovirus early gene, the keratin 12 gene or the keratocan gene, were characterized by critical micelle concentration (CMC), dynamic light scattering (DLS), and atomic force microscopy (AFM). Transgene expression in ocular tissue after gene delivery was analyzed by 5-bromo-4-chloro-3-indolyl-beta-D-galactoside (X-Gal) color staining, 1,2-dioxetane beta-Gal enzymatic activity measurement, and real-time polymerase chain reaction (PCR) analysis. The delivery mechanisms of plasmid-PM on mouse and rabbit corneas were evaluated by EDTA and RGD (arginine-glycine-aspartic acid) peptide.

RESULTS

The sizes of the three plasmid-PM complexes were around 150-200 nm with unimodal distribution. Enhanced stability was found for three plasmid-PM formulations after DNase I treatment. After six doses of eye drop delivery of pK12-Lac Z-PM three times a day, beta-Gal activity was significantly increased in both mouse and rabbit corneas. Stroma-specific Lac Z expression was only found in pKera3.2-Lac Z-PM-treated animals with pretreatment by 5 mM EDTA, an opener of junctions. Lac Z gene expression in both pK12-Lac Z-PM and pKera3.2-Lac Z-PM delivery groups was decreased by RGD peptide pretreatment.

CONCLUSIONS

Cornea epithelium- and stroma-specific gene expression could be achieved using cornea-specific promoters of keratin 12 and keratocan genes, and the gene was delivered with PM formulation through non-invasive, eye drop in mice and rabbits. The transfection mechanism of plasmid-PM may involve endocytosis and particle size dependent paracellular transport.

Efficient expression of vascular endothelial growth factor using minicircle DNA for angiogenic gene therapy

The application of plasmid DNA (pDNA)-based gene therapy is limited by its inefficient transgene expression. In this study, minicircle DNA was evaluated for efficient vascular endothelial growth factor (VEGF) expression in skeletal muscle cells. Production of minicircle DNA encoding VEGF was studied by a semi-quantitative electrophoresis method leading to optimized bacterial culture conditions and producing high purity (86.6%) minicircle DNA. The VEGF minicircle DNA under control of the SV40 promoter (pMini-SV-VEGF) showed an increased amount of VEGF mRNA and up to 8 times more VEGF expression than a conventional plasmid (pSV-VEGF) in two different skeletal muscle cell lines (C2C12 and L8). Minicircle DNA with different promoters, including the SV40, CMV and chicken beta-actin, was tested for VEGF expression in a C2C12 skeletal muscle cell line. The high VEGF expression generated by minicircle DNA stimulated efficient endothelial cell growth in vitro. Furthermore, minicircle DNA expressed higher VEGF compared to conventional plasmid in the tibialis anterior (TA) muscle of mice. Taken together, the results suggest that minicircle DNA is an efficacious gene vector for angiogenic VEGF expression in skeletal muscle and may be useful for treating peripheral arterial disease (PAD).

PEO−PPO Block Copolymer Vectors Do Not Interact Directly with DNA but with Lipid Membranes

Small angle neutron (SANS) and light scattering was used to study the interaction between fragments of double stranded deoxyribonucleic acid (DNA) and a synthetic triblock [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] amphiphilic polymer, known as L64, a potential vector for gene therapy. The mechanism of action of this vector is yet unknown. The contrast variation method was used to separate the partial structure factors of the different components in mixtures of triblock and DNA. It has been found that the copolymer and DNA molecules exhibit repulsive interactions. Further, the interaction between the copolymer and a model lipid membrane was investigated in order to explain the action of the vector. Electrical measurements on black lipid membranes indicated that the main effect of L64 as a vector is to permeabilize the cell's membrane.

Ethanol enhanced in vivo gene delivery with non-ionic polymeric micelles inhalation

Modifications of both carriers and host barriers have been investigated for efficient inhalation gene delivery to lung. Here we used a biocompatible, non-ionic poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) (PEO-PPO-PEO) polymeric micelles (PM) as a carrier and combined it with ethanol to enhance membrane penetration of delivered DNA. The inhalation delivery with six 100 microg doses of pCMV-Lac Z with PM co-formulated with 10%-40% ethanol to nude mice in 2 days at 8 h interval was performed. The beta-galatosidase (beta-Gal) activity was assessed using chlorophenol red-beta-d galactopyranoside (CPRG) and X-gal staining for quantitative and qualitative analysis in tissues. The results showed that beta-Gal activity was significantly increased by 38% in lung around bronchioles when inhalation with PM and 10% ethanol was given. The 10% ethanol also increased the intracellular apparent permeability by 42% in stomach and by 141% in intestine at 48 h after the first dosage of delivery. Also delivery of DNA encoding a functional human cystic fibrosis transmembrane protein (CFTR) using the same inhalation delivery method co-formulated with 10% ethanol, an increased expression of CFTR in lung was detected by immunostaining. We concluded that 10% ethanol co-formulated with the PM system could enhance inhaled gene delivery to airway and gastrointestinal (GI) tract.

Polymer genomics: an insight into pharmacology and toxicology of nanomedicines

Synthetic polymers and nanomaterials display selective phenotypic effects in cells and in the body signal transduction mechanisms involved in inflammation, differentiation, proliferation, and apoptosis. When physically mixed or covalently conjugated with cytotoxic agents, bacterial DNA or antigens, polymers can drastically alter specific genetically controlled responses to these agents. These effects, in part, result from cooperative interactions of polymers and nanomaterials with plasma cell membranes and trafficking of polymers and nanomaterials to intracellular organelles. Cells and whole organism responses to these materials can be phenotype or genotype dependent. In selected cases, polymer agents can bypass limitations to biological responses imposed by the genotype, for example, phenotypic correction of immune response by polyelectrolytes. Overall, these effects are relatively benign as they do not result in cytotoxicity or major toxicities in the body. Collectively, however, these studies support the need for assessing pharmacogenomic effects of polymer materials to maximize clinical outcomes and understand the pharmacological and toxicological effects of polymer formulations of biological agents, i.e. polymer genomics.

Relationships between the physicochemical properties of an amphiphilic triblock copolymers/DNA complexes and their intramuscular transfection efficiency

Poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) triblock copolymer (PEO-PPO-PEO) based plasmid delivery systems are increasingly drawing attention in the field of nonviral gene transfer because of their proven in vivo transfection capability. They result from the simple association of DNA molecules with uncharged polymers. We examined the physicochemical properties of PEO-PPO-PEO/DNA mixtures, in which the PEO-PPO-PEO is Lutrol (PEO75-PPO30-PEO75), formulated under various conditions. We found that interactions between PEO-PPO-PEO and DNA are mediated by the central hydrophobic block within the block copolymer. Dynamic light scattering and cryo-electron microscopy showed that the mean diameter of transfecting particles as well as their stability depended on the PEO-PPO-PEO/DNA ratio and on the ionic composition of the formulating medium. The most active formulation promoting a good tissue-distribution and an optimal transfection was characterized by a reduced electrophoretic mobility, a mean hydrodynamic diameter of approximately 250-300 nm and by a conserved B-DNA form as shown by circular dichroism studies. Our study also revealed that the stability of these formulations strongly depended on a concentration balance between the DNA and the PEO-PPO-PEO, over which the DNA conformation was modified, micron-sized particles were generated, and the transgene expression was declined. We showed that the physicochemical properties of PEO-PPO-PEO/DNA formulations directly impact the level of gene expression in transfected muscles.