Long circulation of intravenously administered plasmid DNA delivered with dendritic poly(l-lysine) in the blood flow

Optimization of DOTAP/chol Cationic Lipid Nanoparticles for mRNA, pDNA, and Oligonucleotide Delivery

Lipid nanoparticles (LNPs) can be used as delivery vehicles for nucleic acid biotherapeutics. In fact, LNPs are currently being used in the Pfizer/BioNTech and Moderna COVID-19 vaccines. Cationic LNPs composed of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)/cholesterol (chol) LNPs have been classified as one of the most efficient gene delivery systems and are being tested in numerous clinical trials. The objective of this study was to examine the effect of the molar ratio of DOTAP/chol, PEGylation, and lipid to mRNA ratio on mRNA transfection, and explore the applications of DOTAP/chol LNPs in pDNA and oligonucleotide transfection. Here we showed that PEGylation significantly decreased mRNA transfection efficiency of DOTAP/chol LNPs. Among non-PEGylated LNP formulations, 1:3 molar ratio of DOTAP/chol in DOTAP/chol LNPs showed the highest mRNA transfection efficiency. Furthermore, the optimal ratio of DOTAP/chol LNPs to mRNA was tested to be 62.5 µM lipid to 1 μg mRNA. More importantly, these mRNA-loaded nanoparticles were stable for 60 days at 4 °C storage without showing reduction in transfection efficacy. We further found that DOTAP/chol LNPs were able to transfect pDNA and oligonucleotides, demonstrating the ability of these LNPs to transport the cargo into the cell nucleus. The influence of various factors in the formulation of DOTAP/chol cationic LNPs is thus described and will help improve drug delivery of nucleic acid-based vaccines and therapies.

Highly Branched Polymers Based on Poly(amino acid)s for Biomedical Application

Polymers consisting of amino acid building blocks continue to receive consideration for biomedical applications. Since poly(amino acid)s are built from natural amino acids, the same building blocks proteins are made of, they are biocompatible, biodegradable and their degradation products are metabolizable. Some amino acids display a unique asymmetrical AB2 structure, which facilitates their ability to form branched structures. This review compares the three forms of highly branched polymeric structures: structurally highly organized dendrimers, dendrigrafts and the less organized, but readily synthesizable hyperbranched polymers. Their syntheses are reviewed and compared, methods of synthesis modulations are considered and variations on their traditional syntheses are shown. The potential use of highly branched polymers in the realm of biomedical applications is discussed, specifically their applications as delivery vehicles for genes and drugs and their use as antiviral compounds. Of the twenty essential amino acids, L-lysine, L-glutamic acid, and L-aspartic acid are asymmetrical AB2 molecules, but the bulk of the research into highly branched poly(amino acid)s has focused on the polycationic poly(L-lysine) with a lesser extent on poly(L-glutamic acid). Hence, the majority of potential applications lies in delivery systems for nucleic acids and this review examines and compares how these three types of highly branched polymers function as non-viral gene delivery vectors. When considering drug delivery systems, the small size of these highly branched polymers is advantageous for the delivery of inhalable drug. Even though highly branched polymers, in particular dendrimers, have been studied for more than 40 years for the delivery of genes and drugs, they have not translated in large scale into the clinic except for promising antiviral applications that have been commercialized.

Non-Viral Targeted Nucleic Acid Delivery: Apply Sequences for Optimization

In nature, genomes have been optimized by the evolution of their nucleic acid sequences. The design of peptide-like carriers as synthetic sequences provides a strategy for optimizing multifunctional targeted nucleic acid delivery in an iterative process. The optimization of sequence-defined nanocarriers differs for different nucleic acid cargos as well as their specific applications. Supramolecular self-assembly enriched the development of a virus-inspired non-viral nucleic acid delivery system. Incorporation of DNA barcodes presents a complementary approach of applying sequences for nanocarrier optimization. This strategy may greatly help to identify nucleic acid carriers that can overcome pharmacological barriers and facilitate targeted delivery in vivo. Barcode sequences enable simultaneous evaluation of multiple nucleic acid nanocarriers in a single test organism for in vivo biodistribution as well as in vivo bioactivity.

Gelated Vorinostat with inner-lysosome triggered release for tumor-targeting chemotherapy

Histonedeacetylase inhibitor (HDACi) has great potential in targeted antitumor therapy by inhibiting tumor migration, invasion, and metastasis. As one of the typical HDACis, vorinostat (Suberoylanilide Hydroxamic Acid, SAHA) was approved as a therapeutic agent for cancer therapy, however, challenges remain due to their poor solubility, short half-life and low efficiency in cellular penetration. Considering the disadvantages of usual drug carriers, folate and vorinostat bound BSA nanogel (FVBN)was fabricated to implement higher solubility, stability, cellular uptake, and lipase-responsive release. With good dispersion and stability, FVBN significantly increased the cellular uptake of vorinostat through folate-mediated endocytosis. FVBN exhibited comparable cytotoxicity with free SAHA, and the growth of tumor cells was blocked in G1/G0 phase just like SAHA performed in cell cycle arrest tests. Moreover, FVBN not only effectively inhibited the growth of melanoma but also observably prevented pulmonary metastasis of melanoma. In the experiment against nude mice bearing solid ovarian cancer, FVBN showed excellent antitumor effect without liver damage, demonstrating the superiority of gelated and inner-lysosome triggered release strategies to the free SAHA, and it is promising to expand the scope of application of HDACi in clinical cancer therapy.

Overcoming the barrier of CD8+T cells: Two types of nano-sized carriers for siRNA transport

Bioengineering immune cells via gene therapy offers treatment opportunities for currently fatal viral infections. Also cell therapeutics offer most recently a breakthrough technology to combat cancer. These primary human cells, however, are sensitive to toxic influences, which make the utilization of optimized physical transfection techniques necessary. The otherwise commonly applied delivery agents such as Lipofectamine^Ⓡ or strongly cationic polymer structures are not only unsuitable for in vivo experiments, but are also highly toxic to immune cells. This study aimed to improve the design of polymeric carrier systems for small interfering RNA, which would allow efficient internalization into CD8⁺T-cells without affecting their viability and thereby removing the current limitations in the field. Here, two new carrier systems for small interfering RNA were tested. One is a cationic diblock copolymer, in which less than 10% of the monomers were modified with triphenylphosphonium cations. This moiety is lipophilic, promotes uptake and it is mostly known for its mitotropic properties. Furthermore, cationic nanohydrogel particles were synthesized in exceedingly small sizes (R_h < 14 nm). After full physicochemical characterization of the two carriers, extensive cytotoxicity studies were performed and the concentration dependent uptake into CD8⁺T-cells was tested in correlation to incubation time and protein content of the surrounding medium. Both carriers facilitated efficient complexation of siRNA as well as significant internalization into primary human cells in less than three hours of incubation. In addition, neither of the delivery systems reduced cell viability making them good candidates to transport siRNA into CD8⁺T-cells efficiently. STATEMENT OF SIGNIFICANCE: This study provides insights into the design of polymeric delivery agents as the method of choice for overcoming the limitations of cell manipulation. Until now, CD8⁺T-cells, which have become a treatment tool for currently fatal diseases, have not yet been made accessible for gene silencing by polymeric siRNA carrier systems. Choosing appropriate modification approaches for two chemically different polymer structures, we were, in both cases, able to achieve significant uptake in these cells even at low concentrations and without inducing cytotoxicity. These results remove current limitations and pave the way for bioengineering via gene therapy.

Clickable Poly(ionic liquids): A Materials Platform for Transfection

The potential applications of cationic poly(ionic liquids) range from medicine to energy storage, and the development of efficient synthetic strategies to target innovative cationic building blocks is an important goal. A post-polymerization click reaction is reported that provides facile access to trisaminocyclopropenium (TAC) ion-functionalized macromolecules of various architectures, which are the first class of polyelectrolytes that bear a formal charge on carbon. Quantitative conversions of polymers comprising pendant or main-chain secondary amines were observed for an array of TAC derivatives in three hours using near equimolar quantities of cyclopropenium chlorides. The resulting TAC polymers are biocompatible and efficient transfection agents. This robust, efficient, and orthogonal click reaction of an ionic liquid, which we term ClickabIL, allows straightforward screening of polymeric TAC derivatives. This platform provides a modular route to synthesize and study various properties of novel TAC-based polymers.

Long-Circulating Polymeric Nanovectors for Tumor-Selective Gene Delivery

Significant advances in the understanding of the genetic abnormalities that lead to the development, progression, and metastasis of neoplastic diseases has raised the promise of gene therapy as an approach to medical intervention. Most of the clinical protocols that have been approved in the United States for gene therapy have used the viral vectors because of the high efficiency of gene transfer. Conventional means of gene delivery using viral vectors, however, has undesirable side effects such as insertion of mutational viral gene into the host genome and development of replication competent viruses. Among non-viral gene delivery methods, polymeric nanoparticles are increasingly becoming popular as vectors of choice. The major limitation of these nanoparticles is poor transfection efficiency at the target site after systemic administration due to uptake by the cells of reticuloendothelial system (RES). In order to reduce the uptake by the cells of the RES and improve blood circulation time, these nanoparticles are coated with hydrophilic polymers such as poly(ethylene glycol) (PEG). This article reviews the use of such hydrophilic polymers employed for improving the circulation time of the nanocarriers. The mechanism of polymer coating and factors affecting the circulation time of these nanocarriers will be discussed. In addition to the long circulating property, modifications to improve the target specificity of the particles and the limitations of steric protection will be analyzed.

Real-time vascular imaging and photodynamic therapy efficacy with micelle-nanocarrier delivery of chlorin e6 to the microenvironment of melanoma

BACKGROUND

Strategies combining anti-vascular therapy and vascular imaging may facilitate the prediction of early response and outcome in cancer treatment.

OBJECTIVE

The aim of this study was to investigate the relationship between the tumor-associated vasculature in melanoma and to develop an approach for melanoma treatment by utilizing the free form and micelle form of the photosensitizer (PS) chlorin e6 in photodynamic therapy (PDT).

METHODS

Green fluorescence protein (GFP) expressing B16-F10 melanoma cells were implanted into the mouse ear dermis. Ce6 in free form or in micelle form was administered via the tail vein. An OV100 imaging system was used to record the red fluorescence of Ce6 to obtain real-time vascular images in the GFP tumor.

RESULTS

Compared to free Ce6, Ce6 linked to the micelle-nanocarrier depicted a much clearer vascular image and had an effective vascular destruction by PDT. Micelle Ce6 was localized in lysosomes and in the endoplasmic reticulum of cultured endothelial cells, implying an active endocytosis of the nano-carrier.

CONCLUSION

Micelle Ce6 can serve as a bifunctional PS for vascular imaging and PDT, which facilitates its delivery in the tumor microenvironment.

Nitroxyl radicals-modified dendritic poly(l-lysine) as a contrast agent for Overhauser-enhanced MRI

Overhauser-enhanced magnetic resonance imaging (OMRI), which is a double resonance technique, creates images of free radical distribution in animals by enhancing the water proton signal intensity by the overhauser effect. In this study, we constructed a contrast agent by combining PROXYL groups that have nitroxyl radicals with PEG-modified dendritic poly(l-lysine) that accumulates in the tumor by enhanced permeability and retention (EPR) effect. Addition of the PROXYL groups at the PEG chains' termini on KG6 was advantageous in OMRI, because the ESR signal of the nitroxyl radical was maintained without decay caused by mobility restriction, even if the PROXYL groups were attached at 25 mol% on one molecule. After intramuscular injection of the molecule modified at 25 mol%, that is, PR25-PEG-KG6, a significant OMRI signal was observed at the injected site. However, no signal was detected in the tumor after intravenous injection of PR25-PEG-KG6 to a tumor-bearing mouse, although PR25-PEG-KG6 itself accumulated in the tumor. The reason was that the nitroxyl radicals were immediately reduced in the blood after the injection, suggesting that use of stable nitroxyl radicals will enable detection of tumors by OMRI after intravenous injection.

Biodegradable nanoparticles composed of dendrigraft poly-L-lysine for gene delivery

We developed novel gene vectors composed of dendrigraft poly-L-lysine (DGL). The transgene expression efficiency of the pDNA/DGL complexes (DGL complexes) was markedly higher than that of the control pDNA/poly-L-lysine complex. However, the DGL complexes caused cytotoxicity and erythrocyte agglutination at high doses. Therefore, γ-polyglutamic acid (γ-PGA), which is a biodegradable anionic polymer, was added to the DGL complexes to decrease their toxicity. The resultant ternary complexes (DGL/γ-PGA complexes) were shown to be stable nanoparticles, and those with γ-PGA to pDNA charge ratios of >8 had anionic surface charges. The transgene expression efficiency of the DGL/γ-PGA complexes was similar to that of the DGL complexes; however, they exhibited lower cytotoxicity and did not induce erythrocyte agglutination at high doses. After being intravenously administered to mice, the DGL6 complex demonstrated high transfection efficiency in the liver, lungs, and spleen, whereas the DGL6/γ-PGA8 complex only displayed high transfection efficiency in the spleen. Future studies should examine the utility of DGL and DGL/γ-PGA complexes for clinical gene therapy.

Polymers for nucleic acid transfer-an overview

For the last five decades cationic polymers have been used for nucleic acids transfection. Our understanding of polymer-nucleic acid interactions and their rational use in delivery has continuously increased. The great improvements in macromolecular chemistry and the recognition of distinct biological extra- and intracellular delivery hurdles triggered several breakthrough developments, including the discovery of natural and synthetic polycations for compaction of nucleic acids into stable nanoparticles termed polyplexes; the incorporation of targeting ligands and surface-shielding of polyplexes to enable receptor-mediated gene delivery into defined target tissues; and strongly improved intracellular transfer efficacy by better endosomal escape of vesicle-trapped polyplexes into the cytosol. These experiences triggered the development of second-generation polymers with more dynamic properties, such as endosomal pH-responsive release mechanisms, or biodegradable units for improved biocompatibility and intracellular release of the nucleic acid pay load. Despite a better biological understanding, significant challenges such as efficient nuclear delivery and persistence of gene expression persist. The therapeutic perspectives widened from pDNA-based gene therapy to application of novel therapeutic nucleic acids including mRNA, siRNA, and microRNA. The finding that different therapeutic pay loads require different tailor-made carriers complicates preclinical developments. Convincing evidence of medical efficacy still remains to be demonstrated. Bioinspired multifunctional polyplexes resembling "synthetic viruses" appear as attractive opportunity, but provide additional challenges: how to identify optimum combinations of functional delivery units, and how to prepare such polyplexes reproducibly in precise form? Design of sequence-defined polymers, screening of combinatorial polymer and polyplex libraries are tools for further chemical evolution of polyplexes.

Microfluidic Assembly of Cationic-β-Cyclodextrin:Hyaluronic Acid-Adamantane Host:Guest pDNA Nanoparticles

Traditionally, transfection complexes are typically formed by bulk mixing, producing particles with high polydispersity and limited control over vector size. Herein, we demonstrate the use of a commercial micro-reactor to assemble pDNA:cationic cyclodextrin:pendant polymer nanoparticles using a layer-by-layer approach. Our studies reveal that the particles formulated via microfluidic assembly have much smaller sizes, lower polydispersity, lower ζ-potentials, and comparable cell viability and transfection profiles in HeLa cells than bulk mixed particles. The complexes also show a flow rate-dependent stability, with particles formed at slower flow rates giving rise to more stable complexes as determined by heparin challenge. Our findings suggest that microfluidic reactors offer an attractive method for assembling reproducible, size-controlled complexes from multi-component transfection complex assemblies.

Preparation of functional water-soluble low-cytotoxic poly(methacrylate)s with pendant cationic L-lysines for efficient gene delivery

In this work, we present the preparation of water-soluble poly(methacrylate)s with pendant cationic L-lysines PHMLs(6-30 K). Plasmid DNA binding affinity as well as particle sizes and zeta potentials of the polyplexes were examined for these PHML vectors, and their cytotoxicities were assayed with HeLa cells by CCK-8 and lactate dehydrogenase kits. Gene transfection efficacy and intracellular uptake of the polyplexes by the PHML vectors were also studied with HeLa cells. As a result, it was revealed that the low cytotoxic PHMLs tended to exhibit gene transfection efficiencies significantly higher than those of the linear structural PLL (15-30 K) control, in particular the molecular weight of a PHML vector remarkably influenced its pDNA binding affinity, transfection efficacy and intracellular uptake of the polyplexes.

Biodistribution and Tumor Localization of PEG-Modified Dendritic Poly(L-Lysine) Oligonucleotide Complexes

A poly(ethylene glycol) (PEG)-modified dendritic poly(L-lysine) (PEG-WeKG6) containing tryptophan residues in its core was synthesized as an oligonucleotide carrier to tumors after systemic injection. PEG- WeKG6 formed a stable complex with double-stranded deoxyoligonucleotide (ODN). The size and the zeta-potential of the complex were smaller than those of a dendritic poly(L-lysine) without PEG (WeKG6). To study the biodistribution of the complexes in tumor-bearing mice after intravenous injection, the den- drimers and the oligonucleotide were labeled with gadolinium and Cy5, respectively. Our results show that PEG modification of the dendrimer improved the stability of ODN in blood circulation. Effective accumulation of the PEG-WeKG6/ODN complex in the tumor tissue was found 24 h after the injection. These results indicate that PEG-WeKG6 is suitable for forming a complex with any genetic or therapeutic material for efficient delivery to tumors.

Development of a low toxicity, effective pDNA vector based on noncovalent assembly of bioresponsive amino-β-cyclodextrin:adamantane-poly(vinyl alcohol)-poly(ethylene glycol) transfection complexes

A host:guest-derived gene delivery vector has been developed, based on the self-assembly of cationic β-CD derivatives with a poly(vinyl alcohol) (MW 27 kDa) (PVA) main chain polymer bearing poly(ethylene glycol) (MW 750) (PEG) or MW 2000 PEG and acid-labile adamantane-modified (Ad) grafts through an acid-sensitive benzylidene acetal linkage. These components were investigated for their ability to promote supramolecular complex formation with pDNA using two different assembly schemes, involving either precomplexation of the pendent Ad-PVA-PEG polymer with the cationic β-CD derivatives before pDNA condensation (method A) or pDNA condensation with the cationic β-CD derivatives prior to addition of Ad-PVA-PEG to engage host:guest complexation (method B). The pendent polymers were observed to degrade under acidic conditions while remaining intact for more than 5 days at pH 7. HeLa cell culture data show that these materials have 10(3)-fold lower cytotoxicities than 25 kDa bPEI while maintaining transfection efficiencies that are superior to those observed for this benchmark cationic polymer transfection reagent when the method A assembly scheme is employed. These findings suggest that degradable cationic polymer constructs employing multivalent host:guest interactions may be an effective and low-toxicity vehicle for delivering nucleic acid cargo to target cells.

Diblock copolymers with tunable pH transitions for gene delivery

A series of diblock copolymers containing an endosomal-releasing segment composed of diethylaminoethyl methacrylate (DEAEMA) and butyl methacrylate (BMA) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The materials were designed to condense plasmid DNA (pDNA) through electrostatic interactions with a cationic poly(N,N-dimethylaminoethyl methacrylate) (DMAEMA) first block. The pDMAEMA was employed as a macro chain transfer agent (macroCTA) for the synthesis of a series in which the relative feed ratios of DEAEMA and BMA were systematically varied from 20% to 70% BMA. The resultant diblock copolymers exhibited low polydispersity (PDI ≤ 1.06) with similar molecular weights (M(n) = 19.3-23.1 kDa). Dynamic light scattering (DLS) measurements in combination with (1)H NMR D(2)O studies demonstrated that the free copolymers assemble into core-shell micelles at physiological pH. Reduction of the solution pH to values representative of endosomal/lysosomal compartments induced an increase in the net cationic charge of the core through protonation of the DEAEMA residues. This protonation promotes micelle destabilization and exposure of the hydrophobic BMA residues that destabilize biological membranes. The pH value at which this micelle-to-unimer transition occurred was dependent on the hydrophobic content of the copolymer, with higher BMA-containing copolymer compositions exhibiting pH-induced transitions to the membrane-destabilizing state at successively lower pH values. The ability of the diblock copolymers to deliver pDNA was subsequently investigated using a GFP expression vector in two monocyte cell lines. High levels of DNA transfection were observed for the copolymer compositions exhibiting the sharpest pH transitions and membrane destabilizing activities, demonstrating the importance of tuning the endosomal-releasing segment composition.

In vitro and in vivo effects of polyethylene glycol (PEG)-modified lipid in DOTAP/cholesterol-mediated gene transfection

Background:

DOTAP/cholesterol-based lipoplexes are successfully used for delivery of plasmid DNA in vivo especially to the lungs, although low systemic stability and circulation have been reported. To achieve the aim of discovering the best method for systemic delivery of DNA to disseminated tumors we evaluated the potential of formulating DOTAP/cholesterol lipoplexes with a polyethylene glycol (PEG)-modified lipid, giving the benefit of the shielding and stabilizing properties of PEG in the bloodstream.

Method:

A direct comparison of properties in vitro and in vivo of 4 different DOTAP/cholesterol-based lipoplexes containing 0%, 2%, 4%, and 10% PEG was performed using reporter gene activity and radioactive tracer lipid markers to monitor biodistribution.

Results:

We found that 10% PEGylation of lipoplexes caused reduced retention in lung and heart tissues of nude mice compared to nonPEGylated lipoplexes, however no significant delivery to xenograft flank tumors was observed. Although PEGylated and nonPEGylated lipoplexes were delivered to cells the ability to mediate successful transfection is hampered upon PEGylation, presumably due to a changed uptake mechanism and intracellular processing.

Conclusion:

The eminent in vivo transfection potency of DOTAP/cholesterol-based lipoplexes is well established for expression in lung tumors, but it is unsuitable for expression in non first pass organs such as xenograft flank tumors in mice even after addition of a PEG-lipid in the formulation.

pH-responsive polymeric sirna carriers sensitize multidrug resistant ovarian cancer cells to doxorubicin via knockdown of polo-like kinase 1

Small interfering RNA (siRNA)-based therapies have great potential for the treatment of debilitating diseases such as cancer, but an effective delivery strategy for siRNA is elusive. Here, pH-responsive complexes were developed for the delivery of siRNA in order to sensitize drug-resistant ovarian cancer cells (NCI/ADR-RES) to doxorubicin. The electrostatic complexes consisted of a cationic micelle used as a nucleating core, siRNA, and a pH-responsive endosomolytic polymer. Cationic micelles were formed from diblock copolymers of dimethylaminoethyl methacrylate (pDMAEMA) and butyl methacrylate (pDbB). The hydrophobic butyl core mediated micelle formation while the positively charged pDMAEMA corona enabled siRNA condensation. To enhance cytosolic delivery through endosomal release, a pH-responsive copolymer of poly(styrene-alt-maleic anhydride) (pSMA) was electrostatically complexed with the positively charged siRNA/micelle to form a ternary complex. Complexes exhibited size (30-105 nm) and charge (slightly positive) properties important for endocytosis and were found to be noncytotoxic and mediate uptake in >70% of ovarian cancer cells after 1 h of incubation. The pH-responsive ternary complexes were used to deliver siRNA against polo-like kinase 1 (plk1), a gene upregulated in many cancers and responsible for cell cycle progression, to ovarian cancer cell lines. Treatment resulted in approximately 50% reduction of plk1 gene expression in the drug-resistant NCI/ADR-RES ovarian cancer cell model and in the drug-sensitive parental cell line, OVCAR8. This knockdown functionally sensitized NCI/ADR-RES cells to doxorubicin at levels similar to OVCAR8. Sensitization occurred through a p53 signaling pathway, as indicated by caspase 3/7 upregulation following plk1 knockdown and doxorubicin treatment, and this effect could be abrogated using a p53 inhibitor. To demonstrate the potential for dual delivery from this polymer system, micelle cores were subsequently loaded with doxorubicin and utilized in ternary complexes to achieve cell sensitization through simultaneous siRNA and drug delivery from a single carrier. These results show knockdown of plk1 results in sensitization of multidrug resistant cells to doxorubicin, and this combination of gene silencing and small molecule drug delivery may prove useful to achieve potent therapeutic effects.

Sequential administration with oxaliplatin-containing PEG-coated cationic liposomes promotes a significant delivery of subsequent dose into murine solid tumor

Recently, we designed a PEG-coated cationic liposome to achieve dual targeting delivery of l-OHP to both tumor endothelial cells and tumor cells in a solid tumor. The targeted liposomal l-OHP formulation showed an efficient antitumor activity in a murine tumor model after three sequential liposomal l-OHP injections. This led us to assume that prior dosing with liposomes might enhance the intra-tumoral accumulation of a subsequent dose, and hence improve the therapeutic efficacy of entrapped l-OHP. The present study shows that while a single liposomal l-OHP injection does not enhance tumor accumulation of subsequent test-PEG-coated cationic liposomes, two sequential injections of liposomal l-OHP do. Cumulative cytotoxic effects of l-OHP delivered by PEG-coated cationic liposomes led to deep diffusion of a subsequent dose of liposomal l-OHP in solid tumor presumably as a result of the enlarged intra-tumoral interstitial space. Our study suggests that sequential injections of a targeted liposomal anticancer drug is of significant clinical and practical importance in enhancing the delivery of adequate quantities of anticancer agents into intractable solid tumors, and thereby may achieve a significant anticancer efficacy.

In vivo siRNA delivery with dendritic poly(L-lysine) for the treatment of hypercholesterolemia

Intravenous delivery of apolipoprotein B-specific siRNA with a sixth-generation of dendritic poly(L-lysine) (KG6) resulted in siRNA-mediated knockdown of ApoB in healthy C57BL/6 mice without hepatotoxicity, and with a significant reduction of serum low-density lipoprotein cholesterol in apolipoprotein E-deficient mice.

NFkappaB decoy delivery using dendritic poly(l-lysine) for treatment of endotoxin-induced hepatitis in mice

Mono-dispersed, 6th generation dendritic poly(l-lysine) (KG6) forms a stable complex with plasmid DNA and this complex can circulate in vivo for extended times before the DNA finally accumulates in the liver. In this study, we attempted to use KG6 as a carrier of NFkappaB decoy oligonucleotide to the liver to treat hepatitis, induced by lipopolysaccharide and d-galactosamine. KG6 formed a complex with the NFkappaB decoy. Serum aspartate aminotransferase and alanine aminotransferase were dramatically suppressed in the hepatitis mouse model after intravenous injection of KG6/NFkappaB decoy complexes. Expression levels of several cytokines and proteins related to the inflammatory reaction were also suppressed by intravenous administration of KG6/NFkappaB decoy complexes. Because [(32)P] NFkappaB decoy was found in non-parenchymal cells after intravenous injection, KG6 has been shown to be a promising carrier molecule of various oligonucleotides to non-parenchymal liver cells, including Kupffer cells.

Development of a novel endosomolytic diblock copolymer for siRNA delivery

The gene knockdown activity of small interfering RNA (siRNA) has led to their use as target validation tools and as potential therapeutics for a variety of diseases. The delivery of these double-stranded RNA macromolecules has proven to be challenging, however, and in many cases, is a barrier to their deployment. Here we report the development of a new diblock copolymer family that was designed to enhance the systemic and intracellular delivery of siRNA. These diblock copolymers were synthesized using the controlled reversible addition fragmentation chain transfer polymerization (RAFT) method and are composed of a positively-charged block of dimethylaminoethyl methacrylate (DMAEMA) to mediate siRNA condensation, and a second endosomal-releasing block composed of DMAEMA and propylacrylic acid (PAA) in roughly equimolar ratios, together with butyl methacylate (BMA). A related series of diblock compositions were characterized, with the cationic block kept constant, and with the ratio of DMAEMA and PAA to BMA varied. These carriers became sharply hemolytic at endosomal pH regimes, with increasing hemolytic activity seen as the percentage of BMA in the second block was systematically increased. The diblock copolymers condensed siRNA into 80-250 nm particles with slightly positive Zeta potentials. SiRNA-mediated knockdown of a model protein, namely glyceraldehyde 3-phosphate dehydrogenase (GAPDH), in HeLa cells generally followed the hemolytic activity trends, with the most hydrophobic second block (highest BMA content) exhibiting the best knockdown. This pH-responsive carrier designed to mediate endosomal release shows significant promise for the intracellular delivery of siRNA.

Efficient delivery of siRNA using dendritic poly(L-lysine) for loss-of-function analysis

RNA interference (RNAi) is a valuable tool for the validation of gene identification and functional genomics. Previously, it was reported that 6th generation dendritic poly(L-lysine) (KG6) transfected DNA into several cultivated cell lines with high efficiency and without any cytotoxic effects. In this study, the potential of KG6 to be an efficient siRNA carrier is investigated. KG6 showed effective knockdown of GAPDH with low cytotoxicity in combination with the weak-base amphiphilic peptide, Endo-Porter. In addition, the knockdown of PEPCK, which is the rate-limiting enzyme for gluconeogenesis, led to a reduction in glucose production in rat hepatoma H4IIEC3 cells. Knockdown of organic cation transporter 1 (OCT1), which is thought to be the gene that influences metformin action, was shown to successfully diminish the ability of metformin to inhibit gluconeogenesis in H4IIEC3 cells. In conclusion, using a combination of KG6 and Endo-Porter, a model system in which genes that influence metformin action can be identified was successfully constructed.

Structural advantage of dendritic poly(l-lysine) for gene delivery into cells

This study aimed to investigate the relationships between structures of gene carrier molecules and their activities for gene delivery into cells. We compared 2 types of poly(L-lysine) as carriers, that is, dendritic poly(L-lysine) (KG6) and linear poly(L-lysine) (PLL). KG6 formed a neutral DNA complex, and its DNA compaction level was weaker than that of PLL. The amount of DNA binding and uptake into cells mediated by PLL was 4-fold higher than that with KG6. However, KG6-mediated gene expression was 100-fold higher than that by PLL. Since pK(a) values of terminal amines of KG6 were lowered even though small amounts of DNA were internalized into cells, sufficient DNA amounts for effective gene expression escaped to the cytosol due to the proton sponge effect in the endosome. In addition, weakly compacted DNA with KG6 was advantageous in accessing RNA polymerase in the cell nucleus. On the other hand, PLL did not show the proton sponge effect in the endosome and resulted in strong compaction of DNA. Even though large DNA amounts were internalized into cells, most of the DNA would not take part in gene expression systems in the nucleus. Amount of induced cytokine production after intravenous injection of DNA complexes with KG6 and PLL was low, and was similar to the case when DNA was injected alone. Therefore, no significant difference in effects on cytokine production was observed between KG6 and PLL.

Biodistribution characteristics of amino acid dendrimers and their PEGylated derivatives after intravenous administration

In this study, we synthesized dendritic poly(L-lysine)s (DPKs), dendritic poly(L-ornithine)s (DPOs), which are constructed as novel amino acid dendrimers, and PEGylated KG6 (the sixth generation of DPKs), and evaluated the physicochemical properties and biodistribution characteristics of these dendrimers. The particle size of DPKs and DPOs was well controlled in the nanometer range. The zeta-potential of these dendrimers was slightly positive and this gradually increased in association with their generation. After intravenous administration to mice, all tested dendrimers cleared rapidly from blood flow and mainly accumulated in the liver and kidney. The hepatic and renal accumulation changed in a generation-dependent manner. In contrast, no significant distributional differences between same generation of DPK and DPO were observed, although the constituent amino acids, particle size, and zeta-potential were different. However, PEGylation of KG6 caused great changes in particle size, zeta-potential, blood retention and organ distribution in vivo, indicating that the PEGylation is applicable strategy to improve biodistribution characteristics of dendrimeric molecules. The information provided by this study will be helpful for the development of future drug delivery systems using amino acid dendrimers as safe drug carriers.

Stabilizing of plasmid DNA in vivo by PEG-modified cationic gold nanoparticles and the gene expression assisted with electrical pulses

This study aimed to investigate the benefits of combining the use of PEG-modified cationic gold nanoparticles with electroporation for in vivo gene delivery. PEG-modified cationic gold nanoparticles were prepared by NaBH(4) reduction of HAuCl(4) in the presence of 2-aminoethanethiol and mPEG-SH. Zeta-potential of the particles was nearly neutral (+0.1 mV). After forming complexes with plasmid DNA at a w/w ratio of 8.4, nanoparticle complexes were 90 nm for at least 60 min and showed a negative zeta-potential. After intravenous injection of DNA-nanoparticle complexes, 20% of gold were detected in blood at 120 min after injection and 5% of DNA were observed in blood after 5 min, suggesting that PEG-modified nanoparticles were stably circulating in the blood flow, but some of the DNA bound to particles degraded during circulation. When electroporation was applied to a lobe of the liver following injection of DNA-nanoparticle complexes, significant gene expression was specifically observed in the pulsed lobe. We concluded that PEG-modified nanoparticles maintained DNA more stably in the blood flow than in the case of naked DNA and electroporation assisted in restricted gene expression of circulating DNA in limited areas of the liver.

Targeting of Polyplexes: Toward Synthetic Virus Vector Systems

Dominating issues in gene vector optimization are specific in recognizing the target cells and exploiting the proper intracellular trafficking routes. Any progress in this area will result in improved specific gene transfer, reduce the required therapeutic vector doses and, in consequence, lower the overall toxicity to the host. To provide polyplexes with the ability to distinguish between non-target and target cells, cell-binding ligands have been incorporated which recognize target-specific cellular receptors. In addition, polyplex domains with unspecific binding capacity (such as surface charges) have to be shielded or removed. Cell-binding ligands can be small molecules, vitamins, carbohydrates, peptides or proteins such as growth factors or antibodies. Such ligands have been incorporated into polyplexes after chemical conjugation to cationic polymers. The choice of the ligand and physical properties of the DNA formulation strongly influence extracellular routing (circulation in blood, tissue distribution), uptake and intracellular delivery of polyplexes. Recent efforts are discussed that aim at the development of polyplexes into virus-like supramolecular complexes; such particles should undergo structural changes compatible with extracellular and intracellular targeting.