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Combination therapy of nucleic acids and chemical drugs for cancer treatment is a promising strategy to enhance the therapeutic efficacy by simultaneously regulating multiple troublesome pathways. In this study, we report on polyethylene glycol-siRNA-polycaprolactone (PEG-siRNA-PCL) micelles that encapsulate hydrophobic drugs for efficient co-delivery of siRNA and drugs to cancer cells. Amphiphilic PEG-siRNA-PCL copolymers were synthesized by annealing antisense siRNA-PCL conjugates with sense siRNA-PEG conjugates. After paclitaxel encapsulation, PEG-siRNA-PCL micelles containing antiapoptotic Bcl-2-specific siRNA were stabilized with linear polyethylenimine via electrostatic interactions. Stabilized PEG-siRNA-PCL micelles showed superior anticancer effects, assessed by caspase-3 activity analysis, apoptotic cell staining, and a cytotoxicity test, to those of paclitaxel-free PEG-siRNA-PCL micelles and unmodified siRNAs. The strong anticancer activity of paclitaxel-incorporated siRNA micelles can be attributed to the synergistic effect of Bcl-2 siRNA and paclitaxel. This work provides an efficient co-delivery platform for combination anticancer therapy with siRNA and chemotherapy.

Multivalent aptamer-siRNA conjugates containing multiple mucin-1 aptamers and BCL2-specific siRNA are synthesized, and doxorubicin, an anthracycline anticancer drug, is loaded into these conjugates through intercalation with nucleic acids. These doxorubicin-incorporated multivalent aptamer-siRNA conjugates are transfected to mucin-1 overexpressing MCF-7 breast cancer cells and their multidrug-resistant cell lines. Doxorubicin-incorporated multivalent aptamer-siRNA conjugates exert promising anticancer effects, such as activation of caspase-3/7 and decrease of cell viability, on multidrug-resistant cancer cells because of their high intracellular uptake efficiency. Thus, this delivery system is an efficient tool for combination oncotherapy with chemotherapeutics and nucleic acid drugs to overcome multidrug resistance., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Recent promising clinical results of RNA therapeutics have drawn big attention of academia and industries to RNA therapeutics and their carrier systems. To improve their feasibility in clinics, systemic evaluations of currently available carrier systems under clinical trials and preclinical studies are needed. In this review, we focus on recent noticeable preclinical studies and clinical results regarding siRNA-based conjugates for clinical translations. Advantages and drawbacks of siRNA-based conjugates are discussed, compared to particle-based delivery systems. Then, representative siRNA-based conjugates with aptamers, peptides, carbohydrates, lipids, polymers, and nanostructured materials are introduced. To improve feasibility of siRNA conjugates in preclinical studies, several considerations for the rational design of siRNA conjugates in terms of cleavability, immune responses, multivalent conjugations, and mechanism of action are also presented. Lastly, we discuss lessons from previous preclinical and clinical studies related to siRNA conjugates and perspectives of their clinical applications., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In this study, we systematically explore the influence of the lipophilic group on the siRNA transfection properties of the polycationic-based delivery vectors. For this, a novel and modular synthetic strategy was developed for the preparation of polymers carrying a cationic site and a lipophilic group at each polymer repeat unit. These bifunctional polymers could form a complex with siRNA and deliver it to human colon carcinoma cells (HT-29-luc). In general, transfection capability increased with an increase in the chain length of the lipophilic moiety. The best transfection agent, a polymer containing ammonium groups and pentyl side chains, exhibited lower toxicity and higher transfection efficiency than branched and linear polyethylenimines (PEI). Moreover, as opposed to PEI, the transfection efficiency of polymer/siRNA complexes remained unchanged in the presence of bafilomycin A1, a proton pump inhibitor, suggesting that the present system did not rely on the "proton sponge" effect for siRNA delivery.

Here, we report quantum dot-incorporating solid lipid nanoparticles (SLNs) for anticancer theranostics with synergistic therapeutic effects of paclitaxel-siRNA combination. The natural components of a low-density lipoprotein (LDL) are reconstituted to produce LDL-mimetic SLNs having a stable core/shell nanostructure incorporating quantum dots and paclitaxel within the lipid shell while anionic siRNA molecules are electrostatically complexed with the outer surface of SLNs. The produced SLN/siRNA complexes efficiently deliver both of paclitaxel and Bcl-2 targeted siRNA into human lung carcinoma cells and exhibit synergistic anticancer activities by triggering caspase-mediated apoptosis as determined by median effect plot analysis. Moreover, the strong fluorescence from quantum dots within SLNs enables in situ visualization of intracellular translocation of SLNs into cancer cells. Our study suggests that LDL-mimetic SLNs can be utilized as a multifunctional and optically traceable nanocarrier for efficient anticancer theranostics., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Recently, small interfering RNA (siRNA) has received much attention for therapeutic applications; however, low transfection efficiency and intrinsic instability limit effective gene silencing. Here we show a new approach based on the incorporation of siRNA/polyelectrolyte complexes into biodegradable poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles to stabilize siRNA within a hydrophobic solid matrix for prolonged gene silencing. To solubilize siRNA in organic media, chitosan oligosaccharides grafted with deoxycholic acids are synthesized and complexed with siRNA, generating a self-assembled polyelectrolyte complex of 123.9 ± 56.8 nm in diameter. The complex is mixed with PLGA solution and emulsified in water to prepare siRNA-loaded PLGA nanoparticles having a diameter of about 230 nm. The excellent structural stability of the prepared nanoparticles leads to efficient cellular uptake followed by effective gene silencing even in the presence of serum proteins. These results suggest that the encapsulation of siRNA into biodegradable polymer matrix can be an effective means of improving the structural stability of siRNA for prolonged therapeutic efficacy., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Because of RNA's ability to encode structure and functional information, researchers have fabricated diverse geometric structures from this polymer at the micro- and nanoscale. With their tunable structures, rigidity, and biocompatibility, novel two-dimensional and three-dimensional RNA structures can serve as a fundamental platform for biomedical applications, including engineered tissues, biosensors, and drug delivery vehicles. The discovery of the potential of small-interfering RNA (siRNA) has underscored the applications of RNA-based micro- and nanostructures in medicine. Small-interfering RNA (siRNA), synthetic double-stranded RNA consisting of approximately 21 base pairs, suppresses problematic target genes in a sequence-specific manner via inherent RNA interference (RNAi) processing. As a result, siRNA offers a potential strategy for treatment of many human diseases. However, due to inefficient delivery to cells and off-target effects, the clinical application of therapeutic siRNA has been very challenging. To address these issues, researchers have studied a variety of nanocarrier systems for siRNA delivery. In this Account, we describe several strategies for efficient siRNA delivery and selective gene silencing. We took advantage of facile chemical conjugation and complementary hybridization to design novel siRNA-based micro- and nanostructures. Using chemical crosslinkers and hydrophobic/hydrophilic polymers at the end of siRNA, we produced various RNA-based structures, including siRNA block copolymers, micelles, linear siRNA homopolymers, and microhydrogels. Because of their increased charge density and flexibility compared with conventional siRNA, these micro- and nanostructures can form polyelectrolyte complexes with poorly charged and biocompatible cationic carriers that are both more condensed and more homogenous than the complexes formed in other carrier systems. In addition, the fabricated siRNA-based structures are linked by cleavable disulfide bonds for facile generation of original siRNA in the cytosol and for target-specific gene silencing. These newly developed siRNA-based structures greatly enhance intracellular uptake and gene silencing both in vitro and in vivo, making them promising biomaterials for siRNA therapeutics.

Development of nano-sized gene delivery vehicles for small interfering RNA (siRNA) delivery is of great importance for their clinical applications such as cancer therapy. Herein, we demonstrate the controlled synthesis of polyethyleneimine (PEI)-coated gold nanoparticles (AuNPs) using catechol-conjugated PEI (PEI-C) for siRNA delivery. Since the conjugated catechol groups are reductive and moderately hydrophobic, PEI-C formed spherical multi-cored micelles in aqueous solution and served as reductive templates for the growth and synthesis of spherical AuNPs with tunable sizes and surface charges. PEI-C was stably anchored on the surface of growing crystal gold seeds with crosslinking, resulting in robust cationic AuNPs. The fabricated PEI-coated AuNPs formed stable complexes with siRNA, and the complexes showed an excellent gene silencing effect in cancer cells. Size and surface charge values of the synthesized AuNPs had a great influence on intracellular uptake and unpacking of siRNA, and the resultant gene silencing efficiency. The PEI-coated AuNPs exhibited an extremely low cytotoxicity due to the reduced density of primary amine groups and the absence of uncomplexed PEI fraction in aqueous solution., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The first attempt to prepare biologically active siRNA-based microhydrogels is reported. The self-assembled microhydrogels were fabricated using sense/antisense complementary hybridization between single-stranded linear and Y-shaped trimeric siRNAs. The siRNA microhydrogels were condensed using a popular cationic polymer such as LPEI to form compact, stable siRNA/polymeric nanoparticles that exhibited superb cellular uptake efficiency and gene silencing activity.

Biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) was conjugated to the 3' end of small interfering RNA (siRNA) via a disulfide bond to synthesize siRNA-PLGA hybrid conjugates. siRNA-PLGA conjugates were spontaneously self-assembled to form a spherical core/shell type micellar structure of ~20 nm in an aqueous environment, probably by hydrophobic interaction of PLGA blocks in the core surrounded by an siRNA shell layer. When linear polyethylenimine was added to the siRNA-PLGA micelles in aqueous solution, stable siRNA-PLGA/LPEI micelles with a size of ~30 nm were produced via ionic complexation between siRNA and LPEI in the outer shell. The cationic siRNA-PLGA/LPEI micelles showed superior intracellular uptake and enhanced gene silencing effect, compared to naked siRNA/LPEI complexes. The hybrid micelle structure based on siRNA and PLGA can be potentially used as an efficient siRNA delivery system for gene silencing., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Di- and triblock siRNA/PEG copolymers were synthesized and complexed with cationic SLN for assessing their gene silencing efficiency as a function of PEG density. A sssiRNA and a sassiRNA were separately conjugated with PEG via a disulfide linkage. AB-type diblock and ABA-type triblock copolymers were successfully prepared by stoichiometric hybridization of sssiRNA-PEG conjugate with sassiRNA and sassiRNA-PEG conjugate, respectively. The resultant di- and triblock copolymers were characterized by means of GPC and gel electrophoresis. The serum stability of siRNA in the copolymers was enhanced as compared to that of naked siRNA. Using cationic SLN as a model carrier, the PEGylation density effect of the siRNA-PEG/SLN complexes on gene silencing and cellular uptake was analyzed., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Simultaneous silencing of multiple up-regulated genes is an attractive and viable strategy to treat many incurable diseases including cancer. Herein we report that multimerized siRNA conjugate composed of two different siRNA sequences in the same backbone shows more efficient inhibition of the two corresponding target genes at one time than physically mixed multimerized siRNA conjugates. Two model siRNAs against VEGF and GFP gene were chemically crosslinked via cleavable and noncleavable linkages for the preparation of dual gene targeted multimeric siRNA conjugates (DGT multi-siRNA). Cleavable DGT multi-siRNA with reducible disulfide linkages exhibited significantly higher gene silencing efficiencies at mRNA and protein expression levels than noncleavable DGT multi-siRNA, the physical mixture of naked siRNA, and that of single gene targeted multimeric siRNA (SGT multi-siRNA) with eliciting negligible immune response. DGT multi-siRNAs against two therapeutic siRNAs, anti-survivin and anti-bcl-2 targeted siRNA, also showed greatly enhanced apoptotic effect. This approach for concurrent suppression of combinatorial therapeutic target genes using cleavable multimeric siRNA structure can be potentially used for improved therapeutic efficacy., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

In this study, dimerized siRNAs linked by a cleavable disulfide bond were synthesized for efficient intracellular delivery and gene silencing. The reducible dimerized siRNAs showed far enhanced complexation behaviors with cationic polymers as compared to monomeric siRNA at the same N/P ratio, as demonstrated by microscopic techniques and gel characterization. Dimerized siRNAs targeting green fluorescent protein (GFP) or vascular endothelial growth factor (VEGF) were complexed with linear polyethylenimine (LPEI), and treated to various cell lines to examine gene transfection efficiencies. In comparison to monomer siRNA/LPEI complexes, dimeric siRNA/LPEI complexes showed greatly enhanced cellular uptake and gene silencing effects in vitro. These results were mainly due to the higher charge density and promoted chain flexibility of the dimerized siRNAs, providing more compact and stable siRNA complexes. In addition, the conjugation strategy of reducible siRNA dimers was further extended: poly(ethylene glycol) (PEG)-modified dimerized siRNAs and heterodimers of siRNAs targeting two different genes (e.g., GFP and VEGF) were synthesized, and their gene silencing efficiencies were characterized. The dimerized siRNA complex system holds great potential for in vivo systemic gene therapy.

Small interfering RNA (siRNA) was conjugated with poly(ethylene glycol) (PEG) at four different terminal ends (sense 3', sense 5', antisense 3', and antisense 5') via cleavable disulfide and noncleavable thioether linkages to evaluate their gene silencing efficiencies upon complexation with Lipofectamine2000. The PEGylation site at the four siRNA termini and PEG molecular weight were not critical factors to significantly affect gene silencing activities. Cleavable siRNA-PEG conjugates showed comparable gene silencing activities to naked siRNA, and exhibited sequence-specific degradation of a target mRNA. Interestingly, noncleavable siRNA-PEG conjugates were processed by Dicer, enabling to exert RNAi effect without showing a target sequence-specific manner. However, only cleavable siRNA-PEG conjugates significantly reduced the extent of INF-alpha release as compared to noncleavable siRNA-PEG conjugates, suggesting that they can be potentially used for therapeutic siRNA applications., (Copyright (c) 2010 Elsevier B.V. All rights reserved.)

Pluronic/polyethylenimine shell crosslinked nanocapsules with embedded magnetite nanocrystals (PPMCs) were developed for magnetically triggered delivery of siRNA. The positively charged PPMCs formed stable nanosized polyelectrolyte complexes via electrostatic interactions with negatively charged siRNA-polyethylene glycol conjugate (siRNA-s-s-PEG) that was linked via a cleavable disulfide linkage. PPMC/siRNA-s-s-PEG polyelectrolyte complexes were efficiently taken up by cancer cells upon exposure to a magnet, thereby enhancing intracellular uptake and silencing effect of siRNA. The present study suggests that these novel nanomaterials could be potentially utilized for magnetically triggered delivery of various nucleic acid-based therapeutic agents.

Small interfering RNA (siRNA) with 19-21 base pairs has been recently recognized as a new therapeutic agent for effectively silencing a specific gene on a post-transcription level. For siRNA therapeutics, safe and efficient delivery issues are significant hurdles to clinical applications. Here we present a new class of biologically active siRNA structure based on chemically self-crosslinked and multimerized siRNA through cleavable disulphide linkages. The multimerized siRNA can produce more stable and compact polyelectrolyte complexes with less cytotoxic cationic carriers than naked siRNA because of substantially increased charge densities and the presence of flexible chemical linkers in the backbone. The cleavable and multimerized siRNA shows greatly enhanced gene-silencing efficiencies in vitro and in vivo through a target-messenger-RNA-specific RNA interference processing without significantly eliciting immune induction. This study demonstrates that the multimerized siRNA structure complexed with selected cationic condensing agents can serve as potential gene-silencing therapeutics for treating various diseases.

For therapeutic applications of small interfering RNA (siRNA), serum stability, enhanced cellular uptake, and facile endosome escape are key issues for designing carriers. In this study, green fluorescent protein (GFP) siRNA was conjugated to a six-arm polyethylene glycol (PEG) derivative via a reducible disulfide linkage (6PEG-siRNA). The 6PEG-siRNA conjugate was also functionalized with a cell penetrating peptide, Hph1 to enhance its cellular uptake property (6PEG-siRNA-Hph1). The 6PEG-siRNA-Hph1 conjugate was electrostatically complexed with cationic self-crosslinked fusogenic KALA peptide (cl-KALA) to form multifunctional polyelectrolyte complex micelles for gene silencing. The resultant siRNA complex formulation with multiple PEG chains showed superior physical stability and resistance to enzymatic degradation. The 6PEG-siRNA-Hph1/cl-KALA complexes exhibited enhanced GFP gene silencing efficiency for MDA-MB-435 cells in the serum containing condition. The current reducible and multifunctional polyelectrolyte complex micelles are expected to have high potential for efficient delivery of therapeutic siRNA.

Background: A variety of synthetic carriers, such as cationic polymers and lipids, have been used as nonviral carriers for small interfering RNA (siRNA) delivery. Although siRNA polyplexes and lipoplexes exhibited good gene silencing efficiencies, they often showed serious cytotoxicities, which are not useful for clinical applications. A double-stranded RNA binding cellular protein with highly specific siRNA binding property and noncytotoxicity was used for siRNA delivery., Methods: A double-stranded RNA binding domain (dsRBD) of human double-stranded RNA activated protein kinase R was genetically produced and utilized to complex siRNA for intracellular delivery. For characterization of the siRNA/dsRBD complexes, decomplexation assay and RNase protection assay were performed. Cytotoxicity and target gene inhibition ability were also examined using human carcinoma cell lines., Results: The recombinantly produced polypeptide dsRBD exhibited its inherent binding activity for siRNA without sequence specificity, and the siRNA/dsRBD complexes protected siRNA from degradation by ribonucleases. Green fluorescent protein (GFP) siRNA/dsRBD complexes showed prominent down-regulation of a target GFP gene, when an endosomal escape function was supplemented by addition of a fusogenic peptide, KALA, in the formulation., Conclusions: The results suggest that dsRBD-based protein carriers could be successfully applied for a wide range of therapeutic siRNAs for intracellular gene inhibition without showing any cytotoxicity.

A polyelectrolyte complex(PEC) micelle-based siRNA delivery system has been developed for vascular endothelial growth factor (VEGF), and its antitumor efficacy has been demonstrated using in-vivo animal models. Penetration and distribution through the avascular regions of human solid tumors after extravasation are important issues for antitumor efficacy, especially for macromolecules such as VEGF siRNA PEC micelles. Using an in-vitro solid tumor model, multicellular layers(MCL) culture of human colorectal cancer cells, we evaluated the penetration kinetics and efficacy of VEGF siRNA PEC micelles(PEC-siRNA) in comparison to unmodified siRNA(N-siRNA). The PEC-siRNA showed full penetration (15-17 layers of cells) with a unique punctuated distribution pattern at 48 h following initial accumulation in the top layers and a significant suppression of mRNA and protein expression in a dose-dependent manner after 72 h exposure. Although the initial penetration of N-siRNA was faster than that of PEC-siRNA, N-siRNA showed complete loss of activity due to its instability within 24 h. Our data support the idea that PEC micelle formulation may provide stable penetration tool through the multilayers of cancer cells and ensure the gene silencing effect of VEGF. This study also demonstrated that MCL could serve as a useful in-vitro model to evaluate the dose- and time-dependent profiles of penetration and efficacy of macromolecular delivery systems in human solid tumor avascular regions.

A polymeric gene carrier was developed to deliver vascular endothelial growth factor (VEGF) small interfering RNA (siRNA) for prostate cancer cells in a target-specific manner. Prostate cancer-binding peptide (PCP) was conjugated with polyethylenimine (PEI) via a poly(ethylene glycol) (PEG) linker (PEI-PEG-PCP). The PEI-PEG-PCP conjugate could effectively condense siRNA to form stable polyelectrolyte complexes (polyplexes) with an average diameter of approximately 150 nm in an aqueous solution. VEGF siRNA/PEI-PEG-PCP polyplexes exhibited significantly higher VEGF inhibition efficiency than PCP-unmodified polycationic carriers (PEI-PEG or PEI) in human prostate carcinoma cells (PC-3 cells). The enhanced gene silencing activity of VEGF siRNA/PEI-PEG-PCP was maintained even under serum conditions, owing to the steric stabilization of the polyplexes with hydrophilic PEG grafts. Confocal microscopic studies revealed that the siRNA/PEI-PEG-PCP polyplexes were delivered into PC-3 cells in a PCP ligand-specific manner.

Gold nanoparticles chemically modified with primary amine groups were developed as intracellular delivery vehicles for therapeutic small interfering RNA (siRNA). The positively charged gold nanoparticles could form stable polyelectrolyte complexes through electrostatic interactions with negatively charged siRNA-polyethylene glycol (PEG) conjugates having a cleavable di-sulfide linkage under reductive cytosol condition. The resultant core/shell type polyelectrolyte complexes surrounded by a protective PEG shell layer had a well-dispersed nanostructure with a hydrodynamic diameter of 96.3+/-25.9 nm, as determined by dynamic light scattering and transmission electron microscopy. Confocal laser scanning microscopy revealed that the nanosized polyelectrolyte complexes were efficiently internalized in human prostate carcinoma cells, and thus enhanced intracellular uptake of siRNA. Furthermore, the siRNA/gold complexes significantly inhibited the expression of a target gene within the cells without showing severe cytotoxicity. The current study demonstrated that positively charged gold nanoparticles could be potentially applied for intracellular delivery of siRNA.

Polyelectrolyte complex (PEC) micelles modified with cancer cell targeting moieties were prepared for intracellular delivery of vascular endothelial growth factor (VEGF) small interfering RNA (siRNA). A luteinizing hormone-releasing hormone (LHRH) peptide analogue was coupled as a cancer targeting ligand to the distal end of the poly(ethylene glycol) (PEG)-siRNA conjugate. The siRNA-PEG-LHRH conjugate self-assembled to form nanosized PEC micelles upon mixing with poly(ethylenimine) (PEI) via ionic interactions. The PEC micelles showed spherical morphology with a hydrodynamic diameter of ca. 150 nm. For LHRH receptor overexpressing ovarian cancer cells (A2780), the PEC micelles with LHRH exhibited enhanced cellular uptake compared to those without LHRH, resulting in increased VEGF gene silencing efficiency via receptor-mediated endocytosis. This study showed that PEC micelles decorated with specific cell-recognizable targeting ligands could be used for targeted delivery of siRNA.

For efficient cancer therapy, small interfering RNA (siRNA) should be stably and efficiently delivered into the target tissue and readily taken up by cancer cells. To address these needs, a polyelectrolyte complex (PEC) micelle-based siRNA delivery system was developed for anti-angiogenic gene therapy. The interaction between poly(ethylene glycol) (PEG)-conjugated vascular endothelial growth factor siRNA (VEGF siRNA-PEG) and polyethylenimine (PEI) led to the spontaneous formation of nanoscale polyelectrolyte complex micelles (VEGF siRNA-PEG/PEI PEC micelles), having a characteristic siRNA/PEI PEC inner core with a surrounding PEG shell layer. Intravenous as well as intratumoral administration of the PEC micelles significantly inhibited VEGF expression at the tumor tissue and suppressed tumor growth in an animal tumor model without showing any detectable inflammatory responses in mice. Upon examination of the PEC micelle distribution and in vivo optical imaging following intravenously injection, enhanced accumulation of the PEC micelles was also observed in the tumor region. This study demonstrates the feasibility of using PEC micelles as a potential carrier for therapeutic siRNAs in local and systemic treatment of cancer.

Cationic solid lipid nanoparticles (SLN), reconstituted from natural components of protein-free low-density lipoprotein, were used to deliver small interfering RNA (siRNA). The cationic SLN was prepared using a modified solvent-emulsification method. The composition was 45% (w/w) cholesteryl ester, 3% (w/w) triglyceride, 10% (w/w) cholesterol, 14% (w/w) dioleoylphosphatidylethanolamine (DOPE), and 28% (w/w) 3beta-[ N-(N',N'-dimethylaminoethane)carbamoyl]-cholesterol (DC-chol). The SLN had a mean diameter of 117+/-12 nm and a surface zeta potential value of +41.76+/-2.63 mV. A reducible conjugate of siRNA and polyethylene glycol (PEG) (siRNA-PEG) was anchored onto the surface of SLN via electrostatic interactions, resulting in stable complexes in buffer solution and in even 10% serum. Under an optimal weight ratio of DC-chol of SLN and siRNA-PEG conjugate, the complexes exhibited higher gene silencing efficiency of GFP and VEGF than that of polyethylenimine (PEI) 25K with showing much reduced cell cytotoxicity. Flow cytometry results also showed that siRNA-PEG/SLN complexes were efficiently taken up by cells. Surface-modified and reconstituted protein-free LDL mimicking SLN could be utilized as noncytotoxic, serum-stable, and highly effective carriers for delivery of siRNA.

Pluronic/poly(ethylenimine) (PEI2K) nanocapsules (NCs) exhibiting a thermally reversible swelling/deswelling volume expansion behavior were synthesized and used for an siRNA delivery nanocarrier as well as an effective endosome breaking agent. Pluronic/PEI2K nanocapsules were in a collapsed state with an average size of 118.9+/-15.3 nm at 37 degrees C, but in a swollen state with that of 412.3+/-83.2 nm at 15 degrees C. The collapsed Pluronic/PEI2K NCs having a highly positive surface zeta potential value were utilized to load siRNA-PEG conjugate on the surface via electrostatic interactions. The siRNA-PEG/NCs nanocomplexes were transfected to the cells at 37 degrees C for efficient cellular uptake. The transfected cells were treated with a brief cold shock to induce an abrupt volume expansion of the NCs within an endosome compartment to physically burst out the endosomal membrane. Far efficient gene silencing effects for both green fluorescent protein (GFP) and vascular endothelial growth factor (VEGF) were observed after the cold shock treatment to the transfected cells.

To develop a small interfering RNA (siRNA) delivery system with low cytotoxicity and high transfection efficiency, siRNA was conjugated to poly(ethylene glycol) via a disulfide linkage (siRNA-PEG) to prepare polyelectrolyte complex micelles (PECMs) by condensing with a cationic fusogenic peptide (KALA). The siRNA-PEG conjugate exhibited enhanced resistance to degradation from nucleases. Anionic siRNA-PEG conjugate and cationic KALA, when mixed in an aqueous phase, spontaneously formed nano-sized PECMs (<200nm) that have an inner core of charge neutralized siRNA/KALA complex surrounded by a PEG corona. Vascular endothelial growth factor (VEGF) siRNA was used to demonstrate VEGF sequence-specific gene inhibition in prostate carcinoma cells (PC-3 cells). The extent of gene silencing was gradually increased with increasing nitrogen to phosphate (N/P) ratio and the concentration of siRNA-PEG/KALA PECMs. These results suggest that the formulation of siRNA-PEG/KALA PECMs could be widely applied for intracellular delivery of various therapeutic siRNAs.