Nanocarriers: a tool to overcome biological barriers in siRNA delivery

INTRODUCTION: siRNA has poor in vivo stability and has a plasma half life of only a few minutes after intravenous administration. These problems can be overcome by conjugating/encapsulating siRNA with various nanosystems. Surface modifications of such nanosystems can further improve the cellular uptake of siRNA-nanosystems. In this review, the authors have highlighted the problems encountered in siRNA delivery, conjugation strategies and nanosystems for siRNA delivery and for improving their in vivo delivery performance. AREAS COVERED: The authors briefly cover various problems encountered in siRNA delivery and discuss nanocarriers for overcoming these biological barriers. EXPERT OPINION: siRNA binding and unpacking are important factors for optimizing the interactions between siRNA and nanosystems. Several crucial conjugation parameters, such as the conjugation site of siRNA, and the nature of molecules to be conjugated (charge, molecular weight and hydrophobicity), should be carefully considered for maximising delivery efficiency of siRNA conjugated nanosystems.     

Supramolecular nanocarrier for gene and siRNA delivery

In this review article, supramolecular nanocarriers for gene and siRNA delivery were introduced. They were formed through the multimolecular assembly of block copolymers, containing the DNA or siRNA inside the core of the micelle structure. Due to the excellent stability under the physiological conditions, low toxic effect, and controllable gene functions, this system should be a promising candidate for in vivo therapeutic applications including the non-lethal diseases and the tissue engineering.     

Nanocarriers: a tool to overcome biological barriers in siRNA delivery

Introduction: siRNA has poor in vivo stability and has a plasma half life of only a few minutes after intravenous administration. These problems can be overcome by conjugating/encapsulating siRNA with various nanosystems. Surface modifications of such nanosystems can further improve the cellular uptake of siRNA-nanosystems. In this review, the authors have highlighted the problems encountered in siRNA delivery, conjugation strategies and nanosystems for siRNA delivery and for improving their in vivo delivery performance.

Areas covered: The authors briefly cover various problems encountered in siRNA delivery and discuss nanocarriers for overcoming these biological barriers.

Expert opinion: siRNA binding and unpacking are important factors for optimizing the interactions between siRNA and nanosystems. Several crucial conjugation parameters, such as the conjugation site of siRNA, and the nature of molecules to be conjugated (charge, molecular weight and hydrophobicity), should be carefully considered for maximising delivery efficiency of siRNA conjugated nanosystems.     

Bioreducible hyaluronic acid conjugates as siRNA carrier for tumor targeting

The successful clinical translation of siRNA-based therapeutics requires efficient carrier systems that can specifically deliver siRNA within the cytosol of the target cells. Although numerous polymeric nanocarriers forming ionic complexes with siRNA have been investigated for cancer therapy, their poor stability and lack of tumor targetability have impeded their in vivo applications. To surmount these limitations, we synthesized a novel type of biodegradable hyaluronic acid-graft-poly(dimethylaminoethyl methacrylate) (HPD) conjugate that can form complexes with siRNA and be chemically crosslinked via the formation of the disulfide bonds under facile conditions. The crosslinked siRNA-HPD (C-siRNA-HPD) complexes exhibited high stability in a 50% serum solution, as compared to the uncrosslinked siRNA-HPD (U-siRNA-HPD) complexes and free siRNA. Both the C-siRNA-HPD and U-siRNA-HPD complexes were efficiently taken up by the CD44-overexpressing melanoma cells (B16F10), but not by the normal fibroblast cells (NIH3T3). When the RFP-expressing B16F10 cells were treated with the complexes or free siRNA, the C-siRNA-HPD complexes showed the highest decrease in RFP expression. In vivo studies demonstrated the selective accumulation of C-siRNA-HPD complexes at the tumor site after their systemic administration into tumor-bearing mice, resulting in an efficient gene silencing effect. Overall, these results suggest that the HPD conjugate could be used as an efficient carrier for the tumor-targeted delivery of siRNA.     

A Double-modulation Strategy in Cancer Treatment With a Chemotherapeutic Agent and siRNA

5-Fluorouracil (5-FU) is broadly considered the drug of choice for treating human colorectal cancer (CRC). However, 5-FU resistance, mainly caused by the overexpression of antiapoptotic proteins such as Bcl-2, often leads ultimately to treatment failure. We here investigated the effect of Bcl-2 gene silencing, using small interfering RNA (siRNA) (siBcl-2), on the efficacy of 5-FU in CRC. Transfection of siBcl-2 by a Lipofectamine2000/siRNA lipoplex effectively downregulated Bcl-2 expression in the DLD-1 cell line (a CRC), resulting in significant cell growth inhibition in vitro upon treatment with 5-FU. For in vivo treatments, S-1, an oral formulation of Tegafur (TF), a prodrug of 5-FU, was used to mimic 5-FU infusion. The combined treatment of polyethylene glycol (PEG)-coated siBcl-2-lipoplex and S-1 showed superior tumor growth suppression in a DLD-1 xenograft model, compared to each single treatment. Surprisingly, daily S-1 treatment enhanced the accumulation of PEG-coated siBcl-2-lipoplex in tumor tissue. We propose a novel double modulation strategy in cancer treatment, in which chemotherapy enhances intratumoral siRNA delivery and the delivered siRNA enhances the chemosensitivity of tumors. Combination of siRNA-containing nanocarriers with chemotherapy may compensate for the limited delivery of siRNA to tumor tissue. In addition, such modulation strategy may be considered a promising therapeutic approach to successfully managing 5-FU-resistant tumors.     

Comparative in vivo study of poly(ethylene imine)/siRNA complexes for pulmonary delivery in mice

Pulmonary siRNA delivery offers a new way to treat various lung diseases. Poly(ethylene imines) (PEIs) are promising cationic nanocarriers and various modifications are still under investigations to improve their cytotoxicity and efficacy for siRNA delivery.In this study, we analyzed two different types of PEI-based nanocomplexes in mice after intratracheal administration regarding their toxicity and efficacy in the lungs. Ubiquitously enhanced green fluorescent protein (EGFP) expressing transgenic and BALB/c mice were intratracheally instilled with 35 μg siRNA complexed with the different types of PEI nanocarriers. Lung toxicity and inflammation were investigated after 24 h, 3 d and 7 d treatment and knockdown of EGFP expression was analyzed by flow cytometry and fluorescence microscopy five days post instillation.Three different polyplexes caused more than 60% knockdown of EGFP expression, but only the fatty acid modified low molecular weight PEI 8.3 kDa (C16-C18-EO25)1.4 specifically reduced EGFP expression in CD45+ leucocytes (25 ± 12%) and CD11b−/CD11c+ lung macrophages (36 ± 14%). Hydrophobic and hydrophilic PEG modifications on PEI caused severe inflammatory response and elevated levels of IgM in broncho-alveolar fluid (BALF). Thus, the PEG modification reduced cytotoxicity, but elevated the immune response and proinflammatory effects. Further investigations of the proinflammatory and immunomodulatory effects of the PEI-modified carriers are necessary to clarify the highly unspecific knockdown effects in the lung in more detail. Nevertheless, the more hydrophobic modification of PEI based non-viral vector system appeared to be a promising approach for improved siRNA therapeutics offering successful pulmonary siRNA delivery.     

Small interfering RNA urokinase silencing inhibits invasion and migration of human hepatocellular carcinoma cells

The serine protease urokinase-type plasminogen activator (u-PA) is involved in a variety of physiologic and pathological processes; in particular, u-PA mRNA is up-regulated in human hepatocellular carcinoma (HCC) biopsies and its level of expression is inversely correlated with patients' survival. To determine the role of u-PA in the invasiveness properties of HCC, we successfully down-regulated u-PA by RNA interference (RNAi) technology, in an HCC-derived cell line at high level of u-PA expression. RNAi is a multistep process involving generation of small interfering RNAs (siRNA) that cause specific inhibition of the target gene. SKHep1C3 cells were transfected with a U6 promoter plasmid coding for an RNA composed of two identical 19-nucleotide sequence motifs in an inverted orientation, separated by a 9-bp spacer to form a hairpin dsRNA capable of mediating target u-PA inhibition. Stable transfectant cells showed a consistently decreased level of u-PA protein. In biological assays, siRNA u-PA-transfected cells showed a reduction of migration, invasion, and proliferation. In conclusion, u-PA down-regulation by RNAi technology decreases the invasive capability of HCC cells, demonstrating that stable expression of siRNA u-PA could potentially be an experimental approach for HCC gene therapy.     

靶向乙酰肝素酶siRNA对大肠癌细胞恶性生物学行为的影响

目的研究化学合成的siRNA干扰乙酰肝素酶对大肠SW620癌细胞生物学行为及其可能的机制。方法实验组选取对数期生长的SW620癌细胞转染靶向乙酰肝素酶siRNA,对照组用非特异性的siRNA处理对数期生长的SW620癌细胞。应用RT-PCR检测乙酰肝素酶基因表达,并利用免疫组化检测乙酰肝素酶蛋白表达情况,侵袭实验检测细胞侵袭力。结果实验组的对数期生长的SW620癌细胞的乙酰肝素酶基因和蛋白含量显著低于对照组,而实验组细胞的侵袭能力也显著低于对照组。对照组的侵袭细胞数显著多于实验组。结论化学合成的siRNA能够降低大肠癌细胞恶性生物学行为,可作为一种新的基因治疗方法用于大肠癌的临床治疗。     

Polyethyleneimine-based core-shell nanogels: a promising siRNA carrier for argininosuccinate synthetase mRNA knockdown in HeLa cells

RNA interference using small interfering RNA (siRNA) is a promising biological strategy for treatment of diverse diseases; however, application of siRNA is severely hindered by its poor stability and low cellular uptake efficiency. We have recently demonstrated that polyethyleneimine (PEI)-based amphiphilic core-shell particles have several distinguishing advantages over native PEI and its derivatives. This paper presents a novel type of PEI-based nanogels with a biodegradable gelatin core. The core-shell nanogels were synthesized via a two-stage reaction: (1) preparation of highly uniform gelatin nanoparticles through appropriate treatment of gelatin solution; and (2) conjugation of branched PEI to the preformed gelatin nanoparticles, followed by repeated cycles of desolvation and drying of the gelatin-PEI nanogels in ethanol/water mixture. The resulting nanogels have a well-defined nanostructure that contains a gelatin core and a PEI shell. They have an average diameter of 200 ± 40nm with high uniformity. The nanogel particles possess positive zeta-potential values of up to +40mV at neutral pH, indicating that they are highly positive and very stable in aqueous medium. The gelatin-PEI nanogels were able to completely condense siRNA at N/P ratios of as low as 5:1, and effectively protected siRNA against enzymatic degradation. Furthermore, the nanogels were four times less toxic than native PEI. Besides low toxicity, the nanogels were able to effectively deliver siRNA into HeLa cells. It was found that increasing the N/P ratio from 10 to 30 significantly increased the intracellular uptake efficiency of siRNA from 41 to 84%. Confocal laser scanning microscopic images confirmed that the nanogels were able to effectively deliver siRNA in the cytoplasm of HeLa cells. The delivered siRNA could inhibit 70% of human argininosuccinate synthetase 1 (ASS1) gene expression. This gene silencing percentage is much higher than that of the commercial Lipofectamine(TM) 2000. Our studies demonstrate that gelatin-PEI core-shell nanogels have promising potential to act as an effective siRNA carrier.     

Cholesteryl oligoarginine delivering vascular endothelial growth factor siRNA effectively inhibits tumor growth in colon adenocarcinoma.

Vascular endothelial growth factor (VEGF) is a multifunctional angiogenic growth factor that is a primary stimulant of the development and maintenance of a vascular network in the vascularization of solid tumors. It has been reported that a blockade of VEGF-mediated angiogenesis is a powerful method for tumor regression. RNA interference represents a naturally occurring biological strategy for inhibition of gene expression. In mammalian systems, however, the in vivo application of small interfering RNA (siRNA) is severely limited by the instability and poor bioavailability of unmodified siRNA molecules. In this study, we tested the hypothesis that a hydrophobically modified protein transduction domain, cholesteryl oligo-d-arginine (Chol-R9), may stabilize and enhance tumor regression efficacy of the VEGF-targeting siRNA. The noncovalent complexation of a synthetic siRNA with Chol-R9 efficiently delivered siRNA into cells in vitro. Moreover, in a mouse model bearing a subcutaneous tumor, the local administration of complexed VEGF-targeting siRNA, but not of scrambled siRNA, led to the regression of the tumor. Hence, we propose a novel and simple system for the local in vivo application of siRNA through Chol-R9 for cancer therapy.     

Biocompatible gelatin nanoparticles for tumor-targeted delivery of polymerized siRNA in tumor-bearing mice

Structural modifications of the siRNA backbone improved its physiochemical properties for incorporating in gene carriers without loss of gene-silencing efficacy. These modifications provide a wider variety of choice of vector systems for siRNA delivery. We developed a tumor-targeted siRNA delivery system using polymerized siRNA (poly-siRNA) and natural polymer gelatin. The polymerized siRNA (poly-siRNA) was prepared through self-polymerization of thiol groups at the 5′-end of sense and anti-sense strands of siRNA and was encapsulated in the self-assembled thiolated gelatin (tGel) nanoparticles (NPs) with chemical cross-linking. The resulting poly-siRNA-tGel (psi-tGel) nanoparticles (average of 145 nm in diameter) protect siRNA molecules from enzymatic degradation, and can be reversibly reduced to release functional siRNA molecules in reductive conditions. The psi-tGel NPs presented efficient siRNA delivery in red fluorescence protein expressing melanoma cells (RFP/B16F10) to down-regulate target gene expression. In addition, the NPs showed low toxicity at a high transfection dose of 125 μg/ml psi-tGel NPs, which included 1 μM of siRNA molecules. In tumor-bearing mice, the psi-tGel NPs showed 2.8 times higher tumor accumulation than the naked poly-siRNA, suggesting tumor-targeted siRNA delivery of psi-tGel NPs. Importantly, the psi-tGel NPs induced effective tumor RFP gene silencing in vivo without remarkable toxicity. The psi-tGel NPs have great potential for a systemic siRNA delivery system for cancer therapy, based on their characteristics of low toxicity, tumor accumulation, and effective siRNA delivery.     

人端粒酶逆转录酶基因沉默对肺腺癌细胞侵袭、增殖、凋亡的影响

目的:探讨靶向人端粒酶逆转录酶(hTERT)基因的小干扰RNA(siRNA)转染对肺腺癌细胞株A549生物学行为的影响。方法:构建靶向hTERT的siRNA表达质粒转染A549细胞,通过Western blot检测蛋白的表达水平,确定有效后,通过Transwell小室检测细胞体外侵袭能力,MTT法检测细胞增殖活性,流式细胞术测定转染后肿瘤细胞的细胞周期和凋亡率。结果:成功构建靶向hTERT的siRNA表达质粒。实验组siRNA转染后的细胞侵袭能力较对照组减弱(P<0.01),生长抑制率明显高于阴性对照组(P<0.01),且表现出时间依赖性。流式细胞术测定显示,实验组siRNA转染48h后,肿瘤细胞凋亡率显著增加(P<0.01)。结论:靶向hTERT的siRNA转染后可以显著降低A549细胞侵袭能力,抑制增殖,诱导细胞凋亡的发生。     

Transfection of shRNA-encoding Minivector DNA of a few hundred base pairs to regulate gene expression in lymphoma cells

This work illustrates the utility of Minivector DNA, a non-viral, supercoiled gene therapy vector incorporating short hairpin RNA from an H1 promoter. Minivector DNA is superior to both plasmid DNA and small interfering RNA (siRNA) in that it has improved biostability while maintaining high cell transfection efficiency and gene silencing capacity. Minivector DNAs were stable for over 48?h in human serum, as compared with only 0.5 and 2?h for siRNA and plasmid, respectively. Although all three nucleic acids exhibited similar transfection efficiencies in easily transfected adhesion fibroblasts cells, only Minivector DNAs and siRNA were capable of transfecting difficult-to-transfect suspension lymphoma cells. Minivector DNA and siRNA were capable of silencing the gene encoding anaplastic lymphoma kinase, a key pathogenic factor of human anaplastic large cell lymphoma, and this silencing caused inhibition of the lymphoma cells. Based on these results, Minivector DNAs are a promising new gene therapy tool.     

A New Potent Secondary Amphipathic Cell�Cpenetrating Peptide for siRNA Delivery Into Mammalian Cells

RNA interference constitutes a powerful tool for biological studies, but has also become one of the most challenging therapeutic strategies. However, small interfering RNA (siRNA)-based strategies suffer from their poor delivery and biodistribution. Cell-penetrating peptides (CPPs) have been shown to improve the intracellular delivery of various biologically active molecules into living cells and have more recently been applied to siRNA delivery. To improve cellular uptake of siRNA into challenging cell lines, we have designed a secondary amphipathic peptide (CADY) of 20 residues combining aromatic tryptophan and cationic arginine residues. CADY adopts a helical conformation within cell membranes, thereby exposing charged residues on one side, and Trp groups that favor cellular uptake on the other. We show that CADY forms stable complexes with siRNA, thereby increasing their stability and improving their delivery into a wide variety of cell lines, including suspension and primary cell lines. CADY-mediated delivery of subnanomolar concentrations of siRNA leads to significant knockdown of the target gene at both the mRNA and protein levels. Moreover, we demonstrate that CADY is not toxic and enters cells through a mechanism which is independent of the major endosomal pathway. Given its biological properties, we propose that CADY-based technology will have a significant effect on the development of fundamental and therapeutic siRNA-based applications.     

SOCS1-siRNA沉默SOCS1基因表达对脐血树突状细胞生物学活性的影响

目的采用RNA干扰技术抑制脐血树突状细胞(DC)SOCS1基因表达,并检测其对树突状细胞生物学活性的影响,为树突状细胞的临床应用奠定基础。方法针对SOCS1基因,采用化学合成法合成SOCS1siRNA,并转染脐血DC。RT-PCR和Western blot检测转染前后DC的SOCS1基因表达;流式细胞术检测细胞表面CD80、CD86及HLA-DR分子表达情况;ELISA法检测细胞培养上清中IL-12水平。结果与对照组相比,siRNA组SOCS1蛋白质表达水平降低,差异有统计学意义;DC表面CD80、CD86及HLA-DR分子表达上调,DC培养上清中IL-12的浓度显著提高。结论 RNA干扰技术能显著下调脐血树突状细胞SOCS1的表达,为以DC SOCS1为靶向的抗肿瘤治疗提供了新思路和新手段。     

Self-assembly of glycerol monooleate with the antimicrobial peptide LL-37: a molecular dynamics study

Over the past decade, the rapid increase in the incidence of antibiotic-resistant bacteria has promoted research towards alternative therapeutics such as antimicrobial peptides (AMPs), but their biodegradability limits their application. Encapsulation into nanocarriers based on the self-assembly of surfactant-like lipids is emerging as a promising strategy for the improvement of AMPs'' stability and their protection against degradation when in biological media. An in-depth understanding of the interactions between the structure-forming lipids and AMPs is required for the design of nanocarriers. This in silico study, demonstrates the self-assembly of the amphiphilic lipid glycerol monooleate (GMO) with the antimicrobial peptide LL-37 into nanocarriers on the molecular scale. Molecular dynamics (MD) simulations show the formation of direct micelles, with either one or two interacting LL-37, and vesicles in this two-component system in agreement with experimental results from small-angle X-ray scattering studies. The hydrophobic contacts between LL-37 and GMOs in water appear responsible for the formation of these nanoparticles. The results also suggest that the enhanced antimicrobial efficiency of LL-37 in these nanocarriers that was previously observed experimentally can be explained by the availability of its side chains with charged amino acids, an increase of the electrostatic interaction and a decrease of the peptide''s conformational entropy upon interacting with GMO. The results of this study contribute to the fundamental understanding of lipid–AMP interactions and may guide the comprehensive design of lipid-based self-assembled nanocarriers for antimicrobial peptides.

Molecular dynamics simulations of glycerol-monooleate (GMO)/LL-37 nanocarriers show that hydrophobic interactions among the molecules drive the formation of GMO/LL-37 micelles.     

Progress on ocular siRNA gene‐silencing therapy and drug delivery systems

Age‐related macular degeneration (AMD) and glaucoma are global ocular diseases with high blindness rate. RNA interference (RNAi) is being increasingly used in the treatment of these disorders with siRNA drugs, bevasiranib, AGN211745 and PF‐04523655 for AMD, and SYL040012 and QPI‐1007 for glaucoma. Administration routes and vectors of gene drugs affect their therapeutic effect. Compared with the non‐viral vectors, viral vectors have limited payload capacity and potential immunogenicity. This review summarizes the progress of the ocular siRNA gene‐silencing therapy by focusing on siRNA drugs for AMD and glaucoma already used in clinical research, the main routes of drug delivery and the non‐viral vectors for siRNA drugs.     

siRNA特异性抑制HEL细胞evi1基因的实验研究

本研究探讨小干扰RNA（small interfering RNA,siRNA）沉默人红白细胞白血病细胞（HEL）的evi1基因后对细胞evi1基因表达的抑制作用及细胞生物学特征变化及其作用机制。体外合成3条evi1基因特异性的siRNA（siRNA-1、siRNA-2、siRNA-3）并转染HEL细胞,并设对照。用四甲基偶氮唑蓝法评价细胞增殖抑制情况,半定量逆转录聚合酶链反应（semiquantitative RT-PCR）检测evi1基因mRNA的表达,台盼蓝染色试验测定细胞活性的变化,流式细胞术检测细胞周期变化和凋亡率。结果显示,细胞转染24、48、72小时后,以siRNA-1作用最强,转染后48小时抑制作用最明显。siRNA浓度为120nmol/L时,抑制率达到最大。转染48小时后siRNA-1对HEL细胞的增殖抑制率为（72.22±2.80）%,evi1-mRNA相对表达率为（27.31±1.11）%,HEL细胞活率为（26.05±2.49）%,与其他各组相比有显著性差异（p〈0.001）。siRNA可使细胞周期阻滞在G0/G1期,S期细胞明显减少,凋亡率明显增高（p〈0.01）。结论：evi1基因特异性siRNA可抑制HEL细胞增殖,使evi1-mRNA表达水平降低,细胞活性下降,HEL细胞周期阻滞在G0/G1期,抑制细胞的有丝分裂,促进细胞凋亡。