Lipidic Systems for In Vivo siRNA Delivery

The ability of small-interfering RNA (siRNA) to silence specific target genes not only offers a tool to study gene function but also represents a novel approach for the treatment of various human diseases. Its clinical use, however, has been severely hampered by the lack of delivery of these molecules to target cell populations in vivo due to their instability, inefficient cell entry, and poor pharmacokinetic profile. Various delivery vectors including liposomes, polymers, and nanoparticles have thus been developed in order to circumvent these problems. This review presents a comprehensive overview of the barriers and recent progress for both local and systemic delivery of therapeutic siRNA using lipidic vectors. Different strategies for formulating these siRNA-loaded lipid particles as well as the general concern about their safe use in vivo will also be discussed. Finally, current advances in the targeted delivery of siRNA and their impacts on the field of RNA interference (RNAi)-based therapy will be presented.     

Formulation and Pharmacokinetics of Self-Assembled Rifampicin Nanoparticle Systems for Pulmonary Delivery

Purpose  To formulate rifampicin, an anti-tuberculosis antibiotic, for aerosol delivery in a dry powder ‘porous nanoparticle-aggregate particle’ (PNAP) form suited for shelf stability, effective dispersibility and extended release with local lung and systemic drug delivery. Methods  Rifampicin was encapsulated in PLGA nanoparticles by a solvent evaporation process, spray dried into PNAPs containing varying amounts of nanoparticles, and characterized for physical and aerosol properties. Pharmacokinetic studies were performed with formulations delivered to guinea pigs by intratracheal insufflation and compared to oral and intravenous delivery of rifampicin. Results  The PNAP formulations possessed properties suitable for efficient deposition in the lungs. In vitro release showed an initial burst of rifampicin, with the remainder available for release beyond eight hours. PNAPs delivered to guinea pigs by insufflation achieved systemic levels of rifampicin detected for six to eight hours. Moreover, rifampicin concentrations remained detectable in lung tissue and cells up to and beyond eight hours. Conversely, after pulmonary delivery of an aerosol without nanoparticles, rifampicin could not be detected in the lungs at eight hours. Conclusions  Our results indicate that rifampicin can be formulated into an aggregated nanoparticle form that, once delivered to animals, achieves systemic exposure and extends levels of drug in the lungs.     

Delivery Systems and Local Administration Routes for Therapeutic siRNA

With the increasing number of studies proposing new and optimal delivery strategies for the efficacious silencing of gene-related diseases by the local administration of siRNAs, the present review aims to provide a broad overview of the most important and latest developments of non-viral siRNA delivery systems for local administration. Moreover, the main disease targets for the local delivery of siRNA to specific tissues or organs, including the skin, the lung, the eye, the nervous system, the digestive system and the vagina, were explored.     

Solid Lipid Nanoparticles and Nanostructured Lipid Carriers: Emerging Lipid Based Drug Delivery Systems

Pharmaceutical Chemistry Journal - In the past decade, research in the area of nanodrug delivery has reached a new height with the advent of lipid based nanodrug delivery systems. Lipids being...     

Targeted Delivery with Peptidomimetic Conjugated Self-Assembled Nanoparticles

Peptides produce specific nanostructures, making them useful for targeting in biological systems but they have low bioavailability, potential immunogenicity and poor metabolic stability. Peptidomimetic self-assembled NPs can possess biological recognition motifs as well as providing desired engineering properties. Inorganic NPs, coated with self-assembled macromers for stability and anti-fouling, and conjugated with target-specific ligands, are advancing imaging from the anatomy-based level to the molecular level. Ligand conjugated NPs are attractive for cell-selective tumor drug delivery, since this process has high transport capacity as well as ligand dependent cell specificity. Peptidomimetic NPs can provide stronger interaction with surface receptors on tumor cells, resulting in higher uptake and reduced drug resistance. Self-assembled NPs conjugated with peptidomimetic antigens are ideal for sustained presentation of vaccine antigens to dendritic cells and subsequent activation of T cell mediated adaptive immune response. Self-assembled NPs are a viable alternative to encapsulation for sustained delivery of proteins in tissue engineering. Cell penetrating peptides conjugated to NPs are used as intracellular delivery vectors for gene expression and as transfection agents for plasmid delivery. In this work, synthesis, characterization, properties, immunogenicity, and medical applications of peptidomimetic NPs in imaging, tumor delivery, vaccination, tissue engineering, and intracellular delivery are reviewed.     

Soluble Self-Assembled Block Copolymers for Drug Delivery

Pharmaceutical Research -     

siRNA体内递送的研究现状

RNAi是用来沉默特定基因的一个强有力的研究工具,并为基因治疗策略带来新希望。目前已经用于治疗肿瘤、乙型肝炎、老年性黄斑变性等疾病。RNAi的效应分子为小分子干扰RNA（siRNA）,然而裸siRNA自身具有电负性、分子量大、极性强、半衰期短,以及容易被内源酶降解和肾小球滤过等缺陷,使其临床应用受到极大的限制。如何通过对siRNA进行化学修饰和载体构建,包括运用病毒性载体和非病毒性载体,以提高siRNA的体内稳定性,成为当前的研究重点。本文对siRNA结构的化学修饰、siRNA的载体递送以及临床试验等研究现状予以综述     

Efficient siRNA Delivery with Non-viral Polymeric Vehicles

Sequence-specific gene silencing using small interfering RNA (siRNA) provides a potent and specific method for gene expression, thus is now being evaluated in clinical trials as a novel therapeutic strategy. As a results, there has been a significant surge of interest in the application of siRNA in therapeutics as a means of silencing the specific gene function. However, for siRNA technology to be valuable and effective, the development of efficient siRNA delivery strategy is essential for improving biological activities such as stability, cellular uptake, sequence-specificity, devoid of nonspecific knockdown and toxic side effects. Accordingly, a number of delivery systems, both viral and nonviral, have been reported and some of them successfully used for the introduction of siRNA into cells both in vitro and in vivo. Here, we discuss the current understanding of synthetic siRNA delivery mechanism and strategies of siRNA delivery by non-viral polymeric vehicles which are currently used in vitro and in vivo.     

Nutraceutics and Delivery Systems

Medical treatment has been shifted to being more prophylactic as a recent trend. Postgenomic research has unveiled the fact that nutritional intervention has been strongly associated with genetic expressions, which are responsible for a variety of biological functions. Based on these findings, the prophylactic effects of dietary supplement and nutrient have been enthusiastically investigated. Preventing or retarding the onset of diseases has become a more attractive and cost effective strategy in the medical arena. Among other approaches to prevent diseases, antioxidants, which are found in many phytochemicals, have received much attention. However, most natural antioxidants such as α-tocopherol, ascorbic acid and others are biologically unstable, poorly soluble in water, and poorly distributed to target sites. Because of these shortcomings further prophylactic applications of dietary supplements have stagnated. This is partially due to a lack of basic awareness of drug delivery system for dietary supplements and nutrients. In this article, we strongly advocate serious consideration of the bioavailability of dietary supplements. Currently, there are some challenging works to improve their bioavailability using delivery systems such as liposomal formulations. We will discuss the target molecules of dietary supplements for prevention of diseases and also introduce the pioneering works of delivery systems for dietary supplements to promote their therapeutic value.     

Ternary Polymeric Nanoparticles for Oral siRNA Delivery

Purpose

Poor stability and inefficient absorption in the intestinal tract are major barriers confronting oral delivery of siRNA. We aimed to uncover if ternary polymeric nanoparticles (cationic polymer/siRNA/anionic component) can overcome these obstacles through changing the formulation-related parameters.

Methods

Ternary polymeric nanoparticles were prepared by ionic gelation of chitosan, N-trimethyl chitosan (TMC), or thiolated trimethyl chitosan (TTMC) with tripolyphosphate (TPP) or hyaluronic acid (HA), and siRNA was simultaneously encapsulated. Structural stabilities and siRNA protection of these nanoparticles were assessed in simulated intestinal milieu. Their transport across ex vivo rat ileum, macrophage uptake, in vitro gene silencing, and in vivo biodistribution after oral administration were investigated.

Results

Ternary polymeric nanoparticles formed by TTMC, siRNA, and TPP (TTMC/siRNA/TPP nanoparticles) showed suitable structural stability and siRNA protection in the intestinal tract, good permeability across ex vivo rat ileum, superior cellular uptake and gene silencing efficiency in Raw 264.7 cells, and high systemic biodistribution after oral administration.

Conclusions

TTMC/siRNA/TPP nanoparticles demonstrated efficient gene silencing in vitro and systemic biodistribution in vivo, therefore, they were expected to be potential vehicles for oral siRNA delivery.     

siRNA的体内递送及药物代谢动力学特性

siRNA作为一种高效的RNA干扰药物在疾病治疗方面前景广阔。但其临床应用还需解决由于高负电荷和分子量等引起的体内递送系统、脱靶效应、免疫激活、毒副作用、改善其药物代谢动力学特性等问题。本文简要综述了siRNA的作用原理、体内递送方式、药代动力学特性、安全问题及临床应用展望。     

Engineering RNA for Targeted siRNA Delivery and Medical Application

RNA engineering for nanotechnology and medical applications is an exciting emerging research field. RNA has intrinsically defined features on the nanometre scale and is a particularly interesting candidate for such applications due to its amazing diversity, flexibility and versatility in structure and function. Specifically, the current use of siRNA to silence target genes involved in disease has generated much excitement in the scientific community. The intrinsic ability to sequence-specifically downregulate gene expression in a temporally- and spatially controlled fashion has led to heightened interest and rapid development of siRNA-based therapeutics. Although methods for gene silencing have been achieved with high efficacy and specificity in vitro, the effective delivery of nucleic acids to specific cells in vivo has been a hurdle for RNA therapeutics. This article covers different RNA-based approaches for diagnosis, prevention and treatment of human disease, with a focus on the latest developments of non-viral carriers of siRNA for delivery in vivo. The applications and challenges of siRNA therapy, as well as potential solutions to these problems, the approaches for using phi29 pRNA-based vectors as polyvalent vehicles for specific delivery of siRNA, ribozymes, drugs or other therapeutic agents to specific cells for therapy will also be addressed.     

外泌体作为siRNA递送载体的研究进展

小干扰RNA （small interference RNA,siRNA）可以选择性靶向和下调致病基因,在治疗人类疾病,特别是恶性肿瘤方面具有很大前景。为了增强siRNA递送系统的靶向性和治疗效果,许多载体已被广泛研究。外泌体存在于机体内源性系统,具有较高的生物相容性、低免疫原性、主动靶向性等优点,是一种很有潜力的siRNA递送载体。本文对外泌体siRNA递送系统的优势与不足、siRNA载入外泌体的方式、外泌体介导siRNA靶向递送及应用等进行了综述,旨在为外泌体作为一种新型靶向载体用于siRNA递送系统的研究提供参考。     

Pseudovirions as Vehicles for the Delivery of siRNA

Over the last two decades, small interfering RNA (siRNA)-mediated gene silencing has quickly become one of the most powerful techniques used to study gene function in vitro and a promising area for new therapeutics. Delivery remains a significant impediment to realizing the therapeutic potential of siRNA, a problem that is also tied to immunogenicity and toxicity. Numerous delivery vehicles have been developed, including some that can be categorized as pseudovirions: these are vectors that are directly derived from viruses but whose viral coding sequences have been eliminated, preventing their classification as viral vectors. Characteristics of the pseudovirions discussed in this review, namely phagemids, HSV amplicons, SV40 in vitro-packaged vectors, influenza virosomes, and HVJ-Envelope vectors, make them attractive for the delivery of siRNA-based therapeutics. Pseudovirions were shown to deliver siRNA effector molecules and bring about RNA interference (RNAi) in various cell types in vitro, and in vivo using immune-deficient and immune-competent mouse models. Levels of silencing were not always determined directly, but the duration of siRNA-induced knockdown lasted at least 3 days. We present examples of the use of pseudovirions for the delivery of synthetic siRNA as well as the delivery and expression of DNA-directed siRNA.     

Glycerol Monooleate-Based Nanocarriers for siRNA Delivery in Vitro

We present studies of the delivery of short interfering ribonucleic acid (siRNA) into a green fluorescent protein (GFP) expressing cell line, using lipid nanocarriers in cubic lyotropic liquid crystal form. These carriers are based on glycerol monooleate (GMO) and employ the use of varying concentrations of cationic siRNA binding lipids. The essential physicochemical parameters of the cationic lipid/GMO/siRNA complexes such as particle size, ζ otential, siRNA uptake stability, lyotropic mesophase behavior, cytotoxicity,and gene silencing efficiency were systematically assessed. We find that the lipid nanocarriers were effectively taken up by mammalian cells and that their siRNA payload was able to induce gene silencing in vitro. More importantly, it was found that the nonlamellar structure of some of the lipid nanocarrier formulations were more effective at gene silencing than their lamellar structured counterparts. The development of cationic lipid functionalized nonlamellar GMO-based nanostructured nanoparticles may lead to improved siRNA delivery vehicles.