Current Pharmaceutical Design - Volume 21, Issue 31, 2015

This review is based on carriers of natural origin such as polysaccharides, proteins, and cell derived entities which have been used for delivery of siRNA. To realize the therapeutic potential of a delivery system, the role of the carrier is of utmost importance. Historical aspects of viral vectors, the first carriers of genes are briefly outlined. Chitosan, one of the extensively experimented carriers, alginates and other polysaccharides have shown success in siRNA delivery. Peptides of natural origin and mimics thereof have emerged as another versatile carrier. Exosomes and mini cells of cellular origin are the newest entrants to the area of siRNA delivery and probably the closest one can get to a natural carrier. In many of the carriers, modifications have provided better efficiency in delivery. The salient features of the carriers and their advantages and disadvantages are also reviewed.

The ‘RNA interference’ has emerged as a potential therapeutic strategy owing to its high specificity to silent any malfunctioned gene in diseases with genetic background. Currently intravenous delivery of siRNA has been a preferred way of administration due to high access of blood to the organs where direct delivery is not possible. Among non-viral delivery systems enabling systemic delivery of siRNA, liposomes and lipid envelope systems appear to be promising due to their biocompatibility over other systems. However, these systems are still challenged by toxicity issues, instability in blood, non-specific distribution and low transfection efficiency after intravenous administration. Therefore, to increase the success of lipid based siRNA delivery, it is essential to understand the importance of various factors affecting the efficiency of siRNA delivery. The current review focuses on the formulation of lipid based siRNA formulations, the challenges posed in systemic delivery and various aspects affecting the transfection efficiency of such formulations. The review also focuses on emerging strategies for lipid based siRNA delivery and overviews clinical prospects for better development of siRNA delivery systems in future. Considering the current trends, it seems that liposomes and lipid based envelope systems for systemic delivery of siRNA will translate into extensive clinical application overcoming the associated challenges in near future.

Various cells of the human physiological system have the capability to release extracellular vesicles (EVs) involved in intercellular transport of proteins and nucleic acids. Exosomes are a subtype of extracellular vesicles having their origin through endocytic pathway. While being involved in intercellular transport of macromolecules, exosomes, due to their presence in several body fluids, can also be utilized as a system to commute RNA molecules and proteins in the body. Recent advances in gene therapy have provided a new outlook in disease therapeutics by modulation of gene expression using oligonucleotide based approach and exosomes have been reported a potential carrier for nucleic acid based therapeutic moieties. In recent years, small interfering RNA (siRNA) has emerged as promising therapeutic alternative for diseases with gene-based pathophysiology, however poor bioavailability limits its therapeutic potential. For effective delivery and enhancement of bioavailability of siRNA, several carriers including dendrimers, liposomes, siRNA conjugates, and siRNA aptamer chimeras, to name a few, have been explored. Exosomes can be considered a promising carrier for effective delivery of siRNA due to their existence in body’s endogenous system and high tolerance. The present review focuses on delivering knowledge about exosomes, siRNA, and capability of exosomes to act as natural carriers for siRNA delivery.

Since its discovery in the late 1990, small interfering RNA (siRNA) have quickly crept into the biopharmaceutical research as a new and powerful tool for the treatment of different human diseases based on altered gene-expression. Despite promising data from many pre-clinical studies, concrete hurdles still need to be overcome to bring therapeutic siRNAs in clinic. The design of stimuli-sensitive nanopreparations for gene therapy is a lively area of the current research. Compared to conventional systems for siRNA delivery, this type of platform can respond to local stimuli that are characteristics of the pathological area of interest, allowing the release of nucleic acids at the desired site. Acidic pH, de-regulated levels of enzymes, altered redox potential and magnetic field are examples of stimuli exploit to design stimuli-sensitive nanoparticles. In this review, we discuss on recent stimulisensitive strategies for siRNA delivery and we highlight on the potential of combining multiple stimuli-sensitive strategies in the same nano-platform for a better therapeutic outcome.

RNA interference has emerged as an innovative technology for gene silencing that degrades mRNAs complementary to the antisense strands of double-stranded, short interfering RNAs (siRNAs). Its therapeutic application has important advantages over small-molecule drugs since offers the possibility of targeting virtually all genes and allows selective silencing of one or several genes. So far, a relative small proportion of cellular proteins can bind and respond to chemical drugs. Based on that, RNA interference-mediated gene silencing is widely considered as a crucial breakthrough in molecular biology with a direct translation to medicine. The liver has been widely chosen as a model system for the development of RNA interference therapy due to the convenience and availability of effective delivery into this tissue. Numerous preclinical models have revealed promising results, but the safety of this technology remains the primary challenge in developing siRNA based treatments. Liver diseases comprise a broad spectrum of genetic and non-genetic pathologies including acute fulminant liver injury that demands urgent medical care, or chronic pathologies such as nonalcoholic fatty liver (NAFLD), alcoholic liver disease, liver cirrhosis, viral hepatitis and hepatocellular carcinoma (HCC). In some cases restoration of liver function is not possible and alternatives to liver transplantation offering novel and efficient therapeutic approaches are urgently needed. In this review, we describe recent insights on the advantages of using RNA interference in preclinical settings as a targeted strategy with potential to markedly improve the treatment of liver diseases.

Drug delivery to the eye is challenging for formulation scientists due to physiological barriers that separate the eye from the rest of the body. A variety of ocular disorders demand the development of optimal drug delivery systems for the administration of drugs and therapeutic agents that can overcome barriers that restrict drug bioavailability. SiRNA inhibits the expression of target genes and has immense potential as a biological tool for the therapeutic inhibition of disease causing genes; however, delivery of siRNA to ocular tissue is a challenge. Recent literature suggests that nanoplatforms show great promise in enhancing ophthalmic drug delivery. A drug delivery system involving nanoparticles and siRNA could surpass problems faced in ocular delivery with improved biodistribution and lower toxicity. This review covers recent research in the area of nanocarrier siRNA drug delivery for various ocular disorders.

The topical application of therapeutic agent has shown promising efficacy in the treatment of skin disorders. The siRNA based therapies have been used for treatment of various disorders including skin diseases. The topical delivery of siRNA based therapies has opened new perspectives for the treatment of skin disorders. The use of siRNA is limited due to the rapid degradation and poor cellular uptake. Also, the stratum corneum, the top layer of skin is the major barrier for the delivery of topical agents. There is unmet need for efficient topical formulation that will deliver the siRNA to the site of action and also overcome the associated siRNA delivery limitations. The topical delivery of siRNA has been achieved using viral or nonviral methods, and the combination of non-viral methods with an active permeation method such as iontophoresis, sonophoresis or microneedles for the treatment of skin disorders. These delivery approaches have been tested in a preclinical setup and few cases the results have shown promise for clinical trials. This review provides an update on the advances in the non-viral delivery approaches for siRNA delivery for skin disorders and use of various delivery approaches for efficient delivery at the disease site.

Brain diseases are the most serious health problems; represent a significant and worldwide public health problem. Small interfering RNAs (siRNAs) can initiate specific silencing of genes and are potential therapeutic agents for many genetically influenced diseases including brain disease. However, on systemic administration the blood-brain barrier (BBB) poses most significant obstacle for the therapeutic siRNAs delivery to the brain. Therefore, the development of successful approaches to enhance siRNA delivery to the brain is of immense interest in clinical and pharmaceutical research. At present, intranasal delivery approach serves as an effective mode of direct delivery of siRNAs to brain by bypassing BBB. In this review, we describe the principles of RNA interference (RNAi) machinery; challenges associated with siRNAs in therapeutics brain targeting and summarize the recent progress made in the use of vector based siRNA technology. Further, it is anticipated that intranasal delivery approach will have a very important role to play in the future for the translation of siRNAs therapeutics from bench to bedside for different brain diseases.

siRNA technology presents a helpful means of gene silencing in mammalian cells. Advancement in the field includes enhanced attentiveness in the characterization of target and off-target effects employing suitable controls and gene expression microarrays. These will permit expansion in the measurement of single and multiple target combinations and also permit comprehensive efforts to understand mammalian cell processes. Another fact is that the delivery of siRNA requires the creation of a nanoparticulate vector with controlled structural geometry and surface modalities inside the targeted cells. On the other hand, dendrimers represent the class of carrier system where massive control over size, shape and physicochemical properties makes this delivery vector exceptional and favorable in genetic transfection applications. The siRNA therapeutics may be incorporated inside the geometry of the density controlled dendrimers with the option of engineering the structure to the specific needs of the genetic material and its indication. The existing reports on the siRNA carrying and deliverance potential of dendrimers clearly suggest the significance of this novel class of polymeric architecture and certainly elevate the futuristic use of this highly branched vector as genetic material delivery system.

With the discovery of RNA interference technology, small-interfering RNA (siRNA) has emerged as new powerful tool for gene therapy because of its high targeting specificity and selectivity. However, one of the limitations to successful gene therapy is the inability to monitor delivery of genes and therapeutic responses at the targeted site. Hence, a combinatorial approach of gene therapy with molecular imaging has been crucial in optimizing gene therapy. Recent advances in nanotechnology have made tremendous efforts to develop multifunctional nanoparticles that contain imaging and therapeutic agents together for image-guided therapy. The nanoparticles serve as contrast agents in imaging for disease detection with simultaneous delivery of therapeutics to cure the diseases. The therapy also helps to monitor the drug accumulation and assimilation in the body, thereby facilitating the evaluation of treatment effects. Here, we present an overview of polymer and lipid-based carriers for siRNA delivery, along with imaging agents as imageguided therapy, in the treatment of breast, lung, liver, ovarian, cervical, and prostate cancers.