Advances in transdermal siRNAs delivery: A review of current research progress

Small interfering RNA (siRNAs) is a double-stranded RNA molecule which can hybridize with a specific mRNA sequence and block the translation of numerous genes to regulate endogenous genes and to defend the genome from invasive nucleic acids. The use of siRNAs has been studied as a treatment option for various skin conditions. One of the main obstacles in the dermal or transdermal delivery of this compound is low skin permeability, and application is limited by its negative charge, high polarity, susceptibility to degradation by nucleases, and difficulty in penetrating the skin barrier. Effective delivery of therapeutic biomolecules to their target is a challenging issue, which can be solved by innovations in drug delivery systems and lead to improvement of the efficiency of many new biopharmaceuticals. Designing of novel transdermal delivery systems garnered tremendous attention in both cosmeceutical and pharmaceutical research and industries, which offers a number of advantages. Developing safe and efficient siRNAs delivery vectors is essential for effective treatment of skin diseases. In recent years, significant progress has been made in the creation of delivery systems using lipids, polymers, cell-penetrating peptides, nanoparticles and other biologically active agents. In this review we will focus on the recent advancements in transdermal siRNAs delivery vectors, such as liposomes, dendrimers, cell-penetrating peptides, and spherical nucleic acid nanoparticles.

Novel nanocarriers for silencing anti-phagocytosis CD47 marker in acute myeloid leukemia cells

Acute myeloid leukemia (AML), a malignant disorder of Hematopoietic stem cells, can escape immunosurveillance by over expression of the cluster of differentiation 47 (CD47) marker, which functions as an inhibitory signal, suppressing phagocytosis by binding to signal regulatory protein α (SIRPα) on macrophages. AML is treated mainly by chemotherapy, which has drastic side effects and poor outcomes for the patients. Most AML patients develop drug resistance, so other methods to treat AML are highly required. Small interfering RNA (siRNA) is considered as an antitumor therapeutic due to its ability to silence genes associated with the overexpressed cancer markers and subsequently re-sensitize cancer cells. However, delivering siRNA into cells faces challenges, and the development of an effective delivery system is desired for successful silencing at the gene level. Herein, we report the usage of different formulations of graphene oxide (GO) as carriers for the delivery of CD47_siRNA (siRNA against CD47) into AML cells in vitro. The polyethylene glycol (PEG) and dendrimers (PAMAM) modified GO with small flake sizes achieved the highest silencing efficiency of the anti-phagocytosis marker CD47 gene, resulted CD47 protein down-regulation in AML cells. Moreover, the concentration at which the GO-based formulations was used has shown no cytotoxicity in AML cells or normal blood cells, which could be used to screen potential drugs for targeted gene therapy in AML.

Phenylboronic Acid-Modified Polyamidoamine Mediated the Transfection of Polo-Like Kinase-1 siRNA to Achieve an Anti-Tumor Efficacy

Background

The construction of tumor-targeting carriers with favorable transfection efficiency was of great significance to achieve the tumor gene therapy. The phenylboronic acid-modified polyamidoamine (namely PP) was employed as a carrier for the delivery of Polo-like kinase-1 siRNA (siPlk-1), inducing an obvious anti-tumor response.

Materials and Methods

The interaction between PP and siPlk-1 was evaluated by gel retardation assay. The transfection efficiency and tumor-targeting ability were analyzed by flow cytometry and confocal laser scanning microscopy, using hepatocarcinoma cell line HepG2 as a model. The anti-proliferation effect of PP/siPlk-1 and related mechanism were studied using the strategies of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, cell apoptosis and cell cycle arrest. The anti-migration effect induced by PP/siPlk-1 delivery was assayed by wound healing and Transwell migration techniques. Finally, quantitative real-time PCR and Western blotting were performed to measure the expression level of Plk-1 and other key targets.

Results

The derivative PP could achieve the condensation of siPlk-1 into stable nanoparticles at nitrogen/phosphate groups ratio (N/P ratio) of >3.0, and it could facilitate the transfection of siPk-1 in a phenylboronic acid-dependent manner. The PP/siPlk-1 nanoparticles exhibited obvious anti-proliferation effect owing to the gene silence of Plk-1, which was identified to be associated with the cell apoptosis and cell cycle arrest at G2 phase. Meanwhile, PP/siPlk-1 transfection could efficiently suppress the migration and invasion of tumor cells.

Conclusion

The derivative PP has been demonstrated to be an ideal tumor-targeting carrier for the delivery of Plk-1 siRNA, exhibiting great potential in the gene therapy of malignant tumors.

Dendrimers as Non-Viral Vectors in Gene-Directed Enzyme Prodrug Therapy

Gene-directed enzyme prodrug therapy (GDEPT) has been intensively studied as a promising new strategy of prodrug delivery, with its main advantages being represented by an enhanced efficacy and a reduced off-target toxicity of the active drug. In recent years, numerous therapeutic systems based on GDEPT strategy have entered clinical trials. In order to deliver the desired gene at a specific site of action, this therapeutic approach uses vectors divided in two major categories, viral vectors and non-viral vectors, with the latter being represented by chemical delivery agents. There is considerable interest in the development of non-viral vectors due to their decreased immunogenicity, higher specificity, ease of synthesis and greater flexibility for subsequent modulations. Dendrimers used as delivery vehicles offer many advantages, such as: nanoscale size, precise molecular weight, increased solubility, high load capacity, high bioavailability and low immunogenicity. The aim of the present work was to provide a comprehensive overview of the recent advances regarding the use of dendrimers as non-viral carriers in the GDEPT therapy.

Development of new self-assembled cationic amino liposomes for efficient gene delivery

A library of 83 structurally diverse cationic amino liposomes is rationally designed and parallelly synthesized for the transfection of plasmid DNA and siRNA. Our designed self-assembled liposomes not only exhibit excellent transfection efficiency in HEK 293T cells and mouse embryonic stem cells, but also show low cytotoxicity.

Nanomaterials-Based siRNA Delivery: Routes of Administration, Hurdles and Role of Nanocarriers

Ribonucleic acid interference (RNAi) is a potential alternative therapeutic approach to knock down the overexpression of genes in several disorders especially cancers with underlying genetic dysfunctions. For silencing of specific genes involved in cell cycle, small/short interfering ribonucleic acids (siRNAs) are being used clinically. The siRNA-based RNAi is more efficient, specific and safe antisense technology than other RNAi approaches. The route of siRNA administration for siRNA therapy depends on the targeted site. However, certain hurdles like poor stability of siRNA, saturation, off-target effect, immunogenicity, anatomical barriers and non-targeted delivery restrict the successful siRNA therapy. Thus, advancement of an effective, secure, and long-term delivery system is prerequisite to the medical utilization of siRNA. Polycationic nanocarriers mediated targeted delivery system is an ideal system to remove these hurdles and to increase the blood retention time and rate of intracellular permeability. In this chapter, we will mainly discuss the different biocompatible, biodegradable, non-toxic (organic, inorganic and hybrid) nanocarriers that encapsulate and shield the siRNA from the different harsh environment and provides the increased systemic siRNA delivery.

Dendrimers Show Promise for siRNA and microRNA Therapeutics

The lack of an appropriate intracellular delivery system for therapeutic nucleic acids (TNAs) is a major problem in molecular biology, biotechnology, and medicine. A relatively new class of highly symmetrical hyperbranched polymers, called dendrimers, shows promise for transporting small TNAs into both cells and target tissues. Dendrimers have intrinsic advantages for this purpose: their physico-chemical and biological properties can be controlled during synthesis, and they are able to transport large numbers of TNA molecules that can specifically suppress the expression of single or multiple targeted genes. Numerous chemical modifications of dendrimers extend the biocompatibility of synthetic materials and allow targeted vectors to be designed for particular therapeutic purposes. This review summarizes the latest experimental data and trends in the medical application of various types of dendrimers and dendrimer-based nanoconstructions as delivery systems for short small interfering RNAs (siRNAs) and microRNAs at the cell and organism levels. It provides an overview of the structural features of dendrimers, indicating their advantages over other types of TNA transporters.

Triptorelin Tethered Multifunctional PAMAM-Histidine-PEG Nanoconstructs Enable Specific Targeting and Efficient Gene Silencing in LHRH Overexpressing Cancer Cells

Cancer treatment using siRNA based therapies pose various limitations such as off-target effects and degradation due to lack of specific delivery in desired cells. The aim of the present study was to develop multifunctional targeted nanoconstructs, which can efficiently and precisely deliver siRNA and silence the desired gene of interest in various LHRH overexpressing cancer cells. Herein, we report the development of triblock, PAMAM-histidine-PEG dendritic nanoconstructs functionalized with triptorelin (an LHRH analog) for targeted siRNA delivery to LHRH overexpressing breast (MCF-7) and prostate (LNCaP) cancer cells. The nanoconstructs were characterized using ¹H NMR and DLS and displayed a very low cationic charge to avoid off-target interactions. The developed nanoconstructs showed negligible cytotoxicity and hemolytic activity with efficient siRNA loading, excellent serum stability, and strongly protected siRNA from degradation. Further, confocal microscopy results confirmed extremely significant (p < 0.001) higher cellular uptake of cy5.5 conjugated targeted nanoparticles (NPs) in both cancer cell lines than nontargeted NPs. Also, targeted NPs specifically delivered cy3-tagged siRNA to MCF-7 cells. Co-localization studies in MCF-7 and LNCaP cells further established that targeted NPs traveled through the endolysosomal pathway and escaped endosomes within 6 h of incubation. Gene silencing studies in luciferase expressing MCF-7 and LNCaP cell lines demonstrated that the targeted NPs exhibited extremely significant (p < 0.001) silencing of luciferase gene. Additionally, receptor blockade studies further confirmed the specificity of targeted NPs and suggested that targeted NPs entered cancer cells via LHRH receptor mediated endocytosis, which was evident through insignificant gene silencing in receptor blocked cells. Thus, the results indicated that PAMAM-histidine-PEG-triptorelin could be a promising approach for siRNA delivery, gene silencing, and tumor therapy in all LHRH overexpressing cancer cells.

Polymer-Nucleic Acid Interactions

Gene therapy is an important therapeutic strategy in the treatment of a wide range of genetic disorders. Polymers forming stable complexes with nucleic acids (NAs) are non-viral gene carriers. The self-assembly of polymers and nucleic acids is typically a complex process that involves many types of interaction at different scales. Electrostatic interaction, hydrophobic interaction, and hydrogen bonds are three important and prevalent interactions in the polymer/nucleic acid system. Electrostatic interactions and hydrogen bonds are the main driving forces for the condensation of nucleic acids, while hydrophobic interactions play a significant role in the cellular uptake and endosomal escape of polymer-nucleic acid complexes. To design high-efficiency polymer candidates for the DNA and siRNA delivery, it is necessary to have a detailed understanding of the interactions between them in solution. In this chapter, we survey the roles of the three important interactions between polymers and nucleic acids during the formation of polyplexes and summarize recent understandings of the linear polyelectrolyte-NA interactions and dendrimer-NA interactions. We also review recent progress optimizing the gene delivery system by tuning these interactions.