siRNA delivery systems for cancer treatment☆
Introduction
RNA interference (RNAi) is a biological mechanism whereby the presence of double-stranded RNA (dsRNA) interferes with the expression of a particular gene that shares a homologous sequence with the dsRNA. The RNAi machinery, first discovered in plants, was later demonstrated in the roundworm Caenorhabditis elegans by delivery of dsRNA using a microinjection technique. The introduction of dsRNA molecules could produce the interfering activity and result in the highly specific inhibition of complementary gene expression in C. elegans [1].
Recent studies have provided insights into the molecular mechanisms of RNAi, in which dsRNA induces the silencing of homologous mRNA. In the cytoplasm of mammalian cells, an enzyme known as Dicer initiates RNA silencing by breakdown of long dsRNA to generate small interfering RNA (siRNA) of about 21–23 nucleotides in length. The resulting siRNAs are incorporated into an RNA-induced silencing complex (RISC) and unwound into a single-stranded RNA (ssRNA), which is followed by the degradation of sense strand ssRNA [2]. The RISC containing ssRNA, a guide or antisense strand, looks for and binds to complementary mRNA molecules. The main components of the RISC complex are the Argonaute 2 protein, which is a member of the Argonaute family of proteins, responsible for mRNA degradation and ssRNA formation [3]. As a catalytic engine within RISC, Argonaute 2 (previously known as eIF2C2) facilitates guiding of the anti-sense ssRNA strand to complementary mRNA sequences and degrades target mRNAs through the PIWI domain of an Ago protein, a structural homolog of RNase H. ATP is not essential for the target cleavage reaction of RISC, although ATP increases the rate of endonuclease activity. The hydrolysis reaction involved in the breakdown of the target mRNA phosphodiester backbone requires a divalent metal ion (Mg2+) and releases the 5'-PO4 and 3'-OH groups [4], [5], [6], [7], [8].
Although siRNA is naturally generated from a long dsRNA, synthetic siRNA can affect RNAi. The introduction of an artificial siRNA of 21 nucleotides triggered gene silencing in mammalian cells [9]. siRNA molecules blocked specific expression of endogenous and heterologous genes in various mammalian cell lines [9]. Moreover, the multiple administrations of synthetic siRNAs achieved long-term silencing of target gene without disrupting the endogenous microRNA pathways [10].
Such work has generated much interest in the potential of synthetic siRNA as a key strategic molecule in biomedical research and in the development of innovative medicines. Indeed, siRNAs have been extensively used for the functional analysis of specific genes, especially genes overexpressed in cancer cells, and for the development of new therapeutics for various incurable diseases.
In this paper, we review therapeutic potentials of nonviral siRNA delivery strategies for treatment of various cancers.
Section snippets
siRNA in clinical trials
Given their specific and potent RNAi triggering activity, siRNAs are emerging as new generation biodrugs. Several studies have supported the therapeutic potential of siRNA. Viral mRNA-targeted siRNA has been shown to be effective in inhibiting different stages of the HIV virus life cycle [11]. The hydrodynamic injection of Fas-specific siRNA prevented liver failure in mice with chronic and severe autoimmune hepatitis [12]. Currently, several potential siRNA candidates are undergoing clinical
siRNA delivery systems for in vivo application
Although researchers and biotechnology companies have reported many siRNA vectors for delivery into the cytoplasm of cells, and although these are satisfactory for most in vitro applications, these delivery technologies are usually inappropriate for in vivo use [14]. Currently, siRNAs in clinical trials are directly administered to local target sites such as the eye and lung, thereby avoiding the complexity of systemic delivery. However, it is necessary to introduce siRNA by a systemic route to
Delivery of therapeutic siRNA in cancer
The RNAi phenomenon and siRNA have provided new opportunities for the development of innovative medicine to treat previously incurable diseases such as cancer. siRNA is of inherent potency because it exploits the endogenous RNAi pathway, allows specific reduction of disease-associated genes, and is applicable to any gene with a complementary sequence [100]. As cancer belongs to the category of genetic diseases, many important genes associated with various cancers have been discovered, their
Future prospects
siRNA therapeutics have several distinct advantages over traditional pharmaceutical drugs. RNAi is an endogenous biological process, so almost all genes can be potently suppressed by siRNA. The identification of highly selective and inhibitory sequences is much faster than the discovery of new chemicals, and it is relatively easy to synthesize and manufacture siRNA on a large scale [14].
Cancers are associated with abnormally high expression of a number of oncogenes. Interference in specific
Acknowledgements
This work was supported by the grants from the Ministry of Education, Science and Technology (F104AA010002-08A0101-00210, F104AA010003-08A0101-00310), the Ministry of Health and Welfare (A04-0041-B21004-07M4-00040B), and National Research Laboratory project.
References (131)
- et al.
Short-interfering RNA-mediated gene silencing in mammalian cells requires Dicer and eIF2C translation initiation factors
Curr. Biol.
(2003) - et al.
Human Argonaute2 mediates RNA cleavage targeted by miRNAs and siRNAs
Mol. Cell.
(2004) - et al.
Evaluation of the safety, tolerability and pharmacokinetics of ALN-RSV01, a novel RNAi antiviral therapeutic directed against respiratory syncytial virus (RSV)
Antiviral Res.
(2008) Progress towards in vivo use of siRNAs
Mol. Ther.
(2006)- et al.
RNA interference by 2',5'-linked nucleic acid duplexes in mammalian cells
Bioorg. Med. Chem. Lett.
(2006) - et al.
Toxicity of cationic lipids and cationic polymers in gene delivery
J. Control. Release,
(2006) - et al.
In vitro and in vivo gene-transferring characteristics of novel cationic lipids, DMKD (O,O'-dimyristyl-N-lysyl aspartate) and DMKE (O,O'-dimyristyl-N-lysyl glutamate)
J. Control. Release
(2006) - et al.
Systemic and specific delivery of small interfering RNAs to the liver mediated by apolipoprotein A-I
Mol. Ther.
(2007) - et al.
Tumor-targeted delivery of siRNA by self-assembled nanoparticles
Mol. Ther.
(2008) - et al.
Efficient gene silencing in metastatic tumor by siRNA formulated in surface-modified nanoparticles
J. Control. Release,
(2008)
Cationic lipids enhance siRNA-mediated interferon response in mice
Biochem. Biophys. Res. Commun.
Polymer-based siRNA delivery: perspectives on the fundamental and phenomenological distinctions from polymer-based DNA delivery
J. Control. Release
Molecular hurdles in polyfectin design and mechanistic background to polycation induced cytotoxicity
Adv. Drug Deliv. Rev.
Biodegradable poly(ethylenimine) for plasmid DNA delivery
J Control. Release
Inhibition of ocular angiogenesis by siRNA targeting vascular endothelial growth factor pathway genes: therapeutic strategy for herpetic stromal keratitis
Am. J. Pathol.
Polymer brush-stabilized polyplex for an siRNA carrier with long circulatory half-life
J. Control. Release
RNA interference in vitro and in vivo using a novel chitosan/siRNA nanoparticle system
Mol. Ther.
Visualizing a correlation between siRNA localization, cellular uptake, and RNAi in living cells
Chem. Biol.
Conjugate for efficient delivery of short interfering RNA (siRNA) into mammalian cells
FEBS Lett.
Exogenous siRNA delivery using peptide transduction domain/cell penetrating peptides
Adv. Drug Deliv.
PEG conjugated VEGF siRNA for anti-angiogenic gene therapy
J. Control. Release
Local and systemic delivery of VEGF siRNA using polyelectrolyte complex micelles for effective treatment of cancer
J. Control. Release
Novel dual inhibitory function aptamer-siRNA delivery system for HIV-1 therapy
Mol. Ther.
Small interfering RNA (siRNA) delivery into murine bone marrow-derived dendritic cells by electroporation
J. Immunol. Methods
RNA interference: from gene silencing to gene-specific therapeutics
Pharmacol. Ther.
Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans
Nature
An RNA-directed nuclease mediates post-transcriptional gene silencing in Drosophila cells
Nature
Argonaute2 is the catalytic engine of mammalian RNAi
Science
Crystal structure of a PIWI protein suggests mechanisms for siRNA recognition and slicer activity
EMBO J.
Structural basis for 5’-end-specific recognition of guide RNA by the A. fulgidus Piwi protein
Nature
Ribo-gnome: the big world of small RNAs
Science
Duplexes of 21-nucleotide RNAs mediate RNA interference in cultured mammalian cells
Nature
Effective RNAi-mediated gene silencing without interruption of the endogenous microRNA pathway
Nature
siRNA-directed inhibition of HIV-1 infection
Nat. Med.
RNA interference targeting Fas protects mice from fulminant hepatitis
Nat. Med.
Interfering with disease: a progress report on siRNA-based therapeutics
Nat. Rev. Drug Discov.
RNAi therapeutics: a potential new class of pharmaceutical drugs
Nat. Chem. Biol.
Strategies for silencing human disease using RNA interference
Nat. Rev. Genet.
RNA-based therapies
Nat. Rev. Drug. Dis.
On future's doorstep: RNA interference and the pharmacopeia of tomorrow
J. Clin. Invest.
Position-specific chemical modification of siRNAs reduces “off-target” transcript silencing
RNA
AsiDesigner: exon-based siRNA design server considering alternative splicing
Nucleic Acids Res.
Activation of the mammalian immune system by siRNAs
Nat. Biotechnol.
Sequence- and target-independent angiogenesis suppression by siRNA via TLR3
Nature
Sequence-dependent stimulation of the mammalian innate immune response by synthetic siRNA
Nat Biotechnol.
Sequence-specific potent induction of IFN-alpha by short interfering RNA in plasmacytoid dendritic cells through TLR7
Nat. Med.
Mechanisms and strategies for effective delivery of antisense and siRNA oligonucleotides
Nucleic Acids Res.
Nonviral in vivo delivery of therapeutic small interfering RNAs
Curr. Opin. Mol. Ther.
siRNA function in RNAi: a chemical modification analysis
RNA,
Sequence, chemical, and structural variation of small interfering RNAs and short hairpin RNAs and the effect on mammalian gene silencing
Antisense Nucleic Acid Drug Dev.
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This review is part of the Advanced Drug Delivery Reviews theme issue on “The Role of Gene– and Drug Delivery in Women's Health – Unmet Clinical Needs and Future Opportunities”.