Cell type-specific delivery of siRNAs with aptamer-siRNA chimeras

Nonviral delivery of synthetic siRNAs in vivo

Sequence-specific gene silencing using small interfering RNA (siRNA) is a Nobel prize-winning technology that is now being evaluated in clinical trials as a potentially novel therapeutic strategy. This article provides an overview of the major pharmaceutical challenges facing siRNA therapeutics, focusing on the delivery strategies for synthetic siRNA duplexes in vivo, as this remains one of the most important issues to be resolved. This article also highlights the importance of understanding the genocompatibility/toxicogenomics of siRNA delivery reagents in terms of their impact on gene-silencing activity and specificity. Collectively, this information is essential for the selection of optimally acting siRNA delivery system combinations for the many proposed applications of RNA interference.

Chemical modification: the key to clinical application of RNA interference?

RNA interference provides a potent and specific method for controlling gene expression in human cells. To translate this potential into a broad new family of therapeutics, it is necessary to optimize the efficacy of the RNA-based drugs. As discussed in this Review, it might be possible to achieve this optimization using chemical modifications that improve their in vivo stability, cellular delivery, biodistribution, pharmacokinetics, potency, and specificity.

Allele dependent silencing of COL1A2 using small interfering RNAs

Osteogenesis imperfecta (OI) is generally caused by a dominant mutation in Collagen I, encoded by the genes COL1A1 and COL1A2. To date there is no satisfactory therapy for OI, but inactivation of the mutant allele through small interfering RNAs (siRNA) is a promising approach, as siRNAs targeting each allele of a polymorphism could be used for allele-specific silencing irrespective of the location of the actual mutations. In this study we examined the allele dependent effects of several tiled siRNAs targeting a region surrounding an exonic COL1A2 T/C polymorphism (rs1800222) in heterozygous primary human bone cells. Relative abundances of COL1A2 alleles were determined by cDNA sequencing and overall COL1A2 abundance was analyzed by quantitative PCR. One of the siRNAs decreased overall COL1A2 abundance by 71% of which 75% was due to silencing of the targeted T-allele. In conclusion, allele-preferential silencing of Collagen type I genes may be a future therapeutic approach for OI.

RNAi for treating hepatitis B viral infection

Chronic hepatitis B virus (HBV) infection is one of the leading causes of liver cirrhosis and hepatocellular carcinoma (HCC). Current treatment strategies of HBV infection including the use of interferon (IFN)-α and nucleotide analogues such as lamivudine and adefovir have met with only partial success. Therefore, it is necessary to develop more effective antiviral therapies that can clear HBV infection with fewer side effects. RNA interference (RNAi), by which a small interfering RNA (siRNA) induces the gene silence at a post-transcriptional level, has the potential of treating HBV infection. The successful use of chemically synthesized siRNA, endogenous expression of small hairpin RNA (shRNA) or microRNA (miRNA) to silence the target gene make this technology towards a potentially rational therapeutics for HBV infection. However, several challenges including poor siRNA stability, inefficient cellular uptake, widespread biodistribution and non-specific effects need to be overcome. In this review, we discuss several strategies for improving the anti-HBV therapeutic efficacy of siRNAs, while avoiding their off-target effects and immunostimulation. There is an in-depth discussion on the (1) mechanisms of RNAi, (2) methods for siRNA/shRNA production, (3) barriers to RNAi-based therapies, and (4) delivery strategies of siRNA for treating HBV infection.

Downregulation of monocyte chemoattractant protein-1 involving short interfering RNA attenuates hapten-induced contact hypersensitivity

Contact hypersensitivity (CHS) is a common skin disease, presenting clinically as allergic contact dermatitis. At inflammatory sites in a typical CHS model in the mouse ear, elevated expression of monocyte chemoattractant protein-1 (MCP-1) has been reported. MCP-1 is a potent chemotactic factor for many types of leukocytes including monocytes/macrophages and T cells. In this study, we aimed at developing a therapy for CHS involving RNA interference targeting MCP-1. A short interfering RNA (siRNA) to mouse MCP-1 successfully inhibited the secretion of MCP-1 by a fibroblastic cell line, L929, and RAW 264.7 cells derived from macrophages, and strikingly suppressed ear swelling in a CHS model. The siRNA systemically administered inhibited the infiltration of both monocytes/macrophages and T cells in the CHS model. Atelocollagen was used in this therapy as a delivery reagent for siRNA into the animal body. Atelocollagen facilitated the incorporation of the siRNA into macrophages/monocytes and fibroblasts, which vigorously secrete MCP-1 protein at inflammatory sites in CHS. This therapy had no adverse effects such as induction of interferon, or liver or renal damage. Our data indicate that the systemic delivery of siRNA targeting MCP-1 is a potent therapeutic strategy for CHS treatment.

Conjugation of nucleosides and oligonucleotides by [3+2] cycloaddition

A procedure is presented for copper(I)-catalyzed [3+2] cycloaddition of nucleosides and nucleotides in near-quantitative yield. Azido-alkyne cycloaddition was applied for the preparation of a range of adenosine dimers and derivatives with versatile functionality, as well as for the smooth condensation of two oligonucleotide strands. The described technology may find valuable application in the synthesis of oligonucleotide dimers and conjugates.

Therapeutic application of RNAi: is mRNA targeting finally ready for prime time?

With unprecedented speed, RNA interference (RNAi) has advanced from its basic discovery in lower organisms to becoming a powerful genetic tool and perhaps our single most promising biotherapeutic for a wide array of diseases. Numerous studies document RNAi efficacy in laboratory animals, and the first clinical trials are underway and thus far suggest that RNAi is safe to use in humans. Yet substantial hurdles have also surfaced and must be surmounted before therapeutic RNAi applications can become a standard therapy. Here we review the most critical roadblocks and concerns for clinical RNAi transition, delivery, and safety. We highlight emerging solutions and concurrently discuss novel therapeutic RNAi-based concepts. The current rapid advances create realistic optimism that the establishment of RNAi as a new and potent clinical modality in humans is near.

Cellular uptake and intracellular release are major obstacles to the therapeutic application of siRNA: novel options by phosphorothioate-stimulated delivery

The cellular uptake of oligomeric nucleic acid-based tools and drugs including small-interfering RNA (siRNA) represents a major technical hurdle for the biologic effectiveness and therapeutic success in vivo. Subsequent to cellular delivery it is crucial to direct siRNA to the cellular location where it enters the RNA interference pathway. Here the authors summarise evidence that functionally active siRNA represents a minor fraction in the order of 1% of total siRNA inside a given target cell. Exploiting possibilities of steering intracellular release or trafficking of siRNA bears the potential of substantially increasing the biological activity of siRNA. The recently described phosphorothioate stimulated cellular delivery of siRNA makes use of the caveolar system ending in the Golgi apparatus, which contrasts all other known delivery systems. Therefore, it represents an attractive alternative to study whether promoted intracellular release is related to increased target suppression and, thus, increased phenotypic biologic effectiveness.

Tumor-targeted delivery of siRNA by self-assembled nanoparticles

We have developed a self-assembled nanoparticle (NP) that efficiently delivers small interfering RNA (siRNA) to the tumor by intravenous (IV) administration. The NP was obtained by mixing carrier DNA, siRNA, protamine, and lipids, followed by post-modification with polyethylene glycol and a ligand, anisamide. Four hours after IV injection of the formulation into a xenograft model, 70-80% of injected siRNA/g accumulated in the tumor, approximately 10% was detected in the liver and approximately 20% recovered in the lung. Confocal microscopy showed that fluorescent-labeled siRNA was efficiently delivered into the cytoplasm of the sigma receptor expressing NCI-H460 xenograft tumor by the targeted NPs, whereas free siRNA and non-targeted NPs showed little uptake. Three daily injections (1.2 mg/kg) of siRNA formulated in the targeted NPs silenced the epidermal growth factor receptor (EGFR) in the tumor and induced approximately 15% tumor cell apoptosis. Forty percent tumor growth inhibition was achieved by treatment with targeted NPs, while complete inhibition lasted for 1 week when combined with cisplatin. The serum level of liver enzymes and body weight monitoring during the treatment indicated a low level of toxicity of the formulation. The carrier itself also showed little immunotoxicity (IMT).

MicroRNAs in disease and potential therapeutic applications

MicroRNAs (miRNAs) are 21-24 nucleotide (nt) duplex RNAs that are created from precursor transcripts by subsequent processing steps mediated by members of the RNAseIII family, Drosha and Dicer. One of the two strands is incorporated into the active sites of the Argonaute family of proteins, where it serves as a guide for Watson-Crick base pairing with complementary sequences in target messenger RNAs (mRNAs). In mammals, the majority of miRNAs guide the RNA-induced silencing complex (RISC) to the 3' untranslated regions (UTRs) of mRNA targets, with the consequence that translation of the target mRNAs is inhibited. The importance of miRNAs in normal cellular development and metabolism is only now being realized. miRNA deficiencies or excesses have been correlated with a number of clinically important diseases ranging from myocardial infarction to cancers. The loss or gain of miRNA function can be caused by a single point mutation in either the miRNA or its target or by epigenetic silencing of primary miRNA transcription units. This review summarizes miRNA biogenesis and biology, explores the potential roles miRNAs can play in a variety of diseases, and suggests some therapeutic applications for restoring or inhibiting miRNA function.

Biology by design: reduction and synthesis of cellular components and behaviour

Biological research is experiencing an increasing focus on the application of knowledge rather than on its generation. Thanks to the increased understanding of cellular systems and technological advances, biologists are more frequently asking not only 'how can I understand the structure and behaviour of this biological system?', but also 'how can I apply that knowledge to generate novel functions in different biological systems or in other contexts?' Active pursuit of the latter has nurtured the emergence of synthetic biology. Here, we discuss the motivation behind, and foundational technologies enabling, the development of this nascent field. We examine some early successes and applications while highlighting the challenges involved. Finally, we consider future directions and mention non-scientific considerations that can influence the field's growth.

The versatility of oligonucleotides as potential therapeutics

Oligonucleotides can in a variety of ways inhibit gene expression by interfering with translation. Oligonucleotides that are complementary to a target mRNA, antisense oligonucleotides, can prevent translation either by cleaving the target or by physically blocking the process. Additionally, oligonucleotides can correct the undesired splicing of pre-mRNA. RNA interference using double-stranded oligoribonucleotides also results in cleavage of the target mRNA. Catalytically competent ribozymes and DNAzymes can have the same effect. Even with no RNA as target, oligonucleotides can be selected as aptamers to bind to any protein to inhibit its activity. Moreover, oligonucleotides can act as decoys particularly for transcription factors to prevent binding to the promoter. A different mode of action is the activation of Toll-like receptors to induce an immune response. Several pathways for drug development are still in their infancy, for example microRNAs and antagomirs.

Interfering with disease: a progress report on siRNA-based therapeutics

RNA interference (RNAi) has rapidly advanced since its initial discovery to form the basis of a new class of therapeutics. De Fougerolles and colleagues discuss the challenges in the development of RNAi-based therapeutics, focusing on lead identification/optimization and effective delivery, and review the latest clinical results.

RNA interference (RNAi) quietly crept into biological research in the 1990s when unexpected gene-silencing phenomena in plants and flatworms first perplexed scientists. Following the demonstration of RNAi in mammalian cells in 2001, it was quickly realized that this highly specific mechanism of sequence-specific gene silencing might be harnessed to develop a new class of drugs that interfere with disease-causing or disease-promoting genes. Here we discuss the considerations that go into developing RNAi-based therapeutics starting from in vitro lead design and identification, to in vivo pre-clinical drug delivery and testing. We conclude by reviewing the latest clinical experience with RNAi therapeutics.

A structure–activity relationship study of siRNAs with structural variations

Specific knock-down of cellular gene expression using small interfering RNAs (siRNAs) is a powerful gene silencing technique in mammalian cells. Early siRNAs were double stranded, and 19-21bp in length, but several variations in siRNA structure have been introduced to achieve better silencing efficiency. In addition, siRNA modules have been incorporated into higher-order RNA structures to generate multi-functional RNA molecules. The effects of such structural variations on the activities of siRNAs have not been thoroughly studied. Here, we present a structure-activity relationship study of siRNA structural variants. Specifically, we focus on the effect on silencing efficiency of the attachment of extra, target-unrelated sequences to the conventional short duplex siRNA structure. Interestingly, while some siRNA structural variants efficiently silence target gene expression, others show a reduction in or a complete lack of silencing activity. Off-target effects and innate immune responses triggered by siRNA structural variants were also measured. In vitro Dicer cleavage reactions show that all siRNA structural variants are substrates of Dicer, but digestion patterns vary. To our knowledge, this is the first systematic structure-activity relationship analysis of siRNAs bearing structural variations. Our results provide useful guidelines for the design of siRNA structural variants and for the construction of complex RNA molecules bearing functional siRNA modules.

Distinct roles of E2F proteins in vascular smooth muscle cell proliferation and intimal hyperplasia

Intimal hyperplasia (IH) and restenosis limit the long-term utility of bypass surgery and angioplasty due to pathological proliferation and migration of vascular smooth muscle cells (VSMCs) into the intima of treated vessels. Consequently, much attention has been focused on developing inhibitory agents that reduce this pathogenic process. The E2F transcription factors are key cell cycle regulators that play important roles in modulating cell proliferation and cell fate. Nonselective E2F inhibitors have thus been extensively evaluated for this purpose. Surprisingly, these E2F inhibitors have failed to reduce IH. These findings prompted us to evaluate the roles of different E2Fs during IH to determine how selective targeting of E2F isoforms impacts VSMC proliferation. Importantly, we show that E2F3 promotes proliferation of VSMCs leading to increased IH, whereas E2F4 inhibits this pathological response. Furthermore, we use RNA probes to show that selective inhibition of E2F3, not global inhibition of E2F activity, significantly reduces VSMC proliferation and limits IH in murine bypass grafts.

Gene therapy progress and prospects: RNA aptamers

Aptamers are oligonucleotides evolved in vitro or in nature to bind target ligands with high affinity and specificity. They are emerging as powerful tools in the fields of therapeutics, drug development, target validation and diagnostics. Aptamers are attractive alternatives to antibody- and small-molecule-based therapeutics owing to their stability, low toxicity, low immunogenicity and improved safety. With the recent approval of the first aptamer drug Macugen by the US FDA, there is great impetus to develop therapeutic aptamers that can target a wide array of disease states. The recent demonstration that aptamer activity can be reversed by the administration of a simple antidote greatly enhances the potential value of aptamers as therapeutic agents.

Gene therapy for stroke: 2006 overview

Gene therapy is a promising approach for treatment of stroke and other cerebrovascular diseases, although it may take many years to realize. Gene therapy could occur prior to a stroke (eg, to stabilize atherosclerotic plaques) and/or following a stroke (eg, to prevent vasospasm after subarachnoid hemorrhage or reduce injury to neurons by ischemic insult). We have transferred the gene coding for vasoactive calcitonin gene-related peptide via cerebrospinal fluid, and demonstrated attenuation of vasospasm after SAH. Transfer of neuroprotective genes or small interfering RNA for neurotoxic genes has good potential for ischemic stroke. In this brief report, we review recent developments in experimental gene therapy for stroke. Fundamental advances, including development of safer, more specific gene transfer vectors, are discussed.

Therapeutic RNA interference for neurodegenerative diseases: From promise to progress

RNA interference (RNAi) has emerged as a powerful tool to manipulate gene expression in the laboratory. Due to its remarkable discriminating properties, individual genes, or even alleles can be targeted with exquisite specificity in cultured cells or living animals. Among its many potential biomedical applications, silencing of disease-linked genes stands out as a promising therapeutic strategy for many incurable disorders. Neurodegenerative diseases represent one of the more attractive targets for the development of therapeutic RNAi. In this group of diseases, the progressive loss of neurons leads to the gradual appearance of disabling neurological symptoms and premature death. Currently available therapies aim to improve the symptoms but not to halt the process of neurodegeneration. The increasing prevalence and economic burden of some of these diseases, such as Alzheimer's disease (AD) or Parkinson's disease (PD), has boosted the efforts invested in the development of interventions, such as RNAi, aimed at altering their natural course. This review will summarize where we stand in the therapeutic application of RNAi for neurodegenerative diseases. The basic principles of RNAi will be reviewed, focusing on features important for its therapeutic manipulation. Subsequently, a stepwise strategy for the development of therapeutic RNAi will be presented. Finally, the different preclinical trials of therapeutic RNAi completed in disease models will be summarized, stressing the experimental questions that need to be addressed before planning application in human disease.

Hydrophobization and bioconjugation for enhanced siRNA delivery and targeting

RNA interference (RNAi) is an evolutionarily conserved process by which double-stranded small interfering RNA (siRNA) induces sequence-specific, post-transcriptional gene silencing. Unlike other mRNA targeting strategies, RNAi takes advantage of the physiological gene silencing machinery. The potential use of siRNA as therapeutic agents has attracted great attention as a novel approach for treating severe and chronic diseases. RNAi can be achieved by either delivery of chemically synthesized siRNAs or endogenous expression of small hairpin RNA, siRNA, and microRNA (miRNA). However, the relatively high dose of siRNA required for gene silencing limits its therapeutic applications. This review discusses several strategies to improve therapeutic efficacy as well as to abrogate off-target effects and immunostimulation caused by siRNAs. There is an in-depth discussion on various issues related to the (1) mechanisms of RNAi, (2) methods of siRNA production, (3) barriers to RNAi-based therapies, (4) biodistribution, (5) design of siRNA molecules, (6) chemical modification and bioconjugation, (7) complex formation with lipids and polymers, (8) encapsulation into lipid particles, and (9) target specificity for enhanced therapeutic effectiveness.

RNAi therapeutics: principles, prospects and challenges

RNA interference (RNAi) was discovered less than a decade ago and already there are human clinical trials in progress or planned. A major advantage of RNAi versus other antisense based approaches for therapeutic applications is that it utilizes cellular machinery that efficiently allows targeting of complementary transcripts, often resulting in highly potent down-regulation of gene expression. Despite the excitement about this remarkable biological process for sequence specific gene regulation, there are a number of hurdles and concerns that must be overcome prior to making RNAi a real therapeutic modality, which include off-target effects, triggering of type I interferon responses, and effective delivery in vivo. This review discusses mechanistic aspects of RNAi, the potential problem areas and solutions and therapeutic applications. It is anticipated that RNAi will be a major therapeutic modality within the next several years, and clearly warrants intense investigation to fully understand the mechanisms involved.

Toxicogenomics of non-viral drug delivery systems for RNAi: potential impact on siRNA-mediated gene silencing activity and specificity

RNA interference (RNAi) is an evolutionary conserved cellular process for the regulation of gene expression. In mammalian cells, RNAi is induced via short (21-23 nt) duplexes of RNA, termed small interfering RNA (siRNA), that can elicit highly sequence-specific gene silencing. However, synthetic siRNA duplexes are polyanionic macromolecules that do not readily enter cells and typically require the use of a delivery vector for effective gene silencing in vitro and in vivo. Choice of delivery system is usually made on its ability to enhance cellular uptake of siRNA. However, recent gene expression profiling (toxicogenomics) studies have shown that separate from their effects on cellular uptake, delivery systems can also elicit wide ranging gene changes in target cells that may impact on the 'off-target' effects of siRNA. Furthermore, if delivery systems also alter the expression of genes targeted for silencing, then siRNA activity may be compromised or enhanced depending on whether the target gene is up-regulated or down-regulated respectively. Citing recent examples from the literature, this article therefore reviews the toxicogenomics of non-viral delivery systems and highlights the importance of understanding the genomic signature of siRNA delivery reagents in terms of their impact on gene silencing activity and specificity. Such information will be essential in the selection of optimally acting siRNA-delivery system combinations for the many applications of RNA interference.

Strategies for silencing human disease using RNA interference

Since the first description of RNA interference (RNAi) in animals less than a decade ago, there has been rapid progress towards its use as a therapeutic modality against human diseases. Advances in our understanding of the mechanisms of RNAi and studies of RNAi in vivo indicate that RNAi-based therapies might soon provide a powerful new arsenal against pathogens and diseases for which treatment options are currently limited. Recent findings have highlighted both promise and challenges in using RNAi for therapeutic applications. Design and delivery strategies for RNAi effector molecules must be carefully considered to address safety concerns and to ensure effective, successful treatment of human diseases.

Administration in non-human primates of escalating intravenous doses of targeted nanoparticles containing ribonucleotide reductase subunit M2 siRNA

The results of administering escalating, i.v. doses of targeted nanoparticles containing a siRNA targeting the M2 subunit of ribonucleotide reductase to non-human primates are reported. The nanoparticles consist of a synthetic delivery system that uses a linear, cyclodextrin-containing polycation, transferrin (Tf) protein targeting ligand, and siRNA. When administered to cynomolgus monkeys at doses of 3 and 9 mg siRNA/kg, the nanoparticles are well tolerated. At 27 mg siRNA/kg, elevated levels of blood urea nitrogen and creatinine are observed that are indicative of kidney toxicity. Mild elevations in alanine amino transferase and aspartate transaminase at this dose level indicate that the liver is also affected to some extent. Analysis of complement factors does not reveal any changes that are clearly attributable to dosing with the nanoparticle formulation. Detection of increased IL-6 levels in all animals at 27 mg siRNA/kg and increased IFN-gamma in one animal indicate that this high dose level produces a mild immune response. Overall, no clinical signs of toxicity clearly attributable to treatment are observed. The multiple administrations spanning a period of 17-18 days enable assessment of antibody formation against the human Tf component of the formulation. Low titers of anti-Tf antibodies are detected, but this response is not associated with any manifestations of a hypersensitivity reaction upon readministration of the targeted nanoparticle. Taken together, the data presented show that multiple, systemic doses of targeted nanoparticles containing nonchemically modified siRNA can safely be administered to non-human primates.

Synthetic RNA circuits

Natural and engineered RNA 'parts' can perform a variety of functions, including hybridizing to targets, binding ligands and undergoing programmed conformational changes, and catalyzing reactions. These RNA parts can in turn be assembled into synthetic genetic circuits that regulate gene expression by acting either in cis or in trans on mRNAs. As more parts are discovered and engineered, it should be increasingly possible to create synthetic RNA circuits that are able to carry out complex logical operations in cells, either superimposed on or autonomous to extant gene regulation.

Combinatorial RNAi: a winning strategy for the race against evolving targets?

The ability to use double-stranded RNA to inhibit gene expression sequence-specifically (RNA interference, or RNAi) is currently revolutionizing science and medicine alike. Numerous pre-clinical studies are evaluating RNAi as a novel therapeutic modality in the battle against gain-of-function autosomal dominant diseases, cancer, and viral infections. One emerging concern is that RNAi mono-therapies might ultimately fail to control viruses that can escape silencing by mutation and/or RNAi suppression. Thus, sophisticated strategies are being developed that aim to avert viral resistance by combining RNAi effectors with each other or with further gene expression inhibitors. Several reports already validate this new concept of “combinatorial RNAi” (coRNAi) and illustrate its versatility by describing co-expression of RNAi triggers directed against single or multiple, viral or cellular, targets. Other studies document the successful delivery of these triggers with additional RNA- or protein-based silencers. Moreover, vectors have been engineered to blend RNAi-mediated gene inhibition with conventional gene replacement strategies. Collectively, these efforts open up exciting new therapeutic avenues but could also augment the inherent risks of RNAi technology, including immune responses, off-targeting, and oversaturation of endogenous pathways. Here, we critically review all coRNAi strategies and discuss the requirements for their transition into clinical application.

Nanoconjugate based on polymalic acid for tumor targeting

A new prototype of polymer-derived drug delivery system, the nanoconjugate Polycefin, was tested for its ability to accumulate in tumors based on enhanced permeability and retention (EPR) effect and receptor mediated endocytosis. Polycefin was synthesized for targeted delivery of Morpholino antisense oligonucleotides into certain tumors. It consists of units that are covalently conjugated with poly(beta-l-malic acid) (M(w) 50,000, M(w)/M(n) 1.3) highly purified from cultures of myxomycete Physarum polycephalum. The units are active in endosomal uptake, disruption of endosomal membranes, oligonucleotide release in the cytoplasm, and protection against enzymatic degradation in the vascular system. The polymer is biodegradable, non-immunogenic and non-toxic. Polycefin was also coupled with AlexaFluor 680 C2-maleimide dye for in vivo detection. Nude mice received subcutaneous injections of MDA-MB 468 human breast cancer cells into the left posterior mid-dorsum or intracranial injections of human glioma cell line U87MG. Polycefin at concentration of 2.5mg/kg was injected via the tail vein. In vivo fluorescence tumor imaging was performed at different time points, 0-180 min up to 24h after the drug injection. The custom-made macro-illumination imaging MISTI system was used to examine the in vivo drug accumulation in animals bearing human breast and brain tumors. In breast tumors the fluorescence signal in large blood vessels and in the tumor increased rapidly until 60 min and remained in the tumor at a level 6 times higher than in non-tumor tissue (180 min) (p<0.003). In brain tumors drug accumulated selectively in 24h without any detectable signal in non-tumor areas. The results of live imaging were corroborated histologically by fluorescence microscopic examination of various organs. In addition to tumors, only kidney and liver showed some fluorescent signal.

Comparison of different strategies to select aptamers against a transmembrane protein target

Binding of aptamers is dependent on their target conformation, which in turn is conditioned by the target's environment. Therefore, selection of aptamers against the active forms of membrane proteins could require their correct membrane insertion in order to maintain their native conformation. Here, we compare different SELEX strategies to identify aptamers against the mutated form of the membrane receptor tyrosine kinase RET(C634Y). (1) selections S1 and S2 against living cells transformed to express the protein yielded a minority of RET-targeted aptamers while the bulk of aptamers recognized more abundant membrane proteins, suggesting that a high level of expression of the target protein is crucial to allow the isolation of aptamers at cell surface; (2) selection S3 against the purified extracellular moiety of RET yielded aptamers unable to recognize RET expressed at the cell membrane; (3) crossover selections S4 and S5 alternating cells and recombinant RET enhanced the enrichment of the aptamers directed against RET; however, these aptamers displayed a weaker affinity for Ret than those obtained with S1 and S2. In our case, using transformed cell lines as the partitioning matrix during SELEX appears to be essential in order to obtain aptamers able to recognize the RET receptor tyrosine kinase in its physiologic environment.

Modulation of scratching behavior by silencing an endogenous cyclooxygenase-1 gene in the skin through the administration of siRNA

BACKGROUND

RNA interference (RNAi) is rapidly becoming a major tool that is revolutionizing research in the bioscience and biomedical fields. To apply the RNAi technique in vivo, it is crucial to develop appropriate methods of guiding the short interfering RNA (siRNA) molecules to the right tissues and cells. Here, we demonstrate an efficient method for performing gene knockdown in the body skin using the in vivo electro-transduction of siRNA. Using this method, we examined whether the targeted silencing of the cyclooxygenase (COX) gene in the skin could modulate the scratching behavior of an atopic dermatitis mouse model.

METHODS

NC/Nga mice were used as the atopic dermatitis model. Using our optimized in vivo electroporation conditions, siRNAs were introduced into the skin; the silencing efficiency was then analyzed by Western blotting, measuring the levels of prostaglandins, and immunohistochemistry. The scratching behaviors of the mice were measured using an automatic system.

RESULTS

Targeted silencing of the COX-1 gene using our in vivo siRNA technique significantly accelerated the scratching behavior of NC/Nga mice, whereas the COX-2 siRNA showed no effect. In addition, the effect of COX-1 siRNA was mimicked by treatment with a COX-1-selective inhibitor (SC-560).

CONCLUSIONS

We have demonstrated the successful silencing of endogenous gene expression in the skin using the intradermal transfection of unmodified siRNA via electroporation. Using this method, we revealed that COX- 1-mediated prostaglandins may act as endogenous inhibitors of scratching behavior.

Inhibition of multiple strains of Venezuelan equine encephalitis virus by a pool of four short interfering RNAs

RNA interference, mediated by short interfering RNAs (siRNAs), has been shown to have activity against a wide range of viruses and is a promising new antiviral therapy. Using multiple siRNAs that target conserved areas of the genome allows for increased chances of antiviral activity against different viral strains and also helps to prevent the emergence of escape mutants. In this study, four siRNAs were designed to target areas of conserved sequence between divergent strains of Venezuelan equine encephalitis virus (VEEV). A pool of these siRNAs inhibited the replication of all six strains of VEEV tested. A single nucleotide mismatch at the extreme 3′ end of one of the siRNA sense strands did not affect antiviral activity but other mutations were not tolerated. Two strains of VEEV were tested for their abilities to overcome the inhibitory effects of RNA interference following 10 consecutive incubations in the presence of siRNAs. One strain remained susceptible throughout the course of the experiment but the other strain became resistant to the activity of siRNAs. Sequence analysis of the siRNA target sites in this strain showed that no mutations had been generated, indicating that the virus may had become resistant in some other manner. In the absence of effective antiviral drugs and vaccines to combat VEEV infection, these siRNAs offer a potential new therapeutic approach but, as with all antimicrobial agents, caution needs to be exercised with respect to the generation of resistance.

RNAi therapeutics: a potential new class of pharmaceutical drugs

The rapid identification of highly specific and potent drug candidates continues to be a substantial challenge with traditional pharmaceutical approaches. Moreover, many targets have proven to be intractable to traditional small-molecule and protein approaches. Therapeutics based on RNA interference (RNAi) offer a powerful method for rapidly identifying specific and potent inhibitors of disease targets from all molecular classes. Numerous proof-of-concept studies in animal models of human disease demonstrate the broad potential application of RNAi therapeutics. The major challenge for successful drug development is identifying delivery strategies that can be translated to the clinic. With advances in this area and the commencement of multiple clinical trials with RNAi therapeutic candidates, a transformation in modern medicine may soon be realized.