Knocking down disease: a progress report on siRNA therapeutics

Chaperonin-Dendrimer Conjugates for siRNA Delivery

The group II chaperonin thermosome (THS) is a hollow protein nanoparticle that can encapsulate macromolecular guests. Two large pores grant access to the interior of the protein cage. Poly(amidoamine) (PAMAM) is conjugated into THS to act as an anchor for small interfering RNA (siRNA), allowing to load the THS with therapeutic payload. THS-PAMAM protects siRNA from degradation by RNase A and traffics KIF11 and GAPDH siRNA into U87 cancer cells. By modification of the protein cage with the cell-penetrating peptide TAT, RNA interference is also induced in PC-3 cells. THS-PAMAM protein-polymer conjugates are therefore promising siRNA transfection reagents and greatly expand the scope of protein cages in drug delivery applications.

Tackling breast cancer chemoresistance with nano-formulated siRNA

Breast cancer is the leading cancer diagnosed in women and the second leading cause of cancer-related deaths in women. Current limitations to standard chemotherapy in the clinic are extensively researched, including problems arising from repeated treatments with the same drugs. The phenomenon that cancer cells become resistant toward certain chemo drugs is called chemotherapy resistance. In this review, we are focusing on nanoformulation of siRNA for the fight against breast cancer chemoresistance.

Pharmacokinetics and biodistribution of recently-developed siRNA nanomedicines

Small interfering RNA (siRNA) is a promising drug candidate, expected to have broad therapeutic potentials toward various diseases including viral infections and cancer. With recent advances in bioconjugate chemistry and carrier technology, several siRNA-based drugs have advanced to clinical trials. However, most cases address local applications or diseases in the filtering organs, reflecting remaining challenges in systemic delivery of siRNA. The difficulty in siRNA delivery is in large part due to poor circulation stability and unfavorable pharmacokinetics and biodistribution profiles of siRNA. This review describes the pharmacokinetics and biodistribution of siRNA nanomedicines, focusing on those reported in the past 5years, and their pharmacological effects in selected disease models such as hepatocellular carcinoma, liver infections, and respiratory diseases. The examples discussed here will provide an insight into the current status of the art and unmet needs in siRNA delivery.

Vector-delivered artificial miRNA effectively inhibited replication of Chikungunya virus

Chikungunya virus (CHIKV) has emerged as one of the most significant arboviral threats in many parts of the world. In spite of large scale morbidity, and long lasting polyarthralgia, no licensed vaccine or antivirals are available for the clinical management of CHIKV infection. In this study, a novel RNA interference based strategy has been adopted for effective inhibition of CHIKV. Four artificial microRNAs (amiRNAs) were designed to target different regions of CHIKV genome. These amiRNAs significantly inhibited CHIKV replication in Vero cells at both RNA and protein levels as assessed by qRT-PCR, immunoblotting and immunofluorescence techniques. Further inhibition of the infectious CHIKV up to 99.8% was demonstrated by plaque reduction assay. Concatemerization of amiRNA resulted in higher inhibition of CHIKV than individual amiRNAs. In addition, we studied the effect of combination of RNAi based therapy with other classical antivirals like chloroquine, ribavirin and mycophenolic acid, that helped in understanding the rational selection of RNAi based combination therapy. These findings provide a promising avenue for the development of novel amiRNA or combination based therapeutics against emerging CHIKV.

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amiRNAs targeting different ORF of CHIKV was designed.

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Significant Inhibition of CHIKV replication through amiRNA was demonstrated.

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Concatenated amiRNAs results in higher viral inhibition.

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Combination of RNAi with classical drugs may obliterate failure of monotherapy.

Artificial Control of Gene Silencing Activity Based on siRNA Conjugation with Polymeric Molecule Having Coil-Globule Transition Behavior

A new strategy for controlling gene silencing activity of siRNA in the cell was developed in the present study. siRNA was linearly conjugated with PNIPAAm, where coil-globule transition of the conjugated PNIPAAm allows thermoresponsive exposure of the vicinal siRNA molecule; a coil form of PNIPAAm (T < LCST) inhibits siRNA interaction with gene silencing-related proteins due to the steric hindrance effect, while a globule form of PNIPAAm (T > LCST) allows a ready access of siRNA to gene silencing pathway. As a result, at T > LCST, PNIPAAm-siRNA elicited effective association of siRNA with a gene silencing-related protein of Ago2, while siRNA recruitment into the gene silencing pathway was significantly suppressed at T < LCST. Ultimately, gene silencing efficacy of PNIPAAm-siRNA was close to unconjugated siRNA at T > LCST (∼80%), while it was dramatically decreased to ∼20% at T < LCST, suggesting that coil-globule transition of the conjugated polymer can control the bioactivity of the vicinal siRNA molecule.

Precision medicine, genomics and drug discovery

The hope for precision medicine has long been on the drug discovery horizon, well before the Human Genome Project gave it promise at the turn of the 21st century. In oncology, the concept has finally been realized and is now firmly embedded in ongoing drug discovery programs, and with many recent therapies involving some level of patient/disease stratification, including some highly personalized treatments. In addition, several drugs for rare diseases have been recently approved or are in late-stage clinical development, and new delivery modalities in cell and gene therapy and oligonucleotide approaches are yielding exciting new medicines for rare diseases of unmet need. For common complex diseases, however, the GWAS-driven advances in annotation of the genetic architecture over the past decade have not led to a concomitant shift in refined treatments. Similarly, attempts to disentangle treatment responders from non-responders via genetic predictors in pharmacogenetics studies have not met their anticipated success. It is possible that common diseases are simply lagging behind due to the inherent time lag with drug discovery, but it is also possible that their inherent multifactorial nature and their etiological and clinical heterogeneity will prove more resistant to refined treatment paradigms. The emergence of population-based resources in electronic health records, coupled with the rapid expansion of mobile devices and digital health may help to refine the measurement of phenotypic outcomes to match the exquisite detail emerging at the molecular level.

Pre-administration of PepFect6-microRNA-146a nanocomplexes inhibits inflammatory responses in keratinocytes and in a mouse model of irritant contact dermatitis

The skin is a difficult to access tissue for efficient delivery of large and/or charged macromolecules, including therapeutic DNA and RNA oligonucleotides. Cell-penetrating peptide PepFect6 (PF6) has been shown to be suitable transport vehicle for siRNAs in cell culture and systemically in vivo in mice. MiR-146a is known as anti-inflammatory miRNA that inhibits multiple factors from the nuclear factor (NF)-κB pathway in various cell types, including keratinocytes. In this study, PF6 was shown to form unimodal nanocomplexes with miR-146a mimic that entered into human primary keratinocytes, where miR-146a inhibited the expression of its direct targets from the NF-κB pathway and the genes known to be activated by NF-κB, C-C motif ligand (CCL)5 and interleukin (IL)-8. The transfection of miR-146a mimic with PF6 was more efficient in sub-confluent keratinocyte cultures, affected keratinocyte proliferation less and had similar effect on cell viability when compared with a lipid based agent. Subcutaneous pre-administration of PF6-miR-146a nanocomplexes attenuated ear-swelling and reduced the expression of pro-inflammatory cytokines and chemokines IL-6, CCL11, CCL24 and C-X-C motif ligand 1 (CXCL1) in a mouse model of irritant contact dermatitis. Our data demonstrates that PF6-miR-146a nanoparticles might have potential in the development of therapeutics to target inflammatory skin diseases.

Immunomodulation of hematological malignancies using oligonucleotides based-nanomedicines

Hematological malignancies are a group of diseases characterized by clonal proliferation of blood-forming cells. Malignant blood cells are classified as myeloid or lymphoid cells depending on their stem cell origin. Lymphoid malignancies are characterized by lymphocyte accumulation in the blood stream, in the bone marrow, or in lymphatic nodes and organs. Several of these diseases are associated with chromosomal translocations, which cause gene fusion and amplification of expression, while others are characterized with aberrant expression of oncogenes. Overall, these genes play a major role in development and maintenance of malignant clones. The discovery of antisense oligonucleotides and RNA interference (RNAi) mechanisms offer new tools to specifically manipulate gene expression. Systemic delivery of inhibitory oligonucleotides molecules for manipulation of gene expression in lymphocytes holds a great potential for facilitating the development of an oligonucleotides -based therapy platform for lymphoid blood cancer. However, lymphocytes are among the most difficult targets for oligonucleotides delivery, as they are resistant to conventional transfection reagents and are dispersed throughout the body, making it difficult to successfully localize or deliver oligonucleotides payloads via systemic administration. In this review, we will survey the latest progress in the field of oligonucleotides based nanomedicine in the heterogeneous group of hematological malignancies with special emphasis on RNA based strategies. We will describe the most advanced non-viral nanocarriers for RNA delivery to malignant blood cells. We will also discuss targeted strategies for cell specific delivery of RNA molecules using nanoparticles and the therapeutic benefit of manipulating gene function in hematological malignancies. Finally, we will focus on the ex vivo, in vivo, and clinical trial strategies, that are currently under development in hematological malignancies - strategies that might increase the arsenal of drugs available to hematologists in the upcoming years.

Recent advances in RNAi-based strategies for therapy and prevention of HIV-1/AIDS

RNA interference (RNAi) provides a powerful tool to silence specific gene expression and has been widely used to suppress host factors such as CCR5 and/or viral genes involved in HIV-1 replication. Newer nuclease-based gene-editing technologies, such as zinc finger nucleases (ZFN), transcription activator-like effector nucleases (TALEN) and the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system, also provide powerful tools to ablate specific genes. Because of differences in co-receptor usage and the high mutability of the HIV-1 genome, a combination of host factors and viral genes needs to be suppressed for effective prevention and treatment of HIV-1 infection. Whereas the continued presence of small interfering/short hairpin RNA (si/shRNA) mediators is needed for RNAi to be effective, the continued expression of nucleases in the gene-editing systems is undesirable. Thus, RNAi provides the only practical way for expression of multiple silencers in infected and uninfected cells, which is needed for effective prevention/treatment of infection. There have been several advances in the RNAi field in terms of si/shRNA design, targeted delivery to HIV-1 susceptible cells, and testing for efficacy in preclinical humanized mouse models. Here, we comprehensively review the latest advances in RNAi technology towards prevention and treatment of HIV-1.

RNA therapeutics: RNAi and antisense mechanisms and clinical applications

RNA therapeutics refers to the use of oligonucleotides to target primarily ribonucleic acids (RNA) for therapeutic efforts or in research studies to elucidate functions of genes. Oligonucleotides are distinct from other pharmacological modalities, such as small molecules and antibodies that target mainly proteins, due to their mechanisms of action and chemical properties. Nucleic acids come in two forms: deoxyribonucleic acids (DNA) and ribonucleic acids (RNA). Although DNA is more stable, RNA offers more structural variety ranging from messenger RNA (mRNA) that codes for protein to non-coding RNAs, microRNA (miRNA), transfer RNA (tRNA), short interfering RNAs (siRNAs), ribosomal RNA (rRNA), and long-noncoding RNAs (lncRNAs). As our understanding of the wide variety of RNAs deepens, researchers have sought to target RNA since >80% of the genome is estimated to be transcribed. These transcripts include non-coding RNAs such as miRNAs and siRNAs that function in gene regulation by playing key roles in the transfer of genetic information from DNA to protein, the final product of the central dogma in biology¹. Currently there are two main approaches used to target RNA: double stranded RNA-mediated interference (RNAi) and antisense oligonucleotides (ASO). Both approaches are currently in clinical trials for targeting of RNAs involved in various diseases, such as cancer and neurodegeneration. In fact, ASOs targeting spinal muscular atrophy and amyotrophic lateral sclerosis have shown positive results in clinical trials². Advantages of ASOs include higher affinity due to the development of chemical modifications that increase affinity, selectivity while decreasing toxicity due to off-target effects. This review will highlight the major therapeutic approaches of RNA medicine currently being applied with a focus on RNAi and ASOs.

Reversal of multidrug resistance in breast cancer MCF-7/ADR cells by h-R3-siMDR1-PAMAM complexes

Multidrug resistance (MDR) among breast cancer cells is the paramount obstacle for the successful chemotherapy. In this study, anti-EGFR antibody h-R3 was designed to self-assembled h-R3-siRNA-PAMAM-complexes (HSPCs) via electrostatic interactions for siRNA delivery. The physicochemical characterization, cell uptake, MDR1 silencing efficiency, cell migration, cell growth and cell apoptosis were investigated. The HSPCs presented lower cytotoxicity, higher cellular uptake and enhanced endosomal escape ability. Also, HSPCs encapsulating siMDR1 knockdowned 99.4% MDR1 gene with up to ∼6 times of enhancement compared to naked siMDR1, increased the doxorubicin accumulation, down-regulated P-glycoprotein (P-gp) expression and suppressed cellular migration in breast cancer MCF-7/ADR cells. Moreover, the combination of anticancer drug paclitaxel (PTX) and siMDR1 loaded HSPCs showed synergistic effect on overcoming MDR, which inhibited cell growth and induced cell apoptosis. This h-R3-mediated siMDR1 delivery system could be a promising vector for effective siRNA therapy of drug resistant breast cancer.

Lipid Nanovectors to Deliver RNA Oligonucleotides in Cancer

The growing knowledge on the mechanisms of gene silencing and gene regulation by non-coding RNAs (ncRNA), mainly small interfering RNA (siRNA) and microRNA (miRNA), is providing a significant boost to the development of new therapeutic strategies for the treatment of cancer. However, the design of RNA-based therapeutics is hampered by biopharmaceutical issues, thus requiring the use of suitable delivery strategies. In this regards, lipid nanovectors have been successfully investigated to deliver RNA in different forms of cancer. Compared to other biomaterials, lipids offer advantages such as biocompatibility, biodegradability, easy production, low cost, limited toxicity and immunogenicity. The possibility to formulate these materials in the form of nanovectors allows overcoming biopharmaceutical issues associated to the therapeutic use of RNA, with the possibility to target tumors. This review takes stock of the main lipid nanovectors proposed to deliver ncRNA. For each considered delivery strategy, the rational design and the most meaningful in vitro and in vivo results are reported and discussed.

Oncogene Knockdown via Active Loading of Small RNAs into Extracellular Vesicles by Sonication

Extracellular vesicles (EVs), including exosomes and microvesicles, have emerged as promising drug delivery vehicles for small RNAs (siRNA and miRNA) due to their natural role in intercellular RNA transport. However, the application of EVs for therapeutic RNA delivery may be limited by loading approaches that can induce cargo aggregation or degradation. Here, we report the use of sonication as a means to actively load functional small RNAs into EVs. Conditions under which EVs could be loaded with small RNAs with minimal detectable aggregation were identified, and EVs loaded with therapeutic siRNA via sonication were observed to be taken up by recipient cells and capable of target mRNA knockdown leading to reduced protein expression. This system was ultimately applied to reduce expression of HER2, an oncogenic receptor tyrosine kinase that critically mediates breast cancer development and progression, and could be extended to other therapeutic targets. These results define important parameters informing the application of sonication as a small RNA loading method for EVs and demonstrate the potential utility of this approach for versatile cancer therapy.

Lipid nanoparticles for targeted siRNA delivery - going from bench to bedside

This review covers the basic aspects of small interfering RNA delivery by lipid nano-particles (LNPs) and elaborates on the current status of clinical trials for these systems. We briefly describe the roles of all LNP components and possible strategies for their improvement. We also focus on the current clinical trials using LNP-formulated RNA and the possible outcomes for therapy in the near future. Also, we present a critical analysis of selected clinical trials that reveals the common logic behind target selection. We address this review to a wide audience, especially to medical doctors who are interested in the application of RNA interference-based treatment platforms. We anticipate that this review may spark interest in this particular audience and generate new ideas in target selection for the disorders they are dealing with.

A versatile post-synthetic method on a solid support for the synthesis of RNA containing reduction-responsive modifications

An original post-synthetic method on a solid support was developed to introduce various disulfide bond containing groups at the 2'-OH of oligoribonucleotides (RNAs). It is based on a thiol disulfide exchange reaction between several readily accessible alkyldisulfanyl-pyridine derivatives and 2'-O-acetylthiomethyl RNA in the presence of butylamine. By this strategy, diverse 2'-O-alkyldithiomethyl RNAs were obtained. These modifications provided high nuclease resistance to RNA and were easily removed with glutathione treatment, thus featuring a potential use for siRNA prodrugs.

Development of antibody-siRNA conjugate targeted to cardiac and skeletal muscles

Despite considerable efforts to develop efficient carriers, the major target organ of short-interfering RNAs (siRNAs) remains limited to the liver. Expanding the application outside the liver is required to increase the value of siRNAs. Here we report on a novel platform targeted to muscular organs by conjugation of siRNAs with anti-CD71 Fab' fragment. This conjugate showed durable gene-silencing in the heart and skeletal muscle for one month after intravenous administration in normal mice. In particular, 1μg siRNA conjugate showed significant gene-silencing in the gastrocnemius when injected intramuscularly. In a mouse model of peripheral artery disease, the treatment with myostatin-targeting siRNA conjugate by intramuscular injection resulted in significant silencing of myostatin and hypertrophy of the gastrocnemius, which was translated into the recovery of running performance. These data demonstrate the utility of antibody conjugation for siRNA delivery and the therapeutic potential for muscular diseases.

Lipid Nanoparticle-mediated siRNA Transfer Against PCTAIRE1/PCTK1/Cdk16 Inhibits In Vivo Cancer Growth

PCTAIRE1/CDK16/PCTK1 plays critical roles in cancer cell proliferation and antiapoptosis. To advance our previously published in vitro results with PCTAIRE1 silencing, we examined the in vivo therapeutic potential of this approach by using small interfering RNA (siRNA) encapsulated by lipid nanoparticles. Therapy experiments of PCTAIRE1 siRNA were performed using human HCT116 colorectal cancer cells and human A2058 melanoma cells. A single dose of PCTAIRE1 siRNA-lipid nanoparticles was found to be highly effective in reducing in vivo PCTAIRE1 expression for up to 4 days as assayed by immunoblotting. Therapy experiments were started 4 days after subcutaneous injection of cancer cells. Treatment with PCTAIRE1 siRNA-lipid nanoparticles (0.5 mg/kg RNA, twice a week) reduced tumor volume and weight significantly compared with the scramble-control group. Histopathological analysis (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) showed increased apoptosis of tumor cells treated with PCTAIRE1-siRNA. Overall, our results demonstrate that siRNA treatment targeting PCTAIRE1 is effective in vivo, suggesting that PCTAIRE1 siRNA-lipid nanoparticles might be a novel therapeutic approach against cancer cells.

Functional inhibition of chemokine receptor CCR2 by dicer-substrate-siRNA prevents pain development

BACKGROUND

Accumulating evidence suggests that the C-C chemokine ligand 2 (CCL2, or monocyte chemoattractant protein 1) acts as a neuromodulator in the central nervous system through its binding to the C-C chemokine receptor 2 (CCR2). Notably, it is well established that the CCL2/CCR2 axis plays a key role in neuron-glia communication as well as in spinal nociceptive transmission. Gene silencing through RNA interference has recently emerged as a promising avenue in research and drug development, including therapeutic management of chronic pain. In the present study, we used 27-mer Dicer-substrate small interfering RNA (DsiRNA) targeting CCR2 and assessed their ability to reverse the nociceptive behaviors induced by spinal CCL2 injection or following intraplantar injection of complete Freund's adjuvant.

RESULTS

To this end, we first developed high-potency DsiRNAs designed to target different sequences distributed across the rat CCR2 (rCCR2) messenger RNA. For optimization, methyl groups were added to the two most potent DsiRNA candidates (Evader and M7 2'-O-methyl modified duplexes) in order to improve in vivo duplex stability and to reduce potential immunostimulatory activity. Our results demonstrated that all modified candidates formulated with the cell-penetrating peptide reagent Transductin showed strong RNAi activity following intrathecal delivery, exhibiting >50% rCCR2 knockdown in lumbar dorsal root ganglia. Accordingly, we found that these DsiRNA duplexes were able to reduce spinal microglia activation and were effective at blocking CCL2-induced mechanical hypersensitivity. Along with similar reductions of rCCR2 messenger RNA, both sequences and methylation patterns were similarly effective in inhibiting the CCL2 nociceptive action for the whole seven days testing period, compared to mismatch DsiRNA. DsiRNAs against CCR2 also reversed the hypernociceptive responses observed in the complete Freund's adjuvant-induced inflammatory chronic pain model.

CONCLUSION

Altogether, these results validate CCR2 as a an appropriate molecular target for pain control and demonstrate that RNAi-based gene therapy represent an highly specific alternative to classical pharmacological approaches to treat central pathologies such as chronic pain.

Transcutaneous iontophoretic delivery of STAT3 siRNA using layer-by-layer chitosan coated gold nanoparticles to treat melanoma

Overexpression of signal transducer and activator of transcription 3 (STAT3) protein prevents apoptosis and enhances proliferation of melanocytes. The aim of this study was to investigate the feasibility of using layer-by-layer assembled gold nanoparticles (LbL-AuNP) as a carrier for iontophoretic delivery of STAT3 siRNA to treat melanoma. Chitosan coated AuNP (AuNP-CS) were prepared by direct reduction of HAuCl4 in the presence of chitosan. The AuNP-CS were then sequentially layered with siRNA and chitosan to form AuNP-CS/siRNA/CS. STAT3 siRNA replaced with scrambled siRNA or sodium alginate were used as controls. The average particle size and zeta-potential of the prepared LbL-AuNP were 150±10nm (PDI: 0.41±0.06) and 35±6mV, respectively. In vitro studies in B16F10 murine melanoma cells showed that AuNP-CS/siRNA/CS inhibited the cell growth by 49.0±0.6% and 66.0±0.2% at 0.25nM and 0.5nM STAT3 siRNA concentration, respectively. Fluorescence microscopy and flow cytometry studies showed a time dependent cell uptake of the LbL-AuNP up to 120min. Clathrin mediated endocytosis was found to be the predominant cell uptake mechanism for LbL-AuNP. STAT3 siRNA loaded LbL-AuNP reduced the STAT3 protein expression by 47.3% in B16F10 cells. Similarly, apoptosis assay showed 29% and 44% of early and late apoptotic events, respectively after treatment with STAT3 siRNA loaded LbL-AuNP. Confocal microscope and skin cryosections showed that application of 0.47mA/cm(2) of anodal iontophoresis enhanced the skin penetration of LbL-AuNP to reach viable epidermis. In conclusion, layer-by-layer chitosan coated AuNP can be developed as a carrier for iontophoretic delivery of STAT3 siRNA to treat melanoma.

The Promise and Challenge of Therapeutic MicroRNA Silencing in Diabetes and Metabolic Diseases

MicroRNAs (miRNAs) are small, non-coding, RNA molecules that regulate gene expression. They have a long evolutionary history and are found in plants, viruses, and animals. Although initially discovered in 1993 in Caenorhabditis elegans, they were not appreciated as widespread and abundant gene regulators until the early 2000s. Studies in the last decade have found that miRNAs confer phenotypic robustness in the face of environmental perturbation, may serve as diagnostic and prognostic indicators of disease, underlie the pathobiology of a wide array of complex disorders, and represent compelling therapeutic targets. Pre-clinical studies in animal models have demonstrated that pharmacologic manipulation of miRNAs, mostly in the liver, can modulate metabolic phenotypes and even reverse the course of insulin resistance and diabetes. There is cautious optimism in the field about miRNA-based therapies for diabetes, several of which are already in various stages of clinical trials. This review will highlight both the promise and the most pressing challenges of therapeutic miRNA silencing in diabetes and related conditions.

Pulmonary administration of small interfering RNA: The route to go?

Ever since the discovery of RNA interference (RNAi), which is a post-transcriptional gene silencing mechanism, researchers have been studying the therapeutic potential of using small interfering RNA (siRNA) to treat diseases that are characterized by excessive gene expression. Excessive gene expression can be particularly harmful if it occurs in a vulnerable organ such as the lungs as they are essential for physiological respiration. Consequently, RNAi could offer an approach to treat such lung diseases. Parenteral administration of siRNA has been shown to be difficult due to degradation by nucleases in the systemic circulation and excretion by the kidneys. To avoid these issues and to achieve local delivery and local effects, pulmonary administration has been proposed as an alternative administration route. Regarding this application, various animal studies have been conducted over the past few years. Therefore, this review presents a critical analysis of publications where pulmonary administration of siRNA in animals has been reported. Such an analysis is necessary to determine the feasibility of this administration route and to define directions for future research. First, we provide background information on lungs, pulmonary administration, and delivery vectors. Thereafter, we present and discuss relevant animal studies. Though nearly all publications reported positive outcomes, several reoccurring challenges were identified. They relate to 1) the necessity, efficacy, and safety of delivery vectors, 2) the biodistribution of siRNA in tissues other than the lungs, 3) the poor correlation between in vitro and in vivo models, and 4) the long-term effects upon (repeated) administration of siRNA. Finally, we present recommendations for future research to define the route to go: towards safer and more effective pulmonary administration of siRNA.

Bioconjugated gold nanoparticles enhance cellular uptake: A proof of concept study for siRNA delivery in prostate cancer cells

The chemistry of gold nanoparticles (AuNPs) facilitates surface modifications and thus these bioengineered NPs have been investigated as a means of delivering a variety of therapeutic cargos to treat cancer. In this study we have developed AuNPs conjugated with targeting ligands to enhance cell-specific uptake in prostate cancer cells, with a purpose of providing efficient non-viral gene delivery systems in the treatment of prostate cancer. As a consequence, two novel AuNPs were synthesised namely AuNPs-PEG-Tf (negatively charged AuNPs with the transferrin targeting ligands) and AuNPs-PEI-FA (positively charged AuNPs with the folate-receptor targeting ligands). Both bioconjugated AuNPs demonstrated low cytotoxicity in prostate cancer cells. The attachment of the targeting ligand Tf to AuNPs successfully achieved receptor-mediated cellular uptake in PC-3 cells, a prostate cancer cell line highly expressing Tf receptors. The AuNPs-PEI-FA effectively complexed small interfering RNA (siRNA) through electrostatic interaction. At the cellular level the AuNPs-PEI-FA specifically delivered siRNA into LNCaP cells, a prostate cancer cell line overexpressing prostate specific membrane antigen (PSMA, exhibits a hydrolase enzymic activity with a folate substrate). Following endolysosomal escape the AuNPs-PEI-FA.siRNA formulation produced enhanced endogenous gene silencing compared to the non-targeted formulation. Our results suggest both formulations have potential as non-viral gene delivery vectors in the treatment of prostate cancer.

The delivery of therapeutic oligonucleotides

The oligonucleotide therapeutics field has seen remarkable progress over the last few years with the approval of the first antisense drug and with promising developments in late stage clinical trials using siRNA or splice switching oligonucleotides. However, effective delivery of oligonucleotides to their intracellular sites of action remains a major issue. This review will describe the biological basis of oligonucleotide delivery including the nature of various tissue barriers and the mechanisms of cellular uptake and intracellular trafficking of oligonucleotides. It will then examine a variety of current approaches for enhancing the delivery of oligonucleotides. This includes molecular scale targeted ligand-oligonucleotide conjugates, lipid- and polymer-based nanoparticles, antibody conjugates and small molecules that improve oligonucleotide delivery. The merits and liabilities of these approaches will be discussed in the context of the underlying basic biology.

Inhibition of miR-21 in glioma cells using catalytic nucleic acids

Despite tremendous efforts worldwide, glioblastoma multiforme (GBM) remains a deadly disease for which no cure is available and prognosis is very bad. Recently, miR-21 has emerged as a key omnipotent player in carcinogenesis, including brain tumors. It is recognized as an indicator of glioma prognosis and a prosperous target for anti-tumor therapy. Here we show that rationally designed hammerhead ribozymes and DNAzymes can target miR-21 and/or its precursors. They decrease miR-21 level, and thus silence this oncomiR functions. We demonstrated that anti-miRNA catalytic nucleic acids show a novel terrific arsenal for specific and effective combat against diseases with elevated cellular miR-21 content, such as brain tumors.

Engineering Periodic shRNA for Enhanced Silencing Efficacy

RNA interference (RNAi) provides a versatile therapeutic approach via silencing of specific genes, particularly undruggable targets in cancer and other diseases. However, challenges in the delivery of small interfering RNA (siRNA) have hampered clinical translation. Polymeric or periodic short hairpin RNAs (p-shRNAs)-synthesized by enzymatic amplification of circular DNA-are a recent development that can potentially address these delivery barriers by showing improved stability and complexation to enable nanoparticle packaging. Here, we modify these biomacromolecules via structural and sequence engineering coupled with selective enzymatic digestion to generate an open-ended p-shRNA (op-shRNA) that is cleaved over ten times more efficiently to yield siRNA. The op-shRNA induces considerably greater gene silencing than p-shRNA in multiple cancer cell lines up to 9 days. Furthermore, its high valency and flexibility dramatically improve complexation with a low molecular weight polycation compared to monomeric siRNA. Thus, op-shRNA provides an RNAi platform that can potentially be packaged and efficiently delivered to disease sites with higher therapeutic efficacy.

Challenges and opportunities for siRNA-based cancer treatment

As one of the life-threatening diseases involving multi-step genetic and epigenetic disorders, cancer has long been a dynamic research area for siRNA-based therapy as half of the current siRNA-based clinical trials are involved in oncology. However, despite consistent enthusiasm in the academic world, siRNA-based cancer treatment still faces obstacles and difficulties in clinical development. In this article, we discuss key challenges facing siRNA-based cancer treatment revealed from recent clinical and preclinical studies, including chemical modification, tumour penetration, endosomal escape, target selection and off-target effects. In addition, opportunities and avenues for translating siRNA technology from bench to oncologic clinics are explored.

Small Players Ruling the Hard Game: siRNA in Bone Regeneration

Silencing gene expression through a sequence-specific manner can be achieved by small interfering RNAs (siRNAs). The discovery of this process has opened the doors to the development of siRNA therapeutics. Although several preclinical and clinical studies have shown great promise in the treatment of neurological disorders, cancers, dominant disorders, and viral infections with siRNA, siRNA therapy is still gaining ground in musculoskeletal tissue repair and bone regeneration. Here we present a comprehensive review of the literature to summarize different siRNA delivery strategies utilized to enhance bone regeneration. With advancement in understanding the targetable biological pathways involved in bone regeneration and also the rapid progress in siRNA technologies, application of siRNA for bone regeneration has great therapeutic potential. High rates of musculoskeletal injuries and diseases, and their inevitable consequences, impose a huge financial burden on individuals and healthcare systems worldwide.

Enzyme- and pH-Responsive Microencapsulated Nanogels for Oral Delivery of siRNA to Induce TNF-α Knockdown in the Intestine

Inflammatory bowel diseases (IBD) manifest from excessive intestinal inflammation. Local delivery of siRNA that targets these inflammatory cytokines would provide a novel treatment approach. Microencapsulated nanogels are designed and validated as platforms for oral delivery of siRNA targeting TNF-α, a common clinical target of IBD treatments. The preferred platform was designed to (i) protect siRNA-loaded nanogels from the harsh acidic environment of the upper GI tract and (ii) enzymatically degrade and release the nanogels once the carrier has reached the intestinal region. This platform consists of microgels composed of poly(methacrylic acid-co-N-vinyl-2-pyrrolidone) (P[MAA-co-NVP]) cross-linked with a trypsin-degradable peptide linker. The P(MAA-co-NVP) backbone is designed to collapse around and protect encapsulated nanogel from degradation at the low pH levels seen in the stomach (pH 2-4). At pH levels of 6-7.5, as typically observed in the intestine, the P(MAA-co-NVP) matrix swells, potentially facilitating diffusion of intestinal fluid and degradation of the matrix by intestinal enzymes such as trypsin, thus "freeing" the therapeutic nanogels for delivery and cellular uptake within the intestine. TNF-α siRNA-loaded nanogels released from this platform were capable of inducing potent knockdown of secreted TNF-α levels in murine macrophages, further validating the potential for this approach to be used for the treatment of IBD.

Silencing Bag-1 gene via magnetic gold nanoparticle-delivered siRNA plasmid for colorectal cancer therapy in vivo and in vitro

Apoptosis disorder is generally regarded as an important mechanism of carcinogenesis. Inducement of tumor cell apoptosis can be an effectual way to treat cancer. Bcl-2-associated athanogene 1 (Bag-1) is a positive regulator of Bcl-2 which is an anti-apoptotic gene. Bag-1 is highly expressed in colorectal cancer, which plays a critical role in promoting metastasis, poor prognosis, especially in anti-apoptotic function, and is perhaps a valuable gene target for colorectal cancer therapy. Recently, we applied a novel non-viral gene carrier, magnetic gold nanoparticle, and mediated plasmid pGPH1/GFP/Neo-Bag-1-homo-825 silencing Bag-1 gene for treating colorectal cancer in vivo and in vitro. By mediating with magnetic gold nanoparticle, siRNA plasmid was successfully transfected into cell. In 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay, magnetic gold nanoparticle had no significant cytotoxicity and by which delivered RNA plasmid inhibited cell viability significantly (P < 0.05). Downregulation of Bag-1 promoted cell apoptosis (∼47.0 %) in vitro and significantly decreased tumor growth when the cells were injected into nude mice. Based on the studies in vivo, the relative expression of Bag-1 was 0.165 ± 0.072 at mRNA level and ∼60 % at protein level. In further study, C-myc and β-catenin, mainly molecules of Wnt/β-catenin pathway, were decreased notably when Bag-1 were silenced in nanoparticle plasmid complex-transfected Balb c/nude tumor xenograft. In conclusion, Bag-1 is confirmed an anti-apoptosis gene that functioned in colorectal cancer, and the mechanism of Bag-1 gene causing colorectal cancer may be related to Wnt/β-catenin signaling pathway abnormality and suggested that magnetic gold nanoparticle-delivered siRNA plasmid silencing Bag-1 is an effective gene therapy method for colorectal cancer.

RNA nanomedicines: the next generation drugs?

RNA therapeutics could represent the next generation personalized medicine. The variety of RNA molecules that can inhibit the expression of any mRNA using, for example, RNA interference (RNAi) strategies, or increase the expression of a given protein using modified mRNA together with new gene editing strategies open new avenues for manipulating the fate of diseased cells while leaving healthy cells untouched. In addition, these therapeutic RNA molecules can maximize the treatment of diseases and minimize its adverse effects. Yet, the promise of RNA therapeutics is hindered by the lack of efficient delivery strategies to selectively target these molecules into specific cells. Herein, we will focus on the challenges and opportunities of the delivery of therapeutic RNAi molecules into cancer cells with special emphasis on solid tumors. Solid tumors represent more than 80 percent of cancers and some are very challenging to treat, not merely due to physiological barriers but also since the tumor microenvironment (TME) is a complex milieu of accessory cells besides the cancerous cells. In this review, we will highlight various limiting factors to successful delivery, current clinical achievements and future outlook focusing on RNAi therapeutics to the TME.

PEGylated cationic hybrid bicellar nanodisc for efficient siRNA delivery

Highly stable PEGylated cationic hybrid bicellar nanodisc for efficient siRNA delivery.

Small molecule-mediated protein knockdown as a new approach to drug discovery

Research into degradation of cellular proteins induced by small molecule agents known as Protacs has gathered pace recently. This article reviews recent progress and assesses the challenges to be addressed to enable clinical evaluation of agents.

Harnessing RNAi-based nanomedicines for therapeutic gene silencing in B-cell malignancies

Despite progress in systemic small interfering RNA (siRNA) delivery to the liver and to solid tumors, systemic siRNA delivery to leukocytes remains challenging. The ability to silence gene expression in leukocytes has great potential for identifying drug targets and for RNAi-based therapy for leukocyte diseases. However, both normal and malignant leukocytes are among the most difficult targets for siRNA delivery as they are resistant to conventional transfection reagents and are dispersed in the body. We used mantle cell lymphoma (MCL) as a prototypic blood cancer for validating a novel siRNA delivery strategy. MCL is an aggressive B-cell lymphoma that overexpresses cyclin D1 with relatively poor prognosis. Down-regulation of cyclin D1 using RNA interference (RNAi) is a potential therapeutic approach to this malignancy. Here, we designed lipid-based nanoparticles (LNPs) coated with anti-CD38 monoclonal antibodies that are specifically taken up by human MCL cells in the bone marrow of xenografted mice. When loaded with siRNAs against cyclin D1, CD38-targeted LNPs induced gene silencing in MCL cells and prolonged survival of tumor-bearing mice with no observed adverse effects. These results highlight the therapeutic potential of cyclin D1 therapy in MCL and present a novel RNAi delivery system that opens new therapeutic opportunities for treating MCL and other B-cell malignancies.

Modulation of hepcidin to treat iron deregulation: potential clinical applications

The secreted peptide hormone hepcidin regulates systemic and local iron homeostasis through degradation of the iron exporter ferroportin. Dysregulation of hepcidin leads to altered iron homeostasis and development of pathological disorders including hemochromatosis, and iron loading and iron restrictive anemias. Therapeutic modulation of hepcidin is a promising method to ameliorate these conditions. Several approaches have been taken to enhance or reduce the effects of hepcidin in vitro and in vivo. Based on these approaches, hepcidin modulating drugs have been developed and are undergoing clinical evaluation. In this article we review the rationale for development of these drugs, the data concerning their safety and efficacy, their therapeutic uses, and potential future prospects.

Effect of surface properties on liposomal siRNA delivery

Liposomes are one of the most widely investigated carriers for siRNA delivery. The surface properties of liposomal carriers, including the surface charge, PEGylation, and ligand modification can significantly affect the gene silencing efficiency. Three barriers of systemic siRNA delivery (long blood circulation, efficient tumor penetration and efficient cellular uptake/endosomal escape) are analyzed on liposomal carriers with different surface charges, PEGylations and ligand modifications. Cationic formulations dominate siRNA delivery and neutral formulations also have good performance while anionic formulations are generally not proper for siRNA delivery. The PEG dilemma (prolonged blood circulation vs. reduced cellular uptake/endosomal escape) and the side effect of repeated PEGylated formulation (accelerated blood clearance) were discussed. Effects of ligand modification on cationic and neutral formulations were analyzed. Finally, we summarized the achievements in liposomal siRNA delivery, outlined existing problems and provided some future perspectives.

Gene-based therapies in lipidology: current status and future challenges

PURPOSE OF REVIEW

Gene-based therapies are designed to modulate gene expression in specific tissues by introducing into cells transgenes, antisense oligonucleotides, RNA interference, microRNAs, or a variety of other oligonucleotide-based compounds and their delivery systems. Several types of gene-based therapies are already available or in clinical development to treat severe lipid-related disorders and associated risk. The review briefly presents the current status and future challenges of these therapies in clinical lipidology, focusing on most advanced and promising agents or mechanisms.

RECENT FINDINGS

Gene-based agents address several unmet medical needs in lipidology such as homozygous familial hypercholesterolemia, familial or multifactorial chylomicronemia, severe hypertriglyceridemia, elevated lipoprotein (a), familial partial lipodystrophy, nonalcoholic fatty liver disease, and hypoalphalipoproteinemia. Most advanced antisense oligonucleotide drugs target apolipoprotein C-III, apolipoprotein (a), angiopoietin-like 3, and diacylglycerol o-acyltransferase-2. Long-term efficacy and safety data are now available for two gene-based agents, mipomersen, approved in the USA for homozygous familial hypercholesterolemia and Glybera, AAV1-LPLS447X gene therapy, conditionally approved in Europe for lipoprotein lipase deficiency.

SUMMARY

Although positive to date, the overall benefit-risk ratio of gene-based therapies is yet to be documented long term across additional patients and conditions. The next generation of such therapies might improve their therapeutic index.

RNase P-Mediated Sequence-Specific Cleavage of RNA by Engineered External Guide Sequences

The RNA cleavage activity of RNase P can be employed to decrease the levels of specific RNAs and to study their function or even to eradicate pathogens. Two different technologies have been developed to use RNase P as a tool for RNA knockdown. In one of these, an external guide sequence, which mimics a tRNA precursor, a well-known natural RNase P substrate, is used to target an RNA molecule for cleavage by endogenous RNase P. Alternatively, a guide sequence can be attached to M1 RNA, the (catalytic) RNase P RNA subunit of Escherichia coli. The guide sequence is specific for an RNA target, which is subsequently cleaved by the bacterial M1 RNA moiety. These approaches are applicable in both bacteria and eukaryotes. In this review, we will discuss the two technologies in which RNase P is used to reduce RNA expression levels.