Advanced Delivery Systems Research Articles

Nanoparticle-mediated systemic delivery of siRNA for treatment of cancers and viral infections.

RNA interference (RNAi) is an endogenous post-transcriptional gene regulatory mechanism, where non-coding, double-stranded RNA molecules interfere with the expression of certain genes in order to silence it. Since its discovery, this phenomenon has evolved as powerful technology to diagnose and treat diseases at cellular and molecular levels. With a lot of attention, short interfering RNA (siRNA) therapeutics has brought a great hope for treatment of various undruggable diseases, including genetic diseases, cancer, and resistant viral infections. However, the challenge of their systemic delivery and on how they are integrated to exhibit the desired properties and functions remains a key bottleneck for realizing its full potential. Nanoparticles are currently well known to exhibit a number of unique properties that could be strategically tailored into new advanced siRNA delivery systems. This review summarizes the various nanoparticulate systems developed so far in the literature for systemic delivery of siRNA, which include silica and silicon-based nanoparticles, metal and metal oxides nanoparticles, carbon nanotubes, graphene, dendrimers, polymers, cyclodextrins, lipids, hydrogels, and semiconductor nanocrystals. Challenges and barriers to the delivery of siRNA and the role of different nanoparticles to surmount these challenges are also included in the review.

A microfluidic reciprocating intracochlear drug delivery system with reservoir and active dose control

Reciprocating microfluidic drug delivery, as compared to steady or pulsed infusion, has unique features which may be advantageous in many therapeutic applications. We have previously described a device, designed for wearable use in small animal models, that periodically infuses and then withdraws a sub-microliter volume of drug solution to and from the endogenous fluid of the inner ear. This delivery approach results in zero net volume of liquid transfer while enabling mass transport of compounds to the cochlea by means of diffusion and mixing. We report here on an advanced wearable delivery system aimed at further miniaturization and complex dosing protocols. Enhancements to the system include the incorporation of a planar micropump to generate reciprocating flow and a novel drug reservoir that maintains zero net volume delivery and permits programmable modulation of the drug concentration in the infused bolus. The reciprocating pump is fabricated from laminated polymer films and employs a miniature electromagnetic actuator to meet the size and weight requirements of a head-mounted in vivo guinea pig testing system. The reservoir comprises a long microchannel in series with a micropump, connected in parallel with the reciprocating flow network. We characterized in vitro the response and repeatability of the planar pump and compared the results with a lumped element simulation. We also characterized the performance of the reservoir, including repeatability of dosing and range of dose modulation. Acute in vivo experiments were performed in which the reciprocating pump was used to deliver a test compound to the cochlea of anesthetized guinea pigs to evaluate short-term safety and efficacy of the system. These advances are key steps toward realization of an implantable device for long-term therapeutic applications in humans.

Development of a Novel Nanoparticle-based Therapeutic Vaccine for Breast Cancer Immunotherapy

Nanoparticles (NPs) have great potential as advanced delivery systems for cancer immunotherapy. PEGylated-Poly- lactide-co-glycolic acid-based (PLGA-PEG) NPs were prepared by double-emulsion solvent evaporation technique, using ovalbumin (OVA) as a model antigen. Glycol Chitosan and block co-polymer Pluronic F127 were used in order to best attain the most efficient parameters for cancer immunotherapy. OVA-loaded PLGA-PEG NPs presented a narrow size distribution with an average size of 167nm witha polidisperity index (PdI)0.167 and zeta potential values close to neutrality (-1.66mV), which is desired for a particulate cancer vaccine to overcome their premature capture by macrophages. The encapsulation efficiency (EE) and loading capacity (LC) of these NPs were 57.5% and 29μg/mg, respectively. PLGA-PEG NPs modified with Pluronic F127 presented slightly higher Z- Average (180nm with a PdI 0.18), and ZP (ZP -1.78mV), but lower EE and LC (32% and 16μg/mg). The effect of NPs on dendritic cell viabilitywas evaluated using Alamar Blue® assays.

Three-Fingered RAVERs: Rapid Accumulation of Variations in Exposed Residues of Snake Venom Toxins

Three-finger toxins (3FTx) represent one of the most abundantly secreted and potently toxic components of colubrid (Colubridae), elapid (Elapidae) and psammophid (Psammophiinae subfamily of the Lamprophidae) snake venom arsenal. Despite their conserved structural similarity, they perform a diversity of biological functions. Although they are theorised to undergo adaptive evolution, the underlying diversification mechanisms remain elusive. Here, we report the molecular evolution of different 3FTx functional forms and show that positively selected point mutations have driven the rapid evolution and diversification of 3FTx. These diversification events not only correlate with the evolution of advanced venom delivery systems (VDS) in Caenophidia, but in particular the explosive diversification of the clade subsequent to the evolution of a high pressure, hollow-fanged VDS in elapids, highlighting the significant role of these toxins in the evolution of advanced snakes. We show that Type I, II and III α-neurotoxins have evolved with extreme rapidity under the influence of positive selection. We also show that novel Oxyuranus/Pseudonaja Type II forms lacking the apotypic loop-2 stabilising cysteine doublet characteristic of Type II forms are not phylogenetically basal in relation to other Type IIs as previously thought, but are the result of secondary loss of these apotypic cysteines on at least three separate occasions. Not all 3FTxs have evolved rapidly: κ-neurotoxins, which form non-covalently associated heterodimers, have experienced a relatively weaker influence of diversifying selection; while cytotoxic 3FTx, with their functional sites, dispersed over 40% of the molecular surface, have been extremely constrained by negative selection. We show that the a previous theory of 3FTx molecular evolution (termed ASSET) is evolutionarily implausible and cannot account for the considerable variation observed in very short segments of 3FTx. Instead, we propose a theory of Rapid Accumulation of Variations in Exposed Residues (RAVER) to illustrate the significance of point mutations, guided by focal mutagenesis and positive selection in the evolution and diversification of 3FTx.

The physicochemical/thermodynamic balance of advanced drug liposomal delivery systems

The aim of this work is to study the morphological characteristics via fractal analysis and the alterations of the thermotropic behavior of dipalmitoylphosphatidylcholine (DPPC) liposomes, caused by the incorporation of cholesterol, poly(amidoamine) (PAMAM) dendrimer, and MPOx (poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline)) gradient block copolymer (9:1 molar ratio). A gamut of light scattering techniques and differential scanning calorimetry were used in order to extract information on the morphological (in different dispersion media) and thermodynamic characteristics of liposomal drug nanocarriers, respectively. The vesicles’ structure of liposomes has a different thermodynamic content, which corresponds to a different thermotropic behavior, in comparison to pure lipid bilayers. The observed metastable phase only for DPPC liposomes has been considered as a “physical impurity”, which leads to “physical incompatibility” and consequently promotes the aggregation of DPPC liposomes in aqueous media. The incorporation of biomaterials such as PAMAM G4 and MPOx, caused alterations in the thermotropic behavior of DPPC liposomes affecting only the main transition specific enthalpy ΔH. All the other calorimetric parameters remained unaltered. These findings supported the hypothesis that the exceptional stability and transition cooperativity of the chimeric liposomal membrane might be due to the reduction of the vesicle size with the smaller membrane curvature that is indicated by the fractal dimensionality of the system. In conclusion, the results from the thermal analysis of the liposomal systems were in line with the picture of their structural characteristics, as indicated by the interplay between physicochemical and thermodynamical parameters, which determines their fractal morphology.

An injectable hydrogel incorporating mesenchymal precursor cells and pentosan polysulphate for intervertebral disc regeneration

Intervertebral disc (IVD) degeneration is one of the leading causes of lower back pain and a major health problem worldwide. Current surgical treatments include excision or immobilisation, with neither approach resulting in the repair of the degenerative disc. As such, a tissue engineering-based approach in which stem cells, coupled with an advanced delivery system, could overcome this deficiency and lead to a therapy that encourages functional fibrocartilage generation in the IVD. In this study, we have developed an injectable hydrogel system based on enzymatically-crosslinked polyethylene glycol and hyaluronic acid. We examined the effects of adding pentosan polysulphate (PPS), a synthetic glycosaminoglycan-like factor that has previously been shown (in vitro and in vivo) to this gel system in order to induce chondrogenesis in mesnchymal precursor cells (MPCs) when added as a soluble factor, even in the absence of additional growth factors such as TGF-β. We show that both the gelation rate and mechanical strength of the resulting hydrogels can be tuned in order to optimise the conditions required to produce gels with the desired combination of properties for an IVD scaffold. Human immunoselected STRO-1+ MPCs were then incorporated into the hydrogels. They were shown to retain good viability after both the initial formation of the gel and for longer-term culture periods in vitro. Furthermore, MPC/hydrogel composites formed cartilage-like tissue which was significantly enhanced by the incorporation of PPS into the hydrogels, particularly with respect to the deposition of type-II-collagen. Finally, using a wild-type rat subcutaneous implantation model, we examined the extent of any immune reaction and confirmed that this matrix is well tolerated by the host. Together these data provide evidence that such a system has significant potential as both a delivery vehicle for MPCs and as a matrix for fibrocartilage tissue engineering applications.

Toward an Impairment Metric for Stereoscopic Video: A Full-Reference Video Quality Metric to Assess Compressed Stereoscopic Video

The quality assessment of impaired stereoscopic video is a key element in designing and deploying advanced immersive media distribution platforms. A widely accepted quality metric to measure impairments of stereoscopic video is, however, still to be developed. As a step toward finding a solution to this problem, this paper proposes a full reference stereoscopic video quality metric to measure the perceptual quality of compressed stereoscopic video. A comprehensive set of subjective experiments is performed with 14 different stereoscopic video sequences, which are encoded using both the H.264 and high efficiency video coding compliant video codecs, to develop a subjective test results database of 116 test stimuli. The subjective results are analyzed using statistical techniques to uncover different patterns of subjective scoring for symmetrically and asymmetrically encoded stereoscopic video. The subjective result database is subsequently used for training and validating a simple but effective stereoscopic video quality metric considering heuristics of binocular vision. The proposed metric performs significantly better than state-of-the-art stereoscopic image and video quality metrics in predicting the subjective scores. The proposed metric and the subjective result database will be made publicly available, and it is expected that the proposed metric and the subjective assessments will have important uses in advanced 3D media delivery systems.

Lycopene from Tomatoes: Vesicular Nanocarrier Formulations for Dermal Delivery

This experimental work aimed to develop a simple, fast, economic, and environmentally friendly process for the extraction of lycopene from tomato and incorporate this lycopene-rich extract into ultradeformable vesicular nanocarriers suitable for topical application. Lycopene extraction was conducted without a cosolvent for 30 min. The extracts were analyzed and incorporated in transfersomes and ethosomes. These formulations were characterized, and the cellular uptake was observed by confocal microscopy. Dermal delivery of lycopene formulations was tested under in vitro and in vivo conditions. Lycopene extraction proved to be quite safe and selective. The vesicular formulation was taken up by the cells, being more concentrated around the nucleus. Epicutaneous application of lycopene formulations decreased the level of anthralin-induced ear swelling by 97 and 87%, in a manner nonstatistically different from the positive control. These results support the idea that the lycopene-rich extract may be a good alternative to the expensive commercial lycopene for incorporation into advanced topical delivery systems.

Advanced Subcompartmentalized Microreactors: Polymer Hydrogel Carriers Encapsulating Polymer Capsules and Liposomes

The design of compartmentalized carriers for advanced drug delivery systems or artificial cells and organelles is of interest for biomedical applications. Herein, a polymer carrier microreactor that contains two different classes of subcompartments, multilayered polymer capsules and liposomes, is presented. 50 nm-diameter liposomes and 300 nm-diameter polymer capsules are encapsulated into a larger polymer carrier capsule, demonstrating control over the spatial positioning of the subcompartments, which are either 'membrane-associated' or 'free-floating' in the aqueous interior. Selective and spatially dependent degradation of the 300 nm-diameter subcompartments (without destroying the structural integrity of the enzyme-loaded liposomes) is also shown, by performing an encapsulated enzymatic reaction using the liposomal subcompartments. These findings cover several important aspects toward the development of engineered compartmentalized carrier vessels for the creation of artificial cell mimics or advanced therapeutic delivery systems.

Matrix-Embedded Cytokines to Simulate Osteoarthritis-Like Cartilage Microenvironments

In vivo, cytokines noncovalently bind to the extracellular matrix (ECM), to facilitate intimate interactions with cellular receptors and potentiate biological activity. Development of a biomaterial that simulates this type of physiological binding and function is an exciting proposition for designing controlled advanced delivery systems for simulating in vivo conditions in vitro. We have decorated silk protein with sulfonated moieties through diazonium coupling reactions to noncovalently immobilize pro-inflammatory cytokines interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in such a biomimetic manner. After adsorption of the cytokines to the diazonium-modified silk matrix, constant release of cytokines up to at least 3 days was demonstrated, as an initial step to simulate an osteoarthritic (OA) microenvironment in vitro. Matrix-embedded cytokines induced the formation of multiple elongated processes in chondrocytes in vitro, akin to what is seen in OA cartilage in vivo. Gene expression profiles with this in vitro tissue model of OA showed significant similarities to profiles from explanted OA cartilage tissues collected from patients who underwent total knee replacement surgery. The common markers of OA, including COL, MMP, TIMP, ADAMTS, and metallothioneins, were upregulated at least 35-fold in the in vitro model when compared to the control-non-OA in vitro generated tissue-engineered cartilage. The microarray data were validated by reverse transcriptase-polymerase chain reaction. Mechanistically, protein interaction studies indicated that TNF-α and IL-1β synergistically controlled the equilibrium between MMPs and their inhibitors, TIMPs, resulting in ECM degradation through the MAPK pathway. This study offers a promising initial step toward establishing a relevant in vitro OA disease model, which can be further modified to assess signaling mechanisms, responses to cell or drug treatments and patient-specific features.

Increasing Student Responsibility And Active Learning In An Undergraduate Capstone Finance Course

This paper focuses on the effectiveness of factors in designing and delivering a complex, capstone course in an undergraduate major in finance. The course uses an instructional delivery system that is contrasted to the standard lecture format and has a broader set of objectives than is usually specified for a finance course. An objective of the instructional design of the course is to harness student responsibility while making them more active participants in the delivery of the content. The goal is to equip them to solve the typical non-structured problems they will deal with in their professional careers. The effect of these factors is measured by analyzing this course compared to all other finance courses taken. The outcomes of this paper show that this method is superior to the standard lecture method across a variety of scales. This provides insight into the future development of this method for this type of course, as well as ideas for developing other advanced instructional delivery systems for similar complex courses.

Liposomes-in-Hydrogel Delivery System with Mupirocin:In VitroAntibiofilm Studies andIn VivoEvaluation in Mice Burn Model

Previously, we have proposed mupirocin-in-liposomes-in-hydrogel delivery system as advanced delivery system with the potential in treatment of burns. In the current studies, we evaluated the system for its cytotoxicity, ability to prevent biofilm formation, act on the mature biofilms, and finally determined its potential as wound treatment in in vivo mice burn model. The system was found to be nontoxic against HaCaT cells, that is, keratinocytes. It was safe for use and exhibited antibiofilm activity against S. aureus biofilms, although the activity was more significant against planktonic bacteria and prior to biofilm formation than against mature biofilms as shown in the resazurin and the crystal violet assays. An in vivo mice burn model was used to evaluate the biological potential of the system and the healing of burns observed over 28 days. The in vivo data suggest that the delivery system enhances wound healing and is equally potent as the marketed product of mupirocin. Histological examination showed no difference in the quality of the healed scar tissue, whereas the healing time for the new delivery system was shorter as compared to the marketed product. Further animal studies and development of more sophisticated in vivo model are needed for complete evaluation.

Gene therapy enters the pharma market: The short story of a long journey

Approximately 20 years ago, gene therapy was first introduced when Michael Blaese and colleagues applied ex vivo modified autologous T cells to children suffering from adenosine deaminase deficiency (ADA‐SCID), a Mendelian genetic error that causes severe combined immunodeficiency syndrome (Blaese et al, 1995). The investigators used retroviral vectors; the most advanced gene delivery system at that time. They transferred a normal copy of adenosine deaminase that, according to the intrinsic features of retroviruses, stably integrated into the cellular genome. While this study demonstrated a proof of concept, years of tremendous efforts both in basic and translational research followed before the first clear evidence for a cure of SCID patients through gene therapy could be reported (Cavazzana‐Calvo et al, 2012). In November 2012, the European Commission has granted marketing authorization for the first gene‐therapy medicine. . . Now gene therapy in Europe has taken the next step. In November 2012, the European Commission has granted marketing authorization for the first gene‐therapy medicine, Glybera® (alipogene tiparvovec), in all 27 European Union member states (http://www.uniqure.com). Glybera has been developed by uniQure (former Amsterdam Molecular Therapeutics) for the treatment of patients with familial lipoprotein lipase deficiency (LPLD, synonym: type I hyperlipidaemia). LPLD is an ultra‐rare disease with a prevalence of 1–2 in 106 individuals in the general populations (Brunzell, 1999). It is an autosomal recessive disease found in all ethnic groups and it is caused by mutations in the LPL gene (chromosome 8p21.3). This gene encodes lipoprotein lipase (LPL), a key enzyme in the catabolism of triglyceride (TG)‐rich lipoproteins that is secreted from adipocytes and muscle cells. In LPLD, TG‐rich lipoproteins accumulate in the plasma leading to chylomicronemia and severe hypertriglyceridemia (TG concentration > 20 mmol/L). The latter causes episodes of abdominal pain, recurrent acute and potentially life‐threatening pancreatitis, eruptive cutaneous xanthomata and hepatosplenomegaly (Brunzell, …

Nanoparticle-based vaccine delivery for cancer immunotherapy.

Development of nano-sized carriers including nanoparticles, nanoemulsions or liposomes holds great potential for advanced delivery systems for cancer immunotherapy, as such nanostructures can be used to more effectively manipulate or deliver immunologically active components to specific target sites. Successful development of nanotechnology based platform in the field of immunotherapy will allow the application of vaccines, adjuvants and immunomodulatory drugs that improve clinical outcomes for immunological diseases. Here, we review current nanoparticle-based platforms in the efficacious delivery of vaccines in cancer immunotherapy.

Positron Emission Tomography (PET) Imaging of Small Interfering RNA (siRNA) Delivery in Drug Development

Pharmacokinetic studies of nanoparticles have provided significant information by which advanced delivery systems have been designed. On the other hand, pharmacokinetics of RNA interference (RNAi) effectors such as small interfering RNA (siRNA) is poorly understood. We have synthesized [(18)F]-labeled siRNA for a pharmacokinetic study using positron emission tomography (PET). PET is a noninvasive bioimaging modality applicable to a microdosing study that is designed to evaluate pharmacokinetics of drug candidates in human at an early stage of drug development. We have demonstrated that the resulting PET images clearly show the biodistribution of siRNA in mice. Naked [(18)F]-siRNA accumulates in the bladder immediately after intravenous administration due to rapid degradation. [(18)F]-siRNA formulated in cationic liposomes rapidly accumulates in the lungs due to positive surface charge of the cationic liposomes. [(18)F]-siRNA formulated in PEGylated liposomes shows long circulation in the bloodstream. Thus, the biodistribution of [(18)F]-siRNA is reflected by the characteristics of each liposomal biodistribution. Importantly, it has been demonstrated that accumulation of siRNA in tumors is able to be evaluated using [(18)F]-siRNA/PET. In addition, [(18)F]-siRNA/PET is also found to be useful to evaluate the effect of chemical modification of siRNA on its biodistribution. Cholesterol-conjugated [(18)F]-siRNA shows long half-life in the bloodstream and accumulates in the liver compared with naked [(18)F]-siRNA. Our findings indicate that the pharmacokinetic PET study of siRNA provides important insights into the development of RNAi medicine.

Improved Burns Therapy: Liposomes‐in‐Hydrogel Delivery System for Mupirocin

Wounds, particularly burns, are prone to colonization of potentially life-threatening bacteria. Local delivery of antimicrobial agents in sufficient quantities and over longer period of time can reduce risk of burn infections. Mupirocin-in-liposomes-in-hydrogels were proposed as advanced delivery system for improved burn therapy. Mupirocin was entrapped in phosphatidylcholine liposomes of various sizes, namely larger (micron size) vesicles entrapping 74% of drug and sonicated vesicles (below 300 nm) entrapping 49% of drug. Liposomes containing mupirocin were incorporated in chitosan hydrogels (10%, w/w). Incorporation of liposomes in hydrogels resulted in prolonged release of liposomally associated mupirocin, as observed in both in vitro and ex vivo studies. The drug release was affected by the vesicle size. Microbiological evaluation of newly developed system confirmed its antimicrobial potential against Staphylococcus aureus and Bacillus subtilis. Bioadhesiveness of the system was compared with the marketed cream containing mupirocin. Our system exhibited superior bioadhesiveness and sustained mupirocin release profiles to marketed product.

Nanoparticles Improve Biological Functions of Phthalocyanine Photosensitizers Used for Photodynamic Therapy

Photodynamic therapy (PDT) is a new technology using photodynamic effect for disease diagnosis and treatment. It is a two-step technique involving the uptake of a photosensitizer by cancer tissue followed by light irradiation that excites the photosensitizer to produce highly reactive oxygen species, the latter execute apoptosis of cancerous cells. As a second-generation of photosensitizers, phthalocyanine demonstrates higher absorption in the 650-800 nm range and short tissue accumulation compared to their first generation. However, many potent phthalocyanine photosensitizers are hydrophobic and poorly water-soluble, which limit their therapeutic applications. As a result, advanced delivery systems and different strategies are called for to improve the effectiveness of PDT. Facts have proved that using nanoparticles as carries of photosensitizers is a very promising route. Nanoparticles have the potentials to increase photosensitizers' aqueous solubility, bioavailability and stability, and deliver photosensitizers to the target tissues. This article reviewed the commonly-used nanoparticles, including colloid gold, quantum dots, paramagnetic nanoparticles, silica-based materials, polymer-based nanoparticles, as potential delivery systems for phthalocyanine photosensitizers, and summarized the improved biological functions of phthalocyanine photosensitizers in PDT.

Leishmaniasis: Prevention, Parasite Detection and Treatment

Leishmaniasis remains a public health problem worldwide, affecting approximately 12 million people in 88 countries; 50 000 die of it each year. The disease is caused by Leishmania, obligate intracellular vector-borne parasites. In spite of its huge health impact on the populations in vast areas, leishmaniasis is one of the most neglected diseases. No safe and effective vaccine currently exists against any form of human leishmaniasis. The spectrum and efficacy of available antileishmanial drugs are also limited. First part of this review discusses the approaches used for the vaccination against leishmaniasis that are based on the pathogen and includes virulent or attenuated parasites, parasites of related nonpathogenic species, whole killed parasites, parasites' subunits, DNA vaccines, and vaccines based on the saliva or saliva components of transmitting phlebotomine vector. Second part describes parasite detection and quantification using microscopy assays, cell cultures, immunodetection, and DNA-based methods, and shows a progress in the development and application of these techniques. In the third part, first-line and alternative drugs used to treat leishmaniasis are characterized, and pre-clinical research of a range of natural and synthetic compounds studied for the leishmanicidal activity is described. The review also suggests that the application of novel strategies based on advances in genetics, genomics, advanced delivery systems, and high throughput screenings for leishmanicidal compounds would lead to improvement of prevention and treatment of this disease.

The Use of Solid Supports to Generate Nucleic Acid Carriers

Nucleic acids are the foundation stone of all cellular processes. Consequently, the use of DNA or RNA to treat genetic and acquired disorders (so called gene therapy) offers enormous potential benefits. The restitution of defective genes or the suppression of malignant genes could target a range of diseases, including cancers, inherited diseases (cystic fibrosis, muscular dystrophy, etc.), and viral infections. However, this strategy has a major barrier: the size and charge of nucleic acids largely restricts their transit into eukaryotic cells. Potential strategies to solve this problem include the use of a variety of natural and synthetic nucleic acid carriers. Driven by the aim and ambition of translating this promising therapeutic approach into the clinic, researchers have been actively developing advanced delivery systems for nucleic acids for more than 20 years. A decade ago we began our investigations of solid-phase techniques to construct families of novel nucleic acid carriers for transfection. We envisaged that the solid-phase synthesis of polycationic dendrimers and derivatized polyamimes would offer distinct advantages over solution phase techniques. Notably in solid phase synthesis we could take advantage of mass action and streamlined purification procedures, while simplifying the handling of compounds with high polarities and plurality of functional groups. Parallel synthesis methods would also allow rapid access to libraries of compounds with improved purities and yields over comparable solution methodologies and facilitate the development of structure activity relationships. We also twisted the concept of the solid-phase support on its head: we devised miniaturized solid supports that provided an innovative cell delivery vehicle in their own right, carrying covalently conjugated cargos (biomolecules) into cells. In this Account, we summarize the main outcomes of this series of chemically related projects.

The promise, pitfalls and progress of RNA-interference-based antiviral therapy for respiratory viruses

Advances in the understanding of RNA biological processing and control are leading to new concepts in human therapeutics with practical implications for many human diseases, including antiviral therapy of respiratory viruses. So-called 'non-coding RNA' exerts specific and profound functional control on regulation of protein production and indeed controls the expression of all genes through processes collectively known as RNA interference (RNAi). RNAi is a naturally occurring intracellular process that regulates gene expression through the silencing of specific messenger RNAs (mRNAs). Methods are being developed that allow the catalytic degradation of targeted mRNAs using specifically designed complementary small interfering RNAs (siRNA). siRNAs are now being chemically modified and packaged into advanced delivery systems so as to acquire drug-like properties and the ability to deliver their effects systemically. Recent in vivo studies have provided proofs of the concept that RNAi may be useful therapeutically. Much of the design of these siRNAs can be accomplished bioinformatically, thus potentially expediting drug discovery and opening new avenues of therapy for many uncommon, orphan, or emerging diseases. Theoretically, any disease that can be ameliorated through knockdown of any endogenous or exogenous protein is a potential therapeutic target for RNAi-based therapeutics. Lung diseases in general are attractive targets for RNAi therapeutics, since the location of affected cells increases their accessibility to topical administration of siRNA, and respiratory viral infections are particularly attractive targets for RNAi-based drug discovery and development. RNAi therapeutics have been shown to exert potent antiviral effects against respiratory syncytial virus (RSV), parainfluenza, influenza, coronaviruses, measles and human metapneumoviruses in vitro and in vivo. Recently, a double-blind placebo-controlled clinical trial of an RNAi-based therapeutic against RSV demonstrated that this technology has therapeutic activity, representing the first proof-of-concept test of efficacy for RNAi's therapeutic effect in humans. This review discusses the science behind RNAi and the potential practical issues in applying this technology to various respiratory viral diseases.