Novel non-endocytic delivery of antisense oligonucleotides

Antisense Oligonucleotide (AS-ODN) Technology: Principle, Mechanism and Challenges

Recently, there is a hopefully tremendous interest in antisense therapeutics for clinical purposes. Single-stranded synthetic antisense oligonucleotides (As-ODNs) with monomers of chemically modified 18-21 deoxynucleotides complement the mRNA sequence in target gene. The target gene expression can be blocked because of created cleavage or disability of the mRNA by binding the As-ODNs to cognate mRNA sequences via sequence-specific hybridization. The idea of antisense therapy has become particular concerning that any sequence longer than a minimal number of nucleotides (17 for DNA and 13 for RNA) can be observed only once within the human genome. The mRNA is omnipresent more probably to manipulate compared to DNA, which results in multiple in vitro and in vivo applications for As-ODNs in the field of regulatory mechanisms of biological processes, cancer, viral infections and hereditary impairments. Although, there are uncertain clinical outcomes on the ability of this approach in treatment procedures despite achieving promising findings based on previous investigations. Accordingly, the efficacy, off-target effects, delivery are issues that should be investigated to obtain satisfactory results. In this review, we will explain the mechanism of action of As-ODNs and various types of modifications and their therapeutic purposes. This article is protected by copyright. All rights reserved.

Structure-activity relationship of serotonin derived tocopherol lipids

Tocopherol-based lipids are widely used for nucleic acid delivery. Using tocopherol molecules, we designed and synthesized 5-HT functionalized lipids by tethering 5-hydroxytryptamine (5-HT), a small molecule ligand as the head group to a natural amphiphilic molecule namely α-tocopherol (Vitamin E). This is with the aim of delivering nucleic acids specifically into cells expressing the serotonin receptors (5-hydroxytryptamine[5-HT]) which are abundant in the central nervous system. In order to achieve target recognition, we adopted an approach wherein two structurally different lipid molecules having serotonin as the head group was conjugated to tocopherol via different linkers thus generating lipids with either free -NH₂ or -OH moiety. The corresponding lipids designated as Lipid A (Tocopheryl carbonate serotonin-NH₂) and Lipid B (Tocopheryl 2-hydroxy propyl ammonium serotonin-OH), were formulated with co-lipids 1,2-dioleoyl-sn-glycero-3-phosphatidyl-ethanolamine (DOPE) and 1,2-dioleoyl-sn-glycero-sn-3-phosphatidylcholine (DOPC) and evaluated for their ability to deliver plasmid DNA through reporter gene expression assays in vitro. Furthermore, the physicochemical characteristics and cellular interactions of the formulations were examined using serotonin-receptor enriched cells in order to distinguish the structural and functional attributes of both lipids. Cell-based gene expression studies reveal that in comparison to Lipid A, a formulation of Lipid B prepared with DOPE as the co-lipid, contributes to efficient uptake leading to significant enhancement in transfection. Specific interactions explored by molecular docking studies suggests the role of the hydroxyl moiety and the enantiospecific significance of serotonin- conjugated tocopherol lipids in recognizing these receptors thus signifying a promising lipid-based approach to target the serotonin receptors in the central nervous system.

Particle size affects the cytosolic delivery of membranotropic peptide-functionalized platinum nanozymes

Delivery of therapeutic agents inside the cytosol, avoiding the confinement in endo-lysosomal compartments and their degradative environment, is one of the key targets of nanomedicine to gain the maximum remedial effects. Current approaches based on cell penetrating peptides (CPPs), despite improving the cellular uptake efficiency of nanocarriers, have shown controversial results in terms of intracellular localization. To elucidate the delivery potential of CPPs, in this work we analyzed the role of the particle size in influencing the ability of a membranotropic peptide, namely gH625, to escape the endo-lysosomal pathway and deliver the particles in the cytosol. To this aim, we carried out a systematic assessment of the cellular uptake and distribution of monodisperse platinum nanoparticles (PtNPs), having different diameters (2.5, 5 and 20 nm) and citrate capping or gH625 peptide functionalization. The presence of gH625 significantly increased the amount of internalized NPs in human cervix epithelioid carcinoma cells, as a function of particle size. However, scanning transmission electron microscopy (STEM) and electron tomography (ET) revealed a prevalent confinement of PtNPs within vesicular structures, regardless of the particle size and surface functionalization. Only in the case of the smallest 2.5 nm particles, the membranotropic peptide was able to partly maintain its functionality, enabling cytosolic delivery of a small fraction of internalized PtNPs, though particle agglomeration in culture medium limited single-particle transport across the cell membrane. Interestingly, membrane crossing by 2.5 nm functionalized-PtNPs seemed to occur by diffusion through the lipid bilayer, with no apparent membrane damage. For larger particle sizes (≥5 nm), their hindrance likely blocked the membranotropic mechanism. Combining the enhanced uptake and partial cytosolic delivery promoted by gH625, we were able to achieve a strong improvement of the antioxidant nanozyme function of 2.5 nm PtNPs, decreasing both the endogenous ROS level and its overproduction following an external oxidative insult.

Simultaneous Imaging of Three Tumor-Related mRNAs in Living Cells with a DNA Tetrahedron-Based Multicolor Nanoprobe

We constructed a DNA tetrahedron based multicolor nanoprobe, which could simultaneously imaging of three tumor-related mRNAs in living cells through fluorescence restoration caused by competitive chain replacement reaction. The oligonucleotides used to construct the tetrahedron were extended by adding three 21-base recognition sequences modified with different fluorophores (FAM, Cy3, and Cy5) in the 5' end. Three 11-base complementary sequences modified with quencher (BHQ1 for FAM and BHQ2 for Cy3 and Cy5) were hybridized with the recognition sequences to quench the fluorescence. In the presence of the specific mRNA targets, the recognition sequences hybridized with the targets to form longer duplexes and the fluorescence was restored. Compared with previously reported nanoprobes based on DNA tetrahedron, the multicolor nanoprobe can effectively avoid false positive results.

What's Next for Gastrointestinal Disorders: No Needles?

A myriad of pathologies affect the gastrointestinal tract, citing this affected area as a significant target for therapeutic intervention. One group of therapeutic agents, antisense and oligonucleotides and small interfering RNAs, offer a promising platform for treating a wide variety of diseases ranging from cancer to auto-immune diseases. Current delivery methods are carried out either systemically or locally into diseased areas, both of which involve needles. The challenge in orally administering this type of treatment lies in the complications that arise due to the vast environmental extremes found within the gastrointestinal tract, owing to the fact that, as the drug travels down the gastrointestinal tract, it is subjected to pH changes and interactions with bacteria and a variety of digestive and protective enzymes including proteases, DNAses, and RNAses. Overcoming these challenges to allow the practical application of these drugs is a priority that has invoked a multitude of research in the chemical, biological, and material sciences. In this review, we will address common gastrointestinal pathologies, the barriers to oral-based therapies and antisense-interfering technologies, the approaches that have already been applied for their delivery, and the current status of antisense drug therapy clinical trials for gastrointestinal-related disorders.

TAT and HA2 facilitate cellular uptake of gold nanoparticles but do not lead to cytosolic localisation

The methods currently available to deliver functional labels and drugs to the cell cytosol are inefficient and this constitutes a major obstacle to cell biology (delivery of sensors and imaging probes) and therapy (drug access to the cell internal machinery). As cell membranes are impermeable to most molecular cargos, viral peptides have been used to bolster their internalisation through endocytosis and help their release to the cytosol by bursting the endosomal vesicles. However, conflicting results have been reported on the extent of the cytosolic delivery achieved. To evaluate their potential, we used gold nanoparticles as model cargos and systematically assessed how the functionalisation of their surface by either or both of the viral peptides TAT and HA2 influenced their intracellular delivery. We evaluated the number of gold nanoparticles present in cells after internalisation using photothermal microscopy and their subcellular localisation by electron microscopy. While their uptake increased when the TAT and/or HA2 viral peptides were present on their surface, we did not observe a significant cytosolic delivery of the gold nanoparticles.

Therapeutic face of RNAi: in vivo challenges

INTRODUCTION

RNA interference is a sequence-specific gene silencing phenomenon in which small interfering RNAs (siRNAs) can trigger gene transcriptional and post-transcriptional silencing. This phenomenon represents an emerging therapeutic approach for in vivo studies by efficient delivery of specific synthetic siRNAs against diseases. Therefore, simultaneous development of synthetic siRNAs along with novel delivery techniques is considered as novel and interesting therapeutic challenges.

AREAS COVERED

This review provides a basic explanation to siRNA signaling pathways and their therapeutic challenges. Here, we provide a comprehensive explanation to failed and successful trials and their in vivo challenges.

EXPERT OPINION

Specific, efficient and targeted delivery of siRNAs is the major concern for their in vivo administrations. Also, anatomical barriers, drug stability and availability, immunoreactivity and existence of various delivery routes, different genetic backgrounds are major clinical challenges. However, successful administration of siRNA-based drugs is expected during foreseeable features. But, their systemic applications will depend on strong targeted drug delivery strategies.

Electroporation and microinjection successfully deliver single-stranded and duplex DNA into live cells as detected by FRET measurements

Förster resonance energy transfer (FRET) technology relies on the close proximity of two compatible fluorophores for energy transfer. Tagged (Cy3 and Cy5) complementary DNA strands forming a stable duplex and a doubly-tagged single strand were shown to demonstrate FRET outside of a cellular environment. FRET was also observed after transfecting these DNA strands into fixed and live cells using methods such as microinjection and electroporation, but not when using lipid based transfection reagents, unless in the presence of the endosomal acidification inhibitor bafilomycin. Avoiding the endocytosis pathway is essential for efficient delivery of intact DNA probes into cells.

A targeted, self-delivered, and photocontrolled molecular beacon for mRNA detection in living cells

The spatiotemporal dynamics of specific mRNA molecules are difficult to image and detect inside living cells, and this has been a significant challenge for the chemical and biomedical communities. To solve this problem, we have developed a targeted, self-delivered, and photocontrolled aptamer-based molecular beacon (MB) for intracellular mRNA analysis. An internalizing aptamer connected via a double-stranded DNA structure was used as a carrier probe (CP) for cell-specific delivery of the MB designed to signal target mRNA. A light activation strategy was employed by inserting two photolabile groups in the CP sequence, enabling control over the MB's intracellular function. After the probe was guided to the target cell via specific binding of aptamer AS1411 to nucleolin on the cell membrane, light illumination released the MB for mRNA monitoring. Consequently, the MB is able to perform live-cell mRNA imaging with precise spatiotemporal control, while the CP acts as both a tracer for intracellular distribution of the MB before photoinitiation and an internal reference for mRNA ratiometric detection.

Microprecision delivery of oligonucleotides in a 3D tissue model and its characterization using optical imaging

Despite significant potential of oligonucleotides (ONs) for therapeutic and diagnostic applications, rapid and widespread intracellular delivery of ONs in cells situated in tissues such as skin, head and neck cavity, and eye has not been achieved. This study was aimed at evaluating the synergistic combination of microneedle (MN) arrays and biochemical approaches for localized intratissue delivery of oligonucleotides in living cells in 3D tissue models. This synergistic combination was based on the ability of MNs to precisely deliver ONs into tissues to achieve widespread distribution, and the ability of biochemical agents (streptolysin O (SLO) and cholesterol conjugation to ONs) to enhance intracellular ON delivery. The results of this study demonstrate that ON probes were uniformly coated on microneedle arrays and were efficiently released from the microneedle surface upon insertion in tissue phantoms. Co-insertion of microneedles coated with ONs and SLO into 3D tissue models resulted in delivery of ONs into both the cytoplasm and nucleus of cells. Within a short incubation time (35 min), ONs were observed both laterally and along the depth of a 3D tissue up to a distance of 500 μm from the microneedle insertion point. Similar widespread intratissue distribution of ONs was achieved upon delivery of ON-cholesterol conjugates. Uniformity of ON delivery in tissues improved with longer incubation times (24 h) postinsertion. Using cholesterol-conjugated ONs, delivery of ON probes was limited to the cytoplasm of cells within a tissue. Finally, delivery of cholesterol-conjugated anti-GFP ON resulted in reduction of GFP expression in HeLa cells. In summary, the results of this study provide a novel approach for efficient intracellular delivery of ONs in tissues.

Selective stimulation of caveolae-mediated endocytosis by an osmotic polymannitol-based gene transporter

Controlling the cellular uptake mechanism and consequent intracellular route of polyplexes is important to improve the transfection efficiency of the non-viral gene delivery. Here, we report a new non-viral vector, polymannitol-based gene transporter (PMT), generated by crosslinking low molecular weight polyethylenimine with mannitol diacrylate, which has low cytotoxicity and good transfection efficiency. Interestingly, the uptake pathway of PMT/DNA complexes was shifted into caveolae-mediated endocytosis, avoiding lysosomal degradation. The mechanism of increased caveolae-mediated endocytosis of PMT/DNA complexes was found to be correlated with mechanosensing signal transduction by the hyperosmotic polymannitol part. Our results suggested that PMT, polymannitol-based gene transporter, is a safe and efficient gene delivery system with a well-modulated uptake pathway and intracellular route for gene therapy.

Radiolabeled oligonucleotides for antisense imaging

Oligonucleotides radiolabeled with isotopes emitting γ-rays (for SPECT imaging) or positrons (for PET imaging) can be useful for targeting messenger RNA (mRNA) thereby serving as non-invasive imaging tools for detection of gene expression in vivo (antisense imaging). Radiolabeled oligonucleotides may also be used for monitoring their in vivo fate, thereby helping us better understand the barriers to its delivery for antisense targeting. These developments have led to a new area of molecular imaging and targeting, utilizing radiolabeled antisense oligonucleotides. However, the success of antisense imaging relies heavily on overcoming the barriers for its targeted delivery in vivo. Furthermore, the low ability of the radiolabeled antisense oligonucleotide to subsequently internalize into the cell and hybridize with its target mRNA poses additional challenges in realizing its potentials. This review covers the advances in the antisense imaging probe development for PET and SPECT, with an emphasis on radiolabeling strategies, stability, delivery and in vivo targeting.

In vitro release characteristics and cellular uptake of poly(D,L-lactic-co-glycolic acid) nanoparticles for topical delivery of antisense oligodeoxynucleotides

The efficacy of antisense oligodeoxynucleotides (AsODNs) is compromised by their poor stability in biological fluids and the inefficient cellular uptake due to their size and negative charge. Since chemical modifications of these molecules have resulted in a number of non-antisense activities, incorporation into particulate delivery systems has offered a promising alternative. The aim of this study was to evaluate various poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles for AsODN entrapment and delivery. PLGA nanoparticles were prepared using the double emulsion solvent evaporation method. The influence of formulation parameters such as PLGA concentration and volume ratio of internal aqueous phase volume (Va1) to organic phase volume (Vo) to external aqueous phase volume (Va2) on particle size, polydispersity index (PDI) and zeta potential (ZP) was investigated using a full factorial study. The particle size increased with increasing PLGA concentrations and volume ratios, with an interaction detectable between the two factors. AsODN entrapment efficiencies ranged between 49.97% and 54.95% with no significant difference between various formulations. By fitting the in vitro release profiles to a dual first order release model it was shown that the AsODN release occurred via two processes: a diffusion controlled process in the early phase (25 to 32% within one day) and a PLGA degradation process in the latter (39 to 70% after 14 days). Cellular uptake studies using primary corneal epithelial cells suggested active transport of nanoparticles via endocytosis. PLGA nanoparticles therefore show potential to successfully entrap AsODNs, transport them into cells and release them over time due to polymer erosion.

Delivery of molecular beacons for live-cell imaging and analysis of RNA

Over the past decade, a variety of oligonucleotide-based probes have been developed that allow for direct visualization of RNA molecules in living cells. Of these, molecular beacons have garnered a particularly high degree of interest due to their simple yet exquisite unimolecular stem-loop design that allows for the efficient conversion of target recognition into a specific fluorescent signal. As a result of their favorable fluorescent enhancement and their high specificity, molecular beacons have been used for a wide range of applications, including the monitoring of RNA expression and localization in living cells, cancer cell detection, and the study of viral infections. In this chapter we describe a general methodology that can be followed for the imaging and analysis of RNA in living cells using molecular beacons. Several commonly employed methods for delivering molecular beacons into the cytosol are discussed including toxin-based cell membrane permeabilization, microinjection, and microporation. Strategies for acquiring ratiometric measurements are also described.

Cytoplasmic delivery of liposomes into MCF-7 breast cancer cells mediated by cell-specific phage fusion coat protein

Earlier, we have shown that doxorubicin-loaded liposomes (Doxil) modified with a chimeric phage fusion coat protein specific toward MCF-7 breast cancer cells identified from a phage landscape library demonstrated a significantly enhanced association with target cells and an increased cytotoxicity. Based on some structural similarities between the N-terminus of the phage potein and known fusogenic peptides, we hypothesized that, in addition to the specific targeting, the phage protein may possess endosome-escaping potential and an increased cytotoxicity of drug-loaded phage protein-targeted liposomes may be explained by an advantageous combination of both, cell targeting and endosomal escape of drug-loaded nanocarrier. The use of the fluorescence resonance energy transfer (FRET) technique allowed us to clearly demonstrate the pH-dependent membrane fusion activity of the phage protein. Endosomal escape and cytosolic delivery of phage-liposomes was visualized with fluorescence microscopy. Endosome acidification inhibition by bafilomycin A 1 resulted in decreased cytotoxicity of the phage-Doxil, while the endosome disruption by chloroquine had a negligible effect on efficacy of phage-Doxil, confirming its endosomal escape. Our results demonstrated an endosome-escaping property of the phage protein and provided an insight on mechanism of the enhanced cytotoxicity of phage-Doxil.

NANOSTRUCTURED PROBES FOR IN VIVO GENE DETECTION

The ability to visualize in real-time the expression dynamics and localization of specific RNAs in vivo offers tremendous opportunities for biological and disease studies including cancer detection. However, quantitative methods such as real-time PCR and DNA microarrays rely on the use of cell lysates thus not able to obtain important spatial and temporal information. Fluorescence proteins and other reporter systems cannot image endogenous RNA in living cells. Fluorescence in situ hybridization (FISH) assays require washing to achieve specificity, therefore can only be used with fixed cells. Here we review the recent development of nanostructured probes for living cell RNA detection, and discuss the biological and engineering issues and challenges of quantifying gene expression in vivo. In particular, we describe methods that use oligonucleotide probes, combined with novel delivery strategies, to image the relative level, localization and dynamics of RNA in live cells. Examples of detecting endogenous mRNAs, as well as imaging their subcellular localization are given to illustrate the biological applications, and issues in probe design, delivery and target accessibility are discussed. The nanostructured probes promise to open new and exciting opportunities in sensitive gene detection for a wide range of biological and medical applications.

Gold nanoparticles delivery in mammalian live cells: a critical review

Functional nanomaterials have recently attracted strong interest from the biology community, not only as potential drug delivery vehicles or diagnostic tools, but also as optical nanomaterials. This is illustrated by the explosion of publications in the field with more than 2,000 publications in the last 2 years (4,000 papers since 2000; from ISI Web of Knowledge, 'nanoparticle and cell' hit). Such a publication boom in this novel interdisciplinary field has resulted in papers of unequal standard, partly because it is challenging to assemble the required expertise in chemistry, physics, and biology in a single team. As an extreme example, several papers published in physical chemistry journals claim intracellular delivery of nanoparticles, but show pictures of cells that are, to the expert biologist, evidently dead (and therefore permeable). To attain proper cellular applications using nanomaterials, it is critical not only to achieve efficient delivery in healthy cells, but also to control the intracellular availability and the fate of the nanomaterial. This is still an open challenge that will only be met by innovative delivery methods combined with rigorous and quantitative characterization of the uptake and the fate of the nanoparticles. This review mainly focuses on gold nanoparticles and discusses the various approaches to nanoparticle delivery, including surface chemical modifications and several methods used to facilitate cellular uptake and endosomal escape. We will also review the main detection methods and how their optimum use can inform about intracellular localization, efficiency of delivery, and integrity of the surface capping.

Fluorescent probes for live-cell RNA detection

Commonly used techniques for analyzing gene expression, such as polymerase chain reaction (PCR), microarrays, and in situ hybridization, have proven invaluable in understanding RNA processing and regulation. However, these techniques rely on the use of lysed and/or fixed cells and are therefore limited in their ability to provide important spatial-temporal information. This has led to the development of numerous techniques for imaging RNA in living cells, some of which have already provided important insight into the dynamic role RNA plays in dictating cell behavior. Here we review the fluorescent probes that have allowed for RNA imaging in living cells and discuss their utility and limitations. Common challenges faced by fluorescent probes, such as probe design, delivery, and target accessibility, are also discussed. It is expected that continued advancements in live cell imaging of RNA will open new and exciting opportunities in a wide range of biological and medical applications.

Microinjection as a tool of mechanical delivery

Microinjection to single cells has been widely used in the studies of transduction-challenged cells, transgenic animal production, and in vitro fertilization to mechanically transfer DNAs, RNA interferences, sperms, proteins, peptides, and drugs. The advantages of microinjection include the precision of delivery dosage and timing, high efficiency of transduction as well as low cytotoxicity. However, manual microinjection is labor intensive and time consuming, which limits the application of this technique to large number of cells in a sample. New cell culture matrix ensuring all cells grow in a desired position and orientation is needed for application of high throughput automatic injection systems, which will significantly increase injection speed, cell survival, and success rates.

Nanovehicular intracellular delivery systems

This article provides an overview of principles and barriers relevant to intracellular drug and gene transport, accumulation and retention (collectively called as drug delivery) by means of nanovehicles (NV). The aim is to deliver a cargo to a particular intracellular site, if possible, to exert a local action. Some of the principles discussed in this article apply to noncolloidal drugs that are not permeable to the plasma membrane or to the blood-brain barrier. NV are defined as a wide range of nanosized particles leading to colloidal objects which are capable of entering cells and tissues and delivering a cargo intracelullarly. Different localization and targeting means are discussed. Limited discussion on pharmacokinetics and pharmacodynamics is also presented. NVs are contrasted to micro-delivery and current nanotechnologies which are already in commercial use. Newer developments in NV technologies are outlined and future applications are stressed. We also briefly review the existing modeling tools and approaches to quantitatively describe the behavior of targeted NV within the vascular and tumor compartments, an area of particular importance. While we list "elementary" phenomena related to different level of complexity of delivery to cancer, we also stress importance of multi-scale modeling and bottom-up systems biology approach.

Modified concatemeric oligonucleotide complexes: new system for efficient oligonucleotide transfer into mammalian cells

Antisense oligonucleotides and double-stranded small interfering RNAs have become an important instrument for the manipulation of gene expression in molecular biology experiments and a promising tool for the development of gene-targeted therapeutics. One of the main impediments in the use of oligonucleotide-based therapeutics is their poor uptake by target cells. The formation of supramolecular concatemeric complexes by oligonucleotides was shown to promote their binding to various mammalian cells [Simonova, O.N.,Vladimirova, A.V., Zenkova, M.A., and Vlassov, V.V. (2006). Biochim. Biophys. Acta 1758, 413-418]. We attempted to improve the efficiency of oligonucleotide concatemer delivery into cells by the attachment of lipophilic cholesterol molecules to the components of concatemeric complexes. Uptake, cellular distribution, and biological activity of the supramolecular complexes formed by delivered antisense oligonucleotides and cholesterol-modified "carrier" oligonucleotides were studied. Our results demonstrate that incorporation of an antisense oligonucleotide into the self-assembling concatemeric system promotes its delivery into cells without the addition of any supplementary transfection agents and allows achieving specific inhibition of the target gene expression.

Single-cell microinjection technology in cell biology

Single-cell microinjection has been successfully used to deliver exogenous proteins, cDNA constructs, peptides, drugs and particles into transfection-challenged cells. With precisely controlled delivery dosage and timing, microinjection has been used in many studies of primary cultured cells, transgenic animal production, in vitro fertilization and RNA inference. This review discusses the advantages and limits of microinjection as a mechanical delivery method and its applications to attached and suspended cells.

Comparison between properties of 2'-O,4'-C-ethylene-bridged nucleic acid (ENA) phosphorothioate oligonucleotides and N3'-P5' thiophosphoramidate oligonucleotides

Synthesis and properties of an oligonucleotide uniformly modified with 2'-O,4-C-ethylene-bridged nucleic acid (ENA) units were compared with those of GRN163, which is modified with N3'-P5' thiophosphoramidates, with the sequence targeting human telomerase RNA subunit. Although an ENA phosphorothioate oligonucleotide, ENA-13, could be synthesized using ENA phosphoramidites on a 100-mg scale, synthesis of GRN163 was very hard even on a 1-micomol scale. In view of both stability of the duplex formation with complementary RNA and the efficiency of cellular uptake by endocytosis, ENA-13 was superior to GRN163. These findings suggest that ENA-13 has useful properties for antisense therapeutic application.

Delivery of antisense oligonucleotides to leukemia cells by RNA bacteriophage capsids

BACKGROUND

Acute myelogenous leukemia (AML) is the most common type of acute leukemia in adults. Because conventional treatments are associated with substantial side effects, novel therapeutic strategies are required. Antisense oligodeoxynucleotides (ODNs) have shown promise as the basis of emerging therapies for fighting cancer, although in vivo application is hampered by high sensitivity to cellular nuclease degradation. Encapsidation of ODNs in a drug-delivery capsule would reduce such degradation, thereby increasing the potency of therapy. MS2 bacteriophage capsid proteins may be used as novel virus-like particles (VLPs) to deliver ODNs. Here we report an analysis of the uptake mechanism of this VLP system and preliminary examples of its use to deliver a number of ODNs, including some targeting p120 messenger RNAs, a biomarker overexpressed in myelogenous leukemia cells.

METHODS

The ODNs were synthesized as covalent extensions to the translational repressor/assembly initiation signal (TR), a 19 nt stem-loop, of the RNA phage MS2. The VLPs were constructed by soaking ODN-TR directly into recombinant RNA-free capsid shells. Targeting of the encapsidated ODNs into cells was achieved by a receptor-mediated endocytosis pathway identified by immunofluorescence microscopy or by transmission electron microscopy with gold-labeled antibodies.

RESULTS

After covalent decoration with transferrin on their surface, the VLPs containing ODNs demonstrated increased effectiveness in killing target leukemia cells expressing transferrin receptors, suggesting that this system is worthy of more extensive analysis.

CONCLUSIONS

The findings suggest that RNA phage VLPs may be useful as a new nanomaterial for targeted delivery of antisense ODNs, or other macromolecular drug candidates.

Transfection effect of microbubbles on cells in superposed ultrasound waves and behavior of cavitation bubble

The combination of ultrasound and ultrasound contrast agents (UCAs) is able to induce transient membrane permeability leading to direct delivery of exogenous molecules into cells. Cavitation bubbles are believed to be involved in the membrane permeability; however, the detailed mechanism is still unknown. In the present study, the effects of ultrasound and the UCAs, Optison on transfection in vitro for different medium heights and the related dynamic behaviors of cavitation bubbles were investigated. Cultured CHO-E cells mixed with reporter genes (luciferase or beta-gal plasmid DNA) and UCAs were exposed to 1 MHz ultrasound in 24-well plates. Ultrasound was applied from the bottom of the well and reflected at the free surface of the medium, resulting in the superposition of ultrasound waves within the well. Cells cultured on the bottom of 24-well plates were located near the first node (displacement node) of the incident ultrasound downstream. Transfection activity was a function determined with the height of the medium (wave traveling distance), as well as the concentration of UCAs and the exposure time was also determined with the concentration of UCAs and the exposure duration. Survival fraction was determined by MTT assay, also changes with these values in the reverse pattern compared with luciferase activity. With shallow medium height, high transfection efficacy and high survival fraction were obtained at a low concentration of UCAs. In addition, capillary waves and subsequent atomized particles became significant as the medium height decreased. These phenomena suggested cavitation bubbles were being generated in the medium. To determine the effect of UCAs on bubble generation, we repeated the experiments using crushed heat-treated Optison solution instead of the standard microbubble preparation. The transfection ratio and survival fraction showed no additional benefit when ultrasound was used. These results suggested that cavitation bubbles created by the collapse of UCAs were a key factor for transfection, and their intensities were enhanced by the interaction of the superpose ultrasound with the decreasing the height of the medium. Hypothesizing that free cavitation bubbles were generated from cavitation nuclei created by fragmented UCA shells, we carried out numerical analysis of a free spherical bubble motion in the field of ultrasound. Analyzing the interaction of the shock wave generated by a cavitation bubble and a cell membrane, we estimated the shock wave propagation distance that would induce cell membrane damage from the center of the cavitation bubble.

Uptake pathways and subsequent intracellular trafficking in nonviral gene delivery

The successful delivery of therapeutic genes to the designated target cells and their availability at the intracellular site of action are crucial requirements for successful gene therapy. Nonviral gene delivery is currently a subject of increasing attention because of its relative safety and simplicity of use; however, its use is still far from being ideal because of its comparatively low efficiency. Most of the currently available nonviral gene vectors rely on two main components, cationic lipids and cationic polymers, and a variety of functional devices can be added to further optimize the systems. The design of these functional devices depends mainly on our understanding of the mechanisms involved in the cellular uptake and intracellular disposition of the therapeutic genes as well as their carriers. Macromolecules are internalized into cells by a variety of mechanisms, and their intracellular fate is usually linked to the entry mechanism. Therefore, the successful design of a nonviral gene delivery system requires a deep understanding of gene/carrier interactions as well as the mechanisms involved in the interaction of the systems with the target cells. In this article, we review the different uptake pathways that are involved in nonviral gene delivery from a gene delivery point of view. In addition, available knowledge concerning cellular entry and the intracellular trafficking of cationic lipid-DNA complexes (lipoplexes) and cationic polymer-DNA complexes (polyplexes) is summarized.

Nanostructured Probes for RNA Detection in Living Cells

The ability to visualize in real-time the expression level and localization of specific RNAs in living cells can offer tremendous opportunities for biological and disease studies. Here we review the recent development of nanostructured oligonucleotide probes for living cell RNA detection, and discuss the biological and engineering issues and challenges of quantifying gene expression in vivo. In particular, we describe methods that use dual FRET (fluorescence resonance energy transfer) or single molecular beacons in combination with peptide-based or membrane-permeabilization-based delivery, to image the relative level, localization, and dynamics of RNA in live cells. Examples of detecting endogenous mRNAs, as well as imaging their subcellular localization and colocalization are given to illustrate the biological applications, and issues in molecular beacon design, probe delivery, and target accessibility are discussed. The nanostructured probes promise to open new and exciting opportunities in sensitive gene detection for a wide range of biological and medical applications.

Cholesterol conjugated oligonucleotide and LNA: a comparison of cellular and nuclear uptake by Hep2 cells enhanced by streptolysin-O

Antisense and antigene oligonucleotides (ONs) are attractive drugs for gene therapy, but major limiting factors for their routine use are inefficient cellular uptake and low accessibility to the target sites. Adding various lipophilic conjugates to the ON improves intracellular delivery as has been previously reported. We studied the cellular delivery of various ON modifications, as well as their cytosolic and nuclear distribution in mammalian Hep2-EGFP-NLS cell line. We compared uptake efficacy of ON and LNA, both conjugated with cholesterol at the 5' end. All ONs were 3' labeled with fluorescent Cy 5 dye. We made a comparison of the ONs uptake efficacy and the kinetics, both adding ONs to the culture medium, and using streptolysin-O (SL-O) permeabilization. The cellular uptake of each ON used in this study was visualized by fluorescent microscopy. We confirmed the results by FACS analysis. We determined the ratio between initial ON-chol concentration (0.4 microM) and the final amount in nucleus.SL-O can highly improve kinetics of ON delivery; not only into the cytoplasm but also to the nucleus, the presumed site of antigene ON action. The most effective nuclear uptake was observed when ON conjugated with cholesterol (ON-chol) and SL-O was used. Nuclear distribution of ON was reached within few minutes. In contrast, ON simply added to the medium reached cytoplasm only and the process of delivery took several hours.

Cell-specific targeting of lipid-based carriers for ODN and DNA

It is well recognized that there is an urgent need for non-toxic systemically applicable vectors for biologically active nucleotides to fully exploit the current potential of molecular medicine in gene therapy. Cell-specific targeting of non-viral lipid-based carriers for ODN and DNA is a prerequisite to attain the concentration of nucleic acids required for therapeutic efficacy in the target tissue. In this review we will address the most promising approaches to selective targeting of liposomal nucleic acid carriers in vivo. In addition, the routes of entry and intracellular processing of these carrier systems are discussed as well as physiological factors potentially interfering with the biological and/or therapeutic activity of their nucleotide pay-load.

Delivery of oligodeoxynucleotides into human saphenous veins and the adjunct effect of ultrasound and microbubbles

Therapy with naked oligodeoxynucleotides (ODNs, molecular weight: 3000 to 7500) provides an elegant means of modulating gene expression without the problems associated with conventional gene therapy, but the relatively low transfer efficiency on intravascular administration is a limitation to clinical application. Ultrasound, which can be potentiated by microbubbles, shows promise as a method of delivering macromolecules such as plasmid DNA and other transgenes into cells. Since uptake of molecules into cells depends on their molecular weight, it might be expected that the delivery of ODNs, which are relatively small, will be facilitated by ultrasound and microbubbles. In the present study, we delivered ODNs into veins using ultrasound and microbubbles. First, we quantified the uptake of fluorescent-labeled ODNs into intact ex vivo human saphenous veins and isolated smooth muscle cells from the veins, evaluating the effect of ultrasound and microbubbles on uptake. Ultrasound potentiated the delivery of ODN in cells, except at high concentrations. When intact veins were studied, we achieved nuclear localization of fluorescent-labeled ODNs in cells. This increased with increasing concentration and incubation time and was not potentiated by ultrasound, even when microbubbles were used. We then applied a therapeutic ODN (antisense to intercellular adhesion molecule 1, ICAM-1) to vein samples and documented a functional inhibition of gene expression in a sequence-specific manner at the protein level with immunohistochemistry and western blot analysis. Again, no significant difference was seen with adjunct ultrasound. These observations suggest high diffusion of ODNs into human saphenous veins in this ex vivo model, indicating potential applications to inhibition of vascular bypass graft occlusion and other vasculopathies. Although microbubble-ultrasound was of value with cells in culture, it was not beneficial with intact veins.

Oligonucleotides and polyribonucleotides: a review of antiviral activity

Current antiviral therapies are insufficient for treating emerging, re-emerging and established viral diseases. In an effort to find new therapeutics, oligo- and polyribonucleotides are being studied for their antiviral capabilities. Studies have shown that uniquely modified single- and double-stranded nucleic acid constructs are effective in inhibiting viral proliferation by various mechanisms. This review gives a brief history and highlights the development of oligo- and polyribonucleotides as antiviral agents primarily in the fields of interferon induction, mRNA complementation and reverse transcriptase inhibition.

Transfection protocol for antisense oligonucleotides affects uniformity of transfection in cell culture and efficiency of mRNA target reduction

In an effort to optimize the transfection of cell lines with antisense oligonucleotides, we examined cellular accumulation of a labeled oligonucleotide by flow cytometry. We were surprised to observe that a routinely used transfection protocol, a fixed lipid/oligonucleotide ratio, resulted in variable transfection efficiency depending on the concentration of oligonucleotide used. A significant population of cells, especially at lower doses of oligonucleotide and cationic lipid, were untransfected. We investigated lipid/oligonucleotide ratios, different lipid preparations, and different cell types and found that these variables did not alter the percentage of cells transfected at these lower doses of oligonucleotide. However, when lipid-oligonucleotide complexes were formed at the high dose and then diluted into a solution of lipid or a complex of lipid and unlabeled, negative control oligonucleotide, a constant percentage of cells was transfected. Under these conditions, mRNA target reduction dose-response curves were also shifted to lower doses. We hypothesize that poor transfection observed at a low concentration of lipid-oligonucleotide complex when diluted in medium is due to loss of active complexes, either by adsorption to the substrate or by changes in physical characteristics of complexes. By maintaining a constant lipid concentration, more consistent transfection was achieved.

Drug delivery of oligonucleotides by peptides

Oligonucleotides are promising tools for in vitro studies where specific downregulation of proteins is required. In addition, antisense oligonucleotides have been studied in vivo and have entered clinical trials as new chemical entities with various therapeutic targets such as antiviral drugs or for tumour treatments. The formulation of these substances were widely studied in the past. With this review we will focus on peptides used as drug delivery vehicles for oligonucleotides. Different strategies are summarised. Cationically charged peptides from different origins were used e.g. as cellular penetration enhancers or nuclear localisation tool. Examples are given for Poly-L-lysine alone or in combination with receptor specific targeting ligands such as asialoglycoprotein, galactose, growth factors or transferrin. Another large group of peptides are those with membrane translocating properties. Fusogenic peptides rich in lysine or arginine are reviewed. They have been used for DNA complexation and condensation to form transport vehicles. Some of them, additionally, have so called nuclear localisation properties. Here, DNA sequences, which facilitate intracellular trafficking of macromolecules to the nucleus were explored. Summarizing the present literature, peptides are interesting pharmaceutical excipients and it seems to be feasible to combine the specific properties of peptides to improve drug delivery devices for oligonucleotides in the future.

Synthesis, properties, and NMR studies of a C8-phenylguanine modified oligonucleotide that preferentially adopts the Z DNA conformation

Carcinogenic aryl hydrazines produce C8-arylated purine adducts. The effect of these adducts on DNA conformation and their role in hydrazine carcinogenesis are unknown. Here, we describe a new synthetic route to produce these adducts that is also compatible with the synthesis of the corresponding phosphoramidites needed for oligonucleotide synthesis. Two oligonucleotides were prepared, an unmodified oligonucleotide, d((5)(')CGCGCGCGCG(3)(')), and a C8-phenylguanine modified oligonucleotide, d((5)(')CGCGCGCGCG(3)(')) (G = 8-phenylguanine). These oligonucleotides were compared using thermal denaturation, circular dichroism, NMR, and molecular modeling. The phenyl modification destabilizes the B DNA form and stabilizes the Z DNA form such that the B:Z ratio is near one under physiological conditions. In light of recent studies that show a role for Z DNA in gene expression and cell transformation, Z DNA stabilization by C8-arylguanine formation from aryl hydrazines may be relevant to their role in carcinogenesis.

Effects of base modifications on antisense properties of 2'-O-methoxyethyl and PNA oligonucleotides

A recently developed antisense splicing assay was used to determine the relative activities of 2'-O-methoxyethoxy (2'-MOE) phosphorothioate oligonucleotides containing base modifications. In the assay, RNase H-inactive oligonucleotides are used to block aberrant splicing and restore correct splicing of an Enhanced Green Fluorescence Protein (EGFP) reporter pre-mRNA stably expressed in HeLa cells. Thus, the extent of EGFP upregulation is proportional to the antisense activity of the tested molecule. The base modifications included C-5 propynyl analogs of uridine and cytidine and phenoxazine and G-clamp analogs of cytosine. Base-modified 2'-MOE oligonucleotides were delivered to the HeLa EGFP-654 test cells by cationic lipid transfection or scrape-loading or without any delivery method (free uptake). When delivered with a cationic lipid, the G-clamp and phenoxazine oligomers showed increases in activity over the unmodified 2'-MOE parent compound. However, when delivered by scrape-loading or without a delivery method, the unmodified oligomer performed best. The results suggest that base modifications do not enhance the free uptake activity of RNase H inactive 2'-MOE oligomers.

Dual FRET molecular beacons for mRNA detection in living cells

The ability to visualize in real-time the expression level and localization of specific endogenous RNAs in living cells can offer tremendous opportunities for biological and disease studies. Here we demonstrate such a capability using a pair of molecular beacons, one with a donor and the other with an acceptor fluorophore that hybridize to adjacent regions on the same mRNA target, resulting in fluorescence resonance energy transfer (FRET). Detection of the FRET signal significantly reduced false positives, leading to sensitive imaging of K-ras and survivin mRNAs in live HDF and MIAPaCa-2 cells. FRET detection gave a ratio of 2.25 of K-ras mRNA expression in stimulated and unstimulated HDF, comparable to the ratio of 1.95 using RT-PCR, and in contrast to the single-beacon result of 1.2. We further revealed intriguing details of K-ras and survivin mRNA localization in living cells. The dual FRET molecular beacons approach provides a novel technique for sensitive RNA detection and quantification in living cells.

Peptide-linked molecular beacons for efficient delivery and rapid mRNA detection in living cells

Real-time visualization of specific endogenous mRNA expression in vivo has the potential to revolutionize medical diagnosis, drug discovery, developmental and molecular biology. However, conventional liposome- or dendrimer-based cellular delivery of molecular probes is inefficient, slow, and often detrimental to the probes. Here we demonstrate the rapid and sensitive detection of RNA in living cells using peptide-linked molecular beacons that possess self-delivery, targeting and reporting functions. We conjugated the TAT peptide to molecular beacons using three different linkages and demonstrated that, at relatively low concentrations, these molecular beacon constructs were internalized into living cells within 30 min with nearly 100% efficiency. Further, peptide-based delivery did not interfere with either specific targeting by or hybridization-induced fluorescence of the probes. We could therefore detect human GAPDH and survivin mRNAs in living cells fluorescently, revealing intriguing intracellular localization patterns of mRNA. We clearly demonstrated that cellular delivery of molecular beacons using the peptide-based approach has far better performance compared with conventional transfection methods. The peptide-linked molecular beacons approach promises to open new and exciting opportunities in sensitive gene detection and quantification in vivo.

Membrane binding and translocation of cell-penetrating peptides

Cell-penetrating peptides (CPPs) have been extensively studied during the past decade, because of their ability to promote the cellular uptake of various cargo molecules, e.g., oligonucleotides and proteins. In a recent study of the uptake of several analogues of penetratin, Tat(48-60) and oligoarginine in live (unfixed) cells [Thorén et al. (2003) Biochem. Biophys. Res. Commun. 307, 100-107], it was found that both endocytotic and nonendocytotic uptake pathways are involved in the internalization of these CPPs. In the present study, the membrane interactions of some of these novel peptides, all containing a tryptophan residue to facilitate spectroscopic studies, are investigated. The peptides exhibit a strong affinity for large unilamellar vesicles (LUVs) containing zwitterionic and anionic lipids, with binding constants decreasing in the order penetratin > R(7)W > TatP59W > TatLysP59W. Quenching studies using the aqueous quencher acrylamide and brominated lipids indicate that the tryptophan residues of the peptides are buried to a similar extent into the membrane, with an average insertion depth of approximately 10-11 A from the bilayer center. The membrane topology of the peptides was investigated using an assay based on resonance energy transfer between tryptophan and a fluorescently labeled lysophospholipid, lysoMC, distributed asymmetrically in the membranes of LUVs. By determination of the energy transfer efficiency when peptide was added to vesicles with lysoMC present exclusively in the inner leaflet, it was shown that none of the peptides investigated is able to translocate across the lipid membranes of LUVs. By contrast, confocal laser scanning microscopy studies on carboxyfluorescein-labeled peptides showed that all of the peptides rapidly traverse the membranes of giant unilamellar vesicles (GUVs). The choice of model system is thus crucial for the conclusions about the ability of CPPs to translocate across lipid membranes. Under the conditions used in the present study, peptide-lipid interactions alone cannot explain the different cellular uptake characteristics exhibited by these peptides.

Cellular uptake and metabolism of DNA frayed wires

DNA frayed wires are a novel, multistranded form of DNA that arises from interactions between single-stranded oligodeoxyribonucleotides with the general sequence d(N(x)G(y)) or d(G(y)N(x)), where y > 10 and x > 5. Frayed wires exhibit greater stability with respect to thermal and chemical denaturation than single- or double-stranded DNA molecules and, thus, may have potential usefulness for DNA drug delivery. However, the stability and uptake of frayed wires have not been investigated in biological systems. Our objective was to examine the cellular uptake and stability of frayed wires in cultured hepatic cells. In these studies, the parent oligonucleotide d(A(15)G(15)) was used to form DNA frayed wires (DNA(FW)) while a random 30-mer oligonucleotide was used as the control nonaggregated DNA (DNA(SS)). Uptake and metabolism studies of DNA(FW) were performed in cultured human hepatoma, HepG2 cells and compared to DNA(SS). Our results indicate that DNA(FW) are not cytotoxic and that their intracellular uptake in HepG2 cells is 2-3.5-fold greater than that of DNA(SS) within the first 2 h (p < 0.05). Similarly, nuclear localization of DNA(FW) is 10-13-fold higher than that of DNA(SS) (p < 0.05). As both internalized and extracellular DNA(FW) appear to be more stable in vitro than DNA(SS), the enhanced uptake may be due to either increased stability or enhanced intracellular transport. These studies also indicate that uptake of DNA(FW) likely occurs via active processes such as receptor-mediated endocytosis similar to mechanisms which have been proposed for DNA(SS). The internalization pathways of DNA(FW) may differ somewhat from that of DNA(SS) insofar as chloroquine does not appear to alter DNA(FW) uptake and degradation, as is the case with DNA(SS).

Innovations in oligonucleotide drug delivery

Oligonucleotides (ONs) are a new class of therapeutic compounds under investigation for the treatment of a variety of disease states, such as cancer and HIV, and for FDA approval of an anti-CMV retinitis antisense molecule (Vitravene trade mark, Isis Pharmaceuticals). However, these molecules are limited not only by poor cellular uptake, but also by a general lack of understanding regarding the mechanism(s) of ON cellular uptake. As a result, various delivery vehicles have been developed that circumvent the proposed mechanism of uptake, endocytosis, while improving target specific delivery and/or drug stability. This review describes various traditional and novel delivery mechanisms that have been employed to improve ON cellular delivery, cost effectiveness, and therapeutic efficacy.

Novel cationic transport agents for oligonucleotide delivery into primary leukemic cells

Novel cationic compounds forming complexes with oligodeoxyribonucleotides (ODNs) were prepared, and their ability to transport ODNs into cultured primary leukemic cells was tested. Two cationic porphyrin derivatives (2 and 3) were found to be at least 1 order of magnitude more efficient in this respect than commercially available agents. The ODN transporting capacity of novel compounds was dependent on the magnitude and the nature of their positive charges as well as on the porphyrin/ODN molar ratio. Porphyrin-ODN complexes were internalized into cells, and their dissociation was demonstrated by accumulation of fluorescein isothiocyanate-ODN fluorescence in the nucleus. Importantly, porphyrin 3 significantly protected complexed ODN against degradation and efficiently mediated the specific antisense effect on targeted v-Myb expression, resulting in reproducible growth inhibition of treated cells. Low toxicity, serum compatibility, and water solubility of porphyrin 3 make this compound a promising novel tool for modulation of gene expression in primary leukemic cells.

Cyclin B synthesis is required for sea urchin oocyte maturation

Sea urchins are members of a limited group of animals in which meiotic maturation of oocytes is completed prior to fertilization. This is different from oocytes of most animals such as mammals and amphibians in which fertilization reactivates an arrested meiotic cycle. Using a recently developed technique for in vitro maturation of sea urchin oocytes, we analyzed the role of cyclin B, the regulatory component of maturation-promoting factor, in the control of sea urchin oocyte meiotic induction and progression. Oocytes of the sea urchin Lytechinus variegatus accumulate significant amounts of cyclin B mRNA and protein during oogenesis. We analyzed cyclin B synthetic requirements in oocytes and early embryos by inhibiting cyclin B synthesis with DNA and morpholino antisense oligonucleotides. Cyclin B synthesis is not necessary for the entry of G2-arrested oocytes into meiosis; however, it is required for the proper progression through meiotic divisions. Surprisingly, mature sea urchin eggs contain significant cyclin B protein following meiosis that serves as a maternal store for early cleavage divisions. We also find that cyclin A can functionally substitute for cyclin B in early embryos but not in oocytes. These studies provide a foundation for understanding the mechanism of meiotic maturation independent of the zygotic cell cycle.

Inhibitor scaffolds as new allele specific kinase substrates

The elucidation of protein kinase signaling networks is challenging due to the large size of the protein kinase superfamily (>500 human kinases). Here we describe a new class of orthogonal triphosphate substrate analogues for the direct labeling of analogue-specific kinase protein targets. These analogues were constructed as derivatives of the Src family kinase inhibitor PP1 and were designed based on the crystal structures of PP1 bound to HCK and N(6)-(benzyl)-ADP bound to c-Src (T338G). 3-Benzylpyrazolopyrimidine triphosphate (3-benzyl-PPTP) proved to be a substrate for a mutant of the MAP kinase p38 (p38-T106G/A157L/L167A). 3-Benzyl-PPTP was preferred by v-Src (T338G) (k(cat)/K(M) = 3.2 x 10(6) min(-)(1) M(-)(1)) over ATP or the previously described ATP analogue, N(6) (benzyl) ATP. For the kinase CDK2 (F80G)/cyclin E, 3-benzyl-PPTP demonstrated catalytic efficiency (k(cat)/K(M) = 2.6 x 10(4) min(-)(1) M(-)(1)) comparable to ATP (k(cat)/K(M) = 5.0 x 10(4) min(-)(1) M(-)(1)) largely due to a significantly better K(M) (6.4 microM vs 530 microM). In kinase protein substrate labeling experiments both 3-benzyl-PPTP and 3-phenyl-PPTP prove to be over 4 times more orthogonal than N(6)-(benzyl)-ATP with respect to the wild-type kinases found in murine spleenocyte cell lysates. These experiments also demonstrate that [gamma-(32)P]-3-benzyl-PPTP is an excellent phosphodonor for labeling the direct protein substrates of CDK2 (F80G)/E in murine spleenocyte cell lysates, even while competing with cellular levels (4 mM) of unlabeled ATP. The fact that this new more highly orthogonal nucleotide is accepted by three widely divergent kinases studied here suggests that it is likely to be generalizable across the entire kinase superfamily.

Synthesis of N-acetyl-D-galactosamine and folic acid conjugated ribozymes

To evaluate potential improvement in tissue specific targeting and cellular uptake of therapeutic ribozymes, we have developed three new phosphoramidite reagents. These reagents can be used in automated solid-phase synthesis to produce oligonucleotide conjugates containing N-acetyl-D-galactosamine (targeting hepatocytes) and folic acid (targeting tumor). N-Acetyl-D-galactosamine was attached through a linker to both 2'-amino-2'-deoxyuridine and D-threoninol scaffolds, and these conjugates were converted to phosphoramidite building blocks. Incorporation of a D-threoninol-based monomer into ribozymes provided multiply labeled ribozyme conjugates. Attachment of the fully protected pteroic acid to the D-threoninol-6-aminocaproyl-L-glutamic acid construct afforded the folic acid conjugate, which was converted into the phosphoramidite and incorporated onto the 5'-end of the ribozyme.

Cellular import mediated by nuclear localization signal Peptide sequences

The cellular delivery of therapeutic agents and their localization within cells is currently a great challenge in medicinal chemistry. A few cationic peptides have shown a strong propensity to cross the cytoplasmic membrane and enter cells. Nuclear localization signal (NLS) sequences are a class of highly cationic peptides that may be exploited for cellular import of linked cargo. A series of NLS sequence peptides were investigated for entry into different cancer cell lines by flow cytometry and confocal microscopy. All NLS peptides demonstrated rapid accumulation within cells when added to the cellular media. Covalent adducts of proteins and oligonucleotides with NLS peptides were also effectively imported within cells. An understanding of the structural and mechanistic properties of these sequences will provide great potential for the rational design of efficient and selective peptidic delivery systems.

Characterization of alginate/poly-L-lysine particles as antisense oligonucleotide carriers

The gel forming characteristics of alginate in the presence of calcium ions and further crosslinking with poly-L-lysine led to the formation of sponge-like nano- and microparticles. The particle size was varied by adjusting the final concentrations of and proportions between the components. The region for particle formation was from 0.04 to 0.08% (w/v) of alginate in the final formulation, the change from the nm to microm size range occurred at a concentration of approx. 0.055% (w/v). Oligonucleotide-loaded microparticles were prepared by two different methods, either by absorption of the drug into the crosslinked polymeric matrix or by incorporation of an oligonucleotide/poly-L-lysine complex into a calcium alginate pre-gel. The release of oligonucleotide from microparticles prepared by the first method was higher. The addition of increasing amounts of poly-L-lysine resulted in larger particles, higher oligonucleotide loading and slower drug release. An increase in the final solid content of the formulation led to larger particles, especially with high concentrated calcium alginate pre-gels. Microparticles based on alginate and poly-L-lysine are potential carriers for antisense oligonucleotides.

Receptor-mediated endocytosis of phosphodiester oligonucleotides in the HepG2 cell line: evidence for non-conventional intracellular trafficking

Having identified an oligonucleotide (ON) receptor in the HepG2 cell line, we have re-examined here the kinetics of ON uptake, subcellular distribution and intracellular localisation in these cells, at concentrations relevant for the study of a receptor-dependent process. Kinetic parameters of ON endocytosis were comparable with those of the receptor-mediated endocytosis tracer, transferrin (uptake equilibrium, saturation with concentration, specific competition and rapid efflux) and were clearly distinct from those of fluid-phase endocytosis. By analytical subcellular fractionation, particulate ON showed a bimodal distribution after 2 h of uptake, with a low-density peak superimposed on the distribution of endosomes, and a high-density peak overlapping lysosomes. After an overnight chase, only the high-density peak remained, but it could be dissociated from lysosomes, based on its refractoriness to displacement upon chloroquine-induced swelling. After 2 h of uptake at 300 nM ON-Alexa, a punctate pattern was resolved, by confocal microscopy, from those of transferrin, of a fluid-phase tracer, and of vital staining of lysosomes by LysoTracker. At 3 microM ON-Alexa, its pattern largely overlapped with the fluid-phase tracer and LysoTracker. Taken together, these data suggest that ON may be internalised at low concentrations by receptor-mediated endocytosis into unique endosomes, then to dense structures that are distinct from lysosomes. The nature of these two compartments and their significance for ON effect deserve further investigation.