Cellular uptake of oligodeoxynucleotide phosphorothioates and their analogs

Responsive core-shell DNA particles trigger lipid-membrane disruption and bacteria entrapment

Biology has evolved a variety of agents capable of permeabilizing and disrupting lipid membranes, from amyloid aggregates, to antimicrobial peptides, to venom compounds. While often associated with disease or toxicity, these agents are also central to many biosensing and therapeutic technologies. Here, we introduce a class of synthetic, DNA-based particles capable of disrupting lipid membranes. The particles have finely programmable size, and self-assemble from all-DNA and cholesterol-DNA nanostructures, the latter forming a membrane-adhesive core and the former a protective hydrophilic corona. We show that the corona can be selectively displaced with a molecular cue, exposing the 'sticky' core. Unprotected particles adhere to synthetic lipid vesicles, which in turn enhances membrane permeability and leads to vesicle collapse. Furthermore, particle-particle coalescence leads to the formation of gel-like DNA aggregates that envelop surviving vesicles. This response is reminiscent of pathogen immobilisation through immune cells secretion of DNA networks, as we demonstrate by trapping E. coli bacteria.

Molecular Transport through a Biomimetic DNA Channel on Live Cell Membranes

Biological membrane channels, considered as molecular gatekeepers, control the transportation of molecules and ions across live cell membranes. Developing synthetic passable channels with predictable structures, high transport efficiency, and low cytotoxicity on live cells is of great interest for replicating the functions of endogenous protein channels, but remains challenging. The development of DNA nanotechnology provides possible solutions for making synthetic channels with precise structures and controllable functionalization. Therefore, in this work, we constructed a phosphorothioate-modified DNA nanopore able to structurally mimic biological channels for molecular transport across live cell membranes. With its stable structure with small hollow size (<2 nm) and the ability to interact with the lipid molecules, this DNA nanopore could show stable insertion into the plasma membrane. We further proved that this membrane-spanning channel could transport ions and antitumor drugs to neurons and cancer cells, respectively, and do so within a certain time window. We expect that this live cell membrane-spanning synthetic DNA nanopore will provide a tool for studying cellular communication, building synthetic cells, and achieving controlled transmembrane transport to cells.

Nucleic acid polymers prevent the establishment of duck hepatitis B virus infection in vivo

Nucleic acid polymers (NAPs) are novel, broad-spectrum antiviral compounds that use the sequence-independent properties of phosphorothioate oligonucleotides (PS-ONs) as amphipathic polymers to block amphipathic interactions involved in viral entry. Using the duck hepatitis B virus (DHBV) model of human hepatitis B virus infection, NAPs have been shown to have both entry and postentry antiviral activity against DHBV infection in vitro in primary duck hepatocytes (PDH). In the current study, various NAPs were assessed for their prophylactic activity in vivo against DHBV infection in ducks. The degenerate NAP REP 2006 prevented the development of widespread and persistent DHBV infection in 14-day-old ducks, while the acidic-pH-sensitive NAP REP 2031 had little or no prophylactic effect. REP 2006 displayed significant toxicity in ducks, which was attributed to CpG-mediated proinflammation, while REP 2031 (which has no CpG motifs) displayed no toxicity. A third NAP, REP 2055, which was designed to retain amphipathic activity at acidic pH and contained no CpG motifs, was well tolerated and displayed prophylactic activity against DHBV infection at doses as low as 1 mg/kg of body weight/day. These studies suggest that NAPs can be easily and predictably tailored to retain anti-DHBV activity and to have minimal toxic effects in vivo. Future studies are planned to establish the therapeutic efficacy of NAPs against persistent DHBV infection.

CpG-Induced IFN-α production of plasmacytoid dendritic cells: time and dosage dependence and the effect of structural modifications to the CpG backbone

Plasmacytoid dendritic cells (pDCs) represent a highly specialized immune cell subset and are considered to be the main sentinels against viral infections and play an important role in the development of immune tolerance. pDCs are able to recognize cytosine-phosphate-guanosine (CpG) motifs within microbial DNA, which are unmethylated CG dinucleotides in a certain sequence context and trigger the secretion of interferon (IFN)-α and other proinflammatory cytokines. Here we used the typical class A CpG oligodeoxynucleotide (ODN) 2216, the B-class ODN 2006, and the newly synthesized CpG ODN TM64 to explore the potency and kinetics of IFN-α stimulation of pDC. TM64 CpG ODN has a hexanucleotide sequence TCGTGT that leads to an increased cellular uptake and features a CpG nucleotide within the sequence that leads to a potent specific B-cell stimulation, thus characteristics similar to a class B CpG. Our data reveals that all CpGs act as both dosage- and time-dependent stimuli of IFN-α secretion. The relationship between concentration of the stimulant and the secreted amount of IFN-α is not linear and results in a plateau formation, with saturation kinetics. Alteration to the backbone can change duration and quantity of overall IFN-α secretion.

Efficient stabilization of phosphodiester (PO), phosphorothioate (PS), and 2'-O-methoxy (2'-OMe) DNA·RNA hybrid duplexes by amino sugars

Antisense strategies that target DNA·RNA hybrid structures offer potential for the development of new therapeutic drugs. The α-sarcin loop region of the 23S [corrected] rRNA domain has been shown to be a high value target for such strategies. Herein, aminoglycoside interaction with three RNA·DNA α-sarcin targeted duplexes (rR·dY, rR·S-dY, and rR·2'OMe-rY) have been investigated to determine the overall effect of aminoglycoside interaction on the stability, affinity, and conformation of these hybrid duplexes. To this end, UV thermal denaturation, circular dichroism spectroscopy, fluorescence intercalator displacement, and ITC as well as DSC calorimetry experiments were carried out. The results suggest the following. (1) Of all the aminoglycosides studied, neomycin confers the highest thermal stability on all three hybrid duplexes studied. (2) There is no appreciable difference in aminoglycoside-induced thermal stability between the unmodified rR·dY and phophorothioate modified rR·S-dY duplexes. (3) The rR·2'OMe-rY duplexes thermal stability is slightly less than the other two hybrids. (4) In all three duplexes, aminoglycoside-induced thermal stability decreased as the number of amino groups decreased. (5) CD scans revealed similar spectra for the rR·dY and rR·S-dY duplexes as well as a more pronounced A-form signal for the rR·2'OMe-rY duplex. (6) FID assays paralleled the CD results, yielding similar affinity values between the rR·dY and rR·S-dY duplexes and higher affinities with the rR·2'OMe-rY duplex. (7) The overall affinity trend between aminoglycosides and the three duplexes was determined to be neomycin > paromomycin > neamine > ribostamycin. (8) ITC K(a) values revealed similar binding constants for the rR·dY and rR·S-dY duplexes with rR·dY having a K(1) of (1.03 ± 0.58) × 10(7) M(-1) and K(2) of (1.13 ± 0.07) × 10(5) M(-1) while rR·S-dY produced a K(1) of (1.17 ± 0.54) × 10(7) M(-1) and K(2) of (1.27 ± 0.69) × 10(5) M(-1). (8) The rR·2'OMe-rY produced a slightly higher binding constant values with a K(1) of (1.25 ± 0.24) × 10(7) M(-1) and K(2) of (3.62 ± 0.18) × 10(5) M(-1). (9) The ΔT(m)-derived K(Tm) of 3.81 × 10(7) M(-1) for rR·S-dY was in relative agreement with the corresponding K(1) of 1.17 × 10(7) M(-1) derived constant from the fitted ITC. These results illustrate that the increased DNA·RNA hybrid duplex stability in the presence of aminoglycosides can help extend the roles of aminoglycosides in designing modified ODNs for targeting RNA.

Cellular uptake and biological activity of peptide nucleic acids conjugated with peptides with and without cell-penetrating ability

A 12-mer peptide nucleic acid (PNA) directed against the nociceptin/orphanin FQ receptor mRNA was disulfide bridged with various peptides without and with cell-penetrating features. The cellular uptake and the antisense activity of these conjugates were assessed in parallel. Quantitation of the internalized PNA was performed by using an approach based on capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). This approach enabled a selective assessment of the PNA moiety liberated from the conjugate in the reducing intracellular environment, thus avoiding bias of the results by surface adsorption. The biological activity of the conjugates was studied by an assay based on the downregulation of the nociceptin/orphanin FQ receptor in neonatal rat cardiomyocytes (CM). Comparable cellular uptake was found for all conjugates and for the naked PNA, irrespective of the cell-penetrating properties of the peptide components. All conjugates exhibited a comparable biological activity in the 100 nM range. The naked PNA also exhibited extensive antisense activity, which, however, proved about five times lower than that of the conjugates. The found results suggest cellular uptake and the bioactivity of PNA-peptide conjugates to be not primarily related to the cell-penetrating ability of their peptide components. Likewise from these results it can be inferred that the superior bioactivity of the PNA-peptide conjugates in comparison with that of naked PNA rely on as yet unknown factors rather than on higher membrane permeability. Several hints point to the resistance against cellular export and the aggregation propensity combined with the endocytosis rate to be candidates for such factors.

Therapeutic applications of synthetic CpG oligodeoxynucleotides as TLR9 agonists for immune modulation

Vertebrate toll-like receptors (TLRs) sense invading pathogens by recognizing bacterial and viral structures and, as a result, activate innate and adaptive immune responses. Ten human functional TLRs have been reported so far; three of these (TLR7, 8, and 9) are expressed in intracellular compartments and respond to single-stranded nucleic acids as natural ligands. The pathogen structure selectively recognized by TLR9 in bacterial or viral DNA was identified to be CpG dinucleotides in specific sequence contexts (CpG motifs). Short phosphorothioate-stabilized oligodeoxynucleotides (ODNs) containing such motifs are used as synthetic TLR9 agonists, and different classes of ODN TLR9 agonists have been identified with distinct immune modulatory profiles. The TLR9-mediated activation of the vertebrate immune system suggests using such TLR9 agonists as effective vaccine adjuvants for infectious disease, and for the treatment of cancer and asthma/allergy. Immune activation by CpG ODNs has been demonstrated to be beneficial in animal models as a vaccine adjuvant and for the treatment of a variety of viral, bacterial, and parasitic diseases. Antitumor activity of CpG ODNs has also been established in numerous mouse models. In clinical vaccine trials in healthy human volunteers or in immunocompromised HIV-infected patients, CpG ODNs strongly enhanced vaccination efficiency. Most encouraging results in the treatment of cancers have come from human phase I and II clinical trials using CpG ODNs as a tumor vaccine adjuvant, monotherapy, or in combination with chemotherapy. Therefore, CpG ODNs represent targeted immune modulatory drugs with a broad range of potential applications.

Cross-species pharmacokinetic comparison from mouse to man of a second-generation antisense oligonucleotide, ISIS 301012, targeting human apolipoprotein B-100

The pharmacokinetics of a 2'-O-(2-methoxyethyl)-modified oligonucleotide, ISIS 301012 [targeting human apolipoprotein B-100 (apoB-100)], was characterized in mouse, rat, monkey, and human. Plasma pharmacokinetics following parental administration was similar across species, exhibiting a rapid distribution phase with t(1/2alpha) of several hours and a prolonged elimination phase with t(1/2beta) of days. The prolonged elimination phase represents equilibrium between tissues and circulating drug due to slow elimination from tissues. Absorption was nearly complete following s.c. injection, with bioavailability ranging from 80 to 100% in monkeys. Plasma clearance scaled well across species as a function of body weight alone, and this correlation was improved when corrected for plasma protein binding. In all of the animal models studied, the highest tissue concentrations of ISIS 301012 were observed in kidney and liver. Urinary excretion was less than 3% in monkeys and human in the first 24 h. ISIS 301012 is highly bound to plasma proteins, probably preventing rapid removal by renal filtration. However, following 25 mg/kg s.c. administration in mouse and 5-mg/kg i.v. bolus administration in rat, plasma concentrations of ISIS 301012 exceeded their respective protein binding capacity. Thus, urinary excretion increased to 16% or greater within the first 24 h. Albeit slow, urinary excretion of ISIS 301012 and its shortened metabolites is the ultimate elimination pathway of this compound, as demonstrated by 32% of dose recovered in total excreta by 14 days in a rat mass balance study. The pharmacokinetics of ISIS 301012 in human is predictable from the pharmacokinetics measured in animals. The pharmacokinetic properties of ISIS 301012 provide guidance for clinical development and support infrequent dose administration.

A novel class of DNA analogs bearing 5'-C-phosphonothymidine units: synthesis and physicochemical and biochemical properties

S(C) and R(C) diastereomers of 5'-C-(O,O-diethyl)-phosphonylthymidine ((R)T and (S)T) were used for the synthesis of the dimers T(R)T and T(S)T, respectively. These dimers were incorporated at selected sites in oligonucleotide constructs. Melting temperature (Tm) experiments demonstrated that relative to the unmodified oligodeoxyribonucleotide, the presence of the (R)T moiety reduced the thermal stability of the duplexes by approximately 5.0 degrees C per modification, whereas their (S)T counterparts only slightly destabilized the duplex structure (deltaTm < or = 1 degree C/modification). The stability of the triple-helical complexes containing one, two, or three modified thymidines is slightly higher than that of the parent complex. Nuclease resistance studies performed with snake venom phosphodiesterase, calf spleen phosphodiesterase, and 3'-exonuclease from human plasma showed that cleavage of the oligonucleotides at the site of the modification was completely suppressed regardless of the stereochemistry of the 5'-C-chiral center. The influence of the (R)T and (S)T modification in the recognition sequence of HindIII, EcoRI, and HpaI restriction endonucleases was also investigated. Although the catalytic activity of HindIII was not affected by the presence of the 5'-C-ethoxyphosphonyl modification, the activities of the two remaining restriction enzymes were partially suppressed depending on the site of modification or the stereochemistry of the modification or both ((R)T vs. (S)T).

Evidence for a specific intracellular localization of an antisense oligonucleotide in k562 cells

In order to be active, antisense oligonucleotides (ASOs) should be delivered to the nuclei of cells. The lack of effect of some ASOs might be explained by poor distribution inside the cell. Here we describe the study of the intracellular distribution of an ASO in a leukemic cell line in which the ASO was not showing an effect. We used fluorescein isothiocyanate-labeled ASO and fluorescent or confocal microscopy. The internalised ASO was localized in a specific intracellular juxtanuclear region, showing no cytoplasmic or nuclear diffusion. Transfection of the ASO improved cellular distribution to the cytoplasm and nuclei and improved the ASO effect.

Molecular and cellular barriers limiting the effectiveness of antisense oligonucleotides

Antisense oligonucleotides present a powerful means to inhibit expression of specific genes, but their effectiveness is limited by factors including cellular delivery, biochemical attack, and poor binding to target. We have developed a systems model of the processes required for an antisense oligonucleotide to enter, gain access to its target mRNA, and exert activity in a cell. The model accurately mimics observed trends in antisense effectiveness with the stability of the oligonucleotide backbone and with the affinity/kinetics of binding to the mRNA over the time course of inhibition. By varying the model parameters within the physically realizable range, we note that the major molecular and cellular barriers to antisense effectiveness are intracellular trafficking, oligonucleotide-mRNA binding rate, and nuclease degradation of oligonucleotides, with a weaker dependence on total cellular uptake than might be expected. Furthermore, the model may serve as a predictive tool to design and test strategies for the cellular use of antisense oligonucleotides. The use of integrated mathematical modeling can play a significant role in the development of antisense and related technologies.

Antisense approach for the treatment of cytomegalovirus infection

Human cytomegalovirus (HCMV) is the most common viral opportunistic infection in patients suffering with acquired immunodeficiency virus (AIDS). HCMV is a systemic infection that may infect several sites in the body, including the retina, gastrointestinal tract, lungs, liver, and central nervous system. Retinitis is the most frequent manifestation of HCMV infection, occurring in 15-40% of all patients. HCMV is progressive and destroys the retina, eventually leading to blindness. Although, there are several drugs available to treat this disease, they are often of limited efficacy and have significant side-effects. Antisense oligonucleotides represent a novel alternative to the currently available drugs. Due to their high affinity and specificity to target the HCMV RNAs, interest in antisense technology to treat HCMV infections has been intense during the past few years. Two antisense drugs are currently in clinical trials, ISIS 2922 (Formivirsen) and GEM 132.

Binding and uptake of immunostimulatory CpG oligodeoxynucleotides by human neuroblastoma cells

Oligodeoxynucleotides (ODNs) that contain unmethylated CpG dinucleotides (CpG-ODN) trigger a strong innate immune response in vertebrates. They have been used to eradicate experimental neuroblastoma, but a direct interaction of CpG-ODN with neuroblastoma cells has not been investigated. We have analyzed uptake, binding, and intracellular distribution of CpG-ODN in the neuroblastoma cells line SKNSH. Our results indicate that cellular uptake of CpG-ODN is dose, time, temperature, and energy dependent but independent of the CpG motif. After internalization, CpGODN localized to the cytoplasm and showed a typical speckled distribution pattern. The intracellular distribution pattern and binding proteins are CpG motif independent as well. Thus, CpG-ODNs are taken up by neuroblastoma cells by a nonspecific transfer mechanism for oligonucleotides and interact with intracellular proteins. These mechanisms might help us to understand the biodistribution of oligo within tumors and might be helpful in evaluating the therapeutic effects of oligonucleotides and rational drug design.

Effect of phosphorothioate chirality on the grooves of DNA double helices: a molecular dynamics study

Phosphorothioate oligonucleotides (PS-ODNs) have gained considerable attention in drug therapy, primarily as potent antisense or antigene oligomers, which bind to specific DNA or mRNA sequences and lead to transcriptional or translational arrest. These are obtained by substituting one of the anionic oxygen of the phosphate group by a sulfur atom, which introduces chirality to the phosphorus atom of the DNA backbone. In this molecular dynamics simulation study, structural parameters like groove widths, environmental parameters like hydration or cation binding, and electrostatic energy surfaces of both the chiral forms of DNA/PS-DNA duplexes were assessed and compared with that of a normal DNA. Results indicate that, PS-S form with its sulfur atoms facing the minor groove has a widened minor groove, while the scenario is reverse for the PS-R form. Further analysis reveals the existence of several factors like large van der Waals radius of sulfur and the effect it has on its neighboring hydration pattern along with the net electrostatic environment, influencing such structural alterations. This also indicates, for the first time, the effect of absolute phosphorothioate chirality on the global structure of a DNA/PS-DNA hybrid that otherwise resembles a regular B-DNA structure.

Optimization of functional efficacy of phosphorothioate-modified oligonucleotides in a human CD8+ T-cell ex vivo expansion model

Antisense oligodeoxyribonucleotides (ODNs) can specifically inhibit gene expression, but their application to fresh human CD8+ T cells is limited by poor spontaneous uptake (<2%). We have examined and optimized the uptake of phosphorothioate-modified oligodeoxyribonucleotides (PS-ODNs) into these cells in an ex vivo expansion model. Optimal antisense treatments were found to be, for fresh CD8+ T cells, 1 micro m PS-ODNs complexed with lipofectin (LF), which resulted in 35% uptake and 10 micro m PS-ODNs in the absence of LF, for cultured cells, which resulted in 95% uptake. The delivered antisenses were functional, as determined by the inhibition of protein expression. In this respect, partially phosphorothioate-modified ODNs (PS-ODNs-P) were twice as effective as completely modified (PS-ODNs-C), and the antisense specific for the cap site showed the highest protein suppression of those tested (68%). Uptake mechanisms were also investigated. To our knowledge, this is the first optimization of the delivery of antisense oligonucleotides into human CD8+ T cells. This protocol could be used to study the function of a particular gene in cytotoxic T lymphocytes and also by those looking for a method to deliver short interfering RNA into cell lines to specifically suppress a gene of interest.

Pharmacokinetics of a tumor necrosis factor-alpha phosphorothioate 2'-O-(2-methoxyethyl) modified antisense oligonucleotide: comparison across species

The pharmacokinetics of a 2'-O-(2-methoxyethyl)-ribose modified phosphorothioate oligonucleotide, ISIS 104838 (human tumor necrosis factor-alpha antisense), have been characterized in mouse, rat, dog, monkey, and human. Plasma pharmacokinetics after i.v. administration exhibited relatively rapid distribution from plasma to tissues with a distribution half-life estimated from approximately 15 to 45 min in all species. Absorption after s.c. injection was high (80-100%), and absorption after intrajejunal administration in proprietary formulations was as high as 10% bioavailability compared with i.v. administration. Urinary excretion of the parent drug was low, with less than 1% of the administered dose excreted in urine after i.v. infusion in monkeys at clinically relevant doses (< or = 5 mg/kg). ISIS 104838 is highly bound to plasma proteins, likely preventing renal filtration. However, shortened oligonucleotide metabolites of ISIS 104838 lose their affinity to bind plasma proteins. Thus, excretion of radiolabel (mostly as metabolites) in urine (75%) and feces (5-10%) was nearly complete by 90 days. Elimination of ISIS 104838 from tissue was slow (multiple days) for all species, depending on the tissue or organ. The highest concentrations of ISIS 104838 in tissues were seen in kidney, liver, lymph nodes, bone marrow, and spleen. In general, concentrations of ISIS 104838 were higher in monkey tissues than in rodents at body weight-equivalent doses. Plasma pharmacokinetics scale well across species as a function of body weight alone. This favorable pharmacokinetic profile for ISIS 104838 provides guidance for clinical development and appears to support infrequent and convenient dose administration.

Ten years of antisense inhibition of brain G-protein-coupled receptor function

Antisense oligonucleotides (AOs) are widely used as tools for inhibiting gene expression in the mammalian central nervous system. Successful gene suppression has been reported for different targets such as neurotransmitter receptors, neuropeptides, ion channels, trophic factors, cytokines, transporters, and others. This illustrates their potential for studying the expression and function of a wide range of proteins. AOs may even find therapeutic applications and provide an attractive strategy for intervention in diseases of the central nervous system (CNS). However, a lack of effectiveness and/or specificity could be a major drawback for research or clinical applications. Here we provide a critical overview of the literature from the past decade on AOs for the study of G-protein-coupled receptors (GPCRs). The following aspects will be considered: mechanisms by which AOs exert their effects, types of animal model system used, detection of antisense action, effects of AO design and delivery characteristics, non-antisense effects and toxicological properties, controls used in antisense studies to assess specificity, and our results (failures and successes). Although the start codon of the mRNA is the most popular region (46%) to target by AOs, targeting the coding region of GPCRs is almost as common (41%). Moreover, AOs directed to the coding region of the GPCR mRNA induce the highest reductions in receptor levels. To resist degradation by nucleases, the modified phosphorothioate AO (S-AO) is the most widely used and effective oligonucleotide. However, the end-capped phosphorothioate AOs (ECS-AOs) are increasingly used due to possible toxic and non-specific effects of the S-AO. Other parameters affecting the activity of a GPCR-targeting AO are the length (mostly an 18-, 20- or 21-mer) and the GC-content (mostly varying from 30 to 80%). Interestingly, one-third of the AOs successfully targeting GPCRs possess a GC/AT ratio of 61-70%. AO-induced reductions in GPCR expression levels and function range typically from 21 to 40% and 41 to 50%, respectively. In contrast to many antisense reviews, we therefore conclude that the functional activity of a GPCR after AO treatment correlates mostly with the density of the target receptors (maximum factor 2). However, AOs are no simple tools for experimental use in vivo. Despite successful results in GPCR research, no general guidelines exist for designing a GPCR-targeting AO or, in general, for setting up a GPCR antisense experiment. It seems that the correct choice of a GPCR targeting AO can only be ascertained empirically. This disadvantage of antisense approaches results mostly from incomplete knowledge about the internalisation and mechanism of action of AOs. Together with non-specific effects of AOs and the difficulties of assessing target specificity, this makes the use of AOs a complex approach from which conclusions must be drawn with caution. Further antisense research has to be carried out to ensure the adequate use of AOs for studying GPCR function and to develop antisense as a valuable therapeutic modality.

bis-Cholesteryl-conjugated phosphorothioate oligodeoxynucleotides are highly selectively taken up by the liver

We previously modulated, by conjugating a single cholesterol, plasma protein binding and liver cell uptake of a phosphorothioate oligodeoxynucleotide (PS-ODN). In this study, we investigated the biological fate of a PS-ODN, denoted ISIS-9389 (3',5'-bis-cholesteryl-conjugated ISIS 3082), provided with two cholesteryl moieties. After intravenous injection of into rats, [(3)H]ISIS-9389 was cleared from plasma with a half-life of 23.6 +/- 0.3 min. After 90 min (approximately 95% cleared), the liver contained 83.0 +/- 0.8% of the dose. Spleen and bone (marrow), which constitute with the liver the reticuloendothelial system, contained 3.1 +/- 0.3 and 4.3 +/- 0.2%, respectively. All other tissues accumulated together <5% of the dose. The hepatic uptake of [(3)H]ISIS-9389 occurred mainly by endothelial cells (51.9 +/- 6.4% of the liver uptake). Parenchymal and Kupffer cells were responsible for 24.9 +/- 7.7 and 23.3 +/- 2.5%, respectively. Preinjected polyinosinic acid and polyadenylic acid reduced hepatic uptake, albeit the latter was less effective. This finding suggests implication of (multiple) scavenger receptors in liver uptake of ISIS-9389. The interaction of ISIS-9389 with plasma proteins, analyzed by size exclusion chromatography, differs from that of unconjugated PS-ODN and PS-ODN with a single cholesterol. Plasma-incubated ISIS-9389 was mainly recovered as a high molecular weight complex. In conclusion, conjugation of PS-ODNs with two cholesteryl moieties results in almost quantitative uptake by the liver. The liver targeting exceeds the already impressive gain in liver uptake achieved by conjugation of a single cholesterol, and is expected to increase the therapeutic activity against liver-associated targets and reduce side effects in nonhepatic tissues.

Cellular uptake of antisense oligonucleotides after complexing or conjugation with cell-penetrating model peptides

The uptake by mammalian cells of phosphorothioate oligonucleotides was compared with that of their respective complexes or conjugates with cationic, cell-penetrating model peptides of varying helix-forming propensity and amphipathicity. An HPLC-based protocol for the synthesis and purification of disulfide bridged conjugates in the 10-100 nmol range was developed. Confocal laser scanning microscopy (CLSM) in combination with gel-capillary electrophoresis and laser induced fluorescence detection (GCE-LIF) revealed cytoplasmic and nuclear accumulationin all cases. The uptake differences between naked oligonucleotides and their respective peptide complexes or conjugates were generally confined to one order of magnitude. No significant influence of the structural properties of the peptide components upon cellular uptake was found. Our results question the common belief that the increased biological activity of oligonucleotides after derivatization with membrane permeable peptides may be primarily due to improved membrane translocation.

Phosphodiester CpG oligonucleotides as adjuvants: polyguanosine runs enhance cellular uptake and improve immunostimulative activity of phosphodiester CpG oligonucleotides in vitro and in vivo

Bacterial DNA and oligonucleotides (ODN) containing CpG-motifs strongly activate cells of the immune system. Accordingly CpG-DNA is a powerful adjuvant in vaccination protocols for B-cell as well as for cytotoxic T-cell responses. A decisive propensity of CpG-DNA is its capacity to induce preferentially T helper type 1 (Th1)-dominated immune responses. To exert its function CpG-DNA has to be taken up by responsive cells, e.g. antigen-presenting cells (APC). The rate of uptake is influenced by the DNA's backbone modification and critically determines activity of CpG-DNA. CpG ODN with a phosphothioate backbone (PTO) are currently used for most in vivo and in vitro studies, since PTO modification protects ODN from the attack of nucleases. However, after administration of PTO-modified CpG-ODN long-lasting effects including lymphadenopathy as well as sustained local interferon-gamma (IFN-gamma) and interleukin-12 (IL-12) production have been reported. To circumvent these restrictions we investigated the effects of DNA sequence as well as DNA backbone modification on cellular uptake and resulting immunostimulation. We show here that uptake of phosphodiester (PO)-CpG-ODN can be strongly enhanced by poly guanosine runs added at the 3' end of the ODN. In addition these ODN showed an improved immunostimulatory activity in vivo and in vitro. This included protection of mice against lethal Th2-dependent leishmaniasis as well as priming of antigen specific Th1 responses. More importantly, guanosine-rich PO-CpG-ODN neither induced lymphadenopathy nor prolonged cytokine production after local administration. Since these improved PO ODN are efficient in vitro and in vivo and lack long lasting undesired effects they could be used preferably as adjuvants in vaccination protocols.

Uptake and quantification of intracellular concentration of lipophilic pro-oligonucleotides in HeLa cells

Several lipophilic prodrugs of oligonucleotides (T12 and T20) bearing enzymolabile protecting groups and labeled with fluorescein were synthesized. Their cellular uptake was studied by three different approaches using fluorescence: fluorescence microscopy, flow cytometry and spectrofluorometry. The corresponding prooligonucleotides (pro-oligos) were rapidly and efficiently taken up by HeLa cells and were found homogeneously in the cytoplasm and in the nucleus. The uptake was proportional to their relative lipophilicity and likely proceeded through a passive diffusion mechanism. Uptake followed a dose-response curve. This prooligo approach led to a 2-log increase of uptake in comparison with a T20 phosphorothioate oligonucleotide. Finally, an intracellular concentration of pro-oligo was estimated between 4 and 6 microM for an external concentration of 1 microM and up to 27 microM for an incubation at 10 microM.

Quantitative three-dimensional analysis and diffusion modeling of oligonucleotide concentrations after direct intraparenchymal brain infusion

We compared quantitative experimental results on the diffusion of 35S-labeled phosphorothioate oligonucleotide (PS-ODN) after intraparenchymal infusion in rat brain, with the distributions predicted by Fick's second law of diffusion. Fischer 344 rats underwent identical intracerebral infusions of 36S-PS-ODN. After 0, 5, 11, 23, and 47 h, groups of animals were sacrificed and sequential brain cryosections subjected to autoradiography. The resulting experimental data were compared to the predicted distributions, for estimation of the apparent free diffusion coefficient, D*. Volumes of distribution and total content of 36 S-PS-ODN in the parenchyma were also computed, to monitor loss of total material. The values for D* were within the expected range for the 21-mer PS-ODN used, but a progressive decrease in D* over time was noted. The model requires D* to remain constant and, thus, does not adequately explain the spread of 35S-PS-ODN following infusion. The progressive slowing of spread over time suggests that at later time points, 35S-PS-ODN may be fixed by tissue binding or cellular uptake in the brain. Loss of material via vascular and CSF clearance may also contribute to the lack of fit. Our results highlight issues to be addressed in the modeling and experimental design of the intraparenchymal infusion process.

Novel non-endocytic delivery of antisense oligonucleotides

Antisense oligonucleotides (ONs) have several properties that make them attractive as therapeutic agents. Hybridization of antisense ONs to their complementary nucleic acid sequences by Watson-Crick base pairing is a highly selective and efficient process. Design of therapeutic antisense agents can be made more rationally as compared to most traditional drugs, i.e., they can be designed on the basis of target RNA sequences and their secondary structures. Despite these advantages, the design and use of antisense ONs as therapeutic agents are still faced with several obstacles. One major obstacle is their inefficient cellular uptake and poor accessibility to target sites. In this article, we will discuss key barriers affecting ON delivery and approaches to overcome these barriers. Current methods of ON delivery will be reviewed with an emphasis on novel non-endocytic methods of delivery. ONs are taken up by cells via an endocytic process. The process of ON release from endosomes is a very inefficient process and, hence, ONs end up being degraded in the endosomes. Thus, ONs do not reach their intended site of action in the cytoplasm or nucleus. Delivery systems ensuring a cytoplasmic delivery of ONs have the potential to increase the amount of ON reaching the target. Here, we shall examine various ON delivery methods that bypass the endosomal pathway. The advantages and disadvantages of these methods compared to other existing methods of ON delivery will be discussed.

Alternative interpretations of the oligonucleotide transport literature: insights from nature

Elucidation of the mechanism of oligonucleotide (ON) cellular internalization has met an impasse at the lipid penetration stage. ON internalization is commonly regarded to involve endocytosis, yet the method by which the ON penetrates the endosome membrane remains a mystery despite more than 10 years of research by multiple laboratories. In addition, the literature regarding this topic is fraught with discrepancies and inconsistencies. Therefore, the goal of this review is to propose and illustrate the feasibility of the notion that the literature discrepancies are perhaps an indication of a complex transport mechanism involving more than one uptake pathway. Accordingly, ON- and cell-differences in uptake may be attributed to differences in the relative importance of these pathways for different cell types and ONs. An example of one such pathway is reviewed and critiqued in this communication with respect to its hypothetical role in ON uptake. Other innovative mechanisms should similarly be considered to stimulate new ideas, discussion and research in this unique and interesting field.

Modulation of plasma protein binding and in vivo liver cell uptake of phosphorothioate oligodeoxynucleotides by cholesterol conjugation

Several studies have shown improved efficacy of cholesteryl-conjugated phosphorothioate antisense oligodeoxynucleotides. To gain insight into the mechanisms of the improved efficacy in vivo, we investigated the disposition of ISIS-9388, the 3'-cholesterol analog of the ICAM-1-specific phosphorothioate oligodeoxynucleotide ISIS-3082, in rats. Intravenously injected [(3)H]ISIS-9388 was cleared from the circulation with a half-life of 49.9 +/- 2.2 min (ISIS-3082, 23.3 +/- 3.8 min). At 3 h after injection, the liver contained 63.7 +/- 3. 3% of the dose. Compared to ISIS-3082, the hepatic uptake of ISIS-9388 is approximately 2-fold higher. Endothelial, Kupffer and parenchymal cells accounted for 45.7 +/- 5.7, 33.0 +/- 5.9 and 21.3 +/- 2.6% of the liver uptake of [(3)H]ISIS-9388, respectively, and intracellular concentrations of approximately 2, 75 and 50 microM, respectively, could be reached in these cells (1 mg/kg dose). Preinjection with polyinosinic acid or poly-adenylic acid reduced the hepatic uptake of [(3)H]ISIS-9388, which suggests the involvement of (multiple) scavenger receptors. Size exclusion chromatography of mixtures of the oligonucleotides and rat plasma indicated that ISIS-9388 binds to a larger extent to high molecular weight proteins than ISIS-3082. Analysis by agarose gel electrophoresis indicated that ISIS-9388 binds more tightly to plasma proteins than ISIS-3082. The different interaction of the oligonucleotides with plasma proteins possibly explains their different dispositions. We conclude that cholesterol conjugation results in high accumulation of phosphorothioate oligodeoxynucleotides in various liver cell types, which is likely to be beneficial for antisense therapy of liver-associated diseases.

Identification, purification and partial characterisation of an oligonucleotide receptor in membranes of HepG2 cells

The low and unpredictable uptake and cytosolic transfer of oligonucleotides (ODN) is a major reason for their limited benefit. Improving the ODN potential for therapy and research requires a better understanding of their receptor-mediated endocytosis. We have undertaken to identify a membrane ODN receptor on HepG2 cells by ligand blotting of cell extracts with [(125)I]ODN and by photolabelling of living cells with a [(125)I]ODN-benzophenone conjugate. A major band at 66 kDa was identified by the two methods. Its labelling was saturable and competed for by unlabelled ODN of various sequences and irrespective of the presence of a phosphodiester or phosphoro-thioate backbone. This protein remained sedimentable after carbonate extraction, indicating strong membrane association. About half of the total cell amount resisted extensive surface proteolysis, suggesting a dual localisation at the plasma membrane and cytoplasmic vesicles. The protein was purified using a biotinylated ODN-benzophenone conjugate by photocrosslinking followed by streptavidin affinity purification. A sequence obtained by Edman degradation showed no homology with known proteins. Using anti-peptide antisera, labelling by western blotting revealed at 66 kDa a band with comparable properties as found by ligand blotting. Thus, a new membrane protein acting as an ODN receptor has been demonstrated.

Histidylated oligolysines increase the transmembrane passage and the biological activity of antisense oligonucleotides

We have designed histidylated oligolysines which increase the uptake, the cytosolic delivery and the nuclear accumulation of antisense oligonucleotides (ODN). Flow cytometry analysis showed a 10-fold enhancement of the ODN uptake in the presence of histidylated oligolysines. The intracellular localizations of fluorescein-labeled ODN and of rhodamine-labeled histidylated oligolysines were investigated by confocal microscopy. Histidylated oligolysines favor the cyto-solic delivery of ODN from endosomes and increase their nuclear accumulation. In contrast, in their absence fluorescent ODN were not observed inside the nucleus but were distributed overwhelmingly within the vesicles in the cytosol. In addition, histidylated oligolysines yielded a more than 20-fold enhancement of the biological activity of antisense ODN towards the inhibition of transient as well as constitutive gene expression. Prevention of endosome lumen acidification using bafilomycin A(1)abolished the effect of histidylated oligolysines, suggesting that protonation of the histidyl residues was involved in the transmembrane passage of ODN.

Cell binding, uptake and cytosolic partition of HIV anti-gag phosphodiester oligonucleotides 3'-linked to cholesterol derivatives in macrophages

The purpose of this study is to evaluate the cell interactions of a new class of compounds composed of phosphodiester oligonucleotides linked to the cholesterol group at position 3, 7, or 22 of the steroid structure. The resulting conjugates were assessed for their capacity to bind, penetrate and partition in the cytoplasmic compartment of murine macrophages. The results showed that lipophilic conjugates bind to cells much faster (t(1/2) < or = 10 min) than do underivatized oligomers. Oligomers tethered to the cholesterol at positions 3 and 7 (PO-GEM-3-Chol and PO-GEM-7-Chol) interacted more efficiently with cell membranes and were better internalized than oligomers attached to the cholesterol moiety at position 22 (PO-GEM-22-Chol). The cytosolic fraction of internalized oligomers was studied by a digitonin-based membrane permeabilization method. The recovered fraction of oligomers that can freely diffuse from the cytosol was comparable for GEM-91, a phosphorothioate congener, and for PO-GEM-7-Chol (50-60% of the internalized oligomers), while that of PO-GEM-3-Chol was less (30% of the internalized oligomers) indicating a higher membrane affinity of the latter derivative as compared to the other investigated compounds. Membrane binding and cell internalization correlated well with the hydrophobicity of the conjugates as characterized by their partition coefficients in a water-octanol system. Due to their capacity of rapid binding and cytosolic partition in cells, cholesterol-derivatized oligonucleotides at position 3 or 7 of the steroid molecule appeared as good candidates for systemic delivery of anti-HIV antisense compounds.

Increased potency of an aptameric G-rich oligonucleotide is associated with novel functional properties of phosphorothioate linkages

We previously showed that inhibition of the expression of CD28 (an essential immune receptor on T cells) mediated by a phosphorothioate (PS)-modified aptameric oligodeoxynucleotide (ODN) sequence, GR1, resulted in reduced T cell responses in vitro and in vivo. Using GR1 sequences differing only in the amount of terminal PS linkages (chimeric SO-ODN), the present study demonstrated that even after a substantial reduction in PS linkages, this 18-mer ODN sequence could still confer functionality in the ODN-mediated inhibition of CD28 expression. We showed that secondary structure and full retention of the ability to form a specific protein-ODN complex and to increase cellular uptake in activated Jurkat T cells were critical parameters in the determination of the magnitude of bioactivity of chimeric SO-ODN. We report that a chimeric SO-ODN with terminal PS linkages that total 9 (ICN 17221) or 12 (ICN 17263) was sufficient to inhibit CD28 expression and suppress in vivo inflammatory ear responses to contact allergen in mice with similar potency to the 17-thioate S-ODN (ICN 16064). Interestingly, all chimeric SO-ODN showed similar in vitro nuclease resistance. These data suggest alternate functional properties for PS linkages, unrelated to nuclease resistance, in enhancing the bioactivity of a G-rich aptamer.

High specific radioactivity labeling of oligonucleotides with 3H-succinimidyl propionate

An easy and rapid method for tritium labeling of deprotected oligonucleotides is proposed. The method consists in performing the reaction of commercial 3H-succinimidyl propionate with a terminal amino group of the oligonucleotide in an organic medium. High specific radioactivity labeling can be achieved with minimal radiolysis during long term storage. The synthesis of the nonradioactive congener having an identical structure to the labeled compound is also described.

Enhanced downregulation of the p75 nerve growth factor receptor by cholesteryl and bis-cholesteryl antisense oligonucleotides

The effects of conjugating cholesterol to either or both ends of a phosphorothioate (PS) oligonucleotide were analyzed in terms of cellular uptake and antisense efficacy. The oligo sequence was directed against the p75 nerve growth factor receptor (p75), and was tested in differentiated PC12 cells, which express high levels of this protein. The addition of a single cholesteryl group to the 5'-end significantly increased cellular uptake and improved p75 mRNA downregulation compared with the unmodified PS oligo. However, only a minor degree of downregulation of p75 protein was obtained with 5' cholesteryl oligos. Three different linkers was used to attach the 5' cholesteryl group but were found not to have any impact on efficacy. Addition of a single cholesteryl group to the 3'-end led to greater p75 mRNA downregulation (31%) and p75 protein downregulation (28%) than occurred with the 5' cholesteryl oligos. The biggest improvement in antisense efficacy, both at the mRNA and protein levels, was obtained from the conjugation of cholesterol to both ends of the oligo. One of the bischolesteryl oligos was nearly as effective as cycloheximide at decreasing synthesis of p75. The bis-cholesteryl oligos also displayed significant efficacy at 1 microM, whereas the other oligos required 5 microM to be effective. The enhanced efficacy of bis-cholesteryl oligos is likely to be due to a combination of enhanced cellular uptake and resistance to both 5' and 3' exonucleases.

Different frequency of gene targeting events by the RNA-DNA oligonucleotide among epithelial cells

A unique hybrid oligonucleotide composed of both RNA and DNA has been shown to correct a point mutation in a site-specific and inheritable manner in extrachromosomal and chromosomal targets. In order to develop new gene therapeutics for skin, we tested two oligonucleotides that were shown to create a point mutation in alkaline phosphatase and beta-globin genes in several epithelial cell types. Highly transformed epithelial cells (HeLa) exhibited a conversion frequency of 5% by both RNA-DNA oligonucleotides. In comparison, other immortalized epithelial cells (HaCaT) or human primary keratinocytes did not show any detectable level of gene conversion by the restriction fragment length polymorphism analysis, indicating less than 1% conversion frequency. The concentration of the oligonucleotide in the nuclei of HeLa cells was similar to that of HaCaT or human primary keratinocytes measured by a radiolabeled or a fluorescein-conjugated oligonucleotide. Moreover, the RNA-DNA oligonucleotide exhibited a prolonged stability in the nucleus. Thus, neither uptake nor nuclear stability of the oligonucleotide appears to be a limiting factor in gene targeting events under our experimental conditions. These results indicate that the frequency of gene targeting varies among different cells, suggesting that cellular recombination and DNA repair activities may be important.

Interaction of oligodeoxynucleotides with mycobacteria: implications for new therapeutic strategies

The use of synthetic oligonucleotides (ONs) to systematically address new pharmacologic targets in mycobacteria would enhance the introduction of new molecular targets for drug intervention. Oligonucleotides' mechanism of action allows researchers to pursue the importance of particular proteins without the requirement of having purified samples. For this approach to be effective, mycobacteria must be able to transport ONs to their cytoplasm, and if this is not the case, the agents must be otherwise delivered. In this report, we characterize the ability of phosphorothioate (PS) and phosphorodiester (PD) ONs to interact with both Mycobacterium smegmatis and Mycobacterium tuberculosis. In addition, the use of delivery enhancer compounds, ethambutol and PAMAM dendrimer, was evaluated on the ON-mycobacteria interaction. ON interaction was demonstrated to be concentration-dependent, suggesting a possibly active component of the oligonucleotide and bacteria interaction. ON interaction could be increased by the coincubation of the bacteria with the delivery adjuvants. Treatment with ethambutol or dendrimers (fourth generation) was demonstrated to increase ON interaction with both species of mycobacteria although not to the same extent. The results of these preliminary experiments indicate that through use of the proper delivery adjuvant, ON interactions with mycobacteria can be increased. These findings may have implications for probing future antimycobacterial therapeutic targets.

Sequence dependency of the internalization and distribution of phosphorothioate oligonucleotides in vascular smooth muscle cells

Antisense studies imply the utilization of oligonucleotides (ODN) for sequence-specific down-regulation of genes. This usually consists in assessing antisense sequences versus control sequences (mismatched, inverted, scrambled, randomized or any sequence unrelated to the relevant target). Even though the investigated biological effect (knockdown of an unwanted protein) is observed only with the antisense sequence and weakly, if at all, with any of the control sequences, this is a necessary but not a sufficient condition to demonstrate an antisense effect. Indeed, biochemical parameters such as stability, uptake and subcellular compartmentalization of ODN in a given cellular system are most often sequence-dependent processes. In this work, a series of phosphorothioate ODN of different lengths and sequences were evaluated as to their binding, internalization and subcellular distribution properties in vascular smooth muscle cells. In addition to membrane binding and nuclear accumulation, the partition of ODN in the cytosol of cells was measured by a method based upon controlled permeabilization of the plasma membrane, permitting the recovery of the cytosolic content with minimal damage to the membranes of the endocytic vesicles and lysosomes. We found that the tested ODN showed striking differences in their uptake and distribution in smooth muscle cells. Our results gave rise to the problem of validating the observed biological effects when different sequences of ODN were compared. Cellular studies such as the one presented in this work could help in choosing the proper control sequences among ODN exhibiting similar cell interactions as compared to the antisense sequences. Moreover, this method could be useful for the selection of antisense sequences that can be efficiently internalized and preferentially distributed in the appropriate compartments in cells for in vitro antisense studies.

Cellular delivery of oligonucleotides by synthetic import peptide carrier

PURPOSE

Inefficient cellular uptake and endosomal entrapment are among the obstacles impeding the therapeutic use of oligonucleotides (ONs). The objectives of this study are to investigate the feasibility of utilizing a synthetic import peptide as a drug carrier for cytoplasmic delivery of ONs and to study its transport mechanisms.

METHODS

A molecular conjugate consisting of a signal import peptide (IP) derived from Kaposi fibroblast growth factor (K-FGF) and a polycationic ON linker, polylysine (PL), was synthesized and complexed with 5' fluorescently-labeled ON. Complex formation was verified by spectral shift assay and cellular uptake of the ON complex was studied fluorometrically. Microscopic studies were performed to visualize the intracellular distribution of the ON.

RESULTS

Cells treated with the ON:IP-PL complex exhibited a dose-dependent increase in ON uptake over free ON-treated controls. The uptake of the complex was shown to occur via an energy-independent, non-endocytic, process since metabolic and endocytic inhibitors and low temperature did not prevent the uptake. Microscopic studies revealed a non-punctate fluorescence pattern, consistent with the non-endocytic transport process. Intense nuclear fluorescence was observed in cells treated with the complex but not with free ON, suggesting enhanced cytoplasmic delivery and nuclear accumulation of the ON by the conjugate. Efficient complex uptake was shown to require both the ON-binding moiety PL and the IP moiety. The delivery system was found to be non-toxic at the concentrations used.

CONCLUSIONS

The peptide carrier was effective in promoting the cellular uptake of ON. The mechanism by which the peptide facilitates ON uptake appears to involve a direct translocation of ON via a non-endocytic process. The peptide carrier has the potential to overcome the problem of ON endosomal entrapment and degradation.

Antiproliferative effect of c-myc antisense phosphorothioate oligodeoxynucleotides in malignant glioma cells

OBJECTIVE

To improve the prognosis for primary malignant tumors of the central nervous system, new therapeutic strategies are needed. Antisense oligodeoxynucleotides (ODNs) offer the potential to block the expression of specific genes within cells. The proto-oncogene c-myc has long been implicated in the control of normal cell growth and its deregulation in the development of neoplasia. We therefore reasoned that a strategy using ODNs complementary to c-myc messenger ribonucleic acid would be a potent inhibitor of glioma cell proliferation.

METHODS

A variety of antisense, sense, and scrambled (15-mer) phosphorothioate ODNs targeted to rat and human c-myc messenger ribonucleic acid were synthesized and added to the media of cultured RT-2 cells (a rat glioblastoma cell line). Cell growth was assessed by 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide dye assay 1 to 5 days after adding the ODNs. c-Myc protein expression was analyzed by Western blot analysis. The stability of the ODNs was confirmed by gel electrophoresis.

RESULTS

Compared with cultures containing standard media, two of three antisense ODNs significantly inhibited the growth of glioma cells, whereas sense and scrambled sequence ODNs did not significantly affect cell growth at the concentrations tested. A human c-myc antisense sequence, which differed from the rat sequence by one base substitution, also had an inhibitory effect on RT-2 cells. Western blot analysis demonstrated that expression of immunoreactive c-Myc protein was also greatly reduced in the rat antisense ODN-treated cells (and not in sense-, scrambled-, or control-treated cells). The degree of reduction of c-Myc protein expression correlated well with the decrease in cell growth observed with several antisense ODNs. Phosphorothioate ODNs were stable in cell culture media for at least 5 days.

CONCLUSION

These results suggest that c-Myc plays a critical role in glioma cell proliferation and demonstrate that antisense ODNs can suppress proto-oncogene expression and inhibit the proliferation of glioma cells. Our results indicate that the antiproliferative activity of these ODNs was mediated predominantly through sequence-specific antisense mechanisms, but that sequence-specific nonantisense effects may also contribute to the strongest effects demonstrated. These findings support a potential role for antisense strategies designed to inhibit c-myc expression in the treatment of malignant gliomas.

Uptake and efflux of intact antisense phosphorothioate deoxyoligonucleotide directed against angiotensin receptors in bovine adrenal cells

Antisense oligonucleotide (AS-ODN) inhibition of angiotensin receptors (AT1-R) offers a potentially novel therapeutic approach for hypertension, left ventricular hypertrophy and other aspects of cardiovascular disease. To clarify questions concerning cellular uptake and retention of these oligos, we quantified the trafficking and stability of phosphorothioated modified AS-ODN to AT1 receptor mRNA in adrenal cells, using visual and chromatographic analysis. The AS-ODN to AT1 receptor mRNA was effective in significantly inhibiting AT1 receptor binding in a dose dependent manner. FITC-labeled ODNs were used to determine the cellular uptake in bovine adrena cortex cells; using confocal microscopy, rapid cellular uptake of 15-mer ODNs was observed. Uptake is initially rapid (30 min to 4 h) followed by a slower uptake process 24 h and after. The cellular accumulation of ODN involves a dynamic balance between influx and efflux processes. Efflux of FITC-ODN had a f1/2 = 4.6 days. Uptake was time and dose dependent. No obvious degradation of intracellular ODNs occurred as shown by intact peaks for 15-mer ODN on thin layer chromatography. The results suggest that the AS-ODN to AT1 receptor mRNA was resistant to cellular nucleases. The FITC-ODN accumulated mainly in the nucleus and remained there intact for up to 3 days. No significant change in target mRNA was observed by quantitative RT-PCR. Therefore the antisense inhibition mechanism of this ODN does not appear to stimulate RNase H or block transcription. Since the ODN accesses the nucleus, the results imply that the ODN inhibits specific mRNA transport into the cytoplasm. The data show that AS-ODN, for inhibition of AT1 receptors, is rapidly taken up and stable in cells and produces specific inhibition of AT1 receptors.

Cellular uptake properties of a 2'-amino/2'-O-methyl-modified chimeric hammerhead ribozyme targeted to the epidermal growth factor receptor mRNA

Catalytic RNA or ribozymes have important potential applications as molecular biological tools in the study of gene expression and as therapeutic inhibitors of disease-causing genes. Very little is known, however, about the cellular uptake mechanisms of exogenously delivered synthetic ribozymes. In this study, we have characterized the uptake properties of a synthetic, 2'-O-methyl-modified ribozyme containing U4/U7 amino groups within the catalytic core of the hammerhead motif. The cellular uptake of the internally [32P]-radiolabeled hammerhead ribozyme in U87-MG glioma cells was temperature, energy, and pH dependent and involved an active process that could be competed with cold ribozyme of the same chemistry and sequence, an all 2'-O-methyl-modified ribozyme of the same sequence, antisense PS-ODNs, and a variety of other polyanions (salmon sperm DNA, spermidine, dextran sulfate, and heparin). Subcellular distribution studies of fluorescently labeled ribozymes confirmed an extranuclear, punctate localization similar to that observed for an endosomal marker, dextran. Our study highlights that hammerhead ribozymes, despite exhibiting a defined secondary structure, enter cells by an endocytic mechanism that appears to be similar to that reported for a variety of antisense ODNs. These observations should facilitate the development of more efficient delivery systems.

Inhibition of Plasmodium falciparum proliferation in vitro by ribozymes

Catalytic RNA (ribozymes) suppressed the growth of the human malarial parasite Plasmodium falciparum in vitro. The phosphorothioated hammerhead ribozymes targeted unique regions of the P. falciparum carbamoyl-phosphate synthetase II gene. The P. falciparum carbamoyl-phosphate synthetase II gene encodes the first and limiting enzyme in the pathway, and its mRNA transcript contains two large insert regions absent in other carbamoyl-phosphate synthetases, including that from humans. These inserts are ideal targets for nucleic acid therapy. Exogenous delivery of ribozymes to cultures reduced malarial viability up to 55% at 0.5 microM ribozyme concentrations, which is significantly greater than control levels (5-15% reduction), suggesting a sequence-specific inhibition. This inhibition was shown to be stage-specific, with optimal inhibitions being detected after 24 h, coincident with maximal production of the carbamoyl-phosphate synthetase enzyme in the course of the life cycle of the parasite. A decrease in total carbamoyl-phosphate synthetase activity was observed only in cultures treated with the ribozymes. The task of developing alternative therapeutic agents against malaria is urgent due to the evolution of drug-resistant strains of P. falciparum, the most virulent of all human malarial parasites. Another critical issue to be addressed is the possibility of eliminating or reducing any systemic toxicity to the host, which can potentially be provided by nucleic acid therapy. This work is the first reported assessment of the ability of ribozymes as antimalarials. Ribozyme inhibition assays can also aid in identifying important antimalarial loci for chemotherapy. The malarial parasite can, in turn, be a useful in vivo host to study the catalysis and function of new ribozyme designs.

[A simple method for the study of cytosolic content of oligonucleotides in cells]

Antisense oligonucleotides are currently used for the specific control of the expression of a selected gene. Their putative targets are located in the cytoplasm (messenger RNA) or the nucleus (pre-messenger RNA or DNA). This approach is conditioned by the presence of the antisense molecule inside the cell at sufficient concentrations and in the appropriate compartments. We propose in this paper a simple method for the study of the cytosolic content of internalized oligonucleotides. This method is based on the selective permeabilization of the plasmic membrane by the detergent digitonin. By complexing to membrane cholesterol, the detergent creates pores through which soluble and diffusible species can escape outside the cells. The selectivity of membrane permeabilization was controlled by using compartment markers: lactate dehydrogenase (LDH) for cytosol, dextrane-rhodamine (DEX) and hexosaminidase (HAM) for endocytic vesicles and lysosomes, respectively. Optimal digitonin concentrations and incubation times have been defined to reach the following pattern of membrane permeabilization: LDH > 80%; DEX and HAM < 15%. The method was applied to monitor the quantity of extractible oligonucleotides from cells after endocytosis. The results showed that phosphodiester and phosphorothioate oligomers are readily available in the cytosol (60-50% of the internalized species), whereas those bearing a hydrophobic moiety (fluorescein, cholesterol) are less diffusible probably owing to membrane binding. Internalization and cytosol partition were found to depend on the chemical nature of the oligonucleotide, and also on the sequence and the cell type. This method could be useful for the selection of antisense molecules that exhibit the best internalization and distribution in cells, and for a more appropriate choice of control sequences in antisense studies.

Antisense inhibition of angiotensinogen in hepatoma cell culture is enhanced by cationic liposome delivery

Abnormalities in expression of renin angiotensin system components, including angiotensinogen, have been implicated in the development and maintenance of hypertension in the spontaneously hypertensive rat model of hypertension. Antisense compounds are being used as physiological tools to provide information on cardiovascular function and hypertension and also show great potential for development as therapeutic agents. We have previously shown that peripheral administration of antisense oligonucleotides to angiotensinogen in vivo decreases hypertensive blood pressures with concomitant changes in angiotensinogen protein and angiotensin II. However, studies using naked phosphorothioated oligonucleotide targeted to the same region did not produce changes in angiotensinogen mRNA in vivo or in cell culture. We now provide data which show that enhanced oligonucleotide delivery utilizing cationic liposomes significantly increases the attenuation of angiotensinogen protein and decreases mRNA in a dose dependent manner. These data provide an understanding of the mechanism of action of the antisense oligonucleotide and also establish optimal conditions and doses for further studies.

Liposomal targeting of bcl-2 antisense oligonucleotides with enhanced stability into human myeloma cell lines

Cationic liposomes improve the delivery of antisense oligonucleotides (ODNs) into cells. However, there is marked variability in the cellular uptake of ODNs into different cell lines. We used liposomes containing dimethyloctadecylammonium bromide (DDAB) and dioleoylphosphatidylethanolamine (DOPE) to increase the delivery of phosphodiester ODNs into four different myeloma cell lines. The delivery by cationic liposomes increased the delivery of bcl-2 antisense ODNs by a factor of 9 to 45 as compared to plain ODNs. The stability of ODNs was increased with liposomes both in the culture medium and within the cells. Intact liposomal ODNs were detected inside the cells up to 24 hours with gel electrophoresis and phosphor imager analysis. Antisense ODNs had no effect on bcl-2 mRNA levels. Also the proliferation of myeloma cells remained unchanged during the 3-day incubation period. Our study shows that liposomal antisense ODNs targeting bcl-2 of human myeloma cells result in increased stability of ODNs with minimal toxicity. However, further modifications are needed to gain biological effects of antisense ODNs on human myeloma cells.