The uptake and distribution of phosphorothioate oligonucleotides into vascular smooth muscle cells in vitro and in rabbit arteries

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.

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.

Formulation and delivery mode affect disposition and activity of tyrphostin-loaded nanoparticles in the rat carotid model

Poor drug residence in the arterial wall hinders clinical implementation of local drug delivery strategies for the treatment of restenosis. A rat carotid model of vascular injury and intraluminal delivery of tyrphostin-containing polylactic acid (PLA) nanoparticles (NPs) were used to determine the relationship between residence properties and biological activity of different formulations and administration modes. The effects of delivery modes (denudation and delivery time) and formulation variables (adsorbed vs encapsulated drug, and NP size) on arterial drug/NP retention were examined. Antirestenotic effects of large (160 nm) and small (90 nm) tyrphostin-containing NPs, surface-absorbed tyrphostin, and systemic treatment were compared. Fluorescent NPs were used to study the spatial distribution of the carrier in the arterial wall. The decrease in arterial tyrphostin level over time fitted a biexponential model. Delivery time and pressure, endothelium integrity, particle size, and drug-polymer association affected local pharmacokinetics and the antirestenotic results after 14 days. The PLA-based tyrphostin NP formulation ensured a prolonged drug residence at the angioplasty site after single intraluminal application. Several readily adjustable formulation and procedural factors considerably modified arterial ingress of the drug-loaded NPs and governed their subsequent redistribution, tissue binding, elimination, and ensuing antirestenotic effect.

Antisense knockdown of inducible nitric oxide synthase inhibits the relaxant effect of VIP in isolated smooth muscle cells of the mouse gastric fundus

1. Our previous results showed that the non-selective nitric oxide synthase (NOS) inhibitor L-N(G)-nitroarginine (L-NOARG) and the selective inducible NOS (iNOS) inhibitor N-(3-(acetaminomethyl)-benzyl)acetamidine (1400W) inhibited the relaxant effect of vasoactive intestinal polypeptide (VIP) in isolated smooth muscle cells of the mouse gastric fundus, suggesting the involvement of iNOS. The identity of the NOS isoform involved in the VIP-induced relaxation in isolated smooth muscle cells of the mouse gastric fundus was now further investigated by use of antisense oligodeoxynucleotides (aODNs) to iNOS. 2. Incubation of isolated smooth muscle cells with fluorescein isothiocyanate (FITC)-labelled aODNs showed that nuclear accumulation occurs quickly and reaches saturation after 60 min. The in vivo intravenous administration of aODNs to iNOS, 24 and 12 h before murine tumour necrosis factor alpha (mTNFalpha) challenge, significantly reduced the nitrite levels induced by the mTNFalpha challenge. 3. Intravenous administration of aODNs to iNOS in mice, 24 and 12 h before isolation of the gastric smooth muscle cells, decreased the inhibitory effect of the NOS inhibitors L-NOARG and 1400W on the relaxant effect of VIP, whereas neither saline nor sODNs had any influence. 4. Preincubation of the isolated smooth muscle cells with aODNs almost abolished the inhibitory effect of L-NOARG and 1400W on the VIP-induced relaxation, whereas sODNs failed. 5. These results illustrate that the inhibitory effect of NOS inhibitors in isolated smooth muscle cells of the mouse gastric fundus is due to inactivation of iNOS. iNOS, probably induced by the isolation procedure of the smooth muscle cells, seems involved in the relaxant effect of VIP in isolated gastric smooth muscle cells.

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.

Antiproliferative effects of steric blocking phosphorodiamidate morpholino antisense agents directed against c-myc

The phosphorodiamidate Morpholino oligomers (PMO) are a new class of antisense agents that inhibit gene expression by binding to RNA and sterically blocking processing or translation. In a search for a Morpholino agent that would inhibit cell proliferation, it was found that oligomers directed against c-myc, a gene involved in control of the cell cycle, were effective. The sequence specificity and mechanism of action of one agent were determined. The 20-mer 126 lowers c-myc protein levels in treated cells and arrests cells in G0/G1 of the cell cycle. It also acts at the RNA level to inhibit normal pre-mRNA splicing and instead produces an aberrantly spliced mRNA. Irrelevant and mispair control oligomers indicated that the observed antiproliferative effect was sequence specific. This was confirmed in a reporter gene model system using a c-myc 5'-untranslated region (5'-UTR) fused to a cDNA copy of the insect luciferase gene. We conclude that 126 is acting through an antisense mechanism involving Watson-Crick hydrogen bonding to its target RNA. A specific antisense agent directed against a cell cycle-associated gene mRNA may be useful as a therapeutic in diseases characterized by excess cell proliferation, such as restenosis following balloon angioplasty or cancer.

Biologically active oligodeoxyribonucleotides. 5. 5'-End-substituted d(TGGGAG) possesses anti-human immunodeficiency virus type 1 activity by forming a G-quadruplex structure

A series of hexadeoxyribonucleotides (6-mers), d(TGGGAG), substituted with a variety of aromatic groups at the 5'-end were synthesized and tested for anti-human immunodeficiency virus type 1 (HIV-1) activity. While unmodified d(TGGGAG) (31) had no anti-HIV-1 activity, compound 23 with a 3,4-di(benzyloxy)benzyl (DBB) group at the 5'-end potently inhibited the HIV-1IIIB-induced cytopathicity of MT-4 cells in vitro (IC50 = 0.37 microM) without cytotoxicity up to 40 microM. A thermal denaturation study on the 5'-end-substituted 6-mers by means of the circular dichroism (CD) spectra demonstrated that the aromatic substituent attached at the 5'-end of the 6-mer strongly enhanced the formation of a parallel helical structure consisting of four strands (quadruplex). On the contrary, compound 36, in which one of the guanosines of 23 was replaced by a thymidine, did not form a quadruplex, thus exhibiting no anti-HIV-1 activity. Moreover, both compound 15, with a tert-butyldiphenylsilyl group solely at its 3'-end, and compound 21, with a relatively small substituent, a benzyl group, at the 5'-end, formed quadruplexes but had no anti-HIV-1 activity. These findings led us to the conclusion that both the quadruplex structure and the aromatic substituent with adequate size at the 5'-end are crucial for the interaction of the 5'-end-substituted 6-mers with the V3 loop as well as the CD4 binding site on viral gp120, resulting in anti-HIV-1 activity.

Enhancement of anti-herpetic activity of antisense phosphorothioate oligonucleotides 5' end modified with geraniol

We have previously shown that antisense phosphorothioate oligonucleotide (SON) targeted against immediate early (IE) pre-mRNA5 of the herpes simplex virus type I (HSV-I) possessed potent anti-herpetic activities in vitro system. However, anti-herpetic activities of SON were not still efficient enough. Lipophilic compounds have been often conjugated with antisense oligonucleotide to enhance the biological activity. In this study, we selected geraniol as a lipophilic compound and newly synthesized SON bearing 5' terminal geraniol (geranyl-SON) toward IE pre-mRNA 5 of the HSV-1 to enhance the anti-herpetic activity. Geraniol is a olefinic terpene alcohol which is found in many essential oils. It possesses lipophilic characteristic. It is thought to be absorbed in tissue. Geraniol enhanced the anti-herpetic activity of SON with less cytotoxicity in a sequence specific manner. Terminal modification with geraniol did not affect binding affinity with complimentary DNA. Cytoplasm distribution of geranyl-SON was confirmed by confocal microscope. While some of the geranyl-SON was seen in the nucleus, unmodified SON had a punctate distribution in the cytoplasm with little in the nucleus. These results suggested that geranyl modification enhances anti-herpetic activity by changing the subcellular distribution of the oligonucleotides. Consequently geraniol-modifica-tion could provide new means for the efficient delivery of oligo-nucleotides.

Limited use of cationic liposomes as tools to enhance the antiherpetic activities of oligonucleotides in vero cells infected with herpes simplex virus type 1

We used commercially available cationic liposomes, lipofectin, DOTAP, and transfectam, to enhance the antiherpetic activities of phosphodiester oligonucleotides (D-oligos) or phosphorothioate oligonucleotides (S-oligos) targeted against immediate-early pre-mRNA4/5 of herpes simplex virus type 1 (HSV-1). With a 5-fold excess of S-oligos/D-oligos, formation of complexes with some of the S-oligos/D-oligos and the cationic liposomes could be visualized on agarose gel. A >5-fold excess of cationic liposomes enhanced the antiherpetic activities of Doligos, whereas there was not enhancement of the antiherpetic activities of S-oligos. As nuclear localization of D-oligos in the presence of cationic liposomes was not clear, we could not clarify the relation between antiherpetic activities of D-oligos and nuclear distribution of oligos. Subcellular distribution of S-oligos in the presence of lipofectin or DOTAP showed nuclear localization by confocal laser scanning microscopy. Transfectam had no effect on the nuclear distribution of S-oligos. These data showed that cationic liposomes would not be appropriate carriers to enhance the antiherpetic activities of S-oligos. Also, distribution of S-oligos into the nucleus does not necessarily enhance their biologic activity. Questions remain about the effectiveness of cationic liposomes in the enhancement of the antivirus activity of S-oligos.

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.

Inhibitory nonsequence-specific effects of cytidine homopolymers on in vivo neointimal formation

Phosphorothioate oligodeoxynucleotides (PS oligos) manifest both antisense and G-quartet aptameric inhibitory effects on vascular smooth muscle cell (SMC) proliferation. In this study, we examined the effects of three cytidine (S-dC) homopolymers lacking any guanosines of various chain length-S-dC28, S-dC18 and S-dC12-on in vitro SMC proliferation and in vivo neointimal formation. S-dC18 significantly inhibited human vascular SMC proliferation, although it had only half the potency as the same dose of S-dC28. Furthermore, S-dC12 at the same concentrations as S-dC18 did not significantly inhibit vascular SMC proliferation. S-dC28 and S-dC18 inhibited PDGF-induced in vitro SMC migration, whereas D-dC12 had no significant effect on PDGF-induced in vitro SMC migration. We determined the effects of S-dC28, S-dC18, and S-dC12 on neointimal SMC formation in the rat carotid balloon injury model. Rat carotid artery neointimal formation after balloon injury was significantly attenuated by S-dC28 treatment compared with the control group and by S-dC18 treatment compared with the control group. S-dC28 and S-dC18 treatment significantly reduced the intima/media area ratio compared with the values of the control groups. However, S-dC12 did not significantly inhibit neointimal formation. We investigated the time course of the inhibitory effects of S-dC28 on rat carotid artery neointimal formation. S-dC28 significantly inhibited rat carotid artery intimal area and intima/media area ratio at 4 weeks and 8 weeks. Fluoresceinated S-dC28 (FITC-S-dC28) was found to be present throughout the rat carotid arterial wall within 6 hours after balloon injury. Taken together, the potent non-G-quartet, nonsequence-specific inhibitory effects of S-dC compounds on in vitro SMC proliferation and in vivo neointimal formation in the rat carotid balloon injury model are chain length dependent and long lasting.

Molecular and cellular characterization of baboon C-Raf as a target for antiproliferative effects of antisense oligonucleotides

C-Raf is a an essential member of the growth factor-ras pathway and a target for intervention strategies aimed at blocking cell proliferative responses. Excessive smooth muscle proliferation is considered one cause of the arterial closure in restenosis. Because of the similarity to the human cardiovascular system, a useful current animal model of the disease is a baboon model. As a foundation for animal studies employing antisense oligonucleotides, efforts were made to characterize the molecular and cellular biology of the baboon system. The nucleotide sequence of baboon c-raf cDNA was determined. Antisense phosphorothioate oligonucleotides specific to the 3'-UTR of c-raf mRNA from human and baboon were compared using primary baboon smooth muscle cells in culture. A particular human antisense oligonucleotide, referred to as ISIS 5132, was different by only 2 of 20 bases from the baboon sequence. The corresponding baboon antisense oligonucleotide ISIS 12959, however, was markedly more effective to inhibit c-raf mRNA, protein production, and DNA synthesis, and the results attest to the species specificity of the approach. After antisense treatment, c-raf mRNA levels dropped rapidly, whereas protein levels decreased with a half-life of roughly 24-48 hours, consistent with the antiproliferative effects. The data are discussed with regard to the profile of protein-protein interactions made by C-Raf and with the view that the baboon system closely parallels the human one at the signal transduction level. As this work progressed, a baboon cDNA homolog of a human c-raf-2 pseudogene was isolated, sequenced, and shown to be transcribed into mRNA.

Morpholino and phosphorothioate antisense oligomers compared in cell-free and in-cell systems

Morpholino and phosphorothioate (S-DNA) antisense oligos were compared in both cell-free and in-cell translation systems. In the most stringent test of specificity in the cell-free system, a globin-targeted S-DNA oligo was found to inhibit its target sequence at concentrations of 10 nM and above, but the sequence-specific component of this inhibition dropped below 50% at concentrations of 100 nM and above. A corresponding Morpholino oligo achieved even higher inhibition at 10 nM, but in contrast to the S-DNA, with the Morpholino, the sequence-specific component of this inhibition remained above 93% at a concentration of 3000 nM. In this same cell-free test system, several S-DNA oligos exhibited substantial undesired nonantisense effects at concentrations of 300 nM and above, whereas corresponding Morpholino oligos exhibited little or no nonantisense activity through a concentration of 3000 nM. In scrape-loaded HeLa cells, both globin-targeted and HBV-targeted S-DNAs (both antisense and control oligos) generally failed to achieve significant translational inhibition at extracellular concentrations up to 3000 nM. In contrast, the Morpholino oligos achieved effective and specific translational inhibition at extracellular concentrations ranging from 30 nM to 3000 nM.

A simple method for delivering morpholino antisense oligos into the cytoplasm of cells

We report a simple and effective means for delivering Morpholino antisense oligos into the cytosol of cultured anchorage-dependent animal cells. This method, referred to as scrape-loading, is carried out in a matter of seconds, uses a common inexpensive laboratory implement, and has minimal detrimental impact on the cells. Using this delivery method, a Morpholino oligo present at 0.1 microM and 1 microM in the extracellular medium inhibited its targeted genetic sequence within cultured Hela cells at levels of 56% and 85%, respectively. Lack of inhibition by two control Morpholino oligos at concentrations up to 3 microM indicates good sequence specificity by this structural type. Also described is a test system for simple, rapid, and sensitive quantitation of antisense activity in cultured cells.