Interaction of cholesterol-conjugated alkylating oligonucleotide derivatives with cellular biopolymers

Self-assembling CpG DNA nanoparticles for efficient antigen delivery and immunostimulation

DNA containing unmethylated deoxycytidylyl-deoxyguanosine (CpG) dinucleotides (CpG DNA) is a potent stimulator of immune responses through triggering of Toll-like receptor 9 (TLR9). In the present study, we synthesized cholesterol-modified CpG oligodeoxynucleotide (Chol-CpG ODN) and investigated its ability to form nanoparticles by self-assembling, then examined their immunostimulatory activity and potency to deliver antigens to antigen presenting cells (APCs). Chol-CpG ODN spontaneously formed particles in aqueous solutions. Cholesterol modification increased the stability of ODN in serum. Chol-CpG ODN was efficiently taken up by mouse macrophage-like RAW264.7 cells and induced a large amount of tumor necrosis factor-α compared with unmodified CpG ODN. Then, ovalbumin (OVA), a model antigen, was incorporated into Chol-CpG ODN nanoparticles. Cholesterol-modified GpC ODN (Chol-GpC ODN) was used to assess the importance of CpG motif on the antigen-specific immune response. Vaccination of mice with OVA/Chol-CpG ODN induced high level interferon-γ production from splenocytes. Furthermore, a high serum level of OVA-specific immunoglobulin G2a was observed in mice receiving OVA/Chol-CpG ODN. Neither CpG ODN nor Chol-GpC ODN was effective at all. These results indicate that self-assembling nanoparticles of Chol-CpG ODN are effective for inducing antigen-specific immune responses because of the high immunostimulatory activity, ability to incorporate antigens and tropism to APCs.

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.

Antisense therapeutics: from theory to clinical practice

The use of antisense (AS) oligonucleotides as therapeutic agents was proposed as far back as the 1960s/1970s when the AS strategy was initially developed. However, it has taken almost a quarter of a century for this potential to be realized. The last few years has seen a rapid increase in the number of AS molecules progressing past Phase I in clinical trials, due in part to our increased knowledge of their structure and chemistry. Here, we describe the most prominent of these modifications with respect to clinical applicability. However, the main focus of this review is clinical application, with a focus on cancer. We will discuss in detail both the status of the current AS clinical trials and the molecules that are likely to be the targets of the next group of AS molecules entering the clinic.

A critical survey of the structure-function of the antisense oligo/RNA heteroduplex as substrate for RNase H

The aim of this review is to draw a correlation between the structure of the DNA/RNA hybrid and its properties as a substrate for the RNase H, as well as to point the crucial structural requirements for the modified AONs to preserve their RNase H potency. The review is divided into the following parts: (1) mechanistic considerations, (2) target RNA folding-AON folding-RNase H assistance in AON/RNA hybrid formation, (3) carbohydrate modifications, (4) backbone modifications, (5) base modifications, (6) conjugated AONs, (7) importance of the tethered chromophore in AON for the AON/RNA hybrid interactions with the RNase H. The structural changes in the AON/RNA hybrid duplexes brought by different modifications of the sugar, backbone or base in the antisense strand, and the effect of these changes on the RNase H recognition of the modified substrates have been addressed. Only those AON modifications and the corresponding AON/RNA hybrids, which have been structurally characterized by spectroscopic means and functionally analyzed by their ability to elicit RNase H potency in comparison with the native counterpart have been presented here.

Cholesteryl-conjugated phosphorothioate oligodeoxynucleotides modulate CYP2B1 expression in vivo

5' cholesteryl-conjugated phosphorothioate oligodeoxynucleotides with sequence complementary to the rat CYP2B1 mRNA were evaluated in adult male Sprague-Dawley rats for their pharmacokinetic properties, toxicity, and ability to modulate CYP2B1 expression in vivo. Following intraperitoneal administration of 35S-labelled oligodeoxynucleotides, volume of distribution for the phosphorothioate was 0.33 l/kg while the 5' cholesteryl-conjugate oligodeoxynucleotide was 0.12 l/kg. The elimination half-life was 23.2 and 55.4 hrs for cholesteryl-modified and unmodified oligodeoxynucleotides, respectively. Cholesteryl-conjugate oligodeoxynucleotide toxicity was detected at a dose of 1.0 mg/kg and consisted primarily of midzonal liver cell enlargement and increased total RNA. Hexobarbital sleep times, a measure of CYP2B1 enzyme activity in vivo, increased from 21.9 minutes in saline-treated animals to 29.5 minutes in cholesterol oligodeoxynucleotide-treated animals. A significant decrease in liver microsomal pentoxyresorufin O-dealkylase enzyme activity, a CYP2B1/2 specific assay, was observed but not a change in p-nitrophenol hydroxylase activity, a specific CYP2E1 assay. These data indicate that in vivo modulation of the CYP2B1 gene can be accomplished with synthetic phosphorothioate oligodeoxynucleotides in a sequence-specific manner. Further, cholesteryl conjugation to the 5' end of the oligodeoxynucleotide enhanced potency despite lesser bioavailability.

Transport of oligonucleotides across natural and model membranes

Oligo- and polynucleotides can not diffuse through lipid membrane, however they are taken up by eukaryotic cells by endocytosis mediated by the nucleic acid specific receptors. The compounds find some way to escape from endosomes and reach nucleic acids in both cell nucleus and cytoplasm. Oligonucleotides bind to a few cell surface proteins which take part in the virus-cell interaction and in the development of immune response. Interaction of nucleic acids with cell surface proteins may play a role in development of some pathologies. The biological role of this interaction is unclear. Efficient delivery of oligonucleotides into eukaryotic cells can be achieved in some conditions by natural mechanisms and by using artificial carriers--membrane vehicles and cationic polymer micelles.

Effect of derivatization of ribophosphate backbone and terminal ribophosphate groups in oligoribonucleotides on their stability and interaction with eukaryotic cells

Various derivatives of oligoribonucleotides were synthesized by the H-phosphonate method. Different modifications of the ribophosphate backbone were designed in order to protect the derivatives against nucleolytic enzymes present in the biological media. These modifications include coupling of fluorescein moiety to 3'-terminal ribose, 2'-O-methylation of ribose, introduction of phosphorothioate internucleotide bonds throughout the molecule, replacement of the two last 3'-terminal phosphodiester bonds by phosphoroamidates and coupling of the last 3'-terminal nucleotide via the 3'-3'-phosphodiester bond. All modifications were tested for their effect on the stability of the derivatives against phosphodiesterase from snake venom and nucleases of the cell culture media. 2'-O-methylated oligoribonucleotides containing either terminal 3'-3'-linkage or two 3'-terminal phosphoroamidate internucleotide bonds appeared to be the most stable under the most severe conditions used. The results demonstrate a possibility to use protected oligoribonucleotide derivatives for experiments in vivo when the use of deoxy-analogues might be ineffective. The uptake of 2'-O-methylated derivatives and their 5'-cholesterol conjugates (coupled via a disulfide bond) by human carcinoma cells did not differ from that of the corresponding oligodeoxyribonucleotides. 85% of the bound derivatives were found in the membrane-cytosolic fraction, while only 15% were found in the nuclear fraction. The oligonucleotide moiety of 2'-O-methyloligoribonucleotide-cholesterol conjugate was not translocated through the cellular membrane. After cleavage of the linkage between cholesterol and oligonucleotide by dithiothreitol the major portion of the oligonucleotide moiety was released into the media. The derivatives, as well as their 5'-cholesterol conjugates, which entered the cells, were stable and protected from action of dithiothreitol dissolved in culture media. These results demonstrate an endocytosis mechanism of penetration as observed in similar experiments using oligodeoxyribonucleotides.