Uptake of polynucleotides by mammalian cells. XIV. Stimulation of the uptake of polynucleotides by poly(L-lysine)

The use of synthetic polymers for delivery of therapeutic antisense oligodeoxynucleotides

Developed over the past two decades, the antisense strategy has become a technology of recognised therapeutic potential, and many of the problems raised earlier in its application have been solved to varying extents. However, the adequate delivery of antisense oligodeoxynucleotides to individual cells remains an important and inordinately difficult challenge. Synthetic polymers appeared on this scene in the middle 1980s, and there is a surprisingly large variety used or proposed so far as agents for delivery of oligodeoxynucleotides. After discussing the principles of antisense strategy, certain aspects of the ingestion of macromolecules by cells, and the present situation of delivery procedures, this article analyses in detail the attempts to use synthetic polymers as carrier matrices and or cell membrane permeabilisation agents for delivery of antisense oligodeoxynucleotides. Structural aspects of various polymers, as well as the results, promises and limitations of their use are critically evaluated.

Polymer chemical structure is a key determinant of physicochemical and colloidal properties of polymer-DNA complexes for gene delivery

Polyplexes are now emerging as potentially useful vectors for gene therapy. To improve our understanding of how the chemical structure of the polymer affects the properties of these systems, a series of structurally related polymers, the linear poly(amidoamine)s (PAAs), have been examined for their abilities to form complexes with DNA. Structure-dependent differences in DNA binding are shown by gel electrophoretic retardation of DNA and thermal transition analyses. Two PAAs, NG28 and NG30, stand out as having high affinity DNA binding characteristics, similar to the model homopolypeptide, poly-L-lysine. In addition, differences in complex formation, particle size and surface charge are displayed for the different polymer-DNA systems. Electron microscopy studies showed that the polymers condensed DNA into similar unit structures but only complexes with NG30 did not undergo agglomeration. This was attributed to an excess of complexed polymer forming a shell of uncomplexed polymer chain segments around a condensed DNA-polymer core. The transfection activities of these polymer complexes differ greatly, and some of these differences can be explained in a multifactorial way by the physicochemical and colloidal properties. It is concluded that polymer chemical structure dictates the apparent affinity of DNA binding, and also several of the important colloidal characteristics of the resulting complexes.

Gel shift assay: demonstration of enhanced binding of oligo(delta)-L-ornithine-oligodeoxynucleotide conjugates to complementary DNA and RNA

An increase in melting temperature for DNA:DNA duplexes had been observed previously (Zhu et al. Antisense Res. Dev. 3:349-356, 1993) when an oligo(delta)ornithine moiety was covalently appended to a short oligodeoxynucleotide. We now report the analysis of duplex formation by electrophoretic gel shift analysis. In the particular example studied, an increase in Tm of 4 degrees C was found to correspond to about a fivefold increase in binding constant. A similar enhancement by the appended cationic peptide was observed when the target strand was RNA. The use of a competitive assay format for avoidance of adsorptive loss at low concentrations (< 10(-7)M) of the oligonucleotide-oligo(delta)ornithine conjugate is presented.

Oligonucleotide-poly-L-ornithine conjugates: binding to complementary DNA and RNA

On the basis of the reported enhanced antisense activity of polylysine-oligonucleotide conjugates, a synthetic 12-mer oligodeoxyribonucleotide has been coupled at its 5' terminus to a series of positively charged (delta-ornithine)n cysteine peptides. Binding between the nucleic acid-peptide conjugate and its complementary DNA target sequence was detected by the impact of complexation on the melting temperature (Tm). It was found that the Tm for the nucleic acid-peptide gradually increased with increasing net charge on the conjugated peptide. Site-directed cleavage with RNase H demonstrates that the peptide-modified oligomer also hybridizes with its RNA target sequence. Increased affinity for target mRNA with net charge was shown by a cell-free translation arrest assay.

Preparation and physical properties of conjugates of oligodeoxynucleotides with poly(delta)ornithine peptides

Oligodeoxynucleotides (12-mers) having either a 3' aminolinker or both 3' and 5' aminolinker groups were synthesized and then reacted with N-iodoacetoxysuccinimide. Separately, a series of peptides, consisting of cysteine carboxyamide and a varying number of residues of ornithine coupled through their side-chain amino groups, was prepared, leaving on the final Fmoc protecting group. Reaction of each Fmoc-peptide with an activated oligodeoxynucleotide yielded the desired conjugates, which were purified by an Fmoc-on/Fmoc-off two-step reversed-phase HPLC procedure. On hybridization with a complementary unmodified 12-mer oligodeoxynucleotide, it was found that there is a gradual increase in melting temperature with the number of ornithine residues, whereas the appended peptide did not perturb the B form of the duplex.

Nucleic acid interaction with VERO cells. A temperature barrier in the interaction pattern

The interaction of VERO cell monolayers with spin (nitroxide)-(labeled polynucleotides (1(N)n) was examined by electron spin resonance (ESR) spectroscopy at various temperatures. Nitroxide labels covalently linked to (A)n, (dUfl)n, (U)n and (A)n . (U)n were used to monitor the interaction. The VERO cells were grown on small quartz plates with a cell viability of 95% or better and then used directly for the ESR studies. The ESR results indicated that the interaction between VERO cells and spin-labeled nucleic acids is temperature dependent. No temperature dependence was found when VERO cells were in contact with nitroxide radicals which were free in solution or covalently bound to Sepharose 4B. The temperature dependence established with nitroxide-labeled nucleic acids indicates that a temperature barrier must exist between 20 and 26 degrees C for the interaction between nucleic acids and VERO cells; namely, at 26 degrees C or above spin-labeled nucleic acids interact significantly with a VERO cell surface; whereas, at 20 degrees C the ESR signal reports no interaction. It is concluded that a temperature-dependent phase transition of membrane components or cell surface products active at 26 degrees C or above play a key role in the nucleic acid cell surface interaction process.

Binding of polynucleotides to fibroblasts. Effects of complex formation with vinyl analogs of nucleic acids

The binding of polynucleotides or of their vinyl analogs to human fibroblasts is changed when complexes are formed between these compounds. The following polymers have been studied: poly(1-vinylcytosine), poly(1-vinyluracil, poly(9-vinyladenine), polyuridylate, polyadenylate and polyinosinate. Only that complex formation (between poly(1-vinylcytosine) and polyinosinate) which is accompanied by aggregation leads to a considerable increase (30 fold) in binding to cells; all the other complex formations have only moderate effects (0.2-3 fold). Furthermore, a comparison of unordered complexes containing polyinosinate whows that enhanced binding to cells is paralleled by an increased cellular resistance to viral infection.

Interaction of normal and unusually modified microbial DNA with cultured mammalian cells. Breakdown and reincorporation vs. uptake of polymerized DNA

The uptake of radioactively labeled bacterial and phage DNA and the incorporation of acid-soluble DNAase I digests of these DNAs by cultures of human foreskin and 3T3 cells were studied. The presence of large amounts of unusually modified pyrimidine residues in donor phage DNAs allowed radioactive donor DNA in the nuclei of DNA-treated cells to be distinguished from host DNA labeled with breakdown products derived from donor DNA. This distinction could be made because it was found that radioactively labeled 5-methylcytosine residues in predigested XP-12 DNA and glucosylated 5-hydroxymethylcytosine residues in predigested T4 DNA could not be incorporated in an unaltered form into animal cell DNA. The results obtained from the study of uptake of these DNAs suggest that approx. 4--40 ng of phage DNA per 10(6) cells was transported to the nuclei of DEAE-dextran-pretreated cells during 3 days of incubation in medium after treatment with the DNA. However, interpretation of the results is complicated by the finding of considerable amounts of donor DNA binding to and persisting at the cell surface, which might attach to nuclei during subcellular fractionation.

Interaction of microbial DNA with cultured mammalian cells. Binding of the donor DNA to the cell surface

Cultured fibroblasts grown in monolayer were incubated for a short time with radioactively labeled microbial DNA and diethylaminoethyl-dextran (DEAE-dextran), poly-L-lysine, or calcium phosphate, agents previously demonstrated by others to markedly enhance transfection. Immediately after such treatment of 1 by 10(-6)-1.5 by 10(6) cells with DNA, approx. 0.05-0.15 mug of donor DNA representing 10-30% of the input DNA became cell associated. In contrast, when the cells are similarly treated with only a DNA solution approx. 0.5-5% of the donor DNA was retained by the cells. More than 95% of the cell-associated donor DNA was shown to be bound to the surface of cells treated with polycation. It was also shown that in the absence of polycation treatment, most of the cell-associated donor DNA was bound to the cell surface.

Stimulation of clonal growth of normal fibroblasts with substrata coated with basic polymers

Improved media have reduced the amount of serum protein required for clonal growth of normal human and chicken fibroblast-like cells. In the presence of limiting amounts of serum protein, attachment of colonies to tissue culture plastic surfaces is weak. Treatment of the culture surface with polylysine or other basic polymers causes the cells to adhere much more tightly. Growth is also improved on the surfaces treated with basic polymers, and further reductions in the concentration of serum as possible. At sufficiently low protein concentrations, growth of some types of cells is totally dependent on the use of a treated surface. Several different types of normal human and chicken fibroblast-like cells show improved growth on polylysine-coated surfaces, but no improvement was obtained in growth of a line of SV-40 transformed WI-38 cells. Acidic and neutral polymers are generally inactive. Collagen and gelatin improve growth slightly, but the effect is much less than that obtained with basic polymers. Both natural and synthetic polymers with an excess of basic groups are active, including histone, polyarginine, polyhistidine, polylysine, polyornithine, and protamine. The only critical requirement appears to be a polymer that carries a positive charge at a physiological pH.

Effect of polyamines on the uptake of poly (2'-fluoro-2'-deoxyuridylic acid) by a mammalian cell line

VERO cells can take up poly(dUfl)1 from the medium. The uptake involves surface adsorption and, most probably, intracellular penetration. Part of the poly(dUfl) is hydrolyzed during incubation with the cells but the hydrolysis products are not incorporated into de novo synthesized nucleic acids. The uptake is reduced by serum and stimulated by polycationic ionenes. The magnitude of stimulation depends on the structure of the ionene and the treatment regimen.