Effect of carrier molecular weight on physicochemical properties and the in vitro immune-stimulatory activity of the CpG-dextran conjugates

The effect of dextran molecular weight on the in vitro physicochemical and immune properties of cytosine-phosphate-guanine (CpG) oligodeoxynucleotide-amino-dextran conjugates is investigated. CpG-1668 was conjugated at the 3'-end to amino-dextran of differing molecular weight (20, 40, 70 or 110-kDa) via a stable bis-aryl hydrazone linkage. Conjugate formation was confirmed by agarose gel electrophoresis and dynamic light scattering measured the size and surface charge of conjugates. Uptake and immune-stimulatory activity of CpG-dextran by antigen-presenting cells was evaluated by flow cytometry and confocal microscopy. Degradation by DNase I was monitored by loss of the fluorescent signal from labelled CpG and changes in size and zeta potential. Hydrazone bond formation (UV 354 nm) showed on average four CpG molecules conjugated per polymer. CpG-dextran prepared from 20 or 40-kDa dextran had a size of 17 nm while 70 or 110-kDa was 30 nm. CpG-dextran was preferentially taken up by dendritic cells, followed by macrophages and then B-cells. Only the 20-kDa dextran conjugate significantly enhanced uptake by bone-marrow derived dendritic cells (BMDCs) compared to free CpG. Confocal microscopy showed that CpG and CpG-dextran accumulates in the endo-lysosomal compartment of BMDCs at 24 h. All conjugates upregulated activation markers (CD40, CD80 or CD86) of BMDCs to a similar level as for free CpG. CpG-dextran 40-kDa produced highest levels of cytokines (TNF-α, IL-6, and IL-12p70) secreted by BMDCs. Enzymatic protection assays showed that the conjugate made from dextran 20-kDa provided no protection for CpG while the higher molecular weight conjugates reduced degradation by DNase I. The 40-kDa dextran conjugate produced the greatest in vitro immune activity, this was due to the conjugate being relatively small in size for cell uptake while sufficiently large enough to protect CpG from nuclease attack. These in vitro studies identify the need to consider the molecular weight of the carrier in bioconjugate design.

Arabinonucleic acids containing C5-propynyl modifications form stable hybrid duplexes with RNA that are efficiently degraded by E. coli RNase H

The promise of the antisense approach to treat a variety of diseases with oligonucleotides and solutions to challenges that have been encountered in their development is attributable to chemical modification of the nucleic acid scaffold. Herein, we describe preliminary data regarding the synthesis of a novel C5-propynyl-β-d-arabinouridine (araU^P) phosphoramidite and its incorporation into oligonucleotides. Substitution of araU^P in dT₁₈ results in minor stabilization of duplexes formed with RNA when modifications are placed consecutively and a uniformly modified araU^P 18-mer increases stability by 34 °C relative to DNA. The modified oligomer exhibits improved nuclease and serum stability when compared to DNA and duplexes formed between RNA and araU^P oligonucleotides are substrates for E. coli RNase H. These preliminary results merit further investigation into C5-propynyl modified arabino nucleic acids for potential therapeutic gene silencing applications.

Synthesis and biophysical properties of 5'-thio-2',4'-BNA/LNA oligonucleotide

Phosphorothioate modification of oligonucleotides is one of the most promising chemical modifications in nucleic acid therapeutics. Structurally similar 5'-thio or phosphorothiolate-modified nucleotides, in which the 5'-bridging oxygen atom is replaced with a sulfur atom, are attracting attention and gaining importance in oligonucleotide-based research. In our present study, we synthesized 5'-thio-2',4'-BNA/LNA monomers bearing thymine or 5-methylcytosine nucleobase. The 5'-thio-2',4'-BNA/LNA monomers were successfully incorporated into target oligonucleotides, and their nuclease stability and binding affinity with complementary strands were evaluated.