Polymer-Conjugated Oligonucleotides

Besides these low-molecular weight molecules, high-molecular mass polymers have been investigated as new conjugating moieties able to endow the bound molecules with their peculiar features. In this way it is possible for example to add more hydrophobic character to the antisense derivative, to increase their cellular penetration. Besides, the presence of larger molecules will reduce their clearance from the body, increasing the time life useful to exercise a therapeutic action. 

Polymers used to modify the oUgonucleotides and enhance their biological efficacy are essentially policationic or biodegradating polymers. Few example of amphiphilic, synthetic macromolecules are also reported. 

The first class, able to form condensed particle by electrostatic interactions with the oligonucleotides, have been widely associated with some simple ligand, as transferrin or folic acid to increase the efficient internalisation of the antisense molecules. The polycationic polymers used are polyamines that become cationic at physiological conditions. 

Poly (L-Lysine) (PLL) has been used to facilitate uptake of oligonucleotides . This polymer interacts with the negatively charged molecules on the cell membrane and it is internalised along with the joined unit. The rate and the amount of oligonucleotide uptake are increased when conjugated with PLL, but, unfortunately, its toxicity and lack of specificity limit its usefulness. 

Polyethyleneimine (PEI) is an organic macromolecule with a very high cation charge density, since every third atom a protonated nitrogen can be present inside the aliphatic backbone. It is a versatile vector, with a very low level of citotoxicity . 

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Synthesis (i) a hydrophobic polymer, terminally modified with a carboxylic acid moiety, was mixed with a coupling agent and reacted with a 50-amino-modified oligonucleotide on solid support (controlled pore glass, CPG) (ii) deprotection and cleavage of the resulting DNA polymer conjugate from solid support (iii) dialysis of cleaved DPA into deionized water to form a mixture... 

DNA-polymer conjugate and the cDNA labeled with a ligand of a cell surface receptor. There is thus an enhanced interest in designing self-assembled structures composed of oligonucleotides for their potential application in drug delivery and biosensing to achieve advances in the biomedicine, industrial, and technological fields [11, 19, 74, 76]. 

If an individual nucleotide is modified in the appropriate way, various enzymatic techniques can be used to polymerize the derivative into an existing oligonucleotide molecule. Alternatively, nucleotide polymers can be treated with chemical activators that can facilitate the attachment of a label at particular reactive sites. Thus, there are two main approaches to modifying DNA or RNA molecules enzymatic or chemical. Both procedures can produce highly active conjugates for sensitive assays to quantify or localize the binding of an oligo probe to its complementary strand in a complex mixture. 

Pu KY, Liu B (2009) Optimizing the cationic conjugated polymer-sensitized fluorescent signal of dye labeled oligonucleotide for biosensor applications. Biosens Bioelectron... 

The chemical modification of nucleic acids at specific sites within individual nucleotides or within oligonucleotides allows various labels to be incorporated into DNA or RNA polymers. This labeling process can produce conjugates having sensitive detec-... 

Folate conjugation with polymers such as polylysine and poly-ethylenimine have allowed the delivery of transgenes and oligonucleotides into cancerous cells, which have been shown to significantly enhance expression of the respective transgenes and antisene effects.80 More recently, this enhancement could be further increased if a... 

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