With an excellent stability profile, ferrocene has always attracted considerable interest for DNA labeling to generate probes for electrochemical detection. Dimethylaminophenothiazin-5-ium chloride, Methylene Blue (MB), has many uses in chemistry and biology. For decades, this compound has been used for applications including redox indicator, photosensitizer, dye for cellular staining procedures, antiseptic and in medicine against Alzheimer's disease. For the detection of biological analytes, MB has also been used as a redox reporter bound to DNA probes.
Enhanced Cellular Uptake
Potential therapeutic oligonucleotides must permeate the cell membrane for optimal activity. The addition of lipophilic groups to an oligonucleotide would be expected to enhance cellular uptake/membrane permeation. The use of cholesteryl oligos and the consequent improvement in activity has been described. We have designed our Cholesteryl products with triethyleneglycol (TEG) spacers for maximum solubility. Vitamin E is both lipophilic and non-toxic even at high doses so would be an excellent candidate as a lipophilic carrier for oligonucleotides. Therefore, as an addition to our cholesteryl product line, we offer simple ?-tocopheryl (vitamin E) labelling. Totally synthetic ?-tocopherol is racemic at its three chiral centers and is used to prepare this product. The 5'-stearyl group may also become a favored lipophilic carrier for experimentation with synthetic oligonucleotides. A directed approach to the delivery of therapeutic oligonucleotides specifically to the liver has been to target the asialoglycoprotein receptor (ASGPR) using a suitable glycoconjugate. Indeed, ASGPR is the ideal target for delivery of therapeutic oligonucleotides to the liver since it combines tissue specificity, high expression levels and rapid internalization and turnover. The use of oligonucleotide glycoconjugates has led to significant advances in therapeutic delivery as evidenced by the work of Alnylam Pharmaceuticals and Ionis Pharmaceuticals using multivalent N-acetylgalactosamine (GalNAc) oligonucleotide conjugates.
Haptens are small molecules for which antibodies have been developed. The binding of a hapeten to its associated antibody is very tight and a hapten labeled oligonucleotide can then be readily captured by the associated antibody, which is often immobilized. Examples of haptens that are used extensively in oligonucleotide synthesis are biotin, fluorescein and the 2,4-dinitrophenyl group.