Aptamers: An Antibody Replacement #Biotechnology #Biopharma #Innovation #MedicalDevice
Aptamers are non-natural ligands, having the ability to bind non-nucleic acid targets such as drugs, proteins, amino acids and other molecules. Naturally they exist as “riboswitch” whose purpose is to regulate gene expression. In 1990, a technique SELEX (systematic evolution of ligands by exponential enrichment) was designed for separation and amplification of such specific nucleic acid molecules which are highly specific for certain molecules.
STEPS OF SELEX
1. First step is to synthesize DNA/RNA library
2. Incubate the molecule with target
3. Isolate the DNA/RNA-target complex
4. Elute out the bound DNA/RNA
5. Concentrate the eluted DNA/RNA
SELEX can be carried out in non-physiological conditions. Hence the provided Aptamers can work in such conditions like low PH or in the presence of solvents. They can recover their native conformation after denaturalization.
Tens of Aptamers, having ability of specific binding to target, are produced as a result of Aptamers cloning. Motif searches are further needed to characterize the sequence of Aptamers and then to choose the one having best specificity and affinity.
Aptamers applicability is highly affected by their proneness to nuclease activity. The solution resulted in the form of spiegelmers. Spiegelmers are mirror image DNA/RNA ligands based on synthetic enantiomeric form of L-2’-deoxyribose and L-Ribose respectively. These synthetic oligonucleotides are highly specific to target but are not recognized by nucleases.
Aptamers are increasingly replacing the techniques involving antibodies.
1. REPORTER-LINKED APTAMER ASSAY: AN ALTERNATIVE TO ELISA:
First RLAA was reported in 1996, used to detect VEGF in serum by using VEGF-binding fluorescein-labelled RNA aptamer instead of immobilized antibody. The results were very similar to ELISA, but process was able to detect the concentrations down up to 1pM. The process avoided any cross reactivity towards other cytokines.
2. APTAMERS IN AFFINITY CHROMATOGRAPHY:
The immobilized Aptamers in stationary phase of affinity chromatography can increase the selectivity in retention of desired target. For example, the use of aptamers has 12,000 times greater recognition for L-Arginine over D-Arginine.
3. APTAMERS AS BIOSENSORS:
Biosensors can provide semi-quantitative or quantitative analytical information using biochemical receptors. When biosensors have aptamers they are termed as aptasensors. The use of aptamers in this field takes advantage of properties like tune ability and high affinity of aptamers.
In parallel to new techniques to improve SELEX, to produce high affinity and more stable aptamers, more stable aptamers are being produced hand in hand with a considerable decrease in time required for their selectivity. Majority of the applications have been reported in the field of clinical diagnostics, the upcoming target is to design aptamers against bioterrorism agents. Most of the applications just include replacement of antibodies, neither of the report has mentioned the true advantages of the aptamers. There is need to look forward towards the production of more advanced aptamers and to discover other specific applications of aptamers.