Aptamer: A Novel Therapeutic Oligonucleotide

The aptamer is an oligonucleotide which is a short version of biological nucleic acids (such as DNA and RNA) with defined sequence of nucleotides. Based on the complexity of molecule, the aptamers lies in-between protein molecules and small chemical molecules. Aptamers have high specificity and affinity towards target proteins. They are screened from random sequences of oligonucleotides based on the highest affinity for target proteins using the SELEX (Systematic Evolution of Ligands by Exponential Enrichment). Researchers have discovered various applications of aptamers that are ready to replace the therapeutic use of biological proteins (such as antibodies) that have complexity in manufacturing and characterization. The present review describes the structural modification in aptamers such as PEGylation, substitution of functional groups, use of an enantiomeric oligonucleotide and its applications. Aptamers can be deactivated, when needed, by the use of reversal agent that contains oligonucleotide sequence complementary to aptamers. This property of aptamers makes them potential therapeutic from a safety point of view. In recent scenario, aptamers are developed for targeted drug delivery systems by conjugating with drug molecules or delivery vesicles such as liposomes. ‘Anti-sense Aptamers’ are being developed to silent the expression of genes responsible for the proliferative growth of tissue in cancer. Other applications of aptamers such as environmental monitoring and laboratory testing are also described in this review.