Nucleic acid-based aptamers: Applications, development And clinical trials

Short single-stranded oligonucleotides called aptamers, often termed as chemical antibodies, have been developed as powerful alternatives to the traditional antibodies with respect to their obvious advantages like high specificity and affinity, longer shelf-life, easy manufacturing procedure, freedom to introduce chemical modifications for further improvement etc. Reiterative selection process of aptamers over 10-15 cycles starting from a large initial pool of random nucleotide sequences make them extremely specific to their targets with high binding affinity. Aptamer-based detection systems are well investigated and ready to take over primitive detection systems. Aptamer chimeras (combination of aptamers with another aptamer or biomacromolecule or chemical moiety) have the potential activity of both the parent molecules and thus hold the capability to perform diverse functions at the same time. Owing to their extremely high specificity and lack of immunogenicity or pathogenicity, a number of other aptamer candidates have recently entered clinical trials and have gained the trust of the pharmaceutical companies. The promising clinical trial results provide new hope to change the conventional style of therapy. Aptamers have attained high therapeutic relevance in a very short time as compared to synthetic drugs or other modes of therapy. This review follows the various trends in aptamer technology including production, selection, modifications and success in clinical fields. It focusses largely on the various applications of aptamers which mainly depends upon their selection procedures. The review also sheds light on various modifications and chimerizations that have been implemented in order to improve the stability and functioning of the aptamers including, introduction of locked nucleic acids (LNAs). The application of various aptamers in detection systems have been discussed elaborately in order to stress on their role as efficient diagnostic agents. The key aspect of this review is focused on success of aptamers on basis of their performance in clinical trials for various diseases