Aptamers as Theranostic Agents: Modifications, Serum Stability and Functionalisation

Abstract

Aptamers, and the selection process known as Systematic Evolution of Ligands by Exponential Enrichment (SELEX) used to generate them, were first described more than twenty years ago. Since then, there have been numerous modifications to the selection procedures. This review discusses the use of modified bases as a means of enhancing serum stability and producing effective therapeutic tools, as well as functionalising these nucleic acids to be used as potential diagnostic agents.

RAID3 - An interleukin-6 receptor-binding aptamer with post-selective modification-resistant affinity

“…Usually, post-selective modification of the pyrimidines disturbs correct aptamer folding and consequently decreases its affinity. 27,28 Strikingly, 2 0 -F-Py modified RAID3 was still able to bind the sIL-6R with an affinity equal to that of the unmodified aptamer. Consequently, this strongly indicates that RAID3 2 0 -F-Py was still able to undergo correct folding with all pyrimidines replaced by their 2 0 -F analogs.…”

“…This phenomenon is rather common with aptamers: most aptamers selected with canonic nucleotides show no or only reduced affinity for their target after post-selective modification of the 2 0 -moiety, and if their affinity should be retained, shortening of the aptamer will finally compromise or destroy it. 27,28 In the present study, we describe the selection, characterization and post-selective modification of an RNA aptamer specific for the IL-6R domain 3 (IL-6R D3) with no apparent sequence similarities to already selected AIR-3 or FAIR-6 and no reduction in affinity, even after minimization. This is, to the best of our knowledge, the first time that the replacement of all 2 0 -OH pyrimidines by their 2 0 -F counterparts in addition to shortening of the initially selected aptamer did not impair the affinity of the aptamer for its target molecule.…”

Applications of Aptamers in Medicine: A Mini Review

“…To increase the serum half-life, chemical modifications have been introduced into sugar moiety or phosphodiester linkage. 3' and/or 5' capping of nucleic acid strands protect aptamer from endonuclease attacks (Shigdar et al, 2013). Incorporation of inverted nucleotide at the 3'-terminus decreases the serum endonuclease activity as 3' exonuclease activity in serum is much higher.…”

“…Another method is the incorporation of fluoro or O-methyl group at the 2' position of the sugar moiety (Davydova et al, 2011). Incorporation of 2'amino pyrimidines, boranophosphate internucleotide linkages, 5-modified pyrimidines, and/or 4'thio pyrimidines increases the nuclease resistance of aptamer (Shigdar et al, 2013).…”

Spiegelmers as potential receptors for cTnI diagnostics

“…7 On the other hand, the most generally examined specimens of human diagnostics, blood plasma and serum, include a panel of nucleases that might expeditiously degrade oligonucleotides severely limiting leveraging aptamers as receptors of biomarker determining assays. 8 With these advantages and drawbacks of aptamers in mind, we previously developed a cTnI selective Spiegelmer 9 for a specic N-terminal epitope of cTnI with a rationally designed selection procedure. Spiegelmers 10 are enantiomeric aptamers, which are composed of L-2 0 -deoxyribose units and thus fully withstand enzymatic degradation.…”