Aptamers are oligonucleotides capable of identifying a target molecule with high affinity and specificity, which grants them enormous potential as therapeutic and diagnostic tools. Aptamers are oligonucleic acid or peptide molecules that bind to a specific target molecule. Aptamers are usually created by selecting them from a large random sequence pool, but natural aptamers also exist in riboswitches. Aptamers can be used for both basic research and clinical purposes as macromolecular drugs.
Nucleic acid aptamers are single-stranded (ssDNA and RNA). Selection is carried out from libraries of oligonucleotides that have a central region of variable size and random sequence and two flanking regions of known sequence to allow PCR amplification. The length of the central region is usually between 30 and 60 nucleotides so that the total length of the aptamer is 70-100 nucleotides.
Aptamers have been engineered through repeated rounds of in vitro selection or equivalently, SELEX (systematic evolution of ligands by exponential enrichment) to bind to various molecular targets such as small molecules, proteins, nucleic acids, and even cells, tissues and organisms. After obtaining the individual aptamers, these are characterized in their interaction with the target protein using biochemical techniques such as SPR, ELISA, slot blot, or Western blot.
Aptamer production is carried out by chemical synthesis, unlike most of the molecules that act similarly. Because interactions of the bases along the chain, these molecules adopt three-dimensional structures allowing them to join stable and specifically to their targets, ranging from small molecules to complex multimeric structures.
In addition to its potential application as molecular sensors, many aptamers that recognize proteins are also capable of interfering with its biological function. In recent years, techniques have been discovered that facilitate intracellular application of aptamers and their use as in-vivo modulators of cellular physiology.
While aptamers are analogous to antibodies in their range of target recognition and variety of applications, they possess several key advantages over their protein counterparts:
Easier and more economical to produce. Aptamers are made through chemical synthesis, a process that is highly reproducible and can be readily scaled up. Their production does not depend on bacteria, cell cultures or animals.
Compared to antibodies, toxicity and low immunogenicity of particular antigens do not interfere with the aptamer selection.
They are capable of greater specificity and affinity than antibodies.
They can easily be modified chemically to yield improved, custom tailored properties.
They can specifically bound to either small molecules and complex multimeric structures.
Their small size leads to a high number of moles of target bound per gram, and they may have improved transport properties allowing cell specific targeting and improved tissue penetration [5-9].
They are much more stable at ambient temperature than antibodies yielding a much higher shelf life, and they can tolerate transportation without any special requirements for cooling, eliminating the need for a continuous cold chain.
Ability to inactivate proteins, without altering genetic material.