Aptamers chemical properties

Due to these properties, aptamers are considered to be chemical antibodies and actually rival or sometimes surpass antibodies. Indeed, the ease and the reproducibilty of the synthesis as well as several other properties make aptamers interesting alternatives it is, for instance, possible to raise aptamers against toxic snbstances. 

The positions that remain unmodified at the end of the in vitro selection procedure (e.g., the purine residnes in a selection carried out with 2 -fluoro-pyrimidine triphosphates) can be modified post-SELEX for further optimization of the aptamers. A systematic stndy of the 64 variants of the six-membered apical loop of an anti-TAR aptamer led to the identification of locked nucleic acid/2 -0-methyl chimeras fully resistant to nncleases that displayed anti-HIV-1 properties in a cell cnlture assay (Di Primo et al., 2007). Identification of the few residues that cannot be modified in an RNA aptamer can be carried ont by chemical interference, a method nsed to identify chemical variants of the aptamer originally selected. Snch an approach led to the synthesis of a modified anti-HIV-1 reverse transcriptase in which all bnt two of the positions of the RNA aptamer were snbstitnted by 2 -0-methyl residnes (Green et al., 1995). This was also the case for the aptamer nsed for age-related macnla degeneration in hnman beings (Ruckman et al., 1998). 

Step and are, at least for DNA aptamers, relatively stable over the time. The in vitro selection can be manipulated to obtain binding properties desirable for specific assays. The aptamers can be produced by chemical synthesis resulting in little or no batch-to-batch variation and reporter or functionalizing molecules can be attached to aptamers at precise locations. Furthermore, they are produced through an in vitro process which does not require animals. 

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