Technology SELEX

The SELEX technology (Systematic Evolution of Ligands by Exponential enrichment) was introduced by Larry Gold and Jack Szostak [1, 2] and provides a powerful tool for the in vitro selection of nucleic acids (aptamers) from combinatorial DNA or RNA libraries against a target molecule. 

Sun S, Technology evaluation SELEX, Gilead Sciences Inc, Curr. Opin. Mol. Ther., 2 100-105, 2000. 

Profile Founded in 1995 with the merger of NeXagen and Vestar, the company utilizes proprietary compounds to develop therapeutics and diagnostics to serve unmet medical needs. From NeXagen, NeXstar acquired the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) combinatorial chemistry technology. 

In vitro evolution or SELEX has proven to be a powerful technology that may have a variety if applications in the development of therapeutics and diagnostics. Chemically modified nucleotides have addressed the concerns about biological stability, but issues related to delivery and mass production still remain as concerns. 

SELEX technology qnickly became an important and widely used tool in molecular biological, pharmaceutical, and medical research, and was often modified to make the selection process more efficient and less time consnming, and to select aptamers with particular binding featnres (affinity, specificity) for different target molecules and for different applications. 

The SELEX process for the selection of target-specific aptamers is a universal process characterized by the repetition of five main steps binding, partition, elution, amplification, and conditioning however, for each aptamer selection, the protocol has to be adapted to the current requirements. The SELEX design and the specific selection conditions depend, for example, on the target, the oligonucleotide hbrary, or the desired features and application of the aptamers to be selected. Therefore, a multitude of SELEX variants have been developed since the first description of this technology in 1990 (Table 2.1). 

Non-SELEX is an attractive alternative to SELEX, due to increased speed and suitability for easy automation. Non-SELEX leads to a final pool with all sequences being unique. The analysis of such sequences would be much more efficient if single-molecule sequencing were used. In this respect, the current effort in the development of single-molecule sequencing technologies is quite encouraging (Bayley, 2006). 

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