X-Aptamers are the next step in the evolution of aptamer technology. They are synthetic affinity reagents that incorporate natural as well as chemically-modified DNA or RNA nucleotides. Common modifications include amino acid functional groups as well as small molecules in virtually any combination. For many years, aptamers were developed using one of several versions of the Systemic Evolution of Ligands by Exponential Enrichment (SELEX) process. Unfortunately, SELEX has inherent limitations, the most notable being limited chemical diversity. Chemical diversity strongly influences the interaction between an affinity reagent and its target and directly affects binding affinity and specificity. Because SELEX relies on enzymatic amplification of an oligonucleotide library, only those chemically modified nucleotides that are compatible with PCR amplification can be used. In addition, the number of distinct, modified nucleotides that can be incorporated into any one SELEX library is severely constrained. This is in stark contrast to the vast chemical diversity of antibodies.
X-Aptamer technology overcomes SELEX limitations and exponentially expands the chemical diversity available for target interaction. X-Aptamers are developed using a patented microbead-based selection process synthesized using combinatorial chemistry as well as a patented synthesizer. In contrast to SELEX, the microbead process does not rely on PCR amplification of the binding sequences and thus enables a rich diversity of chemical functionality that is necessary to achieve excellent specificity and affinity. Many chemical modifications as well as combinations of those modifications that are not compatible with SELEX are available for use with AM Biotech’s bead-based X-Aptamer technology.