Aptamers are small oligonucleotides (10 – 20 kD) that bind with high affinity and specificity to a large number of target molecules. Kd-values for the aptamer-target interactions vary from a few picomolar (pM) to a few nanomolar (nM), which is comparable to the binding of antibodies. They are selected from combinatorial libraries consisting of about 1015 different oligonucleotides in an entirely in vitro system. As no animal is used, the target molecule does not have to be immunogenic and is allowed to be (highly) toxic. After characterization, using standard molecular biological techniques, aptamers are chemically synthesized in small quantities or on large scale.
These “chemical antibodies” can easily be modified in a side directed way for different purposes, such as immobilization on a surface, addition of labels, or changing their pharmacodynamic and pharmacokinetic profiles. Over the last 20 years, aptamers have been widely used in diagnostic (sensors), biotechnology and therapeutic applications. To date, there is one marketed aptamer-based drug for the treatment of wet macula degeneration, and several aptamers are currently in the clinical pipeline.