The stability of aptamers
One of the key benefits of using aptamers instead of antibodies is how you store and use your reagent. Over the past 60 years the stability of oligonucleotides has been rigorously studied and well defined.
Most providers of synthetic oligonucleotides recommend storing the suspended DNA in a neutral buffer, free from divalent metal ions (e.g Tris EDTA) at -20°C. Stored like this, most manufacturers guarantee a shelf life of 2 years. However, even at 37°C, it is estimated that the oligonucleotide would be stable for in excess of 6 weeks. Other studies have shown that aptamer beacons with fluorescent tags have retained their functionality for 5.5 years when stored in lyophilised formats.
Reagent stability is critical for convenient reagent use and simple global logistics. We are working with many partners to help them overcome this exact problem with antibody based assays. Find out about our work with Proaxsis here: Aptamer Group & Proaxsis enter partnership to improve stability of diagnostic tests
In biosensor diagnostic platforms our aptamers have shown excellent stability. Application in plasma matrices has allowed biosensor chips to be reused a number of times without loss of the aptamer’s stability. Ultimately fouling of the chip from the plasma matrix is responsible for the loss of signal in point-of-care and continuous monitoring sensors, not aptamer stability.
As it is becoming more commonplace, to see oligonucleotide-based therapeutics and diagnostics it is crucial to understand the stability of oligonucleotides in vivo and how we can manipulate their chemistry to suit your needs.
DNA was thought to have a very short half-life in vivo (30-60 minutes) due to the abundance of endogenous nucleases. However certain indications that require short half life for acute conditions, such as stroke and inflammation, will benefit from this ability of the aptamer to offer a ‘hit-and-run’ approach. Current unmodified DNA aptamers in the clinic certainly show sufficient half life over a few days to allow the desired treatment. Half-life from in vitro studies
If a longer half life is needed this is often done by modifying the oligonucleotide backbone; removing or replacing functional groups involved in enzymatic degradation. One of the most widely known examples of the application of stabilising modifications is the use of 2’Fluoro and 2’O-Methyl nucleotides in the drug Macugen. Using these modifications has been shown to increase the half-life of the aptamers from minutes (for unmodified RNA) to days.
Other methods (often used in combination with backbone modifications) include the addition of dTdT, or an inverted nucleotide cap, on one end of the aptamer. These caps inhibit endonucleases as they block the binding region on the 5’ or 3’ end. When used in conjunction with backbone modification is it common to see 5-10 fold increases in stability.
By understanding the different characteristics of nucleic acids, we are able to design the perfect solution for your application, whatever the challenge.
If you would like more information or would like to discuss how we can develop aptamers for your application then please get in touch.