Aptamer

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Aptamers (from Latin aptus fit ' and Greek meros , Location' ) are short single-stranded DNA - or RNA - oligonucleotides (25-70 bases ) or peptides comprising a specific molecule can bind structure 3D theirs. If the aptamer is a peptide, it is called a peptide aptamer.

description

Aptamers bind to proteins , e.g. B. growth factors and bacterial toxins, low molecular weight substances such as amino acids and antibiotics , and also virus particles . Aptamers have dissociation constants in the picomolar to nanomolar range. Accordingly, they bind to their target molecules as strongly as antibodies . This high specificity is achieved because the 3D structure of the oligonucleotide folds exactly around the binding partner ("adaptive binding"). The most important interactions besides the accuracy of fit are electrostatic interactions and hydrogen bonds .

Aptamers are produced artificially ( in vitro ) according to the criterion of the highest possible specific binding affinity . For this purpose, large random libraries of oligonucleotides of different base sequences are created, on the order of 10 14 to 10 15 different sequences per µmol . (With an oligonucleotide length of 40 to 70 bases, significantly more variations would be possible, up to 10 42 , but such amounts cannot be produced). These sequences are the " systematic evolution of ligands by exponential enrichment " ( English selection of ligands by exponential enrichment , SELEX ® ) filter out those that bind the desired molecule strongest. The aptamer candidates are mixed with immobilized ligands and the unbound ligands are washed away. What remains are candidates who have a high affinity for the target molecule. These are multiplied via PCR and a new cycle of binding and washing away of the more weakly bound candidates begins. After several passes, one or two oligonucleotides are obtained, which are called aptamers.

Aptamers combine the beneficial properties of small molecules and antibodies. These properties include, among others

  • high specificity and affinity
  • chemical stability
  • low immunogenicity
  • the ability to specifically influence protein-protein interactions

In contrast to monoclonal antibodies, aptamers are chemically synthesized and not biologically expressed, which represents a considerable cost advantage in their synthesis. In the synthesis of numerous modifications, such as the incorporation of can fluorescent - reporter molecules or affinity tags , are made. Is an aptamer with polyethylene glycol (PEG) conjugate , can such. This prevents the originally very small molecules from being filtered or excreted too quickly through the kidneys . This allows the elimination half-life to be increased significantly from minutes to hours. The enzymatic stability of aptamers can also be improved by using chemically modified or stereochemically mirror-image nucleotides ( spiegelmers ).

Applications

Due to their ability to specifically switch off the function of individual proteins in the cell, aptamers are considered molecular tools. Aptamers are used as therapeutics, in medical diagnostics and environmental analysis.

oncology

In oncology in particular, therapeutic approaches are possible with aptamers. There is currently no aptamer-based drug for cancer therapy . However, several clinical studies have started.

Age-related macular degeneration (AMD)

In December 2004, pegaptanib was approved as a drug in the USA , which, after being approved across Europe in February 2006, has been on the market in Germany since May 2006. It is approved for the treatment of wet age-related macular degeneration (AMD). Pegaptanib is a 27- mer RNA aptamer that was developed with the aim of binding to the growth factor VEGF (Vascular Endothelial Growth Factor) in a highly specific manner and with high affinity .

Food analysis

The ability of aptamers to bind to surfaces of bacterial cell walls can be used for enrichment in order to lower the analytical detection limit in subsequent analyzes. Coupled with a real-time quantitative PCR , this can be used in the dairy industry to determine the number of Bacillus cereus spores.

toxicology

Aptamer-based rapid tests can be used as bedside tests in emergency medicine . At the end of 2006, a rapid cocaine test based on aptamer technology was presented.

Individual evidence

  1. ^ AD Ellington, JW Szostak In vitro selection of RNA molecules that bind specific ligands. In: Nature. Volume 346, 1990, pp. 818-822, PMID 1697402 doi: 10.1038 / 346818a0
  2. ↑ C. Tuerk and L. Gold: Systematic evolution of ligands by exponential enrichment: RNA ligands to bacteriophage T4 DNA polymerase. In: Science. Volume 249, 1990, pp. 505-510, PMID 2200121 doi: 10.1126 / science.2200121
  3. ^ A. Vater, S. Klussmann: Toward third-generation aptamers. Spiegelmers and their therapeutic prospects . In: Current Opinion in Drug Discovery & Development . tape 6 , no. 2 , March 2003, p. 253-261 , PMID 12669461 .
  4. ↑ G. Zhou, G. Wilson, L. Hebbard, W. Duan, C. Liddle, J. George, L. Qiao: Aptamers: A promising chemical antibody for cancer therapy. In: Oncotarget. [Electronic publication before going to press] February 2016, doi: 10.18632 / oncotarget.7178 , PMID 26863567 .
  5. ↑ EW Ng et al. : Pegaptanib, a targeted anti-VEGF aptamer for ocular vascular disease. In: Nat. Rev. Drug. Discov. Volume 5, 2006, pp. 123-132, PMID 16518379 doi: 10.1038 / nrd1955 .
  6. ↑ Christin Fischer, Markus Fischer: Aptamer-Based Trapping: Enrichment of Bacillus cereus Spores for Real-Time PCR Detection . In: Otto Holst (Ed.): Microbial Toxins . Springer Science + Business Media LLC, New York, NY 2017, ISBN 978-1-4939-6956-2 , pp. 61-68 , doi : 10.1007 / 978-1-4939-6958-6_6 .
  7. ↑ Christin Fischer, Tim Hünniger, Jan-Hinnerk Jarck, Esther Frohnmeyer, Constanze Kallinich: Food Sensing: Aptamer-Based Trapping of Bacillus cereus Spores with Specific Detection via Real Time PCR in Milk . In: Journal of Agricultural and Food Chemistry . tape 63 , no. 36 , September 16, 2015, p. 8050-8057 , doi : 10.1021 / acs.jafc.5b03738 .
  8. ↑ Juewen Liu, Debapriya Mazumdar, Yi Lu: A Simple and Sensitive “Dipstick” Test in Serum Based on Lateral Flow Separation of Aptamer-Linked Nanostructures . In: Angewandte Chemie . tape 118 , no. 47 , December 4, 2006, p. 8123-8127 , doi : 10.1002 / anie.200603106 .
  9. ^ Test sticks for cocaine Deutschlandfunk. Retrieved May 14, 2019.