:L-Ribonucleic acid aptamer
{{short description|RNA-like molecule}}
{{DISPLAYTITLE:L-Ribonucleic acid aptamer}}
An L-ribonucleic acid aptamer (L-RNA aptamer, trade name Spiegelmer) is an RNA-like molecule built from L-ribose units.{{cite journal|title=RNA-Spiegelmers: a new substance class to efficiently inhibit peptide hormones|author1=Helmling, S.H.|author2=Eulberg, D.E.|author3=Maasch, C.M.|author4=Buchner, K.B.|author5=Klussmann, S.K.|journal=European Journal of Biochemistry|date=July 2003|volume=271|number=S1|doi=10.1111/j.1474-3833.2004.4119.x|doi-access=free}} It is an artificial oligonucleotide named for being a mirror image of natural oligonucleotides. L-RNA aptamers are a form of aptamers. Due to their L-nucleotides, they are highly resistant to degradation by nucleases.{{cite journal |vauthors=Vater A, Klussmann S |title=Turning mirror-image oligonucleotides into drugs: the evolution of Spiegelmer therapeutics |journal=Drug Discovery Today |volume=20 |issue=1 |pages=147–155 | date=January 2015 |pmid=25236655 |doi=10.1016/j.drudis.2014.09.004 |doi-access=free }} L-RNA aptamers are considered potential drugs and are currently being tested in clinical trials.
Features
=Chemical properties=
L-RNA aptamers, built using L-ribose, are the enantiomers of natural oligonucleotides, which are made with D-ribose. Nucleic acid aptamers, including L-RNA aptamers, contain adenosine monophosphate, guanosine monophosphate, cytidine monophosphate, uridine monophosphate, a phosphate group, a nucleobase and a ribose sugar.
=Biological characteristics=
Like other aptamers, L-RNA aptamers are able to bind molecules such as peptides, proteins, and substances of low molecular weight. The affinity of L-RNA aptamers to their target molecules often lies in the pico to nanomolar range and is thus comparable to antibodies.{{clarify|date=June 2012}}{{cite journal |first1=Britta|last1=Wlotzka|first2=Susanne|last2=Leva|first3=Bernd|last3=Eschgfäller|first4=Jens|last4=Burmeister|first5=Frank |last5=Kleinjung|first6=Christine|last6=Kaduk|first7=Peter|last7=Muhn|first8=Holger|last8=Hess-Stumpp|first9=Sven|last9=Klussmann |title=In vivo properties of an anti-GnRH Spiegelmer: an example of an oligonucleotide-based therapeutic substance class |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=99 |issue=13 |pages=8898–902 |date=June 2002 |pmid=12070349 |pmc=124395 |doi=10.1073/pnas.132067399 |bibcode = 2002PNAS...99.8898W |doi-access=free}}
L-RNA aptamers themselves have low antigenicity. In contrast to other aptamers, L-RNA aptamers have high stability in blood serum, since they are less susceptible to be cleaved hydrolytically by enzymes.{{cite journal |vauthors=Klussmann S, Nolte A, Bald R, Erdmann VA, Fürste JP |title=Mirror-image RNA that binds D-adenosine |journal=Nat. Biotechnol. |volume=14 |issue=9 |pages=1112–5 |date=September 1996 |pmid=9631061 |doi=10.1038/nbt0996-1112 |s2cid=41395593 }} They are excreted by the kidneys in a short time due to their low molar mass (which is below the renal threshold).
L-RNA aptamers modified with a higher molar mass, such as PEGylated L-RNA aptamers, show a prolonged plasma half-life.
Production
Unlike other aptamers, L-RNA aptamers are not directly made using systematic evolution of ligands by exponential enrichment (SELEX), as L-nucleic acids are not amenable to enzymatic methods, such as polymerase chain reaction (PCR), used in SELEX. Therefore, the selection is done with mirrored target molecules.
=Reflection of the target molecule=
The first step is the production of the target's enantiomer. In the case of peptides and small proteins that are produced synthetically, an enantiomer is made using synthetic D-amino acids. If the target is a larger protein molecule, beyond synthetic abilities, the enantiomer of an epitope is produced.
=SELEX=
Conventional (up to 1016 different oligonucleotides) existing molecule library serves as a starting point for the subsequent SELEX process.{{clarify|date=June 2012}} Selection, separation, and amplification using the mirror image of the target molecule is performed.
=Sequencing and synthesis=
The sequence of the oligonucleotide selected using SELEX is determined with the help of DNA sequencing. This information is used for the synthesis of the oligonucleotide's enantiomer, the L-RNA aptamer, using L-nucleotides.
Use
L-RNA aptamers have been obtained for the chemokines CCL2 and CXCL12, the complement components C5a and ghrelin. They are currently in preclinical or clinical development. Proof-of-concept for an anti-CCL2/MCP-1 L-RNA aptamers has recently been demonstrated in diabetic nephropathy patients. They can also be used as diagnostic agents.