title: Application of locked nucleic acids to improve aptamer in vivo stability and targeting function.
abstract: Aptamers are powerful candidates for molecular imaging applications due to a number of attractive features, including rapid blood clearance and tumor penetration. We carried out structure-activity relationship (SAR) studies with the Tenascin-C binding aptamer TTA1, which is a promising candidate for application in tumor imaging with radioisotopes. The aim was to improve its in vivo stability and target binding. We investigated the effect of thermal stabilization of the presumed non-binding double-stranded stem region on binding affinity and resistance against nucleolytic degradation. To achieve maximal thermal stem stabilization melting experiments with model hexanucleotide duplexes consisting of unmodified RNA, 2'-O-methyl RNA (2'-OMe), 2'-Fluoro RNA (2'-F) or Locked Nucleic Acids (LNAs) were initially carried out. Extremely high melting temperatures have been found for an LNA/LNA duplex. TTA1 derivatives with LNA and 2'-OMe modifications within the non-binding stem have subsequently been synthesized. Especially, the LNA-modified TTA1 derivative exhibited significant stem stabilization and markedly improved plasma stability while maintaining its binding affinity to the target. In addition, higher tumor uptake and longer blood retention was found in tumor-bearing nude mice. Thus, our strategy to introduce LNA modifications after the selection procedure is likely to be generally applicable to improve the in vivo stability of aptamers without compromising their binding properties.
authors.affiliation: Institute of Chemistry (Biochemistry), Free University Berlin, Thielallee 63, D-14195 Berlin, Germany.
authors.forename: Kathrin S
authors.initials: KS
authors.lastname: Schmidt
authors.forename: Sandra
authors.initials: S
authors.lastname: Borkowski
authors.forename: Jens
authors.initials: J
authors.lastname: Kurreck
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Stephens
authors.forename: Rolf
authors.initials: R
authors.lastname: Bald
authors.forename: Maren
authors.initials: M
authors.lastname: Hecht
authors.forename: Matthias
authors.initials: M
authors.lastname: Friebe
authors.forename: Ludger
authors.initials: L
authors.lastname: Dinkelborg
authors.forename: Volker A
authors.initials: VA
authors.lastname: Erdmann
mesh_terms: D000818:Animals; D052157:Aptamers, Nucleotide; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000378:metabolism*; D009841:Oligonucleotides / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics*; D016376:Oligonucleotides, Antisense / Q000737:chemistry*; D012265:Ribonucleotides / Q000737:chemistry; D013329:Structure-Activity Relationship; D013696:Temperature; D019063:Tenascin / Q000378:metabolism*
chemical_list: D052157:Aptamers, Nucleotide; D009841:Oligonucleotides; D016376:Oligonucleotides, Antisense; D012265:Ribonucleotides; C493194:TTA1 aptamer; D019063:Tenascin; C477371:locked nucleic acid