Biomedical Engineering Reference
In-Depth Information
sequence. was. functionalized. with. both. a. luorophore. and. a. quencher.. Upon. binding. to.
the.trifunctional.molecule,.the.quencher.was.cleaved.by.DTT,.resulting.in.the.“turn-on”.of.
luorescent.signal.
Nucleic.acid.aptamers.have.also.been.linked.with.siRNAs.for.gene.therapy..siRNA.(also.
known.as.short.interfering.RNA).is.a.class.of.short.double-stranded.RNA.molecules.that.
can. interfere. with. the. expression. of. a. speciic. gene.. siRNA. is. comprised. of. a. passenger.
strand.and.a.guide.strand.that.target.the.complementary.mRNA.(Hamilton.and.Baulcombe.
1999)..siRNA-induced.gene.silencing.relies.on.the.formation.of.an.RNA-induced.silencing.
complex.(RISC)..RISC.uses.the.guide.strand.of.siRNA.as.a.template.to.recognize.the.target.
mRNA..Upon.inding.the.target,.RISC.activates.RNase.and.cleaves.the.RNA.(Grunweller.
and. Hartmann. 2005).. While. promising. in. gene. therapy,. direct. siRNA. delivery. remains.
dificult..Functional.ligands.such.as.nucleic.acid.aptamers.have.been.linked.with.siRNAs.
to. help. them. penetrate. through. the. cell. membrane. eficiently.. In. 2006,. McNamara. et. al..
reported. anti-PSMA. aptamer-siRNA. chimeras. for. speciic. siRNA. delivery. (McNamara.
et.al..2006)..This.complex.contains.two.strands..The.longer.one.has.both.PSMA.aptamer.
sequence. and. passenger. strand. sequence.. The. shorter. one. is. the. guide. strand.. Unlike. a.
pretargeting.system,.these.two.strands.were.hybridized.irst.before.being.incubated.with.
cells.. The. binding. of. the. anti-PSMA. aptamer. A10. to. the. target. LNCaP. cells. will. trigger.
the. endocytosis. of. the. aptamer-siRNA. complex. into. the. cell.. A. gene. expression. study.
showed. that. the. relative. gene. expression. of. A10-siRNA-treated. group. was. much. lower.
than.other.control.groups.(80%.less)..As.a.result,.A10-siRNA.chimeras.caused.the.apop-
tosis.of.PSMA-overexpressed.cells.such.as.LNCaP.cells..In.addition.to.in.vitro.cell.assay,.
in.vivo.animal.studies.have.also.been.performed..After.a.series.of.injection.of.A10-siRNA.
chimeras.(200.pmol/injection),.the.tumor.volume.was.reduced.twofold.in.comparison.to.
the.controls..These.results.demonstrate.that.this.irst-generation.A10-siRNA.chimera.can.
eficiently. inhibit. tumor. growth. through. intratumoral. injection.. However,. for. the. treat-
ment. of. advanced. cancer,. systemic. administration. of. aptamer-siRNA. chimeras. will. be.
necessary.. A. second-generation. aptamer-siRNA. chimera. was. developed. to. satisfy. this.
demand.. Compared. with. the. irst-generation. A10-siRNA. chimera,. the. aptamer. portion.
of. this. optimized. complex. was. shortened. from. 71. nucleotides. (nt). to. 39. nt. to. facilitate.
the. chemical. synthesis.. In. addition,. PEGylation. was. applied. to. increase. the. half-life. of.
this.chimera.in.serum.(Dassie.et.al..2009)..Aptamer-siRNA.complexes.have.been.studied.
for. not. only. cancer. therapy,. but. also. the. treatment. of. human. immunodeiciency. virus.
(HIV)-infected. cells. (Zhou. et. al.. 2008,. 2009c).. The. results. showed. that. both. the. aptamer.
and.siRNA.could.suppress.the.replication.and.production.of.HIV.viruses..However,.the.
aptamer-siRNA. chimera. provided. better. eficacy. than. either. the. aptamer. or. the. siRNA.
alone.(Zhou.et.al..2008).
2.4 Conclusions and Perspectives
Nucleic. acid. aptamers. have. recently. been. used. as. afinity. ligands. for. cell. recognition.
applications.because.of.their.remarkable.speciicity,.high.binding.afinity,.small.size,.and.
tunable.stability..Nucleic.acid.aptamers.can.be.directly.used.to.mimic.the.variable.regions.
of.natural.antibodies..They.can.also.be.used.to.functionalize.nanoparticles.through.either.
noncovalent. interactions. or. covalent. bonding.. In. addition,. nucleic. acid. aptamers. can. be.
used. to. develop. multifunctional. nucleic. acid. nanomaterials.. All. these. aptamer-based/
