Biomedical Engineering Reference
In-Depth Information
determine.the.safety.and.tolerability.of.an.ApoB.targeting.siRNA.(PRO-040201).delivery.
to. the. liver.. In. addition,. Tekmira. has. initiated. a. Phase. I. human. clinical. trial. on. a. PLK1.
targeting.siRNA.(TKM-PLK1). in.relapsed.or.refractory. cancer. patients.. Another. Phase. I.
clinical.trial.on.Atu027.has.been.announced.by.Silence.Therapeutics.to.treat.a.broad.range.
of.solid.tumors..Atu027.is.based.on.a.chemically.modiied.siRNA.formulated.in.liposomes.
against.PKN3.(protein.kinase.N3).(Stanton.and.Colletti.2010,.Vaishnaw.et.al..2010).
24.10.1 sirNA and Vehicle-related Side effects
Unwanted. side. effects,. such. as. off-target. gene. silencing. and. immunostimulation,. have.
been.major.concerns.for.siRNA-based.therapeutics.(Agrawal.and.Kandimalla.2004,.Judge.
and. MacLachlan. 2008,. Robbins. et. al.. 2009).. For. instance,. siRNAs. are. known. to. induce.
silencing. of. multiple. genes. via. a. miRNA-like. mechanism. (Dykxhoorn. and. Lieberman.
2006,.Aagaard.and.Rossi.2007)..The.off-target.effects.can.be.ameliorated.by.incorporating.
advanced.bioinformatic.guidance.in.the.designs.of.sequences.and.by.introducing.chemi-
cal. modiications. to. the. siRNA. molecule.. For. example,. a. single. 2′-
O
-methyl. substitution.
was.found.to.signiicantly.reduce.off-target.effects.without.compromising.gene.silencing.
activity.(Judge.et.al..2005,.Robbins.et.al..2007,.Judge.and.MacLachlan.2008).
siRNAs.may.potentially.cause.problems.by.triggering.a.cytokine.response,.which.stems.
from. the. recognition. by. toll-like. receptors. (TLRs). in. cells. of. the. innate. immune. system.
(Agrawal.and.Kandimalla.2004,.Judge.and.MacLachlan.2008,.Robbins.et.al..2009)..It.is.well-
established. that. unmethylated. CpG. motifs. are. able. to. stimulate. the. immune. system. by.
the.TLR9-driven.pathway.(Klinman.2004)..Similarly,.siRNAs.can.be.recognized.by.TLR3.
or.TLR7/8.(Judge.and.MacLachlan.2008,.Robbins.et.al..2009)..In.addition.to.the.TLRs,.the.
helicases.RIG-1.and.Mda5.as.well.as.protein.kinase.R.play.an.important.role.in.the.rec-
ognition.of.siRNAs.by.the.immune.system..The.majority.of.innate.immune.activation.by.
siRNAs.in.vivo.is.mediated.through.TLR7/8.in.immune.cells..It.was.revealed.that.TLR7/8.
binding. is. sequence. speciic,. favoring. GU-rich. sequences. (Judge. et. al.. 2005,. Judge. and.
MacLachlan.2008,.Robbins.et.al..2009)..Therefore,.the.recognition.of.siRNAs.by.TLR7/8.can.
be.avoided.by.choosing.sequences.that.are.not.recognized.by.these.receptors..Additionally,.
TLR7/8-mediated.recognition.and.immune.stimulation.by.siRNA.can.be.reduced.by.the.
2′-
O
-methyl.modiication.on.the.siRNA..In.contrast,.2′-
O
-methylation.of.siRNA.does.not.
block. TLR3. activation. (Kleinman. et. al.. 2008).. Unlike. TLR7/8,. TLR3. is. localized. in. both.
the. cell. surface. and. the. endosome. (Sioud. 2008,. Robbins. et. al.. 2009,. Semple. et. al.. 2010)..
In.a.recent.clinical.trial.of.siRNA.targeting.vascular.endothelial.growth.factor.(VEGF),.it.
was.demonstrated.that.the.observed.decrease.in.vascularization.was.not.a.sequence-.and.
target-dependent. effect. on. angiogenesis,. but. rather. a. result. of. nonspeciic. activation. of.
TLR3.(Kleinman.et.al..2008)..This.inding.highlighted.another.concern.for.the.safe.use.of.
siRNAs-based.therapeutics.in.clinic.(Judge.and.MacLachlan.2008,.Robbins.et.al..2009).
Furthermore,. siRNAs. may. compete. or. interfere. with. endogenous. RNAi. pathways. by.
microRNAs,.leading.to.additional.off-target.effects.of.siRNA.(Dykxhoorn.and.Lieberman.
2006,.Kurreck.2009,.Whitehead.et.al..2009).
24.10.2 Lipid-Mediated Side effect
Synthetic. siRNAs. formulated. in. cationic. LNPs. can. potentially. induce. interferons. and.
inlammatory.cytokines..It.has.been.demonstrated.that.cationic.lipids.can.modify.cellular.
signaling.pathways.and.stimulate.speciic.immune.or.anti-inlammatory.responses..Due.
to.their.charge,.cationic.lipids.are.responsible.for.nonspeciic.interaction.with.negatively.
