Recentprogressofcell-penetratingpeptidesasnewcarriersfor

intracellularcargodeliveryPart1BackgroundPart2CPPsclassificationPart3chemicallinkageofCPPsPart4CPPstransmembranemechanismPart5CPPsApplicationsCONTENTSContentsBackgroundCPPscellmembraneselectivelypermeablebarrierCell-penetratingpeptides(CPPs)fewerthan30aminoacids、entercells、endocytosis、conjugatedbioactivecargos[1]AdvantagesofCPPsBiologicalsafety、cellularuptake、bedesigned、LowcytotoxicityCPPsapplicationsiRNA,nucleicacids,proteins、Nanoparticles、Chemotherapydrugs、Liposomes[2-6]CPPsclassificationCPPsequencesareknowntovaryconsiderablyasseenbyTable1.Similarities:positivelychargedaminoacids(R、K)Themembranolyticproperties:positivelycharge,secondarystructure,specificallyhelicityCPPsclassificationEventhoughCPPshaveagreatsequencevariety,itispossibleto

bemainlydividedintothreesubgroupsdefinedbytheirphysical–

chemicalproperties:cationic,amphipathicandhydrophobic。[7]CationicCPPsCationicpeptidesareaclassofpeptideswithahighpositivenetchargeandfewacidicaminoacidresidues.Typical,thecationicCPPsareincludingR9,Tat,hLFand(RXR)4andsoon.AmphipathicCPPsAmphiphiliccell-penetratingpeptidesarecomposedmainlyoflysine。Therearealsodistributedtootherhydrophilicorhydrophobicaminoacidresiduesinthesequence,whichspatialconformationofα-helixstructure。Amphoterichelixhavinghydrophilicandhydrophobicpropertiesisnecessaryforthestructurethroughthemembrane。suchaspVEC、ARFandproline-richpeptides。CPPsclassificationHydrophobicCPPsPeptideswhichcontainonlyapolarresiduesareconsideredashydrophobic

peptides。Sofar,onlyafewhydrophobicCPPsequenceshavebeendiscoveredsuchasthesignalsequencesfrom

integrinβ3(VTVLALGALAGVGVG)andKaposifibroblastgrowthfactor

(AAVALLPAVLLALLAP)chemicallinkageofCPPschemicallinkageofCPPsExamples

ofcovalentconjugationareneutralcargo(phosphorodiamidate

morpholinooligomers(PMO),peptide

nucleicacids(PNA),smalldrugmolecules)complexes

whichcanbecoupledtoCPPsviaadisulfidebond,an

amidebond,orotherspecificlinkers.Noncovalent

complexesareformedviaelectrostaticand/orhydrophobic

interactionsbetweennegativelychargedcargo

molecules,suchasnucleicacids(siRNA,pDNA,etc.),andapositivelychargedCPP.CPP-cargocomplexesneedtoescape

fromtheendosmalvesiclesinordertoinducea

biologicaleffect.Ways:Onelineofthinkingisthathydrophobicandelectrostaticinteractionsoccurbetweentheendosomalmembraneandthenanoparticles,whichleadstodisruptionof

theendosomes.Anothertheprotonspongetheory,proposesthatendosomesburstduetoosmotic

pressureCPPstransmembranemechanismCPPstransmembranemechanismRoleofEndocytosis.Endocytosis,includingphagocytosis

andpinocytosis.Phagocytosisisacomplex

processusedtouptakelargeparticlessuchas

othercells,viruses,orbacteria,whilepinocytosisis

mainlyusedtouptakesmallerparticles.Endocytosis

occursbytheactionofvariouspathwayswhichcanbe

classifiedintocaveolaeand/orlipid-raft-mediated

endocytosis,

macropinocytosis,cholesterol-dependent

clathrin-mediatedendocytosis,orcaveolae-and

clathrin-independentendocytosisDirecttranslocationthroughthemembranebilayerCPPsApplicationsCPPsApplicationsProperlydevelopedCPPsandtheirconjugates

withtherapeuticsofferaverypromisingpathwayto

deliverlowerconcentrationsoftoxicdrugstocritical

tissuessuchastumors,heart,etc.Smallchemotherapeutic

drugshavealsobeendeliveredbyCPPs(doxorubicin,methotrexate,cyclosporineA,paclitaxel).[8]Cducedabiologicallyactive

Bcl-xLfusionproteincontainingan11aminoacidCPP

fromTATproteinandahemagglutinin(HA)tagthat

allowedinvitroandinvivodeliveryintoneurons[9]Otherfuctionsuchaspromotingintestinalabsorptionofinsulin,Newpeptideforoculartissuetransport-PODandsoon.Conclusioncell-penetratingpeptidescanefficientlytraversethe

plasmamembraneofbothcellsandtissuesandare

successfullyusedasdeliveryvectorsfortherapeutic

molecules.Duetotheirpositivecharge,CPPscan

becovalently

conjugatedtoactivebiomolecules(nucleicacids,peptides,proteins,chemotherapeuticdrugs,etc.).After

efficientcellularinternalization,CPPsareabletorelease

theircargointothecytosolinordertopromote

thedesiredbiologicaleffect.Whencoupledtoacargo,

CPPsuseendocytosisasthemaincellulartranslocation

mechanism.Priortouse,CPPsmustundergobothpharmacologicalandtoxicological

studiesinvivo.Consideringevidencefromnumerous

studies,CPPshavethepotentialtobecomeauniversal

tooltocarrytherapeuticmoleculesacrosscellular

membraneswithoutariskoftoxicityorinflammatory

reactionsReference[1]D.M.Copolovici,K.Langel,E.Eriste,U.Langel,Cell-penetratingpeptides:design,synthesis,andapplications.ACSNano8(2014)1972-1994.[2]H.Raagel,P.Saalik,M.Hansen,U.Langel,M.Pooga,CPP-proteinconstructsinduceapopulationofnon-acidicvesiclesduringtraffickingthroughendo-lysosomalpathway.JControlRelease139(2009)108-117.[3]F.SaidHassane,A.F.Saleh,R.Abes,M.J.Gait,B.Lebleu,Cellpenetratingpeptides:overviewandapplicationstothedeliveryofoligonucleotides.CellMolLifeSci67(2010)715-726.[4]M.Lewin,N.Carlesso,C.H.Tung,X.W.Tang,D.Cory,D.T.Scadden,R.Weissleder,Tatpeptide-derivatizedmagneticnanoparticlesallowinvivotrackingandrecoveryofprogenitorcells.NatBiotechnol18(2000)410-414.[5]E.A.Dubikovskaya,S.H.Thorne,T.H.Pillow,C.H.Contag,P.A.Wender,Overcomingmultidrugresistanceofsmall-moleculetherapeuticsthroughconjugationwithreleasableoctaargininetransporters.ProcNatlAcadSciUSA105(2008)12128-12133.[6]V.P.Torchilin,R.Rammohan,V.Weissig,T.S.Levchenko,TATpeptideonthesurfaceofliposomesaffordstheirefficientintracellulardeliveryevenatlowtemperatureandinthepresenceofmetabolicinhibitors.ProcNatlAcadSciUSA98(2001)8786-8791.[7]S.B.Fonseca