Conscripts of the Infinite Armada Systemic

8/3/2019 Conscripts of the Infinite Armada Systemic

1/11266 | MAY 2010 | voluMe 7 .ature.cm/rcc

MolecularPharmacology andChemistry Program,Memorial SloanKettering CancerCenter, 1275 YorkAenue, New York,NY 10021, USA(D. A. Scheber,C. H. Va,F. E. Escrca,M. R. McDevtt).

Correspondence to:D. A. [email protected]

Cscrpts f the fte armada: sstemc

cacer therap us amaterasDavid A. Scheinberg, Carlos H. Villa, Freddy E. Escorcia and Michael R. McDevitt

Abstract | The ield o clinical nanomaterials is enlarging steadily, with more than a billion US dollars o

unding allocated to research by US goernment agencies in the past decade. The irst generation o anti-

cancer agents using noel nanomaterials has successully entered widespread use. Newer nanomaterials

are garnering increasing interest as potential multiunctional therapeutic agents; these drugs are conerred

noel properties, by irtue o their size and shape. The new eatures o these agents could potentially allow

increased cancer selectiity, changes in pharmacokinetics, ampliication o cytotoxic eects, and simultaneous

imaging capabilities. Ater attachment to cancer target reactie-ligands, which interact with cell-surace

antigens or receptors, these new constructs can delier cytolytic and imaging payloads. The molecules

also introduce new challenges or drug deelopment. While nanoscale molecules are o a similar size toproteins, the paradigms or how cells, tissues and organs o the body react to the non-biological materials

are not well understood, because most cellular and metabolic processes hae eoled to deal with globular,

enzyme degradable molecules. We discuss examples o dierent materials to illustrate interesting principles

or deelopment and uture applications o these nanomaterial medicines with emphasis on the possible

pharmacologic and saety hurdles or accomplishing therapeutic goals.

Scheinberg, D. A. et al. Nat. Rev. Clin. Oncol. 7, 266276 (2010); published online 30 March 2010; doi:10.1038/nrclinonc.2010.38

Introduction

I his 1959 ctr, Thrs pty of room at th bottom,hich is crditd ith iitiatig itrst i aotchoogy,Richard Fyma discssd th probm of maipat-ig ad cotroig thigs o a sma sca, icdig

pacig th mchaica srgo isid th bood ssto obsr, rport, ad prform th srgry.1 I th fid ofaomdici ar o sccssfy approachig so-tios to this chag (Figr 1). May crrt systmicthraptic approachs to cacr ack spcificity ad mostof th actios of ths agts caot b cotrod foo-ig ijctio. Som sotios may b fod i th abiityto crat try itigt drgs.2,3

Ati-cacr agts that tiiz o matrias to atrpharmacokitics (PK), sch as msifid drgs ad ipo-soma costrcts, ar arady i dopmt or approdby th FDA (Sppmtary Tabs 1 ad 2) ad may ofths agts ha b xtsiy rid. Th first of a

gratio of compx, aosca, mtifctioa mdi-cis ha arady b dsigd or ar i hma s.Ths icd th gird targtab toxis that bid tocacr cs, tr thir cytopasm ad dir a zymcapab of shttig do ribosoma sythsis,4 mtistptargtig stratgis to hac ad cotro th rat of

drg diry to a tmor;5 zyms targtd by igadsto cs, hich th act o pro-drg sbstrats to cortthm o-sit to th acti agt,6 a ao-c that sq-tiay dirs diffrt drgs to th tmor7 or targtab

atomic aogrators.8 Othr r mtifctioaaomatria-basd agts i dopmt ha rachdhma tstig (Sppmtary Tab 1).

Hr, rstrict th scop of or discssio to a ra-tiy sma sgmt of th o, systmicay admiistrdaomatria-basd cacr drgs, icdig poymrs,ddrimrs, carbo aotbs, ad arios mtaic ado-mtaic ao-partics, i ordr to istrat crtaiitrstig fatrs that mak aomatria-basd agtsboth appaig ad probmatic (Boxs 1 ad 2). Thsproprtis, icd siz, shap, charg, srfac pattr-ig, poydisprsity, mtiacy ad mticompotstrctrs, biocompatibiity ad biochmica stabiity.913

D to spac cosidratios, i ot discss ariosao-partic or iposoma drg formatios or ocayimpatab dics or dpots or dtctio systms1418 orgird cs, irss, aptamrs or cotid agts,1921fsio protis, or atibodydrg cojgats,4 hichdo dispay may of th abo proprtis ad ha bxtsiy rid shr.

Th appa of aomatria-basd drgs i cacr isbasd o to factors. Firsty, th abiity to cotro thsythsis of th agts i a mafactrig procss tomak mtifctioa ad mtiat mocs, orto atr PK, aoig chags i potcy ad safty, ithstrctrs arragd i distict srfac pattrs xposd

Cmpet terests

D. A. Scheinberg declares associations with the ollowingcompany: Encyse Biosciences Inc. M. R. McDeitt declaresassociations with the ollowing company: ActiniumPharmaceuticals. See the article online or ull details o therelationships. The other authors declare no competing interests.

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2/11nATuRe RevIewS|CliniCAl onCology vOluMe 7 | MAY 2010 | 267

to th iromt. I cacr cs, th dirs siga-ig ad rcptor chags that occr proid targts thatmight b tmpats for mtiat ad mtifctioatargtig igads ad cargo. Scody, th sizs (p tosra hdrd aomtrs i o of th dimsios)ad shaps (hoo sphrs, og rods, stars, tc.) of thmocs, hich ar qit distict from traditioasma moc or proti-basd drgs, yid ry argsrfac to om ratios or th possibiity of cotai-mt for arios cargo (Figr 2). For xamp, a siga carbo aotb (i hich ry atom is a srfaccarbo atom) ith a om simiar to a typica argproti (for xamp, 100150 kDa), i ha mor tha15 tims th srfac ara aaiab for igad attachmtor c itractios tha a arg proti. Bcas of tho-bioogica sorcs of som matrias, ad th dis-tict sizs, acis ad shaps, th pharmacoogy, schas carac ad biodgradatio, toxicoogy ad possibsafty of ths agts i patits might b ry diffr-t from crrt drgs; i ordr for som of th agtsto b sf, it is iky that biocompatib coatigs ad

igads i b a part of thir strctr. ufortaty,gaps i crrt kodg abot aomatria bioogy,toxicoogy ad pharmacoogy, hich ha d to fars ofpossib toxic ffcts ad iromta damag, haarady pt socita, thica ad poitica costraits othir sccssf appicatio.2224 I this rgard, iattmpt to addrss th crrt bfits ad hrds ofths agts ad ftr dirctios for ths kyisss, spciay thos rat to cacr thrapy.

Mtip xamps of aopartics ha mrgdas cadidats for drgs or ha rachd FDA approa(Sppmtary Tabs 1 ad 2). Ths icd thosith itrisic mdicay sf proprtis to ao robst

xtra imagig2527 or promot tmor thrmoysis2831(for xamp, qatm dots, siica aopartics, godaopartics, carbo aotbs), or hich ha o-coat ad coat modificatios ith capsatioof thraptic agts (for xamp, iposoms, ddrim-rs, [co]poymrs). Mor dtais ca b fod i rctartics.11,12,14,15,17,3236

Interaction with cells and tissues

Th siz, shap, ad pattrs of protis prstd tocs ar importat factors i thir rcptor bidig adth sigaig procsss thy cotro. As th physica scaof aomatrias is of th sam ordr as irss, protis,

oigocic acids ad macromocar car machi-ry (Figr 2), o might xpct thy aso i ha dis-ticti ad highy ariab itractios ith cs adtisss dpdt o thir siz, shap, srfac pattr-ig, ad charg.37 Ths itractios i ha a ro iboth th bficia ad pottiay toxic ffcts of thsdrgs. Th grat appa of aomatrias as cacr drgsis th abiity to cotro ths proprtis, ths improigspcificity toards maigat cs ad PK proprtis.

Size

eary stdis ad modig ioig microsca adaosca matrias focsd o th ffct of mocar

Key points

Therapeutic uses o noel materials hae become widespread; many newer

nanoparticles hae emerged as candidates or drugs, each with distinctiechemical and biological compositions, and dierse in vivo behaiors

Newer nanomaterials are garnering increasing interest as potential

multiunctional therapeutic agents, which by irtue o their size, geometric

patterning and shape are conerred noel properties

The synthesis o nanomaterials allows multiunctional and multialent molecules to be generated, which may enhance potency, therapeutic index or selectiity

The arious sizes and shapes o nanomaterials yield ery large surace to

olume ratios or the possibility o containment or arious cargo

The accumulation o nanoparticles in tumors, termed the enhanced

permeability and retention eect was initially described oer two decades ago,

and has been successully applied to nanoparticles

The unusual properties o nanomaterials pose challenges to understanding

their pharmacokinetics as dierent components will hae dierent eatures that

aect their distributions, clearance and catabolism

ight ad siz o th bioogic bhaiors of mics,iposoms, ad poymrs.17,32 Most orgaic aopartics

(sch as poymric partics) ha traditioay bsythsizd sig msio-basd sythtic tchiqsthat ao for capsatio of arios drgs, hiiorgaic aopartics (sch as mtaic partics) aroft prodcd throgh cotrod catio.38 whiths tchiqs ao partic sizs to b cotrod,r sythtic tchiqs ad improd charactriza-tio throgh dyamic ight scattrig, ctro micro-scopy, ad atomic forc microscopy, ha attmptdto proid mor prcis cotro or aosca sizs,ad ha aod diatio of th bioogica ffctsof aomtr sca chags. For th sam matria, sizchags as sma as a f aomtrs ca ad to sigifi-

cat diffrcs i car ptak, toxic ffcts, ad fatithi th c.3943 For xamp, gird partics ofsizs 4060 m r ab to maximay bid ad idcrcptor-mdiatd docytic procsss, hi smarpartics had a impaird abiity to idc mmbrarcptor crossikig.40 Siz aso pays a importatro i dirctig th fat of partics i th atig pr-stig cs of th imm systm.44,45 Ora, iitiastdis sggst that adjstab sizs cod offr a masto dirct diffrt aomatrias ito diffrt carpathays, maximiz affiity of appdd igads, mod-at ptak ito maigat cs, ad miimiz adrsffcts toards orma cs.40,46,47 Siz aso affcts PK

ad ra carac.48,49 Cosistt ith this, ra fi-tratio ad ospcific ptak by th rticodothiasystm (ReS) has b sho to b dpdt opartic siz.5055

Shape

Simiar to th stdy of aomatria siz ffcts, thstdy of aomatria shaps bga ith poymrs thatdmostratd th sigificat impact of th moc-ar architctr of ths matrias o pharmacoogyad fctio.56 As ith impromt i partic sizcotro, tchoogy for cotro of shap has rapidy pro-grssd.13,5759 Th adacmt i sythtic tchiqs

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for o-sphrica partics has sho that partic shap

sigificaty impacts th car ad tiss itractiosof aomatrias. whi a arity of shaps (iptica,sphrica, ad discoid) of mod poystyr particsca idc docytosis, docytosis of shaps that aro-sphrica ar highy dpdt o th oca shapat th itrfac of th c ith th aomatria or thtagtia ag that th aomatria shap maks ithth c.39,60,61 Ths stdis ha prdictd that hsphrica partics bid or rod-ik partics aig pr-pdicar to th car mmbra as apposd to aig-ig para to th srfac, thr is gratr propsity forcar ptak.62,63 Mor rcty, orm-ik partics ofhigh aspct ratio (that is, high gth to idth ratio) r

sho to ihibit phagocytosis, ad cod oy b gfdh cs itractd spcificay at partic ds.64 Bycotrast, stdis of partics ith diamtrs >100 mith aryig aspct ratios (p to thr) fod that highraspct ratios rstd i icrasd ptak by phagocyticcs.42 Itrstigy, carbo aotbs, hich hasay arg aspct ratios (501,000:1) bt ar of rysma diamtrs (12 m) ha highy rapid ad fficitcar ptak. Sra mchaisms ha b dscribdfor ths obsratios.30,63,65,66 Istigators ha fodthat fiamtos mics had circatio tims abot10-fod ogr tha thir sphrica cotrparts.67 By co-trast, circatio tims of carbo aotbs of a simiar

fiamtos shap bt smar diamtr (



atrd biodistribtio profis.76 Idd, a commo strat-gy to aoid ReS ptak of aomatrias is to itrodctra, hydrophiic poythy gyco chais (pgya-tio) to rdc opsoizatio.77 usrprisigy, srfaccharg or zta pottia (th ctrica pottia at thhydrodyamic sippig pa of a partic) is aso aimportat factor ifcig th bioogic bhaior ofaomatrias.78 It sms that gati or tra sr-facs cod b prfrab to aoid ospcific carptak.79,80 Frthrmor, for aomatrias that ar fi-trd by th kidy, charg pays a major ro i tbarrabsorptio, ith positi charg adig to icrasdrttio i th ra cortx.81

Cancer targeting

A importat goa i aomdici is to combi sraof th spcia fatrs of th matrias to impro thagts thraptic idx. Th simpst ay to achithis is by combiig th fctios of targtig, oft ithspcific igads, ad kiig ith a cytotoxic arhad,ith both fctios associatd ith th aomatria

hic (Tab 1 ad Box 3). This might b achid iaacti targtig ith spcific igads (atibodis, pp-tids, tc.), passi targtig that taks adatag ofphysica itractios bt th agts ad th tmormicroiromt (bood fo, ymphatic draiag, tc),or mor compx itractios ith mocs at th tmorsit that might sr to actiat or ras th thrapticmoity (pptidass, pH, tc). Acti (or igad dirctd)targtig impros rati tmor ocaizatio; if thtargt is itraizd it i aso ao fficit caraccmatio of th agt at spcific sits, hich cafrthr icras fficacy.82 effcti cacr thrapis thatar scti for th xprssd targt ar o rotiy

achid ith moocoa atibodis spcific to atigsorxprssd i cacr cs.83 A arg rag of othr tar-gtig moitis has o bcom aaiab ragig frommacromocar bioogics to sythtic sma mocs(Tab 1).8487 Most acti targtig approachs i ao-mdici dircty appd o of ths targtig igadsto a aopartic scaffod.

Types of tumor-associated targets

To dat, hmatopoitic cacr targts (Tab 1)ha yidd th most ciicay sccssf targtigapproachs,83 i part b cas ths maigacis arradiy accssib d to thir itraascar disprsio

ad ar oft mor ssiti to chmothrapy ad radio-thrapy. By cotrast, th diry of aopartics to soidtmors is mor chagig d to th poor ptratio ofth ratiy arg aosca partics throgh th itr-stitia tmor microiromt, dspit th fact maysoid tmor atigs dmostrat grat sctiity forcacr cs. O sotio to this probm is th s oftargts ithi th tmor ascatr icdig asctss-associatd markrs or a arity of itgris.88Targtig th ss has th pharmacoogic adatag ofimmdiat diry for hmatopoitic cacrs, ad asoth bfit that th tmor sss ar drid from thhost ad ar ths gticay stab (ad ths iky to

bcom drg rsistat). Moror, tmor sss dispay amor iform atig profi ths aoig a sig agtto targt a arg arity of tmor typs. I som cass, tar-gtig of th tmor ascatr has rstd i rmodigof th sss to mak thm mor-ffcti trasportrs ofth thraptic agt ad of oxyg, hich might i trmak th tmors mor radiossiti.88,89

a

c

d

b

DendrimerDoxorubicin Carbon nanotube 1nm

Quantum dot

Iron oxideparticle

mAb-modiedcarbon nanotube

Dendrimer

Doxorubicin

mAb-modied carbon nanotubeIron oxide particle

Quantum dot

Liposome

E. coli

Bacteriophage

Dendrimer

Doxorubicin

mAb-modied carbon nanotubeRed blood cell

Iron oxide particle

Quantum dot

Liposome

E. coli

Bacteriophage

Dendrimer

Doxorubicin

10nm

100nm

1,000nm

Figure 2 | Representation o nanomaterials with comparison to biologics, drawnto scale.

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Th accmatio of aopartics i tmors, trmdth hacd prmabiity ad rttio ffct (ePR)90,91as iitiay dscribd or to dcads ago, ad hasb sccssfy appid to aopartics. Approdagts icd r-gird cotioa thrapticsthat tak adatag of ePR to impro th thraptic

idx78 (Sppmtary Tabs 1 ad 2). Som of tharist ao-mdicis, sch as Abraxa or Doxi,ar o macromocar rformatios of pacitaxad doxorbici, rspctiy. ePR dpds poth aky, disorgaizd, ad tortos atr of tmoro-ascatr, hich aos for scti rttio ofpartics i th rag of 60 to 500 m d to thir pro-psity to ak ot of th ascar spac mor radiytha thy ca prmat back ito th circatio Thsffcts occr as a rst of th dficit ymphatic drai-ag of th tmor iromt, bt th ffct may ot bfy rprodcd i physioogic mods sch as i tras-gic mos tmors, orthotopic mods, or timaty i

hmas, spciay i o ascarizd mtastass.9294

no mtifctioa agts ar big dopdsch that passi targtig dirs th acti agt arth srfac of th cacr c ad a scod t, schas th ras of cargo for diffsio ad try ito th c,foos. whi th ePR ffct cod impro th thra-ptic idx of aosca partics by improig ratiaccmatio i soid tmors, th most sccssf ao-mdicis for cacr i iky sti d to s a actitargtig approach i cojctio ith this approach toimpro tmor-to-orma tiss ratios. Frthr impro-mts i thraptic idx ca th b achid by com-biig th patform ith a cytotoxic agt appropriat forth particar cacr big targtd, or a oigocotidscti for a particar actiatd g prodct ithith c. whi ach of th forms of targtig ar ot trycacr spcific, o cod propos agts that proidsqtia icrass i cacr sctiity, first by ePR orascar targtig, scod by igad dirctd diry,ad fiay by c pathay-scti cargo.

PK, manufacturing and regulatory issuesTh sa proprtis of th proposd aomatrias,as as thir mtiacy ad mtifctioaity poschags to drstadig thir PK bcas diffrtcompots i ha diffrt fatrs that affct thdistribtio, carac ad cataboism of aomatrias.Typica PK stdis xami th absorptio, distribtio,mtaboism, ad xcrtio (ADMe) of a drg. Thsfor factors ad th admiistrd dos dtrmi thcoctratio of a drg at its sits of actio, ad ths,th itsity of its ffcts as a fctio of tim. Aftrprototyp aomatrias ar modifid ith diffrtcargos, thir ADMe profi might chag, rqir-

ig itrati tstig to dtrmi th profis.Mtip stps of sythsis ad prificatio ad a thor-ogh physicochmica charactrizatio food by thdtrmiatio of th PK ad th aatio of torabiity(toxicity ad immogicity) by th host i rqirdopmta stps. For may of th matrias,both a dtaid physicochmica dscriptio ad PK datai aimas or hmas ar imitd ad i b xpctdto ary sigificaty amog diffrt matrias ad thcompositio of th strctrs.

Hydrodyamic diamtr ad positi charg i graar irsy ratd to gomrar fitratio rat.54 Forxamp, Kobayashi ad Brchbi50 sd MRI to dmo-

strat that aryig th siz or hydrophobicity of o-targtig Gd-abd ddrimr costrcts atrd throt of ra ad ir xcrtio, rspctiy. Simiary,o-targtd, radioabd qatm dots that r modi-fid ith mta-io chats ad a 600 Dato poythygyco (PeG) moity r rapidy card from th boodad accmatd i th ir ithi a f mits.95,96Simiary, th partic sizs of aopartic C-dots fromCor uirsity ha b td for chags i fitra-tio, or carbo aotb charg proprtis r atrdto mak dramatic chags i thir PK.68,69,9799

Typicay a siz ct off of abot 6 m is s for fitra-tio of gobar matrias. Itrstigy, hor, mch

Table 1 | Ligands or actie cancer targeting

Tpe Mw

(kDa)

Dameter

(m)

Features

Monoclonal antibodies

Whole antibodies 150 1520 High afnity, dialent, many clinicallyapproed examples, contains biologicallyactie constant (Fc) region, long circulation

Engineered fragments (monovalent)

ScF 25 35 Lowered afnity, rapid clearance romcirculation, renal retention, reducedstability, reduced immunogenicity

Fab 50 510 Can be produced genetically orenzymatically by cleaage o monoclonalantibodies

Nanobody 15 23 Smallest antigen-binding ragment, singledomain, can bind cryptic epitopes

Engineered fragments (divalent)

F(ab)2

100 1015 Improed afnity, can be engineered to aariety o sizes and arrangements oprotein domains

Diabodies 5080 510 Mono-specifc or bi-specifc dimer o ScF

Minibodies 80 10 Can be produced genetically

Aptamers

RNA 1030 23 Rapid clearance, automated chemicalsynthesis, susceptible to nucleaseswithout chemical modifcation

DNA 1030 23 Rapid clearance, automated chemicalsynthesis, susceptible to nucleaseswithout chemical modifcation

Receptor ligands

Peptides 0.510 variable Facile synthesis and modifcation, dierselibraries and screening technologies,susceptible to peptidases, renal retention

Whole proteins 30150 variable Produced using recombinant DNA

technologies, can be biologically actie,susceptible to proteases

Small molecules 0.11.0 0.52.0 Chemical synthesis, simple modifcationand coupling chemistries, can bebiologically actie, highly ariable afnities

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argr carbo aotbs ith high aspct ratios ar stifitrd.68,69 Partic charg aso affcts tota body car-ac, mdiatd oft by itractios ith srm protisad cs, as has b obsrd ith Q-dots.53 Kodgof th physicochmica paramtrs ad thir itractiosca ao dsig of partics, for xamp Q-dots, ithigad mbrs ad sizs that prmit ra carac.100

Th atr of th igads ad thir attachmts, adtyps of cargo i ao itrstig approachs to drgdsig. For xamp, th itact agt may accmatat th tmor sit by th ePR ffct, hi its atibodyigad may sctiy bid th tmor c. A arg parti-cat patform may b trappd i th ir ad xcrtdhi th rasd cargo might b card ia th kidy;ach of ths procsss may procd at diffrt rats.As a cosqc of this compxity, stdis of th PKof th itact partic as as th compots, cargoad mtaboits may b rqird. A adatag to thsagts might b that cargos ca b dsigd for triggrdras dr arios coditios, sch as thos that xistisid th targt c. For xamp, pH, rdox, protas-

ssiti or stras-ssiti ikrs or crossikrs thatdgrad or tim or that oos dr car codi-tios ca triggr ras of th cargo. Cytotoxicity, thr-for, cod b focsd dircty o th cacr c. Oapproach that might orcom th so diffsio adcarac of crtai aomatria patforms is to smti-stp pr-targtig approachs i hich th sormatria is admiistrd first, copd ith a iqigad (for xamp, aidi) food atr by a rapidydiffsig ad carig, sma-moc cytotoxic agtcopd ith a scod igad spcificay ab to bid toth first igad ith high affiity (for xamp, bioti).

Dopig a aomatria-basd drg i b a

compx procss (Figr 3). It is aticipatd that mayof th aotchoogy prodcts that i b rgatdby th FDA i spa th rgatory bodaris btpharmacticas, mdica dics, ad bioogics. As acosqc, ths prodcts may b rgatd as com-biatio prodcts. I part, th FDA attmpts to srthat drgs, drg diry systms, mdica dics, adaccis that rach th markt ar saf ad ffcti. ThFDA rgats prodcts, ot tchoogy.101 Thrfor,this distictio i dtrmi th stag at hich th FDArgats a procss to mafactr ad markt oaomatria-basd drgs. Bcas may of th agts may bha simiar to dics ad ha aggr-

gat arg srfac aras ad mtiat moitis thatar xposd to th bood stram, thy may b xpctdto ha simiar ffcts as othr f-sca mdicayimpatd dics (for xamp grafts, cathtrs or as)sch as i th promotio of hmoysis, thrombosis, adpatt aggrgatio, hich i d to b stdid.102 Thmti-compot fatrs of ths agts might makth approa procss compicatd ad possiby ogrtha for traditioa drgs, for hich mor is ko.

Ky qstios for aomatria dopmt i baddrssd by th s of aima mods, th otcoms ofhich may ot trasat for hma s, ad ti-maty i hma sbjcts.93,103If possib, ths PK xpri-

mts ca b prformd i both aimas ad hmassig cassic tracr mthodoogy104 i hich a pr ad-charactrizd prodct, trac-abd ith a stabmoity shod ot atr th ora PK profi. Imagigof th agts i most iky b mpoyd icrasigyto proid ra-tim, ho-body biodistribtios of thtracrs, ths aoig far gratr dtai as to th possibcarac ad toxic ffcts to b xpctd, tha ca bachid ith simp bood masrmts.

As toxicoogica risks aris from th ss ofo aomatrias ad thir arid compositios,

charactrizatio tsts i b cssary. I pri-cip, charactrizatio of th ADMe of th agt i brqird as sa. Th spcific fatrs of aomatria-basd agts (arg siz, rati to sma-mocdrgs, mtip compot atr, poy-disprsity) i,hor, rqir o ad additioa mthods of stdyad stadards.105 Th arg siz of aomatrias cab s dircty ith tchiqs sch as trasmissioctro microscopy (TeM) ad atomic forc micro-scopy (AFM), hich oft brigs isight ito thir shap,poydisprsity ad aggrgatio. Itrisic fatrs of thmatrias prmit dirct masrmt in vitro ad in vivosch as by forscc i th Q-dots or rama spctro-

scopy ith carbo aotbs, or by rgy disprsiX-ray. Radio-tracig (s imagig modaitis sctio) isaso hpf for assssig th proprtis of ths agtsin vivo. larg, mtiat partics or thir appddigads ar possiby immogic, i part, d to thirpoor sobiity ad bcas thy ar oft opsoizdith atig-prstig cs ad trappd i orgassch as th ir, sp ad bo marro. O th othrhad, th imm systm is dsigd to rcogiz bio-ogica pptids ad carbohydrats ith spcific rcp-tors. Ths, aomatrias may ot b rcogizd by thsprocsss bcas of thir chmica mak-p. I additioto improd aaytica mthodoogis, thr is a car

Box 3 | Examples o cancer-associated targets

Hematc ates

B cells: CD19, CD20, CD21, CD22, CD23

T cells: CD4, CD25, CD30

Myeloid precursors: CD33, CD66

Sd tumr ates

Colon: Integrins, A33 glycoprotein, Tag72, epithelial

cell adhesion molecule (EpCAM)

Breast: HER2/neu, Lewis-Y, carcinoembryonic antigen

(CEA)

Prostate: Prostate-speciic membrane antigen (PSMA),

prostate stem-cell antigen (PSCA)

Other: GD2 ganglioside (glioblastoma), MUC1 mucin-

like glycoprotein (pancreatic cancer), olate receptor

(FR), epidermal growth actor receptor (EGFR),

transerrin receptor (TR)

Vascuar ates

vascular endothelial cadherin (vE-cadherin), ascular

endothelial growth actor receptor (vEGFR), integrins

(such as alpha-v-beta-3)

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d to dis a ratioa paradigm to charactriz ao-matrias in vitro ad in vivo.105 Mtip compots i

d to ha ach compot aayzd sparaty adaso assssd as a fia prodct. O sotio to th com-pxity of aatig th pharmacoogy of th matriasfor rgatory ri may b to s compots that bythmss ar arady -charactrizd i hmas ithko toxic ffct profis. Imagig th agts in vivo, iparticar by PeT, hich ca proid ra-tim coc-tratios of th drgs i tisss, i aso aid i dscribigth PK ad pottia for toxic ffcts i gratr dtai.eary trias that mpoy biopsis of targt tisss ca asoproid iaab iformatio o oca PK, spciay ifsd i cojctio ith f body imagig.

Toxic effects of nanomaterial drugsudrstadig ad prdictig th toxicitis of ao-matria agts i hmas is compicatd by thir mti-compot atr, o strctrs ad poydisprsity.Som of th toxic ffcts of ths mti-compotdrgs i b attribtab to th idiida compots.Hor, additioa toxic ffcts may aris bcas th PK proprtis of th matrias dscribd abo mayrst i xpctd itractios ith targt ad o-targt tisss as as ith th orgas iod i car-ac. Prdictios basd o micro-sca partics (schas ihad partics, asbstos, cs, bactria or irss)or from sb-aosca mocs (sch as typica

pharmactica drgs) or from aosca agts (sch asprotis) may ot b graizab to th aomatria-basd agts discssd hr bcas of arg diffrcsi th ay cs rspod to ths o agts. As a co-sqc, thr may b chags i th magitd, qaityad tiss ocatio of toxic ffcts compard ith thorigia drgs. For xamp, th ack of biodgradatioof som compots cod ad to og-trm ifam-matory probms. Idd, cosidrab discssio hassd abot th possib iromta ad coogicacosqcs of idsprad aomatria ss.106,107

whi thr has b cosidrab dbat abot thpossib toxicitis of aomatria-basd drgs, it shodb otd that drgs sd i cacr patits ha typicayhad o thraptic idics. Patits ha b iig totorat sigificat risks of morbidity ad mortaity drigboth th ciica dopmt of th agts ad aftrmarktig approa. Data do ot sggst that aomat-ria drgs ar mor toxic tha thir compots (somof hich ar -ko cytotoxic agts) ad i maycass th agts ar dsigd to rdr th cytotoxic agt

ss toxic by atrig its diry ad carac. Thrfor,i th dopmt of ths agts, it sms raso-ab to st th thrshod for torabiity ad thrapticidx to o highr tha that sd for ati-cacr agtsi crrt s. I additio, for th cacr appicatiosaddrssd hr, qatitis of ijctd matrias ar ikyto b qit sma (mg) so th arg-sca mafactrigisss that may b s ith ss of ths matrias i thctroics or fabricatio idstris ar ss trobsom.Frthrmor, som of th compots of ths agts(iposoms, atibodis, chmothrapy drgs, particatabmi, PeG, spr paramagtic iro oxid, poyactic-co-gtamic acid) ha b idy stdid i hmas

for may yars ad ha b approd by th FDA assaf ad ffcti.

Th possib toxic ffcts of carbo aotbs hab th sbjct of mch spcatio, d to thir pro-fod chmica stabiity, hich might cofr a og ifin vivo if ths agts ar ot card. Moror th highaspct ratio (gth:idth) of carbo aotbs haspromptd som rsarchrs to compar thm to asbs-tos.46 As xpctd from ihaatio stdis, isobra carbo aotbs ca cas ariab amots ofifammatio (as masrd by cytoki ras, rac-ti oxyg spcis atios, compmt actiatio,car morphoogy chags) h ihad or addd

to c ctrs.108115 Th rac of ths fidigs tocacr appicatios is ot car; cacr drgs od bformatd as sob, itraos forms, hich do otsm to sho systmic toxicity.68,69,98,116118 Importaty,hi isob micro-sca mti-a tbs (ithsizs argr tha cod b igstd by macrophags adths mchaisticay simiar to asbstos) casd ifam-matio, aosca matria casd o ifammatio,xdat or graomas, i isob form.46 Hc,at th aosca, ths mocs sm to bha i asimiar mar to protis, hich ar of a simiar siz.I additio, a stdy has sho carbo aotbs tob biodgradab.119

Matching of appropriate targetingligand and cargo to the biology,

biochemistry and expected PK and PD

Construction and testing of purity,solubility, stability, specicityand potency in model in vitro

Scale-up, ADME testingPreparation of IND

Pilot or phase I imaging and therapeutictrials in humans with target neoplasm

Biodistribution andimaging in animal

models in vivo

Pharmacologic andtherapeutic evaluation

in animal models in vivo

Identication and characterization of thetarget molecule, cell and tumor system

including biology and biochemistry

Matching of appropriate nanomaterialvehicle to the biology, biochemistry

and expected PK and PD

Use of intrinsicproperties oftrace labels

Evaluate hemodialysis,thrombogenicity,platelet aggregation,

immunogenicity

Analysis by TEM, DLS,AFM, EDX

Develop novelanalytical methods;establish standards

Figure 3 | Some proposed steps in the deelopment o a nanomaterial anti-canceragent. Abbreiations: ADME, absorption, distribution, metabolism and excretion;AFM, atomic orce microscope; DLS, dynamic light scattering; EDX, energydispersie X-ray; IND, inestigational new drug application; TEM, transmissionelectron microscopy.

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highr potcy ad th possibiity of simtaosimagig ad thrapy, ko as thraostics. Thr ararady agts capab of mtip fctios sch as tar-gtig ad arhad diry, da arhad diry, orimagig ad thrapy i trias. Som of th hrds forftr agts ad ays to so pottia probms arsho i Tab 2. utimaty, isio atray aai-ab biomatrias combid ith sythtic strctrs tocrat mtifctioa agts, hich ar girdto ha dfid diffsio, biodgradatio ad caracrats, immoogic iisibiity, ad cotrod actios.

Review criteria

Articles included in the Reiew were chosen ater an

exhaustie search on the PubMed, Google Scholar and

Science Direct databases or ull-text papers published

in English without a time restriction. The search termsincluded each o the releant nanomaterials by name,

cancer antigens and therapeutic drugs and modalities,

and more general terms or the ields under study.Recent reiews and papers, many o which are cited in

the text, were consulted or additional reerences.

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