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Treza12

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ma rk e r s p r ed i c ti ve f o r t ox i c it y o r t h era p e u tic ou tc o mes o f a p artic u lar t h e r a py as we ll as i nhe rit ab l e ris k o f certai n ca n cers . P h armac og e no mi c m u tati ons i n t he ge rm li ne p r ov i d e s o me e xp la n ati on f o r t h e i n teri nd i v i dual a nd i n terr ac i a l va ri ab ilit y i n d r ug res pon se a nd t ox icit y . F o r ca n cer c h em o t he r ap y , whe r e cy t o t oxi c a g e n ts are a d mi n istere d at do ses cl o se t o t h ei r ma x im a l t o l e r ab l e dose, a nd t h era p e u tic wi ndo ws are relati v el y n a rro w , mi no r d i f f e r ences i n i nd i v i du al d r ug h a nd li ng ma y lea d t o se v ere t ox icitie s. T he r e f o r e, an unde rsta nd i ng o f t h e s ou rces o f t h is v aria b ilit y wou l d l ead t o t he poss i b ilit y o f i nd i v i du alizi ng do sa g es o r i n fl u e n ci ng cli n ical dec i s i ons t ha t can im p r ov e p atie n t care . P h armac og e no mics h as pu tati v e u tilit y i n t he r apy se l e cti on, cli n ical st udy d esi gn, a nd as a t oo l t o im prov e unde r s t and i ng o f t he ph armac o l ogy o f a me d icati on. Th e te rm pha rm acogene ti cs was i n itiall y u se d t o d efi n e i nh erite d d i f f e r e nces i n d r ug e f f ec t s an d t yp icall y f o c u se d on i nd i v i du al ca nd i d ate g e n es . T he fi e l d o f pha rm acog e no mics no w i n cl ud es g e no mewi d e ass o ciat ion s t ud i es and i s used t o d escri b e g e n etic v ariati on s i n all as p ect s of drug a bso r p ti on, d i s tri bu tio n, meta bo lism , a nd e x creti on i n a dd iti on t o drug ta r ge t s and t he ir downs tream p at h wa y s ill u strates s o m e c urr e n t c li n i ca l exa m p l es o f g e no t yp e- gu i d e d ca n cer c h em o t h era p y . V a r iati ons i n t he DNA sequen ces e n c od i ng t h ese p r o tei n s ma y ta k e t h e for m of de l e ti ons, i nse rti ons, re p eats , frames h ift m u tati on s , non se n se m u tati ons, and mi ssense m u tati on s , res u lti ng i n a n i n acti v e , tr un cate d, un sta b le , o r o t he r w i se dys f unc ti on al p r o tei n. T h e m o st c o mm on c h a ng e i nvo l v e s s i ng l e nuc l eo ti de sub stit u ti on s , calle d si ng le- nu cle o ti d e po l y m o r ph i s m s (S N P) , wh i ch o cc u r at a pp r ox imatel y 1 p er 1,000 b ase pai r s on t h e hu m an geno m e. V a ri ab ilit y i n t ox icit y o r acti v it y ca n als o b e me d iated by pos t geno mi c even ts , at t h e le v el o f RNA , p r o tei n, o r f un cti onal acti v it y . P HA RM ACOG E NOM I C S O F TUMOR RESPONSE T u m or response t o che m o t her a py is re gu late d by a c o m p le x, m u lti g e n ic n et work o f genes t ha t enco m p asses i nh ere n t c h aracteristics o f t h e t u m o r , d i f f e r e n ti a ll y ac ti va t ed pa t hway s o f cell si gn ali ng, p r o liferati on a nd DN A

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r e p ai r , f a c t o r s t ha t con tr o l d r ug d eli v er y t o t h e t u m o r cells (e .g., meta bo li s m , tr anspo rt) , and ce ll d eat h. T h ese ma y i n t u r n b e m odu late d by pr e v i ous l y ad mi n i s t e r ed tr ea tme n t o r d r ug e xpo s u re , w h ic h ma y up re gu la te ta r g et p r o t e i ns o r ac ti va t e a lt e r n ati v e p at h wa y s o f d r ug resista n ce . T h e po l yg e n i c na t u r e o f d r ug r espon se im p lies t h at a b etter und ersta nd i ng o f g e no t ype–pheno t ype assoc i a t ion s w ou l d re qu ire m o re t h a n t h e u s u al si ngle - g e n e ph arm acogene ti c s tr a t eg ies em p l oy e d t o d ate . H o we v e r , t h ere are i n sta n ce s whe r e t he geno mi c c on te x t o f a si ng le g e n e wit h i n a ca n cer wil l b e of h i gh im pac t f o r spec ifi c t h era p e u tic a g e n ts (see ) . Pat hw ay D ir ec t ed An ti cance r T h era py On e of th e ea rli es t success s t o ries ill u strati ng p at h wa y - d ri v e n t h era p e u ti cs is w it h CM L . T he ha llm a r k ch r o m o s o mal a bno rmalit y o f t h is d isease is the t r a n sl o cati on o f ch r o m oso m e s 9 a nd 22 t h at u ltimatel y p r odu ces t h e f u si on g e n e BC R - AB L . T h i s d i scov er y i n 1960 e v e n t u all y le d t o t h e d e v el op m ent of t h e ta r ge t ed t y r os i ne - k i nase i nh i b it o r (TKI) imati n i b a nd its s ub se qu e nt F ood a nd D r ug Ad mi n i s tr a ti on (FDA) a pp r ov al f o r treatme n t o f CML i n 2001. T he I n t e r na ti ona l Rando mize d St udy o f I n terfer on a nd STI 571 (I R IS) t r i a l began en r o llm en t i n 2000 a nd c o m p are d imati n i b wit h i n te rf e r o n and l ow - dose cy t a ra b i n e , w h ic h was t h e p re v i ou s sta nd ar d o f ca r e for new l y d i agnosed pa tie n ts wit h c h r on ic- ph ase CML . All e f ficac y e ndpo i n t s f avo r ed im a ti n i b, incl ud i ng c o m p lete c y t og e n etic res pon se o f 76.2% wit h im a ti n i b co m pa re d wit h 14.5 % wit h i n terfer on ( p <0.001 ) .

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Ov e r all su r v i va l ( O S) a ft e r 60 m on t h s o f f o ll o w- up was 89 % wit h imati n i b . T h i s exa m p l e i s j us t on e o f ma ny w h ere a on ce fatal d isease c an now b e cons i de r ed m o r e ak i n t o a c h r on ic d isease , re qu iri ng a d ail y me d icat ion and r egu l a r phys icia n f o ll o w- up, similar t o hyp erte n si on o r d ia b etes . D r ug deve l op m en t h as als o k e p t p ace wit h t h ese a dv a n ces a nd now se ve r a l o t he r agen t s, i nc l ud i ng d asati n i b, n il o ti n i b, bo s u ti n i b, a nd pon ati n i b, have j o i ned im a ti n i b as treatme n t op ti on s f o r CML . Th e i d e a o f chang i ng tr ea tm en t f o c u s fr o m a d isease- b ase d m od el t o a p at hw ay- d ri ven m ode l i s a l so e vo l v i ng. H u ma n e p i d ermal g r o wt h fact o r r ece p t or 2 ( H E R2 ) i s a tr ans mem b ra n e rece p t o r t y r o si n e k i n ase t h at is ov e r e xp r essed o r a m p lifi ed i n up t o 25 % o f b reast ca n cers . T rast u z u ma b is a hu ma n i zed m onoc l ona l an ti body d irecte d a g ai n st HER 2 a nd

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d em on s t r a t ed im p r oved r espon se rates (RR) a nd time t o d isease progr es s i on i n pa ti en t s w it h m etastatic HER 2 po siti v e b reast ca n cer a nd im prov e d d i sease -fr ee su r v i v al (DFS) a nd OS i n HER 2 - po siti v e b reast ca n ce r pa ti en t s tr ea t ed w it h ad j uv a n t trast u z u ma b . Se v eral a dd iti on al a g e n ts ar e now ava il ab l e t o t a r g et t h e HER 2 p at h wa y a nd v ar y i n t h eir ph a r ma co l ogy and m echan i sm o f acti on. La p ati n i b is a n o ral TKI d irect ed a g ai n st H E R2 and t he ep i de r m al g r o wt h fact o r rece p t o r (EGFR) , p e r t u z u m ab i s a hu m an i zed m ono cl on al a n ti body t h at b i nd s at a d i f fere n t l o cati on t han tr as t uzu m ab and i nh i b its t h e d imerizati on a nd s ub se qu e n t acti v ati on o f H E R2 s i gna li ng, a nd a do -trast u z u ma b emta n si n e is a n a n ti body - d r ug con j uga t e t ha t ta r g ets HER 2 - po siti v e cells a nd t h e n relea ses t h e c y t o t ox i c an timit o ti c agen t emta n si n e t h r ough li po s o mal d e g ra d ati on o f t h e li nk i ng co m pound. A ll o f t h ese a g e n ts ill u strate t h e p r og ress a nd ph a r ma co l og i c d i ve r s it y o f pa t h wa y - d irecte d t h era py a nd remai n as sta nd a rd o f ca r e op ti ons f o r HER 2 - po siti v e b reast ca n cer i n eit h er t h e a d j uv a nt and / o r m e t as t a ti c se tti ng s . HER 2 e xp ressi on is no t limite d t o br east c ance r , howeve r . T hough less c o mm on, HER 2 e xp ressi on is see n in nu me rous so li d t u m o r s i nc l ud i ng b la dd e r , g astric , p r o state a nd non– sma ll -cell l ung cance r w it h va r y i ng d e g rees o f i n ci d e n ce d e p e nd i ng on t h e met hod o f de t ec ti on. Based on res u lts fr o m a lar g e , op e n -la b el ph ase III r a ndo mi zed, i n t e r na ti ona l tri al o f 594 p atie n ts wit h g astric o r g ast ro es ophagea l j unc ti on can cer e xp ressi ng HER 2 by eit h er imm unoh i s t oche mi s tr y o r gen e am p lificati on by fl uo resce n ce i n sit u hybr i d iz a ti on, tr as t uzu m ab i s als o a pp r ov e d f o r treatme n t o f metastatic g ast r ic o r gas tr oesophagea l j un cti on a d e no carci no ma t h at e xp resses HER 2. Patie n ts r ando mi zed t o che m o t h era py i n c o m b i n ati on wit h trast u z u ma b had a me d ian O S o f 13.8 m on t hs c o m p are d wit h 1 1.1 m on t h s i n t h e p atie n ts r ecei v i ng che m o t he r apy a l on e ( h azar d rati o [HR] , 0.74 ; 0.60 t o 0.91, p = 0.0046). Nu m e r ous exa m p les als o s uppo rt t h at p at h wa y - d irecte d t h era py w ill c ross t he bounda ri es o f di sease sites a nd t h at t u m o r g e n etics will b ec o me one o f t he b i gges t det ermi n i ng fact o rs f o r treatme n t . Sim p le exp r ess i on o f t he d r u g ta r g et do es no t alwa y s tra n slate i n t o d esir ed cli n ical ou t co m es t hough. Ce t ux ima b a nd p a n it u m u ma b are m ono cl on al a n ti bod i es d ir ec t ed aga i ns t E G FR; ho we v e r , it was f ound t h at c o l o rectal ca n ce r (CRC ) pa ti en t s who d i d no t h a v e d etecta b le EGFR still e xp erie nced r es pon s es t o t hese agen t s s imilar i n e x te n t t o EGFR- po siti v e p atie n ts .

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K i r ste n ra t sa r co m a v ir a l oncog e n e (KRAS) is a do w n stream effect o r o f the EG FR pa t hwa y . Li gand b i nd i ng t o EGFR on t h e cell s u rface acti v ates p at hw ay s i gna li ng t h r ough t h e KRAS-RAF-mit og e n -acti v ate d p r o tei n k i n ase (MA P K ) pa t hwa y , whi c h is t hough t t o c on tr o l cell g r o wt h, d i f f e r e n ti a ti on, and apop t os i s E v e n t u all y it was f ound t h at CRC p atien ts w it h a KRA S m u t a ti on d i d no t d eri v e b e n efit fr o m cet ux ima b o r p a n it u m u m ab. T he RR i n CR C recei v i ng eit h er cet ux ima b o r p a n it u m umab who w er e KRA S w il d t ype w as 10 % t o 40 % c o m p are d wit h n ear zer o p e r ce n t in t hose w it h KRA S m u tati on s T h is fi nd i ng was t h e res u lt o f a r et ro s p e c ti ve ana l ys i s o f s m a ll g r oup o f p atie n ts a nd was c on firme d i n la r g e , prospec ti ve tri a l s. Add iti on all y , it und ersc o res t h e im po rta n ce o f tiss u e c o ll ec ti on f o r b i o m a r k er assessme n t i n trials wit h nov el t h era p e u t ics. A r ece nt c li n i ca l tri a l geno mic a n al y sis s ugg ests t h at m u tati on s i n NRA S ma y als o have va l ue i n p r ed icti ng t h e u tilit y o f EGFR a n ti body t h era py i n c o l or ectal cance r . A lt hough t h e p re d icti v e v al u e o f KRAS m u tati on stat us i n c o l or e c t a l cance r has been well esta b lis h e d i n cli n ical trials , t h e r o le of K R AS i n l ung cance r and o t he r mali gn a n cies is less well el u ci d ate d. L ung ca n ce r s ha r bo ri ng KRA S m u tati on s h a v e b ee n s ho w n t o h a v e less cli n ic al b e n e f it fr o m t he E G F R -t a r ge te d erl o ti n i b i n s o me trials , alt hough t h is h a s no t c ons i s t en tl y been t he cas e acr o ss all trials . A dd iti on all y , l ung ca n cer K R AS m u t a ti on s t a t us does n ot a pp ear t o re p r odu ci b l y p re d ict cli n ical b e n e f it fr o m t he E G F R -t a r ge te d m ono cl on al a n ti bod ies , as is t h e case i n c o l or ectal cance r . Un li ke t he HER 2 e x am p le d isc u sse d p re v i ou sl y , t h e cli n ical app li ca ti on o f so m e g e n etic m u tati on s will d i f fer b etwee n tiss u e o f or i g i n. D ee p e r inves ti ga ti ons and und ersta nd i ng s o f m u tati on s d ri v i ng on c og e nic p at hw ay s can a l so e l uc i da t e mec h a n isms o f resista n ce a nd p ractical t h e r a p euti c s tr a t eg i es f o r tr eat me n t a nd p re v e n ti on. A pp r ox imatel y h alf o f all c u tan eous m e l ano m as ca rr y m u tati on s i n BRAF , wit h t h e m o st c o m mon b ei ng t he V600 E m u t a ti on. V em u rafe n i b is a TKI d irecte d a g ai n st m u tat ed BR A F th a t de m ons tr a t ed im prov eme n ts i n bo t h p r og ressi on -free s u r v i val (PF S ) a nd O S when co m pa r ed wit h t h e c y t o t ox ic a g e n t d acar b azi n e i n pr e v i ous l y un tr ea t ed pa ti en t s wit h metastatic mela no ma carr y i ng t h e BR AF V600E m u t a ti on. V e m u r a f en ib d em on strate d a 63 % relati v e re du cti on i n t h e r is k o f dea t h co m pa r ed w it h d acar b azi n e ( p <0.001 ) al ong wit h a h i ghe r r es pon s e r a t e ( 48 % co m pa r ed wit h 5 % f o r d acar b azi n e) . Base d on t h e se

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A lt hough advances i n bas i c sc ie n ce a nd d r ug d e v el op me n t h a v e tra n slat ed ma ny oncogen i c d ri ve r m u t a t ion s acr o ss t u m o r t yp es i n t o p at h wa y - d irec ted t h e r a p y , t h i s i s no t t he case f o r t h e maj o rit y . T h ere are nu mer ou s e x am p l es of fun ct iona ll y r e l evan t r ecu rre n t d ri v er m u tati on s t h at a f fect p r o tei n ta r gets t h at a r e n o t cu rr en tl y d r uggab le . Re g ar d less o f mali gn a n c y , on e o f t h e most c o mm on l y m u t a t ed t u m o r supp ress o rs is t h e p r o tei n p53. M u tati on s ca n r es u lt i n p53 acqu iri ng oncog e n ic f un cti on s t h at e n a b le p r o liferati on, i nv asi on, m e t as t as i s, and ce ll s u r v i v al as well as c oo r d i n ati ng wit h d i f fer ent pro tei n s , such as E G F R, t o enh a n ce o r i nh i b it its effects . H o we v e r , a cli n ical app li ca ti on o f p53 m u tati on d ata o r d irectl y ta r g eti ng p53 h as b e en limite d, t o da t e . PI K3CA en c od es a catal y tic s ubun it o f phopho i no sit ol - 3 k i n ase ( PI 3K ) , wh i ch i nc l udes f ou r d isti n ct s ub famil y k i n ases i nvo l v e d i n r e gu lati ng ce ll g r ow t h, m o tilit y , p r o liferati on, a nd s u r v i v al . Direct i nh i b it ors o f t he k i nase, as w ell as do w n stream tar g ets , i n cl ud i ng AKT

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c on stit ut i on i s an im po rt an t re gu lat o r o f v aria b ilit y i n d r ug e f fect . D i f f e r e nces i n d r ug e f f ec t s a re m o re p r onoun ce d b etwee n i nd i v i du als c o m p a red t o w it h i n an i nd i v id u al . I nd ee d, st ud ies i n m ono z ygo tic a nd d iz ygo ti c t w i ns i den tifi ed t ha t 20 % t o 80 % o f t h e v ariati on i n d r ug d is po sit ion i s m ed i a t ed by i nh erita n ce . Dr ug -meta bo lizi ng e n z y mes , cell u la r tr anspo rt e r s, and ti ssu e rece p t o rs are gov er n e d by g e n etic v ariat ion. Adv a n ce s i n t he tr ea tm en t o f mo st c o mm on mali gn a n cies h a v e res u lte d in t h e a v ai lab ilit y o f m u lti p l e d i s ti n ct c o m b i n ati on c h em o t h era py re g ime n s w it h simil a r o r equa l an ti can cer efficac y . T h eref o re , d i f fere n ces i n s y ste mic t ox icit y have beco m e a m a j o r d etermi n a n t i n t h e selecti on o f t h era p y . T he maj or it y o f pha rm acogeno mic e x am p les affecti ng a dv erse e v e n ts o r e f f icac y fr o m cy t o t ox i c d r ugs i nvo l v e h e p atic meta bo lizi ng e n z y mes t h a t d et ox i fy o r b i o tr ans f o rm xenob i o tics . , Th i opur i ne Me t hy ltr ans f e r ase On e of th e bes t- s t ud i ed pha r m ac og e n etic s ynd r o me i nvo l v es t h e meta bo li s m o f t he t h i opu ri ne d r ug s —6 -merca p t opu ri n e ( 6 MP) , 6 -t h i ogu a n i ne, and aza t h i op ri ne— w h ic h h a v e wi d e a pp licati on s , i n cl ud i ng mai n te nance t he r apy f o r ch il dhood ALL a nd a du lt le uk emias . T h ese prodrug s m us t be ac ti va t ed t o t h i ogu a n i n e nu cle o ti d es i n o r d er t o h a v e a n ti pro l i f e r a ti ve e f f ec t s. How e v e r , m o st o f t h e v aria b ilit y i n t h e f o rmati on of acti ve m e t abo lit es i s m ed iate d by met hy lati on v ia t h i opu ri n e met hy ltr ans f e r ase (TP M T) . TPMT is a c y t o s o lic e n z y me t h at catal y ze s S -met hy lati on o f t h i opu ri ne agen ts , res u lti ng i n a n i n acti v e meta bo lite . Ery t hrocy t e TP M T ac ti v it y h as a trim od al d istri bu ti on, wit h 90 % o f p atie n ts hav i ng h i gh ac ti v it y , 10 % i n terme d iate acti v it y , a nd 0.3 % wit h v e r y l ow or no de t ec t ab l e ac ti v it y . TPMT d eficie n c y res u lts i n h i gh er i n t r acell u l a r ac ti va ti on o f 6M P t o f o rm t h i ogu a n i n e nu cle o ti d es , res u lti ng in se v e r e o r f a t a l he m a t o l og i c t ox icit y fr o m sta nd ar d do ses o f t h era p y . T he v a r ia b le ac ti v it y r esu lt s fr o m po l y m o r ph ism i n t h e TPMT g e n e , l o cate d on c hro m oso m e l ocus 6p22.3. Gen etic v aria n ts at c odon 238 (TPMT *2 ) , c odon 719 (TP M T *3C ) , o r bo t h c odon s 460 a nd 719 (TPMT *3 A) are t h e m o st cli n i ca ll y s i gn ifi can t , accoun ti ng f o r 95 % o f t h e p atie n ts wit h re duced TP M T ac ti v it y He t e r ozygo tes ( on e wil d t yp e a nd on e v aria n t allele) ar e c o mm on ( 10 % o f pa ti en t s ) , a n d h a v e ele v ate d le v els o f acti v e meta bo lite s

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( t wofo l d m o r e t han ho m ozygou s wil d t yp e) , a nd re qu ire d m o re c u m u lat ive do se r e duc ti ons o f 6M P f o r mai n te n a n ce ALL c h em o t h era py c o m p are d t o ho m o z ygous w il d -t ype pa ti en ts ( ) Patie n ts wit h a ho m o z ygous v a r ia n t TP M T geno t ype a r e a t a f ou rf o l d ris k o f se v ere t ox icit y , c o m p ar ed w it h w il d -t ype pa ti en t s TPMT g e no t yp e tests are no w a v aila b le c o mme rc i a ll y i n a C li n i ca l L abo rat o r y Im p r ov eme n t Ame nd me n ts (CLI A )-ce r ti f ie d env ir on m en t . T o da te , p atie n ts ho m o z ygou s f o r TPMT v aria n t alleles a ppea r t o t o l e r a t e 10 % , a nd h eter o z ygo tes a pp ear t o t o lerate 65 % o f t h e r ec om m ended doses o f 6 M P , wit h no a pp are n t d ecrease i n cli n ical e f f icac y ( ) T h i s h as f o rme d t h e b asis f o r p r o s p ecti v e , TPMT g e no t ype - gu i ded dos i ng o f 6M P t o a vo i d se v ere t ox icit y . Cli n ical P h a r ma cogeno mi cs Im p l e m en tati on C on s o rti u m (CPIC) G u i d eli n es r ec o mm end t ha t ho m ozygous wil d -t yp e p atie n ts b e starte d at t h e f u ll sta nd a rd dose. He t e r ozygous p atie n ts s hou l d start wit h re du ce d do ses at 30% t o 70 % o f t he f u ll dose w it h a d j u stme n ts ma d e after 2 t o 4 wee k s b ase d on m ye l osupp r ess i on and d isease-s p ecific gu i d eli n es . H o m o z ygous v a r ia n t pa ti en t s shou l d s t a rt wit h 10 % o f t h e f u ll do se du e t o t h e e x trem ely h i gh le ve l s o f t he ac ti ve m e t abo lite a nd po te n tial f o r fatal t ox icit y at sta nd a rd doses. Ad j us tm en t s s hou l d b e ma d e after 4 t o 6 wee k s b ase d on m y el o s upp r ess i on and d i seas e-s p ecific gu i d eli n es . D i hydropy rimi d i ne Dehyd r og e n ase (DPD) A lt hough 5 -fl uo r ou r ac il ( 5 FU) h as b ee n a v aila b le f o r ov er 40 y ears , it r emai n s t he co r ne r s t one o f co l o rectal ca n cer c h em o t h era p y , bo t h i n t h e a d j uv a nt and m e t as t a ti c se tti n gs . A dd iti on all y , t h e o ral p r od r ug ca p ecita b i ne u ltim a t e l y unde r go es acti v ati on t o 5 FU a nd is c o mm on l y used i n g ast ro i n t es ti na l and b r eas t m ali gn a n cies . 5 FU is a p r od r ug t h at is acti v ate d i n tr ace ll u l a rl y t o 5 -fl uo r o - 2 ′- d e oxyu ri d i n e m onopho s ph ate (5 F dU MP) , wh i ch i nh i b it s t h ymi dy late s yn t h ase (TS) , am ong o t h er mec h a nis m s o f ac ti on. TS i nh i b iti on res u lts i n im p aire d d e novo py rimi dine s yn t h esi s and supp r ess i on o f DNA s yn t h esis . A pp r ox imatel y 85 % o f a 5FU do se is ca t abo li zed by d i hyd r opy rimi d i n e d e hyd r og e n ase (DPD) t o i n act ive meta bo lit es. T he r e f o r e, D P D is a p rimar y re gu lat o r o f 5 FU acti v it y . DP D d e f icie ncy has been desc ri bed, res u lti ng i n h i gh er 5 FU b l ood le v els , g re ate r

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for mati on o f ac ti ve m e t abo lites , a nd se v ere o r fatal cli n ical t ox icit y , pr e do mi na t e l y m ye l osupp r ess i on, m u c o sitis , a nd cere b ellar t ox icit y I n t h e or y , t h i s t ox i c it y cou l d be re du ce d o r a vo i d e d by scree n i ng f o r DPD acti v it y i n su rr oga t e ti ssues, su c h as p eri ph eral m ononu clear cells . How e v e r , t he t echn i ca l r equ ir e me n ts f o r p re p arati on o f t h ese sam p les m ake it im pr acti ca l f o r m any p r ac ti c e sites . U nd ersta nd i ng t h e m o lec u lar b asi s for DPD de fi c i ency w ill p r ovid e a n a pp r o ac h f o r p r o s p ecti v e i d e n tificati on of p atie n t s a t h i gh ri sk f o r sev ere 5 FU t ox icit y . T h e g e n e e n c od i ng DPD is c o m po se d o f 23 exons, and at least 23 SNPs h a v e b ee n f ound . St ud ies in D P D-d efi c i en t pa ti en t s have i d e n tifie d se v eral d isti n ct m o lec u lar v aria n t s ass o ciate d w it h l ow enzy m e acti v it y . Ma ny o f t h ese are rare , a nd b ase s ub stit ut i ons, sp li c i ng de f ec t s, a nd frame s h ift m u tati on s , h a v e b ee n d esc r i b e d. T he p r eva l en t va ri a ti on is t h e s p lice rec ogn iti on site i n i n tr on 14 (D P YD*2A ) , whe r e a G t o A s ub stit u ti on res u lts i n t h e s k i pp i ng o f e xon 14, r es u lti ng i n an i nac ti ve enzy me . T h is po l y m o r ph ism h as b ee n ass o ciate d w it h seve r e D P D d eficie n c y i n h eter o z ygou s p atie n ts , wit h a ho m o z ygous geno t ype assoc iate d wit h a me n tal retar d ati on s ynd r o me . Patie n ts w it h seve r e 5 F U t ox icit y ma y h ar bo r on e o r m o re v aria n t allele s o f D P D, a nd a r ecen t s t udy show e d t h at 61 % o f ca n cer p atie n ts e xp erie n ci ng se v e r e 5 F U t ox i c iti es had dec rease d DPD acti v it y i n p eri ph eral m ononuc l ea r ce ll s, and D P YD*2 A was c o mm on l y f ound . I n t h e p atie nts w it h gr a de 4 neu tr open i a, 50% h ar bo re d at least on e DPYD *2 A . It is estimate d t ha t i n t he Caucas ia n popu lati on, ho m o z ygo tes f o r t h e v aria n t alleles have an i nc i dence o f 0.1 % a nd h eter o z ygo tes o cc u r at a n i n ci d e n c e of 0.5% t o 2 % . T he r e a r e add iti on al DPD m u tati on s t h at h a v e b ee n ass o ciate d w it h im pa ir ed enzy me acti v it y , i n cl ud i ng DPYD *3 a nd D P YD*13. C PI C gu i de li nes r ec o mme nd sta nd ar d do si ng f o r ho m o z ygous w il d- t ype pa ti en t s. Reduc i ng t h e do se by at least 50 % i n h eter o z ygou s p atie n ts ( *1 / *2A ) i s r eco mme nd e d, f o ll o we d by do se a d j u stme n t b ase d on t ox icit y and / o r pha rm acok i net ic testi ng. T h e u se o f a n alter n ati v e a g e n t is r ec o mm ended i n ho m ozygou s- v aria n t p atie n ts ( *2 A/ *2 A) . T h ere are ma ny pa ti en t s w it h seve r e 5 F U t ox icit y t h at h a v e no rmal DPD acti v it y . Th is h i gh li gh t s t ha t m any f acto rs , i n cl ud i ng m u lti p le g e n es , are po te n tia l ca u ses o f 5 F U t ox i c it y , and t h ere will no t b e on e sim p le test t o a vo i d t h i s im por ta n t c li n i ca l p r ob l e m .

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r e f e rr al pa ti en t s who have ha d b i op sies p erf o rme d elsew h ere , will re qu ir e r e qu estin g t h i s a r ch i ved ti ssu e p ri o r t o o r du ri ng t h e i n itial p atie n t v isit t o f acilitat e mi n imi z i ng tr ea tm en t d ela y s . Alt hough s o me v aria n ts h a v e str ong e v i d e n ce suppo rti ng tr ea tm en t rec o mme nd ati on s , ma ny c u rre n tl y do no t y et . M ul ti d i sc i p li na r y co mmittees c h ar g e d wit h re v iewi ng t h e le v el o f e v i d e n ce f o r each gene ti c r esu lt a nd p r ov i d i ng cli n icall y acti on a b le r ec o mm enda ti ons w ill be essen tial f o r tra n slati ng t h ese m u lti g e n e t u m o r assa y r es u lt s i n t o r ou ti ne c li n ical p ractice . Decisi on t oo ls a nd d e v el op m ent of t r eat men t gu i de li nes w ill f u rt h er assist wit h r ou ti n e i n te g rati on o f t h is tec hno l og y , espec i a ll y f o r on c o l og ists at smaller p ractice sites . O n c o l ogy f ell ow shi p tr a i n i ng p r og r a m s w ill als o n ee d t o b e e xp a nd e d t o e n s u re c o m p et ence o f new p r ac titi one rs i n t h e area o f g e no mic- gu i d e d t h era p ies . Re g a rd le ss o f t hese cha ll enge s , t h e treatme n t p ara d i g m o f g e no mic- d ri ven me d ici ne and i nd i v i dua li z i ng t h era py h as p ermitte d t h e fiel d o f on c o l ogy to m ov e beyond t he limit a ti ons o f non selecti v e c y t o t ox ic t h era py a nd t o war d t h e m or e op tim a l se l ec ti on and do si ng o f on c o l ogy a g e n ts . R E F E R ENC ES 1. Mc L eod H L . Cance r p harmac og e no mics: earl y p r o mise , bu t c on ce r te d e f f o rt needed. S c i e nce 2013 ; 339 : 1563–1566. 2. Ga rr away L A. Geno mics- d ri v e n on c o l ogy : framew o r k f o r a n eme r g i ng pa r ad i g m . J C li n On c o l 2013 ; 31 : 1806–1814. 3. Mand r eka r S J, S a r gen t DJ . Pre d icti v e b i o mar k er v ali d ati on i n pr actice : l essons fr o m r ea l trials . Cli n T rials 2010 ; 7 : 567–573. 4. Evans W E , Re lli ng M V . P h armac og e no mics: tra n slati ng f un cti onal g e no mi cs i n t o r a ti ona l t he r ap e u tics . Scie n ce 1999 ; 286 : 487–491. 5. W ang L , Mc L eod H L , W ei n s h il bou m RM . Ge no mics a nd d r ug r es pon s e. N E ng l J Med 20 1 1 ; 364 : 1 144– 1 153. 6. D r uke r BJ. T r ans l a ti on o f t h e P h ila d el ph ia c h r o m o s o me i n t o t h erap y for CML . B l ood 2008 ; 1 12 : 4808–4817.

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26. W a tt e r s J, Mc L eod H. Ca n cer ph armac og e no mics: c u rre n t a nd f u t u r e a pp licat ions. B i och im B i ophy s Acta 2003 ; 1603 : 99– 1 1 1. 27. Evans W , Re lli ng M. P h armac og e no mics: tra n slati ng f un cti on al g e no mi cs i n t o r a ti ona l t he r ap e u tics . Scie n ce 1999 ; 286 : 487–491. 28. Deenen MJ, Ca t s A, B eij n e n H , et al . Part 2 : ph armac og e n etic v a r ia b ilit y i n d r ug tr anspo rt and ph ase I a n tica n cer d r ug meta bo lism . On c o l og i s t 20 1 1 ; 16 : 820–834. 29. K r yne t sk i E , E vans W . Dr ug met hy lati on i n ca n cer t h era py : less o n s fro m t he TP M T po l y m o r ph i s m . O n c og e n e 2003 ; 22 : 7403–7413. 30. Mc L eod H, K r yne t sk i E Y , Relli ng M V , et al . Ge n etic po l y m o r ph i sm of t h i opu ri ne m e t hy ltr ans f e r a se a nd its cli n ical rele v a n ce f o r c h il dhood ac u te l ymphob l as ti c l euke mi a. Le uk emia 2000 ; 14 : 567–572. 31. Evans W , Hon Y Y , Bomg aars L , et al . Pre pond era n ce o f t h i opu ri n e S - met hy ltr ans f e r ase de fi c i en c y a nd h eter o z ygo sit y am ong p atie n ts i n t o le r a n t t o m e r cap t opu ri ne o r azat h i op ri n e . J Cli n O n c o l 2001 ; 19 : 229 3 – 2301. 32. Relli ng M, Hancock M L , Ri v era GK , et al . Merca p t opu ri n e t h era py i n t o le r a nce and he t e r ozygos ity at t h e t h i opu ri n e S-met hy ltra n sferase g e ne l o c u s . J N a tl Cance r I ns t 1999 ; 91 : 2001–2008. 33. Relli ng M V , Ga r dne r EE , Sa ndbo r n WJ , et al . Cli n ical ph a r ma cogene ti cs im p l e m en t a ti on c on s o rti u m gu i d eli n es f o r t h i opu ri n e met hy ltr ans f e r ase geno t ype and t h i opu ri n e do si ng : 2013 upd ate . Cli n P h a r ma co l T he r 2013 ; 93 : 324–325. 34. Ca ud l e K E , T ho r n C F , Klei n TE , et al . Cli n ical P h armac og e n etics I m p lem en t a ti on Conso rti u m gu i d eli n es f o r d i hyd r opy rimi d i n e d e hydrogenase geno t ype and fl uo r opy rimi d i n e do si ng. Cli n P h armac o l Th e r 2013 ; 94 : 640–645. 35. Mc L eod H, Co lli e - Dug ui d ES , V re k e n P , et al . N o me n clat u re f o r hu ma n D P YD a ll e l es. P ha rm a c og e n etics 1998 ; 8 : 455–459.

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36. W e i X, Eli zondo G, S apon e A , et al . C h aracterizati on o f t h e hu ma n d i hydropy rimi d i ne dehyd r ogen ase g e n e . Ge no mics 1998 ; 51 : 391–400. 37. R idge S , Sl udden J, W ei X , et al . Di hyd r opy rimi d i n e d e hyd r og e n a se ph a r ma cogene ti cs i n pa ti en t s wit h c o l o rectal ca n ce r . Br J Ca n cer 1998 ; 77 : 497–500. 38. Jo hnson M, W ang K, Diasi o R . Pr o f ound d i hyd r opy rimi d i n e d e hydrogenase de fi c i ency r esu lti ng fr o m a nov el c o m pound h eter o z ygo t e g e no t ype. C li n Cance r Res 2002 ; 8 : 768–774. 39. V an Ku il enbu r g A, Me i n sma R , Z o ete kou w L , et al . I n crease d ris k o f gr a d e IV neu tr open i a a ft e r adm i n istrati on o f 5 -fl uo r ou racil du e t o a d i hydropy rimi d i ne dehyd r ogen ase d eficie n c y : h i gh p re v ale n ce o f t h e IV S 14 + 1g > a m u t a ti on. I n t J C a n cer 2002 ; 101 : 253–258. 40. Mü r d t e r TE , S ch r o t h W , Bacc hu s-Ger yb a d ze L , et al . Acti v it y le vels of tam ox if en m e t abo lit es a t t h e estr og e n rece p t o r a nd t h e im p act o f g e n e tic po l y m o r ph i s m s o f phase I and II e n z y mes on t h eir c on ce n trati on le v els i n p lasma . C li n P ha rm aco l T he r 20 1 1 ; 89 : 708–717. 41. Des t a Z , W a r d BA, S oukhov a N V , et al . C o m p re h e n si v e e v al u ati on of tam ox if en sequen ti a l b i o tra n sf o rmati on by t h e hu ma n c y t o c h r o me P 4 5 0 s y stem i n v itr o : p r o mi nen t r ol es f o r CYP 3 A a nd CYP 2 D 6. J P h armac o l Exp The r 2004 ; 310 : 1062–1075. 42. B rad f o r d L D. CY P 2D6 allele fre qu e n c y i n E u r op ea n Ca u casia n s , A sia n s , A fri cans and t he ir des ce nd a n ts . P h armac og e no mics 2002 ; 3 : 229 – 243. 43. C rews KR, Gaed i gk A, D unn e nb e r g er HM , et al . Cli n ical P h a r ma cogene ti cs Im p l e m en tati on C on s o rti u m (CPIC) gu i d eli n es f o r c od ei n e t he r apy i n t he con t ex t o f c y t o c h r o me P 450 2 D 6 (CYP 2 D 6 ) g e no t ype. C li n P ha rm aco l T he r 2012 ; 91 : 321–326. 44. Sc h r o t h W , Goe t z M P , Hama nn U , et al . Ass o ciati on b etwee n C YP2D 6 po l y m o r ph i s m s and ou tc o mes am ong w o me n wit h earl y sta g e br east c ance r tr ea t ed w it h t amox ife n. JAMA 2009 ; 302 : 1429–1436.

17 Alkylatin g A g ents

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17 Alkylatin g A g ents

17 Alkylatin g A g ents

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Kenneth D. T ew PERSPECTIVES Alkylating agents were the first anticancer molecules developed, and they are still used toda y . After more than 50 years of use, the basic chemistry and pharmacology of this drug family is well understood and has not changed substantiall y . The family contains six major classes: nitrogen mustards, aziridines, alkyl sulfonates, epoxides, nitrosoureas, and triazene compounds, although a few nonstandard agents have recently been developed. Most epoxides tend to be quite nonspecific with respect to their reactivity and, as such, few have useful clinical characteristics. This chapter provides perspective on how the limited varieties of alkylating agents continue to be useful in the therapeutic management of cancer patients. The alkylating agents are a diverse group of anticancer agents with the commonality that they react in a manner such that an electrophilic alkyl group or a substituted alkyl group can covalently bind to cellular nucleophilic sites. Electrophilicity is achieved through the formation of carbonium ion intermediates and can result in transition complexes with ta r get molecules. Ultimatel y , reactions result in the formation of covalent linkages by alkylation with a broad range of nucleophilic groups, including bases in DNA, and these are believed responsible for ultimate cytotoxicity and therapeutic e f fect. Although the alkylating agents react with cells in all phases of the cell cycle, their efficacy and toxicity result from interference with rapidly proliferating tissues. From a historical perspective, the vesicant properties of mustard gas used during W orld W ar I were shown to be accompanied by the suppression of lymphoid and hematologic functions in experimental animal s and led to the development of mechlorethamine as the first alkylating agent used in the management of human cance r .

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Subsequentl y , a number of related drugs have been developed, and these have roles in the treatment of a range of leukemias, lymphomas, and solid tumors. Most of the alkylating agents cause dose-limiting toxicities to the

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(5) sulfur atoms of methionine, and (6) thiol groups of cysteinyl residues of protein and glutathione . The least favored reactions will still occu r , but at much slower rates unless they are catalyzed. Alkylation through highly reactive intermediates (e.g., mechlorethamine) would be expected to be less selective in their ta r gets than the less reactive S N 2 reagents (e.g., busulfan). Howeve r , the therapeutic and toxic e f fects of alkylating agents do not correlate directly with their chemical reactivit y . Clinically useful agents include drugs with S N 1 or S N 2 characteristics, and some with both These di f fer in their toxicity profiles and antitumor activit y , but more as a consequence of di f ferences in pharmacokinetics, lipid solubilit y , penetration of the central nervous system (CNS), membrane transport, metabolism and detoxification, and specific enzymatic reactions capable of repairing alkylation sites on DNA. CLASSIFIC A TION The major classes of clinically useful alkylating agents are illustrated in and summarized in the following sections. Doses and schedules of the various agents are shown in .

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Alkyl Sulfonates Busulfan is used for the treatment of chronic myelogenous leukemia. It exhibits S N 2 alkylation kinetics and shows nucleophilic selectivity for thiol groups, suggesting that it may exert cytotoxicity through protein alkylation rather than through DNA. In contrast to the nitrogen mustards and nitrosoureas, busulfan has a greater e f fect on myeloid cells than lymphoid cells, thus the reason for its use against chronic myelogenous leukemia . Aziridines Aziridines are analogs of ring-closed intermediates of nitrogen mustards and are less chemically reactive, but they have equivalent therapeutic properties. Thiotepa has been used in the treatment of carcinoma of the breast, ovar y , for a variety of CNS diseases, and with increasing frequency as a component of high-dose chemotherapy regimens . Thiotepa and its primary desulfurated metabolite triethylenethiophosphoramide (TE P A) alkylate through aziridine ring openings, a mechanism similar to the nitrogen mustards. T riazines Perhaps the newest clinical development in the alkylating agent field is the eme r gence of temozolomide (TMZ). This agent acts as a prodrug and is an imidazotetrazine analog that undergoes spontaneous activation in solution to produce 5-(3-methyltriazen-1-yl) imidazole-4-carboxamide (MTIC), a triazine derivative. It crosses the blood–brain barrier with concentrations in the CNS approximating 30% of plasma concentrations . Resistance to the methylating agent occurs quite frequently and has adversely a f fected the rate and durability of the clinical responses of patients. Howeve r , because of its favorable toxicity and pharmacokinetics, TMZ is being combined with numerous other classes of anticancer drugs in an effort to improve response rates in diseases such as malignant melanomas, gliomas, brain metastasis

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from solid tumors, and refractory leukemias. Many of these trials are currently underwa y . Nitrogen Mustards Bischloroethylamines or nitrogen mustards are extensively administered in the clinic. As an initial step in alkylation, chlorine acts as a leaving group and the β-carbon reacts with the nucleophilic nitrogen atom to form the cyclic, positively cha r ged, reactive aziridinium moiet y . Reaction of the aziridinium ring with an electron-rich nucleophile creates an initial alkylation product. The remaining chloroethyl group achieves bifunctionality through the formation of a second aziridinium. Melphalan (L-phenylalanine mustard), chlorambucil, cyclophosphamide, and ifosfamide (see replaced mechlorethamine as primary therapeutic agents. These derivatives have electron-withdrawing groups substituted on the nitrogen atom, reducing the nucleophilicity of the nitrogen and rendering them less reactive, but enhancing their antitumor e f ficac y . One distinguishing feature of melphalan is that an amino acid transporter responsible for uptake influences its e f ficacy across cell membranes .

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Under physiologic conditions, proton abstraction by a hydroxyl ion initiates spontaneous decomposition of the molecule to yield a diazonium hydroxide

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and an isocyanate (see ). The chloroethyl carbonium ion generated is the active alkylating species. Through a subsequent dehalogenation step, a second electrophilic site imparts bifunctionalit y . Thus, while cross-linking may occur similar to those lesions caused by nitrogen mustards, the chemistry leading to the endpoint is distinct. The isocyanate species generated are also electrophilic, showing nucleophilic selectivity toward sulfhydryl and amino groups that can inhibit a number of enzymes involved in nucleic acid synthesis and thiol balance . Because carbamoylation is considered of minor importance to the therapeutic efficacy of clinically used nitrosoureas, chlorozotocin and streptozotocin were designed to unde r go internal carbamoylation at the 1- or 3-OH group of the glucose ring, with the consequence that no carbamoylating species are produced .

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Streptozotocin is also unusual in that most methylnitrosoureas have only modest therapeutic value. Howeve r , its lack of bone marrow toxicity and strong diabetogenic e f fect in animals led to its use in cancer of the pancreas (see ). The dose-limiting toxicities in humans are gastrointestinal and renal, but the drug has considerably less hematopoietic toxicity than the other nitrosoureas. Because of their lipophilicity and capacity to cross the blood–brain barrie r , the chloroethylnitrosoureas were found to be e f fective against intracranially inoculated murine tumors. Indeed, early preclinical studies showed that many mouse tumors were quite responsive to nitrosoureas. The same extent of efficacy was not found in humans. Subsequent analyses demonstrated that an enzyme responsible for repair of O-6 - alkyl guanine ( O 6 -methylguanine-DNA methyltransferase [MGMT], or the Mer/Mex phenotype ) was expressed at low levels in mice, but at high levels in humans, a contributory factor in the reduced clinical e f ficacy of nitrosoureas in humans. In the 1980s, in particula r , a number of new nitrosoureas were tested in patients in Europe and Japan, but none established a regular role in standard cancer treatment regimens. MGMT promoter methylation is crucial in MGMT gene silencing and can predict a favorable outcome in glioblastoma patients receiving alkylating agents This biomarker is on the ve r ge of entering clinical decision making and is currently used to stratify or even select glioblastoma patients for clinical trials. In other subtypes of glioma, such as anaplastic gliomas, the relevance of MGMT promoter methylation might extend beyond the

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prediction of chemosensitivit y , and could reflect a distinct molecular profile. At this time, the standardization of MGMT assays will be critical in establishing prospective prognostic or predictive effects. In addition, eventual clinical trials will need to determine, for each subtype of glioma, the extent to which methylation patterns are predictive or prognostic and whether such assays could be incorporated into an individualized approach to clinical practice . CLINICAL PHARMACOKINETICS/PHARMACODYNAMICS The pharmacokinetics of the alkylating agents are highly variable depending on the individual agent. Nevertheless, they are generally characterized by high reactivity and short half-lives. Although detailed studies on clinical pharmacology are available , summarizes some of the primary kinetic characteristics of the major clinically useful drugs. Mechlorethamine is unstable and is administered rapidly in a running intravenous infusion to avoid its rapid breakdown to inactive metabolites. In contrast, chlorambucil and cyclophosphamide are su f ficiently stable to be given orall y , and are rapidly and completely absorbed from the gastrointestinal tract, whereas others like melphalan have poor and variable oral absorption. Cyclophosphamide ifosfamide, and dacarbazine are unusual in that they require activation by cytochrome P-450 in the liver before they can alkylate cellular constituents. The nitrosoureas also require activation, albeit nonenzymatic. The major route of metabolism of most alkylating agents is spontaneous hydrolysis, although many can also unde r go some degree of enzymatic metabolism. This is particularly pertinent for phase II metabolic conversions where reactivity with nucleophilic thiols precedes conversion to mercapturates, with the result that most of the alkylating agents are excreted in the urine. One example of complex multistep metabolism is provided by cyclophosphamide (see . Activation by CYP2B6 is followed by the conversion of aldehyde dehydrogenase to reactive alkylating species or possible detoxification through GSH conjugation reactions. The latter is particularly important for acrolein because it is believed to contribute to the bladder toxicities associated with the drug.

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The alkylating agents form covalent bonds with a number of nucleophilic groups present in proteins, RNA, and DNA (e.g., amino, carboxyl, sulfhydryl, imidazole, phosphate). Under physiologic conditions, the chloroethyl group of the nitrogen mustards unde r goes cyclization, with the chloride acting as a leaving group forming an intermediate carbonium ion that attacks nucleophilic sites (see . Bifunctional alkylating agents (with two chloroethyl side chains) can undergo a subsequent cyclization to form a covalent bond with an adjacent nucleophilic group, resulting in DNA–DNA or DNA–protein cross-links. The N7 or O6 positions of guanine are particularly susceptible and may represent primary ta r gets that determine both the cyto t oxic and mutagenic consequences of therap y . The nitrosoureas have a simila r , but distinct, mechanism of action, spontaneously forming both alkylating and carbamoylating agents in aqueous media (see . The carbamoylating moieties are generally believed to be inconsequential to the therapeutic properties of the nitrosoureas. THERAPEUTIC USES The alkylating agents are frequently used in combination therapy to treat a variety of types of cance r . Perhaps the most versatile is cyclophosphamide, whereas the other alkylating agents are of more restricted clinical use. Because of early successes, many disease states are managed with drug combinations that contain several alkylating agents. Cyclophosphamide is employed to t reat a variety of immune-related diseases and to pu r ge bone marrow in autologous marrow transplant situations . A general summary of the clinical uses of the primary alkylating agents is shown in . T OXICITIES The alkylating agents show significant qualitative and quantitative variability in the sites and severities of their toxicities. The primary dose-limiting toxicity is suppression of bone marrow function, with secondary limiting e f fects on the proliferating cells of the intestinal mucosa. Contraindications to the use of alkylating agents would identify patients with severely depressed bone marrow function and patients with hypersensitivity to these drugs. Other listed precautions to these drugs include carcinogenic and mutagenic effects and impairment of fertilit y .

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Precaution is also advised in patients with (1) leukopenia or thrombocytopenia, (2) previous exposure to chemotherapy or radiotherap y , (3) tumor cell infiltration of the bone marro w , and (4) impaired renal or hepatic function. These drugs can also increase toxicity in adrenalectomized patients and interfere with wound healing. A brief summary of dose-limiting toxicities is shown in and a narrative of each follows here. Nausea and V omiting Nausea and vomiting are frequent side e f fects of alkylating agent therapy and are not well controlled by conventional antiemetics . They are a major source of patient discomfort and a significant cause of lack of drug compliance and even discontinuation of therap y . Frequency and extent are highly variable among patients. The overall frequency of nausea and vomiting is directly proportional to the dose of alkylating agent. The onset of nausea may occur within a few minutes of the administration of the drug or may be delayed for several hours. Bone Marrow T oxicity Bone marrow toxicity can involve all of the blood elements, leukocytes, platelets, and red cells . The extent and time course of suppression show marked interindividual fluctuation. Relative platelet sparing is a characteristic of cyclophosphamide treatment. Even at the very high doses (<200 mg/kg) of cyclophosphamide (used in preparation for bone marrow transplantation), some recovery of hematopoietic elements occurs within 21 to 28 days. This stem cell–sparing property is further reflected by the fact that cumulative damage to the bone marrow is rarely seen when cyclophosphamide is given as a single agent, and repeated high doses can be given without progressive lowering of leukocyte and platelet counts. The biochemical basis for the stem cell–sparing e f fect of cyclophosphamide is related to the presence of high levels of aldehyde dehydrogenase in early bone marrow progenitor cells (see . Busulfan is particularly toxic to bone marrow stem cells , and treatment can lead to prolonged hypoplasia. The hematopoietic depression produced by the nitrosoureas is characteristically delayed. The onset of leukocyte and platelet depression occurs 3 to 4 weeks after drug administration and may last an additional 2 to

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3 weeks . Thrombocytopenia appears earlier and usually is more severe than leukopenia. Even if the nitrosourea is given at 6-week intervals, hematopoietic recovery may not occur between courses, and the drug dose often must be decreased when repeated courses are used. Renal and Bladder T oxicity Hemorrhagic cystitis is unique to the oxazaphosphorines (cyclophosphamide and ifosfamide) and may range from a mild cystitis to severe bladder damage with massive hemorrhage . This toxicity is caused by the excretion of toxic metabolites (particularly acrolein) (see in the urine, with subsequent direct irritation of the bladder mucosa. The incidence and severity can be lessened by adequate hydration and continuous irrigation of the bladder with a solution containing 2-mercaptoethane sulfonate (MESNA) and frequent bladder emptying MESNA is given in divided doses every 4 hours in dosages of 60% of those of the alkylating agent. At high cumulative doses, all commonly used nitrosoureas can produce a dose-related renal toxicity that can result in renal failure and death . In patients developing clinical evidence of toxicit y , increases in serum creatinine usually appear after the completion of therapy and may be first detected up to 2 years after treatment. Interstitial Pneumonitis and Pulmonary Fibrosis Long-term busulfan therapy can lead to the gradual onset of feve r , a nonproductive cough, and dyspnea, followed by tachypnea and cyanosis, and progressing to severe pulmonary insu f ficiency and death . If busulfan is stopped before the onset of clinical symptoms, pulmonary function may stabilize, but if clinical symptoms are manifest, the condition may be rapidly fatal. Cyclophosphamide, bischloroethylnitrosourea, and methyl-1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea in cumulative doses exceeding 1,000 mg/m 2 may also lead to similar side effects Other alkylating agents, including melphalan, chlorambucil, and mitomycin C, can lead to pulmonary fibrosis after therap y . This e f fect is probably caused by a direct cytotoxicity of the alkylating agent to pulmonary epithelium, resulting in alveolitis and fibrosis.

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Gonadal T oxicit y , T eratogenesis, and Carcinogenesis Alkylating agents can have profound toxic effects on reproductive tissue .

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agents might be as high as 10%. Acute leukemia has been the most frequently described second malignanc y , and it usually develops 1 to 4 years after drug exposure Other malignancies, including solid tumors, also have been reported to develop in patients treated with alkylating agents . The last four decades have yielded a significant improvement in the survival of children diagnosed with cancer (5-year survival is approximately 80%). As many as two-thirds of the survivors of childhood malignancies can experience delayed drug toxicities that may be severe or even life threatening. Such complications include impairment in growth and development, neurocognitive dysfunction, cardiopulmonary compromise, endocrine dysfunction, renal impairment, gastrointestinal dysfunction, musculoskeletal sequelae, and second cancers . Alopecia The degree of alopecia after cyclophosphamide administration may be quite severe, especially when this drug is used in combination with vincristine sulfate or doxorubicin hydrochloride . Regrowth of hair inevitably occurs after the cessation of therap y , but may be associated with a change in the color and greater curl. Use of a tourniquet or ice pack applied to the scalp during and for a short period after cyclophosphamide administration reduces the impact. Alle r gic Reactions Alkylating agents covalently bind to proteins, and these conjugates can act as haptens and produce alle r gic reactions . An increasing number of reports of skin eruption, angioneurotic edema, urticaria, and anaphylactic reactions after the systemic administration of alkylating agents have appeared. Immunosuppression Alkylating agents suppress both humoral and cellular immunity in a variety of experimental systems The most immunosuppressive is cyclophosphamide, reported to cause (1) selective suppression of B-lymphocyte function, (2) depletion of B-lymphocytes, and (3) suppression of

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busulfan-induced seizures At least one recent study has suggested that a polymorphism in the glutathione S-transferase A2 family may be predictive of transplant-related mortality after allogeneic stem cell transplantation ,

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perhaps indicating that a pharmacogenetic approach might be possible in this disease setting. Moreove r , in a preclinical setting, a proteomic analysis identified thioredoxin as a potentially important adjuvant therapy in enhancing donor cell graft enhancement in bone marrow transplantation .

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The possibility that this approach may benefit patients following alkylating agent–based ablation remains to be tested in a clinical setting. Cyclophosphamide at doses exceeding 100 mg/kg during a 48-hour period (preparatory to bone marrow transplantation) can cause cardiac toxicit y .

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surface antigens. Enzymes frequently associated with the cell surface include peptidases, nitroreductases, and γ-glutamyl transpeptidase; to some degree, each has been ta r geted to cleave circulating alkylating prodrugs, thereby in a localized fashion releasing active alkylating species. Antibody-directed enzyme prodrug therapy is exemplified by the use of an antibody linked to the peptidase carboxypeptidase G-2, which releases an active alkylator from an inactive γ-glutamyl conjugate Linkage of the peptidase to any antibody that localizes selectively to a tumor cell membrane is a viable option. Expression of the peptidase on the cell surface then leads to prodrug activation and cell kill. Such approaches have had limited clinical impact to this time; howeve r , their development does continue. A further rationale for enhancing tumo r -specific delivery takes advantage of the observation that glutathione-S-transferase pi (GSTP1-1) is preferentially expressed in a number of solid tumors and some lymphomas. In this case, the prodrug consists of an unusual alkylating agent conjugated to a substituted glutathione peptidomimetic. GSTP initiates the cleavage, thereby creating a cytotoxic alkylating species The initial canfosfamide design strategy relied on the principle that proton-abstracting sites at the active site of GST could initiate a cleavage reaction that would convert an inactive prodrug into a cytotoxic species. The presence of a histidine residue in proximity to the G binding site was integral to the removal of the sulfhydryl proton from the GSH cosubstrate, resulting in the generation of a nucleophilic sulfide anion. This moiety would be more reactive with electrophiles in the absence of GSH. Unlike other standard nitrogen mustard drugs, canfosfamide contains a tetrakis (chloroethyl) phosphorodiamidate moiet y . Other compounds bearing this structure have been shown to be more cytotoxic than a similar structure with a single bis-(chloroethyl) amine group. As in other nitrogen mustards, the chlorines can act as leaving groups, thus creating aziridinium ions with electrophilic characteristics. Although the exact temporal or sequential formation of the four possible chlorine leaving events is not known, the assumption is that these species possess cytotoxic properties through their capacity to alkylate target nucleophiles, such as DNA bases. T etrafunctionality could result in the formation of cross-links with bonding distances greater than for bifunctional agents. Howeve r , a

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number of caveats apply to this interpretation. For example, alkylating agents, whether mono-, bi-, or putatively tetrafunctional, generally lead to some form of myelosuppression. A number of clinical trials with canfosfamide have now been completed. These include, phase 1 , phase 1/2a phase 2, and phase 3 . The phase 3 study was in platinum refractory ovarian cancer patients and proved negative for enhanced survival. Nevertheless, additional trials are still in progress. Another ta r geting approach delivers the gene for a cytochrome P-450 isoenzyme to tumors by viral vecto r , thereby enhancing specific tumor cell activation of cyclophosphamide Because this therapy has its base in gene delivery technologies, successful development in humans will await further advances in this arena. Laromustine is in the sulfonylhydrazine class of alkylating agents. It is presently in clinical development for the treatment of malignancies such as acute myelogenous leukemia (AML) . Similar to nitrosoureas, laromustine is a prodrug that yields a chloroethylating and a carbamoylating (methyl isocyanate) species. As with nitrosoureas, the cytotoxicity of laromustine is attributed primarily to the chloroethylating-mediated alkylation of DNA and subsequent interstrand cross-links . The carbamoylating species can inhibit DNA repair and other cellular enzyme systems. Phase 1 trials in patients with solid tumors indicated the expected myelosuppression, although few extramedullary toxicities were observed, indicating potential e f ficacy in the treatment of hematologic malignancies. Phase 2 trials have been completed in patients with untreated AML, high-risk myelodysplastic syndrome, and relapsed AML. The most encouraging results have been found in patients older than 60 years with poo r -risk, de novo AML for which no standard treatment exists. Laromustine is currently in phase 2/3 trials for AML and phase 2 trials for myelodysplastic syndrome and solid tumors .

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Laromustine appears to be a promising agent in elderly patients who do not respond to or are not fit for intensive chemotherap y . Although not a new drug, bendamustine is a unique cytotoxic agent with structural similarities to alkylating agents and antimetabolites, but it lacks cross-resistance with other established alkylating agents both in vitro and in the clinic . Its mechanism of action is similar to other mustards in causing

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DNA intra- and interstrand cross-links. In comparison with other more commonly used alkylating agents, such as cyclophosphamide or phenylalanine mustard, more DNA double-strand breaks are formed at equitoxic dosages. T reatment with bendamustine induces a concentration-dependent apoptosis as evidenced by changes in Bcl-2 and Bax expression profiles in chronic B-cell lymphocytic leukemia . DNA damage produced by bendamustine is repaired via base-excision repair mechanisms, implicating an unusual mode of action, which was recently confirmed through gene expression profiling analyses. This also provided an explanation for the lack of cross-resistance with other alkylating agents, as observed in vitro with anthracycline-resistant breast cancer and cisplatin-resistant ovarian cance r . Clinical studies conducted in Germany more than 30 years ago suggested activity in indolent non-Hodgkin lymphoma. Subsequent American trials showed responses in more than 70% of patients with drug refractory disease, with the implication that bendamustine may be the most e f fective drug in this patient population. Combinations of bendamustine and rituximab elicited response rates of 90% to 92%, with complete remission in 55% to 60% in follicular and mantle cell lymphoma. Superiority over chlorambucil in previously untreated patients with chronic lymphocytic leukemia (CLL) led to its recent approval for this disease in the United States. Bendamustine is approved in Germany for the treatment of patients with indolent non-Hodgkin lymphoma, CLL, and multiple myeloma. Activity has also been noted in patients with breast cancer and non–small-cell lung cance r . Bendamustine has been used both as a single agent and in combination with other agents, including etoposide, fludarabine, mitoxantrone, methotrexate, prednisone, rituximab, and vincristine. A multicenter phase 2 trial in lymphomas had an overall response rate of 89%; (35% complete response and 54% partial response). In previously treated patients. the overall response rate was 76% (38% complete response and 38% partial response). The estimated median progression-free survival was 19 months . In CLL patients, the drug is administered at 100 mg/ m 2 intravenously over 30 minutes on days 1 and 2 of a 28-day cycle, for up to six cycles. Efficacy relative to first-line therapies other than chlorambucil has not been established. It is also indicated for the treatment of patients with indolent B-

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t ox icit y and a d i f f e r en t p r o fil e o f a n tit u m o r acti v it y . I n a dd iti on, t h e si d e e f f ects o f c i sp l a ti n s tim u l a t ed t h e d e v el op me n t o f a n tiemetics a nd o t h er s uppor ti ve ca r e m easu r es f o r u se wit h c h em o t h era p y . Pr og ress i n und e r sta nd i ng t he che mi s tr y and ph armac ok i n etics o f cis p lati n h as gu i ded t h e d e v el op m en t o f new ana l og s . I n g e n eral , m od ificati on o f t h e c h l o ri d e lea v i ng g r oups o f c i sp l a ti n r e s u lts i n c o m pound s wit h d iffere n t ph a r ma cok i ne ti cs and r eac ti v it y t o war d s DNA , w h ereas m od ificati on o f the ca rr ie r l igands a lt e r s t he ac ti v it y o f t h e res u lti ng c o m p le x. T h e feat u res o f t h e m or e im po rt an t p l a ti nu m an al og s t h at h a v e b ee n d e v el op e d are s hown i n Ca rbop lati n Th e ca rbop l a ti n m o l ecu l e has t h e same ammi n e carrier li g a nd s as cis p la tin. U si ng a mu ri ne sc r een f o r neph r o t ox icit y , Harra p a nd Cal v ert d isc ov ere d t h at s ub stit u ti ng a cyc l obu t an e d icar boxy late m o iet y f o r t h e tw o c h l o ri d e li g a nd s o f c i sp l a ti n r esu lt ed i n a c o m p le x wit h re du ce d re n al t ox icit y . T his ob se rv ati on was tr ans l a t ed t o t h e cli n ic i n t h e f o rm o f car bop lati n, a m o r e sta b le a nd pha rm acok i ne ti ca l ly p re d icta b le a n al og . T h e res u lts i n humans w e r e ac cu r a t e l y p r ed i c t ed by th e a n imal m od els , a nd marr o w t ox icit y rat he r t h a n n e ph r o t ox i c it y was t he p ri n ci p al si d e effect . At e f fecti v e do ses , ca rbop l a ti n p r oduced l ess na usea , vo miti ng, n e ph r o t ox icit y , a nd n e uro t ox i c it y t han c i sp l a ti n. F u rt h erm o re , t h e m y el o s upp ressi on was cl o sel y assoc i a t ed w it h t he ph armac ok i n etics . T h e w o r k o f Cal v ert et al .

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C o m pounds w it h ac ti v it y i n ci s p lati n -resista n t m od els eme r g e d fr o m m od i f ic a ti ons t o t he ca rri e r g r oup (see left si d e o f t h e a n al og s i n ) . C onnors, i n t he l a t e 1960s, syn t h esize d p lati nu m c oo r d i n ati on c o m pounds w it h v a ry i ng phys i coche mi cal c h aracteristics a nd f ound t h at t h e series t hat po ssess ed a d i a mi nocyc l ohex a n e (DACH) carrier g r oup was acti v e i n m od els o f cance r i n v itr o and i n v i vo . S ub se qu e n t st ud ies s uppo rte d the i d ea t h a t DACH - based p l a ti n um c o m p le x es were non– cr o ss-resista n t wi th cis p latin , and DACH de ri va ti v es e xh i b ite d a un i qu e c y t o t ox icit y p r o file c o m p a red t o c i sp l a ti n and ca rb op lati n i n t h e Nati on al Ca n cer I n stit u te 60 cell li n e sc r een . A ft e r a nu m b er o f d ela y s , a DACH a n al og t h at h a d b ee n s yn t hes i zed by K i dan i and c o llea gu es i n t h e earl y 1970 s , was d e v el op e d i n t he c li n i c . Oxa li p lati n, a c oo r d i n ati on c o m pound o f a DA C H ca rri e r g r oup and an ox alat o lea v i ng g r oup, was acti v e i n cis p lat in - r esista n t t u m o r m ode l s. Li ke c is p lati n, ox ali p lati n p refere n tiall y f o rms a ddu cts a t t he N7 pos iti on o f gu a n i n e a nd, t o a lesser e x te n t , a d e n i n e . How e v e r , t he r e i s ev i dence t h at t h e t h ree- d ime n si on al str u ct u re o f t h e D NA a ddu cts and b i o l og i c r espons e(s) t h e y elicit are d iffere n t fr o m t ho se o f cis p latin . Oxa li p l a ti n de m ons trate d acti v it y i n c o m b i n ati on wit h 5 - f l uorourac il and l eucovo ri n i n c o l on ca n ce r , a d isease t h at is un res pon si ve t o cis p lati n. T h i s fi nd i ng va li d ate d t h e f o c u s on cis p lati n -resista n t pr ecli n i ca l m ode l s t o i den tif y n ew acti v e m o lec u les . O x ali p lati n is a pprov e d f o r t he tr ea tm en t o f a dv a n ce d c o l o rectal ca n ce r , a nd e nh a n ces c ur e r at es i n t he ad j uvan t se tt ing. T h e t h era p e u tic r o le o f ox ali p lati n h as b ee n found t o ex t end t o panc reatic , g astric , a nd es oph a g eal ca n cers , i n al l of wh ic h it i s t he m o r e ac ti ve p lati nu m d eri v ati v e . N e d a p lati n and L obap l a ti n N e d a p lati n i s c i s - d i a mmi neg l y c o lat op lati nu m , d e v el op e d as a less n e phro t ox i c second - gene r a ti on p lati nu m a n al og, h as b ee n s ho w n t o b e acti v e in a r ange o f t u m o r s s imilar t o t h at o f cis p lati n a nd car bop lati n . As a d iammi ne s tr uc t u r e, nedap lati n w ou l d fall am ong t h e cis p lati n a n al og s a n al y ze d i n t he NC I 60 ce ll li n e scree n a nd t h is acti v it y is t h eref o re a n tici p a ted. L obap l a ti n i s a p l a ti nu m (II) c o m p le x i n w h ic h t h e lea v i ng group is l ac ti c ac i d and t he s ta b le ammi n e li g a nd is 1,2 - b is ( ami no m e t hy l) cyc l obu t ane. I n a similar wa y t o ox ali p lati n t h e sta b le

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ammi n e li gand m ay convey so me non– cr o ss-resista n ce c o m p are d t o cis p latin o r ca r bop l a ti n. It i s l i ce n se d i n C h i n a f o r t h e b reast ca n ce r , sma ll -cell l ung cance r , and ch r on i c m y el og e nou s le uk emia . It is un i qu e am ong t h e p lati nu m d r ugs f o r it s app r ov al f o r b reast ca n ce r , bu t t h ere are few pub lis hed c li n i ca l da t a and no ra ndo mize d trials . It h as no t ac h ie v e d a pprov a l i n t he Un it ed St a t es o r E u r op e . N e w e r Pl a ti nu m Str uc t u r es Th e o ct ahed r a l s t e r eoche mi s tr y a dop te d by p lati nu m (IV) c o m pound s h a s le d i nv e s ti ga t o r s t o specu l a t e th at t h e y ma y e xh i b it a d i f fere n t s p ectr u m o f acti v it y t han t ha t o f p l a ti nu m (II) d r ug s . T w o c o m pound s t h at were teste d cli n icall y w it hou t m uch succe ss are o rma p lati n a nd i p r op lati n. T w o o t h e r p lati nu m (I V ) co m pounds t hat e xh i b it nov el str u ct u ral feat u res , satra p la tin (pr e v i ous l y JM216 ) and JM335 ( tra n s-ammi n e[ cyc l ohexy l a mi ne ] d ic h l o r od i hyd r oxo p lati nu m [IV]) , und erwe n t m or e limit ed deve l op m en t . Satra p lati n was t h e first o rall y acti v e p lati nu m c o m pound, and showed so m e acti v it y i n l ung a nd ov aria n ca n cers , bu t d es p ite p r o mi s i ng ac ti v it y i n p r o state ca n ce r , a ph ase III trial was no t s u ccess fu l An a pproach based on t he che mistr y o f t h e p lati nu m-DNA i n teracti on le d t o d esi gn and syn t hes i s by F ar rell et al . o f a nov el class o f c o m pound s c on tai n i ng m u lti p l e p l a ti nu m at o ms (see . T h ese b i- a nd tri nu cl ea r st ru ct ures f o rm adduc t s t ha t sp a n g reater d ista n ces acr o ss t h e mi no r g r oove of DNA and have a p r o fil e o f cell k ill t h at d iffers fr o m t h at o f t h e small m o lec u l es. T hese co m pounds are un i qu e i n t h at t h eir i n teracti on wit h DN A is c on si de r ab l y d i f f e r en t fr om t h at o f cis p lati n, p artic u larl y i n t h e a bund a nce o f i n t e r s tr and c r os s-li nk s f o rme d. Cli n ical d e v el op me n t o f ca nd i d a te co m pounds i s a t a p relimi n ar y sta g e . E f for ts have been m ade t o de si gn nov el p lati nu m a n al og s t h at ca n ci r c u m ven t pu t a ti ve c i sp l a ti n r esista n ce mec h a n isms . A n e x am p le is cis-ammi n e d i ch l o r o ( 2 -m e t hy l py ri d i n e) p lati nu m (II) (als o kno w n as AMD 4 7 3 a nd ZD0473 ) . T h i s co m pound is a stericall y h i nd ere d p lati nu m c o m p le x t h at w as des i gned t o have mi n imal reacti v it y wit h t h i o ls a nd t hu s a vo i d i n acti v a t i on by m o l ecu l es such as g l u tat h i on e . , Res pon ses were

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i d e n ti f ie d w it h it s use i n t he cl i n ic , bu t d e v el op me n t was c u rtaile d b ase d on l ow le ve l s o f ac ti v it y . T he r e ce n t d escri p ti on o f a m ono f un cti on al p lati num (II) a n al og, phenan t h ri p l a ti n, fr o m t h e la b o f Li pp ar d is po te n tiall y o f g r eat i n te r est , based on bo t h po t ency i n v itr o a nd a mec h a n istic p r o file d i f feren t fro m e xis ti ng ana l ogs A r en ewe d a pp reciati on t h at c h em o t h era p e u tic drug s have a con ti nu i ng r o l e i n ma n a g i ng ca n cer is li k el y t o p r o m p t a dd iti ona l c li n i ca l deve l op m en t o f nov el p lati nu m str u ct u res . M E C HAN IS M O F AC TI ON DNA Adduc t F o rm a ti on DNA h a s l ong been t hough t t o b e t h e maj o r t h era p e u tic tar g et f o r p lati num c o m pounds. T he cy t o t ox i c e f fects are d etermi n e d, i n p art , by t h e str u ct u r e a nd r ela t i ve a m oun t o f DNA addu cts f o rme d. Cis p lati n a nd its a n al og s r eact pr e f e r e n ti a ll y a t t he N7 pos iti on o f gu a n i n e a nd a d e n i n e resi du es t o f o rm a v a r iet y o f m ono f unc ti ona l and b if un cti on al a ddu cts T h e m ono a ddu ct s ma y form i n tr as tr and o r i n t e rstra nd cr o ss-li nk s . T h e p re do mi n a n t lesi ons t h at a r e fo rm ed when p l a ti nu m c o m pound s b i nd DNA are d (G p G)Pt i n t r ast r a nd c r oss -li nks. C i sp lati n als o f o rms i n terstra nd cr o ss-li nk s b etwe en gu a n i n e r es i dues l oca t ed on oppo site stra nd s , a nd t h ese acc oun t f o r less t h a n 5% o f t he t o t a l DNA - bound p lati nu m . T h e f o rmati on o f a ddu cts a nd c ro ss - lin ks has been assoc i a te d wit h t h era p e u tic efficac y T h ese a ddu cts m ay con tri bu t e t o t he d r ug ’ s c y t o t ox icit y b eca u se t h e y im p e d e ce r tai n ce ll u l a r p r ocesses t ha t re qu ire t h e se p arati on o f bo t h DNA stra nds, s u c h as rep li ca ti on and tr ansc ri p ti on. T h e a ddu cts f o rme d i n t h e reacti on b et w ee n ca r bop l a ti n and DN A i n c u lt u re d cells are esse n tiall y t h e same as t ho se of c i sp l a ti n ; howeve r , h i gh er c on ce n trati on s o f car bop lati n are r e qu i r e d ( 20 - t o 40 -f o l d f o r c ells) t o ob tai n e qu i v ale n t t o tal p lati nu m-D NA a ddu ct l eve l s due t o it s s l owe r rate o f a qu ati on . O x ali p lati n i n trastra nd a ddu cts f o rm even m o r e s l owly du e t o a sl o wer rate o f c onv ersi on fr o m m ono a dduc t s ; howeve r , t hey are f o rme d at similar DNA se qu e n ces a nd r e g i on s as c i sp l a ti n adduc t s. At e qu it ox ic do ses , ox ali p lati n f o rms fewer DNA a dduc t s t han does c i sp l a ti n. T h is h as b ee n i n ter p rete d t o mea n t h at ox ali p lati n l es i ons a r e m o r e cy t o t ox ic t h a n t ho se f o rme d by cis p lati n.

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Th e d i f f er ences obse r ved i n cy t o t ox icit y b etwee n t h e d iammi n e (e .g., cis p latin , ca r bop l a ti n ) and DA CH p lati nu m c o m pound s ma y no t d e p e nd on t h e t yp e and r e l a ti ve a m oun t s o f t h e a ddu cts f o rme d, bu t on t h e ov erall t hr ee -d i mens i ona l s tr uc t u r e o f t h e a ddu ct a nd its rec ogn iti on by v ari ou s cell u la r p r o t e i ns. T he m a j o r d i f fere n ce b etwee n t h em is t h e p r o tr u si on o f t h e DACH m o i e t y o f oxa li p lati n i n t o t h e maj o r g r oov e o f DNA , w h ic h th us produ ces a bu l k i e r adduc t t han t h at o f cis p lati n. T h is bu l k ie r , m o re hydroph o b i c adduc t see m s t o b e rec ogn ize d d i f fere n tl y by cell u lar p r o te ins i nvo l v e d i n sens i ng DNA da ma g e . T h e f un cti on al c on se qu e n ces are t wofo l d: Pr o t e i ns such as po l y merases t h at rec ogn ize a nd p artici p ate i n r eacti ons on DNA unde r no rmal circ u msta n ces ma y b e p ert u r b e d, w h er eas pro cess es t ha t a r e con tr o ll ed by p r o tei n s t h at rec ogn ize d ama g e d DNA m ay b ec o me ac ti va t ed (t he DNA d ama g e res pon se) . T h e latter g r oup o f p r o t eins fun cti on bo t h i n t he DNA r ep air p r o cess a nd i n cell u lar si gn ali ng t o war d cell s urv i va l/ dea t h dec i s i ons. DNA In t e r s tr and C r oss -Li nk s A lt hough t he DNA adduc t s ar e well-rec ogn ize d t o res u lt i n G-G i n terstr and c ro ss - lin ks, li ke c l ass i ca l a l ky lati ng a g e n ts , p lati nu m d r ug s h a v e t h e ca p acit y t o f o rm i n tr as tr and cro ss-li nk s , al b eit t o a lesser d e g ree . B y b l o c k i ng essen ti a l aspec t s o f D NA meta bo lism , s u c h as re p licati on a nd t r a n sc r i p ti on, i n tr as tr and c r os s-li nk s are h i gh l y c y t o t ox ic . Rece n t st ud ie s h a v e drawn a tt en ti on bo t h t o t h e c y t o t ox icit y o f t h ese lesi on s , a nd t h eir d i f f e r i ng m echan i s m s o f r epa i r , bo t h re p licati on d e p e nd e n t a nd i nd e p e nden t . , T hese s t ud ies ma y h a v e cli n ical im p licati on s i n select ing p atie n ts f o r t he r apy based on th e re p air c o m p ete n ce o f t u m o rs . C ELLU L AR R ESP ON SES T O PL A TINUM-INDUCED DNA DAMA GE M u lti p l e ce ll u l a r ou t co m es ma y f o ll o w t h e f o rmati on o f p lati nu m-DNA a ddu cts , i nc l ud i ng ce ll dea t h by a pop t o sis , n ecr o sis , o r mit o tic catastr ophe, or cell s u r v i va l by ac ti va ti on o f v ari ou s p r o tecti v e mec h a n isms i n cl ud i ng DNA r e pa i r , DNA da m age s i gn ali ng p at h wa y s , cell c y cle arrest , a nd a u t oph a gy (t he l as t m ay have a du al r o le , po ssi b l y c on te x t d e p e nd e n t) . Cell F ate

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Th e cell u l a r e f f ec t s f o ll ow i ng DNA b i nd i ng by p lati nu m d r ug s h a v e b ee n a n al y ze d. T he s t ud i es o f S o r en s on a nd Eastma n , u si ng DNA re p ai r - d e f icie n t Ch i nese ha m s t e r ov ar y (CHO) cells , i nd icate d t h at p assa g e t hrough t he S phase i s necessa r y f o r G 2 arrest a nd cell d eat h, w h ic h s ugg est s t ha t DNA r ep li ca ti on on a d ama g e d tem p late ma y res u lt i n t h e acc u m ula ti on o f f u rt he r da m a ge . A n a b erra n t mit o sis was ob ser v e d b ef o r e a pop t o s is i n t h i s m ode l . DNA D am age Recogn iti on A m ong t he i n iti a ti on even t s t h at u ltimatel y res u lt i n p lati nu m d r ug– i ndu c ed cell d eat h a r e t he b i nd i ng o f p lati nu m-DNA d ama g e rec ogn iti on p r o tei ns, wh ic h t hen seed t he accu m u l a ti on o f a lar g e p r o tei n c o m p le x ca p a b le both of DNA da m age s i gna li ng ( as t o cell c y cle p r o tei n s t o h alt re p licati on ) a nd r e p ai r o f t he da m aged DNA. Am ong t h e DNA- b i nd i ng p r o tei n s are t h e h i gh- mo b ilit y g r oup p r o t e i ns HMG 1 a nd HMG 2 T h ese p r o tei n s ar e ca p a b le o f bend i ng DNA as well as rec ogn izi ng b e n t DNA str u ct u res , s uch as t h at p r oduced by c i sp l a ti n, a nd d i f fere n t s p ecificities f o r cis p lati n a nd f o r ox ali p lati n adduc t s a r e obse rve d i n str u ct u ral st ud ies . Ot h er ca nd i date p lati nu m- DNA da m age r eco g n iti on p r o tei n s i n cl ud e h ist on e H 1, RNA po l y me r a se I tr ansc ri p ti on up stream b i nd i ng fact o r ( h UBF) , t h e T A T A b i nd i ng p r o t e i n (T B P) , and pro tei n s i nvo l v e d i n mismatc h re p air (MMR ). Th e M MR co m p l ex has been im p licate d i n cis p lati n se n siti v it y . St ud i es h a v e s hown t ha t t he M S H2 and MLH 1 p r o tei n s p artici p ate i n t h e r ec ogn iti on o f DNA adduc t s fo rme d by cis p lati n, bu t no t ox ali p lati n, w h i ch c ou l d c on tri bu t e t o d i f f e r ence s i n t h e c y t o t ox icit y p r o files ob ser v e d b et w ee n t hese t wo p l a ti nu m c o m p le x es . DNA D am age Si gna li ng A nu m be r o f s i gna li ng even t s h a v e b ee n s ho w n t o o cc u r after treatme n t o f cells w i th p l a ti nu m d r ugs . F o r e x am p le , t h e A TM- a nd Ra d3 -relate d ( A T R ) pro t e i ns t ha t a r e i nvo lve d i n cell-c y cle c h ec kpo i n t acti v ati on are acti v ate d by c i sp l a ti n. T hese k i n ases pho s pho r y late a nd acti v ate se v eral down st rea m e f f ec t o r s t ha t r egu late cell c y cle , DNA re p ai r , cell s u r v i v al , a nd a pop t os i s, i nc l ud i ng p53, CHK 2, a nd mem b ers o f t h e mit og e n -acti v ate d p r o t e i n k i nase ( MA PK) p at h wa y (e x tracell u lar si gn al-relate d

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k i n ase [ E RK ] , c - Jun a mi no -termi n al k i n ase [JNK] , a nd p38 k i n ase) . Rec ent d ata es pec i a ll y im p li ca t e s i gna li ng t h r ough t h e JNK p at h wa y , a nd i nh i b i tion at t h e lev e l o f JNK see m s esp eciall y rele v a n t t o p lati nu m d r ug c y t o t ox ic ity i n v it ro a nd i n v i vo T he plei o tr op ic n at u re o f t h is stress res pon se only grow s , because each o f t hese mo lec u les s ub se qu e n tl y c on tr o ls t h e acti v i ty a nd e xpress i on o f m any m o r e p r o tei n s . As a res u lt o f t h is c o m p le x it y , acti ng i n t he con t ex t o f va ri ab le g e no mic t u m o r a b errati on s , t h era p e u tic st r ate g ie s d ir ec t ed t o t hese pa t h wa y s h a v e b ee n sl o w t o eme r g e . H o we v e r , cli n ical tri a l s t o i nves ti ga t e sp ecific i nh i b it o rs o f DNA d ama g e res pon se s a r e unde r way and ho l d p r o mise . It is als o rele v a n t t o po i n t ou t t h at t h ese si gn ali ng pa t hways a f f ec t no t j u st t h e t u m o r cell , bu t als o ma y c o mm un i ca t e t o ce ll s i n t he micr o e nv ir on me n t , t h e res pon ses o f w h ic h may als o d et e rmi ne t he e f f ec ti ven ess o f t h era p y . IS DNA T H E ON L Y T ARGE T? E a r l y an a l yses o f t he ac ti on of c y t o t ox ic d r ug s i n cl ud e d a p r ob e o f w h et he r e f f ects on DNA we r e su f fi c i en t t o e xp lai n d r ug e f fects . A p i on eer i n t h is f iel d w a s T ritt on, who p r opo se d t h at e f fects o f DNA-i n tercalati ng a g e nts on t h e p l as m a m e m b r ane cou l d und erlie t h e c y t o t ox icit y o f t h e d r ug. M o r e r ece n tl y , enuc l ea t ed ce ll s we r e s ho w n t o b e s u sce p ti b le t o cis p lati n, a nd a semi n al pape r fr o m V oes t and c o llea gu es s ho we d t h at p lati nu m se n siti v i ty w as d et e rmi ned no t so l e l y by t h e acc u m u lati on o f DNA d ama g e i n t h e t u m or c e ll . I n ana l yz i ng t he c on tri bu ti on o f cells i n t h e micr o e nv ir onment of t u m o r s, he showed t ha t t umo r i n filtrati on wit h mese n c hy mal stem cell s c ou l d c on f e r d r ug r es i s t ance. A searc h f o r secrete d fact o rs d efi n e d p lati nu m-i nduced f a tt y ac i ds, meta bo lic p r odu cts i n t h e t h r o m box a n e s yn t h eta se, and cyc l ooxygen ase- 1 p at h wa y s as d etermi n i ng t h e e f f ecti veness o f d r ug t he r ap y . A p r o te o mic st udy i n cis p lati n -se n siti v e a nd r esista n t ce ll s con firm ed t he s ub sta n tial effects o f d r ug e xpo s u re on li p i d meta bo lit es and t he ir r e l a ti on t o s u sce p ti b ilit y . A c u rre n t f o c u s on t h era pies d i r ecte d t o t he mi c r oenv ir on me n t , i n cl ud i ng imm uno l og ic a nd a n ti-i nf lam ma t o r y i n t e r ven ti ons h as t h e po te n tial t o e xp a nd ou r a b ilit y t o a pp l y p l a ti nu m d r ugs i n t he c li n ic . M E C HAN IS M S O F R ESIS T ANCE

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Th e maj o r limit a ti on t o t he su ccessf u l treatme n t o f s o li d t u m o rs wit h p lati nu m- based che m o t he r apy is t h e emer g e n ce o f d r ug -resista n t t u m o r cells . Deve l op m en t s i n t u mor b i o l ogy h a v e a dv a n ce d ou r t h i nk i ng wit h r e g a rd t o how and when t hese cells eme r g e; h eter og e n eit y wit h i n a t u m o r e v e n at i t s ea rli es t d i agnos i s reflects t h e eme r g e n ce o f treatme n t-resista nt cl on es e ven i n advance o f se lecti on p ress u re a nd t h e realizati on t h at r esista nce m ay no t be spec ific t o t h e DNA- d ama g i ng d r ug. I nd ee d, t h is ma y b e re fl ec t ed c li n i ca ll y i n t h e fi nd i ng t h at after p r og ressi on on i n itial c h em o t he r ap y , t he use o f second -li n e t h era py is u s u all y ass o ciate d wit h a s hor te r du r a ti on o f r esponse. C urr e n tl y desc ri bed m echan i s ms o f p lati nu m d r ug resista n ce ( i n cl ud e r educed ce ll u l a r accumu lati on, i n tracell u lar d et ox ificati on, re p air o f Pt -DNA l es i ons, i nc r eased da ma g e t o lera n ce , a nd t h e acti v ati on o f cell ula r d e f e n se m echan i s m s such as a u t oph a g y . I n a dd iti on, we h a v e alrea dy all ud e d t o exogenous i n fl uenc es on mec h a n ism , as ma y b e me d iate d by o t h e r ce l l s, m e t abo lit es, o f phy sic o c h emical c ond iti on s (s u c h as hypox ia) in t h e t u m o r mi c r oenv ir on m en t . It m u st b e ac kno wle dg e d, ho we v e r , t h at ou r i n si gh ts a r e ve r y limit ed as t o w hy s o me t u m o rs res pond a nd o t h ers do not t o p lati nu m che m o t he r ap y . As g e no me se qu e n ci ng y iel d s i n creasi ng a nd of te n s urp ri s i ng r eve l a ti ons abou t t h e g e n es t h at d ri v e ca n cers a nd t h e c o m p le x it y i nhe r en t i n cancer s o f a si ng le h ist o l og ic t yp e , it is li k el y t h a t wh e n as soc i a t ed w it h ou t co m e s i n la r g e p atie n t popu lati on s , p atter n s wi ll eme r g e t o gu i de se l ec ti on o f t h era p ies . Re du ce d Accu m u l a ti on Plati num up t ake i n ce ll s occu rs by sim p le d iff u si on a nd by carrie r -me d i ated mec h a nis m s. I nh i b iti on o f tr an s po rt mec h a n isms h as a mar k e d e f fect on i n t r acell u l a r p l a ti nu m accu m u lati on, a nd H o well ’ s g r oup h as s ho w n t h e im por ta nce o f t he coppe r tr anspo rters CTR- 1 a nd CTR- 2 i n re gu lati ng th e i nf l ux o f va ri ous p l a ti nu m an al og s i n e uk ar yo tic cells . T h e c on t r i but i on o f t hese m echan isms t o cli n ical p lati nu m d r ug resista n ce is b ei ng e xp l o r ed Accu m u l a ti on ma y als o b e i n fl u e n ce d by e nh a n ce d

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e f f l ux, a nd va ri ous tr anspo rt p r o tei n s are up re gu late d i n cell li n es selecte d for ac qu ir ed r es i s t ance, and i n p lati nu m-resista n t ov aria n ca n cers . In acti v a t i on Plati num co m p l exes a r e h i gh l y reacti v e m o lec u les a nd b i nd ra p i d l y t o m u lti p le ce ll u l a r m ac r o m o l ec ules . Pr o tecti on fr o m s u c h c h emicals i n t he e nv i ron m en t i s a f f o r ded by c ell u lar t h i o ls , i n cl ud i ng small p e p ti d es s u c h as g l u tat h i one ( G S H ) and l a r ge r p r o tei n s as e x em p lifie d by metall o t h i on ei n ( M T). The r e a r e m any r epo rts o f a n ass o ciati on b etwee n p lati nu m d r ug se n siti v it y and g l u t a t h i one l ev el s – ; ho we v e r , re du ci ng i n tracell u lar g l u tat h i one l eve l s w it h d r ugs su c h as bu t h i on i n e s u lf ox imi n e h as res u lte d in on l y l ow t o m odes t po t en ti a tio n o f cis p lati n se n siti v it y . B u t h i on i n e s u l fox imi ne was deve l oped f o r cli n ical u se , a nd s o me im p act on GSH c on te n t o f t u m o r s and no rm a l tiss u es was d em on strate d. H o we v e r , t h e d e p leti on o f G S H was no t co nsiste n t , a nd u ltimatel y , t h e c o st o f p r odu ci ng t h e activ e s t e r eo i so m e r o f t he d r ug was j udg e d p r oh i b iti v e . I n acti v ati on o f t h e p lati nu m d r ugs m ay a l so o cc u r t h r ough b i nd i ng t o t h e M T s , a famil y o f s u l fhydry l-ri ch, l ow– m o l ecu la r -wei gh t p r o tei n s t h at p artici p ate i n h ea vy metal b i nd i ng and de t ox ifi ca ti on ; ho we v e r , t h e c on tri bu ti on o f MT t o cli n ical p l a ti nu m d r ug r es i s t an ce is un clea r , a nd a t h era p e u tic r o le h as not eme r g e d. In c r ease d DNA Repa ir On ce p lati nu m- DNA adduc t s are f o rme d, cells m u st eit h er re p air o r t o ler ate t h e d am age t o su r v i ve. I n gen eral , t h e ca p acit y t o re p air DNA d ama g e seems t o p l ay a r o l e i n de t e rmi n i ng a t u m o r cell ’ s se n siti v it y t o p lati nu m drug s a nd o t he r DNA - da m ag i ng a g e n ts . F o r e x am p le , t u m o rs t h at are unu s u al ly sens iti ve t o c i sp l a ti n, s u c h as testic u lar non semi no mat ou s g erm cell t u m o r s, m ay be de fi c i en t i n t h eir a b ilit y t o re p air p lati nu m-DNA a ddu cts T he i nc r eased r ep air o f p lati nu m-DNA lesi on s i n cis p lati n - r esista n t ce ll li nes as co m pa r ed t o t h eir se n siti v e c oun ter p arts h as b ee n s hown i n seve r a l hu m an cance r cell li n es , bu t tra n slati on o f t h ese ob se rv ati ons t o t he c li n i c has b ee n d i f fic u lt . T h e re p air o f p lati nu m-DN A a ddu cts appea r s t o occu r p r edo mi n a n tl y by nu cle o ti d e e x cisi on re p air (NE R ), wit h a r o l e f o r MMR und er certai n circ u msta n ces . T h e m o lec ula r

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In g ast r i c cance r a l so, h i gh l e vels o f ERCC 1 are ass o ciate d wit h resista nce t o cis p lati n tr ea tm en t . – Ho we v e r , a rece n t ree v al u ati on o f d iscre p a n t r es u lts q ues ti oned t he r e li ab ilit y o f t h e assa y s o f ERCC 1 a nd t h eir r elati onsh i p t o f unc ti on . T h ese d ata s ugg est t h at t h ere is a relati on s h i p b et w ee n E RCC1 exp r ess i on a nd treatme n t , bu t t h at t h e la g i n mar k er d e v el opmen t p r ec l udes im p l em e n tati on o f a p re d icti v e assa y un til a dd iti ona l s t ud i es have been perf o rme d. Pe rh a p s t he m os t s tri k i ng ev i d e n ce t h at DNA re p air is a d etermi n a n t o f p lati nu m d r ug r esponses i s t ha t b reast a nd ov aria n ca n cers o cc u rri ng i n BRC A1 o r BRCA2 m u t a ti on c arriers are p artic u larl y res pon si v e t o cis p l atin or ca rbop l a ti n. T hese cance r s are als o se n siti v e t o i nh i b it o rs o f po l y (AD P - r i bo se )po l y m e r ase ( P AR Pi) , se v eral o f w h ic h are c u rre n tl y i n cli n ical d e v el opmen t . T he m echan i s m o f t h e se n siti v it y t o P ARPi h as b ee n el u ci d ate d. Bo t h t he BRCA1 a nd 2 p r o tei n s f o r p art o f t h e ho m o l ogou s r ec o m b i na ti on r epa ir ( HR ) sy stem t h at ac h ie v es err o r-free re p air o f double st r a nd breaks. Ca rri e r s a r e het er o z ygou s a nd, t h eref o re , h a v e no rmal re pai r fun cti on, bu t l oss o f t he second allele lea d s t o t h e u se o f err o r- p r on e b ac kup s y stems and i s t he r e f o r e oncog e n ic . T h e ca n cers t h at arise are un a b le t o p e rfor m HR and, t he r e f o r e, a re se n siti v e t o d r ug s t h at i ndu ce si ng le stra nd br ea k s , s uch as P AR Pi A mec h a n ism o f resista n ce t o P ARPi h as b e en d esc r i b e d, wh i ch i s due t o r e acti v ati on o f t h e f un cti on o f t h e BRCA 2 lea d i ng t o r es t o r a ti on o f HR a nd se n siti v it y t o P ARPi . T h is reacti v ati on is acc o m pl i shed by an i n tr agen ic d eleti on a nd t h e rest o rati on o f a n op e n r ea d i ng fr a m e. It has f u rt he r b ee n s ho w n t h at s u c h re v erta n t cells are r esista n t t o c i sp l a ti n as we ll a s P ARPi . Fi n all y , rec u rre n t ca n cers i n BRC A2

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s how i ng t ha t t he r e a r e m u lti p le o t h er ca u ses o f cis/car bop lati n resista n c e. C o m b i na ti ons o f p l a ti nu m d ru g s wit h P ARPi are b ei ng acti v el y pu rs u e d in p atie n ts w it h BRCA -r e l a t ed tum o rs a nd als o i n p atie n ts w ho se t u m o rs ar e li k el y t o have acqu ir ed l oss of HR f un cti on ( poo rl y d iffere n tiate d ser ou s ov a r ia n cance r and tri p l e nega ti v e b reast ca n cer) . Au t ophagy Af te r p lati nu m- DNA adduc t f o rmati on, t h e cell d etects t h e DNA d ama ge a nd i n iti a t es s i gna li ng t h r ough m u lti p le p at h wa y s , t h e e f fects o f w h ic h i n cl ud e m ob ili za ti on o f r epa ir p r o tei n s; arrest o f t h e cell c y cle; altere d t r a n sc r i p ti ona l p r og r a m s ; r edi recti on o f e n er gy p r odu cti on a nd c on s u m p ti on ; ac ti va ti on o f cel l d eat h p at h wa y s a nd, sim u lta n e ou sl y , o f p at hw ay s t ha t wou l d coun t e r a cell d eat h d ecisi on, a nd s o t o p ermit s urv i v al . A p r ocess r ecen tl y ch aracterize d t o p erf o rm t h e last f un cti on is a u t oph a g y . I n iti a ll y desc ri bed as a mec h a n ism o f cell d eat h, a u t oph a gy r e pr ese n t s a r egu l a t ed d i sso l u ti on o f cell u lar eleme n ts i n t o a c h aracterist ic set of s u b ce ll u l a r o r gane ll es d etecta b le by electr on micr o sc opy a nd li nked by a p a r ti cu l a r p r o fil e o f gen e e xp ressi on c h a ng es . M u lti p le stim u li pr eci p it a t e t hese changes and h a v e i n c o mm on scarcit y o f nu trie n ts t h at ar e r e qu i r e d f o r su r v i va l , fr o m o x yg e n a nd g l u c o se wit hd rawal t o less s p ecif ic cal or ie dep ri va ti on, and i nh i bi ti on o f meta bo lic p at h wa y s . A u t oph a gy is als o a c onsequence o f cy t o t o xic d r ug treatme n t a nd, m o re rece n tl y , h as b ee n a pp r ec i a t ed as a m eans by w h ic h cells mi gh t s u r v i v e t h e stress o f cell u la r i nsu lt s, and so beco m e resista n t t o treatme n t . Amara v a d i a nd c o llea g u e de m ons tr a t ed t h at a u t oph a gy re v ersal ca n se n sitize t u m o rs to c y t o t ox i c d r ugs and seve r a l trials o f p lati nu m c o m pound s al ong wit h t h e a u t oph a gy i nh i b it o r hyd r oxy c h l o r oqu i n e are i n p r og ress . In c r ease d DNA Da m age T o l e ra n ce

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Th e n et r esu lt o f DNA da m ag e si gn ali ng i n a se n siti v e t u m o r cell is e ng a g em en t o f ce ll dea t h pa t h wa y s , i n cl ud i ng a pop t o sis , a nd t h era p e u ti c b e n e f it . I n a r es i s t an t t u m o r c ell , t h e cell s u r v i v es as a c on se qu e n ce o f one or ma ny o f t hese m echan i s ms , a nd t h is ca n res u lt i n p lati nu m-DNA d am age t o le r a n ce o r m u lti d r ug r es i s t an ce ph e no t yp e , o r bo t h. C on tri bu t o rs t o t he t o le r a n ce mi gh t i nc l ude de fi c ie n t DNA MMR (w h ic h c ou l d e x cise t h e a ddu ct if N E R f a il ed ) , enhan ce d re p licati v e byp ass (w h ic h esse n tiall y i gnor es t he adduc t , a ll ow i ng the cell t o s u r v i v e , bu t c ou l d c on tri bu te t o t he i n c r ease i n m u t a ti on fr equency ob ser v e d i n c h em o t h era py -treate d ca n cer s ) , a nd alte red s i gna li ng t h r ough stress-relate d k i n ases s u c h as JNK , w h ic h can bo t h alt e r tr ansc ri p ti ona l p r o grams a nd acti v ate a u t oph a g y . I nd ee d JNK , by pho s ph or y l a ti ng Bc l- 2 o r Bc l-XL , a nd releasi ng b ecli n - 1 fr o m i nh i b iti on, acts as a key sw it ch t o t u r n on a u t oph a g y . T h e e nh a n ce d DNA d ama g e t o le r a n ce , i n add iti on t o pe rmitti ng p ersiste n ce o f t h e ca n cer cell , ma y have a n a dd iti ona l de l e t e ri ous e f f ec t by f o steri ng f u rt h er m u ta g e n esis wit h i n t he t u m o r , f a c ilit a ti ng it s evo l u ti on t o a m o re mali gn a n t ph e no t yp e . C LINI CAL P HARMACO L O GY P h a r ma cok i ne ti cs Th e ph arm acok i ne ti c d i f f e r en ces ob ser v e d b etwee n p lati nu m d r ug s ma y be att r i bu te d t o t he s tr uc t u r e o f t h eir lea v i ng g r oup s . Plati nu m c o m p le x es c on tai n i ng l eav i ng g r oups t hat are less easil y d is p lace d e xh i b it re du ce d p lasma p r o t e i n b i nd i ng, l onge r p lasma h alf-li v es , a nd h i gh er rates o f re nal clea r a n c e. T hese f ea t u r es a r e e v i d e n t i n t h e ph armac ok i n etic p r op erties o f cis p latin , ca r bop l a ti n, and oxa li p lati n, w h ic h are s u mmarize d i n Plati num d r ug pha rm acok i net ics h a v e b ee n re v iewe d . Cis p latin Af te r i n tr avenous i n f us i on, c is p lati n ra p i d l y d iff u ses i n t o tiss u es a nd is c ov ale nt l y bound t o p l as m a p r o tei n. M o re t h a n 90 % o f p lati nu m is bound t o p las ma p r o t e i n a t 4 hou r s af ter i n f u si on. T h e d isa pp eara n ce o f u lt r a f ilt e r ab l e p l a ti nu m i s r ap i d a nd o cc u rs i n a b i ph asic fas h i on. Half-li ves of 10 t o 30 mi nu t es and 0.7 t o 0.8 hou rs h a v e b ee n re po rte d f o r t h e i n iti al

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a nd te r mi na l phases, r espec ti v el y . Cis p lati n e x creti on is d e p e nd e n t on re nal fun cti on, wh i ch accoun t s f o r t h e maj o rit y o f its elimi n ati on. T h e p erce n ta ge of p lati nu m exc r e t ed i n t he u r in e h as b ee n re po rte d t o b e b etwee n 23 % and 40% at 24 hou r s a ft e r i n f us i on. O n l y a small p erce n ta g e o f t h e t o tal p lati nu m i s exc r e t ed i n t he b i l e . Ca rbop lati n Th e d i f f er ences i n pha rm acok i n etics ob ser v e d b etwee n cis p lati n a nd ca rbop l a ti n depend p rim a ril y on t h e sl o wer rate o f c onv ersi on o f ca rbop l a ti n t o a r eac ti ve spec ies . T hu s , t h e sta b ilit y o f car bop lati n res u lt s in a l ow i nc i dence o f neph r o t ox icit y . Car bop lati n d i f f u ses ra p i d l y i n t o tiss ues a f te r i nf u s i on ; howeve r , it i s c on si d era b l y m o re sta b le i n p lasma . O n l y 24 % of a do s e was bound t o p l as m a p r o tei n at 4 hou rs after i n f u si on. T h e d isa pp e a r ance o f p l a ti nu m fr o m p lasma after s ho rt i n tra v e nou s i n f u si ons o f ca rbop l a ti n has been r epo rt ed t o o cc u r i n a b i ph asic o r tri ph asic ma nn e r . Th e i n it ia l ha lf-li ves f o r t o t a l p lati nu m , w h ic h v ar y c on si d era b l y am ong se v e r al s t ud i es, a r e li s t ed i n T h e h alf-li v es f o r t o tal p lati nu m r a ng e fro m 12 t o 98 mi nu t es d u ri ng t h e first ph ase ( T 1/2 α ) a nd fr o m 1.3 to 1.7 hour s du ri ng t he second ph ase ( T 1 / 2 β) . Half-li v es re po rte d f o r t h e te r mi n al phase r ange fr o m 8.2 t o 40 hou rs . T h e d isa pp eara n ce o f u lt r a f ilt e r ab l e p l a ti nu m i s b i ph asic wit h T 1/2 α a nd T 1/2 β v al u es ra ng i ng fro m 7.6 t o 87 mi nu t es and 1.7 t o 5.9 hou rs , res p ecti v el y . Car bop lati n is e x c r ete d p r edo mi nan tl y by t h e k i dn e y s , a nd c u m u lati v e u ri n ar y e x creti on o f p lati nu m i s 54 % t o 82 % , m os t as un m od ifie d car bop lati n. T h e re n al clea r a n c e o f ca r bop l a ti n i s c l o sel y c o rrelate d wit h t h e g l o mer u lar filtrati on r ate (G F R ) T h i s obse r va ti on e n a b le d Cal v ert et al . t o d esi gn a ca rbop l a ti n - dos i ng f o rm u l a ba se d on t h e i nd i v i du al p atie n t ’ s GFR . Ox ali p l a ti n Af te r o x a li p l a ti n i n f us i on, p lati nu m acc u m u lates i n t o t h ree c o m p artme n t s: p lasma -bound p l a ti nu m , u ltr af iltera b le p lati nu m , a nd p lati nu m ass o ciate d w it h e ry t h r ocy t es. When spec ific a nd se n siti v e mass s p ectr o metric tec hn i ques a r e used, oxa li p l a t in itself is und etecta b le i n p lasma , e v e n at end i nfu si on. T he ac ti ve f o rm s o f t h e d r ug h a v e no t b ee n e x te n si v el y c h a r acteri zed. App r ox im a t e l y 85 % o f t h e t o tal p lati nu m is bound t o p las ma

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pro tei n at 2 t o 5 hou r s a ft e r i n f u si on Plasma elimi n ati on o f t o tal p lati num a nd u lt r afilt e r a t es i s b i phas i c. T h e h alf-li v es f o r t h e i n itial a nd termi n al ph ases ar e 26 mi nu t es and 38.7 hou rs , res p ecti v el y , f o r t o tal p lati nu m a nd 21 mi nu t es and 24.2 hou r s, r e s p ecti v el y , f o r u ltrafiltera b le p lati nu m (see ) . T hus, as w it h car bop lati n, s ub sta n tial d iffere n ces b etwee n t o tal a nd fr ee p l a ti nu m k i ne tics are no t ob ser v e d. As wit h cis p lati n, a pro l onged r e t en ti on o f oxa li p lati n is ob ser v e d i n re d b l ood cells . H o we ve r , un li k e ci sp l a ti n, oxa li p l a ti n do es no t acc u m u late t o a ny si gn ifica n t le v el a f te r multi p l e cou r ses o f tr ea tme n t T h is ma y e xp lai n w hy n e u r o t ox ici ty ass o ciate d w it h oxa li p l a ti n i s re v ersi b le . O x ali p lati n is elimi n ate d pr e do mi nan tl y by t he k i dney s , wit h m o re t h a n 50 % o f t h e p lati nu m b ei ng e x c r ete d i n t he u ri ne a t 48 hou rs . P h a r ma codyna mi cs P h a r ma codyna mi cs r e l a t es ph armac ok i n etic i nd ices o f d r ug e xpo s u re t o b i o l og ic m easu r es o f d r ug e f fect , u s u all y t ox icit y t o no rmal tiss u es o r t umo r cell k ill . T wo i ssues t o be addr esse d i n s u c h st ud ies are w h et h er t h e e f f ecti veness o f t he d r ug can b e e nh a n ce d a nd w h et h er t h e t ox icit y ca n be atte nu ate d by know l edge o f t h e p lati nu m ph armac ok i n etics i n a n i nd i v i du al . T hese ques ti ons a re a pp r op riate t o t h e u se o f c y t o t ox ic a g e n t s w it h r el a ti ve l y na rr ow t he r apeu tic i nd ices . T ox icit y t o no rmal tiss u es ca n be qu a n titat ed as a con ti nuous v aria b le w h e n t h e d r ug ca u ses m y el o s upp r ess i on. T hus, t he e arl y st ud ies o f car bop lati n d em on strate d a cl o se r el a ti onsh i p o f changes i n p latelet c oun ts t o t h e area und er t h e c on ce n t ra ti on -tim e cu r ve ( A UC) i n t h e i nd i v i du al . T h e AUC was itself cl o sel y r e l a t ed t o r ena l f unc ti on, w h ic h was d etermi n e d as creati n i n e clea r a n c e. Based on t hese obs er v ati on s , E go ri n et al . , Cal v ert et al . a nd C h atel ut and co ll eague s der i v e d f o rm u las b ase d on creati n i n e cleara nce t o pr e d i c t e it he r t he pe r cen t ag e c h a ng e i n p latelet c oun t o r a ta r g et AUC. App licati on o f pha rm acodyn amicall y gu i d e d do si ng al go rit h ms f o r ca rbop l a ti n has been w i de l y adop te d as a mea n s o f a vo i d i ng ov er do sa g e (by pro d uc i ng accep t ab l e nad ir p latelet c oun ts) a nd o f ma x imizi ng do se i n te n sit y i n t he i nd i v i dua l . T he re is good e v i d e n ce t h at t h is a pp r o ac h ca n d ec r eas e t he ri sk o f unaccep ta b le t ox icit y . Acc o r d i ng l y , a do si ng strate gy b ase d on r ena l f unc ti on i s r eco mme nd e d f o r t h e u se o f car bop lati n.

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g e n es r el a t ed t o g l u t a t h i one meta bo lism a nd i n se v eral DNA re p air g e n es h a v e b e en i den tifi ed i n l ung can ce r , b reast ca n ce r , a nd v ari ou s GI ca n ce rs. A c on cer n i s t ha t l a r ge r tri a l s h a v e no t alwa y s c on firme d earl y fi nd i ng s . As y et , i nfor m a ti ve S N P s t ha t cou l d b e u se d t o d efi n e t h era p e u tic strate g ies f o r i nd i v i du al pa ti en t s have no t y et b ee n d efi n e d. F O RM U L A TI ON AND AD MINISTR A TION Cis p latin (Pl a ti no l) Cis p latin i s ad mi n i s t e r ed i n a c h l o ri d e-c on tai n i ng s o l u ti on i n tra v e nou sl y ov e r 0.5 t o 2.0 hou r s. T o mi n imize t h e ris k o f n e ph r o t ox icit y , p atie n ts ar e pr e hydr at ed w it h a t l eas t 500 mL o f salt-c on tai n i ng fl u i d. Imme d iatel y b e for e ci sp l a ti n ad mi n i s tr a ti on, ma nn it o l ( 12.5 t o 25.0 g ) is g i v e n p a r e n te ra ll y t o m ax imi ze u ri n e fl o w . A d i u retic s u c h as f u r o semi d e ma y be u se d also , a l ong w it h pa r en t e ral a n tiemetics . T h ese c u rre n tl y i n cl ud e d e x ame thasone t oge t he r w it h a 5 - hyd r oxy tr yp tami n e ( 5 -H T 3 ) a n ta gon is t. A mi n im um o f 1 L o f pos t hyd r at i on fl u i d is u s u all y g i v e n. T h e i n te n sit y o f hydr ati on va ri es so m ewha t w it h t h e do se o f cis p lati n. Hi gh - do se cis p lati n (up t o 200 m g /m 2 pe r cou r se ) ma y b e a d mi n istere d i n a f o rm u lati on c on tai n i ng 3 % sod i u m ch l o ride , bu t t h is met hod is no l ong er wi d el y u se d. Cis p latin m ay a l so be ad mi n i s tere d re g i on all y t o i n crease l o cal d r ug e xpo s ure and d imi n i sh s i de e f fects . Its i n tra p erit on eal u se was d efi n e d by O z o ls et a l . and by Howe ll and c o llea gu es Meas u re d d r ug e xpo s u re in t h e p e r it onea l cav it y i s so m e 50 -f o l d h i gh er c o m p are d t o le v els ac h ie v e d w it h i n tr avenous ad mi n i s tr a ti on. At sta nd ar d do sa g es i n ov aria n ca n cer p atie n ts w it h l ow - vo l u m e d i s ease , a ra ndo mize d i n ter g r oup trial s ugg est ed t h at i n t rape rit onea l ad mi n i s trati on is s up eri o r t o i n tra v e nou s cis p lati n i n c o m b i na ti on w it h i n tr avenou s c y cl opho s ph ami d e . T h e d e v el op me n t of c o m b i na ti ons o f ca r bop l a ti n and p aclita x el h as , ho we v e r , s up erse d e d t h i s tec hn i que i n t he tr ea tm en t o f ov aria n ca n ce r , a nd t h e i n tra p erit on eal r ou t e is now i nf r equen tl y used. Reg i on al u ses als o i n cl ud e i n tra-arterial d eli v er y ( as for h e p ati c t u m o r s, m e l ano m a, a nd g li ob last o ma) , bu t non e h a v e b ee n a dop te d as a s t anda r d m e t hod o f treatme n t . T h ere is g r o wi ng i n terest i n c h em o e mbo li za ti on f o r t he treatme n t o f t u m o rs c on fi n e d t o t h e li v e r , a nd cis p latin i s a co m ponen t o f ma ny popu lar re g ime n s .

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s u mma r i zed i n . Please re v iew t h e p ac k a g e i n serts f o r t h ese drug s fo r f u ll p r esc ri b i ng i n f o rmati on a nd d eli n eati on o f t ox ic effects . Cis p latin Th e si de e f f ec t s assoc i a t ed w it h cis p lati n (at si ng le do ses o f m o re t h a n 50 m g /m 2 ) inc l ude nausea and vo miti ng, n e ph r o t ox icit y , o t o t ox icit y , n e urop a th y , and m ye l osupp r es si on. Rare e f fects i n cl ud e v is u al im p airm ent, seiz ur es , a rr hy t h mi as, acu t e isc h emic v asc u lar e v e n ts , g l u c o se i n t o lera nce, a nd p a n cr ea titi s. T he nausea and vo miti ng stim u late d a searc h f o r n ew a n tieme t i cs. T hese e f f ec t s a r e c u rre n tl y b est ma n a g e d wit h 5 -H T 3 a n ta gonis t s, usua ll y g i ven w it h a g l u c o c o rtic o i d, alt hough o t h er c o m b i na ti ons o f agen t s a r e s t i ll wi d el y u se d. I n t h e wee k s after treatme n t , c on ti nuous an ti e m e ti c t he r apy ma y b e re qu ire d. Ne ph r o t ox icit y is ameli ora t ed bu t no t co m p l e t ely p re v e n te d by hyd rati on. T h e re n al d ama ge t o bo t h g l o m e r u li and t ubu l es is c u m u lati v e , a nd after cis p lati n treatme nt, se ru m cr ea ti n i ne l eve l s a r e no l ong er a relia b le gu i d e t o GFR . A n ac u te ele v ati o n o f se r u m c r ea ti n i ne le v el ma y f o ll o w a cis p lati n do se , bu t t h is i nd e x r et u r ns t o no rm a l w it h time . T ubu le d ama g e ma y b e reflecte d i n a salt - l o si ng synd r o m e t ha t a l so res o l v es wit h time . O t o t ox i c it y i s a cu m u l a ti ve a n d irre v ersi b le si d e e f fect o f cis p lati n t r eatme n t t ha t r esu lt s fr o m dam a g e t o t h e i nn er ea r . T h e i n itial a ud i og ra phic ma n i f est a ti on i s l oss o f h i gh -fre qu e n c y ac u it y ( 4,000 t o 8,000 Hz) . W h e n ac u it y i s a f f ec t ed i n t he r ange o f s p eec h, cis p lati n s hou l d b e d isc on ti nu e d und e r m os t c ir cu m s t ances an d car bop lati n s ub stit u te d w h ere a pp r op riate . Pe r i ph er a l neu r opa t hy i s a l so c u m u lati v e , alt hough less c o mm on t h a n w ith a g e n ts su ch as v i nca a l ka l o i ds. T h is n e u r op at hy is u s u all y re v ersi b le , alt hough r ecove r y i s o ft en s l o w . A nu m b er o f a g e n ts wit h t h e po te n tial f o r pro tecti on fr o m neu r opa t hy h a v e b ee n d e v el op e d, bu t non e is y et u se d w i d el y . Ca rbop lati n

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M y el o s upp r ess i on, wh i ch i s no t u s u all y se v ere wit h cis p lati n, is t h e do s e -limiti ng t ox i c it y o f ca r bop l a ti n. T h e d r ug is m o st t ox ic t o t h e p latelet pr ec ur sor s, bu t neu tr open i a and a n emia are fre qu e n tl y ob ser v e d. T h e l owest p latelet coun t s a ft e r a s i ng l e do se o f car bop lati n are ob ser v e d 17 t o 21 days late r , a nd r ecove r y usua ll y oc c u rs by d a y 28. T h e e f fect is do se d e p e nd e nt, bu t i nd ivi dua l s va r y w i de l y i n t h eir s u sce p ti b ilit y . As s ho w n by E go ri n e t al a nd Ca l ve rt e t a l . , t he sev erit y o f p latelet t ox icit y is b est acc oun ted for by a m easu r e o f t he d r ug e xpo s u re i n a n i nd i v i du al , t h e AUC . B o t h group s de ri ved pha rm aco l og icall y b ase d f o rm u las t o p re d ict t ox icit y a nd gu i d e car bop l a ti n dos i ng. T h at o f Cal v ert a nd c o llea gu es ta r g ets a p articu la r e xpo s ure t o ca r bop l a ti n : Do se (mg ) = t a r ge t AUC (m g • mi n /mL) × (GFR mL/mi n + 25 ) Th is formu l a has been w i de l y u se d t o i nd i v i du alize car bop lati n do si ng a nd p e r mits t a r ge ti ng an accep t abl e le v el o f t ox icit y . Patie n ts w ho are el d erl y , h a v e a poo r pe rf o rm ance s t a t u s , o r h a v e a h ist o r y o f e x te n si v e p retreatm ent h a v e a h i ghe r ri sk o f t ox i c it y e v e n w h e n do sa g e is calc u late d wit h t h ese met hods, bu t t he sa f e t y o f d r ug a d mi n istrati on h as b ee n e nh a n ce d. I n t he c o m b i na ti on o f ca r bop l a ti n and p aclita x el , AUC- b ase d do si ng h as h el p e d to ma x imi ze t he dose i n t ens it y o f car bop lati n. D o sa g es s o me 30 % h i gh er t han t ho se u si ng a dos i ng s tr a t egy b ase d s o lel y on body s u rface area ma y saf ely b e u se d. A de t e rmi na ti on o f wh et h er t h is a pp r o ac h t o do si ng im p r ov es ou tc o m es w ill r equ ir e a r ando mize d trial . Th e o t h er t ox i c iti es o f ca r bopl ati n are g e n erall y mil d er a nd b etter t o lerat ed t h a n t hose o f c i sp l a ti n. Nausea a nd vo miti ng, alt hough fre qu e n t , are less se v e r e , sho rt e r i n du r a ti on, and m o re easil y c on tr o lle d wit h sta nd ar d a n tieme t i cs (i .e., p r och l o r pe razi n e [C o m p azi n e]) , d e x amet h as on e , l or aze p am) t han t ha t a ft e r c i sp lati n treatme n t . Re n al im p airme n t is i nfr e qu e n t , a lt hough a l opec i a is c o mm on, es p eciall y wit h t h e p aclita x el-c on tai n i ng co m b i na ti ons. Ne ur o t ox icit y is als o less c o mm on t h a n wit h cis p latin , a lt hough it i s obse rve d m o re fre qu e n tl y wit h t h e i n creasi ng u se o f h i gh-dose r eg im ens. O t o t ox i ci t y is als o less c o mm on. Ox ali p l a ti n

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Th e do se-limiti ng t ox i c it y o f ox ali p lati n is se n s o r y n e u r op at h y , a c h a r acteri s ti c o f a ll DACH - con tai n i ng p lati nu m d eri v ati v es . T h is si d e e f f ect ta k es t wo f o rm s. Fir s t , a ti ng li ng o f t h e e x tremities , w h ic h ma y als o i nv o lve t h e p e r i o r a l r eg i on, t ha t occu rs earl y a nd u s u all y res o l v es wit h i n a few d a y s . W it h r epea t ed dos i ng, sy m p t o ms ma y last l ong er b etwee n c y cles , but do no t a ppea r t o be cu m u l a ti v e o r o f l ong du rati on. Lar yngoph ar yng eal s p asms a nd co l d dyses t hes i as h a v e als o b ee n re po rte d bu t are no t ass o cia ted w it h si gn ifi can t r esp ir a t o r y sy m p t o ms a nd ca n b e p re v e n te d by p r o l ong i ng t h e dur ati on o f i n f us i on. A second n e u r op at h y , m o re t yp ical o f t h at see n w it h cispl a ti n, a f f ec t s t he ex tremities a nd i n creases wit h re p eate d do ses . D e f i n itiv e phys i o l og i c cha r ac terizati on o f ox ali p lati n -i ndu ce d n e u r op at hy h as proven d i f fi cu lt i n l a r ge stud ies . Electr o m yog rams p erf o rme d i n si x p atie n ts tr ea t ed by E x tr a e t a l . re v eale d a n a xon al se n s o r y n e u r op at h y , but n e rv e co nduc ti on ve l oc iti es w ere un c h a ng e d. S p ecime n s fr o m p eri ph era l n e rv e b i ops i es pe rf o rm ed i n t h is st udy s ho we d d ecrease d m y eli n ati on an d r e p lacem en t w it h co ll agen po c k ets . T h e n e u r o l og ic effects o f ox ali p lati n a pp ea r t o be cu m u l a ti ve i n t h at t h e y b ec o me m o re p r onoun ce d a nd o f gr eate r du r a ti on w it h successiv e c y cles; ho we v e r , un li k e t ho se o f cis p lat in, t h e y a r e r eve r s i b l e w it h d r ug c essati on. I n a re v iew o f 682 p atie n t e xp e r ien ces, B ri enza e t a l re po rte d t h at 82 % o f p atie n ts w ho e xp erie nced gr a d e 2 neu r o t ox i c it y o r h i ghe r h a d t h eir s y m p t o ms re g ress wit h i n 4 t o 6 m on t h s . I n a l a r ge r ad j uvan t trial , d e Gram on t et al . re po rte d t h at 12 % o f p atie n ts had g r ade 3 t ox i c it y at t h e e nd o f a 6 -m on t h treatme n t p eri od a nd t h at t h e m a j o rit y o f t hese pa tie n ts h a d relief , bu t no t alwa y s c o m p lete r es o l u ti on o f t he sy m p t o m s, by 1 y ear late r . T h e p ersiste n ce o f t h e n e uro t ox i c it y has l ed t o app roac h es t o ameli o rate it , i n cl ud i ng t h e u se o f pro tecti ve agen t s. T he use o f c alci u m a nd ma gn esi u m salts i n tra v e nou sl y b e for e a nd a ft e r each i n f us i on h as b ee n s ho w n t o b e i n effecti v e . Ot o t ox i city is no t obse r ved w it h oxa li p l a ti n. Na u sea a nd vo miti ng do o cc u r a nd g e n e r ally r espond t o 5 - H T 3 an ta gon ists . M y el o s upp ressi on is un c o mm on a nd is no t seve r e w it h oxa li p l a ti n as a si ng le a g e n t , bu t it is a feat u re o f c o m b i na ti ons i nc l ud i ng t h i s drug. O x ali p lati n t h era py is no t ass o ciate d with n e phro t ox i c it y . R E F E R ENC ES

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1 1. Co nno r s T , Jones M, Ro ss W , et al . New p lati nu m c o m p le x es wit h a n ti - t umou r ac ti v it y . Che m B i o l I n teract 1972 ; 5 : 415–424. 12. Bur chena l J, Ka l ake r K, Dew K , et al . Rati on ale f o r d e v el op me n t o f p lati nu m ana l ogs. Cance r T r ea t Re p 1979 ; 63 : 1493–1498. 13. K i dan i Y , I nagak i K, T s uk a go s h i S . E x ami n ati on o f a n tit u m o r acti v itie s o f p l a ti nu m co m p l ex es o f 1,2 - d iami no c y cl oh e x a n e is o mers a nd t h ei r r elat ed co m p l exes. Gann 1976 ; 67 : 921–922. 14. Bur chena l J, Ir an i G, Ke r n K , et al . 1,2 -Diami no c y cl oh e x a n e p lati nu m de ri va ti ves o f po t ent ial cli n ical v al u e . Rec Res Ca n cer Res 1980 ; 74 : 146–155. 15. R ixe O, O rt uza r W , A lvarez M , et al . O x ali p lati n, tetra p lati n, cis p latin , and ca r bop l a ti n : sp ectr u m o f acti v it y i n d r ug -resista n t cell li n e s a nd i n t he ce ll li nes o f t he Nat i on al Ca n cer I n stit u te ’ s a n tica n cer d r ug sc r ee n pane l . B i oche m P ha r m ac o l 1996 ; 52 : 1855–1865. 16. Shim ada M, It a m och i H , Ki g awa J . Ne d a p lati n : a cis p lati n d eri v ati ve i n ca n cer t he r ap y . Cance r Man a g Res 2013 ; 5 : 67–76. 17. Foj o T , F a rr e ll N, O rt u zar W , et al . I d e n tificati on o f non -cr o ss- r esista n t p l a ti nu m co m pounds wit h nov el c y t o t ox icit y p r o files u si ng t h e N C I a n t icance r d r ug sc r een a n d cl u stere d ima g e ma p v is u alizati on s . Cri t Re v On c o l He m a t o l 2005 ; 53 : 25–34. 18. Bat es SE , A miri- Ko r des ta n i L , Giacc on e G . Dr ug d e v el op me n t: por tals o f d i scove r y . C li n Can cer Res 2012 ; 18 : 23–32. 19. Ke ll and L . T he deve l op me n t o f o rall y acti v e p lati nu m d r ug s . I n : L i pp e r t B, ed. C i sp l a ti n : Chem istr y a nd Bi o c h emistr y o f a Lea d i ng An tica nce r D r u g . Z u ri ch : V e r l a g Hel v etica C h imica Acta; 1999 : 497. 20. Farr e ll N, Qu Y , B i e r bach U , et al . Str u ct u re-acti v it y relati on s h i p s w it h i n d i- and tri nuc l ea r p l a ti nu m ph ase-I cli n ical a n tica n cer a g e n ts . I n : L i pp e r t B, ed. C i sp l a ti n : Chem istr y a nd Bi o c h emistr y o f a Lea d i ng An tica nce r D r u g . Z u ri ch : V e r l a g Hel v etica C h imica Acta; 1999 ; 477–496.

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c h a ng es . P ha rm aco l Rev 2012 ; 64 : 706–721. 77. Ma J, V e r we ij J, Pl an tin g A , et al . C u rre n t sam p le h a nd li ng met ho d s for mea su r e m en t o f p l a ti nu m-DNA a ddu cts i n le u c o c y tes i n ma n lea d t o d isc r e p a n t r esu lt s i n DNA addu ct le v els a nd DNA re p ai r . Br J Ca n cer 1995 ; 71 : 512–517. 78. Sc he ll ens J, Ma J, Pl an ti ng A , et al . Relati on s h i p b etwee n t h e e xpo s ure t o c i sp l a ti n, DNA - addu ct f o rmati on i n le u c o c y tes a nd t u m ou r r es pon s e i n pa ti en t s w it h so li d t u m ou rs . Br J Ca n cer 1996 ; 73 : 1569–1575. 79. Ozo l s R, Co r den B, Jacob J , et al . Hi gh - do se cis p lati n i n hyp ert onic sali n e . Ann I n t e r n Med 1984 ; 100 : 19–24. 80. Howe ll S , Pf e ifl e C, W ung W , et al . I n tra p erit on eal cis- d iammi ned i ch l o r op l a ti nu m w it h s y stemic t h i o s u lfate p r o tecti on. Ca n cer Res 1983 ; 43 : 1426–1431. 81. A l be rt s D, Li u P , Hann i g a n E , et al . I n tra p erit on eal cis p lati n p l u s i n t r a v e nous cyc l ophospha mide v ers u s i n tra v e nou s cis p lati n p l u s i n t r a v e nous cyc l ophospha mide f o r sta g e III ov aria n ca n ce r . N E ng l J M ed 1996 ; 335 : 1950–1955. 82. Sol o m on B, S ou l en M, Ba u m R , et al . C h em o em bo lizati on o f h e p at o cell u l a r ca r c i no m a w it h cis p lati n, doxo r ub ici n, mit o m y ci n -C , E t h i odol, and po l yv i ny l a l coho l: p r o s p ecti v e e v al u ati on o f res pon se a nd s urv i v al i n a U S popu l a ti on. J V asc I n ter v Ra d i o l 1999 ; 10 : 793–798. 83. Ex tr a J, Ma rt y M, B ri e nza S , et al . P h armac ok i n etics a nd safet y prof ile o f oxa li p l a ti n. S e mi n O n c o l 1998 ; 25 : 13–22. 84. B r i enza S , V i gnoud J, I t z h a k i M , et al . O x ali p lati n (L-OHP): g l obal sa f et y in 682 pa ti en t s. Pr oc A m S o c Cli n O n c o l 1995 ; 14 : 209. 85. And r é T , Bon i C, Moun e d ji-B oud iaf L , et al . O x ali p lati n, f l uorourac il , and l eucovo ri n a s a d j uv a n t treatme n t f o r c o l on ca n ce r . N En gl J Me d 2004 ; 350 : 2343–2351.

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M . W asif S a if and E dwa r d Chu ANTIFO L A TES Re du ce d f o l a t es p l ay a key r o le i n on e-car bon meta bo lism , a nd t h e y are esse n tia l f o r t he b i osyn t hes i s o f pu ri n es , t hy mi dy late , a nd p r o tei n b i o s yn t hes i s. A mi nop t e ri n w as t h e first a n timeta bo lite wit h do c u me n te d cli n ical ac ti v it y i n t he tr ea tme n t o f c h il d re n wit h ac u te le uk emia i n t h e 1940 s . Th i s an tif o l a t e ana l og w as s ub se qu e n tl y re p lace d by met ho tre x at e ( M TX), t he 4 - a mi no, 10 -m e t hy l a n al og o f f o lic aci d, w h ic h remai n s t h e m o st w i de l y used an tif o l a t e an al og, wit h acti v it y a g ai n st a wi d e ra ng e o f ca n ce r s ( , i nc l ud i ng h emat o l og ic mali gn a n cies (ac u te l y m phob l as ti c l euke mi a and non -H odgk i n ’ s l y m pho ma) a nd ma ny s o li d t u m or s ( b r eas t cance r , head and n ec k ca n ce r , o ste og e n ic sarc o ma , b la dde r ca n ce r , and ges t a ti ona l tr ophob lastic ca n cer) . Pemet r e xed i s a py rr o l opy rimi d i n e , m u ltitar g ete d a n tif o late a n al og t h at ta r g ets mu lti p l e enzy m es i nvo l v e d i n f o late meta bo lism , i n cl ud i ng t hy mi dyla t e syn t hase (TS) , d i hyd r o f o late re du ctase (DHFR) , g l y ci n amid e r i bonu cl eo ti de ( GAR ) f o rm y l t ra n sferase , a nd ami no imi d az o le car box am ide (AI C AR ) f o rm y ltr ans f e r ase . T h is a g e n t h as b r o a d -s p ectr u m acti v it y a g ai n st so li d t u m o r s, i nc l ud i ng mali gn a n t mes o t h eli o ma a nd b reast , p a n c r eati c, head and neck, non– small-cell l ung, c o l on, g astric , cer v ical , and b la dd e r cance r s . – Th e t h i rd an tif o l a t e co m pound t o h a v e e n tere d cli n ical p ractice is pr alat r e xa t e ( 10 - p r opa r gy l- 10 - d eazaami nop teri n ) , a 10 - d eazaami nop teri n a n ti fo lat e t ha t was r a ti ona ll y desi gn e d t o b i nd wit h h i gh er a f fi n it y t o t h e r e du ce d f o l a t e ca rri e r ( R F C )- 1 tra n s po rt p r o tei n, w h e n c o m p are d wit h M TX, l ead i ng t o enhanced m e m b ra n e tra n s po rt i n t o t u m o r cells . It is als o

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a n im proved subs tr a t e f o r t he e n z y me f o l y l po l yg l u tam y l s yn t h etase (FPGS), r esu lti ng i n enhanced f o rmati on o f c y t o t ox ic po l yg l u tamate meta bo lit es When co m pa r ed wit h MTX , t h is a n al og is a m o re po te n t i nh i b it or o f m u lti p l e enzy m es i nvo l v e d i n f o late meta bo lism , i n cl ud i ng T S, DH FR , a nd GAR and A I CA R f o rm y ltra n sferases . T h is a g e n t is p rese n tl y a pprov e d f o r t he tr ea tm en t o f rela p se d o r refract o r y p eri ph eral T -cell l y m pho m as Mec h a n i s m o f Ac ti on Th e a n tif o l a t e co m pounds a re ti gh t- b i nd i ng i nh i b it o rs o f DHFR , a k e y e n z y me i n f o l a t e m e t abo li s m . DHFR p la y s a p i vo tal r o le i n mai n tai n i ng t h e i n t r a ce ll u l a r f o l a t e poo l s i n t h eir f u ll y re du ce d f o rm as tet r a hyd r o f o l a t es, and t hese co m pound s ser v e as on e-car bon carriers r e qu i r e d f o r t he syn t hes i s o f t hy mi dy late , pu ri n e nu cle o ti d es , a nd certai n ami no a c i ds. Th e c y t o t ox i c e f f ec t s o f M TX , p emetre x e d, a nd p ralatre x ate are me d iate d by t h ei r respec ti ve po l yg l u t am ate meta bo lites , wit h up t o 5 t o 7 g l u tam yl group s i n a γ - pep ti de li nkage. T h ese po l yg l u tamate meta bo lites e xh i b it pro l onged i n tr ace ll u l a r ha lf-li v es , t h ere by all o wi ng f o r p r o l ong e d d r ug acti on i n t u m o r ce ll s. Mo r eov e r , t h ese po l yg l u tamate meta bo lites are po te n t , d ir ec t i nh i b it o r s o f se veral f o late- d e p e nd e n t e n z y mes , i n cl ud i ng DH FR , T S , A I CAR f o rm y ltra n sferase , a nd GAR f o rm y ltra n sferase . Mec h a n i s m s o f Res i s t ance Th e d e ve l op m en t o f ce ll u l a r resista n ce t o a n tif o lates remai n s a maj o r ob stacle t o it s c li n i ca l e f fi cac y . I n e xp erime n tal s y stems , resista n ce t o a n ti fo lat es a ri ses fr o m seve r a l mec h a n isms , i n cl ud i ng a n alterati on i n a n ti fo lat e tr anspo rt because o f eit h er a d efect i n t h e re du ce d f o late carrier o r fo late r e cep t o r sys t e m s, dec r e ase d ca p acit y t o po l yg l u tamate t h e a n tif o l ate p a r e n t com pound t h r ough e it h er d ecrease d e xp ressi on o f FPGS o r i n c r ease d exp r ess i on o f t he c ata bo lic e n z y me γ- g l u tam y l hyd r o lase , a nd alte r ati ons i n t he t a r ge t enzy mes DHFR a nd / o r TS t h r ough i n crease d e xpr essi on o f w il d -t ype p r o t e i n o r ov ere xp ressi on o f a m u ta n t p r o tei n wi th r e du ce d b i nd i ng a f fi n it y f o r t h e a n tif o late . Ge n e am p lificati on is a c o m mon

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r esista nce m echan i s m obse r v e d i n v ari ou s e xp erime n tal s y stems , i n cl uding t u m or s a m p l es fr o m pa ti en t s. I n i n v itr o a nd i n v i vo e xp erime n tal m od el s y stems, t he l eve l s o f DH F R a nd / o r TS p r o tei n ac u tel y i n crease after e xpo s ure t o M T X and o t he r a ntif o late c o m pound s . T h is ac u te i ndu cti on o f ta r g et p r o t e i n i n r esponse t o d r ug e xpo s u re is me d iate d, i n p art , by a t r a n slatio na l r egu l a t o r y m echan ism , w h ic h ma y re p rese n t a cli n icall y r ele v a n t m echan i s m f o r t he acu te d e v el op me n t o f cell u lar d r ug resista n c e. Cli n ical P ha rm aco l ogy Th e or al b i oava il ab ilit y o f M TX is sat u ra b le a nd erratic at do ses g reater t h a n 25 m g / m 2 . M T X i s co m p letel y a b s o r b e d fr o m p are n teral r ou tes o f a d mi n is t r a ti on, and peak se r um le v els are ac h ie v e d wit h i n 30 t o 60 mi nutes of a d mi n i s tr a ti on. Th e d istri bu ti on o f M T X i n t o t h ir d -s p ace fl u i d c o llecti on s , s u c h as p le u r al e f fu si ons and asc iti c fl u i d, can s ub sta n tiall y alter MTX ph armac ok i n etic s. Th e sl ow r e l ease o f accu m u late d MTX fr o m t h ese t h ir d s p aces ov er tim e pro l ongs t he t e rmi na l ha lf-life o f t h e d r ug, lea d i ng t o po te n tiall y i n crease d cli n ical t ox i c it y . It i s adv i sab le t o e v ac u ate t h ese fl u i d c o llecti on s b ef o re t r eatme n t and m on it o r p l as ma d r ug c on ce n trati on s cl o sel y . Re n al e xc r e ti on i s t he m a i n ro u te o f d r ug elimi n ati on, a nd t h is p r o cess is me d iated by g l o m e r u l a r filtr a ti on a nd t ubu lar secreti on. A bou t 80 % t o 90 % of a n a d mi n i s t e r ed dose i s e li m i n ate d un c h a ng e d i n t h e u ri n e . D o ses o f M TX, t he r e f o r e, shou l d be r edu ce d i n p r opo rti on t o re du cti on s i n creatin ine clea r a n c e. Rena l exc r e ti on o f MTX is i nh i b ite d by p r ob e n eci d, p e n icilli ns, ce ph al o s po ri ns, asp iri n, and non ster o i d al a n ti-i n flammat o r y d r ug s . Pemet r e xed en t e r s t he ce ll v i a t h e RFC s y stem a nd, t o a lesser e x te n t , by t h e fo lat e r ecep t o r p r o t e i n. A s wit h MTX , it und er go es po l yg l u tamati on w it h i n t he ce ll t o t he pen t ag l u tamate f o rm , w h ic h is at least 60 -f o l d m o r e po te n t t han t he pa r en t co m po u nd. T h is a g e n t is mai n l y cleare d by re n al e x c r eti on, and i n t he se tti ng o f re n al dy sf un cti on, t h e termi n al d r ug h alf- li f e is si gn i fican tl y p r o l onged t o up t o 20 hou rs . Pemetre x e d, t h eref o re , s hould b e u se d w it h cau ti on i n pa ti en ts wit h re n al dy sf un cti on. I n a dd iti on, re nal e x c r eti on i s i nh i b it ed i n t he p rese n ce o f o t h er a g e n ts i n cl ud i ng p r ob e n eci d,

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p e n icilli ns, cepha l ospo ri ns, asp iri n, a nd non ster o i d al a n ti-i n flammat o r y drug s . A s w it h o t he r an tif o l a t e ana lo g s , p ralatre x ate is tra n s po rte d i n t o t h e cell b y t h e R FC ca rri e r p r o t e i n and t h e n meta bo lize d by FPGS t o f o rm l ong er c h ai n po l yg l u t a m a t es, w it h up t o f ou r a dd iti on al g l u tamate resi du es attac h e d t o t he pa r en t m o l ecul e . A bou t 34 % o f t h e p are n t d r ug is cleare d in t h e ur i n e du ri ng t he fir s t 24 hou rs after d r ug a d mi n istrati on. As s u c h, ca u ti on i s adv i sed when us i ng p ralatre x ate i n p atie n ts wit h re n al dy s fun c t i on. As w it h M T X and p emetre x e d, t h e c on c o mita n t a d mi n istra tion of o t h e r agen t s such as p r oben eci d, p e n icilli n s , ce ph al o s po ri n s , as p iri n, and non ste ro i da l an ti-i n fl a mm a t o r y d r ug s , ma y i nh i b it re n al cleara n ce . T ox icit y Th e mai n s i de e f f ec t s o f M TX are m y el o s upp ressi on a nd g astr o i n testi n a l (GI) t ox i c it y , wh i ch a r e usua ll y c o m p letel y re v erse d wit h i n 14 d a y s , un le ss drug- eli m i na ti on m echan i s ms are im p aire d. I n p atie n ts wit h c o m p r o mis ed r e n al func ti on, even s m a ll dos es o f MTX ma y res u lt i n seri ou s t ox icit y . M TX- i n d uced neph r o t ox i c it y is t hough t t o res u lt fr o m t h e i n trat ubu lar pr eci p it a ti on o f M T X and it s meta bo lites i n aci d ic u ri n e . A n tif o lates ma y als o e x ert a d ir ec t t ox i c e f f ec t on t h e re n al t ubu les . V i go r ou s hyd rati on a nd ur i n a ry al ka li n i za ti on have g reatl y re du ce d t h e i n ci d e n ce o f re n al fail u re in p atie n ts on h i gh - dose r eg im en s . Ac u te ele v ati on s i n h e p atic e n z y me le vels a nd hype r b ilir ub i ne mi a a r e of te n ob ser v e d du ri ng h i gh - do se t h era p y , but t h ese le ve l s usua ll y r e t u r n t o no rmal wit h i n 10 d a y s . Met ho tre x ate g i v e n c on c o m i t an tl y w it h r ad i o t he r apy ma y i n crease t h e ris k o f s o ft tiss u e n ec ro sis and os t eonec r os i s. Th e or i g i na l r a ti ona l e f o r h i gh - do se MTX t h era py was b ase d on t h e c on ce p t o f se l ec ti ve r escue o f no rmal tiss u es by t h e re du ce d f o late le u c ovor i n ( L V ) . Howeve r , r ec e n t d ata s ugg est t h at h i gh - do se MTX may als o ov er co m e r es i s t ance m e c h a n isms ca u se d by im p aire d acti v e tra n s po r t, d ec r eas ed a f fi n it y o f DH F R f o r MTX , i n crease d le v els o f DHFR res u lti ng fro m g e ne a m p lifi ca ti on, and/o r d ecrease d po l yg l u tamati on o f MTX . Th e mai n t ox i c iti es o f pe m e tre x e d a nd p ralatre x ate i n cl ud e do se-limiti ng m y el o s upp r ess i on, m ucos iti s, a nd s k i n ras h, u s u all y i n t h e f o rm o f t h e

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h a nd-foo t synd r o m e ( H FS) . O t h er t ox icities i n cl ud e re v ersi b le t r a n sam inase mi a, ano r ex i a and fati gu e s ynd r o me , a nd GI t ox icit y . T h es e si d e e f f e c t s a r e r educed by supp leme n tati on wit h f o lic aci d ( 350 μg o ral ly d ail y) a nd v it a mi n B 12 ( 1,000 m g s ub c u ta n e ou sl y g i v e n at least 1 wee k b e for e s ta rti ng t he r ap y , and t h e n re p eate d e v er y t h ree c y cles) . T o d ate , t he r e is no e vidence t o sugges t t ha t v itami n s upp leme n tati on a dv ersel y a f fects the cli n ical e f fi cacy o f pe m e tr exed o r p ralatre x ate . 5- F LUORO P YR I M I D I N ES Th e f l uo r opy rimi d i ne, 5 -fl uo r ou racil ( 5 -FU) was s yn t h esize d by C h arle s H ei d el be r ge r i n t he mi d 1950s. Uracil is a no rmal c o m pon e n t o f RNA; a s s u c h, t h e r a ti ona l e l ead i ng t o th e d e v el op me n t o f t h e d r ug was t h at ca n c e r cells mig h t be m o r e sens iti ve t o d ec oy m o lec u les t h at mimic t h e n at u ral c o m pound t han no rm a l ce ll s. 5 -FU a nd its d eri v ati v es are a n i n te g ral p ar t o f t r eatme n t f o r a b r oad r ange o f s o li d t u m o rs (see ) , i n cl ud i ng G I mali gn a nc i es ( esophagea l , ga stric , p a n creatic , c o l o rectal , a n al , a nd h e p at o cell u l a r cance r s ) , b r eas t , h ea d a nd n ec k, a nd s k i n ca n cers . It c on ti nues t o se r ve as t he m a i n b ac kbon e f o r c o m b i n ati on re g ime n s u se d to t r eat met as t a ti c co l o r ec t a l can cer (mCRC) a nd as a d j uv a n t t h era py o f ear ly -sta g e c o l on cance r . Mec h a n i s m o f Ac ti on 5- F U e n t e r s ce ll s v i a t he f ac ilitate d u racil b ase tra n s po rt mec h a n ism a nd is t h e n a n a bo li zed t o va ri ous cy t o t ox ic nu cle o ti d e f o rms by se v eral b i o c h e m i ca l pa t hways. It i s t hough t t h at 5 -FU e x erts its c y t o t ox ic e f fect s t hrough va ri ous m echan i s m s, i n cl ud i ng ( 1 ) t h e i nh i b iti on o f TS , ( 2 ) i n c orpo r a ti on i n t o RNA, and ( 3 ) i n c o r po rati on i n t o DNA ( . I n a dd iti on t o t hese m echan i s m s, t h e g e no t ox ic stress res u lti ng fr o m TS i nh i b itio n m ay a l so ac ti va t e prog ramme d cell- d eat h p at h wa y s i n s u sce p t ible cells , wh i ch l eads t o t he i ndu cti on o f p are n tal DNA fra g me n tati on. Mec h a n i s m s o f Res i s t ance

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Se v e r al r es i s t ance m echan i s ms t o 5 -FU h a v e b ee n i d e n tifie d i n e xp e r im en t a l and c li n i ca l se tti ng s . Alterati on s i n t h e ta r g et e n z y me TS r e pr ese n t t he m os t co mm on l y d escri b e d mec h a n ism o f resista n ce . I n v itr o, i n v i vo, and c li n i ca l s t ud i es h a v e do c u me n te d a str ong c o rrelati on b etwe en t h e le v e ls o f TS enzy m e ac ti v it y /TS p r o tei n a nd c h em o se n siti v it y t o 5 -FU . In t h is r e ga r d, ce ll li nes and t u m o rs wit h h i gh er le v els o f TS are relati v e ly m or e r e s i s t an t t o 5 -F U. Mu t at i on s i n t h e TS p r o tei n h a v e b ee n i d e n tifie d t h at lead t o r educed b i nd i ng a f fi n it y o f t h e 5 -FU meta bo lite f l uorodeoxyu ri d i ne m onophosph ate (F d UMP) t o t h e TS p r o tei n. Re du ce d e xpr essi on and / o r d imi n i shed acti v it y o f k e y acti v ati ng e n z y mes ma y i n te rf e r e w it h t he f o rm a ti on of c y t o t ox ic 5 -FU meta bo lites . Decrease d e xpr essi on o f mi s m a t ch r epa ir e n z y mes , s u c h as hu ma n m u tL ho m o l og 1 (h M LH1 ) and hu m an m u tS ho m o l og 2 ( h MSH 2 ) , a nd i n crease d e xp ress ion of t h e c a t abo li c enzy m e d i hyd r opy rimi d i n e d e hyd r og e n ase (DPD) are ass o ciate d w it h fl uo r opy rimi d i n e resista n ce . At t h is time , t h e relati v e c on t r i but i on o f each o f t hese m ec h a n isms i n t h e d e v el op me n t o f cell u lar r esista nce t o 5 -F U i n t he ac t u al cli n ical setti ng remai n s un clea r . Cli n ical P ha rm aco l ogy 5- F U is no t o r a ll y ad mi n i s t e re d, g i v e n its erratic b i o a v aila b ilit y res u lti ng fro m h i gh l eve l s o f t he ca t abo lic e n z y me DPD p rese n t i n t h e gu t m u c o s a. Af te r i n tr avenous bo l us dose s , meta bo lic elimi n ati on is ra p i d, wit h a h al f -li f e of 8 t o 14 mi nu t es. Mo r e t h a n 85 % o f a n a d mi n istere d do se o f 5 -FU is e n z y ma t i ca ll y i nac ti va t ed by D PD , t h e rate-limiti ng e n z y me i n t h e cata bo lism o f 5 -F U. A ph a r m acogene ti c synd r o me h as b ee n i d e n tifie d i n w h ic h p artial o r c o m p et e de fi c i ency i n t he D PD e n z y me is p rese n t i n 3 % t o 5 % a nd 0.1 % o f t h e g e n er a l popu l a ti on, r espe cti v el y . As DPD catal y zes t h e rate-limiti ng ste p i n t he ca t abo li c pa t hway of 5 -FU , a d eficie n c y o f DPD ca n res u lt i n a cli n icall y dange r ous i nc r ease in t h e a n a bo lic p r odu cts o f 5 -FU . Unfor t una t e l y , pa ti en t s w it h DPD d eficie n c y do no t ma n ifest a ph e no t ype on l y un til t hey a r e tr ea t ed w it h 5 -FU , a nd i n t h at setti ng, t h e y ca n d e v el op se v e r e G I t ox i c it y i n t he f o rm o f m u c o sitis a nd / o r d iarr h ea , m y el o s upp r ess i on, neu r o l og ic t ox icit y , a nd i n rare cases , d eat h. I n p atie nts b ei ng t r e a t ed w it h 5 -F U o r an y o t h er fl uo r opy rimi d i n e , it is im po rta n t t o

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c on si d er D P D de fi c i ency i n p atie n ts w ho p rese n t wit h e x cessi v e , se v ere t ox icit y . It i s now i nc r eas i n gl y a pp reciate d t h at DPD m u tati on s are unable t o acc o u n t f o r a ll o f t he obse r v e d cases o f e x cessi v e 5 -FU t ox icit y , b ecau se up t o 50 % o f pa ti en t s who exp erie n ce 5 -FU t ox icit y will h a v e no do c u me n t ed a lt e r a ti ons i n t he DPD g e n e . M o re ov e r , i nd i v i du als wit h nor mal D P D enzy m e ac ti v it y ma y b e d ia gno se d wit h h i gh p lasma le v els o f 5- F U, resu lti ng i n i nc r eased to x icit y . Alt hough DPD e n z y me acti v it y ca n be assa y e d fr o m pe ri phe r a l b l ood m ononu clear cells i n a s p ecialize d la bor at o r y , r ou ti ne pheno t yp i c a nd g e no t yp ic scree n i ng s f o r DPD d e f icie ncy p ri o r t o 5 -F U t he r apy are no t y et a v aila b le . Bi o m odu l a ti on o f 5 -F U Si gn i f ica n t e f f o rt s have f ocus e d on e nh a n ci ng t h e a n tit u m o r acti v it y o f 5 -F U t hrough b i oche mi ca l m odu lati on i n w h ic h 5 -FU is c o m b i n e d wit h v a r i ou s agen t s, i nc l ud i ng l eu c ovo ri n, MTX , N- pho s phon acet y l - L-as p art ic aci d, i n t e rf e r on - α, i n t e rf e r on -γ , a nd a w ho le ho st o f o t h er a g e n ts F o r t he p ast 20 to 25 yea r s, t he r educ e d f o late L V h as b ee n t h e mai n b i o c h emic al m odu lat o r o f 5 -F U. An a lt e r n ati v e a pp r o ac h h as b ee n t o alter t h e sc h e dule of 5-FU ad mi n i s tr a ti on. G i ve n t h e S- ph ase s p ecificit y o f t h is a g e n t , pro l onged exposu r e o f t u m o r cells t o 5 -FU w ou l d i n crease t h e fracti on o f cells b ei ng exposed t o t he d r ug. O v erall res pon se rates are si gn ifica n tl y h i gh e r i n pa ti en t s tr ea t ed w it h i n f u si on al sc h e du les o f 5 -FU t h a n i n t ho se t r eate d w it h bo l us 5 -F U, and th is im p r ov eme n t i n res pon se rate h as t r a n slate d i n t o an im p r oved prog ressi on -free s u r v i v al . M o re ov e r , t h e ove r all sa f et y p r o fil e i s im p r oved w it h i n f u si on al re g ime n s . A hyb ri d sc h e du le of bo l u s a nd i n f us i ona l 5 -F U wa s o ri g i n all y d e v el op e d i n Fra n ce , a nd t h is r e g ime n has shown supe ri o r c li n ical acti v it y c o m p are d wit h bo l u s 5 -FU sc h e du l es. T h i s hyb ri d sched ule h as no w b ee n sim p lifie d by u si ng on l y the 46-hour i n f us i on o f 5 -F U and c o m p letel y elimi n ati ng t h e 5 -FU bo l u s doses. T ox icit y i on. Th e d e r m a t o l og i c H FS i s m o re c o mm on l y ob ser v e d wit h i n f u si on al 5 -F U t h e r a p y . Acu t e neu r o l og i c symp t o ms h a v e als o b ee n re po rte d, a nd t h e y

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i n cl ud e so m no l ence, ce r ebe llar ata x ia , a nd upp er m o t o r si gn s . T reatme nt w it h 5-FU can, on r a r e occas io n s , ca u se c o r on ar y v as o s p asm , res u lti ng i n a s yndro m e o f ches t pa i n, ca r d iac e n z y me ele v ati on s , a nd elect ro car d i og r aph i c changes. Car d iac t ox icit y seems t o b e relate d m o re to i nfu si ona l 5 -F U t han bo l us a dmi n istrati on . C APE CI T AB I N E Ca p ecit ab i ne i s an o r a l fl uo r opy rimi d i n e car b amate t h at was rati on all y d esi gn e d t o a ll ow f o r se l ec ti ve 5 -FU acti v ati on i n t u m o r tiss u e . T h is o r al a g e n t w a s i n iti a ll y app r oved i n a n t h rac y cli n e-a nd ta x a n e-resista n t b reast ca n ce r a nd subsequen tl y app r ov e d f o r u se i n c o m b i n ati on wit h do ceta x e l as sec ond-l i ne t he r apy i n m e t as tatic b reast ca n cer a nd i n c o m b i n ati on wit h la p ati n i b, a t y r os i ne - k i nase i nh i b it o r o f hu ma n e p i d ermal g r o wt h fact o r r ece p t or t ype 2 ( H E R2 ) and ep i d ermal g r o wt h fact o r rece p t o r (EGFR) i n wo me n w it h H E R2 - pos iti ve metastatic b reast ca n cer f o ll o wi ng p r og ress ion on t r ast uzu m ab - based t he r ap y . T h is a g e n t is als o a pp r ov e d by t h e U . S . F ood a nd D r ug Ad mi n i s tr a ti on (FDA) f o r t h e first-li n e treatme n t o f mC R C a nd as a d j uvan t t he r apy f o r s t ag e III c o l on ca n cer w h e n fl uo r opy rimi d i ne t h e r a py a l one i s p r e f e rr ed . I n E u r op e a nd t h r oughou t m u c h o f t h e w o rl d, t h e c o m b i na ti on o f capec it ab i n e p l u s ox ali p lati n (XELOX) is a pp r ov e d f o r t h e t r eatm en t o f m CRC as we ll as f o r t h e a d j uv a n t t h era py o f sta g e III c o l on ca nce r I n add iti on, r e ce n t st ud ies h a v e do c u me n te d t h e non i nf eri o rit y o f capec it ab i n e t o 5 -FU w h e n c o m b i n e d wit h cis p lati n i n t he t r eatme n t o f m e t as t a ti c gas tric ca n ce r . Cli n ical P ha rm aco l ogy Ca p ecit ab i ne i s r ap i d l y and ex te n si v el y a b s o r b e d by t h e gu t m u c o sa , wit h n ea r l y 80 % o r a l b i oava il ab ilit y . It is i n acti v e i n its p are n t f o rm a nd und e r goes enzy m a ti c conve r s i on v ia t h ree s u ccessi v e ste p s . Of no te , t h e t h i rd a nd fi na l s t ep occu r s i n t u m o r tiss u e a nd i nvo l v es t h e c onv ersi on o f 5 ′ -d e oxy - 5 -fl uo r ou ri d i ne t o 5- FU by t h e e n z y me t hy mi d i n e pho s pho r y las e (T P ), wh i ch i s exp r essed a t m u c h h i gh er le v els i n t u m o rs w h e n c o m p are d w it h c orrespond i ng no rm a l tiss u e . Ca p ecita b i n e a nd ca p ecita b i n e

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meta bo lit es a r e p rim a ril y excr ete d by t h e k i dn e y s , a nd i n c on trast t o 5 -F U, ca u ti on m us t be t aken i n t he prese n ce o f re n al dy sf un cti on, wit h a pp r op ri ate do se m od ifi ca ti on. T he use o f ca p ecita b i n e is a b s o l u tel y c on trai nd icate d in p atie n ts whose c r ea ti n i ne c l ea ra n ce is less t h a n 30 mL p er mi nu te . T h e F DA a nd Roche have added a b lac k box war n i ng a nd stre ng t h e n e d t h e pr eca u tio ns sec ti on on t he cap ecita b i n e la b el a bou t t h e d r ug–d r ug i n te r acti on be t ween wa rf a ri n a nd ca p ecita b i n e- b ase d c h em o t h era p y . It is g e n e r ally r eco mm ended t o d o wee k l y m on it o ri ng o f t h e c o a gu lati on p a r ameter s ( p r o t h r o m b i n time/i n ter n ati on al no rmalize d rati o [PT/INR]) f o r all p atie n t s r ece i v i ng conco mita n t warfari n a nd ca p ecita b i n e , wit h a n a ppropria t e ad j us tm en t o f war fari n do se . T ox icit y Simila r t o wha t i s obse r ved wit h i n f u si on al 5 -FU , t h e mai n si d e e f fects o f ca p ecita b i ne i nc l ude d i a rr hea a nd HFS . Of no te , t h e i n ci d e n ce o f m y el o s upp r ess i on, neu tr openi c fe v e r , m u c o sitis , al op ecia , a nd n a u sea/ vo miti ng i s l owe r w it h ca p ecita b i n e w h e n c o m p are d wit h 5 -FU . E le v ati ons i n i nd ir ec t se r u m b ilir ub i n ca n b e ob ser v e d, bu t are u s u all y t r a n sie n t and c li n i ca ll y asy m p t o matic . Patie n ts i n t h e U n ite d States a pp e a r t o b e unab l e t o t o l e r a t e as h i gh do ses o f ca p ecita b i n e as E u r op ea n p atie nts, eit h e r as m ono t he r apy o r i n co m b i n ati on wit h o t h er c y t o t ox ic c h em o t he r ap y . A lt hough t h e und erl y i ng reas on s f o r t h is d iscre p a n c y ar e no t known, it m ay i n pa rt be relate d t o t h e i n crease d f o rtificati on o f t h e U S d iet w it h f o l a t e and t he i nc r e ase d f o c u s on v itami n a nd f o lic aci d s upp le men t a ti on. S -1 S -1 is a n o r a l fl uo r opy rimi d ine t h at c on sists o f te g af u r (FT) , a p r od r ug o f 5 -F U, c o m b i ned w it h t wo 5 -F U b i o c h emical m odu lat o rs: 5 -c h l o r o - 2,4 - d i hydroxypy ri d i ne ( g im e r ac il o r CDHP) , a c o m p etiti v e i nh i b it o r o f DP D, a nd o te rac il po t ass i u m , wh i ch i nh i b its pho s pho r y lati on o f 5 -fl u r ou racil i n t h e GI tr ac t , t he r eby dec r eas i ng seri ou s GI t ox icities s u c h as n a u sea/ vo miti ng, m ucos iti s, a nd d iarr h ea . As wit h o t h er o ral a g e n ts , S- 1 o f f e r s se ve r a l advan t ages ove r 5 -FU , i n cl ud i ng ease o f a d mi n istrati on, no r is k s as soc i a t ed w it h use o f c e n tral v e nou s access s u c h as i n fecti on,

nan nan

nan nan

C DHP i nh i b it s D P D, t hus a ll o wi ng h i gh er c on ce n trati on s o f 5 -FU t o e n t e r t h e a n ab o li c pa t hway and en ha n ce its t h era p e u tic effect . A dd iti on all y , t he i nh i b itio n o f D P D l eads t o a decrease d am oun t o f FBAL f o rmati on, w h ic h pr es u ma b l y l eads t o r educed ne u r o t ox icit y . Oteracil is t h e fi n al c o m ponent of t h e S -1 f o rm u l a ti on, and it i nh i b its o r o tate pho s pho ri bo s y ltra n sferase i n t h e GI m ucosa, wh i ch p r even ts t h e f o rmati on o f fl uo r ou ri d i n e m onophospha t e (F UM P) , t her e by d ecreasi ng GI t ox icit y . Th e ma x im u m t o l e r a t ed dose was esta b lis h e d at 80 m g / m 2 i n tw o d i v i d e d do ses fo r a Japanese popu l a ti on a nd 25 m g / m 2 twice a d a y f o r a Ca u casi an popu lati on. T h i s i n t e r e t hn i c v aria b ilit y o f S- 1 ph armac ok i n etics a nd ph a r ma codyna mi cs has been a ttri bu te d t o d iffere n ces i n t h e CYP 2 A 6 g e no t ypes St ud i es have de m on strate d a h i gh fre qu e n c y o f allelic v ari ants C YP2A 6 *4, *7, and *9 i n E a st Asia n s t h a n i n Ca u casia n s , w h ic h mi gh t be ass o ciate d w it h r educed enzy matic acti v it y a nd d ecrease d acti v ati on o f F T . On t h e o t he r hand, h i ghe r FT meta bo lism is see n i n Ca u casia n p atie n ts due t o h i gh er CY P 2A6 ac ti v it y . H o we v e r , i nv esti g at o rs h a v e esta b lis h e d sim ila r 5- F U e xposu r e be t ween t hese tw o et hn ic g r oup s . T h ese fi nd i ng s were e xp lai ned by h i ghe r CDH P e x po s u re i n Asia n s , res u lti ng i n i n crease d D PD i nh i b itio n and s l owe r ca t abo lism o f 5 -FU , d es p ite h a v i ng l o w CYP 2 A 6 acti v it y , whe r eas Caucas i ans h a d h i gh er CYP 2 A 6 acti v it y bu t faster 5 -F U clea r a n c e.

nan nan

Cli n ical T ox i c it y Cli n ical s t ud i es have shown t h at t h e GI t ox icities ass o ciate d wit h S- 1, s uch as d ia rrhea, nausea, vo miti ng, a nd hyp er b ilir ub i n emia , are m o re p r o mi n e nt i n W ester n pa ti en t s, whe r eas h emat o l og ic t ox icities are m o re p re v ale n t i n Ja p a n es e pa ti en t s. T he d i f f e r en ce i n safet y p r o file ca nno t b e e xp lai n e d by d i f f e r e nces i n 5 -F U exposu r e, b eca u se ph armac ok i n etic st ud ies h a v e s hown t h at ov er a ll d r ug exposu r es a re simila r . A po te n tial e xp la n ati on mi gh t i nvo l v e i n t e r e t hn i c va ri a ti ons i n TS p r o m o ter e nh a n cer re g i on po l y m o r ph i s m s, wh i ch a r e more fre qu e n tl y see n i n Asia n s o r i n Ca u casi ans on a h i ghe r f o l a t e d i e t . C Y T A RA B I N E C y ta r a b i ne ( a r a - C ) i s a deoxycy ti d i n e nu cle o si d e a n al og is o late d fr o m t he s pong e C r yp t o t e t hya c r yp t a , a nd it d i f fers fr o m its phy si o l og ic c oun ter p ar t by v i r t ue o f a s t e r eo t yp i c i nve rsi on o f t h e 2 ′- hyd r oxy l g r oup o f t h e s ug ar m o iet y A r eg im en o f a r a - C, c o m b i n e d wit h a n a n t h rac y cli n e a nd g i v e n as a 5- or 7 - day con ti nuous i n f us i on, is c on si d ere d t h e sta nd ar d i ndu cti on t r eatme n t f o r acu t e m ye l o i d l euk emia (AML) . Ara-C is acti v e a g ai n st o t he r h emat o l og i c m a li gnanc i es, su c h as non -H odgk i n ’ s l y m pho ma , c h r on ic m y el ogenous l euke mi a, and ac u te l y m pho c y tic le uk emia (see . How e v e r , t h i s agen t has abso l u tel y no acti v it y a g ai n st s o li d t u m o rs . Mec h a n i s m o f Ac ti on Ar a - C e n t e r s ce ll s v i a nuc l eo si d e tra n s po rt p r o tei n s , t h e m o st im po rta n t one b ei ng t he equ ili b r a ti ve i nh i b it o r -se n siti v e (ES) rece p t o r . O n ce i n si d e t h e cell , a r a -C r equ ir es ac ti va ti on f o r its c y t o t ox ic e f fects T h e first meta bo li c s t ep i s t he conve r s i on o f ara-C t o t h e m onopho s ph ate f o rm ara-c y ti d i n e m onophospha t e ( a r a -CMP) by t h e e n z y me d e oxy c y ti d i n e k i n as e (d C K) w it h subsequen t phospho r y lati on t o t h e d i- a nd tri pho s ph ate meta bo lit es, r espec ti ve l y . A ra-c y ti d i n e tri pho s ph ate (ara-CTP) is a po te nt i nh i b it or o f DNA po l y m e r ases α, β , a nd γ , w h ic h i n t u r n i n terferes wit h DNA c ha i n e l onga ti on, DNA s yn t h esis , a nd DNA re p ai r . Ara-CTP is al so i n c orpo r a t ed d ir ec tl y i n t o DN A a nd f un cti on s as a DNA c h ai n termi n at o r , i n te rf e r in g w it h cha i n e l onga ti on. Cata bo lism o f ara-C i nvo l v es tw o k e y

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b e g i n s wit h i n 12 hou r s a ft e r t h e start o f d r ug i n f u si on, a nd is c h aracteriz ed by f e v e r , m ya l g i a, bone pa i n, mac u l op a pu lar ras h, c on j un cti v itis , malais e, a nd o cc as i ona l ches t pa i n. Th e a d mi n i s tr a ti on o f a r a - C a t h i gh do ses ( 2 t o 3 g / m 2 wit h eac h do se) i s ass o ciate d w it h p r o f ound m y el o s upp ressi on Se v ere GI t ox icit y i n t h e for m of m ucos iti s and / o r d i a r rh ea is als o ob ser v e d. Ne u r o l og ic t ox icit y i s si gn i f ic an tl y m o r e co mm on wit h h i gh - do se ara-C t h a n wit h sta nd ar d doses, a nd pr es en t s w it h se i zu r es, cer e b ral a nd cere b ellar dy sf un cti on, a nd p e r i ph e ra l neu r opa t h y . C li n i ca l si gn s o f cere b ellar dy sf un cti on o cc u r i n u p t o 15% o f pa ti en t s and i nc l ud e dy sart h ria , dy smetria , a nd ata x ia . C h a nge in ale r t n ess and cogn iti ve ab ilit y , mem o r y l o ss , a nd fr on tal l ob e release si gns r e f lect c e r eb r a l t ox i c it y . Desp ite d isc on ti nu ati on o f t h era p y , cli n ical r ec ov e ry i s i nco m p l e t e i n up t o 30 % o f a f fecte d p atie n ts . P u lm on ar y c o m p lic a ti ons m ay i nc l ude non car d i og e n ic pu lm on ar y e d ema , ac u te r es p i r at o r y d i s tr ess, and pneu m on ia , res u lti ng fr o m Stre p t o c o cc u s v iri d a ns i nf ecti on. O t he r s i de e f f ec t s as s o ciate d wit h h i gh - do se ara-C i n cl ud e c on j un c t i v iti s ( o ft en r espons i v e t o t op ical c o rtic o ster o i d s) , a p ai n f u l HF S, a nd r a r el y , anaphy l ac ti c r eac ti on s . GE MC I T AB I N E G emcita b i ne ( 2′,2′ - d ifl uo r odeoxy c y ti d i n e) is a d ifl uo ri n ate d d e oxy c y ti d i ne a n al og. D esp it e it s s imil a rit y in str u ct u re , meta bo lism , a nd mec h a n ism o f acti on t o a r a - C, t he spec tr u m o f a n tit u m o r acti v it y o f g emcita b i n e is m uch bro a d e r . T h i s co m pound h as si gn ifica n t cli n ical acti v it y a g ai n st se ve r al hu ma n so li d t u m o r s, i nc l ud i ng p a n creatic , b ile du ct , g all b la dd e r , small cell a nd non–s m a ll- ce ll l ung, b l add e r , ov ar y , a nd b reast ca n cers as well as h emat o l og i c m a li gnanc i es, na mel y H odgk i n ’ s a nd non -H odgk i n ’ s l y m pho m a ( see . Mec h a n i s m o f Ac ti on Th e t r an spo rt o f ge m c it ab i ne i n t o cells re qu ires t h e nu cle o si d e tra n s po rt e r s y stem . Ge m c it ab i ne i s i nac tive i n its p are n t f o rm a nd re qu ires i n tracell ula r acti v ati on f o r it s cy t o t ox i c e f fects . T h e ste p s i nvo l v e d i n t h e meta bo lic acti v ati on o f ge m c it ab i ne a r e similar t o t ho se ob ser v e d wit h ara-C , wit h

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bo t h drugs be i ng ac ti va t ed by t h e same e n z y matic mac h i n er y t o t h e acti ve t r i pho s pha t e m e t abo lit e ( see ) . Gemcita b i n e tri pho s ph ate is t h e n i n c orpo r a t ed i n t o DNA, r esu lti ng i n c h ai n termi n ati on a nd t h e i nh i b iti on o f DNA s yn t hes i s and f unc ti on, or t h e tri pho s ph ate f o rm ca n d irectl y i nh i bit DNA p ol y m e r ases α, β , and γ , w h ic h i n t u r n, i n terferes wit h DNA c h ai n el ong ati on, DNA syn t hes i s, a n d DNA re p ai r . T h e tri pho s ph ate meta bo li te is als o a po t en t i nh i b it o r o f ri bonu cle o ti d e re du ctase , w h ic h f u rt h er me d iat es i nh i b itio n o f DNA b i osyn t he sis by re du ci ng t h e le v els o f k e y d e oxynuc l eo ti de poo l s . Mec h a n i s m s o f Res i s t ance Se v e r al m echan i s m s o f r es i s ta n ce t o g emcita b i n e h a v e b ee n d escri b e d i n v a r i ou s p r ec li n i ca l expe rim en tal m od els Gemcita b i n e is a po lar nu cle o si de ana l og t ha t r equ ires t h e acti v it y o f hu ma n e qu ili b rati v e nu cle o si de tr anspo rt e r 1 ( h E N T 1 ) t o e n ter cells a nd e x ert its c y t o t ox ic e f f ects . Pr ec li n i ca l da t a i n hu ma n p a n creatic ca n cer cell li n es s ho we d t hat g emcitabi ne r es i s t ance i s neg ati v el y c o rrelate d wit h h ENT 1 e xp ressi on and ca n b e in duced by spec ifi c i nh i b it o rs o f h ENT 1 Cli n ical d ata als o s uppor t t he concep t t ha t a l ack o f h ENT 1 ma y b e p re d icti v e o f resista n c e to g emcitabi ne. CO - 101, a li p i d - d r ug c on j ug ate o f g emcita b i n e , was rati onally d esi gn e d t o en t e r ce ll s i ndepend e n tl y o f h ENT 1. U n f o rt un atel y , tw o st udies i n p a n c rea ti c cance r f a il ed t o sho w a ny b e n efit o f CO- 101. Add iti ona ll y , seve r a l enzy m es i nvo l v e d i n t h e i n tracell u lar meta bo lism o f g emcitabi ne have been im p licate d i n t h e d e v el op me n t o f cell u lar d r ug r esista nce, i nc l ud i ng r educed e xp ressi on a nd / o r d eficie n c y i n d CK e n z yme acti v it y as we ll as i nc r eased e x p ressi on a nd / o r acti v it y o f t h e cata bo lic e n z y mes cy ti d i ne dea mi nase a nd d CMP d eami n ase . Rece n t st ud ies h a v e als o i d e n tifi ed a subse t o f CD44 - po siti v e ca n cer stem cells wit h i n p a n c r eati c t u m o r s t ha t sus t a i n t u m o r f o rmati on a nd g r o wt h, a nd are r esista n t t o ge m c it ab i ne t he r a p y . Cli n ical P ha rm aco l ogy

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G emcita b i ne i s ad mi n i s t e r ed via t h e i n tra v e nou s r ou te , t yp icall y ov er a 30 -mi nu te i n tr avenous i n f us i on, a nd it und e r go es e x te n si v e meta bo lism by d eami na ti on t o t he ca t abo li c m eta bo lite , d ifl uo r od e oxyu ri d i n e ( d F d U) , with m or e t h a n 90 % o f t he m e t abol ize d d r ug b ei ng rec ov ere d i n u ri n e . Plasma clea r a n c e i s abou t 30 % l owe r i n w o me n a nd i n el d erl y p atie n ts , a nd t h is ph a r ma cok i ne ti c d i f f e r ence ma y res u lt i n a n i n crease d ris k o f t ox icit y i n t h ese r e spec ti ve pa ti en t popu lati on s . T h e i n itial fi nd i ng s fr o m p il o t ph a r ma cok i ne ti c s t ud i es sugg este d t h at g emcita b i n e , w h e n g i v e n at a fi xed do se r at e (F DR ) i n tr avenous i n f u si on o f 10 m g / m 2 p er mi nu te , p r odu ce d t h e h i ghes t accu m u l a ti on o f a cti v e d F d CTP meta bo lites i n p eri ph eral b l ood m ononuc l ea r ce ll s, wh i ch l ed t o a ra ndo mize d ph ase II trial t h at c o m p ar ed g emcitabi ne 1,500 m g / m 2 by FDR o r 2,200 m g / m 2 o f g emcita b i n e ov er 30 mi nu tes . A lt hough t h i s phase II st udy s ugg este d a n im p r ov e d ov erall s urv i v al w it h F DR, a subsequen t ph ase III trial faile d t o c on firm t h e s urv i v al advan t age o f ge m c ita b i n e by FDR ov er its c onv e n ti on al a d mi n is t r a ti on schedu l e . T ox icit y G emcita b i ne i s a r e l a ti ve l y w ell-t o lerate d d r ug w h e n u se d as a si ng le a gent. Th e mai n dose -limiti ng t ox i c it y is m y el o s upp ressi on, wit h n e u tr op e n ia m or e c o mm on l y expe ri enced t h a n t h r o m bo c y t op e n ia . T ox icit y is sc h e dule d e p e nd e n t , w it h l onge r i n f us i on s p r odu ci ng g reater h emat o l og ic t ox icit y . T r a n sie n t fl u li ke sy m p t o m s, incl ud i ng fe v e r , h ea d ac h e , art h ral g ias , a nd m y al g ia s, occu r i n 45 % o f pa tie n ts . Ast h e n ia a nd tra n sie n t tra n sami n ase mia ma y o cc u r . Rena l mi c r oang i op at hy s ynd r o mes , i n cl ud i ng h em o l y tic- u re mic s yndro m e and t h r o m bo ti c t h r o m bo c y t op e n ic pu r pu ra , h a v e b ee n re po rte d r a r el y . 6-THIO P UR I N ES Th e d e ve l op m en t o f t he pu ri n e a n al og s i n ca n cer c h em o t h era py b e g a n i n t h e ea r ly 1950s w it h t he syn t h esis o f t h e t h i opu ri n es , 6 -merca p t opu ri n e ( 6 -M P) a nd 6 -t h i oguan i ne ( 6 -T G ) . 6 -MP h as a n im po rta n t r o le i n mai n te n a nce t h e r a py f o r acu t e l y m phob l ast ic le uk emia , w h ereas 6 -TG is acti v e i n r emissi on i nduc ti on and i n mai n te n a n ce t h era py f o r AML (see .

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Mec h a n i s m o f Ac ti on Th e t h i opu ri nes, 6 - M P and 6 -TG , act similarl y wit h res p ect t o t h eir cellu la r b i o c h e m i s tr y I n t he ir r espe cti v e m onopho s ph ate nu cle o ti d e f o rms , t hey i nh i b it e nzy m es i nvo l ved i n d e novo pu ri n e s yn t h esis a nd pu ri n e i n te r c onve r s i on r eac ti ons. T h e tri pho s ph ate nu cle o ti d e f o rms ca n g et d i r ectl y i nco r po r a t ed i n t o e it h er cell u lar RNA o r DNA , lea d i ng t o t h e i nh i b itio n o f RNA and DNA syn t h esis a nd f un cti on, res p ecti v el y . Mec h a n i s m s o f Res i s t ance Th e d e ve l op m en t o f ce ll u l a r resista n ce t o 6 -t h i opu ri n es res u lts fr o m a d ec r eas ed l eve l o f key cy t o t ox ic nu cle o ti d e meta bo lites , eit h er t h r ough d ec r eas ed f o rm a ti on o r i nc r e ase d b rea kdo w n. Resista n t cells h a v e b ee n i d e n ti f ie d t ha t exp r ess e it he r co m p lete o r p artial d eficie n c y o f t h e acti v a ting e n z y me hypoxan t h i ne - guan i n e pho s pho ri bo s y ltra n sferase (HGP R T) . I n cli n ical sa m p l es de ri ved fr o m p atie n ts wit h AML , d r ug resista n ce h as been ass o ciate d w it h i nc r eased con ce n trati on s o f a mem b ra n e- bound al k ali n e pho s ph at ase o r a con j uga ti ng e n z y me , 6 -t h i opu ri n e met hy ltra n sferase (T PM T), t he end -r esu lt be i ng re du ce d f o rmati on o f c y t o t ox ic t h i opu ri n e nu cle o ti des. Fi na ll y , t he dec rease d e xp ressi on o f mismatc h re p air e n z y m es, i n cl ud i ng hM L H1 and hM S H2, h as b ee n ass o ciate d wit h cell u lar d r ug r esista nce. Cli n ical P ha rm aco l ogy Or al a bso r p ti on o f 6 - M P i s h i gh l y erratic , a nd t h e relati v el y poo r o ral b i o a v ail ab ilit y i s m a i n l y r e l a t ed t o ra p i d first- p ass meta bo lism i n t h e li v e r . Th e maj o r r ou t e o f d r ug e limi n ati on is v ia meta bo lism by se v eral e n z y ma t i c pa t hways. 6 - M P i s ox i d ize d t o t h e i n acti v e meta bo lite 6 -t h i ou r ic aci d by xan t h i ne ox i dase. E nh a n ce d 6 -MP t ox icit y ma y res u lt fr o m t h e c on c o m i t an t ad mi n i s tr a ti on o f 6 -MP a nd t h e x a n t h i n e ox i d ase i nh i b it o r all opur i no l . I n pa ti en t s r ece i v i ng bo t h 6 -MP a nd all opu ri no l , t h e 6 -MP dose m u st b e r educed by a t l eas t 50 % t o 75 % . 6 -MP als o und e r go es S-met hy lati on by t he enzy m e T P MT t o y iel d 6 -met hy lmerca p t opu ri n e . 6-TG is a d mi n i s t e r ed o r a ll y i n t h e treatme n t o f AML . Its o ral b i o a v ail ab ilit y i s e rr a ti c, w it h p ea k p lasma le v els o cc u rri ng 2 t o 4 hou rs

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a f te r i n g es ti on. T he ca t abo li s m o f 6 -TG d iffers fr o m 6 -MP i n t h at it is not a d i r ect s ubs tr a t e f o r xan t h i ne ox i d ase . TP M T enzy m e ac ti v it y m ay var y c on si d era b l y am ong p atie n ts as a res u l t o f po i n t mut a ti ons o r l oss o f a lleles o f TPM T A pp r ox imatel y 0.3 % o f t he Ca u casia n popu l a ti on exp r ess es eit h er a ho m o z ygou s d eleti on o r a m u ta tion of bo t h a ll e l es o f t he TP M T g e n e . I n t h ese p atie n ts , g r o ssl y ele v ate d t h i opur i ne nuc l eo ti des concen trati on s , p r o f ound m y el o s upp ressi on wit h p a n c y t open i a, and ex t ens i ve GI s y m p t o ms are ob ser v e d after on l y a b rief c our se of t h i opu ri ne tr ea tm en t . A n estimate d 10 % o f p atie n ts ma y b e at i n c r ease d ri sk f o r t ox i c it y be ca u se o f h eter o z ygou s l o ss o f t h e g e n e o r a m u ta n t a ll e l e cod i ng f o r a l ess e n z y maticall y acti v e TPM T . T ox icit y Th e maj o r dose -r e l a t ed t ox i c ities o f t h e t h i opu ri n es are m y el o s upp ressi on a nd GI to x i c it y i n t he f o rm o f n a u sea/ vo miti ng, a no re x ia , d iarr h ea , a nd st o matiti s . I n TP M T - de fi c ie n t p atie n ts , do sa g e re du cti on t o 5 % t o 25 % o f t h e sta nda r d dosage i s necessa r y t o p re v e n t se v ere e x cessi v e t ox icit y . Th i opur i ne hepa t o t ox i c it y oc c u rs i n up t o 30 % o f a du lt p atie n ts a nd pr ese n ts m a i n l y as cho l es t a tic ja und ice , alt hough ele v ati on s o f h e p atic t r a n sam inases m ay a l so be se e n. C o m b i n ati on s o f t h i opu ri n es wit h o t h er known hepa t o t ox i c agen t s shou l d b e a vo i d e d, a nd li v er f un cti on s hou l d be cl o sel y m on it o r ed. T he t h i opu ri n es are als o po te n t s upp ress o rs o f cell-me d iated imm un it y , and p r o lo ng e d t h era py res u lts i n a n i n crease d pr e d is pos iti on t o bac t e ri a l and p arasitic i n fecti on s . F LUDA R AB I N E Fl ud a r a b i ne ( 9 -β - D - a r ab i nosy l- 2 -fl uo r o a d e n i n e m onopho s ph ate , F-ara- A M P) i s an ac ti ve agen t i n t h e treatme n t o f c h r on ic l y m pho c y tic le uk e mia ( C LL) (see ) It is als o acti v e a g ai n st i ndo le n t non - Hodgk i n ’ s l y m pho m a, p r o l y m pho c y tic le uk emia , c u ta n e ou s T -cell l y m pho m a, and W a l dens tr ö m macr og l obu li n emia . T h is a g e n t h as als o s hown p r o mi s i ng ac ti v it y i n m a n tle cell l y m pho ma . I n c on trast t o its acti v it y i n he m a t o l og i c m a li gn a n cies , t h is c o m pound h as v irt u all y no acti v it y aga i ns t so li d t u m o r s.

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Mec h a n i s m o f Ac ti on Th e acti ve cy t o t ox i c m e t abo l i te is t h e tri pho s ph ate meta bo lite F-ara- A T P , wh ic h com pe t es w it h deoxyad e no si n e tri pho s ph ate ( d A TP) f o r i n c orpo r a ti on i n t o DNA and ser v es as a h i gh l y e f fecti v e c h ai n termi n at o r . In a dd iti on, F- a r a - A TP d ir ec tl y i nh i b its e n z y mes i nvo l v e d i n DNA r e p licati on, i nc l ud i ng DNA po l y merases , DNA p rimase , DNA li g ase I , and r i bonu cl eo ti de r educ t ase . F-ara- A TP is als o i n c o r po rate d i n t o RNA , ca u si ng t he i nh i b iti on o f RNA f un cti on, p r o cessi ng, a nd mRNA tra n slat ion. In c on t r a s t t o o t he r an tim e t abo lites , fl ud ara b i n e is acti v e a g ai n st nond i v i d i ng ce ll s. I n f ac t , t he p rimar y e f fect o f fl ud ara b i n e ma y res u lt fr om acti v ati on o f apop t os i s, t h r ough a n as y et ill- d efi n e d mec h a n isms . T h i s f i nd i ng m ay exp l a i n t he ac ti v it y o f fl ud ara b i n e i n i ndo le n t l y m phop r o lif e r a ti ve d i seases w it h relati v el y l o w g r o wt h fracti on s . Mec h a n i s m s o f Res i s t ance Th e d ec reased exp r ess i on o f th e acti v ati ng e n z y me d CK res u lti ng i n d imi n is hed i n tr ace ll u l a r f o rmati on o f F-ara-AMP is on e o f t h e mai n r esista nce m echan i s m s i den ti f ie d i n p recli n ical m od els . A h i gh d e g ree o f c ro ss -r e s i s t ance deve l ops t o m u lti p le nu cle o si d e a n al og s , re qu iri ng acti v ati on by dCK, i nc l ud i ng c y tara b i n e , g emcita b i n e , cla d ri b i n e , a nd cl of a r a b i ne. Reduced ce ll u l a r tra n s po rt o f d r ug h as als o b ee n i d e n tifie d as a r esista nce m echan i s m . Cli n ical P ha rm aco l ogy Pea k c oncen tr a ti ons o f F- a r a -A are reac h e d 3 t o 4 hou rs after i n tra v e nous a d mi n is t r a ti on . T he m a i n r ou te o f elimi n ati on is v ia t h e k i dn e y s , wit h a bou t 25 % o f a g i ven dose o f d r ug b ei ng e x crete d un c h a ng e d i n t h e u ri n e . T ox icit y M y el o s upp r ess i on and imm uno s upp ressi on are t h e maj o r si d e effects o f f l ud a r a b i ne as h i gh li gh t ed by do se-limiti ng a nd po ssi b l y c u m u lati v e l y m phopen i a and t h r o m bocy t op e n ia . S upp ressi on o f t h e imm un e s y stem a f f ects T - ce ll f unc ti on m o r e t h a n B-cell f un cti on. Fe v ers , o fte n i n t h e

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setti ng o f neu tr open i a, occu r i n 20 % t o 30 % o f p atie n ts . L y m pho c y te c oun ts , s pec ifi ca ll y CD4 - pos i t i v e cells , d ecrease ra p i d l y after t h e i n itiati on of t h e r a p y , and r ecove r y o f C D 4 - po siti v e cells t o no rmal le v els ma y ta ke l ong e r t han 1 yea r . Co mm on oppo rt un istic p at hog e n s i n cl ud e t h e v aricel la -z o ste r v ir us, Cand i da, and P n e u m o c y stis cari n i i . I n g e n eral , p atie n ts are em p i r ic a ll y p l aced on su lf a met hox az o le trimet hop rim p r ophy la x is t o pr e v e n t t he deve l op m en t o f P . cari n ii i n fecti on. C LADR I B I N E Cla dr i b i ne ( 2 - CdA ) i s a pu ri n e d e oxy a d e no si n e a n al og, a nd it is t h e d r ug o f c ho ice f or ha ir y ce ll l euke mia wit h acti v it y i n l o w- g ra d e l y m phop r o lif e r a ti ve d i so r de rs (see Sal v a g e treatme n t o f p atie n ts p r ev i ous l y tr ea t ed w it h i n terfer on - α o r s p le n ect o m y is as e f fecti ve as f i r st - li ne tr ea tm en t . Re tr eat me n t wit h cla d ri b i n e res u lts i n a c o m p lete r es pon s e i n up t o 60 % o f r e l ap si ng p atie n ts . I n a dd iti on, t h is a g e n t h as pro misi ng ac ti v it y i n pa ti en t s wit h CLL a nd non -H odgk i n ’ s l y m pho ma . Mec h a n i s m o f Ac ti on Upon e n tr y i n t o t he ce ll , 2 - Cd A und e r go es a n i n itial c onv ersi on t o cla dr i b i ne -m onophospha t e ( Cd -AMP) v ia t h e reacti on catal y ze d by d C K, a nd C d- A M P i s subsequen tl y meta bo lize d t o t h e acti v e meta bo lite , cla dr i b i ne -tri phospha t e. T he tri pho s ph ate meta bo lite c o m p etiti v el y i nh i bits i n c orpo r a ti on o f t he no rm a l d A TP nu cle o ti d e i n t o DNA , a p r o cess t h at r es u lts in t he t e rmi na ti on o f ch ai n el ong ati on . Pr og ressi v e acc u m u lati on of t h e t r i phospha t e m e t abo lit e lea d s t o a n im b ala n ce i n d e oxy ri bonu cle otide poo ls , t he r eby i nh i b iti ng f u rt h er DNA s yn t h esis a nd re p ai r . Fi n all y , t h e t r i pho s pha t e m e t abo lit e i s a po te n t i nh i b it o r o f ri bonu cle o ti d e re du ctase , wh ic h fu rt he r f ac ilit a t es t he i nh i b iti on o f DNA b i o s yn t h esis . Mec h a n i s m s o f Res i s t ance Resista nce t o 2 - CdA has been attri bu te d t o altere d i n tracell u lar d r ug meta bo li s m . A r educ ti on i n t h e acti v it y o f d CK , t h e e n z y me res pon si b le f o r g e n e r atin g cy t o t ox i c nuc l eo ti d e meta bo lites , is a maj o r d etermi n a n t o f ac qu i r ed r es i s t ance. T he m onopho s ph ate a nd tri pho s ph ate meta bo lites ar e d e pho s pho r y l a t ed by t he cy t op lasmic e n z y me 5 ′- nu cle o ti d ase . I n teresti n g l y ,

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r esista n t ce ll s de ri ved fr o m a p atie n t wit h CLL e xh i b ite d bo t h l o w le v el s o f d C K e x pr ess i on and h i gh l eve ls o f 5 ′- nu cle o ti d ase . Cli n ical P ha rm aco l ogy 2- C dA i s o r a ll y b i oava il ab l e, wit h 50 % o f a n a d mi n istere d do se o rall y a b s orb e d. App r ox im a t e l y 50 % o f a n a d mi n istere d do se o f d r ug is cleare d by t h e k i dneys, and 20 % t o 3 5% o f t h e d r ug is e x crete d un c h a ng e d i n t he ur i n e . O f no t e, t h i s nuc l eos i d e ca n cr o ss t h e b l ood–b rai n b arrier wit h p e n et r at ion i n t o t he ce r eb r osp i n al fl u i d. T ox icit y A t c onv e n ti ona l doses, m ye los upp ressi on is do se limiti ng. After a si ng l e c our se of d r ug, r ecove r y fr o m t h r o m bo c y t op e n ia u s u all y o cc u rs wit h i n 2 to 4 w ee k s , whe r eas r ecove r y fr o m n e u tr op e n ia ta k es p lace i n 3 t o 5 wee k s . GI t ox iciti es a r e gene r a ll y mil d, wit h n a u sea/ vo miti ng a nd d iarr h ea . Mil d -t o- m od e ra t e neu r o t ox i c it y occu rs i n 15 % o f p atie n ts a nd is at least p artl y r e v e r si b l e w it h d i scon ti nua ti on o f t h e d r ug. Imm uno s upp ressi on acc ounts for t h e lat e m o r b i d it y obse r v e d i n 2 -C d A – treate d p atie n ts . L y m pho c y te c oun ts , pa rti cu l a rl y CD4 - pos i t i v e cells , d ecrease wit h i n 1 t o 4 wee k s o f drug a d mi n i s tr a ti on and m ay remai n d e p resse d f o r se v eral y ears . After d isc on ti nua ti on o f 2 - CdA, a m e d ia n time o f up t o 40 m on t h s ma y b e r e qu i r e d f o r co m p l e t e r ecove r y o f no rmal CD 4 - po siti v e c oun ts . Alt hough oppor t un i s ti c i n f ec ti ons occu r , t h e y do s o less fre qu e n tl y t h a n wit h f l ud a r a b i ne t he r ap y . I n f ec ti ou s c o m p licati on s c o rrelate wit h d ecreases i n t h e C D 4- pos iti ve coun t , and the y i n cl ud e h er p es z o ste r , Ca nd i d a , P n e u m ocys ti s , P seudo m onas aer ug i no s a , Listeria m ono c y t og e n e s , C ryp t o c occus neo f o rm an s , Asp e r g ill u s , P . cari n ii , a nd c y t o me g al ov ir u s . C LO F ARAB I N E Cl of a r a b i ne i s a pu ri ne deoxy a d e no si n e nu cle o si d e a n al og, a nd it is a pprov e d f o r t he tr ea tm en t o f p e d iatric p atie n ts wit h rela p se d o r refract o r y ac u te l ymphob l as ti c l euke mi a (see ) . O ngo i ng st ud ies are e xp l or i ng t he bene fit o f c l o f a ra b i n e al on e a nd i n c o m b i n ati on wit h o t h er