Paclitaxel Stent Coating Inhibits Neointimal Hyperplasia at
`4 Weeks in a Porcine Model of Coronary Restenosis
`Alan W Heldman MD Linda Cheng PhD G Mark Jenkins MD Phillip F Heller PhD
`DongWoon Kim MD Melvin Ware Jr LAT Cynthia Nater BS Ralph H Hruban MD
`Banafsheh Rezai MD Benjamin S Abella MD Katherine E Bunge MD James L Kinsella PhD
`Steven J Sollott MD Edward G Lakatta MD Jeffrey A Brinker MD
`William L Hunter MD Jeffrey P Froehlich MD
`
`stents remain
`BackgroundDespite limiting elastic recoil and late vascular
`remodeling after angioplasty coronary
`vulnerable to restenosis caused primarily by neointimal hyperplasia Paclitaxel a microtubulestabilizing drug has been
`smooth muscle cell migration and proliferation contributing to neointimal hyperplasia We
`shown to inhibit vascular
`tested whether paclitaxelcoated coronary stents are effective at preventing neointimal proliferation in a porcine model
`of restenosis
`
`Methods and ResultsPalmazSchatz stents were dip coated with paclitaxel 0 02 15 or 187 pgstent by immersion
`in ethanolic paclitaxel and evaporation of the solvent Stents were deployed with mild oversizing in the left anterior
`descending coronary artery LAD of 41 minipigs The treatment effect was assessed 4 weeks after stent
`implantation
`late loss index mean luminal diameter decreased with increasing paclitaxel dose P<00028 by
`The angiographic
`ANOVA declining by 843 from 0352 to 0055 P<005 at the highest
`tested 187 pgstent versus control
`the neointimal area decreased by 395 high dose versus control P<005 with
`Accompanying this change
`dose P<0040 by ANOVA whereas the luminal area increased by 904 high dose versus control
`P<005 with escalating dose P<00004 by ANOVA Inflammatory cells were seen infrequently and there were no
`cases of aneurysm or thrombosis
`ConclusionsPaclitaxelcoated
`inhibition of neointimal hyperpla
`coronary stents produced a significant dose dependent
`in the pig LAD 28 days after implantation later effects require further study These results
`sia and luminal encroachment
`therapeutic benefit of paclitaxelcoated coronary stents in the prevention and treatment of
`demonstrate the potential
`human coronary restenosis Circulation 200110322892295
`
`increasing
`
`level
`
`Key Words paclitaxel
`
`stents
`
`angioplasty
`
`restenosis
`
`remains a frequent cause of late failure after
`Restenosis
`successful coronary angioplasty Coronary
`initially
`stents reduce restenosis by limiting the extent of elastic recoil
`and late vascular remodeling2 Despite these improvements
`the incidence of restenosis remains high because of neointi
`mal hyperplasia which is induced by all
`forms of dilating
`mechanical
`injury and is aggravated
`by the presence of the
`stent instent restenosis 3 Combining the mechanical sup
`to limit neointimal
`port of a stent with a treatment
`ingrowth
`improve therapeutic outcomes This combined
`should further
`has been used successfully in intracoronary brachy
`approach
`therapy43 Late thrombosis and edge stenosis
`the candy
`wrapper effect
`that may limit
`are potential complications
`the effectiveness of this approach36
`
`antineoplastic
`
`inhibitors of neointimal hyperplasia like
`Pharmacological
`represent an alternative to radiation therapy78
`paclitaxel
`Paclitaxel Taxol is a derivatized diterpenoid that exerts an
`effect by interfering with cell microtubule
`function910 Paclitaxel alters the dynamic equilibrium be
`and a and 13tubulin by favoring the
`tween microtubules
`formation of abnormally stable microtubules11 This leads to
`the inhibition of cell division and migration intracellular
`signaling and protein secretion which all
`rely on the rapid
`and efficient
`of microtubules Systemic
`depolymerization
`in the rat showed that a significant
`application of paclitaxel
`70 reduction in neointimal proliferation could be achieved
`
`than antineoplastic
`at blood concentrations 100 times lower
`In rat7 and humans cultured cell models paclitaxel
`
`levels 7
`
`oHdtiqtuoijpaproiumoa
`
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`guest
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`on
`
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`
`20
`
`2017
`
`Received September 28 2000 revision received December
`
`Medicine and the National
`
`15 2000 accepted December
`
`19 2000
`
`From the Division of Cardiology AWH GMJ BSA KEB JAB and Department of Pathology RHH BR Johns Hopkins School of
`Institute on Aging National Institutes of Health LC PFH DWK MW CN JLK SJS EGL JPF Baltimore
`Md and Angiotech Pharmaceuticals Inc Vancouver BC Canada WLH
`
`Presented in part at the 70th Scientific Sessions of the American Heart Association Orlando Fla November 1013 1997 and published in abstract
`I11288
`form Circulation 199796suppl
`to Alan W Heldman MD Division of Cardiology Carnegie 565 Johns Hopkins Hospital
`Correspondence
`Email aheldmanjhmiedu
`© 2001 American Heart Association Inc
`
`600 N Wolfe St Baltimore MD 21287
`
`Circulation is available at httpwwwcirculationahaorg
`
`2289
`
`Abraxis EX2035
`Actavis LLC v Abraxis Bioscience LLC
`1PR201701101 1PR201701103 1PR201701104
`
`

`

`2290
`
`Circulation
`
`May 8 2001
`
`prevented growth factorstimulated vascular smooth muscle
`cell migration and proliferation consistent with its effects on
`formation in vivo As an alternative to systemic
`neointimal
`therapy local drug delivery offers the advantages of allowing
`high local concentrations of drug at the treatment site while
`local de
`minimizing systemic toxic effects For paclitaxel
`livery might be achieved by a drug delivery catheters or by a
`coated stent12
`
`to the arterial wall can
`
`The sustained delivery of paclitaxel
`be achieved with polymeric stent coatings but these coatings
`inflammation and thrombosis12 After an initial
`may induce
`stents we resorted to
`failed attempt with polymercoated
`stents with paclitaxel dissolved in a
`dip coating metallic
`volatile solvent ethanol Evaporation of the solvent
`that adheres
`to the surface of the
`fine residue of paclitaxel
`stent By limitation of the coating to paclitaxel
`associated with certain polymers were
`able complications
`avoided The dip coating technique also allows paclitaxel
`have
`immediate contact with the vessel wall
`
`leaves a
`
`the undesir
`
`to
`
`favoring its
`tissue This strategy for local
`rapid accumulation by arterial
`drug delivery resembles shortterm irradiation4 by optimizing
`the conditions for blocking the earliest cellular events
`
`trig
`
`gered by injury1314
`
`Methods
`
`Stent Preparation
`Johnson were coated by dipping
`PalmazSchatz
`stents Johnson
`and evaporating the solvent This
`the stent into ethanolic paclitaxel
`procedure left a fine residue of paclitaxel covering the surface of the
`stent Results of local extravascular paclitaxel delivery studies in the
`rat 10 ttg paclitaxel effectively inhibited neointimal growth unpub
`lished results were used to establish 4 treatment groups control 0
`low dose 02 ttgstent
`intermediate dose 15 ttgstent
`ttgstent
`and high dose 187 ttgstent Coated stents were checked
`for the
`uniformity of drug application by selecting several stents at random
`and measuring pacli
`from each batch extracting them in ethanol
`liquid chromatography HPLC Gilson
`taxel by highperformance
`Paclitaxel was eluted from a 25cmX46mm pentafluorophenyl
`consisting of 45
`column ES Industries in a mobile
`acetonitrile and 55 water flowing at 15 mLmin and monitored at
`227 nm with a UV detector Gilson model 116 Paclitaxelcoated
`stents were mounted on 30 mm balloons PS1530 balloon delivery
`catheter Johnson
`Johnson with a manufacturer supplied crimp
`ing tool Sterilization was carried out with ethylene oxide gas Drug
`losses associated with the mounting and crimping procedure were
`evaluated by extracting the demounted stents in ethanol and subject
`to HPLC Loss of paclitaxel
`to the blood was
`ing the extract
`at 37°C in pig
`determined
`stents
`by incubating
`paclitaxelcoated
`whole blood treated with 1 mmolL EDTA to prevent clotting The
`incubation time was varied to establish a paclitaxel washout curve
`
`phase
`
`Stent Deployment
`care and
`All animal protocols were approved by the animal
`use
`Institute on Aging NIH and Johns
`committees of the National
`Hopkins University and were conducted according to established
`guidelines for the humane use and treatment of laboratory animals
`Male and female NIH minipigs n=43 weighing 35 to 45 kg were
`pretreated with aspirin 325 mg and diltiazem Cardizem CD 180
`mg the day before stent implantation Aspirin 325 mg was given
`the evaluation period The animals were sedated
`with ketamine 20 mgkg IM and acetylpromazine 022 mgkg IM
`and given sodium pentobarbital 4 mgkg IV to facilitate
`supine
`positioning and endotracheal
`with 1 to 2 isoflurane in oxygen flowing at 2 Lmin An 8F
`intubation Anesthesia was maintained
`
`daily throughout
`
`arterial sheath was inserted into the right carotid artery under sterile
`
`technique and heparin 5000 U was administered
`surgical
`intraarterial bolus The
`stent was delivered to the left anterior
`descending coronary artery LAD through an 8F Judkins
`right
`guiding catheter and deployed by two 30 second balloon inflations at
`8 atm The segment of artery to be stented was selected
`to allow
`12 times oversizing by visual estimation Angulated and branch
`ing segments were stented
`this degree of
`to permit
`if necessary
`implantation was done by a single pair of operators
`oversizing Stent
`
`as an
`
`AWH and MW who were blinded to the treatment groups
`
`Coronary angiography was performed in 2 views generally antero
`posterior and 30° left anterior oblique immediately before and after
`
`stent
`
`implantation
`
`Angiographic Analysis
`Angiograms were performed during the initial catheterization and at
`4week followup The angiographic mean luminal diameter MLD
`within the stented segment was measured by computerized coronary
`angiography ImageComm by 2 blinded investigators AWH and
`BSA Two views were measured and averaged
`for each arterial
`segment Neointimal encroachment of the lumen was evaluated from
`the late loss index LLI defined as LLI=MLD0MLD4wksMLD0
`where MLD and MED4wks are the MLDs immediately after stenting
`and at followup respectively
`
`overnight
`
`Histological Preparation and
`Histomorphometric Analysis
`After the terminal angiogram the heart was excised and perfusion
`fixed with 10 formalin at 100 mm Hg for 15 minutes After
`immersionfixation a segment of the LAD containing the
`stent was dissected from the myocardium The LAD segment was
`embedded in acrylic plastic and cut
`into 3 blocks containing the
`proximal middle and distal portions of
`the
`stent Three cross
`from each of these blocks with a tungsten carbide
`sections were cut
`knife and stained with elastic van Gieson or Movat pentachrome
`and distal
`tissue from adjacent proximal
`Arterial
`nonstented
`segments of the LAD were paraffin embedded
`and stained with the
`above dyes or hematoxylin and eosin Histomorphometric
`analysis of
`the tissue sections was performed by computerized video imaging
`with an Axioplan microscope Zeiss and a black and white MTI
`video camera DageMTI
`Inc Video images were analyzed with
`IBAS 20 software IBAS Kontron Electronik
`The vessel
`injury
`score was determined by the method of Schwartz et a115 The luminal
`and neointimal
`areas were evaluated for each of the tissue cross
`averaged and expressed as the absolute area
`in square
`sections
`millimeters The neointimal
`and medial wall
`thicknesses in milli
`meters were measured halfway between each pair of strut openings
`tissue cross sections
`and averaged
`inbetween distance
`over all
`thickness was also measured at each strut site strut
`Neointimal
`lumen distance All morphometric analyses were made by investi
`gators LC and CN blinded to the treatment groups
`
`at
`
`Determination of Postdeployment Paclitaxel Levels
`the intermediate 16 ttgstent
`PalmazSchatz
`stents dip coated
`doses were deployed in the LAD
`and high 177 ttgstent paclitaxel
`and left
`in place for 10 to 15 minutes The heart was removed and
`perfused with 10 formalin before dissection of the stented arterial
`segment to preserve the tissue architecture and minimize drug losses
`segment of LAD were each
`The excised stent and surrounding
`extracted with 1 mL of absolute ethanol
`for 72 hours at
`room
`ethanol extracts was determined
`Paclitaxel
`in the
`by HPLC
`
`temperature
`
`quantitatively
`
`Statistical Analysis
`data were analyzed by comparing
`and histological
`Angiographic
`stents by use of a 1 way ANOVA
`and paclitaxelcoated
`control
`Pairwise comparisons involving the control and different
`test which
`groups were performed according to the post hoc Dunnett
`The
`level of significance was
`corrects for multiple comparisons
`taken as P<005 Results are reported as mean±SEM
`
`treatment
`
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`

`Heldman et al
`
`Paclitaxel
`
`Inhibits Neointimal Hyperplasia
`
`2291
`
`A o
`
`4$ 03
`
`02
`
`01
`
`00
`
`n=11
`
`n= 8
`
`n=11
`
`n=5
`
`0
`
`02
`
`15
`
`187
`
`Paclitaxel pgstent
`
`n= 5
`
`n=11
`
`TABLE 1 Stent Oversize Ratio Vascular
`Stent Circumference
`
`Injury Score and
`
`Oversize Ratio
`
`Injury Score
`
`Stent
`
`Circumference mm
`
`128±003
`
`123±002
`
`124±002
`
`129±007
`
`107±009
`
`27±021
`
`28±013
`
`11±023
`
`769±016
`
`769± 026
`
`772± 048
`
`745±011
`
`Paclitaxel
`
`AgStent
`
`0 0
`
`2
`
`15
`
`187
`
`Oversize ratio indicates MLD
`
`after
`
`stentingMLD
`
`before stenting stent
`
`the linear distance from
`circumference
`of the stent Results are reported as m
`
`strut to strut around the circumference
`
`25
`
`ean±SEM
`
`20 I
`
`n=11
`
`n=8
`
`15
`
`10
`
`05
`
`00
`
`To
`
`5 E
`
`c
`nz
`
`0
`
`02
`
`15
`
`187
`
`Paclitaxel Astent
`
`Figure 2 A LLI vs paclitaxel dose B MLD at 4week followup
`vs paclitaxel dose Results are reported as mean±SEM
`P<005 vs control Dunnetts test
`
`dilatations were found in any of the treatment groups Angio
`gams were evaluated for the MLD and LLI during the 4 week
`period Figure 2 Application of ANOVA to the LLI data
`between the treatment groups was
`revealed that the difference
`significant P<00028 The LLI was dose dependent between
`from 0352 to
`the control and high paclitaxel doses the LLI fell
`0055 declining by 84 P<005 by Dunnetts
`test The
`change in MLD with increasing drug dose was inversely related
`in LLI The gain in MLD rose to 146 of the
`control group at the high paclitaxel dose P<005 by Dunnetts
`test and was highly significant across all group comparisons
`P<00012 by ANOVA
`
`to the decline
`
`Histomorphometric Analysis
`
`Representative
`
`from the different
`arterial cross sections
`ment groups are shown in Figure 3 In the control Figure 3A
`and low dose Figure 3B groups the stent strut sites were
`clearly visible between the neointima and internal elastic lamina
`causing mild compression of the medial wall A progressive
`formation was observed with
`decline in the extent of neointimal
`
`treat
`
`Results
`
`dial
`
`infarction
`
`in the LAD with
`Fortythree pigs underwent stent placement
`paclitaxelcoated PalmazSchatz
`stents All pigs survived to
`completion of the 4 week study without evidence of myocar
`on gross inspection Fortyone pigs in 4
`11 in the control 0 ptg
`treatment groups were analyzed
`the low dose 02 ptgstent
`15 at the intermediate
`stent 8 at
`dose 15 ptgstent
`the high dose 187 ptgstent
`and 7 at
`Because efficacy was judged by the ability to inhibit neoin
`timal hyperplasia induced by injury animals with low injury
`scores and incomplete engagement of the stent struts were
`eliminated from further analysis This occurred in 2 pigs in
`the control group with injury scores of 017 and 021 the
`mean injury score
`remaining 41 animals was
`119±008 mean± SEM Uniformity of the applied injury
`was evident from the similarity in oversize ratios 126 ± 002
`P<0231 by ANOVA and
`injury scores P<0755 by
`ANOVA which were not significantly different
`in the 4
`treatment groups Table 1
`
`for
`
`the
`
`Angiographic Analysis
`The 4 week followup angiogams Figure 1 showed a graded
`effect of paclitaxel dose with the largest reduction in neointimal
`
`at
`
`the high dose In the control angiogam a
`encroachment
`distinctive narrowing of the stented LAD segment was evident
`that was less severe at
`the intermediate dose At the high dose
`between
`a stepdown in the luminal diameter occurred
`stented and nonstented
`segments indicating effective
`of neointimal growth andor mild arterial dilatation in the
`drug applied region No hyperplastic edge effects or aneurysmal
`
`the
`
`inhibition
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`
`Figure 1 Four week followup angiograms of stented LADs A No paclitaxel control B intermediate dose paclitaxel 15 Agstent
`and C high dose paclitaxel 187 Agstent Arrows show approximate midpoint of stent
`
`

`

`of stented
`
`Figure 3 Photomicrographs
`LAD cross sections magnification x40
`A No paclitaxel control B low dose
`paclitaxel 02 Agstent C intermediate
`dose paclitaxel 15 Agstent and D
`high dose paclitaxel 187 Agstent
`lumen in A
`Black material partially filling
`is barium gelatin dye contrast medium
`indicate bound
`Solid and open arrows
`aries formed by internal and external
`elastic laminae respectively L indicates
`lumen N neointima M tunica media
`and A tunica adventitia
`
`and medial wall hemorrhage The frequency of these changes
`increased with the applied drug dose implicating paclitaxel
`in
`
`their origin Infiltration of cells with inflammatory morphology
`was seen infrequently in the cross sections and was not corre
`lated with the paclitaxel dose A small number of sections
`showed a perivascular inflammation that was probably injury
`related The identification of endothelial cells was limited by the
`technique however endothelium like cells
`tissue processing
`were occasionally seen surrounding the lumen forming an
`incomplete barrier in all of the treatment groups
`Figure 4A shows the dose dependence of the neointimal area
`calibrated to the drug dose applied to the stent Consistent with
`the relationship found in the LLI the high dose treatment group
`formation com
`showed
`reduction of neointimal
`a significant
`pared with controls 39 P<005 by Dunnetts
`test
`the
`significance with all group comparisons included was P<00402
`by ANOVA A similar dose dependence
`was observed
`in the
`index Figure 4C Neointimal
`neointimal
`thickness
`thickness
`declined significantly between the control and high dose groups
`55 inbetween and 75 strut lumen P<005 by Dunnetts
`test and was significant over all groups P<00058 inbetween
`strutlumen by ANOVA As shown in Figure
`and P<00001
`4D medial wall thickness was also reduced by 26 at the high
`drug dose compared with the control group P<005 by Dun
`thickness was not
`netts test The decrease in medial wall
`significant by ANOVA P<009 however suggesting that
`than those
`medial wall cells may be less sensitive to paclitaxel
`found in the neointima
`
`the
`
`The change in luminal area with increasing drug dose was
`inversely related to the decline in the LLI and neointimal area
`Figure 4B The luminal area at the high dose was 190 of
`that for the control group P<005 by Dunnetts test and the
`difference in luminal area was highly significant
`group comparisons P<00004 by ANOVA An uninten
`stent was
`ruled out on the
`tional bias in oversizing the
`the mean stent circumference
`determined by
`grounds that
`summation of the strut to strut distances was not signifi
`in the 4 treatment groups Table 1
`
`cantly different
`
`across all
`
`2292
`
`Circulation
`
`May 8 2001
`
`increasing drug dose This inhibition was particularly evident at
`the high dose Figure 3D where the strut sites protruded into
`the lumen attached to the vessel wall by a narrow pedestal of
`acellular material Expansion of the stent would have initially
`forced the struts into the medial wall
`
`like the control group
`these changes involved expansion of the vessel
`suggesting that
`wall ectasia or dilatation Incomplete deployment of the stent
`as the cause of this effect was ruled out by the similarity in
`Table 1
`oversize ratios injury scores and stent circumferences
`Illumination of the acellular material with polarized light re
`it was noncrystalline which excluded paclitaxel or a
`vealed that
`metabolite as its probable source Similar less intensely stained
`deposits were seen surrounding the strut sites at the lower doses
`Figure 3C but were completely absent from the control group
`Other histological changes Table 2 included medial wall cell
`necrosis with associated calcified deposits and focal neointimal
`
`TABLE 2
`
`Paclitaxel Histopathology
`
`Tissue Event
`
`0
`
`02
`
`15
`
`187
`
`Paclitaxel Dose µgStent
`
`Focal
`
`hemorrhage
`
`Neointima
`
`Medial wall
`
`Tissue necrosis
`
`Amorphous deposits
`
`Neointima
`
`Medial wall
`
`Inflammation
`
`Thrombosis
`
`<1
`
`ND
`
`ND
`
`ND
`
`ND
`
`03
`
`ND
`
`9
`
`ND
`
`ND
`
`18
`
`6
`
`2
`
`<1
`
`31
`
`ND
`
`07
`
`ND
`
`6
`
`30
`
`ND
`
`25
`
`28
`
`13
`
`68
`
`53
`
`ND
`
`ND
`
`The arterial cross section was divided into N pie shaped sectors where N is
`
`the total number of stent struts The frequency of a histopathological event was
`nx100N where n is the number of sectors in which the event appeared For
`each pig an average score was computed from the proximal middle and distal
`arterial cross sections Data acquired from all pigs were used to compute the
`average score at a given dose ND indicates not detectable
`The presence of
`inflammation was detected as anything more than a very mild noncircumfer
`infiltrate around the strut21
`
`ential
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`

`Heldman et al
`
`Paclitaxel
`
`Inhibits Neointimal Hyperplasia
`
`2293
`
`results suggest
`
`that a significant
`
`associated with the tissue At
`the drug was
`recovered
`recovery was larger
`than observed at
`
`of
`
`the intermediate dose only
`and
`the variation in
`the high dose These
`loss of the applied paclitaxel
`occurred before it
`reached the tissue
`In a separate set of in vitro experiments drug retention on
`only 52 of the
`the stent after balloon mounting averaged
`applied dose 197 ptgstent
`losses up to
`and additional
`17 occurred during ex vivo manipulation
`subsequent
`to
`mounting These losses may have resulted from cracking and
`flaking of the paclitaxel
`film caused by distortion of the stent
`during crimping Simple handling of the stent before mount
`ing resulted in <5 drug loss Additional
`losses to the blood
`lipids may occur during the brief 30second exposure to
`the coronary circulation before deployment This was dem
`in which a 30 second
`onstrated in washout experiments
`exposure to pig blood at 37°C resulted in loss of <5 of the
`applied paclitaxel dose
`
`Discussion
`In this study a pig model of coronary stent
`restenosis was
`local paclitaxel delivery would prevent
`used to test whether
`neointimal hyperplasia induced by vascular stretch injury
`PalmazSchatz
`stents were coated with a range of paclitaxel
`doses and were deployed with mild oversizing in the LAD
`Preliminary experiments that applied paclitaxel by use of a
`
`n=7
`
`II
`
`187
`
`n=7
`
`n= 11
`
`n= 8
`
`n= 15
`
`20
`
`15
`
`10
`
`05
`
`A E
`
`1 00
`
`0
`
`02
`15
`Paclitaxel µgstent
`
`30
`
`20 I
`
`ii
`
`n=8
`
`n=15
`
`0
`
`02
`15
`Paclitaxel µgstent
`
`187
`
`n= 11
`
`n= 8
`
`In Between
`CI StrutLumen
`
`n=15
`
`n= 7
`
`0
`
`02
`
`15
`
`187
`
`To
`
`s
`
`1 o
`
`00
`
`04
`
`03
`
`02
`
`01
`
`00
`
`0
`
`mm
`
`NeointimalThickness
`
`paproiumoa
`
`pHdmw
`
`ag
`
`nonbiodegradable
`ethylene
`vinyl acetate polymeric stent
`coating were marked by an intense inflammatory response
`severe luminal narrowing thrombosis and death To reduce
`these risks we chose to eliminate the polymer and apply
`to the bare stent with a dip coating technique see
`Methods We assumed that
`this approach would be optimal
`for rapid drug elution and high drug tissue concentrations
`because there is no barrier to prevent paclitaxel
`from gaining
`immediate access to the injured arterial
`in
`Locally applied paclitaxel produced a dose dependent
`hibition of neointimal
`formation as revealed by the pattern of
`in the angiographic and histomorphometric
`change
`during the 4 week evaluation period Analysis of the data by
`ANOVA showed that
`inhibition of the tissue hyperplastic
`response was significant neointimal area P<0040 LLI
`P<00028 or highly significant
`luminal area P<00004
`over all
`treatment groups In pairwise comparisons involving
`Dunnetts test statistical significance was routinely observed
`when the high dose treatment group was compared with the
`controls Specifically the LLI Figure 2A and luminal area
`Figure 4B showed the largest differences 84 for LLI
`90 for luminal area whereas the percentage
`MLD 46 and neointimal
`area 39 were less pro
`
`tissue
`
`indices
`
`change in the
`
`paclitaxel
`
`Paclitaxel vigistent
`
`n= 11
`
`n= 8
`
`n=15n= 7
`
`T
`
`015
`
`010
`
`I
`
`005
`
`2 000
`
`0
`
`02
`
`15
`
`187
`
`Paclitaxel µgstent
`
`thickness
`
`of A neointimal area B lumina
`Figure 4 Dose dependence
`area C neointimal
`and D medial wall
`thickness Neo
`intimal thickness in mm was measured as linear distance from
`lumen to 1 stent strut site strut lumen or 2 a point halfway
`between each pair of stent strut sites inbetween Results are
`reported as mean±SEM P<005 vs control Dunnetts test
`
`taxel
`
`Postdeployment Paclitaxel Levels
`Shortterm studies to determine the postdeployment pacli
`levels Table 3 showed that at the high paclitaxel dose
`of the drug originally deposited on the stent was
`recovered Of this slightly less than 50 of the dose was
`
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`
`on
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`
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`
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`
`Postimplantation Paclitaxel Recovery
`
`Instrument
`
`Recovery
`
`n
`
`6
`
`4
`
`Stent Ag
`
`Tissue Ag
`
`P9
`
`Total Ag
`
`336±175
`594
`6368±845
`530
`
`228±139
`402
`5543±1392
`462
`
`002 ± 0005
`
`03
`
`093±0860
`
`08
`
`565±217
`100
`12002±1503
`100
`
`338
`
`678
`
`TABLE 3
`
`Applied Dose
`
`n 1
`
`67±16
`
`177±85
`
`Paclitaxel
`
`removed from dissecting instruments
`
`

`

`2294
`
`Circulation
`
`May 8 2001
`
`in
`
`nounced Although the effects of paclitaxel on each of the
`consistent eg the changes
`indices were qualitatively
`in
`neointimal and luminal area were inversely related inhibi
`the high dose 078 mm2 versus
`tion of neointimal growth at
`control alone could not account
`for the increase in luminal
`area 135 mm2 versus control Exposure to the high dose of
`paclitaxel eliminated direct contact between the strut sites and
`medial wall Figure 3D implying that
`the vessel wall had
`undergone dilatation relative to the stent This was consistent
`records which showed a stepdown
`with angiographic
`luminal diameter between the drug applied stented and
`nonstented regions Figure 1C From the discrepancy be
`tween the neointimal and luminal area changes wall dilata
`for as much as 42 of the luminal increase at
`tion accounted
`the high paclitaxel dose and 36 at
`the intermediate dose
`can be traced to a
`the gain in luminal diameter
`thickness Figure 4D which was
`reduction in medial wall
`significant only at the high paclitaxel dose This suggests that
`in addition to neointimal growth inhibition and arterial wall
`dilatation16 a third component of the mechanism of action of
`involves the loss of vascular smooth muscle cells
`
`Part of
`
`paclitaxel
`from a quiescent nondividing population in the medial wall
`This effect probably represents true necrosis of the medial
`wall with perhaps a smaller contribution from apoptosis
`The cytostatic effects of paclitaxel on neointimal
`formation
`were complicated by local cytotoxic effects that manifested
`as a decrease in medial wall thickness focal neointimal and
`
`cells were an infrequent
`
`cellular
`
`during the
`
`require subsequent
`
`medial wall hemorrhage
`and cell necrosis
`Inflammatory
`finding at all paclitaxel doses Table
`2 arguing against the drug eluting coating as a stimulus to
`inflammation At the high dose of paclitaxel a reduction in
`cell numbers andor extracellular protein mass may have been
`responsible for the decline in medial wall thickness Various
`repair mechanisms
`responding to arterial dilatation
`and
`these
`changing wall
`tension may compensate for
`changes The acellular material eg fibrin bridging the gap
`between the medial wall and strut sites Figure 3D may be a
`repair mechanisms acting to stabi
`manifestation of cellular
`lize the arterial wall against further dilatation Although none
`of
`the pigs died from vascular complications
`4 week period concern
`about possible evolving complica
`long
`tions aneurysm wall rupture will
`to evaluate
`term experiments
`safety of this treatment
`the
`strategy Longterm studies should reveal whether cellular
`repair mechanisms respond to injury and cytotoxicity
`by
`this might reduce the longterm therapeu
`overcompensation
`tic benefit of paclitaxel particularly at the high dose at which
`medial wall necrosis and neointimal
`inhibition were signifi
`cant The requirement
`for longterm followup is underscored
`by the disparity between 1 month data1718
`and longterm
`results619 obtained with intracoronary brachytherapy which
`increase in neointi
`is complicated by a late dose dependent
`mal
`formation
`and delayed healing of
`
`the endothelium
`
`Further study will determine whether local paclitaxel delivery
`a sustained benefit or whether complications similar
`produces
`to those associated with brachytherapy diminish its therapeu
`
`tic potential
`
`An important property of paclitaxel
`is its insolubility in
`water which minimizes loss to the blood during catheteriza
`
`tion <5 during a 30 second exposure and facilitates tissue
`
`after contact with the arterial wall The lipophilic
`
`it
`
`uptake
`nature of paclitaxel may enhance cellular uptake by enabling
`to pass through the hydrophobic barrier of cell mem
`branes2021 A significant
`fraction may also be retained by
`membrane lipids and remain there as a depot for continuous
`release In diseased human vessels variations in the lipid
`content of plaque may alter the drug distribution pattern and
`from the standpoint of
`reduce its efficacy Another concern
`tissue levels of paclitaxel
`therapeutics is whether adequate
`
`a resurgence of neointimal
`can be maintained to prevent
`longer periods of time The compound coating
`growth over
`material used in some sustained release devices
`can extend
`the period of paclitaxel availability weeks months and
`maintain inhibitory control
`of paclitaxel
`in the presence
`washout andor metabolism It can also protect against drug
`losses from the stent during the procedures leading up to and
`including implantation mounting crimping handling Tests
`with our dip coated stents showed that most of the drug loss
`occurred before stent expansion and deployment arguing for
`modification of
`This might be
`coating
`procedure
`the
`
`in a fast release polymer
`achieved by encapsulating paclitaxel
`to the stent after mounting Al
`or by applying paclitaxel
`stent used
`in this study may have
`though the dip coated
`for efficacy barrierfree drug elution and safety
`
`advantages
`
`biocompatibility it
`
`should not be regarded as a final
`
`preclinical design
`
`Research
`
`Acknowledgments
`Inc
`funding was provided by Angiotech Pharmaceuticals
`and Develop
`Vancouver Canada through a Cooperative Research
`ment Award CRADA with the National
`Institutes of Health and
`Johns Hopkins University The authors express their appreciation to
`Frances OConnor
`for help in performing the statistical analysis
`
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`by
`
`guest
`
`on
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`
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`
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`

`

`Heldman et al
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`Paclitaxel
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`2295
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