stent-based immunosuppressive therapies for the prevention of restenosis
TRANSCRIPT
Cardiovascular Radiation Medicine 4 (2003) 98–107
Stent-based immunosuppressive therapies for the prevention
of restenosis
Meenakshi Aggarwala, Philip S. Tsaoa, Alan Yeunga, Andrew J. Carterb,*
aStanford University Medical Center, Stanford, CA, USAb Interventional Cardiology Research, Providence Heart Institute, Providence St. Vincent Medical Center,
Providence Health System, 9205 Southwest Barnes Road, Portland, OR, 97225, USA
Received 11 June 2003; received in revised form 31 July 2003; accepted 31 July 2003
1. Introduction
The long-term clinical efficacy of intracoronary stenting
is limited by restenosis, which occurs in 15% to 30% of
patients [1,2]. In-stent restenosis is due solely to neointimal
hyperplasia [3–6]. Stent-induced mechanical arterial injury
and a foreign body response to the prosthesis incites acute
and chronic inflammation in the vessel wall (Fig. 1). The
subsequent elaboration of cytokines and growth factors
induces multiple signaling pathways via mTOR to activate
smooth muscle cell migration and proliferation. The expres-
sion of inflammatory cytokines from proliferating T cells
and macrophages are associated with the release of growth
factors, such as platelet-derived growth factor, basic fibro-
blast growth factor, endothelial cell growth factor, or trans-
forming growth factor-beta, which induce smooth muscle
cell proliferation and migration as well as secretion of
matrix proteins. The long-term effects of smooth muscle
cell migration, proliferation and matrix formation is the
development of neointimal hyperplasia that may obstruct
the stent lumen resulting in restenosis. Thus, pharmacolog-
ical compounds or other agents that target inflammation and
cellular proliferation may be ideal candidates as stent-based
therapies for the prevention of restenosis.
The promising early clinical results of the potent stent-
based immunosuppressive therapy, sirolimus, lead a number
of investigators to explore the effects of other immunosup-
pressive agents as stent-based therapies for the prevention of
restenosis. The purpose of this manuscript is to review the
relevant preclinical and clinical data in the field of stent-
based immunosuppressive therapies for the prevention of
restenosis. An understanding of the physical properties and
1522-1865/03/$ – see front matter D 2003 Elsevier Inc. All rights reserved.
doi:10.1016/S1522-1865(03)00165-3
* Corresponding author. Interventional Cardiology Research, Provi-
dence Heart Institute, Providence St. Vincent Medical Center, Providence
Health System, 9205 Southwest Barnes Road, Portland, OR, 97225, USA.
Tel.: +1-503-216-5206.
E-mail address: [email protected] (A.J. Carter).
pharmacological effects of these compounds as well as the
proposed drug delivery stent systems will improve our
interpretation of clinical outcomes with this class of drug-
eluting stents. The reader will appreciate that a ‘‘class
effect’’ is unlikely to be observed as these immunosuppres-
sive compounds each with uniquely different molecular
weight, solubility, and mechanism of action (Table 1) are
explored as stent based therapies for the prevention of
restenosis. This information will also serve as a helpful
comparison to other potentially effective stent-based thera-
pies such as paclitaxel.
2. Dexamethasone
Dexamethasone is a potent glucocorticoid with anti-
inflammatory and antiproliferative properties. In vitro stud-
ies with cultured bovine [7] and human [8] smooth muscle
cells demonstrated that steroids are effective in suppressing
smooth muscle cell proliferation. The mechanism of action
by which steroids inhibit smooth muscle cell proliferation is
multifold. Steroids by virtue of their anti-inflammatory
property reduce collection of inflammatory cells at the site
of vessel wall trauma. The steroid induced anti-inflamma-
tory actions include inhibition of leukocyte adhesion to
endothelial cells, reduction in leukocyte aggregation, sup-
pression of platelet derived growth factor, and reduced
production of cytokines, nuclear proteins, fibroblasts and
macrophages [9]. In vivo experiments with systemic admin-
istration of glucocorticoids have demonstrated reduction in
intimal hyperplasia [10] and atherosclerotic plaque forma-
tion [11]. Unfortunately, these results have not been repro-
duced in human clinical trials [12,13], most likely due to
inadequate concentration of drug at the intervention site,
thus, suggesting the need for more effective local drug
delivery. The human clinical trials failed to demonstrate a
reduction in post-PTCA restenosis by systemic administra-
tion of steroids for 1 or 7 days. The prolonged and high dose
Fig. 1. Photomicrographs of a human coronary artery after stent placement.
Note the severe inflammatory and foreign-body response to the stent with
diffuse inflammatory cell infiltration, and multiple giant cells (courtesy of
Dr. Andrew Farb, Armed Forces Institute of Pathology, Washington, DC).
Table 1
General mechanisms of action of immunosuppressive drugs
Small Molecules
CsA, tacrolimus (FK506)
Inhibition of calcineurin phosphatase
Mycophenolate mofetil (MMF)
Inhibition of inosine monophosphate dehydrogenase (IMPDH)
Sirolimus
Inhibition of mTOR1 and 2
Steroids
Pleiotropic effects including blocking activation of nuclear factor-
kappa B (NF-nB)
CsA, cyclosporine.
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107 99
systemic intravenous and intramuscular administration of
glucocorticoids in humans is limited by potential for side
effects. Consequently, dexamethasone-eluting stents are a
prospective technique to allow for local delivery of high
concentration of glucocorticoids while limiting their sys-
temic side effects.
Lincoff et al. [14] are one of the first groups to study the
efficacy of intracoronary delivery of dexamethasone via a
polymer-coated dexamethasone-eluting stent in a porcine
coronary injury model. A 125-Am diameter tantalum wire
configured into a 16 mm long balloon expandable coil stent
was used. Each stent was sprayed and coated with a mixture
of poly-L-lactic acid (PLLA) and dexamethasone in a 2:1
ratio with 0.8 mg of dexamethasone and 0.4 mg of PLLA
per stent. Two different formulations of PLLAwere used—a
low molecular weight polymer of 80 kD and a high
molecular weight polymer of 321 kD. At 28 days after
implant, the stents coated with low molecular weight PLLA
produced a severe inflammatory response at the polymer
tissue interface. This infiltrate consisted of mononuclear
cells, lymphocytes and multinucleated giant cells. On the
contrary, arteries with high molecular weight PLLA stents
did not demonstrate an acute or chronic inflammatory
response. Nonetheless, neither high molecular weight
PLLA nor combination of high molecular weight PLLA–
dexamethasone resulted in a decrease in neointimal hyper-
plasia. The proportion of dexamethasone initially contained
within the stent coating was estimated in the arterial wall with
8% at 1 h and 10% at 24 h after implantation. Dexamethasone
concentration in the arterial tissue was 90,000 to 300,000
times higher than the serum levels at 24 h after stent
implantation. At 28 days, the arterial tissue dexamethasone
concentration remained 3000 times higher relative to the
serum levels. This study demonstrated that dexamethasone
could be delivered via a polymer-coated stent in a safe and
sustained manner though the dose appeared insufficient to
produce a reduction in neointimal hyperplasia [14].
Strecker et al. [15] evaluated the effect of polymer-coated
dexamethasone eluting stents on neointimal hyperplasia in a
canine model. Balloon expandable flexible tantalum stents
were coated with a pure polylactide (dl-PLA) or a polylac-
tide-co-polymer (PLA-Co-TMC). The ratio of polymer to
dexamethasone was 84:16 with each stent containing ap-
proximately 4 mg of dexamethasone per cm stent coating.
Digital subtraction angiography (DSA) was performed at 3,
6, 9, 12 and 24 weeks after stent implantation. Arteries with
dexamethasone coated stents demonstrated about 30% less
neointimal thickness within the stented area at 24 weeks
when compared with noncoated stents (183 vs. 263 Am). On
angiography, dexamethasone-coated stents revealed 29%
less stenosis than noncoated stents at 24 weeks.
More recent data has demonstrated that methylpredniso-
lone-coated stents decrease neointimal hyperplasia in a
porcine coronary model [16]. Ten percent (g/g) of methyl-
prednisolone in a polyfluoroalkoxy phosphazene polymer
(PFM-P75) was sprayed onto the surface of stainless steel
balloon expandable coronary stents. A barrier coat of
1% (g/v) PFM-P75 was then applied to allow sustained
release of methylprednisolone. At 4 weeks, the coronary
arteries with methylprednisolone eluting stents had a de-
creased inflammatory score surrounding the stent filaments
(0.46 + 0.54 vs. 2.34 + 0.75, P < .001) and significantly less
neointimal hyperplasia vs. controls (2.53 + 0.85 vs.
4.29 + 1.28 mm2, respectively). In vitro methylpredniso-
lone-release curves revealed 50% methylprednisolone re-
lease from the stent within 33 days. In summary, the studies
by Lincoff et al. [14], Strecker et al. [15] and Ping et al.
[16] provide preliminary data that steroid-eluting stents are
safe and may inhibit in-stent neointimal hyperplasia. This
preclinical work, while inconclusive, nonetheless has set
the stage for clinical trials of steroid eluting stents.
Study of Antirestenosis with the Biodivysio Dexameth-
asone Eluting Stent, STRIDE, is a multicenter trial evalu-
ating the safety and efficacy of Biodivysio Drug Delivery
Phosphorylcholine Coated (DD PC) stent with dexa-
methasone in de novo coronary lesions [17]. Seventy-one
patients at a mean age of 61.9 years were enrolled at eight
centers in Belgium. Their clinical profile consisted of 63%
having hyperlipidemia, 56% had hypertension, 41% had
history of previous MI and 28% had unstable angina
pectoris. The Biodivysio DD PC stent was dipped in a
15 mg/ml dexamethasone solution for at least 5 min and air-
dried for 5 min, resulting in 45 Ag of dexamethasone per
mm stent. Three different lengths of stents were available—
11, 15 or 18 mm. Patients received ASA indefinitely and
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107100
ticlodipine 250 mg/day for 28 days. The primary endpoint
was angiographic restenosis at 6 months with secondary
endpoints of major adverse cardiac events at 30 days and
6 months. Forty-one percent of the treated lesions were in
the LAD and 30% in the RCA. Preliminary results have
revealed four major adverse cardiac events at 30 days (one
in hospital death secondary to stent thrombosis, one non-
stent cardiac death, one non-Q wave MI, and one recurrence
of chest pain requiring target vessel revascularization).
Long-term clinical follow-up is in progress, although pre-
liminary data indicates only a modest reduction of angio-
graphic late lumen loss for patients with dexamethasone-
eluting stents at 6 months. Interestingly, the authors
reported potentially more favorable effects for dexametha-
sone-eluting stents in patients with unstable angina as
compared to those with stable angina at the time of initial
revascularization procedure. Future prospective, random-
ized studies with dexamethasone eluting stents are planned
to confirm these initial findings (BRILLIANT).
3. Sirolimus
Sirolimus (formerly rapamycin, Wyeth Ayerst) is a natu-
rally occurring macrolide antibiotic. It was originally
extracted from soil in Easter Island. It is produced by natural
fermentation from the fungus Streptomyces. Sirolimus is a
potent immunosuppressive agent, approved by the FDA in
1999 for treating allograft rejection in renal transplant
patients. More recently, the antiproliferative effects of siroli-
mus were recognized leading to its use in drug-coated stents.
In theory, sirolimus has a dual mechanism of action to
potentially inhibit neointimal formation and reduce resteno-
sis (Fig. 2). Sirolimus has both potent anti-inflammatory and
antiproliferative properties. Initial studies have demonstrated
Fig. 2. This figure illustrates the fundamental mechanism of action for t
that sirolimus is a cytostatic inhibitor of cytokine and growth
factor mediated cell proliferation [18,19]. Sirolimus inhibits
the cell cycle at the G1/S phase by binding to a cellular
receptor FKBP12 which in turn blocks molecular target of
rapamycin (mTOR) activation. Consequently, down regula-
tion of the cyclin dependent kinase p27kip1 is prevented and
phosphorylation of the retinoblastoma protein is inhibited.
Experimental data by Marx et al. [20], Poon et al. [21] and
Gallo et al. [22] has helped to demonstrate the mechanism of
action of sirolimus on vascular smooth muscle cells. Marx
et al. [20] demonstrated sirolimus mediated inhibition of rat
and human vascular smooth muscle cell proliferation in
vitro. Gallo et al. [22] demonstrated that systemic adminis-
tration of sirolimus was effective in reducing neointimal
hyperplasia in a porcine balloon injury model. In addition to
the biological properties of sirolimus, its physical properties
are ideal for the application as a locally delivered agent.
Sirolimus is a hydrophobic compound with a molecular
weight of 942 and thus, low solubility in aqueous solutions.
Due to its lipophilicity, the drug passes easily through the
cell membrane allowing for intramural distribution and
prolonged arterial tissue retention. Together the structural
properties and biological effects of sirolimus suggest that the
compound may be ideally suited for stent-based delivery in
the prevention of restenosis.
Experimental studies were implemented in 1998 to
determine the feasibility and efficacy of sirolimus-eluting
stents. In 1999, we performed preclinical studies to deter-
mine the efficacy of sirolimus-eluting stents alone or in
combination with dexamethasone to reduce in-stent neo-
intimal hyperplasia using a porcine coronary model [23]. At
28 days, a 50% reduction in neointimal proliferation was
demonstrated with sirolimus-eluting stents compared to
bare metal, P < .0001. The combination of sirolimus with
dexamethasone failed to produce a synergistic effect. The
he anti-proliferative and immunosuppressive compound sirolimus.
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107 101
reduction in neointimal hyperplasia translated to a signifi-
cant reduction in in-stent restenosis for sirolimus-eluting
stents compared to bare metal (26F 11% vs. 55F 20%,
respectively). Sirolimus alone or in combination with dexa-
methasone profoundly suppressed strut-associated inflam-
mation. Endothelialization scores were the same for both
the sirolimus and metal stents. Arterial wall protein expres-
sion at 7 days, assessed by Western blot, revealed a
profound reduction in PCNA expression and pRb phos-
phorylation with sirolimus-eluting stents. These molecular
effects of sirolimus result in inhibition of neointimal hyper-
plasia. In addition, we demonstrated a 70% reduction in the
inflammatory cytokine MCP-1 with sirolimus-eluting stents
(Fig. 3). This preclinical study showed that sirolimus-
eluting stents could significantly reduce in-stent restenosis
by cytostatic inhibition of the cell cycle and reduction in
inflammatory cytokines.
The clinical trials with sirolimus-eluting stents have
confirmed its success in reducing in-stent restenosis. The
First-In-Man trial with sirolimus-eluting stents was con-
ducted by Sousa et al. [24,25] to assess the safety and
feasibility of the sirolimus eluting Bx Velocity stent in the
treatment of de novo coronary lesions. Forty-five patients
with stable angina were enrolled at two centers—Sao Paulo,
Brazil (30 patients) and Rotterdam, Netherlands (15 patients).
Patients were treated with either a 3.0 or 3.5 mm diameter,
18 mm long, fast release (FR) or slow release (SR) sirolimus-
eluting stent (15 FR and 15 SR in Brazil and 15 SR in
Rotterdam). The FR formulation delivered the drug in less
than 15 days and the SR formulation delivered the drug in
90 days. All patients received ASA indefinitely and clopi-
dogrel for 60 days. Coronary angiography and IVUS were
performed immediately after the procedure, at 4, 12 and at
24 months. The angiographic and IVUS results at 4 and
12 months showed 0% binary restenosis. One year in-stent
MLD (FR, 2.73F 0.3 mm and SR, 2.87F 0.4 mm) and
Fig. 3. Western blot of porcine coronary artery specimens at 7 days after
placement of bare metal (St), sirolimus (SRL) and dexamethasone (Dex)
eluting stents. MCP-1 expression is not detectable in noninjured aorta (A).
The relative expression of MCP-1 is significantly less for sirolimus treated
arteries in comparison with arteries treated with bare metal stents.
%DS (FR, 8.9F 6.1% and SR, 6.7F 7%) remained essen-
tially unchanged compared to 4-month follow-up. Sousa
et al. [24,25] recently reported the 24-month clinical, angio-
graphic and IVUS follow-up for the 30 patients who received
either the FR release or SR formulation in Sao Paulo, Brazil.
After 2 years, no patient developed in-stent restenosis, and
90% were free of repeat target vessel revascularization. No
patient deaths occurred during the study period. One patient
had myocardial infarction at 14 months secondary to target
vessel occlusion, which prevented further angiographic as-
sessment. Angiographic assessment was deferred in another
patient due to developing pneumonia the week prior to
scheduled angiography. Angiography and IVUS in 28 of
30 patients demonstrated a similar MLD, % diameter steno-
sis and neointimal hyperplasia volume at 24 months in
comparison with 12 months. In-lesion and in-stent MLD
were greater in the SR group than the FR group while plaque
volume was similar for each group by IVUS. In the SR
group, in-stent and in-lesion MLD increased at 2 years vs.
1 year. No patient had in-stent restenosis (z50% diameter
stenosis). This is the longest follow up to date available on
sirolimus-eluting stents in man. These preliminary results did
not show a ‘‘late catch up’’ in restenosis and in fact suggest a
sustained effect of stent-based sirolimus in reducing reste-
nosis. These promising first-in-man results encouraged con-
firmation with randomized, placebo-controlled, multicenter
clinical trials.
The Randomized study with the sirolimus-coated Bx
VElocity balloon expandable stent in the treatment of
patients with de novo native coronary Lesions (RAVEL)
was a prospective, multicenter, randomized, double blind
clinical trial comparing bare metal and sirolimus-coated
stents [26]. This trial enrolled 238 patients from 15 centers
in Europe and 4 centers in Latin America. The patients were
randomized to a single sirolimus-coated stent (140 Ag/cm2)
or the bare metal Bx Velocity stent. The primary endpoint
was minimum lumen diameter measured by quantitative
coronary angiography (QCA) at 6-months. Prerequisite
native vessel diameter was 2.5 to 3.5 mm. Baseline demo-
graphics, anginal status and pre- and postprocedural vessel
diameter in both the sirolimus and control group were
similar. QCA analysis within the stent at 6 months demon-
strated 0% restenosis rate in the sirolimus-treated group
compared to 26% in the control, P < .0001. Late loss in the
sirolimus-treated group was a mere 0.01 mm compared to
0.80 mm for control, P < .0001. This resulted in a MLD at
follow up of 2.42 mm for the sirolimus treated group vs.
1.64 mm for control. No major adverse cardiac events were
seen in 96.7% of the sirolimus-treated group whereas only
72.9% of the bare metal group was event free. Serruys et al.
recently demonstrated that sirolimus-eluting stents inhi-
bited restenosis irrespective of the vessel size. In a subset
of 95 patients (48 sirolimus-eluting stents, 47 bare metal
stents), a motorized intravascular ultrasound pullback
along with quantitative coronary analysis was performed
at 6 months. There was no evidence of edge effect as
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107102
documented by intravascular ultrasound analysis in 95 of
the 237 patients or as demonstrated by QCA at 6 months.
Data from the subset of patients undergoing intravascular
ultrasound was reviewed to assess the incidence of incom-
plete stent apposition (ISA) at 6 months. ISA was defined
as z1 strut clearly separated from vessel wall with evi-
dence of blood speckles behind the strut. The incidence of
ISA in patients receiving sirolimus-eluting stent was 20% at
6 months compared to 4% in the group receiving a bare metal
stent (P < .015) with diabetics being more prone to ISA.
Nonetheless, ISA was not associated with adverse clinical
events. It is unclear whether ISA is the result of late acquired
malapposition or a consequence of an acute incomplete
deployment. In this trial, IVUS was not performed at time
of stent deployment, thereby making it difficult to determine
the underlying mechanism. After 1 year, a 94.2% event free
survival (freedom from death, myocardial infarction, target
vessel revascularization, target lesion revascularization) was
reported for the sirolimus-treated group compared to 71.2%
for the control group. These results set a stage for larger
randomized trials to be conducted in the United States.
SIROLIMUS-Coated BX Velocity Balloon-Expandable
Stent in the Treatment of Patients with De Novo Coronary
Artery Lesions (SIRIUS study) is a prospective, multicenter,
randomized, double-blind clinical trial that was conducted
in 55 centers in the United States. Eleven hundred and one
patients with focal de novo native coronary arterial lesions
(2.5–3.5 mm diameter, 15 to 30 mm long) were randomized
to treatment with sirolimus-coated (109 Ag/cm2) or baremetal
Bx Velocity stents between February and August 2001.
Patients received ASA indefinitely and either clopidogrel or
ticlodipine for 3 months postprocedure. The primary end-
point of the SIRIUS study was target vessel failure (cardiac
death, myocardial infarction, target lesion revascularization)
at 9 months postprocedure. Secondary endpoints included
angiographic in-stent and in-segment binary restenosis at
8 months, angiographic in-stent and in-segment minimum
lumen diameter at 8 months, major adverse cardiac events
up to 5 years and economic factors (index hospitalization
costs, length of stay and repeat hospitalizations) for up to
12 months. This trial differs from RAVEL in that it was a
larger cohort of patients, involved longer lesions, allowed
two stents per lesion, required a longer duration of anti-
platelet therapy (3 months vs. 2 months for RAVEL) and
will provide economic data. The results of the SIRIUS trial
were presented during the XIIIth Annual Transcatheter
Cardiovascular Therapeutics, September 2002 [27].
Patient demographics were similar in both groups with
respect to age, hypertension, hyperlipidemia and diabetes.
Approximately 60% of the patients had single vessel dis-
ease, 40% a lesion in the left anterior descending coronary
artery, and 60% of the lesions were classified as ACC/AHA
lesion class B2 or C. The average lesion length was 14.3 mm
for the sirolimus-treated group and 14.6 mm for the bare
metal group. On average, 1.4 stents were implanted per
patient with overlapping of stents in approximately 25% of
cases. Quantitative angiographic analysis of the in-stent
segment at 8 months demonstrated a late loss of 0.14 mm
for the sirolimus-eluting group compared to 0.92 mm for the
bare metal group, resulting in an 85% reduction in late loss
and 94% decline in in-stent restenosis, P < .001. Quantita-
tive angiographic analysis of the treated segment (stent plus
5 mm proximal or distal) demonstrated a 67% reduction in
late loss and a 72% decrease in restenosis for the sirolimus-
eluting group in comparison with the BX Velocity, P < .001.
Thus, quantitative angiographic analysis of the treated
segment at 8 months demonstrated less effective suppres-
sion of neointimal hyperplasia at both the proximal and
distal peri-stent area compared to in-stent suppression of
neointimal hyperplasia by sirolimus-eluting stents. This
resulted in restenosis at the stent margins, which, in partic-
ular at the proximal margin, was not significantly different
between the sirolimus and control group. Further subgroup
analysis by reference vessel size revealed that smaller
vessels (2.3 mm diameter) were more prone to restenosis at
the proximal edge. There were two cases of stent thrombosis
in the sirolimus-treated group (0.4%) with four episodes of
stent thrombosis in the control group (0.8%). The primary
endpoint of target vessel failure (TVF) at 270 days was
8.6% for the sirolimus group compared to 21.0% for the
bare metal, P =.017, resulting in a reduction of TVF by 59%
for sirolimus treated patients. Clinical events of death and
MI were similar between the two groups at 270 days but
target lesion revascularization was decreased by 72% in the
sirolimus group, P < .001.
The larger sample size of the SIRIUS trial enabled
subgroup analysis of outcomes for specific lesion and patient
subsets. In general, the overall treatment effect of the
sirolimus-eluting stent was similar in several important
patient and anatomical subsets with a 75% relative reduction
in target lesion revascularization at 9-months. Within the
sirolimus group, target lesion revascularization was in-
creased in smaller vessels (2.3 mm or less) relative to
moderate (2.3 to 3.0 mm) or large vessels (3.0 mm or greater)
predominantly due to proximal margin peri-stent restenosis.
The frequency of target lesion revascularization was also
dependent on lesion length with an average frequency of
0.3 events per millimeter of stent length. In comparison with
BX Velocity, the sirolimus-eluting stent reduced the frequen-
cy of target lesion revascularization 70% independent of
lesion length. In diabetic patients the frequency of target
lesion revascularization was nearly twofold greater than
nondiabetic patients for sirolimus and bare metal stents.
Diabetic patients with reference vessel dimensions less than
2.3 mm had a 23% incidence of target lesion revasculariza-
tion in the sirolimus group as compared with 48% in the BX
Velocity group, P < .0001. From the various subgroup anal-
yses, it was concluded that sirolimus-eluting stents are safe
and effective in reducing neointimal hyperplasia in a more
complex group of patients and lesions. The suboptimal
efficacy in neointimal suppression at the proximal stent
margin in smaller vessels will require further evaluation and
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107 103
perhaps modification of current stent deployment techni-
ques to include limiting the proximal zone of balloon injury
and insuring complete lesion coverage. Diabetic patients,
who benefited from sirolimus-eluting stents but to a lesser
extent than the nondiabetic subgroup, continue to pose a
challenge for durable long-term outcomes with stents. At
present, a dose escalation study, 3-D or Diabetic Double
Dose Study, is in-progress to determine if a 2X concentra-
tion of sirolimus (approximately 300 Ag/cm2 drug per stent
surface area) is safe and potentially more effective in the
challenging patient population.
With initial success in de novo native coronary lesions,
investigators have started to evaluate the role of sirolimus-
eluting stents in the management of in-stent restenosis
(ISR) [28,29]. Sousa et al. evaluated 30 patients, 16 in Brazil
and 14 in Netherlands, between February and May 2001 for
ISR in native coronary arteries. Patients were treated with
z1 sirolimus eluting Bx Velocity stent. Angiographic and
IVUS analysis was performed on day of implantation and at
6month follow up. Thirty patients received a total of 41 stents
with mean lesion length of 17.2F 5.7 mm. No acute post-
procedure cardiac events were noted. At 12 months, there
were no cases of stent thrombosis. Six-month data is under
evaluation. In contrast, Serruys et al. have suggested a
different response with a more frequent clinical event rate
including reintervention and stent thrombosis, particularly in
patients with more complex ISR as well as failed brachyther-
apy. Therefore, additional studies will be needed to determine
the utility of sirolimus-eluting stents for ISR and the relative
efficacy in comparison with vascular brachytherapy.
The utility of sirolimus-eluting stents in the treatment of
in-stent restenosis will be compared to endovascular bra-
chytherapy in a prospective multicenter randomized clinical
trial, the SISR study. The SISR study, A Multicenter,
Randomized Study of the Sirolimus-Eluting Bx Velocity
Balloon Expandable Stent vs. Intravascular Brachytherapy
in the Treatment of Patients with In-stent Restenosis, is
a 350-patient clinical trial comparing Cypherk sirolimus-
eluting stent placement to endovascular brachytherapy with
gamma or beta-emitting systems for ISR lesions in reference
vessels 2.75- to 3.75-mm diameter with lesion length of
<40 mm excluding chronic total occlusion. This pivotal
randomized clinical trial is designed to determine superior-
ity for Cypher sirolimus eluting stent by a reduction in 9-
month target vessel failure in comparison with endovascular
brachytherapy. The enrollment in the SISR trial is expected
to commence during the first quarter of 2003.
The Cypher sirolimus eluting is presently under investi-
gation in more complex lesion subsets typical of the ‘‘real
world’’ practice of interventional cardiology. At present,
registry studies are ongoing in patients with bifurcation
lesions, unprotected left main disease and acute myocardial
infarction. The efficacy of direct stenting with Cypher
sirolimus-eluting stents will be investigated in a randomized
clinical trial of 455 patients conducted in Canada and
Europe (E and C-SIRIUS). Multicenter randomized clinical
trials are planned for patients with multivessel coronary
disease amenable to stenting or CABG (ARTS II, FREE-
DOM) to determine equivalence of these revascularization
therapies. The FREEDOM study will be sponsored by the
NHLBI and conducted in 14 centers throughout the United
States to determine if multivessel Cypher sirolimus-eluting
stent placement provides similar outcomes to CABG at
3 years in diabetic patients with symptomatic coronary
artery disease. Ultimately, these studies will provide the
scientific evidence necessary to broaden clinical applica-
tions of sirolimus-eluting stents in the day-to-day practice
of interventional cardiology.
4. Tacrolimus
Tacrolimus is a potent immunosuppressant, which was
discovered in 1984 [30] and is approved by FDA for use in
management of liver transplantation and kidney allograft
rejection. Tacrolimus is a metabolite of the actinomycete
Streptomyces tsukubaensis. It is lipophilic and highly bound
to plasma proteins [32].
The cellular receptor, FKBP12, is the initial binding site
for both tacrolimus and sirolimus. However, unlike siroli-
mus, the tacrolimus–FKBP complex inhibits the activity of
calcineurin, a serine threonine phosphatase. The inhibition
of calcineurin leads to inactivation of transcription factors
(NF-AT) responsible for cytokine gene activation. Conse-
quently, inhibiting the transcription of many cytokines such
as interleukin (IL) 2, IL-3, IL-4, IL-5, tumor necrosis factor
alpha and granulocyte-macrophage colony-stimulating fac-
tor [31]. The potent inhibition of cytokine expression by
tacrolimus suggests a potential utility in the prevention of
restenosis. Mechanical injury to macrophage laden athero-
sclerotic plaques leads to cytokine gene expression by
macrophages and/or smooth muscles in the plaque [33].
The increase in cytokine level stimulates vascular smooth
muscle activation and proliferation ultimately leading to
neointimal formation and restenosis [33]. In addition, the
activated smooth muscle cells produce cytokines resulting
in a vicious cycle with continued stimulation of vascular
smooth muscle cell proliferation. The suppression of
cytokine production by tacrolimus may translate to a
reduction in in-stent restenosis. It is thought that tacrolimus
may have an advantage over other agents in that it may
preferentially inhibit the proliferation of vascular smooth
muscle cells without impairing endothelial cell regenera-
tion, thereby enabling stent integration into the arterial
wall. The local delivery of tacrolimus via a drug-eluting
stent should minimize the nephrotoxicity and neurotoxicity
associated with systemic administration of the agent while
allowing for the drug to be delivered to the intended site
of action.
Clinical trials with tacrolimus-eluting stents have been
initiated at the Heart Centre Sieburg, Germany. The PRES-
ENT study—PREliminary Safety Evaluation of Nanoporous
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107104
Tacrolimus-eluting stents—is a two arm nonrandomized
prospective Phase I safety study comparing nanoporous
ceramic coated-stents with tacrolimus-eluting nanoporous
ceramic-coated stents. Tacrolimus at a dose of 60 Ag per
stent was used, to treat patients with a single focal native de
novo coronary arterial lesion. Preliminary data from this
study supports safety but suggests a need for additional dose
finding studies (E. Grube, MD, personal communication).
In addition to the aforementioned PRESENT trial,
JOMED is conducting the EVIDENT trial (Endo-Vascular
Investigation Determining the Safety of a New Tacrolimus
Eluting Stent Graft) to evaluate the safety of a tacrolimus-
eluting coronary stent graft for the treatment of saphenous
vein graft stenosis. The drug delivery platform is JOMED’s
balloon expandable PTFE coronary stent graft. The dose of
tacrolimus is 325 Ag per stent, which is significantly higher
than the 60 Ag dose in PRESENT trial. Professor Eberhard
Grube is also the principal investigator for the EVIDENT
trial, like PRESENT, which is being conducted at the Heart
Centre in Sieburg, Germany. To date, the preliminary results
of these trials indicates a lack of efficacy for this agent at the
present doses suggesting further dose finding or selection of
an alternative delivery method may be necessary to achieve
efficacy for this stent-based therapy.
5. Everolimus
Everolimus is similar to sirolimus in that they are both
immunosuppressive and antiproliferative agents. Everoli-
Fig. 4. This figure provides a comparison of the basic structure, molecular weigh
its analogues.
mus suppresses antigen-mediated T cell proliferation and
therefore has been used as an immunosuppressant. Ever-
olimus is a cytostatic agent, which acts by binding to the
intracellular receptor FKBP-12 resulting in late G1 cell
cycle arrest of vascular smooth cell proliferation. Unlike
sirolimus, everolimus has increased solubility in organic
solvents and has a two- to threefold lower affinity for the
receptor FKBP12. Structurally, the two compounds differ in
a side chain which for sirolimus is a hydrogen and for
everolimus is CH2(CH2)OH (Fig. 4). Preclinical data con-
ducted by Honda et al. [34] has demonstrated that ever-
olimus may be as effective as sirolimus in the prevention of
in-stent restenosis in a porcine coronary model.
The first clinical trial, to assess the safety and efficacy, of
everolimus-eluting stent was initiated at the Heart Center in
Siegburg, Germany by Dr. Eberhard Grube called ‘‘First
Use To Underscore Reduction in Restenosis with Ever-
olimus’’ (FUTURE I) [35]. The stent platform in this trial
is the Challenge stent, which is coated by a bioerodable
polymer-carrying everolimus. This was a prospective, ran-
domized and single-blinded trial of everolimus-eluting stent
in 40 patients with de novo coronary lesions, 2.75–4.0 mm
in diameter and <18 mm in length. Randomization was in a
2:1 ratio with 27 patients receiving a everolimus-eluting
stent and 13 patients receiving a bare metal stent. The pri-
mary endpoint was major adverse cardiac events at 30 days
and secondary endpoint is angiographic restenosis at
6 months. The preliminary results of FUTURE 1 were
presented by Dr. Eberhard Grube at the American College
of Cardiology, March 2003. Major adverse cardiac events at
t, physical properties, and approved clinical indication for rapamycin and
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107 105
30 days did not differ significantly between the everolimus
group and control group. Angiographic study at 6-months
demonstrated late loss of 0.10 mm in the everolimus group
and 0.83 mm in the bare metal group. Although angio-
graphic restenosis (>50% diameter stenosis) was not ob-
served the everolimus group, this was not significantly
different from the 9.1% incidence of restenosis in the
control group. The results from the FUTURE I trial
demonstrated the feasibility and safety of this unique
bioerodable polymeric everolimus elluting stent. The FU-
TURE II is a multicenter prospective clinical trial, which
will consist of 200 patients to be randomized in a double-
blinded manner to an everolimus-eluting stent or a bare
metal stent. The primary end point of FUTURE II will be
angiographic late lumen loss at 6 months. Secondary
endpoints will be major adverse cardiac events at 1 and 6
months and 1 year.
6. Abt-578
ABT-578 is a synthetic analogue of sirolimus. The
molecular structure of ABT-578 contains a tetrazole ring
as compared to a hydroxyl group in sirolimus. Its mecha-
nism of action is similar to sirolimus in that ABT-578 binds
the intracellular receptor FKBP-12 and exerts an antiproli-
ferative effect via mTOR. In vitro data with ABT-578 has
demonstrated inhibition of growth-factor-mediated vascular
smooth muscle cell proliferation. Preclinical data has also
shown reduction in neointima formation at 28 days with
ABT-578 in the porcine coronary model. A Phase I clinical
trial with ABT-578-eluting phosphorylcholine-coated stent
is currently in-progress (ENDEAVOR I).
7. Myophenolic acid (MPA)
MPA (C7H20O6; MW 320.3) is an antibiotic, first derived
from cultures of the Penicillium species by Gosio in 1896
[36]. MPA has antineoplastic, antibacterial, antifungal, anti-
viral and excellent immunosuppressive properties. MPA is
the active metabolite of mycophenolic mofetil (MMF), an
FDA-approved drug, indicated for the prophylaxis of organ
rejection in patients receiving allogeneic renal, cardiac or
hepatic transplants. It is available for both oral (capsules,
tablets and oral suspension) and IV administration at rec-
ommended doses of 1–1.5 g b.i.d. (daily dose of 2–3 g) for
transplant patients.
MPA is a noncompetitive reversible inhibitor of IMPDH
(inosine monophosphate dehydrogenase). This NAD-
dependant enzyme is the rate-limiting enzyme in the de
novo pathway for purine biosynthesis and leads to depletion
of guanine nucleotides. This decrease in GTP results in
decreased DNA synthesis, allosteric feedback inhibition of
purine and pyrimidine biosynthesis, inhibition of glycosyl-
ation of adhesion molecules, and decreased cyclin depen-
dant kinase activity resulting in G0/G1 arrest [37].
MPA is known to exert antiproliferative activity on
lymphocytes, macrophages and smooth muscle cells [38].
In addition, depletion of guanine nucleotides inhibits trans-
fer of mannose and fructose to glycoproteins, preventing the
glycosylation of lymphocyte and monocyte glycoproteins
that are involved in adhesion to endothelial cells, thus,
inhibits recruitment of leukocytes into sites of inflammation
and graft rejection [39].
MPA is effective in the prevention of graft vascular
disease in rat models of aortic [40,41] and renal [42,43]
transplantation. Both the adventitial inflammatory compo-
nent and neointimal proliferation were inhibited by MPA in
the aortic transplant animals. In the renal transplant study,
allospecific IgM and IgG responses were absent in the
treated group. MPA, on its own and when given with
rapamycin was able to inhibit neointimal formation after
balloon injury [44]. In a study of heterotopic primate cardiac
xenografts [45], mycophenolate was more effective than
azathioprine when combined with cyclosporine and steroids
in preventing graft vascular disease. MPAwas also shown to
ameliorate the atherogenic potential of a high cholesterol diet
and to reduce macrophage and foam cell infiltration and
smooth muscle cell infiltration and proliferation [46].
MPA is incorporated in a proprietary polymer coating on
the Duraflex drug-eluting stent system developed by Avan-
tec Vascular (Sunnyvale, CA). The polymer employed by
Avantec has a long history in medical device industry
including blood-contacting and permanent implants. The
polymer coating is thin (V5 A), durable, and flexible and
can be modified to control the release rates of both hydro-
philic and hydrophobic drugs. The combination of the
coating technology with the inert nature of the polymer
results in no chemical interaction between the drug and the
polymer. The total amount of drug loaded on an 18 mm long
Duraflex stent is 300 Ag (3.3 Ag/mm2). The release of MPA
has been modified to provide a range of drug elution from
the stent for periods of 14 to 45 days.
In vitro studies have confirmed the broad therapeutic
window of MPA by measuring the antiproliferative effect
of MPA on human smooth muscle cells (SMCs) (prolifer-
ation assay) and the cytostatic effect of MPA on human
SMCs (viability assay). These studies suggest that MPA is
effective in inhibiting cell proliferation by a cytostatic
mechanism. MPA did not induce cell death even at con-
centrations 1000 times higher than the IC50 for inhibition of
SMC proliferation.
The IMPACT clinical trial (Inhibition with MPA of
Coronary Restenosis Trial) in February, 2002. This non-
randomized open label study was designed to evaluate the
safety and efficacy of the MPA-eluting Duraflex Stent
System in 150 patients with focal native de novo coronary
arterial lesions. The preliminary results of the IMPACT trial
presented during the EuroPCR in May 2003 indicated the
feasibility and safety of this drug-eluting stent but suggested
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107106
minimal effect on late lumen loss. Further study is in-
progress to evaluate MPA-eluting stents with different
elution characteristics to increase early drug tissue concen-
tration as well as MPA in combination with other agents.
8. Conclusions
Stent based delivery of immunosuppressive agents has
established itself as a viable strategy for the reduction of in-
stent restenosis. The present data substantiates varying
degrees of clinical efficacy for stent-based immunosuppres-
sive therapies likely related to structural properties (MW,
solubility) and specific biologic effects based on mecha-
nism of action. Agents with a multiplicity of biologic
effects, such as sirolimus and other rapamycin analogs,
appear to produce the most potent suppression of neo-
intimal formation (90% inhibition) and thus the greatest
clinical benefit for reduction of restenosis. A ‘‘class effect’’
for these structurally and functionally divergent immuno-
suppressive compounds has not been observed with stent-
based delivery for the prevention of neointimal formation
and restenosis. For the sirolimus-eluting stent, the combi-
nation of efficacy and safety, with reduced restenosis and
absence of a pathobiological response, should make this a
core technology for the interventional cardiologist. As other
therapeutic agents and combination drug-eluting stents are
being explored, we must remember that all drugs and
carrier vehicles are not equivalent. The use of sirolimus
and other drug eluting stents in high-risk subset groups,
insulin-requiring diabetics, and in complex lesions, such as
at points of bifurcation requires additional study in larger
randomized clinical trials. In the coming years, emphasis
will shift to advancement of stent design for drug delivery
and ease of use as well as operator technique which will
demand vigilance at time of stent placement and deploy-
ment—goal to limit area of injury, avoid gaps in between
stents and perform optimal stent expansion. The stent–
carrier–drug composite system is a breakthrough medical
technology that will transform the principles and practice of
vascular medicine.
References
[1] Williams DO, Holubkov R, Yeh W, Bourassa MG, Al-Bassam M,
Block PC, Coady P, Cohen H, Cowley M, Dorros G, Faxon D,
Holmes DR, Jacobs A, Kelsey SF, King SB, Myler R, Slater J, Stanek
V, Vlachos HA, Detre KM. Percutaneous coronary intervention in the
current era compared with 1985–1986: the National Heart, Lung, and
Blood Institute Registries. Circulation 2000;102(24):2945–51.
[2] Mehran R, Dangas G, Abizaid AS, Mintz GS, Lansky AJ, Satler LF,
Pichard AD, Kent KM, Stone GW, Leon MB. Angiographic patterns
of in-stent restenosis: classification and implications for long-term
outcome. Circulation 1999;100(18):1872–8.
[3] Mehran R, Dangas G, Mintz GS, Waksman R, Hong MK, Abizaid A,
Abizaid AS, Kornowski R, Lansky AJ, Laird JR, Kent KM, Pichard
AD, Salter LF, Stone GW, Leon MD. In-stent restenosis: ‘‘The Great
Equalizer’’—disappointing clinical outcomes with ALL intervention-
al strategies. J Am Coll Cardiol 1999;33(Suppl. A):63A.
[4] Waksman R. Beta radiation to INHIBIT recurrance of in-stent reste-
nosis: clinical and angiographic results of the multicenter randomized
double blind study. Late breaking clinical trials at the American Heart
Association. New Orleans, LA, 2000.
[5] Kuntz RE. The beta-cath system trial. Late breaking clinical trials at
American College of Cardiology. Orlando, FL, 2001.
[6] Hoffmann R, Mintz GS, Dussaillant GR, Popma JJ, Pichard AD,
Satler LF, Kent KM, Griffin J, Leon MB. Patterns and mechanisms
of in-stent restenosis. A serial intravascular ultrasound study. Circu-
lation 1996;94(6):1247–54.
[7] Longenecker JP, Kilty LA, Johnson LK. Glucocorticoid influence
on growth of vascular wall cells in culture. J Cell Physiol 1982;
113:192–202.
[8] Voisard R, Seitzer U, Baur R, Dartsch PC, Osterhues H, Hoher M,
Hombach V. Corticosteroid agents inhibit proliferation of smooth
muscle cells from human atherosclerotic arteries in vitro. Int J Cardiol
1994;43(3):257–67.
[9] Cronstein BN, Kimmel SC, Levin RI, Martiniuk F, Weissmann G. A
mechanism for the antiinflammatory effects of corticosteroids: the
glucocorticoid receptor regulates leukocyte adhesion to endothelial
cells and expression of endothelial-leukocyte adhesion molecule 1
and intercellular adhesion molecule 1. Proc Natl Acad Sci U S A
1992;89(21):9991–5.
[10] Chervu A, Moore WS, Quinones-Baldrich WJ, Henderson T. Efficacy
of corticosteroids in suppression of intimal hyperplasia. J Vasc Surg
1989;10(2):129–34.
[11] Hollander W, Kramsch DM, Franzblau C. Suppression of athe-
romatous fibrous plaque formation by anti-proliferative and anti-
inflammatory drugs. Circ Res 1974;34:I-131–4 (supplement).
[12] Stone GW, Rutherford BD, McConahay DR, Johnson WL, Giorgi LV,
Ligon RW, Hartzler GO. A randomized trial of corticosteroids for the
prevention of restenosis in 102 patients undergoing repeat coronary
angioplasty. Catheter Cardiovasc Diagn 1989;18(4):227–31.
[13] Pepine CJ, Hirshfeld JW, Macdonald RG, Henderson MA, Bass TA,
Goldberg S, Savage MP, Vetrovec G, Cowley M, Taussig AS. A
controlled trial of corticosteroids to prevent restenosis after coronary
angioplasty. M-HEART Group. Circulation 1990;81(6): 1753–61.
[14] Lincoff AM, Furst JG, Ellis SG, Tuch RJ, Topol EJ. Sustained local
delivery of dexamethasone by a novel intravascular eluting stent to
prevent restenosis in the porcine coronary injury model. J Am Coll
Cardiol 1997;29(4):808–16.
[15] Strecker EP, Gabelmann A, Boos I, Lucas C, Xu Z, Haberstroh J,
Freudenberg N, Stricker H, Langer M, Betz E. Effect on intimal
hyperplasia of dexamethasone released from coated metal stents com-
pared with non-coated stents in canine femoral arteries. Cardiovasc
Intervent Radiol 1998;21(6):487–96.
[16] Ping QB, Yanming H, Wang L, Vermeire I, Verbeken E, Schacht E,
de Scheerder IK. Methylprednisolone coated stents decrease neo-
intimal hyperplasia in a porcine coronary model. J Am Coll Cardiol
2001;37(Suppl. 1):74A.
[17] Liu X, Huang Y, Scheerder ID. Study of antirestenosis with the Bio-
divysio dexamethasone eluting stent (STRIDE): a multicenter trial.
J Am Coll Cardiol 2002;39(Suppl. 1):15A.
[18] Meiser BM, Morris RE. Identification of a new pharmacologic action
for an old compound. Med Sci Res 1989;17:609–10.
[19] Gregory CR, Huie P, Billingham ME, Morris RE. Rapamycin inhibits
arterial intimal thickening caused by both alloimmune and mechanical
injury. Its effect on cellular, growth factor, and cytokine response in
injured vessels. Transplantation 1993;55(6):1409–18.
[20] Marx SO, Jayaraman T, Go LO, Marks AR. Rapamycin-FKBP inhib-
its cell cycle regulators of proliferation in vascular smooth muscle
cells. Circ Res 1995;76(3):412–7.
[21] Poon M, Marx SO, Gallo R, Badimon JJ, Taubman MB, Marks AR.
Rapamycin inhibits vascular smooth muscle cell migration. J Clin
Invest 1996;98(10):2277–83.
M. Aggarwal et al. / Cardiovascular Radiation Medicine 4 (2003) 98–107 107
[22] Gallo R, Padurean A, Jayaraman T, Marx S, Roque M, Adelman S,
Chesebro J, Fallon J, Fuster V, Marks A, Badimon JJ. Inhibition
of intimal thickening after balloon angioplasty in porcine coronary
arteries by targeting regulators of the cell cycle. Circulation 1999;
99(16):2164–70.
[23] Suzuki T, Kopia G, Hayashi S, Bailey LR, Llanos G, Wilensky R,
Klugherz BD, Papandreou G, Narayan P, Leon MB, Yeung AC, Tio F,
Tsao PS, Falotico R, Carter AJ. Stent-based delivery of sirolimus
reduces neointimal formation in a porcine coronary model. Circula-
tion 2001;104(10):1188–93.
[24] Sousa JE, Costa MA, Abizaid A, Abizaid AS, Feres F, Pinto IM,
Seixas AC, Staico R, Mattos LA, Sousa AG, Falotico R, Jaeger J,
Popma JJ, Serruys PW. Lack of neointimal proliferation after implan-
tation of sirolimus-coated stents in human coronary arteries: a quan-
titative coronary angiography and three-dimensional intravascular
ultrasound study. Circulation 2001;103(2):192–5.
[25] Sousa JE, Costa MA, Abizaid AC, Rensing BJ, Abizaid AS, Tana-
jura LF, Kozuma K, Van Langenhove G, Sousa AG, Falotico R,
Jaeger J, Popma JJ, Serruys PW. Sustained suppression of neointi-
mal proliferation by sirolimus-eluting stents: one-year angiographic
and intravascular ultrasound follow-up. Circulation 2001;104(17):
2007–11.
[26] Morice MC, Serruys PW, Sousa JE, Fajadet J, Ban Hayashi E, Perin
M, Colombo A, Schuler G, Barragan P, Guagliumi G, Molnar F,
Falotico R. A randomized comparison of a sirolimus-eluting stent
with a standard stent for coronary revascularization. N Engl J Med
2002;346(23):1773–80.
[27] Leon MB. Sirius: SIRIUS 400. Late breaking clinical trials at Euro
PCR. Paris, France, 2002.
[28] Sousa JE, Abizaid AA, Sousa A, Costa MA, Evelyn R, Benno R, Mu-
zaffer D, Marinella C, Rodolfo S, Abizaid AA, Serruys PW, Tanajura
LF. Sirolimus-coated stents for the treatment of in-stent restenosis: the
first-in-man experience. Circulation 2001;104(17 [Suppl. II]):II-625.
[29] Degertekin M, Regar E, Tanabe K, Smits PC, van der Giessen WJ,
Carlier SG, de Feyter P, Vos J, Foley DP, Ligthart JMR, Popma JJ,
Serruys PW. Sirolimus-eluting stent for treatment of complex in-stent
restenosis. The first clinical experience. J Am Coll Cardiol 2003;41:
184–9.
[30] Shapiro R. The development of tacrolimus in renal transplantation.
Transplant Proc 2001;33:3158–60.
[31] Starzl TE, Todo S, Fung JJ, et al. Transplant Proc 22 [entire issue].
[32] Gummert JF, Ikonen T, Morris RE. Newer immunosuppressive drugs:
a review. J Am Soc Nephrol 1999;10(6):1366–80.
[33] Libby P, Schwartz D, Brogi E, Tanaka H, Clinton SK. A cascade
model for restenosis. A special case of atherosclerosis progression.
Circulation 1992;86(6 [Suppl. III]):III47–52.
[34] Honda H, Kar S, Honda T, Takizawa K, Meguro T, Fishbein MC,
Makkar R, Eigler N, Litvack F. Everolimus eluting stents significantly
inhibit neointimal hyperplasia in an experimental pig coronary model.
Am J Cardiol 2002;90(Suppl. 6A):73H.
[35] Grube E, Gerckens U, Buellesfeld L, Bootsveld A, Techen G, Staber-
ock M, Selbach G, Mueller R. First human experience using a new
everolimus stent coating: early findings of the FUTURE trial. Am J
Cardiol 2002;90(Suppl. 6A):71H.
[36] Gosio B. Ricerche Batteriologiche e chimiche sulle alterazioni del
mais. Revista di Igiene e Sanita Pubblica Ann 1896;7:825–68.
[37] Laurent AF, Dumont S, Poindron P, Muller CD. Mycophenolic acid
suppresses protein N-linked glycosylation in human monocytes and
their adhesion to endothelial cells and to some substrates. Exp Hem-
atol 1996;24(1):59–67.
[38] Allison AC, Eugui EM. Purine metabolism and immunosuppres-
sive effects of mycophenolate mofetil (MMF). Clin Transplant 1996;
10(1 Pt 2):77–84.
[39] Hauser IA, Johnson DR, Thevenod F, Goppelt-Strube M. Effect of
mycophenolic acid on TNF alpha-induced expression of cell adhesion
molecules in human venous endothelial cells in vitro. Br J Pharmacol
1997;122(7):1315–22.
[40] Morris RE, Hoyt EG, Murphy MP, Eugui EM, Allison AC. Myco-
phenolic acid morpholinoethylester (RS-61443) is a new immunosup-
pressant that prevents and halts heart allograft rejection by selective
inhibition of T- and B-cell purine synthesis. Transplant Proc 1990;
22(4):1659–62.
[41] Raisanen-Sokolowski A, Aho P, Myllarniemi M, Kallio E, Hayry P.
Inhibition of early chronic rejection in rat aortic allografts by myco-
phenolate mofetil (RS61443). Transplant Proc 1995;27(1):435.
[42] Azuma H, Binder J, Heemann U, Schmid C, Tullius SG, Tilney NL.
Effects of RS61443 on functional and morphological changes in
chronically rejecting rat kidney allografts. Transplantation 1995;
59(4):460–6.
[43] Azuma H, Binder J, Heemann U, Tullius SG, Tilney NL. Effect of
RS61443 on chronic rejection of rat kidney allografts. Transplant Proc
1995;27(1):436–7.
[44] Gregory CR, Huang X, Pratt RE, Dzau VJ, Shorthouse R, Billingham
ME, Morris RE. Treatment with rapamycin and mycophenolic
acid reduces arterial intimal thickening produced by mechanical in-
jury and allows endothelial replacement. Transplantation 1995;59(5):
655–61.
[45] O’Hair D, McManus RP, Komorowski R. Inhibition of chronic vas-
cular rejection in primate cardiac xenografts using mycophenolate
mofetil. Ann Thorac Surg 1994;58(5):1311–5.
[46] Romero F, Rodriguez-Iturbe B, Pons H, Parra G, Quiroz Y, Rincon J,
Gonzalez L. Mycophenolate mofetil treatment reduces cholesterol-
induced atherosclerosis in the rabbit. Atherosclerosis 2000;152(1):
127–33.