Initial experience with paclitaxel-coated stents

RhoA inhibitor-eluting stent attenuates restenosis by inhibiting YAP signaling

OBJECTIVE

Current drug-eluting stent (DES) treatment is promising, but it still has the drawback of in-stent restenosis, which remains a clinically relevant problem. Efforts should be made to discover new signaling molecules and novel potential targets for the prevention of arterial restenosis. In this study, we fabricated a novel DES targeting the RhoA pathway and further examined this promising strategy in vitro and in a rabbit carotid model.

METHODS

Active RhoA expression is correlated with the synthetic smooth muscle phenotype, and the RhoA inhibitor rhosin suppresses this phenotypic modulation at both transcriptional and translational levels. We further demonstrated that the RhoA inhibitor rhosin might act through the YAP pathway in smooth muscle cell phenotype modulation by a gain-of-function assay. Moreover, we fabricated a RhoA inhibitor-eluting stent and tested it in a rabbit carotid model.

RESULTS

Compared with a bare-metal stent, the RhoA inhibitor-eluting stent significantly attenuated neointimal formation at 6 months. However, overexpression of YAP by lentivirus blocked the antirestenosis effect of the RhoA inhibitor-eluting stent and repressed smooth muscle-specific genes.

CONCLUSIONS

RhoA inhibitor-eluting stents attenuate neointimal formation through inhibition of the YAP signaling pathway. This novel DES may represent a potential strategy for the treatment of in-stent restenosis.

Rescuing Impaired Re-endothelialization of Drug-Eluting Stents Using the Hepatocyte Growth Factor

BACKGROUND

Current commercially available drug-eluting stents (DESs) are criticized for the problem of stent thrombosis by induced impaired re-endothelialization (RE). The solving of this challenge could be boosted by endothelial progenitor cells (EPCs). The purpose of this study was to examine the effects of hepatocyte growth factor (HGF) on this process.

METHODS

The abundance and functional capacity of circulating EPC was analyzed by a fluorescence-activated cell sorter and western blot. The in vivo effect of HGF on DES patency, RE, and neointimal formation was investigated in a hypercholesterolemic rabbit model.

RESULTS

After 7 days of HGF administration, the number of CD34+/CD133+ progenitor cells had increased significantly. HGF also significantly inhibited the onset of senescence of EPC due to a decrease in protein expression of p53 and p21. In the in vivo study, HGF-treated DES had a higher patency rate than the control group (11/12 vs. 6/12, P = 0.032). Moreover, the HGF-treated group exhibited better RE (control group: 69.5 ± 12.9%, HGF group: 88.8 ± 8.4%, P = 0.006), but significantly smaller areas of neointima (control group: 0.68 ± 0.15 mm², HGF group: 0.45 ± 0.18 mm², P = 0.02).

CONCLUSION

HGF efficiently ameliorates the vascular response to stent implantation, and has an important redeeming influence on the deleterious endothelial effects of DES.

Acrylic Copolymers as Candidates for Drug-Eluting Coating of Vascular Stents

The aim of the present work is the synthesis and characterization of polymer materials showing good adhesion, drug loading, and delivery properties, for potential cardiovascular application. In particular, poly(methylmethacrylate-co-acrylic acid) copolymers are prepared in different compositions by a radical polymerization and investigated as potential materials to coat metallic stents and to carry out a local drug release. Films obtained by dissolving the copolymer in an appropriate organic solvent (also loaded with an anti-restenosis drug, such as tacrolimus) are investigated: physicochemical properties, adhesiveness to metallic stent material, and kinetics of drug release in physiological environment are studied.

The pathophysiology and burden of restenosis

The introduction of percutaneous transluminal coronary angioplasty (PTCA) revolutionized the surgical treatment of coronary artery disease. However, despite increased surgical experience and technical breakthroughs, restenosis occurs in 30%-50% of patients undergoing simple balloon angioplasty and in 10%-30% of patients who receive an intravascular stent. Animal and human data indicate that restenosis is a response to injury incurred during PTCA. The need for reintervention in a high percentage of patients due to restenosis remains an important limitation to the long-term success of PTCA. Stenting reduces initial elastic recoil and limits negative arterial remodeling; however, bare-metal stents may promote intimal hyperplasia by eliciting an immune and proliferative response. Consistent with these data, clinical studies suggest that drug-eluting stents, coated with anti-inflammatory or antiproliferative agents, reduce the risk for restenosis. Stenting represents a considerable cost burden. Treatment strategy should focus on selective use of expensive drug-eluting stents in populations where they have been found to be more clinically effective than bare-metal stents--patients who are at high risk for restenosis or who develop restenosis with bare-metal stents. Recent studies suggest that the pharmacologic management of restenosis is now feasible. Together, the judicious use of stents and oral pharmacotherapy promise to reduce the risk for restenosis, even among high-risk patients.

Antiproliferative Agents Alter Vascular Plasminogen Activator Inhibitor-1 Expression

OBJECTIVE

Drug eluting stents (DES) reduce the incidence of restenosis after coronary angioplasty. Enthusiasm has been tempered by a possible increased risk of in-stent thrombosis. We examined the effects of paclitaxel and rapamycin on the endothelial transcriptome to identify alterations in gene expression associated with thrombosis.

METHODS AND RESULTS

Gene expression profiling was performed on human coronary artery endothelial cells treated with rapamycin or paclitaxel. Plasminogen activator inhibitor-1 (PAI-1) was the most consistently induced transcript in rapamycin-treated human coronary artery endothelial cells. RT-PCR and ELISA were performed to confirm positive findings. Transgenic mice engineered to express enhanced green fluorescent protein under control of the human PAI-1 promoter were also treated. Rapamycin and paclitaxel treated endothelial cells produced dose-dependent increases in PAI-1. There was a variable effect on endothelial tissue-type plasminogen activator (t-PA) expression. Enhanced expression of PAI-1 and enhanced green fluorescent protein were detected in coronary arteries, the aorta, and kidney of the mice.

CONCLUSIONS

Antiproliferative agents stimulate the expression of prothrombotic genes. PAI-1 expression may also play a role in the prevention of restenosis through an antimigratory mechanism. The effects of antiproliferatives on vascular gene expression deserve further scrutiny in view of the increasing utilization of drug-eluting stents.

In Situ Visualization of Paclitaxel Distribution and Release by Coherent Anti-Stokes Raman Scattering Microscopy

Visualization of three-dimensional distribution of drug molecules and subsequent changes during the release process is critical for understanding drug delivery mechanisms as well as designing tailor-made release profiles. This study utilized coherent anti-Stokes Raman scattering (CARS) imaging to examine paclitaxel distribution in various polymer films with lateral resolution of 0.3 microm and depth resolution of 0.9 microm. Raman bands in the CH stretch vibration and fingerprint regions were used to distinguish paclitaxel from the polymers. The detection sensitivity was measured to be 29 mM by imaging paclitaxel molecules dissolved in N,N-dimethylformamide solution. Release of paclitaxel from a polymer matrix was monitored at an acquisition speed of 1 frame/s. Our results show that CARS microscopy can be used effectively for in situ imaging of native drug molecules in a delivery system.

Drug-eluting stents for infrainguinal occlusive disease: progress and challenges

High restenosis rate is still the major limitation of peripheral arterial interventions. Within the last years, drug-eluting stents have gained wide acceptance in the coronary arteries, however, these devices are not currently available for arteries outside the coronary vasculature. This article summarizes the special role of the superficial femoral artery in restenosis, with efforts being made to reduce the restenosis rate in this artery, focusing on stents and drug-eluting stents.

Zotarolimus (ABT-578) eluting stents

Drug-eluting stents have revolutionized the field of interventional cardiology and have provided a significant innovation for preventing coronary artery restenosis. Polymer coatings that deliver anti-proliferative drugs to the vessel wall are key components of these revolutionary medical devices. This article focuses on the development of stents which elute the potent anti-proliferative agent, zotarolimus, from a synthetic phosphorylcholine-based polymer known for its biocompatible profile. Zotarolimus is the first drug developed specifically for local delivery from stents for the prevention of restenosis and has been tested extensively to support this indication. Clinical experience with the PC polymer is also extensive, since more than 120,000 patients have been implanted to date with stents containing this non-thrombogenic coating. This review provides background on pre-clinical studies with zotarolimus, on the development of the biocompatible PC polymer and on the clinical trials conducted using two stent platforms which deliver this drug to patients with coronary artery disease.

Traitement endovasculaire par « kissing stent » des lésions oblitérantes du carrefour aorto-iliaque

PURPOSE

To evaluate short and medium-term results of endovascular repair of the aortoiliac bifurcation for occlusive disease by the kissing stent technique.

METHOD

Twenty patients were included in this retrospective study between May 1999 and November 2002 (13 men, mean age 58 years, range 42-86). Fifteen were treated for bilateral common iliac artery stenosis (75%), four for unilateral common iliac artery occlusion with or without controlateral stenosis (20%), and one for bilateral common iliac artery occlusion (5%). Each patient had a clinical examination and dupplex-scan prior to discharge, at three months, twelve months then yearly.

RESULTS

All procedures were successful. Forty balloon expandable stents were deployed in the kissing position (mean length and diameter, 45 mm and 9 mm). Nine other stents were also deployed either in the abdominal aorta (one patient) either in the lower portion of the common iliac artery. Intra-operative complications were represented by one hematoma of the groin region treated surgically, one emboli of the femoral bifurcation treated by Forgarty balloon embolectomy, three dissections of the common iliac arteries treated by stenting, and one internal iliac artery occlusion not treated. Mean follow-up was 21 months (range 3-36). Three significant restenoses (>50%) were diagnosed during this period and one patient had an additional transluminal procedure. No intra-stent occlusion was found. Primary and secondary cumulative patencies at 12 and 36 months were respectively 94.7%, 84,4% and 100%, 89%.

CONCLUSION

We confirm the feasibility, and the reliability of endovascular aorto-iliac kissing stent reconstruction in occlusive disease for selected patients.

Strut Position, Blood Flow, and Drug Deposition

Background— The intricacies of stent design, local pharmacology, tissue biology, and rheology preclude an intuitive understanding of drug distribution and deposition from drug-eluting stents (DES).

Methods and Results— A coupled computational fluid dynamics and mass transfer model was applied to predict drug deposition for single and overlapping DES. Drug deposition appeared not only beneath regions of arterial contact with the strut but surprisingly also beneath standing drug pools created by strut disruption of flow. These regions correlated with areas of drug-induced fibrin deposition surrounding DES struts in porcine coronary arteries. Fibrin deposition immediately distal to individual isolated drug-eluting struts was twice as great as in the proximal area and for the stent as a whole was greater in distal segments than proximal segments. Adjacent and overlapping stent struts increased computed arterial drug deposition by far less than the sum of their combined drug load. In addition, drug eluted from the abluminal stent strut surface accounted for only 11% of total deposition, whereas, remarkably, drug eluted from the adluminal surface accounted for 43% of total deposition. Thus, local blood flow alterations and location of drug elution on the strut were far more important in determining arterial wall drug deposition and distribution than were drug load or arterial wall contact with coated strut surfaces.

Conclusions— Simulations that coupled strut configurations with flow dynamics correlated with in vivo effects and revealed that drug deposition occurs less via contact between drug coating and the arterial wall than via flow-mediated deposition of blood-solubilized drug.

Cypher drug-eluting stent treatment of tibioperoneal obstructive disease: A case report

Stent placement in a tibial artery for suboptimal angioplasty results has had a high rate of restenosis and occlusion due to neointimal hyperplasia. Drug-eluting stents may provide a new therapeutic option in this situation. We describe the use of a Cypher drug-eluting stent after suboptimal angioplasty result in a claudicant with a severe tibioperoneal trunk lesion and single-vessel runoff to the foot with 6-month follow-up.

Advanced c-myc antisense (AVI-4126)-eluting phosphorylcholine-coated stent implantation is associated with complete vascular healing and reduced neointimal formation in the porcine coronary restenosis model

An advanced six-ring morpholino backbone c-myc antisense (AVI-4126) was shown to inhibit c-myc expression and intimal hyperplasia after local catheter delivery in a porcine balloon injury model. The purpose of this study was to investigate the effects of an AVI-4126-eluting phosphorylcholine-coated (PC) stent on c-myc expression restenosis and vascular healing after stent implantation in porcine coronary arteries. PC stents were loaded with AVI-4126 using soak trap. Nine pigs underwent AVI-4126 PC coronary stent implantation (two stents/animal). Two to six hours postprocedure, three pigs were sacrificed and stented segments were analyzed by Western blot for c-myc expression. In chronic experiments, six pigs (12 stent sites) were sacrificed at 28 days following intervention and vessels were perfusion-fixed. High-performance liquid chromatography analysis of plasma samples showed minimal presence of the antisense. Western blot analysis of the stented vessels demonstrated inhibition of c-myc expression at 2 and 6 hr after procedure. Quantitative histologic morphometry showed that the neointimal area was significantly reduced (by 40%) in the antisense-coated group compared with control (2.3 +/- 0.7 vs. 3.9 +/- 0.8 mm(2), respectively; P = 0.0077). Immunostaining and electron microscopy demonstrated complete endothelialization, without fibrin deposition, thrombosis, or necrosis in all implanted stents. In the porcine coronary model, an advanced c-myc-eluting PC stent blocked c-myc expression and significantly inhibited myointimal hyperplasia and allowed complete reendothelialization and healing response.

Drug eluting stents in the infrainguinal circulation

The short-term efficacy of drug-eluting stents has been validated in the coronary circulation, particularly with the drugs rapamycin and paclitaxel. The physical environment of the infrainguinal arteries is very different from the coronary circulation. Self-expanding stents are necessary in the femoropopliteal segment, which is subject to recurrent external forces. These include flexion at the knee, compression within the adductor hiatus, rotation and longitudinal compression. Thus, the properties required of a drug coating is likely be very different from those used in coronary arteries. This would appear to be borne out by SIROCCO, the only published study to date evaluating drug-eluting stents in the noncoronary circulation. SIROCCO began as a prospective randomized 36 patient trial comparing rapamycin coated to uncoated self-expanding SMART stents in the femoropopliteal segment. The first phase of SIROCCO demonstrated reduction of intimal hyperplasia by rapamycin. However, the study is being repeated to optimize the rate of drug elution, and multiple stent fractures seen in the first phase of the study necessitated modification of stent design. Considerable further study of drug eluting stents will be required in each vascular bed to determine the ideal stent/drug combination, and to establish clinical efficacy.

HIF at the crossroads between ischemia and carcinogenesis

Tissue hypoxia occurs where there is an imbalance between oxygen supply and consumption in both, solid tumors as a result of exponential cellular proliferation and in atherosclerotic diseases as a result of inefficient blood supply. Hypoxia-inducible factor 1 (HIF-1) is central in normal angiogenesis and cancer angiogenesis. HIF-1 is a transcriptional activator composed of an O(2)- and growth factor-regulated HIF-1alpha subunit and a constitutively expressed HIF-1beta subunit. Upon activation, HIF-1 drives the expression of genes controlling cell survival and governing the formation of new blood vessels. A better understanding of the regulation of HIF-1alpha levels by the receptor tyrosine kinases/phosphatidylinositol 3-kinase signaling pathway and by the HIF prolyl hydoxylases has provided new insights into the development of anticancer and revascularization therapeutics. We will focus on the potential of a new pharmacology for regulating HIF pathways in both, cancer and ischemic cardiac diseases. The consequences of the switch of HIF activation in these two disease states and the signaling pathway overlap that atherosclerosis and cancer angiogenesis share are discussed.

Everolimus and mycophenolate mofetil are potent inhibitors of fibroblast proliferation after lung transplantation1

BACKGROUND

Dysregulated fibroblast proliferation is thought to play an important role in the progression of bronchiolitis obliterans (BO) after lung transplantation. Augmented immunosuppression is often used to treat BO. We investigated the effect of methylprednisolone (mPRED), cyclosporine A (CsA), tacrolimus (FK506), azathioprine (AZA), mycophenolate mofetil (MMF), and everolimus (rapamycin derivative [RAD]) on the proliferative capacity of fibroblasts cultured from transbronchial biopsies of lung transplant recipients.

METHODS

Primary cultures of human lung fibroblasts were obtained from 14 transbronchial biopsies of lung transplant recipients. Subconfluent cells were serum starved for 24 hr followed by growth stimulation in the presence or absence of the respective drug in six concentrations ranging as follows: 0.01 to 100 mg/L for mPRED; 0.01 to 50 mg/L for CsA and AZA; 0.001 to 5 mg/L for FK506 and MMF; and 0.00001 to 1 mg/L for RAD. Proliferation was quantified by [3H]thymidine incorporation and direct cell count. A toxic drug effect was excluded by trypan blue.

RESULTS

Drug concentrations (mg/L) causing a 50% inhibition of fibroblast proliferation were mPRED 4; CsA 20; FK506 0.3; AZA 7; MMF 0.3; and RAD 0.0006. Drug concentrations (mg/L) causing inhibition of fetal bovine serum-induced proliferation were mPRED 60; CsA 45; FK506 3; AZA 35; MMF 1; and RAD 0.003.

CONCLUSIONS

RAD and MMF were the most potent antifibroproliferative drugs and were effective at concentrations achieved clinically, supporting their use for the treatment of patients with early BO. Our method holds promise as an in vitro model to assess the likely in vivo responses of human lung fibroblasts to specific immunosuppressive drugs.

Evolving revascularization approaches for myocardial ischemia

Stable angina pectoris secondary to ischemic heart disease is a common and disabling condition. Medical therapy aims to relieve symptoms, improve exercise capacity, and decrease cardiac events by reducing myocardial oxygen demand or improving coronary blood supply to the ischemic myocardium. If medical treatment is inadequate, invasive revascularization procedures to improve coronary perfusion are considered. Percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass graft (CABG) surgery are well-established and widely used myocardial revascularization techniques. Recent advances in PTCA have attempted to address the problem of restenosis, initially through the deployment of bare metal intracoronary stents and, more recently, with drug-eluting stents. Developments in CABG have focused on reducing the invasiveness of the procedure and minimizing the incidence of serious complications. Refinements include the use of mechanical stabilizers, endoscopic harvesting of conduit vessels, robotic telemanipulation systems, and fully automated anastomotic devices. Surgical laser transmyocardial revascularization and therapeutic angiogenesis represent newer approaches to coronary revascularization. Therapeutic angiogenesis aims to deliver an angiogenic growth factor or cytokine to the myocardium to stimulate collateral blood vessel growth throughout the ischemic tissue. The angiogenic factor may be administered as a recombinant protein or as a transgene within a plasmid or gene-transfer vector. Ongoing angiogenic gene therapy clinical trials are evaluating which factors, vectors, and delivery techniques hold the greatest promise for management of patients with chronic stable angina.

Late stent thrombosis after implantation of a sirolimus-eluting stent

Late stent thrombosis in the era of routine high-pressure stent deployment and combined antiplatelet therapy with thienopyridines and aspirin has become a rare but feared complication. We describe a patient with acute myocardial infarction due to late stent thrombosis 6 weeks after deployment of a sirolimus-eluting stent and 2 weeks after the discontinuation of clopidogrel. This is the first report of late thrombosis of a sirolimus-eluting stent.

Small-scale systems for in vivo drug delivery

Recent developments in the application of micro- and nanosystems for drug administration include a diverse range of new materials and methods. New approaches include the on-demand activation of molecular interactions, novel diffusion-controlled delivery devices, nanostructured 'smart' surfaces and materials, and prospects for coupling drug delivery to sensors and implants. Micro- and nanotechnologies are enabling the design of novel methods such as radio-frequency addressing of individual molecules or the suppression of immune response to a release device. Current challenges include the need to balance the small scale of the devices with the quantities of drugs that are clinically necessary, the requirement for more stable sensor platforms, and the development of methods to evaluate these new materials and devices for safety and efficacy.

Pilot trial of oral rapamycin for recalcitrant restenosis

BACKGROUND

Sirolimus-coated stents are a promising new therapy for restenosis. We treated a select group of patients at especially high risk for restenosis with oral sirolimus.

METHODS AND RESULTS

Patients were treated with an oral sirolimus-loading dose of 6 mg after coronary angioplasty, followed by 2 mg/d for 4 weeks. Serum electrolytes, lipid profile, renal panel, and complete blood cell count were measured at 1, 3, and 5 weeks after drug initiation. Oral sirolimus was prescribed to 22 patients who had a total of 28 lesions and were at high risk for restenosis. Of the 22 study patients, 11 (50%) discontinued oral sirolimus early because of side effects or laboratory abnormalities. Hypertriglyceridemia and leukopenia were the most frequent adverse events, occurring in 3 patients each. All adverse drug effects were reversible after discontinuation. Follow-up was obtained in 100% of patients at a mean of 9.9+/-1.8 months, ranging from 6.5 to 11.8 months. Target lesion revascularization (TLR) occurred in 15 of 28 lesions (53.6%) and 13 of 22 patients (59.1%). There was no difference in TLR for patients receiving a complete course of sirolimus (n=8; 72.7%) compared with patients who terminated treatment prematurely (n=5; 45.5%; P=NS). Clinically driven repeat cardiac catheterization was obtained in 15 (68.2%) patients; restenosis (>50% diameter stenosis at follow-up) was present in 13 (86.7%).

CONCLUSIONS

Oral sirolimus does not appear to provide benefit to patients with recalcitrant restenosis. Adverse drug effects are frequent, underscoring the importance of local drug delivery to achieve high tissue concentrations without systemic adverse drug effects.