The effect of variable dose and release kinetics on neointimal hyperplasia using a novel paclitaxel-eluting stent platform: the Paclitaxel In-Stent Controlled Elution Study (PISCES)

Intravascular drug release kinetics dictate arterial drug deposition, retention, and distribution

Millions of patients worldwide have received drug-eluting stents to reduce their risk for in-stent restenosis. The efficacy and toxicity of these local therapeutics depend upon arterial drug deposition, distribution, and retention. To examine how administered dose and drug release kinetics control arterial drug uptake, a model was created using principles of computational fluid dynamics and transient drug diffusion-convection. The modeling predictions for drug elution were validated using empiric data from stented porcine coronary arteries. Inefficient, minimal arterial drug deposition was predicted when a bolus of drug was released and depleted within seconds. Month-long stent-based drug release efficiently delivered nearly continuous drug levels, but the slow rate of drug presentation limited arterial drug uptake. Uptake was only maximized when the rates of drug release and absorption matched, which occurred for hour-long drug release. Of the two possible means for increasing the amount of drug on the stent, modulation of drug concentration potently impacts the magnitude of arterial drug deposition, while changes in coating drug mass affect duration of release. We demonstrate the importance of drug release kinetics and administered drug dose in governing arterial drug uptake and suggest novel drug delivery strategies for controlling spatio-temporal arterial drug distribution.

Release profiles in drug-eluting stents: issues and uncertainties

This review presents the current data on drug release from drug-eluting stents and the effects of the release profiles on animal and human data for coronary stenosis. Data for the two most important drugs, sirolimus (rapamycin) and paclitaxel, are presented, the polymers used are described and the observed release profiles are discussed for various polymer carriers. The current literature on the tissue compatibility of the polymers commonly used in drug-eluting stents is also discussed. The range of release rates from stents studied to date is limited for sirolimus, but somewhat broader for paclitaxel. Animal and human data comparing the different release profiles are limited to about 6 months for animals and 2-4 years for humans. From the data available, it appears that for both sirolimus and paclitaxel, a slow-releasing drug-eluting stent leads to slightly more favorable angiographic outcomes than more rapid release. Most of the complications arising from the use of drug-eluting stents are attributed to incomplete healing; one possible clinical consequence of this delay in healing is that anti-platelet therapy needs to be maintained over a much longer period than is the case for bare metal stents.

Percutaneous coronary revascularization using a trilayer metal phosphorylcholine-coated zotarolimus-eluting stent

The ZoMaxx Coronary Stent System elutes the antiproliferative agent zotarolimus via a biocompatible phosphorylcholine polymer loaded onto a novel, thin, stainless steel stent platform containing an 0.0007-inch inner layer of tantalum that enhances fluoroscopic radiopacity. The objective of this single-arm prospective clinical trial was to assess the safety and performance of the ZoMaxx stent for the treatment of coronary artery stenosis. Forty consecutive patients with ischemic coronary occlusive disease due to single de novo obstructive lesions of native coronary arteries were treated with 3 x 18 mm ZoMaxx stents at the Dante Pazzanese de Cardiologie in Saõ Paulo, Brazil, between April and July 2005. Independent core laboratories analyzed quantitative coronary angiography and intravascular ultrasound results immediately after stent implantation, and after 4 months. The lesion, procedure, and device-deployment success rates were all 100% (40 of 40). There were no major adverse cardiac events during the study. Follow-up quantitative coronary angiography at 4 months revealed in-stent and in-segment late lumen losses of 0.20 +/- 0.35 and 0.17 +/- 0.35 mm, respectively. Follow-up intravascular ultrasound at 4 months revealed 6.5 +/- 6.2% neointimal volume obstruction. There were no instances of late acquired stent incomplete apposition or stent thrombosis. In conclusion, the ZoMaxx Coronary Stent can be safely implanted for the treatment of de novo coronary artery stenosis. The inhibition of neointima formation as measured by follow-up angiography and IVUS after 4 months suggests therapeutic potential for the reduction of restenosis.

Gene therapy progress and prospects: therapeutic angiogenesis for ischemic cardiovascular disease

During the past decade, both in vitro and in vivo studies have provided new insights into the cellular and molecular mechanisms that govern angiogenesis and arteriogenesis. However, therapeutic angiogenesis clinical trials using recombinant protein or gene therapy formulations of single angiogenic growth factors have yielded at best only modest success to date. Among the second generation of angiogenic agents are therapeutic transgenes that enhance expression of two or more proangiogenic cytokines. These include synthetic constructs that mimic that activity of endogenous transcriptional regulators and other upstream, regulatory factors that have the potential to induce formation of morphologically and physiologically functional vessels. These agents are now beginning to be evaluated in clinical trials for patients with advanced ischemic cardiac and peripheral vascular disease.

The Cobalt chromium STent with Antiproliferative for Restenosis II (COSTAR II) trial study design: advancing the active-control evaluation of second-generation drug-eluting stents

BACKGROUND

Randomized clinical trials have demonstrated the superiority of drug-eluting stents (DESs) compared with bare-metal stents in reducing the need for revascularization and major adverse cardiac events (MACEs) in low-risk patients with single-vessel lesions. Rapid DES uptake has necessitated shifting the paradigm to active DES-controlled noninferiority study models with most studies using surrogate angiographic measurements to attain adequate statistical power. No previous prospective trial has specifically compared a new DES with an active-control DES in a high-risk patient population using primary clinical end points.

OBJECTIVE

COSTAR II is designed to compare use of the investigational Costar stent (Conor MedSystems, Palo Alto, CA) with the Taxus (Boston Scientific, Maple Grove, MN) stent in single- and multivessel percutaneous coronary intervention. The primary end point is the clinical composite of MACE at 8 months supported by consistent results in the evaluation of 8-month MACE rates in the single- and multivessel cohorts and of in-segment late loss in a small angiographic substudy at 9 months.

METHODS

A total of 1700 patients, 50% with single-vessel and 50% with multivessel disease, are randomized in a 3:2 ratio to receive either Costar or Taxus stent(s) in this prospective, multicenter, noninferiority study design. Because no prior data were available to determine control multivessel MACE rates, an imputed placebo statistical analysis plan incorporating a variable delta based on actually observed control DES MACE rates will be implemented. The results of COSTAR II will provide information about a novel coronary stent device as well as unique data regarding both control and test DES use in more complex "real-world" patients.

Drug eluting stents

Dual antiplatelet therapy should not be discontinued without referral to a cardiologist

Progressive stent technologies: new approaches for the treatment of cardiovascular diseases

The CYPHER (Cordis, Johnson & Johnson) sirolimus-eluting stent and the TAXU (Boston Scientific) paclitaxel-eluting stent have been extensively evaluated and have been proven to be significant novel tools for the treatment of coronary artery disease. Several sirolimus derivatives have already emerged, receiving CE Mark approval. However, in the future, it is likely that drugs presently under investigation will address additional mechanisms associated with neointimal formation, either as single agents or in combination with antiproliferative compounds. Concurrently, alterations on stent platform design (helicoidal, open-closed cell), coatings (biodegradable, bioabsorbable, nanoporous) and polymers are being explored.

The paclitaxel-eluting stent in percutaneous coronary intervention: part I: background and clinical comparison to bare metal stents

The development of coronary artery stents that release (elute) a drug locally into the diseased vasculature has revolutionized the practice of interventional cardiology. These devices were designed to minimize the incidence of in-stent restenosis that may occur with bare metal stents. The paclitaxel-eluting stent is the most recent drug-eluting stent approved for use in the United States and is a bare metal stent coated with paclitaxel that is gradually released from the stent into the vessel wall with undetectable systemic concentrations of the drug. Paclitaxel functions to stabilize the assembly of microtubules, thereby interfering with cell division, motility, and shape, and ultimately inhibiting smooth muscle cell proliferation and migration, key processes in the development of neointimal hyperplasia during in-stent restenosis. Clinical trials have repeatedly demonstrated the superiority of the paclitaxel-eluting stent over the bare metal stent in terms of reducing restenosis rates and percent stenosis diameter as well as other angiographic end points. Although the rates of major adverse cardiac events are reduced with the paclitaxel-eluting stent compared with the bare metal stent, this is primarily the result of a reduction in the need for target vessel revascularization, whereas rates of myocardial infarction and death have not been shown to be significantly affected.

Drug-eluting stents: factors governing local pharmacokinetics

Stent-based drug delivery system is a revolutionary approach to mitigate the negative affects of balloon angioplasty, improve immune responsiveness and prevent hyperplastic growth of smooth muscle in the restenotic state. Its success is therefore empirically associated with effective delivery of potent therapeutics to the target site at a therapeutic concentration, for a sufficient time, and in a biologically active form. However, local delivery with drug-eluting stents imparts large dynamic concentration gradients across tissues that can be difficult to identify, characterize and control. This review explores the factors such as physiological transport forces, drug physicochemical properties, local biological tissue properties and stent design that governs the local pharmacokinetics within the arterial wall by drug-eluting stent. Rational design and optimization of drug-eluting stents for local delivery thus requires a careful consideration of all these factors.

Drug-Eluting Stents

Percutaneous coronary intervention has evolved dramatically over the past 25 years as coronary stents replaced stand-alone balloon angioplasty. Improvements in stents were made in the 1990s, but a breakthrough occurred in early 2000 with the development of stents that eluted pharmacology agents directly into the vessel wall by means of a controlled release from a durable polymer coating. Various drug-eluting stents were developed,each varying with its delivery platform, polymer coating (or absence of coating),and drug selected for elution. This article describes the clinically available and late developmental drug-eluting stent programs targeted for treating patients who have coronary artery disease.

Paclitaxel-eluting stents

Percutaneous coronary intervention and stent implantation is rapidly becoming the most commonly used form of revascularization. The long term results of this procedure are limited by restenosis which is a phenomenon predominantly caused by proliferation of smooth muscle cells. Many devices and pharmaceutical agents have been unsuccessful in preventing this problem. Paclitaxel is an antiproliferative drug that has been extensively studied for the prevention of restenosis. This article will review the trial results of the currently available stent platforms and discuss some of the ongoing studies and future directions for the development of new paclitaxel-eluting stents.

Sirolimus and Paclitaxel on polymer-based drug-eluting stents: similar but different

Recent clinical studies that investigated the efficacy of the two U.S. Food and Drug Administration-approved drug-eluting stent (DES) platforms Cypher (Cordis, Johnson and Johnson, Miami Lakes, Florida) and Taxus (Boston Scientific, Boston, Massachusetts) suggest that there are differences between both DES concerning neointimal growth. Both DES elute compounds that inhibit the cell cycle, but at different stages: Cypher stents elute sirolimus, which induces G1 cell cycle inhibition, and Taxus stents release paclitaxel, which predominantly leads to M-phase arrest. In an attempt to explain the differences observed in human studies, the properties of these stent-based compounds on critical molecular and cellular events associated with the pathophysiology of in-stent restenosis are discussed in detail with the conclusion that both sirolimus and paclitaxel are different in their pleiotropic anti-restenotic effects. This may be in part responsible for the differences observed in recent clinical studies.

Technology Insight: an overview of research in drug-eluting stents

Drug-eluting stents (DESs) have revolutionized interventional cardiology over the past few years to the extent that balloon angioplasty and bare stents did in the 1980s and 1990s. The first DESs became commercially available in Europe in 2002 and in the US in 2003, and it is estimated that up to 80% of patients who undergo stent implantation in the US now receive a DES. Two devices, Cypher sirolimus-eluting stents (Cordis Corporation, Miami Lakes, FL) and Taxus paclitaxel-eluting stents (Boston Scientific Corporation, Natick, MN), are currently licensed for sale in both regions. Multiple new devices using different drugs, carriers and stents are currently undergoing clinical trials to establish their efficacy and obtain approval for commercialization. While the remarkable reduction of restenosis has accounted for the success of DESs, concerns remain regarding long-term follow-up; published 3-year follow-up results are available for fewer than 200 patients overall. Reports of late stent thrombosis have emerged, particularly in relation to discontinuation of antiplatelet therapy. In patients treated with DESs, long-term administration of at least one antiplatelet agent must be continued following completion of the mandatory dual antiplatelet regimen. In this review, we summarize the findings available for DESs so far, discuss emerging safety and efficacy data, and look at the future directions for these devices.